Use of cationic copolymers in the manufacture of paper, paperboard, tissue, etc.

Abstract

The invention relates to the use of a cationic copolymer having a standard viscosity of ≥ 2 mPas and a charge density of at most 5 meq / g, obtained by polymerizing (meth)acrylamide and a cationic monomer, for reducing anionic substances and / or 5 anionic particulate material in an aqueous phase of a thick fiber stock having a consistency of ≥ 20 g / l in the manufacture of a fibrous web, such as paper, paperboard, tissue, etc. The invention also relates to a method for manufacturing a fibrous web, such as paper, paperboard, tissue, etc., using the cationic copolymer.

Description

Technical Field

[0001] The present invention relates to the use of a cationic copolymer obtained by polymerizing (meth)acrylamide and a cationic monomer in the manufacture of paper, paperboard, tissue paper, etc., according to the preamble of the appended independent claims. Background Technology

[0002] It is known that anionic particulate materials and anionic substances, such as anionic hydrophobic colloids, form deposits on process surfaces during the manufacture of paper, paperboard, tissues, etc. These deposits can lead to web breakage, therefore, regular cleaning and sanitation of the most affected surfaces (e.g., drying cylinders, calenders, wires, and felts) is a preventative measure. This results in downtime and production losses. Even when not causing web breakage, the deposits can degrade the quality of the produced fiber webs. This degraded quality can manifest as porosity and / or dark spots in the final fiber web, even to the point where the produced web is unsuitable for its intended end use and must be discarded.

[0003] Problems caused by anionic particulate matter and anionic substances are typically mitigated by adding one or more fixatives to the fiber raw material before it is formed into the fiber web. Fixatives are usually synthetic cationic polymers. Cationic polymers react with anionic hydrophobic colloids and anionic particulate matter in a polyelectrolyte complexation manner. Cationic polymers can form aggregates with dissolved and colloidal substances and attach them to the fibers, fillers, and fine powders in the paper raw material. This phenomenon is commonly referred to as fixation.

[0004] Synthetic cationic polymers used as fixatives are typically polymers with low molecular weight and high cationic charge density, such as copolymers of dialkylamines and epichlorohydrins, polydiallyl dimethylammonium chloride (p-DADMAC), polyethyleneimine, and polyethyleneamine. Even low molecular weight cationic polyacrylamides with high charge density can be used. The molecular weights of these synthetic cationic polymers can range from approximately 10,000 Daltons to hundreds of thousands of Daltons. Low molecular weight polymers used as fixatives are usually added in relatively large quantities to achieve effective results. This can lead to increased chemical costs. Furthermore, adding large amounts of synthetic polymers may not be advantageous considering the sustainability of the entire process.

[0005] Therefore, there is a continuous need for new and effective fixatives in the manufacture of fiber webs such as paper, paperboard, and tissue paper. Summary of the Invention

[0006] The purpose of this invention is to minimize or even eliminate the drawbacks present in the prior art.

[0007] Another object of the present invention is to provide effective control over anionic particulate matter and anionic substances that cause deposition in the manufacture of paper, paperboard, tissue paper, etc.

[0008] Another object of the present invention is particularly to improve the fixation of anionic specific materials and / or anionic substances on fibers and reduce their amount in the aqueous phase of fiber raw materials in the manufacture of paper, paperboard, tissues, etc.

[0009] These objectives are achieved by the invention having the features provided in the characterizing portion of the independent claim. Some preferred embodiments of the invention are provided in the dependent claims.

[0010] Unless otherwise expressly stated, the features set forth in the dependent claims and embodiments in the specification may be freely combined with each other.

[0011] The exemplary embodiments and their advantages provided herein are related to the uses and methods according to the invention through applicable sections, even if not always mentioned separately.

[0012] The typical use of the cationic copolymers of the present invention, obtained by polymerizing (meth)acrylamide and cationic monomers, having a standard viscosity of ≥2 mPas and a charge density of up to 5 meq / g, is for reducing anionic substances and / or anionic particulate materials in the aqueous phase of thick fiber raw materials with a consistency of ≥20 g / l in the manufacture of fiber webs such as paper, paperboard, tissue paper, etc.

[0013] Typical methods according to the present invention for reducing anionic substances and / or anionic particulate materials in the aqueous phase of fibrous raw materials in the manufacture of fibrous webs such as paper, paperboard, tissue paper, etc. include:

[0014] -Provide water-based thick fiber raw materials with a consistency ≥20g / l;

[0015] - A cationic copolymer with a standard viscosity of ≥2 mPas and a charge density of up to 5 meq / g, obtained by polymerizing (meth)acrylamide and cationic monomers, is added to the aqueous thick fiber raw material.

[0016] -Optional dilution of fiber raw materials

[0017] - The fiber raw material is formed into a fiber web and the web is dried.

[0018] It has now been unexpectedly found that cationic copolymers obtained by polymerizing (meth)acrylamide and cationic monomers (having a standard viscosity of ≥2 mPas and a charge density of up to 5 meq / g) are surprisingly effective in attaching anionic substances and / or anionic particulate materials to fiber webs. Contrary to expectations, the specific copolymers of the present invention reduce the amount of anionic particulate materials and anionic substances in the aqueous phase of the thick fiber feedstock, and this has been observed as a significant reduction in the turbidity of the aqueous phase. It is believed that the high molecular weight (expressed by its standard viscosity) of the cationic copolymer enables the copolymer to interact effectively with the anionic particulate materials and anionic substances present in the aqueous phase of the thick fiber feedstock. Effective interaction reduces the total amount of copolymer used, which improves the sustainability of the fiber web manufacturing process. Furthermore, the cationic copolymers used in the present invention have a relatively low cationicity. This means a reduced risk of over-cationization in the process and improved process operability. For example, the risk of unwanted foam buildup due to over-cationization can be avoided.

[0019] In the context of this application, the term "anionic substance and / or anionic particulate material" generally includes anionic colloids and anionic hydrophobic substances, such as anionic trash; stickies, including small and large stickies; anionic hydrophobic colloidal substances, anionic hydrophobic aggregates, resins (pitch), etc. Stickies include synthetic anionic hydrophobic substances or particulate materials derived from, for example, adhesives; printing inks; coating adhesives, such as latex; waxes used in cardboard boxes for packaging; and hydrophobic interior and surface adhesives. Resins include natural anionic hydrophobic substances, such as wood extracts, sterols, fatty acids, resin acids, fatty acid esters, including their salts and other forms. Anionic colloids include anionic solid particles having a particle size in the range of 1-200 nm, preferably 1-100 nm, such as synthetic polymer particles. Anionic substances and / or anionic particulate materials can have a wide range of particle sizes. The present invention is particularly effective in immobilizing anionic substances and / or anionic particulate materials having a particle size of 0.1-150 μm, preferably 1-150 μm, such as 3-100 μm, especially by immobilizing them on fibers.

[0020] According to one embodiment of the invention, a cationic copolymer of (meth)acrylamide and a cationic monomer can preferably be used to immobilize and reduce the amount of anionic substances and / or anionic particulate materials selected from anionic colloidal resin particles and / or latex adhesive particles. It has been observed that when the cationic copolymer is used according to the invention, the immobilization results are particularly improved when the fiber raw material contains anionic colloidal resin particles and / or latex adhesives, and their amount in the aqueous phase of the fiber raw material is effectively reduced.

[0021] Cationic copolymers are preferably used alone as the sole agent for reducing the amount of anionic substances and / or anionic particulate materials in thick fiber raw materials. No anionic additives are required, which simplifies the use of cationic copolymers.

[0022] Cationic copolymers are suitable for fiber feedstocks containing cellulose fibers obtained through chemical pulping, mechanical pulping, recycled cellulose fibers, and / or broke paper. Cationic copolymers are particularly suitable for fiber feedstocks containing, or composed of, recycled cellulose fibers and / or cellulose fibers obtained through mechanical pulping.

[0023] According to one embodiment of the present invention, the charge density of the fiber raw material is negative before and after the cationic copolymer is added to the fiber raw material.

[0024] Preferably, the viscous fiber raw material does not contain a significant amount of inorganic filler particles, such as calcium carbonate or talc particles. The amount of inorganic filler particles can be ≤10% by weight, preferably ≤5% by weight, more preferably ≤2% by weight (calculated from the dry weight of the fiber raw material). The amount of inorganic particles can be, for example, in the range of 0-10% by weight, preferably 0.1-5% by weight, more preferably 0.5-2% by weight.

[0025] In the context of this application, the terms "fixation," "fixing," and "fix" refer to the quantitative reduction of anionic substances and / or anionic particulate materials in an aqueous phase. These can be removed from the aqueous phase of the fiber raw material and, at least temporarily or permanently, bound or attached to the fibers and, possibly, filler particles.

[0026] The cationic copolymer of (meth)acrylamide and cationic monomer used in this invention has a standard viscosity of ≥2 mPas. According to a preferred embodiment, the cationic copolymer can have a standard viscosity of ≥2.2 mPas, preferably ≥2.5 mPas, more preferably ≥3.5 mPas. For example, the cationic copolymer can have a standard viscosity in the range of 2-7 mPas, preferably 2.2-6 mPas, more preferably 2.3-5 mPas, even more preferably 2.5-4.5 mPas, and sometimes even more preferably 3-4 mPas. The standard viscosity of the copolymer is directly related to its molecular weight. The higher the standard viscosity, the longer the copolymer chain. Surprisingly, it has been observed that long copolymer chains can effectively compensate for the low cationicity of the copolymer and provide good fixation results.

[0027] The standard viscosity was measured at 25°C using a Brookfield LV viscometer equipped with a UL adapter, using a UL Adapter Spindle and a rotation speed of 60 rpm, in a 1M NaCl aqueous solution with a polymer content of 0.1% by weight. The general relationship between the standard viscosity of the copolymer and its average molecular weight is given in Table 1.

[0028] Table 1 shows the relationship between standard viscosity and average molecular weight.

[0029]

[0030] The relationships shown in Table 1 are based on standard viscosity and intrinsic viscosity measurements and use the Mark-Houwink-Sakurada constant K = 2.57 × 10⁻⁶. -4 dl / g and a = 0.67.

[0031] The cationic copolymer of (meth)acrylamide and cationic monomers used in this invention has a charge density of up to 5 meq / g. According to a preferred embodiment, the cationic copolymer can have a charge density of up to 4 meq / g, preferably up to 3 meq / g. The charge density can be, for example, in the range of 0.5-5 meq / g, preferably 1-4 meq / g, more preferably 1-3 meq / g, and even more preferably 2-3 meq / g. The relatively low cationicity of the cationic copolymer not only provides economic advantages (because the amount of expensive cationic monomers in copolymer production can be minimized), but also reduces the risks and associated operability problems related to over-cationization in fiber web manufacturing.

[0032] A cationic copolymer of (meth)acrylamide and a cationic monomer can be obtained by polymerizing (meth)acrylamide with up to 95 mol%, preferably up to 90 mol%, more preferably up to 55 mol%, or even more preferably up to 50 mol%. According to a preferred embodiment, a cationic copolymer is obtained by polymerizing (meth)acrylamide with 4-95 mol%, preferably 5-90 mol%, more preferably 5-55 mol%, or even more preferably 8-50 mol% or 10-50 mol% of a cationic monomer. For example, preferably, a cationic copolymer is obtained by polymerizing (meth)acrylamide with 19-50 mol%, preferably 19-40 mol%, more preferably 15-35 mol% or 19-33 mol% of a cationic monomer.

[0033] Preferably, the cationic copolymer does not contain structural units with anionic charges. This means that the total ionicity of the cationic copolymer corresponds to the amount of cationic monomer used.

[0034] The cationic monomer can be selected from diallyl dimethylammonium chloride (DADMAC), 2-(dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl]trimethylammonium chloride (ADAM-Cl), 2-(dimethylamino)ethyl acrylate benzyl chloride, 2-(dimethylamino)ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3-(acryloylamino)propyl]trimethylammonium chloride (APTAC), and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC). According to a preferred embodiment, the cationic monomer is [2-(acryloyloxy)ethyl]trimethylammonium chloride (ADAM-Cl).

[0035] According to a preferred embodiment, the cationic copolymer is a linear polymer. In other words, the cationic copolymer is unbranched and preferably not crosslinked. During the polymerization reaction, the amount of crosslinking agent is less than 0.002 mol%, preferably less than 0.0005 mol%, more preferably less than 0.0001 mol%. According to one embodiment, the polymerization reaction is completely free of crosslinking agent. Linear copolymers effectively reduce the risk of forming insoluble polymer particles, which can degrade the quality of the produced paper or paperboard.

[0036] The cationic copolymer of (meth)acrylamide and the cationic monomer is water-soluble and can be obtained by free radical polymerization of (meth)acrylamide and the cationic monomer. The term "water-soluble" herein means that the copolymer is completely miscible with water. When mixed with excess water, the resulting copolymer solution is preferably substantially free of discrete polymer particles or spheres. Excess water means that the resulting polymer solution is not a saturated solution.

[0037] Cationic copolymers can be obtained, for example, by solution polymerization, suspension polymerization, reverse emulsion polymerization, gel polymerization, or dispersion polymerization. According to a preferred embodiment, a cationic copolymer is obtained by gel polymerization, which produces a copolymer in gel form or a highly viscous liquid. Following gel polymerization, the resulting gel-form copolymer is pulverized, such as crushed or shredded, and then dried and optionally ground, thereby obtaining a dry, particulate copolymer.

[0038] Cationic copolymers of (meth)acrylamide and cationic monomers are typically dissolved and / or diluted in water before being used in the manufacture of paper, paperboard, tissues, etc. Therefore, the cationic copolymer of (meth)acrylamide and cationic monomers is typically dissolved and / or diluted in water to form a diluted treatment solution, which is then added to the fiber raw material. The active polymer content of this diluted treatment solution can be 0.1-4% by weight, preferably 0.3-3% by weight, more preferably 0.5-2% by weight. The diluted treatment solution can be further diluted before being introduced into the manufacturing process of paper, paperboard, tissues, etc.

[0039] Cationic copolymers are added to the thickened fiber feedstock to provide effective interaction with anionic substances and / or anionic particulate materials in the aqueous phase. The thickened fiber feedstock is understood herein as a fiber feedstock or furnish having a consistency of ≥20 g / L, preferably ≥25 g / L, more preferably ≥30 g / L. The thickened fiber feedstock may have a consistency greater than 20 g / L, preferably greater than 25 g / L, more preferably greater than 30 g / L. For example, the consistency of the thickened fiber feedstock may be in the range of 20-70 g / L, preferably 25-65 g / L, more preferably 30-60 g / L. Preferably, the cationic copolymer is added to the thickened fiber feedstock before diluting the feedstock with water discharged from the line section of the manufacturing process. According to one embodiment, the cationic copolymer may be used in an amount of 50-2000 g / ton, preferably 100-1000 g / ton, more preferably 200-600 g / ton. Detailed Implementation

[0040] experiment

[0041] Fixed test procedure

[0042] A fixation test was performed to examine how the turbidity of the pulp sample changed with the dosage of the fixation chemical. Hydrophobic colloidal particles were considered part of the turbidity in the aqueous phase of the pulp sample. When cationic fixation chemicals were added to the pulp sample, they fixed the hydrophobic colloidal particles to the fiber surface. This was considered a reduction in the turbidity of the aqueous phase of the pulp sample.

[0043] First, dilute the pulp to a consistency of approximately 10 g / L. Warm the diluted pulp to 45°C. Add the specified amount of fixed chemicals to the warm, diluted pulp sample (100 ml), and vigorously shake the pulp sample in a tightly sealed plastic container for 15 seconds using two magnetic stirrers as mixing aids. Then, filter the pulp sample by gravity using black ribbon filter paper, and measure the turbidity of the filtrate using a HACH, 2100AN IS Laboratory Turbidimeter. The results obtained are considered fully applicable to raw materials with higher consistency (stock).

[0044] At certain fixed chemical dosage levels, the lower the turbidity, the better the performance of the fixing chemical; that is, the more effective the chemical is in fixing hydrophobic colloidal particles onto the fiber surface.

[0045] The polymer used

[0046] The fixation efficiency of various cationic polyacrylamides obtained by polymerizing acrylamide and cationic monomers was tested. The properties of the tested cationic polyacrylamides are given in Table 2.

[0047] Table 2 shows the properties of the cationic polyacrylamide tested.

[0048]

[0049] *Standard viscosity, measured according to the definition in the instruction manual.

[0050] Commercially available polyamines, commonly used as fixatives, are used as a reference. Polyamines are used in 50% active solutions and have a viscosity of 500-1000 mPas measured by a Brookfield viscometer at 25°C. Commercially available polyamines have low average molecular weights, making the measurement of their standard viscosity difficult or meaningless.

[0051] Example 1

[0052] The pulp was thermomechanical pulp (TMP) from a Finnish paper mill. The pulp was diluted to a consistency of 9.7 g / L. The pulp pH was 7.5. Fixation tests were performed as described above. Fixation tests (0-test) without any added fixation chemicals gave turbidity values ​​of 73-76 NTU.

[0053] The polymers tested and the obtained fixation test results are given in Table 3 and Figure 1 As shown in the image.

[0054] From Table 3 and Figure 1 It can be seen that, for the fixation of thermomechanical pulp, the performance of all tested polyacrylamides is much better than that of the reference (i.e., polyamine, which is commonly used as a fixation chemical in papermaking).

[0055] Table 3 shows the results of the fixed-point tests in Example 1. Polymer dosage is given in terms of active polymer per ton of dry pulp.

[0056]

[0057] Example 2

[0058] The pulp was groundwood pulp (GW) from a Finnish paper mill. The pulp was diluted to a consistency of 8.8 g / L. Fixation tests were performed as described above. Fixation tests (0-test) without any added fixation chemicals gave turbidity values ​​of 63-75 NTU.

[0059] The polymers tested and the obtained fixation test results are given in Table 4 and Figure 2 As shown in the image.

[0060] Table 4 shows the polymers used in Example 2 and the results of the fixation test. The polymer dosage is given in terms of active polymer per ton of dry pulp.

[0061]

[0062] From Table 4 and Figure 2 It is easy to see that all the polyacrylamides tested performed much better than the reference (i.e., polyamine, which is commonly used as a fixation chemical in papermaking) in fixing groundwood pulp.

[0063] Example 3

[0064] The pulp was groundwood pulp (GW) from a Finnish paper mill. The pulp was diluted to a consistency of 10 g / L. Fixation tests were performed as described above. In addition to turbidity, the charge and particle count of the filtrate were measured. Particle counts (all hydrophobic aggregates and colloids) were measured using a flow cytometry (FCM)-based Kemira Flyto™, a widely used measurement technique that allows for rapid analysis of particles in fluid samples. Flow cytometry can be used to identify, measure, and count all particles, hydrophobic aggregates, small hydrophobic particles, and hydrophobic colloids (as a specific subset if all are present as hydrophobic particles) ranging in size from approximately 0.1 μm to 100 μm from process samples (such as process water, filtrate, and pulp suspensions) used in the manufacture of pulp and paper. Particle types were distinguished by selective staining with a fluorescent dye. The "All Particles" value also includes hydrophobic particles and colloids. Hydrophobic aggregates can include, for example, white pitch contaminated with hydrophobic materials, sticky substances, fine powders, and fillers. Sticky substances can also fall into the subgroup of hydrophobic colloids. Therefore, this method can be used to simultaneously analyze colloids, small particles, fine powders, fillers, and aggregates.

[0065] The polymers tested and the results obtained are given in Table 5.

[0066] As shown in Table 5, at addition levels of 150 g / t and 300 g / t, all tested cationic copolymers significantly reduced the negative charge and turbidity of the filtrate. The number of particles in the filtrate was also significantly reduced. For example, the fixation test (0-test) conducted without any fixation chemicals yielded a turbidity of approximately 28 NTU and a charge of -23.0 μeq / l. The particle count in the 0-test was approximately 79 million, of which 3.25 million were hydrophobic aggregates and 16 million were hydrophobic colloids. Adding CPAM5 at a dosage of 300 g / t reduced the number of hydrophobic aggregates from 3.25 million in the 0-test to less than half (1.59 million), and reduced the amount of hydrophobic colloids from 16 million in the 0-test to less than one-tenth (approximately 1.29 million). All the results obtained indicate the excellent fixation performance of the cationic copolymers. Furthermore, it can be seen that increasing the charge of the cationic copolymer, i.e., the amount of cationic monomers present in the polymerization, can significantly improve the fixation efficiency.

[0067] Table 5 shows the polymers used in Example 3 and the results of the fixation test. Polymer dosage is given in terms of active polymer per metric ton of dry pulp.

[0068]

[0069] *No polymer additives

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the embodiments described above, but rather that the invention may vary within the scope of the appended claims.

Claims

1. The use of a linear cationic copolymer obtained by polymerizing (meth)acrylamide and a cationic monomer for reducing anionic substances and / or anionic particulate materials in the aqueous phase of a thick fiber raw material having a consistency of ≥ 20 g / L in the manufacture of fiber webs, said linear cationic copolymer having: -Standard viscosity ≥ 2 mPa·s - Charge density in the range of 0.5-3 meq / g, and Dosage: -50-600 g / ton.

2. The use according to claim 1, characterized in that, The linear cationic copolymer has a standard viscosity of ≥ 2.2 mPa·s.

3. The use according to claim 1, characterized in that, The copolymer has a standard viscosity in the range of 2-7 mPa·s.

4. The use according to claim 1, characterized in that, The fiber web is paper, paperboard, or paper towel.

5. The use according to claim 1, characterized in that, The linear cationic copolymer is obtained by polymerizing (meth)acrylamide and up to 95 mol% of cationic monomers.

6. The use according to claim 5, characterized in that, The linear cationic copolymer is obtained by polymerizing (meth)acrylamide and 4-95 mol% of cationic monomers.

7. The use according to claim 1, characterized in that, The cationic monomer is selected from diallyl dimethyl ammonium chloride (DADMAC), 2-(dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl]trimethyl ammonium chloride (ADAM-Cl), 2-(dimethylamino)ethyl acrylate benzyl chloride, 2-(dimethylamino)ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3-(acryloylamino)propyl]trimethyl ammonium chloride (APTAC), and [3-(methacryloylamino)propyl]trimethyl ammonium chloride (MAPTAC).

8. The use according to claim 1, characterized in that, The linear cationic copolymer is obtained by solution polymerization, suspension polymerization, reverse emulsion polymerization, gel polymerization or dispersion polymerization.

9. The use according to claim 1, characterized in that, The anionic substance and / or anionic particulate material comprises anionic colloidal resin particles and / or latex adhesive particles.

10. The use according to claim 1, characterized in that, Fiber raw materials include cellulose fibers obtained through chemical pulping, mechanical pulping, and / or recycled cellulose fibers.

11. The use according to claim 10, characterized in that, The fiber raw materials include recycled cellulose fibers and / or cellulose fibers obtained by mechanical pulping.

12. The use according to claim 1, characterized in that, The linear cationic copolymer does not contain structural units with anionic charges.

13. A method for reducing anionic substances and / or anionic particulate materials in the aqueous phase of fiber raw materials in the manufacture of fiber webs, the method comprising: - Provide water-based thick fiber raw materials with a consistency of ≥ 20 g / l; - Add 50-600 g / ton of a linear cationic copolymer obtained by polymerizing (meth)acrylamide and a cationic monomer to the aqueous thick fiber raw material, the copolymer having a standard viscosity of ≥ 2 mPa·s and a charge density in the range of 0.5-3 meq / g; -Optionally dilute the thick fiber raw material; - The fiber raw material is formed into a fiber web and the web is dried.

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