A water-absorbing core for sanitary napkins or diapers, and a method for manufacturing and use thereof

Abstract

This invention relates to the field of disposable absorbent hygiene products, and more particularly to an absorbent core for sanitary napkins or diapers, its preparation method, and its application. The absorbent core comprises a first base paper, a second base paper, and granular superabsorbent polymer (SAP) disposed between the two. In preparation, dry base paper is used as the raw material for both the first and second base papers. The first base paper is impregnated with a superabsorbent polymer coating liquid containing superabsorbent polymers and adhesives. Before the first base paper dries after impregnation and coating, it is wrinkled using a scraper or embossing technique. Then, the granular superabsorbent polymer is placed on the second base paper, covered by the first base paper, and the mixture is pressed and dried to obtain the absorbent core. This invention improves the in-plane diffusion capacity of liquids and the stability of SAP fixation, reduces the risk of backflow and powder shedding, and is suitable for absorbent hygiene products such as sanitary napkins and diapers.

Description

Technical Field

[0001] This invention relates to the field of disposable absorbent hygiene products, and more particularly to an absorbent core for sanitary napkins or diapers, sanitary napkins and diapers containing the absorbent core, and a method for preparing the absorbent core. Background Technology

[0002] Disposable absorbent hygiene products such as sanitary napkins, baby diapers, and adult incontinence care products typically consist of a liquid-permeable top layer, a liquid-impermeable bottom layer, and an absorbent core sandwiched between the two. The absorbent core primarily functions to receive, diffuse, absorb, and lock in bodily fluids; its performance directly affects the product's absorption speed, dryness, rewetting rate, softness, and wearing comfort. Most existing absorbent cores employ a composite structure with upper and lower substrates sandwiching superabsorbent resin. The upper and lower substrates can be made of dust-free paper, wood pulp paper, fluff pulp paper, toilet paper, hydrophilic nonwoven fabric, or their composite materials. The superabsorbent resin is typically a polyacrylate granular superabsorbent resin.

[0003] In the prior art, there are already methods for preparing absorbent paper by combining crepe paper with superabsorbent polymer (SAP). For example, Chinese invention patent application CN110219197A discloses a method for compounding absorbent paper using a cylinder paper machine. This technology provides an upper single-layer crepe paper and a lower single-layer semi-formed paper. SAP particles are spread on the lower single-layer semi-formed paper. Then, the upper single-layer crepe paper and the lower single-layer semi-formed paper are pressed together to form a double-layer paper, which is then dried and crepe-set to obtain the finished absorbent paper. This method can obtain ultra-thin, soft, breathable, dry, and high-quality absorbent paper, which can be used in absorbent products such as sanitary napkins and diapers. The prior art describes the use of creping base paper and superabsorbent polymer (SAP) composite in the processing of absorbent paper. However, it mainly involves creping base paper and semi-finished base paper. It does not disclose the process of using dry base paper as the raw material, impregnating the base paper with a coating liquid containing superabsorbent polymer and adhesive, and then performing creping or embossing before drying after impregnation and coating. It also does not disclose the technical solution of using wet or semi-dry impregnation and coating base paper to composite with SAP to simultaneously improve the diffusion performance of the base paper and the interfacial fixation of granular superabsorbent polymer.

[0004] Other existing technologies improve the absorbent core performance from the perspective of superabsorbent polymer (SAP) layer distribution and flow-guiding structure. For example, Chinese invention patent application CN105250083A discloses a composite absorbent paper for absorbent sanitary products, which includes an upper release layer, an upper superabsorbent polymer (SAP) layer, a high-loft nonwoven fabric, a lower SAP layer, and a lower release layer, laminated sequentially. Flow-guiding grooves are provided in the upper and lower SAP layers to improve absorption characteristics and increase core utilization. This document points out that after rapid absorption of liquid by the SAP at the liquid-receiving area, gelation can easily occur, leading to slower fluid diffusion, poorer dryness, and increased leakage risk; the application of flow-guiding grooves in the SAP layer improves the liquid diffusion problem. While this solution addresses issues of gel retardation and absorbent core utilization, its improvements focus on the macroscopic distribution of the superabsorbent polymer layer and the design of the flow channels, rather than improving the liquid diffusion capacity and SAP fixation stability of the base paper itself through impregnation coating, wet or semi-dry wrinkling, and control of the composite sequence.

[0005] From a practical production perspective, the absorbent cores of low-thickness, low-basis-weight sanitary napkins or diapers place higher demands on the softness, liquid absorption and diffusion capacity, and SAP (superabsorbent polymer) fixation ability of the base paper. While ordinary dry base paper offers good processing convenience when used as the top and bottom covering substrates, its surface hydrophilic diffusion properties and interfacial fixation ability for granular superabsorbent polymers are limited. Simply increasing the amount of hot melt adhesive or ordinary adhesive to fix the SAP may create localized water-blocking areas, affecting liquid entry into the core and diffusion along the base paper. Conversely, reducing the amount of adhesive can lead to SAP migration, accumulation, or powdering during slitting, transportation, and use, affecting core stability.

[0006] Furthermore, existing creping paper processing methods primarily focus on improving paper softness, fluffiness, or air permeability, while existing composite absorbent paper processes mainly emphasize the placement of the SAP layer and the lamination of the upper and lower substrates. When these two methods are combined, there remains a problem of insufficient coordination between the creping structure and the absorbent coating, SAP fixation, and core lamination. In particular, after the base paper has dried into its bast state, existing technologies do not provide a clear solution for how to allow superabsorbent polymers and adhesives to penetrate the fiber pores of the base paper surface through subsequent impregnation coating, and how to crease the paper in time before it dries, so that the base paper retains its liquid permeability while achieving better in-plane diffusion and SAP-assisted fixation capabilities.

[0007] Therefore, it is necessary to provide a new absorbent core for sanitary napkins or diapers and its preparation method, using dry base paper as the raw material for the first and second base papers, impregnating and coating the first base paper with superabsorbent polymer and adhesive, and then performing creping or embossing before drying after impregnation and coating, then setting granular superabsorbent resin on the second base paper and covering it with the first base paper, and forming the absorbent core by pressing and drying, thereby taking into account liquid diffusion, SAP stability, softness and processing continuity under conditions of lower thickness and lower basis weight. Summary of the Invention

[0008] This invention aims to provide an absorbent core for sanitary napkins or diapers and its preparation method. By using dry base paper as the raw material for the first and second base papers, the first base paper is impregnated and coated with at least a superabsorbent polymer and an adhesive. Before the first base paper dries after impregnation and coating, it is wrinkled by a scraper or embossing. Then, granular superabsorbent resin is placed on the second base paper and covered and laminated by the first base paper. This improves the liquid diffusion capacity, SAP fixation stability, softness and processing continuity of the absorbent core under low thickness and low basis weight conditions.

[0009] Firstly, in order to achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] An absorbent core for sanitary napkins or diapers, the absorbent core comprising a first base paper, a second base paper, and granular superabsorbent resin disposed between the first base paper and the second base paper, the absorbent core being prepared by the following method:

[0011] 1) Dry base paper is used as the raw material for both the first and second base papers;

[0012] 2) At least the first base paper is impregnated with a superabsorbent polymer coating liquid, wherein the superabsorbent polymer coating liquid includes superabsorbent polymer and adhesive;

[0013] 3) After impregnation and coating, the first base paper is wrinkled by scraping or embossing to form a wrinkled surface;

[0014] 4) Place granular superabsorbent resin on the second base paper, then cover the granular superabsorbent resin with the first base paper, and prepare the absorbent core by pressing and drying.

[0015] Preferably, the wrinkled surface of the first base paper is positioned facing the granular superabsorbent resin, so that the granular superabsorbent resin comes into contact with the surface of the first base paper after impregnation, coating and wrinkling treatment.

[0016] And / or, the wrinkled surface formed on the first base paper before it dries after impregnation coating, together with the superabsorbent coating liquid that has been impregnated into the pores of the surface fibers of the first base paper, constitutes a liquid diffusion structure for promoting the diffusion of liquid within the surface of the first base paper.

[0017] And / or, the moisture content of the first base paper is 25%-60% before it dries after impregnation coating; or, the moisture content of the first base paper is 10%-25% after pre-dehydration treatment but before it is completely dried after impregnation coating.

[0018] And / or, the doctor blade wrinkling includes wet wrinkling or semi-dry wrinkling; wherein, wet wrinkling is a wrinkling method in which the moisture content of the first base paper is 25%-60% when it comes into contact with the doctor blade, and semi-dry wrinkling is a wrinkling method in which the moisture content of the first base paper is 10%-25% when it comes into contact with the doctor blade.

[0019] Preferably, the superabsorbent polymer includes one or more of sodium polyacrylate, potassium polyacrylate, polyacrylate superabsorbent polymers, low crosslinked polyacrylate microgels, and starch-grafted polyacrylate superabsorbent polymers.

[0020] And / or, the adhesive comprises one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, cellulose ether, starch derivative, waterborne polyurethane, acrylic emulsion, and polyacrylate emulsion;

[0021] And / or, in the superabsorbent polymer coating liquid, the mass fraction of the superabsorbent polymer is 0.5%-5.0%, and the mass fraction of the adhesive is 0.1%-3.0%; preferably, the mass fraction of the superabsorbent polymer is 1.0%-4.0%, and the mass fraction of the adhesive is 0.2%-1.0%.

[0022] And / or, the viscosity of the superabsorbent polymer coating liquid is 100-1800 mPa·s, and the pH is 6.0-8.5;

[0023] And / or, the granular superabsorbent resin is one or more of sodium polyacrylate superabsorbent resin, potassium polyacrylate superabsorbent resin, and starch-grafted polyacrylate superabsorbent resin.

[0024] Preferably, the first base paper is impregnated, coated, wrinkled and dried to form a superabsorbent polymer coating layer. The dry weight of the superabsorbent polymer coating layer is 0.3-4.0 g / m², the thickness is 1-30 μm, and it retains liquid permeability without forming a closed water-blocking film.

[0025] And / or, the wrinkling rate of the first base paper is 5%-25%; and / or, the surface texture density formed by the wrinkling of the first base paper is 5-35 lines / cm;

[0026] And / or, the basis weight of the first and second base papers is 15-40 g / m², respectively;

[0027] And / or, the particle size of the granular superabsorbent resin is 150-850 μm, and the spreading amount is 20-60 g / m²;

[0028] And / or, the absorbent core has a basis weight of 70-100 g / m² and a thickness of 0.3-0.5 mm;

[0029] And / or, the second base paper is an uncoated and unwrinkled flat base paper before the granular superabsorbent resin is applied; or, the second base paper is subjected to impregnation coating, wrinkling, or impregnation coating followed by wrinkling treatment before the granular superabsorbent resin is applied.

[0030] Preferably, the first base paper and / or the second base paper is a composite base paper containing bamboo pulp fiber, wherein the composite base paper includes one or more of bamboo pulp fiber, fluff pulp fiber, wood pulp fiber, cotton fiber, viscose fiber, and hydrophilic chemical nonwoven fiber;

[0031] Preferably, based on dry fiber weight, the composite base paper comprises 15%-60% bamboo pulp fiber, 20%-75% fluff pulp fiber, and 0%-50% wood pulp fiber.

[0032] Preferably, the granular superabsorbent resin is at least partially fixed by an adhesive component in the first base paper formed by drying the impregnating coating liquid.

[0033] And / or, the absorbent core does not contain a continuous hot melt adhesive layer, or the dry amount of hot melt adhesive in the absorbent core is not greater than 1.0 g / m².

[0034] Secondly, the present invention also provides a method for preparing the absorbent core, comprising the following steps:

[0035] Dry base paper is used as the raw material for both the first and second base papers.

[0036] At least the first base paper is impregnated with a super absorbent agent coating liquid, so that the super absorbent agent coating liquid enters the fiber pores of the first base paper surface and forms a wet coating layer on the surface of the first base paper;

[0037] Before the first base paper is dried after impregnation and coating, the first base paper is wrinkled by scraping or embossing to form a wrinkled surface.

[0038] Granular superabsorbent resin is placed on the second base paper;

[0039] The first base paper is covered on the granular superabsorbent resin, with the wrinkled surface of the first base paper facing the granular superabsorbent resin.

[0040] The absorbent core is obtained by pressing, drying, rolling and slitting.

[0041] Preferably, the impregnation coating is carried out by one or more of the following methods: pad coating, immersion coating, tank impregnation coating, scraping off residual liquid after impregnation, and dehydration by roller after impregnation.

[0042] And / or, the liquid retention rate of the first base paper after impregnation and coating is 20%-120%;

[0043] And / or, the doctor blade wrinkling uses a drying cylinder, Yankee cylinder, or heated roller as the carrier roller. After the first base paper is attached to the surface of the carrier roller, it is peeled off by a doctor blade to form the wrinkled surface. The doctor blade angle is 15°-35°, and the surface temperature of the carrier roller is 60-130°C; or, the embossing wrinkling uses an embossing roller with micro-textures, the embossing pressure is 0.05-0.35MPa, and the embossing temperature is 40-90°C.

[0044] And / or, the linear pressure of the pressing is 3-30 N / mm, and the pressing temperature is 40-100℃;

[0045] And / or, the drying temperature is 70-130℃, and the moisture content of the absorbent core after drying is 4%-10%.

[0046] Thirdly, the present invention also provides a sanitary napkin, comprising a liquid-permeable surface layer, a liquid-impermeable bottom layer, and an absorbent core disposed between the liquid-permeable surface layer and the liquid-impermeable bottom layer, wherein the absorbent core is the absorbent core described above.

[0047] Fourthly, the present invention also provides a diaper, comprising a liquid-permeable surface layer, a liquid-impermeable bottom layer, and an absorbent core disposed between the liquid-permeable surface layer and the liquid-impermeable bottom layer, wherein the absorbent core is the absorbent core described above.

[0048] This invention uses dry base paper as the raw material for both the first and second base papers, facilitating continuous processing using conventional base paper rolls. By impregnating and coating at least the first base paper, a coating solution containing superabsorbent polymers and adhesives penetrates the fiber pores of the first base paper and distributes across the paper surface. The superabsorbent polymers enhance the first base paper's wettability, traction, and temporary storage capacity for body fluids, while the adhesives help improve the interfacial bonding stability between the first base paper and the granular superabsorbent resin during subsequent pressing and drying processes. The first base paper is prepared before drying after impregnation and coating. The process involves crease-forming or embossing the base paper to create a wrinkled surface in a wet or semi-dry state. This improves the softness and fluffiness of the base paper and allows the impregnating coating liquid to redistribute along the wrinkled surface, forming a liquid diffusion structure that facilitates the diffusion of the liquid within the surface of the first base paper. During the lamination process, granular superabsorbent polymer (SAP) is first placed on the second base paper and then covered by the impregnated and creased first base paper. This ensures full contact between the granular SAP and the functionalized wrinkled surface of the first base paper, achieving synergistic absorption, diffusion, and fixation after pressing and drying. Therefore, this invention reduces the use of continuous hot melt adhesive layers, lowers the risk of SAP migration, accumulation, and powdering, alleviates localized gel blockage, increases primary and secondary absorption rates, reduces rewetting, and enhances softness and comfort while maintaining a low core thickness. It is suitable for disposable absorbent hygiene products such as sanitary napkins, diapers, pull-ups, and adult care products. Attached Figure Description

[0049] Figure 1 This is a product photo of the absorbent core of the present invention.

[0050] Figure 2 This is a photo of the product after it has absorbed water according to the present invention. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings, embodiments, and comparative examples. The following embodiments are designed based on continuous laboratory-scale pilot-scale equipment and sheet composite experiments. The base paper, granular superabsorbent resin, polyacrylate superabsorbent polymer, adhesive, impregnation tank, doctor blade creping device, embossing roller, pressing roller, and hot air drying device used are all conventional materials or equipment in the art. Those skilled in the art can implement the present invention without creative effort based on the types of raw materials, proportions, coating methods, moisture content, pressing and drying conditions disclosed in this specification. It should be understood that the following embodiments do not limit the scope of protection of the present invention. Any equivalent substitutions made within the technical concept defined by the claims of the present invention for the type of base paper, type of superabsorbent polymer, type of adhesive, creping method, SAP application amount, and pressing and drying conditions should fall within the scope of protection of the present invention.

[0052] The absorbent core provided by this invention includes a first base paper, a second base paper, and granular superabsorbent resin disposed between the first and second base papers. Both the first and second base papers are made from dried base paper. Unlike adding SAP directly at the wet end of papermaking or using semi-finished paper web lamination, this invention preferentially uses already rolled, low-moisture base paper that is easy to store and continuously unwound. At least the first base paper is impregnated and coated on the subsequent lamination line, allowing the superabsorbent polymer coating liquid containing superabsorbent polymers and adhesives to penetrate the surface fiber pores of the first base paper and form a wet functional layer on its surface. Subsequently, before the first base paper dries after impregnation and coating, it is wrinkled using a doctor blade or embossing technique to create a wrinkled surface. This wrinkled surface primarily improves the softness, fluffiness, intraplane diffusion capacity of the liquid, and contact stability with the granular superabsorbent resin; the carrying and coating function of the granular superabsorbent resin is still jointly accomplished by the first and second base papers as sheet-like substrates.

[0053] I. Raw Materials and Testing Methods

[0054] The dry base paper used in the examples includes bamboo pulp composite base paper, fluff pulp composite base paper, and wood pulp composite base paper. The basis weight of the first and second base papers is controlled at 18-38 g / m², respectively. The granular superabsorbent polymer (SAP) is sodium polyacrylate with a particle size of 150-850 μm, preferably 300-600 μm. The artificial urine is an aqueous solution of sodium chloride with a mass fraction of 0.9%.

[0055] The testing method is as follows.

[0056] Quantitative test: Take 10 samples of 100mm×100mm, weigh them and convert the weight to g / m², and take the average value.

[0057] Thickness test: The thickness of the sample was measured under a pressure of 0.5 kPa. Ten points were tested in each group, and the average value was taken.

[0058] 30s diffusion distance test: Lay the sample flat, add 5mL of artificial urine to the center, and measure the longitudinal and lateral diffusion distances after 30s.

[0059] Single absorption time test: Add 5 mL of artificial urine to the center of the sample at once and record the time when the surface gloss of the liquid disappears and there is no obvious free liquid.

[0060] Secondary absorption time test: After the first absorption is completed, let stand for 5 minutes, then add 5 mL of artificial urine again, and record the time for complete absorption.

[0061] Reabsorption test: After the sample absorbs 10 mL of artificial urine, it stands for 5 min, covers the surface with filter paper and applies a pressure of 1.2 kPa for 1 min, and weighs the increase in weight of the filter paper.

[0062] SAP powder shedding rate test: Take a sample of a specified area, place it on a vibrating screen and vibrate for 5 minutes, collect the shed particles and powder, and calculate the percentage of the shed mass to the theoretical mass of SAP in the sample.

[0063] Softness test: The bending length method is used to evaluate the softness of the core. The smaller the bending length, the better the softness.

[0064] II. Implementation Examples

[0065] Example 1: Semi-dry blade-creased absorbent core of bamboo pulp composite first base paper

[0066] Dry bamboo pulp composite base paper is used as the raw material for the first and second base papers. Based on dry fiber weight, the base paper is prepared from 30 parts bamboo pulp fiber, 50 parts fluff pulp fiber and 20 parts wood pulp fiber. The basis weight of the first and second base papers is 24 g / m², and the initial moisture content of the base paper is 6.5%.

[0067] Preparation of the superabsorbent coating solution: Sodium polyacrylate was added to deionized water and stirred for 40 min to obtain a sodium polyacrylate dispersion with a mass fraction of 2.0%; polyvinyl alcohol (PVA) and sodium carboxymethyl cellulose (CMC) with a mass fraction of 0.6% and 0.25% were added, and stirring was continued for 30 min to obtain a coating solution with a viscosity of 720 mPa·s and a pH of 7.1. In this coating solution, sodium polyacrylate acts as the superabsorbent agent, while PVA and CMC act as adhesives and film-forming modifiers.

[0068] The first base paper is passed through a trough-type impregnation coating device, allowing the coating liquid to penetrate the fiber pores on the surface of the first base paper. It is then dehydrated by rollers, with the liquid content controlled at 65%. Before the first base paper is completely dried after impregnation and coating, it enters a heated roller and doctor blade creping device. At the time of creping, the moisture content of the first base paper is 18%. The surface temperature of the heated roller is 95℃, and the doctor blade angle is 25°. After creping, the creping rate of the first base paper is 13%, and the surface texture density is 18 lines / cm. Subsequently, granular superabsorbent polymer (SAP) with a particle size of 300-600μm is uniformly applied to the second base paper at 32g / m². The first base paper is then placed on top of the SAP, with the impregnated and creped surface of the first base paper facing the SAP. The paper is then pressed at a linear pressure of 12N / mm and a temperature of 65℃, followed by hot air drying at 95℃, winding, and slitting to obtain the absorbent core. The obtained core had a weight of 84 g / m² and a thickness of 0.41 mm.

[0069] Example 2: Wet-state doctor blade creping and absorbent core of high fluff pulp base paper

[0070] Dry base paper was used as both the first and second base papers. The base paper consisted of 20 parts bamboo pulp fiber, 65 parts fluff pulp fiber, and 15 parts wood pulp fiber. The basis weight of both the first and second base papers was 28 g / m². A superabsorbent polymer coating solution was prepared, comprising 1.5% sodium polyacrylate, 0.5% low-crosslinked polyacrylate microgel, 0.8% starch derivative, and 0.2% cellulose ether, with a viscosity of 860 mPa·s and a pH of 7.0.

[0071] After the first base paper is dip-coated, the liquid content is controlled at 90%. Before drying, it enters the doctor blade creping device. The moisture content of the paper web at the time of creping is 36%, which is wet creping. The surface temperature of the carrier roller is 80℃, the doctor blade angle is 22°, the creping rate is 18%, and the surface texture density is 15 lines / cm. The SAP application rate is 42g / m². The second base paper is an uncoated, smooth base paper. After pressing and hot air drying, an absorbent core with a basis weight of 101g / m² and a thickness of 0.49mm is obtained.

[0072] Example 3: Semi-dry embossed and wrinkled absorbent core for low-thickness sanitary napkins

[0073] Dry base paper was used as both the first and second base paper. The base paper consisted of 45 parts bamboo pulp fiber, 40 parts fluff pulp fiber, and 15 parts wood pulp fiber, with a basis weight of 22 g / m² for each layer. The superabsorbent coating solution included 2.2% potassium polyacrylate, 0.5% waterborne polyurethane, and 0.2% sodium carboxymethyl cellulose, with a viscosity of 640 mPa·s and a pH of 7.3.

[0074] After impregnation, the first base paper is dehydrated by rollers with a liquid content of 55%. It then enters the micro-texture embossing roller at a moisture content of 16% for embossing and wrinkling. The embossing pressure is 0.18 MPa, the embossing temperature is 65℃, the wrinkling rate is 10%, and the surface texture density is 22 lines / cm. The SAP application rate is 30 g / m². After covering, pressing, and drying, a low-thickness absorbent core with a basis weight of 77 g / m² and a thickness of 0.36 mm is obtained.

[0075] Example 4: Absorbent core with simultaneous impregnation and coating of second base paper

[0076] This embodiment demonstrates that the second base paper can also undergo impregnation and coating treatment. Both the first and second base papers are dry base papers made from 30 parts bamboo pulp fiber, 50 parts fluff pulp fiber, and 20 parts wood pulp fiber, with a single-layer basis weight of 23 g / m². The impregnation and coating solution for the first base paper includes 1.8% sodium polyacrylate and 0.8% polyvinyl alcohol, while the impregnation and coating solution for the second base paper includes 1.0% sodium polyacrylate and 0.5% starch derivative.

[0077] After the first base paper is impregnated and coated, it is wrinkled by a doctor blade at a moisture content of 20%. The second base paper is only impregnated and coated and then pre-dried at low temperature without wrinkling. The SAP application rate is 34 g / m². During lamination, the SAP is first applied to the coated surface of the second base paper, and then the wrinkled surface of the first base paper is covered. After pressing and drying, an absorbent core is obtained with a basis weight of 86 g / m² and a thickness of 0.42 mm.

[0078] Example 5: Absorbent core without bamboo pulp fiber

[0079] Dry base paper made from 70 parts fluff pulp fiber and 30 parts wood pulp fiber was used as both the first and second base papers, with a basis weight of 25 g / m² for each layer. The superabsorbent polymer (SAP) coating solution consisted of 1.8% sodium polyacrylate, 0.6% polyacrylate emulsion, and 0.2% cellulose ether, with a viscosity of 780 mPa·s. After impregnation and coating, the first base paper had a liquid retention rate of 60%, and wrinkling occurred at a moisture content of 19%, with a wrinkling rate of 12%. The SAP application rate was 34 g / m². After lamination, pressing, and drying, an absorbent core with a basis weight of 88 g / m² and a thickness of 0.43 mm was obtained.

[0080] This embodiment illustrates that the core effect of the present invention does not depend on bamboo pulp fiber. Ordinary fluff pulp / wood pulp base paper can also achieve improved diffusion and SAP stability through impregnation coating and creping before drying. The solution containing bamboo pulp fiber can be regarded as the preferred solution to further improve the taste suppression and differentiation performance.

[0081] III. Comparative Example

[0082] Comparative Example 1: Direct Composite Core of Ordinary Dry Base Paper

[0083] Using the same amount of first base paper, second base paper, and SAP as in Example 1, but without impregnation coating or wrinkling treatment of the first base paper, the SAP is directly placed on the second base paper, and then the first base paper is covered, and the mixture is pressed and dried to obtain a conventional composite core.

[0084] Comparative Example 2: Impregnation coating only, but without wrinkles

[0085] Using the same coating solution and SAP application rate as in Example 1, the first base paper was directly dried after impregnation coating without doctor blade wrinkling or embossing, and then laminated with the second base paper and SAP. This comparative example is used to demonstrate the effect of simple impregnation coating.

[0086] Comparative Example 3: Unimpregnated coating, only wrinkled

[0087] The same first and second base papers as in Example 1 were used. The first base paper was not impregnated and coated, but only wrinkled by a doctor blade at an appropriate moisture content, and then laminated with the second base paper and SAP. This comparative example was used to demonstrate the effect of simple wrinkling.

[0088] Comparative Example 4: Wrinkling after complete drying following impregnation coating

[0089] Using the same coating solution as in Example 1, the first base paper was impregnated and coated, then completely dried to a moisture content of 6%, before being wrinkled with a doctor blade. It was subsequently laminated with a second base paper and SAP. This comparative example demonstrates the effectiveness of the "wrinkling before drying" process sequence.

[0090] Comparative Example 5: Superabsorbent polymer coating liquid without adhesive

[0091] The same base paper and process as in Example 1 were used, but the coating solution contained only 2.0% sodium polyacrylate and no polyvinyl alcohol, sodium carboxymethyl cellulose, or other adhesives. This comparative example was used to demonstrate the effect of adhesives on SAP-assisted fixation and improved dust removal.

[0092] Comparative Example 6: High-heat melt adhesive fixing core

[0093] The same standard dry base paper and SAP application method as Comparative Example 1 were used, but a 3.0 g / m² hot melt adhesive was applied between the first and second base papers to fix the SAP. This comparative example was used to demonstrate the effect of conventional high-adhesion fixation methods on diffusion and absorption performance.

[0094] IV. Summary of Process Parameters for Examples and Comparative Examples

[0095]

[0096] The data in the table above are consistent with the preparation conditions of each embodiment and comparative example. The amount of SAP spread, thickness and amount of hot melt adhesive were all set according to the corresponding test group, and there were no inconsistencies in the parameters of the same group.

[0097] V. Performance Test Results

[0098]

[0099] The performance test results show that Examples 1-5 all exhibited good liquid diffusion performance, short absorption time, low reabsorption, and low SAP dusting rate. Comparing Example 1 and Comparative Example 1, the 30s longitudinal diffusion distance of Example 1 increased from 55mm to 124mm, the lateral diffusion distance increased from 33mm to 76mm, the first absorption time decreased from 16.8s to 7.6s, the second absorption time decreased from 25.6s to 10.5s, the reabsorption decreased from 0.36g to 0.13g, and the SAP dusting rate decreased from 4.9% to 0.8%. These results demonstrate that the present invention, through a combination of impregnation coating, pre-drying wrinkling, and overlay lamination processes, can simultaneously improve liquid diffusion, absorption efficiency, and SAP fixation stability.

[0100] Comparative Example 2, with only impregnation coating but no wrinkling, had a longitudinal diffusion distance of 82 mm, superior to Comparative Example 1 but significantly lower than Example 1. This indicates that impregnation coating can improve the wettability of the first base paper and the contact stability of SAP, but lacks the surface diffusion structure formed by wrinkling before drying, resulting in insufficient in-plane diffusion of the liquid. Comparative Example 3, with only wrinkling but no impregnation coating, had a shorter bending length, indicating improved softness. However, the SAP dusting rate was 3.7%, significantly higher than Example 1, indicating that the SAP-assisted fixation effect is insufficient when no adhesive and superabsorbent polymer enter the surface fiber pores of the first base paper. Comparative Example 4, with impregnation coating, complete drying, and then wrinkling, performed better than Comparative Examples 2 and 3 but lower than Example 1. This indicates that wrinkling before drying after impregnation coating allows the coating liquid to better combine with the surface wrinkled structure, forming a more effective liquid diffusion structure. Comparative Example 5, without adhesive, had diffusion performance close to Example 1, but the SAP dusting rate was 3.1%, indicating that the adhesive significantly contributes to the auxiliary fixation of granular superabsorbent resin. Comparative Example 6 uses high-temperature hot melt adhesive for fixation. Its SAP powder shedding rate is low, but its diffusion distance, absorption time, and re-permeation amount are all poor. This indicates that a higher amount of hot melt adhesive can easily hinder liquid diffusion and entry into the SAP layer.

[0101] In summary, the technical effects of this invention stem from the following synergistic effects.

[0102] First, using dried base paper as the raw material for both the first and second base papers allows for compatibility with existing base paper unwinding, impregnation, creping, powdering, lamination, drying, winding, and slitting equipment, facilitating continuous production.

[0103] Second, the first base paper is impregnated with a coating containing superabsorbent polymers and adhesives, allowing the coating liquid to penetrate the pores of the surface fibers of the first base paper, rather than forming an outer coating only on the paper surface. The superabsorbent polymers improve the wettability, traction, and temporary storage capacity of the liquid, while the adhesives improve the interfacial stability between the first base paper and the particulate superabsorbent resin.

[0104] Third, before the first base paper dries after impregnation and coating, it is wrinkled by a doctor blade or embossing to form a wrinkled surface in the wet or semi-dry state, which can improve the softness and the ability of liquid to spread in the surface, and make the impregnation coating liquid more fully integrated with the surface structure of the first base paper.

[0105] Fourth, the granular superabsorbent resin is first placed on the second base paper and then covered by the first base paper. This helps to protect the surface structure formed by wrinkling before the coating dries after impregnation and coating, and allows the granular superabsorbent resin to fully contact the functionalized surface of the first base paper.

[0106] Fifth, the present invention can eliminate the need for a continuous hot melt adhesive layer, or use only a low amount of hot melt adhesive of no more than 1.0 g / m², thereby reducing the water blockage problem caused by traditional high hot melt adhesive fixing methods, and improving liquid diffusion and absorption efficiency while maintaining a low SAP powder shedding rate.

[0107] Therefore, this invention can achieve rapid liquid diffusion, shortened primary and secondary absorption time, reduced rewetting, reduced SAP powder shedding rate, and improved softness under conditions of low basis weight and low thickness of absorbent core with a basis weight of 70-100g / m² and a thickness of 0.3-0.5mm. It is suitable for use in disposable absorbent hygiene products such as sanitary napkins, baby diapers, pull-up pants, and adult incontinence care products.

Claims

1. An absorbent core for sanitary napkins or diapers, the absorbent core comprising a first base paper, a second base paper, and granular superabsorbent resin disposed between the first base paper and the second base paper, characterized in that, The absorbent core is prepared by the following method: 1) Dry base paper is used as the raw material for both the first and second base papers; 2) At least the first base paper is impregnated with a superabsorbent polymer coating liquid, wherein the superabsorbent polymer coating liquid includes superabsorbent polymer and adhesive; 3) After impregnation and coating, the first base paper is wrinkled by scraping or embossing to form a wrinkled surface; 4) Place granular superabsorbent resin on the second base paper, then cover the granular superabsorbent resin with the first base paper, and prepare the absorbent core by pressing and drying.

2. The absorbent core according to claim 1, characterized in that, The wrinkled surface of the first base paper is positioned facing the granular superabsorbent resin, so that the granular superabsorbent resin comes into contact with the surface of the first base paper after impregnation, coating and wrinkling treatment. And / or, the wrinkled surface formed on the first base paper before it dries after impregnation coating, together with the superabsorbent coating liquid that has been impregnated into the pores of the surface fibers of the first base paper, constitutes a liquid diffusion structure for promoting the diffusion of liquid within the surface of the first base paper. And / or, the moisture content of the first base paper is 25%-60% before it dries after impregnation coating; or, the moisture content of the first base paper is 10%-25% after pre-dehydration treatment but before it is completely dried after impregnation coating. And / or, the doctor blade wrinkling includes wet wrinkling or semi-dry wrinkling; wherein, wet wrinkling is a wrinkling method in which the moisture content of the first base paper is 25%-60% when it comes into contact with the doctor blade, and semi-dry wrinkling is a wrinkling method in which the moisture content of the first base paper is 10%-25% when it comes into contact with the doctor blade.

3. The absorbent core according to claim 1, characterized in that, The superabsorbent polymer includes one or more of sodium polyacrylate, potassium polyacrylate, polyacrylate superabsorbent polymers, low cross-linked polyacrylate microgels, and starch-grafted polyacrylate superabsorbent polymers. And / or, the adhesive comprises one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, cellulose ether, starch derivative, waterborne polyurethane, acrylic emulsion, and polyacrylate emulsion; And / or, in the superabsorbent polymer coating liquid, the mass fraction of the superabsorbent polymer is 0.5%-5.0%, and the mass fraction of the adhesive is 0.1%-3.0%; preferably, the mass fraction of the superabsorbent polymer is 1.0%-4.0%, and the mass fraction of the adhesive is 0.2%-1.0%. And / or, the viscosity of the superabsorbent polymer coating liquid is 100-1800 mPa·s, and the pH is 6.0-8.5; And / or, the granular superabsorbent resin is one or more of sodium polyacrylate superabsorbent resin, potassium polyacrylate superabsorbent resin, and starch-grafted polyacrylate superabsorbent resin.

4. The absorbent core according to claim 1, characterized in that, The first base paper is impregnated, coated, wrinkled and dried to form a superabsorbent polymer coating layer. The dry weight of the superabsorbent polymer coating layer is 0.3-4.0 g / m², the thickness is 1-30 μm, and it retains liquid permeability without forming a closed water-blocking film. And / or, the wrinkling rate of the first base paper is 5%-25%; And / or, the surface texture density formed after the first base paper is wrinkled is 5-35 lines / cm; And / or, the basis weight of the first and second base papers is 15-40 g / m², respectively; And / or, the particle size of the granular superabsorbent resin is 150-850 μm, and the spreading amount is 20-60 g / m²; And / or, the absorbent core has a basis weight of 70-100 g / m² and a thickness of 0.3-0.5 mm; And / or, the second base paper is an uncoated and unwrinkled flat base paper before the granular superabsorbent resin is applied; or, the second base paper is subjected to impregnation coating, wrinkling, or impregnation coating followed by wrinkling treatment before the granular superabsorbent resin is applied.

5. The absorbent core according to claim 1, characterized in that, The first base paper and / or the second base paper are composite base papers containing bamboo pulp fibers, and the composite base paper includes one or more of bamboo pulp fibers, fluff pulp fibers, wood pulp fibers, cotton fibers, viscose fibers, and hydrophilic chemical nonwoven fibers. Preferably, based on dry fiber weight, the composite base paper comprises 15%-60% bamboo pulp fiber, 20%-75% fluff pulp fiber, and 0%-50% wood pulp fiber.

6. The absorbent core according to claim 1, characterized in that, The granular superabsorbent resin is at least partially fixed by the adhesive component in the first base paper formed by the drying of the impregnation coating liquid; And / or, the absorbent core does not contain a continuous hot melt adhesive layer, or the dry amount of hot melt adhesive in the absorbent core is not greater than 1.0 g / m².

7. A method for preparing the absorbent core according to any one of claims 1-6, characterized in that, Includes the following steps: Dry base paper is used as the raw material for both the first and second base papers. At least the first base paper is impregnated with a super absorbent agent coating liquid, so that the super absorbent agent coating liquid enters the fiber pores of the first base paper surface and forms a wet coating layer on the surface of the first base paper; Before the first base paper is dried after impregnation and coating, the first base paper is wrinkled by scraping or embossing to form a wrinkled surface. Granular superabsorbent resin is placed on the second base paper; The first base paper is covered on the granular superabsorbent resin, with the wrinkled surface of the first base paper facing the granular superabsorbent resin. The absorbent core is obtained by pressing, drying, rolling and slitting.

8. The method according to claim 7, characterized in that, The impregnation coating is carried out using one or more of the following methods: pad coating, immersion coating, tank impregnation coating, scraping off residual liquid after impregnation, and dehydration by rollers after impregnation. And / or, the liquid retention rate of the first base paper after impregnation and coating is 20%-120%; And / or, the doctor blade wrinkling uses a drying cylinder, Yankee cylinder, or heated roller as the carrier roller. After the first base paper is attached to the surface of the carrier roller, it is peeled off by a doctor blade to form the wrinkled surface. The doctor blade angle is 15°-35°, and the surface temperature of the carrier roller is 60-130°C; or, the embossing wrinkling uses an embossing roller with micro-textures, the embossing pressure is 0.05-0.35MPa, and the embossing temperature is 40-90°C. And / or, the linear pressure of the pressing is 3-30 N / mm, and the pressing temperature is 40-100℃; And / or, the drying temperature is 70-130℃, and the moisture content of the absorbent core after drying is 4%-10%.

9. A sanitary napkin, characterized in that, It includes a liquid-permeable top layer, a liquid-impermeable bottom layer, and an absorbent core disposed between the liquid-permeable top layer and the liquid-impermeable bottom layer, wherein the absorbent core is the absorbent core as described in any one of claims 1-6.

10. A diaper, characterized in that, It includes a liquid-permeable top layer, a liquid-impermeable bottom layer, and an absorbent core disposed between the liquid-permeable top layer and the liquid-impermeable bottom layer, wherein the absorbent core is the absorbent core as described in any one of claims 1-6.

Images