Decorative base paper and method for producing a decorative base paper

Abstract

The application belongs to the technical field of decorative base paper preparation, and particularly relates to a decorative base paper and a preparation method thereof, which comprises the following steps: uniformly mixing paper pulp for preparing the decorative base paper and titanium dioxide to obtain mixed pulp; adding liquid polyaluminum chloride into the mixed pulp, so that the Zeta potential of the mixed pulp reaches 0-10 mV, excluding 0 mV; then adding polyamide epoxy chloropropane resin into the mixed pulp, uniformly mixing, adding sodium carboxymethyl cellulose, so that the Zeta potential of the mixed pulp reaches 2-5 mV; finally, adding polyacrylamide into the mixed pulp, and then beating to obtain the decorative base paper. The method can simultaneously realize that the decorative base paper has good uniformity, good titanium dioxide retention rate and smoothness of water filtration.

Description

Technical Field

[0001] This invention belongs to the field of decorative base paper preparation technology, specifically relating to a decorative base paper and a method for preparing decorative base paper. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Sodium carboxymethyl cellulose (CMC) is an important wet-end additive in papermaking. Its excellent water retention and film-forming properties can significantly improve the uniformity, surface smoothness and printability of paper. Therefore, it has important application value in paper types with high requirements for surface performance, such as decorative base paper.

[0004] However, current high-speed paper machine wet-end chemistry systems typically rely on a binary / microparticle retention and filtration system composed of cationic polymers (such as polyacrylamide, PAE, etc.) and anionic microparticles (such as polyacrylamide (PAM)) to achieve efficient retention and good filtration of fillers and fine fibers. When anionic CMC is added, the numerous carboxyl groups on its molecular chain undergo strong charge neutralization and complexation with the cationic polymers in the system, leading to the following problems: The excessive neutralization of the charge of cationic polymers prevents them from effectively bridging fiber and filler particles and disrupts the charge basis for forming a flocculation network with subsequent anionic microparticles, leading to a sharp decline in the efficiency of the entire retention and filtration system. Decorative base paper typically adds large amounts of expensive titanium dioxide to improve opacity. The failure of the main retention system directly results in a significant reduction in the retention rate of titanium dioxide in the paper machine's white water system, which not only increases raw material costs but also increases the load on the white water system. Pulp dispersed by CMC is difficult to form adequate, reflocculated flocs, leading to difficulties in pulp filtration, reduced paper machine dewatering capacity, limited operating speed, increased energy consumption, and even paper breaks.

[0005] To resolve the aforementioned contradictions, existing technologies typically involve sacrificing some performance, such as reducing or abandoning the use of CMC, which results in paper uniformity and printability not being optimal; or adjusting the process by moving the CMC addition point to the surface sizing stage, but this only improves surface performance and cannot solve the problem of uniformity inside the paper, and also increases sizing costs. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a decorative base paper and a method for preparing the decorative base paper.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing decorative base paper, comprising the following steps: The pulp used to prepare decorative base paper is mixed evenly with titanium dioxide to obtain a mixed pulp. Add liquid polyaluminum chloride to the mixed slurry to make the zeta potential of the mixed slurry reach 0-10mV, excluding 0mV; Then polyamide epichlorohydrin resin is added, mixed well, and sodium carboxymethyl cellulose is added to make the zeta potential of the mixed slurry reach 2-5mV. Finally, add polyacrylamide to the mixed slurry, stir for the set time, and then form the paper.

[0008] Secondly, the present invention provides a decorative base paper prepared by the aforementioned preparation method.

[0009] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention adds a specific type of PAC before PAE and CMC. As a cationic polymer with high charge density, PAC preferentially neutralizes anionic interfering substances in the system and effectively blocks the interference of subsequently added CMC on the main retention aid system (polyacrylamide (PAM)). Because the main retention aid system is protected, titanium dioxide can be efficiently flocculated and retained by polyacrylamide (PAM), avoiding loss caused by the addition of CMC, resulting in stable optical performance and cost savings.

[0010] The method of this invention allows for the addition of sufficient CMC, enabling CMC to fully utilize its advantages in water retention and film formation, significantly improving paper uniformity and surface properties. The slurry system of this invention exhibits stable charge, allowing the slurry to form good flocs, recovering the water filtration performance from the negative impacts of CMC addition, resulting in stable paper machine operating speed, low breakage rate, and reduced energy consumption. Detailed Implementation

[0011] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0012] To address the technical problems mentioned in the background art, the present invention provides a method for preparing decorative base paper, comprising the following steps: The pulp used to prepare decorative base paper is mixed evenly with titanium dioxide to obtain a mixed pulp. Add liquid polyaluminum chloride to the mixed slurry to make the zeta potential of the mixed slurry reach 0-10mV, excluding 0mV; Then polyamide epichlorohydrin resin is added, mixed well, and sodium carboxymethyl cellulose is added to make the zeta potential of the mixed slurry reach 2-5mV. Finally, add polyacrylamide to the mixed slurry, stir for the set time, and then form the paper.

[0013] Liquid polyaluminum chloride (PAC), as a high-charge-density cationic polymer, contains a large number of polynuclear aluminum hydroxy complexes in its molecular structure. These PACs can rapidly neutralize negatively charged anionic interfering substances in pulp systems, such as lignin sulfonates, pectin, and hemicellulose degradation products. These anions consume subsequently added cationic additives, leading to a decrease in the filtration efficiency of the additives. Through electrostatic adsorption and complexation, PAC can convert soluble anionic impurities into insoluble precipitates, preventing their accumulation and circulation within the system.

[0014] Sodium carboxymethyl cellulose (CMC), as an anionic surface sizing agent, will ineffectively bind with cationic polyacrylamide (PAM) as the primary retention aid if added directly to pulp. Preferential addition of PAC can form a cationic protective layer on the fiber surface, preventing contact between CMC and PAM, allowing PAM to bind more effectively with fine fibers and fillers. Simultaneously, sufficient CMC can be added to ensure paper uniformity, surface smoothness, and printability.

[0015] The dense flocculent structure formed by PAC accelerates the dewatering process of pulp in the wire section and improves filtration performance. The cationic groups of PAC can combine with anionic substances such as resin acids and fatty acids in the pulp to form stable complexes, reducing resin deposition in the wire and press sections and lowering the frequency of paper breaks. The epoxy groups in PAE molecules can undergo cross-linking reactions with the hydroxyl groups on the fiber surface, forming a stable covalent network during drying, significantly improving paper strength. The cationic segments of PAE can also bridge fine fibers and fillers, helping to improve the retention rate of titanium dioxide and other fillers.

[0016] The relatively high molecular weight of PAM can play a long-chain bridging role between the fibers, fillers and PAE-formed flocs. The resulting large floc structure can significantly improve the filtration speed and effectively enhance the dewatering efficiency of the mesh section.

[0017] Furthermore, the order in which liquid polyaluminum chloride, carboxymethyl cellulose, polyamide epichlorohydrin resin, and polyacrylamide are added in this invention is also a significant innovation, specifically: First, PAC is added to quickly neutralize the negative charge on the surface of fibers and titanium dioxide using strong cations, eliminating electrostatic repulsion between particles and allowing the dispersed fine fillers to initially aggregate. At the same time, the zeta potential of the pulp is quickly adjusted to a reasonable range, establishing a preliminary flocculation environment and occupying negative charge adsorption sites in advance, preventing subsequent anionic additives from directly occupying the fiber surface. Then, anionic CMC is added. At this point, after charge neutralization by PAC, the potential of the pulp system tends to be mild. Adding anionic CMC at this time will not cause a violent charge reversal. The long molecular chains of CMC interweave between the initially formed flocs, forming a flexible framework, improving paper sheet uniformity, and enhancing the hydrophilicity and water absorption properties of the paper, while also improving the retention of fine titanium dioxide.

[0018] If CMC is added first, the anions will directly encapsulate the negatively charged titanium dioxide particles and fibers, making it difficult for the cationic PAC to adsorb, thus completely losing its charge neutralization effect. Then, a weak cationic PAE is added. At this point, the floc skeleton has been formed, and PAE is evenly attached to the fiber interlacing sites without destroying the stable floc structure formed by PAC+CMC in the early stage. It prioritizes strengthening the fiber's own binding force and can also ensure the improvement of paper wet strength. If PAE is added in advance, it will occupy a large number of PAC adsorption sites, weakening the charge regulation and filler retention effect. Finally, cationic PAM is added as a large floc forming agent in the later stage. After the previous multiple additives are laid, the small flocs are finally associated into stable flocs of uniform size through macromolecular bridging, which ensures the retention rate and does not cause the uniformity to deteriorate due to the flocs being too large.

[0019] In some embodiments, the amount of titanium dioxide added accounts for 70%-85% of the oven-dry slurry mass, preferably 75%-80%.

[0020] In some embodiments, the basicity of the liquid polyaluminum chloride is 50%-70%, and the mass percentage of Al2O3 is 10%-18%.

[0021] When the alkalinity is <50%, PAC mainly exists as low-polymerization monomers and dimers, with low positive charge density and weak ability to neutralize anionic waste, thus failing to effectively form flocs. When the alkalinity is >70%, PAC will over-polymerize to form insoluble Al(OH)3 precipitates, resulting in the loss of effective components. In the alkalinity range of 50%-70%, PAC mainly exists as Al with a Keggin structure. 13 O4(OH) 24 7+ The presence of the thiomer, the most active form of PAC, with a positive charge density of up to +7, can efficiently neutralize anionic impurities in the pulp, ensuring the effective retention of substances such as titanium dioxide.

[0022] If the basicity is too low, the positive charge will be insufficient, weakening the ability to capture titanium dioxide particles. If the basicity is too high, precipitation or abnormal viscosity may occur during storage. An alumina content of 10-18% ensures sufficient aluminum content while avoiding excessive volume addition due to too low a content, which would increase the pumping burden. Setting the upper limit at 18% avoids problems such as high viscosity and pumping difficulties. Liquid PAC in the 10-18% range has good fluidity and is easier to mix with water.

[0023] In some embodiments, the amount of liquid polyaluminum chloride added is 0.5%-2% of the oven-dry slurry mass.

[0024] In some embodiments, the amount of polyamide epichlorohydrin resin added accounts for 0.3%-1% of the oven-dry slurry mass, preferably 0.4%-0.7%.

[0025] In some embodiments, the amount of sodium carboxymethyl cellulose added is 0.2%-0.8% of the oven-dry pulp mass.

[0026] Preferably, the aqueous solution of sodium carboxymethyl cellulose with a mass fraction of 2% has a viscosity of 100-300 mPa·s at 25°C.

[0027] In some embodiments, the amount of polyacrylamide added is 0.2%-0.6% of the oven-dry pulp mass.

[0028] Secondly, the present invention provides a decorative base paper prepared by the aforementioned preparation method.

[0029] The present invention will be further described below with reference to the embodiments.

[0030] The liquid polyaluminum chloride used in the following examples and comparative examples was purchased from Weifang Weihui Chemical Co., Ltd. The polyamide epichlorohydrin resin was purchased from Transfar Group Co., Ltd. The polyacrylamide was purchased from Shandong Tianjian Water Treatment Co., Ltd. Hydrated alumina was purchased from Shandong Anbai Chemical Co., Ltd.

[0031] Example 1 A method for preparing decorative base paper includes the following steps: (1) Mix the broadleaf eucalyptus pulp with a beating degree of 35°SR with 80% titanium dioxide (relative to the oven-dry pulp mass) and mix them evenly in a desoldering machine to obtain a mixed pulp.

[0032] (2) Add liquid polyaluminum chloride with an alkalinity of 65% and an Al2O3 mass percentage of 15% to the mixed slurry. The amount of liquid polyaluminum chloride added is 1.2% of the oven-dry slurry. The stirring speed is 1000 r / min and the stirring time is 5 min. Then, the zeta potential of the slurry is measured to be 6.7 mV using a zeta potential meter.

[0033] (3) Then add 0.5% of polyamide epichlorohydrin resin (PAE) by weight of oven-dry slurry to the slurry obtained in step (2), with a stirring speed of 1000 r / min and a stirring time of 5 min.

[0034] (4) Add 0.5% of CMC by weight of oven-dry slurry to the slurry obtained in step (3). The viscosity of CMC is 212 mPa·s (viscosity of 2% aqueous solution at 25℃). After addition, the stirring rate is 1000 r / min and the stirring time is 5 min. The zeta potential of the slurry is measured to be 4.1 mV using a zeta potential meter.

[0035] (5) Add 0.4% of the dry slurry mass of polyacrylamide (PAM) to the slurry obtained in step (4) to form a microparticle system. Stir at a speed of 1000 r / min for 5 minutes.

[0036] (6) The pulp obtained in step (4) is then sheeted on a standard paper forming machine at a rate of 80 g / m. 2 The hand-made sheets were dried at 92℃, and then treated in a constant temperature and humidity chamber at a temperature of 23±1℃ and a humidity of 50±2%RH for 24 hours before their performance was tested according to relevant standards.

[0037] Example 2 A method for preparing decorative base paper includes the following steps: (1) Mix the broadleaf eucalyptus pulp with a beating degree of 35°SR with 80% titanium dioxide (relative to the oven-dry pulp mass) and mix them evenly in a desoldering machine to obtain a mixed pulp.

[0038] (2) Add liquid polyaluminum chloride with an alkalinity of 50% and an Al2O3 mass percentage of 10% to the mixed slurry. The amount added is 0.5% of the oven-dry slurry. The stirring speed is 1000 r / min and the stirring time is 5 min. Then, the zeta potential of the slurry is measured to be 4.3 mV using a zeta potential meter.

[0039] (3) Then add 0.5% of polyamide epichlorohydrin resin (PAE) by weight of oven-dry slurry to the slurry obtained in step (2), with a stirring speed of 1000 r / min and a stirring time of 5 min.

[0040] (4) Add CMC with a viscosity of 300 mPa·s (viscosity of 2% aqueous solution at 25°C) to the slurry obtained in step (3). The amount of CMC added is 0.2% of the dry slurry mass. After addition, the stirring rate is 1000 r / min and the stirring time is 5 min. The zeta potential of the slurry is measured to be 3 mV using a zeta potential meter.

[0041] (5) Add 0.4% of the dry slurry mass of polyacrylamide (PAM) to the slurry obtained in step (4) to form a microparticle system. Stir at a speed of 1000 r / min for 5 minutes.

[0042] (6) Subsequently, the sheet was copied onto a standard sheet forming machine with a fixed weight of 80 g / m. 2 The hand-made sheets were dried at 92℃, and then treated in a constant temperature and humidity chamber at a temperature of 23±1℃ and a humidity of 50±2%RH for 24 hours before their performance was tested according to relevant standards.

[0043] Example 3 A method for preparing decorative base paper includes the following steps: (1) Mix the broadleaf eucalyptus pulp with a beating degree of 35°SR with 80% titanium dioxide (relative to oven-dry pulp) and mix them evenly in a desoldering machine to obtain a mixed pulp.

[0044] (2) Add liquid polyaluminum chloride with an alkalinity of 70% and an Al2O3 mass percentage of 18% to the mixed slurry. The amount of liquid polyaluminum chloride added is 2% of the oven-dry slurry. The stirring speed is 1000 r / min and the stirring time is 5 min. Then, the zeta potential of the slurry is measured to be 8.6 mV using a zeta potential meter.

[0045] (3) Then add 0.5% of polyamide epichlorohydrin resin (PAE) by weight of oven-dry slurry to the slurry obtained in step (2), with a stirring speed of 1000 r / min and a stirring time of 5 min.

[0046] (4) Add CMC with a viscosity of 100 mPa·s to the slurry obtained in step (3). The amount of CMC added is 0.8% of the dry slurry mass. After addition, the stirring speed is 1000 r / min and the stirring time is 5 min. The zeta potential of the slurry is measured to be 2.2 mV using a zeta potential meter.

[0047] (5) Add 0.4% of the dry slurry mass of polyacrylamide (PAM) to the slurry obtained in step (4) to form a microparticle system. Stir at a speed of 1000 r / min for 5 minutes.

[0048] (6) Subsequently, the sheet was copied onto a standard sheet forming machine with a fixed weight of 80 g / m. 2 The hand-made sheets were dried at 92℃, and then treated in a constant temperature and humidity chamber at a temperature of 23±1℃ and a humidity of 50±2%RH for 24 hours. After that, the performance was tested according to relevant international standards.

[0049] Comparative Example 1 The only difference from Example 1 is that step (4) is moved to step (2), and the rest of the steps are the same as in Example 1.

[0050] Specifically: (2) Add 0.5% of CMC by weight of oven-dry slurry to the mixed slurry. The viscosity of CMC is 212 mPa·s (viscosity of 2% aqueous solution at 25℃). After addition, the stirring rate is 1000 r / min and the stirring time is 5 min.

[0051] (3) Then add liquid polyaluminum chloride with an alkalinity of 65% and an Al2O3 mass percentage of 15% to the slurry obtained in step (2). The amount of liquid polyaluminum chloride added is 1.2% of the oven-dry slurry. The stirring rate is 1000 r / min and the stirring time is 5 min.

[0052] (4) Add 0.5% of polyamide epichlorohydrin resin (PAE) by weight of oven-dry slurry to the slurry obtained in step (3), with a stirring speed of 1000 r / min and a stirring time of 5 min.

[0053] Comparative Example 2 The only difference from Example 1 is that step (2) is omitted, while the rest of the steps are the same as in Example 1.

[0054] Comparative Example 3 The only difference from Example 1 is that step (4) is omitted, while the rest of the steps are the same as in Example 1.

[0055] Comparative Example 4 The only difference from Example 1 is that steps (2) and (3) are swapped, and the rest of the steps are the same as in Example 1.

[0056] Specifically: (2) Add 0.5% of polyamide epichlorohydrin resin (PAE) to the mixed slurry, stirring at a speed of 1000 r / min for 5 min.

[0057] (3) Then add liquid polyaluminum chloride with an alkalinity of 65% and an Al2O3 mass percentage of 15% to the slurry obtained in step (2), the amount added is 1.2% of the oven-dry slurry, the stirring speed is 1000 r / min, and the stirring time is 5 min; then, the zeta potential of the slurry is measured to be 6.7 mV using a zeta potential meter.

[0058] Comparative Example 5 The only difference from Example 1 is that step (4) is swapped with step (3), and the rest of the steps are the same as in Example 1.

[0059] Specifically: (3) Then add 0.5% of CMC by weight of oven-dry slurry to the slurry obtained in step (2). The viscosity of CMC is 212 mPa.s (viscosity of 2% aqueous solution at 25℃). After adding, the stirring rate is 1000 r / min and the stirring time is 5 min.

[0060] (4) Add 0.5% of polyamide epichlorohydrin resin (PAE) by weight of oven-dry slurry to the slurry obtained in step (3), and stir at a speed of 1000 r / min for 5 min.

[0061] Comparative Example 6 The only difference from Example 1 is that steps (4) and (5) are swapped, and the rest of the steps are the same as in Example 1.

[0062] Specifically: (4) Add 0.4% of the dry slurry mass of polyacrylamide (PAM) to the slurry obtained in step (3) to form a microparticle system. Stir at a speed of 1000 r / min for 5 minutes.

[0063] (5) Add 0.5% of the dry slurry mass of CMC to the slurry obtained in step (4). The viscosity of CMC is 212 mPa.s. After adding, the stirring speed is 1000 r / min and the stirring time is 5 min.

[0064] Comparative Example 7 The only difference from Example 1 is that the liquid polyaluminum chloride in step (2) is replaced with hydrated alumina in equal amounts, and the other steps are the same as in Example 1.

[0065] Comparative Example 8 The only difference from Example 1 is that the liquid polyaluminum chloride in step (2) is replaced with sulfuric acid, and the amount of sulfuric acid added is 0.53% of the dry slurry mass. All other steps are the same as in Example 1.

[0066] The performance of the decorative base paper prepared in the examples and comparative examples was tested below, and the test results are shown in Tables 1, 2 and 3.

[0067] The testing methods for each performance aspect are as follows: The test method for the total retention rate (%) of the slurry is as follows: ; The test method for ash retention rate (%) is as follows: ; The test methods for opacity, L, a, and b are GB / T1543-1988, using the Elrepho optical performance measuring instrument; The test methods for pulp ash content and paper ash content (%) are GB / T742-2008; The test method for dynamic filtration time is to use the Schubert beating degree test method and record the filtration time, referring to GB / T3332-1982; The uniformity test method is visual inspection. Place the paper in front of a light source and observe the uniformity of the light passing through the paper. The evaluation criteria for uniformity are as follows: Advantages: When observed under transmitted light, the light transmittance of the entire paper surface is very uniform, with almost no obvious bright spots (thin areas) or dark spots (thick areas), and no "cloud-like" or fiber flocculation phenomena. Good (Medium): When the light is transmitted, slight and uneven differences in light transmission can be seen, with a few inconspicuous cloud-like patterns or scattered small spots, but the overall surface is still relatively flat. Average (Poor): The light transmission is obviously uneven, with obvious "cloud-like" patterns, strong contrast between bright and dark spots, and even local thinness (with holes close together), and disordered fiber distribution.

[0068] The test method for tensile strength N / 15mm is GB / T12914-2018; The test method for air permeability is GB / T5402-2003; The test method for water absorption height (mm / 15min) is GB / T461.3-2005.

[0069] Table 1 Comparison of slurry retention rates

[0070] Table 2 Comparison of optical properties of finished paper

[0071] Table 3 Comparison of Physical Indicators

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing decorative base paper, characterized in that: Includes the following steps: The pulp used to prepare decorative base paper is mixed evenly with titanium dioxide to obtain a mixed pulp. Add liquid polyaluminum chloride to the mixed slurry to make the zeta potential of the mixed slurry reach 0-10mV, excluding 0mV; Then polyamide epichlorohydrin resin is added, mixed well, and sodium carboxymethyl cellulose is added to make the zeta potential of the mixed slurry reach 2-5mV. Finally, add polyacrylamide to the mixed slurry, stir for the set time, and then form the paper.

2. The method for preparing decorative base paper according to claim 1, characterized in that: The amount of titanium dioxide added accounts for 70%-85% of the oven-dry slurry mass; Alternatively, the amount of titanium dioxide added accounts for 75%-80% of the oven-dry slurry mass.

3. The method for preparing decorative base paper according to claim 1, characterized in that: The basicity of the liquid polyaluminum chloride is 50%-70%, and the mass percentage of Al2O3 is 10%-18%.

4. The method for preparing decorative base paper according to claim 1, characterized in that: The amount of liquid polyaluminum chloride added is 0.5%-2% of the dry slurry mass.

5. The method for preparing decorative base paper according to claim 1, characterized in that: The amount of polyamide epichlorohydrin resin added accounts for 0.3%-1% of the oven-dry pulp mass.

6. The method for preparing decorative base paper according to claim 5, characterized in that: The amount of polyamide epichlorohydrin resin added accounts for 0.4%-0.7% of the oven-dry pulp mass.

7. The method for preparing decorative base paper according to claim 1, characterized in that: The amount of sodium carboxymethyl cellulose added is 0.2%-0.8% of the oven-dry pulp mass.

8. The method for preparing decorative base paper according to claim 7, characterized in that: The aqueous solution of sodium carboxymethyl cellulose with a mass fraction of 2% has a viscosity of 100-300 mPa·s at 25°C.

9. The method for preparing decorative base paper according to claim 1, characterized in that: The amount of polyacrylamide added is 0.2%-0.6% of the oven-dry pulp mass.

10. A decorative base paper, prepared by any one of the preparation methods described in claims 1-9.

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