Water-absorbing and dissolvable sanitary paper and method for producing the same

Abstract

The application belongs to the technical field of toilet paper preparation, and particularly relates to water-absorbing and soluble toilet paper and a preparation method thereof, which comprises the following steps: S1, dosing and spreading pulp: long-fiber pulp board and short-fiber pulp board are taken according to a weight ratio to prepare long-fiber pulp and short-fiber pulp; S2, pulp refining: the long-fiber pulp is delivered to a refiner for refining, and the short-fiber pulp is delivered to a fiber defibrator for defibration; S3, pulp mixing: the long-fiber pulp and the short-fiber pulp after the treatment in step S2 are mixed to obtain mixed pulp, then modified inorganic fillers and composite strength improvers are added, water is added to dilute the pulp to a concentration of 0.1-0.3%, the pH of the pulp is adjusted to be less than or equal to 7, and a papermaking base material is obtained; S4, web forming; S5, pressing and drying; S6, doctor blade creping; and S7, winding into paper. The water-absorbing and soluble toilet paper provided by the application has reliable strength in a dry state, can maintain a complete structure in a wet state, and can be quickly dispersed after meeting water.

Description

Technical Field

[0001] This invention belongs to the field of toilet paper preparation technology, and particularly relates to a water-absorbent and soluble toilet paper and its preparation method. Background Technology

[0002] Toilet paper, an indispensable daily necessity, is used frequently and widely in homes, public places, medical institutions, and other areas. Traditional toilet paper is mostly discarded after use, becoming solid waste. This not only increases the burden and pressure of solid waste disposal but can also pollute soil and water bodies if improperly handled. Furthermore, if used traditional toilet paper remains in the environment for extended periods, it can become a breeding ground for bacteria. This is especially true for medical institutions and public places with high hygiene and environmental requirements, where the large volume of toilet paper used and the lack of immediate waste disposal facilities can lead to rapid bacterial growth and a decline in environmental sanitation. In contrast, water-soluble toilet paper dissolves instantly in water and can be flushed away immediately, entering the wastewater treatment system. This not only reduces the chance of bacterial growth and helps maintain environmental hygiene but is also convenient to use, dissolving or degrading rapidly in water without causing long-term water pollution. Therefore, the development of water-soluble toilet paper is becoming an urgent need and is undeniably necessary.

[0003] The primary technical challenge in the production of absorbent soluble toilet paper is balancing paper solubility and strength, specifically, the balance between paper strength, particularly wet strength, and water solubility. First, the paper needs a certain level of strength, including both dry and wet strength. Dry strength refers to the paper's resistance to tearing and tensile stress in a dry state, a core indicator ensuring its basic functionality. Insufficient strength leads to the paper easily crumbling into dust during wiping, resulting in incomplete cleaning or paper residue. Only with good dry strength can the paper guarantee its structural stability and durability under normal usage conditions. Wet strength refers to the paper's ability to maintain its physical integrity and structural strength when wet or soaked in water; that is, the paper's ability to resist tearing, stretching, or breaking after absorbing moisture. For toilet paper, appropriate wet strength is necessary, primarily because it needs to withstand use in humid environments. The paper must be resistant to damage and minimize the risk of paper residue or contamination even in humid conditions or with small amounts of water residue. However, if the paper's wet strength is too high, it may be difficult to decompose in the sewer, causing blockages. If the paper's wet strength is too low, it will crumble into dust upon contact with water, failing to effectively cover excrement, oil stains, water stains, and other dirt, thus failing to complete the cleaning task. For toilet paper used in sanitation facilities, it is also necessary to ensure that the paper remains intact in a moist environment to avoid fiber residue causing infection. Therefore, it is necessary to adjust the raw material composition of the paper so that absorbent soluble toilet paper maintains its structural integrity in a wet state, gradually dispersing over tens of seconds to several minutes after contact with water, rather than disintegrating instantly.

[0004] However, increasing paper strength, especially wet strength, can lead to a decrease in water solubility, primarily due to fundamental conflicts in their chemical and physical mechanisms. High dry strength in paper indicates a dense fiber structure, strong hydrogen bonds between fibers, high adhesive strength from additives, and slow dissolution and separation upon contact with water. The wet strength of paper is formed by wet-strength agents, such as polyamide epichlorohydrin resin and urea-formaldehyde resin, which primarily connect fibers into a three-dimensional network structure through chemical bonds. This enhances the bonding force between fibers and allows the paper to maintain its structural integrity even when wet. This strong cross-linked structure prevents water molecule penetration and reduces the damage of water to the hydrogen bonds between fibers, thus maintaining paper strength. The water solubility of paper, on the other hand, is formed because the fibers or water-soluble additives in water-soluble paper, such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), and soluble sugars, are bound together by relatively weak physical forces, such as hydrogen bonds and van der Waals forces. Upon contact with water, these intermolecular forces are disrupted, causing the paper to dissolve rapidly. Therefore, wet strength depends on strong chemical bonds, requiring the formation of a stable, strongly cross-linked structure through covalent or ionic bonds. These bonds resist the disruption by water molecules. Water solubility, on the other hand, depends on weak interactions, relying on physical forces easily disrupted by water molecules, 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, however, requires a loose paper structure to facilitate water molecule penetration and the untangling of molecular chains, accelerating dissolution. Therefore, adding wet strength agents intensifies the cross-linking reaction, enhancing fiber bonding, but simultaneously reducing the paper's water solubility. Conversely, adding water-soluble additives can improve the paper's hydrophilicity and solubility, but weakens the bonding between fibers, reducing wet strength. Thus, in the preparation of absorbent soluble toilet paper, the contradiction between paper's "solubility" and "strength," especially the balance between wet strength and water solubility, is the core technical challenge in producing 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, and provides a toilet paper that has excellent mechanical properties in the dry state, can maintain structural integrity in the wet state, and can be quickly dispersed when exposed to water. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned technical problems by providing a water-absorbent and water-soluble toilet paper and its preparation method. This method aims to achieve a toilet paper that is reliably strong when dry, maintains structural integrity when wet, and can be quickly dispersed when exposed to water by controlling the balance between paper strength and water solubility.

[0007] In view of this, the present invention provides a method for preparing water-absorbing and soluble toilet paper, comprising the following steps:

[0008] S1, Ingredients and Pulp Preparation: Take long fiber pulp boards and short fiber pulp boards according to the weight ratio of (1.5~3): (7~9). After pre-wetting and dispersing the long fiber pulp boards and short fiber pulp boards with water respectively, long fiber pulp and short fiber pulp are prepared.

[0009] S2, Pulping: Long fiber slurry is fed to a pulper for pulping, and the freeness of the pulp after pulping is 25~32°SR; short fiber slurry is fed to a fiber de-fiber machine for de-fibering, and the freeness of the pulp after de-fibering is 37~45°SR.

[0010] S3, Pulp Preparation: The long-fiber pulp and short-fiber pulp processed in step S2 are mixed to obtain a mixed pulp. Then, 1-3% of modified inorganic filler and 0.05-0.15% of composite strength improver by weight of oven-dry pulp are added. Water is added to dilute the mixed pulp to a pulp concentration of 0.1-0.3%, and the pH of the pulp is adjusted to ≤7 with acid or alkali to obtain the papermaking base material. The modified inorganic filler has a core-shell structure, with CaCO3 as the core particles and an outer shell formed by polyacrylic acid. The composite strength improver is a composite material composed of modified PAE and cationic starch.

[0011] S4, copied from the internet;

[0012] S5, pressing and drying;

[0013] S6, scraper wrinkles;

[0014] S7, rolled into paper.

[0015] Furthermore, step S3 includes:

[0016] (I) The long fiber slurry after step S2 is mixed with the short fiber slurry to obtain a mixed slurry;

[0017] (II) Add the modified inorganic filler to deionized water to prepare a dispersion A with a solid content of 10-15 wt%, and adjust the pH of dispersion A to 7.5-8.5 with acid or alkali;

[0018] (III) Disperse the composite strength improver in deionized water to prepare a dispersion B with a solid content of 5-10 wt%, and adjust the pH of dispersion B to 6-7 with acid or alkali.

[0019] (IV) Add dispersion B slowly to dispersion A over 5-10 minutes while stirring at a low speed of 100-200 rpm. After adding dispersion B, continue stirring for 10-20 minutes, then let stand for 5-10 minutes to obtain dispersion C.

[0020] (V) Add dispersion C to the mixed slurry, dilute the mixed slurry with water to a slurry concentration of 0.1~0.3%, and adjust the pH of the slurry to ≤7 with acid or alkali to obtain the papermaking base material.

[0021] Furthermore, in step S1, the long fibers account for 18 to 25 wt% of the total fiber weight.

[0022] Furthermore, the core layer of the modified inorganic filler is composed of light calcium carbonate particles with a particle size of 1~3μm.

[0023] Furthermore, the preparation process of the modified inorganic filler is as follows:

[0024] (a) Disperse the inorganic filler in deionized water and add an appropriate amount of dispersant. Stir to ensure uniform dispersion to obtain an inorganic filler suspension. Then, adjust the pH of the inorganic filler suspension to 8-9 using acid or alkali. The content of the inorganic filler is 10-20 wt%, and the content of the dispersant is 0.1-0.5 wt%.

[0025] (b) Add the partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1~0.5wt%;

[0026] (c) Under stirring, the aqueous polyacrylic acid solution is slowly added to the inorganic filler suspension. The mixture is then heated to 30-40°C and stirred at 100-400 rpm for 1-2 hours. The pH of the mixture is then adjusted to 6.5-7.5 using acid or alkali. The mixture is then stirred at 100-400 rpm for 0.5-1 hour to obtain the modified inorganic filler suspension.

[0027] (d) The modified inorganic filler is obtained by centrifugation and drying of the suspension of the modified inorganic filler.

[0028] Furthermore, step (c) includes:

[0029] Under stirring, an aqueous solution of polyacrylic acid is slowly added to the inorganic filler suspension. The mixture is then heated to 30-40°C and stirred continuously at 100-400 rpm for 1-2 hours. The pH of the mixture is then adjusted to 6.5-7.5 using acid or alkali. Subsequently, an aqueous solution of CaCl2 is slowly added dropwise, with the amount of CaCl2 added being 1-5 wt% of the amount of polyacrylic acid. Stirring is continued at 100-400 rpm for 0.5-1 hour to obtain a suspension of modified inorganic filler.

[0030] Furthermore, the preparation process of the composite strength improver is as follows:

[0031] (1) First, the cationic starch is dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 10~30wt%. Then, the cationic starch suspension is heated at a rate of 5~10℃ / min to the gelatinization start temperature of the cationic starch, and the cationic starch suspension is kept at this temperature for 10~20min.

[0032] (2) Then add a certain amount of modified PAE and water to prepare a suspension with a total content of 5~10wt% of modified PAE and cationic starch, wherein the weight ratio of modified PAE to cationic starch is (0.3~0.6):1. Then place the mixture in an ultrasonic device and ultrasonically treat it for 15~30 minutes at a power of 400~600W to obtain a suspension of composite strength improver.

[0033] Furthermore, in the preparation process of the composite strength improver, after ultrasonic treatment in step (2), the ultrasonically treated mixture is concentrated at below 50°C to a suspension with a total content of 20~40wt% of modified PAE and cationic starch. Then, it is placed in a low-temperature freezing device for cyclic freezing treatment 3~5 times at a freezing temperature below -10°C. After freezing, it is placed at room temperature to thaw completely before the next cycle of freezing treatment is performed.

[0034] Furthermore, the preparation process of the modified PAE is as follows:

[0035] First, a polyamide polyamine intermediate solution with a solid content of 30-40% is prepared;

[0036] Then, add 0.05-0.1 parts by weight of modifier to the polyamide polyamine intermediate solution and dilute with water to a solid content of 20-25%. Slowly add 10-20 parts by weight of epichlorohydrin while stirring. After the addition is complete, heat the reaction system to 65-85°C and stir and keep it at this temperature until the viscosity of the reaction system is 30-40 mPa·s. Then, adjust the pH of the reaction system to 3.5-4.5 with acid. Then, add 0.1-0.2 parts by weight of modifier again and keep it at this temperature for 20-30 minutes while stirring. Stop heating and dilute with water to a solid content of 10-15% to obtain the modified PAE resin.

[0037] The water-absorbing and soluble toilet paper is prepared using the above-described method.

[0038] The beneficial effects of this invention are:

[0039] In the absorbent and soluble toilet paper provided by this invention, its structural disintegration is not caused solely by physical water absorption and swelling or chemical bond breaking, but by a degradation process triggered by the synergistic effect of multiple mechanisms. This process involves both physical disintegration and chemical degradation. For example, water molecules entering the paper structure cause expansion and separation between fibers, weak interfacial peeling, and structural disintegration caused by the expansion of inorganic fillers after absorbing water. In particular, modified inorganic fillers first absorb water and expand in an aqueous environment. Through the pH responsiveness of the shell PAA, particles undergo interfacial swelling and surface dissociation, thereby promoting the overall disintegration of the fiber structure and causing the material to break down and decompose from a macroscopic perspective. At the same time, the paper's structural disintegration process also involves chemical structural changes, such as pH-triggered swelling and dissolution of the modified inorganic filler shell, and the dissociation of weak cross-linked structures between modified PAE and cationic starch, fibers, etc. This leads to the material's disintegration, component dissolution, or depolymerization at the microscopic level. This composite degradation mechanism enables the paper to maintain reliable strength in a dry state, retain structural integrity in a wet state, and rapidly disperse upon contact with water. This results in a dynamic performance transformation of toilet paper that is stable during use and can be controlled and effectively dispersed or dissolved under given conditions (such as in toilet water). Detailed Implementation

[0040] The technical solutions in the embodiments of this application will be clearly described below with reference to specific examples. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0041] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification.

[0042] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0043] A method for preparing absorbent and soluble toilet paper, comprising the following steps:

[0044] S1, Ingredients and Pulp Dispersion: Take long fiber pulp boards and short fiber pulp boards according to the weight ratio of (1.5~3): (7~9), pre-wet the long fiber pulp boards and short fiber pulp boards with water respectively, and then disperse them in a hydraulizer to obtain long fiber pulp and short fiber pulp.

[0045] S2, Refining: Long fiber slurry is fed to a refining machine for refining. The refining power is 30~60kwh / t, and the freeness of the slurry after refining is 25~32°SR. Short fiber slurry is fed to a fiber de-fiber machine for de-fibering for 5~10min. The freeness of the slurry after de-fibering is 37~45°SR.

[0046] S3, Pulp Preparation: The long-fiber pulp and short-fiber pulp processed in step S2 are mixed to obtain a mixed pulp. Then, 1-3% of modified inorganic filler and 0.05-0.15% of composite strength improver by weight of oven-dry pulp are added. Water is added to dilute the mixed pulp to a pulp concentration of 0.1-0.3%, and the pH of the pulp is adjusted to ≤7 with acid or alkali to obtain the papermaking base material. The modified inorganic filler has a core-shell structure, with CaCO3 as the core particles and an outer shell formed by polyacrylic acid. The composite strength improver is a composite material composed of modified PAE and cationic starch.

[0047] S4, Online Papermaking: The papermaking base material is conveyed to the headbox for online papermaking to form pages;

[0048] S5, Pressing and Drying: After the wet paper sheet is pressed to remove moisture, it is initially shaped to obtain a wet paper sheet. The wet paper sheet is then dehydrated by two vacuum boxes and transferred to the drying cylinder by vacuum press rollers, where it is dried on the surface of the drying cylinder.

[0049] S6, doctor blade crease: After the paper is dried, it is creased with a doctor blade, and after the creases are peeled off, it enters the paper winding equipment.

[0050] S7, Wrapped into paper: After initial winding and rewinding on a paper rolling machine, the paper is slit to obtain absorbent and soluble toilet paper.

[0051] Furthermore, the basis weight of each layer of the absorbent and soluble toilet paper described in this invention is 13.5~18.5 g / m³. 2 The absorbent and soluble toilet paper has 2 to 4 layers.

[0052] Preferably, the long fibers are selected from one or more of coniferous wood, sisal, flax fiber, etc.

[0053] Preferably, the average fiber length of the long fiber is 2~4.5mm.

[0054] Preferably, the short fibers are selected from one or more of broadleaf wood, sugarcane bagasse, wheat straw, reed fiber, etc.

[0055] Preferably, the average fiber length of the short fibers is 0.5~1mm.

[0056] More preferably, in step S1, the long fibers account for 18 to 25 wt% of the total fiber weight.

[0057] Generally, in the industry, when manufacturing ordinary toilet paper, long fibers account for about 40-60 wt% of the total fiber weight; when manufacturing ordinary absorbent soluble toilet paper, long fibers account for about 20-30 wt% of the total fiber weight; and when manufacturing high-strength absorbent soluble toilet paper, long fibers account for about 30-40% of the total fiber weight.

[0058] Compared to existing technologies, this invention improves paper strength by incorporating trace amounts of modified inorganic fillers and composite strength enhancers. This reduces the proportion of long fibers in the total fiber weight of the high-strength absorbent soluble toilet paper prepared by this invention to 18-25 wt%. Consequently, the absorbent soluble toilet paper prepared by this invention has a relatively low content of long fibers and a relatively high content of short fibers, resulting in better paper softness and rapid dissolution in water. Furthermore, since short fibers are cheaper than long fibers, the manufacturing cost is also reduced.

[0059] More importantly, this invention modifies calcium carbonate by adding an appropriate amount of polyacrylic acid (PAA) to coat it as an inorganic filler. Since PAA is a weakly acidic polymer with a significant pH-responsive characteristic, coating it onto the surface of calcium carbonate particles creates a core-shell structure. This endows the modified inorganic filler particles with different stability and dissolution behaviors in different pH environments. For example, in acidic or neutral environments, the PAA shell structure is stable and does not easily dissolve prematurely. However, in alkaline environments, such as toilet flushing water, the PAA shell swells or destabilizes and detaches, thereby promoting the exposure of calcium carbonate and assisting in the rapid disintegration of the paper structure, thus increasing the overall water dissolution rate. Simultaneously, calcium carbonate, as an inorganic mineral filler, although insoluble in water, is porous and hydrophilic. Therefore, the calcium carbonate particles themselves can act as "weak bonding points" in the paper, easily becoming the starting point for structural breakage under the influence of water, thereby accelerating the dissociation rate and disintegration of the paper in water.

[0060] Furthermore, in the modified inorganic filler, the PAA coating improves the hydrophilicity and charge properties of the calcium carbonate particles, preventing particle agglomeration and improving their dispersion uniformity in pulp and retention in wet paper. Moreover, the PAA coating also provides the modified inorganic filler with a certain degree of flexibility and binding ability, assisting in the formation of a more stable hydrogen bond network between fibers in the dry state, and moderately enhancing the dry and wet strength of the paper without significantly reducing its water absorption and solubility.

[0061] Based on this, by combining modified PAE with cationic starch to form a composite strength improver, the paper strength and water solubility can be adjusted to a suitable level, so as to achieve reliable strength of paper in dry state, maintain structural integrity in wet state, and be able to disperse quickly when exposed to water.

[0062] Furthermore, step S1 includes:

[0063] Long fiber pulp boards are pre-wetted with water and then placed in a hydrapulper for pulping with added water to obtain long fiber pulp with a concentration of 3-5 wt%. End fiber pulp boards are pre-wetted with water and then placed in a hydrapulper for pulping with added water to obtain short fiber pulp with a concentration of 3-5 wt%.

[0064] Furthermore, in step S1, after slurry preparation, long fiber slurry and short fiber slurry can be separately sent to a slag remover for slag removal treatment.

[0065] In step S2, controlling the beating degree of long fiber pulp at 25~32°SR allows the long fibers to retain appropriate length and strength, enhancing the dry strength and tensile strength of the paper. Controlling the beating degree of short fiber pulp at 37~45°SR provides a good foundation for the water solubility and dispersion speed of the paper, thereby improving fiber bonding and paper uniformity, taking into account the initial strength of the paper, and enhancing its solubility after contact with water.

[0066] Furthermore, step S3 includes:

[0067] (I) The long fiber slurry after step S2 is mixed with the short fiber slurry to obtain a mixed slurry;

[0068] (II) Add the modified inorganic filler to deionized water to prepare a dispersion A with a solid content of 10-15 wt%, and adjust the pH of dispersion A to 7.5-8.5 with acid or alkali;

[0069] (III) Disperse the composite strength improver in deionized water to prepare a dispersion B with a solid content of 5-10 wt%, and adjust the pH of dispersion B to 6-7 with acid or alkali.

[0070] (IV) Add dispersion B slowly to dispersion A over 5-10 minutes while stirring at a low speed of 100-200 rpm. After adding dispersion B, continue stirring for 10-20 minutes, then let stand for 5-10 minutes to obtain dispersion C.

[0071] (V) Add dispersion C to the mixed slurry, dilute the mixed slurry with water to a slurry concentration of 0.1~0.3%, and adjust the pH of the slurry to ≤7 with acid or alkali to obtain the papermaking base material.

[0072] Furthermore, in step S3, the modified inorganic filler is a modified inorganic filler that has been modified by polyacrylic acid. The modified inorganic filler has CaCO3 as the core inorganic filler particles and is coated with a shell layer formed by polyacrylic acid, thereby constituting a core-shell type functional filler with pH response performance. The shell layer in the core-shell structure remains stable under neutral or weakly acidic conditions, and can swell or destabilize and deshell in alkaline water environments, such as toilet flush water, thereby regulating the supporting effect and release behavior of the inorganic filler on the paper structure.

[0073] Preferably, the core layer of the modified inorganic filler is composed of lightweight calcium carbonate particles.

[0074] More preferably, the light calcium carbonate particles are spherical or nearly spherical in shape, and the particle size of the light calcium carbonate particles is 1~3μm.

[0075] As some examples of the present invention, the preparation process of the modified inorganic filler is as follows:

[0076] (a) Disperse the inorganic filler in deionized water and add an appropriate amount of dispersant. Stir to ensure uniform dispersion to obtain an inorganic filler suspension. Then, adjust the pH of the inorganic filler suspension to 8-9 using acid or alkali. The content of the inorganic filler is 10-20 wt%, and the content of the dispersant is 0.1-0.5 wt%.

[0077] (b) Add the partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1~0.5wt%;

[0078] (c) Under stirring, the aqueous polyacrylic acid solution is slowly added to the inorganic filler suspension. The mixture is then heated to 30-40°C and stirred at 100-400 rpm for 1-2 hours. The pH of the mixture is then adjusted to 6.5-7.5 using acid or alkali. The mixture is then stirred at 100-400 rpm for 0.5-1 hour to obtain the modified inorganic filler suspension.

[0079] (d) The modified inorganic filler is obtained by centrifugation and drying of the suspension of the modified inorganic filler.

[0080] As some other examples of the present invention, in the process of preparing the modified inorganic filler, after obtaining the suspension of the modified inorganic filler through 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 dispersion A in step S3. In this case, the amount of the suspension of the modified inorganic filler added is calculated based on the weight of the modified inorganic filler contained therein.

[0081] As a preferred example of the present invention, other Ca atoms may be introduced during the preparation of the modified inorganic filler. 2+ Ions act as physical cross-linking factors to facilitate the cross-linking of carboxyl-Ca groups. 2+ -Carboxyl bridging constructs 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.

[0082] Specifically, other calcium compounds can be introduced by adding CaCl2. 2+ Ions act as physical cross-linking factors, and their specific implementation is as follows:

[0083] In step (c): Under stirring, the aqueous solution of polyacrylic acid is slowly added to the inorganic filler suspension. The mixture is then heated to 30-40°C and stirred continuously at 100-400 rpm for 1-2 hours. The pH of the mixture is then adjusted to 6.5-7.5 using acid or alkali. Then, an aqueous solution of CaCl2 is slowly added dropwise, with the amount of CaCl2 added being 1-5 wt% of the amount of polyacrylic acid. At the same time, stirring is continued at 100-400 rpm for 0.5-1 hours to obtain a suspension of modified inorganic filler.

[0084] Preferably, the concentration of the CaCl2 aqueous solution is 0.05~0.2 mol / L. Compared with other soluble calcium salts, CaCl2 has strong water solubility, fast ion release rate, good diffusion, which helps to achieve uniform cross-linking, and is chemically stable, less prone to causing side reactions, and has a wide range of raw material sources.

[0085] Preferably, the weight-average molecular weight (Mw) of the polyacrylic acid is 100,000 to 300,000 Daltons (Da).

[0086] Preferably, the degree of neutralization of the partially neutralized polyacrylic acid is 45% to 60%.

[0087] Preferably, the ratio of the inorganic filler to polyacrylic acid is (50~200):1.

[0088] As some examples of the present invention, the dispersant is selected from one or more of sodium lignosulfonate, sodium hexametaphosphate, sodium tripolyphosphate, polyoxyethylene alkyl ether, etc.

[0089] In this invention, partially neutralized polyacrylic acid is selected to form the shell structure. In contrast, unneutralized polyacrylic acid has a low charge density, weak adsorption capacity, and is less likely to react with Ca. 2+ Ionic bonding, however, also has the disadvantages of being prone to aggregation and viscosity, making it difficult to form a stable dispersion system; while partially neutralized polyacrylic acid, being moderately negatively charged, can effectively adsorb Ca on the surface of CaCO3. 2+ The ions do not easily cause strong electrorepulsion or aggregation. Furthermore, partially neutralized polyacrylic acid retains some carboxyl groups (-COOH), which can form hydrogen bonds, and also contains a certain amount of -COO groups. - It can be used with Ca 2+ Electrostatic complexation, a bifunctional group synergistic adsorption method, more easily yields a stable, dense, and controllable shell. Furthermore, the use of partially neutralized polyacrylic acid allows the shell to maintain moderate shrinkage at neutral pH, while rapidly extending, uncoating, or swelling under alkaline conditions. This widens the pH control range of the modified inorganic filler and regulates the paper's water solubility. In fact, in China, to prevent acidic water from corroding tap water pipes, water treatment plants adjust the pH of tap water to weakly alkaline by adding chlorine, lime, sodium bicarbonate, and other regulators during water treatment. This provides the conditions for the water solubility and dissociation of the absorbent soluble paper described in this invention.

[0090] Furthermore, in the preparation process of the modified inorganic filler, the pH of the inorganic filler suspension is first adjusted to 8-9 using acid or alkali, so that the inorganic filler is dispersed in a weakly alkaline environment. In a weakly alkaline environment, it is beneficial for the inorganic filler particles to carry an appropriate amount of negative charge on their surface, thereby enhancing the electrostatic repulsion between particles and preventing particle aggregation or precipitation, thus 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 particle stability and facilitating the subsequent formation of core-shell structures.

[0091] Furthermore, the composite strength improver is a mixture of modified PAE and cationic starch, and its preparation process is as follows:

[0092] (1) First, disperse the cationic starch in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 10~30wt%. Then, heat the cationic starch suspension at a rate of 5~10℃ / min to near the gelatinization start temperature of the cationic starch and keep the cationic starch suspension at this temperature for 10~20min.

[0093] (2) Then add a certain amount of modified PAE and water to prepare a suspension with a total content of 5~10wt% of modified PAE and cationic starch, wherein the weight ratio of modified PAE to cationic starch is (0.3~0.6):1, and the weight of modified PAE is based on the solid content in its aqueous solution; then place the mixture in an ultrasonic device, and after ultrasonic treatment for 15~30min at a power of 400~600W, obtain a suspension of composite strength improver.

[0094] It should be noted that, in the preparation of the absorbent and soluble toilet paper, the composite strength improver is added in the form of a suspension, and the amount added is calculated based on the actual total weight of the modified PAE and cationic starch therein.

[0095] As a preferred example of the present invention, in the preparation process of the composite strength improver, after ultrasonic treatment in step (2), the ultrasonically treated mixture can be concentrated at below 50°C to a suspension with a total content of 20~40wt% of modified PAE and cationic starch. Then, it is placed in a low-temperature freezing device for cyclic freezing treatment 3~5 times, with a freezing temperature below -10°C. After freezing, it is placed at room temperature for natural thawing and then subjected to the next cycle of freezing treatment.

[0096] As some examples of the present invention, the gelatinization start temperature T of the cationic starch 糊化 The temperature is typically 55-65℃, but varies depending on the type of starch. It can be measured using instruments such as differential calorimeters and polarizing microscopes.

[0097] Preferably, during the preparation of the composite strength improver, the gelatinization start temperature T of the cationic starch is determined. 糊化 After the process is completed, the cationic starch suspension can be heated to T. 糊化 -3℃~T 糊化 .

[0098] In the preparation process of the above-mentioned composite strength improver, the cationic starch suspension is heated to the gelatinization start temperature T. 糊化 Nearby, and for a certain period of time, in T 糊化 Near the specified temperature, the crystalline regions of starch can still be maintained, but the hydrogen bonds in the amorphous regions break, causing the chain segments to loosen. The short-range ordered structure inside the starch granules begins to disintegrate. Therefore, this process can achieve "pre-activation" of the internal structure of starch granules, exposing more active groups, such as hydroxyl groups, and enhancing their interaction with modified PAE. At the same time, it disrupts the long-range and short-range ordered structure of starch, improves its solubility in water, and enhances the water solubility of the prepared absorbent and soluble paper.

[0099] Furthermore, by treating the mixture of modified PAE and cationic starch in an ultrasonic device, the ultrasonic cavitation effect can be used to further shear the cationic starch segments, forming some oligosaccharides and flowable hydrophilic segments, thereby reducing its average molecular weight, improving its flowability, and enhancing its water solubility, making it easier to miscible and compound with modified PAE or other components. For modified PAE, under ultrasonic action, the epoxy groups in PAE can be opened and react with the starch hydroxyl groups, strengthening the crosslinking density between modified PAE and cationic starch, which improves the paper strength when used in absorbent paper. For the mixture of modified PAE and cationic starch, the ultrasonic cavitation effect can be used to break the aggregation of the two substances, promoting full mixing and bonding between modified PAE and cationic starch molecules, and improving the compounding efficiency and bonding ability between PAE and starch.

[0100] Based on this, cyclic cryogenic freezing can be used to induce microstructural "reorganization". Specifically, during freezing, the growth of ice crystals squeezes the polymer chains in the system into narrow spaces, causing the molecular chains between cationic starch and PAE to align, entangle, and rearrange hydrogen bonds. During thawing, the ice crystals melt and release liquid water, causing local rapid swelling and releasing voids. This creates a structure with interwoven micropores and chain networks, disrupting the original stacking of polymer chains. Ultimately, through multiple cycles, a multi-level structure is induced, characterized by enhanced inter-chain interactions, more uniform pore structure, enhanced film-forming properties, and easy dissolution triggering. This multi-level structure is denser and more adhesive in the dry state, allowing it to better combine with modified inorganic fillers with fiber or core-shell structure in pulp, effectively improving paper strength. However, it can absorb water and swell / disintegrate when exposed to water, which is beneficial for paper hydrolysis or dissolution. Ultimately, it helps to enhance the affinity and adhesion between cationic starch, pulp fiber, and modified PAE, and helps to form a paper strength support network, thus perfecting the "early strength and late disintegration" performance requirements of water-absorbent and soluble paper.

[0101] Furthermore, the preparation process of the modified PAE is as follows:

[0102] First, in an oil bath at 110-140℃, 10-15 parts by weight of diethylenetriamine and 8-12 parts by weight of adipic acid are added to the reaction vessel. After the reaction materials are mixed evenly with stirring, the temperature is raised to 160-180℃ and kept at that temperature for 2-4 hours. Then, the heating is stopped and the temperature of the reaction system is allowed to cool down naturally to 100℃. 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.

[0103] Then, add 0.05-0.1 parts by weight of modifier to the above polyamide polyamine intermediate solution and dilute with water to a solid content of 20-25%. Slowly add 10-20 parts by weight of epichlorohydrin while stirring. After the addition is complete, heat the reaction system to 65-85°C and stir and keep it at this temperature until the viscosity of the reaction system is 30-40 mPa·s. Then, adjust the pH of the reaction system to 3.5-4.5 with acid. Then, add 0.1-0.2 parts by weight of modifier again and keep it at this temperature for 20-30 minutes while stirring. Stop heating and dilute with water to a solid content of 10-15% to obtain the modified PAE resin.

[0104] As some examples of the present invention, the modifier is selected from polyhydroxy functional monomers or oligomers, such as polyvinyl alcohol, polyglycerol acrylate, and polyether alcohols.

[0105] Preferably, the modifier is polyvinyl alcohol.

[0106] In the preparation process of the modified PAE, hydroxyl groups can be introduced into the main chain or cross-linking nodes and the end of the molecular chain of PAE by adding the modifier twice. This results in an increase in hydrogen bonds in the molecular structure of the modified PAE and a decrease in the number of covalent bonds that the modified PAE can generate in paper. The strengthening effect and mechanism of PAE on paper transitions to that of a dry strength agent, and the ability to bind with fibers and cationic starch through hydrogen bonds is improved. While improving the dry and wet strength of paper, the controllable solubility and dispersion properties of absorbent and soluble paper are maintained.

[0107] Overall, the structural disintegration of the absorbent and soluble toilet paper provided by this invention is not caused solely by physical water absorption and swelling or chemical bond breaking, but by a degradation process triggered by the synergistic effect of multiple mechanisms. This process involves both physical disintegration and chemical degradation. For example, water molecules entering the paper structure cause expansion and separation between fibers, weak interfacial peeling, and structural disintegration caused by the expansion of inorganic fillers after absorbing water. In particular, modified inorganic fillers first absorb water and expand in an aqueous environment. Through the pH responsiveness of the shell PAA, particles undergo interfacial swelling and surface dissociation, thereby promoting the overall disintegration of the fiber structure and causing the material to break down and decompose from a macroscopic perspective. At the same time, the paper's structural disintegration process also involves chemical structural changes, such as pH-triggered swelling and dissolution of the modified inorganic filler shell, and the dissociation of weak cross-linked structures between modified PAE and cationic starch, fibers, etc. This leads to the material's disintegration, component dissolution, or depolymerization at the microscopic level. This composite degradation mechanism enables the paper to maintain reliable strength in a dry state, retain structural integrity in a wet state, and rapidly disperse upon contact with water. This results in a dynamic performance transformation of toilet paper that is stable during use and can be controlled and effectively dispersed or dissolved under given conditions (such as in toilet water).

[0108] Example 1

[0109] Preparation of modified PAE:

[0110] 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 the reaction vessel. After the reaction materials were mixed evenly with stirring, the temperature was raised to 170°C and kept at that temperature for 3 hours. Then, the heating was stopped and the temperature of the reaction system was allowed to cool down to 100°C naturally. 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.

[0111] Then, 0.08 parts by weight of polyvinyl alcohol were added to the above polyamide polyamine intermediate solution, and water was added to dilute it to a solid content of 20%. 15 parts by weight of epichlorohydrin were slowly added under stirring. After the addition was complete, the reaction system was heated to 75°C and stirred and kept at this temperature until the viscosity of the reaction system was 36 mPa·s. The pH of the reaction system was then adjusted to 4 using acid. Then, 0.15 parts by weight of polyvinyl alcohol were added again, and the mixture was kept at this temperature for 25 minutes under stirring. Heating was then stopped, and water was added to dilute it to a solid content of 15%, thus obtaining the modified PAE resin.

[0112] Example 2

[0113] Preparation of composite strength improver:

[0114] (1) First, the cationic starch was dispersed in an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 20wt%. Then, the cationic starch suspension was heated at a rate of 7℃ / min to the gelatinization start temperature of cationic starch, 55℃, and the cationic starch suspension was kept at this temperature for 20min.

[0115] (2) Then add a certain amount of the modified PAE and water prepared in Example 1 above to prepare a suspension with a total content of 10wt% of modified PAE and cationic starch, wherein the weight ratio of modified PAE to cationic starch is 0.4:1. Then place the mixture in an ultrasonic device and ultrasonically treat it for 20 minutes at a power of 500W to obtain a suspension of composite strength improver.

[0116] Example 3

[0117] Preparation of composite strength improver:

[0118] The suspension of the composite strength improver prepared in Example 2 was concentrated at 45°C to a suspension with a total content of 30wt% of modified PAE and cationic starch. Then, it was placed in a low-temperature freezing device for three cycles of freezing treatment at a freezing temperature of -20°C. After freezing, it was allowed to thaw naturally at room temperature before the next cycle of freezing treatment was performed.

[0119] Example 4

[0120] Preparation of modified inorganic fillers:

[0121] (a) Disperse inorganic filler calcium carbonate particles in deionized water, add an appropriate amount of dispersant, stir to ensure uniform dispersion to obtain an inorganic filler suspension, and then adjust the pH of the inorganic filler suspension to 8.5 using acid or alkali; wherein the content of inorganic filler is 20 wt% and the content of dispersant is 0.3 wt%;

[0122] (b) Add the partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.3 wt%;

[0123] (c) Under stirring, the aqueous solution of polyacrylic acid is slowly added to the inorganic filler suspension, wherein the ratio of inorganic filler to polyacrylic acid is 100:1. The mixture is then heated to 40°C and stirred at 300 rpm for 2 hours. The pH of the mixture is then adjusted to 7 using acid or alkali, and stirred at 300 rpm for 0.5 hours to obtain the modified inorganic filler suspension.

[0124] (d) The modified inorganic filler is obtained by centrifugation and drying of the suspension of the modified inorganic filler.

[0125] Example 5

[0126] Preparation of modified inorganic fillers:

[0127] (a) Disperse inorganic filler calcium carbonate particles in deionized water, add an appropriate amount of dispersant, stir to ensure uniform dispersion to obtain an inorganic filler suspension, and then adjust the pH of the inorganic filler suspension to 8.5 using acid or alkali; wherein the content of inorganic filler is 20 wt% and the content of dispersant is 0.3 wt%;

[0128] (b) Add the partially neutralized polyacrylic acid to deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.3 wt%;

[0129] (c) Under stirring, an aqueous solution of polyacrylic acid is slowly added to the inorganic filler suspension, wherein the ratio of inorganic filler to polyacrylic acid is 100:1. The mixture is then heated to 40°C and stirred at 300 rpm for 2 hours. The pH of the mixture is then adjusted to 7 using acid or alkali. Then, an aqueous solution of CaCl2 is slowly added dropwise, with the amount of CaCl2 added being 3 wt% of the amount of polyacrylic acid. The mixture is stirred at 300 rpm for 0.5 hours to obtain a suspension of modified inorganic filler.

[0130] (d) The modified inorganic filler is obtained by centrifugation and drying of the suspension of the modified inorganic filler.

[0131] Example 6

[0132] Preparation method of water-absorbing and soluble toilet paper:

[0133] S1, Ingredients and Pulp Preparation: Take long fiber pulp board and short fiber pulp board in a weight ratio of 1.5:9. After pre-wetting and dispersing the long fiber pulp board and short fiber pulp board with water respectively, long fiber pulp and short fiber pulp are prepared.

[0134] S2, Refining: Long fiber slurry is fed to a refiner for refining, and the freeness of the slurry after refining is 25°SR; short fiber slurry is fed to a fiber de-fiber machine for de-fibering, and the freeness of the slurry after de-fibering is 37°SR.

[0135] S3, Pulp preparation: The long fiber pulp and short fiber pulp after step S2 are mixed to obtain a mixed pulp. Then, 1% of the modified inorganic filler prepared in Example 4 above and 0.05% of the composite strength improver prepared in Example 2 above are added to the total weight of the oven-dry pulp board. Water is added to dilute the mixed pulp to a pulp concentration of 0.2%, and the pH of the pulp is adjusted to 6 with acid or alkali to obtain the papermaking base material.

[0136] S4, Online Papermaking: The papermaking base material is conveyed to the headbox for online papermaking to form pages;

[0137] S5, Pressing and Drying: After the wet paper sheet is pressed to remove moisture, it is initially shaped to obtain a wet paper sheet. The wet paper sheet is then dehydrated by two vacuum boxes and transferred to the drying cylinder by vacuum press rollers, where it is dried on the surface of the drying cylinder.

[0138] S6, doctor blade crease: After the paper is dried, it is creased with a doctor blade, and after the creases are peeled off, it enters the paper winding equipment.

[0139] S7, Wrapped into paper: After initial winding and rewinding on a paper rolling machine, the paper is slit to obtain a 3-layer absorbent and soluble toilet paper product.

[0140] Example 7

[0141] Preparation method of water-absorbing and soluble toilet paper:

[0142] S1, Ingredients and Pulp Preparation: Take long fiber pulp board and short fiber pulp board in a weight ratio of 3:7. After pre-wetting and dispersing the long fiber pulp board and short fiber pulp board with water respectively, long fiber pulp and short fiber pulp are prepared.

[0143] S2, Pulping: Long fiber slurry is fed to a pulper for pulping, and the freeness of the pulp after pulping is 30°SR; short fiber slurry is fed to a fiber de-fiber machine for de-fibering, and the freeness of the pulp after de-fibering is 40°SR.

[0144] S3, Pulp Preparation: The long fiber pulp and short fiber pulp after step S2 are mixed to obtain a mixed pulp. Then, 3% of the total weight of the oven-dry pulp board prepared in Example 4 above and 0.15% of the total weight of the oven-dry pulp board prepared in Example 2 above are added. Water is added to dilute the mixed pulp to a pulp concentration of 0.3%, and the pH of the pulp is adjusted to 6 with acid or alkali to obtain the papermaking base material.

[0145] S4, Online Papermaking: The papermaking base material is conveyed to the headbox for online papermaking to form pages;

[0146] S5, Pressing and Drying: After the wet paper sheet is pressed to remove moisture, it is initially shaped to obtain a wet paper sheet. The wet paper sheet is then dehydrated by two vacuum boxes and transferred to the drying cylinder by vacuum press rollers, where it is dried on the surface of the drying cylinder.

[0147] S6, doctor blade crease: After the paper is dried, it is creased with a doctor blade, and after the creases are peeled off, it enters the paper winding equipment.

[0148] S7, Wrapped into paper: After initial winding and rewinding on a paper rolling machine, the paper is slit to obtain a 3-layer absorbent and soluble toilet paper product.

[0149] Example 8

[0150] Preparation method of water-absorbing and soluble toilet paper:

[0151] S1, Ingredients and Pulp Preparation: Take long fiber pulp board and short fiber pulp board in a weight ratio of 2:8. After pre-wetting and dispersing the long fiber pulp board and short fiber pulp board with water respectively, long fiber pulp and short fiber pulp are prepared.

[0152] S2, Refining: Long fiber slurry is fed to a refiner for refining, and the freeness of the slurry after refining is 32°SR; short fiber slurry is fed to a fiber de-fiber machine for de-fibering, and the freeness of the slurry after de-fibering is 45°SR.

[0153] S3, Pulp Preparation: The long fiber pulp and short fiber pulp after step S2 are mixed to obtain a mixed pulp. Then, 2% of the total weight of the oven-dry pulp board prepared in Example 4 above and 0.1% of the total weight of the oven-dry pulp board prepared in Example 2 above are added. Water is added to dilute the mixed pulp to a pulp concentration of 0.2%, and the pH of the pulp is adjusted to 6 with acid or alkali to obtain the papermaking base material.

[0154] S4, Online Papermaking: The papermaking base material is conveyed to the headbox for online papermaking to form pages;

[0155] S5, Pressing and Drying: After the wet paper sheet is pressed to remove moisture, it is initially shaped to obtain a wet paper sheet. The wet paper sheet is then dehydrated by two vacuum boxes and transferred to the drying cylinder by vacuum press rollers, where it is dried on the surface of the drying cylinder.

[0156] S6, doctor blade crease: After the paper is dried, it is creased with a doctor blade, and after the creases are peeled off, it enters the paper winding equipment.

[0157] S7, Wrapped into paper: After initial winding and rewinding on a paper rolling machine, the paper is slit to obtain a 3-layer absorbent and soluble toilet paper product.

[0158] Example 9

[0159] Preparation method of water-absorbing and soluble toilet paper:

[0160] The only difference between it and Example 8 above is that the pulp preparation process in step S3 is as follows:

[0161] S3, pulp preparation:

[0162] (I) The long fiber slurry after step S2 is mixed with the short fiber slurry to obtain a mixed slurry;

[0163] (II) Add the modified inorganic filler to deionized water to prepare a dispersion A with a solid content of 15 wt%, and adjust the pH of dispersion A to 8 with acid or alkali; wherein, the amount of modified inorganic filler added is 2% of the total weight of the oven-dry paddle.

[0164] (III) Take a suspension of composite strength improver with a solid content of 10 wt%, and denote it as dispersion B. Adjust the pH of dispersion B to 6 with acid or alkali. The amount of composite strength improver added is 0.1% of the total weight of the oven-dry paddle.

[0165] (IV) Add dispersion B slowly to dispersion A within 10 minutes according to the proportion, while stirring at a low speed of 200 rpm. After the addition of dispersion B is complete, continue stirring for 20 minutes, and then let it stand for 10 minutes to obtain dispersion C.

[0166] (V) Add dispersion C to the mixed slurry, dilute the mixed slurry with water to a slurry concentration of 0.2%, and adjust the pH of the slurry to 6 with acid or alkali to obtain the papermaking base material.

[0167] Example 10

[0168] Preparation method of water-absorbing and soluble toilet paper:

[0169] The only difference between it and Example 7 above is that the pulp preparation process in step S3 is as follows:

[0170] S3, pulp preparation:

[0171] (I) The long fiber slurry after step S2 is mixed with the short fiber slurry to obtain a mixed slurry;

[0172] (II) Add the modified inorganic filler to deionized water to prepare a dispersion A with a solid content of 10 wt%, and adjust the pH of dispersion A to 8.5 with acid or alkali.

[0173] (III) Disperse the composite strength improver in deionized water to prepare a dispersion B with a solid content of 10 wt%, and adjust the pH of dispersion B to 6 with acid or alkali.

[0174] (IV) Add dispersion B slowly to dispersion A within 5 minutes according to the ratio, while stirring at a low speed of 200 rpm. After the addition of dispersion B is complete, continue stirring for 10 minutes, and then let it stand for 5 minutes to obtain dispersion C.

[0175] (V) Add dispersion C to the mixed slurry, dilute the mixed slurry with water to a slurry concentration of 0.2%, and adjust the pH of the slurry to 6 with acid or alkali to obtain the papermaking base material.

[0176] Example 11

[0177] The only difference between it and Example 8 above is that the composite strength improver used is prepared by Example 3 above.

[0178] Example 12

[0179] The only difference between it and Example 8 above is that the modified inorganic filler used is prepared by Example 5 above.

[0180] Comparative Example 1

[0181] Preparation of absorbent and soluble toilet paper:

[0182] The main difference between it and embodiment 8 above is that no modified inorganic filler is added during the slurry preparation process.

[0183] Comparative Example 2

[0184] Preparation of absorbent and soluble toilet paper:

[0185] The main difference between it and embodiment 8 above is that the filler added during the slurry preparation process is unmodified calcium carbonate filler.

[0186] Comparative Example 3

[0187] Preparation of absorbent and soluble toilet paper:

[0188] The main difference between this and embodiment 8 above is that the preparation process of the added composite strength improver during the slurry preparation process 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 20wt%. Then, a certain amount of modified PAE and water prepared in embodiment 1 above are added to prepare a suspension with a total content of modified PAE and cationic starch of 10wt%, wherein the weight ratio of modified PAE to cationic starch is 0.4:1. After that, the mixture is placed in an ultrasonic device and ultrasonically treated for 20 minutes at a power of 500W to obtain a suspension of composite strength improver.

[0189] Comparative Example 4

[0190] Preparation of absorbent and soluble toilet paper:

[0191] The main difference between it and embodiment 8 above is that the PAE in the added composite strength improver during the pulp preparation process is unmodified PAE.

[0192] Comparative Example 5

[0193] Preparation of absorbent and soluble toilet paper:

[0194] The main difference between this and embodiment 8 above is that the preparation process of the composite strength improver added during the pulping process is as follows:

[0195] 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%. Then, the cationic starch suspension was heated at a rate of 7 ℃ / min to the gelatinization start temperature of cationic starch, 55 ℃, and the cationic starch suspension was kept at this temperature for 20 min.

[0196] (2) Then add a certain amount of the modified PAE and water prepared in Example 1 above to prepare a suspension with a total content of 10wt% of modified PAE and cationic starch. After stirring evenly, a suspension of composite strength improver is obtained.

[0197] Performance testing

[0198] Paper samples were taken and tested from Examples 6 and 12 and Comparative Example 1 and 5, respectively, and the data obtained are shown in Table 1 below:

[0199] Among them, (1) the longitudinal and transverse tensile strengths were determined according to JIS P 8113 (2006);

[0200] (2) The transverse wet tensile strength was determined according to JIS P 8135 (1998). During the test, the two ends of the test sample were fixed on the clamps of the testing machine. Then, a flat brush containing water was used to apply water horizontally to the center of the test sample with a width of 10 mm. Then, a tensile load was immediately applied to the product in the up and down direction for testing.

[0201] (3) Flushing performance: According to the national standard GB / T 40181-2021 "Test method and evaluation of flushability of disposable sanitary nonwoven materials", the simulated flushing method of a toilet is adopted. The test method is as follows:

[0202] Place the paper sample in a toilet bowl for 10 seconds to ensure it is evenly wetted with water at pH 7.5. Then flush the sample down the toilet. Collect the dispersed liquid in a container at the toilet outlet. Pour the dispersed liquid onto a 5-mesh filter screen and collect the solids on the screen. After drying and humidifying, calculate the dispersibility performance. Dispersibility performance = 100% - dispersion residue, dispersion residue = (weight of solids on the screen / weight of sample) x 100%.

[0203] The dissociation time was determined according to JIS P 4501 (1993), and the rotor speed was 600 rpm during the test.

[0204] Table 1. Paper performance test results

[0205]

[0206] The embodiments described in this application are as follows. Unless otherwise specified, the embodiments and features described in the embodiments can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A process for the production of water-absorbing, dissolvable toilet paper, characterized in that, The method comprises the steps of: S1, batching and dispersing: taking long fiber pulp board and short fiber pulp board according to a weight ratio of (1.5-3):(7-9), respectively pre-wetting and dispersing the long fiber pulp board and the short fiber pulp board to obtain long fiber pulp and short fiber pulp; S2, refining: conveying the long fiber pulp to a refiner for refining, and the beating degree of the pulp after refining is 25-32°SR; conveying the short fiber pulp to a fiber defibrator for defibration, and the beating degree of the pulp after defibration is 37-45°SR; S3, pulp mixing: mixing the long fiber pulp and the short fiber pulp after step S2 to obtain mixed pulp, then adding 1-3% of the total weight of the pulp board of modified inorganic fillers and 0.05-0.15% of the total weight of the pulp board of composite strength improver, diluting the mixed pulp to a pulp concentration of 0.1-0.3% by adding water, and adjusting the pH of the pulp to ≤7 by using acid or base to obtain papermaking base material; wherein the modified inorganic filler has a core-shell structure, CaCO3 is the core layer particle, and the outer layer is coated with a shell layer formed by polyacrylic acid; the composite strength improver is a composite of modified PAE and cationic starch; S4, wire molding; S5, pressing and drying; S6, doctor blade creping; S7, winding into paper; The preparation process of the modified inorganic filler is as follows: (a) dispersing the inorganic filler into deionized water, adding an appropriate amount of dispersant, stirring to make the dispersion uniform to obtain an inorganic filler suspension, and then using acid or base to adjust the pH of the inorganic filler suspension to 8-9; wherein the content of the inorganic filler is 10-20wt%, and the content of the dispersant is 0.1-0.5wt%; (b) adding partially neutralized polyacrylic acid into deionized water to prepare a polyacrylic acid aqueous solution with a concentration of 0.1-0.5wt%; (c) slowly adding the polyacrylic acid aqueous solution into the inorganic filler suspension under stirring, then heating the mixture to 30-40℃, and continuously stirring at a speed of 100-400rpm for 1-2h at this temperature, then adjusting the pH of the mixture to 6.5-7.5 using acid or base, and then continuing to stir at a speed of 100-400rpm for 0.5-1h to obtain a modified inorganic filler suspension; (d) the modified inorganic filler suspension is treated by centrifugation and drying to obtain the modified inorganic filler; The preparation process of the composite strength improver is as follows: (1) first, disperse the cationic starch into an appropriate amount of water to obtain a cationic starch suspension with a cationic starch content of 10-30wt%, then heat the cationic starch suspension to the gelatinization starting temperature of the cationic starch at a speed of 5-10℃ / min, and keep the cationic starch suspension at this temperature for 10-20min; (2) Then a certain amount of modified PAE and water are added to prepare a suspension with a total content of 5-10 wt% of modified PAE and cationic starch, wherein the weight ratio of modified PAE to cationic starch is (0.3-0.6):1, and then the mixture is placed in an ultrasonic device, and after ultrasonic treatment at a power of 400-600 W for 15-30 min, a suspension of the composite strength improver is obtained; 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, which is polyvinyl alcohol, is added to the polyamide polyamine intermediate solution, and water is added to dilute it to a solid content of 20-25%, and then 10-20 parts by weight of epoxy chloropropane is slowly added under stirring, after the addition is completed, the reaction system is heated to 65-85℃, and stirred and kept at this temperature until the viscosity of the reaction system is 30-40 mPa·s, then 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 the modifier is added again, after stirring and keeping for 20-30 min, the heating is stopped, and water is added to dilute it to a solid content of 10-15%, and the modified PAE resin is obtained.

2. The method of making absorbent and dissolvable sanitary paper according to claim 1, characterized in that, Step S3 includes: (I) mixing the long fiber pulp after step S2 with the short fiber pulp to obtain a mixed pulp; (II) adding the modified inorganic filler to deionized water to prepare a dispersion A with a solid content of 10-15 wt%, and adjusting the pH of the dispersion A to 7.5-8.5 using an acid or a base; (III) dispersing the composite strength improver in deionized water to prepare a dispersion B with a solid content of 5-10 wt%, and adjusting the pH of the dispersion B to 6-7 using an acid or a base; (IV) slowly adding the dispersion B to the dispersion A in proportion within 5-10 min while stirring at a low speed of 100-200 rpm, after the addition of the dispersion B is completed, continuing to stir for 10-20 min, and then standing for 5-10 min to obtain a dispersion C; (V) adding the dispersion C to the mixed pulp, diluting the mixed pulp to a pulp concentration of 0.1-0.3% by adding water, and adjusting the pH of the pulp to ≤7 using an acid or a base to obtain a papermaking base.

3. The method of making absorbent and dissolvable sanitary paper according to claim 1, characterized in that, In step S1, the long fibers account for 18-25 wt% of the total weight of the fibers.

4. The method of making absorbent and dissolvable sanitary paper according to claim 1, characterized in that, The core layer of the modified inorganic filler is composed of light calcium carbonate particles with a particle size of 1-3 μm.

5. The method of making absorbent and dissolvable sanitary paper according to claim 1, characterized in that, The step (c) in the preparation process of the modified inorganic filler includes: Under stirring, the polyacrylic acid aqueous solution is slowly added to the inorganic filler suspension, and then the mixture is heated to 30-40℃, and continuously stirred at a speed of 100-400 rpm for 1-2 h at this temperature, and then the pH of the mixture is adjusted to 6.5-7.5 using an acid or a base, and then a CaCl2 aqueous solution is slowly added dropwise, and the addition amount of CaCl2 is 1-5 wt% of the amount of polyacrylic acid, and at the same time, the stirring is continued at a speed of 100-400 rpm for 0.5-1 h to obtain a suspension of the modified inorganic filler.

6. The method of making absorbent and dissolvable sanitary paper according to claim 1, characterized in that, In the preparation of the composite strength modifier, after the ultrasonic treatment in step (2), the mixed solution after ultrasonic treatment is concentrated to a suspension with a total content of modified PAE and cationic starch of 20-40 wt% at 50°C or lower, and then is subjected to cyclic freezing treatment for 3-5 times in a low-temperature freezing device, with a freezing temperature of -10°C or lower. After freezing, the suspension is naturally thawed completely at room temperature and then is subjected to the next cycle of freezing treatment.

7. The sanitary paper prepared by the method according to any one of claims 1 to 6.

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