EP3697963B1 - Method for producing multiple ply paper - Google Patents

Description

The invention relates to a method for producing multi-layer paper, comprising dewatering two aqueous fiber suspensions to obtain two fiber webs, spraying at least one fiber web with an aqueous spray solution or spray suspension, joining the two fiber webs to form a layer composite, dewatering the layer composite under pressure to form a partially dewatered layer composite, and dewatering the partially dewatered layer composite using heat to form a multi-layer paper, wherein the aqueous spray solution or spray suspension contains a water-soluble polymer P. Further objects are a multi-layer paper obtainable by the method and a paper machine suitable for the method, which contains a spray device containing the aqueous spray solution or spray suspension with polymer P.

Multi-layer papers are made from paper stock mixtures or fiber mixtures with the same or different material composition by pressing together individual, still wet paper webs or paper layers. An important quality feature of multi-layer packaging papers or cardboard is their strength. This is largely determined by the internal cohesion of the materials used. The layer adhesion in the sense of the cohesion in the border area between the individual paper layers can represent a weak point. The trend towards using increased amounts of recycled raw material leads to ever shorter paper fiber lengths and therefore fundamentally poorer paper strengths. There is also a trend in folding box cardboard to use ever more voluminous fiber mixtures to increase flexural rigidity. Both trends increase the need to increase layer adhesion.

To increase the adhesion between layers, adhesive starch or starch derivatives are often used. For example, a native or modified starch based on wheat, corn, potato or tapioca is sprayed onto a paper web in the form of an aqueous suspension. In the drying section of a paper machine, gelatinization then occurs and solidification is achieved in this way. The use of native starch often has the disadvantage that only a low solids content can be used due to its high viscosity in aqueous solution. Subsequent exposure to heat can also cause the starch composite to become partially or completely irreversibly brittle.

EP0953679A discloses polymers to improve the strength of single- and multi-layer papers, which are obtainable by polymerization of at least 5% by weight (meth)acrylic acid and are applied to a paper layer by spraying, among other things. In some of the examples, a first fibrous web, which is made from a fibrous slurry from old corrugated cardboard and has a moisture content of 86%, is sprayed with various terpolymers obtained by polymerization of acrylic acid, acrylamide and acrylonitrile. Then a second fibrous web, which is also made from a fibrous slurry made from old corrugated cardboard and has a moisture content of 96%, is bonded to the sprayed first fibrous web by pressing. It is then dried and the paper strength of the resulting two-ply paper is determined according to J-TAPPI No. 19-77. The decisive factor is EP0953679A is the spraying of its polymers in dispersed form. The examples mentioned show that when the same polymers are sprayed in solution form, which is achieved by increasing the pH value from 2.7 to 7.0, only about a third of the previous strength value is obtained.

After JP 2007-063682 A To improve the adhesion of multi-ply papers, polymers obtained by polymerizing N-vinylformamide and subsequent, at least partial hydrolysis of the formamide groups are used in combination with starch. The examples disclose spraying a first fibrous web, which is made from a fibrous slurry from old corrugated cardboard and has a moisture content of 82%, with various suspensions or solutions containing a starch and/or a polymer solution. A second fibrous web, which is also made from a fibrous slurry from old corrugated cardboard and has a moisture content of 92%, is then bonded to the sprayed first fibrous web by pressing. It is then dried at 105°C and the paper strength of the resulting two-ply papers is determined according to J-TAPPI No. 19-77. Also mentioned as polymers in the examples are a polyallylamine and polymers obtained by polymerization of N-vinylformamide and subsequent, at least partial, hydrolysis of the formamide groups.

The JP 2002 294595 A describes a method for producing combination paper which achieves both a sufficient improvement in ply bonding strength and an improvement in the strength (internal strength) in the Z direction of a paper sheet itself, comprising the steps of combining each wet paper web layer after the formation of the paper layer, thereafter pressing the combined layer, and further drying the pressed layer.

The EN 42 41 117 A1 describes the use of copolymers which are formed by polymerizing a) 5 to 99 mol% of N-vinylcarboxamides, b) 95 to 1 mol% of monoethylenically unsaturated carboxylic acids and/or alkali metal, alkaline earth metal, ammonium or amine salts thereof and optionally c) up to 30 mol% of other monoethylenically unsaturated compounds and optionally d) up to 2 mol% of crosslinking agent and subsequent partial or complete cleavage of the formyl groups from the N-vinylcarboxamide units in the copolymer to form amine or ammonium groups.

The WO 2005/121451 A1 describes a machine for producing a fibrous web, which is characterized in that a measuring arrangement for measuring the ash content is installed within the machine, in particular within the wire section, the press section, the drying section or after the drying section in front of a calender.

The DE 198 29 757 A1 describes aqueous adhesive dispersions containing A) 0.1-10 wt. % adhesive polymer in the form of a dispersion, based on the total weight of the dispersion, B) 0.1-100 parts by weight of component A), of an anionic or cationic polyelectrolyte and C) 0-50 parts by weight, based on 100 parts by weight of components A), of at least one polyalkylene glycol with a molecular weight of 200-100,000 g/mol.

The EP1378603A2 describes a method for converting a paper machine in which a state-of-the-art size pressing station is replaced by a contactless application station for liquid or pasty agents.

The known processes for producing multi-layer paper or cardboard do not yet fully meet the requirements.

The invention is based on the object of providing a method for producing multi-layer paper or cardboard, with which multi-layer paper or cardboard with improved strength is obtained. This method should also be simple to carry out. Furthermore, the strength should be present when subjected to greater shear forces. Splitting, particularly along the original fiber webs, should also be made more difficult. Further desirable properties are maintaining the strength under the influence of heat or increased humidity when storing the produced multi-layer paper or cardboard or during its further processing.

1. (A) Entwässern einer ersten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf einem ersten Sieb, wodurch eine erste Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
2. (B) Entwässern einer zweiten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf einem zweiten Sieb, wodurch eine zweite Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
3. (C) Besprühen der ersten Faserstoffbahn, der zweiten Faserstoffbahn oder der ersten Faserstoffbahn und der zweiten Faserstoffbahn auf mindestens einer Flächenseite mit einer Sprühlösung oder Sprühsuspension aus einer Sprühvorrichtung, wodurch mindestens eine besprühte Faserstoffbahn, die eine besprühte Flächenseite hat, entsteht,
4. (D) Zusammenfügen der ersten Faserstoffbahn mit der zweiten Faserstoffbahn, von denen mindestens eine der beiden eine besprühte Faserstoffbahn ist, derart, dass mindestens eine besprühte Flächenseite der beiden Faserstoffbahnen die Kontaktflächenseite zur anderen Faserstoffbahn bildet und die Faserstoffbahnen in ihrer gesamten Breite übereinander liegen, wodurch ein Lagenverbund entsteht,
5. (E) Entwässern des Lagenverbunds durch Pressen, wodurch ein teilentwässerter Lagenverbund entsteht,
6. (F) Entwässern des teilentwässerten Lagenverbunds durch Wärmezufuhr, wodurch das getrocknete mehrlagige Papier entsteht,

• wobei die Sprühlösung oder Sprühsuspension enthält
  • (c-a) Wasser
  • (c-b) mindestens ein wasserlösliches Polymer P, das erhältlich ist durch Polymerisieren von
    1. (i) 40 bis 85 mol% eines Monomers der Formel I
       
       in der R¹ = H oder C₁-C₆-Alkyl bedeutet,
    2. (ii) 15 bis 60 mol% eines oder mehrerer ethylenisch ungesättigter Monomere, die von einem Monomer der Formel I verschieden sind,
    wobei die Gesamtmenge aller Monomere (i) und (ii) 100 mol% beträgt, und optional durch ein sich anschliessendes teilweises oder vollständiges Hydrolysierens der in das Polymer P einpolymerisierten Einheiten der Monomere der Formel (I) unter Bildung von primären Aminogruppen oder Amidingruppen,
• wobei der Anteil von Wasser mindestens 75 Gew.-% bezogen auf die Sprühlösung oder die Sprühsuspension beträgt.

A process for producing dried multi-ply paper has been found comprising the steps

1. (A) dewatering a first aqueous pulp suspension having a dry matter content of between 0.1% and 6% on a first screen to form a first pulp web having a dry matter content of between 14% and 25%,
2. (B) dewatering a second aqueous pulp suspension having a dry matter content of between 0.1% and 6% by weight on a second screen to form a second pulp web having a dry matter content of between 14% and 25% by weight,
3. (C) spraying the first fibrous web, the second fibrous web or the first fibrous web and the second fibrous web on at least one surface side with a spray solution or spray suspension from a spray device, thereby producing at least one sprayed fibrous web having a sprayed surface side,
4. (D) joining the first fibrous web to the second fibrous web, of which at least one of the two is a sprayed fibrous web, such that at least one sprayed surface side of the two fibrous webs forms the contact surface side to the other fibrous web and the fibrous webs lie one above the other across their entire width, thereby forming a layer composite,
5. (E) dewatering the composite layer by pressing, resulting in a partially dewatered composite layer,
6. (F) dewatering the partially dewatered layer composite by applying heat, thereby producing the dried multi-layer paper,

• wherein the spray solution or spray suspension contains
  • (approx) water
  • (cb) at least one water-soluble polymer P obtainable by polymerizing
    1. (i) 40 to 85 mol% of a monomer of formula I
       
       in which R ¹ = H or C ₁ -C ₆ alkyl,
    2. (ii) 15 to 60 mol% of one or more ethylenically unsaturated monomers other than a monomer of formula I,
    wherein the total amount of all monomers (i) and (ii) is 100 mol%, and optionally by subsequent partial or complete hydrolysis of the units of the monomers of formula (I) polymerized into the polymer P to form primary amino groups or amidine groups,
• wherein the proportion of water is at least 75% by weight based on the spray solution or the spray suspension.

Dry content is understood here as the ratio of the mass of a sample after drying to the mass of the sample before drying, expressed in weight percentages (wt.%). The dry content is preferably determined by drying at 105°C until the mass is constant. Drying is carried out at 105°C (± 2°C) in a drying cabinet until the mass is constant. Mass is constant here when, at dry contents of 1 to 100 wt.% the rounded first decimal place of the percentage value no longer changes and for dry contents of 0 to less than 1 wt.% the rounded second decimal place of the percentage value no longer changes. Drying takes place at ambient pressure, possibly 101.32 KPa, without any correction being made for deviations caused by weather and altitude. In the examples section under dry content determination you will find further information on practical implementation.

In step (A), the first aqueous pulp suspension is understood to mean a composition containing (a-a) water and (a-b) first pulp containing cellulose fibers. An alternative term for pulp suspension is paper pulp.

Mechanical and/or chemical processes can be used to obtain the aqueous fiber suspension. For example, grinding an aqueous fiber suspension is a mechanical process for shortening fibers and, in the case of cellulose fibers, also for defibrillating the fibers. The dewatering ability of the aqueous fiber suspension is determined by the degree of grinding achieved. One method for measuring the degree of grinding of a fiber suspension is to determine the dewatering kinetics according to Schopper Riegler in units of degrees Schopper Riegler (°SR).

Native and/or recycled fibers can be used as fibers. All fibers from wood or annual plants that are commonly used in the paper industry can be used. Suitable annual plants for the production of fibers are, for example, rice, wheat, sugar cane and kenaf. Wood pulp, e.g. from softwood or hardwood, includes, for example, groundwood, thermomechanical pulp (TMP), chemo-thermomechanical pulp (CTMP), pressure groundwood, semi-chemical pulp, high-yield pulp and refiner mechanical pulp (RMP). Coarse groundwood pulp typically has a freeness of 40-60 °SR compared to normal groundwood pulp with 60-75 °SR and fine groundwood pulp with 70-80 °SR. Pulps, e.g. from softwood or hardwood, include chemically digested sulfate, sulfite or soda pulps. Pulp can also be bleached or unbleached. Unbleached pulp, also known as unbleached kraft pulp, is preferred. Unrefined pulp typically has 13-17 °SR compared to low or medium refined pulp with 20-40 °SR and highly refined pulp with 50-60 °SR. Recovered fibers can come from waste paper, for example. The waste paper can optionally be subjected to a deinking process beforehand. Mixed waste paper can typically have around 40 °SR compared to waste paper from a deinking process with around 60 °SR. Recovered fibers from waste paper can be used alone or in a mixture with other, particularly native fibers.

An aqueous pulp suspension can be obtained, for example, by recycling existing paper or cardboard, for example by pulping waste paper in a pulper together is mechanically treated with water until the aqueous pulp suspension has the desired consistency. Another example of the combination of two fiber sources is the mixing of a primary pulp suspension with recycled broke from a coated paper that is produced using the primary pulp suspension.

In addition to water, the aqueous pulp suspension may contain other components that may be deliberately added to it or may be present through the use of waste paper or existing paper.

In paper production, a dry matter content of 2% to 4% by weight based on the aqueous fiber suspension (corresponds roughly to a fiber concentration of 20 to 40 g/L if almost exclusively fiber is present) is usually referred to as thick stock. This is usually distinguished from a dry matter content of 0.1% to less than 2% by weight based on the aqueous fiber suspension (corresponds roughly to a fiber concentration of 1 to less than 20 g/L if almost exclusively fiber is present), in particular 0.5% to 1.5% by weight (5 to 15 g/L). The dry matter content or dry weight of an aqueous fiber suspension includes all components that are non-volatile or, preferably, non-volatile when the dry matter content is determined by drying at 105°C to constant mass.

A possible further component of the first aqueous fiber suspension is (a-c) an organic polymer that is different from a fiber. The organic polymer (a-c) can be neutral, cationic or anionic.

A neutral organic polymer (ac) can be uncharged-neutral because it does not contain any polymer units with a functional group that carries a charge at least at a pH of 7. A functional group that carries a charge at least at a pH of 7 is understood here to mean an atom or a connected group of atoms that is covalently bound to the rest of the polymer unit. The functional group permanently carries a charge or acts on its own, i.e. independently of other components of the polymer unit or other polymer units, in its uncharged form in pure water as an acid or as a base. The acid effect leads to the formation of a negative charge on the corresponding functional group of the polymer unit when deprotonated with a base. This can happen, for example, with NaOH, KOH or NH ₃ , which are typically used in aqueous solution and lead to the corresponding sodium, potassium or ammonium salts. The base effect leads to the formation of a positive charge on the corresponding functional group of the polymer unit when protonated with an acid. This can be done, for example, with HCl, H ₂ SO ₄ , H ₃ PO ₄ , HCOOH or H ₃ CCOOH, which are typically used in aqueous solution, and give the corresponding chloride, hydrogen sulfate/sulfate, dihydrogen phosphate / hydrogen phosphate / phosphate, formate or acetate salts. An example of a functional group with a permanent positive charge is (-CH ₂ -) ₄ N ⁺ (a tetraalkylated nitrogen) such as that in diallyldimethylammonium or in 2-(N,N,N-trimethylammonium)ethyl acrylate. Examples of a functional group that leads to the creation of negative charges in the polymer unit are -COOH (a carboxylic acid), -SO ₂ OH (a sulfonic acid), -PO(OH) ₂ (a phosphonic acid), -O-SO ₂ OH (a monoesterified sulfuric acid) or -O-PO(OH) ₂ (a monoesterified phosphoric acid). Examples of a functional group which leads to the formation of positive charges in the polymer unit are -CH ₂ -CH(NH ₂ )- or -CH ₂ -NH ₂ (a primary and basic amino group), (-CH ₂ -) ₂ NH (a secondary and basic amino group), (-CH ₂ -) ₃ N (a tertiary and basic amino group) or (-) ₂ CH-N=CH-NH-CH(-) ₂ (a basic amidine group, in particular also in the form of a cyclic amidine).

Examples of a neutral organic polymer (a-c) which does not contain any polymer units having a functional group carrying a charge at least at a pH of 7 are polyacrylamide, poly(acrylamide-co-acrylonitrile), poly(vinyl alcohol) or poly(vinyl alcohol-co-vinyl acetate).

A neutral organic polymer (ac) can also be amphoteric-neutral because it contains polymer units with a functional group that carries a negative charge at least at a pH of 7, as well as polymer units with a functional group that carries a positive charge at least at a pH of 7, and furthermore the number of all negative charges and the number of all positive charges of the functional groups balance each other out. An organic polymer in which the number of positive charges differs from the number of negative charges by less than 7 mol% units is also considered to be amphoteric-neutral herein, where 100 mol% units are the number of all polymerized monomers to produce the organic polymer. For example, an organic polymer which is produced by polymerizing 30 mol% acrylic acid and 70 mol% N-vinylformamide and in which half of the polymerized N-vinylformamide units are hydrolyzed is considered to be amphoteric-neutral with a difference of 5 mol% units between the functional groups - COOH and -CH ₂ -CH(NH ₂ )-. In the case of the polymerization of 10 mol% itaconic acid (HOOC-CH ₂ -C(=CH ₂ )-COOH), 10 mol% acrylic acid and 80 mol% N-vinylformamide to form an organic polymer in which 44% of the polymerized N-vinylformamide units are hydrolyzed, the polymer is considered to be amphoteric-neutral with a difference of 5 mol% units between the functional groups -COOH and -CH ₂ -CH(NH ₂ )-.

A cationic organic polymer (ac) can be purely cationic, ie it contains polymer units with a functional group that carries a positive charge at least at a pH of 7, but it does not contain polymer units with a functional group that carries a negative charge at least at a pH of 7. Examples of a purely cationic Organic polymer (ac) are poly(allylamine), poly(diallylamine), poly(diallyldimethylammonium chloride), poly(acrylamide-co-diallyldimethylammonium chloride) or poly(acrylamide-co-2-(N,N,N-trimethylammonium)ethyl acrylate chloride).

A cationic organic polymer (ac) can also be amphoteric-cationic, ie it contains polymer units with a functional group that carries a positive charge at least at a pH of 7, as well as polymer units with a functional group that carries a negative charge at least at a pH of 7, and the number of all positive charges is higher than the number of all negative charges of the functional groups. An organic polymer is considered to be amphoteric-cationic herein if the number of positive charges differs from that number of negative charges by equal to or more than 7 mol% units, where 100 mol% units are the number of all polymerized monomers to produce the organic polymer. For example, an organic polymer obtained by polymerization of 30 mol% acrylic acid and 70 mol% N-vinylformamide, in which 57% of the polymerized N-vinylformamide units are hydrolyzed, is considered to be amphoteric-cationic with a difference of 10 mol% units between the functional groups -COOH and -CH ₂ -CH(NH ₂ )-.

An anionic organic polymer (a-c) can be purely anionic, i.e. it contains polymer units with a functional group that carries a negative charge at least at a pH of 7, but it does not contain polymer units with a functional group that carries a positive charge at least at a pH of 7. Examples of a purely anionic organic polymer (a-c) are poly(acrylic acid), poly(styrene-co-n-butyl acrylate-co-acrylic acid) or poly(acrylamide-co-acrylonitrile-co-acrylic acid).

An anionic organic polymer (ac) can also be amphoteric-anionic, ie it contains polymer units with a functional group that carries a negative charge at least at a pH of 7, as well as polymer units with a functional group that carries a positive charge at least at a pH of 7, and the number of all negative charges is higher than the number of all positive charges of the functional groups. An organic polymer is considered to be amphoteric-anionic herein if the number of negative charges differs from that number of positive charges by equal to or more than 7 mol% units, where 100 mol% units are the number of all polymerized monomers to produce the organic polymer. For example, an organic polymer obtained by polymerization of 30 mol% acrylic acid and 70 mol% N-vinylformamide, in which 29% of the polymerized N-vinylformamide units are hydrolyzed, is considered to be amphoteric-anionic with a difference of 10 mol% units between the functional groups -COOH and -CH ₂ -CH(NH ₂ )-.

The organic polymer (a-c) can also be differentiated according to whether it is linear, branched or crosslinked. Crosslinking can be achieved, for example, by adding a crosslinker during the polymerization of the starting monomers or by adding a crosslinker after polymerization, in particular just before the organic polymer (a-c) is added to the aqueous fiber suspension. For example, polyacrylamide can be crosslinked during polymerization by adding the crosslinker methylenebisacrylamide to acrylamide or by adding a crosslinker such as glyoxal after polymerization. If necessary, both types of crosslinking can be combined. A crosslinked organic polymer that has a high degree of crosslinking, typically during monomer polymerization, is particularly worthy of mention here. This is present in the first aqueous fiber suspension as particles, in particular as so-called organic microparticles.

The organic polymer (a-c) can also be differentiated into natural, modified-natural or synthetic. A natural organic polymer is usually obtained from nature, with appropriate isolation steps being used where appropriate but no targeted chemical-synthetic modification. An example of a natural organic polymer (a-c) is unmodified starch. Cellulose is not an example of a natural organic polymer (a-c) - this is a fiber material (a-b). A modified-natural organic polymer is modified by a chemical-synthetic process step. An example of a modified-natural organic polymer (a-c) is cationic starch. A synthetic organic polymer (a-c) is obtained chemically-synthetically from individual monomers. An example of a synthetic organic polymer (a-c) is polyacrylamide.

An organic polymer (a-c) here also includes two or more different organic polymers. Accordingly, an organic polymer (a-c) as a possible further component of a first aqueous fiber suspension is then divided into a first organic polymer (a-c-1), a second organic polymer (a-c-2), ... etc.

A possible further component of the first aqueous fiber suspension is (ad) a filler. A filler (ad) is an inorganic particle, in particular an inorganic pigment. All pigments based on metal oxides, silicates and/or carbonates that are usually used in the paper industry can be considered as inorganic pigments, in particular pigments from the group consisting of calcium carbonate, which can be used in the form of ground lime, chalk, marble (GCC) or precipitated calcium carbonate (PCC), talc, kaolin, bentonite, satin white, calcium sulfate, barium sulfate and titanium dioxide. An inorganic particle is also a colloidal solution of polysilicic acids, in which the silica particles typically have a particle size between 5 and 150 nm.

A filler (a-d) here also includes two or more different fillers. Accordingly, a filler (a-d) as a possible further component of the first aqueous fiber suspension is then divided into a first filler (a-d-1), a second filler (a-d-2), ... etc.

Preferably, inorganic pigments with 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 average particle size (volume average) of the inorganic pigments and the particles of the powder composition is generally determined in this document using the quasi-elastic light scattering method (DIN-ISO 13320-1), for example using a Mastersizer 2000 from Malvern Instruments Ltd.

A possible further component of the first aqueous fiber suspension is (ae) another paper auxiliary. Another paper auxiliary (ae) is different from the aforementioned components (ab), (ac) and (ad). Another paper auxiliary (ae) is, for example, a machine sizing agent, a water-soluble salt of a trivalent metal cation, a defoamer, a non-polymeric wet strength agent, a biocide, an optical brightener or a paper dye. Examples of a machine sizing agent are alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA) and resin size. Examples of a water-soluble salt of a trivalent metal cation are aluminum(III) salts, in particular AlCl ₃ such as AlCl ₃ ·6 H ₂ O, Al ₂ (SO ₄ ) ₃ such as Al ₂ (SO ₄ ) ₃ ·18 H ₂ O, or KAI(SO ₄ ) ₂ ·12 H ₂ O.

Another paper auxiliary (a-e) here also includes two or more different other paper auxiliary agents. Accordingly, another paper auxiliary (a-e) as a possible further component of the first aqueous fiber suspension is then divided into a first other paper auxiliary (a-e-1), a second other paper auxiliary (a-e-2), ... etc.

During paper production, more than one organic polymer (a-c) and more than one filler (a-d) are often added to the first aqueous pulp suspension. In the case of an organic polymer (a-c), this serves, for example, to influence technical properties of the paper production process itself or technical properties of the paper produced. For example, retention agents, dewatering agents, wet strength agents or dry strength agents are used.

Examples of a retention agent are cationic, amphoteric or anionic organic polymers (ac). Examples are an anionic polyacrylamide, a cationic polyacrylamide, a cationic starch, a cationic polyethyleneimine or a cationic polyvinylamine. A retention agent is, for example, a filler (ad) which is an anionic microparticle, in particular colloidal silica or bentonite. Combinations of the above examples are also possible. A combination in particular is a dual system which consists of a cationic polymer with an anionic microparticle or an anionic polymer with a cationic microparticle. A preferred retention agent is a synthetic organic polymer (ac) or a dual system. In the case of a dual system as a retention agent, for example, there is already a cationic first organic polymer (ac-1) in combination with a first filler (ad-1), for example a suitable bentonite, and if necessary a second filler (ad-2) is then calcium carbonate.

The first fiber suspension preferably contains an organic polymer (a-c) which is a synthetic organic polymer. Very preferred is an organic polymer (a-c) which is a polyacrylamide. Particularly preferred is an organic polymer (a-c) which is a cationic polyacrylamide. Very particularly preferred is an organic polymer (a-c) which is a cationic polyacrylamide and acts as a retention agent.

Preferably, the weight amount of organic polymer (a-c) is 0.001 wt.% to 0.2 wt.% based on the weight amount of first fiber (a-b) in the first fiber suspension. The weight amount of first fiber (a-b) refers to the dry content of first fiber (a-b) and the weight amount of organic polymer (a-c) refers to the solid content of organic polymer (a-c). The solid content of the organic polymer (a-c) is determined from a material sample of the organic polymer (a-c) by drying this sample in a circulating air drying cabinet at 140°C for 120 minutes. For example, in the case of an aqueous polymer solution, suspension or emulsion, the sample is placed in a metal lid for drying. Drying is carried out at ambient pressure, optionally 101.32 KPa, without correction for deviation resulting from weather and sea level. Very preferably, the amount by weight of organic polymer (a-c) is 0.005 wt.% to 0.1 wt.% based on the amount by weight of first fiber (a-b) in the first fiber suspension, particularly preferably 0.01 wt.% to 0.08 wt.%, very particularly preferably 0.02 wt.% to 0.06 wt.% and especially preferably 0.3 wt.% to 0.05 wt.%.

Preferably, the amount by weight of organic polymer (a-c) which is a cationic polyacrylamide is 0.001 wt.% to 0.2 wt.% based on the amount by weight of first fiber (a-b) in the first fiber suspension.

Preferably, no anionic organic polymer is added to the first fiber suspension.

Examples of a dry strength agent are a synthetic organic polymer (a-c) such as polyvinylamine, polyethyleneimine, polyacrylamide or glyoxylated polyacrylamide or a natural organic polymer (a-c) such as unmodified starch.

The dry matter content of the first aqueous fiber suspension is preferably between 0.11 wt.% and 5 wt.%, very preferably between 0.12 wt.% and 4 wt.%, particularly preferably between 0.13 wt.% and 3 wt.%, 2 wt.%, 1 wt.%, 0.6 wt.% or 0.35 % by weight as an upper limit and most preferably between 0.14 % by weight and 0.30 % by weight.

The first sieve, which has a first sieve top and a first sieve bottom, has sieve meshes as openings. The first aqueous fiber suspension is applied to the sieve via the headbox. The headbox ensures that the fiber suspension is applied evenly and across the entire width of the sieve. The sieve top is an essentially flat surface at the moment of the headbox, i.e. apart from the sieve meshes or other material-related unevenness and a certain radius bend in the case of a ring sieve. This allows the production of a uniformly thin, as homogeneous as possible fiber web. After the first fiber suspension has been applied, parts of the water (a-a) of the first aqueous fiber suspension run off through the sieve meshes, whereupon a sheet forms on the first sieve top and the first fiber web is created. A fiber web produced in this way is flat, i.e. it has a very small height in relation to its length and width. The fiber of the fiber suspension and possible other components that are to be present in the ultimately produced paper, for example a filler, are ideally retained entirely or at least substantially in the forming fiber web. Possible other components of the fiber suspension that are added to support the retention of the other components, to support the dewatering of the fiber suspension or to support uniform sheet formation, for example an organic polymer, have their effect during this process. Most of the time, these possible other components of the fiber suspension also remain entirely or at least substantially in the resulting fiber web. The dry portion of the fiber web, which determines the dry content of the fiber web, contains the retained components of fiber, possible other components that are to be present in the ultimately produced paper, and the possible other components. Depending on their retention behavior, these components are, for example, the aforementioned fiber, organic polymers, fillers and other paper auxiliaries. At the end of step (A), the fiber web is strong enough to be removed from the screen.

The screen contains, for example, a metal or plastic mesh. The screen is preferably an endless screen. After the resulting fiber web is separated from an endless screen, the endless screen runs back to the material application, where new fiber suspension is applied to the running endless screen. The screen is very preferably an endless screen that runs around several rollers. Well-known screen types for endless screens are the fourdrinier screen, the double-wire former with an endless lower screen and an additional endless upper screen, the round screen and the round screen former. A fourdrinier screen is preferred.

The dewatering of the fiber suspension on the top of the screen can be supported by applying a negative pressure on the bottom of the screen. The negative pressure is understood as a lower pressure than the pressure on the top of the sieve, which corresponds, for example, to the ambient pressure.

The dry content of the first fibrous web is preferably 15 wt.% to 24 wt.%, very preferably 16 wt.% to 23 wt.%, particularly preferably 17 wt.% to 22 wt.%, very particularly preferably 17.5 wt.% to 22 wt.% and especially preferably 18 wt.% to 21 wt.%.

The square meter weight of a fibrous web is defined here as the mass of components per square meter of fibrous web that remain after drying, preferably as a constant mass during the aforementioned dry content determination at a drying temperature of 105°C. The square meter weight of a fibrous web is preferably between 20 and 120 g/m ² . The sum of all square meter weights of the fibrous webs is not the grammage of the dried multi-ply paper ultimately produced from it, because at least one of the layers is still sprayed as a fibrous web with a slight increase in grammage, the layer composite could lose some of the aforementioned components after drying during dewatering by pressing and, more formally, during dewatering via heated cylinders with a slight reduction in grammage, or the said dewatering or other steps could still result in stretching or compression of the dried multi-ply paper or its wetter precursors. In the latter case, one square meter of the fibrous web would no longer correspond to one square meter of the dried multi-ply paper. However, the weight per square metre of the flat first fibrous web can approximately correspond to the proportion of the layer that results from this fibrous web in the further process to the total grammage of the dried multi-ply paper. The weight per square metre of the first fibrous web is, for example, 30 to 100 g/m ² , 30 to 60 g/m ² , 65 to 105 g/m ² , 35 to 50 g/m ² or 70 to 90 g/m ² .

In step (B), the second aqueous fiber suspension is understood to mean a composition containing (b-a) water and (b-b) second fiber containing cellulose fibers. The statements and preferences for step (A) also apply mutatis mutandis to step (B), whereby an organic polymer (b-c) or a first organic polymer (b-c-1) and a second organic polymer (b-c-2) etc., a filler (b-d) or a first filler (b-d-1) and a second filler (b-d-2) etc., another paper auxiliary (b-e) or a first other paper auxiliary (b-e-1) and a second other paper auxiliary (b-e-2), a second screen having a second screen top side and a second screen bottom side, a second fiber web and a square meter weight of the second fiber web are meant.

Preferably, the second fiber material (bb) is the same as the first fiber material (ab). Preferably, the organic polymer (bc) is the same as the organic polymer (ac) or the first organic polymer (bc-1) is the same as the first organic polymer (ac-1), very preferably the first organic Polymer (bc-1) is equal to the first organic polymer (ac-1) and the second organic polymer (bc-2) is equal to the second organic polymer (ac-2). Preferably, the second organic polymer (bc) is contained in the same amount by weight per second fiber (bb) as the first organic polymer (ac) per first fiber (ab). Preferably, the amount by weight of organic polymer (ac), which is a cationic polyacrylamide, is 0.001 wt. % to 0.2 wt. % based on the amount by weight of first fiber (ab) in the first fiber suspension and the amount by weight of organic polymer (bc), which is a cationic polyacrylamide, is 0.001 wt. % to 0.2 wt. % based on the amount by weight of second fiber (bb) in the second fiber suspension. Preferably, the filler (bd) is the same as the filler (ad) or the first filler (bd-1) is the same as the first filler (ad-1), very preferably the first filler (bd-1) is the same as the first filler (ad-1) and the second filler (bd-2) is the same as the second filler (ad-2). Preferably, the other paper auxiliary (be) is the same as the other paper auxiliary (ae) or the first other paper auxiliary (be-1) is the same as the first other paper auxiliary (ae-1), very preferably the first other paper auxiliary (be-1) is the same as the first other paper auxiliary (ae-1) and the second other paper auxiliary (be-2) is the same as the second other paper auxiliary (ae-2). Preferably, the composition of the second fiber suspension is the same as the composition of the first fiber suspension. Preferably, the weight per square meter of the first fibrous web is higher than the weight per square meter of the second fibrous web, very preferably the weight per square meter of the first fibrous web is 65 to 105 g/m ² and the weight per square meter of the second fibrous web is 30 to 60 g/m ² .

Preferably, an organic polymer (a-c) is added as a retention agent to the first aqueous fiber suspension containing (a-a) water and (a-b) first fiber before dewatering in step (A), and an organic polymer (b-c) is added as a retention agent to the second aqueous fiber suspension containing (b-a) water and (b-b) second fiber before dewatering in step (B). Very preferably, the amount of polymer (a-c) added is 0.001% by weight to 0.2% by weight based on the first fiber (a-b), and the amount of organic polymer (b-c) added is 0.001% by weight to 0.2% by weight based on the second fiber (b-b). Particularly preferably, the amount of polymer (a-c) added is 0.020 wt.% to 0.15 wt.% and the amount of polymer (b-c) added is 0.0020 wt.% to 0.15 wt.%. In these amounts, the polymer (a-c) and the polymer (b-c) are very particularly preferably a cationic polymer and especially preferably a cationic polyacrylamide.

Preferably, in step (A), the first fiber suspension is applied to the top of the first screen and dewatering is supported by applying a negative pressure to the first screen bottom, in step (B), the second fiber suspension is applied to the top of the second screen and dewatering is supported by applying a negative pressure to the second screen bottom, or in step (A), the first fiber suspension is applied to the top of the first screen and dewatering is supported by applying a negative pressure to the first screen bottom, and in step (B), the second fiber suspension is applied to the top of the second sieve and dewatering is supported by applying a negative pressure to the underside of the second sieve. Very preferably, in step (A), the first fiber suspension is applied to the top of the first sieve and dewatering is supported by applying a negative pressure to the underside of the first sieve, and in step (B), the second fiber suspension is applied to the top of the second sieve and dewatering is supported by applying a negative pressure to the underside of the second sieve.

In step (C), at least one surface side of the first fibrous web or the second fibrous web is sprayed with a spray solution or spray suspension. This creates at least one sprayed fibrous web with one sprayed surface side. Preferably, the first fibrous web and the second fibrous web are sprayed, very preferably sprayed simultaneously and particularly preferably sprayed simultaneously by spraying from a spray device onto both fibrous webs.

The spraying in step (C) with the spray solution or spray suspension preferably takes place from a spray device. The spray device contains, for example, one or more nozzles. The spray solution or spray suspension is sprayed from the nozzle(s) onto the surface side of the fibrous web to be sprayed. The spray solution or spray suspension is preferably under an overpressure compared to the ambient pressure, for example 0.5 to 15 bar, preferably 0.5 to 4.5 bar and very preferably 0.8 to 2.5 bar. The overpressure is built up at the latest shortly before it exits the nozzle. A container for storing the spray solution or spray suspension can be part of the spray device.

In step (D), the joining of the first fibrous web with the second fibrous web creates the layer composite. One surface side of the first fibrous web comes into permanent contact with one surface side of the second fibrous web. At least one of these two surface sides is a sprayed surface side. When joining, the surface sides come into contact at least to the extent that the fibrous webs then adhere weakly to one another. When joining, the fibrous webs are arranged or brought together in such a way that the fibrous webs lie on top of one another across their entire width or the fibrous webs cover each other completely. Joining corresponds to completely placing the first fibrous web and the second fibrous web on top of one another. For example, joining takes place spatially and temporally almost immediately before pressing in step (E). Preferably, in step (C) the first fibrous web and the second fibrous web are sprayed, whereby at least two sprayed fibrous webs are formed, and in step (D) the first fibrous web is joined to the second fibrous web in such a way that the sprayed surface side of the first fibrous web forms the contact surface side to the second fibrous web and the sprayed surface side of the second fibrous web forms the contact surface side to the first fibrous web.

In step (E), the layer composite is pressed, which leads to further dewatering and a corresponding increase in the dry content. Step (E) begins when the layer composite from step (C) reaches the so-called couching line. During couching, dewatering takes place by exerting mechanical pressure on the layer composite. Removing water through mechanical pressure is more energy-efficient than removing water by adding heat or by drying. By placing the layer composite on a water-absorbent belt, e.g. a felt-like fabric, the dewatering is supported by the absorption of the pressed water. A roller is suitable for exerting pressure on the layer composite. In particular, passing the layer composite through two rollers, possibly resting on the water-absorbent belt, is suitable. The surface of the roller consists of, for example, steel, granite or hard rubber. The surface of a roller can be coated with a water-absorbent material. The water-absorbent materials have a high degree of absorbency, porosity, strength and elasticity. After contact with the layer composite, the water-absorbent materials are ideally dewatered again on a side facing away from the layer composite, e.g. using a squeegee.

At the end of step (E), a partially dewatered layer composite is created. At the end of step (E), the partially dewatered layer composite is strong enough to be fed to the next step without mechanical support. The partially dewatered layer composite has, for example, a dry content of between 35% by weight and 65% by weight. The partially dewatered layer composite preferably has a dry content of between 37% by weight and 60% by weight, very preferably between 38% by weight and 55% by weight, particularly preferably between 39% by weight and 53% by weight, very particularly preferably between 40% by weight and 52% by weight.

In step (F), the partially dewatered layer composite from step (E) is further dewatered by supplying heat, which produces the dried multi-layer paper at the end of step (F). The heat is supplied to the partially dewatered layer composite, for example, by heated cylinders over which the partially dewatered layer composite is guided, by IR radiators, by warm air which is guided over the partially dewatered layer composite, or by a combination of two or all three measures. Preferably, the heat is supplied at least by heated cylinders. The cylinders can be heated by electricity or, in particular, steam. Typical temperatures of the cylinders are 120 to 160°C. A cylinder can have a coating on its surface which results in a better surface quality of the dried multi-layer paper. The dried multi-layer paper has the highest strength in comparison with the first fibrous web or the combined strengths of all fibrous webs, with a layer composite or with a partially dewatered layer composite. It is assumed that from a dry content of 80% by weight, the hydroxyl groups of cellulose fibers are increasingly bonded via hydrogen bonds, which supplements the previous mechanical felting of the fibers. One measure of the strength of the dried multi-layer paper is, for example, the internal strength.

A dried multi-ply paper is defined herein as a sheet material having a grammage, ie a basis weight of the dried paper, of up to 600 g/m ² . The term paper in the narrower sense is typically used for grammages up to 225 g/m ² , while the term cardboard is used for grammages from 150 g/m ² .

The grammage of the dried multi-ply paper is preferably 20 to 400 g/m ² , very preferably 40 to 280 g/m ² , particularly preferably 60 to 200 g/m ² , very particularly preferably 80 to 160 g/m ² , especially preferably 90 to 140 g/m ² and very especially preferably 100 to 130 g/m ² .

The dried multi-layer paper preferably has two, three or four layers, very preferably two or three layers and particularly preferably two layers. With two layers, there is exactly one first fibrous web and one second fibrous web in the process. With three layers, there is an additional fibrous web as the third fibrous web and with four layers, there is another additional fibrous web as the fourth fibrous web. A third and optionally a fourth fibrous web are connected to the layer composite of the first fibrous web and the second fibrous web with or without spraying. This is followed by the respective further dewatering of steps (E) and (F).

The first fibrous web and the second fibrous web each make a contribution to the grammage of the dried multi-ply paper. These contributions can be the same or different. The contributions are approximately calculated from the square meter weights of the respective fibrous web. The contribution of the first fibrous web to the grammage of the dried multi-ply paper is preferably higher than the contribution of the second fibrous web, very preferably the ratio is 3 or more parts of first fibrous web to 2 or fewer parts of second fibrous web. The ratio of 3 or more parts of first fibrous web to 2 or fewer parts of second fibrous web is particularly preferably 4 parts of first fibrous web to 1 part of second fibrous web.

The dry content of the dried multi-ply paper is, for example, at least 88% by weight. The dry content of the dried multi-ply paper is preferably between 89% by weight and 100% by weight, very preferably between 90% by weight and 98% by weight, particularly preferably between 91% by weight and 96% by weight, very particularly preferably between 92% by weight and 95% by weight and especially preferably between 93% by weight and 94% by weight.

The process for producing dried multi-ply paper may include further steps. For example, step (F) may be followed by calendering the dried multi-ply paper.

A polymer P is water-soluble if its solubility in water under standard conditions (20 °C, 1013 mbar) and pH 7.0 is at least 5 wt.%, preferably at least 10 wt.%. The weight percentages refer to the solid content of polymer P. The solid content of polymer P is determined after its production as an aqueous polymer solution. A sample of the polymer solution in a metal lid is dried in a circulating air drying cabinet at 140°C for 120 minutes. Drying takes place at ambient pressure, if necessary 101.32 KPa, without correction for deviations caused by weather and altitude.

The spray solution here is a solution of the polymer P in the solvent water. If another liquid is present that does not mix sufficiently with water to dissolve, this mixture is also referred to as a spray solution. On the other hand, there are no solid particles in the spray solution. Solid particles down to colloidal dimensions, i.e. <10 ^-5 cm, are also absent. The spray dispersion here is a solution of the polymer P in the solvent water, which also contains water-insoluble solid particles. If another liquid is present that does not mix sufficiently with water to dissolve, this mixture is also referred to as a spray suspension. The temperature is 23°C and the ambient pressure is approximately 101.32 KPa.

The spray solution or spray suspension preferably has a pH of 5.5 or greater. The spray solution or spray suspension very preferably has a pH between 5.8 and 12, particularly preferably between 6.2 and 11, very particularly preferably between 6.4 and 10, especially preferably between 6.8 and 9 and particularly especially preferably between 7.2 and 8.8.

Due to the high water content, the density of the spray solution or spray suspension can be approximately assumed to be 1 g/cm ³ .

• (c-a) Wasser
• (c-b) mindestens ein Polymer P
• (c-c) optional ein weiterer Lagenverbinder, der von einem Polymer P verschieden ist,
• (c-d) optional ein Sprühhilfsmittel, das von einem Polymer P und dem weiteren Lagenverbinder verschieden ist,
• wobei der Gehalt an Wasser (c-a) mindestens 80 Gew.-% beträgt bezogen auf das Gewicht der Sprühlösung oder Sprühsuspension.

The spray solution or spray suspension preferably contains

• (approx) water
• (cb) at least one polymer P
• (cc) optionally a further layer connector which is different from a polymer P,
• (cd) optionally a spraying aid which is different from a polymer P and the further layer connector,
• wherein the water content (ca) is at least 80 wt.% based on the weight of the spray solution or spray suspension.

The spray solution or spray suspension preferably contains between at least 85% by weight and 99.99% by weight of water (ca) based on the total weight of the spray solution or spray suspension, very preferably between at least 95% by weight and 99.95% by weight of water, particularly preferably between 98% by weight and 99.9% by weight of water and most preferably between 99% by weight and 99.7% by weight of water.

The spray solution or spray suspension preferably contains between 0.01% by weight and less than 15% by weight of polymer P (c-b) based on the total weight of the spray solution or spray suspension, very preferably between 0.05% by weight and less than 5% by weight of polymer P, particularly preferably between 0.1% by weight and less than 2% by weight of polymer P, very particularly preferably between 0.15% by weight and less than 1% by weight of polymer P and especially preferably between 0.3% by weight and less than 0.8% by weight of polymer P. The weight of polymer P in a spray solution or spray suspension refers to the solid content of polymer P.

The further layer connector (c-c), which is different from a polymer P, is, for example, an organic polymer. A natural polysaccharide, a modified polysaccharide, a protein or a polyvinyl alcohol is preferred. A mixture of several layer connectors is also included. A natural polysaccharide is, for example, natural starch or guar gum. A modified polysaccharide is, for example, a chemically modified starch or a cellulose ether. A protein is, for example, glutin or casein. A cellulose ether is, for example, carboxymethyl cellulose.

A natural starch is, for example, a starch from corn, wheat, oats, barley, rice, millet, potatoes, peas, cassava, sorghum or sago. A degraded starch has a reduced weight-average molecular weight compared to the natural starting starch. The starch can be degraded enzymatically, by oxidation, acid action or base action. Enzymatic degradation and degradation by acid action or base action in the presence of water leads to increased levels of oligosaccharides or dextrins via hydrolysis. Some degraded starches are commercially available. The degradation of starch is a chemical process. Chemical modification is the functionalization of a natural starch by covalently attaching a chemical group or breaking down covalent bonds in the starch. A chemically modified starch is obtainable, for example, by esterification or etherification of a natural starch followed by starch degradation. The esterification can be supported by an inorganic or organic acid. For example, an anhydride of the acid or a chloride of the acid is used as a reagent. A common procedure for etherifying a starch involves treating the starch with an organic reagent that contains a reactive halogen atom, an epoxy functionality or a sulfate group in an alkaline, aqueous reaction mixture. Known types of etherification of starches are alkyl ethers, uncharged hydroxyalkyl ethers, carboxylic acid alkyl ethers or 3-trimethylammonium-2-hydroxypropyl ether. A chemically modified starch is, for example, phosphated degraded starch and acetylated degraded starch. A chemically modified starch can be neutral, anionic or cationic.

The further layer connector (cc) can be neutral, anionic or cationic. Neutral is divided into uncharged-neutral and amphoteric-neutral. The distinction is made according to the definitions given for the organic polymer (ac). Uncharged-neutral means that it a pH of 7 there are no charge-bearing atoms or functional groups. Amphoteric-neutral means that at a pH of 7 there are atoms or functional groups with a positive charge as well as atoms or functional groups with a negative charge, but the charges differ by less than 7 mol% overall, with all charges adding up to 100 mol%. Cationic is divided accordingly into purely cationic and amphoteric-cationic. Anionic is divided accordingly into purely anionic and amphoteric-anionic. Very preferred is a further layer connector (cc) which is uncharged-neutral, amphoteric-neutral, purely anionic, amphoteric-anionic or amphoteric cationic. Particularly preferred is a further layer connector (cc) which is neutral or anionic. Very particularly preferred is a further layer connector (cc) which is uncharged-neutral or purely anionic. Especially preferred is a further layer connector (cc) which is uncharged-neutral.

The spray solution or spray suspension preferably contains between 0% by weight and 15% by weight of a further layer connector (c-c) based on the total weight of the spray solution or spray suspension. Very preferably, the amount of further layer connector (c-c) is between 0.05% by weight and less than 5% by weight of further layer connector (c-c), particularly preferably between 0.1% by weight and less than 2% by weight of further layer connector (c-c), very particularly preferably between 0.15% by weight and less than 1% by weight of further layer connector (c-c) and especially between 0.3% by weight and less than 0.8% by weight of further layer connector (c-c).

Preferably, the amount by weight of a further layer connector (c-c) is equal to or less than the amount by weight of polymer P (c-b), determined as the solid content of polymer P (c-b) and as the solid content of further layer connector (c-c), in a spray solution or spray suspension, very preferably equal to or less than half the amount by weight of polymer P (c-b), particularly preferably equal to or less than a third of the amount by weight of polymer P (c-b) and very particularly preferably equal to or less than a quarter of the amount by weight of polymer P (c-b).

The spray solution or spray suspension preferably contains no further layer connector (c-c) which is a cationic starch. The spray solution or spray suspension particularly preferably contains no further layer connector (c-c) which is a starch. The spray solution or spray suspension particularly preferably contains no further layer connector (c-c) which is purely cationic. The spray solution or spray suspension very particularly preferably contains no further layer connector (c-c) which is cationic. The spray solution or spray suspension especially preferably contains no further layer connector (c-c) which is an organic polymer and is different from polymer P.

The spraying aid (cd), which is different from a polymer P and the further layer connector, is, for example, a viscosity regulator, a pH regulator, a defoamer or a biocide.

The spray solution or spray suspension preferably contains between 0% by weight and less than 2% by weight of spray auxiliary agent (c-d) based on the total weight of the spray solution or spray suspension. Very preferably, the amount of spray auxiliary agent (c-d) is between 0.001% by weight and less than 1% by weight of spray auxiliary agent (c-d), particularly preferably between 0.005% by weight and less than 0.8% by weight of spray auxiliary agent (c-d) and very particularly preferably between 0.01% by weight and less than 0.5% by weight of spray auxiliary agent (c-d).

Preferably, the amount by weight of a spray auxiliary agent (c-d) is equal to or less than one tenth of the amount by weight of polymer P (c-b), determined as the solids content of polymer P (c-b), in a spray solution or spray suspension, very preferably equal to or less than one twentieth of the amount by weight of polymer P (c-b), particularly preferably equal to or less than one thirtieth of the amount by weight of polymer P (c-b) and very particularly preferably equal to or less than one fortieth of the amount by weight of polymer P (c-b).

The spray solution or spray suspension preferably does not contain any polydiallyldimethylammonium chloride or pentaethylenehexamine which is substituted with an alkyl having at least 5 C atoms or with an arylalkyl. The spray solution or spray suspension very preferably does not contain any homo- or copolymer of protonated or quaternized dialkylaminoalkyl acrylate, homo- or copolymer of protonated or quaternized dialkylaminoalkyl methacrylate, homo- or copolymer of protonated or quaternized dialkylaminoalkylacrylamide, homo- or copolymer of protonated or quaternized dialkylaminoalkyl methacrylamide, homo- or copolymer of diallyldimethylammonium chloride or pentaethylenehexamine which is substituted with an alkyl having at least 5 C atoms or with an arylalkyl.

The spray solution or spray suspension preferably does not contain any filler according to the previous definition of filler (a-d).

• (c-a) Wasser
• (c-b) wasserlösliches Polymer P,
• (c-c) ein weiterer Lagenverbinder, der von einem Polymer P verschieden ist,
• (c-d) ein Sprühhilfsmittel,
• wobei der Gehalt an Wasser (c-a) mindestens 80 Gew.-% bezogen auf das Gewicht der Sprühlösung oder Sprühsuspension ist und der Gehalt an Sprühhilfsmittel (c-d) zwischen 0 Gew.-% bis unter 2 Gew.-% bezogen auf das Gewicht der Sprühlösung oder Sprühsuspension ist.

Preferably, the spray solution consists of

• (approx) water
• (cb) water-soluble polymer P,
• (cc) another layer connector other than a polymer P,
• (cd) a spraying aid,
• wherein the water content (ca) is at least 80 wt.% based on the weight of the spray solution or spray suspension and the spray auxiliary content (cd) is between 0 wt.% to less than 2 wt.% based on the weight of the spray solution or spray suspension.

The application amount of spray solution or spray suspension is preferably 0.05 to 5 g/m ² based on the solids content of the spray solution or spray suspension and based on the sprayed area. Very preferred is 0.1 to 3 g/m ² , particularly preferred is 0.3 to 1.5 g/m ² , very particularly preferred is 0.4 to 1.0 g/m ² and especially preferred is 0.5 to 0.8 g/m ² .

Solution, precipitation, suspension or emulsion polymerization are available for polymerizing the monomers (i) and (ii) to form polymer P. Solution polymerization in aqueous media is preferred. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, e.g. an alcohol. Examples of an alcohol are methanol, ethanol or n-propanol. The polymerization takes place radically, for example by using radical polymerization initiators, for example peroxides, hydroperoxides, so-called redox catalysts or azo compounds that decompose into radicals. The polymerization is carried out, for example, in water or a water-containing mixture as a solvent in a temperature range of 30 to 140°C, and it can be carried out under ambient pressure, reduced pressure or increased pressure. For solution polymerization, a water-soluble polymerization initiator is preferably selected, for example 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

When polymerizing the monomers (i) and (ii) to form polymer P, polymerization regulators can be added to the reaction. Typically, 0.001 to 5 mol% based on the total amount of all monomers (i) and (ii) are used. Polymerization regulators are known from the literature and are, for example, sulfur compounds, sodium hypophosphite, formic acid or tribromochloromethane. Individual examples of sulfur compounds are mercaptoethanol, 2-ethylhexylthioglycolate, thioglycolic acid and dodecyl mercaptan.

Preferably, the polymer P has a weight-average molecular weight Mw between 75,000 and 5,000,000 Daltons. Very preferably, the polymer P has a weight-average molecular weight Mw between 100,000 and 4,500,000 Daltons, particularly preferably between 180,000 and 2,500,000 Daltons, and especially preferably between 210,000 and 1,500,000 Daltons. The weight-average molecular weight can be determined using static light scattering, for example at a pH of 9.0 in a 1000 millimolar saline solution.

Preferably, the polymer P has a cationic equivalent of less than 3 meq/g, very preferably less than 2.4 meq/g, particularly preferably less than 2.2 and more than 0.1 meq/g, and especially preferably from 2.0 meq/g to 0.5 meq/g. The cationic equivalent is preferably determined by titration of an aqueous solution of the polymer P, adjusted to a pH of 3, with an aqueous potassium polyvinyl sulfate solution. More preferably, the determination of the cationic equivalent is carried out by i) providing a predetermined volume of an aqueous solution of the polymer P, adjusted to a pH of 3, in a particle charge detector, for example the particle charge detector PCD-02 manufactured by Mütek, ii) titrating the provided aqueous solution with an aqueous potassium polyvinyl sulfate solution, for example with a concentration of N/400, to the point where the streaming potential is zero, and iii) calculating the electrical charge.

Examples of monomers (i) of the formula I are N-vinylformamide (R ¹ = H), N-vinylacetamide (R ¹ = C ₁ -alkyl), N-vinylpropionamide (R ¹ = C ₂ -alkyl) and N-vinylbutyramide (R ¹ = C ₃ -alkyl). The C ₃ -C ₆ -alkyls can be linear or branched. An example of C ₁ -C ₆ -alkyl is methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 2-methylpropyl, 3-methylpropyl, 1,1-dimethylethyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl or n-hexyl. R ¹ is preferably H or C ₁ -C ₄ alkyl, very preferably H or C ₁ -C ₂ alkyl, particularly preferably H or C ₁ alkyl and very particularly preferably H, ie the monomer (i) is N-vinylformamide. A monomer of the formula I in the singular also includes a mixture of different monomers of the formula I as monomer (i). The numerical proportion of the monomer with R ¹ = H in the total number of all monomers (i) of the formula I is preferably 85 to 100%, very preferably 90% to 100%, particularly preferably 95% to 100% and very particularly preferably 99-100%.

The total amount of all monomers (i) is preferably 45 to 85 mol% based on all monomers polymerized to obtain the polymer P, i.e. all monomers (i) and (ii) or, according to the following specifications of (ii), consequently (i), (ii-A), (ii-B), (ii-C) and (ii-D) or (i), (ii-1), (ii-2), (ii-3), (ii-4), (ii-5), (ii-6), (ii-7) and (ii-8), very preferably 50 to 83 mol%, particularly preferably 55 to 82 mol%, very particularly preferably 60 to 81 mol% and especially preferably 62 to 80 mol%.

An ethylenically unsaturated monomer is herein a monomer that contains at least one C ₂ unit whose two carbon atoms are connected by a carbon-carbon double bond. In the case of hydrogen atoms as the only substituent, this is ethylene. In the case of substitution with 3 hydrogen atoms, a vinyl derivative is present. In the case of substitution with two hydrogen atoms, an E/Z isomer or an ethene-1,1-diyl derivative is present. Monoethylenically unsaturated monomer here means that exactly one C ₂ unit is present in the monomer.

The total amount of all monomers (ii) is preferably 15 to 55 mol% based on all monomers polymerized to obtain the polymer P, i.e. all monomers (i) and (ii) or, according to the following specifications of (ii), consequently (i), (ii-A), (ii-B), (ii-C) and (ii-D) or (i), (ii-1), (ii-2), (ii-3), (ii-4), (ii-5), (ii-6), (ii-7) and (ii-8), very preferably 17 to 50 mol%, particularly preferably 18 to 45 mol%, very particularly preferably 19 to 40 mol% and especially preferably 20 to 38 mol%.

By polymerizing monomers of formula I, the polymer P initially contains amide groups resulting from these monomers. In the case of N-vinylformamide, ie formula I with R ¹ = H, this is the formamide group -NH-C(=O)H. As is known, for example in EP0438744A1 , page 8 / lines 26 to 34, the amide group can be hydrolyzed acidically or alkaline, splitting off the carboxylic acid and forming a primary amino group in the polymer P. A basic hydrolysis of the amide group is preferred. If not all amide groups are hydrolyzed, it is known that condensation of the primary amino group with an adjacent Amide group enables the formation of a cyclic, six-membered amidine. In this respect, the hydrolysis of an amide group leads to the formation of a primary amino group or an amidine group on the polymer P according to the following reaction scheme.

In the case of polymerization of ethylene derivatives substituted directly on the ethylene function with cyano, e.g. acrylonitrile, the polymer P contains additional cyano groups. The primary amino group in the polymer P formed by hydrolysis can, as is known, react with one of these cyano groups to form a cyclic, 5-membered amidine. In this case, the hydrolysis of an amide group leads to an amidine group on the polymer P according to the following reaction scheme. The ethylene derivative substituted with cyano in the following reaction scheme is polymerized acrylonitrile.

In both cases shown, the hydrolysis of an amide group originating from a monomer of formula I leads to a primary amino group or an amidine group. A primary amino group or an amidine group is positively charged at pH = 7 and corresponds to a cationic charge in the polymer P.

The conditions for hydrolysis of the amide groups in the polymer P, which originate from monomers of the formula I, can also lead to the hydrolysis of other groups in the polymer P which are sensitive to hydrolysis under these conditions. As is known, for example in EP0216387A2 , column 6 / lines 7 to 43, or in WO 2016/001016 A1 , page 17 / lines 1 to 8, hydrolyze acetate groups in polymer P, which originate from vinyl acetate as monomer (ii). Accordingly, a secondary hydroxy group is formed in polymer P, as shown below.

Examples of the one or more ethylenically unsaturated monomers (ii) are (ii-A) an anionic monomer, (ii-B) an uncharged monomer, (ii-C) a cationic monomer and (ii-D) a zwitterionic monomer. An anionic monomer carries at least one negative charge at pH = 7, an uncharged monomer carries no charge at pH = 7, a cationic monomer carries at least one positive charge at pH = 7, and a zwitterionic monomer carries at least one anionic charge and at least one cationic charge at pH = 7. The question of whether an atom or functional group in a monomer carries a charge at pH = 7 can be approximately decided by considering the behavior of the atom or functional group in a comparable molecular environment of a non-monomer. An anionic monomer (ii-A) is preferably acrylic acid, methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts. An uncharged monomer (ii-B) is preferably acrylonitrile, methacrylonitrile or vinyl acetate.

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-A) an anionic monomer, (ii-B) an uncharged monomer, (ii-C) a cationic monomer, (ii-D) 0 - 10 mol% a zwitterionic monomer, wherein the total amount of all monomers (i) and (ii-A) to (ii-D) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-A) to (ii-D).

• wobei mindestens ein ethylenisch ungesättigtes Monomer ein anionisches Monomer oder ein ungeladenes Monomer ist,
• wobei die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) 100 mol% beträgt und mol% sich auf die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) bezieht.

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-A) an anionic monomer, (ii-B) an uncharged monomer, (ii-C) a cationic monomer, (ii-D) 0 - 10 mol% a zwitterionic monomer,

• wherein at least one ethylenically unsaturated monomer is an anionic monomer or an uncharged monomer,
• wherein the total amount of all monomers (i) and (ii-A) to (ii-D) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-A) to (ii-D).

• wobei mindestens ein ethylenisch ungesättigtes Monomer ein anionisches Monomer oder ein ungeladenes Monomer ist,
• wobei die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) 100 mol% beträgt und mol% sich auf die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) bezieht.

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-A) an anionic monomer, wherein at least 50% of all anionic monomers are acrylic acid, methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts based on the total number of anionic monomers, (ii-B) an uncharged monomer, wherein at least 50% of all uncharged monomers are vinyl acetate, acrylonitrile or methacrylonitrile based on the total number of all uncharged monomers, (ii-C) a cationic monomer, (ii-D) 0 to 10 mol% a zwitterionic monomer,

• wherein at least one ethylenically unsaturated monomer is an anionic monomer or an uncharged monomer,
• wherein the total amount of all monomers (i) and (ii-A) to (ii-D) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-A) to (ii-D).

• wobei mindestens ein ethylenisch ungesättigtes Monomer ein anionisches Monomer oder ein ungeladenes Monomer ist, und die Menge an anionischen Monomeren und an ungeladenen Monomeren 15 bis 60 mol% beträgt,
• wobei die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) 100 mol% beträgt und mol% sich auf die Gesamtmenge aller Monomere (i) und (ii-A) bis (ii-D) bezieht.

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-A) an anionic monomer, wherein at least 50% of all anionic monomers are acrylic acid, methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts based on the total number of anionic monomers, (ii-B) an uncharged monomer, wherein at least 50% of all uncharged monomers are vinyl acetate, acrylonitrile or methacrylonitrile based on the total number of all uncharged monomers, (ii-C) 0 to 15 mol% a cationic monomer, (ii-D) 0 to 10 mol% a zwitterionic monomer,

• wherein at least one ethylenically unsaturated monomer is an anionic monomer or an uncharged monomer, and the amount of anionic monomers and uncharged monomers is 15 to 60 mol%,
• wherein the total amount of all monomers (i) and (ii-A) to (ii-D) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-A) to (ii-D).

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-A) an anionic monomer, wherein at least 50% of all anionic monomers are acrylic acid, methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts based on the total number of anionic monomers, (ii-B) an uncharged monomer, wherein at least 50% of all uncharged monomers are vinyl acetate, acrylonitrile or methacrylonitrile based on the total number of all uncharged monomers, where the total amount of all monomers (i), (ii-A) and (ii-B) is 100 mol% and mol% refers to the total amount of all monomers (i), (ii-A) and (ii-B).

The one or more ethylenically unsaturated monomers (ii) are preferably selected from (ii-1) Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts, (ii-2) Acrylonitrile or methacrylonitrile, (ii-3) vinyl acetate, (ii-4) a monoethylenically unsaturated sulfonic acid, a monoethylenically unsaturated phosphonic acid, a monoethylenically unsaturated mono- or diester of phosphoric acid or a monoethylenically unsaturated carboxylic acid having 4 to 8 carbon atoms other than methacrylic acid, or their alkali metal, alkaline earth metal or ammonium salts, (ii-5) a quaternized, monoethylenically unsaturated monomer, a monoethylenically unsaturated monomer which carries at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7, or a diallyl-substituted amine which has exactly two ethylenic double bonds and is quaternized or protonated at pH 7, or their salt form, (ii-6) a monoethylenically unsaturated monomer which carries no charge at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, or an ethylenically unsaturated monomer whose exactly two ethylenic double bonds are conjugated and which carries no charge at pH 7, (ii-7) 0 to 2 mol% a monomer having at least two ethylenically unsaturated double bonds that are not conjugated, and which is different from a diallyl-substituted amine having exactly two ethylenic double bonds, (ii-8) 0 to 10 mol% an ethylenically unsaturated monomer other than monomers (i) and (ii-1) to (ii-7), wherein the total amount of all monomers (i) and (ii-1) to (ii-8) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-1) to (ii-8).

Monomers (ii-1) and (ii-4) are examples of an anionic monomer (ii-A). Monomers (ii-2), (ii-3) and (ii-6) are examples of an uncharged monomer (ii-B). Monomers (ii-5) are examples of a cationic monomer (ii-C). Monomers (ii-8) can be an example of a zwitterionic monomer (ii-D).

Alkali metal, alkaline earth metal or ammonium salts have, for example, sodium ions, potassium ions, magnesium ions, calcium ions or ammonium ions as cations. Accordingly, alkali metal or alkaline earth metal bases, ammonia, amines or alkanolamines have been used to neutralize the free acids. For example, sodium hydroxide, potassium hydroxide, soda, potash, sodium hydrogen carbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine have been used. Alkali metal and ammonium salts are preferred, very preferably sodium, potassium or (NH ₄ ) ⁺ salts.

The monomers (ii-4) do not include a monomer which simultaneously carries a group which is protonated at pH 7 or carries a quaternized nitrogen.

For the monomers (ii-4), monoethylenically unsaturated sulfonic acids are, for example, vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, methallysulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropylsulfonic acid or styrenesulfonic acid.

For the monomers (ii-4), monoethylenically unsaturated phosphonic acids are, for example, vinylphosphonic acid, vinylphosphonic acid monomethyl ester, allylphosphonic acid, allylphosphonic acid monomethyl ester, acrylamidomethylpropylphosphonic acid or acrylamidomethylenephosphonic acid.

For the monomers (ii-4), monoethylenically unsaturated mono- or diesters of phosphoric acid are, for example, monoallylphosphoric acid ester, methacrylethylene glycol phosphoric acid or methacrylethylene glycol phosphoric acid.

For the monomers (ii-4) there are monoethylenically unsaturated carboxylic acids having 4 to 8 C atoms which are different from methacrylic acid, for example dimethacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid or crotonic acid.

The monomers (ii-5) do not include a monomer that simultaneously carries a group that is deprotonated at pH 7. In the case of a monomer (ii-5), salt form means that a corresponding anion ensures charge neutrality in the case of a quaternized nitrogen or in the case of protonation. Such anions are, for example, chloride, bromide, hydrogen sulfate, sulfate, hydrogen phosphate, methyl sulfate, acetate or formate. Chloride and hydrogen sulfate are preferred, chloride is particularly preferred.

For the monomers (ii-5), quaternized, monoethylenically unsaturated monomers are, for example, [2-(acryloyloxy)ethyl]trimethylammonium chloride, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [3-(acryloyloxy)propyl]trimethylammonium chloride, [3-(methacryloyloxy)propyl]trimethylammonium chloride, 3-(acrylamidopropyl)trimethylammonium chloride or 3-(methacrylamidopropyl)trimethylammonium chloride. Preferred quaternizing agents used are dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride or benzyl chloride. Methyl chloride is particularly preferred.

For the monomers (ii-5), monoethylenically unsaturated monomers which carry at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7 are, for example, esters of α,β-ethylenically unsaturated monocarboxylic acids with amino alcohols, mono- and diesters of α,β-ethylenically unsaturated dicarboxylic acids with amino alcohols, amides of α,β-ethylenically unsaturated monocarboxylic acids with dialkylated diamines, vinylimidazole or alkylvinylimidazole.

In the case of esters of α,β-ethylenically unsaturated monocarboxylic acids with amino alcohols, the acid component is preferably acrylic acid or methacrylic acid. The amino alcohols, preferably C ₂ -C ₁₂ amino alcohols, can be C ₁ -C ₈ -mono- or C ₁ -C ₈ -dialkylated on the amine nitrogen. Examples are dialkylaminoethyl acrylates, dialkylaminoethyl methacrylates, dialkylaminopropyl acrylates or dialkylaminopropyl methacrylates. Individual examples are N-methylaminoethyl acrylate, N-methylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminopropyl acrylate, N,N-dimethylaminopropyl methacrylate, N,N-diethylaminopropyl acrylate, N,N-diethylaminopropyl methacrylate, N,N-dimethylaminocyclohexyl acrylate or N,N-dimethylaminocyclohexyl methacrylate.

In the mono- and diesters of α,β-ethylenically unsaturated dicarboxylic acids with amino alcohols, the acid component is preferably fumaric acid, maleic acid, monobutyl maleate, itaconic acid or crotonic acid. The amino alcohols, preferably C ₂ -C ₁₂ amino alcohols, can be C ₁ -C ₈ -mono- or C ₁ -C ₈ -dialkylated on the amine nitrogen.

Amides of α,β-ethylenically unsaturated monocarboxylic acids with dialkylated diamines are, for example, dialkylaminoethylacrylamides, dialkylaminoethylmethacrylamides, dialkylaminopropylacrylamides or dialkylaminopropylacrylamides. Individual examples 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 or N-[2-(diethylamino)ethyl]methacrylamide.

For the monomers (ii-5) diallyl-substituted amines that have exactly two ethylenic double bonds and are quaternized or protonated at pH 7, for example diallylamine or diallyldimethylammonium chloride.

Examples of the monomers (ii-6) are monoesters of α,β-ethylenically unsaturated monocarboxylic acids with C ₁ -C ₃₀ alkanols, monoesters of α,β-ethylenically unsaturated monocarboxylic acids with C ₂ -C ₃₀ alkanediols, diesters of α,β-ethylenically unsaturated dicarboxylic acids with C ₁ -C ₃₀ alkanols or C ₂ -C ₃₀ alkanediols, primary amides of α,β-ethylenically unsaturated monocarboxylic acids, N-alkylamides of α,β-ethylenically unsaturated monocarboxylic acids, N,N-dialkylamides of α,β-ethylenically unsaturated monocarboxylic acids, nitriles of α,β-ethylenically unsaturated monocarboxylic acids, Acrylonitrile and methacrylonitrile are different, dinitriles of α,β-ethylenically unsaturated dicarboxylic acids, esters of vinyl alcohol with C ₁ or C ₃ -C ₃₀ monocarboxylic acids, esters of allyl alcohol with C ₁ -C ₃₀ monocarboxylic acids, N-vinyllactams, nitrogen-free heterocycles with one α,β-ethylenically unsaturated double bond, vinylaromatics, vinyl halides, vinylidene halides, C ₂ -C ₈ monoolefins or C ₄ -C ₁₀ olefins with exactly two double bonds that are conjugated.

Monoesters of α,β-ethylenically unsaturated monocarboxylic acids with C ₁ -C ₃₀ -alkanols are, for example, methyl acrylate, methyl methacrylate, methyl ethacrylate (= methyl-2-ethyl acrylate), ethyl acrylate, ethyl methacrylate, ethyl ethacrylate (= ethyl-2-ethyl acrylate), n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, tert-butyl ethacrylate, n-octyl acrylate, n-octyl methacrylate, 1,1,3,3-tetramethylbutyl acrylate, 1,1,3,3-tetramethylbutyl methacrylate or 2-ethylhexyl acrylate.

Monoesters of α,β-ethylenically unsaturated monocarboxylic acids with C ₂ -C ₃₀ alkanediols are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl ethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl acrylate or 6-hydroxyhexyl methacrylate.

Primary amides of α,β-ethylenically unsaturated monocarboxylic acids are, for example, acrylamide or methacrylamide.

N-alkyl amides of α,β-ethylenically unsaturated monocarboxylic acids are, for example, N-methylacrylamide, N-methylmethacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-(n-propyl)acrylamide, N-(n-propyl)methacrylamide, N-(n-butylacrylamide, N-(n-butyl)methacrylamide, N-(tert-butyl)acrylamide, N-(tert-butyl)methacrylamide, N-(n-octyl)acrylamide, N-(n-octyl)methacrylamide, N-(1,1,3,3-tetramethylbutyl)acrylamide, N-(1,1,3,3-tetramethylbutyl)methacrylamide, N-(2-ethylhexyl)acrylamide or N-(2-ethylhexylmethacrylamide.

N,N-dialkylamides of α,β-ethylenically unsaturated monocarboxylic acids are, for example, N,N-dimethylacrylamide or N,N-dimethylmethacrylamide.

Esters of vinyl alcohol with C ₁ or C ₃ -C ₃₀ monocarboxylic acids are, for example, vinyl formate or vinyl propionate.

Examples of N-vinyllactams are 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 or N-vinyl-7-ethyl-2-caprolactam.

Examples of vinyl aromatics include styrene and methylstyrene.

Examples of vinyl halides are vinyl chloride and vinyl fluoride.

Examples of vinylidene halides are vinylidene chloride and vinylidene fluoride.

Examples of C ₂ -C ₈ monoolefins are ethylene, propylene, isobutylene, 1-butene, 1-hexene or 1-octene.

Examples of C ₄ -C ₁₀ olefins with exactly two double bonds that are conjugated are butadiene and isoprene.

The monomers (ii-7) act as crosslinkers. Examples of the monomers (ii-7) are triallylamine, methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, pentaerythritol triallyl ether, N,N-divinylethyleneurea, tetraallylammonium chloride, polyalkylene glycols or polyols such as pentaerythritol, sorbitol and glucose esterified at least twice with acrylic acid and/or methacrylic acid.

Examples of monomers (ii-8) are the sulfobetaine 3-(dimethyl(methacryloylethyl)ammonium)propanesulfonate, the sulfobetaine 3-(2-methyl-5-vinylpyridinium)propanesulfonate, the carboxybetaine N-3-methacrylamidopropyl-N,N-dimethyl-beta-ammonium-propionate, the carboxybetaine N-2-acrylamidoethyl-N,N-dimethyl-beta-ammonium-propionate, 3-vinylimidazole-N-oxide, 2-vinylpyridine-N-oxide or 4-vinylpyridine-N-oxide.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-1) 15 to 50 mol% Acrylic acid or methacrylic acid or their alkali metal, Contain alkaline earth metal or ammonium salts, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-1) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. A content of (i) of 50 to 83 mol%, of (ii) of 17 to 50 mol% and of (ii-1) of 17 to 50 mol% is very preferred. A content of (i) of 55 to 82 mol%, of (ii) of 18 to 45 mol% and of (ii-1) of 18 to 45 mol% is particularly preferred. A content of (i) of 60 to 81 mol%, of (ii) of 19 to 40 mol% and of (ii-1) of 19 to 40 mol% is very particularly preferred. Particularly preferred is a content of (i) of 62 to 80 mol%, of (ii) of 20 to 38 mol% and of (ii-1) of 20 to 38 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-2) 0 to 35 mol% acrylonitrile or methacrylonitrile, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-2) in mol% refers to the total number of all monomers (i) and (ii), ie all monomers used in the polymerization. The total number of all monomers is 100 mol%. Depending on the hydrolysis conditions selected for the polymer P, cyano or nitrile groups of the polymerized monomers (ii-2) can also partially be converted to carboxamide groups. or carboxylic acid groups. Furthermore, in the case of hydrolysis, a cyano or nitrile group can also react with a polymerized monomer (i) to form a cyclic, 5-membered amidine. Very preferred is 0 to 34 mol% of the monomers (ii-2), particularly preferred is 0.1 to 34 mol% and very particularly preferred is 1 to 27 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-3) 0 to 35 mol% contain vinyl acetate, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-3) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. In the case of hydrolysis, the acetate groups of the polymerized monomers (ii-3) can partially or completely hydrolyze to secondary hydroxy groups. Very preferred is 0 to 34 mol% of the monomers (ii-3), particularly preferred is 0.1 to 34 mol% and very particularly preferred is 1 to 27 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-4) 0 to 10 mol% a monoethylenically unsaturated sulfonic acid, a monoethylenically unsaturated phosphonic acid, a monoethylenically unsaturated mono- or diester of phosphoric acid or a monoethylenically unsaturated carboxylic acid having 4 to 8 carbon atoms other than methacrylic acid, or whose alkali metal, alkaline earth metal or ammonium salts are contained, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-4) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. Very preferred is 0 to 5 mol% of the monomers (ii-4), particularly preferred is 0.1 to 5 mol% and very particularly preferred is 1 to 3 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-5) 0 to 20 mol% a quaternized, monoethylenically unsaturated monomer, a monoethylenically unsaturated monomer which carries at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7, or a diallyl-substituted amine which has exactly two ethylenic double bonds and is quaternized or protonated at pH 7, or their salt form, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-5) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. Very preferred is 0 to 34 mol% of the monomers (ii-5), particularly preferred is 0.1 to 34 mol% and very particularly preferred is 1 to 27 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-6) 0 to 35 mol% a monoethylenically unsaturated monomer which carries no charge at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, or an ethylenically unsaturated monomer whose exactly two double bonds are conjugated, which carries no charge at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-6) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. Very preferred is 0 to 34 mol% of the monomers (ii-6), particularly preferred is 0.1 to 34 mol% and very particularly preferred is 1 to 27 mol%.

Preference is given to a polymer P in which less than 5 mol% of acrylamide is used as monomer (ii) during polymerization, very preferably less than 1 mol% of acrylamide and particularly preferably no acrylamide is used.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-7) 0 to 1 mol% a monomer which has at least two ethylenically unsaturated double bonds which are not conjugated and which is different from a diallyl-substituted amine which has exactly two ethylenic double bonds, and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-7) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. Very preferred is 0 to 0.5 mol% of the monomers (ii-7), particularly preferred is 0.001 to 0.5 mol% and very particularly preferred is 0.01 to 0.1 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I, (iii) 15 to 50 mol% one or more ethylenically unsaturated monomers, which are different from a monomer of formula I, where among the monomers (ii) (ii-8) 0 to 5 mol% an ethylenically unsaturated monomer other than monomers (i) and (ii-1) to (ii-7), and optionally by subsequent partial or complete hydrolysis of the units of the monomers (i) polymerized into the polymer P.

The content of the monomers (ii-7) in mol% refers to the total number of all monomers (i) and (ii), i.e. all monomers used in the polymerization. The total number of all monomers is 100 mol%. Very preferred is 0 to 3 mol% of the monomers (ii-8), particularly preferred is 0.1 to 3 mol% and very particularly preferred is 1 to 2 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I (ii-1) 15 to 50 mol% Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts, (ii-2) 0 to 35 mol% Acrylonitrile or methacrylonitrile, (ii-3) 0 to 35 mol% vinyl acetate, (ii-4) 0 to 35 mol% a monoethylenically unsaturated sulfonic acid, a monoethylenically unsaturated phosphonic acid, a monoethylenically unsaturated mono- or diester of phosphoric acid or a monoethylenically unsaturated carboxylic acid having 4 to 8 carbon atoms other than methacrylic acid, or their alkali metal, alkaline earth metal or ammonium salts, (ii-5) 0 to 35 mol% a quaternized, monoethylenically unsaturated monomer, a monoethylenically unsaturated monomer which carries at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7, or a diallyl-substituted amine which has exactly two ethylenic double bonds and is quaternized or protonated at pH 7, or their salt form, (ii-6) 0 to 35 mol% a monoethylenically unsaturated monomer which carries no charge at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, or an ethylenically unsaturated monomer whose exactly two ethylenic double bonds are conjugated and which carries no charge at pH 7, (ii-7) 0 to 2 mol% a monomer having at least two ethylenically unsaturated double bonds which are not conjugated and which is different from a diallyl-substituted amine having exactly two ethylenic double bonds, (ii-8) 0 to 10 mol% an ethylenically unsaturated monomer other than monomers (i) and (ii-1) to (ii-7), and optionally by subsequent partial or complete hydrolysis of the units of the monomers of the formula (I) polymerized into the polymer P to form primary amino groups or amidine groups, the ester group of polymerized vinyl acetate being partially or completely hydrolyzed, the total amount of all monomers (i) and (ii-1) to (ii-8) being 100 mol% and mol% referring to the total amount of all monomers (i) and (ii-1) to (ii-8). Very preferred is a content of (i) of 50 to 83 mol% and of (ii-1) of 17 to 50 mol%. Particularly preferred is a content of (i) of 55 to 82 mol% and of (ii-1) of 18 to 45 mol%. Very particular preference is given to a content of (i) of 60 to 81 mol% and of (ii-1) of 19 to 40 mol%. Particularly preferred is a content of (i) of 62 to 80 mol% and of (ii-1) of 20 to 38 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I (ii-1) 15 to 50 mol% Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts, (ii-2) 0 to 35 mol% Acrylonitrile or methacrylonitrile, (ii-3) 0 to 35 mol% Vinyl acetate, and optionally by a subsequent partial or complete hydrolysis of the units of the monomers of the formula (I) polymerized into the polymer P to form primary amino groups or amidine groups, the ester group of polymerized vinyl acetate being partially or completely hydrolyzed, the total amount of all monomers (i), (ii-1), (ii-2) and (ii-3) being 100 mol% and mol% referring to the total amount of all monomers (i), (ii-1), (ii-2) and (ii-3). A content of (i) of 50 to 83 mol% and of (ii-1) of 17 to 50 mol% is very preferred. A content of (i) of 55 to 82 mol% and of (ii-1) of 18 to 45 mol% is particularly preferred. Very particular preference is given to a content of (i) of 60 to 81 mol% and of (ii-1) of 19 to 40 mol%. Particularly preferred is a content of (i) of 62 to 80 mol% and of (ii-1) of 20 to 38 mol%.

Preferred is a polymer P which is obtainable by polymerizing (iii) 50 to 85 mol% a monomer of formula I (ii-1) 15 to 50 mol% Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts, (ii-2) 0 to 35 mol% Acrylonitrile or methacrylonitrile, and optionally by subsequent partial or complete hydrolysis of the units of the monomers of the formula (I) polymerized into the polymer P to form primary amino groups or amidine groups, where the total amount of all monomers (i), (ii-1) and (ii-2) is 100 mol% and mol% refers to the total amount of all monomers (i), (ii-1) and (ii-2). Very preferred is a content of (i) of 50 to 83 mol% and of (ii-1) of 17 to 50 mol%. Particularly preferred is a content of (i) of 55 to 82 mol% and of (ii-1) of 18 to 45 mol%. Very particularly preferred is a content of (i) of 60 to 81 mol% and of (ii-1) of 19 to 40 mol%. Particularly preferred is a content of (i) of 62 to 80 mol% and of (ii-1) of 20 to 38 mol%.

The method is preferably carried out in a paper machine. The paper machine preferably has equipment which comprises a first wire section with the first wire, which has a first wire top and a first wire bottom, a second wire section with the second wire, which has a second wire top and a second wire bottom, a spray device containing the spray solution or spray suspension, a press section and a drying section with heated cylinders, and in the paper machine these are arranged in the order first wire section and second wire section, followed by the spray device, then the press section and then the drying section. The spray device is preferably located at the end of the first wire section and second wire section. In the paper machine the step (A) in the first wire section, step (B) takes place in the second wire section, step (C) takes place before the press section, preferably at the end of the first wire section and the second wire section, step (D) takes place before or at the beginning of the press section, step (E) takes place in the press section and step (F) takes place in the drying section. The spraying device preferably comprises at least one nozzle, very preferably one or more nozzles, which enable the spray solution or spray suspension to be sprayed under an overpressure of 0.5 to 4.5 bar compared to the ambient pressure. The first fiber suspension and the second fiber suspension pass through the paper machine with dewatering on a wire, spraying of at least one surface side, joining, dewatering by pressing and dewatering by supplying heat to form a multi-layer paper in the direction from the wire sections towards the drying section.

The preferences for the process for producing multi-ply paper also apply to the other objects of the invention.

1. (A) Entwässern einer ersten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf einem ersten Sieb, wodurch eine erste Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
2. (B) Entwässern einer zweiten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf einem zweiten Sieb, wodurch eine zweite Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
3. (C) Besprühen der ersten Faserstoffbahn, der zweiten Faserstoffbahn oder der ersten Faserstoffbahn und der zweiten Faserstoffbahn auf mindestens einer Flächenseite mit einer Sprühlösung oder Sprühsuspension, wodurch mindestens eine besprühte Faserstoffbahn, die eine besprühte Flächenseite hat, entsteht,
4. (D) Zusammenfügen der ersten Faserstoffbahn mit der zweiten Faserstoffbahn, von denen mindestens eine der beiden eine besprühte Faserstoffbahn ist, derart, dass mindestens eine besprühte Flächenseite der beiden Faserstoffbahnen die Kontaktflächenseite zur anderen Faserstoffbahn bildet und die Faserstoffbahnen in ihrer gesamten Breite übereinander liegen, wodurch ein Lagenverbund entsteht,
5. (E) Entwässern des Lagenverbunds durch Pressen, wodurch ein teilentwässerter Lagenverbund entsteht,
6. (F) Entwässern des teilentwässerten Lagenverbunds durch Wärmezufuhr, wodurch das getrocknete mehrlagige Papier entsteht,

wobei die Sprühlösung oder Sprühsuspension enthält

• (c-a) Wasser
• (c-b) mindestens ein wasserlösliches Polymer P, das erhältlich ist durch Polymerisieren von
  1. (i) 40 bis 85 mol% eines Monomers der Formel I
     
     in der R¹ = H oder C₁-C₆-Alkyl bedeutet,
  2. (ii) 15 bis 60 mol% eines oder mehrerer ethylenisch ungesättigter Monomere, die von einem Monomer der Formel I verschieden sind,
  wobei die Gesamtmenge aller Monomere (i) und (ii) 100 mol% beträgt, und optional durch ein sich anschliessendes teilweises oder vollständiges Hydrolysierens der in das Polymer P einpolymerisierten Einheiten der Monomere der Formel (I) unter Bildung von primären Aminogruppen oder Amidingruppen, wobei der Anteil von Wasser mindestens 75 Gew.-% bezogen auf die Sprühlösung oder die Sprühsuspension beträgt.

Another object of the invention is a dried multi-layer paper which is obtainable by a process comprising the steps

1. (A) dewatering a first aqueous pulp suspension having a dry matter content of between 0.1% and 6% on a first screen to form a first pulp web having a dry matter content of between 14% and 25%,
2. (B) dewatering a second aqueous pulp suspension having a dry matter content of between 0.1% and 6% by weight on a second screen to form a second pulp web having a dry matter content of between 14% and 25% by weight,
3. (C) spraying the first fibrous web, the second fibrous web or the first fibrous web and the second fibrous web on at least one surface side with a spray solution or spray suspension, thereby producing at least one sprayed fibrous web having a sprayed surface side,
4. (D) joining the first fibrous web to the second fibrous web, of which at least one of the two is a sprayed fibrous web, such that at least one sprayed surface side of the two fibrous webs forms the contact surface side to the other fibrous web and the fibrous webs lie one above the other across their entire width, thereby forming a layer composite,
5. (E) dewatering the composite layer by pressing, resulting in a partially dewatered composite layer,
6. (F) dewatering the partially dewatered layer composite by applying heat, thereby producing the dried multi-layer paper,

wherein the spray solution or spray suspension contains

• (approx) water
• (cb) at least one water-soluble polymer P obtainable by polymerizing
  1. (i) 40 to 85 mol% of a monomer of formula I
     
     in which R ¹ = H or C ₁ -C ₆ alkyl,
  2. (ii) 15 to 60 mol% of one or more ethylenically unsaturated monomers other than a monomer of formula I,
  wherein the total amount of all monomers (i) and (ii) is 100 mol%, and optionally by a subsequent partial or complete hydrolysis of the units of the monomers of the formula (I) polymerized into the polymer P to form primary amino groups or amidine groups, wherein the proportion of water is at least 75 wt.% based on the spray solution or the spray suspension.

The multi-ply dried paper is preferably obtainable from a process in which the spray solution or spray suspension has a pH of 5.5 or greater.

Preferably, the dry matter content is determined by drying at 105°C to constant mass.

The dried multi-ply paper preferably has a dry matter content of at least 88% by weight.

The dried multi-ply paper is preferably made of two plies, very preferably of one ply with a grammage of 20 to 60 g/ ^m2 and one ply with 60 to 100 g/ ^m2 .

The dried multi-ply paper preferably has an internal strength of 200 to 450 J/ ^m2 , very preferably of 210 to 400 J/ ^m2 and particularly preferably of 230 to 380 J/ ^m2 , the internal strength corresponding to that of Tappi specification T833 pm-94.

• (c-a) Wasser
• (c-b) mindestens ein wasserlösliches Polymer P, das erhältlich ist durch Polymerisieren von
  1. (i) 40 bis 85 mol% eines Monomers der Formel I
     
     in der R¹ = H oder C₁-C₆-Alkyl bedeutet,
  2. (ii) 15 bis 60 mol% eines oder mehrerer ethylenisch ungesättigter Monomere, die von einem Monomer der Formel I verschieden sind,
  • wobei die Gesamtmenge aller Monomere (i) und (ii) 100 mol% beträgt,
  • und optional durch ein sich anschliessendes teilweises oder vollständiges Hydrolysierens der in das Polymer P einpolymerisierten Einheiten der Monomere der Formel (I) unter Bildung von primären Amino- oder Amidingruppen,
  • wobei der Anteil von Wasser mindestens 75 Gew.-% bezogen auf die Sprühlösung oder die Sprühsuspension beträgt,
  • und die Papiermaschine geeignet ist für ein Verfahren zur Herstellung von getrocknetem mehrlagigem Papier enthaltend die Schritte
    1. (A) Entwässern einer ersten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf dem ersten Sieb, wodurch eine erste Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
    2. (B) Entwässern einer zweiten wässrigen Faserstoffsuspension, die einen Trockengehalt zwischen 0,1 Gew.-% und 6 Gew.-% aufweist, auf dem zweiten Sieb, wodurch eine zweite Faserstoffbahn, die einen Trockengehalt zwischen 14 Gew.-% und 25 Gew.-% aufweist, entsteht,
    3. (C) Besprühen der ersten Faserstoffbahn, der zweiten Faserstoffbahn oder der ersten Faserstoffbahn und der zweiten Faserstoffbahn auf mindestens einer Flächenseite mit der Sprühlösung oder Sprühsuspension aus der Sprühvorrichtung, wodurch mindestens eine besprühte Faserstoffbahn, die eine besprühte Flächenseite hat, entsteht,
    4. (D) Zusammenfügen der ersten Faserstoffbahn mit der zweiten Faserstoffbahn, von denen mindestens eine der beiden eine besprühte Faserstoffbahn ist, derart, dass mindestens eine besprühte Flächenseite der beiden Faserstoffbahnen die Kontaktflächenseite zur anderen Faserstoffbahn bildet und die Faserstoffbahnen in ihrer gesamten Breite übereinander liegen, wodurch ein Lagenverbund entsteht,
    5. (E) Entwässern des Lagenverbunds durch Pressen, wodurch ein teilentwässerter Lagenverbund entsteht,
    6. (F) Entwässern des teilentwässerten Lagenverbunds durch Wärmezufuhr, wodurch das getrocknete mehrlagige Papier entsteht.

A paper machine is also described, the equipment of which comprises a first wire section with a first wire having a first wire top and a first wire bottom, a second wire section with a second wire having a second wire top and a second wire bottom, a spray device, a press section and a drying section with heatable cylinders, and in the paper machine these are arranged in the order of first wire section and second wire section, followed by the spray device, then the press section and then the drying section, wherein the spray device contains a spray solution or spray suspension,
wherein the spray solution or spray suspension contains

• (approx) water
• (cb) at least one water-soluble polymer P obtainable by polymerizing
  1. (i) 40 to 85 mol% of a monomer of formula I
     
     in which R ¹ = H or C ₁ -C ₆ alkyl,
  2. (ii) 15 to 60 mol% of one or more ethylenically unsaturated monomers other than a monomer of formula I,
  • where the total amount of all monomers (i) and (ii) is 100 mol%,
  • and optionally by subsequent partial or complete hydrolysis of the units of the monomers of formula (I) polymerized into the polymer P to form primary amino or amidine groups,
  • wherein the proportion of water is at least 75% by weight based on the spray solution or the spray suspension,
  • and the paper machine is suitable for a process for producing dried multi-ply paper comprising the steps
    1. (A) dewatering a first aqueous pulp suspension having a dry content of between 0.1% and 6% on the first wire to form a first pulp web having a dry content of between 14% and 25%,
    2. (B) dewatering a second aqueous pulp suspension having a dry content of between 0.1% and 6% on the second wire to form a second pulp web having a dry content of between 14% and 25%,
    3. (C) spraying the first fibrous web, the second fibrous web or the first fibrous web and the second fibrous web on at least one surface side with the spray solution or spray suspension from the spray device, thereby producing at least one sprayed fibrous web having a sprayed surface side,
    4. (D) joining the first fibrous web to the second fibrous web, of which at least one of the two is a sprayed fibrous web, such that at least one sprayed surface side of the two fibrous webs forms the contact surface side to the other fibrous web and the fibrous webs lie one above the other across their entire width, thereby forming a layer composite,
    5. (E) dewatering the composite layer by pressing, resulting in a partially dewatered composite layer,
    6. (F) Dewatering the partially dewatered layer composite by applying heat, thereby producing the dried multi-layer paper.

The spray solution or spray suspension in the spray device preferably has a pH of 5.5 or greater.

Preferably, the dry matter content is determined by drying at 105°C to constant mass.

A paper machine is preferred which has a device for generating a negative pressure on the first screen bottom or the second screen bottom. A paper machine is very preferred which has a device for generating a negative pressure on the first screen bottom and a device for generating a negative pressure on the second screen bottom.

A paper machine is preferred whose first wire section and whose second wire section are arranged such that the first fibrous web and the second fibrous web are sprayed together from a spray device, the spraying takes place between the end of the two wire sections and the beginning of the press section and the two sprayed surface sides of the first fibrous web and the second fibrous web come into contact with each other when they are joined together.

Another invention is a process for producing dried multi-layer paper in which, in comparison with the previous process, the polymer P there is replaced by a polymer PA. The objects of this other invention are, in addition to the process mentioned, the corresponding paper obtainable by this process and a paper machine suitable for this process, which contains a spray device containing the aqueous spray solution or spray suspension with polymer PA. The polymer PA, which is different from a polymer P, is a Michael system-modified polymer containing primary amine groups, an alkylated polyvinylamine containing primary amine groups, or a graft polymerization polymer containing primary amine groups.

ist in der WO 2007/136756 beschrieben.A Michael system-modified polymer containing primary amine groups is obtainable by reacting Michael systems with a starting polymer containing primary amine groups. This reaction to the polymer type of formula II shown

is in the WO 2007/136756 described.

wobei R² und R³ unabhängig voneinander für H, Alkyl, Alkenyl, Carbonyl, Carboxyl oder Carboxamid stehen und X¹ für eine elektronenziehende Gruppe oder ein elektronenziehendes Amin steht.Michael systems are understood to be compounds with an unsaturated double bond that is conjugated to an electron-withdrawing group. Suitable Michael systems are described by formula III.

where R ² and R ³ independently represent H, alkyl, alkenyl, carbonyl, carboxyl or carboxamide and X ¹ represents an electron-withdrawing group or an electron-withdrawing amine.

Examples of Michael systems are acrylamide, N-alkylacrylamide, methacrylamide, N,N-dimethylacrylamide, N-alkylmethacrylamide, N-(2-methylpropanesulfonic acid acrylamide, N-(glycolic acid)acrylamide, N-[3-(propyl)trimethylammonium chloride]acrylamide, acrylonitrile, methacrylonitrile, acrolein, methyl acrylate, alkyl acrylate, methyl methacrylate, alkyl methacrylate, aryl acrylate, aryl methacrylates, [2-(methacryloyloxy)ethyl]-trimethylammonium chloride, N-[3-(dimethyl-amino)propyl]methacrylamide, N-ethylacrylamide, 2-hydroxyethyl acrylate, 3-sulfopropyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, pentafluorophenyl acrylate, ethylene diacrylate, ethylene dimethacrylate, heptafluorobuty-1-acrylate, poly(methyl methacrylate), Acryloylmorpholine, 3-(acryloyloxy)-2-hydroxypropyl methacrylate, dialkyl maleate, dialkyl itaconate, dialkyl fumarate, 2-cyanoethyl acrylate, carboxyethyl acrylate, phenylthioethyl acrylate, 1-adamantyl methacrylate, dimethylaminoneopentyl acrylate, 2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate and dimethylaminoethyl methacrylate.

Acrylamide is the preferred Michael system. The Michael systems are used in an amount of 1 to 75 mol% based on the primary amino groups and/or amidine groups. The reaction conditions for the conversion are given in the WO2007/136756 described, the disclosure of which is expressly incorporated by reference.

wobei

X-

ein Anion, vorzugsweise, Chlorid, Bromid oder lodid,

Y

Carbonyl oder Methylen oder eine Einfachbindung,

R4

Wasserstoff, lineares oder verzweigtes C₁-C₂₂-Alkyl,

R5

lineares oder verzweigtes C₁-C₁₅-Alkylen, oder lineares oder verzweigtes C₁-C₁₅-Alkenylen,

R6

lineares oder verzweigtes C₁-C₁₂-Alkylen, das gegebenenfalls mit Hydroxyl substituiert ist, bevorzugt -CH₂CH(OH)CH₂- oder -CH₂-CH₂-,

R7

Wasserstoff, lineares oder verzweigtes C₁-C₂₂-Alkyl, bevorzugt Methyl oder Ethyl,

R8

Wasserstoff, lineares oder verzweigtes C₁-C₂₂-Alkyl, lineares oder verzweigtes C₁-C₂₂-Alkoxy, lineares oder verzweigtes C₁-C₂₂ Dialkylamin, bevorzugt Amino,

R9

lineares oder verzweigtes C₁-C₁₂-Alkylen, bevorzugt -CH₂-CH₂-,

R10

Wasserstoff, lineares oder verzweigtes C₁-C₂₂-Alkyl, bevorzugt Methyl oder Ethyl, ist.

An alkylated polyvinylamine containing primary amine groups is obtained by reacting the primary amino groups and/or amidine groups of the polyvinylamines. This reaction is described in the WO 2009/017781 described as well as reaction conditions. The reaction products preferably contain structural units selected from the group of polymer units (IV), (V), (VI), (VII) and (VIII)

where

X-

an anion, preferably chloride, bromide or iodide,

Y

Carbonyl or methylene or a single bond,

R4

Hydrogen, linear or branched C ₁ -C ₂₂ alkyl,

R5

linear or branched C ₁ -C ₁₅ alkylene, or linear or branched C ₁ -C ₁₅ alkenylene,

R6

linear or branched C ₁ -C ₁₂ alkylene which is optionally substituted by hydroxyl, preferably -CH ₂ CH(OH)CH ₂ - or -CH ₂ -CH ₂ -,

R7

Hydrogen, linear or branched C ₁ -C ₂₂ alkyl, preferably methyl or ethyl,

R8

Hydrogen, linear or branched C ₁ -C ₂₂ alkyl, linear or branched C ₁ -C ₂₂ alkoxy, linear or branched C ₁ -C ₂₂ dialkylamine, preferably amino,

R9

linear or branched C ₁ -C ₁₂ -alkylene, preferably -CH ₂ -CH ₂ -,

R10

hydrogen, linear or branched C ₁ -C ₂₂ alkyl, preferably methyl or ethyl.

Reaction products containing units of formula IV are obtainable by polymer-analogous reaction of the primary amino groups of polyvinylamines with alkylating agents. The alkylation can also be carried out with alkyl glycidyl ethers, glycidol (2,3-epoxy-1-propanol) or chloropropanediol. Preferred alkyl glycidyl ethers are butyl glycidyl ether, 2-ethylhexyl glycidyl ether, hexadecyl glycidyl ether and C ₁₂ /C ₁₄ glycidyl ether. The reaction with alkyl glycidyl ethers is generally carried out in water, but can also be carried out in aqueous/organic solvent mixtures.

Reaction products containing units of the formula V and VII are obtainable by polymer-analogous reaction of the primary amino groups of the polyvinylamines with alkylating agents or acylating agents.

Such alkylating agents are selected from chloroacetic acid, salts of chloroacetic acid, bromoacetic acid, salts of bromoacetic acid, halogen-substituted alkanoic acid acrylamides and halogen-substituted alkenoic acid acrylamides, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 2-(diethylamino)ethyl chloride hydrochloride, (dialkylamino)alkyl chlorides such as 2-(dimethylamino)ethyl chloride, 3-chloro-2-hydroxypropylalkyl-dimethylammonium chlorides such as 3-chloro-2-hydroxypropyllauryldimethylammonium chloride, 3-chloro-2-hydroxypropyl-cocoalkyl-dimethylammonium chloride, 3-chloro-2-hydroxypropylstearyldimethylammonium chloride, (haloalkyl)trimethylammonium chlorides such as (4-chlorobutyl)trimethylammonium chloride, (6-chlorohexyl)trimethylammonium chloride, (8-chlorooctyl)trimethylammonium chloride and glycidylpropyltrimethylammonium chloride. Such acylating agents are selected from succinic anhydride, substituted succinic anhydrides substituted with linear or crosslinked C ₁ -C ₁₈ alkyl or linear or crosslinked C ₁ -C ₁₈ alkenyl, maleic anhydride, glutaric anhydride, 3-methylglutaric anhydride, 2,2-dimethylsuccinic anhydride, cyclic alkylcarboxylic anhydrides, cyclic alkenylcarboxylic anhydrides and alkenylsuccinic anhydrides (ASA).

A graft polymerization polymer containing primary amine groups is, for example, hydrolyzed graft polymers of, for example, N-vinylformamide on polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylformamides, polysaccharides such as starch, oligosaccharides or monosaccharides. The graft polymers are obtainable by, for example, radically polymerizing N-vinylformamide in an aqueous medium in the presence of at least one of the grafting bases mentioned, optionally together with other copolymerizable monomers, and then hydrolyzing the grafted vinylformamide units in a known manner to form polymerized vinylamine units. Such graft polymers are used, for example, in the DE-A-19515943 , DE-A-4127733 and DE-A-10041211 described.

Examples

The percentages in the examples are by weight unless otherwise stated.

A) Additive A-1) Methods for characterizing polymers

The solids content is determined by distributing 0.5 to 1.5 g of the polymer solution in a 4 cm diameter metal lid and then drying it in a circulating air drying cabinet at 140°C for 120 minutes. The ratio of the mass of the sample after drying under the above conditions to the weighed sample mass multiplied by 100 gives the solids content of the polymer solution in wt.%. Drying is carried out at ambient pressure, if necessary 101.32 KPa, without correction for deviations caused by weather and altitude.

The degree of hydrolysis is the proportion in % of the hydrolyzed N-CHO groups of the N-vinylformamide monomers used in the polymerization in relation to the total amount of N-vinylformamide used in the polymerization. The degree of hydrolysis of the homopolymers or copolymers in which N-vinylformamide is used in the polymerization and which are subjected to hydrolysis is determined by enzymatic analysis of the formic acid or formates released during hydrolysis (test set from Boehringer Mannheim).

The polymer content indicates the content of polymer without counterions in the aqueous solution in wt.%, i.e. counterions are not taken into account. The polymer content is the sum of the weight fractions of all structural units of the polymer in g that are present in 100 g of the aqueous solution. It is determined mathematically. For this purpose, potentially charge-bearing structural units in the charged form are included, i.e. e.g. amino groups in the protonated form and acid groups in the deprotonated form. Counterions of the charged structural units such as a sodium cation, chloride, phosphate, formate, acetate, etc. are not taken into account. The calculation can be carried out in such a way that, for a batch, starting from the amounts of monomers used, possibly a degree of hydrolysis of certain monomers and possibly a proportion of reactants that is converted in a polymer-analogous manner by reacting with the polymer to form a covalent bond, the molar amounts of the structural units of the polymer present at the end of the reaction are determined and these are converted into weight fractions using the molar masses of the structural units. For this purpose, a complete, i.e. 100% conversion of all monomers or reactants used is assumed. The sum of the weight fractions gives the total amount of polymer in this batch. The polymer content is the ratio of the total amount of polymer to the total mass of the batch. In addition to the aforementioned total amount of polymer, the total mass of the batch therefore contains reaction medium, possibly cations or anions and everything added to the reaction batch that is not assumed to be incorporated into the polymer. Substances removed from the reaction batch are deducted (e.g. any distilled water, etc.).

The total content of primary amino groups and/or amidine groups can be determined in a similar way to the procedure described above for the polymer content. The molar composition of the structural units of the polymer present at the end of the reaction is determined based on the amounts of monomers used, the analytically determined degree of hydrolysis, the ratio of amidine groups to primary amino groups determined using ¹³ C NMR spectroscopy and, if applicable, the proportion that was converted in a polymer-analogous manner by reaction with the polymer to form a covalent bond. Using the molar mass of the individual structural units, the molar proportion of primary amino groups and/or amidine units in meq that is present in 1 g of polymer can be calculated. When determining using ¹³ C NMR spectroscopy, the area of the formate group HCOO- (173 [ppm]) can be compared with the area of the amidine group -N=CH-N- (152 ppm).

The K values are determined according to H. Fikentscher, Cellulose Chemistry, Volume 13, 48-64 and 71-74 measured under the conditions specified. The figures in brackets indicate the concentration of the polymer solution based on the polymer content and the solvent. The measurements were carried out at 25°C and a pH of 7.5.

The weight-average molecular weight Mw is determined using static light scattering. For this purpose, the sample is dissolved in a 1000 millimolar sodium chloride solution at a pH of 9.0. The Mw is given in Daltons.

The water used in the examples of polymerizations under A-2) and hydrolyses under A-3) is completely demineralized.

A-2) Polymerizations Example P-P1: P1 (Polymer VFA = 100 mol%, K value 90)

234 g of N-vinylformamide are provided as feed 1.

As feed 2, 1.2 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride are dissolved in 56.8 g of water at room temperature.

1080.0 g of water and 2.5 g of 75 wt.% phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube. 2.1 g of 25 wt.% sodium hydroxide solution are added at a speed of 100 rpm to achieve a pH of 6.6. The initial charge is heated to 73°C and the pressure in the apparatus is reduced to such an extent that the reaction mixture just begins to boil at 73°C (approx. 350 mbar). Then feeds 1 and 2 are started simultaneously. At a constant 73°C, feed 1 is added in one hour and 15 minutes and feed 2 in 2 hours. After the addition of feed 2 is complete, the reaction mixture is post-polymerized for a further three hours at 73°C. During the entire polymerization and post-polymerization, approx. 190 g of water are distilled off. The mixture is then cooled to room temperature under normal pressure.

A slightly yellow, viscous solution with a solids content of 19.7 wt.% and a polymer content of 19.5 wt.% is obtained. The K value of the polymer is 90 (0.5 wt.% in water). The Mw is 0.34 million Daltons. The pH value is expected to be between 6 and 7 due to the buffer used.

Example P-P2: P2 (copolymer VFA/Na-acrylate = 70 mol%/30 mol%, K-value 122)

As feed 1, a mixture of 330 g of water, 217.8 g of aqueous 32 wt. % Na acrylate solution adjusted to pH 6.4, and 124.2 g of N-vinylformamide is provided.

As feed 2, 0.3 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is dissolved in 66.8 g of water at room temperature.

As feed 3, 0.2 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is dissolved in 17.4 g of water at room temperature.

668.3 g of water and 1.9 g of 75 wt.% phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube. 3.1 g of 25 wt.% sodium hydroxide solution are added at a speed of 100 rpm so that a pH of 6.6 is reached. The mixture is heated to 73°C and the pressure in the apparatus is to approx. 340 mbar so that the reaction mixture just begins to boil at 73°C. Then feeds 1 and 2 are started simultaneously. At a constant 73°C, feed 1 is added over two hours and feed 2 over 3 hours. After the addition of feed 2 has ended, the reaction mixture is post-polymerized for a further hour at 73°C. Then feed 3 is added over 5 minutes and post-polymerized for a further two hours at 73°C. During the entire polymerization and post-polymerization, approx. 190 g of water are distilled off. The mixture is then cooled to room temperature under normal pressure. A slightly yellow, viscous solution with a solids content of 15.9 wt.% and a polymer content of 15.6 wt.% is obtained. The K value of the copolymer is 122 (0.1 wt.% in 5 wt.% aqueous NaCl solution). The Mw is 2.2 million Daltons.

Example P-P3: P3 (copolymer VFA/Na-acrylate = 70 mol%/30 mol%, K-value 85)

As feed 1, a mixture of 240.0 g of water, 176.5 g of aqueous 32% Na acrylate solution adjusted to pH 6.4, and 100.6 g of N-vinylformamide is provided.

As feed 2, 5.8 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride are dissolved in 164.2 g of water at room temperature.

As feed 3, 5.8 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride are dissolved in 164.2 g of water at room temperature.

330 g of water and 1.2 g of 85% by weight phosphoric acid were placed in a 2 L glass apparatus with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube. 4.2 g of 25% by weight sodium hydroxide solution were added at a speed of 100 rpm to achieve a pH of 6.6. The initial charge was heated to 80°C and the pressure in the apparatus was reduced to approx. 450 mbar so that the reaction mixture just began to boil at 80°C. Then feeds 1 and 2 were started simultaneously and added synchronously over 2 hours. The mixture was then post-polymerized for a further hour at 80°C. Then feed 3 was added in 5 minutes and post-polymerized for a further two hours at 80°C. During the entire polymerization and post-polymerization, approx. 190 g of water was distilled off. The mixture was then cooled to room temperature under normal pressure.

A slightly yellow, viscous solution with a solids content of 16.0 wt.% and a polymer content of 15.7 wt.% is obtained. The K value of the copolymer is 85 (0.5 wt.% in 5 wt.% aqueous NaCl). The Mw is 0.8 million Daltons. The pH value is expected to be between 6 and 7 due to the buffer used.

Example P-P4: P4 (copolymer VFA/Na-acrylate = 70 mol%/30 mol%, K-value 152)

As feed 1, 0.4 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is dissolved in 81.2 g of water at room temperature.

As feed 2, 0.6 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is dissolved in 104.7 g of water at room temperature.

212 g of water are provided as feed 3.

950 g of water and 1.4 g of 75 wt. % phosphoric acid are placed in a 2 L glass apparatus equipped with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube. At a speed of 100 rpm, 2.5 g of a 25 wt. % sodium hydroxide solution are added so that a pH of 6.5 is achieved. 144.7 g of an aqueous 32 wt. % Na acrylate solution, adjusted to pH 6.4, and 82.5 g of N-vinylformamide are added to this buffer solution. The initial mixture is heated to 63°C and the pressure in the apparatus is reduced to approx. 230 mbar so that the reaction mixture just begins to boil at 63°C. Then feed 1 is added over 5 minutes. The mixture is kept at 63°C for 3 hours while water is constantly distilled off. The temperature is then increased to 75°C and the pressure is adjusted to approx. 390 mbar so that continuous distillation is ensured. After 3.5 hours, feed 2 is added over 15 minutes. The temperature is then kept at 75°C for a further 1.25 hours. Feed 3 is then added over 20 minutes, the vacuum is broken and the mixture is cooled to room temperature. During the polymerization and post-polymerization, approximately 270 g of water are distilled off.

A slightly yellow, viscous solution with a solids content of 10.2 wt.% and a polymer content of 9.9 wt.% is obtained. The K value of the copolymer is 152 (0.1 wt.% in 5 wt.% aqueous NaCl). The Mw is 4.1 million Daltons.

Example P-P5: P5 (copolymer VFA/Na-acrylate = 60 mol%/40 mol%, K value 90)

As feed 1, a mixture of 423.5 g of aqueous 32 wt. % Na acrylate solution adjusted to pH 6.4 and 155.1 g of N-vinylformamide is provided.

As feed 2, 2.1 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride are dissolved in 227.9 g of water at room temperature.

573.4 g of water and 3.0 g of 85% by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube. At a speed of 100 rpm, 5.2 g of 25% by weight sodium hydroxide solution are added so that a pH of 6.6 is reached. The initial charge is heated to 77°C and the pressure in the apparatus is reduced to approx. 450 mbar so that the reaction mixture just begins to boil at 77°C. Then feeds 1 and 2 are started simultaneously. At a constant 77°C, feed 1 is added in 1.5 hours and feed 2 in 2.5 hours. After the addition of feed 2 is complete, the reaction mixture is post-polymerized for a further 2.5 hours at 80°C. During the entire polymerization and post-polymerization, approx. 200 g of water are distilled off. The mixture is then cooled to room temperature under normal pressure. A slightly yellow, viscous solution with a solids content of 25.0 wt.% and a polymer content of 24.5 wt.% is obtained. The K value of the copolymer is 90 (0.5 wt.% in 5 wt.% aqueous NaCl solution). The Mw is 0.9 million Daltons.

Example P-P6: P6 (copolymer VFA/Na-acrylate = 80 mol%/20 mol%, K-value 86)

As feed 1, a mixture of 293.7 g of water, 243.0 g of aqueous 32 wt. % Na acrylate solution adjusted to pH 6.4, and 237.2 g of N-vinylformamide is provided.

As feed 2, 1.4 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride are dissolved in 203.6 g of water at room temperature.

659.4 g of water and 3.5 g of 75 wt. % phosphoric acid are placed in a 2 L glass apparatus equipped with anchor stirrer, descending condenser, internal thermometer and nitrogen inlet tube.

At a speed of 100 rpm, 6.0 g of a 25 wt. % sodium hydroxide solution are added so that a pH of 6.6 is achieved. The initial charge is heated to 80°C and the pressure in the apparatus is reduced to approx. 460 mbar so that the reaction mixture just begins to boil at 80°C. Then feeds 1 and 2 are started simultaneously. At a constant 80°C, feed 1 is added in 2 h and feed 2 in 2.5 h. After the addition of feed 2 has ended, the reaction mixture is post-polymerized for a further 2.5 h at 80°C. During the entire polymerization and post-polymerization, approx. 170 g of water are distilled off. The mixture is then cooled to room temperature under normal pressure.

A slightly yellow, viscous solution with a solids content of 21.5 wt.% and a polymer content of 21.3 wt.% is obtained. The K value of the copolymer is 86 (0.5 wt.% in 5 wt.% aqueous NaCl solution). The Mw is 0.7 million Daltons.

A-3) Hydrolysis of polymers containing vinylformamide in polymerized form Example H-H1P1: H1P1 (polymer VFA[32] from P1)

603.3 g of the polymer solution obtained according to Example P-P1 are mixed with 8.6 g of a 40% by weight aqueous sodium bisulfite solution in a 1 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 94.9 g of a 25% aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 3.5 h. The product obtained is cooled to room temperature and adjusted to pH 3.0 with 31.7 g of 37% by weight hydrochloric acid.

A slightly yellow, viscous solution with a polymer content of 14.0 wt.% is obtained. The degree of hydrolysis of the polymerized vinylformamide units is 32 mol%.

Example H-H2P1: H2P1 (polymer VFA[100] from P1)

300.0 g of the polymer solution obtained according to Example P-P1 are heated to 80°C in a 1 L four-neck flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm. Then 157.3 g of a 25% by weight aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 3 hours. The product obtained is cooled to room temperature and adjusted to pH 7 with 37% hydrochloric acid.

A slightly yellow, viscous solution with a polymer content of 7.2 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 100 mol%.

Example H-H3P2: H3P2 (copolymer VFA[50]/Na-acrylate = 70 mol%/30 mol% of P2)

1224.3 g of the polymer solution obtained according to Example P-P2 are mixed in a 2 L four-necked flask equipped with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 704.4 g of water and 8.9 g of a 40 wt. % aqueous sodium bisulfite solution and then heated to 80°C. Then 140.4 g of a 25% by weight sodium hydroxide solution are added. The mixture is kept at 80°C for 5 hours. It is then cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly yellow, slightly cloudy and viscous solution with a polymer content of 7.1 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 50 mol%.

Example H-H4P3: H4P3 (copolymer VFA[100]/Na-acrylate = 70 mol%/30 mol% of P3)

600.0 g of the polymer solution obtained according to Example P-P3 are mixed with 4.5 g of a 40 wt.% aqueous sodium bisulfite solution in a 2 L four-neck flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 150.0 g of a 25% aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 7 hours. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly yellow, viscous solution with a polymer content of 7.7 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 100 mol%.

Example H-H5P3: H5P3 (copolymer VFA[51]/Na-acrylate = 70 mol%/30 mol% of P3)

600.0 g of the polymer solution obtained according to Example P-P3 are mixed with 4.5 g of a 40 wt.% aqueous sodium bisulfite solution in a 2 L four-neck flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 72.0 g of a 25% aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 3.5 h. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly yellow, slightly cloudy and viscous solution with a polymer content of 10.4 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 51 mol%.

Example H-H6P3: H6P3 (copolymer VFA[30]/Na-acrylate = 70 mol%/30 mol% of P3)

600.0 g of the polymer solution obtained according to Example P-P3 are mixed with 4.5 g of a 40% by weight aqueous sodium bisulfite solution in a 2 L four-neck flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 45.5 g of a 25% aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 7 hours. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly yellow, slightly cloudy and viscous solution with a polymer content of 11.7 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 30 mol%.

Example H-H7P4: H7P4 (copolymer VFA[51]/Na-acrylate = 70 mol%/30 mol% of P4)

159.8 g of the polymer solution obtained according to Example P-P4 are mixed with 0.7 g of a 40 wt. % aqueous sodium bisulfite solution in a 500 mL four-neck flask equipped with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 11.8 g of a 25% aqueous sodium hydroxide solution are added. The mixture is kept at 80°C for 4.5 hours. The product obtained is diluted with 71.4 g of water and cooled to room temperature. Then a pH of 8.5 is adjusted with 4.7 g of 37% hydrochloric acid.

A slightly yellow, slightly cloudy and viscous solution with a polymer content of 5.0 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 51 mol%.

Example H-H8P5: H8P5 (copolymer VFA[100]/Na-acrylate = 60 mol%/40 mol% of P5)

1102.9 g of the polymer solution obtained according to Example P-P5 were mixed with 10.5 g of a 40 wt.% aqueous sodium bisulfite solution in a four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 355.6 g of a 25 wt.% sodium hydroxide solution are added. The mixture is kept at 80°C for 7 h and then cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly cloudy, viscous solution with a polymer content of 11.5 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 100 mol%.

Example H-H9P6: H9P6 (copolymer VFA[35]/Na-acrylate = 80 mol%/20 mol% of P6)

600.0 g of the polymer solution obtained according to Example P-P6 are mixed with 4.5 g of a 40% by weight aqueous sodium bisulfite solution in a 2 L four-neck flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm and then heated to 80°C. Then 83.3 g of a 25% by weight sodium hydroxide solution are added. The mixture is kept at 80°C for 3.5 h. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

A slightly yellow, slightly cloudy and viscous solution with a polymer content of 15.3 wt.% is obtained. The degree of hydrolysis of the vinylformamide units is 35 mol%.

A-4) Overview of individual polymers produced

Table TabA1 polymer non-hydrolyzed N-CHO of the original N-vinylformamide [mol%] ^a) hydrolyzed N-CHO of the original N-vinylformamide [mol%] ^b) Sodium acrylate [mol%] ^c) Mw [million Daltons] Degree of hydrolysis [mol%] P1 100 (0) 0 0.34 (0) H1P1 68 32 0 - 32 H2P1 0 100 0 - 100 P2 70 (0) 30 2.2 (0) H3P2 35 35 30 - 50 P3 70 (0) 30 0.8 (0) H4P3 0 70 30 - 100 H5P3 35 35 30 - 51 H6P3 49 21 30 - 30 P4 70 (0) 30 4.1 (0) H7P4 35 35 30 - 51 P5 60 (0) 40 0.9 (0) H8P5 0 60 40 - 100 P6 80 (0) 20 0.7 (0) H9P6 52 28 20 0.5 35

Footnotes:

1. a) non-hydrolyzed N-CHO groups of the N-vinylformamide used in the polymerization calculated based on the amount of N-vinylformamide used in the polymerization minus hydrolyzed N-CHO groups of the N-vinylformamide used in the polymerization
2. b) hydrolyzed N-CHO groups of the N-vinylformamide used in the polymerization calculated based on the amount of N-vinylformamide used in the polymerization and the specific degree of hydrolysis
3. c) Sodium acrylate in polymerized form calculated based on the amount of sodium acrylate used in polymerization

B) Preparation of suspensions or solutions for spraying

To prepare the suspensions or solutions for spraying, the corresponding aqueous solutions from the examples containing the polymer mentioned and optionally the starch mentioned as a solid are added with stirring to a glass vessel with a 4-liter mark in which there are already 2 liters of drinking water. In the case of the aqueous solutions from the examples containing the polymer mentioned, enough of this aqueous solution is added to add 20 g of polymer based on the polymer content or, in the case of the combination with starch, 10 g of polymer based on the polymer content. In the case of the combination with starch, 10 g of starch based on the solid content of the starch are added. After the addition, the mixture is slurried or dissolved. Drinking water is then added until the 4-liter mark on the edge of the vessel is reached. The preparation of the pure starch suspension is described below. The reference solution without additives (= L(0) in Table TabB1) consists only of drinking water. The compositions of the spray solutions L are given in Table TabB1 and those of the spray suspensions S in Table TabB2.

Example S-St1: St1 (strength)

A starch suspension of the commercial starch Cargill*size 35802 (cationic starch, available from Cargill, powder insoluble/partially soluble in water) is prepared by slurrying 20 g of the solid powder of this starch in 2 L of drinking water at room temperature and further dilution with drinking water to a total volume of 4 L. The starch concentration in the aqueous suspension is 5 g / L based on solids content. The pH value of the aqueous suspension is 7.3. Table TabB1 Spray solution L additives contained Concentration polymer [g / L] ^c) L0(-) ^a) - 0 L1(P1) ^a) P1 5 L2(H1P1) ^a) H1P1 5 L3(H2P1 ⁾ H2P1 5 L4(H3P2) ^b) H3P2 5 L5(H4P3) ^b) H4P3 5 L6(H5P3) ^b) H5P3 5 L7(H6P3) ^b) H6P3 5 L8(P3) ^b) P3 5 L9(H7P4) ^b) H7P4 5 L10(H8P5) ^b) H8P5 5 L11(H9P6) ^b) H9P6 5

1. a) vergleichend
2. b) erfindungsgemäss
3. c) Konzentration bezogen auf Polymergehalt der wässrigen Lösung des Beispiels

Tabelle TabB2 Sprühsuspension S enthaltene Additive Konzentration Stärke [ g / L] Konzentration Polymer [g / L] ^c) S1(St1) ^a) St1 5 - S2(St1+P1) ^a) St1 + P1 2,5 2,5 S3(St1+H1P1) ^a) St1 + H1P1 2,5 2,5 S4(St1+H2P1) ^a) St1 + H2P1 2,5 2,5 S5(St1+H3P2) ^b) St1 + H3P2 2,5 2,5 S6(St1+H4P3) ^b) St1 + H4P3 2,5 2,5 S7(St1+H5P3) ^b) St1 + H5P3 2,5 2,5 S8(St1+H6P3) ^b) St1 + H6P3 2,5 2,5 S9(St1 +P3) ^b) St1 + P3 2,5 2,5 S10(St1+H7P4) ^b) St1 + H7P4 2,5 2,5 S11(St1+H8P5) ^b) St1 + H8P5 2,5 2,5 S12(St1+H9P6) ^b) St1 + H9P6 2,5 2,5 Footnotes:

1. a) comparative
2. b) according to the invention
3. c) Concentration based on polymer content of the aqueous solution of the example

Table TabB2 Spray suspension S additives contained Concentration starch [ g / L] Concentration polymer [g / L] ^c) S1(St1) ^a) St1 5 - S2(St1+P1) ^a) St1 + P1 2.5 2.5 S3(St1+H1P1) ^a) St1 + H1P1 2.5 2.5 S4(St1+H2P1) ^a) St1 + H2P1 2.5 2.5 S5(St1+H3P2) ^b) St1 + H3P2 2.5 2.5 S6(St1+H4P3) ^b) St1 + H4P3 2.5 2.5 S7(St1+H5P3) ^b) St1 + H5P3 2.5 2.5 S8(St1+H6P3) ^b) St1 + H6P3 2.5 2.5 S9(St1 +P3) ^b) St1 + P3 2.5 2.5 S10(St1+H7P4) ^b) St1 + H7P4 2.5 2.5 S11(St1+H8P5) ^b) St1 + H8P5 2.5 2.5 S12(St1+H9P6) ^b) St1 + H9P6 2.5 2.5

1. a) vergleichend
2. b) erfindungsgemäss
3. c) Konzentration bezogen auf Polymergehalt der wässrigen Lösung des Beispiels

Footnotes:

1. a) comparative
2. b) according to the invention
3. c) Concentration based on polymer content of the aqueous solution of the example

C) Papers C-1) Physical characterizations Determination of dry matter content

To determine the dry matter content (DW), the mass of the wet sample (MF) is determined from a damp paper sample on a calibrated top-loading rapid balance that can weigh to 0.01 g. The damp paper sample preferably has an area of at least 10 cm x 10 cm. The damp paper sample is then placed in a calibrated drying cabinet that can maintain a set temperature to within ± 2°C and dried at a set temperature of 105°C until the mass is constant. This is typically the case after 90 minutes. The dried paper sample, while still warm, is then transferred to a desiccator that contains a suitable drying agent such as silica gel. After cooling to room temperature, the mass of the dried paper sample (MT) is determined on the aforementioned balance. The dry matter content of the paper sample is calculated using DW = 100 · MT / MF and is given in wt.%. The percentage is often given with one decimal place. If this percentage value no longer changes with the rounded first decimal place, this is an indication that constant mass has been achieved for dry contents of 1 to 100 wt.%. For dry contents of 0 to less than 1 wt.%, the rounded second decimal place of the percentage value is the corresponding indication. Drying takes place at ambient pressure, possibly 101.32 kPa, without correction being made for deviations resulting from the weather and altitude. During drying, the normal ambient air pressure is maintained, possibly 101.32 kPa. No correction is made for slightly different air pressures caused by the weather and altitude. In the case of a moist sample which does not yet have the consistency of a sheet, e.g. a fiber suspension or paper pulp, the moist sample is dried in an appropriate dish with a large surface area.

Internal strength of a preserved dried paper sheet

A dried sheet of paper obtained is examined after storage in a climate chamber at a constant 23 °C and 50 % humidity for 12 hours. The internal strength is determined using a procedure that corresponds to Tappi specification T833 pm-94. Ten paper strips with a width of 2.5 cm and a length of 12.7 cm are cut from two sheets of paper in DIN A4 format, which were previously obtained from the dried paper web of the test machine. Each individual paper sample is attached to the paper with double-sided adhesive tape. attached to a separate base plate and a metal angle. The metal angle is knocked out with a pendulum, whereby the paper sample to be tested is split in a plane parallel to the paper surface. The energy required for this process is measured. The device used for the measurement is an Internal Bond Test Station from TMI (Testing Machines Inc. Islandia, New York USA). The double-sided adhesive tape is a product from 3M (width 25.4 mm, type Scotch No. 140). The measuring device supplies the energy required for the splitting, based on a standardized area in J / m ² . The average value is calculated from 10 individual measurements.

C-2) Production of paper raw material

The raw material for paper production is a paper pulp that is produced by beating paper webs in a pulper. The paper pulp is obtained by dissolving it in drinking water and mechanically processing the paper webs in the pulper at a dry content of approx. 3.5 - 4% by weight. The paper pulp then typically has a fineness of around 50° Schopper Riegler. The paper webs are packaging base papers of the "Testliner 2" specification with a basis weight of 120 g / m ² , which come from Thurpapier in Weinfelden (Switzerland).

C-3) Production of papers by spray treatment of the wet paper web

The papers produced consist of two layers: a top layer with a grammage of 40 g / m ² and a base layer with a grammage of 80 g / m ² . This paper is produced on a test paper machine of the Paper Technology Foundation (PTS) in Heidenau. To make the two-ply possible, the test machine is equipped with a headbox for the lower wire and an additional headbox for the upper wire in addition to a headbox for the lower wire. The paper pulp is diluted with drinking water to a dry content of 0.35 wt.%. The paper pulp is then pumped into the two headboxes and from there applied to the upper wire in the form of a fourdrinier wire and the lower wire in the form of a fourdrinier wire. The wire for the top layer and the wire for the base layer run towards each other at an angle of 60° and form a narrow gap at the end. The top layer and the base layer come into contact and form enough adhesion to detach from the wires deflected after the gap. The layers that are weakly adhering to one another then run into the press section and are couched together on the side facing away from the screens in the press section of the machine, i.e. pressed together while dewatering. The resulting paper web is then sent through the heated cylinders of the drying section, where temperatures of up to 100°C can be reached, and the dried paper is rolled up at the end of the drying section. The dry content of the dried paper obtained is typically 93-94% by weight for the previously described material type, the specified grammage and a machine speed of 0.85 m ² per minute. The contact pressures in the press section can be varied, resulting in different dry contents after the press section. This are between 40 wt.% and 52 wt.% depending on the contact pressure in the test paper machine. The dry content before the press can be varied by using a chemical dewatering agent and/or by applying a vacuum to the undersides of the upper and lower wire. This allows the dry content before the press in the test paper machine to be varied in a range between 15 wt.% and 22 wt.%.

1. 1. In der Einstellung "B", bei der es sich um die Basiseinstellung handelt, ist die dosierte Retentionsmittelmenge (Percol 540, RTM BASF, kationisch modifiziertes Polyacrylamid, emulgiert in Kohlenwasserstoffen und Wasser, Dichte ca. 1 g /cm³, pH-Wert 3-6, cremefarben, Festgehalt 44 Gew.-%) sehr gering und liegt bei ca. 100 g Festgehalt Retentionsmittel pro Tonne Papier für den Gesamtstoff aus dem Oberlage und Unterlage hergestellt werden (0,01 Gew.-%). Dabei wird der Oberlage und Unterlage jeweils die gleiche relative Menge an gleichem Retentionsmittel zudosiert. Der Trockengehalt vor der Presse beträgt unter diesen Bedingungen ca. 15,8 Gew.-%.
2. 2. In der Einstellung "V", bei der ein Vakuum zum Einsatz kommt, bleibt das Retentionsmittel und die Retentionsmittelmenge konstant bei 100 g pro Tonne Papier wie vorgehend bei der Einstellung nach Punkt 1. angegeben. Auf der jeweiligen Unterseite des jeweiligen Siebes nach den beiden Stoffaufläufen wird jedoch zusätzlich ein Vakuum angelegt. Das Vakuum wird so eingestellt, dass die gewünschten Effekte in ausreichender Ausprägung auftreten, ohne dass dabei eine Störung der Formation auftritt. Diese Situation entspricht einer Einstellung des Vakuums, die hier zu einem Trockengehalt der nassen Papierbahnen vor der Presse von ca. 18,2 Gew.-% führt.
3. 3. In der Einstellung "R", bei der zusätzliches Retentionsmittel zum Einsatz kommt, wird das Vakuum nach der Einstellung unter Punkt 2. abgeschaltet. Das Retentionsmittel bei der Einstellung nach Punkt 1. wird in seiner Menge auf ca. 370 g Festgehalt Retentionsmittel pro Tonne Papier des Gesamtstoffs erhöht (0,037 Gew.-%). Der Trockengehalt der nassen Papierbahnen vor der Presse erreicht dabei mit ca. 18,2 Gew.-% den zuvor mit Vakuum nach Punkt 2. erreichten Wert.

Three settings are used:

1. 1. In setting "B", which is the basic setting, the amount of retention agent dosed (Percol 540, RTM BASF, cationically modified polyacrylamide, emulsified in hydrocarbons and water, density approx. 1 g/ ^cm3 , pH value 3-6, cream-colored, solids content 44% by weight) is very low and is approx. 100 g of solids content of retention agent per ton of paper for the total material from which the top layer and base layer are made (0.01% by weight). The same relative amount of the same retention agent is dosed to the top layer and base layer. The dry content before the press under these conditions is approx. 15.8% by weight.
2. 2. In the "V" setting, where a vacuum is used, the retention agent and the amount of retention agent remain constant at 100 g per ton of paper as specified in the setting according to point 1. However, an additional vacuum is applied to the underside of the respective screen after the two headboxes. The vacuum is set so that the desired effects are sufficiently pronounced without disrupting the formation. This situation corresponds to a vacuum setting that leads to a dry content of the wet paper webs before the press of approx. 18.2% by weight.
3. 3. In the "R" setting, where additional retention aid is used, the vacuum is switched off after the setting under point 2. The amount of retention aid in the setting according to point 1 is increased to approx. 370 g of solids content of retention aid per ton of paper of the total material (0.037% by weight). The dry matter content of the wet paper webs before the press reaches the value previously achieved with vacuum according to point 2, at approx. 18.2% by weight.

For spray treatment of the wet paper web with spray solutions or spray suspensions, the spray solution or spray suspension is sprayed between the top layer and the base layer using a nozzle before the top layer and the base layer come into contact with each other ("bP" = "before press"). A two-component nozzle from Schlick is used for this. Spraying takes place before the press section. The position of the nozzle is approx. 15 cm from the couching line, i.e. the line where pressing takes place while dewatering, in the press section. The distance to the wire run-up of the base layer is therefore approx. 35 cm. The pressure for opening the nozzle valve and atomizing the spray solution or spray suspension is 1 bar. The spray width with even coverage is 35 cm. However, when preparing the dried paper sheets for later analysis, 5 cm at the edge are not taken into account. The spray solution or spray suspension is sprayed at two different Application quantities. The first quantity is in a range of around 0.1 L/ ^m2 , which corresponds to an application quantity of 0.5 g/ ^m2 at an approximate concentration of 5 g/L. The second quantity is in a range of around 0.2 L/ ^m2 , which corresponds to an application quantity of 1.0 g/ ^m2 at an approximate concentration of 5 g/L. The density of the spray solution or spray suspension can be approximately assumed to be 1 g/ ^cm3 due to the high dilution.

C-4) Tests and measurements of the dried papers obtained

Dried papers are produced on the paper machine as described in C-3), taking into account the respective information in Tables TabC1 - Tab C3 on the concentration of the spray solution or spray dispersion and the machine settings. Tables TabC1 to TabC3 also give the measured internal strengths of dried paper test sheets as described in C-1). Table TabC1 "bP" - 0.1 L / m ² Internal strength [J / m ² ] Example No. Spray solution Setting "B" Setting "V" Setting "R" R1 L0(-) ^a) 148 154 142 C1-1 L1(P1) ^a) 153 144 155 C1-2 L2(H1P1) ^a) 159 163 153 C1-3 L3(H2P1 ⁾ 156 152 149 C1-4 L4(H3P2) ^b) 232 281 285 C1-5 L5(H4P3) ^b) 227 283 289 C1-6 L6(H5P3) ^b) 226 281 293 C1-7 L7(H6P3) ^b) 216 261 267 C1-8 L8(P3) ^b) 221 278 273 C1-9 L9(H7P4) ^b) 215 264 268 C1-10 L10(H8P5) ^b) 219 269 273 C1-11 L11(H9P6) ^b) 233 279 284 Footnotes: a) comparative
b) according to the invention

In Table TabC1, it can be seen that, compared to the comparative examples, the papers produced with spray solutions according to the invention have a significantly improved internal strength. Furthermore, increasing the dry content after the wire section by means of negative pressure or increased retention polymer quantity leads to a further improvement in the internal strength of the papers produced with spray solutions according to the invention, while these measures have little and inconsistent effect in the comparative examples. Table TabC2 "bP" - 0.2 L / m ² Internal strength [J / m ² ] Example No. Spray solution Setting "B" Setting "V" Setting "R" R2 L0(-) ^a) 152 142 139 C2-1 L1(P1) ^a) 161 168 153 C2-2 L2(H1P1) ^a) 168 174 163 C2-3 L3(H2P1 ⁾ 163 169 174 C2-4 L4(H3P2) ^b) 254 299 305 C2-5 L5(H4P3) ^b) 248 231 322 C2-6 L6(H5P3) ^b) 243 297 291 C2-7 L7(H6P3) ^b) 238 284 279 C2-8 L8(P3) ^b) 252 302 299 C2-9 L9(H7P4) ^b) 242 297 293 C2-10 L10(H8P5) ^b) 238 264 267 C2-11 L11(H9P6) ^b) 249 297 294 Footnotes: a) comparative
b) according to the invention

Table TabC2 shows that even when the application quantity is doubled, the papers produced with spray solutions according to the invention have significantly improved internal strength compared to the comparative examples. Increasing the dry content after the wire section by means of negative pressure or increased retention polymer quantity almost always leads to a further improvement in the internal strength of the papers produced with spray solutions according to the invention, while these measures have little or no effect on the comparative examples. Table TabC3 "bP" - 0.1 L / m ² Internal strength [J / m ² ] Example No. Spray solution or spray suspension Setting "B" Setting "V" Setting "R" R1 L0(-) ^a) 148 154 142 C3-1 S1(St1) ^a) 167 161 165 C3-2 S2(St1+P1) ^a) 161 169 167 C3-3 S3(St1+H1P1) ^a) 156 147 163 C3-4 S4(St1+H2P1) ^a) 161 165 154 C3-5 S5(St1+H3P2) ^b) 198 254 245 C3-6 S6(St1+H4P3) ^b) 202 248 237 C3-7 S7(St1+H5P3) ^b) 204 247 239 C3-8 S8(St1+H6P3) ^b) 205 243 249 C3-9 S9(St1+P3) ^b) 205 249 255 C3-10 S10(St1+H7P4) ^b) 204 239 247 C3-11 S11(St1+H8P5) ^b) 201 239 243 C3-12 S12(St1+H9P6) ^b) 209 242 252 Footnotes: a) comparative
b) according to the invention

Table TabC3 shows, as in Table TabC1 and Table TabC2, that the papers produced with spray dispersions according to the invention have significantly improved internal strength compared to the comparative examples. Increasing the dry content after the wire section by means of negative pressure or increased retention polymer quantity leads to a further improvement in the internal strength of the papers produced with spray dispersions according to the invention, whereas these measures have little and inconsistent effect in the comparative examples. In comparison with Table TabC1, Table TabC3 shows that replacing half of the amount of polymer used with cationic starch no longer leads to an equivalent improvement in the internal strength of the papers.

Claims (14)

1. A method for the manufacture of dried multi-layer paper comprising the steps

   (A) Dewatering a first aqueous fiber suspension, which has a dry matter content between 0.1 wt.% And 6 wt.%, on a first sieve, whereby a first fibrous sieve, which has a dry matter content between 14 wt.% and 25 wt .-%, arises,

   (B) Dewatering a second aqueous fiber suspension, which has a dry matter content between 0.1 wt.% And 6 wt.%, on a second sieve, whereby a second fibrous sieve, which has a dry matter content between 14 wt.% and 25 wt .-%, arises,

   (C) Spraying the first fibrous web, the second fibrous web or the first fibrous web and the second fibrous web on at least one surface side with a spray solution or spray suspension, thereby producing at least one sprayed fibrous web which has a sprayed surface side,

   (D) Joining the first fibrous web with the second fibrous web, of which at least one of the two is a sprayed fibrous web, in such a way that at least one sprayed surface side of the two fibrous webs forms the contact surface side to the other fibrous web and the entire width of the fibrous webs lie one above the other, whereby a layer bond is created,

   (E) Dewatering the layer compound by pressing, whereby a partially dehydrated layer compound is formed,

   (F) Dehydrating the partially dehydrated layer compound by supplying heat, which creates the dried multilayer paper.

   wherein the spray solution or spray suspension contains

   (c-a) water

   (c-b) at least one water-soluble polymer P, which can be obtained by polymerizing

   (i) 40 to 85 mol% of a monomer of Formula I

   

   in which R¹ = H or C₁-C₆-alkyl,

   (ii) 15 to 60 mol% of one or more ethylenically unsaturated Monomers which are different from a monomer of formula I, the total amount of all monomers (i) and (ii) being 100 mol%, and optionally by a subsequent partial or complete hydrolysis of the units of the monomers of formula (I) polymerized into the polymer P to form primary amino or amidine groups,

   wherein the proportion of water is at least 75% by weight, based on the spray solution or the spray suspension.
2. A method according to claim 1, wherein the spray solution or spray suspension has a pH Value of 5.5 or greater.
3. A method according to claim 1 or 2, wherein in step (E) the partially dehydrated layer composite has a dry content of between 35% by weight and 65% by weight, and/or wherein in step (F) the dried multi-ply paper has a dry content of at least 88% by weight.
4. A method according to any one of claims 1 to 3, wherein the polymer P is obtainable by polymerizing

   (i) 40 to 85 mol%, preferably 50 to 85 mol%, of a monomer of formula I,

   (ii) 15 to 60 mol%, preferably 15 to 50 mol%, of one or more ethylenically unsaturated monomers which are different from a monomer of the formula I,

   wherein the one or more ethylenically unsaturated monomers are selected from

   (ii-1) Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts,

   (ii-2) Acrylonitrile or methacrylonitrile,

   (ii-3) Vinyl acetate,

   (ii-4) of a monoethylenically unsaturated sulfonic acid, a m noethylenically unsaturated sulfonic acid, a monoethylenically unsaturated phosphonic acid, a monoethylenically unsaturated mono- or diester of phosphoric acid or a monoethylenically unsaturated carboxylic acid with 4 to 8 carbon atoms, which is different from methacrylic acid, or their alkali metal, alkaline earth metal or ammonium salts,

   (ii-5) a quaternized, monoethylenically unsaturated monomer, a monoethylenically unsaturated monomer which carries at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7, or a diallyl-substituted amine which has exactly two ethylenic double bonds and is quaternized or at pH 7 is protonated, or its salt form,

   (ii-6) a monoethylenically unsaturated monomer which carries no charge at pH 7 and which is different from acrylonitrile, methacrylonitrile and vinyl acetate, or an ethylenically unsaturated monomer whose exactly two ethylenic double bonds are conjugated and which carries no charge at pH 7,

   (ii-7) 0 to 2 mol% of a monomer containing at least two ethylenically unsaturated double bonds which are not conjugated and which is different from a diallyl-substituted amine which has exactly two ethylenic double bonds,

   (ii-8) 0 to 10 mol% of an ethylenically unsaturated monomer derived from the monomers (ii-1) to (ii-7) is different,

   wherein the total amount of all monomers (i) and (ii-1) to (ii-8) is 100 mol% and mol% relates to the total amount of all monomers (i) and (ii-1) to (ii-8),

   and optionally by subsequent partial or complete hydrolysis of the units of the monomers of the formula (I) polymerized into the polymer P to form primary amino groups or amidine groups, wherein in the case of the presence of polymerized-in units of vinyl acetate these also hydrolyse partially or completely.
5. A method according to any one of claims 1 to 4, wherein
   which contains one or more ethylenically unsaturated monomers

   (ii-1) 15 to 50 mol% acrylic acid or methacrylic acid or alkali metal, alkaline earth metal or ammonium salts thereof, and/or

   (ii-2) 0 to 35 mol% of acrylonitrile or methacrylonitrile, and/or

   (ii-3) 0 to 35 mol% vinyl acetate, and/or

   (ii-4) 0 to 10 mol% of a monoethylenically unsaturated sulfonic acid, a monoethylenically unsaturated phosphonic acid, a monoethylenically unsaturated mono- or diester of phosphoric acid or a monoethylenically unsaturated carboxylic acid with 4 to 8 carbon atoms, which is different from methacrylic acid, or their alkali metal, alkaline earth metal or ammonium salts, and/or

   (ii-5) 0 to 20 mol% of a quaternized, monoethylenically unsaturated monomer, a monoethylenically unsaturated monomer which carries at least one secondary or tertiary amino group and whose at least one secondary or tertiary amino group is protonated at pH 7, or a diallyl-substituted amine which has exactly two ethylenic double bonds and is quaternized or at pH 7 is protonated, or its salt form, and/or

   (ii-6) from 0 to 35 mol% of a monoethylenically unsaturated monomer which, at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, or of an ethylenically unsaturated monomer whose exactly two double bonds are conjugated, which carries no charge at pH 7 and is different from acrylonitrile, methacrylonitrile and vinyl acetate, and/or

   (ii-7) 0 to 1 mol% of a monomer which carries at least two ethylenically unsaturated bonds and is different from acrylonitrile, methacrylonitrile and vinyl acetate double bonds which are not conjugated and which is different from a diallyl-substituted amine having exactly two ethylenic double bonds, and/o

   (ii-8) 0 to 5 mol% of an ethylenically unsaturated monomer derived from the monomers (i) and (ii-1) to (ii-7) is different, where mol% refers to the total number of all monomers used in the polymerization and the total number of all monomers is 100 mol%.
6. A method according to any one of claims 1 to 5, wherein the polymer P is obtainable by
   polymerization of

   (i) 50 to 85 mol% of a monomer of Formula I

   (ii-1) 15 to 50 mol% of acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts,

   (ii-2) 0 to 35 mol% Acrylonitrile or methacrylonitrile

   wherein the total amount of all monomers (i) and (ii-1) to (ii-2) is 100 mol% and mol% refers to the total amount of all monomers (i) and (ii-1) to (ii-2), and optionally by a subsequent partial or complete hydrolysis of the units of the monomers of formula (I) polymerized into the polymer P to form primary amino groups or amidine groups.
7. A method according to any one of claims 1 to 6, wherein in steps (A) and (B) in each case up to a dry content of 17 wt .-% to 22 wt .-%.
8. A process according to any one of the claims 1 to 7, wherein an organic polymer (a-c) is added as a retention agent to the first aqueous pulp suspension containing (a-a) water and (a-b) first pulp prior to dewatering in step (A), and an organic polymer (b-c) is added as a retention agent to the second aqueous pulp suspension containing (b-a) water and (b-b) second pulp prior to dewatering in step (B), containing (b-a) water and (b-b) second fibrous material, an organic polymer (b-c) is added as a retention agent before dewatering in step (B), the amount of organic polymer (a-c) added preferably being 0.001% by weight.-% to 0.2 % by weight based on the first pulp (a-b) and preferably the amount of added organic polymer (b-c) is 0.001 % to 0.2 % by weight based on the second pulp (b-b).
9. A method according to any one of claims 1 to 8, wherein the first sieve is a Fourdrinier wire and the second sieve is a Fourdrinier wire.
10. A method according to any one of the claims 1 to 9, in step (A) the first fibrous suspension is applied to the first sieve with a first top side of the sieve and a first underside of the sieve on the first top side of the sieve, and the dewatering is supported by applying a vacuum to the first underside of the sieve, in step (B), the second fibrous suspension is applied to the second sieve with a second sieve top side and a second sieve bottom on the second sieve top, and dewatering is supported by applying a vacuum to the second sieve bottom, or in step (A) first fibrous suspension and in step (B) the second fibrous suspension is applied to the corresponding first sieve top side and second sieve top side, and the respective dehydrating is supported by applying a vacuum to the corresponding first sieve bottom and second sieve bottom.
11. A method according to any one of claims 1 to 10, wherein the method is carried out in a paper machine, the equipment of which has a first sieve section with the first sieve, which has a first sieve top and a first sieve underside, a second sieve section with the second sieve, which has a second sieve top side and a second underside of the sieve has a spray device containing the spray solution or spray suspension, a press section and a dryer section with heated cylinders, and in the paper machine these in the order of the first sieve section and second sieve section, followed by the spray device, then the press section and then the dryer section are arranged.
12. A method according to any one of claims 1 to 11, wherein in step (C) the spray solution or spray suspension for spraying is placed under an overpressure of 0.5 to 4.5 bar relative to the ambient pressure, and/or
    whereby in step (C) spraying with the spray solution or spray suspension from a spraying device takes place.
13. A method according to any one of claims 1 to 12, wherein in step (C) the first fibrous web and the second fibrous web are sprayed, whereby at least two sprayed fibrous webs are formed, and in step (D) the first fibrous web is joined to the second fibrous web in this way that the sprayed surface side of the first fibrous web forms the contact surface side to the second fibrous web and the sprayed surface side of the second fibrous web forms the contact surface side to the first fibrous web.
14. A method according to any one of claims 1 to 13, wherein the dry content is determined by drying at 105°C to constant mass.