High-hiding titanium dioxide for decorative paper and method for its production

Abstract

The present application relates to the technical field of fillers, and particularly relates to high-hiding titanium dioxide for decorative paper and a preparation method thereof. The present application takes the rutile titanium dioxide without inorganic surface treatment as raw material, continuously carries out sodium tripolyphosphate pretreatment, aluminum sulfate deposition, sodium metaaluminate pulse nucleation, sodium bicarbonate / carbon dioxide phase transition gate and polyaluminum chloride epitaxial coating in the same system, and titanium dioxide with aluminum / phosphorus composite coating on the surface is prepared; by controlling the feeding sequence, pH and temperature, the retention rate of titanium dioxide in the decorative base paper, the opacity after hot pressing and the light resistance stability are improved, and the obtained titanium dioxide is suitable for melamine impregnated decorative paper.

Description

Technical Field

[0001] This invention relates to the field of filler technology, specifically to high-opacity titanium dioxide for decorative paper and its preparation method. Background Technology

[0002] Decorative paper is widely used in the veneer decoration of engineered wood products. Its core performance indicators include hiding power, whiteness, light aging resistance, and printability. To achieve ideal opacity and cover the dark surface of the engineered wood substrate, titanium dioxide, as the most critical functional pigment, directly determines the final quality of the decorative paper through its dispersion state, coating structure, and retention efficiency in the pulp. Traditionally, the paper industry has focused on high whiteness and high hiding power for titanium dioxide. However, in the impregnation and hot pressing process, titanium dioxide must also withstand the combined effects of high temperatures, resin curing, and acidic environments, which places more stringent demands on the thermal stability and interfacial compatibility of the titanium dioxide surface.

[0003] In existing technologies, to improve the dispersibility and retention of titanium dioxide in pulp systems, inorganic substances such as phosphates, aluminates, or silicates are typically used for surface treatment. For example, by depositing hydrated alumina in the presence of sodium tripolyphosphate, a negatively charged coating layer can be constructed on the surface of titanium dioxide, which can then adsorb pulp fibers or filler particles using electrostatic interactions, thereby improving retention. However, the simple phosphate-aluminate co-coating system exhibits significant shortcomings in the impregnation and hot-pressing process of decorative paper. On the one hand, high temperatures and acidic resin environments can disrupt the interfacial stability of the coating layer, leading to agglomeration of titanium dioxide particles or their detachment from the fiber surface, reducing the opacity after hot-pressing and curing. On the other hand, traditional coating processes struggle to form a uniform, dense, and thermochemically stable multilayer structure on the surface of titanium dioxide, resulting in the failure to effectively isolate photoactive sites in the titanium dioxide lattice. Under long-term ultraviolet irradiation, these sites are prone to catalyzing resin degradation, causing yellowing and severely affecting the decorative effect and service life of the decorative paper.

[0004] To improve the density and weather resistance of the coating layer, some studies have attempted to use silicon-aluminum composite coating or introduce rare earth elements such as cerium and zirconium for modification. However, these methods are often complex and costly, and may introduce heavy metal elements, failing to meet increasingly stringent environmental protection requirements. Furthermore, in the wet end of pulp systems, the retention rate of titanium dioxide is closely related to the surface charge characteristics and steric hindrance effect of the coating layer. Traditional methods of adding all coating agents at once or simply adjusting the feeding sequence make it difficult to precisely control the growth position and thickness of different functional layers on the surface of titanium dioxide particles, easily leading to uneven coating, localized excessive thickness, or the formation of free precipitates. These free precipitates not only waste raw materials but also cause white water pollution during paper forming and reduce the effective utilization rate of titanium dioxide.

[0005] Therefore, how to simultaneously improve the retention efficiency of titanium dioxide in decorative paper, the opacity after hot pressing, and the resistance to light aging, while simplifying the process and controlling costs, through reasonable coating layer structure design and precise interface reaction control, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a high-opacity titanium dioxide for decorative paper and its preparation method, so as to solve the problems of low retention rate of existing titanium dioxide for decorative paper in pulp system, insufficient opacity after hot pressing and curing, and poor light aging resistance.

[0007] To achieve the above objectives, the present invention provides high-opacity titanium dioxide for decorative paper, wherein the high-opacity titanium dioxide is obtained by using titanium dioxide as the initial raw material, and by neutralization and precipitation coating with sodium tripolyphosphate and aluminum sulfate, hydrolysis coating with sodium aluminate, and epitaxial coating with sodium bicarbonate and polyaluminum chloride. Based on 1000 parts by weight of titanium dioxide, the amounts of sodium tripolyphosphate, aluminum sulfate, sodium aluminate, sodium bicarbonate, and polyaluminum chloride added are 7-9 parts, 28-32 parts, 2-3 parts, 1.0-1.6 parts, and 11-14 parts, respectively. Preferably, the polyaluminum chloride, based on commercial solids, is preferably spray-dried polyaluminum chloride with an alumina mass fraction of 26%-30% and a basicity of 65%-85%.

[0008] Preferably, sodium tripolyphosphate, aluminum sulfate, sodium aluminate, sodium bicarbonate, and polyaluminum chloride are all added to the reaction system in the form of aqueous solutions.

[0009] Preferably, the titanium dioxide is rutile titanium dioxide, specifically Longbai Group's Snow Lotus BLR-501, with a TiO2 content of 98.5% and a specific gravity of 4.2 g / cm³. 3 .

[0010] Furthermore, the present invention also provides the following steps for preparing high-opacity titanium dioxide for decorative paper: (1) Disperse titanium dioxide in water to form a slurry, add sulfuric acid to adjust the pH to be stable at 2.9-3.1, and add sodium tripolyphosphate solution to the slurry. The sodium tripolyphosphate solution is added within 18-22 min, and sulfuric acid aqueous solution is added during this process to maintain the pH of the system stable at 3.0-3.2. After the addition is completed, keep stirring for 20-30 min. (2) Without solid-liquid separation, the slurry obtained in step (1) is heated to 61-65℃ and aluminum sulfate solution octadechydrate is added. The aluminum sulfate solution is added within 28-32 minutes. During this process, sodium hydroxide aqueous solution is added to maintain the pH of the system at 4.3-4.5. After the addition is completed, stirring is maintained for 20-30 minutes. (3) Without solid-liquid separation, the slurry obtained in step (2) is cooled to 59-61℃ and the pH of the system is adjusted to 6.1-6.3. The first coating liquid is added within 2-4 minutes, and the pH of the system is kept stable at 8.0-8.2 during this process. After the addition is completed, stirring is continued for 8-12 minutes. (4) Without solid-liquid separation, add sodium bicarbonate solution to the slurry obtained in step (3), and then pass carbon dioxide through it to lower the pH of the system to 7.4-7.9 and maintain it. The sodium bicarbonate solution is added within 6-10 minutes. After the addition is completed, keep stirring for 8-15 minutes. (5) Heat the slurry obtained in step (4) to 76-80℃, add the second coating liquid, and add the second coating liquid within 40-50 min. During this process, maintain the pH of the system at 7.6-8.0. After the addition is completed, continue to maintain it for 30-40 min. (6) The slurry obtained in step (5) is filtered, washed, dried, crushed and depolymerized by airflow to obtain high opacity titanium dioxide for decorative paper.

[0011] Preferably, the first coating solution is a sodium aluminate solution, and the second coating solution is a polyaluminum chloride solution.

[0012] Preferably, the concentration of the sulfuric acid aqueous solution is 19%-21%.

[0013] Preferably, the concentration of the sodium hydroxide aqueous solution is 9.5%-10.5%.

[0014] The beneficial effects of this invention are: This invention utilizes sodium tripolyphosphate pre-occupancy and acidic aluminum sulfate deposition to first form a relatively stable inner interface on the surface of titanium dioxide particles. Subsequently, sodium aluminate is added briefly to form initial aluminum oxide hydroxyl deposition sites. Then, the pH and carbonate environment of the system are controlled by sodium bicarbonate and carbon dioxide, which promotes the outer layer deposition from rapid liquid phase precipitation to controlled interface growth. Finally, polyaluminum chloride is introduced for subsequent deposition growth, thereby improving the uniformity and interface stability of the coating layer. The resulting titanium dioxide can achieve a high retention rate, high opacity after hot pressing, and good light aging resistance in decorative paper applications.

[0015] After the inner layer anchoring is completed, this invention uses rapid pulsed addition of sodium aluminate, addition of sodium bicarbonate solution, introduction of carbon dioxide, and slow-release extension of polyaluminum chloride to finally form a continuous, uniform outer layer coating structure with a certain thickness. This multi-layer interface step-by-step transition design enables functional complementarity and structural enhancement between different coating layers, resulting in significant improvement in the yellowing value and overall color difference of the heat-cured paper sample after UV aging, and substantial improvement in its light aging resistance.

[0016] This invention continuously completes the pre-occupation of sodium tripolyphosphate, the acidic anchoring of aluminum sulfate, and subsequent multilayer construction within the same dispersion system, avoiding the damage to interfacial active sites caused by intermediate filtration and washing operations. This continuous process ensures that each coating reaction always takes place on the particle surface, reducing the formation of free precipitates and enabling the coating layer to form a strong chemical bond and spatial configuration match with the titanium dioxide matrix. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0018] Raw material source description: Rutile titanium dioxide-based powder: Longbai Group Snow Lotus BLR-501.

[0019] Example 1: A method for preparing high-opacity titanium dioxide for decorative paper, the specific steps of which are as follows: S1: At room temperature, slowly add 40g of sulfuric acid to 160g of deionized water to prepare a 20% sulfuric acid aqueous solution; slowly add 20g of sodium hydroxide granules to 180g of deionized water, and after cooling, prepare a 10% sodium hydroxide aqueous solution; dissolve 8g of sodium tripolyphosphate in 120g of deionized water to prepare a sodium tripolyphosphate solution; dissolve 30g of aluminum sulfate octadecylhydrate in 200g of deionized water to prepare an aluminum sulfate solution; dissolve 2g of sodium aluminate in 40g of deionized water to prepare the first coating solution; dissolve 1.2g of sodium bicarbonate in 60g of deionized water to prepare a sodium bicarbonate solution; dissolve 13g of solid polyaluminum chloride in 187g of deionized water to prepare the second coating solution; all the above solutions should be prepared and used immediately. S2: Add 4000g of deionized water to a glass-lined reactor equipped with mechanical stirring, temperature control, and online pH detection. Heat to 55℃ and add 1000g of rutile titanium dioxide-based powder at 500r / min. After dispersing for 30min, add sulfuric acid aqueous solution (20%) to stabilize the pH of the slurry at 2.9-3.1. Then, while keeping the temperature and stirring speed constant, add 128g of sodium tripolyphosphate solution at a constant speed about 2cm below the liquid surface and close to the outer edge of the impeller within 20min, and simultaneously add sulfuric acid aqueous solution (20%) to keep the pH of the system at 3.0-3.2. After the addition is completed, continue to keep warm and stir for 25min. S3: Heat the slurry obtained in S2 to 63℃, keep the stirring speed at 500r / min, add 230g of aluminum sulfate solution at a constant speed of about 2cm below the liquid surface over 30min, and simultaneously add sodium hydroxide aqueous solution (10%) dropwise to keep the pH of the system stable at 4.3-4.5. After the addition is completed, continue to keep it at 4.3-4.5 for 25min. S4: Cool the slurry obtained in S3 to 60℃, and add sodium hydroxide aqueous solution (10%) at 500r / min to raise the pH of the system to 6.1-6.3; then quickly add 42g of the first coating solution within 3min and continue stirring for 10min. During this process, if the pH is higher than 8.3, add sulfuric acid aqueous solution (20%) to stabilize the pH of the system at 8.0-8.2. S5: At 60℃ and 500r / min, add 61.2g of sodium bicarbonate solution to the slurry obtained in S4 within 8min; after the addition is completed, introduce carbon dioxide at 0.15L / min from about 2cm below the liquid surface for 5min, and control the pH of the system at 7.5-7.8 according to online pH detection; after the carbon dioxide is introduced, continue stirring for 12min. S6: Heat the slurry obtained in S5 to 78℃ and keep stirring at 500r / min. Add 200g of the second coating liquid at a constant speed over 45min from about 2cm below the liquid surface, while simultaneously adding sodium hydroxide aqueous solution (10%) dropwise to keep the pH of the system stable at 7.7-8.0. Continue stirring for 35min after the addition is complete. S7: The slurry obtained in S6 is cooled to 45°C, and sulfuric acid aqueous solution (20%) is added to reduce the pH of the system to 6.3-6.7. Then, it is filtered and the filter cake is washed with deionized water until the pH of the filtrate is between 6 and 7. The filter cake is then dried at 110°C for 12 hours, mechanically crushed, and then subjected to airflow depolymerization to obtain the high-opacity titanium dioxide product for decorative paper.

[0020] Example 2: A method for preparing high-opacity titanium dioxide for decorative paper, the specific steps of which are as follows: S1: At room temperature, slowly add 38g of sulfuric acid to 158g of deionized water to prepare a 19% sulfuric acid aqueous solution; slowly add 19g of sodium hydroxide granules to 179g of deionized water, and after cooling, prepare a 9.5% sodium hydroxide aqueous solution; dissolve 7g of sodium tripolyphosphate in 120g of deionized water to prepare a sodium tripolyphosphate solution; dissolve 28g of aluminum sulfate octadecylhydrate in 200g of deionized water to prepare an aluminum sulfate solution; dissolve 2g of sodium aluminate in 40g of deionized water to prepare the first coating solution; dissolve 1.0g of sodium bicarbonate in 60g of deionized water to prepare a sodium bicarbonate solution; dissolve 11g of solid polyaluminum chloride in 189g of deionized water to prepare the second coating solution; all the above solutions should be prepared and used immediately. S2: Add 3900g of deionized water to a glass-lined reactor equipped with mechanical stirring, temperature control, and online pH detection. Heat to 54℃, add 1000g of rutile titanium dioxide-based powder at 450r / min, disperse for 28min, then add 18g of 19% sulfuric acid aqueous solution to stabilize the pH of the slurry at 2.9-3.1, and continue stirring for 10min. Subsequently, while maintaining the temperature and stirring speed, add 127g of sodium tripolyphosphate solution at a constant speed within 18min, approximately 2cm below the liquid surface and close to the outer edge of the impeller, and simultaneously add sulfuric acid aqueous solution (19%) to maintain the pH of the system at 3.0-3.2. After the addition is completed, continue stirring at the same temperature for 20min. S3: Heat the slurry obtained in S2 to 61℃, keep the stirring speed at 450r / min, add 228g of aluminum sulfate solution at a constant speed from about 2cm below the liquid surface over 28min, and simultaneously add sodium hydroxide aqueous solution (9.5%) dropwise to keep the pH of the system stable at 4.3-4.5; after the addition is completed, continue aging for 20min. S4: Cool the slurry obtained in S3 to 59°C, and add sodium hydroxide aqueous solution (9.5%) at 450 r / min to raise the pH of the system to 6.1-6.3; then quickly add 42 g of the first coating solution within 2 min and continue stirring for 8 min. During this process, if the pH is higher than 8.3, add sulfuric acid aqueous solution (19%) to stabilize the pH of the system at 8.0-8.2. S5: At 59℃ and 450r / min, add 61.0g of sodium bicarbonate solution to the slurry obtained in S4 within 6min; after the addition is completed, introduce carbon dioxide at 0.12L / min from about 2cm below the liquid surface for 4min, and control the pH of the system at 7.4-7.7 according to online pH detection; continue stirring for 10min after the carbon dioxide is introduced. S6: Heat the slurry obtained in S5 to 76℃ and keep stirring at 450r / min. Add 200g of the second coating liquid at a constant rate of about 2cm below the liquid surface over 42min, while simultaneously adding sodium hydroxide aqueous solution (9.5%) dropwise to keep the pH of the system stable at 7.6-7.9. Continue to maintain the temperature for 30min after the addition is completed. S7: Reduce the temperature of the slurry obtained in S6 to 45°C, add sulfuric acid aqueous solution (19%) to reduce the pH of the system to 6.3-6.7; then filter and wash the filter cake three times with deionized water until the pH of the filtrate is 6-7; then dry the filter cake at 105°C for 10 hours, and after mechanical crushing, perform airflow depolymerization to obtain the finished high-opacity titanium dioxide for decorative paper.

[0021] Example 3: A method for preparing high-opacity titanium dioxide for decorative paper, the specific steps of which are as follows: S1: At room temperature, slowly add 42g of sulfuric acid to 162g of deionized water to prepare a 21% sulfuric acid aqueous solution; slowly add 21g of sodium hydroxide granules to 181g of deionized water, and after cooling, prepare a 10.5% sodium hydroxide aqueous solution; dissolve 9g of sodium tripolyphosphate in 120g of deionized water to prepare a sodium tripolyphosphate solution; dissolve 32g of aluminum sulfate octadecylhydrate in 200g of deionized water to prepare an aluminum sulfate solution; dissolve 3g of sodium aluminate in 42g of deionized water to prepare the first coating solution; dissolve 1.6g of sodium bicarbonate in 60g of deionized water to prepare a sodium bicarbonate solution; dissolve 14g of solid polyaluminum chloride in 186g of deionized water to prepare the second coating solution; all the above solutions should be prepared and used immediately. S2: Add 4100g of deionized water to a glass-lined reactor equipped with mechanical stirring, temperature control, and online pH detection. Heat to 56℃, add 1000g of rutile titanium dioxide-based powder at 550r / min, disperse for 35min, then add sulfuric acid aqueous solution (21%) to stabilize the pH of the slurry at 2.9-3.1, and continue stirring for 10min. Subsequently, while maintaining the temperature and stirring speed, add 129g of sodium tripolyphosphate solution at a constant speed over 22min from about 2cm below the liquid surface and close to the outer edge of the impeller, and simultaneously add sulfuric acid aqueous solution (21%) to maintain the pH of the system at 3.0-3.2. After the addition is completed, continue stirring at the temperature for 30min. S3: Heat the slurry obtained in S2 to 65℃, keep the stirring speed at 550r / min, add 232g of aluminum sulfate solution at a constant speed from about 2cm below the liquid surface over 32min, and simultaneously add sodium hydroxide aqueous solution (10.5%) dropwise to keep the pH of the system stable at 4.3-4.5; after the addition is completed, continue aging for 30min. S4: Cool the slurry obtained in S3 to 61°C, and add sodium hydroxide aqueous solution (10.5%) at 550 r / min to raise the pH of the system to 6.1-6.3; then quickly add 45g of the first coating solution within 4 min and continue stirring for 12 min. During this process, if the pH is higher than 8.3, add sulfuric acid aqueous solution (21%) to stabilize the pH of the system at 8.0-8.2. S5: At 61℃ and 550r / min, add 61.6g of sodium bicarbonate solution to the slurry obtained in S4 within 10min; after the addition is completed, introduce carbon dioxide at 0.18L / min from about 2cm below the liquid surface for 6min, and control the pH of the system at 7.6-7.9 according to online pH detection; after the carbon dioxide is introduced, continue stirring for 15min. S6: Heat the slurry obtained in S5 to 80℃ and keep stirring at 550r / min. Add 200g of the second coating liquid at a constant rate of about 2cm below the liquid surface over 48min, while simultaneously adding sodium hydroxide aqueous solution (10.5%) dropwise to keep the pH of the system stable at 7.8-8.0. Continue stirring for 40min after the addition is complete. S7: Reduce the temperature of the slurry obtained in S6 to 47°C, add sulfuric acid aqueous solution (21%) to reduce the pH of the system to 6.3-6.7; then filter and wash the filter cake three times with deionized water until the pH of the filtrate is 6-7; then dry the filter cake at 115°C for 14 hours, and after mechanical crushing, perform airflow depolymerization to obtain the finished high-opacity titanium dioxide for decorative paper.

[0022] Comparative Example 1: The difference from Example 1 is that sodium tripolyphosphate solution is not added in S2. In S3, 128g of sodium tripolyphosphate solution and 230g of aluminum sulfate solution are simultaneously added to the slurry from about 2cm below the liquid surface within 30 minutes, while 58g of 10% sodium hydroxide aqueous solution is added dropwise to stabilize the pH of the system at 4.3-4.5. The other conditions are the same as in Example 1.

[0023] Comparative Example 2: The difference from Example 1 is that in S3, the pH of the system was changed from 4.3-4.5 to 6.8-7.0 during the addition of 230g of aluminum sulfate solution; the other conditions were the same as in Example 1.

[0024] Comparative Example 3: The difference from Example 1 is that after S2 in Example 1, the slurry is first filtered and washed once with deionized water, and then redispersed with 4000g of deionized water before entering S3. That is, the pre-occupation of oligophosphate and the subsequent acid-confined aluminum-phosphorus anchoring are not completed continuously in the same system; the other conditions are the same as in Example 1.

[0025] Comparative Example 4: The difference from Example 1 is that no second coating solution is added in S6, and an equal amount of deionized water is used instead; the other conditions are the same as in Example 1.

[0026] Comparative Example 5: The difference from Example 1 is that the outer layer construction sequence of Example 1 is reversed; specifically, the first coating liquid is not added in S4, but the first coating liquid is added after the second coating liquid is added; the other conditions are the same as in Example 1.

[0027] Comparative Example 6: The difference from Example 1 is that sodium tripolyphosphate solution, aluminum sulfate solution, first coating solution, sodium bicarbonate solution and second coating solution were added together; the other conditions were the same as in Example 1.

[0028] Performance testing Titanium dioxide obtained from the examples and comparative examples were used as powder samples for testing. Decorative base paper samples were prepared as follows: Metsä Birch bleached hardwood sulfate pulp was soaked in deionized water at 20°C for 4 hours, and then decomposed using a laboratory pulp decomposer for 10 minutes to obtain pulp. Pulp was taken based on 20g of oven-dry fiber, and 28 parts of titanium dioxide (i.e., 5.6g of the titanium dioxide corresponding to the examples or comparative examples) were added to 100 parts of oven-dry fiber. Deionized water was then added to prepare a decorative paper pulp with a total pulp concentration of 0.8%, and the pulp was stirred at 1500 rpm for 15 minutes at 25°C. The resulting pulp was diluted to 0.2% and continuously formed using a laboratory paper forming machine to obtain a basis weight of 70g / m³. 2 The wet paper sheets were dehydrated under vacuum and then dried at 105°C to constant weight to obtain decorative base paper samples; The hot-pressed paper sample was prepared as follows: The above-mentioned decorative base paper was immersed in MELDUR M-8 / UT modified melamine-formaldehyde impregnation resin with a solid content of 55% at 25°C for 8s. The weight gain of the impregnation was controlled to be 130% by double-roll extrusion. It was pre-dried in a hot air box at 150°C for 90s to control the volatile content to 8%. Then, a single sheet of pre-impregnated paper was sandwiched between two 50μm polytetrafluoroethylene release films and placed between mirror stainless steel plates. It was hot-pressed at 165°C and 0.9MPa for 28s. After pressing, it was cooled at 0.5MPa for 30s and the release film was peeled off to obtain the hot-pressed paper sample for opacity, whiteness, color and aging tests. In addition, blank decorative base paper samples without titanium dioxide were prepared to correct the background ash content of the pulp; all other tests were performed in triplicate, and the average value of the results was taken. Particle size distribution: 0.20 g of each powder sample was weighed and tested according to GB / T 19077-2024 "Particle size analysis by laser diffraction". Deionized water was used as the dispersion medium, the circulation tank volume was 200 mL, the stirring speed of the dispersion tank was 2000 r / min, the light shading was controlled at 10%, the ultrasonic dispersion time was 60 s, the circulation time was 60 s before measurement, and the test was repeated 3 times. D10, D50 and D90 were recorded, and D50 was used as the key evaluation index. Ash content, basis weight, and titanium dioxide retention rate of decorative base paper: The decorative base paper samples corresponding to the examples and comparative examples were treated for 24 hours in the standard atmosphere specified in GB / T 10739-2023 "Standard Atmospheric Conditions for the Treatment and Testing of Paper, Paperboard and Pulp Specimens". Then, the basis weight of the paper was determined according to GB / T 451.2-2023 "Paper and Paperboard Part 2: Determination of Basis Weight". The ash content was then determined according to GB / T 22877-2023 "Determination of Ash Content (Residue from Ignition) of Paper, Paperboard, Pulp and Cellulose Nanomaterials (525°C)". The ash content of the blank decorative base paper without titanium dioxide was taken as the background ash content A0, the ash content of the decorative base paper in the examples or comparative examples was taken as A1, the total dry paper mass of the same batch of decorative base paper was taken as M1, and the mass of titanium dioxide added in a single batch (5.6 g) was taken as M. p Calculate the titanium dioxide retention rate; Opacity of heat-cured paper samples: The heat-cured paper samples corresponding to the examples and comparative examples were treated in the standard atmosphere specified in GB / T10739-2023 for 24 hours, and tested according to GB / T 1543-2005 "Determination of opacity (paper backing) of paper and paperboard (diffuse reflection method)". Three 100mm×100mm samples were cut for each sample, and 10 different positions were tested on each sample. The average value was taken as the opacity result. CIE whiteness of heat-cured paper samples: The heat-cured paper samples corresponding to the examples and comparative examples were treated for 24 hours under the conditions specified in GB / T10739-2023, and tested according to GB / T 22880-2008 "Determination of CIE whiteness of paper and paperboard, D65 / 10° (outdoor daylight)". Three 100mm×100mm samples were cut for each sample, and 10 different positions were tested on each sample. The average value was taken as the CIE whiteness result. Yellowing value and overall color difference after UV aging: Three 70mm × 150mm samples were cut from the heat-cured paper samples corresponding to the examples and comparative examples, respectively. Aging was performed according to GB / T 16422.3-2022 "Laboratory Light Source Exposure Tests for Plastics - Part 3: Fluorescent Ultraviolet Lamps", under UVA-340 ultraviolet lamp conditions, with an irradiance of 0.89 W / m² at 340 nm. 2The aging process consisted of 6 cycles of UV irradiation at 60℃ for 8 hours and condensation at 50℃ for 4 hours, for a total of 6 cycles and a total aging time of 72 hours. Before and after aging, the L color of the sample was measured under D65 light source and 10° observer conditions according to GB / T 3979-2008 "Methods for Measurement of Object Color". a b The value is then used to calculate the overall color difference ΔE according to GB / T 7921-2008 "Uniform Color Space and Color Difference Formula". ab, and simultaneously record the change in yellowing value Δb. ; Volume fraction of the sedimentation layer of titanium dioxide slurry after 24 hours: Weigh 40g of titanium dioxide samples corresponding to the examples and comparative examples, add them to 60g of deionized water, disperse at 2000r / min for 10min at 25℃, immediately transfer to a 100mL stoppered graduated cylinder, gently shake three times to remove large air bubbles, and record the initial total volume V0; after the graduated cylinder has stood at 25℃ for 24 hours, record the volume of the bottom sedimentation layer V. s The settlement layer volume fraction (%) is calculated according to the formula: Vs / V0×100%; the above test results are shown in Table 1.

[0029] Table 1 Performance Test Results As can be seen from the data in Table 1, the high-coverage titanium dioxide for decorative paper prepared by this invention exhibits a good balance between particle size distribution, ash content of the decorative base paper and titanium dioxide retention rate, opacity after hot pressing, whiteness after hot pressing, change in yellowing value after aging, overall color difference, and static stability of the pulp. This may be because the interfacial sites formed in the previous stage provide a more stable deposition base for the subsequent stage, ensuring that the outer layer structure is no longer a simple liquid-phase precipitation but rather grows gradually along the established interface. This balances the requirements for opacity after hot pressing, lightfastness, and retention and dispersion performance in the pulp system required for decorative paper applications.

[0030] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 3, regardless of whether the pre-occupation of sodium tripolyphosphate is absent or whether filtration, washing, and redispersion are introduced after pre-occupation, the ash content of the decorative base paper, the titanium dioxide retention rate, the opacity after hot pressing, and the static stability of the pulp all deteriorate simultaneously. The main reason is that the pre-occupation of polyphosphate ions must not only exist but also be completed continuously in the same system as the subsequent acid-confined aluminum-phosphorus anchoring, and there is a significant synergistic effect between the two.

[0031] As can be seen from the data in Table 1 for Example 1 and Comparative Example 2, simply changing the system conditions during the aluminum sulfate deposition stage from an acidic window to a near-neutral range did not maintain the level of coverage, effective retention, and water slurry stability after hot pressing, even though aluminum-containing deposits could still be formed in the system. Furthermore, the overall color improvement after aging was insufficient. The main reason for this is that under near-neutral conditions, aluminum sulfate octadechydrate is more prone to rapid hydrolysis in the liquid phase, forming deposits that deviate from the particle surface, making it difficult to preferentially adhere to the rutile titanium dioxide surface to construct a thin and stable aluminum-phosphorus anchoring inner layer.

[0032] As can be seen from the data in Table 1 for Example 1 and Comparative Example 4, when the sodium aluminate pulse nucleation and sodium bicarbonate phase transformation steps are retained, but the polyaluminum chloride slow-release epitaxy is lacking, some superficial chemical indicators can still be maintained at a high level. However, the overall performance of opacity after hot pressing, yellowing value change after aging, overall color difference, and retention dispersion is still lower than that of Example 1. The main reason is that the sodium aluminate pulse nucleation and sodium bicarbonate and carbon dioxide phase transformation can initially establish the outer layer structure, but without the polyaluminum chloride slow-release epitaxy, the continuity and interface stability of the outer layer coverage are still insufficient, making it difficult to simultaneously achieve both the light scattering interface after hot pressing and the isolation of photoactive sites without significantly increasing the coating thickness.

[0033] As can be seen from the data in Example 1 and Comparative Example 5 in Table 1, when the order of outer layer construction was reversed from adding sodium aluminate first, then controlling with sodium bicarbonate and carbon dioxide, and finally adding polyaluminum chloride, significant adverse changes occurred in the opacity after hot pressing, titanium dioxide retention rate, and static stability of the water slurry. The change in yellowing value and overall color difference after aging also increased further. The main reason for this is that there is a significant sequential dependence between the pulse nucleation of sodium aluminate, the phase transformation of sodium bicarbonate and carbon dioxide, and the slow-release epitaxy of polyaluminum chloride, which is a typical synergistic effect rather than a simple separation of several aluminum-containing raw materials.

[0034] As can be seen from the data in Example 1 and Comparative Example 6 in Table 1, the most significant imbalance in application performance occurs when sodium tripolyphosphate solution, aluminum sulfate solution, first coating solution, sodium bicarbonate solution, and second coating solution are added simultaneously. This is particularly evident in increased particle size, decreased opacity after hot pressing, increased yellowing value and overall color difference, and deteriorated stability of the water slurry after standing. The main reason for this is that the simultaneous addition completely disrupts the progressive logic of first site fixation, then anchoring, then nucleation, then regulation, and finally extension. Thus, it is clear that this invention is not a simple superposition of multiple known components, but rather creates an unpredictable overall synergistic effect by providing reaction sites and spatial constraints for the next step through the previous step.

[0035] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A high-opacity titanium dioxide for decorative paper, characterized in that, The high-opacity titanium dioxide is obtained by using titanium dioxide as the initial raw material, followed by neutralization and precipitation coating with sodium tripolyphosphate and aluminum sulfate, hydrolysis coating with sodium aluminate, and epitaxial coating with sodium bicarbonate and polyaluminum chloride. Based on 1000 parts by weight of titanium dioxide, the amounts of sodium tripolyphosphate, aluminum sulfate, sodium aluminate, sodium bicarbonate, and polyaluminum chloride added are 7-9 parts, 28-32 parts, 2-3 parts, 1.0-1.6 parts, and 11-14 parts, respectively.

2. The high-opacity titanium dioxide for decorative paper according to claim 1, characterized in that, Sodium tripolyphosphate, aluminum sulfate, sodium aluminate, sodium bicarbonate, and polyaluminum chloride are all added to the reaction system in the form of aqueous solutions.

3. The high-opacity titanium dioxide for decorative paper according to claim 1, characterized in that, The titanium dioxide is rutile titanium dioxide, specifically Longbai Group's Snow Lotus BLR-501, with a TiO2 content of 98.5% and a specific gravity of 4.2 g / cm³. 3 .

4. A method for preparing high-opacity titanium dioxide for decorative paper according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Disperse titanium dioxide in water to form a slurry, and add sodium tripolyphosphate solution to the slurry, while maintaining the pH of the system at 3.0-3.2 during the process; (2) Heat the slurry obtained in step (1) to 61-65℃, add aluminum sulfate solution, and keep the pH of the system stable at 4.3-4.5 during this process; (3) Without solid-liquid separation, the slurry obtained in step (2) is cooled to 59-61℃ and the first coating liquid is added. During this process, the pH of the system is kept stable at 8.0-8.

2. After the addition is completed, stirring is continued for 8-12 minutes. (4) Without solid-liquid separation, add sodium bicarbonate solution to the slurry obtained in step (3), and then pass carbon dioxide through it. After the addition is completed, keep stirring for 8-15 minutes. (5) Heat the slurry obtained in step (4) to 76-80℃, add the second coating liquid, and maintain the pH of the system at 7.6-8.0 during this process. After the addition is completed, continue to maintain the temperature for 30-40 minutes. (6) The slurry obtained in step (5) is filtered, washed, dried, crushed and depolymerized by airflow to obtain high opacity titanium dioxide for decorative paper.

5. The preparation method according to claim 4, characterized in that, After the sodium tripolyphosphate solution in step (1) is added, stirring should be maintained for 20-30 minutes.

6. The preparation method according to claim 4, characterized in that, After the aluminum sulfate solution in step (2) is added, stirring should be maintained for 20-30 minutes.

7. The preparation method according to claim 4, characterized in that, Step (3) The first coating solution is sodium aluminate solution, and stirring should be maintained for 8-12 minutes after addition; the second coating solution is polyaluminum chloride solution, and stirring should be maintained for 30-40 minutes after addition.

8. The preparation method according to claim 4, characterized in that, After the sodium bicarbonate solution in step (4) is added, keep stirring for 8-15 minutes.

9. The preparation method according to claim 4, characterized in that, The washing in step (6) is performed with deionized water until the pH of the filtrate is between 6 and 7.

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