Heat-sensitive titanium dioxide for papermaking and preparation method thereof

Abstract

The invention discloses heat-sensitive titanium dioxide for papermaking and a preparation method of the heat-sensitive titanium dioxide. The titanium dioxide sequentially comprises a titanium dioxide base material, an inorganic coating layer and an organic coating layer from inside to outside, the inorganic coating layer comprises a boehmite alumina film layer doped with a group 9 element; the organic coating layer is a film layer formed by introducing a spiropyran compound; the titanium dioxide has a reversible thermosensitive characteristic and shows different colors at different temperatures. According to the invention, inorganic coating and organic modification treatment are comprehensively adopted, and the inorganic coating enables the Group 9 elements to be doped in the Al coating layer, so that the dispersibility of titanium dioxide is effectively enhanced; according to organic modification, a spiropyran compound is introduced to the surface of titanium dioxide, so that titanium dioxide and paper prepared from titanium dioxide have heat sensitivity, the high-dispersion heat-sensitive titanium dioxide is obtained, and the application scene of the high-dispersion heat-sensitive titanium dioxide in the field of specialty paper is expanded.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide preparation technology, specifically relating to a thermosensitive titanium dioxide for papermaking and its preparation method. Background Technology

[0002] Titanium dioxide (TiO2) has long held a core position as a filler and coating material in the paper industry due to its superior whiteness, hiding power, and chemical stability. In ordinary paper, it enhances whiteness and opacity by efficiently scattering light, while also improving the paper's folding endurance, tear resistance, and surface smoothness, meeting basic requirements for printing and packaging. In the field of specialty papers, titanium dioxide serves as a substrate carrier for functional materials such as thermosensitive and photosensitive paper, supporting the development of high-end products such as anti-counterfeiting paper and thermal recording paper. However, the application of traditional titanium dioxide faces two major technical bottlenecks: First, unmodified particles are prone to agglomeration, leading to uneven dispersion in pulp, reduced hiding power and whiteness consistency, and increased paper surface roughness, which exacerbates ink consumption. While inorganic coating modification of titanium dioxide, such as conventional hydrated alumina coating and silicon-aluminum coating, is technically mature and cost-effective, and can effectively improve the dispersion stability of titanium dioxide, it has limitations such as difficulty in controlling the microstructure of the coating layer and the weather resistance being greatly affected by the coating conditions, thus limiting its improvement in dispersibility. Second, titanium dioxide has weak bonding force with fibers and low retention rate, requiring excessive addition of fillers to compensate for loss during production, which not only wastes resources but also further exacerbates the agglomeration problem, creating a vicious cycle.

[0003] Thermal paper is a high-end product, typically achieved by adding heat-sensitive agents. While there are many types of existing paper heat-sensitive agents, they have significant shortcomings. Traditional heat-sensitive agents are mainly bisphenol A (BPA) and its substitutes. Although BPA is inexpensive, it has a high melting point and low photosensitive color development, requiring the use of sensitizers. Furthermore, it poses potential health risks, such as endocrine disorders and cancer. Substitutes, such as benzyl paraben (PHBB), offer high heat sensitivity but are expensive and have poor light and oil resistance, leading to easy fading of images and unsuitability for long-term storage. Novel color developers, such as particulate dispersions of BPA polymers, overcome the difficulties of processing BPA monomers, but still pose potential toxicity risks and have relatively low technological maturity. Other phenolic compounds, such as salicylic acid, can be used as color developers, but their wide melting point range and premature image formation negatively impact the quality of the thermal paper. Based on the above-mentioned technical problems, this application aims to provide a titanium dioxide with high dispersibility and thermosensitive properties to meet its application needs in the papermaking field, especially in the field of specialty paper. Summary of the Invention

[0004] The purpose of this invention is to provide a thermosensitive titanium dioxide for papermaking and a preparation method to overcome the shortcomings of the prior art.

[0005] The objective of this invention is achieved through the following technical solution: A thermosensitive titanium dioxide for papermaking comprises, from the inside out, a titanium dioxide substrate, an inorganic coating layer, and an organic coating layer; the inorganic coating layer includes a boehmite alumina film layer doped with a Group 9 element; the organic coating layer is a film layer formed by introducing a spirocyclic pyran compound. The titanium dioxide has reversible thermosensitive properties, exhibiting different colors at different temperatures.

[0006] Preferably, the titanium dioxide is white or light-colored at temperatures above 130°C; The titanium dioxide appears dark at temperatures below 100°C.

[0007] Preferably, the spirocyclic pyran compound has the following general structural formula:

[0008] Wherein R1 is independently selected from at least one of H, dimethyl, and methoxy; R2 is independently selected from at least one of methyl, dimethyl, trimethyl, and hydroxyethyl; and R3 is independently selected from at least one of nitro, halogen, and methoxy.

[0009] Preferably, the spirocyclic pyran compound is selected from one or more combinations of the following compounds: 1',3'-Dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole], spiro[1,3,3-trimethylindole-(6'-bromobenzodihydropyran)], spiro[1,3,3-trimethylindole-(6'-nitrobenzodihydropyran)], spiro[1,3,3-trimethylindole-(8'-methoxybenzodihydropyran)], N-(hydroxyethyl)-3,3-dimethyl-6-nitroindolinespiropyran, spiro[1,3,3-trimethylindole-benzodihydropyran].

[0010] Preferably, the coating amount of the boehmite alumina film doped with Group 9 elements, calculated as alumina, is 3.0~6.0% of the mass of the titanium dioxide substrate; The doping amount of the group 9 element, calculated as group 9 element, is 0.1 to 1.0% of the mass of the titanium dioxide substrate.

[0011] Preferably, the coating amount of the organic coating layer is 1.0 to 3.0% of the mass of the titanium dioxide substrate.

[0012] Another aspect of this application provides a method for preparing the thermosensitive titanium dioxide for papermaking as described above, comprising the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. A boehmite alumina coating with Group 9 element doping; S3. Perform organic coating of spirocyclic pyran compounds.

[0013] Preferably, step S2 further includes: A soluble aluminum source, a soluble Group 9 element source, and a pH adjuster are added concurrently to a titanium dioxide slurry to deposit alumina and obtain a Group 9 element-doped boehmite alumina film. Preferably, the pH of the parallel flow is controlled to be 6.5~8.0.

[0014] Preferably, step S3 employs a wet coating method to organically coat the spirocyclic pyran compound.

[0015] Preferably, step S3 further includes: The slurry coated with a boehmite alumina film containing Group 9 elements was separated into solid and liquid phases, dried, and then slurried with a nonprotonated solvent. The spirocyclic pyran compound was added, and the mixture was refluxed at 60-80°C for 2-4 hours.

[0016] This application combines inorganic coating and organic modification. Inorganic coating allows Group 9 elements to be doped into the Al coating layer, effectively enhancing the dispersibility of titanium dioxide. Organic modification introduces spirocyclic pyran compounds onto the surface of titanium dioxide, giving the titanium dioxide and the paper made from it heat-sensitive properties, thereby obtaining highly dispersed heat-sensitive titanium dioxide and expanding its application scenarios in the field of specialty paper.

[0017] This invention achieves a leap in performance through multi-dimensional innovation. Regarding improved dispersibility, by doping the Al coating layer with a Group 9 element using an inorganic coating, aggregation caused by electrostatic adsorption is blocked, ultimately resulting in a product with significantly improved dispersion stability. In terms of thermosensitive functional design, the technology breaks through the traditional limitation of titanium dioxide serving only as a color developer carrier. By introducing spirocyclic pyran compounds, titanium dioxide is endowed with autonomous thermal response capabilities, enabling temperature-controlled switching between color development and occultation, expanding its application scenarios in the field of specialty papers.

[0018] The technological innovation of highly dispersed thermal titanium dioxide profoundly addresses the practical needs of the paper industry. From an environmental perspective, traditional titanium dioxide production is energy-intensive and highly polluting. Modification technology, by increasing retention rate, can reduce filler usage, lower white water discharge and wastewater treatment costs, and contribute to the industry's green transformation. From an economic perspective, global titanium dioxide prices are significantly affected by ore supply and economic cycle fluctuations. High retention rate technology can reduce unit paper production costs and enhance companies' resilience. From a market perspective, the demand for specialty papers continues to grow, especially for high-end products such as thermal and photosensitive papers, which have increasingly stringent functional requirements for fillers, driving the evolution of titanium dioxide towards composite and functional applications. In the future, with the further integration of nanotechnology, microencapsulation processes, and smart material design, the highly dispersed thermal titanium dioxide provided in this application is expected to open up broader application spaces in fields such as anti-counterfeiting packaging, smart labels, and environmentally responsive paper, becoming one of the key materials for the transformation and upgrading of the paper industry. Attached Figure Description

[0019] Figure 1 These are photos of the dispersibility test process for titanium dioxide samples. Figure 2 This is a color photograph of titanium dioxide before oven treatment in Example 3; Figure 3 This is a color photograph of titanium dioxide after oven treatment in Example 3; Figure 4 This is a color photograph of titanium dioxide in Comparative Example 1 before oven treatment; Figure 5 This is a color photo of titanium dioxide after oven treatment, as shown in Comparative Example 1. Detailed Implementation

[0020] This application provides a thermosensitive titanium dioxide for papermaking, which, from the inside out, comprises a titanium dioxide substrate, an inorganic coating layer, and an organic coating layer; the inorganic coating layer includes a boehmite alumina film layer doped with a group 9 element; and the organic coating layer is a film layer formed by introducing a spirocyclic pyran compound.

[0021] The Group 9 elements are selected from at least one of cobalt (Co), iridium (Ir), or rhodium (Rh). Although Mt is also a Group 9 element, it is radioactive and therefore is not applicable to this application.

[0022] This titanium dioxide has reversible thermosensitive properties, exhibiting different colors at different temperatures.

[0023] The titanium dioxide provided in this application combines inorganic coating and organic modification treatments. The inorganic coating incorporates Group 9 elements into the Al coating layer, effectively enhancing the dispersibility of the titanium dioxide. The organic modification introduces spirocyclic pyran compounds onto the surface of the titanium dioxide, giving the titanium dioxide and the paper made from it heat-sensitive properties, as described in detail below: 1. During the inorganic coating process of titanium dioxide, the boehmite alumina (AlOOH) film deposited on its surface has abundant O atoms and numerous defect sites. These sites possess high chemical reactivity. Group 9 elements such as Ir particles, due to their small size, large specific surface area, and high energy and reactivity of their surface atoms, can chemically react with the O atoms or defect sites on the AlOOH surface to form strong chemical bonds. This firmly fixes the Ir particles to the surface, altering the surface charge distribution of titanium dioxide, increasing the absolute value of the Zeta potential, enhancing the electrostatic repulsion between particles, and reducing agglomeration. Simultaneously, it may optimize surface chemical properties, promoting binding with polymeric dispersants and creating a steric hindrance effect, further preventing particle contact. Furthermore, the synergistic effect of Ir doping and Al coating can form a more stable and dense coating layer, optimizing surface properties and enhancing dispersant adsorption. This significantly improves the dispersion stability of titanium dioxide in the medium, reduces agglomeration, and ultimately enhances the dispersibility of titanium dioxide.

[0024] The method of improving the dispersibility of titanium dioxide by using alumina film doped with group 9 elements can, compared with other inorganic coatings, more effectively prevent particle agglomeration by changing the surface properties and electronic structure of the film, significantly improve dispersibility and may improve weather resistance.

[0025] Titanium dioxide doped with Group 9 elements (cobalt, rhodium, and iridium) exhibits several unique advantages over other elements in improving dispersibility, providing a new path for optimizing titanium dioxide performance. Specifically: On the one hand, Group 9 elements exhibit more precise control over electronic structure. Cobalt's 3d orbital electrons can participate in surface electron transfer, forming Co-O-Ti bonds, increasing the surface negative charge density, raising the zeta potential, and effectively reducing particle aggregation through electrostatic repulsion. Rhodium and iridium, with their high electronegativity and strong oxidizing properties, can be used for surface modification to reduce surface defects in titanium dioxide, lower surface free energy, weaken van der Waals forces between particles, enhance interactions with dispersants, and improve dispersion stability.

[0026] On the other hand, regarding lattice distortion effects, the ionic radii of Group 9 elements differ significantly from those of titanium, leading to more intense lattice expansion and distortion during doping, further refining the particle size. For example, cobalt ion doping results in smaller particle sizes, increased specific surface area, and enhanced light scattering ability, thereby improving dispersibility and hiding power. Simultaneously, rhodium and iridium doping introduce defects such as oxygen vacancies, regulating surface activity, improving wettability, and promoting dispersion.

[0027] Furthermore, in terms of process adaptability, doping with Group 9 elements may simplify the surface coating process, achieving a "dense-loose" bilayer structure that balances weather resistance and dispersibility. Simultaneously, it reduces sensitivity to pH, allowing titanium dioxide to maintain good dispersibility over a wide pH range.

[0028] 2. Organic modification using spirocyclic pyran compounds: Spirocyclic pyran compounds can exist on the surface of titanium dioxide through chemical reactions (hydroxyl condensation) / physical adsorption (hydrogen bonding, etc.), giving the finished titanium dioxide thermosensitive properties. The thermosensitive mechanism of spirocyclic pyran compounds is based on the reversible change in molecular structure upon heating. At room temperature or low temperature, spirocyclic pyran consists of two aromatic heterocycles, such as indoline and benzopyran, linked by spiro carbon atoms to form a closed ring. The spiro carbon atoms are sp3 hybridized, the molecule is stable and does not absorb visible light, and is colorless or light-colored. Upon heating, the CO bonds within the molecule heterocleave, the spiro ring structure opens to form an open-ring chromophore. During this process, the hybridization state of the spiro carbon atoms changes from sp3 to sp2, the molecule enters a conjugated equilibrium state, the absorption spectrum redshifts, and the color deepens. Moreover, this color change is reversible; when the temperature decreases or heating is stopped, the open-ring chromophore reforms the CO bonds, restoring the closed-ring form, and the color returns to its original state.

[0029] The non-redox leuco properties of spiropyran compounds bring novel color-changing effects to thermal paper, and have potential application value, especially in scenarios that require highly sensitive and stable color-changing materials.

[0030] Furthermore, products obtained by combining spiropyran compounds as heat sensitizers with titanium dioxide can enhance the heat-sensitive structure and extend service life, as detailed below: On the one hand, combining spirocyclic pyrans with titanium dioxide disperses spirocyclic pyran molecules on the surface or within the pores of the titanium dioxide. This dispersion helps reduce the interactions between spirocyclic pyran molecules, preventing degradation due to aggregation. Simultaneously, the rigid structure of titanium dioxide provides physical support for the spirocyclic pyran molecules, enhancing their structural stability. On the other hand, the polar groups such as hydroxyl groups on the surface of titanium dioxide can form hydrogen bonds with the polar parts of the spirocyclic pyran molecules (such as oxygen atoms on the pyran ring). This hydrogen bonding further stabilizes the structure of the spirocyclic pyran molecules, reducing structural changes caused by factors such as light and heat, thereby extending their service life.

[0031] Preferably, titanium dioxide is white (white being the natural color of titanium dioxide) or light-colored at temperatures above 130°C. Titanium dioxide appears dark at temperatures below 100°C.

[0032] Spirocyclic pyran compounds have the following general structural formula:

[0033] Wherein R1 is independently selected from at least one of H, dimethyl, and methoxy; R2 is independently selected from at least one of methyl, dimethyl, trimethyl, and hydroxyethyl; and R3 is independently selected from at least one of nitro, halogen, and methoxy.

[0034] Preferably, the spirocyclic pyran compound is selected from one or more combinations of the following compounds: 1',3'-Dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole], spiro[1,3,3-trimethylindole-(6'-bromobenzodihydropyran)], spiro[1,3,3-trimethylindole-(6'-nitrobenzodihydropyran)], spiro[1,3,3-trimethylindole-(8'-methoxybenzodihydropyran)], N-(hydroxyethyl)-3,3-dimethyl-6-nitroindolinespiropyran, spiro[1,3,3-trimethylindole-benzodihydropyran].

[0035] The structural formula of 1',3'-dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole] is as follows:

[0036] The structural formula of spiro[1,3,3-trimethylindole-(6'-nitrobenzodihydropyran)] is as follows:

[0037] The structural formula of spiro[1,3,3-trimethylindole-benzodihydropyran] is as follows:

[0038] The structural formula of N-(hydroxyethyl)-3,3-dimethyl-6-nitroindolinespiropyran is as follows:

[0039] The specific color of titanium dioxide at high temperatures can be affected by using different spiropyran compounds, which is mainly related to the structure of the spiropyran compound. However, the amount of spiropyran compound coating will affect the depth of the color.

[0040] As those skilled in the art will understand, each film layer requires a certain amount of coating to completely cover the surface of the titanium dioxide and achieve its intended function; however, the coating amount cannot be too large. Preferably, the coating amount of the alumina film layer doped with Group 9 elements is 3.0 to 6.0% of the mass of the titanium dioxide substrate, based on alumina; and the doping amount of the Group 9 element is 0.1 to 1.0% of the mass of the titanium dioxide substrate, based on the Group 9 element.

[0041] Preferably, the coating amount of the organic coating layer is 1.0 to 3.0% of the mass of the titanium dioxide substrate.

[0042] This application also provides a method for preparing the thermosensitive titanium dioxide for papermaking as described above, comprising the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. A boehmite alumina coating with Group 9 element doping; S3. Perform organic coating of spirocyclic pyran compounds.

[0043] This application employs a wet coating method for inorganic coating, which offers strong controllability and results in relatively stable coatings. For the same purpose, a wet coating method is also preferred for organic coating.

[0044] The concentration of the titanium dioxide-based material slurry, calculated as titanium dioxide, is preferably 250-350 g / L. This concentration is suitable for inorganic coating. A certain high temperature can promote inorganic coating; the preferred coating temperature is 75-85℃.

[0045] Preferably, step S2 further includes: A soluble aluminum source, a soluble Group 9 element source, and a pH adjuster are added concurrently to a titanium dioxide slurry to deposit alumina, thereby obtaining a Group 9 element-doped boehmite alumina film.

[0046] As those skilled in the art will understand, the boehmite alumina film is formed under neutral to slightly alkaline conditions, preferably with the concurrent flow pH controlled at 6.5–8.0. Soluble Group 9 element sources such as IrCl4 also undergo hydrolysis under these pH conditions, precipitating out and doping into the alumina film.

[0047] Preferably, the soluble aluminum source, the soluble Group 9 element source, and the pH adjuster are added in parallel over a period of 90 to 150 minutes, followed by a curing period of 40 to 80 minutes.

[0048] To maintain slurry stability, before adding soluble aluminum source, soluble Group 9 element source and pH adjuster in parallel flow, the slurry pH should first be adjusted to 6.5~8.0 and matured for 20~40 minutes.

[0049] Since alumina is deposited under slightly alkaline conditions, alkaline aluminum sources, such as sodium aluminate or potassium aluminate, are preferred as the soluble aluminum source. It is preferably added in solution form, with a solution concentration of 150-180 g / L (based on alumina). The amount of soluble aluminum source added, based on alumina, is 3.0-6.0% of the mass of the titanium dioxide substrate.

[0050] Soluble Group 9 element sources, such as iridium sources, can be Ir₂O₃, IrO₂, IrCl₄, and IrCl₃·3H₂O. Ir₂O₃ and IrO₂ are insoluble in water but soluble in acids. Ir₂O₃ is soluble in sulfuric acid or hydrochloric acid, and IrO₂ is soluble in hydrochloric acid. Therefore, Ir₂O₃ and IrO₂ can be added to the slurry in the form of acid solutions. After addition to the slurry, they are redeposited on the titanium dioxide surface under conditions of 6.5–8.0, becoming doped into the alumina film.

[0051] IrCl4 and IrCl3·3H2O are soluble in both water and acid, therefore, they can be added to the slurry in the form of aqueous or acidic solutions, with a solution concentration of 60-80 g / L (based on iridium oxide). Other Group 9 element sources are similar to iridium sources and are also preferably added in solution form.

[0052] The amount of soluble Group 9 element source added is 0.1 to 1.0% of the mass of the titanium dioxide substrate, based on the Group 9 element source.

[0053] pH adjusters can be inorganic acids, inorganic bases, etc., and the preferred solution concentration is 90~110g / L.

[0054] As those skilled in the art will understand, to facilitate washing and meet the requirements of downstream products, preferably, after inorganic coating, the pH of the slurry is adjusted to 4.5-5.5, and then matured for 20-40 minutes.

[0055] Preferably, step S3 further includes: The slurry coated with boehmite alumina film containing Group 9 elements is separated into solid and liquid phases (preferably by pressure filtration), dried, and then slurried with a non-protonated solvent. Spirocyclic pyran compounds are added and refluxed at 60-80°C for 2-4 hours. Under high-temperature reflux reaction conditions, the spirocyclic pyran compounds are firmly bonded to titanium dioxide.

[0056] Because the reaction time is relatively long, reflux can greatly ensure that the solvent does not evaporate.

[0057] Aprotic solvents such as dimethyl sulfoxide, acetone, diethyl ether, and toluene can be used for organic coating modification. When the slurry coated with the inorganic coating layer is dehydrated and then slurried again with an aprotic solvent, water can be used to avoid adverse effects of water on the binding of spirocyclic pyran compounds and titanium dioxide.

[0058] As those skilled in the art will understand, after organic coating modification, the process also includes steps of alcohol washing, flash evaporation, and steam powdering to obtain the target titanium dioxide.

[0059] Example 1 The slurry with qualified particle size from the sand mill is introduced into the coating tank, the concentration is controlled at 300 g / L, and the temperature is raised to 80℃; within 40 min, NaOH solution is added to adjust the pH to 7.0, and it is matured for 30 min; within 120 min, IrCl3·3H2O solution (0.5% by mass of titanium dioxide substrate), NaAlO2 solution (5.3% by mass), and H2SO4 solution are added in parallel, the pH is controlled at 7.0, and then it is matured for 60 min; within 40 min, H2SO4 solution is added to adjust the pH to 5.0, and then it is matured for 30 min.

[0060] The slurry was washed with water and dried; the filter cake was pulped with toluene at a concentration of 200 g / L, and a reflux condenser was used at a temperature of 70°C. N-(hydroxyethyl)-3,3-dimethyl-6-nitroindoline spiropyran, accounting for 2% of the mass fraction of the titanium dioxide substrate, was added and refluxed for 3 h; the mixture was washed with alcohol, and then flash-evaporated and steam-dried to obtain the target titanium dioxide.

[0061] Example 2 The slurry with qualified particle size from the sand mill is introduced into the coating tank, the concentration is controlled at 300 g / L, and the temperature is raised to 80℃; within 40 min, NaOH solution is added to adjust the pH to 7.0, and it is matured for 30 min; within 120 min, IrCl3·3H2O solution (0.5% by mass of titanium dioxide substrate), NaAlO2 solution (5.3% by mass), and H2SO solution are added in parallel, the pH is controlled at 7.0, and then it is matured for 60 min; within 40 min, H2SO4 is added to adjust the pH to 5.0, and then it is matured for 30 min.

[0062] The slurry was washed with water and dried; the filter cake was pulped with toluene at a concentration of 200 g / L, and a reflux condenser was used at a temperature of 70 °C. 1',3'-dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole], accounting for 2% of the mass fraction of the titanium dioxide substrate, was added and refluxed for 3 h; the mixture was washed with alcohol, and then flash-evaporated and steam-dried to obtain the target titanium dioxide.

[0063] Example 3 The slurry with qualified particle size from the sand mill is introduced into the coating tank, the concentration is controlled at 300 g / L, and the temperature is raised to 80℃; within 40 min, NaOH solution is added to adjust the pH to 7.0, and it is matured for 30 min; within 120 min, IrCl3·3H2O solution (0.5% by mass of titanium dioxide substrate), NaAlO2 solution (5.3% by mass), and H2SO4 are added concurrently, the pH is controlled at 7.0, and it is matured for 60 min; within 40 min, H2SO4 solution is added to adjust the pH to 5.0, and it is matured for 30 min.

[0064] The slurry was washed with water and dried; the filter cake was pulped with toluene at a concentration of 200 g / L, and a reflux condenser was used at a temperature of 70 °C. Spiro[1,3,3-trimethylindole-(6'-nitrobenzenedihydropyran)] at a mass fraction of 2% of the titanium dioxide substrate was added and refluxed for 3 h; the mixture was washed with alcohol, and then flash-evaporated and steam-dried to obtain the target titanium dioxide.

[0065] Example 4 Example 4 is similar to Example 1, except that the amount of Ir introduced is adjusted from 0.5% to 0.3%.

[0066] Example 5 Example 5 is similar to Example 1, except that the amount of Ir introduced is adjusted from 0.5% to 0.7%.

[0067] Example 6 Example 6 is similar to Example 1, except that the amount of organic modification is adjusted from 2% to 1%.

[0068] Example 7 Example 7 is similar to Example 1, except that the amount of organic modification is adjusted from 2% to 3%.

[0069] Example 8 Example 8 is similar to Example 1, except that the inorganic doped Ir element is changed to Rh element (the rhodium source is rhodium nitrate).

[0070] Comparative Example 1 (Conventional alumina coating) The slurry with qualified particle size from sand milling was introduced into a coating tank, with the concentration controlled at 300 g / L, and heated to 80℃. Within 40 min, NaOH solution was added to adjust the pH to 7.0, and the mixture was allowed to mature for 30 min. Within 120 min, NaAlO2 solution (5.3% by mass of titanium dioxide substrate) and H2SO4 were added concurrently, maintaining the pH at 7.0, and the mixture was allowed to mature for 60 min. Within 40 min, H2SO4 solution was added to adjust the pH to 5.0, and the mixture was allowed to mature for 30 min. The slurry was then washed with water, flash-evaporated, and steam-powdered to obtain the target titanium dioxide.

[0071] Comparative Example 2 (without organic coating compared to Example 1) The slurry with qualified particle size from sand milling was introduced into a coating tank, with the concentration controlled at 300 g / L, and heated to 80℃. Within 40 min, NaOH solution was added to adjust the pH to 7.0, and the mixture was allowed to mature for 30 min. Within 120 min, a mixture of 0.5% IrCl3·3H2O solution, 5.3% NaAlO2 solution, and H2SO4 (by mass fraction of titanium dioxide substrate) was added concurrently, maintaining the pH at 7.0, and the mixture was allowed to mature for 60 min. Within 40 min, H2SO4 solution was added to adjust the pH to 5.0, and the mixture was allowed to mature for 30 min. The slurry was then washed with water, flash-evaporated, and steam-dried to obtain the target titanium dioxide.

[0072] Comparative Example 3 (without iridium doping compared to Example 1) The slurry with qualified particle size from the sand mill is introduced into the coating tank, the concentration is controlled at 300 g / L, and the temperature is raised to 80℃; within 40 min, NaOH solution is added to adjust the pH to 7.0, and it is matured for 30 min; within 120 min, NaAlO2 solution and H2SO4 with a mass fraction of 5.3% of titanium dioxide substrate are added in parallel, the pH is controlled at 7.0, and it is matured for 60 min; within 40 min, H2SO4 solution is added to adjust the pH to 5.0, and it is matured for 30 min.

[0073] The slurry was washed with water and dried; the filter cake was pulped with toluene at a concentration of 200 g / L, and a reflux condenser was used at a temperature of 70°C. N-(hydroxyethyl)-3,3-dimethyl-6-nitroindoline spiropyran, accounting for 2% of the mass fraction of the titanium dioxide substrate, was added and refluxed for 3 h; the mixture was washed with alcohol, and then flash-evaporated and steam-dried to obtain the target titanium dioxide.

[0074] Comparative Example 4 (using kaolin, a common filler in paper mills, instead of titanium dioxide) Kaolin was used, and toluene was used for pulping. The concentration was controlled at 200 g / L. A reflux condenser was used, and the temperature was controlled at 70℃. N-(hydroxyethyl)-3,3-dimethyl-6-nitroindoline spiropyran, accounting for 2% of the mass fraction of kaolin, was added and refluxed for 3 h. After alcohol washing, the modified kaolin was obtained by flash evaporation and steam evaporation.

[0075] Experimental results The titanium dioxide obtained in Examples 1-8 and Comparative Examples 1-4 were used for papermaking, and their application performance was evaluated.

[0076] 1. Dispersion test The dispersibility test (sedimentation test) was conducted in an aqueous system using a 250mL graduated cylinder. 5% titanium dioxide powder was mixed with water, and the height of the powder was recorded at different time points, in mL. Figure 1 As shown in Table 1, the left side is a photograph of the state inside the graduated cylinder when titanium dioxide and water are just mixed, and the right side is a photograph of the state inside the graduated cylinder after standing for a period of time.

[0077] Table 1

[0078] As can be seen from the data of Examples 1-8 and Comparative Example 1, doping with Ir and introducing spirocyclic pyran compounds can significantly improve the dispersibility of titanium dioxide, and the improvement is greater with Ir doping.

[0079] 2. Thermosensitivity test Test method: Weigh 30g of titanium dioxide, treat it in a 140℃ oven for 1 hour, observe its color change, and then naturally cool it to room temperature before observing its color change again. The results are shown in Table 2. Figures 2-5 As shown.

[0080] Table 2

[0081] in, Figure 2 and Figure 3 These are color photos of titanium dioxide before and after oven treatment in Example 3. The color of the titanium dioxide changed significantly after oven treatment.

[0082] Figure 4 and Figure 5 The images show the colors of titanium dioxide in Comparative Example 1 before and after oven treatment. The color of the titanium dioxide did not change significantly after oven treatment.

[0083] As can be seen from the color changes in Examples 1-8 and Comparative Examples 1-4, the introduction of spirocyclic pyran compounds in the embodiments of this application makes the titanium dioxide thermosensitive, exhibiting color development at high temperatures. Furthermore, this thermosensitive property is reversible, restoring the original color upon cooling. In contrast, the comparative examples, which did not introduce spirocyclic pyran compounds, do not exhibit thermosensitive properties.

[0084] 3. Thermosensitive color change life test of powder materials Test method: Weigh 30g of titanium dioxide, treat it in an oven at 140℃ for 1 hour, observe its color change, and then naturally cool it to room temperature, observe its color change again. One cycle is considered as one test, and the experiment is repeated.

[0085] The results are shown in Table 3.

[0086] Table 3

[0087] Analysis of the number of cycles in Examples 1-8 and Comparative Example 4 shows that combining spirocyclic pyran compounds with titanium dioxide helps extend the lifespan of reversible thermosensitive materials. Compared with kaolin, another commonly used filler in the papermaking industry, combining spirocyclic pyran compounds with titanium dioxide has significant advantages.

[0088] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A thermosensitive titanium dioxide for papermaking, characterized in that, From the inside out, it includes a titanium dioxide substrate, an inorganic coating layer, and an organic coating layer; the inorganic coating layer includes a boehmite alumina film layer doped with group 9 elements; the organic coating layer is a film layer formed by introducing spirocyclic pyran compounds; The titanium dioxide has reversible thermosensitive properties, exhibiting different colors at different temperatures.

2. The thermosensitive titanium dioxide for papermaking as described in claim 1, characterized in that, The titanium dioxide appears white or light-colored at temperatures above 130°C. The titanium dioxide appears dark at temperatures below 100°C.

3. The thermosensitive titanium dioxide for papermaking as described in claim 1, characterized in that, The spirocyclic pyran compound has the following general structural formula: ； Wherein R1 is independently selected from at least one of H, dimethyl, and methoxy; R2 is independently selected from at least one of methyl, dimethyl, trimethyl, and hydroxyethyl; and R3 is independently selected from at least one of nitro, halogen, and methoxy.

4. The thermosensitive titanium dioxide for papermaking as described in claim 1, characterized in that, The spirocyclic pyran compound is selected from one or more combinations of the following compounds: 1',3'-Dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole], spiro[1,3,3-trimethylindole-(6'-bromobenzodihydropyran)], spiro[1,3,3-trimethylindole-(6'-nitrobenzodihydropyran)], spiro[1,3,3-trimethylindole-(8'-methoxybenzodihydropyran)], N-(hydroxyethyl)-3,3-dimethyl-6-nitroindolinespiropyran, spiro[1,3,3-trimethylindole-benzodihydropyran].

5. The thermosensitive titanium dioxide for papermaking as described in claim 1, characterized in that, The amount of boehmite alumina film doped with Group 9 elements, calculated as alumina, is 3.0~6.0% of the mass of the titanium dioxide substrate; The doping amount of the group 9 element, calculated as group 9 element, is 0.1 to 1.0% of the mass of the titanium dioxide substrate.

6. The thermosensitive titanium dioxide for papermaking as described in claim 1, characterized in that, The amount of the organic coating layer is 1.0 to 3.0% of the mass of the titanium dioxide substrate.

7. A method for preparing the thermosensitive titanium dioxide for papermaking as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Preparation of titanium dioxide-based material slurry; S2. A boehmite alumina coating with Group 9 element doping; S3. Perform organic coating of spirocyclic pyran compounds.

8. The method for preparing the thermosensitive titanium dioxide for papermaking as described in claim 7, characterized in that, Step S2 further includes: A soluble aluminum source, a soluble Group 9 element source, and a pH adjuster are added concurrently to a titanium dioxide slurry to deposit alumina and obtain a Group 9 element-doped boehmite alumina film. Preferably, the pH of the parallel flow is controlled to be 6.5~8.

0.

9. The method for preparing the thermosensitive titanium dioxide for papermaking as described in claim 7, characterized in that, Step S3 involves using a wet coating method to organically coat the spirocyclic pyran compound.

10. The method for preparing the thermosensitive titanium dioxide for papermaking as described in claim 9, characterized in that, Step S3 further includes: The slurry coated with a boehmite alumina film containing Group 9 elements was separated into solid and liquid phases, dried, and then slurried with a nonprotonated solvent. The spirocyclic pyran compound was added, and the mixture was refluxed at 60-80°C for 2-4 hours.

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