Production of paper, card and board

Abstract

The present invention relates to a process for producing paper, card and board. The present invention is based on the discovery that controlling solids content during the process in a specified manner provide enhanced initial web strength of the paper prior to drying and allows for higher machine speeds in the paper production process as compared to known processes.

Claims

1. A process for producing paper, card and board having an enhanced initial wet web strength, comprising: draining a paper stock comprising filler and at least one water-soluble polymer and having a fibrous concentration of 3.5 to 15 g/l on a wire section to form a sheet, and pressing the sheet on a press section to a solids content of G(x) wt % or greater, wherein G(x) is computed by the following equation:
G(x)=48+(x−15).Math.0.4, x is the numerical value of the filler content of the dry paper, card or board, the water-soluble polymer is obtainable by Hofmann degradation of an acrylamide- and/or methacrylamide-containing polymer with or without subsequent postcrosslinking, and the acrylamide- and/or methacrylamide-containing polymer is obtainable by free-radically polymerizing a monomer mixture comprising: (a) 50 to 90 mol % of acrylamide and/or methacrylamide, (b) 10 to 50 mol % of one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation, and/or diallyldimethylammonium chloride, and (c) optionally up to 1.0 wt %, based on the total weight of monomers (a) and (b), of one or more compounds having two or more ethylenically unsaturated moieties whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation, and the sheet has an INF index of 3.2 to 3.9 Nm/g.

2. The process of claim 1, wherein (b) is diallyldimethylammonium chloride.

3. The process of claim 1, wherein said monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation are selected from the group consisting of nitriles of α,β-ethylenically unsaturated mono- and dicarboxylic acids, amides of α,β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N,N-dialkyl derivatives, N-vinyllactams, nitrogenous heterocycles, vinylaromatics, C.sub.2-C.sub.8 monoolefins, α,β-ethylenically unsaturated mono- and dicarboxylic acids and salts thereof, anhydrides of α,β-ethylenically unsaturated mono- and dicarboxylic acids, ethylenically unsaturated sulfonic acids and salts thereof, and ethylenically unsaturated phosphonic acids and salts thereof.

4. The process of claim 1, wherein the acrylamide- and/or methacrylamide-containing polymer contains monomer (c).

5. The process of claim 4, wherein said compounds having two or more ethylenically unsaturated moieties whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation are selected from the group consisting of methylenebisacrylamides, triallylamine, tetraallylammonium chloride, and N,N′-divinylpropyleneurea.

6. The process of claim 1, wherein the acrylamide- and/or methacrylamide-containing polymer does not contain monomer (c).

7. The process of claim 1, further comprising preparing the paper stock comprising filler and at least one water-soluble polymer at a fibrous concentration of 20 to 40 g/l, and diluting the prepared stock comprising filler and at least one water-soluble polymer to a fibrous concentration of 3.5 to 15 g/l.

8. The process of claim 7, wherein the water-soluble polymer is added to a paper stock comprising filler and having a fibrous concentration of 20 to 40 g/l.

9. The process of claim 7, wherein the water-soluble polymer is added to a paper stock having a fibrous concentration of 20 to 40 g/l followed by adding the filler.

10. The process of claim 7, wherein the paper stock comprises a fibrous material having a freeness of ≦30° SR.

11. The process of claim 7, wherein the water-soluble polymer is added in an amount of 0.05 to 5.00 wt %, based on fibrous material.

12. The process of claim 7, wherein the water-soluble polymer is obtainable by subsequent postcrosslinking with a crosslinker selected from multifunctional epoxides, multifunctional carboxylic esters, multifunctional isocyanates, multifunctional acrylic or methacrylic esters, multifunctional acrylic or methacrylic amides, epichlorohydrin, multifunctional acyl halides, multifunctional nitriles, α,ω-chlorohydrin ethers of oligo- or polyethylene oxides or of other multifunctional alcohols, divinyl sulfone, maleic anhydride or w-halocarbonyl chlorides, multifunctional haloalkanes and carbonates.

13. The process of claim 1, wherein the draining of the paper stock on a wire section and the of the sheet on a press section are conducted in a papermaking machine.

14. The process of claim 1, wherein x ranges from 20 to 40 wt %.

15. The process of claim 1, wherein x ranges from 20 to 30 wt %.

16. The process of claim 1, wherein x ranges from 15 to 20 wt %.

17. The process of claim 1, wherein x ranges from 25 to 40 wt %.

18. The process of claim 1, wherein the fibrous material has a freeness of 20 to 30° SR.

19. The process of claim 1, wherein the paper stock contains 0.5 to 50 kg of the at least one water-soluble polymer per metric ton of dry fibrous material.

20. The process of claim 1, wherein the filler comprises at least one metal oxide, silicate and/or carbonate.

Description

EXAMPLES

(1) The polymers are prepared in three consecutive steps: a) preparing the prepolymer b) Hofmann degrading the prepolymer and optionally postcrosslinking.

(2) Preparation of Polymer I

(3) a) Preparing Prepolymer I (70 Mol % of Acrylamide and 30 Mol % of DADMAC (Diallyldimethylammonium Chloride)—Unbranched)

(4) A 2 l glass apparatus equipped with an anchor stirrer, a reflux condenser, an internal thermometer and a nitrogen inlet tube was initially charged with 295.5 g of distilled water, 189.6 g of a 65 wt % aqueous solution of DADMAC and 1.0 g of 75 wt % phosphoric acid. The pH was adjusted to 3 by adding 0.4 g of sodium hydroxide. Nitrogen was introduced to remove oxygen from the initial charge while the initial charge was heated to the polymerization temperature of 75° C. At the same time, the following feeds were prepared: Feed 1: mixture of 253.0 g of a 50 wt % acrylamide solution, 60.0 g of distilled water and 0.9 g of sodium hydroxide Feed 2: 100 g of a 0.6% wt % aqeuous bisulfite solution Feed 3: 100 g of a 0.88 wt % aqueous sodium persulfate solution

(5) The three feeds were started at the same time. Feed 1 was added over a period of 2 hours, while feeds 2 and 3 were added over 5 hours. Thereafter, the temperature of the mixture was raised to 85° C. On completion of the addition of feeds 2 and 3 the batch was maintained at 85° C. for a further hour before being cooled down.

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

(7) b) Hofmann Degrading the Prepolymer

(8) 250.0 g of prepolymer I, obtained by a), were initially charged to a three-neck flask equipped with an internal thermometer and a blade stirrer and were cooled down to 8° C. with an ice/sodium chloride mixture under constant agitation.

(9) The following feed was prepared: 234.5 g of a 14.1 wt % aqueous NaOCl solution and 20.5 g of distilled water were initially charged to a glass beaker and cooled down to 5° C. with an ice bath. Under constant agitation, 71.1 g of a 50 wt % aqueous sodium hydroxide solution were added dropwise such that the temperature could be maintained below 10° C.

(10) This feed was added dropwise to the cooled initial prepolymer charge from a cooled dropping funnel (<10° C.) in 80 minutes such that the temperature was maintained in the range 8-10° C. during the addition. Thereafter, the reaction mixture was warmed to 20° C. within 10 minutes and maintained at 20° C. for 30 minutes. Thereafter, 558.1 g of this mixture were added dropwise to 135 g of 37% hydrochloric acid under constant agitation and with vigorous evolution of gas.

(11) Finally, the pH of the solution obtained was adjusted to pH 3.5 with 10.0 g of 25 wt % aqueous sodium hydroxide solution.

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

(13) Preparation of Polymer II (Postcrosslinked)

(14) 309.8 g of polymer I were initially charged to a 500 ml three-neck flask equipped with a blade stirrer and were adjusted to pH 8.5 by adding 6.8 g of 50 wt % aqueous sodium hydroxide solution. Thereafter, the mixture was heated to 45° C. and admixed with 0.9 g of Grillbond G 1701 (from EMS). After 30 minutes' stirring at 45° C., the temperature was raised to 55° C. and the batch was maintained at 55° C. for 2 hours. During this period, the viscosity was observed to increase. After 2 hours, the batch was cooled down to room temperature, and adjusted to pH 3.0 by adding 8.0 g of 37% hydrochloric acid.

(15) Polymer II was obtained as a clear, slightly viscous solution having a polymer content of 8.2 wt % and a viscosity of 190 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT).

(16) Preparation of Polymer III

(17) a) Preparing Prepolymer III (70 Mol % of Acrylamide and 30 Mol % of DADMAC, Triallylamine as Monomer c)

(18) A 2 l glass apparatus equipped with an anchor stirrer, a reflux condenser, an internal thermometer and a nitrogen inlet tube was initially charged with 155.8 g of distilled water, 189.6 g of a 65 wt % aqueous solution of DADMAC and 1.0 g of 75 wt % phosphoric acid. The pH was adjusted to 3 by adding 0.4 g of sodium hydroxide. Nitrogen was introduced to remove oxygen from the initial charge while the initial charge was heated to the polymerization temperature of 75° C.

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

(20) The 3 feeds were started at the same time. Feed 1 was added over a period of 3 hours, while feeds 2 and 3 were run in over 6 hours. On completion of the addition of feed 2, the temperature was raised to 85° C. and the batch was maintained at 85° C. for a further hour before being cooled down.

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

(22) b) Hofmann Degradation of Prepolymer III

(23) 250.0 g of prepolymer III, obtained by a), were initially charged to a three-neck flask equipped with an internal thermometer and a blade stirrer and were cooled down to 8° C. with an ice/sodium chloride mixture under constant agitation.

(24) The following feed was prepared: 234.5 g of a 14.1 wt % aqueous NaOCl solution and 20.5 g of distilled water were initially charged to a glass beaker and cooled down to 5° C. with an ice bath. Under constant agitation, 71.1 g of a 50 wt % aqueous sodium hydroxide solution were added dropwise such that the temperature could be maintained <10° C.

(25) This feed was added dropwise to the initial charge from a cooled dropping funnel (<10° C.) in 80 minutes such that the temperature was maintained in the range 8-10° C. during the addition. Thereafter, the reaction mixture was warmed to 20° C. within 10 minutes and maintained at 20° C. for 60 minutes. Thereafter, 566.2 g of this mixture were added dropwise to 135 g of 37% hydrochloric acid under constant agitation and with vigorous evolution of gas.

(26) Finally, the pH of the solution obtained was adjusted to pH 3.5 with 12.2 g of 25 wt % aqueous sodium hydroxide solution.

(27) Polymer III was obtained as a clear, slightly viscous solution having a polymer content of 8.6 wt % and a viscosity of 23 mPas (Brookfield LV viscosity, spindle 1, 60 rpm, RT).

(28) Polymer IV (Postcrosslinked)

(29) 301.8 g of polymer III were initially charged to a 500 ml three-neck flask equipped with a blade stirrer and were adjusted to pH 8.5 by adding 6.2 g of 50 wt % aqueous sodium hydroxide solution. Thereafter, the mixture was heated to 45° C. and admixed with 0.43 g of Grillbond G 1701 (from EMS). After 30 minutes' stirring at 45° C., the temperature was raised to 55° C. and the batch was maintained at 55° C. for 3 hours. During this period, the viscosity was observed to increase. After 3 hours, the batch was cooled down to room temperature, and adjusted to pH 3.0 by adding 7.4 g of 37% hydrochloric acid.

(30) Polymer IV was obtained as a clear, slightly viscous solution having a polymer content of 8.2% and a viscosity of 419 mPas (Brookfield LV viscosity, spindle 2, 60 rpm, RT).

(31) Preparation of Polymer V

(32) a) Preparing Prepolymer V (70 Mol % of Acrylamide and 30 Mol % of DADMAC, Triallylamine as Monomer c)

(33) A 2 l glass apparatus equipped with an anchor stirrer, a reflux condenser, an internal thermometer and a nitrogen inlet tube was initially charged with 155.8 g of distilled water, 189.6 g of a 65 wt % aqueous solution of DADMAC and 1.0 g of 75 wt % phosphoric acid. The pH was adjusted to 3 by adding 0.4 g of NaOH. Nitrogen was introduced to remove oxygen from the initial charge while the initial charge was heated to the polymerization temperature of 75° C. At the same time the following feeds were prepared: Feed 1: 0.25 g of triallylamine was dissolved in 160.0 g of distilled water by addition of 0.75 g of 75 wt % phosphoric acid. Thereafter, 253.0 g of a 50 wt % acrylamide solution were added and the pH was adjusted to 4.0 with 0.6 g of 25 wt % aqueous sodium hydroxide solution. Feed 2: 120 g of a 0.6% wt % aqeuous bisulfite solution Feed 3: 120.6 g of a 0.88 wt % aqueous sodium persulfate solution

(34) The 3 feeds were started at the same time. Feed 1 was added over a period of 3 hours, while feeds 2 and 3 were run in over 6 hours. On completion of the addition of feed 2, the temperature was raised to 85° C. On completion of the addition of feeds 2 and 3, the batch was maintained at 85° C. for a further hour before being cooled down.

(35) The prepolymer was obtained as a clear, viscous solution having a solids content of 25.5 wt % and a viscosity of 12 400 mPas (Brookfield LV viscosity, spindle 4, 6 rpm, RT).

(36) b) Hofmann Degradation of the Prepolymer

(37) 250.0 g of prepolymer V, obtained by a), were initially charged to a three-neck flask equipped with an internal thermometer and a blade stirrer and were cooled down to 8° C. with an ice/sodium chloride mixture under constant agitation.

(38) At the same time the following feed stream was prepared:

(39) 234.5 of a 14.1 wt % aqueous NaOCl solution and 20.5 g of distilled water were initially charged to a glass beaker and cooled down to 5° C. with an ice bath. Under constant agitation, 71.1 g of a 50 wt % NaOH solution were added dropwise such that the temperature could be maintained <10° C.

(40) This feed was added dropwise to the initial charge from a cooled dropping funnel (<10° C.) in 80 minutes such that the temperature was maintained in the range 8-10° C. during the addition. Thereafter, the reaction mixture was warmed to 20° C. within 10 minutes and maintained at 20° C. for 60 minutes. Thereafter, 566.2 g of this mixture were added dropwise to 135 g of 37% hydrochloric acid under constant agitation and with vigorous evolution of gas.

(41) Finally, the pH of the solution obtained was adjusted to pH 3.5 with 16.0 g of 25 wt % aqueous sodium hydroxide solution.

(42) Polymer V was obtained as a clear, slightly viscous solution having a polymer content of 8.5% and a viscosity of 22 mPas (Brookfield LV viscosity, spindle 1, 60 rpm, RT).

(43) Polymer VI (Postcrosslinked)

(44) 314.4 g of polymer V were initially charged to a 500 ml three-neck flask equipped with a blade stirrer and were adjusted to pH 8.5 by adding 6.4 g of 50 wt % aqueous sodium hydroxide solution. Thereafter, the mixture was heated to 45° C. and admixed with 0.44 g of Grillbond G 1701 (from EMS). After 30 minutes' stirring at 45° C., the temperature was raised to 55° C. and the batch was maintained at 55° C. for 3 hours. During this period, the viscosity was observed to increase. After 3 hours, the batch was cooled down to room temperature, and adjusted to pH 3.0 by adding 7.6 g 37% hydrochloric acid.

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

(46) Polymer VII (85 Mol % of Acrylamide and 15 Mol % of Acrylic Acid)

(47) In accordance with JP63042998 (see table on page 624), the C-4 Hofmann product was emulated.

(48) Polymer VIII (not in Accordance with the Present Invention) (Comparative Example Corresponds to Polymer I from EP Application Numbered 11170740.2)

(49) A 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet tube was initially charged with 400 g of deionized water. In addition, the following feeds were provided: Feed 1: The following components were mixed in a glass beaker: 250 g of deionized water 95.6 g of 50 wt % aqueous acrylamide solution 121.9 g of 80 wt % aqueous solution of acryloyloxyethyltrimethylammonium chloride 148.1 g of 32 wt % aqueous sodium acrylate solution 0.2 g of 1 wt % aqueous solution of diethylenetriaminepentaacetic acid. About 32 g of 37% hydrochloric acid were added to set pH 4.1. Feed 2: 60.0 g of 1 wt % aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride Feed 3: 16.5 g of 1 wt % aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride

(50) The initial charge was heated to 63° C. and a water jet pump was used to reduce the pressure until the water just started to boil. Feeds 1 and 2 were started at the same time, feed 1 being added in 2 hours and feed 2 in 3 hours to the initial charge at constant internal temperature. Upon completion of feed 2 the reaction was maintained at 63° C. for a further hour and then heated to 72° C. while the vacuum was reduced accordingly. The reaction mixture was maintained at 72° C. for a further 2 hours, at which point feed 3 was added all at once to initiate a 2 hour period of secondary polymerization at 72° C. The vacuum was then lifted and the batch was diluted with 500 g of deionized water and cooled down to room temperature. 208 g of water were distilled off during the entire polymerization.

(51) A clear, colorless, viscous solution was obtained of polymer VIII composed of 40 mol % acrylamide, 30 mol % acryloyloxyethyltrimethylammonium chloride and 30 mol % sodium acrylate. Solids content: 14.5 wt % Viscosity: 10 600 mPas (Brookfield, spindle 7, 50 rpm, room temperature) K value 120 (0.1% solution of polymer in 5 wt % aqueous sodium chloride solution)

(52) Polymer IX (not in Accordance with the Present Invention): (Comparative Example Corresponds to Polymer II from EP Application Numbered 11170740.2)

(53) A 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet tube was initially charged with 400 g of deionized water. In addition, the following feeds were provided: Feed 1: The following components were mixed in a glass beaker: 250 g of deionized water 119.5 g of 50 wt % aqueous acrylamide solution 113.8 g of 80 wt % aqueous solution of acryloyloxyethyltrimethylammonium chloride 108.6 g of 32 wt % aqueous sodium acrylate solution 0.2 g of 1 wt % aqueous solution of diethylenetriaminepentaacetic acid. About 38 g of 37% hydrochloric acid were added to set pH 4.1. Feed 2: 63.5 g of 1% aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride Feed 3: 17.0 g of 1% aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride.

(54) The initial charge was heated to 66° C. and a water jet pump was used to reduce the pressure until the water just started to boil. Feeds 1 and 2 were started at the same time, feed 1 being added in 2 hours and feed 2 in 3 hours to the initial charge at constant internal temperature. Upon completion of feed 2 the reaction was maintained at 66° C. for a further hour and then heated to 78° C. while the vacuum was reduced accordingly. The reaction mixture was maintained at 78° C. for a further 2 hours, at which point feed 3 was added all at once to initiate a 2 hour period of secondary polymerization at 78° C. The vacuum was then lifted and the batch was diluted with 500 g of deionized water and cooled down to room temperature. 200 g of water were distilled off during the entire polymerization.

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

(56) Polymer X (not in Accordance with the Present Invention) (Corresponds to Polymer III from EP Application Numbered 11170740.2)

(57) A 2 I 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet tube was initially charged with 400 g of deionized water. In addition, the following feeds were provided: Feed 1: The following components were mixed in a glass beaker: 250 g of deionized water 71.7 g of 50 wt % aqueous acrylamide solution 130.1 g of 80 wt % aqueous solution of acryloyloxyethyltrimethylammonium chloride 187.8 g of 32 wt % aqueous sodium acrylate solution 0.2 g of 1 wt % aqueous solution of diethylenetriaminepentaacetic acid. About 34 g of 37% hydrochloric acid were added to set pH 4.1. Feed 2: 60.3 g of 1 wt % aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride Feed 3: 16.0 g of 1 wt % aqueous solution of 2,2′-azobis(2-amidinopropane) dihydrochloride.

(58) The initial charge was heated to 63° C. and a water jet pump was used to reduce the pressure until the water just started to boil. Feeds 1 and 2 were started at the same time, feed 1 being added in 2 hours and feed 2 in 3 hours to the initial charge at constant internal temperature. Upon completion of feed 2 the reaction was maintained at 63° C. for a further hour and then heated to 72° C. while the vacuum was reduced accordingly. The reaction mixture was maintained at 72° C. for a further 2 hours, at which point feed 3 was added all at once to initiate a 2 hour period of secondary polymerization at 72° C. The vacuum was then lifted and the batch was diluted with 500 g of deionized water and cooled down to room temperature. 200 g of water were distilled off during the entire polymerization.

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

(60) Testing of Above-Described Polymers I to X in Enhancing the Initial Wet Web Strength of Paper

(61) To simulate the sheet-forming process on the laboratory scale, the thin stuff in the examples has to be adjusted to a fibrous concentration of 3.5 g/l.

(62) Pretreatment of Fibrous Suspension

(63) Bleached birchwood sulfate pulp was beaten in a laboratory pulper at a fibrous concentration of 4% until it was free of fiber bundles and had reached a freeness of 30° SR. The beaten stuff was subsequently admixed with an optical brightener (Blankophor® PSG) and also with a fully destructurized cationic starch (HiCat® 5163 A) and left exposed to the action thereof for 5 minutes. The cationic starch had been destructurized beforehand as a 10% starch slurry in a jet cooker at 130° C. for 1 minute.

(64) The amount of optical brightener added was 0.5 wt % of commercial product, based on the dry matter content of the fibrous suspension. The amount of cationic starch added was 0.8% of starch (solids), based on the dry matter content of the fibrous suspension. The fiber content of the fibrous suspension after starch and optical brightener had been added was 3.5% (35 g/l).

Examples 1 to 7

(65) Seven glass beakers were each filled with 50 g of the above-described pretreated fibrous suspension. Each of the glass beakers had added to it 1.75 g of a 1 wt % aqueous solution of one of the above-described polymers I to VII under gentle stirring of the fibrous suspension (corresponds to 1% of polymer (solids) per fibrous material (solids)). The fibrous suspensions were each subsequently reduced to a fibrous concentration of 0.35% by addition of water. This was followed by addition of a 20 wt % carbonate pigment slurry (PCC, Syncarb F474 from Omya). The amount of pigment suspension (corresponds to filler suspension) added was adjusted in multiple preliminary tests such that the pigment content of the laboratory sheets subsequently formed was about 20%. The fibrous suspension two minutes after pigment addition was processed on a Rapid-Köthen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire frame and placed between two suction felts. The pack consisting of suction felts and the wet paper was subsequently pressed in a static press at a press pressure of 6 bar. In each case, pressing was done to a 50 wt % solids content of the wet sheets.

Examples 8, 9 and 10 (not According to the Invention)

(66) Three glass beakers were each filled with 50 g of the above-described pretreated fibrous suspension. Each of the glass beakers had added to it 1.75 g in each case of a 1 wt % aqueous solution of one of the above-described polymers I-III under gentle stirring of the fibrous suspension (corresponds to 1% of polymer (solids) per fibrous material (solids)). The fibrous suspensions were each subsequently reduced to a fibrous concentration of 0.35% by addition of water. This was followed by addition of a 20 wt % carbonate pigment slurry (PCC, Syncarb F474 from Omya). The amount of pigment suspension added was adjusted in multiple preliminary tests such that the pigment content of the laboratory sheets subsequently formed was about 20%. The fibrous suspension two minutes after pigment addition was processed on a Rapid-Köthen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire frame and placed between two suction felts. The pack consisting of suction felts and the wet paper was subsequently pressed in a static press at a press pressure of 6 bar. By adapting the residence time within the press arrangement, pressing was in each case carried on to a solids content of the wet sheets which is discernible from Table 1.

Examples 11, 12 and 13

(67) Three glass beakers were each filled with 50 g of the above-described pretreated fibrous suspension. Each of the glass beakers had added to it 1.75 g of a 1 wt % aqueous solution of one of the above-described polymers VIII to X under gentle stirring of the fibrous suspension (corresponds to 1% of polymer (solids) per fibrous material (solids)). The fibrous suspensions were each subsequently reduced to a fibrous concentration of 0.35% by addition of water. This was followed by addition of a 20 wt % carbonate pigment slurry (PCC, Syncarb F474 from Omya). The amount of pigment suspension (corresponds to filler suspension) added was adjusted in multiple preliminary tests such that the pigment content of the laboratory sheets subsequently formed was about 20%. The fibrous suspension two minutes after pigment addition was processed on a Rapid-Köthen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire frame and placed between two suction felts. The pack consisting of suction felts and the wet paper was subsequently pressed in a static press at a press pressure of 6 bar. In each case, pressing was done to a 50 wt % solids content of the wet sheets.

Examples 14, 15 and 16 (not According to the Invention—Addition to Thin Stuff)

(68) Three glass beakers containing 50 g of the pretreated fibrous suspension (thick stuff) were diluted with 450 g of water to a fibrous concentration of 0.35% (corresponds to 3.5 g/l).

(69) To 500 g in each case of the diluted fibrous suspension (thin stuff) were added 1.75 g of a 1 wt % aqueous solution of polymer I, II or III (corresponds to 1 wt % of polymer (solids) based on fibrous material (solids)).

(70) This was followed by addition of a 20 wt % carbonate pigment slurry (PCC, Syncarb F474 from Omya) to the mixture. The amount of pigment suspension added was adjusted in multiple preliminary tests such that the pigment content of the laboratory sheets subsequently formed was about 20%.

(71) The fibrous suspension two minutes after pigment addition was processed on a Rapid-Köthen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire frame and placed between two suction felts. The pack consisting of suction felts and the wet paper was subsequently pressed in a static press at a press pressure of 6 bar. By adapting the residence time of the papers within the press arrangement, pressing was in each case carried on to a 50 wt % solids content of the wet sheets.

Examples 17 and 18 (Reference)

(72) Three glass beakers were each filled with 50 g of the above-described pretreated fibrous suspension. The fibrous suspensions were each subsequently reduced to a fibrous concentration of 0.35% by addition of water. This was followed by addition of a 20 wt % carbonate pigment slurry (PCC, Syncarb F474 from Omya). The amount of pigment suspension (corresponds to filler suspension) added was adjusted in multiple preliminary tests such that the pigment content of the laboratory sheets subsequently formed was about 20%. The fibrous suspension two minutes after pigment addition was processed on a Rapid-Köthen sheet-former to ISO 5269/2 into sheets having a grammage of 100 g/sqm. The wet sheets were subsequently removed from the wire frame and placed between two suction felts. The pack consisting of suction felts and the wet paper was subsequently pressed in a static press at a press pressure of 6 bar. The pressing time was varied to produce not only sheets of differing dry matter content (see Table 1)

(73) Performance Testing: Determination of Initial Wet Web Strength

(74) Initial wet web strength must not be confused with a paper's wet strength and initial wet strength since both these properties are measured on papers which, after drying, are moistened back to a defined water content. Initial wet strength is an important parameter in the assessment of papers without permanent wet strength. A dried and subsequently remoistened paper has a completely different wet strength than a moist paper directly after it has passed through the wire and press sections of a papermachine.

(75) Initial wet web strength is determined on wet paper using the Voith method (cf. M. Schwarz and K. Bechtel “Initiale Gefügefestigkeit bei der Blattbildung”, in Wochenblatt für Papierfabrikation 131, pages 950-957 (2003) No. 16). The wet sheets after pressing in the static press were knocked off onto a plastics support and transferred to a cutting support. Test strips having a defined length and width were then cut out of the sheet. They were pressed under constant pressure until the desired dry matter content was reached. To investigate the sheets of paper obtained according to the examples reported above, four dry matter contents ranging between 42% and 58% were established in each case. These values were used to determine initial wet web strength at 50% dry matter using a fitting method described in the abovementioned literature reference. The actual measurement of initial wet web strength took place on a vertical tensile tester using a special clamping device. The force determined in the tension machine was converted into the grammage-independent INF index. For an exact description of the clamping device, the measuring procedure, the determination of the dry matter in the paper and the data processing, the abovementioned literature reference can be enlisted.

(76) The results of the tests are reproduced in Table 1.

(77) TABLE-US-00001 TABLE 1 Results of performance testing for production of paper having a filler content of 20 wt %. According to the computation of the limiting dry matter content G(x) = G(20), the invention requires pressing to a solids content of at least 50 wt %: G(20) = 48 + (20 − 15) .Math. 0.4 = 50 INF index Solids content Example Polymer [Nm/g] pressed [%]  1 I 3.9 50.3  2 II 3.5 50.5  3 III 3.3 50.2  4 IV 3.4 50.9  5 V 3.5 51.2  6 VI 3.6 50.6  7 VII 3.2 51.3  8 I 1.8 48.6 not according to the invention  9 II 1.9 49.1 not according to the invention 10 III 2.1 49.2 not according to the invention 11 VIII 3.3 50.3 not according to the invention 12 IX 3.1 50.5 not according to the invention 13 X 2.9 50.2 not according to the invention 14 (addition to thin stuff) I 1.8 50.2 not according to the invention 15 (addition to thin stuff) II 1.5 50.0 not according to the invention 16 (addition to thin stuff) III 1.7 51.2 not according to the invention 17 1.1 48.4 reference 18 1.4 50.6 reference