Method for producing paper

Abstract

A method of producing paper and board by using at least one water-soluble amphoteric polymer is provided. The water-soluble amphoteric polymer is obtained by copolymerizing a monomer mixture containing a) at least one N-vinylcarboxamide, b) at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form, c) optionally at least one monoethylenically unsaturated monomer other than components (a) and (b), and d) optionally at least one compound having two or more ethylenically unsaturated double bonds, and then partly or wholly hydrolyzing the COR.sup.1 groups of the polymer. The cationic monomer units and the anionic monomer units differ in their respective molar fractions, each based on the total number of moles of all monomer units, by not more than 10 mol % in absolute terms.

Claims

1. A method of producing paper and board, said method comprising providing an aqueous slurry comprising a filler, at least one water-soluble amphoteric polymer and a microparticle, admixing the aqueous slurry to a paper stock, dewatering the paper stock by sheet formation in a wire section to obtain a paper sheet, until the paper sheet has a dry matter content of not less than 18 wt %, and then pressing the paper sheet and drying, wherein the water-soluble amphoteric polymer is obtained by a process comprising copolymerizing a monomer mixture comprising a) at least one N-vinylcarboxamide of formula ##STR00007## where R.sup.1 and R.sup.2 are each independently H or a C.sub.1 to C.sub.6 alkyl, b) at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form, c) optionally at least one monoethylenically unsaturated monomer other than said components (a) and (b), and d) optionally at least one compound having two or more ethylenically unsaturated double bonds, and then partly or wholly hydrolyzing the COR.sup.1 groups of the polymer, wherein cationic monomer units and anionic monomer units differ in respective molar fractions, each based on a total number of moles of all monomer units, by not more than 10 Mol % in absolute terms; wherein the filler is calcium carbonate; and wherein the microparticle is chosen from: a copolymer formed from acrylamide and one or more anionic monomers; and/or inorganic microparticles of bentonite, colloidal silica, and/or silicate.

2. The method according to claim 1, wherein the monomer mixture consists of: based on a total weight of monomers in the monomer mixture, a) 5 to 95 wt %, of least one N-vinylcarboxamide b) 5 to 95 wt %, of the at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form, c) 0 to 90 wt % of the at least one monoethylenically unsaturated monomer other than said components (a) and (b), and d) 0 to 5 wt % of the at least one compound having two or more ethylenically unsaturated double bonds.

3. The method according to claim 1, wherein the water-soluble amphoteric polymer is obtained by copolymerizing a) N-vinylformamide, b) at least one monoethylenically unsaturated monomer selected from the group consisting of acrylic acid, methacrylic acid, an alkali metal salt of acrylic acid and/or methacrylic acid and an ammonium salt of acrylic acid and/or methacrylic acid, and c) optionally other monoethylenically unsaturated monomers.

4. The method according to claim 1, wherein the water-soluble amphoteric polymer comprises (i) 1 to 98 mol % of vinylcarboxamide units, (ii) (ii) 1 to 98 mol % of units of monoethylenically unsaturated sulfonic acids, phosphonic acids, phosphoric esters, derivatives thereof or units of monoethylenically unsaturated mono- and dicarboxylic acids, thereof and dicarboxylic anhydrides, (iii) 1 to 98 mol % of vinylamine units and/or amidine units, and (iv) (iv) up to 50 mol % of units of other monoethylenically unsaturated compounds.

5. The method according to claim 1, wherein the water-soluble amphoteric polymer comprises (i) 5 to 70 mol % of vinylcarboxamide units, (ii) 5 to 45 mol % of units of acrylic acid, methacrylic acid, a salt of acrylic acid and/or a salt of methacrylic acid, and (iii) 10 to 60 mol % of units form vinylamine units and optionally amidine units.

6. The method according to claim 1, wherein a proportion of the microparticles in the aqueous slurry is 0.01-1 wt % based on the filler.

7. The method according to claim 1, wherein a proportion of the water-soluble amphoteric polymer is 0.01-1 wt %, based on the filler.

8. The method according to claim 1, wherein the aqueous slurry comprises water, 5-70 wt % of the filler based on the aqueous slurry, 0.001-1 wt % of the water-soluble amphoteric polymer based on the filler, and 0.01-1 wt % of the microparticles based on the filler.

9. The method according to claim 1, wherein the sheet formation in the wire section is carried on until the paper sheet has a dry matter content of not less than 19 wt %.

Description

EXAMPLES

(1) The degree of hydrolysis of the water-soluble amphoteric polymers was quantified by enzymatic analysis of the formates/formic acid released in the hydrolysis (test kit from Boehringer Mannheim).

(2) The structural composition of the polymers was computed from the monomer mixture used, the degree of hydrolysis and the vinylamine/amidine ratio determined via .sup.13C NMR spectroscopy. The composition ratio is in mol %, unless otherwise stated.

(3) Dry matter content is determined in accordance with DIN EN ISO 638 DE using the oven-drying method. The dry matter content of the sheet of paper is to be understood as meaning the ratio of the mass of a sample dried to constant mass at a temperature of (1052) C. under defined conditions, to the mass of the sample before drying. The dry matter content is reported as proportional parts by mass in percent.

(4) The dry matter content of the total paper stock and of fiber is determined similarly to the determination of the dry matter content of the sheet of paper. This results in the reported total paper solids and fiber solids, respectively.

(5) The K values were determined after H. Fikentscher, Cellulosechemie, volume 13, 48-64 and 71-74 under the conditions reported in each case. The particulars between parentheses indicate the solvent and the concentration of the polymer solution.

(6) Solids contents were determined for the polymers by 0.5 to 1.5 g of the polymer solution being distributed in a 4 cm diameter tin lid and then dried at 140 C. in a circulating air drying cabinet for two hours. The ratio of the mass of the sample after drying under the above conditions to the mass at sample taking is the solids content of the polymer.

(7) Ash content: ISO 2144

(8) Average molecular weight M.sub.w is to be understood as meaning here, hereinabove and hereinbelow the mass-average molecular weight M.sub.w as determinable by light scattering. The molecular weight was determined on the nonhydrolyzed precursor.

(9) Materials used:

(10) bentonite (Hydrocol from BASF)

(11) colloidal silica (EKA NP from Akzo Nobel)

(12) acrylamide-containing structured anionic microparticle (Telioform M300 from BASF) retention aid: Percol 540 from BASF SE) cationic polyacrylamide as 1 wt % solution

(13) Preparation of Slurries A1-A16

(14) The following amphoteric polymers were used to prepare slurries:

(15) TABLE-US-00001 TABLE 1 Water-soluble amphoteric polymers used Composition vinylformamide units/acrylic acid Average molecular weight Polymer units/vinylamine + amidine units [dalton] P1 40/30/30 500 000 P2 5/45/50 400 000 P3 65/20/15 650 000 P4 30/40/30 400 000 P5 30/30/40 400 000 P6 40/30/30 500 000

(16) Slurry A1

(17) 0.7 g of a 12 wt % aqueous solution of polymer P1 were initially charged to a glass beaker and then diluted with 30 g of water. This was followed by the admixture of 150 g of a 20 wt % slurry of precipitated calcium carbonate (PCC) in water. During the admixture of the PCC slurry and thereafter, the mixture was stirred with a Heiltof stirrer at 1000 revolutions per minute (rpm). About 30 seconds after the admixture of the PCC slurry, a 1 wt % slurry of bentonite (Hydrocol from BASF) was admixed under agitation from the stirring assembly. The admixed amount of bentonite slurry was reckoned such that the proportion of bentonite solids corresponded to 0.3 wt % based on FCC solids. Following a further 30 seconds, the speed of the Heiltof stirrer was reduced to 200 rpm. The bentonite slurry was prepared in accordance with the recommendations in the Hydrocol technical infosheet for service as a microparticle component to augment flocculation processes. This applies particularly to sufficiently swelling the bentonite before use. Mixture pH is subsequently adjusted to 8.5.

(18) Slurries A2-A8

(19) The preparation of slurry A1 was repeated using microparticles and the P2 to P6 polymers indicated in table 1 but maintaining the amounts/concentrations. Slurry 6 was prepared with ground calcium carbonate instead of precipitated calcium carbonate. The compositions of the slurries obtained are reported in table 2.

(20) TABLE-US-00002 TABLE 2 Preparation of slurries Slurry Polymer Filler Microparticle A1 P1 PCC bentonite A2 P2 PCC bentonite A3 P3 PCC bentonite A4 P4 PCC bentonite A5 P5 PCC bentonite A6 P6 GCC bentonite A7 P6 PCC silica sol A8 P2 PCC silica sol PCC: precipitated calcium carbonate GCC: ground calcium carbonate

(21) Slurry A9

(22) 0.7 g of a 12 wt % aqueous solution of polymer P6 were initially charged to a glass beaker and then diluted with 30 g of water. This was followed by the admixture of 150 g of a 20 wt % slurry of precipitated calcium carbonate (PCC) in water. During the admixture of the PCC slurry and thereafter, the mixture was stirred with a Heiltof stirrer at 1000 revolutions per minute (rpm). About 30 seconds after the admixture of the PCC slurry, a 1 wt % solution of an acrylamide-containing structured anionic micropolymer (Telioform M300 from BASF) was admixed under agitation from the stirring assembly. The admixed amount of micropolymer solution was reckoned such that the proportion of micropolymer solids in the PCC slurry corresponded to 0.07 wt % based on FCC solids. Following a further 30 seconds, the speed of the Heiltof stirrer was reduced to 200 rpm and left at that level until the further use of the slurry. Mixture pH is subsequently adjusted to 8.5.

(23) Slurry A10

(24) The preparation of slurry A9 was repeated except that polymer P2 was used instead of polymer P6.

(25) Slurry A11

(26) 9 g of a 1 wt % slurry of bentonite (Hydrocol from BASF) was initially charged to a glass beaker. The bentonite slurry was prepared in accordance with the recommendations in the Hydrocol technical infosheet for service as a microparticle component to augment flocculation processes. This was followed by the admixture of 150 g of a 20 wt % slurry of precipitated calcium carbonate (PCC) in water. The ratio of bentonite solids to PCC solids in the resulting slurry was 3:1000. During the admixture of the PCC slurry and thereafter, the mixture was stirred with a Heiltof stirrer at 1000 revolutions per minute (rpm). About 30 seconds after the admixture of the PCC slurry, 21 g of a 0.4 wt % aqueous solution of polymer P6 was admixed under agitation from the stirring assembly. Following a further 30 seconds, the speed of the Heiltof stirrer was reduced to 200 rpm and left at that level until the further use of the slurry. Mixture pH is subsequently adjusted to 8.5.

(27) Slurries A12-A14

(28) The preparation of slurry A1 was repeated using microparticles and the P polymers indicated in table 1 but maintaining the amounts/concentrations. Slurry A16 was prepared with ground calcium carbonate instead of precipitated calcium carbonate. The compositions of the slurries obtained are reported in table 3.

(29) TABLE-US-00003 TABLE 3 Preparation of slurries Microparticle Slurry Polymer Filler Microparticle [g] A11 P6 PCC bentonite 0.09 A12 P2 PCC bentonite 0.09 A13 P6 PCC silica sol 0.09 A14 P2 PCC silica sol 0.09 PCC: precipitated calcium carbonate

(30) Slurry A15

(31) 21 g of a 0.1 wt % solution of an acrylamide-containing structured anionic micropolymer (M300 from BASF) was initially charged to a glass beaker. This was followed by the admixture of 150 g of a 20 wt % slurry of precipitated calcium carbonate (PCC) in water. The ratio of micropolymer solids to PCC solids in the resulting slurry was 0.7:1000. During the admixture of the PCC slurry and thereafter, the mixture was stirred with a Heiltof stirrer at 1000 revolutions per minute (rpm).

(32) About 30 seconds after the admixture of the PCC slurry, 21 g of a 0.4 wt % aqueous solution of polymer P6 was admixed under agitation from the stirring assembly. Following a further 30 seconds, the speed of the Heiltof stirrer was reduced to 200 rpm and left at that level until the further use of the slurry. Mixture pH is subsequently adjusted to 8.5.

(33) Slurry A16

(34) The preparation of slurry A15 was repeated except that polymer P2 was used instead of polymer P6.

(35) Slurry A17 (Not in Accordance with the Present Invention)

(36) The preparation of slurry A1 was repeated except that no microparticles were added.

(37) Slurry A18 (Not in Accordance with the Present Invention)

(38) The preparation of slurry A2 was repeated except that no microparticles were added.

(39) Slurry A19 (Not in Accordance with the Present Invention)

(40) The preparation of slurry A11 was repeated except that no water-soluble amphoteric polymer was added.

(41) Pretreatment of Fibrous Suspension

(42) A mixture of bleached birchwood sulfate and bleached pinewood sulfate in a ratio of 70/30 was beaten in a laboratory pulper at a solids concentration of 4 wt % to a freeness of 29-32 and freedom from fiber bundles. The fibrous stuff pH was in the range from 7 to 8 at this stage. The beaten stuff was subsequently diluted with water to a solids concentration of 0.8 wt %. The dilute fibrous stuff was subsequently admixed with an optical brightener (Blankophor PSG) and also with a cationic starch (HiCat 5163 A).

(43) The cationic starch had been destructurized beforehand as a 10 wt % starch slurry in a jet cooker at 130 C. for 1 minute. The amount of optical brightener added was 0.3 wt % of commercial product, based on total paper stock solids. The amount of cationic starch added was 0.8 wt % of starch solids, based on total paper stock solids.

(44) Production of Sheets of Paper by the Method of the Invention:

(45) To determine the performance of the above-described aqueous slurries in the production of filler-containing papers, each dilute paper stock suspension was initially charged at 500 ml and admixed with a cationic polyacrylamide (Percol) as retention aid plus in each case one of the filler slurries described in the inventive and comparative examples. The amount of retention aid added was 0.01 wt % of Percol based on total paper stock solids. The amount of filler slurry added to the paper stock suspension was adjusted in several preliminary tests such that the ash content of the sheets of paper fabricated from furnish plus slurry was 25 wt %.

(46) Sheets produced for comparison each comprise about 25 wt % of an untreated PCC and also 25 wt % of an untreated GCC.

(47) The sheets of paper were produced at a basis weight of 100 g/m.sup.2 on a dynamic sheet-former from TechPap of France. The paper stock suspension was sprayed onto a wire clamped into an upright fast-rotating drum. Drainage and sheet formation in this system is determined not only by the sheet structure but particularly by the centrifugal forces within the rotating drum. The speed of rotation of the drum can be varied to likewise vary the centrifugal force acting on the nascent sheet structure. The result is a variation in sheet drainage that leads to a variation in the dry matter content of the wet paper web. The reference is here to the dry matter content of the wet paper web immediately after removal from a water-permeable support (wire) clamped into the drum of the dynamic sheet-former.

(48) The speed of the drum was varied in 5 stages between 600 and 1100 revolutions per minute, making it possible to establish dry matter contents in the range between 14 wt % and 21 wt %. The filler quantity admixed for sheet formation has to be slightly increased with increasing drum speed, since filler retention decreases with increasing drainage. A small portion of the still wet sheet web is used for immediate determination of the dry matter content after removal of the wet paper sheet from the wire of the dynamic sheet-former.

(49) Performance Testing:

(50) Determination of Initial Wet Web Strength

(51) The initial wet web strength must not be confused with a paper's wet strength and initial wet strength, since both properties are measured on dried paper remoistened back to a defined water content. Initial wet strength is an important parameter in assessing paper that does not have permanent wet strength. Paper that has been dried and remoistened has a completely different wet strength than moist as-produced paper after passing through the wire and press sections of the papermachine.

(52) Initial wet web strength is determined on wet paper using in each case the Voith method (cf. M. Schwarz and K. Bechtel Initiale Gefgefestigkeit bei der Blattbildung, in Wochenblatt fr 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 IWWS 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.

(53) The results of the tests are reported in table 4.

(54) TABLE-US-00004 TABLE 4 Dry matter IWWS(50%) content before index Example Slurry press [wt %] [Nm/g] reference PCC 1 PCC untreated 14.6 1.8 reference PCC 2 PCC untreated 15.3 1.7 reference PCC 3 PCC untreated 17.1 2.1 reference PCC 4 PCC untreated 18.6 1.9 reference PCC 5 PCC untreated 19.5 1.7 reference GCC 6 GCC untreated 14.9 2.1 reference GCC 7 GCC untreated 16.1 2.0 reference GCC 8 GCC untreated 17.8 1.8 reference GCC 9 GCC untreated 18.6 1.7 reference GCC 10 GCC untreated 19.4 1.9 1 1 14.8 2.4 2 1 15.7 2.2 3 1 17.2 2.4 4E 1 18.3 3.9 5E 1 19.5 4.2 6 2 15.3 2.2 7 2 16.8 2.4 8 2 17.5 2.5 9E 2 18.2 3.6 10E 2 19.4 3.9 11 3 15.5 1.9 12 3 16.2 2.3 13 3 17.6 2.6 14E 3 18.4 3.4 15E 3 20.1 3.8 16 4 15.3 2.1 17 4 15.9 2.1 18 4 17.4 2.4 19E 4 18.5 3.6 20E 4 19.7 3.8 21 5 14.9 2.1 22 5 16.3 2.4 23 5 17.2 2.3 24E 5 18.9 3.6 25E 5 19.8 3.7 26 6 15.8 2.2 27 6 16.5 2.3 28 6 17.3 2.7 29E 6 18.7 4.1 30E 6 19.5 4.5 31 7 15.2 2.3 32 7 16.6 2.3 33 7 17.4 2.6 34E 7 18.6 3.5 35E 7 19.4 3.8 36 8 14.5 1.9 37 8 15.3 2.4 38 8 16.8 2.4 39E 8 18.3 3.6 40E 8 19.5 3.7 41 9 15.6 2.1 42 9 16.4 2.1 43 9 17.3 2.2 44E 9 18.3 3.6 45E 9 19.6 3.5 46 10 15.6 1.8 47 10 16.4 2.1 48 10 17.3 2.3 49E 10 18.7 3.4 50E 10 19.6 3.7 51 11 15.7 2.2 52 11 16.4 2.2 53 11 17.7 2.4 54E 11 18.6 3.6 55E 11 19.9 3,7 56 12 14.8 2.2 57 12 16.1 2.3 58 12 17.1 2.6 59E 12 18.2 3.5 60E 12 18.9 3.8 61 13 15.2 2.3 62 13 16.7 2.4 63 13 17.6 2.7 64E 13 18.6 3.8 65E 13 19.4 4.0 66 14 15.3 2.1 67 14 16.4 2.3 68 14 17.3 2.3 69E 14 18.4 3.5 70E 14 19.3 3.9 71 15 14.8 2.0 72 15 15.6 2.1 73 15 16.9 2.4 74E 15 18.4 3.5 75E 15 19.1 3.5 76 16 15.4 1.8 77 16 16.6 2.1 78 16 17.6 2.4 79E 16 18.4 3.3 80E 16 19.6 3.6 81 17 16.1 2.2 82 17 16.9 2.2 83 17 17.3 2.3 84 17 18.7 2.3 85 17 19.8 2.4 86 18 15.7 2.1 87 18 16.4 2.4 88 18 17.2 2.3 89 18 18.4 2.5 90 18 19.3 2.4 91 19 15.6 2.2 92 19 16.7 2.1 93 19 17.8 2.4 94 19 18.6 2.2 95 19 19.7 2.3

(55) Examples in accordance with the present invention are all marked E in the table.

(56) The following inferences can be drawn from the data listed in table 4:

(57) The examples conducted in accordance with the present invention exhibit a distinctly enhanced wet web strength index IWWS (50%) for the sheets. When the dry matter content is clearly therebelow, the IWWS (50%) index is only slightly above that of an untreated filler slurry.

(58) Reference examples PCC 4 and PCC 5 and reference examples GCC 9 and GCC 10 show that just adjusting the dry matter content to above 18 wt % (in the case via the adjustment of the speed of rotation of the dynamic sheet-former) without additional treatment of the filler slurry with a 2-component system does not lead to a significant increase in the IWWS (50%) index. Examples 84, 85, 89, 90, 94 and 95 show that treating the filler with either just the water-soluble amphoteric polymer or just the microparticles likewise fails to cause any effect on exceeding the dry matter content above 18%.