A wet-end papermaking process for improving paper surface smoothness

Abstract

The present invention discloses a wet-end papermaking process for improving the surface smoothness of paper, belonging to the field of papermaking technology. The wet-end papermaking process for improving the surface smoothness of paper comprises the following steps: (1) mixing a papermaking raw material slurry with a nanometer dual-phase self-assembly system, wherein the nanometer dual-phase self-assembly system comprises the following components: Janus nanoparticles having a particle size of 20 to 150 nanometers and a surface structure with a hydrophilic and hydrophobic distribution; and a hydrogen bond network auxiliary factor selected from polyvinyl alcohol and sodium carboxymethyl cellulose with a molecular weight range of 5000 to 100000 Da. The present invention significantly improves the surface roughness of paper by using Janus nanoparticles and metal ion-induced self-assembly technology. Experimental results show that the surface roughness (Ra value) of paper using the present invention is significantly lower than that of the traditional process, and the smoothness and glossiness of the paper are improved. The present invention is particularly suitable for applications with high requirements on the paper surface, such as high-end printing and fine processing.

Description

Technical Field

[0001] The invention belongs to the technical field of papermaking, and in particular 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 diversified. 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 improve its surface quality, but also significantly improve its printability and performance in subsequent processing. However, current paper surface modification technology still faces some challenges in solving this problem. Nanomaterials have a strong tendency to agglomerate due to their ultra-small size and high specific surface area, which makes their uniform dispersion in the slurry a major problem. Traditional dispersion methods often rely on high concentrations of surfactants, but these surfactants may pollute the environment or leave residues in subsequent processing, affecting the final quality of the paper. Summary of the Invention

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

[0004] The present invention provides a wet-end papermaking process for improving the surface smoothness of paper, the process comprising the following steps:

[0005] (1) Mixing papermaking raw material slurry with a nanometer two-phase self-assembly system, wherein the nanometer two-phase self-assembly system comprises the following components:

[0006] Janus nanoparticles have a particle size of 20 to 150 nanometers and a surface structure with alternating hydrophilic and hydrophobic distributions;

[0007] A hydrogen bond network auxiliary factor selected from one or more of polyvinyl alcohol and sodium carboxymethyl cellulose, with a molecular weight range of 5000 to 100000 Da;

[0008] (2) adding the nano two-phase self-assembly system to the front section of the wet end mesh at a ratio of 0.1% to 1.5% of the dry weight of the slurry, and stirring and mixing thoroughly;

[0009] (3) Introducing multivalent metal ions into the slurry to induce Janus nanoparticles to form a network structure with auxiliary factors, wherein the metal ions are selected from Ca 2+ Mg 2+ 、Al 3+ One or more of the following, with a concentration of 0.01% to 0.2% of the total mass of the slurry;

[0010] (4) In the wet end forming area, the shear force field formed by the slurry flow is used to induce the Janus nanoparticles to be oriented and adsorbed along the fiber surface;

[0011] (5) After pressing and drying, a nanoparticle self-assembled layer with a thickness of 30 to 100 nanometers is formed on the surface of the paper. This layer evenly covers the fiber junction area and fills the surface micropores, significantly improving the surface smoothness.

[0012] Preferably, the Janus nanoparticles are formed by heterogeneously modifying the surface of a silica substrate, wherein amino functional groups are grafted onto one side of the surface and alkyl or fluoroalkyl segments are grafted onto the other side of the surface.

[0013] Preferably, the addition ratio of the hydrogen bond network auxiliary factor is 50% to 200% of the mass of the Janus nanoparticles.

[0014] 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.

[0015] Preferably, the absolute value of the surface Zeta potential of the Janus nanoparticles is not less than 25 mV.

[0016] Preferably, the total solid content of the slurry after adding the self-assembly system is 2.5%, and the slurry temperature is controlled at 45°C.

[0017] Preferably, the shear induction process is completed in the paper machine mesh section, the fluid flow rate is not less than 1.5 m / s, and the shear rate is controlled at 200 to 800 s -1 within the range.

[0018] Preferably, the self-assembly system does not contain any surfactant additives, excluding alkylamides, quaternary ammonium salts, sulfonates, and fluorocarbon surfactants.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] (1) This approach significantly improves the surface roughness of paper by using Janus nanoparticles and metal ion-induced self-assembly technology. Experimental results show that the surface roughness (Ra value) of paper produced using this approach is significantly lower than that of conventional processes, improving the smoothness and glossiness of the paper. This approach is particularly suitable for applications requiring high surface quality, such as high-end printing and fine processing.

[0021] (2) The present invention avoids the use of surfactants commonly used in traditional wet-end papermaking processes, reducing the use and residue of surfactants. Experimental results show that in the wet-end process of the present invention, the residual amount of surfactant in the paper is almost zero, while the residual amount of surfactant in traditional processes is higher, which may cause environmental problems and subsequent processing pollution. Therefore, this solution provides a more environmentally friendly and sustainable paper production process.

[0022] (3) Due to the significant improvement in surface smoothness, the printability of the paper has been significantly improved. The improvement in glossiness, ink absorption uniformity, ink adhesion and other properties ensures the excellent performance of the paper in the high-precision printing process.

[0023] (4) This solution does not rely on traditional surfactants. Instead, it uses a green process that combines the self-assembly of nanoparticles with a 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 the modern papermaking industry for environmental protection and green production.

[0024] (5) The process of the present invention is simple to operate and can be directly integrated with existing paper machine equipment without requiring large-scale equipment modifications. By adjusting the dispersion and arrangement of nanoparticles in the slurry, the surface quality and overall performance of the paper can be improved without adding additional equipment complexity. Therefore, it has high economic efficiency and production adaptability.

[0025] (6) While improving the surface quality, the present invention does not negatively impact the paper's physical properties, such as substrate strength and water absorption, thereby ensuring that the paper's overall performance is optimized. This makes the modified paper not only suitable for high-end printing but also maintains excellent performance in areas such as packaging and electronic paper. DETAILED DESCRIPTION

[0026] Example

[0027] Example 1: A wet-end papermaking process for improving the surface smoothness of paper, the process comprising the following steps:

[0028] (1) Mixing papermaking raw material slurry with a nanometer two-phase self-assembly system, wherein the nanometer two-phase self-assembly system comprises the following components:

[0029] Janus nanoparticles, based on a silica substrate with a particle size of 50 nanometers, have amino groups grafted onto one side of the surface and alkyl groups grafted onto the other. The particle surface zeta potential is 28 mV.

[0030] As the hydrogen bonding network cofactor, polyvinyl alcohol (PVA) was selected with a molecular weight of 50,000 Da and an addition amount of 100% of the mass of Janus nanoparticles;

[0031] (2) adding the nano two-phase self-assembly system to the front section of the wet end mesh at a ratio of 0.1% to 1.5% of the dry weight of the slurry, and stirring and mixing thoroughly;

[0032] (3) Introducing Ca into the slurry 2+ Salt solution, with a concentration of 0.1% (i.e. 0.1% of the total mass of the slurry), and a pH value controlled at 6.5;

[0033] (4) In the wet end forming area, the shear force field formed by the slurry flow is used to induce the Janus nanoparticles to be oriented and adsorbed along the fiber surface;

[0034] (5) After pressing and drying, a nanoparticle self-assembled layer with a thickness of 30 to 100 nanometers is formed on the surface of the paper. This layer evenly covers the fiber junction area and fills the surface micropores, significantly improving the surface smoothness.

[0035] The shear induction process is completed in the wire section of the paper machine, and the shear rate in the wire section is controlled at 500s -1 , the flow rate is 2m / s.

[0036] Example 2: Janus nanoparticles: Using a silica substrate, the particles are 100 nm in diameter, with amino groups grafted onto one side and fluoroalkyl groups grafted onto the other. The particle surface zeta potential is 32 mV.

[0037] Hydrogen bond network cofactor: Sodium carboxymethyl cellulose (CMC) with a molecular weight of 70,000 Da was selected, and the addition amount was 150% of the mass of Janus nanoparticles.

[0038] Metal ions: Al 3+ Salt solution, concentration is 0.15% (i.e. 0.15% of the total mass of the slurry), and the pH value is controlled at 5.0.

[0039] The total solid content of the slurry is controlled at 2.8%, and the slurry temperature is maintained at 42°C.

[0040] Shear force: The shear rate in the web section is controlled at 700s -1 , the flow rate is 1.7m / s.

[0041] Example 3: Janus nanoparticles: Using a silica substrate, the particles are 80 nanometers in diameter, with amino groups grafted onto one side and alkyl groups grafted onto the other. The particle surface zeta potential is 26 mV.

[0042] Hydrogen bond network cofactor: Polyvinyl alcohol (PVA) with a molecular weight of 60,000 Da was selected, and the addition amount was 120% of the mass of Janus nanoparticles.

[0043] Metal ion: Mg is used2+ The salt solution has a concentration of 0.08% (i.e. 0.08% of the total mass of the slurry) and a pH value controlled at 7.0.

[0044] The total solid content of the slurry is controlled at 2.5%, and the slurry temperature is maintained at 43°C.

[0045] Shear force: The shear rate in the web section is controlled at 400s -1 , the flow rate is 1.9m / s.

[0046] Example 4: Janus nanoparticles: Using a silica substrate, the particles are 150 nm in diameter, with amino groups grafted onto one side and fluoroalkyl groups grafted onto the other. The particle surface zeta potential is 30 mV.

[0047] Hydrogen bond network cofactor: Sodium carboxymethyl cellulose (CMC) with a molecular weight of 80,000 Da was selected and the addition amount was 200% of the mass of Janus nanoparticles.

[0048] Metal ions: Use Ca 2+ Salt solution, concentration is 0.05% (i.e. 0.05% of the total mass of the slurry), and the pH value is controlled at 6.0.

[0049] The total solid content of the slurry is controlled at 2.7%, and the slurry temperature is maintained at 44°C.

[0050] Shear force: The shear rate in the web section is controlled at 600s -1 , the flow rate is 2.2m / s.

[0051] Comparative Example

[0052] Comparative Example 1: Nanomaterials: Conventional nano-silica particles with a particle size of 100 nanometers were used without any surface modification and could not be arranged in a directional manner on the fiber surface.

[0053] Surfactant: Alkylamide surfactant was used at a concentration of 0.3% (0.3% of the total mass of the slurry) to promote the dispersion of particles.

[0054] Metal ions: No metal ions added.

[0055] The total solid content of the slurry is 3.0%, and the slurry temperature is controlled at 45°C.

[0056] Shear force: The shear rate in the wire section of a traditional paper machine is about 250s -1 , the flow rate is 1.2m / s.

[0057] Comparative Example 2: Nanomaterial: Ordinary nano titanium dioxide with a particle size of 200 nanometers was used without surface modification.

[0058] Surfactant: Use sulfonate surfactant at a concentration of 0.5% (0.5% of the total mass of the slurry) to stabilize the dispersion of titanium dioxide.

[0059] Metal ions: No metal ions added.

[0060] The total solid content of the slurry is 4.0%, and the slurry temperature is controlled at 50°C.

[0061] Shear force: The shear rate in the wire section of a traditional paper machine is about 300s -1 , the flow rate is 1.5m / s.

[0062] Comparative Example 3: Nanomaterial: Conventional micron-grade kaolin with a particle size of 1 to 2 µm was used to fill paper.

[0063] Surfactant: No surfactant was used.

[0064] Metal ions: No metal ions added.

[0065] The total solid content of the slurry is 3.5%, and the slurry temperature is controlled at 48°C.

[0066] Shear force: The shear rate in the wire section of a traditional paper machine is about 350s -1 , the flow rate is 1.8m / s.

[0067] Comparative experiment

[0068] Experiment 1: To verify the effect of different processes on the surface smoothness of paper, compare the surface roughness Ra values ​​between Examples 1-4 and Comparative Examples 1-3, and evaluate the advantages of the present invention in improving the surface quality of paper. The experimental steps are as follows: 1. Sample preparation: According to the process parameters of Examples 1-4 and Comparative Examples 1-3, paper samples were produced respectively. Ensure that the slurry solid content, temperature, shear rate and other conditions of each sample meet the respective process requirements. 2. Surface roughness measurement: Select at least 5 different points on the surface of each paper sample for measurement. Use a surface roughness measuring instrument (such as the measuring instruments produced by German WILCOX or Mitutoyo) to scan, and the measurement accuracy is . Measure 3 times at each point and take the average value as the Ra value of that point. For each sample, the average Ra value of the 5 measurement points is finally calculated as the roughness value of the sample. 3. Data processing: Statistical analysis is performed on the Ra value of each process group, and the average Ra value and standard deviation of each group are calculated. 4. Data calculation and result presentation: 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. The calculation formula is:

[0069]

[0070] in, is the number of measurement points, is the height deviation of the i-th point relative to the plane reference.

[0071] The experimental results are shown in Table 1.

[0072] Table 1

[0073] serial 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

[0074] It can be seen from the experimental results that the surface roughness of the paper of Examples 1-4 is significantly lower than that of Comparative Examples 1-3. The specific analysis is as follows: Example 4 shows the best surface smoothness, with an Ra value of 0.65µm, which is significantly lower than the 1.50µm of the traditional process. The results show that the surface of the paper is significantly improved when using Janus nanoparticles and metal ion-induced network structures. The Ra value of Example 3 is 0.78µm, which is still significantly better than the traditional process, indicating that metal ions and nano self-assembly systems have an important effect on improving surface smoothness. Example 1 and Example 2 also show significantly better surface smoothness than the traditional process, which are 0.85µm and 0.92µm, respectively. In comparison, Comparative Example 3 in the traditional process performed the worst, with an Ra value of 1.50µm, which shows that traditional nano titanium dioxide and micron-sized fillers cannot effectively improve surface smoothness.

[0075] Experiment 2: Verify the differences in surfactant residues in paper produced by different processes. The experimental steps are as follows:

[0076] 1. Sample Preparation: Paper samples were produced according to the process parameters described in Examples 1-4 and Comparative Examples 1-3, ensuring that the pulp solids content, temperature, shear rate, and other conditions for each sample met the respective process requirements. For each paper sample, 10 sheets of paper, each measuring 10 x 10 cm, were sampled for surfactant extraction.

[0077] 2. Surfactant Extraction: Take 1g of paper sample (i.e., a small piece measuring 10x10cm) and place it in 50mL of ethanol (or isopropanol). Ultrasonic extraction is performed for 30 minutes. The extract is filtered to remove solid particles. The filtered liquid sample is analyzed by gas chromatography.

[0078] 3. Gas Chromatography Analysis: Use a gas chromatograph (GC) to analyze the residual surfactant in the extract. Calculate the residual surfactant in the paper sample based on the peak area of ​​the chromatogram and the calibration curve (in mg / g paper).

[0079] 4. Data processing: Statistical analysis was performed on the surfactant residues in each process group, and the average residue and standard deviation of each group were calculated.

[0080] 5. Data Calculation and Results Presentation: Calculation Formula for Surfactant Residue: Calculate the surfactant mass concentration (mg / mL) in the extract using gas chromatography analysis. Then, calculate the surfactant residue per gram of paper sample (mg / g paper) using the following formula:

[0081]

[0082] The experimental results are shown in Table 2.

[0083] Table 2

[0084] serial 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

[0085] From the experimental results, it can be seen that the residual amount of surfactant in the paper of Examples 1-4 is significantly lower than that of Comparative Examples 1-3. The specific analysis is as follows:

[0086] The residual amount of surfactant in Example 4 is only 0.01 mg / g paper, which shows that the process of the present invention has a significant advantage in avoiding surfactant contamination.

[0087] The residual amount of surfactant in Example 3 is only 0.01 mg / g 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.

[0088] Example 1 and Example 2 also showed relatively low residual amounts, which were 0.02 and 0.03 mg / g paper, respectively, demonstrating the superiority of the solution of the present invention in reducing surfactant residues.

[0089] In comparison, Comparative Example 3 in the traditional process showed the highest residue amount of 0.53 mg / g paper, which shows that the traditional process relies on a large amount of surfactants and has a more serious residual pollution problem.

[0090] 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 to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in 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: The process includes the following steps: (1) Mixing papermaking raw material slurry with a nanometer two-phase self-assembly system, wherein the nanometer two-phase self-assembly system comprises the following components: Janus nanoparticles have a particle size of 20 to 150 nanometers and a surface structure with alternating hydrophilic and hydrophobic distributions; A hydrogen bond network auxiliary factor selected from one or more of polyvinyl alcohol and sodium carboxymethyl cellulose, with a molecular weight range of 5000 to 100000 Da; The self-assembly system does not contain any surfactant additives; (2) adding the nano two-phase self-assembly system to the front section of the wet end mesh at a ratio of 0.1% to 1.5% of the dry weight of the slurry, and stirring and mixing thoroughly; (3) Introducing multivalent metal ions into the slurry to induce Janus nanoparticles to form a network structure with auxiliary factors, wherein the metal ions are selected from Ca 2+ Mg 2+ 、Al 3+ One or more of the following, with a concentration of 0.01% to 0.2% of the total mass of the slurry; (4) In the wet end forming area, the shear force field formed by the slurry flow is used to induce the Janus nanoparticles to be oriented and adsorbed along the fiber surface; (5) After pressing and drying, a self-assembled layer of nanoparticles with a thickness of 30 to 100 nanometers is formed on the surface of the paper. This layer evenly covers the fiber junction area and fills the surface micropores, significantly improving the surface smoothness; The Janus nanoparticles are formed by heterogeneously modifying the surface of a silica substrate, with amino functional groups grafted onto one side of the surface and alkyl or fluoroalkyl segments grafted onto the other side of the surface; The addition ratio of the hydrogen bond network auxiliary factor is 50% to 200% of the mass of the Janus nanoparticles; 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.

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

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

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

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