Paper reinforcing agent and application thereof

Abstract

The invention discloses a paper reinforcing agent and application thereof, and belongs to the technical field of papermaking. The paper reinforcing agent is prepared by mixing raw starch, cationic polyacrylamide and water. The paper reinforcing agent is directly used for forming a wet paper sheet in a dry part adding mode, so that the performance of a paper base material is remarkably improved, and the internal bonding strength, the ring crush compression resistance index and the bursting strength of the paper base material are remarkably superior to those of the paper base material which is only added with GPAM at a wet part or only sprayed with starch emulsion at a dry part; the paper base material is even superior to a paper base material prepared by a preparation method of adding GPAM at a wet part and spraying starch emulsion at a dry part.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of papermaking, and particularly relates to a paper strengthening agent and application thereof. BACKGROUND

[0002] In order to pursue environmental protection and cost-effectiveness, recycled fibers are generally used as the main pulp (OCC) in modern papermaking industry. However, as the recycling times of fibers increase, the performance of the pulp itself becomes poorer, and various problems such as short fibers, poor strength, and many impurities are encountered, which seriously affect the key mechanical performance indicators such as internal bonding strength and ring crush strength of the produced paperboard (especially high-strength packaging paperboard). Therefore, in order to improve the strength of the paperboard, modern technology often sprays starch on the wet paper sheet to improve the strength, but the use of single spraying starch has limited effect on improving the strength performance of the paperboard, and it is difficult to meet the high requirements of modern packaging paper. In addition, chemicals that can enhance the effect are also added to meet the strength requirements.

[0003] At present, spraying starch and wet strength agent are commonly used in the papermaking process.

[0004] Spraying starch is generally used after the formation of the paper sheet (without drying), and 3-8% of raw starch milk is attached to the fibers in the form of spraying. Through pressing, the starch particles further penetrate the surface and interlayer of the paper sheet. During the subsequent high-temperature drying process, the starch particles are completely gelatinized by water absorption and swelling. The -OH on the starch molecular chain forms a large number of hydrogen bonds with the -OH on the cellulose molecules, greatly enhancing the bonding force between the fibers. The starch particles that have not penetrated deeply also form a continuous film on the surface of the fibers, which can effectively improve the ring crush strength of the paper. However, the surface of the unmodified starch particles generally has weak negative charge, and there is still electrostatic repulsion between the fibers, which makes it difficult to firmly adsorb on the surface of the fibers and easily flow away with water during pressing and dewatering, resulting in a decrease in retention rate and insufficient interlayer bonding force, thereby increasing the cost of raw materials.

[0005] The main component of wet strength agent is cationic polyacrylamide (GPAM), which is generally added in the wet part. The principle is that the cationic groups on the molecular chain are electrostatically adsorbed on the surface of the fibers, forming a stable and dense three-dimensional network structure. At the same time, -CONH2 and -OH are combined through hydrogen bonds to enhance the bonding force between the fibers. However, GPAM is consumed by the large amount of anions "garbage" present in the pulp, and a large part of the strengthening agent may flow away with the white water, resulting in a decrease in the strengthening effect and causing waste of cost. In addition, the introduction of a large amount of cations into the pulp may form large fiber flocs, affecting the uniformity of the paper, and the strengthening effect of GPAM depends on the addition method in the pulp. If the addition point and mixing intensity are not good, the effect will be poor. Therefore, the existing technology lacks an effective method that can simultaneously solve the key problems of low strengthening efficiency of spraying starch, low retention rate of strengthening agent, high cost, and complex use method.

[0006] In summary, it is of great significance to develop a new type of reinforcing agent for papermaking to improve the performance of paper. SUMMARY

[0007] Therefore, the present application aims to provide a paper reinforcing agent and its application. The paper reinforcing agent is directly added to the forming paper sheet by dry part, which significantly improves the performance of the paper substrate.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] The present application provides a paper reinforcing agent, which is prepared by mixing raw starch, cationic polyacrylamide (GPAM) and water.

[0010] The traditional spraying starch component is single, which depends on the physical penetration of starch particles on the surface of paper fibers. However, the paper reinforcing agent (GPAM-starch blend system) of the present application significantly improves the paper strength index through the synergistic effect of starch and GPAM.

[0011] The GPAM in the paper reinforcing agent of the present application has cationic groups which can be closely adsorbed on the surface of the weakly negatively charged starch particles, forming a stable "carrier-functional molecule" complex. A large number of cationic groups can make the blend system present a positive charge, so that the paper reinforcing agent is more firmly adsorbed on the surface of the paper fibers, greatly improving the retention rate of starch particles on the fibers and effectively solving the problem of poor internal bonding strength caused by starch loss.

[0012] In addition, the paper reinforcing agent of the present application utilizes the mechanical entrapment characteristics of the paper fiber network itself to efficiently "escort" GPAM to the surface of the fibers, thereby greatly reducing the invalid consumption of GPAM caused by charge neutralization, dissolution and loss with water, and fundamentally improving the retention rate of GPAM in the paper sheet.

[0013] Preferably, the mass ratio of the cationic polyacrylamide and raw starch is (0.1-0.4) : 10.

[0014] The present application controls the concentration of starch to ensure uniform dispersion of starch particles in water, so that the starch particles remain in the original state without gelatinization, have low viscosity, are not easy to block the nozzle, and are easy to transport and mix.

[0015] In some embodiments of the present application, the preparation method of the paper reinforcing agent preferably comprises the following steps:

[0016] The raw starch is configured into a starch emulsion and mixed with a GPAM aqueous solution to prepare the paper reinforcing agent.

[0017] Preferably, the concentration of the starch emulsion is 1wt%-15wt%; more preferably, 3wt%-8wt%.

[0018] Preferably, the concentration of the GPAM aqueous solution is 1wt%-12wt%; more preferably, 2wt%-10wt%. The above preparation method makes the GPAM and starch particles in the GPAM-starch blended system bind more closely, and the "carrier-functional molecule" complex more stable.

[0019] More preferably, the mass ratio of the absolute dry GPAM in the GPAM aqueous solution to the absolute dry starch in the starch emulsion is (0.1-0.4):10.

[0020] More preferably, the mixing temperature is 10°C-40°C; more preferably, 25°C-35°C; further preferably, 30°C.

[0021] More preferably, the mixing is mechanical stirring mixing.

[0022] Preferably, the rotation speed of the mechanical stirring is 300-500 rpm.

[0023] Preferably, the mechanical stirring time is 15-30 min; more preferably, 30 min.

[0024] Preferably, the raw starch is selected from one or more of corn starch, cassava starch, potato starch, and pea starch; more preferably, corn starch.

[0025] Preferably, the cationic monomer in the cationic polyacrylamide is selected from one or more of methacryloyloxyethyl trimethyl ammonium chloride, diallyl dimethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, and methacrylamidopropyl trimethyl ammonium chloride; more preferably, diallyl dimethyl ammonium chloride or methacrylamidopropyl trimethyl ammonium chloride.

[0026] Preferably, the cationic monomer content in the cationic polyacrylamide is 5wt%-25wt%.

[0027] More preferably, the molecular weight of the cationic polyacrylamide is 10-1000 KDa.

[0028] Preferably, the raw material of the paper strength agent further comprises a pH buffer.

[0029] The addition amount of the pH buffer is 0.01wt%-0.1wt% of the total raw material system of the paper strength agent.

[0030] The pH buffer includes but is not limited to sodium bicarbonate and the like.

[0031] The pH buffer is used to maintain the stability of the system.

[0032] The application also provides the use of the paper strength agent in paper production.

[0033] Preferably, the paper strength agent is sprayed on the surface of the forming wet paper sheet during paper production. The use of the paper strength agent in the production of paper substrates can significantly improve the internal bonding strength, ring crush strength index and burst strength of the paper substrates.

[0034] The application verifies the excellent performance of the paper strength agent by preparing the enhanced paper substrates under laboratory conditions.

[0035] In some embodiments of the application, the method for preparing the enhanced paper substrates comprises the following steps:

[0036] The paper strength agent is uniformly sprayed on the surface of the wet paper sheet (such as the junction of the core layer and the surface layer), and is hot-pressed with another wet paper sheet to form a composite, and then is dried to obtain the enhanced paper substrates.

[0037] The spraying can be performed by using the devices well known in the art, and the application does not make special limitations thereto.

[0038] The use of the paper strength agent integrates the two enhancement processes, which are traditionally completed in the wet part (paper slurry) and the dry part (the surface of the forming wet paper sheet), into a single process completed in the dry part, thereby simplifying the process flow and reducing the complexity and difficulty of the method.

[0039] By spraying the positively charged blending system (paper strength agent) on the surface of the wet paper sheet, the application can avoid the problem that the GPAM is neutralized and consumed by the large amount of anionic charges in the paper slurry and is lost with water due to the addition in the wet part, and the positive charges of the blending system can be electrostatically adsorbed to the fibers of the paper, thereby simultaneously improving the retention rate of the starch and GPAM in the paper strength agent.

[0040] The paper strength agent can further penetrate into the intermolecular space of the paper fibers and tightly entangle with the fiber molecules.

[0041] The drying process in the method for preparing the enhanced paper substrates makes the starch particles completely gelatinized by absorbing water under high temperature conditions.

[0042] If the drying temperature is too high, the forming paper sheet will be dried too fast, which will result in a large amount of starch particles not being completely gelatinized, thereby affecting the enhancement effect. If the temperature is too low, the drying time will be too long, which is not conducive to the gelatinization of the starch.

[0043] Preferably, the drying temperature is 100-130℃; more preferably, 110℃.

[0044] Preferably, the drying time is 30 min.

[0045] After gelatinization, starch granules penetrate into the fiber molecules in the forming wet paper sheet, and solidify with the starch-adsorbed GPAM molecules. With the penetration and distribution of starch granules, GPAM molecules are directly and efficiently transported and fixed in the fiber-interlaced network. Moreover, the gelatinized starch molecules greatly prevent the loss of GPAM due to moisture migration, thanks to their excellent film-forming and adhesive properties. Under the action of drying and heating, the hydroxyl groups on the starch granules and fiber molecules further combine through hydrogen bonds.

[0046] The starch in the paper strength agent of the present application serves as a carrier to load and fix the easily lost GPAM molecules, so that they can be efficiently trapped in the fiber network of the forming paper together with the starch after spraying, and the retention rate of GPAM can be increased from 40-60% in conventional wet-end addition to more than 90%. After spraying, the GPAM in the forming wet paper sheet exerts its "bridging" effect of the long molecular chain to build a stable strength skeleton; and the gelatinized starch forms a dense film on the fiber surface and between the layers, which interpenetrate each other to form a composite strengthening system of CPAM-starch, while greatly improving the interlayer bonding strength.

[0047] Finally, a stable three-dimensional interpenetrating structure of "electrostatic adsorption + hydrogen bonding + physical entanglement" is formed between GPAM, fibers and starch, breaking the use boundary between traditional wet-end strengthening and dry-end strengthening. It can not only play the effect of wet-end strengthening through electrostatic adsorption, but also play the role of dry-end solidification through starch gelatinization and film formation, thereby comprehensively improving the strength performance of the paper substrate.

[0048] The use of the paper strength agent of the present application effectively solves the problem of waste of chemicals in traditional processes (wet-end and dry-end strengthening). Under the condition of ensuring the strength of the paper, the amount of chemicals is reduced, the production cost is reduced, and the cost is reduced and the benefit is increased.

[0049] The preparation method of the present application is simple and efficient, and the process adaptability is high. Only the single starch in the spraying point on the original process production line needs to be replaced with a blended system of "GPAM-starch" (the paper strength agent of the present application), and the paper strength agent of the present application is suitable for the original equipment of the paper mill, avoiding the additional equipment cost and installation cost caused by the introduction of new technology.

[0050] Compared with existing technologies, the paper strengthening agent provided by this invention is made from a mixture of raw starch, cationic polyacrylamide, and water. This paper strengthening agent is directly added to the wet end of the paper sheet, significantly improving the performance of the paper substrate. The resulting internal bond strength, ring crush strength index, and bursting strength are significantly better than those obtained by adding GPAM only in the wet end or by spraying starch emulsion only in the dry end, and even better than paper substrates prepared by methods that add GPAM in the wet end and spray starch emulsion in the dry end. Detailed Implementation

[0051] To further illustrate the present invention, the paper strengthening agent provided by the present invention and its application are described in detail below with reference to embodiments.

[0052] Example 1

[0053] Prepare a 5% concentration of corn starch milk, add 4% GPAM (5% cationic monomer, 4% aqueous solution with a viscosity of 6 cps) at an addition rate of 10-40 kg / t of oven-dried starch (the amount of oven-dried GPAM is 10-40 kg / t relative to the amount of oven-dried starch), and stir vigorously at 30℃ for 30 min to obtain spray starch enhancer A.

[0054] Under laboratory conditions, using cardboard core layer pulp as raw material, a pulp concentrate with a consistency of 1% was prepared after descaling and beating. A traditional wet-process sheet forming basis weight of 50 g / m³ was used. 2 After vacuum dehydration, ensuring the paper web moisture content is 70%-80%, the first formed paper sheet is peeled off and set aside. The same process is repeated for the second paper sheet. After vacuum dehydration, starch reinforcing agent A is sprayed onto the second paper sheet, and vacuum dehydration is performed again. Then, the first paper sheet is completely laminated onto the second paper sheet. Finally, pressing and drying (110℃, 30 min) are performed to obtain the paper substrate.

[0055] Based on the amount of paper used per ton (t), the amount of oven-dried starch used is 10 kg / t of paper, and the amount of 4% GPAM used is 2.5~10 kg / t of paper. Meanwhile, based on the amount of paper used per ton, starch usage of 0~20 kg / t of paper and GPAM usage of 0 kg / t of paper serve as a blank control. This embodiment focuses on using a starch usage of 10 kg / t or 20 kg / t of paper and GPAM usage of 0 kg / t of paper as a blank control group.

[0056] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 1.

[0057] Table 1 Performance test results of sprayed starch enhancer A in Example 1

[0058]

[0059] Example 2

[0060] Prepare a 5% concentration of corn starch milk, add 8% GPAM (10% cationic monomer, 8% aqueous solution with a viscosity of 20 cps) at an addition rate of 10~40 kg / t of oven-dried starch, and stir vigorously at 30℃ for 30 min to obtain spray starch enhancer B.

[0061] Under laboratory conditions, using cardboard core layer pulp as raw material, a pulp concentrate with a consistency of 1% was prepared after descaling and beating. A traditional wet-process sheet forming basis weight of 50 g / m³ was used. 2 After vacuum dehydration, ensuring the paper web moisture content is between 70% and 80%, the first formed paper sheet is peeled off and set aside. The same process is repeated for the second paper sheet. After vacuum dehydration, starch reinforcing agent B is sprayed onto the second paper sheet, and vacuum dehydration is performed again. Then, the first paper sheet is completely laminated onto the second paper sheet. Finally, pressing and drying (110℃, 30 min) are performed to obtain the paper substrate.

[0062] Based on paper usage per ton (t), the oven-dry starch usage is 10 kg / t paper, and the 8% GPAM usage is 1.25~5 kg / t paper. Meanwhile, based on paper usage per ton, starch usage of 0~20 kg / t paper and GPAM usage of 0 kg / t paper serve as a control group. This embodiment focuses on using 10 kg / t or 20 kg / t paper starch and 0 kg / t paper GPAM as the control group.

[0063] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 2.

[0064] Table 2 Performance test results of sprayed starch enhancer B in Example 2

[0065]

[0066] Example 3

[0067] Prepare a 5% concentration of corn starch milk, add 2% GPAM (15% cationic monomer, 2% aqueous solution with a viscosity of 10cps) at an addition rate of 10~40 kg / t of oven-dried starch, and stir vigorously at 30℃ for 30 min to obtain spray starch enhancer C.

[0068] Under laboratory conditions, using cardboard core layer pulp as raw material, a pulp concentrate with a consistency of 1% was prepared after descaling and beating. A traditional wet-process sheet forming basis weight of 50 g / m³ was used. 2 After vacuum dehydration, ensuring the paper web moisture content is between 70% and 80%, the first formed paper sheet is peeled off and set aside. The same process is repeated for the second paper sheet. After vacuum dehydration, starch reinforcing agent C is sprayed onto the second paper sheet, and vacuum dehydration is performed again. Then, the first paper sheet is completely laminated onto the second paper sheet. Finally, pressing and drying (110℃, 30 min) are performed to obtain the paper substrate.

[0069] Based on paper usage per ton (t), the oven-dry starch usage is 10 kg / t of paper, and the 2% GPAM usage is 5-20 kg / t of paper. Meanwhile, based on paper usage per ton, starch usage of 0-20 kg / t of paper and GPAM usage of 0 kg / t of paper serve as a control group. This embodiment focuses on using a starch usage of 10 kg / t or 20 kg / t of paper and GPAM usage of 0 kg / t of paper as a control group.

[0070] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 3.

[0071] Table 3 Performance test results of sprayed starch enhancer C in Example 3

[0072]

[0073] Example 4

[0074] Prepare a 5% concentration of corn starch milk, add 10% GPAM (25% cationic monomer, 10% aqueous solution viscosity of 16cps) at an addition rate of 10~40 kg / t of oven-dried starch, and stir vigorously at 30℃ for 30 min to obtain spray starch enhancer D.

[0075] Under laboratory conditions, using cardboard core layer pulp as raw material, a pulp concentrate with a consistency of 1% was prepared after descaling and beating. A traditional wet-process sheet forming basis weight of 50 g / m³ was used. 2 After vacuum dehydration, ensuring the paper web moisture content is 70%-80%, the first formed paper sheet is peeled off and set aside. The same process is repeated for the second paper sheet. After vacuum dehydration, starch reinforcing agent D is sprayed onto the second paper sheet, and vacuum dehydration is performed again. Then, the first paper sheet is completely laminated onto the second paper sheet. Finally, pressing and drying (110℃, 30 min) are performed to obtain the paper substrate.

[0076] Based on paper usage per ton (t), the oven-dry starch usage is 10 kg / t of paper, and the 10% GPAM usage is 1-4 kg / t of paper. Meanwhile, based on paper usage per ton, starch usage of 0-20 kg / t of paper and GPAM usage of 0 kg / t of paper serve as a control group. This embodiment focuses on using a starch usage of 10 kg / t or 20 kg / t of paper and GPAM usage of 0 kg / t of paper as the control group.

[0077] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 4.

[0078] Table 4 Performance test results of sprayed starch enhancer D in Example 4

[0079]

[0080] The results in Tables 1-4 above show that if sprayed starch is used alone, the internal bond strength, ring crush strength index and bursting strength of the paper substrate are all low. Even if the amount of oven-dried starch is increased, the improvement in these properties is not significant, and they are all lower than the properties of the paper substrate prepared using the sprayed starch reinforcing agent described in this invention.

[0081] Comparative Example 1 (GPAM added to the wet end)

[0082] Under laboratory conditions, using cardboard core layer pulp as raw material, a pulp concentrate with a consistency of 1% was prepared after descaling and beating. A traditional wet-process sheet forming basis weight of 50 g / m³ was used. 2 Add 2% GPAM (5-20 kg / t paper) to the 1% pulp, vacuum dewater, and ensure the paper web moisture content is 70%-80%. Remove the first formed paper sheet for later use. Repeat the above operation for the second paper sheet, then completely laminate the first paper sheet onto the second paper sheet. Then press and dry (110℃, 30 min) to obtain the paper substrate.

[0083] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 5.

[0084] Table 5 Performance test results of the paper substrate prepared in Comparative Example 1

[0085]

[0086] Comparative Example 2

[0087] Under laboratory conditions, using cardboard core pulp as raw material, a pulp with a consistency of 1% was prepared after descaling and beating.

[0088] The traditional wet tableting method was used to measure 50g / m³. 2 Add 2% GPAM (5-20 kg / t paper) to the 1% pulp. After vacuum dewatering, ensure the paper web moisture content is 70%-80%. Peel off the first formed paper sheet for later use. Repeat the above operation for the second paper sheet. After vacuum dewatering, spray 5% raw starch milk at an addition rate of 10 kg / t paper onto the second paper sheet and vacuum dewater it again. Then, completely adhere the first paper sheet onto the second paper sheet. Then, press and dry (110℃, 30 min) to obtain the paper substrate.

[0089] The interlayer bond strength of paper was tested using GB / T 26203-2023 "Determination of internal bond strength of paper and paperboard (Scott type)", the bursting strength of paper was tested using GB / T 454-2020 "Determination of bursting strength of paper", and the ring crush strength of paper was tested using GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". The results are shown in Table 6.

[0090] Table 6 Performance test results of the paper substrate prepared in Comparative Example 2

[0091]

[0092] The wet-end addition in Tables 5 and 6 above refers to adding GPAM directly to the pulp with a pulp concentration of 1% used to prepare the paper, while the dry-end addition refers to spraying starch emulsion onto the surface of the formed wet paper sheet.

[0093] The above results show that, compared with Example 3, the paper substrates prepared by the wet-end reinforcement method described in Comparative Example 1 and the wet-end and dry-end superposition reinforcement method described in Comparative Example 2 have significantly lower internal bond strength, ring crush strength index and bursting strength than those of Example 3.

[0094] In summary, the reinforcing agent described in this invention has excellent effects and can be directly added to the dry end after wet paper sheet forming. This makes the internal bond strength, ring crush strength index and bursting strength of the paper substrate significantly better than those obtained by adding GPAM only in the wet end or by spraying starch emulsion only in the dry end, and even better than those obtained by the preparation method of adding GPAM in the wet end and spraying starch emulsion in the dry end.

[0095] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A paper strength agent, characterized by, It is made by mixing raw starch, cationic polyacrylamide and water.

2. The paper strength enhancer according to claim 1, characterized by, The mass ratio of the cationic polyacrylamide and raw starch is (0.1-0.4):

10.

3. The paper strength enhancer according to claim 1, wherein The raw starch is selected from one or more of corn starch, cassava starch, potato starch, pea starch.

4. The paper strength enhancer according to claim 1, wherein The cationic monomer in the cationic polyacrylamide is selected from one or more of methacryloyloxyethyl trimethyl ammonium chloride, diallyl dimethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, methacrylamide propyl trimethyl ammonium chloride.

5. The paper strength enhancer according to claim 4, wherein The content of the cationic monomer in the cationic polyacrylamide is 5wt%-25wt%.

6. The paper strength enhancer according to claim 5, wherein The molecular weight of the cationic polyacrylamide is 10-1000 KDa.

7. The paper strength enhancer according to any one of claims 1 to 6, characterized in that, The raw material of the paper strength agent further comprises a pH buffer.

8. The paper strength enhancer according to claim 7, characterized in that, The addition amount of the pH buffer is 0.01wt%-0.1wt% of the total raw material system of the paper strength agent.

9. The paper strength agent of any one of claims 1-8 for use in paper production.

10. Use according to claim 9, characterized in that, The paper strength agent is sprayed on the surface of the forming wet paper sheet during paper production. The paper strength agent is sprayed on the surface of the forming wet paper sheet during paper production.

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