EP3164543A1

EP3164543A1 - Aqueous surface-coating agent for paper and paperboard

Info

Publication number: EP3164543A1
Application number: EP15731313.1A
Authority: EP
Inventors: Christoph Hamers; Maria Heuken
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2014-07-03
Filing date: 2015-06-23
Publication date: 2017-05-10
Also published as: CN106661843A; KR20170026594A; WO2016001016A1; US20180209099A1

Abstract

The present invention pertains to an aqueous surface-coating agent for paper and paperboard, the aqueous surface-coating agent comprising 1-55 wt.% of solid content and containing (A) 0-20 parts by weight of starch (solid), (B) 0.01-20 parts by weight of a zirconium carbonate composition, and (C) 0.01-40 parts by weight of a synthetic water soluble polymer (solid) comprising one or more monomers with monoethylenic double bonds in the polymerized form. The present invention further pertains to a paper and paperboard manufacturing method using the aqueous surface-coating agent, and corrugated board made from said paper.

Description

The invention relates to an aqueous surface-coating agent for paper and paperboard having a solids content of from 1 to 55% by weight

(A) 0 to 20 parts by weight of starch (solid),

(B) 0.01 to 20 parts by weight of a zirconium carbonate compound,

(C) 0.01 to 40 parts by weight of synthetic water-soluble polymer (solid) containing one or more monomers having monoethylenic double bonds in copolymerized form.

The present invention further relates to a process for producing paper and paperboard using the aqueous surface coating agent and corrugated board made from this paper.

In the packaging paper sector, the strength of the paper is an important requirement, as an important basis for this is recycled fibers, which lose their length due to recycling and thus gradually decrease the strength of the paper. In order to improve the paper properties, aids such as wet and dry strength agents such as cationic and anionic polyacrylamide or polyvinylamine, retention aids and sizing agents are often added to the stock. However, the action of cationic solidifying agent is partially offset in the pulp by anionic compounds from the recycling process. For this reason, an attempt is made to achieve additional strength by the addition of aids to the paper sheet, for example in the size press.

Surface sizing involves coating the paper sheet. As a surface sizing agent are often gelatin or starch derivatives in use. Such starch added as a surface sizing agent also has a strengthening effect. However, it is not possible to increase the strength by strength as desired.

Thus, WO 2004/027149 teaches a consolidation of the paper sheet by crosslinking starch and zinc borate applied to the paper sheet in the size press.

Further, EP 2 432 934 teaches to improve paper and board strength by spraying a paper sheet of paper fibers and polyvinyl alcohol fibers with zirconium carbonate and then drying. A disadvantage of all these crosslinking agents is that the process of crosslinking begins already in the mixture and causes only a limited solidification. It was an object of the present invention to provide a surface-coating agent which first cross-links on the fiber and effects a high strength of the paper. Accordingly, the above-mentioned surface coating agent and a process for producing paper and paperboard using the aqueous surface coating agent and corrugated board made from this paper have been found. Under pulp (also referred to as pulp), a mixture of water and pulp is understood below, which may further contain depending on the stage in the production process of the paper filler and paper auxiliaries. If it is a reference to dry paper stock, the total paper pulp of pulp and optionally filler and optionally paper auxiliaries without water to understand (pulp solid).

Depending on the area-related mass, colloquially also referred to as basis weight, the name changes for the molded body made of fiber. The aim is below paper has a basis weight of 7 g / m ² to 225 g / m ² and ² be understood by paperboard having a basis weight of from 225 g / m.

According to the invention, the surface-coating agent contains a zirconium carbonate compound. The zirconium carbonate compound is, for example, ammonium zirconium carbonate, or potassium zirconium carbonate. These are anionic, inorganic hydroxylated zirconium compounds which are available as water-based solutions and are commonly used for paper coatings, coating colors and ink formulations.

Strength in this context should be understood as meaning any native, modified or degraded starch. Native starches may consist of amylose, amylopectin or mixtures thereof. Modified starches may be oxidized starch, starch esters or starch ethers.

Starch types are native starches such as potato, wheat, maize, rice or tapioca starches, with potato starch being preferred. It is likewise possible to use chemically modified starches, such as hydroxyethyl or hydroxypropyl starches, or starches which contain anionic groups, such as phosphate starch, or else cationized starches which contain quaternary ammonium groups, a degree of substitution DS of from 0.01 to 0.2 being preferred. The degree of substitution DS indicates the number of cationic groups contained on average per glucose unit in the starch. Particularly preferred are amphoteric starches which contain both quaternary ammonium groups and anionic groups such as carboxylate and / or phosphate groups and which may optionally also be chemically modified, for. B. hydroxylalkylated or alkylesterified. The starches can be used individually but also in any mixtures with each other.

Preferably, an open-digest (degraded) starch is used. When starch has been completely digested, the starch granules have completely burst, the starch being present in a molecularly disperse form. The average molecular weights _{M.sub.w of} a degraded starch are, for example, in the range from 0.4 million to 8 million daltons, preferably in the range from 0.5 to 3 million daltons, particularly preferably in the range from 0.6 to 2 million daltons. The degradation can take place thermally, which is usually understood as boiled starch. Furthermore, the degradation can be enzymatic. Finally, the degradation can also be oxidative. Particular preference is given to using an enzymatically degraded starch. The average molecular weight Mw (determined by GPC) of the synthetic water-soluble polymer is preferably <1 million daltons, for example 20,000 daltons to 1 million daltons, preferably 35,000 daltons to 1 million daltons. These polymers have, for example, K values (determined according to H. Fikentscher in 5% aqueous saline solution at pH 7, a polymer concentration of 0.5% by weight and a temperature of 25 ° C.) in the range from 20 to 250, preferably 30 to 80.

The synthetic water-soluble polymer preferably comprises one or more monomers in a polymerized form selected from acrylamide, vinyl alcohol, vinyl acetate and an N-vinylcarboxamide of the formula in which R ¹ , R ² = H or C ¹ to C ₆ alkyl. The synthetic water-soluble polymers may be uncharged or charged. The latter carry cationic and / or anionic radicals.

According to a preferred embodiment, the synthetic water-soluble polymer comprises one or more monomers in copolymerized form selected from acrylamide and an N-vinylcarboxamide of the formula (I), with the proviso that no vinyl alcohol is contained in copolymerized form.

In connection with the monomers, vinyl alcohol means a copolymerized unit [CH 2 CHOH], which is usually obtained by using as monomer a vinyl ester, e.g. Vinyl formate or vinyl acetate and the resulting polymer is subjected to hydrolysis, in which the copolymerized vinyl ester monomers are hydrolyzed to units [CH 2 CHOH].

According to a preferred embodiment, suitable synthetic water-soluble polymers are the polymers of a vinylcarboxamide of the above formula (I).

According to one embodiment, polymers which contain vinylamine units as synthetic water-soluble polymers are suitable. The cationic polymers containing vinylamine units are water-soluble. The solubility in water under normal conditions (20 ° C., 1013 mbar) and pH 7.0 is, for example, at least 5% by weight, preferably at least

10% by weight. The vinylamine units containing cationic polymers are cationic due to their amino group. The charge density of the cationic polymers containing vinylamine units (without counterion) is at least 0.1 meq / g and is preferably in the range of 4 to

10 meq / g.

The cationic polymers containing vinylamine units usually have average molecular weights Mw in the range from 10,000 to 10,000,000 daltons, preferably in the range from 15,000 to 5,000,000 daltons, particularly preferably in the range from 20,000 to 3,000,000 daltons. The average molecular weight M _w is understood here and below as meaning the mass-average molecular weight, as can be determined by GPC.

Cationic polymers containing vinylamine units are known, cf. the DE 35 06 832 A1 and DE 10 2004 056 551 A1 referred to in the prior art. For example, the cationic polymer containing vinylamine units is preferably used as the reaction products obtainable by polymerizing

(aO) at least one monomer of the formula in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,

(cO) optionally monoethylenically unsaturated monomers other than the monomers (aO), and

(dO) if appropriate, compounds which have at least two ethylenically unsaturated double bonds in the molecule and subsequent partial or complete hydrolysis of polymerized in the polymer units of the monomers (I) to form amino groups and / or obtainable

by Hofmann degradation of polymers having acrylamide and / or methacrylamide units.

Hydrolysis of the carboxylic acid amide radicals of the copolymerized units of the monomers (I) converts the group -NR ² -CO-R ¹ into the group -NR ² -H. Examples of monomers of group (aO) are N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinyl-N-methylpropionamide and N-vinylpropionamide. The monomers of group (aO) can be used alone or in a mixture in the copolymerization with the monomers of the other groups. The copolymers may optionally contain monomers of group (cO) in a polymerized form for modification, for example esters of ethylenically unsaturated C3 to Cs carboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isobutyl methacrylate, methyl methacrylate, ethyl methacrylate and vinyl esters, for example Vinyl acetate or vinyl propionate, or other monomers such as N-vinylpyrrolidone, N-vinylimidazole, acrylamide and / or methacrylamide.

A further modification of the copolymers is possible by using in the copolymerization monomers (dO) which contain at least two double bonds in the molecule, e.g. Methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, triallylamine, pentaerythritol triallyl ether, polyalkylene glycols esterified at least twice with acrylic acid and / or methacrylic acid or polyols such as pentaerythritol, sorbitol or glucose. If at least one monomer of group (dO) is used in the copolymerization, the amounts employed are up to 2 mole%, e.g. 0.001 to 1 mole%. In a likewise preferred embodiment, the synthetic water-soluble polymer employed are reaction products obtainable by polymerizing

(a) vinyl acetate and

(cO) optionally monoethylenically unsaturated monomers other than the monomers (aO) and vinyl acetate, and

(dO) optionally compounds which have at least two ethylenically unsaturated double bonds in the molecule and optionally subsequent partial or complete hydrolysis of the units of the monomers (I) and the vinyl acetate units polymerized into the polymer.

The synthetic water-soluble polymer according to a preferred embodiment carries acid groups, so is preferably an anionic polymer. The anionic charge density of the synthetic water-soluble polymer (without counter ion) is at least -0.1 to 10 meq / g, and is preferably in the range of -0.1 to -4 meq / g.

According to a further preferred embodiment, the synthetic water-soluble polymer, in particular consists of, one or more monomers in copolymerized form selected from (A) one or more monomers selected from acrylamide, vinyl alcohol, vinyl acetate and an N-vinylcarboxamide of the formula in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,

(B) monoethylenically unsaturated monomers containing one or more acid groups and / or their alkali metal, alkaline earth metal or ammonium salts, and

(c) optionally one or more monoethylenically unsaturated monomers other than the monomers (a) and (b), and

(D) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule.

When the monomers (a) and (b) or (a), (b) and (c) are copolymerized in the presence of a compound (d), branched copolymers are obtained. The proportions and reaction conditions are to be chosen so that water-soluble polymers are still obtained. Under certain circumstances it may be necessary to use polymerization regulators. All known regulators can be used, such as thiols, sec. Alcohols, sulfites, phosphites, hypophosphites, thioacids, aldehydes, etc. (further details can be found, for example, in EP-A 438 744, page 5, lines 7-12).

The branched copolymers contain, for example

(a) 10 to 95 mol% of units of the formula I,

(b) 5 to 90 mol% of units of an acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts,

(C) 0 to 30 mol% of units of at least one monoethylenically unsaturated monomer, which is different from the monomers (a) and (b), and

(D) 0 to 2 mol%, preferably 0.001 to 1 mol% of units of at least one compound copolymerized with at least two ethylenically unsaturated double bonds.

Examples of monomers of group (a) are d Examples of monomers of group (a) are N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide,

N-vinyl-N-ethylacetamide, N-vinyl-N-methyl-propionamide and N-vinyl-propionamide. Furthermore, acrylamide is suitable as monomer (a).

Suitable monomers of group (b) are in particular monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms and the water-soluble salts of these carboxylic acids. Examples of this group of monomers include acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid and crotonic acid. As monomers of group (b) Also suitable are sulfo-containing monomers such as vinylsulfonic acid, acrylamido-2-methyl-propanesulfonic acid and styrenesulfonic acid and vinylphosphonic acid. The monomers of this group can be used alone or in admixture with each other, in partially or completely neutralized form in the copolymerization. For neutralization, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines are used. Examples of these are sodium hydroxide, potassium hydroxide, soda, potash, sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine. The monomers of group (b) are preferably used in the copolymerization in partially neutralized form.

The copolymers may, for modification, optionally contain monomers of group (c) in a polymerized form, e.g. Esters of ethylenically unsaturated C 3 to C 8 carboxylic acids, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isobutyl methacrylate, methyl methacrylate, ethyl methacrylate, and vinyl esters, for example. Vinyl acetate or vinyl propionate, or other monomers such as N-vinylpyrrolidone, N-vinylimidazole.

The copolymers may, for modification, optionally contain monomers of group (d) in a polymerized form, e.g. Methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, triallylamine, pentaerythritol triallyl ether, polyalkylene glycols esterified at least twice with acrylic acid and / or methacrylic acid or polyols such as pentaerythritol, sorbitol or glucose. If at least one monomer of group (d) is used in the copolymerization, the amounts employed are up to 2 mole%, e.g. 0.001 to 1 mole%.

The polymerization of the monomers is carried out in a known manner in the presence of free-radical polymerization initiators and optionally in the presence of polymerization regulators, cf. EP-B 672 212, page 4, lines 13-37 or EP-A 438 744, page 2, line 26 to page 8, line 18.

Preferably, as the synthetic water-soluble polymer, an anionic copolymer obtainable by copolymerizing

(a1) N-vinylformamide,

(b1) acrylic acid, methacrylic acid and / or their alkali metal or ammonium salts and

(c1) optionally one or more monoethylenically unsaturated monomers other than the monomers of groups (a) and (b).

The synthetic water-soluble polymer preferably contains

(a) 10 to 95 mol% of the units of the formula I.

(B) 5 to 90 mol% of units of a monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms in the molecule and / or their alkali metal, alkaline earth metal or ammonium salts and

(c) 0 to 30 mol% of units of at least one monoethylenically unsaturated monomer other than the monomers of groups (a) and (b). Particular preference is given to copolymers and terpolymers comprising acrylic acid and vinylformamide in copolymerized form. As the synthetic water-soluble polymer, it is preferable to use a synthetic water-soluble polymer obtainable by copolymerizing

(a2) 50 to 90 mol% of N-vinylformamide,

(b2) 10 to 50 mol% of acrylic acid, methacrylic acid and / or their alkali or ammonium salts and

(c2) 0 to 30 mol% of at least one monoethylenically unsaturated monomer other than the monomers of groups (a) and (b).

Likewise preferably used as a synthetic water-soluble polymer is an anionic copolymer, which is obtainable by copolymerizing

(a1) vinyl acetate and

(c) optionally one or more monoethylenically unsaturated monomers other than the monomers of groups (a) and (b), followed by partial or complete hydrolysis of the vinylacetate units incorporated in the polymer.

Also preferred as synthetic water-soluble polymers are copolymers obtainable by copolymerizing a monomer mixture comprising, preferably consisting of (a1) acrylamide

(c1) optionally one or more monoethylenically unsaturated monomers which are different from the monomers of groups (a) and (b). The synthetic water-soluble polymer contains, for example

(a) 10 to 95 mole percent of acrylamide

(c) 0 to 30 mol% of units of at least one monoethylenically unsaturated monomer other than the monomers of groups (a) and (b).

Copolymers of acrylamide with a compound selected from acrylic acid, methacrylic acid and their alkali metal or ammonium salts, preferably of acrylamide with acrylic acid, are particularly preferably used as the synthetic water-soluble polymer. These synthetic water-soluble polymers generally contain at least

30 wt .-%, preferably at least 40 wt .-%, and in a particularly preferred form at least 50 wt .-% and generally at most 90 wt .-%, preferably at most 85 wt .-%, and in a particularly preferred form at most 80% by weight of acrylamide copolymerized, based on the total weight of the monomers.

These synthetic water-soluble polymers further generally contain at least 70% by weight, more preferably at least 60% by weight, and most preferably at least 40% by weight and generally at most 10% by weight, preferably at most 15% by weight .-%, and in a particularly preferred form at most 20 wt .-% of a compound selected from acrylic acid, methacrylic acid and their alkali metal or ammonium salts, preferably acrylic acid, copolymerized, based on the total weight of the monomers.

According to a further preferred embodiment, suitable synthetic water-soluble polymers are also polyacrylic acids.

Particularly suitable are water-soluble polyacrylic acids which have a low molecular weight. Low molecular weight refers to an average molecular weight (M _w ) of less than 50,000, preferably less than 20,000, and most preferably less than 10,000, for example less than 5,000. Such polyacrylic acids may contain, as comonomers, further monocarboxylic acids, dicarboxylic acid monomers, and their anhydrides, and monoethylenically unsaturated monomers which are not carboxylic acids in polymerized form.

Examples of monocarboxylic acids are methacrylic acid, vinylacetic acid (3-butenoic acid) and acyloxypropionic acid. Suitable dicarboxylic acid monomers are, for example, maleic acid, itaconic acid, mesaconic acid, fumaric acid and citraconic acid. The anhydrides of carboxylic acids such as maleic anhydride, are useful.

Monoethylenically unsaturated monomers which are not carboxylic acids may be present in amounts which are soluble in the reaction mixture and the polymer produced is soluble in water. In any case, the carboxyl-free monomer is less than 80% and preferably less than 50% by weight of the total weight of all monomers employed. Examples of suitable monoethylenically unsaturated monomers which are not carboxylic acids are alkyl esters of acrylic or methacrylic acid, such as methyl, ethyl or butyl acrylate or methyl, butyl or isobutyl methacrylate; Hydroxyalkyl esters of acrylic or methacrylic acids, such as hydroxyethyl or hydroxypropyl acrylate or methacrylate; Acrylamide, methacrylamide, phosphoethyl methacrylate, allyl or methallyl alcohols, esters and ethers; Acrylonitrile, vinyl acetate, styrene, vinylsulfonic acid or salts thereof, allylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid or salts thereof.

Preference is given to polyacrylic acids which are acrylic acid polymers or acrylic acid copolymers which contain up to 30% by weight, based on all ethylenically unsaturated monomers, of ethylenically unsaturated comonomers selected from the group consisting of methacrylic acid, one acid (anhydride), vinylsulfonic acid, allylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid, in copolymerized form.

The polyacrylic acid is preferably homopolymers of acrylic acid.

A process for the preparation of such polyacrylic acids is described in EP 405 818 and WO 2012/104325, to which reference is expressly made.

According to these methods, molecular weight regulators or chain transfer agents are added during the free-radical polymerization of acrylic acid. Preferred chain transfer agents are hypophosphorous acid or a salt thereof, such as sodium hypophosphite monohydrate.

Thus, polyacrylic acids are suitable which are obtainable by polymerization of monoethylenically unsaturated monocarboxylic acids and optionally other monomers with sodium persulfate as a starter in the presence of hypophosphite as a regulator in which an alkaline neutralizing agent during the polymerization in an amount sufficient to at least 20% of the acidic Neutralize groups, is present.

Suitable examples are polyacrylic acids obtainable by polymerization of acrylic acid in feed mode with peroxodisulfate as a starter in the presence of hypophosphite as a regulator in water as a solvent, in the water and optionally one or more ethylenically unsaturated comonomers submitted and acrylic acid in acidic, not neutralized form, optionally one or more ethylenically unsaturated comonomers, an aqueous peroxodisulfate solution and an aqueous hypophosphite solution are added continuously, and after completion of the acrylic acid feed to the aqueous solution, a base is added, wherein the comonomer content 30 wt .-% , based on the total monomer content, does not exceed.

Suitable synthetic water-soluble polymers are also amphoteric copolymers with overall anionic charge, which are obtainable by copolymerizing

(a) at least one monomer selected from acrylamide and one

N-vinylcarboxamide of the formula in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,

(B) at least one monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms in the molecule and / or their alkali metal, alkaline earth metal or ammonium salts and, if appropriate

(c) other monoethylenically unsaturated monomers other than the monomers (a) and (b), and optionally

(d) compounds which have at least two ethylenically unsaturated double bonds in the molecule, and subsequent partial cleavage of groups -CO-R ¹ from the monomers of the formula I copolymerized in the copolymer to form amino groups, the content of amino groups in the copolymer being at least 5 mol% below the content of copolymerized acid groups of the monomers (b) is. In the hydrolysis of N-vinylcarboxamide polymers, amidine units are formed in a secondary reaction by reacting vinylamine units with an adjacent vinylformamide unit. In the following, the indication of vinylamine units in the amphoteric copolymers always means the sum of vinylamine and amidine units.

The amphoteric compounds thus obtained contain, for example

(a) 10 to 95 mol% of units of a monomer of the formula I.

(c) 0 to 30 mol% of units of at least one monoethylenically unsaturated monomer other than the monomers (a) and (b),

(d) 0 to 2 mol% of units of a compound containing at least two ethylenically unsaturated double bonds, and

(E) copolymerized 0 to 42 mol% of vinylamine units, wherein the content of amino groups in the copolymer is at least 5 mol% below the content of copolymerized acid group-containing monomers (b). The hydrolysis of the anionic copolymers can be carried out in the presence of acids or bases or else enzymatically. In the case of hydrolysis with acids, the vinylamine groups formed from the vinylcarboxamide units are in salt form. The hydrolysis of vinylcarboxamide copolymers is described in detail in EP-A 438 744, page 8, line 20 to page 10, line 3. The remarks made there apply correspondingly to the preparation of the amphoteric polymers to be used according to the invention.

The aqueous surface-coating composition according to the invention comprises, preferably at least 95% by weight, in particular consisting of 100% by weight, of the composition (A), (B) and (C) according to the invention and water, the solids content of the surface-coating agent 1 to 55 wt .-%, preferably 5 to 20 wt .-%, in particular 10 to 15 wt .-% is.

The aqueous surface-coating agent according to the invention preferably contains

1 to 20 parts by weight, preferably 2 to 12 parts by weight, in particular 3 to 8 parts by weight of starch (solid),

0.01 to 20 parts by weight, preferably 0.2 to 10 parts by weight, in particular 0.5 to

2 parts by weight of a zirconium carbonate compound, (C) 0.01 to 40 parts by weight, preferably 0.5 to 20 parts by weight, in particular 2 to

10 parts by weight of synthetic water-soluble polymer (solid) containing one or more monomers having monoethylenic double bonds in polymerized form. The surface coating agent according to the invention is applied to raw paper. The amount of coating agent is applied with a coating weight of preferably 0.1 to 10 g / m ² .

The surface coating agent is prepared by mixing the individual components. According to a preferred variant, the cooked starch is added and the synthetic water-soluble polymer is mixed in, followed by the zirconium carbonate compound.

The aqueous surface-coating agent of the present invention may additionally contain a surface sizing agent based on an aqueous dispersion. The aqueous dispersions may have anionic or cationic charge and have a particle size between 50 and 500 nm.

Suitable dispersions are, for example, which are obtainable by copolymerization of ethylenically unsaturated monomers, in particular acrylonitrile and (meth) acrylates, and optionally up to 10% by weight of further monomers, such as styrene, by means of free-radically initiated emulsion polymerization in the presence of degraded starch. It is possible to use chain transfer agents. Such aqueous dispersions are described in EP 0 273 770 EP 0 257 412,

WO 99/42490, WO 2002/14393, WO 2007/000419, WO 2007/000420 and WO 201 1/039185 the disclosure of which is expressly incorporated by reference.

The aqueous surface-coating agent of the present invention preferably has a viscosity in the range of 1 to 200 mPa.s (12% solids content and Brookfield Spindle 2 at 100 RPM at which solids content (Brookfield LV viscosity, spindle 4, 6 rpm, RT).) The surface coating composition of the invention is suitable For the coating of base paper, the paper obtained hereafter is characterized by high strengths.

In this case, the surface coating compositions according to the invention can be processed with all process methods suitable for surface sizing. The application with the surface coating agent according to the invention takes place in a film and / or size press or according to a non-contact application method with a spray bar or curtain coating method. The coating can be done by means of a doctor blade or a nozzle.

It is generally possible to coat base paper in a separate film and / or size press. Preferably, the film and / or size press is arranged inline in the paper machine. As a rule, it is integrated in the drying unit. The paper sheet preferably has a water content of <60% by weight at the time of application.

The order is made in the usual quantities. For the application, the surface coating agent usually the size press liquor in an amount of 0.05 to 3 wt .-% based on solid substance added and depends on the desired degree of sizing of the papers to be equipped.

The present invention further relates to a process for the production of paper and paperboard comprising the steps of a) treating paper stock with paper auxiliaries and / or filler,

b) dewatering of the paper stock treated according to a) with sheet formation and c) coating of the paper web obtained according to b) with the surface coating composition according to the invention

d) and drying the according to c) coated paper web.

According to the invention, native and / or recovered fibers can be used as the fibrous material. All fibers of coniferous and hardwoods commonly used in the paper industry can be used, for example. unbleached pulp and fiber from all year-round plants. Wood pulp includes, for example, groundwood, thermo-mechanical pulp (TMP), chemo-thermo-mechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp, and refiner mechanical pulp (RMP). As pulp, for example, sulphate, sulphite and soda pulps come into consideration. Suitable annual plants for the production of fibrous materials are, for example, rice, wheat, sugar cane and kenaf.

Waste paper is preferably used for the production of pulps, which is used either alone or in admixture with other fibers. A preferred process for the production of paper and paperboard comprising the steps of a) treating paper stock with paper auxiliaries and / or filler,

d) and drying the paper web coated according to c),

with the proviso that no polyvinyl alcohol fibers are part of the pulp.

In the case of waste paper, a pulp with a freeness of 20 to 50 SR can be used. As a rule, a pulp with a freeness of about 40 SR is used, which is ground during the production of the pulp. Preferably, pulp is used which has a freeness of <40 SR.

The process according to the invention preferably serves for the production of filler-containing paper. The filler content of the paper is generally 1 to 20% by weight, preferably 5 to 20% by weight, in particular 10 to 15% by weight, based on dry paper stock. Under filler is, as usual in papermaking, inorganic pigment to understand.

In addition to the filler, usually at a pulp concentration of 5 to 15 g / l, customary paper auxiliaries may be added to the paper stock. Conventional For example, sizing agents, wet strength agents, cationic or anionic retention agents based on synthetic polymers, as well as dual systems, dehydrating agents, optical brighteners, defoamers, biocides and paper dyes. These conventional paper additives can be used in the usual amounts.

As a sizing agent, mention may be made of alkylketene dimers (AKD), alkenylsuccinic anhydrides (ASA) and rosin size.

Wet strength agents are synthetic dry strength agents such as polyvinylamine or natural dry strength agents such as starch.

Suitable retention agents are, for example, anionic microparticles (colloidal silicic acid, bentonite), anionic polyacrylamides, cationic polyacrylamides, cationic starch, cationic polyethyleneimine or cationic polyvinylamine. In addition, any combination thereof is conceivable, for example, dual systems consisting of a cationic polymer with an anionic microparticle or an anionic polymer with a cationic microparticle. In order to achieve a high filler retention, it is recommended to add retention aids of this kind, which can be added to the thick material, for example, but also to the thin material.

The dewatering takes place on the screen of the paper machine under sheet formation. The paper web obtained hereafter passes through the press section, in which the paper web is dried as a rule to a solids content <40 wt .-%. Subsequently, further dehydration by drying.

The coating step according to the invention takes place during the drying phase. Depending on the paper machine, a drying unit may already be present in front of the coating device, preferably a size press. The present application further relates to the paper coated with the surface-coating agent according to the invention. Corrugated board made with this paper shows improved strength properties.

Examples

The following examples are intended to explain the present invention in more detail. The percentages in the examples are by weight unless otherwise specified.

The K value of the polymers was determined according to Fikentscher, Cellulose-Chemie, Volume 13, 58-64 and 71-74 (1932) at a temperature of 20 ° C. Where K = k-1000.

The solids content was determined by annealing a sample of the product (about 3 g) in a preheated convection oven at 120 ° C, that is, it was dried to constant weight. In the examples and in the comparative examples, the following polymers were used.

Polymer (1) Vinylformamide / acrylic acid copolymer (90/10 mol / mol) In the original, 46.8 kg of water were mixed with 0.35 kg of 85% strength by weight aqueous phosphoric acid and 0.65 kg of 25% strength by weight. -% sodium hydroxide solution adjusted to pH 6.6. 200 g of Afranil T (liquid) (defoamer) were added. Then, the template was purged with nitrogen, heated to 80 ° C and a pressure of 450 mbar was set. As soon as distillate occurred, 32.5 kg of vinylformamide (99% pure), 14.8 kg of a 32% strength aqueous sodium acrylate solution and 8.9 kg of water were metered in from an inlet over 4 hours. At the same time were 7.4 kg one

10 wt% aqueous 2,2 ^' azobis (2-amidinopropane) hydrochloride solution added over 4 h. After the end of the feeds, an additional hour yet polymerized, then an additional 7.4 kg of a 10 wt% aqueous ^2,2'-azobis (2-amidinopropane) hydrochloride solution were metered in over a period of 15 minutes and then a further 2 hours postpolymerized. During the polymerization, 8.9 kg of water were distilled off. The product obtained hereafter can be characterized as follows:

K value 50.2 (determined in a 5% strength by weight aqueous sodium chloride solution at a pH of 7 and a polymer concentration of 1%)

Solids content (FG): 36% by weight

Polymer (2) Polyvinylformamide

In the template, the pH was adjusted to 6.5 with 62.7 kg of water, 0.36 kg of 85 wt .-% aqueous phosphoric acid and 0.59 kg of a 25 wt .-% sodium hydroxide solution. Then the template was purged with nitrogen, heated to 80 ° C and set a pressure of 450 mbar. As soon as distillate appeared, 38.0 kg of vinylformamide (99% pure) were metered in over 3 hours.

At the same time 0.83 kg of a 10 wt% aqueous (2,2 ^'azobis (2-amidinopropane) were hy- drochloridlösung metered in from a feed over a period of 3 hours. 30 minutes after the start of the two feeds began, the feed of 15.7 kg of water for 3 hours 30. After the monomer feed had ended, the reaction mixture was kept at 80 ° C. for a further 3 hours During the entire polymerization 15.7 kg of water were distilled off The product obtained hereunder can be characterized as follows:

K value: 42.9 (determined in water at a pH of 7 and a polymer concentration of 1%)

FG: 34.33%

Polymer (3) Hydrolysed copolymer of vinyl acetate / crotonic acid (90/10)

The original 70 kg of water and 40 kg of 25 wt .-% sodium hydroxide solution were presented. Over 60 minutes 6 kg Luviset ^® CA 66 (BASF, VAc / crotonic 90/10 mol / mol) were added portionwise 21 dissolved with stirring.

After completion of the addition, the solution was heated to 80 ° C internal temperature and maintained at the temperature for a further 5 hours. Subsequently, the solution was cooled and adjusted by the addition of 2.2 kg of 32% hydrochloric acid, a pH of 6. The product obtained hereafter can be characterized as follows:

Hydrolysis degree VAc: 68%.

22.5% non-volatile component (NFA); Polymer content 18.0% by weight

Polymer (4) Copolymer of Acrylamide and Acrylic Acid (90:10 mokmol)

In the template were added 80 kg of water 1, 38 kg of a dilute solution Trilon ^® C (BASF, diluted to 1 wt .-% solids), and 375 g of sodium hypophosphite monohydrate (solid) is heated to 60 ° C, while nitrogen was passed through.

9.8 kg of a 32 wt .-% aqueous sodium acrylate solution (33.34 mol) and 42.5 kg of a 50 wt .-% aqueous acrylamide (301, 07 mol) were added over a period of 2h20 'added. At the same time 12.6 kg of a 4% strength by weight aqueous (2,2 were ^'azobis (2-amidinopro- pan) hydrochloride solution over 2:20' metered in. One hour after the additions were 2.76 kg of a 4 wt % aqueous (2,2 ^' azobis (2-amidinopropane) hydrochloride solution was added within 5 minutes, then it was heated to 80 ° C internal temperature and thus started the postpolymerization.The mixture was kept at 80 ° C for 2 hours.

Then, by adding 0.36 kg of 32% hydrochloric acid, the pH was adjusted to 6.3. The product obtained hereafter can be characterized as follows:

K value: 28.8 (determined in a 5% strength by weight aqueous sodium chloride solution at a pH of 7 and a polymer concentration of 2%)

Ratio in polymer AM / AA: 90/10 mol / mol

FG: 17%

Polymer (5) Hydrolyzed Copolymer of Vinylacetate (VAc) and Vinylformamide (VFA)

In the template was adjusted with 31, 7 kg of water, 0.22 kg of 85 wt .-% phosphoric acid and 0.42 kg of a 25 wt .-% sodium hydroxide solution, a pH of 6.5. 2.33 kg of a 10% aqueous solution of Mowiol i- gen ^® 40-88 (Kuraray) were added.

Then, the template was purged with nitrogen and heated to 65 ° C.

8.35 kg of vinylformamide (99%) were added over 3 hours. At the same time, the supply of 15.0 kg of vinyl acetate began over 0.5 h and 8.18 kg of a 2 wt% aqueous ^2,2'-azobis (2-amidinopropane) hydrochloride solution over 8h.

After the end of the initiator feed, 5.0 kg of water were added and polymerization was continued for one hour. Then, 10.5 kg of a 2 wt% aqueous ^2,2'-azobis (2-amidinopropane) - hydrochloride solution added over 15 minutes and 5.0 kg of water was added after the end of the feed. The batch was heated to 70 ° C internal temperature and further polymerized for 2h, then 25 kg of water were added. The pressure was lowered slightly and 15 kg of water were distilled off. There was obtained a copolymer of vinyl acetate and VFA (47.6 / 52.4 mokmol). The product mixture can be characterized as follows:

K value: 54.6 (determined in formamide and a polymer concentration of 1%)

FG: 22.8% Subsequently, the resulting product mixture was heated to 80 ° C internal temperature. Then, 0.6 kg of sodium bisulfite solution (40% in water) was added. After reaching 80 ° C 3.2 kg of 25 wt .-% sodium hydroxide solution are added in 15 minutes. The mixture was hydrolyzed for 3 h at this temperature and then cooled and adjusted to a pH of 8.2 with 8.7 kg of a 32 wt .-% aqueous hydrochloric acid. An end product was obtained with a content of 45.7% polyvinyl alcohol, 6.7% polyvinyl acetate and 27.8% polyvinyl formamide and 19.8% polyvinylformamide.

NFA: 22.4% Polymer Content: 9.8% Polymer (6) Copolymer of Vinylacetate and VFA (50/50)

In the initial charge, 31.7 kg of water, 0.22 kg of 85% strength by weight phosphoric acid and 0.42 kg of a 25% strength by weight sodium hydroxide solution (pH 6.5, 2.33 kg of a 10% aqueous solution of Mowiol 40-88 (Kuraray) was added, then the template was purged with nitrogen and heated to 65 ° C. 8.35 kg of vinylformamide (99%) were metered in over 3 h, at the same time the reaction began supply of 15.0 kg of vinyl acetate over 0.5 h and 8, 18 kg of a 2% strength by weight aqueous (2,2 ^'azobis (2-amidinopropane) hydrochloride solution) over 8 hours. After the end of the initiator feed was added 5.0 kg water was added and further merized poly- one hour. Then, 10.5 kg of a 2 wt% aqueous ^2,2'-azobis (2-amidinopropane) hy- drochloridlösung added over 15 minutes and after the end of the inlet 5, The batch was heated to an internal temperature of 70 ° C. and further polymerized for 2 hours, then 25 kg of water were added, the pressure was lowered slightly and it became 15 kg of water distilled off.

K value: 54.6 (determined in formamide and a polymer concentration of 1%)

FG: 22.8%

Ratio in the polymer: 47.6 / 52.4

Polymer (7)

As polymer 7, a polyacrylic acid having an average molecular weight of (GPC) about 4000 g / mol and a degree of neutralization of 50 was used.

Starch solution production:

A corn starch with the trade name Merizet ^® 120 (from Tate & Lyle) which has been degraded enzymatically as follows was used. A 12% slurry of Merizet 120 was prepared in 65 ° C water with stirring in a 1 000 L vessel and 0.012% enzyme 120 PL Novozyme added. After 20 minutes, 100 ml of acetic acid was metered into the starch solution to terminate the starch degradation. The starch solution had a viscosity of 55 mPas at 100 RPM (spindle 2).

Determination of the weight average (M _w ) of the starch solution

The aqueous starch solutions were diluted with DMSO and stabilized in this manner. The determination of the molecular weight distribution was carried out by means of GPC-MALLS (gel chromatography with multi-angle laser light scattering). The GPC-MALLS consists of a Water 515 Pump Module, Degasser, Waters 717 Autosampier, GPC Column Heating (Jet Stream). The MALLS Dector is Dawn-Heleos (Wyatt Technology, Santa Barbara, USA) equipped with a K 5 flow cell and a He-Ne laser m of 10 to 658 nm and equipped with 16 detectors with an angle of 15 to 162 °. The following GPC columns were used in series Suprema S 30000, S 1000 and S 10 (PSS, Mainz, Germany). The samples were eluted with a DMSO-containing 0.09 M NaNO 3 solution at a flow rate of 0.5 ml / min and a temperature of 70 ° C in the GPC columns. As software evaluation ASTRA 5.3.0.18 was used.

Determination of the weight average (M _w ) of the polymers The molecular weight distribution was determined by means of GPC-UV (gel chromatography with UV and fluorescence detector). The GPC consists of a Water 515 Pump Module, Degasser, Waters 717 Autosampier, GPC Column Heating (Jet Stream). The UV detector is equipped with an Agilent (DRI 1200 UV) and an Agilent fluorescence detector (1200 VWD - 260 nm). The following GPC columns were used in series TSKgel GMPWXL. The samples were washed with a 0.01 M NaN3 solution at a flow rate of 0.8 ml / min

Temperature of 35 ° C eluted in the GPC columns. The polymer solutions were filtered before injection with a 0.2 micrometer Millipore filter. The concentration of the polymer solution was 1 .5% Further compounds used as auxiliaries:

Bacote 20 ^® (from zirconium Chemicals) is an alkaline solution of Ammoniumzirkoni- carbonate (zirconates (2), bis [carbonato (2) -0] dihydroxydiammonium) having a solids content of 20%.

Preparation of surface coating agent

Surface coating agents were prepared with polymers 1-7 and the 12 wt% starch solution prepared above. For this purpose, the starch solution was initially charged and the polymer solution and Bacote 20 were added. The composition of the surface coating agent was chosen so that the amounts indicated in the table were obtained in parts by weight starch (solid), parts by weight polymer (solid) and parts by weight Bacote 20. The compositions were each supplemented with water such that a solids content of 12 wt .-% was achieved. In each case 2 parts by weight of Bacote 20 were used, which corresponds to the equivalent of 0.4 parts by weight of ammonium zirconium carbonate. Surface Thickness Polymer Bacote 20 coating agent [parts by weight]

1 (comparison) 12 - -

2 n.e. 8 4 parts by weight of polymer 1 -

3 8 4 parts by weight of polymer 1 2 parts by weight of T

4 n.e. 8 4 parts by weight of polymer 2 -

5 8 4 parts by weight of polymer 2 2 parts by weight of T

6 n.e. 8 4 parts by weight of polymer 3 -

7 8 4 parts by weight of polymer 3 2 parts by weight of T

8 n.e. 8 4 parts by weight of polymer 4

9 8 4 parts by weight of polymer 4 2 parts by weight of T

1 1 n.e. 8 4 parts by weight of polymer 5

12 8 4 parts by weight of polymer 5 2 parts by weight of T

13 n.e. 8 4 parts by weight of polymer 6

14 8 4 parts by weight of polymer 6 2 parts by weight of T

15 n.e. 8 4 parts by weight of polymer 7

16 8 4 parts by weight of polymer 7 2 parts by weight

n.e .: not according to the invention

Parts by weight: parts by weight

paper coating

Since no large-scale experiment was carried out, dry base paper was coated with the surface coating agent. Since the paper is then dried again, the influence on the paper properties is irrelevant. The base paper used was a paper made from 100% recovered paper (mixture of grades: 1.02, 1 .04, 4.01) with a weight per unit area of 100 g / m2, and which has no surface strength.

The base paper was coated in the formulations described in Table 1 by means of a film press at 800 m / min on a test coater with IR dryers. The coating weights were determined gravimetrically. The indication of the coating weight refers to the dried coating quantity after leaving the IR dryer. Subsequently, the paper strength of the example papers was examined. It was coated with different amounts of surface coating agent.

Technical application testing of raw papers

Before testing the paper, it was stored for 24 h at 50% humidity and the following strength tests were carried out

- CMT according to DIN EN 23035 (Corona medium test)

The results of the coating with a coating weight of 2 g / m ² are shown in Table 2. This corresponds to an application rate of 0.7 g / m ² polymer (solid) and 1.3 g / m ² starch (solid) and in the examples according to the invention plus Barcote 20. Table 2: Application results of the paper with the surface coating agents of Examples 2 -16 with a coating weight of 2 g / m ²

1): Increase in% compared to uncoated base paper

The results of the coating with a coating weight of 4 g / m ² are shown in Table 3. This corresponds to an application rate of 1.3 g / m ^{2 of} polymer (solid) and 2.7 g / m ^{2 of} starch (solid) and in the examples according to the invention plus Barcote 20.

Table 3: Application results of the paper with the surface coating agents of Examples 2 -16 with a coating weight of 4 g / m ²

Paper Example Polymer CMT Factor [N m ² / g] Boost ¹ > [%]

1 Comparison 1 - 2.20 19

2b 2 n.e. 1 2.25 22

3b 3 1 2,43 31

4b 4 n.e. 2 2.25 22

5b 5 2 2,50 35

6b 6 n.e. 3

7b 7 3

8b 8 n.e. 4 2.24 22

9b 9 4 2.29 25

1 1 b 1 1 n.e. 5 2.23 21

12b 12 5 2.43 32

13b 13 n.e. 6 2,1 1 19

14b 14 6 2.22 21

15b 15 n.e. 7 2.23 21

16b 16 7 2,40 31 1): Increase in% compared to uncoated base paper

The results of the coating with a coating weight of 6 g / m ² are shown in Table 4. This corresponds to an application rate of 2 g / m ^{2 of} polymer (solid) and 4 g / m ^{2 of} starch (solid) and in the examples according to the invention plus Barcote 20.

Table 4: Application results of the paper with the surface coating agents of Examples 2 -16 with a coating weight of 6 g / m ²

1): Increase in% compared to uncoated base paper

Claims

claims

1 . Aqueous surface-coating agent for paper and cardboard having a solids content of 1 to 55 wt .-% containing

(A) 0 to 20 parts by weight of starch,

(B) 0.01 to 20 parts by weight of a zirconium carbonate compound,

(C) 0.01 to 40 parts by weight of synthetic water-soluble polymer containing one or more monomers having monoethylenic double bonds in copolymerized form.

An aqueous surface coating composition according to claim 1, characterized in that the synthetic water-soluble polymer has an average molecular weight M _w ^ 1 million daltons.

3. An aqueous surface coating composition according to claim 1 or 2, characterized in that the synthetic water-soluble polymer monomers in copolymerized form selected from acrylamide, vinyl alcohol, vinyl acetate and an N-vinylcarboxylic acid amide of the formula in which R ¹ , R ² = H or C ¹ to C 6 alkyl, contains.

4. Aqueous surface-coating agent according to any one of claims 1 to 3, characterized in that the synthetic water-soluble polymer is an anionic polymer.

5. An aqueous surface coating composition according to any one of claims 1 to 4, characterized in that the synthetic water-soluble polymer is obtainable by copolymerizing a monomer mixture comprising

(a) one or more monomers selected from acrylamide and an N-vinylcarboxylic acid amide of the formula in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,

(B) one or more acid groups containing monoethylenically unsaturated monomers and / or their alkali metal, alkaline earth metal or ammonium salts and

(c) optionally one or more monoethylenically unsaturated monomers other than the monomers (a) and (b), and (D) optionally one or more compounds having at least two ethylenically unsaturated double bonds in the molecule.

6. Aqueous surface-coating agent according to any one of claims 1 to 5, characterized in that the synthetic water-soluble polymer is a co- or terpolymer comprising the monomers acrylic acid and vinylformamide in copolymerized form.

The aqueous surface-coating agent according to any one of claims 1 to 6, characterized in that the aqueous surface-coating agent has a viscosity in the range of 1 to 200 mPa · s.

8. An aqueous surface coating composition according to any one of claims 1 to 7 containing

(A) 1 to 20 parts by weight of starch,

(B) 0.01 to 20 parts by weight of a zirconium carbonate compound,

(C) 0.01 to 40 parts by weight of synthetic water-soluble polymer containing one or more monomers having monoethylenic double bonds in copolymerized

Shape.

9. A process for the production of paper and paperboard comprising the steps a) the treatment of paper stock with paper auxiliaries and / or filler,

b) dewatering of the paper stock treated according to a) with sheet formation and c) coating of the paper web obtained according to b) with a surface coating agent according to one of claims 1 to 8

d) and drying the according to c) coated paper web.

10. Paper and paperboard obtainable by the process according to claim 9.

1 1. Use of the paper according to claim 10 for the production of corrugated cardboard.