Water-absorbing soluble toilet paper and preparation method thereof

Abstract

The invention belongs to the technical field of toilet paper preparation, and particularly relates to water-absorbing soluble toilet paper and a preparation method thereof.The preparation method comprises the steps that S1, proportioning and pulp dispersing are conducted, specifically, a long fiber pulp board and a short fiber pulp board are taken according to the weight ratio, and long fiber pulp and short fiber pulp are prepared; s2, pulping: conveying the long fiber pulp into a pulping machine for pulping; conveying the short fiber slurry into a fiber fluffer for fluffing; s3, pulp preparation: mixing the long fiber pulp and the short fiber pulp treated in the step S2 to obtain mixed pulp, then adding modified inorganic filler and a composite strength improver, adding water to dilute until the concentration of the pulp is 0.1-0.3%, and adjusting the pH value of the pulp to be less than or equal to 7 to obtain a papermaking base material; s4, making paper with pulp on a net; s5, squeezing and drying; s6, wrinkling with a scraper; s7, winding into paper. The water-absorbing soluble toilet paper provided by the invention is reliable in strength in a dry state, can keep a complete structure in a wet state, and can be quickly dispersed after meeting water.

Description

Technical Field

[0001] The invention belongs to the technical field of toilet paper preparation, and in particular relates to water-absorbent and soluble toilet paper and a preparation method thereof. Background Art

[0002] As an indispensable daily necessity, toilet paper is used very frequently and is widely used in various fields such as homes, public places, and medical institutions. Traditional toilet paper is often discarded after use and becomes solid waste. This not only increases the burden and pressure of solid waste disposal, but may also pollute soil and water bodies due to improper disposal. At the same time, if traditional toilet paper is left in the environment for a long time after use, it may become a breeding ground for bacteria. This is especially true for medical institutions and public places with high hygiene and environmental protection requirements. Due to the large amount of toilet paper used and the lack of immediate garbage disposal equipment, the piles of toilet paper after large amounts of use are prone to rapid bacterial growth, leading to a decrease in environmental hygiene. Water-absorbing soluble toilet paper, on the other hand, dissolves immediately when it comes into contact with water and can be immediately flushed away, entering the sewage treatment system with sewage. This not only reduces the chance of bacterial growth and helps maintain environmental hygiene, but is also convenient to use and can quickly dissolve or degrade in water bodies, without causing long-term water pollution. Therefore, the preparation of water-absorbing soluble toilet paper is becoming an urgent need and is of great necessity that cannot be ignored.

[0003] The primary technical challenge faced in the production of water-soluble toilet paper is balancing paper solubility and strength. Specifically, this refers to the balance between paper strength, especially wet strength, and water solubility. First, paper must possess a certain level of strength, including both dry and wet strength. Dry strength refers to the paper's resistance to tearing and stretching in a dry state, and is a core indicator for ensuring its ability to fulfill its basic functions. Insufficient dry strength can easily lead to crumbling and fragmentation when wiped, resulting in incomplete cleaning or residual paper debris. Only with good dry strength can paper ensure structural stability and durability under normal use. Wet strength, on the other hand, refers to the paper's ability to maintain its physical integrity and structural strength when wet or submerged in water. In other words, the paper's ability to resist tearing, stretching, or rupture after absorbing water. For toilet paper, the need for appropriate wet strength is primarily based on its need to withstand use in wet environments. It must ensure that the paper is resistant to damage, residual paper debris, or the risk of contamination when used in a wet environment or with minimal residual water. However, if the wet strength of the paper is too high, it may be difficult to break down in sewers, causing blockages. If the wet strength of the paper is too low, it will crumble into slag upon contact with water. This will prevent the paper from effectively covering waste, oil stains, water spots, dirt, and other materials being wiped, rendering it ineffective for cleaning. For paper used in sanitary facilities, it is also crucial to ensure that the paper remains intact in a wet environment to prevent residual fibers from causing infection. Therefore, it is necessary to adjust the raw material composition of the paper so that water-soluble toilet paper maintains its structural integrity when wet, gradually disintegrating over tens of seconds to minutes upon contact with water, rather than instantly disintegrating.

[0004] However, increasing paper strength, especially wet strength, also leads to a decrease in water solubility. This is primarily due to a fundamental conflict between chemical and physical mechanisms. High dry strength in paper implies a dense fiber structure, strong hydrogen bonding between fibers, high adhesive strength of additives, and slow dissolution and separation in water. The mechanism by which wet strength is achieved is that wet strength agents, such as polyamide-epichlorohydrin resin and urea-formaldehyde resin, primarily chemically connect fibers into a three-dimensional network, enhancing interfiber bonding and maintaining the structural integrity of the paper even when wet. This strongly cross-linked structure blocks water penetration and reduces the damage to interfiber hydrogen bonds, thereby maintaining paper strength. Water solubility, on the other hand, is achieved by weak physical forces, such as hydrogen bonds and van der Waals forces, between fibers or water-soluble additives in water-soluble paper. These forces disrupt the intermolecular forces upon contact with water, causing the paper to dissolve rapidly. Therefore, wet strength relies on strong chemical bonds, requiring stable, strongly cross-linked structures formed through covalent or ionic bonds that are resistant to water molecules. Water solubility, on the other hand, relies on weak interactions and physical forces easily disrupted by water, such as hydrogen bonds and van der Waals forces, to achieve rapid dissolution. The cross-linked structure of wet strength agents densifies the paper, reducing water penetration channels and thus maintaining strength. Water solubility, on the other hand, requires a loose structure to facilitate water molecule penetration and the disentanglement of molecular chains, accelerating dissolution. Therefore, the addition of wet strength agents intensifies the cross-linking reaction and enhances fiber bonding, while also reducing the paper's water solubility. Adding water-soluble additives can increase the paper's hydrophilicity and solubility, but weakens the bonding between fibers and reduces wet strength. Therefore, in the preparation of water-soluble toilet paper, the contradiction between the paper's "solubility" and "strength," particularly the balance between wet strength and water solubility, is a core technical challenge in the production of this type of paper.

[0005] Based on this, the present invention improves the strength and water solubility of paper by optimizing the raw material composition and preparation process of paper, providing a toilet paper that has excellent mechanical properties in a dry state, can maintain structural integrity in a wet state, but can quickly disperse when exposed to water. Summary of the Invention

[0006] The purpose of the present invention is to address the above-mentioned technical problems and provide a water-soluble toilet paper and a preparation method thereof, so as to achieve toilet paper that has reliable strength in a dry state, can maintain structural integrity in a wet state, and can quickly disperse when exposed to water by regulating the balance between paper strength and water solubility.

[0007] In view of this, the present invention provides a method for preparing water-absorbent and soluble toilet paper, comprising the steps of: S1, batching and slurry preparation: taking a long fiber pulp sheet and a short fiber pulp sheet in a weight ratio of (1.5-3):(7-9), pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water, and dispersing them to prepare a long fiber slurry and a short fiber slurry; S2, refining: the long fiber pulp is conveyed to the refiner for refining, and the beating degree of the pulp after refining is 25~32°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking, and the beating degree of the pulp after deflaking is 37~45°SR; S3, slurry preparation: mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry, then adding 1-3% of the total weight of the absolute dry paddle board and 0.05-0.15% of the total weight of the absolute dry paddle board as a composite strength improver, adding water to dilute the mixed slurry to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or alkali to obtain a papermaking base material; wherein the modified inorganic filler has a core-shell structure, CaCO3 is a core layer particle, and the outer layer is coated with a shell layer formed by polyacrylic acid; the composite strength improver is a composite formed by compounding modified PAE and cationic starch; S4, copied online; S5, pressing and drying; S6, scraper wrinkling; S7, rolled into paper.

[0008] Furthermore, step S3 includes: (I) mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A having a solid content of 10-15 wt%, and adjusting the pH of the dispersion A to 7.5-8.5 with an acid or base; (III) dispersing the composite strength improver in deionized water to prepare a dispersion B having a solid content of 5 to 10 wt%, and adjusting the pH of the dispersion B to 6 to 7 with an acid or an alkali; (IV) Slowly adding dispersion B to dispersion A in proportion over 5 to 10 minutes while stirring at a low speed of 100 to 200 rpm. After the addition of dispersion B is completed, stirring is continued for 10 to 20 minutes, and then the mixture is allowed to stand for 5 to 10 minutes to obtain dispersion C; (V) Adding the dispersion C to the mixed slurry, diluting the mixed slurry with water to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or an alkali to obtain a papermaking base material.

[0009] Furthermore, in step S1, the long fibers account for 18-25 wt% of the total fiber weight.

[0010] Furthermore, the core layer of the modified inorganic filler is composed of light calcium carbonate particles, and the particle size of the light calcium carbonate particles is 1-3 μm.

[0011] Furthermore, the preparation process of the modified inorganic filler is as follows: (a) dispersing an inorganic filler in deionized water, adding an appropriate amount of a dispersant, and stirring to uniformly disperse the inorganic filler to obtain an inorganic filler suspension, and then adjusting the pH of the inorganic filler suspension to 8 to 9 using an acid or a base; wherein the content of the inorganic filler is 10 to 20 wt % and the content of the dispersant is 0.1 to 0.5 wt %; (b) adding partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1 to 0.5 wt %; (c) slowly adding the polyacrylic acid aqueous solution to the inorganic filler suspension under stirring, then heating the mixture to 30-40° C. and continuously stirring at 100-400 rpm for 1-2 hours at the same temperature, adjusting the pH of the mixture to 6.5-7.5 with an acid or base, and then continuing to stir at 100-400 rpm for 0.5-1 hour to obtain a suspension of the modified inorganic filler; (d) The suspension of the modified inorganic filler is centrifuged and dried to obtain the modified inorganic filler.

[0012] Furthermore, the step (c) includes: Under stirring, the polyacrylic acid aqueous solution is slowly added to the inorganic filler suspension, and then the mixed solution is heated to 30~40°C and continuously stirred at a speed of 100~400 rpm at this temperature for 1~2 hours. After that, the pH of the mixed solution is adjusted to 6.5~7.5 using an acid or a base, and then the CaCl2 aqueous solution is slowly added dropwise, and the amount of CaCl2 added is 1~5wt% of the amount of polyacrylic acid. At the same time, stirring is continued at a speed of 100~400 rpm for 0.5~1 hour to obtain a suspension of modified inorganic filler.

[0013] Furthermore, the preparation process of the composite strength improver is as follows: (1) First, cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension having a cationic starch content of 10-30 wt%, and then the cationic starch suspension is heated at a rate of 5-10 °C / min to the gelatinization starting temperature of the cationic starch, and the cationic starch suspension is maintained at this temperature for 10-20 min; (2) Then, a certain amount of modified PAE and water were added to prepare a suspension having a total content of modified PAE and cationic starch of 5-10 wt%, wherein the weight ratio of modified PAE to cationic starch was (0.3-0.6):1. The mixed solution was then placed in an ultrasonic device and ultrasonically treated for 15-30 min at a power of 400-600 W to obtain a suspension of the composite strength improver.

[0014] Furthermore, in the preparation process of the composite strength improver, after the ultrasonic treatment in step (2), the ultrasonically treated mixed solution is concentrated at below 50°C to a suspension having a total content of modified PAE and cationic starch of 20-40 wt%, and then placed in a low-temperature freezing device for cyclic freezing treatment 3-5 times, with the freezing temperature being below -10°C. After freezing, the mixture is placed at room temperature for natural thawing and then subjected to the next cycle of freezing treatment.

[0015] Furthermore, the preparation process of the modified PAE is as follows: First, a polyamide-polyamine intermediate solution with a solid content of 30-40% is prepared; Then, 0.05-0.1 parts by weight of a modifier is added to the polyamide-polyamine intermediate solution, and water is added to dilute the solution to a solid content of 20-25%. 10-20 parts by weight of epichlorohydrin are slowly added under stirring. After the addition is complete, the reaction system is heated to 65-85° C., stirred and kept warm at this temperature until the viscosity of the reaction system reaches 30-40 mPa·s. The pH of the reaction system is adjusted to 3.5-4.5 using an acid solution, and then 0.1-0.2 parts by weight of a modifier is added again. After keeping warm under stirring for 20-30 minutes, heating is stopped, and the solution is diluted with water to a solid content of 10-15%, thereby obtaining a modified PAE resin.

[0016] The water-absorbing and soluble toilet paper is prepared by the method for preparing the water-absorbing and soluble toilet paper.

[0017] The beneficial effects of the present invention are: In the water-absorbent soluble toilet paper provided by the present invention, the structural disintegration is not caused solely by physical water absorption and expansion or chemical bond rupture, but is a degradation process triggered by the synergistic action of multiple mechanisms. This process includes both physical disintegration, such as the expansion and separation of fibers caused by water molecules entering the paper structure, weak interfacial debonding, and structural collapse caused by the inorganic filler absorbing water and swelling. In particular, the modified inorganic filler first absorbs water and expands in an aqueous environment. The pH responsiveness of the shell PAA causes the particles to undergo interfacial swelling and surface dissociation, thereby promoting the overall disintegration of the fiber structure and causing the material to break up and decompose from the macroscopic structure. At the same time, the structural disintegration process of the paper also includes chemical structural changes, such as the swelling and dissolution of the modified inorganic filler shell triggered by pH changes, and the dissociation of the weak cross-linked structure between the modified PAE and cationic starch and fibers, which leads to the disintegration of the material from the microstructural level, dissolution or depolymerization of components. This composite degradation mechanism is used to achieve the properties of paper that are reliable in dry state, maintain structural integrity in wet state, and quickly disperse when exposed to water, thereby making the toilet paper stable during use and able to controllably and effectively disperse or dissolve under given conditions (such as toilet water). DETAILED DESCRIPTION

[0018] The following will be combined with the specific embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0019] In the description of this application, it should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to this application. For ease of description, technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be considered part of the specification.

[0020] It should be noted that, in this application, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0021] A method for preparing water-absorbing and soluble toilet paper comprises the following steps: S1, batching and slurrying: taking a long fiber pulp sheet and a short fiber pulp sheet according to a weight ratio of (1.5-3):(7-9), pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water respectively, and then dispersing them in a hydraulic pulper to obtain a long fiber pulp and a short fiber pulp; S2, refining: the long fiber pulp is conveyed to the refiner for refining, the refining power is 30~60kwh / t, and the beating degree of the pulp after refining is 25~32°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking for 5~10 minutes, and the beating degree of the pulp after deflaking is 37~45°SR; S3, slurry preparation: mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry, then adding 1-3% of the total weight of the absolute dry paddle board and 0.05-0.15% of the total weight of the absolute dry paddle board as a composite strength improver, adding water to dilute the mixed slurry to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or alkali to obtain a papermaking base material; wherein the modified inorganic filler has a core-shell structure, CaCO3 is a core layer particle, and the outer layer is coated with a shell layer formed by polyacrylic acid; the composite strength improver is a composite formed by compounding modified PAE and cationic starch; S4, papermaking on the web: conveying the papermaking base material to the headbox for papermaking on the web; S5, pressing and drying: The wet paper pair is pressed to remove moisture and is initially formed to obtain a wet paper pair. The wet paper web is dehydrated by suction in two vacuum boxes and then transferred to the drying cylinder via vacuum pressing rollers, where it is dried on the surface of the drying cylinder. S6, scraper wrinkling: After the paper is dried, it is scraper wrinkled and peeled off, and then enters the paper winding equipment; S7, winding into paper: After the initial rolling and rewinding on the paper rolling equipment, the paper is cut into pieces to obtain water-absorbing and soluble toilet paper.

[0022] Furthermore, the basis weight of each layer of the water-soluble toilet paper of the present invention is 13.5-18.5 g / m 2 The water-absorbing and soluble toilet paper has 2 to 4 layers.

[0023] Preferably, the long fibers are selected from one or more of softwood, sisal, and flax fibers.

[0024] Preferably, the average fiber length of the long fibers is 2 to 4.5 mm.

[0025] Preferably, the short fibers are selected from one or more of hardwood, bagasse, wheat straw, reed fibers and the like.

[0026] Preferably, the average fiber length of the short fibers is 0.5-1 mm.

[0027] More preferably, in step S1, the long fibers account for 18-25 wt% of the total fiber weight.

[0028] Generally speaking, when ordinary toilet paper is manufactured in the industry, the proportion of long fibers in the total fiber weight is about 40~60wt%; when ordinary water-absorbent soluble toilet paper is manufactured, the proportion of long fibers in the total fiber weight is about 20~30wt%; when high-strength water-absorbent soluble toilet paper is manufactured, the proportion of long fibers in the total fiber weight is about 30~40%.

[0029] Compared with the prior art, in the present invention, the strength of the paper is improved by adding a trace amount of modified inorganic filler and composite strength improver, and the proportion of long fibers in the total fiber weight of the high-strength water-absorbing and soluble toilet paper prepared by the present invention is reduced to 18~25wt%. In this way, the content of long fibers in the water-absorbing and soluble toilet paper prepared by the present invention is relatively low, and the content of short fibers is relatively high, which can make the paper have better softness and can dissolve quickly after entering water. At the same time, since the price of short fibers is lower than that of long fibers, the preparation cost can also be reduced.

[0030] More importantly, the present invention incorporates an appropriate amount of polyacrylic acid (PAA) to coat calcium carbonate as a modified inorganic filler. Since PAA is a weakly acidic polymer with pronounced pH-responsive properties, coating the surface of calcium carbonate particles creates a core-shell structure, endowing the modified inorganic filler particles with varying stability and dissolution behavior in different pH environments. For example, in acidic or neutral environments, the PAA shell is structurally stable and resists premature dissolution. However, in alkaline environments, such as flushing water, the PAA shell swells or destabilizes and detaches, exposing the calcium carbonate and aiding in the rapid disintegration of the paper structure, thereby increasing the overall water dissolution rate. Furthermore, calcium carbonate, as an inorganic mineral filler, is insoluble in water but porous and hydrophilic. Therefore, the calcium carbonate particles themselves act as "weak points" in the paper, easily initiating structural fractures under the action of water, thereby accelerating the paper's dissolution rate and disintegration in water.

[0031] Furthermore, the PAA coating in the modified inorganic filler improves the surface hydrophilicity and charge properties of the calcium carbonate particles, preventing particle agglomeration and improving their uniformity of dispersion in the pulp and retention in the wet paper. Furthermore, the PAA coating provides the modified inorganic filler with a certain degree of flexibility and bonding ability, aiding in the formation of a more stable hydrogen bond network between fibers in the dry state. This moderately enhances the dry and wet strength of the paper without significantly reducing its water absorption and solubility.

[0032] On this basis, by combining modified PAE with a composite strength improver made from cationic starch, the strength and water solubility of the paper are regulated to appropriate levels, achieving the goal of reliable strength in a dry state, maintaining structural integrity in a wet state, and quickly dispersing when exposed to water.

[0033] Furthermore, the step S1 includes: After pre-wetting the long fiber pulp sheet with water, it is placed in a hydraulic pulper and water is added for pulping to obtain a long fiber pulp with a concentration of 3-5wt%; after pre-wetting the end fiber pulp sheet with water, it is placed in a hydraulic pulper and water is added for pulping to obtain a short fiber pulp with a concentration of 3-5wt%.

[0034] Furthermore, in the step S1, after slurrying, the long fiber slurry and the short fiber slurry can be respectively sent to a cleaner for slag removal.

[0035] In step S2, controlling the beating degree of the long fiber slurry within 25-32°SR can enable the long fibers to retain appropriate length and strength, thereby enhancing the dry strength and tensile strength of the paper. Controlling the beating degree of the short fiber slurry within 37-45°SR can provide a good foundation for the water solubility and dispersion speed of the paper, thereby improving the fiber bonding strength and paper uniformity, taking into account the initial strength of the paper, and improving its solubility in water.

[0036] Furthermore, step S3 includes: (I) mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A having a solid content of 10-15 wt%, and adjusting the pH of the dispersion A to 7.5-8.5 with an acid or base; (III) dispersing the composite strength improver in deionized water to prepare a dispersion B having a solid content of 5 to 10 wt%, and adjusting the pH of the dispersion B to 6 to 7 with an acid or an alkali; (IV) Slowly adding dispersion B to dispersion A in proportion over 5 to 10 minutes while stirring at a low speed of 100 to 200 rpm. After the addition of dispersion B is completed, stirring is continued for 10 to 20 minutes, and then the mixture is allowed to stand for 5 to 10 minutes to obtain dispersion C; (V) Adding the dispersion C to the mixed slurry, diluting the mixed slurry with water to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or an alkali to obtain a papermaking base material.

[0037] Furthermore, in step S3, the modified inorganic filler is a modified inorganic filler obtained by modifying the inorganic filler with polyacrylic acid. The modified inorganic filler has CaCO3 as the core layer inorganic filler particles, and the outer layer is coated with a shell layer formed by polyacrylic acid, thereby constituting a core-shell functional filler with pH responsiveness. The shell layer in the core-shell structure remains stable under neutral or weakly acidic conditions, and may swell or destabilize and deshell in an alkaline water environment, such as toilet flushing water, thereby regulating the supporting effect and release behavior of the inorganic filler on the paper structure.

[0038] Preferably, the core layer of the modified inorganic filler is composed of light calcium carbonate particles.

[0039] More preferably, the light calcium carbonate particles are spherical or nearly spherical in shape, and have a particle size of 1 to 3 μm.

[0040] As some examples of the present invention, the preparation process of the modified inorganic filler is as follows: (a) dispersing an inorganic filler in deionized water, adding an appropriate amount of a dispersant, and stirring to uniformly disperse the inorganic filler to obtain an inorganic filler suspension, and then adjusting the pH of the inorganic filler suspension to 8 to 9 using an acid or a base; wherein the content of the inorganic filler is 10 to 20 wt % and the content of the dispersant is 0.1 to 0.5 wt %; (b) adding partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1 to 0.5 wt %; (c) slowly adding the polyacrylic acid aqueous solution to the inorganic filler suspension under stirring, then heating the mixture to 30-40° C. and continuously stirring at 100-400 rpm for 1-2 hours at the same temperature, adjusting the pH of the mixture to 6.5-7.5 with an acid or base, and then continuing to stir at 100-400 rpm for 0.5-1 hour to obtain a suspension of the modified inorganic filler; (d) The suspension of the modified inorganic filler is centrifuged and dried to obtain the modified inorganic filler.

[0041] As some other examples of the present invention, in the process of preparing the modified inorganic filler, after preparing the suspension of the modified inorganic filler in step (c), the suspension of the modified inorganic filler can also be directly added to the mixed slurry after being prepared according to the preparation requirements of the dispersion A in step S3. In this case, the addition amount of the suspension of the modified inorganic filler is calculated based on the weight of the modified inorganic filler contained therein.

[0042] As a preferred example of the present invention, other Ca 2+ Ions act as physical cross-linking factors to form 2+-Carboxyl bridging forms a reversible cross-linked structure, thereby improving the shell strength and stability while retaining the ability of the modified inorganic filler to achieve pH-responsive structural expansion, cleavage and core release in an alkaline environment.

[0043] Specifically, other Ca can be introduced by adding CaCl2 2+ Ions are used as physical cross-linking factors. The specific approach is: In step (c): under stirring, the polyacrylic acid aqueous solution is slowly added to the inorganic filler suspension, and then the mixed solution is heated to 30-40° C. and continuously stirred at a speed of 100-400 rpm at this temperature for 1-2 hours. After that, the pH of the mixed solution is adjusted to 6.5-7.5 using an acid or a base, and then a CaCl2 aqueous solution is slowly added dropwise, wherein the amount of CaCl2 added is 1-5wt% of the amount of polyacrylic acid used, and stirring is continued at a speed of 100-400 rpm for 0.5-1 hour to obtain a suspension of modified inorganic filler.

[0044] Preferably, the concentration of the CaCl2 aqueous solution is 0.05 to 0.2 mol / L. Compared to other soluble calcium salts, CaCl2 has strong water solubility, fast ion release rate, and good diffusivity, which facilitates uniform cross-linking. It also has stable chemical properties, is less likely to induce side reactions, and has a wide range of raw material sources.

[0045] Preferably, the weight average molecular weight (Mw) of the polyacrylic acid is 100,000 to 300,000 Daltons (Da).

[0046] Preferably, the neutralization degree of the partially neutralized polyacrylic acid is 45% to 60%.

[0047] Preferably, the ratio of the added amount of the inorganic filler to the polyacrylic acid is (50-200):1.

[0048] As some examples of the present invention, the dispersant is selected from one or more of sodium lignin sulfonate, sodium hexametaphosphate, sodium tripolyphosphate, polyoxyethylene alkyl ether, and the like.

[0049] In the present invention, partially neutralized polyacrylic acid is selected to form the shell structure. In comparison, unneutralized polyacrylic acid has a low charge density and weak adsorption capacity, and is not easy to react with Ca 2+ Ion binding, at the same time, there are also the disadvantages of easy aggregation and viscosity, which is not conducive to the formation of a stable dispersion system; while the partially neutralized polyacrylic acid is moderately negatively charged, which can effectively adsorb Ca on the surface of CaCO3 2 + ions, and is not easy to cause strong electric repulsion or aggregation. In addition, partially neutralized polyacrylic acid retains some carboxyl groups (-COOH) that can form hydrogen bonds, and also contains a certain amount of -CO - , can be combined with Ca2+ Electrostatic complexation, a dual-functional group synergistic adsorption method, makes it easier to obtain a stable, dense, and controllable shell. Furthermore, the use of partially neutralized polyacrylic acid allows the shell to maintain moderate contraction at neutral pH, while rapidly stretching, uncoating, or expanding and swelling under alkaline conditions, widening the pH control range of the modified inorganic filler and regulating the water solubility of the paper. In fact, in China, to prevent acidic water from corroding tap water pipes, water plants will adjust the pH of tap water to a weak alkaline state during the water treatment process by adding regulators such as chlorine, lime, and sodium bicarbonate. This provides conditions for the water solubility and dissociation of the water-absorbing soluble paper described in the present invention.

[0050] In addition, during the preparation of the modified inorganic filler, the pH of the inorganic filler suspension is first adjusted to 8-9 using an acid or base, so that the inorganic filler is dispersed in a weakly alkaline environment. In a weakly alkaline environment, the surface of the inorganic filler particles is conducive to an appropriate amount of negative charge, which enhances the electrostatic repulsion between the particles, thereby avoiding aggregation or precipitation between the particles and maintaining dispersion stability. At the same time, the weakly alkaline environment is also conducive to the combination of polyacrylic acid and calcium carbonate particles, enhancing the stability of the particles and facilitating the subsequent formation of a core-shell structure.

[0051] Furthermore, the composite strength improver is a mixture of modified PAE and cationic starch, and its preparation process is as follows: (1) First, cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 10-30 wt%. The cationic starch suspension is then heated at a rate of 5-10 °C / min to near the gelatinization starting temperature of the cationic starch, and the cationic starch suspension is maintained at this temperature for 10-20 min. (2) Then, a certain amount of modified PAE and water were added to prepare a suspension with a total content of modified PAE and cationic starch of 5-10 wt%, wherein the weight ratio of modified PAE to cationic starch was (0.3-0.6):1, and the weight of modified PAE was the solid content in its aqueous solution as the actual weight; then, the mixed solution was placed in an ultrasonic device, and after ultrasonic treatment for 15-30 min at a power of 400-600 W, a suspension of the composite strength improver was obtained.

[0052] It should be noted that, when preparing the water-soluble toilet paper, the composite strength improver is added in the form of a suspension thereof, and the added amount is calculated based on the actual total weight of the modified PAE and cationic starch therein.

[0053] As a preferred example of the present invention, in the preparation process of the composite strength improver, after the ultrasonic treatment in step (2), the mixed solution after ultrasonic treatment can be concentrated below 50°C to a suspension having a total content of modified PAE and cationic starch of 20-40wt%, and then placed in a low-temperature freezing device for cyclic freezing treatment 3-5 times, with the freezing temperature being below -10°C. After freezing, the mixed solution is placed at room temperature for natural thawing and then subjected to the next cycle of freezing treatment again.

[0054] As some examples of the present invention, the gelatinization starting temperature T of the cationic starch is 糊化 It is usually 55~65℃, which varies depending on the type of starch. It can be measured by relevant instruments such as differential calorimeter scanner, polarizing microscope, etc.

[0055] Preferably, in the preparation process of the composite strength improver, after determining the gelatinization starting temperature T 糊化 After passing through, the cationic starch suspension can be heated to T 糊化 -3℃~T 糊化 .

[0056] In the preparation process of the composite strength improver, the cationic starch suspension is heated to the gelatinization starting temperature T 糊化 Nearby, and keep for a certain period of time, in T 糊化 When the temperature is near 4000℃, the crystalline region of starch can still be maintained, but the hydrogen bonds in the amorphous region are broken, resulting in loose chain segments and the short-range ordered structure inside the starch granules begins to disintegrate. Therefore, this process can achieve "pre-activation" of the internal structure of the starch granules, exposing more active groups, such as hydroxyl groups, to enhance the interaction between them and the modified PAE. At the same time, it disrupts the long-range and short-range ordered structures of starch, improves its solubility in water, and improves the water solubility of the prepared absorbent soluble paper.

[0057] In addition, by placing the mixed system of modified PAE and cationic starch in an ultrasonic device for treatment, for cationic starch, the ultrasonic cavitation effect can be used to further shear the cationic starch chain segments to form partial oligosaccharides and mobile hydrophilic segments, thereby reducing its average molecular weight, improving its fluidity, and enhancing its water solubility, making it easier to dissolve and compound with modified PAE or other components; for modified PAE, under the action of ultrasound, the epoxy groups in PAE can be promoted to open the ring and react with the starch hydroxyl groups, thereby strengthening the crosslinking density between the modified PAE and cationic starch, and improving its ability to improve the strength of paper after being used in water-soluble paper; for the mixed system of modified PAE and cationic starch, the ultrasonic cavitation effect can be used to break the aggregation of the two substances, promote the full mixing and combination between the modified PAE and cationic starch molecules, and improve the compounding efficiency and binding ability between PAE and starch.

[0058] On this basis, cyclic low-temperature freezing treatment can be used to utilize freezing / thawing to cause "reorganization" of the microstructure. Specifically, during the freezing process, the growth of ice crystals will squeeze the polymer chains in the system into a narrow space, prompting the molecular chains between cationic starch and PAE to undergo directional arrangement, entanglement, and hydrogen bond rearrangement. During thawing, the ice crystals melt, releasing liquid water, causing local rapid swelling and releasing voids, forming a microscopic pore-chain network interlaced distribution structure between the two, disrupting the original stacking of the polymer chains. Ultimately, through multiple cycles, a multi-level structure is induced to form with enhanced interchain interactions, more uniform pore structure, enhanced film-forming properties, and easy dissolution triggering. This multi-level structure is denser and more cohesive in the dry state, and can better combine with modified inorganic fillers with fibers or core-shell structures in the pulp, which can effectively improve the strength of the paper. However, it can absorb water and swell / disintegrate when exposed to water, which is beneficial to the hydrolysis or dissolution of the paper. Ultimately, it helps to enhance the affinity and adhesion between cationic starch, pulp fibers, and modified PAE, helps to form a paper strength support network, and improves the "early strength and late disintegration" performance requirements required for water-absorbent and soluble paper.

[0059] Furthermore, the preparation process of the modified PAE is as follows: First, in an oil bath at 110-140°C, 10-15 parts by weight of diethylenetriamine and 8-12 parts by weight of adipic acid are added to a reactor. After the raw materials are uniformly mixed under stirring, the temperature is raised to 160-180°C and kept warm for 2-4 hours. Then, heating is stopped. After the temperature of the reaction system naturally cools to 100°C, water is added to dilute the mixture to a solid content of 30-40%, and the mixture is stirred until homogeneous to obtain a polyamide polyamine intermediate solution. Then, 0.05-0.1 parts by weight of a modifier is added to the above-mentioned polyamide polyamine intermediate solution, and water is added to dilute the solution to a solid content of 20-25%. 10-20 parts by weight of epichlorohydrin are slowly added under stirring. After the addition is completed, the reaction system is heated to 65-85° C. and stirred and kept warm at this temperature until the viscosity of the reaction system reaches 30-40 mPa·s. The pH of the reaction system is adjusted to 3.5-4.5 using an acid solution, and then 0.1-0.2 parts by weight of a modifier is added again. After keeping warm under stirring for 20-30 minutes, heating is stopped, and the solution is diluted with water to a solid content of 10-15% to obtain a modified PAE resin.

[0060] As some examples of the present invention, the modifier is selected from polyhydroxyl functional monomers or oligomers, such as polyvinyl alcohol, polyglycerol acrylate, and polyether alcohol substances.

[0061] Preferably, the modifier is polyvinyl alcohol.

[0062] During the preparation of the modified PAE, hydroxyl groups can be introduced into the main chain or cross-linking node of PAE and the end of the molecular chain by adding the modifier twice, respectively. This increases the number of hydrogen bonds in the molecular structure of the modified PAE and reduces the number of covalent bonds that the modified PAE can generate in paper. The strengthening effect and mechanism of PAE on paper transition to a dry strength agent, and the ability to combine with fibers and cationic starch through hydrogen bonds is enhanced. While taking into account the improvement of the dry and wet strength of the paper, the controllable solubility and dispersibility of the water-absorbing soluble paper is maintained.

[0063] In general, in the water-absorbent soluble toilet paper provided by the present invention, the structural disintegration is not caused solely by physical water absorption and expansion or chemical bond breaking, but is a degradation process triggered by the synergistic action of multiple mechanisms. This process includes both physical disintegration, such as the expansion and separation of fibers caused by water molecules entering the paper structure, weak interfacial debonding, and structural collapse caused by the inorganic filler absorbing water and swelling. In particular, the modified inorganic filler first absorbs water and expands in an aqueous environment. The pH responsiveness of the shell PAA causes the particles to undergo interfacial swelling and surface dissociation, thereby promoting the overall disintegration of the fiber structure and causing the material to break up and decompose from the macroscopic structure. At the same time, the structural disintegration process of the paper also includes chemical structural changes, such as the swelling and dissolution of the modified inorganic filler shell triggered by pH changes, and the dissociation of the weak cross-linked structure between the modified PAE and cationic starch and fibers, which leads to the disintegration of the material from the microstructural level, dissolution or depolymerization of components. This composite degradation mechanism is used to achieve the properties of paper that are reliable in dry state, can maintain structural integrity in wet state, but can quickly disperse when exposed to water, thereby making the toilet paper stable during use and able to controllably and effectively disperse or dissolve under given conditions (such as toilet water).

[0064] Example 1 Preparation of modified PAE: First, in an oil bath at 120°C, 10 parts by weight of diethylenetriamine and 10 parts by weight of adipic acid were added to a reactor. After the raw materials were mixed uniformly under stirring, the temperature was raised to 170°C and kept warm for 3 hours. The heating was then stopped. After the temperature of the reaction system naturally cooled to 100°C, water was added to dilute the mixture to a solid content of 35%, and the mixture was stirred until homogeneous to obtain a polyamide polyamine intermediate solution. Then, 0.08 parts by weight of polyvinyl alcohol was added to the above-mentioned polyamide polyamine intermediate solution, and the solution was diluted with water to a solid content of 20%. 15 parts by weight of epichlorohydrin was slowly added under stirring. After the addition was completed, the reaction system was heated to 75° C. and stirred and kept warm at this temperature until the viscosity of the reaction system reached 36 mPa·s. The pH of the reaction system was adjusted to 4 using an acid solution, and then 0.15 parts by weight of polyvinyl alcohol was added again. After keeping warm under stirring for 25 minutes, heating was stopped and the solution was diluted with water to a solid content of 15% to obtain a modified PAE resin.

[0065] Example 2 Preparation of composite strength improver: (1) First, cationic starch was dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 20 wt%. The cationic starch suspension was then heated at a rate of 7 °C / min to the gelatinization starting temperature of 55 °C, and the cationic starch suspension was maintained at this temperature for 20 min. (2) Then, a certain amount of the modified PAE prepared in Example 1 and water were added to prepare a suspension having a total content of 10 wt% of the modified PAE and cationic starch, wherein the weight ratio of the modified PAE to the cationic starch was 0.4:1. The mixed solution was then placed in an ultrasonic device and ultrasonically treated for 20 minutes at a power of 500 W to obtain a suspension of the composite strength improver.

[0066] Example 3 Preparation of composite strength improver: The suspension of the composite strength improver prepared in Example 2 was concentrated at 45°C to a suspension having a total content of modified PAE and cationic starch of 30 wt%, and then placed in a low-temperature freezing device for cyclic freezing treatment three times at a freezing temperature of -20°C. After freezing, it was placed at room temperature for natural thawing and then subjected to the next cycle of freezing treatment again.

[0067] Example 4 Preparation of modified inorganic fillers: (a) dispersing inorganic filler calcium carbonate particles in deionized water, adding an appropriate amount of a dispersant, and stirring to uniformly disperse to obtain an inorganic filler suspension, and then adjusting the pH of the inorganic filler suspension to 8.5 using an acid or a base; wherein the content of the inorganic filler is 20 wt % and the content of the dispersant is 0.3 wt %; (b) adding partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.3 wt %; (c) slowly adding the polyacrylic acid aqueous solution to the inorganic filler suspension under stirring, wherein the ratio of the inorganic filler to the polyacrylic acid is 100:1, heating the mixture to 40°C and stirring at 300 rpm for 2 hours at the same temperature, adjusting the pH of the mixture to 7 with an acid or base, and continuing stirring at 300 rpm for 0.5 hours to obtain a suspension of the modified inorganic filler; (d) The suspension of the modified inorganic filler is centrifuged and dried to obtain the modified inorganic filler.

[0068] Example 5 Preparation of modified inorganic fillers: (a) dispersing inorganic filler calcium carbonate particles in deionized water, adding an appropriate amount of a dispersant, and stirring to uniformly disperse to obtain an inorganic filler suspension, and then adjusting the pH of the inorganic filler suspension to 8.5 using an acid or a base; wherein the content of the inorganic filler is 20 wt % and the content of the dispersant is 0.3 wt %; (b) adding partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.3 wt %; (c) Under stirring, slowly add the polyacrylic acid aqueous solution to the inorganic filler suspension, wherein the ratio of the added amount of inorganic filler to polyacrylic acid is 100:1, and then heat the mixture to 40°C and continue stirring at 300 rpm at this temperature for 2 hours. Then, use an acid or base to adjust the pH of the mixture to 7, and then slowly add an aqueous solution of CaCl2 dropwise, wherein the amount of CaCl2 added is 3wt% of the amount of polyacrylic acid used, and continue stirring at 300 rpm for 0.5 hours to obtain a suspension of modified inorganic filler.

[0069] (d) The suspension of the modified inorganic filler is centrifuged and dried to obtain the modified inorganic filler.

[0070] Example 6 Preparation method of water-absorbent soluble toilet paper: S1, batching and slurry preparation: taking a long fiber pulp sheet and a short fiber pulp sheet at a weight ratio of 1.5:9, pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water, and dispersing them to prepare a long fiber slurry and a short fiber slurry; S2, refining: the long fiber pulp is conveyed to the refiner for refining, and the beating degree of the pulp after refining is 25°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking, and the beating degree of the pulp after deflaking is 37°SR; S3, slurry preparation: the long fiber slurry treated in step S2 is mixed with the short fiber slurry to obtain a mixed slurry, and then the modified inorganic filler prepared in the above embodiment 4 accounting for 1% of the total weight of the absolute dry paddle board and the composite strength improver prepared in the above embodiment 2 accounting for 0.05% of the total weight of the absolute dry paddle board are added, and water is added to dilute the mixed slurry to a slurry concentration of 0.2%, and the pH of the slurry is adjusted to 6 with an acid or an alkali to obtain a papermaking base material; S4, papermaking on the web: conveying the papermaking base material to the headbox for papermaking on the web; S5, pressing and drying: The wet paper pair is pressed to remove moisture and is initially formed to obtain a wet paper pair. The wet paper web is dehydrated by suction in two vacuum boxes and then transferred to the drying cylinder via vacuum pressing rollers, where it is dried on the surface of the drying cylinder. S6, scraper wrinkling: After the paper is dried, it is scraper wrinkled and peeled off, and then enters the paper winding equipment; S7, winding into paper: After the initial rolling and rewinding on the paper rolling equipment, the paper is cut into pieces to obtain a three-layer water-absorbent and soluble toilet paper product.

[0071] Example 7 Preparation method of water-absorbent soluble toilet paper: S1, batching and slurrying: taking a long fiber pulp sheet and a short fiber pulp sheet in a weight ratio of 3:7, pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water, and dispersing them to prepare a long fiber slurry and a short fiber slurry; S2, refining: the long fiber pulp is conveyed to the refiner for refining, and the beating degree of the pulp after refining is 30°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking, and the beating degree of the pulp after deflaking is 40°SR; S3, slurry preparation: the long fiber slurry treated in step S2 is mixed with the short fiber slurry to obtain a mixed slurry, and then the modified inorganic filler prepared in the above embodiment 4 accounting for 3% of the total weight of the absolute dry paddle board and the composite strength improver prepared in the above embodiment 2 accounting for 0.15% of the total weight of the absolute dry paddle board are added, and water is added to dilute the mixed slurry to a slurry concentration of 0.3%, and the pH of the slurry is adjusted to 6 with an acid or an alkali to obtain a papermaking base material; S4, papermaking on the web: conveying the papermaking base material to the headbox for papermaking on the web; S5, pressing and drying: The wet paper pair is pressed to remove moisture and is initially formed to obtain a wet paper pair. The wet paper web is dehydrated by suction in two vacuum boxes and then transferred to the drying cylinder via vacuum pressing rollers, where it is dried on the surface of the drying cylinder. S6, scraper wrinkling: After the paper is dried, it is scraper wrinkled and peeled off, and then enters the paper winding equipment; S7, winding into paper: After the initial rolling and rewinding on the paper rolling equipment, the paper is cut into pieces to obtain a three-layer water-absorbent and soluble toilet paper product.

[0072] Example 8 Preparation method of water-absorbent soluble toilet paper: S1, batching and slurrying: taking a long fiber pulp sheet and a short fiber pulp sheet in a weight ratio of 2:8, pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water, and dispersing them to prepare a long fiber slurry and a short fiber slurry; S2, refining: the long fiber pulp is conveyed to the refiner for refining, and the beating degree of the pulp after refining is 32°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking, and the beating degree of the pulp after deflaking is 45°SR; S3, slurry preparation: the long fiber slurry treated in step S2 is mixed with the short fiber slurry to obtain a mixed slurry, and then the modified inorganic filler prepared in the above embodiment 4 accounting for 2% of the total weight of the absolute dry paddle board and the composite strength improver prepared in the above embodiment 2 accounting for 0.1% of the total weight of the absolute dry paddle board are added, and water is added to dilute the mixed slurry to a slurry concentration of 0.2%, and the pH of the slurry is adjusted to 6 with an acid or an alkali to obtain a papermaking base material; S4, papermaking on the web: conveying the papermaking base material to the headbox for papermaking on the web; S5, pressing and drying: The wet paper pair is pressed to remove moisture and is initially formed to obtain a wet paper pair. The wet paper web is dehydrated by suction in two vacuum boxes and then transferred to the drying cylinder via vacuum pressing rollers, where it is dried on the surface of the drying cylinder. S6, scraper wrinkling: After the paper is dried, it is scraper wrinkled and peeled off, and then enters the paper winding equipment; S7, winding into paper: After the initial rolling and rewinding on the paper rolling equipment, the paper is cut into pieces to obtain a three-layer water-absorbent and soluble toilet paper product.

[0073] Example 9 Preparation method of water-absorbent soluble toilet paper: The only difference between this embodiment and the above-mentioned embodiment 8 is that the slurry preparation process in step S3 is: S3, slurry preparation: (I) mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A having a solid content of 15 wt%, and adjusting the pH of the dispersion A to 8 with an acid or base; wherein the amount of the modified inorganic filler added is 2% of the total weight of the dry paddle; (III) taking a suspension of a composite strength improver having a solid content of 10 wt %, referred to as dispersion B, and adjusting the pH of dispersion B to 6 with an acid or base; wherein the amount of the composite strength improver added is 0.1% of the total weight of the dry paddle; (IV) Slowly adding dispersion B to dispersion A in proportion over 10 minutes while stirring at a low speed of 200 rpm. After the addition of dispersion B is completed, stirring is continued for 20 minutes, and then the mixture is allowed to stand for 10 minutes to obtain dispersion C; (V) Dispersion C is added to the mixed slurry, water is added to dilute the mixed slurry to a slurry concentration of 0.2%, and the pH of the slurry is adjusted to 6 with an acid or an alkali to obtain a papermaking base material.

[0074] Example 10 Preparation method of water-absorbent soluble toilet paper: The only difference between this embodiment and the above-mentioned embodiment 7 is that the slurry preparation process in step S3 is: S3, slurry preparation: (I) mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A having a solid content of 10 wt%, and adjusting the pH of the dispersion A to 8.5 with an acid or a base; (III) dispersing the composite strength improver in deionized water to prepare a dispersion B having a solid content of 10 wt%, and adjusting the pH of the dispersion B to 6 with an acid or a base; (IV) Slowly adding dispersion B to dispersion A in proportion over 5 minutes while stirring at a low speed of 200 rpm. After the addition of dispersion B is completed, stirring is continued for 10 minutes, and then the mixture is allowed to stand for 5 minutes to obtain dispersion C; (V) Dispersion C is added to the mixed slurry, water is added to dilute the mixed slurry to a slurry concentration of 0.2%, and the pH of the slurry is adjusted to 6 with an acid or an alkali to obtain a papermaking base material.

[0075] Example 11 The only difference between this embodiment and the above-mentioned embodiment 8 is that the composite strength improver used is prepared from the above-mentioned embodiment 3.

[0076] Example 12 The only difference between this embodiment and the above-mentioned embodiment 8 is that the modified inorganic filler used is prepared from the above-mentioned embodiment 5.

[0077] Comparative Example 1 Preparation of water-absorbent soluble toilet paper: The main difference between this embodiment and the above-mentioned embodiment 8 is that no modified inorganic filler is added during the slurry preparation process.

[0078] Comparative Example 2 Preparation of water-absorbent soluble toilet paper: The main difference between this embodiment and the above-mentioned embodiment 8 is that during the slurry preparation process, the added filler is an unmodified calcium carbonate filler.

[0079] Comparative Example 3 Preparation of water-absorbent soluble toilet paper: The main difference between it and the above-mentioned embodiment 8 is that: during the slurry preparation process, the preparation process of the added composite strength improver is as follows: first, the cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 20 wt%, and then a certain amount of the modified PAE prepared in the above-mentioned embodiment 1 and water are added to prepare a suspension with a total content of modified PAE and cationic starch of 10 wt%, wherein the weight ratio of the modified PAE to the cationic starch is 0.4:1, and then the mixed solution is placed in an ultrasonic device, and after ultrasonic treatment for 20 minutes at a power of 500 W, a suspension of the composite strength improver is obtained.

[0080] Comparative Example 4 Preparation of water-absorbent soluble toilet paper: The main difference between this embodiment and the above-mentioned embodiment 8 is that during the slurry preparation process, the PAE in the added composite strength improver is unmodified PAE.

[0081] Comparative Example 5 Preparation of water-absorbent soluble toilet paper: The main difference between this embodiment and the above embodiment 8 is that during the slurry preparation process, the preparation process of the added composite strength improver is as follows: First, cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 20 wt%. The cationic starch suspension is then heated at a rate of 7°C / min to 55°C, the gelatinization starting temperature of the cationic starch, and the cationic starch suspension is maintained at this temperature for 20 minutes. (2) Then, a certain amount of the modified PAE prepared in Example 1 and water were added to prepare a suspension having a total content of 10 wt% of the modified PAE and cationic starch, and the mixture was stirred evenly to obtain a suspension of the composite strength improver.

[0082] Performance testing The papers in Examples 6 to 12 and Comparative Examples 1 to 5 were sampled and tested, and the obtained data are shown in Table 1 below: Wherein, (1) longitudinal and transverse dry tensile strengths were measured according to JIS P 8113 (2006); (2) Transverse wet tensile strength is measured in accordance with JIS P 8135 (1998). During the test, after fixing both ends of the test sample to the chuck of the testing machine, a flat brush containing water is used to apply water horizontally to the center of the test sample with a width of 10 mm. Immediately thereafter, a tensile load is applied to the product in the vertical direction for testing. (3) Flushability: According to the national standard GB / T 40181-2021 "Test method and evaluation of flushability of disposable sanitary nonwoven materials", the flushing method is simulated by a flush toilet. The test method is as follows: Place the paper sample in a flush toilet for 10 seconds to evenly wet it with water (pH 7.5). Then flush the sample down the toilet. Use a container at the toilet outlet to collect the dispersed liquid. Pour the dispersed liquid onto a 5-mesh filter screen. Collect the solids on the screen, dry and adjust the humidity, and calculate the flushability. Where, flushability = 100% - dispersion residual rate, dispersion residual rate = (weight of solids on the screen / sample weight) x 100%; The dissociation time was measured according to JIS P 4501 (1993). During the measurement, the rotor speed was 600 rpm.

[0083] Table 1 Paper performance test results The embodiments of the present application have been described. Unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A method for preparing water-soluble toilet paper, characterized in that: Including steps: S1, batching and slurry preparation: taking a long fiber pulp sheet and a short fiber pulp sheet in a weight ratio of (1.5-3):(7-9), pre-wetting the long fiber pulp sheet and the short fiber pulp sheet with water, and dispersing them to prepare a long fiber slurry and a short fiber slurry; S2, refining: the long fiber pulp is conveyed to the refiner for refining, and the beating degree of the pulp after refining is 25~32°SR; the short fiber pulp is conveyed to the fiber deflaker for deflaking, and the beating degree of the pulp after deflaking is 37~45°SR; S3, slurry preparation: mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry, then adding 1-3% of the total weight of the absolute dry paddle board and 0.05-0.15% of the total weight of the absolute dry paddle board as a composite strength improver, adding water to dilute the mixed slurry to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or alkali to obtain a papermaking base material; wherein the modified inorganic filler has a core-shell structure, CaCO3 is a core layer particle, and the outer layer is coated with a shell layer formed by polyacrylic acid; the composite strength improver is a composite formed by compounding modified PAE and cationic starch; S4, copied online; S5, pressing and drying; S6, scraper wrinkling; S7, rolled into paper.

2. The method for preparing water-soluble toilet paper according to claim 1, wherein: The step S3 comprises: (I) mixing the long fiber slurry treated in step S2 with the short fiber slurry to obtain a mixed slurry; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A having a solid content of 10-15 wt%, and adjusting the pH of the dispersion A to 7.5-8.5 with an acid or base; (III) dispersing the composite strength improver in deionized water to prepare a dispersion B having a solid content of 5 to 10 wt%, and adjusting the pH of the dispersion B to 6 to 7 with an acid or an alkali; (IV) Slowly adding dispersion B to dispersion A in proportion over 5 to 10 minutes while stirring at a low speed of 100 to 200 rpm. After the addition of dispersion B is completed, stirring is continued for 10 to 20 minutes, and then the mixture is allowed to stand for 5 to 10 minutes to obtain dispersion C; (V) Adding the dispersion C to the mixed slurry, diluting the mixed slurry with water to a slurry concentration of 0.1-0.3%, and adjusting the pH of the slurry to ≤7 with an acid or an alkali to obtain a papermaking base material.

3. The method for preparing water-soluble toilet paper according to claim 1, wherein: In step S1, the long fibers account for 18-25 wt% of the total fiber weight.

4. The method for preparing water-soluble toilet paper according to claim 1, wherein: The core layer of the modified inorganic filler is composed of light calcium carbonate particles, and the particle size of the light calcium carbonate particles is 1-3 μm.

5. The method for preparing water-soluble toilet paper according to claim 1, 2 or 4, characterized in that: The preparation process of the modified inorganic filler is as follows: (a) dispersing an inorganic filler in deionized water, adding an appropriate amount of a dispersant, and stirring to uniformly disperse the inorganic filler to obtain an inorganic filler suspension, and then adjusting the pH of the inorganic filler suspension to 8 to 9 using an acid or a base; wherein the content of the inorganic filler is 10 to 20 wt % and the content of the dispersant is 0.1 to 0.5 wt %; (b) adding partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1 to 0.5 wt %; (c) slowly adding the polyacrylic acid aqueous solution to the inorganic filler suspension under stirring, then heating the mixture to 30-40° C. and continuously stirring at 100-400 rpm for 1-2 hours at the same temperature, adjusting the pH of the mixture to 6.5-7.5 with an acid or base, and then continuing to stir at 100-400 rpm for 0.5-1 hour to obtain a suspension of the modified inorganic filler; (d) The suspension of the modified inorganic filler is centrifuged and dried to obtain the modified inorganic filler.

6. The method for preparing water-soluble toilet paper according to claim 5, characterized in that: The step (c) comprises: Under stirring, the polyacrylic acid aqueous solution is slowly added to the inorganic filler suspension, and then the mixed solution is heated to 30~40°C and continuously stirred at a speed of 100~400 rpm at this temperature for 1~2 hours. After that, the pH of the mixed solution is adjusted to 6.5~7.5 using an acid or a base, and then the CaCl2 aqueous solution is slowly added dropwise, and the amount of CaCl2 added is 1~5wt% of the amount of polyacrylic acid. At the same time, stirring is continued at a speed of 100~400 rpm for 0.5~1 hour to obtain a suspension of modified inorganic filler.

7. The method for preparing water-soluble toilet paper according to claim 1, wherein: The preparation process of the composite strength improver is as follows: (1) First, cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension having a cationic starch content of 10-30 wt%, and then the cationic starch suspension is heated at a rate of 5-10 °C / min to the gelatinization starting temperature of the cationic starch, and the cationic starch suspension is maintained at this temperature for 10-20 min; (2) Then, a certain amount of modified PAE and water were added to prepare a suspension having a total content of modified PAE and cationic starch of 5-10 wt%, wherein the weight ratio of modified PAE to cationic starch was (0.3-0.6):

1. The mixed solution was then placed in an ultrasonic device and ultrasonically treated for 15-30 min at a power of 400-600 W to obtain a suspension of the composite strength improver.

8. The method for preparing water-soluble toilet paper according to claim 7, characterized in that: In the preparation process of the composite strength improver, after the ultrasonic treatment in step (2), the ultrasonically treated mixed solution is concentrated at below 50°C to a suspension having a total content of modified PAE and cationic starch of 20-40 wt%, and then placed in a low-temperature freezing device for cyclic freezing treatment 3-5 times, with the freezing temperature being below -10°C. After freezing, the mixture is placed at room temperature for natural thawing and then subjected to the next cycle of freezing treatment.

9. The method for preparing water-soluble toilet paper according to claim 7, characterized in that: The preparation process of the modified PAE is as follows: First, a polyamide-polyamine intermediate solution with a solid content of 30-40% is prepared; Then, 0.05-0.1 parts by weight of a modifier is added to the polyamide-polyamine intermediate solution, and water is added to dilute the solution to a solid content of 20-25%. 10-20 parts by weight of epichlorohydrin are slowly added under stirring. After the addition is complete, the reaction system is heated to 65-85° C., stirred and kept warm at this temperature until the viscosity of the reaction system reaches 30-40 mPa·s. The pH of the reaction system is adjusted to 3.5-4.5 using an acid solution, and then 0.1-0.2 parts by weight of a modifier is added again. After keeping warm under stirring for 20-30 minutes, heating is stopped, and the solution is diluted with water to a solid content of 10-15%, thereby obtaining a modified PAE resin.

10. The toilet paper prepared by the method for preparing water-soluble toilet paper according to any one of claims 1 to 9.

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