Micro-crosslinking amphoteric polyacrylamide aqueous solution dry strength agent and preparation method thereof

Abstract

The invention relates to the technical field of papermaking, in particular to a micro-crosslinking amphoteric polyacrylamide aqueous solution dry strength agent and a preparation method thereof. The preparation method of the micro-crosslinked amphoteric polyacrylamide aqueous solution dry strength agent provided by the embodiment of the invention comprises the following steps: S1, mixing water, acrylamide, a cationic functional monomer, an anionic functional monomer, a cationic oligomer and a crosslinking agent to obtain a pre-polymerized solution; s2, sequentially adding an oxidizing agent, an azo initiator and a chain regulator into the pre-polymerized solution in a nitrogen environment, and heating to 51-56 DEG C to initiate a polymerization reaction to obtain a polymerized solution; s3, adding an exchange increasing agent into the polymerization solution, raising the temperature to 87-93 DEG C, continuously reacting, and adding a reducing agent to stop the polymerization reaction after the preset viscosity is reached, so as to obtain a product solution. The embodiment of the invention provides a micro-crosslinking amphoteric polyacrylamide aqueous solution dry strength agent and a preparation method thereof. The performance of the dry strength agent is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of papermaking, in particular to a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent and a preparation method thereof. Background Art

[0002] The anions in the amphoteric polyacrylamide can remove other cations (such as Ca 2+ and Mg 2+ The anionic groups can repel other anions in the system, thus preventing their cationic groups from prematurely interacting with other materials in the system. When there are too many cationic additives in the system, which makes the fiber have a certain degree of cationic properties, these anionic groups can balance the cationic groups already adsorbed on the fiber, so that the cationic groups on the molecule are in closer contact with the anionic groups on the fiber. When the additive content in the system increases due to the recycling of fine components, the system charge balance established by the amphoteric polyacrylamide can enable the paper machine system to maintain good operating performance. The relative molecular weight range of amphoteric polyacrylamide is relatively wide, ranging from several thousand to tens of millions, and it can play a role in a variety of pulps.

[0003] However, in the papermaking process, the wet-end chemical conditions may be more complex, including high temperature, high shear force and high conductivity. Amphoteric polyacrylamide has poor stability and is prone to partial degradation. Especially when the white water is recycled in the system, the charge caused by anionic waste and other substances increases, thereby significantly increasing the amount of amphoteric polyacrylamide dry strength agent used and increasing the cost of use. Summary of the Invention

[0004] The embodiment of the present invention provides a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent and a preparation method thereof, which improves the performance of the dry strength agent.

[0005] In a first aspect, an embodiment of the present invention provides a method for preparing a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, comprising: S1, mixing water, acrylamide, cationic functional monomer, anionic functional monomer, cationic oligomer, and crosslinking agent to obtain a prepolymer solution; S2, adding an oxidant, an azo initiator, and a chain regulator to the prepolymerization solution in sequence under a nitrogen environment, raising the temperature to 51-56° C. to initiate a polymerization reaction, thereby obtaining a polymerization solution; S3, adding a crosslinking agent to the polymerization solution, and heating it to 87-93° C. to continue the reaction. After reaching a preset viscosity, a reducing agent is added to stop the polymerization reaction to obtain a product solution.

[0006] In one possible design, the cross-linking agent includes one or more combinations of aziridine and hexamethylene diisocyanate.

[0007] In a possible design, the amount of the cross-linking agent is 0.05% to 0.3% by mass of the prepolymer solution, preferably 0.08% to 0.14%.

[0008] In one possible design, the total weight of the acrylamide, the cationic functional monomer, the anionic functional monomer, and the cationic oligomer accounts for 13-18 wt %, preferably 14.5 wt %, of the prepolymerization solution.

[0009] In one possible design, the mass ratio of the acrylamide, the cationic functional monomer, the anionic functional monomer, and the cationic oligomer is (8~14):(0.8~4):(0.4~1.3):(0.2~1.0), preferably (10~12.5):(1.3~2.0):(0.6~0.9):(0.3~0.6).

[0010] In one possible design, the cationic functional monomer includes one or more combinations of diethylaminoethyl acrylate, diethylaminoethyl methacrylate, and N,N-diallylethanolamine; The anionic functional monomer includes one or more of 2-ethyl acrylic acid and butenedioic acid; The cationic oligomer includes one or more of polymethacrylamidopropyl dodecyldimethylammonium chloride, methacrylamidopropyl trimethylammonium chloride and polyacryloyloxyethyl dimethylbenzyl ammonium chloride; The cross-linking agent includes one or more of pentaerythritol triallyl ether and malondialdehyde; The oxidant comprises one or more of potassium persulfate and sodium persulfate; The azo initiator includes one or more of azobisisocyanovaleric acid and azobisisoheptonitrile; The chain regulator includes one or more of dodecyl mercaptan and sodium formate; The reducing agent includes one or more of potassium bisulfite, sodium metasulfite and ferrous sulfate.

[0011] In one possible design, the amount of the cross-linking agent is 0.008% to 0.03% of the mass of the pre-polymerization solution; The amount of the oxidant is 0.03% to 0.11% of the mass of the prepolymerization solution; The amount of the azo initiator is 0.005% to 0.016% of the mass of the prepolymerization solution; The amount of the chain regulator is 0.005% to 0.02% of the mass of the prepolymer solution; The amount of the reducing agent is 0.02% to 0.05% of the mass of the prepolymerization solution.

[0012] In a possible design, S1 further includes: adding a pH adjuster to the prepolymerization solution to adjust the pH value of the prepolymerization solution to 2-2.8.

[0013] In a possible design, the preset viscosity is 4000-11000 mPa·s.

[0014] In a second aspect, an embodiment of the present invention provides a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, which is prepared according to any of the above preparation methods.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention has a simple preparation process, short reaction time, easy control of the reaction process, low cost, high conversion rate, and high production efficiency, making it more suitable for industrial production. The method of the present invention can produce a novel slightly cross-linked amphoteric polyacrylamide aqueous solution with an effective content, moderate apparent viscosity, and significant enhancement of paper tensile strength. The present invention can produce an effective content of 13% to 18%, which is lower than the 15% to 20% effective content of conventional cationic polyacrylamide aqueous solutions and amphoteric polyacrylamide aqueous solutions used as papermaking dry strength agents on the market, and the cost is lower. The apparent viscosity is 4000 to 11000 mPa·s, which is lower than the 5000 mPa·s to 20000 mPa·s apparent viscosity of conventional cationic polyacrylamide aqueous solutions and amphoteric polyacrylamide aqueous solutions used as papermaking dry strength agents on the market, and the dispersion and dilution speed during use is faster.

[0016] (2) When the novel micro-crosslinked amphoteric polyacrylamide aqueous solution prepared by the present invention is used as a papermaking dry strength agent, the tensile strength of the paper is significantly improved, and the amount of papermaking dry strength agent used is reduced. According to on-site tensile strength test comparison, the amount of the novel micro-crosslinked amphoteric polyacrylamide aqueous solution prepared by the present invention when used as a papermaking dry strength agent is reduced by about 18-29% compared with the amount of conventional cationic polyacrylamide and amphoteric polyacrylamide, and the tensile strength is increased by about 21%, the efficiency of the on-site dilution equipment is increased by about 30%, and the energy consumption of the dilution equipment is reduced by about 26%. Compared with other conventional cationic polyacrylamide aqueous solutions and amphoteric polyacrylamide aqueous solutions, the novel micro-crosslinked amphoteric polyacrylamide aqueous solution of the present invention as a papermaking dry strength agent can effectively improve the tensile strength of paper, reduce the load of wastewater treatment in the papermaking process, and increase the number of times white water is recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 The present invention provides a flow chart of a method for preparing a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, comprising: S1, mixing water, acrylamide, cationic functional monomer, anionic functional monomer, cationic oligomer, and crosslinking agent to obtain a prepolymer solution; S2, adding an oxidant, an azo initiator, and a chain regulator to the prepolymerization solution in sequence under a nitrogen environment, raising the temperature to 51-56° C. to initiate a polymerization reaction, thereby obtaining a polymerization solution; S3, adding a crosslinking agent to the polymerization solution, and raising the temperature to 87-93°C, continuing the reaction, and after reaching the preset viscosity, adding a reducing agent to stop the polymerization reaction to obtain a product solution.

[0021] In this embodiment, first, cationic oligomers act as co-stabilizers, effectively controlling the viscosity and temperature of the aqueous solution polymerization reaction. Second, by employing a high-temperature initiation system (comprising an oxidant and an azo initiator) (51-56°C), the oxidant is used to initiate polymerization in the early stages of the reaction to synthesize the novel slightly cross-linked amphoteric polyacrylamide aqueous solution. The exothermic reaction allows the azo initiator to decompose and release free radicals, accelerating the reaction rate in the latter stages to ensure complete reaction. Third, the addition of a cross-linking enhancer restores the molecular structure of some cross-links destroyed by the high-temperature reaction to a spatial network, further stabilizing the polyacrylamide molecular structure, especially under high-temperature conditions, and enhancing its cross-linking effectiveness. The combined effects of these three factors increase the viscosity of the polymerization system. The reaction is terminated by adding a reducing agent in the later stages, ensuring that the novel slightly cross-linked amphoteric polyacrylamide aqueous solution can be synthesized using the present invention.

[0022] It should be noted that the crosslinking agent can also promote the grafting of free radicals in each functional monomer onto the main chain obtained by S2 polymerization, thereby increasing the density of active groups grafted on the polymer, thereby increasing the density of hydrogen bonds formed between the polymer and the fiber, and ultimately achieving a significant increase in tensile strength.

[0023] In some embodiments of the present invention, the cross-linking agent includes one or more combinations of aziridine and hexamethylene diisocyanate.

[0024] In this example, aziridine and hexamethylene diisocyanate were used as crosslinking agents, significantly improving the tensile strength of the resulting paper. It should be noted that while other esters and heterocyclic compounds can also enhance tensile strength to a certain extent, the aforementioned two substances provide the most significant improvement in paper tensile strength.

[0025] In some embodiments of the present invention, the amount of the cross-linking agent is 0.05% to 0.3% by weight of the prepolymer solution, preferably 0.08% to 0.14%.

[0026] In the present invention, the dosage of the cross-linking agent is preferably 0.08% to 0.14%. Too much or too little of the cross-linking agent will result in the apparent viscosity of the prepared novel slightly cross-linked amphoteric polyacrylamide aqueous solution being too high or too low, respectively.

[0027] In some embodiments of the present invention, the total weight of acrylamide, cationic functional monomer, anionic functional monomer and cationic oligomer accounts for 13-18 wt %, preferably 14.5 wt %, of the prepolymerization solution.

[0028] In the present invention, the conversion rate of each raw material can reach more than 99.5%, and the mass ratio of each functional monomer raw material to the prepolymer solution is the effective content. The present application can control the effective content by controlling the amount of each raw material, water and other additives. The effective content of the present application is controlled at 13~18wt%. The mass fraction of the additives added in the subsequent steps is extremely low. Therefore, the effective content of the final product is also basically in the range of 13~18wt%. The product within this effective content range can play a sufficient dry strength role. However, the effective content of the polyacrylamide dry strength agent obtained by the existing preparation method is too high, which is not conducive to the control of the reaction process, resulting in too fast reaction and high apparent viscosity. The product provided by the present application has a lower effective content than the existing dry strength agent and has better effect. In summary, the product of the present application saves costs and increases the effects of tensile strength and easy dilution.

[0029] In some embodiments of the present invention, the mass ratio of acrylamide, cationic functional monomer, anionic functional monomer, and cationic oligomer is (8-14): (0.8-4): (0.4-1.3): (0.2-1.0), preferably (10-12.5): (1.3-2.0): (0.6-0.9): (0.3-0.6).

[0030] In some embodiments of the present invention, the cationic functional monomer includes one or more combinations of diethylaminoethyl acrylate, diethylaminoethyl methacrylate, and N,N-diallylethanolamine; The anionic functional monomer includes one or more of 2-ethyl acrylic acid and butenedioic acid; The cationic oligomer includes one or more of polymethacrylamidopropyl dodecyldimethylammonium chloride, methacrylamidopropyl trimethylammonium chloride, and polyacryloyloxyethyl dimethylbenzyl ammonium chloride; The cross-linking agent includes one or more of pentaerythritol triallyl ether and malondialdehyde; The oxidizing agent includes one or more of potassium persulfate and sodium persulfate; Azo initiators include one or more of azobisisocyanovaleric acid and azobisisoheptonitrile; The chain regulator includes one or more of dodecyl mercaptan and sodium formate; The reducing agent includes one or more of potassium bisulfite, sodium metasulfite and ferrous sulfate.

[0031] In the present invention, the cationic oligomer copolymerizes with acrylamide, stabilizing the viscosity and temperature of the polymerization system. The cationic and anionic functional monomers copolymerize with acrylamide to produce a zwitterionic polyacrylamide with opposite charges and an overall positive charge. Excessive or insufficient amounts of anionic functional monomers can reduce fiber bonding.

[0032] In some embodiments of the present invention, the amount of the cross-linking agent is 0.008% to 0.03% of the mass of the prepolymer solution; The amount of oxidant used is 0.03%~0.11% of the mass of the prepolymerization solution; The dosage of azo initiator is 0.005%~0.016% of the mass of prepolymer solution; The amount of chain regulator used is 0.005%~0.02% of the mass of the prepolymer solution; The amount of reducing agent used is 0.02% to 0.05% of the mass of the prepolymerization solution.

[0033] In some embodiments of the present invention, S1 further includes: adding a pH adjuster to the prepolymerization solution to adjust the pH value of the prepolymerization solution to 2-2.8.

[0034] The pH adjuster includes one or more of sulfamic acid, hydrochloric acid, and acetic acid, preferably acetic acid. This is because hydrochloric acid is a strong acid, sulfamic acid is easily hydrolyzed, and acetic acid is an organic acid with a weaker acidity. This prevents rapid heat release during the pH adjustment process, thereby maintaining a stable system temperature.

[0035] In some embodiments of the present invention, the preset viscosity is 4000-11000 mPa·s.

[0036] According to some more specific embodiments, the preparation process of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution includes: S1, with deionized water, 8% to 14% of acrylamide, 0.8% to 1.4% of the mass of the prepolymerization solution of cationic functional monomer diethylaminoethyl methacrylate, 0.4% to 1.3% of the mass of the prepolymerization solution of anionic functional monomer butenedioic acid, 0.2% to 1.0% of the mass of the prepolymerization solution of cationic oligomer poly (methacrylamide propyl dodecyl dimethyl ammonium chloride), and 0.008% to 0.03% of the mass of the prepolymerization solution of a crosslinking agent pentaerythritol triallyl ether are thoroughly stirred and mixed to obtain a prepolymerization solution with a mass percentage content of 13% to 18% of the total reactants, and acetic acid is used to adjust the pH of the prepolymerization solution to 2.0-2.8; S2, transferring the obtained prepolymer solution into a glass reactor, inserting a digital thermometer, and introducing high-purity nitrogen into the reactor for 20-30 minutes, then heating the reactor to 51-56° C. in a water bath, and sequentially adding 0.03%-0.11% of the mass of the prepolymer solution of potassium persulfate as an oxidant, 0.005%-0.16% of the mass of the prepolymer solution of azobisisocyanovaleric acid as an azo initiator, and 0.005%-0.02% of the mass of the prepolymer solution of sodium formate as a chain regulator to the prepolymer solution to initiate a polymerization reaction; S3, adding 0.05% to 0.3% by weight of the prepolymer solution of hexamethylene diisocyanate as a crosslinking agent to continue the reaction at 87-93° C., and adding 0.02% to 0.05% by weight of the prepolymer solution of potassium bisulfite as a reducing agent when the solution viscosity reaches a specified range of 4000 to 11000 mPa·s to obtain the polyacrylamide aqueous solution.

[0037] The method of the present invention is a feasible method for producing a novel slightly cross-linked amphoteric polyacrylamide aqueous solution suitable for industrial production of a papermaking dry strength agent. The novel slightly cross-linked amphoteric polyacrylamide aqueous solution obtained by the present invention has a moderate effective content, high conversion rate, low monomer content, excellent solubility, high production efficiency, and low cost. Compared with other cationic polyacrylamides and amphoteric polyacrylamide-treated paper pulp, it can increase paper tensile strength, require less papermaking dry strength agent, and effectively reduce the wastewater treatment load during the papermaking process after pulp treatment.

[0038] It should be noted that the present invention has no special requirements for the addition of initiators. It is sufficient to add an oxidizing agent, an azo initiator, a chain regulator, and a reducing agent to the prepolymerization solution in sequence to initiate the polymerization reaction. That is, during the addition of these substances, as long as the previous substance is completely dissolved or dispersed in the solution, the subsequent substance can be added.

[0039] It should be noted that the mass of the prepolymer solution can be determined first according to the demand, and then the mass of each raw material can be determined based on the mass of the prepolymer solution.

[0040] The embodiment of the present invention provides a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, which is prepared according to any of the above preparation methods.

[0041] In order to more clearly illustrate the technical solutions and advantages of the present invention, several embodiments are described in detail below.

[0042] Experimental materials: Acrylamide (AM), cationic functional monomer (diethylaminoethyl methacrylate), anionic functional monomer (butenedioic acid), cationic oligomer (polymethacrylamidopropyl dodecyldimethylammonium chloride), crosslinking agent (pentaerythritol triallyl ether), acetic acid, oxidizing agent (potassium persulfate), azo initiator (azobisisocyanovaleric acid), chain regulator (sodium formate), crosslinking extender (hexamethylene diisocyanate), reducing agent (potassium bisulfite), deionized water.

[0043] Experimental instruments and equipment: High-purity nitrogen, electronic balance, precision pH meter, 1000mL glass reactor, digital thermometer, high-pressure nitrogen bottle, Brookfield viscometer, refrigerator, mechanical stirrer, magnetic stirrer, stopwatch, scientific calculator, glass rod, 250mL beaker, 500mL beaker, 10mL syringe, lifting platform, constant temperature water bath.

[0044] Test method: (a) Determination of apparent viscosity of aqueous solution: Preheat and calibrate the Brookfield viscometer. Set the test spindle type to LV-04 and the speed to 30 rpm. Install the test spindle correctly. Weigh approximately 200 g of the new slightly cross-linked amphoteric polyacrylamide aqueous solution into a 250 mL beaker and place it on a lifting platform. Adjust the height so that the liquid level submerges the spindle groove. Measure the apparent viscosity of the solution at a temperature of 23-25°C.

[0045] (b) Paper tensile strength determination A novel slightly cross-linked amphoteric polyacrylamide aqueous solution was used as a papermaking dry strength additive. A 0.15% (mass fraction) aqueous solution was prepared with water. During the papermaking process, a diluted solution of the aqueous solution was added to the mixed slurry. The tensile strength of the paper was measured after forming.

[0046] Use a standard paper cutter to cut the sample accurately.

[0047] Place the cut specimen flat on the test preparation table, push the specimen into the fixture with both hands, and level it so that the specimen is horizontal on the same plane. The pneumatic fixture will automatically clamp the specimen and perform automatic testing. When the test is completed, it will automatically reset, release the fixture, and place the next specimen until the test is completed.

[0048] The tensile strength data displayed on the reading interface is the tensile strength of the sample, in units of (N·m / g).

[0049] Example 1 (1) 12% of acrylamide by weight of the prepolymer solution, 0.8% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.4% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.2% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.008% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 13.5% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.0 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 20 minutes, and then the temperature was raised to 51° C. in a water bath. 0.05% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.012% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.02% of the mass of the prepolymer solution was used as a chain regulator. The polymerization reaction was initiated; (3) When the polymerization solution in step (2) reacts to 87° C., 0.25% of the mass of the prepolymerization solution is added as a crosslinking agent, hexamethylene diisocyanate, to continue the reaction. When the viscosity of the solution reaches the specified range of 8860 mPa·s, 0.03% of the mass of the prepolymerization solution is added as a reducing agent, potassium bisulfite, to obtain the polyacrylamide aqueous solution.

[0050] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0051] Example 2 (1) 12% of acrylamide by weight of the prepolymer solution, 1.0% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.7% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.5% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.013% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage of 14.5% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.8 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 30 minutes, and then the temperature was raised to 56° C. in a water bath. 0.1% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.008% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.01% of the mass of the prepolymer solution was used as a chain regulator. Sodium formate was added to the prepolymer solution in sequence to initiate the polymerization reaction; (3) The polymerization solution of step (2) is reacted to 93° C., and 0.25% of the mass of the prepolymerization solution of hexamethylene diisocyanate as a crosslinking agent is added to continue the reaction. When the viscosity of the solution reaches the specified range of 10030 mPa·s, 0.035% of the mass of the prepolymerization solution of potassium bisulfite as a reducing agent is added to obtain the polyacrylamide aqueous solution.

[0052] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0053] Example 3 (1) 11% of acrylamide by weight of the prepolymer solution, 1.2% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 1.0% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.8% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.018% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were fully stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 13.2% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.5 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 25 minutes, and then the temperature was raised to 53° C. in a water bath. 0.11% of the mass of the prepolymer solution as an oxidizing agent, 0.016% of the mass of the prepolymer solution as an azo initiator, azobisisocyanovaleric acid, and 0.005% of the mass of the prepolymer solution as a chain regulator, sodium formate, were added to the prepolymer solution in sequence to initiate a polymerization reaction; (3) The polymerization solution in step (2) is reacted to 90° C., and 0.15% of the mass of the prepolymerization solution as a crosslinking agent, hexamethylene diisocyanate, is added to continue the reaction. When the solution viscosity reaches the specified range of 10960 mPa·s, 0.05% of the mass of the prepolymerization solution as a reducing agent, potassium bisulfite, is added to obtain the polyacrylamide aqueous solution.

[0054] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0055] Example 4 (1) 10% of acrylamide by weight of the prepolymer solution, 1.4% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 1.3% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 1.0% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.025% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 14.8% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.7 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 26 minutes, and then the temperature was raised to 55° C. in a water bath. 0.06% of the mass of the prepolymer solution was added to the prepolymer solution as an oxidizing agent, potassium persulfate, 0.015% of the mass of the prepolymer solution was added to the prepolymer solution as an azo initiator, azobisisocyanovaleric acid, and 0.008% of the mass of the prepolymer solution was added to the prepolymer solution to initiate a polymerization reaction; (3) The polymerization solution of step (2) is reacted to 89° C., and 0.1% of the mass of the prepolymerization solution of hexamethylene diisocyanate as a crosslinking agent is added to continue the reaction. When the viscosity of the solution reaches the specified range of 9630 mPa·s, 0.04% of the mass of the prepolymerization solution of potassium bisulfite as a reducing agent is added to obtain the polyacrylamide aqueous solution.

[0056] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0057] Example 5 (1) 13% of acrylamide by weight of the prepolymer solution, 0.9% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.6% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.9% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.02% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage of 15.7% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.8 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 30 minutes, and then the temperature was raised to 56° C. in a water bath. 0.08% of the mass of the prepolymer solution was added to the prepolymer solution as an oxidizing agent, potassium persulfate, 0.01% of the mass of the prepolymer solution was added to the prepolymer solution as an azo initiator, azobisisocyanovaleric acid, and 0.018% of the mass of the prepolymer solution was added to the prepolymer solution to initiate a polymerization reaction; (3) The polymerization solution of step (2) is reacted to 93° C., and 0.3% of the mass of the prepolymerization solution of hexamethylene diisocyanate as a crosslinking agent is added to continue the reaction. When the viscosity of the solution reaches the specified range of 6390 mPa·s, 0.02% of the mass of the prepolymerization solution of potassium bisulfite as a reducing agent is added to obtain the polyacrylamide aqueous solution.

[0058] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0059] Example 6 (1) 13% of acrylamide by weight of the prepolymer solution, 1.3% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.8% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.7% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.016% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution were thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 16.0% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.8 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 30 minutes, and then the temperature was raised to 51° C. in a water bath. 0.09% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.013% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.013% of the mass of the prepolymer solution was used as a chain regulator. Sodium formate was added to the prepolymer solution in sequence to initiate the polymerization reaction; (3) The polymerization solution of step (2) is reacted to 93° C., and 0.2% of the mass of the prepolymerization solution of hexamethylene diisocyanate as a crosslinking agent is added to continue the reaction. When the viscosity of the solution reaches the specified range of 5650 mPa·s, 0.025% of the mass of the prepolymerization solution of potassium bisulfite as a reducing agent is added to obtain the polyacrylamide aqueous solution.

[0060] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0061] Example 7 (1) 14% of acrylamide by weight of diethylaminoethyl methacrylate solution, 1.1% of cationic functional monomer by weight of prepolymer solution, 1.2% of anionic functional monomer butenedioic acid by weight of prepolymer solution, 0.4% of cationic oligomer polymethacrylamide propyl dodecyl dimethyl ammonium chloride by weight of prepolymer solution, and 0.03% of crosslinking agent pentaerythritol triallyl ether by weight of prepolymer solution were mixed with deionized water to obtain a prepolymer solution with a mass percentage of 15.7% of the total reactants, and the pH of the prepolymer solution was adjusted to 2.8 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 30 minutes, and then the temperature was raised to 51-56° C. in a water bath. 0.03% of the mass of the prepolymer solution as an oxidizing agent, 0.007% of the mass of the prepolymer solution as an azo initiator, azobisisocyanovaleric acid, and 0.016% of the mass of the prepolymer solution as a chain regulator, sodium formate, were added to the prepolymer solution in sequence to initiate a polymerization reaction; (3) The polymerization solution of step (2) is reacted to 93° C., and 0.12% of the mass of the prepolymerization solution as a crosslinking agent, hexamethylene diisocyanate, is added to continue the reaction. When the solution viscosity reaches the specified range of 4320 mPa·s, 0.045% of the mass of the prepolymerization solution as a reducing agent, potassium bisulfite, is added to obtain the polyacrylamide aqueous solution.

[0062] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this example was conducted, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution used in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0063] Comparative Example 1 Comparative Example 1 is substantially the same as Example 1, except that no cross-linking agent is added in step (3), and the reducing agent is added directly when the viscosity reaches the specified range.

[0064] Specifically, (1) 12% of acrylamide by weight of the prepolymer solution, 0.8% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.4% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.2% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.008% of pentaerythritol triallyl ether as a cross-linking agent by weight of the prepolymer solution are thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 13.5% of the total reactants, and the pH of the prepolymer solution is adjusted to 2.0 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 20 minutes, and then the temperature was raised to 51° C. in a water bath. 0.05% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.012% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.02% of the mass of the prepolymer solution was used as a chain regulator. The polymerization reaction was initiated; (3) When the polymerization solution in step (2) reacts until the solution viscosity reaches the specified range of 8860 mPa·s, 0.03% of the mass of the prepolymerization solution as a reducing agent, potassium bisulfite, is added to obtain the polyacrylamide aqueous solution.

[0065] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this comparative example was carried out, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0066] Comparative Example 2 Comparative Example 2 is substantially the same as Example 1, except that the cross-linking agent is added after the prepolymer solution is obtained in step (1).

[0067] Specifically, (1) 12% of acrylamide by weight of the prepolymer solution, 0.8% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.4% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.2% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.008% of pentaerythritol triallyl ether as a crosslinking agent by weight of the prepolymer solution are fully stirred and mixed with deionized water to obtain a prepolymer solution with a total reactant content of 13.5%, 0.25% of hexamethylene diisocyanate as a crosslinking agent by weight of the prepolymer solution are added, and the pH of the prepolymer solution is adjusted to 2.0 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 20 minutes, and then the temperature was raised to 51° C. in a water bath. 0.05% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.012% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.02% of the mass of the prepolymer solution was used as a chain regulator. The polymerization reaction was initiated; (3) When the polymerization solution in step (2) reacts until the solution viscosity reaches the specified range of 8860 mPa·s, 0.03% of the mass of the prepolymerization solution as a reducing agent, potassium bisulfite, is added to obtain the polyacrylamide aqueous solution.

[0068] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this comparative example was carried out, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0069] Comparative Example 3 Comparative Example 3 is substantially the same as Example 1, except that the cross-linking enhancer is replaced by a common cross-linking agent, N,N-methylenebisacrylamide.

[0070] Specifically, (1) 12% of acrylamide by weight of the prepolymer solution, 0.8% of diethylaminoethyl methacrylate as a cationic functional monomer by weight of the prepolymer solution, 0.4% of butylated acid as an anionic functional monomer by weight of the prepolymer solution, 0.2% of polymethacrylamide propyl dodecyl dimethyl ammonium chloride as a cationic oligomer by weight of the prepolymer solution, and 0.008% of pentaerythritol triallyl ether as a cross-linking agent by weight of the prepolymer solution are thoroughly stirred and mixed with deionized water to obtain a prepolymer solution having a mass percentage content of 13.5% of the total reactants, and the pH of the prepolymer solution is adjusted to 2.0 with acetic acid; (2) The prepolymer solution obtained in step (1) was transferred into a glass reactor, a digital thermometer was inserted, high-purity nitrogen was introduced into the reactor for 20 minutes, and then the temperature was raised to 51° C. in a water bath. 0.05% of the mass of the prepolymer solution was used as an oxidizing agent, potassium persulfate, 0.012% of the mass of the prepolymer solution was used as an azo initiator, azobisisocyanovaleric acid, and 0.02% of the mass of the prepolymer solution was used as a chain regulator. The polymerization reaction was initiated; (3) When the polymerization solution in step (2) reacts to 87° C., 0.25% of the mass of the prepolymerization solution as the extender N,N-methylenebisacrylamide is added to continue the reaction. When the solution viscosity reaches the specified range of 8860 mPa·s, 0.03% of the mass of the prepolymerization solution as the reducing agent potassium bisulfite is added to obtain the polyacrylamide aqueous solution.

[0071] The performance test of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution prepared in this comparative example was carried out, and the results are shown in Table 1. The amount of the novel slightly cross-linked amphoteric polyacrylamide aqueous solution in Table 1 refers to the amount used for 1 ton of absolutely dry paper.

[0072] Table 1: Performance indicators of the novel slightly cross-linked amphoteric polyacrylamide aqueous solutions prepared in Examples 1 to 7 and Comparative Examples 1 to 3.

[0073]

[0074] Table 2: Relationship between the amount of oxidant used and the apparent viscosity of the aqueous solution of the new slightly cross-linked amphoteric polyacrylamide.

[0075]

[0076] Table 3: Relationship between the amount of azo initiator used and the apparent viscosity of the aqueous solution of the new slightly cross-linked amphoteric polyacrylamide.

[0077]

[0078] Table 4: Relationship between the amount of chain regulator and the apparent viscosity of the aqueous solution of the novel slightly cross-linked amphoteric polyacrylamide.

[0079]

[0080] Table 5: Relationship between the amount of reducing agent used and the apparent viscosity of the aqueous solution of the new slightly cross-linked amphoteric polyacrylamide.

[0081]

[0082] Finally, it should be noted that the above embodiments and comparative examples are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments and comparative examples, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments and comparative examples, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments and comparative examples of the present invention.

Claims

1. A method for preparing a slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, characterized in that: include: S1, mixing water, acrylamide, cationic functional monomer, anionic functional monomer, cationic oligomer, and crosslinking agent to obtain a prepolymer solution; S2, adding an oxidant, an azo initiator, and a chain regulator to the prepolymerization solution in sequence under a nitrogen environment, raising the temperature to 51-56° C. to initiate a polymerization reaction, thereby obtaining a polymerization solution; S3, adding a crosslinking agent to the polymerization solution, and heating it to 87-93° C. to continue the reaction. After reaching a preset viscosity, a reducing agent is added to stop the polymerization reaction to obtain a product solution.

2. The preparation method according to claim 1, characterized in that The cross-linking agent includes one or more combinations of aziridine and hexamethylene diisocyanate.

3. The preparation method according to claim 1, characterized in that The amount of the cross-linking agent used is 0.05% to 0.3% of the mass of the prepolymer solution, preferably 0.08% to 0.14%.

4. The preparation method according to claim 1, characterized in that The total weight of the acrylamide, the cationic functional monomer, the anionic functional monomer, and the cationic oligomer accounts for 13-18 wt % of the prepolymerization solution, preferably 14.5 wt %.

5. The preparation method according to claim 1 or 4, characterized in that The mass ratio of the acrylamide, the cationic functional monomer, the anionic functional monomer, and the cationic oligomer is (8-14): (0.8-4): (0.4-1.3): (0.2-1.0), preferably (10-12.5): (1.3-2.0): (0.6-0.9): (0.3-0.6).

6. The preparation method according to claim 1, characterized in that The cationic functional monomer includes one or more combinations of diethylaminoethyl acrylate, diethylaminoethyl methacrylate and N,N-diallylethanolamine; The anionic functional monomer includes one or more of 2-ethyl acrylic acid and butenedioic acid; The cationic oligomer includes one or more of polymethacrylamidopropyl dodecyldimethylammonium chloride, methacrylamidopropyl trimethylammonium chloride and polyacryloyloxyethyl dimethylbenzyl ammonium chloride; The cross-linking agent includes one or more of pentaerythritol triallyl ether and malondialdehyde; The oxidant comprises one or more of potassium persulfate and sodium persulfate; The azo initiator includes one or more of azobisisocyanovaleric acid and azobisisoheptonitrile; The chain regulator includes one or more of dodecyl mercaptan and sodium formate; The reducing agent includes one or more of potassium bisulfite, sodium metasulfite and ferrous sulfate.

7. The preparation method according to claim 1, characterized in that The amount of the cross-linking agent is 0.008% to 0.03% of the mass of the prepolymer solution; The amount of the oxidant is 0.03% to 0.11% of the mass of the prepolymerization solution; The amount of the azo initiator is 0.005% to 0.016% of the mass of the prepolymerization solution; The amount of the chain regulator is 0.005% to 0.02% of the mass of the prepolymer solution; The amount of the reducing agent is 0.02% to 0.05% of the mass of the prepolymerization solution.

8. The preparation method according to claim 1, characterized in that S1 further includes: adding a pH adjuster to the prepolymerization solution to adjust the pH value of the prepolymerization solution to 2-2.

8.

9. The preparation method according to claim 1, characterized in that The preset viscosity is 4000~11000 mPa·s.

10. A slightly cross-linked amphoteric polyacrylamide aqueous solution dry strength agent, characterized in that: Prepared according to any one of the preparation methods of claims 1-9.

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