Papermaking filler wrapping agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of papermaking, in particular to a papermaking filler wrapping agent and a preparation method and application thereof. The papermaking filler wrapping agent comprises a cationic polyester polyacrylamide emulsion and a high molecular weight water-soluble polymer. The papermaking filler wrapping agent has the advantages that the papermaking filler wrapping agent is insensitive to shearing action, the retention rate of filler such as calcium carbonate is high, the paper strength is not reduced, and produced paper products are good in batch stability.

Description

Technical Field

[0001] The present invention relates to the technical field of papermaking, and in particular to a papermaking filler wrapping agent, a preparation method and an application thereof. Background Art

[0002] In the papermaking process, paper is typically made from an aqueous cellulose suspension or pulp. Cultural papers, for example, often require the addition of calcium carbonate or other fillers during the manufacturing process to fill the gaps between fibers, achieving objectives such as increased hiding power, a smoother surface, and reduced costs. These paper products often contain multiple layers, such as filler and fiber layers, requiring multiple cycles of lamination to achieve high-quality products.

[0003] After the initial cooking and beating process of papermaking, fibers are transformed into a mixture of long and short fibers. Short fibers, consisting of fiber fragments only tens of microns long, easily escape the filter cloth through the gaps between fibers during the papermaking process and return to the fiber suspension. Fillers, typically particles measuring a few microns or even tens to hundreds of nanometers, carry a negative surface charge, matching the charge on the fiber surface. This mutual repulsion leads to low retention during the papermaking process. During the papermaking process, how to convert the fibers or fillers in the suspension into the paper layer as much as possible is a critical challenge for paper industry technicians.

[0004] Early processes used non-ionic polymers without charge, such as starch and polyacrylamide. Due to the large molecular weight of the polymer, it has a certain flocculation effect in aqueous solution, which helps to improve the retention of fillers. However, since its effect is the van der Waals force, it is relatively weak and the retention effect is not ideal.

[0005] US Patent Publication No. US4753710A discloses a system for improving fiber and filler retention. A high-molecular-weight linear cationic polymer is first added to an aqueous fiber suspension, followed by shearing followed by the addition of bentonite. The high-molecular-weight linear cationic polymer carries a positive charge, which attracts the negative surface charges of the fibers and filler, causing the fibers and filler to flocculate. The shearing action partially deflocculates the fibers and filler, improving the retention of fine fibers and filler. WIPO Patent Publication No. WO1998029604A1 discloses a system for flocculating fine fibers in a fiber suspension using a cationic polymer. The floccules are then deflocculated under mechanical shear, and then reflocculated using an anionic branched polymer, significantly improving the fiber retention rate in the system. Both of these filler encapsulation systems are sensitive to shear, with floccules easily deflocculating under shear. Furthermore, as shear increases, floc size rapidly decreases, resulting in poor batch stability in actual paper production operations.

[0006] US Patent Publication No. US20020066540A1 discloses a method for improving fiber and filler flocculation. A cationic polymer, silica sol, and non-swelling organic microparticles are added to the system to flocculate the fibers and fillers, resulting in a paper product with high retention. However, this system is a ternary system, requiring time-consuming and labor-intensive modifications to existing binary paper machines. Furthermore, the ternary system requires higher system stability, and even slight changes in raw material parameters and ratios can affect product performance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a papermaking filler wrapping agent and a preparation method and application thereof, and the prepared paper product has good stability.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a papermaking filler packaging agent, including a cationic polyester polyacrylamide emulsion and a high molecular weight water-soluble polymer.

[0009] Another technical solution adopted by the present invention is: a method for preparing the above-mentioned papermaking filler coating agent, wherein the cationic polyester polyacrylamide emulsion is prepared by reacting acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt and alkenyl cationic polyester.

[0010] Another technical solution adopted by the present invention is: use of the above-mentioned papermaking filler packaging agent in the preparation of high-ash paper products.

[0011] The beneficial effects of the present invention are as follows: the papermaking filler coating agent of the present invention includes a cationic polyester polyacrylamide emulsion and a high molecular weight water-soluble polymer, has the advantages of being insensitive to shearing, having a high retention rate for fillers such as calcium carbonate, not reducing paper strength, and having good batch stability of produced paper products. DETAILED DESCRIPTION

[0012] To explain the technical content, achieved objectives and effects of the present invention in detail, the following describes them in conjunction with the implementation methods.

[0013] A papermaking filler packaging agent comprises a cationic polyester polyacrylamide emulsion and a high molecular weight water-soluble polymer.

[0014] The papermaking filler coating agent of the present invention comprises a cationic polyester polyacrylamide emulsion and a high molecular weight water-soluble polymer. The cationic polyester polyacrylamide emulsion contains long-chain cationic polyester segments, both the ends and the head of the cationic polyester carry positive charges. The segments on the side chains have a large degree of freedom of movement, and when fully expanded, they have a large active area, making it easy to contact filler particles. When in contact with negatively charged fillers, the positive and negative charges attract each other, causing the fillers to aggregate. Simultaneously, the ester groups in the cationic polyester segments and the hydroxyl acrylic acid esters on the main chain have a good adsorption effect on the filler. Combined with the positive charges at the head and the end, the adsorption of the filler is more secure, and the polymer can resist the deagglomeration effect caused by mechanical shearing, thereby stabilizing the polymer's coating effect on the filler.

[0015] Cationic polyester polyacrylamide emulsion can form a binary encapsulation additive system with a high molecular weight water-soluble polymer. It can be operated according to the existing papermaking process without changing the process or modifying the paper machine. It is convenient and fast to switch, has a high filler retention rate, and has good paper uniformity, high paper strength, and batch stability. It is suitable for papermaking equipment with most filler binary encapsulation additive systems.

[0016] Furthermore, the weight ratio of the cationic polyester polyacrylamide emulsion to the high molecular weight water-soluble polymer is 1:0.5-3.

[0017] Furthermore, the high molecular weight water-soluble polymer includes at least one of polyacrylamide, cationic polyacrylamide, cationic starch, cationic guar gum and guar gum.

[0018] Furthermore, the molecular weight of the polyacrylamide is 10 million Da to 20 million Da, preferably 12 million Da to 15 million Da.

[0019] Furthermore, the molecular weight of the cationic polyacrylamide is 10 million Da to 12 million Da, and the degree of substitution of the quaternary ammonium salt is 0.25 mol% to 0.3 mol%.

[0020] Furthermore, the molecular weight of the cationic starch is 6 million Da to 7 million Da, and the degree of substitution of the quaternary ammonium salt is 0.25 mol% to 0.3 mol%.

[0021] Furthermore, the molecular weight of the cationic guar gum is 8 million Da to 10 million Da, and the degree of substitution of the quaternary ammonium salt is 0.25 mol% to 0.3 mol%.

[0022] Furthermore, the molecular weight of guar gum is 18 million Da to 20 million Da.

[0023] Another technical solution adopted by the present invention is: the preparation method of the above-mentioned papermaking filler packaging agent, the cationic polyester polyacrylamide emulsion is prepared by reacting acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt and alkenyl cationic polyester.

[0024] As can be seen from the above description, hydroxy acrylates provide excellent adhesion, which is beneficial for improving interlayer adhesion and tensile strength of paper products. The alkenyl quaternary ammonium salts of the present invention can provide low molecular weight cations, which are a good supplement to the ternary cations of alkenyl cationic polyesters.

[0025] Furthermore, the preparation method of the cationic polyester polyacrylamide emulsion comprises the following steps: S1: dissolving acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt, alkenyl cationic polyester and chain transfer agent in deionized water to prepare an aqueous phase; dissolving an emulsifier in a solvent to prepare an oil phase; S2. The oil phase and the water phase are mixed and emulsified and reacted in sequence to obtain a cationic polyester polyacrylamide emulsion.

[0026] Furthermore, the solvent is n-decane.

[0027] Furthermore, the weight ratio of acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt, alkenyl cationic polyester and chain transfer agent is 80-100:5-50:5-15:10-20:0.01-0.02.

[0028] Furthermore, the weight ratio of acrylamide to deionized water is 80-100:300-500.

[0029] Furthermore, the weight ratio of the emulsifier to n-decane is 30-40:600-800.

[0030] Furthermore, the emulsification in S2 is specifically as follows: stirring the oil phase and adding the water phase dropwise until the two phases are emulsified.

[0031] Furthermore, the reaction in S2 is specifically as follows: heating to 70-90° C., adding an initiator, and keeping the temperature to react for 5-8 hours.

[0032] Furthermore, the initiator is azobisisobutylamidine hydrochloride.

[0033] Furthermore, the hydroxy acrylate includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and hydroxybutyl methacrylate.

[0034] Furthermore, the alkenyl quaternary ammonium salt includes at least one of acryloyloxypropyltrimethylammonium halide, methacryloyloxypropyltrimethylammonium halide and allyltrimethylammonium halide, and the halogen atom includes at least one of chlorine, bromine and iodine.

[0035] Furthermore, the chain transfer agent is Bruno Bock EVABOPOL® 1400.

[0036] As can be seen from the above description, the present invention uses a special chain transfer agent when preparing the cationic polyester polyacrylamide emulsion, controls the molecular weight of the cationic polyester polyacrylamide within a certain range, and controls the size of the encapsulated filler while ensuring the filler retention rate, thereby avoiding unevenness in the paper product caused by excessively large particle size, thereby achieving the purpose of uniform and smooth paper products. At the same time, on the basis of increasing the filler ratio of the paper product, the interlayer bonding strength and tensile strength thereof are not reduced and are even slightly improved.

[0037] Furthermore, the emulsifier is a combination of EFS-1006 and EFS-1320 from Shanghai Zhongcheng Fine Chemical Co., Ltd., with a weight ratio of 1:1.3 to 1.5; Furthermore, the structural formula of the alkenyl cationic polyester is formula (1): Formula (1); Wherein R1 is a straight-chain alkyl group having 1 to 18 carbon atoms, R2 is a straight-chain alkyl group having 1 to 4 carbon atoms, R3 and R4 are segments of lactone ring-opening polymerization, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and 8≤m+n≤50; R5 is methylene or 4-methylene-phenyl, and X and Y are halogen atoms, respectively, including chlorine, bromine and iodine.

[0038] From the above description, we can see that Furthermore, the preparation method of the alkenyl cationic polyester comprises the following steps: adding an alkenyl halide, a base and dimethyl carbonate to the cationic polyester to react to obtain the alkenyl cationic polyester.

[0039] Furthermore, the molar ratio of alkenyl halide, base and dimethyl carbonate is 1-1.05:0.01-0.04:10-60.

[0040] Furthermore, the preparation method of the alkenyl cationic polyester includes the following steps: adding an alkenyl halide, a base and dimethyl carbonate to the cationic polyester, stirring and heating to 50-60°C, reacting for 4-8 hours, filtering to remove the solid base, then adjusting the pH to 5-7 with dilute acid, then removing the dimethyl carbonate by reduced pressure distillation, and cooling to 20-30°C to obtain the alkenyl cationic polyester.

[0041] From the above description, it can be seen that adjusting the pH to 5-7 with dilute acid can neutralize the alkali in the system and reduce impurities.

[0042] Furthermore, the alkenyl halide is any one of 4-vinylbenzyl chloride, 4-vinylbenzyl bromide, 3-chloro-1-propene, 3-bromo-1-propene, and 3-iodo-1-propene.

[0043] Furthermore, the base is any one of sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

[0044] Furthermore, the dilute acid is any one of hydrochloric acid with a concentration of 5 wt %, hydrobromic acid with a concentration of 5 wt %, and hydroiodic acid with a concentration of 5 wt %.

[0045] As can be seen from the above description, the dilute acid of the present invention uses hydrochloric acid, hydrobromic acid and hydroiodic acid, which are consistent with the anion part of the alkenyl cationic polyester, avoiding the introduction of other ions that affect the performance of the finished product.

[0046] Furthermore, the preparation method of the cationic polyester includes the following steps: after mixing N-alkyldiethanolamine, lactone and a catalyst for reaction, 2,3-epoxypropyltrialkylammonium halide, boron trifluoride etherate and dimethyl carbonate are added and the mixture is reacted to obtain the cationic polyester.

[0047] Furthermore, the molar ratio of N-alkyldiethanolamine to lactone is 1:8-50.

[0048] Furthermore, the molar ratio of N-alkyldiethanolamine, 2,3-epoxypropyltrialkylammonium halide, dimethyl carbonate and boron trifluoride etherate is 1:1.95-2.1:40-50:0.02-0.05.

[0049] Furthermore, the catalyst is butyl titanate, and the molar ratio of butyl titanate to N-alkyldiethanolamine is 1:20-100.

[0050] Furthermore, the preparation method of cationic polyester includes the following steps: mixing N-alkyldiethanolamine, lactone and catalyst at 110~140℃ for reaction for 2~8h, then cooling to 30~40℃, adding 2,3-epoxypropyltrialkylammonium halide, boron trifluoride ether and dimethyl carbonate, stirring for 0.5~1h, then heating to 50~60℃, reacting for 3~5h, removing dimethyl carbonate by reduced pressure distillation, and cooling to 20~30℃ to obtain cationic polyester.

[0051] Furthermore, the alkyl group of the N-alkyldiethanolamine is a straight-chain alkyl group having 1 to 18 carbon atoms.

[0052] From the above description, it can be seen that when the number of carbon atoms is 1-18, the water solubility of N-alkyldiethanolamine after being connected to lactone and cationized needs to be better.

[0053] Furthermore, the lactone includes at least one of γ-butyrolactone, α-methyl-γ-butyrolactone, δ-valerolactone, γ-valerolactone, ε-caprolactone and γ-caprolactone.

[0054] Furthermore, the alkyl group of the 2,3-epoxypropyltrialkylammonium halide is a linear alkyl group having 1 to 4 carbon atoms, and the halide ion is any one of a chloride ion, a bromide ion and an iodide ion.

[0055] From the above description, it can be seen that when the linear alkyl group is 1-4, the water solubility after cationization needs to be better.

[0056] Another technical solution adopted by the present invention is: a papermaking filler wrapping agent is prepared by adopting the preparation method of the above-mentioned papermaking filler wrapping agent.

[0057] Another technical solution adopted by the present invention is: use of the above-mentioned papermaking filler packaging agent in the preparation of high-ash paper products.

[0058] Example 1 of the present invention is: a method for preparing a papermaking filler wrapping agent, the steps are as follows: S1. Add 1 mol of N-methyldiethanolamine, 40 mol of γ-butyrolactone, and 0.01 mol of butyl titanate to a reactor, heat to 110° C., react for 8 hours, and then cool to 30° C.; add 2.1 mol of 2,3-epoxypropyltrimethylammonium chloride and 46 mol of dimethyl carbonate to a reactor, add 0.05 mol of boron trifluoride etherate, stir for 0.5 hour, heat to 60° C., react for 3 hours, remove dimethyl carbonate by distillation under reduced pressure, and cool to 20° C. to obtain cationic polyester A1; S2. Add 1.05 mol of 3-chloro-1-propene, 0.01 mol of sodium carbonate, and 50 mol of dimethyl carbonate to cationic polyester A1, stir and heat to 60° C., react for 4 hours, filter to remove solid sodium carbonate, add 5 wt % hydrochloric acid dropwise to adjust the pH to 7, remove dimethyl carbonate by vacuum distillation, and cool to 30° C. to obtain alkenyl cationic polyester B1; The structural formula of the alkenyl cationic polyester B1 is formula (1): Formula (1); wherein R1 is a methyl group, R2 is a methyl group, R3 and R4 are segments of the ring-opening polymerization of γ-butyrolactone, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and m+n=40; ​​R5 is a methylene group, and X and Y are chlorine; S3. 100 g of acrylamide, 5 g of hydroxyethyl acrylate, 5 g of acryloyloxypropyltrimethylammonium chloride, 20 g of the alkenyl cationic polyester B1 obtained in step S2, and 0.01 g of the chain transfer agent EVABOPOL® 1400 were uniformly mixed, and the mixture was dissolved in 500 g of deionized water to prepare an aqueous phase C1. 12 g of emulsifier EFS-1006 and 18 g of emulsifier EFS-1320 were dissolved in 600 g of n-decane to prepare an oil phase D1. S4, add the oil phase D1 to the reactor, stir and gradually add the aqueous phase C1 dropwise until the two phases are emulsified, raise the temperature to 90°C, add 0.03g of initiator azobisisobutylamidine hydrochloride, keep the temperature for reaction for 5 hours, and then cool to 30°C to obtain cationic polyester polyacrylamide emulsion E1; S5. Separately store 10 g of cationic polyester polyacrylamide emulsion E1 and 13.33 g of cationic starch (molecular weight of 7 million Da, degree of quaternary ammonium salt substitution of 0.3 mol%) to obtain a papermaking filler coating agent F1.

[0059] Example 2 of the present invention is: a method for preparing a papermaking filler wrapping agent, the steps are as follows: S1. Add 1 mol of N-octadecyldiethanolamine, 8 mol of γ-caprolactone, and 0.05 mol of butyl titanate to a reactor, heat to 140° C., react for 2 hours, and then cool to 40° C.; add 1.95 mol of 2,3-epoxypropyltributylammonium bromide and 40 mol of dimethyl carbonate to a reactor, add 0.02 mol of boron trifluoride etherate, stir for 1 hour, heat to 50° C., react for 5 hours, remove dimethyl carbonate by distillation under reduced pressure, and cool to 20° C. to obtain cationic polyester A2; S2, 1.02 mol of 4-vinylbenzyl bromide, 0.04 mol of potassium bicarbonate and 10 mol of dimethyl carbonate were added to cationic polyester A2, stirred and heated to 50°C, reacted for 8 hours, filtered to remove solid potassium bicarbonate, 5 wt% of hydrobromic acid was added dropwise to adjust the pH to 6, dimethyl carbonate was removed by vacuum distillation, and the temperature was lowered to 20°C to obtain vinyl cationic polyester B2; The structural formula of the alkenyl cationic polyester B2 is formula (1): Formula (1); wherein R1 is a linear alkyl group having 18 carbon atoms, R2 is a butyl group, R3 and R4 are segments of a ring-opening polymerization of γ-caprolactone, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and m+n=8; R5 is a 4-benzyl group, and X and Y are bromine; S3, 80 g acrylamide, 50 g hydroxybutyl methacrylate, 15 g allyltrimethylammonium bromide, 15 g alkenyl cationic polyester B2 obtained in step S2, and 0.02 g chain transfer agent Bruno Bock EVABOPOL® 1400 were mixed uniformly, and the mixture was dissolved in 300 g deionized water to prepare aqueous phase C2; ​​15 g emulsifier EFS-1006 and 19.5 g emulsifier EFS-1320 were dissolved in 700 g n-decane to prepare oil phase D2; S4. Add the oil phase D2 to the reactor, stir and gradually add the aqueous phase C2 dropwise until the two phases are emulsified, raise the temperature to 70°C, add 0.07g of initiator EVABOPOL®1400, keep the temperature for reaction for 8 hours, and then cool to 20°C to obtain cationic polyester polyacrylamide emulsion E2; S5. Separately store 10 g of cationic polyester polyacrylamide emulsion E2 and 5 g of cationic polyacrylamide (molecular weight of 12 million Da, degree of quaternary ammonium salt substitution of 0.25 mol%) to obtain a papermaking filler encapsulating agent F2.

[0060] Example 3 of the present invention is: a method for preparing a papermaking filler wrapping agent, the steps are as follows: S1. Add 1 mol of N-ethyldiethanolamine, 50 mol of γ-valerolactone, and 0.02 mol of butyl titanate to a reactor, heat to 130° C., react for 6 hours, and then cool to 35° C.; add 2 mol of 2,3-epoxypropyltriethylammonium iodide and 50 mol of dimethyl carbonate to a reactor, add 0.04 mol of boron trifluoride etherate, stir for 1 hour, heat to 57° C., react for 4.5 hours, remove dimethyl carbonate by distillation under reduced pressure, and cool to 25° C. to obtain cationic polyester A3; S2, 1 mol of 3-iodo-1-propylene, 0.03 mol of potassium carbonate and 60 mol of dimethyl carbonate were added to cationic polyester A3, stirred and heated to 55°C, reacted for 6 hours, filtered to remove solid potassium carbonate, 5 wt% of hydroiodic acid was added dropwise to adjust the pH to 5, dimethyl carbonate was removed by vacuum distillation, and the temperature was lowered to 20°C to obtain alkenyl cationic polyester B3; The structural formula of the alkenyl cationic polyester B3 is formula (1); Formula (1); wherein R1 is ethyl, R2 is ethyl, R3 and R4 are segments of the ring-opening polymerization of γ-valerolactone, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and m+n=50; R5 is methylene, and X and Y are iodine; S3. 90 g acrylamide, 30 g hydroxypropyl acrylate, 10 g methacryloyloxypropyltrimethylammonium iodide, 20 g alkenyl cationic polyester B3, and 0.015 g chain transfer agent EVABOPOL® 1400 were mixed uniformly, and the mixture was dissolved in 400 g deionized water to prepare aqueous phase C3. 14 g emulsifier EFS-1006 and 21 g emulsifier EFS-1320 were dissolved in 800 g n-decane to prepare oil phase D3. S4, add the oil phase D3 to the reactor, stir and gradually add the aqueous phase C3 dropwise until the two phases are emulsified, raise the temperature to 80°C, add 0.05g of initiator azobisisobutylamidine hydrochloride, keep the temperature for reaction for 6 hours, and then cool to 25°C to obtain cationic polyester polyacrylamide emulsion E3; S5. Separately store 10 g of cationic polyester polyacrylamide emulsion E3 and 30 g of polyacrylamide (molecular weight of 20 million Da) to obtain a papermaking filler coating agent F3.

[0061] Example 4 of the present invention is: a method for preparing a papermaking filler packaging agent, the steps are as follows: S1. 1 mol of N-lauryldiethanolamine, 28 mol of δ-valerolactone, and 0.03 mol of butyl titanate were added to a reaction kettle, heated to 120° C., reacted for 4 hours, and then cooled to 35° C.; 2.05 mol of 2,3-epoxypropyltrimethylammonium bromide and 48 mol of dimethyl carbonate were added to a reaction kettle, and 0.03 mol of boron trifluoride etherate was added. After stirring for 0.5 hour, the temperature was raised to 53° C., reacted for 4 hours, and then the dimethyl carbonate was removed by distillation under reduced pressure. The temperature was then lowered to 25° C. to obtain cationic polyester A4; S2. Add 1.01 mol of 3-bromo-1-propene, 0.02 mol of sodium bicarbonate, and 40 mol of dimethyl carbonate to cationic polyester A4, stir and heat to 50° C., react for 7 hours, filter to remove solid sodium bicarbonate, dropwise add 5 wt % hydrobromic acid to adjust the pH to 7, remove dimethyl carbonate by distillation under reduced pressure, and cool to 25° C. to obtain alkenyl cationic polyester B4; The structural formula of the alkenyl cationic polyester B4 is formula (1): Formula (1); wherein R1 is a linear alkyl group having 12 carbon atoms, R2 is a methyl group, R3 and R4 are segments of the ring-opening polymerization of δ-valerolactone, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and m+n=28; R5 is a methylene group, and X and Y are bromine; S3. 100 g acrylamide, 20 g hydroxyethyl methacrylate, 13 g acryloyloxypropyltrimethylammonium bromide, 20 g alkenyl cationic polyester B4, and 0.02 g chain transfer agent EVABOPOL® 1400 were uniformly mixed, and the mixture was dissolved in 350 g deionized water to prepare aqueous phase C4. 13 g emulsifier EFS-1006 and 17 g emulsifier EFS-1320 were dissolved in 750 g n-decane to prepare oil phase D4. S4, add the oil phase D4 to the reactor, stir and gradually add the aqueous phase C4 dropwise until the two phases are emulsified, raise the temperature to 75°C, add 0.06g of initiator azobisisobutylamidine hydrochloride, keep the temperature for reaction for 8 hours, and then cool to 24°C to obtain cationic polyester polyacrylamide emulsion E4; S5. Separately store 10 g of cationic polyester polyacrylamide emulsion E4 and 12 g of cationic guar gum (molecular weight of 9 million Da, degree of quaternary ammonium salt substitution of 0.28 mol%) to obtain a papermaking filler coating agent F4.

[0062] Example 5 of the present invention is: a method for preparing a papermaking filler wrapping agent, the steps are as follows: S1. Add 1 mol of N-butyldiethanolamine, 20 mol of ε-caprolactone, and 0.03 mol of butyl titanate to a reactor, heat to 125° C., react for 5 hours, and then cool to 30° C.; add 2.1 mol of 2,3-epoxypropyltriethylammonium chloride and 40 mol of dimethyl carbonate to a reactor, add 0.02 mol of boron trifluoride etherate, stir for 1 hour, heat to 50° C., react for 5 hours, remove dimethyl carbonate by distillation under reduced pressure, and cool to 20° C. to obtain cationic polyester A5; S2. Add 1.02 mol of 4-vinylbenzyl chloride, 0.01 mol of potassium carbonate, and 35 mol of dimethyl carbonate to cationic polyester A5, stir and heat to 58° C., react for 5 hours, filter to remove solid potassium carbonate, add 5 wt % hydrochloric acid dropwise to adjust the pH to 6.5, remove dimethyl carbonate by distillation under reduced pressure, and cool to 20° C. to obtain alkenyl cationic polyester B5; The structural formula of the alkenyl cationic polyester B5 is formula (1): Formula (1); wherein R1 is butyl, R2 is ethyl, R3 and R4 are segments of the ring-opening polymerization of ε-caprolactone, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and m+n=20; R5 is 4-benzyl, and X and Y are chlorine; S3. 85 g acrylamide, 10 g hydroxypropyl acrylate, 8 g allyltrimethylammonium chloride, 12 g alkenyl cationic polyester B5, and 0.01 g chain transfer agent EVABOPOL® 1400 were uniformly mixed, and the mixture was dissolved in 500 g deionized water to prepare aqueous phase C5. 12.5 g emulsifiers EFS-1006 and EFS-1320 were dissolved in 640 g n-decane to prepare oil phase D5. S4, add the oil phase D5 to the reactor, stir and gradually add the aqueous phase C5 dropwise until the two phases are emulsified, raise the temperature to 85°C, add 0.04g of initiator, keep the temperature for reaction for 6 hours, and then cool to 30°C to obtain cationic polyester polyacrylamide emulsion E5; S5. Separately store 10 g of cationic polyester polyacrylamide emulsion E5 and 13.33 g of guar gum (molecular weight of 18 million Da) to obtain a papermaking filler coating agent F5.

[0063] Example 6 of the present invention is: a papermaking filler packaging agent prepared by the preparation method of Example 1.

[0064] Comparative Example 1 of the present invention is: The only difference between Comparative Example 1 and Example 1 is that no chain transfer agent is added in step A2, and cationic polyester polyacrylamide emulsion E6 and papermaking filler packaging agent F6 are obtained.

[0065] Comparative Example 2 of the present invention is: The only difference between Comparative Example 2 and Example 1 is that the alkenyl cationic polyester is replaced by an equimolar amount of acryloyloxypropyltrimethylammonium chloride to obtain cationic polyacrylamide emulsion E7 and papermaking filler packaging agent F7.

[0066] Example 7 of the present invention is: Use of a papermaking filler encapsulating agent in preparing high-ash paper products, comprising the following steps: Step 1: Disperse or dissolve the cationic polyester polyacrylamide emulsion and the high molecular weight water-soluble polymer in deionized water to the corresponding concentrations. The specific operation is described as follows: Cationic polyester polyacrylamide emulsions E1 to E6, cationic polyacrylamide emulsion E7 and Will calcium carbonate synergist SF1010 were diluted with deionized water to a concentration of 2 wt% aqueous dispersion; The high molecular weight water-soluble polymer was dissolved in deionized water to form an aqueous solution of appropriate concentration for ease of use, depending on the type and weight of the high molecular weight water-soluble polymer used in Examples 1-5 and Comparative Examples 1-2. The concentrations of the aqueous solutions of the high molecular weight water-soluble polymer used in Examples 1-5 were 2 wt % cationic starch aqueous solution, 4 wt % cationic polyacrylamide aqueous solution, 0.34 wt % acrylamide aqueous solution, 2.67 wt % cationic guar gum aqueous solution, and 2 wt % guar gum aqueous solution, respectively, to prepare binary packaging agents F1-F7 for papermaking fillers. The pulp is diluted with deionized water to 1 wt% to prepare a pulp suspension; the calcium carbonate solution is a 15 wt% mixed water suspension of light calcium carbonate and heavy calcium carbonate (the ratio of light calcium carbonate to heavy calcium carbonate is 1:1).

[0067] Step 2: Take 34.66g of calcium carbonate suspension, add 1.5g of 2wt% aqueous solution of E1-E7 and Will calcium carbonate synergist SF1010 to the calcium carbonate solution, stir for 2 minutes, then add 2g of the corresponding high molecular weight water-soluble polymer aqueous solution of Examples 1-5 and Comparative Examples 1-2, continue stirring for 1 minute to obtain a coated calcium carbonate suspension, add the obtained calcium carbonate suspension to 1000g of pulp suspension, and stir at high speed for 5 minutes to obtain a uniform filler fiber mixed slurry. Take 180g of the obtained mixed slurry and add it to a sheet machine with 5.5L of water in advance, stir with air for 10s, and quickly drain to form round paper pieces; the obtained round paper pieces are dried at 105°C, taken out and equilibrated under conditions of 25±2°C and 50±5% humidity to obtain paper sheet samples.

[0068] test: 1. Each paper sample was tested 5 times in parallel and the average value was taken. The interlayer bonding strength and tensile strength were tested at different positions of the same paper. The test results are shown in Table 1. The blank sample was added with only the same amount of cationic starch solution as in Example 1.

[0069] 2. After diluting a 15wt% light calcium carbonate aqueous suspension to 0.4wt%, take 1kg of each suspension and add 15g of E1-E7 and an aqueous solution of Will calcium carbonate synergist SF1010. Stir for 2 minutes, then add 20g of the corresponding high molecular weight water-soluble polymer aqueous solution. After stirring for 1 minute, the particle size of the encapsulated sodium carbonate is measured using a laser particle size analyzer. Vigorous stirring is required during the laser particle size analyzer test to ensure uniform distribution of the sample dilution. To verify the shear resistance of the additives, the static particle size distribution of samples SF1010, F1, and F7 was tested under static conditions. These samples are designated SF1010-2, F1-2, and F7-2, respectively. The test results are shown in Table 2. A blank sample was supplemented with the same amount of cationic starch as the other samples.

[0070] Table 1

[0071] As shown in Table 1, the blank sample has a significantly lower grammage and ash content than the other samples. F7 shows a slight increase in grammage and a moderate increase in ash content, indicating that the addition of F7 improves calcium carbonate retention. F1-F5 and Will SF1010 have similar grammages, with the ash content of F1-F5 increasing by approximately two points compared to SF1010, all showing significant improvements compared to the blank. F6, on the other hand, shows a significant increase in grammage, attributed to its higher molecular weight and excellent calcium carbonate retention. Table 2 also demonstrates that F6's larger particle size for calcium carbonate encapsulation increases paper product heterogeneity, resulting in no improvement in interlaminar bond strength and tensile strength compared to the blank, with significantly greater variance than the other samples. Will SF1010 shows a significant increase in ash content compared to the blank, as well as a modest improvement in tensile strength and interlaminar bond strength. However, all other properties are slightly inferior to those of F1-F5, with slightly greater variance in interlaminar bond strength and tensile strength. Interlayer bond strength characterizes the interfiber interaction, while tensile strength characterizes the tear resistance of paper products. Both are related to the interfiber bond strength. Theoretically, as the amount of filler in a paper product increases, both interlayer bond strength and tensile strength decrease. However, the various samples tested in this paper exhibited good interlayer bond strength and tensile strength, demonstrating that the addition of the binary encapsulation additive not only increases the ash content of the paper but also significantly improves its quality.

[0072] Table 2

[0073] As can be seen from Table 2, the blank sample calcium carbonate coating particle size is lower than Will SF1010 and F1~F6 described in the present invention, and is equivalent to F7. This shows that the samples F1~F5 of the present invention have obvious coating effects. At the same time, from the comparison results of SF1010 and SF1010-2, F1 and F1-2, and F7 and F7-2, it can be seen that the coating particle sizes of SF1010 and F1 in the shear state are only slightly smaller than those of SF1010-2 and F1-2 in the static state, respectively, and both have good coating effects, indicating that SF1010 and F1 have good shear resistance, but it is obvious that the coating ability of SF1010 is slightly worse than that of samples F1-F5 described in the present invention, which is consistent with the results of paper weight and ash content in Table 1; while F7 has a good coating effect in the static state, is very easy to disperse in the shear state, and the final particle size distribution is close to that of the blank sample, indicating that F7 has weak shear resistance.

[0074] In summary, the papermaking filler wrapping agent of the present invention has a good wrapping effect on calcium carbonate. While increasing the ash content of the finished paper, it not only does not reduce the interlayer bonding and tensile strength of the paper product, but even improves them.

[0075] In summary, the papermaking filler encapsulating agent provided by the present invention, and its preparation method and application, have the following advantages: 1. The papermaking filler wrapping agent includes cationic polyester polyacrylamide emulsion, which can aggregate the filler, firmly adsorb the filler, resist the deagglomeration effect of mechanical shearing, and stabilize the wrapping effect of the polymer on the filler.

[0076] 2. Cationic polyester polyacrylamide emulsion and high molecular weight water-soluble polymer form a binary encapsulation additive system, which improves the filler retention rate, paper uniformity and paper strength.

[0077] 3. The preparation method of the present invention is applicable to most papermaking equipment.

[0078] 4. When preparing cationic polyester polyacrylamide emulsion, a special chain transfer agent is used to control the size of the wrapped filler while ensuring the filler retention rate, thereby increasing the interlayer bonding strength and tensile strength of the paper product without reducing it while increasing the filler ratio.

[0079] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the description of the present invention, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A papermaking filler wrapping agent, characterized in that: It includes cationic polyester polyacrylamide emulsion and high molecular weight water-soluble polymer.

2. The method for preparing the papermaking filler packaging agent according to claim 1, wherein The cationic polyester polyacrylamide emulsion is prepared by reacting acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt and alkenyl cationic polyester.

3. The method for preparing the papermaking filler wrapping agent according to claim 2, wherein: The preparation method of the cationic polyester polyacrylamide emulsion comprises the following steps: S1: dissolving acrylamide, hydroxy acrylate, alkenyl quaternary ammonium salt, alkenyl cationic polyester and chain transfer agent in deionized water to prepare an aqueous phase; dissolving an emulsifier in a solvent to prepare an oil phase; S2. The oil phase and the water phase are mixed and emulsified and reacted in sequence to obtain a cationic polyester polyacrylamide emulsion.

4. The method for preparing the papermaking filler wrapping agent according to claim 2, wherein: The hydroxy acrylate includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and hydroxybutyl methacrylate.

5. The method for preparing the papermaking filler wrapping agent according to claim 2, wherein: The alkenyl quaternary ammonium salt includes at least one of acryloyloxypropyl trimethyl ammonium halide, methacryloyloxypropyl trimethyl ammonium halide and allyl trimethyl ammonium halide.

6. The method for preparing the papermaking filler wrapping agent according to claim 2, wherein: The structural formula of the alkenyl cationic polyester is formula (1): Formula (1); Wherein R1 is a straight-chain alkyl group having 1 to 18 carbon atoms, R2 is a straight-chain alkyl group having 1 to 4 carbon atoms, R3 and R4 are segments of lactone ring-opening polymerization, and the number of repeating units thereof is m and n, respectively, wherein m and n are natural numbers and 8≤m+n≤50; R5 is methylene or 4-methylene-phenyl, and X and Y are halogen atoms.

7. The method for preparing the papermaking filler wrapping agent according to claim 2, wherein: The preparation method of the alkenyl cationic polyester comprises the following steps: adding alkenyl halide, base and dimethyl carbonate into the cationic polyester to carry out reaction to obtain the alkenyl cationic polyester.

8. The method for preparing the papermaking filler packaging agent according to claim 7, wherein: The preparation method of the cationic polyester comprises the following steps: mixing N-alkyldiethanolamine, lactone and a catalyst for reaction, adding 2,3-epoxypropyltrialkylammonium halide, boron trifluoride etherate and dimethyl carbonate and continuing the reaction to obtain the cationic polyester.

9. The method for preparing the papermaking filler wrapping agent according to claim 8, wherein: The alkyl group of the N-alkyldiethanolamine is a straight-chain alkyl group having 1 to 18 carbon atoms.

10. Use of the papermaking filler encapsulating agent according to claim 1 in the preparation of high-ash paper products.

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