Paper reinforcing agent and preparation method thereof

Abstract

The invention relates to the technical field of papermaking additives, in particular to a paper reinforcing agent and a preparation method thereof.The preparation method comprises the following steps that S1, a cationic polymer is subjected to alkali treatment, guar gum is added in a stirring state for a reaction, and the mass ratio of the cationic polymer to the guar gum is (2.5-7.5): (0.5-1.5); s2, adding an amphoteric polyacrylamide dry strength agent into the solution after the reaction in the S1, heating to 70 DEG C, and adding a modifier to react to generate a modified polymer N; s3, after the polymer N is diluted, a glyoxal modified polyacrylamide dry strength agent with the same mass ratio is added, and a paper reinforcing agent solution is obtained after mixing reaction. Compared with the simple compounding of any one or more of a traditional amphoteric PAM dry strength agent, a starch reinforcing agent, a guar gum reinforcing agent and a glyoxal modified polyacrylamide dry strength agent, the paper reinforcing agent disclosed by the invention has more efficient reinforcing performance in the production and use of packaging paper; compared with a traditional amphoteric PAM dry strength agent, the amphoteric PAM dry strength agent has more excellent water filtering performance.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking additives, and in particular to a paper strengthening agent and a preparation method thereof. Background Art

[0002] Paper dry strength agents, also known as dry strength agents, refer to a class of water-soluble polymers that can form hydroxyl bonds with the fiber surface. Their main function is to enhance the internal bonding between fibers, thereby improving the physical strength indicators of paper such as tensile strength, bursting strength, folding resistance and stiffness. Common dry strength agents include starch-modified, polyacrylamide, glyoxal-modified polyacrylamide, etc. Most of these dry strength agents are hydrophilic polymers. They are dispersed between fibers to increase the number of bonds between fibers, thereby achieving the purpose of improving paper strength.

[0003] Starch-modified dry strength agents have been widely used in the papermaking industry due to their wide range of raw material sources and affordable prices. Their molecular structure is similar to that of fiber in papermaking fiber raw materials, and they have good compatibility and are easy to combine with fibers, thereby significantly improving the physical properties of paper such as tensile strength, bursting strength and tear resistance. They are also cheaper than synthetic dry strength agents.

[0004] With the further iteration of manufacturing technology, guar gum products, which were once relegated to the second line due to high cost issues, have begun to enter the papermaking arena. Guar gum, a raw material, has a molecular structure similar to cellulose and is easier to absorb fibers than starch, which can significantly improve the strength of paper sheets. It is also helpful for paper water resistance, improving uniformity, and reducing gray spots on paper sheets. It is used in special papers such as cigarette paper and drawing paper.

[0005] Polyacrylamide dry strength agents have won the favor of the market due to their simple manufacturing process, moderate price and simple use conditions. Their long molecular chain can form hydrogen bonds with fibers, significantly improving the dry strength of paper. At the same time, polyacrylamide dry strength agents also have retention and filtration effects, which can improve the retention rate of fibers and fillers and reduce raw material loss.

[0006] Glyoxal-modified polyacrylamide dry strength agents combine the advantages of glyoxal and polyacrylamide, forming a strong chemical bond with the fibers. They have excellent reinforcement effects and can synergize with traditional polyacrylamide dry strength agents to significantly improve the dry and wet strength of paper.

[0007] However, in actual applications, starch-based dry strength agents still have a significant gap in strength improvement compared with polyacrylamide-based dry strength agents. They are prone to corruption during high temperatures in summer. Large-scale use may not only lead to difficulties in water filtration and affect production efficiency, but is also extremely unfavorable for COD control in water treatment. Therefore, papermaking companies are working hard to reduce the proportion of such raw materials used.

[0008] Although raw guar gum is superior to starch-based dry strength agents in improving strength, its swelling properties lead to high viscosity of the prepared solution and poor fluidity, which affects on-site addition. It also has a significant impact on the water filtration performance of the paper sheet after addition. Therefore, raw guar gum is generally rarely used directly in the production of packaging paper and cultural paper to improve paper strength. It is only added to some special-purpose paper types such as cigarette paper and drawing paper.

[0009] Although polyacrylamide dry strength agents have better reinforcing performance than starch and guar gum dry strength agents, their molecular weight control and formula adjustment have a significant impact on the paper strengthening effect, and need to be matched according to the actual paper machine system, and their universality is not good. This type of dry strength agent has a high cost-effectiveness when used at low dosages, but large-scale use not only has limited strength improvement, but also will cause many problems such as confusion of anions and cations in the paper machine system, increased system foam, and difficulty in water filtration that affects production.

[0010] Glyoxal-modified polyacrylamide dry strength agent is less cost-effective than polyacrylamide dry strength agent, so it is rarely used alone as a dry strength agent in actual production. It is generally used in combination with traditional polyacrylamide dry strength agent as a synergist to further improve the strength of paper and is used to produce some high-grade paper grades with high strength requirements. The production process of this type of dry strength agent is relatively complicated, the product has a short shelf life, is inconvenient to store and transport, and has a high cost, so it has not been widely used.

[0011] With the advancement of cost reduction and efficiency improvement in enterprises, strict control of raw material costs and people's demand for higher quality paper grades, enterprises are in urgent need of seeking a more efficient paper enhancement solution to further improve the dry strength of paper. Summary of the invention

[0012] In view of this, the purpose of the present invention is to provide a paper strengthening agent and a preparation method thereof, which combines the advantages of guar gum, amphoteric polyacrylamide dry strength agent, and glyoxal-modified polyacrylamide dry strength agent, and adopts a specific process reaction to synthesize a new type of polymer, which has more efficient strengthening performance and water filtration performance.

[0013] Based on the above purpose, the present invention provides a method for preparing a paper strengthening agent, comprising the following steps:

[0014] S1, treating the cationic polymer with alkali, and then adding guar gum to react under stirring, wherein the mass ratio of the cationic polymer to the guar gum is 2.5-7.5:0.5-1.5;

[0015] S2, add amphoteric polyacrylamide dry strength agent to the solution after reaction in S1, raise the temperature to 70°C, add modifier to react and generate modified polymer N;

[0016] S3. After diluting the polymer N, add glyoxal-modified polyacrylamide dry strength agent in an equal mass ratio, and obtain a paper strengthening agent solution after mixing and reaction.

[0017] Optionally, the cationic polymer includes one or a mixture of two or more of polyhydroxypropyl dimethyl ammonium chloride, a copolymer of acrylamide and dimethyl diallyl ammonium chloride, polydichloroethyl ether tetramethylethylenediamine, and polydimethyl diallyl ammonium chloride.

[0018] Preferably, the guar gum in S1 has a molecular weight of 1-2 million and a protein content of less than or equal to 4.5%; the molecular weight of the polyhydroxypropyl dimethyl ammonium chloride is 25000-40000 and the charge density is 6.9-7 mmol / g; the molecular weight of the acrylamide and dimethyl diallyl ammonium chloride copolymer is 80000-150000, and the molecular weight of the polydimethyl diallyl ammonium chloride is 50000-100000.

[0019] Optionally, the molecular weight of the amphoteric polyacrylamide dry strength agent is 200,000-500,000, and the amphoteric polyacrylamide dry strength agent added in S2 is an amphoteric polyacrylamide dry strength agent solution with a mass fraction of 15-20%.

[0020] Preferably, the mass ratio of the cationic polymer to the 20% amphoteric polyacrylamide dry strength agent solution is 5-10:20-30.

[0021] Preferably, the modifier includes modifier A and / or modifier B, the mass ratio of modifier A to modifier B is 0.5-2:0.5-2.5, modifier A includes any one or a mixture of two or more of 2,3-epoxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyldodecyldimethylammonium chloride, propylene oxide, epichlorohydrin, and ethylene oxide; modifier B includes any one or a mixture of two or more of 3-chloro-2-hydroxypropyl sodium sulfonate, chloroacetic acid, and sodium chloroacetate.

[0022] Preferably, the mass ratio of the modifier A to the modifier B is 1:2.

[0023] Preferably, the modifier added to S2 is a 25% by mass modifier A solution and a 25% by mass modifier B solution, and the mass ratio of the 20% amphoteric polyacrylamide dry strength agent solution to the modifier A solution and the modifier B solution is 20-30:0.5-2:0.5-2.5.

[0024] Optionally, the glyoxal-modified polyacrylamide is a copolymer of glyoxal-crosslinked acrylamide and a cationic monomer, with a weight average molecular weight of 10-300 W Daltons, a ratio of acrylamide units to cationic monomer units of 5:95-95:5, and a ratio of glyoxal units to acrylamide units of 60:40-5:95.

[0025] Optionally, the glyoxal-modified polyacrylamide added in S3 is a glyoxal-modified polyacrylamide solution with a mass fraction of 1-5%.

[0026] The invention also provides a paper reinforcing agent, which is prepared by adopting the preparation method of the paper reinforcing agent.

[0027] Beneficial effects of the present invention:

[0028] 1. The paper strengthening agent of the present invention has more efficient strengthening performance in packaging paper production compared with any one or a simple compound of conventional amphoteric PAM dry strength agents, starch strengthening agents, guar gum strengthening agents and glyoxal-modified polyacrylamide dry strength agents; and has better water filtration performance compared with conventional amphoteric PAM dry strength agents.

[0029] 2. The present invention adopts a special cationic polymer and adds a certain amount of alkali. After fully dissolved, a specific proportion of raw guar gum is slowly sprinkled into the polymer under stirring. Compared with direct dissolution in deionized water, the polymer has a higher dissolution concentration and a shorter dissolution time (the raw guar gum dissolves slowly in water and has a high solution viscosity. The solution has no fluidity when the concentration exceeds 2%). DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0031] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should have the common meanings understood by people with ordinary skills in the field to which the present invention belongs. "Include" or "comprising" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects.

[0032] The amphoteric polyacrylamide (PAM) polymers used in the following examples are all amphoteric dry strength agents produced by Fumiao Technology, mainly composed of a copolymer of acrylamide, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallyl ammonium chloride, and acrylic acid monomers, with a molecular weight of 500,000.

[0033] The polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) used in the following examples is a polymer product synthesized by Fumiao Technology with dimethylamine, epichlorohydrin and ethylenediamine as main raw materials, with a molecular weight of 25000-40000 and a charge density of 6.95 mmol / g.

[0034] Acrylamide and dimethyldiallyl ammonium chloride copolymer (PDM5025) produced by Fumiao Technology is mainly obtained by copolymerization of acrylamide and dimethyldiallyl ammonium chloride, with a cationic degree of 10% and a mass average molecular weight of 80,000-150,000.

[0035] Polydimethyldiallylammonium chloride (PDAC-1250) is a homopolymer of polydimethyldiallylammonium chloride produced by Fumiao Technology with a molecular weight of 50,000-100,000.

[0036] The raw material guar gum is provided by Jiangmen Xinhui District Hongzhou Chemical Ink Factory Co., Ltd., with a molecular weight of 1 million to 2 million and a protein content of less than or equal to 4.5%.

[0037] Glyoxal-modified polyacrylamide is a copolymer of glyoxal-crosslinked acrylamide and cationic monomers, with a weight average molecular weight of 10-300 W Daltons, a ratio of acrylamide units to cationic monomer units of 5 / 95-95 / 5, and a ratio of glyoxal units to acrylamide units of 60 / 40-5 / 95.

[0038] Example 1

[0039] Screening of cationic polymers

[0040] The cationic polymers in Table 1 below were respectively configured into a cationic polymer solution with a mass fraction of 50%, and after adding 0.5g of sodium hydroxide to fully dissolve, 0.5g of raw guar gum was slowly sprinkled in under stirring, reacted for 10 minutes, 30g of 20% amphoteric PAM dry strength agent was added, the temperature was raised to 70°C, and the reaction was performed for 2 hours to generate polymer product N. Polymer product N was diluted with deionized water to a polymer N solution with a mass fraction of 1%, and mixed with 1% glyoxal-modified polyacrylamide in an equal mass ratio, and reacted for 2 minutes to obtain the final enhancer solution. The following evaluation method 1 was then used to evaluate the application of the enhancement effect and water filtration effect, and the test results are shown in Table 1.

[0041] Table 1 Performance test results of various cationic polymers at different addition amounts

[0042]

[0043] The test results in Table 1 above show that a certain proportion of PA-8050, PDM5025, and PDAC-1250 as special cationic polymers can promote the enhancement effect, but a large amount of PDM5025 and PDAC-1250 have side effects on water filtration. PA-8050 is the most preferred.

[0044] Example 2

[0045] Screening of the amount of PA-8050 and amphoteric PAM dry strength agent added

[0046] After adding 0.5g of sodium hydroxide to 10-20g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, slowly sprinkle 0.5g of raw guar gum under stirring, react for 10min, add 20-30g of 20% amphoteric PAM dry strength agent, heat to 70℃, react for 2 hours, and generate polymer product N. Polymer product N is diluted with deionized water to a polymer N solution with a mass fraction of 1%, mixed with 1% glyoxal-modified polyacrylamide in an equal mass ratio, reacted for 2min, and the final enhancer solution is obtained. Then, the following evaluation method 1 is used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 2 below.

[0047] Table 2 Performance test results of PA-8050 and amphoteric PAM dry strength agent at different addition amounts

[0048]

[0049] The results in Table 2 above show that the addition ratio of PA-8050 to 20% amphoteric PAM dry strength agent affects the reinforcement and water drainage performance, and the preferred ratio is 10g PA-8050+30g 20% ​​amphoteric PAM dry strength agent.

[0050] Example 3

[0051] Screening of guar gum raw material addition amount

[0052] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, slowly sprinkle 0.5-1.5g of raw guar gum under stirring, react for 10min, add 30g of 20% amphoteric PAM dry strength agent, heat to 70℃, react for 2 hours, and generate polymer product N. Polymer product N is diluted with deionized water to a polymer N solution with a mass fraction of 1%, mixed with 1% glyoxal-modified polyacrylamide in an equal mass ratio, reacted for 2min, and the final enhancer solution is obtained. After that, the enhancement effect and water filtration effect are evaluated, and the test results are shown in Table 3.

[0053] Table 3 Performance test results of different addition amounts of guar gum raw materials

[0054]

[0055] The results in Table 3 above show that the increase in the proportion of raw guar gum added has a certain improvement in strength, but has a more obvious effect on water filtration performance. When the proportion exceeds a certain level, the water filtration performance of the slurry decreases significantly. Considering the strength and water filtration performance, the addition of guar gum raw material at a ratio of 1.0g is preferred.

[0056] Example 4

[0057] Screening of the amount of modifier A and modifier B added separately

[0058] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, 1.0g of raw guar gum was slowly sprinkled in under stirring, reacted for 10min, 30g of 20% amphoteric PAM dry strength agent was added, and after fully mixing, 0.5-2.0g of 25% 2,3-epoxypropyltrimethylammonium chloride or 25% 3-chloro-2-hydroxypropyl sulfonate sodium was slowly dripped in under stirring, and the temperature was raised to 70°C, and reacted for 2 hours to generate polymer product N. Polymer product N was diluted with deionized water to a polymer N solution with a mass fraction of 1%, and mixed with 1% glyoxal-modified polyacrylamide in an equal mass ratio, and reacted for 2min to obtain the final enhancer solution. Then, the following evaluation method 1 was used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 4 below.

[0059] Table 4 Performance test results of modifier A and modifier B at various addition amounts

[0060]

[0061]

[0062] The results in Table 4 above show that at the same addition amount, the effect of modifier B is better than that of modifier A, and adding more modifier A has a counter-effect on both the enhancement effect and the water filtration effect.

[0063] Example 5

[0064] Screening of combined addition amount of modifier A and modifier B

[0065] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, 1.0g of raw guar gum was slowly sprinkled in under stirring, reacted for 10min, 30g of 20% amphoteric PAM dry strength agent was added, and after fully mixing, 0.5-2.0g of 25% sodium 3-chloro-2-hydroxypropyl sulfonate and 0.5-2.0g of 25% 2,3-epoxypropyl trimethyl ammonium chloride were slowly dripped in under stirring, and the temperature was raised to 70°C, and reacted for 2 hours to generate polymer product N. Polymer product N was diluted with deionized water to a polymer N solution with a mass fraction of 1%, and mixed with 1% glyoxal-modified polyacrylamide in an equal mass ratio, reacted for 2min, and the final enhancer solution was obtained. Then, the following evaluation method 1 was used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 5.

[0066] Table 5 Performance test results of modifier A and modifier B combined addition amount

[0067]

[0068]

[0069] The results in Table 5 above show that there is a synergistic effect when modifier A and modifier B are added in a specific ratio, preferably 1g modifier A+2g modifier B.

[0070] Example 6

[0071] Screening of Concentration of Glyoxal-modified Polyacrylamide

[0072] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, 1.0g of raw guar gum was slowly sprinkled in under stirring, reacted for 10min, 30g of 20% amphoteric PAM dry strength agent was added, and after fully mixing, 2.0g of 25% sodium 3-chloro-2-hydroxypropyl sulfonate and 1.0g of 25% 2,3-epoxypropyl trimethyl ammonium chloride were slowly dripped in under stirring, and the temperature was raised to 70°C, and reacted for 2 hours to generate polymer product N. Polymer product N was diluted with deionized water to a polymer N solution with a mass fraction of 1%, and mixed with 0.5-5% glyoxal-modified polyacrylamide in an equal mass ratio, reacted for 2min, and the final enhancer solution was obtained. Then, the following evaluation method 1 was used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 6 below.

[0073] Table 6 Performance test results of glyoxal-modified polyacrylamide at different concentrations

[0074]

[0075] The results in Table 6 above show that the reaction concentration of glyoxal-modified polyacrylamide has a significant effect on the final product state and application performance. When the concentration is higher than 1%, the solution stability is significantly reduced, which is mainly reflected in the turbidity of the solution and even the formation of flocculent precipitation, a sudden drop in viscosity, etc., and the enhanced water filtration performance is significantly reduced.

[0076] Example 7

[0077] Selection of mass ratio of glyoxal-modified polyacrylamide to polymer product N

[0078] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution and fully dissolving it, 1.0g of raw guar gum was slowly sprinkled in under stirring, reacted for 10min, 30g of 20% amphoteric PAM dry strength agent was added, and after fully mixing, 2.0g of 25% sodium 3-chloro-2-hydroxypropyl sulfonate and 1.0g of 25% 2,3-epoxypropyl trimethyl ammonium chloride were slowly dripped in under stirring, and the temperature was raised to 70°C, and reacted for 2 hours to generate polymer product N. Polymer product N was diluted with deionized water to a polymer N solution with a mass fraction of 1%, and mixed with 0.5-3 times the mass ratio of 1% glyoxal-modified polyacrylamide, reacted for 2min, and the final enhancer solution was obtained. Then, the following evaluation method 1 was used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 7.

[0079] Table 7 Performance test results of glyoxal-modified polyacrylamide and polymer product N at different mass ratios

[0080]

[0081] The results in Table 7 above show that as the mass ratio of glyoxal-modified polyacrylamide in the formula increases, the water filtration performance is significantly improved, but the strength decreases slightly; while as the mass ratio of glyoxal-modified polyacrylamide in the formula decreases, the strength recovers slightly but the water filtration performance decreases significantly; the optimal combination for balancing the enhanced performance and the water filtration performance is 1:1.

[0082] Example 8

[0083] After adding 0.5g of sodium hydroxide to 10g of 50% polyhydroxypropyl dimethyl ammonium chloride (hereinafter referred to as PA-8050) solution to fully dissolve, 1.0g of raw guar gum was slowly sprinkled in under stirring, reacted for 10min, 30g of 20% amphoteric PAM dry strength agent was added, and after fully mixing, 2.0g of 25% sodium 3-chloro-2-hydroxypropyl sulfonate and 1.0g of 25% 2,3-epoxypropyl trimethyl ammonium chloride were slowly dripped in under stirring, and the temperature was raised to 70°C, reacted for 2 hours, and polymer product N was generated. Then, the following evaluation method 2 was used to evaluate the application of enhancement effect and water filtration effect, and the test results are shown in Table 8 below.

[0084] Table 8 Comparison of the preferred final solution of Example 7 and Example 8 using two evaluation methods

[0085]

[0086] The results in Table 8 above show that the enhancer prepared in Example 7 is relatively better.

[0087] Comparative Example

[0088] The raw materials guar gum, amphoteric PAM dry strength agent, glyoxal-modified polyacrylamide, and polyhydroxypropyltrimethylammonium chloride were diluted with deionized water to a concentration of 1% as the final solution. Then, the following evaluation method 1 was used to evaluate the application of the enhancement effect and the water filtration effect. The test results are shown in Table 9 below.

[0089] Table 9 Comparison results of four single raw materials and Example 7 at the same dry addition amount

[0090]

[0091] The results in Table 9 above show that, when 4.0 kg of dry agent is added per ton of absolute dry slurry, the application effect of the final enhancer solution prepared by the present invention is significantly better than that of a single addition method of the four main raw materials at the same dry addition amount.

[0092] The laboratory evaluation method for evaluating the enhancement effect and water filtration effect of paper dry strength agents is as follows:

[0093] Preparation of hand-sheet paper: Take the thick stock without dry strength agent and bottom white water from the mixed pulp pool of the on-site coated white paper machine bottom layer (packaging paper pulp system, 100% OCC pulp); 2Weigh the concentrated pulp into a beaker, add 4 kg (dry weight) of the final solution prepared in Examples 1-7 and the comparative example per ton of pulp, stir for 30 seconds, dilute with white water to 1% screen concentration, add 0.2 kg of Fumiao Technology retention aid VD8240 solution per ton of paper, continue stirring for 60 seconds, transfer to a sheet making machine to make wet paper sheets, press at 106 kPa for 30 seconds and 501 kPa for 20 seconds, then the paper sheets are formed, take out and transfer to a 95°C paper sample dryer for drying for 5-10 minutes, and keep the temperature and humidity constant for 24 hours.

[0094] Results test:

[0095] The paper tear resistance index is tested according to GBT 454-2002 Determination of paper tear resistance.

[0096] The test of paper tensile index adopts GB / T 12914-2018 Determination of tensile strength of paper and paperboard Constant rate tensile method (20mm / min)

[0097] Test of water filtration performance of slurry: According to "GB3332 Determination of slurry beating degree" test the beating degree of the slurry after reaction in ①. The lower the beating degree, the better the water filtration effect.

[0098] Laboratory evaluation method for evaluating the enhancement effect and water filtration effect of paper dry strength agent 2 is as follows:

[0099] Preparation of hand-sheet paper: Take the thick stock without dry strength agent and bottom white water from the mixed pulp pool of the on-site coated white paper machine bottom layer (packaging paper pulp system, 100% OCC pulp); 2 Weigh the concentrated pulp into a beaker, add 2 kg (dry weight) of the polymer product N prepared in Example 7 per ton of pulp, stir for 15 seconds, add 2 kg (dry weight) of 1% glyoxal-modified polyacrylamide solution per ton of pulp, stir for 15 seconds, dilute with white water to 1% online concentration, add 0.2 kg of Fumiao Technology retention aid VD8240 solution per ton of paper, continue stirring for 60 seconds, transfer to a sheet making machine to make wet paper sheets, press at 106 kPa for 30 seconds and 501 kPa for 20 seconds, then the paper sheets are formed, take out and transfer to a 95°C paper sample dryer for drying for 5-10 minutes, and keep the temperature and humidity constant for 24 hours.

[0100] Results test:

[0101] The paper tear resistance index is tested according to GBT 454-2002 Determination of paper tear resistance.

[0102] The test of paper tensile index adopts GB / T 12914-2018 Determination of tensile strength of paper and paperboard Constant rate tensile method (20mm / min)

[0103] Test of water filtration performance of slurry: According to "GB3332 Determination of slurry beating degree" test the beating degree of the slurry after reaction in ①. The lower the beating degree, the better the water filtration effect.

[0104] Those skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a paper strengthening agent, characterized in that: The steps include: S1, treating the cationic polymer with alkali, and then adding guar gum to react under stirring, wherein the mass ratio of the cationic polymer to the guar gum is 2.5-7.5:0.5-1.5; S2, add amphoteric polyacrylamide dry strength agent to the solution after reaction in S1, raise the temperature to 70°C, add modifier to react and generate modified polymer N; S3. After diluting the polymer N, add glyoxal-modified polyacrylamide dry strength agent in an equal mass ratio, and obtain a paper strengthening agent solution after mixing and reaction.

2. The method for preparing the paper strengthening agent according to claim 1, characterized in that: The cationic polymer includes one or a mixture of two or more of polyhydroxypropyl dimethyl ammonium chloride, a copolymer of acrylamide and dimethyl diallyl ammonium chloride, polydichloroethyl ether tetramethylethylenediamine, and polydimethyl diallyl ammonium chloride.

3. The method for preparing the paper strengthening agent according to claim 2, characterized in that: The guar gum described in S1 has a molecular weight of 1-2 million and a protein content of less than or equal to 4.5%. The molecular weight of the polyhydroxypropyl dimethyl ammonium chloride is 25000-40000 and the charge density is 6.9-7 mmol / g. The molecular weight of the acrylamide and dimethyl diallyl ammonium chloride copolymer is 80000-150000, and the molecular weight of the polydimethyl diallyl ammonium chloride is 50000-100000.

4. The method for preparing the paper strengthening agent according to claim 1, characterized in that: The molecular weight of the amphoteric polyacrylamide dry strength agent is 200000-500000, and the amphoteric polyacrylamide dry strength agent added in S2 is an amphoteric polyacrylamide dry strength agent solution with a mass fraction of 15-20%.

5. The method for preparing the paper strengthening agent according to claim 4, characterized in that: The mass ratio of the cationic polymer to the 20% amphoteric polyacrylamide dry strength agent solution is 5-10:20-30.

6. The method for preparing the paper strengthening agent according to claim 5, characterized in that: The modifier includes modifier A and / or modifier B, the mass ratio of modifier A to modifier B is 0.5-2:0.5-2.5, modifier A includes any one of 2,3-epoxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyldodecyldimethylammonium chloride, propylene oxide, epichlorohydrin, and ethylene oxide, or a mixture of two or more thereof; modifier B includes any one of 3-chloro-2-hydroxypropane sodium sulfonate, chloroacetic acid, and sodium chloroacetate, or a mixture of two or more thereof.

7. The method for preparing the paper strengthening agent according to claim 6, characterized in that: The modifier added to S2 is a 25% modifier A solution and a 25% modifier B solution. The mass ratio of the 20% amphoteric polyacrylamide dry strength agent solution to the modifier A solution and the modifier B solution is 20-30:0.5-2:0.5-2.

5.

8. The method for preparing the paper strengthening agent according to claim 1, characterized in that: The glyoxal-modified polyacrylamide is a copolymer of glyoxal-crosslinked acrylamide and a cationic monomer, with a weight average molecular weight of 10-300 W Daltons, a ratio of acrylamide units to cationic monomer units of 5:95-95:5, and a ratio of glyoxal units to acrylamide units of 60:40-5:

95.

9. The method for preparing the paper strengthening agent according to claim 8, characterized in that: The glyoxal-modified polyacrylamide added to S3 is a glyoxal-modified polyacrylamide solution with a mass fraction of 1-5%.

10. A paper strengthening agent, characterized in that: The paper strengthening agent is prepared by the preparation method of the paper strengthening agent according to any one of claims 1 to 9.

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