Method for producing multi-layer paper

Abstract

A method for producing dried multilayer paper is provided comprising dewatering a first aqueous fibrous suspension, thereby creating a first fibrous web; dewatering a second aqueous fibrous suspension, thereby creating a second fibrous web; spraying one or more of a first fibrous web and a second fibrous web with a spray solution or spray suspension, thereby producing at least one sprayed fibrous web; assembling the first fibrous web with the second fibrous web; dehydrating the resulting layer compound by pressing; then dehydrating by supplying heat, which creates the dried multilayer paper. The spray solution or spray suspension contains water and at least one water-soluble polymer P. The polymer P is obtained by polymerizing: 40 to 85 mol % of a monomer of Formula I ##STR00001##
in which R.sup.1=H or C.sub.1-C.sub.6-Alkyl; and 15 to 60 mol % of one or more ethylenically unsaturated monomers.

Claims

1. A method for the manufacture of dried multi-layer paper comprising the steps (A) Dehydrating a first aqueous fibre suspension, which has a dry matter content between 0.1 wt. % And 6 wt. %, on a first sieve, whereby a first fibrous web, which has a dry matter content between 14 wt. % and 25 wt. %, arises, (B) Dehydrating a second aqueous fibre suspension, which has a dry matter content between 0.1 wt. % and 6 wt. %, on a second sieve, whereby a second fibrous web, 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) Dehydrating 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 comprises (c-a) Water, and (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 ##STR00011## in which R.sup.1=H or C.sub.1-C.sub.6-Alkyl, (ii) 15 to 60 mol % of one or more ethylenically unsaturated monomers which are different from a monomer of the 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 the 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 wherein the spray solution or spray suspension is free of starch.

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, wherein in step (E) the partially dehydrated layer compound has a dry content between 35% wt. and 65% wt.

4. A method according to claim 1, wherein in step (F) the dried multilayer paper has a dry content of at least 88% wt.

5. A method according to claim 1, wherein the polymer P is obtainable by polymerizing (i) 40 to 85 mol % of a monomer of Formula I, (ii) 15 to 60 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) 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, (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 % 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, (ii-8) 0 to 10 mol % of ethylenically unsaturated monomer which is different than monomers (ii-1) to (ii-7), 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 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, where in the presence of polymerized units of vinyl acetate these also partially or completely hydrolyse.

6. A method according to claim 1, wherein in the polymerization (i) 50 to 85 mol % of a monomer of Formula I, (ii) 15 to 50 mol % of one or more ethylenically unsaturated monomers which are different from a monomer of the Formula I, are used.

7. A method according to claim 1, wherein the one or more ethylenically unsaturated monomers comprise (ii-1) 15 to 50 mol % Acrylic acid or methacrylic acid or their alkali metal, alkaline earth metal or ammonium salts, where mol % refers to the total number of all monomers used in the polymerization and the total number of all monomers is 100 mol %.

8. A method according to claim 1, wherein the polymer P is obtainable by polymerizing 50 to 85 mol % of 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, wherein the total amount of all monomers (i) and (ii-1) to (ii-2) is 100 mol % and mol % relates to the total amount of all monomers (i) and (ii-1) to (ii-2), 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.

9. A method according to claim 1, wherein in steps (A) and (B) dehydrating is conducted in each case up to a dry content of 17 wt. % to 22 wt. %.

10. A method according to claim 1, wherein an organic polymer (a-c) is added to the first aqueous fibre suspension, containing (a-a) water and (a-b) first fibre, before dehydration in step (A) as a retention agent, and the second aqueous fibre suspension, containing (b-a) water and (b-b) second fibre, before dehydration in step (B) an organic polymer (b-c) added as a retention agent.

11. A method according to claim 10, wherein the amount of added organic polymer (a-c) is 0.001 wt. % to 0.2 wt. % based on the first fibre (a-b) and the amount of added organic polymer (b-c) 0.001 wt. % to 0.2 wt. % based on the second fibre (b-b).

12. A method according to claim 1, wherein the first sieve is a Fourdrinier wire and the second sieve is a Fourdrinier wire.

13. A method according to claim 1, wherein 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 dewatering is supported by applying a vacuum to the corresponding first sieve bottom and second sieve bottom.

14. A method according to claim 1, 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.

15. A method according to claim 1, 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.

16. A method according to claim 1, 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.

17. A method according to claim 1, wherein in step (C) the spraying with the spray solution or spray suspension takes place from a spray device.

18. A method according to claim 1, wherein the dry content is determined by drying at 105° C. to constant mass.

19. A dried multi-layer paper obtainable by a process according to claim 1.

Description

EXAMPLES

(1) The percentages in the examples are percentages by weight, unless stated otherwise.

(2) A) Additive

(3) A-1) Methods for Characterizing the Polymers

(4) The solids content is determined by distributing 0.5 to 1.5 g of the polymer solution in a metal lid with a diameter of 4 cm and then drying in a forced 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 % by weight. Drying is carried out at ambient pressure, possibly 101.32 KPa, which is carried out without a correction for a deviation resulting from weather and sea level.

(5) The degree of hydrolysis is the proportion in % of the hydrolyzed N—CHO groups of the N-vinylformamide monomers used in the polymerization of the total amount of N-vinylformamide used in the polymerization. The determination of 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 the hydrolysis (test set from Boehringer Mannheim).

(6) The polymer content indicates the content of polymer without counter ions in the aqueous solution in % by weight, i.e. Counter ions are not considered. The polymer content is the sum of the parts by weight of all structural units of the polymer in g which are present in 100 g of the aqueous solution. It is determined mathematically. For this purpose, potentially charge-bearing structural units are included in the charged form, i.e. e.g. Amino groups in the protonated form and acid groups in the deprotonated form. Counter ions of the charged structural units such as sodium cation, chloride, phosphate, formate, acetate etc. are not considered. The calculation can be carried out in such a way that, for a batch, the application quantity of the monomers, if appropriate a degree of hydrolysis of certain monomers and, optionally a proportion of reactants, the polymer analogue by reaction with the polymer under formation a covalent bond is applied, which determines Structural units of the polymer present at the end of the reaction and these are converted into parts by weight using the molar masses of the structural units. For this, a complete, i.e. 100% conversion of all monomers used or generally reactants are assumed. The sum of the parts by weight gives the total amount of polymer in this approach. The polymer content results from 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 consequently contains reaction medium, optionally cations or anions, and everything added to the reaction batch which is not assumed to be incorporated into the polymer. Substances removed from the reaction mixture (e.g. water which may have been distilled off, etc.) are drawn off.

(7) The total content of primary amino groups and/or amidine groups can be carried out analogously as per the procedure described above for the polymer content. The molar composition is based on the amounts of monomers used, the analytically determined degree of hydrolysis, the ratio of amidine groups to primary amino groups determined by .sup.13C-NMR-spectroscopy and, if appropriate, the proportion which has been polymer-analogously applied with the polymer to form a covalent bond, the molar composition of the structural units of the polymer present at the end of the reaction. With the help of the molar mass of the individual structural units, the molar proportion of primary amino groups and/or amidine units in meq which is in 1 g of polymer can be calculated. When determined by means of 13C NMR spectroscopy, the area of the formate group HCOO— (173 [ppm]) can be related to the area of the amidine group —N═CH—N— (152 ppm).

(8) The K values are measured according to H. Fikentscher, Cellulosechemie, Vol. 13, 48-64 and 71-74 under the conditions specified in each case. The information in parentheses indicates 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 value of 7.5.

(9) The weight average molecular weight Mw is determined with static light scattering. To do this, the sample is dissolved in a 1000 millimolar saline solution at a pH value of 9.0. The Mw is given in Daltons.

(10) The water used in the examples of polymerizations under A-2) and hydrolysis under A-3) is completely desalinated.

(11) A-2) Polymerisations

Example P-P1: P1 (Polymer VFA=100 mol %, K-Value 90)

(12) 234 g of N-vinylformamide is provided as feed 1.

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

(14) 1080.0 g of water and 2.5 g of 75% strength by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending cooler, internal thermometer and nitrogen inlet tube. At a speed of 100 rpm, 2.1 g of a 25% strength by weight sodium hydroxide solution are added, so that a pH of 6.6 is reached. 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 at the same time. At a constant 73° C., feed 1 is metered in one hour and 15 minutes and feed 2 in 2 hours. After the addition of feed 2 has ended, the reaction mixture is polymerized at 73° C. for a further three hours. About 190 g of water are distilled off during the entire polymerization and post-polymerization. The mixture is then cooled to room temperature under normal pressure.

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

Example P-P2: P2 (Copolymer VFA/Na Acrylate=70 Mol %/30 Mol %, K Value 122)

(16) A mixture of 330 g of water, 217.8 g of aqueous 32% by weight Na-acrylate solution, which is adjusted to pH 6.4, and 124.2 g of N-vinylformamide are provided as feed 1.

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

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

(19) 668.3 g of water and 1.9 g of 75% strength by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending cooler, internal thermometer and nitrogen inlet tube.

(20) At a speed of 100 rpm, 3.1 g of a 25% wt. strength by weight sodium hydroxide solution are added, so that a pH of 6.6 is reached. The initial charge is heated to 73° C. and the pressure in the apparatus is reduced to approx. 340 mbar, so that the reaction mixture just begins to boil at 73° C. Then feeds 1 and 2 are started at the same time. At a constant 73° C., feed 1 is metered in two hours and feed 2 in 3 hours. After the addition of feed 2 has ended, the reaction mixture is post-polymerized at 73° C. for a further 2 hours. Then feed 3 is added in 5 minutes and polymerization is continued at 73° C. for a further two hours. About 190 g of water are distilled off during the entire polymerization and post-polymerization. The mixture is then cooled to room temperature under normal pressure.

(21) A slightly yellow, viscous solution is obtained with a solids content of 15.9% by weight and a polymer content of 15.6% by weight. The K value of the copolymer is 122 (0.1% by weight in 5% by weight 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)

(22) A mixture of 240.0 g of water, 176.5 g of aqueous 32% Na acrylate solution, which is adjusted to pH 6.4, and 100.6 g of N-vinylformamide are provided as feed 1.

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

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

(25) 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 cooler, internal thermometer and nitrogen inlet tube. At a speed of 100 rpm, 4.2 g of a 25% wt. strength by weight sodium hydroxide solution are added, so that a pH of 6.6 is reached. The initial charge is heated to 80° C. and the pressure in the apparatus is reduced to approx. 450 mbar, so that the reaction mixture just begins to boil at 80° C. Then feeds 1 and 2 are started simultaneously and metered in synchronously in 2 hours. The mixture is then polymerized at 80° C. for a further one hour. The feed 3 is then added in 5 minutes and the polymerization is continued at 80° C. for a further two hours. About 190 g of water are distilled off during the entire polymerization and post-polymerization. The mixture is then cooled to room temperature under normal pressure.

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

Example P-P4: P4 (Copolymer VFA/Na Acrylate=70 Mol %/30 Mol %, K Value 152)

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

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

(29) 212 g of water is provided as feed 3.

(30) 950 g of water and 1.4 g of 75% strength by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending cooler, internal thermometer and nitrogen inlet tube.

(31) At a speed of 100 rpm, 2.5 g of a 25% wt. strength by weight sodium hydroxide solution are added, so that a pH of 6.5 is reached. To this buffer solution 144.7 g of an aqueous 32% by weight Na-acrylate solution, which is adjusted to pH 6.4, and 82.5 g of N-vinylformamide are added. The initial charge 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 in 5 minutes. The batch is kept at 63° C. for 3 hours with constant distillation of water. The temperature is then increased to 75° C. and the pressure is set to approximately 390 mbar, so that continuous distillation is still ensured. After 3.5 h, feed 2 is added in 15 min. The temperature is then kept at 75° C. for a further 1.25 h. The feed 3 is then added in 20 min, the vacuum is broken, and the batch is cooled to room temperature. About 270 g of water are distilled off during the polymerization and post-polymerization.

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

Example P-P5: P5 (Copolymer VFA/Na Acrylate=60 Mol %/40 Mol %, K Value 90)

(33) A mixture of 423.5 g of aqueous 32% by weight Na acrylate solution, which is adjusted to pH 6.4, and 155.1 g of N-vinylformamide are provided as feed 1.

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

(35) 573.4 g of water and 3.0 g of 85% strength by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending cooler, internal thermometer and nitrogen inlet tube.

(36) At a speed of 100 rpm, 5.2 g of a 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 at the same time. At a constant 77° C., feed 1 is metered in 1.5 hours and feed 2 in 2.5 hours. After the addition of feed 2 has ended, the reaction mixture is post-polymerized at 80° C. for a further 2.5 hours. About 200 g of water are distilled off during the entire polymerization and post-polymerization. The mixture is then cooled to room temperature under normal pressure.

(37) A slightly yellow, viscous solution is obtained with a solids content of 25.0% by weight and a polymer content of 24.5% by weight. The K value of the copolymer is 90 (0.5% by weight in 5% by weight 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)

(38) A mixture of 293.7 g of water, 243.0 g of aqueous 32% by weight Na-acrylate solution, which is adjusted to pH 6.4, and 237.2 g of N-vinylformamide are provided as feed 1.

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

(40) 659.4 g of water and 3.5 g of 75% strength by weight phosphoric acid are placed in a 2 L glass apparatus with anchor stirrer, descending cooler, internal thermometer and nitrogen inlet tube.

(41) At a speed of 100 rpm, 6.0 g of a 25% wt. strength by weight sodium hydroxide solution are added, so that a pH of 6.6 is reached. 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 at the same time. At constant 80° C., feed 1 is metered in 2 h and feed 2 in 2.5 h. After the addition of feed 2 has ended, the reaction mixture is polymerized at 80° C. for a further 2.5 h. About 170 g of water are distilled off during the entire polymerization and post-polymerization. The mixture is then cooled to room temperature under normal pressure.

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

(43) A-3) Hydrolysis of Polymers Containing Vinyl Formamide in Copolymerized Form

Example H-H1P1: H1P1 (Polymer VFA[32] from P1)

(44) 603.3 g of the polymer solution obtained according to Example P-P1 are mixed 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 with 8.6 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then 94.9 g of a 25% aqueous sodium hydroxide solution is added. The mixture is kept at 80° C. for 3.5 hours. The product obtained is cooled to room temperature and adjusted to pH 3.0 with 31.7 g of 37% strength by weight hydrochloric acid.

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

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

(46) 300.0 g of the polymer solution obtained according to Example P-P1 are mixed 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 then heated to 80° C. Then 157.3 g of a 25% by weight aqueous sodium hydroxide solution is 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.

(47) A slightly yellow, viscous solution with a polymer content of 7.2% by weight 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 % from P2)

(48) 1224.3 g of the polymer solution obtained according to Example P-P2 are in a 2 L four-necked flask 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% by weight solution aqueous sodium bisulfite solution and then heated to 80° C. Then add 140.4 g of a 25% by weight sodium hydroxide solution. The mixture is kept at 80° C. for 5 hours. It is then cooled to room temperature and adjusted to pH 8.5 using 37% hydrochloric acid.

(49) A slightly yellow, slightly cloudy and viscous solution with a polymer content of 7.1% by weight 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 % from P3)

(50) 600.0 g of the polymer solution obtained according to Example P-P3 are mixed in a 2 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 4.5 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then 150.0 g of a 25% aqueous sodium hydroxide solution is added.

(51) 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.

(52) A slightly yellow, viscous solution with a polymer content of 7.7% by weight 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 % from P3)

(53) 600.0 g of the polymer solution obtained according to Example P-P3 are mixed in a 2 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 4.5 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then 72.0 g of a 25% aqueous sodium hydroxide solution is added. The mixture is kept at 80° C. for 3.5 hours. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

(54) A slightly yellow, slightly cloudy and viscous solution with a polymer content of 10.4% by weight 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 % from P3)

(55) 600.0 g of the polymer solution obtained according to Example P-P3 are mixed in a 2 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 4.5 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then 45.5 g of a 25% aqueous sodium hydroxide solution is 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.

(56) A slightly yellow, slightly cloudy and viscous solution with a polymer content of 11.7% by weight 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 % from P4)

(57) 159.8 g of the polymer solution obtained according to Example P-P4 are mixed in a 500 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 0.7 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then 11.8 g of a 25% aqueous sodium hydroxide solution is 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. A pH of 8.5 is then set with 4.7 g of 37% hydrochloric acid.

(58) A slightly yellow, slightly cloudy and viscous solution with a polymer content of 5.0% by weight 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 % from P5)

(59) 1102.9 g of the polymer solution obtained according to Example P-P5 are mixed in a four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 10.5 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then add 355.6 g of a 25% by weight sodium hydroxide solution. The mixture is kept at 80° C. for 7 hours and then cooled to room temperature and adjusted to pH 8.5 using 37% hydrochloric acid.

(60) A slightly cloudy, viscous solution with a polymer content of 11.5% by weight 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 % from P6)

(61) 600.0 g of the polymer solution obtained according to Example P-P6 are mixed in a 2 L four-necked flask with a blade stirrer, internal thermometer, dropping funnel and reflux condenser at a stirrer speed of 80 rpm with 4.5 g of a 40% by weight aqueous sodium bisulfite solution and then on heated to 80° C. Then add 83.3 g of a 25% by weight sodium hydroxide solution. The mixture is kept at 80° C. for 3.5 hours. The product obtained is cooled to room temperature and adjusted to pH 8.5 with 37% hydrochloric acid.

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

(63) A-4) Overview of Individual Polymers Produced

(64) TABLE-US-00001 TABLE TabA1 Unhydrolyzed hydrolysed N-CHO of N-CHO of the original the original Sodium Mw Hydrolysis N-vinylformamide N-vinylformamide acrylate [Mio. degree Polymer [Mol %] .sup.a) [mol %] .sup.b) [Mol %] .sup.c) Dalton] [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: .sup.a) Non-hydrolysed N-CHO groups of the N-vinylformamide used in the polymerization calculated based on the amount of N-vinylformamide used in the polymerization minus hydrolysed N-CHO groups of the N-vinylformamide used in the polymerization .sup.b) hydrolysed N-CHO groups of the N-vinylformamide used in the polymerization, calculated based on the amount of N-vinylformamide used in the polymerization and determined degree of hydrolysis .sup.c) Polymerized sodium acrylate calculated based on the amount of sodium acrylate used in the polymerization

(65) B) Preparation of Suspensions or Solutions for Spraying

(66) To prepare the suspensions or solutions for spraying, the corresponding aqueous solutions from the examples containing the polymer mentioned and, if appropriate, the starch mentioned are added as a solid with stirring into a glass vessel with a 4-liter marking, in which there are already 2 litres of drinking water. For this purpose, in the case of the aqueous solutions from the examples containing the polymer mentioned, so much of this aqueous solution is added that 20 g or, in the case of the combination with starch, 10 g of polymer, based on the polymer content, are added. In the case of a combination with starch, 10 g of starch based on the solids content of the starch are added. After the addition is complete, the slurry is mixed or dissolved. Drinking water is then added until the 4-litre mark on the rim 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)

(67) A starch suspension of the commercial starch Cargill*size 35802 (cationic starch, available from Cargill, powder insoluble/partially soluble in water) is prepared by slurring 20 g of the solid powder of this starch in 2 L drinking water at room temperature and further dilution with drinking water up to 4 L total volume. The starch concentration in the aqueous suspension is 5 g/L based on the solids content. The pH Value of the aqueous suspension is 7.3.

(68) TABLE-US-00002 TABLE TabB1 Concentration Spray contained Polymer solution L additives [g/L] .sup.c) L0(-) .sup.a) — 0 L1(P1) .sup.a) P1 5 L2(H1P1) .sup.a) H1P1 5 L3(H2P1) .sup.a) H2P1 5 L4(H3P2) .sup.b) H3P2 5 L5(H4P3) .sup.b) H4P3 5 L6(H5P3) .sup.b) H5P3 5 L7(H6P3) .sup.b) H6P3 5 L8(P3) .sup.b) P3 5 L9(H7P4) .sup.b) H7P4 5 L10(H8P5) .sup.b) H8P5 5 L11(H9P6) .sup.b) H9P6 5 Footnotes: .sup.a) comparative .sup.b) inventively .sup.c) Concentration based on the polymer content of the aqueous solution of the example

(69) TABLE-US-00003 TABLE TabB2 Concentration Concentration contained strength Polymer Spray suspension S additives [g/L] [g/L] .sup.c) S1(St1) .sup.a) St1 5 — S2(St1 + P1) .sup.a) St1 + P1 2.5 2.5 S3(St1 + H1P1) .sup.a) St1 + H1P1 2.5 2.5 S4(St1 + H2P1) .sup.a) St1 + H2P1 2.5 2.5 S5(St1 + H3P2) .sup.b) St1 + H3P2 2.5 2.5 S6(St1 + H4P3) .sup.b) St1 + H4P3 2.5 2.5 S7(St1 + H5P3) .sup.b) St1 + H5P3 2.5 2.5 S8(St1 + H6P3) .sup.b) St1 + H6P3 2.5 2.5 S9(St1 + P3) .sup.b) St1 + P3 2.5 2.5 S10(St1 + H7P4) .sup.b) St1 + H7P4 2.5 2.5 S11(St1 + H8P5) .sup.b) St1 + H8P5 2.5 2.5 S12(St1 + H9P6) .sup.b) St1 + H9P6 2.5 2.5 Footnotes: .sup.a) comparative .sup.b) inventively .sup.c) Concentration based on the polymer content of the aqueous solution of the example

(70) C) Paper

(71) C-1) Physical Characterizations

(72) Dry Content Determination

(73) To determine the dry matter content (TG), the mass of the moist sample (MF) is determined from a moist paper sample on a calibrated top-pan high-speed scale that can be used to weigh to 0.01 g. The moist paper sample preferably has an area of at least 10 cm×10 cm. The moist paper sample is then placed in a calibrated drying cabinet, which can maintain a set temperature to a deviation of ±2° C., and dried to constant mass at a set temperature of 105° C. This is typically the case after 90 minutes. The still warm dried paper sample is then transferred to a desiccator which contains a suitable drying agent such as silica gel. After cooling at room temperature, the mass of the dried paper sample (MT) is determined on the aforementioned scale. The dry content of the paper sample is calculated according to TG=100.Math.MT/MF and is stated in % by weight. The percentage is often given with a decimal place. If this percentage value does not change with the rounded first decimal place, this is an indication of the achievement of constant mass at dry contents of 1 to 100% by weight. For dry contents from 0 to less than 1% by weight, the rounded second decimal place of the percentage value is the corresponding indication. Drying is carried out at ambient pressure, possibly 101.32 KPa, which is carried out without a correction for a deviation resulting from weather and sea level. During the drying process, the atmospheric pressure normally prevailing in the environment is maintained, possibly at 101.32 kPa. A correction for a slightly different air pressure due to weather and sea level is not made. In the case of a moist sample that does not yet have a paper consistency, e.g. a pulp suspension or a paper pulp, the moist sample is dried in an appropriate dish with a large surface.

(74) Internal Strength of an Obtained Dried Paper Sheet

(75) A dried paper sheet obtained is examined after a storage period in the climatic room at a constant 23° C. and 50% humidity for 12 hours. The internal strength is carried out according to a procedure which corresponds to the Tappi regulation T833 μm-94. 10 paper strips with a width of 2.5 cm and a length of 12.7 cm are cut from two sheets of paper in A4 format, which are previously obtained from the dried paper web of the trial machine. Each individual paper sample is attached to a separate base plate and a metal bracket with double-sided adhesive tape. The metal angle is knocked out with a pendulum, whereby the paper sample to be examined is split in a plane parallel to the paper surface. The energy that is required for this process is measured. The device used for the measurement is an internal bond test station from TMI (Testing Machines Inc. Islandia, N.Y. 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/m2. The mean is formed from 10 individual measurements each.

(76) C-2) Production of the Paper Raw Material

(77) A paper pulp, which is produced by opening paper webs in a pulper, which serves as the raw material for paper making. The pulp is obtained by dissolving it in drinking water and by mechanically processing the paper webs in the pulper at approx. 3.5-4% by weight dry matter. The paper pulp typically has a degree of fineness around 50° Schopper Riegler. The paper webs are packaging base papers of the “Testliner 2” specification with a basis weight of 120 g/m2, which comes from Thurpapier in Weinfelden (Switzerland).

(78) C-3) Production of the Papers with Spray Treatment of the Wet Paper Web

(79) The papers produced consist of two layers: a top layer with a grammage of 40 g/m.sup.2 and a base with a grammage of 80 g/m.sup.2. This paper is produced on a test paper machine from the Paper Technology Foundation (PTS) in Heidenau. In order to make the two-layer system possible, the test machine is equipped with a headbox for the bottom wire and an additional headbox for the top wire. The paper pulp is diluted to a dry content of 0.35% by weight with drinking water. The paper pulp is then pumped into the two headboxes and from there applied to the top sieve in the form of a sieve and the bottom sieve in the shape of a sieve. The sieve for the top layer and the sieve for the base run towards each other at an angle of 60° and form a narrow gap at the end. The top layer and the underlay come into contact and form enough adhesion to separate from the sieves deflected after the gap. Then the weakly adhering layers run into the press section and are compressed on the side facing away from the sieves in the press section of the machine, i.e. pressed together under drainage. The resulting paper web is then sent through the heated cylinders of the dryer section, in which temperature peaks can be reached up to 100° C., and the dried paper is rolled up at the end of the dryer section. The dry content of the dried paper obtained is typically 93-94% by weight for the previously described type of fabric, the stated grammage and a machine speed of 0.85 m.sup.2 per minute. The contact pressures in the press section can be varied, which results in different dry contents after the press section. Depending on the contact pressure in the test paper machine, these are between 40% by weight and 52% by weight. The dry content in front of the press can be varied by using a chemical dewatering agent and/or by applying a vacuum to the undersides of the top and bottom sieves. As a result, the dry contents in front of the press in the test paper machine can be varied in a range between 15% by weight and 22% by weight.

(80) Three Settings are Used:

(81) 1. In setting “B”, which is the basic setting, the metered amount of retention aid (Percol 540, RTM BASF, cationically modified polyacrylamide, emulsified in hydrocarbons and water, density approx. 1 g/cm.sup.3, pH-Value 3-6, cream-colored, solids content 44% by weight) is very low and is approximately 100 g of solids retention agent per tonne of paper for the entire fabric from the top and bottom layers (0.01% by weight). The same relative amount of the same retention agent is metered into the top and bottom layers. The dry content in front of the press is approx. 15.8% by weight under these conditions.

(82) 2. In the setting “V”, in which a vacuum is used, the retention agent and the retention agent amount remain constant at 100 g per ton of paper as stated above in the setting according to point 1. However, an additional vacuum is created on the underside of the respective sieve after the two headboxes. The vacuum is set in such a way that the desired effects occur in a sufficient form without the formation being disturbed. This situation corresponds to a setting of the vacuum, which here leads to a dry content of the wet paper webs in front of the press of approximately 18.2% by weight.

(83) 3. In the setting “R”, where additional retention agent is used, the vacuum is switched off after the setting under point 2. The amount of the retention aid in the setting according to item 1 is increased to about 370 g of the retention aid retention content per ton of paper of the total substance (0.037% by weight). The dry content of the wet paper webs in front of the press reached about 18.2% by weight which is the value previously achieved with vacuum according to point 2.

(84) For spray treatment of the wet paper web with spray solutions or spray suspensions, the spray solution or the spray suspension is sprayed with a nozzle before the top layer and the base come into contact between the top layer and the base (“BP”=“before press”). A two-fluid nozzle by the company Schlick is used for this. Spraying takes place before the press section. The position of the nozzle is approx. 15 cm from the gum line, i.e. the line on which is pressed under drainage in the press section. The distance to the sieve top of the pad is therefore approx. 35 cm. The pressure to open the nozzle valve and atomize the spray solution or spray suspension is 1 bar. The spray width with even coverage is 35 cm. Nevertheless, when processing the dried paper sheets for later analysis, 5 cm at the edge are not considered. The spray solution or spray suspension is sprayed with two different application quantities. The first quantity is in a range around 0.1 L/m.sup.2, this corresponds to an application quantity of 0.5 g/m.sup.2 at an approximate concentration of 5 g/L. The second quantity is in a range around 0.2 L/m.sup.2, this corresponds to an application quantity of 1.0 g/m.sup.2 at an approximate concentration of 5 g/L. Due to the high dilution, the density of the spray solution or spray suspension can be assumed to be approximately 1 g/cm.sup.3.

(85) C-4) Experiments and Measurement of the Dried Papers Obtained

(86) Dried papers are produced on the paper machine as described in C-3) considering the respective information in Tables TabC1-Tab C3 for concentration of the spray solution or spray dispersion and the machine setting. Tables TabC1 to TabC3 also give the measured internal strengths of dried paper test sheets as described in C-1).

(87) TABLE-US-00004 TABLE TabC1 “bP“-0.1 L/m.sup.2 Internal strength [J / m.sup.2 ] Example Spray Setting Setting Setting No. solution “B“ “V“ “R“ R1 L0(-) .sup.a) 148 154 142 C1-1 L1(P1) .sup.a) 153 144 155 C1-2 L2(H1P1) .sup.a) 159 163 153 C1-3 L3(H2P1) .sup.a) 156 152 149 C1-4 L4(H3P2) .sup.b) 232 281 285 C1-5 L5(H4P3) .sup.b) 227 283 289 C1-6 L6(H5P3) .sup.b) 226 281 293 C1-7 L7(H6P3) .sup.b) 216 261 267 C1-8 L8(P3) .sup.b) 221 278 273 C1-9 L9(H7P4) .sup.b) 215 264 268 C1-10 L10(H8P5) .sup.b) 219 269 273 C1-11 L11(H9P6) .sup.b) 233 279 284 Footnotes: .sup.a) comparative .sup.b) inventively

(88) In comparison with the comparative examples, Table TabC1 shows that the papers produced with spray solutions according to the invention have a significantly improved internal strength. Furthermore, the increase in the dry content after the wire section by means of negative pressure or an increased amount of retention polymer in the papers produced with the spray solutions according to the invention leads to a further improvement in the internal strength, while these measures have little and inconsistent effects in the comparative examples.

(89) TABLE-US-00005 TABLE TabC2 “bP“ - 0.2 L/m.sup.2 Internal strength [J/m.sup.2 ] Example Spray Setting Setting Setting No. solution “B“ “V“ “R“ R2 L0(-) .sup.a) 152 142 139 C2-1 L1(P1) .sup.a) 161 168 153 C2-2 L2(H1P1) .sup.a) 168 174 163 C2-3 L3(H2P1) .sup.a) 163 169 174 C2-4 L4(H3P2) .sup.b) 254 299 305 C2-5 L5(H4P3) .sup.b) 248 231 322 C2-6 L6(H5P3) .sup.b) 243 297 291 C2-7 L7(H6P3) .sup.b) 238 284 279 C2-8 L8(P3) .sup.b) 252 302 299 C2-9 L9(H7P4) .sup.b) 242 297 293 C2-10 L10(H8P5) .sup.b) 238 264 267 C2-11 L11(H9P6) .sup.b) 249 297 294 Footnotes: .sup.a) comparative .sup.b) inventively

(90) The table TabC2 shows that even when the application quantity is doubled, the papers produced with the spray solutions according to the invention have a significantly improved internal strength compared to the comparative examples. Increasing the dry content after the wire section by means of negative pressure or an increased amount of retention polymer almost always leads to a further improvement in the internal strength of the papers produced with the spray solutions according to the invention, while these measures have little and inconsistent effects in the comparative examples.

(91) TABLE-US-00006 TABLE TabC3 “bP“-0.1 L/m.sup.2 Internal strength [J/m.sup.2 ] Example Spray solution or Setting Setting Setting No. spray suspension “B“ “V“ “R“ R1 L0(-) .sup.a) 148 154 142 C3-1 S1(St1) .sup.a) 167 161 165 C3-2 S2(St1 + P1) .sup.a) 161 169 167 C3-3 S3(St1 + H1P1) .sup.a) 156 147 163 C3-4 S4(St1 + H2P1) .sup.a) 161 165 154 C3-5 S5(St1 + H3P2) .sup.b) 198 254 245 C3-6 S6(St1 + H4P3) .sup.b) 202 248 237 C3-7 S7(St1 + H5P3) .sup.b) 204 247 239 C3-8 S8(St1 + H6P3) .sup.b) 205 243 249 C3-9 S9(St1 + P3) .sup.b) 205 249 255 C3-10 S10(St1 + H7P4) .sup.b) 204 239 247 C3-11 S11(St1 + H8P5) .sup.b) 201 239 243 C3-12 S12(St1 + H9P6) .sup.b) 209 242 252 Footnotes: .sup.a) comparative .sup.b) inventively

(92) In table TabC3, as in table TabC1 and table TabC2, it can be seen that the papers produced with spray dispersions according to the invention have a significantly improved internal strength compared to the comparative examples. The increase in the dry content after the wire section by means of negative pressure or an increased amount of retention polymer in the papers produced with the spray suspensions according to the invention leads to a further improvement in the internal strength, while these measures have little and inconsistent effects in the comparative examples. In comparison with Table TabC1, Table TabC3 shows that replacing half of the number of polymers used with cationic starch no longer leads to an improvement in the internal strength of the paper of the same size.