EP2888404B1 - Method for producing paper, paperboard and cardboard - Google Patents

Description

The invention relates to a process for the production of paper, paperboard and paperboard comprising dewatering a filler-containing paper stock containing at least one water-soluble polymer which is obtainable by the Hofmann degradation of an acrylamide and / or methacrylamide-containing polymer, with sheet formation in the wire section and subsequent Pressing the paper in the press section.

The development of new processes for the production of paper takes place at various points in the process. Improved papers are achieved by new ingredients or modified dosing. But even faster and faster paper machines make new demands on the manufacturing process.

A limiting factor on the way to further increasing the speed of paper machines is the initial wet texture strength. It limits the maximum applicable force that can be exerted on a sheet just formed in the paper machine that has passed through the wire and press sections of the machine and is being transferred to the dryer section. In this case, the sheet must be removed from the press rollers. In order to be able to reliably ensure tear-free operation of a paper machine, the applied peel force at this point must be significantly smaller than the initial wet texture strength of the wet paper. An increase in the initial wet structure strength allows the use of higher take-off forces and thus a faster operation of the paper machine, cf. EP-B-0 780 513 ,

Initial wet web strength refers to the strength of a wet paper that has never been dried. This is the strength of a wet paper, as is the case in papermaking after passing through the wire and press section of the paper machine.

In the press section, the wet nonwoven fabric is doffed onto the press felt by a suction cup (suction roll or static vacuum element). The task of the press felt is the transport of the fibrous web by press nips of various modifications. Depending on the design of the press section and the composition of the paper stock, the dry content of the web is up to a maximum of 55%. The dry content increases with the pressure exerted on the continuous paper web in the press. Printing and thus the dry content of the paper web can be varied over a relatively large range in many paper machines.

It is known that the initial wet structural strength can be increased by increasing the solids content of the paper at the point between the press and dryer sections in the manufacturing process. There is also the possibility of the solids content improve this point of the process through additives to increase drainage. But there are limits to this possibility.

The WO 2009/156274 teaches the use of amphoteric copolymers obtainable by copolymerization of N-vinylcarboxamide with anionic comonomers and subsequent hydrolysis of the vinylcarboxamide as a stock additive to increase the initial wet strength of paper. The treatment takes place, for example, in thick matter or in thin paper during the papermaking process.

The older registration WO 2012/175392 teaches the use of acrylamide-based amphoteric copolymers obtainable by copolymerizing acrylamide with anionic comonomers as a stock additive to increase the initial wet strength of paper. The treatment takes place in the thick matter in the papermaking process. In addition, the press section of the paper machine must be set so that the dry content of the wet paper web after leaving the press section exceeds a minimum value dependent on the composition of the material.

Furthermore, for example, the use of polymers obtained by the Hofmann degradation of an acrylamide- and / or methacrylamide-containing polymer for solidification is known.

The invention has for its object to increase in the production of paper, the initial wet structural strength of the still wet paper web before the transition to the dryer section, in order to achieve higher machine speeds compared to known methods in the papermaking process.

• wobei x für den Zahlwert des Füllstoffgehalt des trockenen Papier, Pappe oder Kartons (in Gew.-%)
• und G(x) für den Zahlwert des minimalen Feststoffgehalt (in Gew.-%), auf den das Blatt gepresst wird, steht,
• wobei das wasserlösliche Polymer durch den Hofmannabbau eines Acrylamid- und/oder Methacrylamid-haltigen Polymers und gegebenenfalls einer anschließenden Nachvernetzung erhältlich ist,
• mit der Maßgabe, dass bei einem Füllstoffgehalt von 15 Gew.-% oder kleiner in der Presspartie auf mindestens einen Feststoffgehalt von 48 Gew.-% gepresst wird,
• wobei das wasserlösliche Polymer dem Papierstoff mit einer Faserstoffkonzentration im Bereich von 20 bis 40 g/l und vor Zugabe eines Füllstoffs zugesetzt wird.

Accordingly, a process for the production of paper, paperboard and paperboard has been found comprising dewatering a filler-containing paper stock containing at least one water-soluble polymer with formation of sheets in the wire section and then pressing the paper in the press section, resulting in a stock having a pulp concentration in the press section Range from 20 to 40 g / l dosing the at least one water-soluble polymer, then the stock diluted to a pulp concentration in the range of 5 to 15 g / l, the diluted paper stock dewatered to form a sheet and the sheet in the press section to a solids content G (x) Wt% or greater and G (x) calculates after $$\mathrm{G}\left(\mathrm{x}\right)=48+\left(\mathrm{x}-15\right)\cdot 0.4$$

• where x is the numerical value of the filler content of the dry paper, board or cardboard (in% by weight)
• and G (x) is the number of minimum solids (in% by weight) on which the sheet is pressed,
• wherein the water-soluble polymer is obtainable by the Hofmann degradation of an acrylamide- and / or methacrylamide-containing polymer and optionally a subsequent post-crosslinking,
• with the proviso that at a filler content of 15% by weight or less in the press section is pressed to at least a solids content of 48% by weight,
• wherein the water-soluble polymer is added to the pulp at a pulp concentration in the range of 20 to 40 g / l and before the addition of a filler.

Under pulp, a mixture of water and pulp is understood below, which additionally contains, depending on the stage in the manufacturing process of the paper, paperboard or cardboard, the water-soluble polymer, filler and optionally paper auxiliaries.

The dry content of the paper is understood as meaning the solids content of paper, board, cardboard and fibrous material with the heat-barrier method as determined in accordance with DIN EN ISO 638 DE.

In the context of this application, the term pigment is used synonymously with the term filler, since in the production of paper the pigments are used as fillers. Under filler is, as usual in papermaking, inorganic pigment to understand.

The inventive method is used to produce paper, cardboard and cardboard comprising dewatering a filler-containing paper stock. The filler content (x) of the paper, paperboard and cardboard can be 5 to 40% by weight, based on the paper, paperboard or cardboard.

According to a preferred embodiment, a process for the production of paper is preferred whose filler content is 20 to 30 wt .-%. Such papers are, for example, wood-free papers.

According to a further preferred embodiment, a process for the production of paper is preferred whose filler content is 10 to 20 wt .-%. Such papers are used primarily as packaging papers.

According to a further preferred embodiment, a process for the production of paper is preferred whose filler content is 5 to 15 wt .-%. Such papers are used primarily for newspaper printing.

According to another preferred embodiment, preference is given to a process for producing paper whose filler content is from 25 to 40% by weight, for example SC papers.

zu $$\mathrm{G}\left(30\right)=48+\left(30-15\right)\cdot \mathrm{0,4}=54$$

bzw. zu $$G\left(15\right)=48+\left(15-15\right)\cdot \mathrm{0,4}=48.$$

The aqueous paper pulp containing at least one water-soluble polymer, pulp and filler is dewatered in the wire section to form a sheet and the sheet is pressed in the press section, that is, further dehydrated. The dewatering in the press section takes place up to a minimum solids content, but can also go beyond that. This lower limit of the solids content up to which the product must be pressed is also referred to hereinafter as the limit dry content or else as the minimum solids content G (x) and is based on the pressed sheet which is a mixture of paper stock and water. This Grenztrockengehalt to which at least dehydrated, it depends on the amount of filler. Thus, the limit dry content G (x) for a paper with a filler content of 30 or 15 wt .-% calculated according to the formula $$\mathrm{G}\left(\mathrm{x}\right)=48+\left(\mathrm{x}-15\right)\cdot 0.4$$

to $$\mathrm{G}\left(30\right)=48+\left(30-15\right)\cdot 0.4=54$$

or too $$G\left(15\right)=48+\left(15-15\right)\cdot 0.4=\mathrm{48th}$$

In other words, in the production of paper having a filler content of 30% by weight, according to the invention, a solids content of at least 54% by weight is pressed in the press section in order to obtain paper with good initial wet structural strength.

In contrast, according to the invention, in the production of paper having a filler content of 15 or smaller in the press section, a solids content of at least 48% by weight is pressed in order to obtain paper with good initial wet structural strength.

According to one embodiment of the invention, for the production of paper, paperboard and paperboard having a filler content of 17 to 32% by weight in the press section, at least a solids content in the range of 49 to 55% by weight is pressed.

According to another embodiment of the invention, for the production of paper, paperboard and cardboard having a filler content of 15% by weight or less in the press section, at least a solids content of 48% by weight is pressed.

The fibers are treated according to the invention by metering the water-soluble polymer into the pulp at a pulp concentration in the range from 20 to 40 g / l. In a pulp concentration of 20 to 40 g / l (corresponds to a pulp concentration of 2 to 4 wt .-% based on the aqueous pulp) is usually understood in the papermaking the thick material. This is distinguished from the thin material, which is to be understood below as a fiber concentration in the range of 5 to 15 g / l. Following treatment with water-soluble polymer, the stock is diluted with water to a pulp concentration in the range of 5 to 15 g / l.

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. Pulp, bleached and unbleached pulp and pulp from all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical 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. Preferably, unbleached pulp, also referred to as unbleached kraft pulp, is used. Suitable annual plants for the production of fibrous materials are for example rice, wheat, sugarcane and kenaf. Waste paper may also be used to make the pulps, either alone or blended with other pulps. For example, the waste paper can come from a deinking process. But it is not necessary that the waste paper to be used is subjected to such a process. Furthermore, it is also possible to start from fiber blends of a primary material and recycled coated broke.

In the case of bleached or unbleached pulp, a pulp having a freeness of 20 to 30 SR can be used. In general, a pulp with a freeness of about 30 SR is used, which is ground during the production of the pulp. Preferably, pulp is used which has a freeness of ≤30 SR.

The treatment of the pulp with the water-soluble polymer is carried out in aqueous suspension, preferably in the absence of other process chemicals commonly used in papermaking. It takes place in the papermaking process by adding at least one water-soluble polymer to an aqueous paper stock having a pulp concentration of 20 to 40 g / l. Particularly preferred is a process variant in which a water-soluble polymer is added to the aqueous paper stock at a time which is prior to the addition of the filler. Very particularly preferably, the addition takes place after the addition of the dry strength agent, for example the starch.

The water-soluble polymers are preferably added in an amount of 0.05 to 5.00 wt .-%, based on pulp (solid).

Typical application rates are, for example, 0.5 to 50 kg, preferably 0.6 to 10 kg of at least one water-soluble polymer, per ton of dry pulp. Particularly preferably, the amounts of water-soluble polymer used is 0.6 to 3 kg of polymer (solid), based per ton of dry pulp.

The exposure time of the water-soluble polymer to a pure pulp after metering to sheet formation is, for example, 0.5 second to 2 hours, preferably 1.0 second to 15 minutes, more preferably 2 to 20 seconds.

In addition to the water-soluble polymer, inorganic pigment is added as a filler to the pulp. Suitable inorganic pigments are all pigments customarily usable in the paper industry on the basis of metal oxides, silicates and / or carbonates, in particular of pigments from the group consisting of calcium carbonate which is in the form of ground (GCC) lime, chalk, marble or precipitated calcium carbonate ( PCC), talc, kaolin, bentonite, satin white, calcium sulfate, barium sulfate and titanium dioxide. It is also possible to use mixtures of two or more pigments.

According to the invention, inorganic pigments having an average particle size (volume average) ≦ 10 μm, preferably from 0.3 to 5 μm, in particular from 0.5 to 2 μm, are used. The determination of the average particle size (volume average) of the inorganic pigments and of the particles of the powder composition is carried out in the context of this document generally by the method of quasi-elastic light scattering (DIN-ISO 13320-1), for example with a Mastersizer 2000 from. Malvern Instruments Ltd. ,

The inorganic pigment is preferably metered after the addition of the water-soluble polymer. In this case, according to a preferred embodiment, the addition takes place in the stage in which the pulp is already present as a thin material, ie at a pulp concentration of 5 to 15 g / l.

According to a further preferred embodiment, the inorganic pigment is metered both in the thin and in the thick matter, wherein the ratio of the two addition amounts (adding thick matter / adding thin material) is preferably 5/1 to 1/5.

In addition to the water-soluble polymer, conventional paper auxiliaries may optionally be admixed with the paper stock, generally at a pulp concentration of 5 to 15 g / l. Conventional paper auxiliaries are, for example, sizing agents, wet strength agents, synthetic cationic or anionic retention aids Polymers as well as dual systems, dehydrating agents, other dry strength agents, optical brighteners, defoamers, biocides and paper dyes. These conventional paper additives can be used in the usual amounts.

The sizing agents include alkylketene dimers (AKD), alkenylsuccinic anhydrides (A-SA) and rosin size.

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.

Dry strength agents are synthetic dry strength agents such as polyvinylamine, polyethyleneimine, glyoxylated polyacrylamide (PAM), amphoteric polyacrylamides or natural dry strength agents such as starch.

In the paper machine, these dry contents are set when passing through the press section. In the press section, the wet nonwoven fabric is doffed onto the press felt by a suction cup (suction roll or static vacuum element). The task of the press felt is the transport of the fibrous web by press nips of various modifications. The dry content of the web is, depending on the design of the press section and the composition of the pulp, up to a maximum of 55%. The dry content increases with the pressure exerted on the continuous paper web in the press. Printing and thus the dry content of the paper web can be varied over a relatively large range in many paper machines.

The water-soluble polymer used according to the invention is obtainable by the Hofmann degradation of an acrylamide- and / or methacrylamide-containing polymer and optionally a subsequent postcrosslinking.

prepolymer

These acrylamide- and / or methacrylamide-containing polymers, also referred to below as prepolymers, are obtainable by free-radical copolymerization of a monomer mixture comprising acrylamide and / or methacrylamide.

The monomers acrylamide and methacrylamide are based on the monomer composition of the prepolymer individually or as a mixture in proportions of 10 mol% to 100 mol%, preferably in proportions of 20 to 90 mol%, more preferably in proportions of 30 to 80 mol% in copolymerized Form included.

• a) Acrylamid und/oder Methacrylamid (Monomere a)
• b) gegebenenfalls ein oder mehrere monoethylenisch ungesättigte Monomer, deren korrespondierende Struktureinheit im Polymer unter den Reaktionsbedingungen des Hofmann-Abbaus stabil ist, und/oder DADMAC (Diallyldimethylammoniumchlorid) (Monomere b),
• (c) gegebenenfalls einer oder mehrerer Verbindungen mit zwei oder mehr ethylenisch ungesättigten Resten, und deren korrespondierende Struktureinheiten im Polymer unter den Reaktionsbedingungen des Hofmann-Abbaus stabil sind, wobei DADMAC nicht umfasst ist (Monomere c).

Preferably, the monomer mixture comprises the following composition:

• a) acrylamide and / or methacrylamide (monomers a)
• b) optionally one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation and / or DADMAC (diallyldimethylammonium chloride) (monomers b),
• (C) optionally one or more compounds having two or more ethylenically unsaturated radicals, and their corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation, wherein DADMAC is not included (monomers c).

Monoethylenically unsaturated monomers whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation are, for example, nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, such as acrylonitrile and methacrylonitrile, amides of α, β-ethylenically unsaturated monocarboxylic acids and their N Alkyl and N, N-dialkyl derivatives, N-vinyl lactams, nitrogen-containing heterocycles, vinyl aromatics, C ₂ -C ₈ monoolefins, α, β-ethylenically unsaturated mono- and dicarboxylic acids and their salts, anhydrides of α, β-ethylenically unsaturated mono - and dicarboxylic acids, ethylenically unsaturated sulfonic acids and their salts, ethylenically unsaturated phosphonic acids and their salts.

Examples of members of this group (b) are e.g. N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, n-propyl (meth) acrylamide, N- (n-butyl) (meth) acrylamide, tert-butyl (meth) acrylamide, n-octyl (meth ) acrylamide, 1,1,3,3-tetramethylbutyl (meth) acrylamide, ethylhexyl (meth) acrylamide, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N-vinylformamide, N-vinylacetamide, N-methyl-N-vinylacetamide and mixtures thereof. Further suitable monomers (b) are N- [2- (dimethylamino) ethyl] acrylamide, N- [2- (dimethylamino) ethyl] methacrylamide, N- [3- (dimethylamino) propyl] acrylamide, N- [3- ( Dimethylamino) propyl] methacrylamide, N- [4- (dimethylamino) butyl] acrylamide, N- [4- (dimethylamino) butyl] methacrylamide, N- [2- (diethylamino) ethyl] acrylamide, N- [2- (diethylamino) ethyl] methacrylamide and mixtures thereof.

Suitable monomers (b) are furthermore N-vinyllactams and derivatives thereof which may have, for example, one or more C ₁ -C ₆ -alkyl substituents (as defined above).

These include N-vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-5-methyl-2-pyrrolidone, N-vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl-7-methyl-2-caprolactam, N-vinyl-7-ethyl-2-caprolactam and mixtures thereof.

Also suitable as monomers (b) are N-vinylimidazoles and alkylvinylimidazoles, in particular methylvinylimidazoles such as, for example, 1-vinyl-2-methylimidazole, 3-vinylimidazole N-oxide, 2- and 4-vinylpyridine N-oxides and betaine derivatives and quaternization products thereof monomers.

Also suitable is diallyldimethylammonium chloride (DADMAC).

Further suitable additional monomers are ethylene, propylene, isobutylene, butadiene, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and mixtures thereof.

Also suitable are monomers which carry at least one acid function, ie at least one sulfonic acid group, phosphonic acid group or carboxylic acid group. Also suitable are the salts of the abovementioned compounds. By way of example may be mentioned:
Vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, acrylamidomethylenephosphonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, CH ₂ = CH-NH-CH ₂ -PO ₃ H, monomethyl vinylphosphonate, allylphosphonic acid, monomethyl allylphosphonate, acrylamidomethylpropylphosphonic acid.

Also suitable are monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms and the water-soluble salts such as Akalimetall-, alkaline earth metal or ammonium salts of these carboxylic acids and the monoethylenically unsaturated carboxylic anhydrides into consideration. This group of monomers includes, for example, acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, α-chloroacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, glutaconic acid, aconitic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid and crotonic acid.

The acid group-carrying monomers can be present in unneutralized, partially neutralized or completely neutralized form, wherein the phosphonic acids one or both protons can be neutralized by suitable bases.

Suitable bases for the partial or complete neutralization of the acid groups of the monomers are, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines. Examples are sodium hydroxide, potassium hydroxide, Sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, magnesium hydroxide, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine and morpholine.

The monomers of this group (b) can be used alone or in a mixture.

Preferred monoethylenically unsaturated monomers whose corresponding structural units are stable in the polymer reaction conditions of Hofmann degradation are, for example, nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, such as acrylonitrile and methacrylonitrile, amides of α, β-ethylenically unsaturated monocarboxylic acids and their N- Alkyl and N, N-dialkyl derivatives, N-vinyl lactams and DADMAC.

The prepolymers preferably contain at least 5 mol%, preferably at least 10 mol% and preferably at most 90 mol%, preferably at most 70 mol% and in a particularly preferred form at most 50 mol% of one or more monoethylenically unsaturated monomers, the corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation, (monomers b) copolymerized, based on the total moles of monomers (a and b).

In addition, the prepolymers can be used in amounts of up to 5% by weight, preferably up to 3% by weight, in particular up to 1% by weight, very particularly preferably up to 1% by weight and at least 0.0001% by weight, in particular at least 0.001% by weight, based on the total weight of the monomers a and b used for the polymerization, of compounds having two or more ethylenically unsaturated radicals whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation, in copolymerized form DADMAC is not included (monomers c).

Such modification of the prepolymers by copolymerizing compounds having two or more ethylenically unsaturated radicals whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation is achieved, for example, with methylenebisacrylamide, triallylamine, tetraallylammonium chloride or N, N'-divinylpropyleneurea.

Particularly preferably, the monomer mixture used to prepare the prepolymer has the following composition: 30 to 95 mol% Acrylamide and / or methacrylamide (monomers a) and 5 to 70 mol% one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation and / or diallyldimethylammonium chloride (monomers b) and up to 1.0 wt .-% based on the total weight of the monomers a and b of one or more compounds having two or more ethylenically unsaturated radicals whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation.

In a further preferred embodiment, the monomer mixture used to prepare the prepolymer has the following composition: 50 to 90 mol% Acrylamide and / or methacrylamide and 10 to 50 mol% one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation and / or diallyldimethylammonium chloride (monomers b) and up to 1.0 wt .-% based on the total weight of the monomers a and one or more compounds having two or more ethylenically unsaturated radicals whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation.

In particular, a monomer mixture of the following composition is preferred for the production of the prepolymer: 60 to 80 mol% Acrylamide and / or methacrylamide (monomer a) 20 to 40 mol% Diallyldimethylammonium chloride (monomer b) and optionally from 0.001 to 0.1% by weight, based on the total amount of monomer a and monomer b, of one or more compounds selected from methylenebisacrylamide, triallylamine, tetraallylammonium chloride, N, N'-divinylpropyleneurea.

The prepolymers can be prepared by solution, precipitation, suspension, gel or emulsion polymerization. Preference is given to solution polymerization in aqueous media. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, e.g. an alcohol such as methanol, ethanol, n-propanol, isopropanol, etc.

The polymerization temperatures are preferably in a range of about 30 to 200 ° C, more preferably 40 to 110 ° C. The polymerization is usually carried out under atmospheric pressure, but it can also proceed under reduced or elevated pressure. A suitable pressure range is from 0.1 to 10 bar.

The acid group-containing monomers (b) are preferably used in the salt form.

To prepare the polymers, the monomers can be polymerized by means of free-radical initiators.

As initiators for the radical polymerization, the peroxo and / or azo compounds customary for this purpose can be used, for example alkali or ammonium peroxydisulfates, diacetyl peroxide, dibenzoyl peroxide, succinyl peroxide, di-tert-butyl peroxide, tert-butyl perbenzoate, tert-butyl perpivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl permalate, cumene hydroperoxide, diisopropyl peroxydicarbamate, bis (o-toluoyl) peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, tert-butyl perisobutyrate, tert-butyl peracetate, di-tert-amyl peroxide tert-butyl hydroperoxide, azo-bis-isobutyronitrile, azo-bis (2-amidonopropane) dihydrochloride or 2-2'-azobis (2-methyl-butyronitrile). Also suitable are initiator mixtures or redox initiator systems, such as, for example, ascorbic acid / iron (II) sulfate / sodium peroxodisulfate, tert-butyl hydroperoxide / sodium disulfite, tert-butyl hydroperoxide / sodium hydroxymethanesulfinate, H ₂ O ₂ / CuI.

To adjust the molecular weight, the polymerization can be carried out in the presence of at least one regulator. As a regulator, the usual compounds known in the art, such. B. sulfur compounds, for. As mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid, sodium hypophosphite, formic acid or dodecyl mercaptan and Tribromchlormethan or other compounds which act regulating the molecular weight of the polymers obtained, are used.

The molecular weight of the water-soluble prepolymer is, for example, at least 50,000, preferably at least 100,000 daltons and in particular at least 500,000 daltons. The molecular weights of the prepolymer are then e.g. 50,000 to 10 million, preferably 100,000 to 5 million (as determined by light scattering). This molar mass range corresponds, for example, to K values of 50 to 300, preferably 70 to 250 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25 ° C. and a polymer concentration of 0.1% by weight).

Hofmann degradation

Hofmann degradation (also referred to as Hofmann rearrangement) is understood by one skilled in the art to be the degradation of primary acid amides to amines with the loss of one carbon atom (Rompp Online, version 3.12). In Hofmann degradation, the amide groups of the prepolymer are reacted with hypohalites under alkaline conditions and then the carbamates formed are decarboxylated by acidification to give amino groups.

Such polymers are for example made EP-A-0 377 313 and WO-A-2006/075115 known. The preparation of polymers containing vinylamine groups is described, for example, in WO-A-2006/075115 , Page 4, line 25 to page 10, line 22 and in the examples on pages 13 and 14, the contents of which are expressly incorporated by reference.

The Hofmann degradation is preferably carried out in aqueous solution. 0.1 to 2.0, preferably 0.8 to 1.1, particularly preferably 1.0 molar equivalents of hypohalite are used per mole equivalent of amide group. The strong base is used in amounts of 1.0 to 4.0 molar equivalents per molar equivalent of amide group, preferably 1.5 to 3.0 molar equivalents, more preferably 2.0 to 2.5 molar equivalents.

For example, sodium hypochlorite (NaOCl) and sodium hypobromite (NaOBr) are used as hypohalites, with NaOCl being preferred. Alkali hydroxides, alkaline earth hydroxides and alkaline earth oxides are used as the strong base.

Hofmann degradation of the polymer occurs e.g. in the temperature range of -15 to 90 ° C, preferably -5 to 40 ° C optionally in the presence of quaternary ammonium salts as a stabilizer to prevent side reaction of the resulting amino groups with the amide groups of the starting polymer. After completion of the reaction with alkali metal hydroxide / alkali metal hypochlorite, the aqueous reaction solution is passed into a reactor in which an acid is introduced for the decarboxylation of the reaction product. The pH of the reaction product containing vinylamine units is adjusted to a value of 2 to 7.

The water-soluble polymer obtained by the Hofmann degradation of an acrylamide- and / or methacrylamide-containing polymer can be used in the process according to the invention.

According to another variant, the polymer obtained by the Hofmann degradation of an acrylamide- and / or methacrylamide-containing polymer is additionally postcrosslinked.

postcrosslinking

To increase the molecular weight of the Hofmann degraded polymer and to achieve branched polymer structures, the Hofmann degraded polymer can be post-reacted with crosslinkers. Crosslinkers are compounds which carry at least two reactive groups which can react with the primary amino groups of the Hofmann product.

Suitable crosslinkers are, for example, multifunctional epoxides, such as bisglycidyl ethers of oligo- or polyethyleneoxides or other multifunctional alcohols, such as glycerol or sugars, multifunctional carboxylic acid esters, polyfunctional isocyanates, polyfunctional acrylic or methacrylic acid esters, polyfunctional acrylic or methacrylic acid amides, epichlorohydrin, multifunctional acid halides, multifunctional nitriles, a, ω-chlorohydrin ethers of oligo- or polyethylene oxides or other multifunctional alcohols such as glycerol or sugars, divinylsulfone, maleic anhydride or ω-halocarboxylic acid, multifunctional haloalkanes in particular α, ω-dichloroalkanes and carbonates such as ethylene carbonate or propylene carbonate into consideration. Other crosslinkers are in WO 97/25367 , Pages 8 to 16 described.

Preferred crosslinkers are multifunctional epoxides such as bisglycidyl ethers of oligo- or polyethylene oxides or other multifunctional alcohols such as glycerol or sugars.

The crosslinkers are optionally used in amounts of up to 5.0% by weight, preferably from 20 ppm to 2% by weight, based on the polymer obtained by the Hofmann degradation.

The method according to the invention enables a tear-free operation of the paper machine. The resulting in the process paper web or paper sheet shows a significantly increased wet structural strength.

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

Examples

1. a) Herstellung des Präpolymers
2. b) Hofmann Abbau des Präpolymers
   und gegebenenfalls einer Nachvernetzung.

The preparation of the polymers takes place in the three successive steps:

1. a) Preparation of the prepolymer
2. b) Hofmann degradation of the prepolymer
   and optionally a post-crosslinking.

Preparation of Polymer I a) Preparation of the prepolymer I (70 mol% acrylamide and 30 mol% DADMAC (diallyldimethylammonium chloride) - unbranched)

A 2 l glass apparatus with anchor stirrer, reflux condenser, internal thermometer and nitrogen inlet tube was charged with 295.5 g of distilled water, 189.6 g of a 65% strength by weight aqueous solution of DADMAC and 1.0 g of 75% strength by weight phosphoric acid. By adding 0.4 g of sodium hydroxide, the pH was adjusted to 3. By introducing nitrogen, the template was deoxygenated while being heated to the polymerization temperature of 75 ° C. At the same time the following feeds were produced: Feed 1: Mixture of 253.0 g of a 50% strength by weight acrylamide solution, 60.0 g of distilled water and 0.9 g of sodium hydroxide Feed 2: 100g of a 0.6% wt .-% aqueous bisulfite solution Feed 3: 100g of a 0.88% by weight aqueous sodium persulfate solution

The three feeds were started at the same time. Feed 1 was metered in over a period of 2 hours while feeds 2 and 3 were metered in over a period of 5 hours. Subsequently, the temperature of the mixture was raised to 85 ° C. After the end of feeds 2 and 3, the batch was held at 85 ° C. for a further hour and then cooled.

A clear, viscous prepolymer solution having a solids content of 25.6% by weight and a viscosity of 50,000 mPas (Brookfield LV viscosity, spindle 4, 6 rpm, RT) was obtained.

b) Hofmann degradation of the prepolymer

250.0 g of the obtained according to a) prepolymer I were placed in a three-necked flask with internal thermometer and blade stirrer and cooled with constant stirring with the aid of an ice / salt mixture to 8 ° C.

The following feed was prepared: 234.5 g of a 14.1% strength by weight aqueous NaOCl solution and 20.5 g of distilled water were placed in a beaker and cooled to 5 ° C. using an ice bath. While stirring continuously, 71.1 g of a 50% strength by weight sodium hydroxide solution were slowly added dropwise so that the temperature could be kept below 10 ° C.

This feed was added dropwise from a cooled dropping funnel (<10 ° C) in 80 minutes to the cooled prepolymer sample so that the temperature during the addition was kept in the range 8-10 ° C. Subsequently, the reaction mixture was heated to 20 ° C within 10 minutes and kept at 20 ° C for 30 minutes. Subsequently, 558.1 g of this mixture were added dropwise with constant stirring to 135 g of 37% hydrochloric acid, with a strong evolution of gas was observed. Finally, the pH of the resulting solution was adjusted to pH 3.5 with 10.0 g of 25% strength by weight sodium hydroxide solution.

A clear, slightly viscous solution of polymer I having a polymer content of 8.6% by weight and a viscosity of 39 mPas (Brookfield LV viscosity, spindle 1, 60 rpm, RT) was obtained.

Preparation of Polymer II (postcrosslinked)

309.8 g of the polymer I were initially charged in a 500 ml three-necked flask with paddle stirrer and adjusted to pH 8.5 by addition of 6.8 g of a 50% strength by weight sodium hydroxide solution. Subsequently, the mixture was heated to 45 ° C and 0.29 g of Grillbond G 1701 (EMS) was added. After stirring for 30 minutes at 45 ° C, the temperature was raised to 55 ° C and the mixture was maintained at 55 ° C for 2 hours. Within this time, an increase in viscosity was observed. At the end of the 2 hours, the reaction was cooled to room temperature and the pH was adjusted to pH 3.0 by the addition of 8.0 g of 37% hydrochloric acid.

A clear, slightly viscous solution of polymer II having a polymer content of 8.2% by weight, a viscosity of 190 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT) was obtained.

Preparation of Polymer III a) Preparation of Prepolymer III (70 mol% acrylamide and 30 mol% DADMAC, triallylamine as monomer c)

155.8 g of distilled water, 189.6 g of a 65% strength by weight aqueous solution of DADMAC and 1.0 g of 75% strength by weight phosphoric acid were placed in a 2 l glass apparatus with anchor stirrer, reflux condenser, internal thermometer and nitrogen inlet tube. By adding 0.4 g of NaOH, the pH was adjusted to 3. By introducing nitrogen, the template was deoxygenated while being heated to the polymerization temperature of 75 ° C.

The following feeds were provided: Feed 1: 0.5 g of triallylamine was dissolved in 160.0 g of distilled water with the addition of 0.75 g of 75 wt .-% phosphoric acid. Subsequently, 253.0 g of a 50 wt .-% strength acrylamide solution was added and the pH was adjusted to 4.0 by means of 0.4 g of 25 wt .-% sodium hydroxide solution. Feed 2: 120 g of a 0.6 wt .-% aqueous bisulfite solution Feed 3: 120.6 g of a 0.88% by weight aqueous sodium persulfate solution

The 3 feeds were started at the same time. Feed 1 was added in 3 hours while feeds 2 and 3 were fed in 6 hours. After the end of the addition of feed 2, the temperature was raised to 85 ° C and held for a further hour at this temperature and then cooled.

A clear, viscous prepolymer solution having a solids content of 25.5% and a viscosity of 15,800 mPas (Brookfield LV viscosity, spindle 4, 6 rpm, RT) was obtained.

b) Hofmann degradation of the prepolymer III

250.0 g of the according to a) prepolymer III were placed in a three-necked flask with paddle stirrer and internal thermometer and cooled with constant stirring with the aid of an ice / salt mixture to 8 ° C.

At the same time, the following feed was prepared: For this purpose, 234.5 of a 14.1 wt .-% aqueous NaOCl solution and 20.5 g of distilled water were placed in a beaker, and cooled by means of an ice bath to 5 ° C. With constant stirring, 71.1 g of a 50% strength by weight sodium hydroxide solution were slowly added dropwise so that the temperature could be kept <10 ° C.

This feed was added dropwise from a cooled dropping funnel (<10 ° C) in 80 minutes to the original that the temperature during the addition in the range 8-10 ° C could be maintained. Subsequently, the reaction mixture was heated to 20 ° C in 10 min and kept at 20 ° C for 60 min. Subsequently, 566.2 g of this mixture were added dropwise with constant stirring to 135 g of 37% hydrochloric acid, with a strong evolution of gas was observed. Finally, the pH of the resulting solution was adjusted to pH 3.5 with 12.2 g of 25% strength by weight sodium hydroxide solution.
A clear, slightly viscous solution of polymer III having a polymer content of 8.6% by weight and a viscosity of 23 mPas (Brookfield LV viscosity, spindle 1.60 rpm, RT) was obtained.

Polymer IV (postcrosslinked)

301.8 g of the polymer III were placed in a 500 ml three-necked flask with paddle stirrer and adjusted by addition of 6.2 g of a 50 wt .-% sodium hydroxide solution to pH 8.5. The mixture was then heated to 45 ° C and 0.43 g Grillbond G 1701 (EMS) added. After stirring for 30 minutes at 45 ° C, the temperature was raised to 55 ° C and the mixture was maintained at 55 ° C for 3 hours. Within this time, an increase in viscosity was observed. At the end of the 3 hours, the reaction was cooled to room temperature and the pH was adjusted to 3.0 by the addition of 7.4 g of 37% hydrochloric acid.
A clear, slightly viscous solution of polymer IV having a polymer content of 8.2%, a viscosity of 419 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT) was obtained.

Preparation of Polymer V a) Preparation of the prepolymer V (70 mol% acrylamide and 30 mol% DADMAC, triallylamine as monomer c)

155.8 g of distilled water, 189.6 g of a 65% strength by weight aqueous solution of DADMAC and 1.0 g of 75% strength by weight phosphoric acid were placed in a 2 l glass apparatus with anchor stirrer, reflux condenser, internal thermometer and nitrogen inlet tube. By adding 0.4 g of NaOH, the pH was adjusted to 3. By introducing nitrogen, the template was deoxygenated while being heated to the polymerization temperature of 75 ° C. At the same time the following feeds were produced: Feed 1: 0.25 g of triallylamine was dissolved in 160.0 g of distilled water with the addition of 0.75 g of 75 wt .-% phosphoric acid. Subsequently, 253.0 g of a 50 wt .-% strength acrylamide solution was added and the pH adjusted by means of 0.6 g of 25 wt .-% sodium hydroxide solution to 4.0. Feed 2: 120 g of a 0.6 wt .-% aqueous bisulfite solution Feed 3: 120.6 g of a 0.88% by weight aqueous sodium persulfate solution

The 3 inlets were started synchronously. Feed 1 was added in 3 hours while feeds 2 and 3 were fed in 6 hours. After the end of feed 2, the temperature was raised to 85 ° C. After the end of feeds 2 and 3, the batch was held at 85 ° C. for a further hour and then cooled. A clear, viscous prepolymer solution having a solids content of 25.5% and a viscosity of 12,400 mPas (Brookfield LV viscosity, spindle 4, 6 rpm, RT) was obtained.

b) Hofmann degradation of the prepolymer

250.0 g of the according to a) prepolymer V were placed in a three-necked flask with paddle stirrer and internal thermometer and cooled with constant stirring with the aid of an ice / salt mixture to 8 ° C.
At the same time, the following feed was produced:
234.5 of a 14.1% strength by weight aqueous NaOCl solution and 20.5 g of distilled water were introduced into a beaker and cooled to 5 ° C. by means of an ice bath. While stirring continuously, 71.1 g of a 50% strength by weight NaOH solution were added dropwise so that the temperature could be kept <10 ° C.

This feed was added dropwise from a cooled dropping funnel (<10 ° C) in 80 minutes to the template that the temperature during the addition in the range 8-10 ° C could be maintained. Subsequently, the reaction mixture was heated to 20 ° C in 10 min and kept at 20 ° C for 60 min. Subsequently, 566.2 g of this mixture were added dropwise with constant stirring to 135 g of 37% hydrochloric acid, with a strong evolution of gas was observed. Finally, the pH of the resulting solution was adjusted to pH 3.5 with 16.0 g of 25% strength by weight sodium hydroxide solution.
A clear, slightly viscous solution of polymer V having a polymer content of 8.5%, a viscosity of 22 mPas (Brookfield LV viscosity, spindle 1, 60 rpm, RT) was obtained.

Polymer VI (postcrosslinked)

314.4 g of the polymer V were placed in a 500 ml three-necked flask with paddle stirrer and adjusted by the addition of 6.4 g of a 50 wt .-% sodium hydroxide solution to pH 8.5. The mixture was then heated to 45 ° C and 0.44 g Grillbond G 1701 (EMS) was added. After stirring for 30 minutes at 45 ° C, the temperature was raised to 55 ° C and the mixture was maintained at 55 ° C for 3 hours. Within this time, an increase in viscosity was observed. At the end of the 3 hours, the reaction was cooled to room temperature and the pH was adjusted to 3.0 by the addition of 7.6 g of 37% hydrochloric acid.

A clear, slightly viscous solution of polymer VI having a polymer content of 8.1%, a viscosity of 190 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT) was obtained.

Polymer VII (85 mol% acrylamide and 15 mol% acrylic acid)

Corresponding JP63042998 (see table on page 624) the Hofmann product C-4 was readjusted.

Polymer VIII (not according to the invention) (comparative example corresponds to polymer I from EP application no. 11170740.2)

In a 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet 400 g of deionized water were submitted. Furthermore, the following feeds were provided: Feed 1: In a beaker, the following components were mixed: 250 g of deionized water 95.6 g 50% strength by weight aqueous acrylamide solution 121.9 g 80 wt .-%, aqueous solution of acryloyloxyethyltrimethylammonium chloride 148.1 g 32 wt .-%, aqueous sodium acrylate solution 0.2 g of 1% strength by weight aqueous solution of diethylenetriaminepentaacetic acid. The addition of about 32 g of 37% strength hydrochloric acid adjusted the pH to 4.1 Feed 2: 60.0 g of a 1 wt .-% aqueous solution of 2,2'-azobis (2-amide inopropane) di hydrochloride Feed 3: 16.5 g of a 1 wt .-% aqueous solution of 2,2'-azobis (2-amide inopropane) -di hydrochloride

The original was heated to 63 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held at 63 ° C. for a further hour, then the mixture was heated to 72 ° C. and the vacuum was reduced correspondingly. The reaction mixture was kept at 72 ° C for a further 2 hours, then feed 3 was added all at once and postpolymerized at 72 ° C for a further 2 hours. Then the vacuum was released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 208 g of water were distilled off.

A clear, colorless, viscous solution of the polymer VIII having the composition of 40 mol% acrylamide, 30 mol% acryloyloxyethyltrimethylammonium chloride and 30 mol% sodium acrylate was obtained. Solids content: 14.5% by weight Viscosity: 10,600 mPas (Brookfield, spindle 7, 50 rpm, room temperature) K value 120 (0.1% solution of the polymer in a 5% by weight aqueous saline solution) Polymer IX (not according to the invention): (Comparative example corresponds to polymer II from EP application no. 11170740.2)

In a 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet 400 g of deionized water were submitted. Furthermore, the following feeds were provided: Feed 1: In a beaker, the following components were mixed: 250 g of deionized water 119.5 g of 50% strength by weight aqueous acrylamide solution 113.8 g 80% strength by weight aqueous solution of acryloyloxyethyltrimethylammonium chloride 108.6 g 32 wt .-%, aqueous sodium acrylate solution 0.2 g of 1% strength by weight aqueous solution of diethylenetriaminepentaacetic acid. The addition of about 38 g of 37% strength hydrochloric acid adjusted the pH to 4.1 Feed 2: 63.5 g of a 1% aqueous solution of 2,2'-azobis (2-amide inopropane) -di hydrochloride Feed 3: 17.0 g of a 1% aqueous solution of 2,2'-azobis (2-amide inopropane) -di hydrochloride

The original was heated to 66 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held for a further hour at 66 ° C, then was heated to 78 ° C and correspondingly reduced the vacuum. The reaction mixture was kept for a further 2 hours at 78 ° C, then feed 3 was added all at once and postpolymerized at 78 ° C for a further 2 hours. Then the vacuum was released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 200 g of water were distilled off.

A clear, colorless, viscous solution of the polymer IX having the composition of 50 mol% acrylamide, 28 mol% acryloyloxyethyltrimethylammonium chloride and 22 mol% sodium acrylate was obtained. Solids content: 14.1% by weight Viscosity: 42,000 mPas (Brookfield, spindle 7, 50 rpm, room temperature) K value 125 (0.1% solution of the polymer in a 5% aqueous saline solution)

Polymer X (not according to the invention) (corresponds to polymer III from EP application no. 11170740.2)

In a 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet 400 g of deionized water were submitted. Furthermore, the following feeds were provided: Feed 1: In a beaker, the following components were mixed: 250 g of deionized water 71.7 g 50% strength by weight aqueous acrylamide solution 130.1 g 80% strength by weight aqueous solution of acryloyloxyethyltrimethylammonium chloride 187.8 g 32 wt .-%, aqueous sodium acrylate solution 0.2 g of 1% strength by weight aqueous solution of diethylenetriaminepentaacetic acid. The pH was adjusted to 4.1 by adding about 34 g of a 37% strength hydrochloric acid Feed 2: 60.3 g of a 1 wt .-% aqueous solution of 2,2'-azobis (2-amide inopropane) -di hydrochloride Feed 3: 16.0 g of a 1 wt .-% aqueous solution of 2,2'-azobis (2-amide inopropane) -di hydrochloride

The original was heated to 63 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held at 63 ° C. for a further hour, then the mixture was heated to 72 ° C. and the vacuum was reduced correspondingly. The reaction mixture was kept at 72 ° C for a further 2 hours, then feed 3 was added all at once and postpolymerized at 72 ° C for a further 2 hours. Then the vacuum was released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 200 g of water were distilled off.

A clear, colorless, viscous solution of the polymer X having the composition of 30 mol% of acrylamide, 32 mol% of acryloyloxyethyltrimethylammonium chloride and 38 mol% of sodium acrylate was obtained. Solids content: 14.8% by weight Viscosity: 12,000 mPas (Brookfield, spindle 7, 50 rpm, room temperature) K value 117 (0.1% solution of the polymer in a 5% by weight aqueous saline solution)

Testing the polymers I to X described above to increase the initial wet strength of paper

To simulate the sheet formation process on a laboratory scale, the pulp concentration of the thin material in the examples must be set at 3.5 g / l.

Pretreatment of the pulp suspension

Bleached birch sulphate was beaten open at a pulp concentration of 4% in the laboratory pulper until a freeness of 30 ° SR was reached. An optical brightener (Blankophor® PSG) and a fully digested cationic starch (HiCat® 5163 A) were then added to the open material and allowed to act for 5 minutes. The digestion of the cationic starch was previously carried out as a 10% starch slurry in a jet cooker at 130 ° C and 1 minute residence time. The metered amount of the optical brightener was 0.5 wt .-% commercial goods, based on the solids content of the pulp suspension. The dosage of the cationic starch was 0.8% starch (solid), based on the solids content of the pulp suspension. The pulp content of the pulp suspension after addition of starch and optical brightener was 3.5% (35 g / l).

Examples 1 to 7

Seven beakers were filled with 50 g each of the pretreated pulp suspension described above. 1.75 g of a 1% strength by weight aqueous solution of one of the above-described polymers I to VII were metered into each of the beakers with slight stirring of the pulp suspension (corresponding to 1% polymer (solid) on pulp (solid)). Subsequently, the pulp suspensions were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension (equivalent to filler suspension) was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. It was pressed in each case up to a solids content of 50 wt .-% of the wet leaves.

Examples 8, 9 and 10 (not according to the invention)

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. To each of the beakers each metered 1.75 g a 1% strength by weight aqueous solution of one of the above-described polymers I-III with gentle stirring of the pulp suspension (corresponds to 1% polymer (solid) on pulp (solid)). Subsequently, the pulp suspensions were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By adjusting the residence time within the press arrangement, in each case up to a solids content of the wet leaves was pressed, which is shown in Table 1.

Examples 11, 12 and 13

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. 1.75 g of a 1% strength by weight aqueous solution of one of the polymers VIII to X described above were metered into each of the beakers with slight stirring of the pulp suspension (corresponding to 1% polymer (solid) on pulp (solid)). Subsequently, the pulp suspensions were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension (equivalent to filler suspension) was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. It was pressed in each case up to a solids content of 50 wt .-% of the wet leaves.

Example 14, 15 and 16 (not according to the invention - dosage in the thin material)

Three beakers with 50 g of the pretreated pulp suspension (thick stock) were diluted to a pulp concentration of 0.35% (equivalent to 3.5 g / l) by the addition of 450 g of water.

To each 500 g of the diluted pulp suspension (thin) each 1.75 g of a 1 wt .-% aqueous solution of polymer I, II or III were added (equivalent to 1 wt .-% polymer (solid) based on pulp (solid).

Thereafter, in each case a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added to the mixture. The added amount of the pigment suspension was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%.

The pulp suspension was processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By adjusting the reference time of the papers within the press arrangement, in each case up to a solids content of 50% by weight of the wet leaves was pressed.

Examples 17, 18 (reference)

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. Subsequently, the pulp suspensions were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension (equivalent to filler suspension) was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By varying the contact time both leaves with different dry content were produced (see Table 1)

Application testing: Determination of initial wet texture strength

The wet strength and the initial wet strength of paper are to be distinguished from the initial wet texture strength because both properties are measured on papers which are moistened again to a defined water content after drying. The initial wet strength is an important parameter in the assessment of non-permanent wet-strength papers. A dried and then moistened paper has a very different wet strength than a damp paper directly after passing through the wire and press section of a paper machine is present.

The determination of the initial wet structural strength on the wet paper takes place in each case according to the Voith method (cf. M.Schwarz and K. Bechtel "Initial structural strength in sheet formation", in Wochenblatt fur Papierfabrikation 131, pages 950-957 (2003) No. 16 , For this purpose, the wet leaves were beaten after pressing in the static press on a plastic backing and transferred to a cutting pad. Subsequently, the sample strips were cut with a defined length and width from the sheet. Under constant pressure they were pressed until the desired dry content was reached. For the examination of the paper sheets obtained according to the examples given above, in each case four dry contents in the range between 42% and 58% were set. From these values, the initial wet texture strength at 50% dry content was determined using an adjustment method described in the above reference. The actual measurement of the initial wet structural strength was made on a vertical tensile testing machine with a special clamping device. The force determined in the tractor was converted into the area-mass-independent so-called INF index. For a detailed description of the clamping device, the measuring procedure, the determination of the dry content in the paper and the data processing, the reference cited above can be used.

The results of the tests are shown in Table 1

Table 1: Results of the performance test for the production of paper with a filler content of 20 wt .-%. According to the calculation of the limit dry content G (x) = G (20), according to the invention, a solids content of at least 50% by weight is to be pressed: G (20) = 48 + (20-15) 0.4 = 50 example polymer INF index [Nm / g] Solids content up to the pressed [%] 1 I 3.9 50.3 2 II 3.5 50.5 3 III 3.3 50.2 4 IV 3.4 50.9 5 V 3.5 51.2 6 VI 3.6 50.6 7 VII 3.2 51.3 8 not according to the invention I 1.8 48.6 9 not according to the invention II 1.9 49.1 10 not according to the invention III 2.1 49.2 11 not according to the invention VIII 3.3 50.3 12 not according to the invention IX 3.1 50.5 13 not according to the invention X 2.9 50.2 14 (dosage in the thin) not according to the invention I 1.8 50.2 15 (dosage in the thin) not according to the invention II 1.5 50.0 16 (dosage in the thin) not according to the invention III 1.7 51.2 17 Reference 1.1 48.4 18 Reference 1.4 50.6

Claims (8)

1. A process for production of paper, card and board comprising draining a filler-containing paper stock comprising at least one water-soluble polymer with sheet formation in the wire section and then pressing the paper in the press section, wherein a paper stock having a fibrous concentration in the range from 20 to 40 g/l has the at least one water-soluble polymer added to it, then the paper stock is diluted to a fibrous concentration in the range from 5 to 15 g/l, the diluted paper stock is drained to form a sheet and the sheet is pressed in the press section to a solids content G(x) wt% or greater and G(x) computes according to $$\mathrm{G}\left(\mathrm{x}\right)=48+\left(\mathrm{x}-15\right)\cdot 0.4$$

   

   where x is the numerical value of the filler content of the dry paper, card or board (in wt%) and

   G(x) is the numerical value of the minimum solids content (in wt%) to which the sheet is pressed,

   wherein the water-soluble polymer is obtainable by Hofmann degradation of an acrylamide- and/or methacrylamide-containing polymer with or without subsequent postcrosslinking,
   with the proviso that, for a filler content of 15 wt% or less, there is pressing in the press section to at least a solids content of 48 wt%, wherein the water-soluble polymer is added to the paper stock having a fibrous concentration in the range from 20 to 40 g/l and before adding a filler.
2. The process according to claim 1 wherein the paper stock by way of fibrous material exclusively comprises a fibrous material having a freeness of ≤30° SR.
3. The process according to either one of claims 1 and 2 wherein the water-soluble polymer is added in an amount of 0.05 to 5.00 wt%, based on fibrous material.
4. The process according to any one of claims 1 to 3 wherein the acrylamide- and/or methacrylamide-containing polymer is obtainable by free-radically polymerizing a monomer mixture comprising

   a) acrylamide and/or methacrylamide,

   b) optionally one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation, and/or diallyldimethylammonium chloride,

   c) optionally one or more compounds having two or more ethylenically unsaturated moieties, and whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation.
5. The process according to any one of claims 1 to 5 wherein the acrylamide- and/or methacrylamide-containing polymer is obtainable by free-radically polymerizing a monomer mixture consisting of 50 to 90 mol% of acrylamide and/or methacrylamide, and 10 to 50 mol% of one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation, and/or diallyldimethylammonium chloride, and also up to 1.0 wt%, based on the total weight of monomers a and b, of one or more compounds having two or more ethylenically unsaturated moieties whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation.
6. The process according to any one of claims 1 to 5 wherein the acrylamide- and/or methacrylamide-containing polymer is obtainable by free-radically polymerizing a monomer mixture consisting of:

   60 to 80 mol% of acrylamide and/or methacrylamide (monomer a)

   20 to 40 mol% of diallyldimethylammonium chloride (monomer b)

   and also optionally from 0.001 to 0.1 wt%, based on the total amount of monomer a and monomer b, of one or more compounds selected from methylenebisacrylamides, triallylamine, tetrallylammonium chloride, N, N'-divinylpropyleneurea.
7. The process according to any one of claims 1 to 6 wherein the water-soluble polymer is obtainable by Hofmann degradation of an acrylamide- and/or methacrylamide-containing polymer and subsequent postcrosslinking with a crosslinker selected from multifunctional epoxides, multifunctional carboxylic esters, multifunctional isocyanates, multifunctional acrylic or methacrylic esters, multifunctional acrylic or methacrylic amides, epichlorohydrin, multifunctional acyl halides, multifunctional nitriles, α,ω-chlorohydrin ethers of oligo- or polyethylene oxides or of other multifunctional alcohols, divinyl sulfone, maleic anhydride or ω-halocarbonyl chlorides, multifunctional haloalkanes and carbonates.
8. The process according to any one of claims 1 to 7 for production of paper, card and board having a filler content of 17 to 32, which process comprises pressing in the press section to at least a solids content in the range from 49 to 55.