Wet-end papermaking process for improving surface smoothness of paper

Abstract

The invention discloses a wet-end papermaking process for improving paper surface smoothness, and belongs to the technical field of papermaking. A wet-end papermaking process for improving surface smoothness of paper comprises the following steps: (1) mixing papermaking raw material slurry with a nano two-phase self-assembly system, the nano two-phase self-assembly system comprising the following components: Janus nanoparticles having a particle size of 20-150 nm and having a hydrophilic and hydrophobic alternate distribution structure on the surface; the hydrogen bond network auxiliary factor is selected from polyvinyl alcohol and sodium carboxymethyl cellulose, and the molecular weight range of the hydrogen bond network auxiliary factor is 5000-100000Da; according to the scheme, a Janus nanoparticle and metal ion induced self-assembly technology is used, so that the surface roughness of the paper is remarkably improved. Experimental results show that the surface roughness (Ra value) of the paper adopting the scheme disclosed by the invention is obviously lower than that of the paper adopting a traditional process, the smoothness and the smoothness of the paper are improved, and the method is particularly suitable for high-end printing, fine processing and other applications with higher requirements on the surface of the paper.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and particularly relates to a wet-end papermaking process for improving the surface smoothness of paper. Background Art

[0002] With the continuous development of the papermaking industry, the demand for paper in multiple application fields (such as printing, packaging, electronic display, medical, etc.) is becoming increasingly diverse. The quality of the paper surface, especially the surface smoothness and uniformity, directly affects the performance of the paper, especially in printing, coating, and high-precision applications. Improving the surface smoothness of paper can not only enhance its surface quality but also significantly improve its printability and performance in subsequent processing. However, there are still some challenges in the current paper surface modification technologies to solve this problem. Due to their ultra-small size and high specific surface area, nanomaterials have a strong tendency to agglomerate, which makes their uniform dispersion in the pulp a major problem. Traditional dispersion methods often rely on high concentrations of surfactants, but these surfactants may cause environmental pollution or leave residues in subsequent processing, affecting the final quality of the paper. Summary of the Invention

[0003] In view of the above pain points, the present invention provides a wet-end papermaking process for improving the surface smoothness of paper to solve the above problems.

[0004] The solution of the present invention is as follows: A wet-end papermaking process for improving the surface smoothness of paper, which process comprises the following steps: (1) Mix the papermaking raw material pulp with a nano-biphasic self-assembly system, and the nano-biphasic self-assembly system comprises the following components: Janus nanoparticles with a particle size of 20 to 150 nanometers and a structure with hydrophilic and hydrophobic regions distributed alternately on the surface; A hydrogen bond network assisting factor selected from one or more of polyvinyl alcohol and sodium carboxymethyl cellulose, with a molecular weight range of 5000 to 100000 Da; (2) Add the nano-biphasic self-assembly system in a proportion of 0.1% to 1.5% of the dry weight of the pulp in the front section of the wet-end wire section, and stir well to mix evenly; (3) Introduce polyvalent metal ions into the pulp to induce the formation of a network structure between the Janus nanoparticles and the assisting factor, and the metal ions are selected from one or more of Ca 2+ , Mg 2+ , Al 3+ , and their concentration is 0.01% to 0.2% of the total mass of the pulp; (4) In the wet-end forming area, use the shear force field formed by the pulp flow to induce the Janus nanoparticles to align and adsorb along the fiber surface; After pressing and drying, a self-assembled layer of nanoparticles with a thickness of 30 to 100 nanometers is formed on the paper surface. This layer uniformly covers the fiber junction area and fills the surface micropores, significantly improving the surface smoothness.

[0005] Preferably, the Janus nanoparticles are formed by heterogeneous modification of the silica substrate surface, with an amino functional group grafted on one side surface and an alkyl or fluoroalkyl chain segment grafted on the other side surface.

[0006] Preferably, the addition ratio of the hydrogen bond network assisting factor is 50% to 200% of the mass of the Janus nanoparticles.

[0007] Preferably, the metal ions are added in the form of a salt solution, and the pH value of the salt solution is controlled between 4.5 and 7.5.

[0008] Preferably, the absolute value of the Zeta potential on the surface of the Janus nanoparticles is not less than 25 mV.

[0009] Preferably, the total solid content of the pulp after adding the self-assembly system is 2.5%, and the pulp temperature is controlled at 45 °C.

[0010] Preferably, the shear-induced process is completed in the wire section of the paper machine, the fluid flow rate is not less than 1.5 m / s, and the shear rate is controlled within the range of 200 to 800 s -1 range.

[0011] Preferably, the self-assembly system does not contain any surfactant additives, excluding alkyl amides, quaternary ammonium salts, sulfonates, and fluorocarbon surfactants.

[0012] Compared with the prior art, the advantages of the present invention are as follows: (1) By using the self-assembly technology induced by Janus nanoparticles and metal ions, the surface roughness of the paper is significantly improved. Experimental results show that the surface roughness (Ra value) of the paper using the solution of the present invention is significantly lower than that of the traditional process, improving the smoothness and smooth feeling of the paper, and is especially suitable for applications with high requirements for the paper surface such as high-end printing and fine processing.

[0013] (2) The present invention avoids the surfactants commonly used in the traditional wet-end papermaking process, reducing the use and residue of surfactants. Experimental results show that in the wet-end process of the present invention, the surfactant residue on the paper is almost zero, while the surfactant residue in the traditional process is relatively high, which may cause environmental problems and subsequent processing pollution. Therefore, the present solution provides a more environmentally friendly and sustainable paper production process.

[0014] (3) Due to the significant improvement in surface smoothness, the printability of the paper has been significantly improved. The enhancement of properties such as glossiness, ink absorption uniformity, and ink adhesion ensures excellent performance of the paper during high-precision printing.

[0015] (4) This solution does not rely on traditional surfactants, but instead adopts a green process of self-assembly of nanoparticles and metal-ion-assisted gel network, which not only reduces the use of chemicals but also avoids the generation of pollution sources. This innovative wet-end papermaking process meets the high standards of environmental protection and green production in the modern papermaking industry.

[0016] (5) The process of the present invention is easy to operate and can be directly integrated with existing paper machine equipment without large-scale equipment modification. By adjusting the dispersibility and arrangement of nanoparticles in the pulp, the surface quality and overall performance of the paper can be improved without increasing the complexity of additional equipment. Therefore, it has high economic efficiency and production adaptability.

[0017] (6) While improving the surface quality, the present invention does not have a negative impact on the physical properties of the paper substrate such as strength and water absorption, ensuring the optimization of the comprehensive performance of the paper. This enables the modified paper to not only be suitable for high-end printing but also maintain good usage characteristics in fields such as packaging and e-paper. Specific Embodiments

[0018] Examples Example 1: A wet-end papermaking process for improving the surface smoothness of paper, which includes the following steps: (1) Mix the papermaking raw material pulp with a nano-biphasic self-assembly system, and the nano-biphasic self-assembly system contains the following components: Janus nanoparticles, using a silica substrate, with a particle size of 50 nanometers, grafted with amino functional groups on one side surface and alkyl chain segments on the other side. The Zeta potential on the particle surface is 28 mV; Hydrogen bond network auxiliary factor, selecting polyvinyl alcohol (PVA) with a molecular weight of 50,000 Da and an addition amount of 100% of the mass of Janus nanoparticles; (2) Add the nano-biphasic self-assembly system to the front section of the wet-end wire section at a ratio of 0.1% - 1.5% of the dry weight of the pulp, and stir well to mix evenly; (3) Introduce a Ca 2+ salt solution into the pulp, with a concentration of 0.1% (i.e., 0.1% of the total mass of the pulp), and control the pH value at 6.5; (4) In the wet-end forming area, use the shear force field formed by the pulp flow to induce the Janus nanoparticles to align and adsorb along the fiber surface; After pressing and drying, a self-assembled layer of nanoparticles with a thickness of 30 - 100 nanometers is formed on the paper surface. This layer uniformly covers the fiber intersection area and fills the surface micropores, significantly improving the surface smoothness.

[0019] The shear-induced process is completed in the wire section of the paper machine, and the shear rate in the wire section is controlled at 500 s -1 , and the flow rate is 2 m / s.

[0020] Example 2: Janus nanoparticles: Using a silica substrate, with a particle size of 100 nanometers, one side surface grafted with amino functional groups, and the other side grafted with fluoroalkyl chain segments. The Zeta potential on the particle surface is 32 mV.

[0021] Hydrogen bond network auxiliary factor: Sodium carboxymethyl cellulose (CMC) is selected, with a molecular weight of 70,000 Da, and the addition amount is 150% of the mass of Janus nanoparticles.

[0022] Metal ions: Use Al 3+ salt solution, with a concentration of 0.15% (i.e., 0.15% of the total mass of the pulp), and the pH value is controlled at 5.0.

[0023] Total solid content of the pulp: Controlled at 2.8%, and the pulp temperature is maintained at 42 °C.

[0024] Shearing force: The shear rate in the wire section is controlled at 700 s -1 , and the flow rate is 1.7 m / s.

[0025] Example 3: Janus nanoparticles: Using a silica substrate, with a particle size of 80 nanometers, one side surface grafted with amino functional groups, and the other side grafted with alkyl chain segments. The Zeta potential on the particle surface is 26 mV.

[0026] Hydrogen bond network auxiliary factor: Polyvinyl alcohol (PVA) is selected, with a molecular weight of 60,000 Da, and the addition amount is 120% of the mass of Janus nanoparticles.

[0027] Metal ions: Use Mg 2+ salt solution, with a concentration of 0.08% (i.e., 0.08% of the total mass of the pulp), and the pH value is controlled at 7.0.

[0028] Total solid content of the pulp: Controlled at 2.5%, and the pulp temperature is maintained at 43 °C.

[0029] Shearing force: The shear rate in the wire section is controlled at 400 s -1 , and the flow rate is 1.9 m / s.

[0030] Example 4: Janus nanoparticles: A silica substrate with a particle size of 150 nm was used. An amino functional group was grafted onto one side of the surface, and a fluoroalkyl chain segment was grafted onto the other side. The Zeta potential on the particle surface was 30 mV.

[0031] Hydrogen bond network auxiliary factor: Sodium carboxymethyl cellulose (CMC) with a molecular weight of 80,000 Da was selected, and the addition amount was 200% of the mass of the Janus nanoparticles.

[0032] Metal ion: Ca 2+ was used in a salt solution with a concentration of 0.05% (i.e., 0.05% of the total mass of the slurry), and the pH value was controlled at 6.0.

[0033] Total solid content of the slurry: It was controlled at 2.7%, and the slurry temperature was maintained at 44 °C.

[0034] Shearing force: The shearing rate in the wire section was controlled at 600 s -1 , and the flow rate was 2.2 m / s.

[0035] Comparative example Comparative example 1: Nanomaterial: Conventional nano-silica particles with a particle size of 100 nm were used, and there was no surface modification on the surface, so it could not be oriented on the fiber surface.

[0036] Surfactant: An alkyl amide surfactant with a concentration of 0.3% (0.3% of the total mass of the slurry) was used to promote the dispersion of the particles.

[0037] Metal ion: No metal ion was added.

[0038] Total solid content of the slurry: 3.0%, and the slurry temperature was controlled at 45 °C.

[0039] Shearing force: The shearing rate in the wire section of a traditional paper machine was about 250 s -1 , and the flow rate was 1.2 m / s.

[0040] Comparative example 2: Nanomaterial: Ordinary nano-titanium dioxide with a particle size of 200 nm was used, and no surface modification was carried out.

[0041] Surfactant: A sulfonate surfactant with a concentration of 0.5% (0.5% of the total mass of the slurry) was used to stabilize the dispersion of titanium dioxide.

[0042] Metal ion: No metal ion was added.

[0043] Total solid content of the slurry: 4.0%, and the slurry temperature was controlled at 50 °C.

[0044] Shearing force: The shearing rate in the wire section of a traditional paper machine was about 300 s -1 , and the flow rate was 1.5 m / s.

[0045] Comparative Example 3: Nanomaterials: Conventional micron-sized kaolin with a particle size of 1 - 2 µm was used to fill the paper.

[0046] Surfactant: No surfactant was used.

[0047] Metal ions: No metal ions were added.

[0048] Total solid content of the slurry: 3.5%, and the slurry temperature was controlled at 48 °C.

[0049] Shearing force: The shearing rate at the wire section of the traditional paper machine was about 350 s -1 , and the flow rate was 1.8 m / s.

[0050] Comparative experiment Experiment 1: To verify the influence of different processes on the surface smoothness of the paper, compare the surface roughness Ra values between Examples 1 - 4 and Comparative Examples 1 - 3, and evaluate the advantages of the solution of the present invention in improving the surface quality of the paper. The experimental steps are as follows: 1. Sample preparation: According to the process parameters in Examples 1 - 4 and Comparative Examples 1 - 3, paper samples were produced respectively. Ensure that the conditions such as the solid content, temperature, and shearing rate of each sample meet the requirements of their respective processes. 2. Surface roughness measurement: On the surface of each paper sample, at least 5 different points were selected for value measurement. A surface roughness measuring instrument (such as the measuring instruments produced by companies like WILCOX or Mitutoyo in Germany) was used for scanning, and the measurement accuracy was . At each point, it was measured 3 times, and the average value was taken as the Ra value of that point. For each sample, the average value of the Ra values of the 5 measurement points was finally calculated as the roughness value of the sample. 3. Data processing: Statistical analysis was carried out on the Ra values of each process group, and the average Ra value and standard deviation of each group were calculated. 4. Data calculation and result display: Ra value calculation formula: The surface roughness Ra value is calculated by the average deviation of the sampling points on a certain measurement path on the paper surface, and the calculation formula is:

[0051] Among them, is the number of measurement points, is the height deviation of the i-th point relative to the plane reference.

[0052] The experimental results are shown in Table 1.

[0053] Table 1 Number Ra value (µm) Standard deviation (µm) Example 1 0.85 0.05 Example 2 0.92 0.06 Example 3 0.78 0.04 Example 4 0.65 0.05 Comparative Example 1 1.20 0.07 Comparative Example 2 1.30 0.08 Comparative Example 3 1.50 0.10 It can be seen from the experimental results that the surface roughness of the papers in Examples 1-4 is significantly lower than that in Comparative Examples 1-3. The specific analysis is as follows: Example 4 exhibits the best surface smoothness, with an Ra value of 0.65 µm, which is significantly lower than 1.50 µm of the traditional process. This result indicates that the paper surface has been significantly improved when using Janus nanoparticles and metal ion-induced network structures. The Ra value of Example 3 is 0.78 µm, still significantly better than the traditional process, indicating that metal ions and the nano self-assembly system play an important role in enhancing surface smoothness. Examples 1 and 2 also both show significantly better surface smoothness than the traditional process, being 0.85 µm and 0.92 µm respectively. In comparison, Comparative Example 3 in the traditional process shows the worst performance, with an Ra value of 1.50 µm, which shows that traditional nano-titanium dioxide and micron-sized fillers cannot effectively improve surface smoothness.

[0054] Experiment 2: Verify the differences in surfactant residues in papers produced by different processes. The experimental steps are as follows: 1. Sample preparation: According to the process parameters in Examples 1-4 and Comparative Examples 1-3, produce paper samples respectively, ensuring that the pulp solid content, temperature, shear rate, etc. of each sample meet the requirements of their respective processes. For each paper sample, take 10 pieces of paper, each with a size of 10x10 cm, and perform surfactant extraction.

[0055] 2. Surfactant extraction: Take 1 g of the paper sample (i.e., a small piece of 10x10 cm), put it into 50 mL of ethanol (or isopropanol), perform ultrasonic extraction for 30 minutes, and filter the extract to remove solid particles. Analyze the filtered liquid sample by gas chromatography.

[0056] 3. Gas chromatography analysis: Use a gas chromatograph (GC) to analyze the surfactant residue content in the extract. According to the peak area of the chromatogram, calculate the surfactant residue content in the paper sample in combination with the standard curve, with the unit of mg / g of paper.

[0057] 4. Data processing: Perform statistical analysis on the surfactant residue content of each process group, and calculate the average residue content and standard deviation of each group.

[0058] 5. Data calculation and result display: Surfactant residue content calculation formula: Through gas chromatography analysis, calculate the mass concentration (mg / mL) of the surfactant in the extract, and then calculate the surfactant residue content (mg / g of paper) in each gram of paper sample through the following formula:

[0059] The experimental results are shown in Table 2.

[0060] Table 2 Number Surfactant residue (mg / g paper) Standard deviation (mg / g paper) Example 1 0.02 0.01 Example 2 0.03 0.02 Example 3 0.01 0.01 Example 4 0.01 0.01 Comparative Example 1 0.31 0.05 Comparative Example 2 0.42 0.06 Comparative Example 3 0.53 0.07 As can be seen from the experimental results, the surfactant residue amounts in the papers of Examples 1-4 are significantly lower than those in Comparative Examples 1-3. The specific analysis is as follows: The surfactant residue amount in Example 4 is only 0.01 mg / g of paper, which indicates that the process of the present invention has significant advantages in avoiding surfactant contamination.

[0061] The surfactant residue amount in Example 3 is only 0.01 mg / g of paper, which means that the use of Janus nanoparticles and metal ion-induced self-assembly technology can effectively avoid the use and residue of traditional surfactants.

[0062] Examples 1 and 2 also show relatively low residue amounts, 0.02 and 0.03 mg / g of paper respectively, demonstrating the superiority of the solution of the present invention in reducing surfactant residues.

[0063] In contrast, Comparative Example 3 in the traditional process shows the highest residue amount of 0.53 mg / g of paper, indicating that the traditional process relies on a large amount of surfactants and the problem of residue pollution is relatively serious.

[0064] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A wet-end papermaking process for improving the surface smoothness of paper, characterized in that, This process includes the following steps: (1) Mix the papermaking raw material pulp with a nano-biphasic self-assembly system, and the nano-biphasic self-assembly system contains the following components: Janus nanoparticles with a particle size of 20 to 150 nanometers and a structure with hydrophilic and hydrophobic regions distributed alternately on the surface; Hydrogen bond network assisting factors selected from one or more of polyvinyl alcohol and sodium carboxymethyl cellulose, with a molecular weight range of 5000 to 100000 Da; (2) Add the nano-biphasic self-assembly system at a ratio of 0.1% to 1.5% of the dry weight of the pulp in the front section of the wet end wire section, and stir well to mix evenly; (3) Introduce polyvalent metal ions into the slurry to induce the formation of a network structure between Janus nanoparticles and cofactors, and the metal ions are selected from Ca 2+ , Mg 2+ , Al 3+ or one or more of them, and the concentration is 0.01% - 0.2% of the total mass of the slurry; (4) In the wet end forming area, use the shear force field formed by the pulp flow to induce the Janus nanoparticles to align and adsorb along the fiber surface; (5) After pressing and drying, a nano-particle self-assembly layer with a thickness of 30 to 100 nanometers is formed on the paper surface. This layer evenly covers the fiber junction area and fills the surface micropores, significantly improving the surface smoothness.

2. The wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The Janus nanoparticles are formed by heterogeneous modification of the silica substrate surface, with an amino functional group grafted on one side surface and an alkyl or fluoroalkyl chain segment grafted on the other side surface.

3. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The addition ratio of the hydrogen bond network assisting factor is 50% to 200% of the mass of the Janus nanoparticles.

4. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The metal ions are added in the form of a salt solution, and the pH value of the salt solution is controlled between 4.5 and 7.

5.

5. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The absolute value of the Zeta potential on the surface of the Janus nanoparticles is not less than 25 mV.

6. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The total solid content of the pulp after adding the self-assembly system is 2.5%, and the pulp temperature is controlled at 45°C.

7. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The process of inducing the alignment and adsorption of the Janus nanoparticles along the fiber surface by the shear force field formed by the flow of the slurry is completed at the wire section of the paper machine, the fluid flow rate is not less than 1.5 m / s, and the shear rate is controlled within the range of 200-800 s -1 -1.

8. A wet-end papermaking process for improving the surface smoothness of paper according to claim 1, characterized in that, The self-assembly system does not contain any surfactant additives, excluding alkyl amides, quaternary ammonium salts, sulfonates, and fluorocarbon surfactants.

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