Papermaking agent system, method for making a papermaking agent system and its use

Abstract

The invention relates to a papermaking agent system in liquid form, which comprises (i) cationic starch solution, prepared by cooking a starch mixture comprising a starch component and a water component, and (ii) polymer composition, which has anionic and cationic groups and a cationic net charge of >0.1 meq/g. The polymer composition comprises or originates from at least one of constituents a), b) or c). Constituent a) contains an amphoteric polymer, which is a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, and anionic and cationic groups attached to the copolymer. Constituent b) contains a first polymer, which is a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, and anionic or cationic groups attached to the copolymer, as well as a second polymer, which comprises groups with opposite charge than the first polymer. Constituent c) contains a third polymer, which comprises a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, as well as hydrolytically unstable cationic groups attached to the copolymer. Constituent a), b) or c) is added to one of the components of the starch mixture or to the starch mixture before the cooking of the starch mixture, and/or constituent a) or b) is added to the cationic starch solution after cooking of the starch mixture. The invention relates also to the use of the papermaking agent system and to a method for its preparation.

Claims

1. Papermaking agent system in liquid form, which comprises (i) cationic starch solution, prepared by cooking a starch mixture comprising a starch component and a water component, and (ii) polymer composition, which has anionic and cationic groups and which has a cationic net charge of >0.1 meq/g, at pH 7, the polymer composition comprising, or originating from constituent c), where constituent c) contains a third polymer, which comprises a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, as well as hydrolytically unstable cationic groups attached to the copolymer, wherein the hydrolytically unstable cationic groups originate from monomers selected from the group consisting of 2-(dimethylamino)ethyl acrylate, [2-(acryloyloxy)ethyl] trimethylammonium chloride, 2-dimethylaminoethyl methacrylate and [2-(methacryloyloxy)ethyl] trimethylammonium chloride; wherein constituent c) is added to one of the components of the starch mixture or to the starch mixture before the cooking of the starch mixture and a part of the hydrolytically unstable cationic groups are hydrolysed into anionic groups during the cooking; and wherein the amount of hydrolysed groups is at least 4 mol-% of the total cationic groups in polymer.

2. Papermaking agent system according to claim 1, characterised in that the third polymer of constituent c) is a dispersion polymer, which is obtained by polymerising cationic polyacrylamide within an organic coagulant matrix.

3. Papermaking agent system according to claim 1, characterised in that the third polymer of constituent c) comprises both hydrolytically unstable cationic groups and hydrolytically stable cationic groups.

4. Papermaking agent system according to claim 3, characterised in that the constituent c) is a mixture of at least one first third polymer, which comprises hydrolytically unstable cationic groups, and at least one second third polymer, which comprises hydrolytically stable cationic groups.

5. Papermaking agent system according to claim 1, characterised in that the polymer composition has a net charge of 0.5-5.5 meq/g, preferably 1-1.5 meq/g, at pH 7.

6. Papermaking agent system according to claim 1, characterised in that it comprises polymer composition in amount of 0.1-50 weight-%, preferably 0.1-30 weight-%, more preferably 0.2-15 weight-%, calculated from total amount of starch.

7. Papermaking agent system according to claim 1, characterised in that the polymer composition comprises 10-95 weight-%, preferably 15-90 weight-%, more preferably 20-80 weight-%, still more preferably 25-75 weight-%, of structural units derived from acrylamide and/or methacrylamide monomers, calculated from the total dry weight of the polymer composition.

8. Papermaking agent system according to claim 1, characterised in that the starch component in the starch mixture has an amylopectin content in the range of 65-90%, preferably 70-85%, and an amylose content in the range of 10-35%, preferably 15-30%.

9. Papermaking agent system according to claim 1, characterised in that at least 70 weight-% of the starch units of the starch component in the starch mixture has an average molecular weight (MW) over 20 000 000 g/mol, preferably 50 000 000 g/mol, 100 000 000 g/mol.

10. Papermaking agent system according to claim 1, characterised in that starch component in the starch mixture has a degree of substitution (DS) in the range of 0.01-0.20, preferably 0.01-0.1, more preferably 0.015-0.06.

11. Papermaking agent system according to claim 1, characterised in that starch component has a charge density of 0.06-1.0 meq/g.

12. Method for making a papermaking agent system in liquid form, which comprises (i) preparing a cationic starch solution by cooking a starch mixture, which comprises a starch component and a water component, and (ii) obtaining a polymer composition, which has anionic and cationic groups and which has net charge of >0.1 meq/g, the polymer composition originating from constituent c), where constituent c) contains a third polymer, which comprises a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, as well as hydrolytically unstable cationic groups attached to the copolymer, wherein the hydrolytically unstable cationic groups originate from monomers selected from the group consisting of 2-(dimethylamino)ethyl acrylate, [2-(acryloyloxy)ethyl] trimethylammonium chloride, 2-dimethylaminoethyl methacrylate and [2-(methacryloyloxy)ethyl] trimethylammonium chloride; wherein constituent c) is added to one of the components of the starch mixture or to the starch mixture before the cooking of the starch mixture and a part of the hydrolytically unstable cationic groups are hydrolysed into anionic groups during the cooking; and wherein the amount of hydrolysed groups is at least 4 mol-% of the total cationic groups in polymer.

13. Method according to claim 12, characterised in adding the constituent c) in dry form or in liquid form.

14. Method according to claim 12, characterised in that the papermaking agent system is added to the thick stock having consistency of at least 20 g/l.

15. Papermaking agent system in liquid form, which comprises (i) cationic starch solution, prepared by cooking a starch mixture comprising a starch component and a water component, wherein the starch component in the starch mixture has an amylopectin content in the range of 65-90%, preferably 70-85%, and an amylose content in the range of 10-35%, preferably 15-30%; and (ii) polymer composition, which has anionic and cationic groups and which has a cationic net charge of >0.1 meq/g, at pH 7, the polymer composition comprising, or originating from constituent c), where constituent c) contains a third polymer, which comprises a copolymer comprising structural units derived from acrylamide and/or methacrylamide monomers, as well as hydrolytically unstable cationic groups attached to the copolymer, wherein the hydrolytically unstable cationic groups originate from monomers selected from the group consisting of 2-(dimethylamino)ethyl acrylate, [2-(acryloyloxy)ethyl] trimethylammonium chloride, 2-dimethylaminoethyl methacrylate and [2-(methacryloyloxy)ethyl] trimethylammonium chloride; wherein constituent c) is added to one of the components of the starch mixture or to the starch mixture before the cooking of the starch mixture and a part of the hydrolytically unstable cationic groups are hydrolysed into anionic groups during the cooking; and wherein the amount of hydrolysed groups is at least 4 mol-% of the total cationic groups in polymer.

Description

(1) The invention is described in more detail below with reference to the enclosed schematic drawing, in which

(2) FIG. 1 shows schematically the manufacture of the papermaking agent system according to the present invention.

(3) FIG. 1 shows schematically the manufacture of the papermaking agent system according to the present invention. Starch component is fed from a storage vessel 101 to a mixing tank 102 where it is mixed with water component and a starch mixture is obtained. Starch mixture is transferred to a cooking stage 103 whereby a starch solution is obtained and transferred to a storage tank 104.

(4) In FIG. 1 possible feeding points for the various constituents a), b) and c) of the polymer composition are marked with letters A, B and C, respectively.

(5) Constituent a) comprising an amphoteric copolymer with both anionic and cationic groups can be added before cooking stage 103 or after cooking stage 103 if at least part of the cationic groups are hydrolytically stable. In case all the cationic groups of the amphoteric copolymer are hydrolytically unstable the constituent a) is added after the cooking stage 103.

(6) Constituent b) comprising a first polymer, which is a copolymer having cationic or anionic groups attached to the copolymer, and a second polymer having groups of opposite charge attached to it. The first and second polymer may be added simultaneously or sequentially after each other. If at least part of the cationic groups in constituent b) are hydrolytically stable, both the first polymer and the second polymer may be added before the cooking stage 103. In case all the cationic groups in constituent b) are hydrolytically unstable both the first and the second polymer may be added after the cooking stage 103, or alternatively, the polymer comprising the anionic groups may be added before the cooking stage 103 and the polymer comprising the cationic groups may be added after the cooking stage 103.

(7) Constituent c) comprising a third polymer, which is a copolymer with hydrolytically unstable cationic groups is added before the cooking stage 103. During the cooking the hydrolytically unstable cationic groups are converted to anionic groups. The constituent c) comprises preferably also hydrolytically stable cationic groups, which may be attached to the same copolymer backbone as the hydrolytically unstable cationic groups. The constituent c) may also comprise a second third polymer, which comprises the hydrolytically stable groups.

(8) The constituents, which are added to starch mixture before the cooking stage 103 may be added either to the starch mixture, after the mixing of the starch component and the water component, or to one of the components of the mixture, before they are mixed together. In the latter case, the addition is done preferably to the water component.

EXPERIMENTAL

(9) Some embodiments of the invention are described in the following non-limiting examples.

Example 1

(10) Papermaking Agent Systems

(11) In all tests, starch is cationic corn starch, having DS 0.043 and moisture content of 12.2%. Ash content of the dry starch material is 2.77%. 10% starch slurry has pH value of 6. Starch is cooked at 1% concentration at 97-100° C. at atmospheric pressure for 90 min and then cooled to 25° C.

(12) In order to obtain a papermaking agent system comprising cationic starch solution and a polymer composition following polymer constituents are added into starch mixture prior cooking:

(13) Alternative 1: Aqueous cationic dispersion polymer of cationic polyacrylamide, CPAM, and poly-DADMAC. Proportion of CPAM is 17.5 weight-% of the dispersion. CPAM comprises 70 mol-% of acrylamide, 26 mol-% of DADMAC and 4 mol-% of cationic acrylate ester monomer. MW of CPAM is about 5 000 000 g/mol and charge density is 3.0 meq/g. Proportion of poly-DADMAC is 17.5 weight-% of the dispersion. Charge density of the poly-DADMAC is 6.2 meq/g and the average molecular weight about 300 000 g/mol. Total polymer content is 35 weight-%. Dry solids content is 38 weight-%. Measured charge density is 4.52 meq/g dry material, at pH 2.9.

(14) Alternative 2: Amphoteric polymer, which is an aqueous solution of co-polymer of acrylamide, APTAC and acrylic acid. Cationicity of amphoteric polymer is 10 mol-% and anionicity 5 mol-% of total monomers. Viscosity of the polymer is 13 700 mPas at 19.4% concentration at pH 4.0. Charge density is 1.2 meq/g dry product, at pH 3, and 0.6 meq/g dry product, at pH 7.

(15) Alternative 3: Cationic non-hydrolysable polymer for enhancing the efficiency of starch is an aqueous solution of non-thermosetting polyamidoamine-epichlorohydrin co-polymer. Viscosity of the polymer is 45 mPas at 25% concentration, charge density is 4.2 meq/g dry product, at pH 4.

(16) Retention polymer is commercial cationic polyacrylamide Fennopol K 3400 R (Kemira Oyj). The product is dry powder, which is dissolved at 0.5% concentration by mixing the powder with water and agitating the solution for 1 h at 25° C.

(17) Characterisation of Furnish and Process Water

(18) pH, conductivity, turbidity, charge and chemical oxygen demand of furnish and process water samples are characterised by using measurements and devices defined in Table 1.

(19) TABLE-US-00001 TABLE 1 Measurements and devices used for characterisation of the furnish and process water. Measurement Device pH Knick Portamess, Van London-pHoenix company, Texas, USA Conductivity Knick Portamess Knick Portamess, Van London- pHoenix company, Texas, USA Turbidity WTW Turb 555 IR, WTW Wissenschaftlich- Technische Werkstätten GmbH, Weilheim, Germany Charge Mütek PCD 03, BTG Instruments GmbH, Herrsching, Germany Chemical Oxygen DR Lange Lasa 100, Hach Lange GmbH, Düsseldorf, Demand (COD) Germany

(20) Zeta potential for furnish and process water samples is measured as follows: Pulp samples for zeta potential measurements are diluted to approximately 1% consistency with clear filtrate of paper machine process water. Zeta potential is determined using Mütek SZP-06 System Zeta Potential device (BTG Instruments GmbH, Herrsching, Germany). This device applies a vacuum to draw pulp stock against a screen and forms a pad of fines and fibres between two electrodes. A pulsating vacuum causes the aqueous phase to oscillate through the plug, thus shearing off the counterions and generating a streaming potential. The zeta potential is calculated by using the measured streaming potential, conductivity, and the pressure difference. The chemical treatment time, before each measurement, was obtained in 5 min.

(21) The fines content of the furnish is measured by employing Dynamic Drainage Jar, DDJ (Paper Research Materials, Inc., Seattle, Wash.), with 60M wire screen, which has 210 μm diameter screen holes. Consistency of the furnish is approximately 1 and the furnish slurry volume is 500 ml in DDJ experiment. Stirring speed is 1000 rpm and stirring is started 45 s before drainage. 100 g of the screened material is filtrated and weighed after drying.

(22) Characteristics of SC-paper furnish employed in the study are given in table 2. SC-paper furnish comprises approximately 75% of ground wood pulp and approximately 25% of long fibre kraft pulp.

(23) TABLE-US-00002 TABLE 2 Characteristics of SC-paper furnish employed in the Examples. Mixing chest Clear White SC-paper furnish furnish filtrate water pH 7.1 7.6 7.8 Turbidity (NTU) 95 21 23 Conductivity filtrate (μS/cm) 2270 1700 2000 Charge (μeq/l) −43.9 −50 −41.1 Zeta potential (mV) −18.7 — — Consistency (g/l) 33.8 — — Ash content (%) 18.3 — — COD (mg/l) 1512 1199 1252 Fines content (%) (60M wire) 49 — —
Manufacture of Sheets and their Testing

(24) SC-paper sheets are formed with Moving Belt Former (MBF), shown in FIG. 2. MBF is PC-controlled sheet former which utilises a real paper machine wire. Drainage occurs due to pulsating suction. The wire 1 itself is immobile and a moving perforated belt 2 is arranged under the wire 1, which generates suction effect similar to those occurring at the wire section of a paper machine. MBF forms a single sheet 3 instead of continuous paper web. The furnish suspension is added to a mixing vessel 4 with mixer 5 and mixed with fillers and retention chemicals. Drainage begins when the drainage foil 6 moves away and furnish suspension comes into contact with the wire 1. Moving belt 2 wipes water away from the wire 1 and the vacuum box 7 generates suction that pulsates to the wire 1 when the holes of the moving belt 2 passes the wire.

(25) The wire type employed the study is DL2874 two-layer wire with 5100 m.sup.3/(m.sup.2h) air permeability. The vacuum is 29 kPa, the stirring speed 2000 rpm, and stirring time 40 s

(26) The mixing chest furnish is diluted to consistency of 4.6 g/l % with clear paper machine filtrate. Cationic starch and polymer composition are added to the diluted furnish 3 min before 290 ml of the diluted furnish and 290 ml white water are added to the mixing vessel of the MBF, where the furnish mixture is kept under constant mixing. Filler, which comprises clay and ground calcium carbonate in a ratio of 50:50, is added 20 s before the drainage. The consistency is 6.4 g/l after the filler addition. The retention polymer is added 10 s before drainage. Mixing is stopped approximately 5 s before the drainage. After the sheet formation, the sheets are dried 2 min with a hot plate dryer (Lorentzen & Wettre). After the drying, sheets are pre-conditioned for 24 h at 23° C. in 50% relative humidity.

(27) SC-paper paper sheets are calendered once on both sides before paper testing with a nip pressure of 150 kN/m and a temperature of 80° C.

(28) The properties of the paper sheets are measured using the methods and devices disclosed in Table 3. Initial wet web strength is determined from undried fine paper sheets with an ash content of approximately 25%. The sheets are pressed 5 min at 4.5 bar pressure, and the wet tensile strength is measured immediately after pressing.

(29) TABLE-US-00003 TABLE 3 Methods and devices used for measuring paper sheet properties. Measurement Standard, Device Grammage ISO 536, Mettler Toledo Ash content ISO 1762, Precisa PrepAsh 229 Tensile strength ISO 1924-3, Lorentzen & Wettre Tensile tester Scott bond T 569, Huygen Internal Bond tester
Results

(30) A line is adjusted to the obtained results. From the line it is possible read comparable tensile strength values and retention polymer consumption at standard retention level of 78.2% and at standard grammage of 80.8 g/m.sup.2. Ash content of the produced sheets is 36±1%. Dosage starch, polymer composition and retention polymer is given in relation to the produced paper. 0-test is performed without any addition of starch or polymer composition.

(31) The results for the paper sheets comprising different amounts of starch and various polymer compositions are given in Table 4.

(32) TABLE-US-00004 TABLE 4 Results for Example 1. Tensile Retention Tensile energy Scott polymer index, absorption Bond, consump- System Nm/g index, J/kg J/m.sup.2 tion, g/t 0-test 10.3 85 131 280 Cationic starch, 6.4 kg/t 10.3 94 132 223 Alternative 1, 29 g/t + 10.8 101 140 181 cationic starch, 6.4 kg/t Alternative 1, 58 g/t + 10.9 104 138 190 cationic starch, 6.4 kg/t Alternative 2, 256 g/t + 11.4 111 133 153 cationic starch, 6.4 kg/t Alternative 2, 1.6 kg/t + 10.9 106 137 154 cationic starch, 6.4 kg/t Alternative 3, 320 g/t + 10.8 102 133 170 cationic starch, 6.4 kg/t Alternative 3, 1.6 kg/t + 10.3 85 139 191 cationic starch, 6.4 kg/t

Example 2

(33) Hydrolytic Stability of Amphoteric Polyacrylamides

(34) Hydrolytic stability of amphoteric polyacrylamides at 100° C. is tested. Amphoteric polyacrylamides, which contain different cationic monomer in the polymer, are used in the stability test. The following polymers are used.

(35) Polymer 1: Aqueous solution of co-polymer of 85 mol-% acrylamide, 10 mol-% acryloyloxyethyltrimethylammonium chloride (ADAM-Cl) and 5 mol-% acrylic acid.

(36) Polymer 2: Aqueous solution of co-polymer of 85 mol-% acrylamide, 10 mol-% [3-(acryloylamino)propyl] trimethylammonium chloride (APTAC) and 5 mol-% acrylic acid.

(37) Polymer 3: Aqueous solution of co-polymer of 85 mol-% acrylamide, 10 mol-% diallyldimethylammonium chloride (DADMAC) and 5 mol-% acrylic acid.

(38) Measured values of the polymer solutions are given in Table 5.

(39) TABLE-US-00005 TABLE 5 Properties of the polymer solutions used in Example 2. Poly- Dry Charge, Charge, mer Cat. solids Viscosity pH 3 (meq/ pH 7 (meq/ # Monomer (%) (mPas) pH g dry) g dry) 1 ADAM-CI 19.8 10 500 3.9 1.20 0.55 2 APTAC 19.4 13 700 4.0 1.21 0.60 3 DADMAC 20.0  5 200 3.8 1.24 0.60

(40) The polymers are first diluted with 100 mmol/l potassium phosphate buffer, pH 7.4, and then further with water in a manner that concentration of the polymer solutions is 1.00% and concentration of potassium phosphate is 50 mmol/l. pH of each solution is measured at 25° C. Solutions are kept in sealed autoclave bottles for 24 hours at 100° C. The bottles are then cooled and pH measured at 25° C. Charge densities of the polymers are determined by Mütek PDC 03 pH—particle charge detector (BTG Instruments GmbH, Herrsching, Germany) equipped with Mütek PCD Titrator Three-titrator unit (BTG Instruments GmbH, Herrsching, Germany), using 0.001 M PES-Na as titrant polymer for net cationic polymers and 0.001 N poly-DADMAC as titrant polymer for net anionic polymers, both titrant polymers supplied by BTG Instruments GmbH, Herrsching, Germany. Charge densities are determined at pH 3. The results are given in Table 6.

(41) TABLE-US-00006 TABLE 6 Results of hydrolytic stability experiments of amphoteric polyacrylamides. Cat. pH before 24 h pH after 24 h Charge, pH 3 Polymer # Monomer at 100° C. at 100° C. (meq/g dry) 1 ADAM-CI 7.4 7.2 −0.15 2 APTAC 7.3 7.3 1.20 3 DADMAC 7.3 7.3 1.22

(42) The results show that amphoteric polyacrylamide, which contains ADAM-CI as cationic monomer loses completely its cationic charge in conditions comparable to conditions prevailing during starch cooking. Amphoteric polyacrylamides, which contain APTAC or DADMAC as cationic monomer, do not show any significant change in their cationic charge.

Example 3

(43) Hydrolytic Stability of Cationic Dispersion Polymer

(44) Hydrolytic stability of cationic dispersion polymer is tested at 100° C. The dispersion polymer is the following:

(45) Cationic dispersion polymer corresponds to Alternative 1 in Example 1.

(46) The dispersion polymer is diluted first with 100 mmol/l potassium phosphate buffer, pH 7.4, and then further with water in a manner that concentration of the polymer solution is 1.00% and concentration of potassium phosphate is 50 mmol/l. A clear transparent solution is obtained. pH of the solution is measured at 25° C., pH 7.3. Solution is kept in a sealed autoclave bottle for 24 hours at 100° C. Gel lump is formed in to the bottom of the autoclave bottle during the storage time at 100° C. The bottle is then cooled and pH is measured at 25° C. pH is 7.2. pH of the mixture is adjusted to 2.9 with hydrochloric acid and the mixture is mixed for 10 min with magnetic stirrer. The lump is dissolved during the stirring period. Charge density of the polymer is determined by Mütek PDC 03 pH—particle charge detector (BTG Instruments GmbH, Herrsching, Germany), equipped with Mütek PCD Titrator Three-titrator unit (BTG Instruments GmbH, Herrsching, Germany), using 0.001 M PES-Na as titrant polymer for net cationic polymer, titrant polymer supplied by BTG Instruments GmbH, Herrsching, Germany. Charge density is 4.33 meq/g dry material at pH 2.9.

(47) Charge density of the dispersion polymer decreases by 0.19 meq/g during heating. The decrease shows that a part of the cationic groups of the dispersion polymer are hydrolysed during the heating, whereby the cationic dispersion polymer is changed into an amphoteric dispersion polymer. The formation of amphoteric polymer can be observed by the formation of gel lump and then by dissolution of the lump at pH 2.9. The reason for the lump formation is the formation of poly-ion complex of cationic poly-DADMAC groups and anionic groups of hydrolysed polyacrylamide. The dissolution of the lump is a result of breakage of the poly-ion complex, when the formed carboxylic acid anions turn non-ionic at pH 2.9. Amphotericity can be as low as about 4 mol-% of cationic charges.

(48) Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.