Retention assisting method of nano titanium dioxide filler based on paper-based facing material

Abstract

The invention relates to the field of papermaking, and particularly provides a retention method of a nano titanium dioxide filler based on a paper-based facing material. The retention method comprises the following steps: S100, mixing nano titanium dioxide with dopamine under an alkaline condition, so as to obtain titanium dioxide coated with polydopamine; s200, mixing the titanium dioxide coated with the polydopamine with the cationic guar gum containing the boron group, so as to obtain a composite retention aid; and S300, adding the composite retention aid into the paper pulp, and carrying out wet end retention treatment and net forming treatment to obtain the paper-based facing material. The efficient retention aid is prepared by polymerizing and coating the nano titanium dioxide with dopamine under the alkaline condition and compounding with the cationic guar gum containing the boron group, so that the retention aid rate and dispersity of the nano titanium dioxide at the wet end are improved, and the performance of the paper-based facing material is improved; and on the other hand, the retention aid dosage is reduced, the process is mild and environment-friendly, and the adaptability of subsequent procedures is considered.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and more specifically, to a method for aiding the retention of nano-titanium dioxide fillers based on paper-based finishing materials. Background Technology

[0002] Decorative paper requires high surface gloss, whiteness, and strength. Nano-titanium dioxide, due to its high refractive index and excellent optical properties, is widely used in high-end decorative base paper and functional paper-based materials. However, nanoparticles are prone to loss or aggregation during the wet-end process, resulting in low retention rate and uneven dispersion, which restricts material performance and production efficiency. Traditional retention aid systems have limited retention efficiency for nano-titanium dioxide, making it difficult to achieve both high retention rate and good web-forming performance.

[0003] Therefore, there is an urgent need for a retention aid method for nano-titanium dioxide fillers that can balance high retention rate and good web-forming performance in order to solve the above problems. Summary of the Invention

[0004] This invention provides a retention aid method for nano-titanium dioxide fillers based on paper-based finishing materials. By polymerizing and coating nano-titanium dioxide with dopamine under alkaline conditions, and then compounding it with boron-containing cationic guar gum, a highly efficient retention aid is prepared. This method can significantly improve the retention rate and dispersion uniformity of nano-titanium dioxide in the wet-end stage, thereby enhancing the performance of paper-based finishing materials. At the same time, it reduces the amount of retention aid used, the process is mild, environmentally friendly and energy-saving, and the finished finishing paper can be adapted to subsequent processes, showing significant cost advantages and industrial application value.

[0005] This invention provides a retention aid method for nano-titanium dioxide filler based on paper-based finishing materials. The retention aid method includes the following steps: S100, mixing nano-titanium dioxide with dopamine under alkaline conditions to obtain polydopamine-coated titanium dioxide; S200, mixing polydopamine-coated titanium dioxide with boron-containing cationic guar gum to obtain a composite retention aid; S300, adding the composite retention aid to pulp, and performing wet-end retention treatment and web forming treatment to obtain the paper-based finishing material.

[0006] In any of the above technical solutions, the preparation method of boron-containing cationic guar gum in step S200 includes the following steps: S210, dissolving cationic guar gum in deionized water and performing a first stirring treatment to obtain a guar gum solution; S220, adding boric acid solution to the guar gum solution and performing a second stirring treatment to obtain a second solution, and cooling the second solution to room temperature to obtain boron-containing cationic guar gum.

[0007] In any of the above technical solutions, in step S210, the rotation speed of the first stirring treatment is 300-500 rpm, and the time is 20-30 min.

[0008] In any of the above technical solutions, in step S220, the concentration of the boric acid solution is 10-30 mM; the second stirring treatment speed is 300-500 rpm, and the time is 10-15 min.

[0009] In any of the above technical solutions, in step S220, after the second stirring treatment, the solution further includes: S221, adjusting the second solution to 6.5-7.5 using sodium hydroxide or hydrochloric acid.

[0010] In any of the above technical solutions, in step S100, the concentration of dopamine monomer is 1-3 g / L; the alkaline condition is a pH value of 8.5-9.0; and the particle size of nano-titanium dioxide is 20-50 nm.

[0011] In any of the above technical solutions, in step S200, the mass ratio of polydopamine-coated titanium dioxide to boron-containing cationic guar gum is 1:(8-12); the mixing temperature is 40-50℃ and the time is 25-45min.

[0012] In any of the above technical solutions, in step S300, the pulp concentration is 1-3 wt%; the amount of composite retention aid added is 1.0-2.0 wt% of the dry fiber mass; the ultrasonic frequency of wet-end retention aid is 15-25 kHz; the stirring speed of the web forming process is 1500-2500 rpm; the temperature of the wet-end retention aid process is 55-65℃, and the time is 3-5 min; the dewatering pressure of the web forming process is 0.1-0.3 MPa.

[0013] In any of the above technical solutions, S300 further includes adjusting the pH value to 5.0-6.0 after the wet end retention treatment and before web formation.

[0014] This invention provides an application of a retention aid method for nano-titanium dioxide fillers in paper-based decorative materials, wherein the paper-based decorative materials prepared by any of the above retention aid methods are used for decorative paper.

[0015] The technical effects that can be achieved by adopting the technical solution of the present invention are as follows: 1. This invention significantly improves the retention efficiency and dispersion stability of nano-titanium dioxide at the wet end by constructing a multi-point crosslinking network of a polydopamine coating layer and boron-containing cationic guar gum. The polydopamine coating effectively improves the hydrophilicity and surface activity of the particles, preventing aggregation, while the cationic guar gum forms a stable bond with the polydopamine through boron-diol coordination, thereby constructing a three-dimensional network structure between fibers. This achieves efficient capture and uniform distribution of particles in the pulp, solving the problems of low nanoparticle retention and poor dispersion in traditional retention aid systems. 2 The retention aid method used in this invention has the advantages of mild process conditions and environmental friendliness. The entire process does not require high temperature and high pressure or organic solvents. At the same time, the raw materials selected are all low toxicity or natural sources. The resulting retention aid can be fully adapted to the existing paper wet end process system, which not only reduces the environmental burden in the production process, but also has good potential for green and sustainable development. 3. The paper-based decorative material prepared by this retention-aid method exhibits excellent mechanical strength, a smooth surface, and a uniform coating, significantly improving the visual effect and service life of the decorative paper. The optical properties of nano-titanium dioxide are fully preserved and released, combined with good web formation quality and fiber bonding structure, enabling the paper to not only possess a high-end decorative effect but also be compatible with subsequent deep processing procedures. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart illustrating the steps of the retention method of the present invention; Figure 2 This is a schematic flowchart of the preparation method of the boron-containing cationic guar gum of the present invention; Figure 3 This is a schematic diagram of the multi-point crosslinking mechanism between polydopamine-coated TiO2 and boron-containing cationic guar gum in this invention; Figure 4 This is a schematic diagram of the spatial distribution of the composite retention aid in the fiber network and the three-dimensional cross-linked network structure of the colloidal matrix. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0019] To make the above-mentioned objectives, features and advantages of this aspect more apparent and understandable, specific embodiments of this aspect are described in detail below.

[0020] Decorative paper requires high surface gloss, whiteness, and strength. Nano-titanium dioxide, due to its high refractive index and excellent optical properties, is widely used in high-end decorative base paper and functional paper-based materials. However, nanoparticles are prone to loss or aggregation during the wet-end process, resulting in low retention rate and uneven dispersion, which restricts material performance and production efficiency. Traditional retention aid systems have limited retention efficiency for nano-titanium dioxide, making it difficult to achieve both high retention rate and good web-forming performance.

[0021] Therefore, there is an urgent need for a retention aid method for nano-titanium dioxide fillers that can balance high retention rate and good web-forming performance in order to solve the above problems.

[0022] In view of this, to overcome the problems of low retention rate, poor dispersibility, and harsh process conditions of nano-titanium dioxide in the prior art, this embodiment provides a retention aid method for nano-titanium dioxide fillers based on paper-based finishing materials, which has the advantages of mild process, environmental protection and energy saving, high retention efficiency and uniform dispersion, such as... Figure 1 As shown, the retention assistance method includes the following steps: S100. Under alkaline conditions, nano-titanium dioxide is mixed with dopamine to obtain polydopamine-coated titanium dioxide. S200. Polydopamine-coated titanium dioxide is mixed with boron-containing cationic guar gum to obtain a composite retention aid. S300. Add the composite retention aid to the pulp, perform wet-end retention treatment and web forming treatment to obtain paper-based decorative material.

[0023] Specifically, this method achieves efficient retention and uniform dispersion of nano-titanium dioxide through multi-point cross-linking of polydopamine and boron-containing guar gum, significantly improving the whiteness, opacity, and mechanical strength of paper-based finishing materials. The retention aid dosage is low, the process is mild and environmentally friendly, and it is compatible with subsequent lamination, calendering, and printing processes, demonstrating excellent prospects for industrial application and cost-effectiveness.

[0024] Preferably, in step S100, nano-titanium dioxide with a particle size of 20-50 nm is mixed with dopamine monomer at a concentration of 1-3 g / L in an alkaline environment with a pH of 8.5-9.0. Dopamine rapidly self-polymerizes within this pH range to form a uniform and dense polydopamine coating, effectively improving the surface hydrophilicity and dispersion stability of the titanium dioxide particles. The coating thickness can be precisely controlled by the dopamine concentration to ensure that the particles do not agglomerate at the wet end and are easily adsorbed onto the fiber surface. Nano-titanium dioxide with a particle size of 20-50 nm has a high specific surface area, which is beneficial to the full coverage of the coating and subsequent multi-point crosslinking with guar gum, thus laying a solid foundation for efficient retention.

[0025] like Figure 3 As shown, under alkaline conditions, -Ti-OH groups are generated on the surface of TiO2 particles; within the pH range of 8.5-9.0, dopamine can spontaneously polymerize to form a polydopamine coating, in which the catechol functional groups can be adsorbed onto the TiO2 surface via hydrogen bonds. When the pH is adjusted to 6.5-7.5, B(OH)3 and B(OH)4... - The two reach a formation equilibrium, B(OH)4 - It can coordinate with the ortho-bisphenol group in polydopamine to form a stable cyclic borate bond.

[0026] Preferably, in step S200, polydopamine-coated titanium dioxide and boron-containing cationic guar gum are mixed at a mass ratio of 1:(8-12) at 40-50°C for 25-45 minutes. This allows for multi-point crosslinking and steady-state adsorption. The boric acid groups on the guar gum form coordination bonds or boron-diol bridging with the catechol groups in the polydopamine coating, which not only enhances the bonding force between the titanium dioxide particles and the guar gum but also constructs a three-dimensional network structure between the fibers. Suitable temperature and time can accelerate the crosslinking reaction while ensuring uniform dispersion, ultimately yielding a composite retention aid with strong adhesion, stable dispersion, and rich in functional boron bonds, laying the foundation for efficient wet-end retention.

[0027] Furthermore, such as Figure 2 As shown, the preparation method of boron-containing cationic guar gum in step S200 includes the following steps: S210. Dissolve cationic guar gum in deionized water and perform a first stirring treatment to obtain a guar gum solution; S220. Add boric acid solution to guar gum solution and simultaneously perform a second stirring treatment to obtain a second solution. After cooling the second solution to room temperature, cationic guar gum containing boron groups is obtained.

[0028] Preferably, in step S210, the cationic guar gum is fully dissolved in deionized water at a stirring rate of 300-500 rpm and a stirring time of 20-30 min. This ensures that the guar gum molecules are fully hydrated, swelled, and uniformly dispersed, breaking up agglomerates and obtaining a solution with stable viscosity and good flowability. This homogeneous and stable guar gum solution provides an ideal molecular configuration and active sites for subsequent boric acid crosslinking, which helps to improve the crosslinking efficiency and stability of the final composite retention aid.

[0029] Preferably, in step S220, a 10-30 mM boric acid solution is added to a homogeneous guar gum solution and stirred at 300-500 rpm for 10-15 min to allow the boric acid molecules to fully react with the hydroxyl groups of guar gum to undergo a diol-boron ester crosslinking reaction. Subsequently, the mixture is cooled to room temperature to form a boron-containing cationic guar gum. This process can introduce reversible boron-diol coordination bonds between guar gum chains, enhancing its molecular network structure and adhesion properties, and improving the crosslinking density and stability of the composite retention aid. At the same time, the cationic properties of guar gum are preserved, which is beneficial for efficient bonding with fibers and polydopamine-coated titanium dioxide in wet-end processes, thereby significantly improving the retention effect and dispersion uniformity.

[0030] Furthermore, in step S221, the pH of the second solution is adjusted to 6.5-7.5, which can stabilize the boron-diol coordination bond and prevent the dissociation of boron ester bonds or degradation of guar gum chains under excessively acidic or alkaline conditions. At the same time, within this pH range, guar gum maintains a good cationic charge density, which is conducive to the formation of electrostatic adsorption and coordination cross-linking co-bridged network with the fiber surface and the polydopamine-coated titanium dioxide, thereby further improving the stability, adhesion strength and wet-end retention efficiency of the composite retention aid.

[0031] Preferably, in step S300, a composite retention aid is added at a pulp concentration of 1-3 wt% and a dry fiber mass of 1.0-2.0 wt%. This is achieved through ultrasonic retention at 15-25 kHz for 3-5 minutes at 55-65°C, combined with stirring at 1500-2500 rpm and a dewatering pressure of 0.1-0.3 MPa. This rapidly promotes the efficient combination of the composite retention aid with fibers and nano-titanium dioxide in a three-dimensional network, significantly improving particle capture rate and dispersion uniformity. Suitable ultrasonic and temperature conditions accelerate the penetration of the retention aid and break down micro-agglomerates. Stirring and pressure synergistically optimize the dewatering rate and paper structure, resulting in a finished product with high whiteness, high strength, and excellent web quality. Furthermore, the process is characterized by short processing time, low energy consumption, and high production efficiency, demonstrating significant value for industrial application.

[0032] Adjusting the pH to 5.0-6.0 after wet-end retention and before web formation allows for a slightly acidic environment that further optimizes the cationic charge density on the guar gum and polydopamine coatings, enhancing their electrostatic adsorption and hydrogen bonding with the fiber surface and nano-titanium dioxide particles. Simultaneously, this pH range promotes the sedimentation and uniform spreading of micro-molecular particles, contributing to the formation of a denser, more uniform fiber network layer. The result is improved retention stability and web formation quality, reduced surface defects, and enhanced smoothness and subsequent processing performance of the decorative paper.

[0033] like Figure 4 As shown, during the wet-end retention stage, the ultrasonically treated polydopamine-coated TiO2 particles first undergo preliminary bonding with the fiber surface, adsorbing onto the cellulose fiber surface through electrostatic interactions or hydrogen bonding. Subsequently, the branched segments of guar gum achieve multi-point cross-linking with the polydopamine layer through borate ester bonds. Simultaneously, the positively charged branches in guar gum intertwine with the negatively charged surfaces of the cellulose microfibers, further enhancing the bonding strength. After the web-forming process is completed, the dehydration pressure is 0.1-0.3 MPa. The three-dimensional network formed in the paper-based structure has good porosity, and the TiO2 particles are uniformly distributed at the fiber intersections, thus constructing a continuous, uniform, and dense filler coating on the surface of the paper-based finishing material.

[0034] In summary, the paper-based decorative material prepared by this invention has high whiteness, high opacity, and excellent tensile strength, and the surface coating is uniform and smooth. It is suitable for the production of various decorative papers and can be directly used in wallpaper, floor covering, furniture covering, and packaging materials. It not only improves visual effect and durability, but also takes into account production cost and environmental protection requirements.

[0035] Example 1 This embodiment provides a method for aiding the retention of nano-titanium dioxide fillers based on paper-based finishing materials, including the following steps: S100, In a buffer solution with a pH of 8.5, 20 nm nano-titanium dioxide was mixed with 1 g / L of dopamine monomer to obtain polydopamine-coated titanium dioxide. S210. Dissolve cationic guar gum in deionized water and stir at 300 rpm for 20 min to obtain guar gum solution. S220. Add 10mM boric acid solution to guar gum solution and stir at 300rpm for 10min to obtain a second solution. Cool the second solution to room temperature and adjust to 6.5 with sodium hydroxide or hydrochloric acid to obtain boron-containing cationic guar gum. S200. Polydopamine-coated titanium dioxide and boron-containing cationic guar gum are mixed at a mass ratio of 1:8 and at 40°C for 45 min to obtain a composite retention aid. S300. Add the composite retention aid to 1 wt% of pulp. The amount of composite retention aid added is 1.0 wt% of the dry fiber mass. Perform wet-end retention treatment at a frequency of 15 kHz, a temperature of 55 ℃, and a time of 3 min. Adjust the pH value to 5.0. Then, perform web forming treatment at a speed of 1500 rpm and a dewatering pressure of 0.1 MPa to obtain the paper-based decorative material.

[0036] Example 2 This embodiment provides a method for aiding the retention of nano-titanium dioxide fillers based on paper-based finishing materials, including the following steps: S100, In a buffer solution with a pH of 9.0, 30 nm nano-titanium dioxide was mixed with 2 g / L of dopamine monomer to obtain polydopamine-coated titanium dioxide. S210. Dissolve cationic guar gum in deionized water and stir at 400 rpm for 25 min to obtain guar gum solution. S220. Add 20mM boric acid solution to guar gum solution and stir at 400rpm for 13min to obtain a second solution. Cool the second solution to room temperature and adjust to 7.0 with sodium hydroxide or hydrochloric acid to obtain boron-containing cationic guar gum. S200. Polydopamine-coated titanium dioxide and boron-containing cationic guar gum are mixed at a mass ratio of 1:10 and at 45°C for 30 min to obtain a composite retention aid. S300. Add the composite retention aid to 2wt% of pulp. The amount of composite retention aid added is 1.5wt% of the dry fiber mass. Perform wet-end retention treatment at a frequency of 20kHz, a temperature of 60℃, and a time of 4min. Adjust the pH value to 5.5. Then, perform web forming treatment at a speed of 2000rpm and a dewatering pressure of 0.2MPa to obtain the paper-based decorative material.

[0037] Example 3 This embodiment provides a method for aiding the retention of nano-titanium dioxide fillers based on paper-based finishing materials, including the following steps: S100. In a buffer solution with a pH of 9.0, 50 nm nano-titanium dioxide was mixed with 3 g / L of dopamine monomer to obtain polydopamine-coated titanium dioxide. S210. Dissolve cationic guar gum in deionized water and stir at 500 rpm for 30 min to obtain guar gum solution. S220. Add 30mM boric acid solution to guar gum solution and stir at 500rpm for 15min to obtain a second solution. Cool the second solution to room temperature and adjust to 7.5 with sodium hydroxide or hydrochloric acid to obtain boron-containing cationic guar gum. S200. Polydopamine-coated titanium dioxide and boron-containing cationic guar gum are mixed at a mass ratio of 1:12 and at 50°C for 25 min to obtain a composite retention aid. S300. Add the composite retention aid to 3wt% of pulp. The amount of composite retention aid added is 2.0wt% of the dry fiber mass. Perform wet-end retention treatment at a frequency of 25kHz, a temperature of 65℃, and a time of 5min. Adjust the pH value to 6.0. Then, perform web forming treatment at a speed of 2500rpm and a dewatering pressure of 0.3MPa to obtain the paper-based decorative material.

[0038] Comparative Example 1 This comparative example provides a method for aiding the retention of nano-titanium dioxide filler based on paper-based finishing materials. The steps are the same as in Example 3, except that steps S210, S220, and S200 are omitted.

[0039] Comparative Example 2 This comparative example provides a paper-based finishing material, which is purchased externally.

[0040] Performance testing The retention rate, paper whiteness and hiding power, and mechanical properties of Examples 1-3 and Comparative Examples 1-2 were tested. The test results are shown in Table 1, and the test methods are as follows: Retention rate: During the paper machine production process, finished paper samples and corresponding white water samples are collected separately. The amount of TiO2 added in the original pulp of the same batch is recorded as m. 原 The mass of TiO2 measured in the finished paper is recorded as m. 纸 Both units are grams. The residual TiO2 in the white water sample can be measured by filtration and weighing or by ICP-OES, denoted as m. 白水 The retention rate is calculated as follows: Retention rate (%) = (m 纸 / m 原 ) × 100% Balance verification can also be performed, i.e., m 原 =m 纸 +m 白水 ±ε.

[0041] Paper whiteness and hiding power: The prepared dried paper sample was cut into 10cm×10cm pieces and placed in the whiteness meter measuring chamber at a temperature of 23±2℃ and a relative humidity of 50±2%. After calibrating the instrument, the measurement was performed; the whiteness percentage (%) and CIE L were recorded. * a * b * Three-color parameters; determination of opacity: place the paper sample on a black background and a white background respectively to measure the reflectance, and calculate the opacity (%) according to ISO 2471.

[0042] Tensile strength and elongation at break: Paper samples were cut to size 15mm × 100mm, equilibrated for 24 hours under suitable conditions, and tested using a universal testing machine equipped with a 5kN load cell. The clamping distance was set to 50mm, the tensile rate was 1mm / s, and the maximum tensile force F at break was recorded. max (N) and the corresponding elongation at fracture ΔL (mm).

[0043] Tensile strength = F max / w; (w is the sample width (m)); Elongation at break = (ΔL / L0) × 100%; (L0 = 50mm clamping distance).

[0044] Tear strength: Cut a 63mm×63mm paper sample according to the standard, and pre-cut a 12.7mm long opening in the middle. The paper sample is hooked at the opening. The tear tester releases the pendulum and measures the energy (mN·m) during tearing. Record the corresponding tear strength.

[0045] Table 1 The composite retention aid system of Examples 1-3 can significantly improve the retention rate of nano-TiO2 at the wet end, while obtaining paper-based finishing materials with high whiteness and high opacity, and significantly enhancing the mechanical strength of the paper. Comparative Example 2, which was purchased externally, had a low retention rate due to the large loss of nano-TiO2, resulting in insufficient whiteness and opacity, and the paper strength was also significantly worse. Comparative Example 1, which did not have guar gum crosslinking, had a slightly improved retention rate, but it was far less than that of the embodiments of the present invention, indicating that single PDA coating is still difficult to form a stable "three-dimensional network capture" mechanism.

[0046] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for aiding the retention of nano-titanium dioxide fillers based on paper-based finishing materials, characterized in that, The retention assistance method includes the following steps: S100. Under alkaline conditions, nano-titanium dioxide is mixed with dopamine to obtain polydopamine-coated titanium dioxide. S200. The polydopamine-coated titanium dioxide is mixed with boron-containing cationic guar gum to obtain a composite retention aid. S300. The composite retention aid is added to the pulp, and wet-end retention treatment and web forming treatment are performed to obtain the paper-based finishing material.

2. The retention-aiding method according to claim 1, characterized in that, The preparation method of the boron-containing cationic guar gum in step S200 includes the following steps: S210. Dissolve cationic guar gum in deionized water and perform a first stirring treatment to obtain a guar gum solution; S220. Add boric acid solution to the guar gum solution and simultaneously perform a second stirring treatment to obtain a second solution. After cooling the second solution to room temperature, the boron-containing cationic guar gum is obtained.

3. The retention-aiding method according to claim 2, characterized in that, In step S210, The first stirring treatment is performed at a speed of 300-500 rpm for a time of 20-30 min.

4. The retention-aiding method according to claim 2, characterized in that, In step S220, The concentration of the boric acid solution is 10-30 mM; The second stirring treatment is performed at a speed of 300-500 rpm for 10-15 minutes.

5. The retention-aiding method according to claim 2, characterized in that, In step S220, after the second stirring treatment, the following is further included: S221. Adjust the pH of the second solution to 6.5-7.5 using sodium hydroxide or hydrochloric acid.

6. The retention-aiding method according to claim 1, characterized in that, In step S100, The concentration of the dopamine monomer is 1-3 g / L; The alkaline conditions are a pH value between 8.5 and 9.0; The particle size of the nano-titanium dioxide is 20-50 nm.

7. The retention-aiding method according to claim 1, characterized in that, In step S200, The mass ratio of the polydopamine-coated titanium dioxide to the boron-containing cationic guar gum is 1:(8-12). The mixing process is carried out at a temperature of 40-50°C for 25-45 minutes.

8. The retention-aiding method according to claim 1, characterized in that, In step S300, The concentration of the pulp is 1-3 wt%; The amount of the composite retention aid added is 1.0-2.0 wt% of the dry fiber mass; The ultrasonic frequency of the wet end retention aid is 15-25kHz; The stirring speed for the web forming process is 1500-2500 rpm; The temperature for the wet end retention treatment is 55-65℃, and the time is 3-5 minutes. The dehydration pressure of the web forming process is 0.1-0.3 MPa.

9. The retention-aiding method according to claim 1, characterized in that, The S300 also includes adjusting the pH value to 5.0-6.0 after the wet end retention treatment and before web formation.

10. The retention-aiding method according to any one of claims 1-9, characterized in that, The paper-based finishing material is used for decorative face paper.

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