WO2016087597A1

WO2016087597A1 - Paper or cardboard equipped with a barrier layer

Info

Publication number: WO2016087597A1
Application number: PCT/EP2015/078552
Authority: WO
Inventors: Carmen-Elena Cimpeanu; Hermann Seyffer
Original assignee: Basf Se
Priority date: 2014-12-04
Filing date: 2015-12-03
Publication date: 2016-06-09

Abstract

The invention relates to a process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer, which comprises coating of a paper or a cardboard with an aqueous coating material. The aqueous coating material comprises an aqueous dispersion of a polymer P, which is obtainable by radically initiated aqueous emulsion polymerization of at least 75 parts of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate, and optionally other monomers, wherein the sum total of the parts by weight of all monomers is 100, in the presence of 10 to 85 parts of ligninsulfonic acid. The obtained paper or cardboard equipped with a barrier layer shows beneficial water vapor permeability.

Description

Paper or cardboard equipped with a barrier layer Description The current invention relates to a process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer, the paper equipped with a barrier layer or the cardboard equipped with a barrier layer, an use of the paper equipped with a barrier layer or the cardboard equipped with a barrier layer for hindering a migration of a hydrophobic substance and allowing a migration of water vapor, and a process for preparing an aqueous dispersion of a polymer P' in the presence of ligninsulfonic acid.

JP-S63-097612 A describes a highly water-absorptive polymer, which has the ability to absorb water by 250 g/g and physiological saline (stated as 0.85 % sodium chloride in water) by 45 g/g. It is obtained by polymerizing a monomer selected from a group consisting of an acrylic ester, a methacrylic ester, acrylamide and methacrylamide in the presence of lignin and optionally a cross-linking agent. Optionally, this is followed by a partial hydrolysis leading to a rate of hydrolysis between 10 and 80%. The lignin can be ligninsulfonate, thiolignin or natural lignin. In its example 1 , 5 g methyl acrylate and 0.05 g Ν,Ν-methylenebisacrylamide are polymerized in the presence of 3 g ligninsulfonate in an aqueous solution at pH 4.7 under radical initiation by hydrogen peroxide and ferrous ammonium sulphate hexahydrate. The obtained reaction product is filtered, washed with water and afterwards hydrolized by aqueous sodium hydroxide solution at 100°C. In its example 2, the final hydrolysis is extended. In its example 3, the example 1 is repeated except of using 4 g of ligninsulfonate and 6 g of methyl acrylate. In its example 4, 4 g of ligninsulfonate, 6 g methyl acrylate, 0.06 g N,N-bismethylenebisacryl- amide, hydrogen peroxide and ferrous ammonium sulphate are reacted at pH 7 similarly to its example 1. In its final inventive example 5, example 4 is repeated except of using a modified ligninsulfonate.

WO-2013/120790 describes an aqueous polymer dispersion comprising a chain growth addition polymer obtainable via free-radically initiated emulsion polymerization from one or more ethylenically unsaturated, free-radically polymerizable monomers, wherein the chain growth addition polymer is formed to an extent of not less than 50 wt% from primary monomers selected from the group consisting of vinylaromatic compounds, conjugated aliphatic dienes, vinyl esters of saturated Ci- to C2o-carboxylic acids, esters of acrylic acid or of methacrylic acid with monohydric Ci- to C2o-alcohols, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds, or mixtures thereof, wherein the monomers are polymerized in the presence of lignosulfonate and wherein the chain growth addition polymer is branched or crosslinked via copolymeri- zation of at least one branching or crosslinking monomer other than the primary monomers and selected from monomers having two or more free-radically polymerizable, ethylenically unsaturated groups. The prepared polymer dispersions are used for paper coating compositions. The coated papers are tested for surface strength, e.g. by IGT dry pick resistance, by IGT wet pick resistance and Offset test. All disclosed examples are based on the combination of styrene and butyl acrylate (t-butyl or n-butylacrylate) as the major vinyl-group containing monomers.

Paper and cardboard are ecologically friendly materials, which are based on renewable raw materials. They are breathable, if they are used as a packaging material. A gas exchange between the goods, which are packaged, and the environment can take place, especially an exchange of moisture as water vapor. Hence, the dreaded for- mation of mildew is inhibited. A sign for the formation of mildew is a must, which would be noticeable for example at foods containing cereals.

There are also goods, especially foods, which are greasy or oily. At a packaging out of paper or cardboard, these greasy or oily goods cause grease spots, which lead to an unattractive appearance. A barrier against migration of grease or oil is desirable for these uses of a packaging out of a paper or a cardboard.

Furthermore, the problem of a migration of hydrophobic volatile ingredients out of a packaging as well as through a packaging is known. These undesirable volatile ingre- dients can originate from mineral oil contaminations of a recycled paper or cardboard used as raw material as well as from a printing ink, an adhesive or a solvent. A barrier against the migration of volatile hydrophobic substances is desirable.

A barrier, which is typically in the form of an additional layer, is used to avoid or at least delay the migration out of a material or through a material. However, many barrier layers avoid or delay the migration of all substances at a comparable rate. For example, a desirable exchange of moisture as water vapor is typically significantly hindered by a barrier layer against grease or oil. It is an object of the present invention to provide an ecologically friendly packaging material, which possess a barrier layer, wherein the barrier layer blocks the migration of grease or oil and of hydrophobic volatile ingredients, whereas a relevant exchange of moisture is still possible. The object is achieved, according to the invention, by a process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer, which comprises the steps of

(a) providing an aqueous coating material, which comprises

- an aqueous dispersion of a polymer P, which is obtainable by

radically initiated aqueous emulsion polymerization of

(i) at least 75 parts by weight of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate, (ii) 0 to 20 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate,

(iii) 0 to 5 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups,

(iv) 0 to 5 parts by weight of an acid monomer, which contains one ethylenically unsaturated group and at least one acid group,

(v) 0 to 9 parts by weight of a further monomer, which contains an ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv),

wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100,

in the presence of an initial ligninsulfonic acid in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v),

- 0 to 70 parts by weight of an additional ligninsulfonic acid, which is added after the generation of the aqueous dispersion of a polymer P, based on the sum total of the parts by weight of the monomers (i) to (v), and wherein the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), and

- 0 to 50 parts by weight of an inorganic pigment based on the sum total of the parts by weight of the monomers (i) to (v);

(b) coating a paper or a cardboard with the aqueous coating material from step (a) to obtain a water-containing layer on at least one surface of the paper or of the cardboard;

(c) drying of the water-containing layer on the paper or the cardboard from step (b) to obtain the paper equipped with a barrier layer or the cardboard equipped with a barrier layer. An ethylenically unsaturated group herein defines a C2-unit, wherein the two carbon atoms are connected by a carbon-carbon-double bond. For example, in case of a complete substitution with hydrogen atoms, it is ethylene. In case of substitution with 3 hydrogen atoms, it is a vinyl group. In case of substitution with 2 hydrogen atoms, it is an E/Z isomer or an ethen-1 ,1 -diyl group.

An amount of a weight herein refers to the solids content, if not otherwise stated. The solids content is herein defined as the weight obtained when a defined amount, for example 5 g, is dried at 140°C in a drying cabinet to a constant weight. Preferably, the amount of the acrylate ester is at least 85 parts by weight, especially at least 90 parts by weight and very especially at least 96 parts by weight, wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100. The upper limit of the amount of the further acrylate ester is accordingly reduced, if the amount of the acrylate ester is at least 85 parts by weight.

Preferably, the amount of the acrylate ester is at least 85 parts by weight and the amount of the further acrylate ester is from 0 to 15 parts by weight.

Preferably, the acrylate ester is a mixture of at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate. In particular, methyl acrylate is a member of the mixture. In particular, ethyl acry- late or ethyl methacrylate is a member of the mixture. Very particular, ethyl acrylate is a member of the mixture. In particular, ethyl acrylate or ethyl methacrylate is a member of the mixture and the combined amount of ethyl acrylate and ethyl methacrylate is at least 40%, especially 50%, based on the parts by weight of the acrylate ester. Very particular, ethyl acrylate is a member of the mixture and the amount of ethyl acrylate is at least 40%, especially 50%, based on the parts by weight of the acrylate ester. Very particular, methyl acrylate and ethyl acrylate are members of the mixture. Very particular, methyl methacrylate and ethyl acrylate are members of the mixture.

The further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacry- late, is for example in regard the C3-C18 alkyl linear or branched and the alkyl is for example n-propyl, 1 -methyl-ethyl, n-butyl, 1 -methyl-propyl, 2-methyl-propyl, 1 ,1 -dimethyl- ethyl, n-pentyl, 1 -methyl-butyl, 3-methyl-butyl, n-hexyl, 1 -methyl-pentyl, 2-methyl- pentyl, 4-methyl-pentyl, 2-ethyl-butyl, n-heptyl, 1-methyl-hexyl, n-octyl, 1-methyl-heptyl, 2-ethyl-hexyl, 5,5-dimethyl-hexyl, 1 ,1 ,3,3-tetramethyl-butyl, n-nonyl, 2-ethyl-heptyl, n- decyl, undecyl, n-dodecyl, tridecyl, tetradecyl, pentadecyl, n-hexadecyl or n-octadecyl. A mixture of further acrylate esters is also suitable. Preferred is C3-Ci2-alkyl, in particular C3-Cs-alkyl and very particular C4-alkyl.

Preferably, the amount of the further acrylate ester is from 0 to 15 parts by weight, in particular from 0 to 8 parts by weight and very particular from 0 to 4 parts by weight, wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100.

The crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups, is for example an alkanediol diacrylate like butanediol diacrylate, a polyethylene glycol diacrylate, an alkane triol triacrylate, pentaerythritol tetracrylate, allyl acrylate or allyl methacrylate, a divinylbenzene, 2,4,6-triallyloxy-1 ,3,5-triazine, methylene bis(acrylamide) [=N-[(prop-2-enoylamino)methyl]prop-2-enamide] or methylene bis(methacrylamide). A mixture of crosslinking monomers is also suitable.

Preferably, the amount of the crosslinking monomer is from 0 to 2 parts by weight, in particular from 0 to 0.9 parts by weight and very particular from 0 to 0.25 parts by weight, wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100.

The acid group of the acid monomer is for example a carboxylic acid group, a sulfonic acid group or a phosphonic acid group. Examples for the acid monomer, which contains one ethylenically unsaturated group and at least one acid group, are acrylic acid, methacrylic acid, itaconic acid, crotonic acid (trans-butenoic acid), isocrotonic acid (cis- butenoic acid), vinylacetic acid, (E)-4-methoxy-4-oxo-but-2-enoic acid, (Z)-4-ethoxy-4- oxo-but-2-enoic acid, vinyllactic acid, maleic acid, 2-methylmaleic acid, aconitic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, para-vinylphenyl sulfonic acid, meta-vinyl sulfonic acid, ortho-vinylphenyl sulfonic acid or vinyl phosphonic acid. A mixture of acid monomers is also suitable. Dependent on the pH value, the acid group can be deprotonated to be in the form of an anion, which forms with a cationic counterion a salt. The cationic coun- terion is for example a sodium ion, a potassium ion, a magnesium ion, a calcium ion, ammonium or an alkylated ammonium. Dependent on the pH value, an acid monomer, which possesses at least two acid groups, which structurally allows a cyclic anhydride form, can be in its cyclic form. This is for example the case at maleic acid, itaconic acid or aconitic acid. Preferably, the acid group is a carboxylic acid group. Preferred is an α,β-ethylenically unsaturated C3-C6 carboxylic acid, in particular acrylic acid, methacrylic acid or itaconic acid, very particular acrylic acid or methacrylic acid.

Preferably, the amount of the acid monomer is from 0 to 2 parts by weight, in particular from 0 to 0.9 parts by weight and very particular from 0 to 0.25 parts by weight, wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100.

The further monomer, which contains an ethylenically unsaturated group and which is different to the acrylate ester, the further acrylate ester, the crosslinking monomer or the acid monomer, is for example a vinylaromatic compound such as styrene or me- thylstyrene, an ethylenically unsaturated carboxamide such as acrylamide or methac- rylamide, an ethylenically unsaturated carbonitrile such as acrylonitrile or methacryloni- trile, a vinyl ester of a saturated Ci-Ci8-carboxylic acid such as vinyl acetate, a cycloal- kyl acrylate, a cycloalkyl methacrylate, an allyl ester of a saturated carboxylic acid, a vinyl ether, a vinyl ketone, a dialkyl ester of an ethylenically unsaturated dicarboxylic acid, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, a N,N-dialkylaminoalkyl- acrylamide, a Ν,Ν-dialkylaminoalkylmethacrylamide, a Ν,Ν-dialkylaminoalkyl acrylate, a Ν,Ν-dialkylaminoalkyl methacrylate, ureido methacrylate, ureido acrylate, glycidyl acrylate, glycidyl methacrylate, vinyl chloride, vinylidene chloride, an alkene such as ethylene or propylene including a conjugated aliphatic diene such as butadiene or iso- prene, or a cycloalkene such as cyclohexene including a conjugated aliphatic cy- clodiene such as cyclopentadiene. A mixture of further monomers is also suitable. Pre- ferred is styrene or methylstyrene, an ester of vinyl alcohol and a C1-C15 monocarbox- ylic acid, a C5-C10 cycloalkyl acrylate, a C5-C10 cycloalkyl methacrylate, di(Ci-Cio alkyl) maleinate, di(Ci-Cio alkyl) fumarate, an ethylenically unsaturated C3-Cs-mono- carbonitrile, an ethylenically unsaturated C4-C8-dicarbonitrile, an ethylenically unsatu- rated C3-C8 monocarboxamide, an ethylenically unsaturated C4-C8 dicarboxamide, ureido methacrylate, ureido acrylate, glycidyl acrylate, glycidyl methacrylate, alkene, a cycloalkane or a conjugated aliphatic C4-C9 diene.

Preferably, the amount of the further monomer is from 0 to 5 parts by weight, in particu- lar from 0 to 3 parts by weight and very particular from 0 to 2 parts by weight, wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100.

Especially preferred is an aqueous dispersion of a polymer P, which is obtainable by radically initiated aqueous emulsion polymerization of

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate,

(ii) 0 to 20 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate,

in the presence of an initial ligninsulfonic acid in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and one member of the at least two members of the mixture is ethyl acrylate or ethyl methacrylate,

(ii) 0 to 20 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate, (iii) 0 to 5 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups,

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and two members of the at least two members of the mixture are methyl methacrylate and ethyl acrylate,

(iv) 0 to 5 parts by weight of an acid monomer, which contains one ethyleni- cally unsaturated group and at least one acid group,

(i) at least 85 parts by weight of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate,

(ii) 0 to 15 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate,

(iii) 0 to 2 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups, (iv) 0 to 2 parts by weight of an acid monomer, which contains one ethyleni- cally unsaturated group and at least one acid group,

(v) 0 to 5 parts by weight of a further monomer, which contains an ethyleni- cally unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv),

(i) at least 90 parts by weight of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate, (ii) 0 to 8 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate,

(iii) 0 to 2 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups,

(iv) 0 to 0.9 parts by weight of an acid monomer, which contains one eth- ylenically unsaturated group and at least one acid group,

(v) 0 to 3 parts by weight of a further monomer, which contains an ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv),

(i) at least 96 parts by weight of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate,

(ii) 0 to 4 parts by weight of a further acrylate ester, which is a C3-C18 alkyl acrylate or a C3-C18 alkyl methacrylate,

(iii) 0 to 0.25 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups,

(iv) 0 to 0.25 parts by weight of an acid monomer, which contains one ethylenically unsaturated group and at least one acid group,

(v) 0 to 2 parts by weight of a further monomer, which contains an ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv), wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100,

in the presence of an initial ligninsulfonic acid in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the mono- mers (i) to (v).

(iii) 0 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups,

(iv) 0 parts by weight of an acid monomer, which contains one ethylenically unsaturated group and at least one acid group,

(v) 0 parts by weight of a further monomer, which contains an ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv),

in the presence of an initial ligninsulfonic acid in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v). Ligninsulfonic acid herein refers to ligninsulfonic acid itself and salts thereof. The reason is that dependent on the pH value of the aqueous environment, ligninsulfonic acid is in its acid form or partly up to completely deprotonated as a ligninsulfonate salt. Typical cationic counterions of the ligninsulfonate salts are sodium, ammonium, calcium or magnesium. Preferably, ligninsulfonic acid is present as a salt, especially as sodium or calcium ligninsulfonate. Typically, ligninsulfonic acid salts are formed during sulfite pulping of wood, wherein sulfonation takes place at some of the C3-side chains of the formal phenylpropane-based units of lignin. For example, literature provides a range of around 2 sulfonic acids groups per 5 to 8 phenylpropane units and for example a range of a molecular weight of 10000 to 200000 g/mol. Ligninsulfonate salts are a major component of sulfite pulping wastes, from which ligninsulfonic acid or its salts can be isolated and purified.

The amount of initial ligninsulfonic acid as well as the amount of additional ligninsulfonic acid is calculated based on ligninsulfonic acid. It is understood that there is only very small difference to a calculation based on the completely deprotonated ligninsulfonate polyanion and a small difference to a calculation based on a ligninsulfonate metal salt, wherein the metal is ammonium, sodium, magnesium or calcium. In a case of doubt, the value calculated for ligninsulfonic acid is decisive.

The radically initiated aqueous emulsion polymerization of the monomer (i) and the other monomers (ii) to (v) takes place in the presence of an initial ligninsulfonic acid in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v). Preferably, the amount of initial ligninsulfonic acid is from 10 to 65 parts by weight, in particular from 10 to 45 parts and very particular from 12 to 40 parts by weight.

Preferably, the amount of the additional ligninsulfonic acid, which is added after the generation of the aqueous dispersion of the polymer P, is from 0 to 55 parts by weight, especially 0 to 45 parts by weight and very especially 0 to 35 parts by weight, based on the sum total of the parts by weight of the monomers (i) to (v).

Preferably, the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 10 to 65 parts by weight, especially 20 to 65 parts by weight and very especially 20 to 45 parts by weight, based on the sum total of the parts by weight of the monomers (i) to (v).

Preferably, the amount of initial ligninsulfonic acid is from 10 to 65 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 55 parts by weight and the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 20 to 65 parts by weight based on the sum total of the parts by weight of the mon- omers (i) to (v).

Preferably, the amount of initial ligninsulfonic acid is from 10 to 45 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 35 parts by weight and the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 20 to 45 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

The radically initiated aqueous emulsion polymerization of the monomer (i) and the other monomers (ii) to (v) in the presence of the initial ligninsulfonic acid comprises the steps of providing the monomers and the initial ligninsulfonic acid, of emulsifying the monomers in an aqueous medium and of polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid. The steps of providing the monomers and the initial ligninsulfonic acid, of emulsifying the monomers in an aqueous medium and of polymerizing the monomers in the presence of a free-radical initia- tor and the initial ligninsuflonic acid can be conducted in parallel. For example, parts or all of the monomers to be polymerized are fed over a certain time to a reactor, where emulsification in an aqueous medium and polymerization already takes place. The step of polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid takes place preferably in a reactor. The medium for polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid contains water. The aqueous medium for emulsifying the monomers forms typically at least a part of the medium for polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid. Preferably, the initial ligninsulfonic acid is already in the aqueous medium of the reactor prior to addition of the monomers. The monomers are emulsified during the radically initiated aqueous emulsion polymerization in an aqueous medium, i.e. they are dispersed in the aqueous medium supported for example by external stirring of the resulting mixture. The emulsifying of the monomers in an aqueous medium can take place in the same reactor, where the polymerizing occurs, or can be conducted in a separate apparatus with a subsequent transfer of the at least partly emulsified monomers to the reactor, where the polymerizing occurs. In the latter situation, the emulsification of the monomers continues in the reactor, where the polymerizing occurs.

Preferably, the majority of the monomers is present in a liquid state at the radically in i- tiated aqueous emulsion polymerization once polymerizing occurs.

The aqueous medium contains for example water, which is demineralized. The aqueous medium can contain a further solvent as diluent or to modify the solubility of the monomers. The further solvent is non-polymerizable under the applied conditions, liq- uid at 21 °C and at 101 .32 kPa, and is for example an alcohol such as methanol, etha- nol, n-propanol, isopropanol, n-butanol or isobutanol, or a ketone such as acetone, methyl ethyl ketone, diethyl ketone or isobutyl methyl ketone. A mixture of further solvents is also suitable. Preferred is an aqueous medium, which content of a further solvent is below 10% by weight based on the overall amount of water and the further sol- vent in the radically initiated aqueous emulsion polymerization, in particular below 1 %.

A non-polymerizable component in the radically initiated aqueous emulsion polymerization is understood as a component, which does not act as a monomer for the polymer P under the conditions of an aqueous radically initiated emulsion polymerization, i.e. even if the component is covalently incorporated into the polymer P, the polymer chain growth is stopped by the component. In contrast, a monomer for the polymer P enables after its covalent incorporation a further polymer chain growth, i.e. the reaction with a further monomer. In order to promote the dispersing of the monomers in the aqueous medium, a dispersing auxiliary, which is different to ligninsulfonic acid, can be used. The dispersing auxiliary serves also to support the stabilization of the aqueous dispersion of the polymer P by keeping the formed particles of the polymer P dispersed. A dispersing auxiliary is an emulsifier, a protective colloid or a mixture of both of them. The emulsifier and the protective colloid are differentiated by their weight-average molar mass M_w. An emulsifier has a weight-average molar mass M_w in general below 2000, while the weight-average molar mass M_w of the protective colloid may be up to 50 000, in particular from above 2000 to up to 50000. Preferably, the dispersing auxiliary is an emulsifier.

A suitable emulsifier is a surface-active substance. An emulsifier is non-ionic, anionic, or cationic. In case of employing a mixture of emulsifiers, their compatibility has to assured, which can be evaluated in case of doubt by preliminary tests. Typically, an anionic emulsifier is compatible with another anionic emulsifier or a non-ionic emulsifier. Similarly, a cationic emulsifier is typically compatible with another cationic emulsifier or a non-ionic emulsifier.

A non-ionic emulsifier is for example an ethoxylated C8-C36 fatty alcohol having a degree of ethoxylation of from 3 to 50 (= ethylene oxide units [EO]: 3-50), an ethoxylated mono-, di- and tri-C4-Ci2 alkylphenol having a degree of ethoxylation of from 3 to 50. A customary nonionic emulsifier is for example an Emulgin B grade (a cetyl/stearyl alcohol ethoxylate, RTM BASF), a Dehydrol LS grade (a fatty alcohol ethoxylate, EO units: 1-10, RTM BASF), a Lutensol A grade (a Ci₂Ci₄-fatty alcohol ethoxylate, EO units: 3-8, RTM BASF), a Lutensol AO grade (a C13C15-OXO alcohol ethoxylate, EO units: 3-30), a Lutensol AT grade (a Ci6Cis-fatty alcohol ethoxylate, EO units: 1 1-80), a Lutensol ON grade (a Cio-oxo alcohol ethoxylate, EO units: 3-1 1 ) or a Lutensol TO grade (a C13-OXO alcohol ethoxylate, EO units: 3-20).

An anionic emulsifier is for example an alkali metal salt of a dialkyl ester of sulfosuccin- ic acid, an alkali metal ion or ammonium salt of a C8-C12 alkyl sulfate, an alkali metal ion or ammonium salt of a C12-C18 alkylsulfonic acid, an alkali metal ion or ammonium salt of a C9-C18 alkylarylsulfonic acid, a sulfuric acid monoester of an ethoxylated C12- C18 alkanol (EO units: 4-30) or a sulfuric acid monoester of an ethoxylated (C4-C12 al- kyl)phenol (EO units: 3-50).

As further anionic emulsifiers, compounds of the general formula I

wherein R^a and R^b are each a H atom or C₄-C2₄-alkyl and are not both H atoms at the same time, and Mi⁺ and M₂ ⁺ can be alkali metal ions and/or ammonium, are also useful. In the general formula I, R^a and R^b are preferably linear or branched alkyl radicals having from 6 to 18 carbon atoms, in particular 6, 12 or 16 carbon atoms, or hydrogen atoms, where R^a and R^b are not both hydrogen atoms at the same time. Mi⁺ and M2⁺ are preferably sodium, potassium or ammonium, with sodium being particularly preferred. A compound of general formula I, in which Mi⁺ and M2⁺ are both sodium, R^a is a branched alkyl radical having 12 carbon atoms and R^b is hydrogen or R^a is particularly advantageous. Use is frequently made of industrial mixtures which have a proportion of from 50 to 90% by weight of the monoalkylated product, for example Dowfax^® 2A1 (RTM The Dow Chemical Corp.). The compounds of general formula I are commonly known, e.g. from US-A 4 269 749, and commercially available.

A comprehensive description of suitable emulsifiers may be found in Houben-Weyl, Methoden der organischen Chemie, volume XIV/1 , Makromolekulare Stoffe, Georg- Thieme-Verlag, Stuttgart, 1961 , pages 192 to 208.

Similar to an emulsifier, a protective colloid is non-ionic, anionic or cationic. A protective colloid is for example a polyvinyl alcohol), a poly(alkylene glycol), poly(acrylic acid) or an alkali metal salt thereof, a poly(methacrylic acid) or an alkali metal salt thereof or a gelatin derivative. An anionic protective colloid can also be a copolymer, which is different to the polymer P, containing at least one of acrylic acid, methacrylic acid, ma- leic acid, 2-acrylamido-2-methylpropane sulfonic acid, para-vinylphenyl sulfonic acid and salt forms thereof, preferably an alkali metal salt thereof, in polymerized form. A cationic protective colloid is for example a homopolymer or a copolymer, which is different to the polymer P, and the N-protonated or N-alkylated derivative of a homopolymer or a copolymer of N-vinylpyrrolidone, N-vinylformamide in its at least partly hydro- lysed form, N-vinylacetamide in its at least partly hydrolysed form, N-vinylcarbazole, 1- vinylimidazole, 2-vinylimidazole, 2-vinylpyridine, 4-vinylpyridine or an amine-group- bearing acrylate, methacrylate, acrylamide or methacrylamide, wherein the nitrogen of the amine-group is protonated at a pH below 7 or is permanently positively charged, for example by alkylation.

A comprehensive description of suitable protective colloids may be found in Houben- Weyl, Methoden der organischen Chemie, volume XIV/1 , Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961 , pages 41 1 to 420.

Preferably, the radically initiated aqueous emulsion polymerization occurs in the presence of the initial ligninsulfonic acid and a dispersing aid, which is different to ligninsul- fonic acid and which is an emulsifier, in particular an anionic emulsifier and very particular an anionic emulsifier with a weight-average molar mass M_w below 1000. Preferably, the radically initiated aqueous emulsion polymerization occurs in the presence of less than 2 parts by weight of a protective colloid different to ligninsulfonic acid, in particular in the absence of a protective colloid different to ligninsulfonic acid. The parts by weight are based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100 parts. For polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid, the aqueous medium is preferably heated to the temperature at which the polymerization of the monomers is to take place or to a temperature which is, for example, from 5 to 20°C below the polymerization temperature. The free-radical initiator can be fed in parallel to the monomers or for example parts of the free-radical initiator are added initially at once, for example 15% or 30% by weight of the overall amount of the free-radical initiator. For example, as soon as the polymerization temperature desired is reached or within a time span of from 1 to 15 minutes, preferably from 5 to 15 minutes, after the polymerization temperature is reached, the metering of the monomers to be polymerized is started. They can be fed continuously within, for example, from 60 minutes to 10 hours, in general within from 2 to 4 hours. It is also possible for example for 1 % to 10% by weight of all or parts of the monomers to be included in the initial charge in addition to the free-radical initiator and the initial ligninsulfonic acid. The remaining monomers and the remaining initiator are then metered separately into the initial charge under polymerization conditions after the polymerization has started.

The temperature for polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid is chosen at least so high that the specifically em- ployed free-radical initiator generates free radicals. Other criteria for the temperature might apply in addition. The temperature is for example from 50 to 130°C, in particular from 60 to 100°C. The polymerizing of the monomers can be carried out under a pressure, which is above atmospheric pressure, for example at pressures up to 15 bar, for example in the range from 2 to 10 bar.

The polymerizing of the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid can be conducted under exclusion of oxygen, for example under an inert atmosphere such as nitrogen. Additionally, other steps of the radically initiated aqueous emulsion polymerization can be conducted under exclusion of oxygen, especially the step of emulsifying the monomers in an aqueous medium.

A free-radical initiator forms free radicals under the reaction conditions used in the radically initiated aqueous emulsion polymerization. A free-radical initiator is for example a peroxodisulfate, a peroxosulfate, an azo initiator, an organic peroxide, an organic hy- droperoxide, hydrogen peroxide or a redox initiator system, which consists of at least one reducing agent and an oxidizing agent. It is understood that the free radical initiator can also be a high-energy radiation such as electron beams or irradiation with UV light, which leads to transformation of components at the radically initiated aqueous emulsion polymerization into free radicals. A mixture of free radical initiators is also suitable. An example of a peroxodisulfate is sodium peroxodisulfate, potassium peroxodisulfate or ammonium peroxodisulfate. An example of a peroxosulfate is sodium peroxosulfate, potassium hydrogenperoxosulfate or potassium peroxosulfate. An example for an azo initiator is 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl- valeronitrile), 2,2'- azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(isobutyro- nitrile), 2,2'-azobis(2-methylbutyronitrile) or 2,2^'-azobis(N,N'-dimethyleneisobutyr- amidine) dihydrochloride. An example for an organic peroxide is dibenzoyl peroxide, tert-butyl perpivalate, tert-butyl-per 2-ethylhexanoate, di-tert-butyl peroxide, diamyl peroxide, dioctanoyl peroxide, didecanoyl peroxide, dilauroyl peroxide, bis(o-toluyl) peroxide, succinyl peroxide, tert-butyl peracetate, tert-butyl permaleate, tert-butyl perisobu- tyrate, tert-butyl peroctanoate or tert-butyl perbenzoate. An example of an organic hydroperoxide is tert-butyl hydroperoxide. An example of a redox initiator system's oxidiz- ing agent is the above mentioned free radical initiator with the exception of high-energy radiation. An example of a redox initiator's reducing agent is an alkali metal salt of sul- furous acid such as sodium sulfite or sodium hydrogen sulfite, an alkali metal salt of disulfurous acid such as sodium disulfite, an bisulfite adduct of an aliphatic aldehyde or ketone such as acetone bisulfite, hydroxymethanesulfinic acid and salts thereof or ascorbic acid. The redox initiator system can be used with concomitant use of a soluble metal compound, whose metallic component can occur in a plurality of valency states. An example for a redox initiator system is ascorbic acid/iron(ll) sulfate/sodium perox- odisulfate, tert-butyl hydroperoxide/sodium disulfite, tert-butyl hydroperoxide/sodium hydroxymethanesulfinic acid or tert-butyl hydroperoxide/ascorbic acid. The individual components, for example the reducing agent, may also be a mixture such as a mixture of the sodium salt of hydroxymethanesulfinic acid and sodium disulfite.

The free-radical initiator is preferably used in the form of an aqueous solution, the lower concentration being determined by the amount of water acceptable in the final disper- sion and the upper concentration by the solubility of the relevant free-radical initiator in water. Preferred is a water-soluble free-radical initiator, in particular a hydroperoxide and very particular hydroperoxide in a redox initiator system.

The free-radical initiator is used for example in an amount - unless it is high energy radiation - of up to 2 parts by weight, preferably of at least 0.1 parts by weight, in particular from 0.1 to 1.5 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100.

In the radically initiated aqueous emulsion polymerization, the step of polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid can be followed by a step of removing residual, unreacted monomers. The removal of residual, unreacted monomers is conducted until the desired residual amount of one or more of the employed monomers is achieved. The step of removal of residual, unreacted monomers can be for example an aftertreating of the polymerized monomers with a further radical initiator or an aftertreating of the aqueous dispersion of polymer P by distillation, for example steam distillation. At aftertreating of the polymerized monomers with a further radical initiator, the initially formed reaction product, i.e. the pol- ymerized monomers (i) to (v) and the initial ligninsulfonic acid, is subjected to an after- treatment after the actual polymerization and is reacted with a further radical initiator. This further radical initiator can be the free-radical initiator of the step of polymerizing the monomers or a different free-radical initiator. Preferably, the further radical initiator generates nonionic radicals, in particular hydroxyl radicals or alkoxy radicals. A hydrox- yl radical is formed for example from hydrogen peroxide or an organic hydroperoxide. An alkoxy radical is formed for example from an organic alkyl peroxide. A further radical initiator, which forms non-ionic radicals, is for example hydrogen peroxide, dibenzo- yl peroxide, tert-butyl perpivalate, tert-butyl per-2-ethylhexanoate, di-tert-butyl peroxide, diamyl peroxide, dioctanoyl peroxide, didecanoyl peroxide, dilauroyl peroxide, bis(o- toluyl) peroxide, succinyl peroxide, tert-butyl peracetate, tert-butyl permaleate, tert-butyl perisobutyrate, tert-butyl per-n-octanoate, tert-butyl perbenzoate or tert-butyl hydroperoxide. A further radical initiator is preferably a peroxide compound, which is hydrogen peroxide, an organic hydroperoxide or an organic peroxide. Particularly preferred is a redox initiator system comprising the further radical initiator, which is a peroxide compound, which is hydrogen peroxide, an organic hydroperoxide or an organic peroxide, as oxidizing agent in combination with an inorganic or organic reducing agent. An inorganic or organic reducing agent is for example an alkali metal salt of sulfurous acid such as sodium sulfite or sodium hydrogen sulfite, an alkali metal salt of disulfurous acid such as sodium disulfite, a bisulfite adduct of an aliphatic aldehyde and a ketone such as an acetone bisulfite or a salt thereof or hydroxylmethanesulfinic acid or a salt thereof, or ascorbic acid. The redox initiator systems for the aftertreatment can be used with concomitant use of a soluble metal compound, whose metallic component may occur in a plurality of valency states. A redox initiator system for the aftertreatment is for example tert-butyl hydroperoxide/sodium disulfite, tert-butyl hydroperoxide/sodium hydroxymethanesulfinic acid or tert-butyl hydroperoxide/ascorbic acid. The redox initiator system's oxidizing agent or reducing agent may also be a mixture, for example a mixture of the sodium salt of hydroxymethanesulfinic acid and sodium disulfite. Especially preferred is a further radical initiator, which is a redox initiator system of hydrogen peroxide/ascorbic acid or of tert-butyl hydroperoxide/ascorbic acid.

The amount of a further radical initiator, which is used for the aftertreatment, is for example from 0.001 to 0.5 parts by weight, in particular from 0.002 to 0.1 parts by weight, based on the sum total of the parts by weight of the monomers (i) to (v), which is al- ways 100.

The addition of the further radical initiator for the aftertreatment is effected after the main polymerization of the monomers has taken place, i.e. after for example more than 70% by weight, in particular at least 90% by weight, very particularly 100% by weight, of all monomers have been added and more than 70% by weight, in particular at least 90% by weight, very particularly at least 95% of all monomers have undergone polymerization in the presence of a free-radical initiator. The aftertreatment with the further radical initiator is preferably effected at a temperature of at least 55°C, for example at 55°C to 130°C, in particular of at least 65°C, for example at 65°C to 85°C.

Preferred is a step of removing residual, unreacted monomers, which is an aftertreating of the polymerized monomers with a further radical initiator. Especially preferred is at this step a further radical initiator, which is hydrogen peroxide, an organic hydroperoxide or an organic peroxide. In particular, the further radical initiator is a redox initiator system of hydrogen peroxide/ascorbic acid or of tert-butyl hydroperoxide/ascorbic acid. The radically initiated aqueous emulsion polymerization can also be conducted in the presence of a polymer seed. A polymer seed is an aqueous dispersion of finely divided polymer particles. The weight average particle diameter of the polymer particles of the polymer seed is for example not more than 80 nm, particularly not more than 60 nm, very particularly not more than 50 nm or not more than 40 nm, especially preferred in the range from 20 to 40 nm. Determining the weight average particle diameter is known to a person skilled in the art and is effected for example via the method of an analytical ultracentrifuge. Weight average particle diameter herein is the weight average D_wso value determined by the method of the analytical ultracentrifuge (cf. S.E. Harding et al., Analytical Ultracentrifugation in Biochemistry and Polymer Science, Royal Society of Chemistry, Cambridge, Great Britain 1992, Chapter 10, Analysis of Polymer Dispersions with an Eight-Cell-AUC-Multiplexer: High Resolution Particle Size Distribution and Density Gradient Techniques, W. Maechtle, pages 147 to 175). It is advantageous for the polymer seed used to be monomodal and to have a narrow particle size distribution. Narrow particle size distribution herein is to be understood as meaning that the ratio of the weight average particle diameter D_wso and number average particle diameter DN5O determined by the method of the analytical ultracentrifuge [D_W5O/DNSO] is not more than 2.0, preferably not more than 1.5 and more preferably not more than 1.2 or not more than 1.1 . Preparing a polymer seed is known to a person skilled in the art and is typically effected by initially charging a relatively small amount of monomers and a relatively large amount of emulsifiers together with deionized water in a reaction vessel and adding a sufficient amount of polymerization initiator at the reaction temperature. The preference according to the present invention is for the use of a polymer seed having a glass transition temperature of not less than 50°C, particularly not less than 60°C, very particularly not less than 70°C, especially not less than 80°C or not less than 90°C. Glass transition temperature for the polymer seed is determined by the norm ISO 1 1357-2. Particular preference is given to a polystyrene polymer seed or to a poly(methyl methacrylate) polymer seed. The amount of the polymer seed is based on the polymer solids content of the aqueous polymer seed dispersion. It is therefore reported as parts by weight of polymer seed solids per the sum total of the parts by weight of the monomers (i) to (v), which is always 100. Preferably, a polymer seed is used in an amount of 0.1 to 4 parts by weight and more preferably 1 to 3 parts by weight of the monomers (i) to (v). The polymer seed can partly or completely be charged to the aqueous medium prior to addition of the monomers, with the remainder if any, being added in the course of polymerizing the monomers. Preferably, all of the polymer seed is initially charged to the aqueous medium prior to polymerizing the monomers.

Preferred is a radically initiated aqueous emulsion polymerization, wherein a polymer seed is present during the polymerizing of the monomers in the presence of a free- radical initiator and the initial ligninsulfonic acid. In order to modify the properties of the resulting polymer P, a chain transfer agent can be present during the radically initiated aqueous emulsion polymerization. In the presence of the chain transfer agent, a polymer which has a lower weight-averaged molar mass and a smaller K value is obtained in comparison to the polymer obtained in the absence of the chain transfer agent. The K value can be determined in 5% strength aqueous sodium chloride solution at pH 7, 25°C and a polymer concentration of 0.1 % by weight according to H. Fikentscher, Cellulose-Chemie, volume 13, 58-64 and 71-74 (1932). A chain transfer agent is for example a non-polymerizable sulfur-containing organic compound, which is free of a sulfur-oxygen-bond or wherein the sulfur atom is not part of a heterocylic ring, an aldehyde, which is free of a carbon-carbon double bond, a non-polymerizable carboxylic acid, a non-polymerizable alcohol or a non- polymerizable phosphor-containing compound. An example for a non-polymerizable sulfur-containing organic compound, which is free of a sulfur-oxygen-bond or wherein the sulfur atom is not part of a heterocylic ring, is dodecyl mercaptan, thiodiglycol, ethylthioethanol, di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide, diisopropyl disul- fide, 2-mercaptoethanol, 1 ,3-mercaptopropanol, 3-mercaptopropane-1 ,2-diol, 1 ,4- mercaptobutanol, thioglycolic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, thioacetic acid or thiourea. Dodecyl mercaptan is a member of the class of alkyl thiols. An example for an aldehyde, which is free of a carbon-carbon double bond, is formaldehyde, acetaldehyde or propionaldehyde. An example for a non-polymerizable car- boxylic acid is formic acid or a salt thereof such as sodium formate or ammonium formate. An example for a non-polymerizable alcohol is isopropanol or 2-butanol. An example for a non-polymerizable phosphorous compound is sodium hypophosphite. A mixture of chain transfer agents is also suitable. If a chain transfer agent is used in the radically initiated aqueous emulsion polymerization, the amount is typically 0.01 to 3, preferably from 0.1 to 1.0 parts by weight based on sum total of the parts by weight of the monomers (i) to (v), which is always 100. The chain transfer agent can be initially added to the aqueous medium prior to the monomers, metered into the polymerization together with or separately from the monomers during the radically initiated aqueous emulsion polymerization or portioned between these variants. Preferably, the chain transfer agent is metered into the monomers. The pH value of the aqueous medium at the polymerizing of the monomers in the presence of a free-radical initiator and the initial lignosulfonic acid is for example in the range from 2 to 7, in particular from 3 to 6 and very particular from 4 to 5. As previously mentioned, monomers and other components in the radically initiated aqueous emul- sion polymerization, which comprise acid groups, can be present in the radically initiated aqueous emulsion polymerization in the form of their free acids and in specific cases in an anhydride form, or partially or completely neutralized in a salt form depending on the pH value. Adjustments of the pH value of the aqueous medium are preferably conducted with an alkali metal hydroxide solution or ammonia solution. Preference is given to use aqueous sodium hydroxide solution, aqueous potassium hydroxide solution or ammonia solution as a neutralizing agent.

After the step of polymerizing the monomers in the presence of a free-radical initiator and the initial ligninsulfonic acid and the optional step of removing residual, unreacted monomers, the reaction product can be filtered to remove possible coagulum from the aqueous dispersion of the polymer P.

At the end of the radically initiated aqueous emulsion polymerization, the pH value of the aqueous dispersion of the polymer P can be adjusted, for example to a pH value of between 6 and 10, in particular between 6 and 8.

In the aqueous polymer dispersion of the polymer P, the dispersed particles of the polymer P have an average particle diameter of preferably 85 to 500 nm, in particular of 90 to 450 nm and especially of 100 to 350 nm. The average particle diameter of the polymer particles can be determined by dynamic light scattering on a 0.005% to 0.01 % by weight aqueous polymer dispersion at 23°C by means of an Autosizer IIC from Malvern Instruments, England and be based on the cumulant z-average diameter of the measured autocorrelation function as per ISO standard 13321 . A biocide can be added to the aqueous dispersion of a polymer P to inhibit microbial activity. A biocide is for example 1 ,2-benzisothiazol-3(2H)-one, 2-methyl-4-isothiazolin- 3-one or 5-chloro-2-methyl-4-isothiazolin-3-one. A mixture of biocides is also suitable.

The solids content of the aqueous polymer dispersion of the polymer P, which includes the initial ligninsulfonic acid, is for example in the range from 20% to 80%, in particular in the range from 40% to 70% by weight, in particular from 40 to 60% by weight. The corresponding solids content can be effected for example through appropriate adjustment of the amount of aqueous medium in relation to the monomers, the initial ligninsulfonic acid and other components in the radically initiated aqueous emulsion polymerization. The aqueous dispersion of the polymer P, which is polymerized in the presence of the initial ligninsulfonic acid, possesses a glass transition temperature once it is dried, for example when a film is formed. The glass transition temperature can be determined by differential scanning calorimetry, in particular the norm ISO 1 1357-2. This measured glass transition temperature is lower than a calculated glass transition temperature of a polymer, which is based on the same monomers as the polymer P and polymerized under the same conditions but in the absence of the initial ligninsulfonic acid. The presence of the initial ligninsulfonic acid shows a plasticizer effect in regard to the glass transition temperature.

The Fox equation can be used for the calculation of the glass transition of the polymer, i.e. in the absence of initial lignosulfonate during polymerization. After Fox (T.G. Fox, Bull. Am. Phys. Soc. 1956 [Ser. I I] 1 , page 123 and according to Ullmann's Ency- clopadie der technischen Chemie, vol. 19, page 18, 4^th edition, Verlag Chemie, Wein- heim, 1980), the reciprocal of the glass transition temperature of uncrosslinked or lightly crosslinked copolymers is given to a good approximation by:

1/Tg = X /Tg¹ + X²/Tg2 + .... Xⁿ/T_g",

where x¹ , x², .... xⁿ are the mass fractions of the monomers 1 , 2, .... n constructing the polymers A and B and T_g ¹ , T_g ², .... T_g ⁿ are the glass transition temperatures, in degrees Kelvin, of the homopolymers each constructed of only one of the monomers 1 , 2, .... n. The mass fractions are based on the sum total of all monomers from which the polymers A and B of the polymer mixture are constructed.

The T_g values of the homopolymers of most monomers are known and listed for example in Ullmann's Encyclopedia of Industrial Chemistry, vol. 5, A21 , page 169, VCH Weinheim, 1992; further sources of glass transition temperatures of homopolymers are for example J. Brandrup, E.H . Immergut, Polymer Handbook, 1 ^st Ed., J. Wiley, New York 1966, 2^nd Ed. J.Wiley, New York 1975, and 3^rd Ed. J. Wiley, New York 1989).

The glass transition temperatures of the dried aqueous polymer dispersions D1 to D7, D12 and D13 as shown in the experimental part in table 2-A provide starting points for choosing the monomers and the amount of initial ligninsulfonic acid.

Preferred is a process, wherein the monomers (i), (ii), (iii), (iv) and (v) and the amount of initial ligninsulfonic acid are chosen in a way, that the dried aqueous dispersion of the polymer P, which is polymerized in the presence of the initial ligninsulfonic acid, possesses a glass transition temperature in the range from 0°C to 70°C as determined by the norm ISO 1 1357-2. In particular, the glass transition temperature is in the range from 0°C to 60°C, especially from 5°C to 45°C and very especially from 5 to 35°C. Preferably, the combined amount of the initial ligninsulfonic acid and an additional ligninsulfonic acid, which is added after the generation of an aqueous dispersion of a polymer P, is from 10 to 65 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. In particular, the combined amount is from 10 to 45 parts by weight and very particular from 12 to 40 parts by weight. Accordingly adjusted to the combined amount, the amount of additional ligninsulfonic acid is preferably from 0 to 55 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. In particular, the amount of additional ligninsulfonic acid is from 0 to 35 parts by weight and very particular from 0 to 28 parts by weight.

Preferred is a process, wherein the amount of initial ligninsulfonic acid is from 10 to 65 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 55 parts by weight and the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 10 to 65 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. An inorganic pigment is for example a metal salt, in particular a calcium sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, an aluminate, a silicate, an aluminum oxide, a titanium dioxide, a zinc oxide, a zinc sulfide, a silicon dioxide or an argillaceous earth, which is different to the aforementioned substances. A mixture of inorganic pigments is also suitable. Preferred is an inorganic pigment, which is a white pigment. A white pigment is defined herein as a pigment, which has no significant absorption of light at a wavelength of from 400 nm to around 800 nm. Accordingly, a human being perceives the white pigment as colorless. There are several inorganic pigments, which are metal salts, which comprise two or more anionic groups, two or more cationic metals, or both of them. An example thereof is a calcium aluminate sulfate or a two- or three-layered phyllosilicate such as kaolinite, halloysite, talc, montmorillonite, hectorite, nontronite or saponite. Preferred is an inorganic pigment, which is a calcium sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, an aluminate, a silicate, an aluminum oxide, a titanium dioxide, a zinc oxide, a zinc sulfide or a silicon dioxide. Especially preferred is an inorganic pigment, which is a calcium sulfate, a cal- cium aluminate sulfate, a barium sulfate, a magnesium carbonate, a calcium carbonate, silica, alumina, an aluminum hydrate, a silicate, a titanium dioxide, a zinc oxide, a kaolin, a talc or a silicon dioxide. The calcium carbonate may be a natural ground calcium carbonate (GCC), a precipitated calcium carbonate (PCC), a lime or a chalk. Suitable calcium carbonate pigments are available, for example as Covercarb 60 (RTM Omya), Hydrocarb 60 (RTM Omya) or Hydrocarb 90 ME. Other suitable inorganic pigments are also available, for example as Hydrogloss 90 (clay, RTM KaMin) or Finntalc C10 (talc, RTM Mondo Minerals).

Preferably, the inorganic pigment is platelet-shaped. An example of a platelet-shaped pigment is talc, clay or mica. Mica is a specific class of phyllosilicates, which comprises muscovite, paragonite, phlogopite, biotite, lepidolite or margarite. Talc is preferred. Pre- ferred aspect ratios (ratio of length to thickness) are above 2, in particular above 5 and very particular above 10.

Preferably, the amount of the inorganic pigment is from 0 to 35 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. In particular, the amount of the inorganic pigment is from 0 to 20 parts and very particular from 0 to 10 parts.

The coating material is prepared for example by mixing the aqueous dispersion of the polymer P with other optional components. An additional amount of water can be added to adjust the concentration of the coating material for an optimal coating step, for example to adjust the desired viscosity. Further water can be introduced into the coating material from the formulations of the inorganic pigment, for example as aqueous slurry. Further water can also be introduced by the additional ligninsulfonic acid or op- tionally a further auxiliary ingredient in an aqueous formulation. A solids content of the coating material is typically in the range from 10% to 70% by weight based on the coating material, in particular from 20% to 60% by weight and very particular from 40 to 60% by weight. A high solids content is desired to reduce the amount of water, which has to be removed at the drying step of the water-containing layer on the paper or the cardboard. The pH of the paper coating material is preferably adjusted to values of from 6 to 10, in particular from 7 to 9.5.

The coating material contains optionally a further auxiliary ingredient. The optional further auxiliary ingredient, which is different to the aqueous dispersion of the polymer P, ligninsulfonic acid, the inorganic pigment or water, is for example a thickener, a further polymeric binder, an optical brightener, a flow control agent, a further dispersing auxiliary, a surfactant, a lubricant, a further neutralizing agent, a defoamer, a deaerator, a preservative or a dye. A mixture of further auxiliary ingredients is also suitable. A thickener helps to further optimize viscosity and water retention of the coating material. A thickener is for example a cross-linked polyacrylate or a cellulose derivative such as carboxymethylcellulose. A thickener is preferably used in an amount of from 0.01 to 1 , in particular from 0.1 to 0.5 parts by weight, based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. A further polymeric binder can be a starch-based binder or a further emulsion polymer. A starch-based binder is for example a native, a chemically modified or a degraded starch. The chemically modified starch may be a starch ester or a starch ether. For a starch-based binder, preferred is a native starch, in particular native cereal, corn or potato starch. A further emulsion polymer is for example a copolymer of styrene and butadiene or a copolymer of styrene and an acrylate. An optical brightener is for example a stilbene derivative, in particular a di-, tetra- or hexasulfonate bistriazinyl-substituted 4,4'-diaminostilbene. A further dispersing auxiliary is for example an emulsifier or a protective colloid as described at the process for preparing an aqueous dispersion of the polymer P and can be added inde- pendently from a dispersing auxiliary in the process for preparing an aqueous dispersion of the polymer P. A lubricant is for example a stearate such as calcium stearate or a wax. A further neutralizing agent is used to adjust the pH value of the coating material as previously mentioned. The further neutralizing agent can be added independently from a neutralizing agent employed in the process for preparing an aqueous dispersion of the polymer P and is for example sodium hydroxide or ammonium hydroxide. A preservative is for example a further biocide, which can be added independently from a biocide in the process for preparing an aqueous dispersion of the polymer P. A dye is for example an organic pigment with a strong absorption at a wavelength between 400 nm and 800 nm or a soluble compound with a strong absorption at a wavelength between 400 nm and 800 nm.

Preferred is a process, wherein the coating material comprises 0 to 30 parts by weight of a further auxiliary ingredient, which is different to the aqueous dispersion of the pol- ymer P, ligninsulfonic acid, the inorganic pigment or water, based on the sum total of the parts by weight of the monomers (i) to (v), which is always 100. In particular, the coating material comprises 0 to 15 parts by weight of a further auxiliary ingredient, very particular 0 to 10 parts by weight and especially 0 to 5 parts by weight. Paper or cardboard are both common expressions for a plane material produced basically from plant fibers with a grammage for example up to 600 g/m². The expression paper is used typically more for a grammage up to 225 g/m², whereas the expression cardboard is used typically more for a grammage above 150 g/m². The lower limit of the grammage is for example 5 g/m², in particular 20 g/m². The paper surface or a cardboard surface can be uncoated or coated. The process can be applied to provide a single coat, i.e. the barrier layer is the sole coat. The process can also be applied to provide a base coat, i.e. the barrier layer is the basis followed by a further coating, which provides a further layer. The process can also be applied to provide a top coat, i.e. the paper or the cardboard already possess a base coat. Preferably, the process for manufacturing a paper equipped with a barrier layer or a cardboard layer equipped with a barrier layer is preferably applied to an uncoated paper or an uncoated cardboard. In particular, the process provides the barrier layer as the sole coat of the paper or the cardboard. The coating material is applied in general in an amount from 1 to 50 g, preferably from 5 to 30 g based on the solids content of the coating material per square meter of the paper or the cardboard. The coating material can be applied by a customary application method, for example by means of a size press, a film press, a blade coater, an air brush, a knife coater, a curtain coater or a spray coater.

Drying of the water-containing layer on the paper or the cardboard is conducted for example by heating the layer. A film formation is enabled by an evaporation of water and an optional further solvent. The surface temperature of the water-containing layer of the paper or the cardboard during the drying step has to enable a film formation from the water-containing layer. Preferably, the surface temperature during the drying step reaches or exceeds at the water-containing layer of the paper or the cardboard the glass transition temperature of the aqueous dispersion of the polymer P, which is pol- ymerized in the presence of the initial ligninsulfonic acid. For a fast film formation, the temperature exceeds significantly the glass transition temperature, for example by at least 25°C. The heating is conducted for example by infrared irradiating. In the case of a continuous process, the paper or the cardboard with the water-containing layer is for example led through a dryer duct, which is equipped with an infrared irradiating device. The thickness of the dried coating, i.e. the barrier layer, is preferably at least 1 μηη, in particular in the range from 1 to 50 μηη, very particular in the range from range from 2 to 30 μηη and especially in the range from 5 to 30 μηη.

Optionally, the paper or the cardboard contains a hydrophobic compound, which pos- sess a solubility of less than 1 % by weight in water at 20°C and at 101.3 kPa and a molecular weight of less than 1500 g/mol, in particular less than 1000 g/mol, and which is in liquid or solid state at 20°C and at 101.3 kPa. The presence of such a compound is for example caused by a contamination. The origin of such a contamination is for example the use of a paper pulp for making the paper or the cardboard, which is based on a recycled paper or a recycled cardboard. The latter one can contain hydrocarbons from a mineral oil component, which has been used in an applied printing ink. Said recycled paper or recycled cardboard can contain a fatty acid ester, which is a residual of a former use. Similarly, the recycled paper or recycled cardboard can contain a fatty acid triglyceride, which is a residual of a former use including a contact with vegetable or animal fats. Due to the hydrophilic nature of cellulose, which is for example the main component in the paper or the cardboard, a hydrophobic compound is less fixed to the paper or the cardboard and is in combination with a not too high molecular weight more mobile than a hydrophilic compound. The hydrophobic compound is for example an aliphatic or aromatic hydrocarbon, a fatty acid ester or a fatty acid triglyceride. In particular, the hydrophobic compound is a saturated or unsaturated aliphatic C5-C24 hydrocarbon, a C6-C22 aromatic hydrocarbon, which is unsubstitued or substituted with one or more C1-C4 alkyl, a saturated or unsaturated C4-C22 carboxylic acid esterified with a saturated or unsaturated C1-C22 alco- hoi or a glycerin esterified by three saturated or unsaturated C4-C22 carboxylic acids.

Preferred is a process, wherein the paper or the cardboard contains a hydrophobic compound, which possesses a solubility of less than 1 % by weight in water at 20°C and at 101.3 kPa and a molecular weight of less than 1500 g/mol, and which is in liquid or solid state at 20°C and at 101.3 kPa. Preferred is a process, wherein the hydrophobic compound is an aliphatic or aromatic hydrocarbon, a fatty acid ester or a fatty acid triglyceride.

Preferred is a process, wherein the paper or the cardboard contains a hydrophobic compound, which possesses a solubility of less than 1 % by weight in water at 20°C and at 101.3 kPa and a molecular weight of less than 1500 g/mol, and which is in liquid or solid state at 20°C and at 101.3 kPa, wherein the hydrophobic compound is mobile in the paper or the cardboard. Preferred is a process, wherein the paper or the cardboard contains

- a hydrophobic compound, which possesses a solubility of less than 1 % by weight in water at 20°C and at 101 .3 kPa, a molecular weight of less than 1500 g/mol and a vapor pressure at 20°C of below 1.5 kPa, and which is in liquid or solid state at 20°C and at 101.3 kPa, and

- a further hydrophobic substance, which possesses a solubility of less than 1 % by weight in water at 20°C and at 101 .3 kPa, a molecular weight of less than 500 g/mol and a vapor pressure at 20°C of between 1.5 kPa and 101 .3 kPa, and which is in liquid or solid state at 20°C and at 101.3 kPa. The barrier layer preferably possesses an oil penetration through a paper or a cardboard at a coat weight of 19 to 22 g/m² on a paper or a cardboard at 60°C after 24 hours, which is determined by a grid pattern test as described in the experimental part, of less than 20%, in particular of less than 10%, very particular of less than 2% and especially of less than 1 %.

The barrier layer preferably possesses a water vapor permeability at a coat weight of 19 to 22 g/m² on a paper or a cardboard, which is determined as laid down in DIN 53122, of more than 200 g/(m²d), in particular of more than 270 g/(m²d), very particular of more than 320 g/(m²d) and especially of more than 400 g/(m²d).

The barrier layer preferably possesses a permeability to gaseous n-hexane at a coat weight of 19 to 22 g/m² on a paper or a cardboard at 23°C, which is determined according to the method of measurement as described in the experimental part, of less than 50 g/(m²d), in particular of less than 20 g/(m²d), very particular of less than 16 g/(m²d) and especially of less than 5 g/(m²d).

The barrier layer preferably possesses an oil penetration as defined above of less than 20%, a water vapor permeability as defined above of more than 200 g/(m²d) and a permeability to gaseous n-hexane as defined above of less than 50 g/(m²d).

The above described preferences are described for a process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer. These preferences for the process apply also to the further embodiments of the invention. A further embodiment of the invention relates to a paper equipped with a barrier layer or a cardboard equipped with a barrier layer, which is obtainable by the process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer.

The paper equipped with a barrier layer or the cardboard equipped with a barrier layer is preferably employed as a construction material for a container suitable for packaging. The container possesses an interior room completely surrounded by a wall. The goods to be packed are to be placed in the interior room and are separated by the wall from the environment. The wall itself can be either uniform, i.e. formally consist out of one segment, or divided into two or more segments. Due to its function as packaging, the wall is thin in relation to a diameter of the interior room once the interior room is filled with the goods to be packed. The area of the wall directed to the interior room equals approximately the area of the wall directed away from the interior room due to the thin nature of the wall. The complete area of the wall provides a barrier against the environment in regard to migration of grease or oil and hydrophobic volatile ingredients. However, at least 45% to 100% of the area of the wall based on the overall area of the wall is a segment, which is the paper equipped with a barrier layer or the cardboard equipped with a barrier layer, or which is a multilayer arrangement, wherein the paper equipped with a barrier layer or the cardboard equipped with a barrier layer is covered at least partly by a further layer. The minimum ensures that the container allows the exchange of moisture as water vapor from or to the interior room. Preferably, 85% to 100%, in particular 100% of the area of the wall based on the overall area of the wall is a segment, which is the paper equipped with a barrier layer or the cardboard equipped with a barrier layer, or which is a multilayer arrangement, wherein the paper equipped with a barrier layer or the cardboard equipped with a barrier layer is covered at least partly by a further layer. Preferably, the segment is the paper equipped with a barrier layer or the cardboard equipped with a barrier layer. The further layer allows the exchange of moisture as water vapor.

The container is for example a bag or a box. The in maximum 55% of the alternative material for the wall is for example a metal foil or an arrangement comprising the metal foil, a polyamide film or an arrangement comprising the polyamide film or a polyester film or an arrangement comprising the polyester film. The further layer is for example a layer of a further paper or a further cardboard, which is laminated to the paper equipped with a barrier or the cardboard equipped with a barrier. The further layer is for example used to provide more mechanical strength for the container or to provide an area for a labelling such as by picture or a trademark. The further layer is preferably different to a metal foil, a polyamide film, a polyester film or a polyolefin film such as a polyethylene or polypropylene film. The goods, which are foreseen to be packed into the interior room of the container, are for example food products, in particular foods containing cereals.

Preferred is a container suitable for packaging, which possess an interior room com- pletely surrounded by a wall, wherein from 45% to 100% of the area of the wall based on the overall area of the wall is a segment, which is the paper equipped with a barrier layer or the cardboard equipped with the barrier layer, or which is a multilayer arrangement, wherein the paper equipped with a barrier layer or the cardboard equipped with a barrier layer is covered at least partly by a further layer.

A further embodiment of the invention is an use of a paper equipped with a barrier layer or a cardboard equipped with a barrier layer for hindering a migration of a hydrophobic compound, which possess a solubility of less than 1 % by weight in water at 20°C and at 101 .3 kPa and a molecular weight of less than 1500 g/mol, and which is in liquid or solid state at 20°C and at 101.3 kPa.

Preferred is the use for hindering the migration of the hydrophobic substance and allowing a migration of water vapor.

A further embodiment of the invention is a process for preparing an aqueous dispersion of a polymer P', which comprises the steps of

- providing the monomers

(i) at least 75 parts by weight of an acrylate ester, which is methyl acrylate, ethyl acrylate, methyl methacrylate or ethyl methacrylate,

(iii) 0 to 5 parts by weight of a crosslinking monomer, which contains at least two non-conjugated ethylenically unsaturated groups and is different to methylene bisacrylamide,

(iv) 0 to 5 parts by weight of an α,β-ethylenically unsaturated C3-C6 carbox- ylic acid,

(v) 0 to 9 parts by weight of a further monomer, which contains a ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii), (iv), acrylamide or methacrylamide,

- emulsifying the monomers in an aqueous medium, and

- polymerizing the monomers in the presence of a radical initiator and an initial lig- ninsulfonic acid,

wherein an initial ligninsulfonic acid is present in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v). The monomer-composition of polymer P' differs from the monomer-composition of polymer P in view of cited JP-S63-097612 A by excluding methylene bisacrylamide as an option for the crosslinking polymer and by excluding acrylamide or methacrylamide as an option for the further monomer.

Preferred is a process for preparing an aqueous dispersion of a polymer P', wherein the monomers to be provided are

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acry- late, methyl methacrylate and ethyl methacrylate,

(v) 0 to 9 parts by weight of a further monomer, which contains an ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii), (iv), acrylamide or methacrylamide,

wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100.

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and one member of the at least two members of the mixture is ethyl acrylate or ethyl methac- rylate,

wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100. Preferred is a process for preparing an aqueous dispersion of a polymer P', wherein the monomers to be provided are

(i) at least 75 parts by weight of an acrylate ester, which is a mixture of at least two members of the group consisting of methyl acrylate, ethyl acry- late, methyl methacrylate and ethyl methacrylate, and two members of the at least two members of the mixture are methyl methacrylate and ethyl acrylate,

A further embodiment of the invention is an aqueous dispersion of a polymer P', which is obtainable by the process for preparing an aqueous dispersion of the polymer P'.

A further embodiment of the invention is a process for preparing an aqueous dispersion of a polymer P", which comprises the steps of

- providing the monomers

(v) 0 to 9 parts by weight of a further monomer, which contains a ethylenically unsaturated group and which is different to the monomers (i), (ii), (iii) or (iv),

wherein the sum total of the parts by weight of the monomers (i), (ii), (iii), (iv) and (v) is always 100, - emulsifying the monomers in an aqueous medium, and

wherein an initial ligninsulfonic acid is present in an amount of from 10 to 85 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

The monomer-composition of polymer P" differs from the monomer-composition of polymer P in view of cited JP-S63-097612 A by requiring the presence of methyl meth- acrylate and ethyl acrylate. Polymer P" is a preference versus the broader defined pol- ymer P.

A further embodiment of the invention is an aqueous dispersion of a polymer P", which is obtainable by the process for preparing an aqueous dispersion of the polymer P". The invention is illustrated by the non-limiting examples below.

Experimental part

Unless the context suggests otherwise, percentages are always by weight. A reported content is based on the content in aqueous solution or dispersion if not stated otherwise.

Synthesis of aqueous polymer dispersions

Materials:

MA methyl acrylate

MMA methyl methacrylate

EA ethyl acrylate

BDA butanediol diacrylate

AA acrylic acid

LNSS lignosulfonate, sodium salt

MD maltodextrin

SDS dodecyl sulfate, sodium salt

LDBS linear C10-C13 alkylbenzenesulfonate, sodium salt

APBDS alkylated phenoxybenzenedisulfonate, sodium salt

TBHP tert-butyl hydroperoxide

SFAS formaldehydesulfoxylate dihydrate, sodium salt

SPDS peroxodisulfate, sodium salt The used sodium salt of lignosulfonate is 'Ligninsulfonat Hansa Na 50' (RTM of Chem- ische Werke Zell-Wildhausen GmbH) and obtained from hard and soft wood as an aqueous solution with a content of 47.7% and pH = 7. The used maltodextrin is 'C Dry MD 01915' (RTM Cargill) and obtained as a dried powder from corn starch with a solids content of 94.7% and DE = 15-99.

The used sodium salt of dodecyl sulfate is 'Disponil SDS 15' (RTM BASF, an aqueous solution with a content of 15% by weight). The used sodium salt of a linear C10-C13 al- kylbenzene sulfonate is 'Disponil LDBS 20' (RTM BASF, an aqueous solution with content of 20% by weight).

The used sodium salt of an alkylated phenoxybenzene disulfonate is 'Dowfax 2A1 ' (RTM Dow Chemical, an aqueous solution with a content of 45% by weight).

The used sodium salt of formaldehydesulfoxylate dihydrate is 'Rongalit C (RTM BASF) as an aqueous solution with a content of 10% by weight.

The other used materials are commercially available for example from Aldrich Inc. or from BASF SE.

Example D-1 : Aqueous polymer dispersion No. D1

After flushing a reactor with nitrogen, 83.00 g demineralized water, 6.67 g aqueous Disponil SDS 15 (15% by weight) and 254.24 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 180.00 g methyl methacry- late and 220.00 g ethyl acrylate is added as a monomer feed over 2 hours into the re- actor. Concomitantly to the monomer feed, 120.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 91 .20 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 76.57 g demineralized water is added and the mixture is kept for 55 minutes at 70 °C for completion of the polymeriza- tion. Afterwards, another 40.00 g aqueous tert-butyl hydroperoxide (10% by weight) are fed over 30 min and then 20.56 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 15.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-2: Aqueous polymer dispersion No. D2

After flushing a reactor with nitrogen, 83.00 g demineralized water, 6.67 g aqueous Disponil SDS 15 (15% by weight) and 254.24 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 176.00 g methyl methacry- late, 220.00 g ethyl acrylate and 4.00 g butanediol diacrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 120.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 91.20 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 76.57 g demineralized water is added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 40.00 g aqueous tert-butyl hydroperoxide (10% by weight) are fed over 30 min and then 20.56 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 15.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-3: Aqueous polymer dispersion No. D3

After flushing a reactor with nitrogen, 83.00 g demineralized water, 6.67 g aqueous Disponil SDS 15 (15% by weight) and 254.24 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 178.00 g methyl methacry- late, 220.00 g ethyl acrylate and 2.00 g butanediol diacrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 120.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 91.20 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 76.57 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 40.00 g aqueous tert-butyl hydroperoxide (10% by weight) is fed over 30 min and then 20.56 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 15.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-4: Aqueous polymer dispersion No. D4

After flushing a reactor with nitrogen, 60.17 g demineralized water, 5.83 g aqueous Dis- ponil SDS 15 (15% by weight) and 444.92 g aqueous Ligninsulfonat Hansa Na 50

(47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 157.50 g methyl methacry- late and 192.5 g ethyl acrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 105.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 79.80 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 67.00 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 35.00 g aqueous tert-butyl hydroperoxide (10% by weight) are fed over 30 min and then 18.00 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 20.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion. Example D-5: Aqueous polymer dispersion No. D5

After flushing a reactor with nitrogen, 60.17 g demineralized water, 5.83 g aqueous Disponil SDS 15 (15% by weight) and 444.92 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 154.00 g methyl methacry- late, 192.5 g ethyl acrylate and 3.50 butanediol diacrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 105.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 79.80 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 67.00 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 35.00 g aqueous tert-butyl hy- droperoxide (10% by weight) is fed over 30 min and then 18.00 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 15.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion. Example D-6: Aqueous polymer dispersion No. D6

After flushing a reactor with nitrogen, 60.17 g demineralized water, 5.83 g aqueous Dis- ponil SDS 15 (15% by weight) and 444.92 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 155.75 g methyl methacry- late, 192.5 g ethyl acrylate and 1 .75 g butanediol diacrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 105.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 79.80 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 67.00 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 35.00 g aqueous tert-butyl hydroperoxide (10% by weight) is fed over 30 min and then 18.00 g demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 15.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-7: Aqueous polymer dispersion No. D7

After flushing a reactor with nitrogen, 42.98 g demineralized water, 4.83 g aqueous Dis- ponil SDS 15 (15% by weight) and 491 .53 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 130.50 g methyl methacry- late and 159.50 g ethyl acrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 87.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 66.12 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 55.51 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another 29.00 g aqueous tert-butyl hydroperoxide (10% by weight) is fed over 30 min and then 18.00 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 14.90 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-8: Aqueous polymer dispersion No. D8

After flushing a reactor with nitrogen, 450.0 g demineralized water and 3.0 g aqueous Disponil LDBS 20 (20% by weight) are placed in the reactor. The resulting mixture is heated to 86 °C. Afterwards, 21 .43 g aqueous sodium peroxodisulfate (7% by weight) are added and stirred for 5 minutes. A mixture of 240.0 g water, 26.67 g aqueous Dowfax 2A1 (45% by weight), 6.00 g acrylic acid, 264.00 g methyl methacrylate and 330.00 g ethyl acrylate as an emulsion feed is added into the reactor over 2 hours. After the end of the emulsion feed, the mixture is kept for 45 min at 86 °C for the comple- tion of the polymerization. Afterwards, the reactor is cooled to room temperature to obtain an aqueous polymer dispersion.

Example D-9: Aqueous polymer dispersion No. D9

After flushing a reactor with nitrogen, 427.50 g demineralized water and 142.1 1 g C Dry MD 01915 (94.7% by weight) are placed in the reactor. The resulting mixture is heated to 86 °C. Afterwards, 3.21 g aqueous sodium peroxodisulfate (7% by weight) are added and stirred for 5 minutes. A mixture of 180.0 g water, 20.00 g aqueous Dowfax 2A1 (45% by weight), 4.50 g acrylic acid, 198.00 g methyl methacrylate and 247.5 g ethyl acrylate as an emulsion feed is added into the reactor over 2 hours. Concomitantly to the emulsion feed, 12.86 g aqueous sodium peroxodisulfate (7% by weight) as an imitator feed is also added over the 2 hours into the reactor. After the end of the emulsion feed and the initiator feed, the mixture is kept at 86 °C for 45 minutes for the completion of the polymerization. Afterwards, 35.00 g of water are added and the reactor is cooled to room temperature to obtain an aqueous polymer dispersion.

Example D-10: Aqueous polymer dispersion No. D10

100 g of the aqueous dispersion No. D8 is mixed at room temperature with 31 .5 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) for 15 minutes. Example D-1 1 : Aqueous polymer dispersion No. D1 1

100 g of the aqueous dispersion No. D8 is mixed at room temperature with 63.0 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) for 15.

Example D-12: Aqueous polymer dispersion No. D12

After flushing a reactor with nitrogen, 83.00 g demineralized water, 6.67 g aqueous Disponil SDS 15 (15% by weight) and 254.24 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. 400.00 g methyl acrylate are added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 120.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 91.20 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 76.57 g demineralized water are added and the mixture is kept for 55 minutes at 70° C for completion of the polymerization. Afterwards, another 40.00 g tert- butyl hydroperoxide (10% by weight) are fed over 30 min and then 20.56 g of deminer- alized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 20.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-13: Aqueous polymer dispersion No. D13

After flushing a reactor with nitrogen, 81.73 g demineralized water, 18.67 g aqueous Disponil SDS 15 (15% by weight) and 127.12 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. A mixture of 180.00 g methyl- methacrylate and 220.00 g ethyl acrylate is added as a monomer feed over 2 hours into the reactor. Concomitantly to the monomer feed, 120.00 g aqueous tert-butyl hydroperoxide (10% by weight) as a first initiator feed and 91.20 g aqueous Rongalit C (10% by weight) as a second initiator feed are also added over the 2 hours into the reactor. After the end of the monomer feed and the two initiator feeds, 76.57 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another aqueous 40.00 g tert-butyl hydroperoxide (10% by weight) are fed over 30 min and then 20.56 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 20.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-14: Aqueous polymer dispersion No. D14

After flushing a reactor with nitrogen, 142.24 g demineralized water, 18.67 g aqueous Disponil SDS 15 (15% by weight) and 127.12 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) are placed in the reactor. The pH value is adjusted to 4.5 with acetic acid. The resulting mixture is heated to 70° C. At 70°C 68.57 g sodium peroxodisulfate (7% by weight) are added to the reactor and stirred for 2 minutes. Afterwards, a mixture of 180.00 g methyl-methacrylate and 220.00 g ethyl acrylate is added as a monomer feed over 2 hours into the reactor. After 1 h from the starting of monomer feed, a mixture of 17.14 g sodium peroxodisulfate (7% by weight) and 32.86 g water is also added over 1 hour into the reactor. After the end of the monomer feed and the initiator feed, 77.00 g demineralized water are added and the mixture is kept for 55 minutes at 70 °C for completion of the polymerization. Afterwards, another aqueous 40.00 g tert-butyl hydroperoxide (10% by weight) are fed over 30 min and then 22.00 g of demineralized water are added and the polymerization mixture is stirred for 90 min. During cooling of the reactor to room temperature, 20.00 g aqueous sodium hydroxide (25% by weight) are added to obtain an aqueous dispersion.

Example D-15: Aqueous polymer dispersion No. D15

100 g of the aqueous dispersion No. D13 is mixed at room temperature with 13.6 g aqueous Ligninsulfonat Hansa Na 50 (47.7% by weight) for 15 minutes. Tables 1-A, 1 -B and 1 C summarize the employed amounts of monomers and other ingredients for the polymer dispersions No. D1 to D15.

Table 1-A:

Footnotes: a) according to the invention

b) comparative

c) LNSS present at beginning of polymerization

d) LNSS added to aqueous dispersion after end of polymerization Table 1-B

Footnotes: compare table

Table 1-C

monomer dispersion No.

/ other D13 ^a> D14 ^a> D15 ^a> ingredient

MMA 45.0 45.0 45.0

EA 55.0 55.0 55.0

BDA - - -

AA - - - initial 15 30 15 LNSS ^c>

MD - - -

SDS 0.7 0.7 0.7

LDBS - - -

APBDS - - -

TBHP 3.0 1 .0 3.0

SFAS 2.3 - 2.3

SPDS - 1 .5 -

Footnotes: compare table

Physical properties of the aqueous polymer dispersions Solids contents are determined by drying a defined amount of the particular aqueous polymer dispersion (about 5 g) at 140°C in a drying cabinet to constant weight. Two separate measurements are carried out in each case and averaged.

The glass transition temperature Tg is determined by differential scanning calorimetry in analogy to DIN EN ISO 1 1357-2. A sample is poured out a room temperature and evaporates in laboratory atmosphere over night. Afterwards, a drying at 120 °C for 1 hour takes place. The DSC apparatus Q2000 from TA Instruments Inc. is run with a program of heating to 150°C, maintaining for 2 minutes, fast cooling to -130°C and afterwards heating with 20 K / minute. The analysis of Tg occurs in accordance with ISO 1 1357-2 (half height).

A measure of the particle size of the dispersed polymer particles is the light transmit- tance value. For determining the light transmission value of an aqueous polymer dispersion, the aqueous polymer dispersion to be investigated in each case is measured in 0.1 % strength by weight aqueous dilution in a cell having an edge length of 2.5 cm using light of 600 nm wavelength and is compared with the corresponding transmit- tance of water under the same measuring conditions. The transmittance of water is specified as 100%. The more finely divided the dispersion, the higher is the light transmittance value which is measured by the method described above. From the measured values, it is possible to calculate the mean particle size, cf. B. Verner, M. Barta, B. Sedlacek, Tables of Scattering Functions for Spherical Particles, Prague, 1976, Edice Marco, Rada D-DATA, SVAZEK D-1.

The sheer stability is determined by placing 100 g of the composition to be tested in a 1 liter square flask. Stirring is performed for 5 minutes at 8000 rpm with a stirrer from Pentraulik Maschinen- und Apparate GmbH, which is equipped with a jagged stirring- disk. After this shearing, filtration over a 125μηη sieve takes place followed by drying at 70°C for 2 hours. The residue from the filtration is extrapolated to 1 kg of the composition to be tested. This value is an indicator for shear stability. The less residue from the filtration, the less coagulate has been generated during shearing and the better the shear stability.

Tables 2-A, 2-B and 2-C show physical properties of the synthesized aqueous polymer dispersions. Table 2-A

Footnotes: a) according to the invention

b) comparative

c) not determined

Table 2-B

Footnotes: compare table

Table 2-c

physical dispersion-No.

property D13 ^a> D14 ^a> D15 ^a> solids 48.8 47.1 49.4 content

[%]

Tg [°C] 20.8 - c) - c) light 52.2 - c) - c) transmit- tance [%]

shear sta>1 % >1 % >1 % bility Footnotes: compare table 2-A

Preparation of papers coated with the aqueous polymer dispersions Procedure

a) The aqueous polymer dispersion as obtained in the synthetic procedure is diluted with water in such a way that no streaks from the wire-wound rod are visible when the the base paper (Magnostar (RTM Sappi), uncoated, 70 g/m²) is coated. The base paper is then placed on the paper underlay of the coating table in portrait format. The wire-wound rod is placed ca. 8 cm from the bottom edge of the paper. A small amount of coating colour is applied to the paper in front of the rod, and applied to the strip of the base paper by pressing the rod down gently with both hands and mowing it at a constant speed across the paper. The strip of paper is then hung up to dry in an oven and dried for 1 min at 130°C.

b) After the paper has been left to cool down, 5 x 5 cm samples are taken from the uncoated upper edge of the base paper and from the coated area. Both samples are weighed and the coat weight relative to the area is calculated. If the value obtained is less than the prescribed value, different combinations of pressure, coating speed, choice of wire-wound rod and the dilution of the coating colour can be selected until the desired result is obtained when the procedure is repeated.

c) The coat weight relative to area in g/m² is calculated from the mass of the coated sample less the uncoated sample.

Physical properties of the papers coated with the aqueous polymer dispersions

Several physical properties of the papers coated with the aqueous polymer dispersions are determined.

The oil penetration through a coated paper is determined by a grid pattern test. The tests employs a glass plate (25 x 15 cm), a further glass plate (10 x 10 cm), a paper sheet (25 x 15 cm sized, commercial photocopy paper) with a 10 x 10 grid pattern (10 x 10 cm, 100 squares, each 1 cm²), the coated paper to be tested in a paper size of 25 x 15 cm, a blotting paper (10 x 10 cm, standard commercial paper towel for hand-drying), a drying oven and the coated paper to be tested in a paper size of 25 x 15 cm. The reagent is oleic acid with a content of around 0.2- 0.5% parts by weight of the dye Sudan Blue. The procedure starts with the glass plate (25 x 15 cm) as a base, on which the paper sheet with a 10 x 10 grid pattern is placed. Upon this grid pattern paper lies the coated paper to be tested with the coated side showing up. The blotting paper is placed onto the coated side of the coated paper to be tested in such a position that the grid pattern lies completely underneath. The blotting paper is soaked with 1 .5-2 ml. of the blue-colored oleic acid and covered with the further glass plate. The obtained pile is put into an oven at 60°C and checked for oil penetration after 1 h and 24h. For the eval- uation, the stained squares of the paper with the grid pattern are count and the sum of the stained area is estimated in percent.

The water vapor permeability of a coated paper determined is laid down in DIN 53122. The standard laboratory atmosphere, under which the coated paper is tested, is performed at 23 ± 1 °C and at 85 ± 2 % relative humidity of the air (atmosphere D). Five specimens with a diameter of 90 mm each are punched out of the coated paper to be tested. The specimens with the coated side upwards are placed on metal dishes filled with silica gel. Afterwards, the dishes are sealed at the edges with a wax blend as de- scribed in DIN 53122. The dishes are placed in a desiccator or a climate chamber set to atmosphere D and kept overnight. The specimens are weight every 24 hours and the results are plot against the time. The test is discontinued if at least three consecutive points lie on a straight line. The permeability to water vapor is calculated by the method laid down in DIN 53122 and stated in g/(m²d).

The hexane permeability is determined by pouring 9 ml. of n-hexane into a vessel, which contains a sponge. The vessel is closed with a lid, which has an opening and a sealing ring (internal diameter of the opening: 63 mm). The opening is tightly closed with the coated paper to be tested with the coated side directed towards the sponge. The coated paper to be tested does not come into contact with the hexane-drenched sponge. The weight decrease of the vessel is measured. The atmosphere outside the vessel is the laboratory atmosphere and the temperature is 23°C. The weight decrease in grams is measured for 2 days. It is converted to 1 m² of paper area and to 1 day and then reported as g/(m²d). The weight decrease is a measure of the hexane exiting through the barrier material via the gas phase, and thus is a measure of the barrier performance against gaseous mineral oil constituents.

Tables 3-A, 3-B and 3-C summarize the determined physical properties of the papers coated with one of the polymer dispersions No. D1 to D15.

Table 3-A

Footnotes: a) according to the invention

b) comparative Table 3-B

Footnotes: compare table

The measured results of the papers Pa1 to Pa15 produced with coating materials containing one of the polymer dispersions-No. D1 to D15 show

(a) that all polymer dispersion-No. D1 to D15 provide a barrier for gaseous n- hexane.

(b) that a content of sodium ligninsulfonate in the polymer dispersion leads to a water vapor permeability, e.g. Pa8 and Pa9 based on dispersions D8 and D9, which are both free of sodium ligninsulfonate, show clearly the lowest values. This is despite of 30% by weight of a maltodextrin in D9.

(c) that if all the content of sodium ligninsulfonate is added after polymerization, i.e.

Pa10 and Pa1 1 based on dispersions D10 with 30% by weight of sodium ligninsulfonate and D1 1 with 60% by weight of sodium ligninsulfonate, a good water vapor permeability is achieved but the barrier for oil diminishes in parallel, (d) that once a certain amount of sodium ligninsulfonate is added to the polymeriza- tion, the water permeability can further be increased under maintenance of a barrier for oil and a barrier for gaseous n-hexane. This is done by addition of a certain amount of additional sodium ligninsulfonate after the polymerization, i.e. the comparison of Pa13 based on D13 with 15% by weight of sodium ligninsulfonate versus Pa15 based on D15 with 15% by weight of sodium ligninsulfonate plus 15% by weight of post-polymerization-added sodium ligninsulfonate.

(e) that the same amount of sodium ligninsulfonate achieves a higher water vapor permeability under maintenance of a barrier for oil and a barrier for gaseous n- hexane, if all of the sodium ligninsulfonate acid is added to the polymerization, i.e. the comparison of Pa15 based on D15 with 15% by weight of sodium ligninsulfonate plus 15% by weight of post-polymerization-added sodium ligninsulfonate acid versus Pa1 based on D1 with 30% by weight of sodium ligninsul- fonate.

(f) that Pa1 based on D1 with at 30% by weight of sodium ligninsulfonate added to the polymerization achieves a better water vapor permeability than Pa13 based on D13 with 15% of sodium ligninsulfonate added to the polymerization. Furthermore, Pa4 based on D4 with 60% by weight of sodium ligninsulfonate added to the polymerization or Pa7 based on D7 with even 80% by weight of sodium ligninsulfonate added to the polymerization achieve no further increase of the water vapor permeability. Instead, a slightly beginning decline of the barrier for oil and the barrier for gaseous n-hexane at Pa7 based on D7 is noted.

(g) that Pa1 in comparison to Pa2 and Pa3 provides better water vapor permeability as well as Pa4 in comparison to Pa5 and Pa6. Thus, the presence of a crosslink- ing monomer in D2 and D3 as well as in D5 and D6 leads to slightly inferior results.

(h) that Pa14 in comparison to Pa1 provides related results in regard to water vapor permeability, a similar barrier for oil and a similar gaseous barrier for n-hexane. Thus, the different radical initiator versus D1 at D14 during the initial polymerization, i.e. sodium peroxodisulfate versus a redox initiator system comprising tert- butyl hydroperoxide at D1 , leads only to a minor difference.

(i) that Pa1 based on D1 with a mixture of 55% by weight of ethyl acrylate and 45% by weight of methyl methacrylate provides better results than Pa12 based on D12 with 100% methyl acrylate. However, Pa12 still shows good water vapor permeability, a barrier for oil and a barrier for gaseous n-hexane.

Claims

A process for manufacturing a paper equipped with a barrier layer or a cardboard equipped with a barrier layer, which comprises the steps of

(a) providing an aqueous coating material, which comprises

- an aqueous dispersion of a polymer P, which is obtainable by

radically initiated aqueous emulsion polymerization of

(c) drying of the water-containing layer on the paper or the cardboard from step (b) to obtain the paper equipped with a barrier layer or the cardboard equipped with a barrier layer.

A process according to claim 1 , wherein the amount of the acrylate ester is at least 85 parts by weight.

3. A process according to claim 1 or 2, wherein the amount of the acrylate ester is at least 85 parts by weight and the amount of the further acrylate ester is from 0 to 15 parts by weight.

A process according to any preceding claim, wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate.

A process according to any preceding claim, wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and

wherein ethyl acrylate or ethyl methacrylate is one member of the at least two members.

6. A process according to any preceding claim, wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate,

wherein ethyl acrylate or ethyl methacrylate is one member of the at least two members, and

wherein the combined amount of ethyl acrylate and ethyl methacrylate is at least

40% based on the parts by weight of the acrylate ester.

7. A process according to any preceding claim, wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acry- late, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and

wherein ethyl acrylate and methyl methacrylate are members of the mixture.

8. A process according to any preceding claim, wherein the amount of crosslinking monomer is from 0 to 2 parts by weight.

9. A process according to any preceding claim, wherein the amount of initial ligninsul- fonic acid is from 10 to 65 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 55 parts by weight and the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 10 to 65 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

10. A process according to any preceding claim, wherein the amount of initial ligninsulfonic acid is from 10 to 65 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 55 parts by weight and the combined amount of the initial lig- ninsulfonic acid and the additional ligninsulfonic acid is from 20 to 65 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

1 1. A process according to any preceding claim, wherein the amount of initial ligninsul- fonic acid is from 10 to 45 parts by weight, the amount of additional ligninsulfonic acid is from 0 to 35 parts by weight and the combined amount of the initial ligninsulfonic acid and the additional ligninsulfonic acid is from 20 to 45 parts by weight based on the sum total of the parts by weight of the monomers (i) to (v).

12. A process according to any preceding claim, wherein the monomers (i), (ii), (iii), (iv) and (v) and the amount of initial ligninsulfonic acid are chosen in a way, that the dried aqueous dispersion of the polymer P, which is polymerized in the pres- ence of the initial ligninsulfonic acid, possesses a glass transition temperature in the range from 0°C to 70°C as determined by the norm ISO 1 1357-2.

13. A process according to any preceding claim, wherein the coating material comprises

- 0 to 30 parts by weight of a further auxiliary ingredient, which is different to the aqueous dispersion of the polymer P, ligninsulfonic acid, the inorganic pigment or water, based on the sum total of the parts by weight of the monomers (i) to (v).

14. A process according to any preceding claim, wherein the paper or the cardboard contains a hydrophobic compound, which possesses a solubility of less than 1 % by weight in water at 20°C and at 101.3 kPa and a molecular weight of less than 1500 g/mol, and which is in liquid or solid state at 20°C and at 101 .3 kPa.

15. A process according to the preceding claim, wherein the hydrophobic compound is an aliphatic or aromatic hydrocarbon, a fatty acid ester or a fatty acid triglyceride.

16. A paper equipped with a barrier layer or a cardboard equipped with a barrier layer, which is obtainable by a process as defined in anyone of claims 1 to 15.

17. A container suitable for packaging, which possess an interior room completely surrounded by a wall, wherein from 45% to 100% of the area of the wall based on the overall area of the wall is a segment, which is the paper equipped with a barrier layer or the cardboard equipped with a barrier layer as defined in claim 16, or which is a multilayer arrangement, wherein the paper equipped with a barrier layer or the cardboard equipped with a barrier layer as defined in claim 16 is covered at least partly by a further layer.

18. The use of a paper equipped with a barrier layer or a cardboard equipped with a barrier layer as defined in claim 16 for hindering a migration of a hydrophobic compound, which possess a solubility of less than 1 % by weight in water at 20°C and at 101 .3 kPa and a molecular weight of less than 1500 g/mol, and which is in liquid or solid state at 20°C and at 101 .3 kPa.

19. The use according to the preceding claim for hindering the migration of the hydrophobic substance and for allowing a migration of water vapour.

A process for preparing an aqueous dispersion of a polymer P', which comprises the steps of

- providing the monomers

- emulsifying the monomers in an aqueous medium, and

A process according to claim 20, wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate.

22. A process according to claim 21 , wherein the acrylate ester is a mixture comprising at least two members out of the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and

23. An aqueous dispersion of a polymer P', which is obtainable by the process as defined in claim 20, 21 or 22.