Liquid sanitary napkin and method of making same

Abstract

The present application relates to sanitary napkin technical field, disclose a kind of liquid sanitary napkin and preparation method thereof.The liquid sanitary napkin includes liquid face layer, flow guide layer, liquid core layer and leakage prevention bottom layer in turn from top to bottom, liquid core layer is the reaction type amphiphilic ion flow guide polyurethane foaming sheet material compressed by double roller and processed;The foaming sheet material is prepared by foaming and curing by raw material containing reactive zwitterionic polyol chain extender, and the chain extender is obtained by reacting N-methyldiethanolamine with organic sodium salt containing 3-chloro-2-hydroxypropane sulfonate sodium.The liquid core layer can also be provided with through-hole array, longitudinal flow guide groove, arc-shaped flow resistance groove and micro blind hole array.The present application can improve the speed of menstrual blood infiltration, reduce surface residual liquid and reperfusion, and make the core body not easy to form a group, fault or deformation after absorbing liquid under pressure, with the advantages of fast absorption, good dryness and comfortable use.

Description

Technical Field

[0001] This invention relates to the field of sanitary napkin technology, specifically to a liquid sanitary napkin and its preparation method. Background Technology

[0002] Sanitary napkins typically consist of a top layer, a diversion layer, an absorbent core, and a leak-proof bottom layer. The structure and material properties of the absorbent core directly affect the rate of menstrual blood absorption, the uniformity of diffusion, the amount of backflow, and the dryness and comfort during use. Traditional sanitary napkins often use a composite of fluff pulp and superabsorbent polymer (SAP) to form the absorbent core. Although it has a certain absorbency, menstrual blood is highly viscous and contains protein, mucus, and cellular components, which can easily accumulate in the top layer or at the core entrance. At the same time, traditional cores are prone to local swelling, clumping, discontinuity, or displacement after absorbing liquid, which can easily cause surface dampness, backflow, and side leakage under pressure, walking, or bending.

[0003] Chinese invention patent application CN116421766A discloses a method for preparing a liquid sanitary napkin absorbent core. The method involves formulating a HIPE emulsion using acrylate monomers, a crosslinking agent, a photoinitiator, and a surfactant. Different emulsions are then coated onto fabric, followed by light exposure, steam treatment, dehydration, and drying to form the absorbent core, thereby improving liquid transfer capacity and dryness. This method primarily relies on the acrylate system and emulsion polymerization to form a porous absorbent structure. The process involves steps such as emulsion preparation, coating, light exposure, and steam treatment. However, it does not address the reactive zwitterionic conductivity modification of the polyurethane foam pore framework, nor does it solve the problems of blood adhesion and blockage at the pore inlet and insufficient core morphological stability under pressure after liquid absorption.

[0004] Chinese invention patent application CN118578700A discloses a method for preparing a liquid sanitary napkin. The absorbent core is prepared by using polyurethane prepolymer made from polyether polyol and isocyanate, foamed and cured to form a foamed sheet, and further combined with a porous soft absorbent sheet to form a monolithic absorbent core. Different pore sizes are used to promote liquid passage and reduce backflow. Although this method involves polyurethane foam sheets, it mainly achieves absorption and drainage through the combination of the foamed sheet and the porous soft absorbent sheet. It does not disclose the covalent embedding of reactive zwitterionic polyhydroxy chain extenders containing sulfonic acid groups, carboxylic acid groups, and quaternary ammonium cations into the polyurethane foam framework, nor does it disclose a technical solution for improving the stability of repeated liquid absorption and drainage through double-roller compression opening combined with a partitioned pore structure.

[0005] Chinese invention patent application CN110236796A discloses a side-leakage-preventing sanitary napkin. It features a strip-shaped groove in the center of the surface layer, an annular groove around the outer periphery of the strip-shaped groove, and perforations at the bottom of the grooves. Protective strips are also provided on both sides. The strip-shaped groove, annular groove, and protective strips work together to prevent side leakage. This solution primarily reduces lateral liquid overflow from the surface grooves and side protection structure of the sanitary napkin. However, it does not improve the rapid absorption of menstrual blood, the drainage within the foam pores, the ability to repeatedly absorb liquid and remain dry, or the resistance to deformation when wet by addressing the issue of menstrual blood stagnation at the core material's inlet, surface dampness, and clumping and deformation of the core after absorbing liquid. Furthermore, its structural leak-proof effect fails to address the problems of menstrual blood retention at the core's inlet, surface dampness, and the core clumping and deforming after absorbing liquid.

[0006] Therefore, although existing technologies have improved liquid sanitary napkins by using polymer absorbent materials, porous foam structures, or surface leak-proof structures, problems still exist such as unstable menstrual blood seepage rate, significant surface residual liquid and backflow, easy deformation of the core under pressure after absorption, and uneven diffusion of liquid within the core. Based on this, it is necessary to provide a new liquid sanitary napkin and its preparation method. By performing reactive zwitterionic conductivity modification on the liquid core material and combining it with open-pore treatment and partitioned pore design, it can simultaneously possess the properties of rapid absorption, surface dryness, uniform diffusion, and resistance to deformation. Summary of the Invention

[0007] To address the shortcomings of the existing technology, the present invention provides a liquid sanitary napkin and its preparation method.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A liquid sanitary napkin, from top to bottom, comprises a liquid-permeable surface layer, a diversion layer, a liquid core layer, and a leak-proof bottom layer. The liquid core layer is a reactive zwitterionic diffusing polyurethane foam sheet processed by double-roll compression and perforation. The foam sheet is obtained by foaming and curing raw materials containing a reactive zwitterionic polyhydroxy chain extender. The reactive zwitterionic polyhydroxy chain extender is obtained by reacting N-methyldiethanolamine with an organic sodium salt, wherein the organic sodium salt contains at least one of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate.

[0010] Most existing sanitary napkins rely on fluff pulp / superabsorbent polymer or ordinary foam core to absorb menstrual blood. Menstrual blood has a high viscosity and contains protein, mucus and cellular components, which can easily stagnate on the surface or at the core entrance, resulting in slow absorption, surface dampness and backflow. After the core absorbs liquid and is compressed, it is also prone to local expansion, collapse, clumping or displacement, leading to uneven diffusion, increased risk of side leakage, and reduced comfort.

[0011] Preferably, the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium chloroacetate in the organic sodium salt is (1-5):(1-3).

[0012] Preferably, the liquid core layer is provided with an array of through holes, a longitudinal flow guide groove, an arc-shaped flow obstruction groove, and an array of micro blind holes.

[0013] Preferably, the through-hole array is elliptical in shape along the length of the sanitary napkin, with a through-hole diameter of 0.5-3.0 mm and a center-to-center distance of 2-5 mm between adjacent through-holes; the longitudinal guide groove is located on both sides of the through-hole array, with a length of 80-120 mm, a width of 1-3 mm, and a depth of 0.5-1.5 mm; the arc-shaped flow-blocking groove is located at the rear end of the through-hole array, with a depth of 0.5-1.2 mm and a groove width of 1-3 mm; the micro-blind hole array is located in the front inlet area and / or the rear liquid storage and diffusion area, with a hole diameter of 0.2-0.5 mm and a depth of 0.3-0.8 mm.

[0014] A method for preparing the liquid sanitary napkin includes the following steps:

[0015] (1) Preparation of reactive zwitterionic polyhydroxy chain extender: N-methyldiethanolamine was reacted with an organic sodium salt in a solvent under nitrogen protection, and then desalted and dried;

[0016] (2) The polyol, the reactive zwitterionic polyhydroxy chain extender, the foaming agent, the catalyst and the mixture are mixed to obtain component A, which is then mixed with isocyanate and foamed and cured to obtain polyurethane foam sheet;

[0017] (3) The foamed sheet is subjected to double-roller compression and perforation treatment, then rinsed, dried and cut to obtain the liquid core layer;

[0018] (4) The liquid permeable surface layer, the flow guiding layer, the liquid core layer and the leak-proof bottom layer are stacked and then combined to obtain a liquid sanitary napkin.

[0019] Preferably, the organic sodium salt in step (1) is a combination of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate, and the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium chloroacetate is 3:2; the reaction conditions are: pH 8.0-8.5, temperature 70-80℃, and time 8-10h.

[0020] Preferably, the polyol in step (2) includes polyether triol and polyoxypropylene polyether triol; the isocyanate is a mixture of 4,4'-diphenylmethane diisocyanate and carbodiimide-modified MDI; and a post-curing treatment is performed after foaming and curing.

[0021] Preferably, the conditions for the double-roller compression opening process in step (3) are as follows: the gap between the two rollers is adjusted to 30%-60% of the initial thickness of the foamed sheet, the roller speed is 1-5m / min, and the compression-release is repeated 3-10 times; after compression opening, the sheet is rinsed with deionized water until the conductivity is less than 100μS / cm, and then dried until the moisture content is less than 1.0wt%.

[0022] Preferably, the liquid core layer obtained in step (3) is further processed with a through-hole array, a longitudinal flow guide groove, an arc-shaped flow obstruction groove and / or a micro blind hole array.

[0023] Preferably, the through-hole array is elliptical in shape along the length of the sanitary napkin, and the diameter of the through-hole is 0.5-3.0 mm; the longitudinal guide groove is located on both sides of the through-hole array, with a depth of 0.5-1.5 mm; the arc-shaped flow-blocking groove is located at the rear end of the through-hole array, with a depth of 0.5-1.2 mm; and the micro-blind hole array is located in the front inlet area and / or the rear liquid storage and diffusion area, with a diameter of 0.2-0.5 mm.

[0024] This invention does not simply replace the traditional absorbent core with ordinary polyurethane foam material. Instead, it introduces a reactive zwitterionic polyhydroxy chain extender into the polyurethane foaming reaction, allowing the hydroxyl groups in the molecule to participate in the isocyanate reaction, and covalently fixing zwitterionic hydrophilic groups such as sulfonic acid groups, carboxylic acid groups, and quaternary ammonium cations into the polyurethane cell framework. As a result, the inner walls of the liquid core layer's cells are no longer ordinary hydrophobic or weakly hydrophilic surfaces, but rather form an interface with stable menstrual blood conduction capabilities. When menstrual blood contacts the core layer, the hydrophilic groups such as sulfonic acid groups and carboxylic acid groups on the inner walls of the cells can undergo hydrogen bonding, ionic solvation, and wetting interactions with the water and polar components in the menstrual blood, enabling the menstrual blood to be quickly captured and guided into the cell interior, reducing the retention of menstrual blood on the surface layer.

[0025] Simultaneously, the zwitterionic groups form a stable hydration layer on the inner wall of the cell, reducing the adhesion and blockage of proteins, mucus, and cellular components in menstrual blood at the cell inlet, ensuring a smooth entry path for the liquid during multiple absorption processes. Unlike ordinary surfactant-based hydrophilic finishing, the zwitterionic flow-conducting groups of this invention are fixed in the polyurethane molecular chains and cell framework through a chemical reaction, making them less prone to migration or loss during washing, liquid absorption, and pressure application. Therefore, they can maintain a longer-lasting liquid absorption rate and drying effect.

[0026] Furthermore, this invention forms a three-dimensional interconnected pore structure through foaming, and opens some closed pores through a double-roller compression and opening process, creating numerous porous channels inside the liquid core layer capable of accommodating and transporting menstrual blood. A through-hole array is set in the middle of the liquid core layer, allowing menstrual blood to quickly seep into the core layer. Longitudinal guide channels promote the diffusion of menstrual blood along the length of the core layer. A micro-blind hole array provides local temporary storage space. Arc-shaped flow-blocking channels reduce the risk of menstrual blood instantly concentrating and migrating towards the ends. These pore structures work together to ensure that menstrual blood does not remain or accumulate on the surface, but rather quickly enters the core, disperses evenly inside, and is temporarily stored, thereby reducing surface residual liquid and lowering the risk of backflow and side leakage.

[0027] Furthermore, the liquid core layer uses a continuous polyurethane elastic foam skeleton as a support structure. Unlike fluff pulp / superabsorbent polymer cores, it does not clump, break, or harden due to localized swelling after absorbing liquid. Under pressure, walking, and bending conditions, the foam skeleton maintains a certain degree of resilience and shape recovery, keeping the core relatively flat and preventing collapse or displacement. This invention simultaneously achieves the technical effects of rapid menstrual blood absorption, dry surface, uniform diffusion, and resistance to deformation. Visually, this results in less residual liquid after adding liquid, a smaller red residue area, and no clumping or hardening of the core, leading to better dryness and a more comfortable fit when worn.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention provides a liquid sanitary napkin and its preparation method. The invention uses a reactive zwitterionic conductive polyurethane foam sheet as the liquid core layer, and a reactive zwitterionic polyhydroxy chain extender participates in the isocyanate reaction during the polyurethane foaming and curing process, thereby covalently fixing hydrophilic conductive groups such as sulfonic acid groups, carboxylic acid groups, and quaternary ammonium cations into the polyurethane cell skeleton. Compared with ordinary surfactant hydrophilic finishing, these conductive groups are less likely to migrate or be lost during rinsing, liquid absorption, and pressure application, enabling the inner wall of the cell to maintain good menstrual blood wetting and conductivity for a long time, thereby increasing the speed at which menstrual blood enters the core layer.

[0030] 2. In this invention, the organic sodium salt is preferably a compound system of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate, so that the reactive zwitterionic polyhydroxy chain extender has both sulfonate and carboxylate hydrophilic structures. The sulfonate structure is beneficial for forming a stable hydration layer and improving rapid wetting ability, while the carboxylate structure is beneficial for improving the affinity between polar components in menstrual blood and the follicle wall. The combination of the two can reduce the adhesion and blockage of proteins, mucus and cellular components in menstrual blood at the follicle inlet, so that the liquid can still be smoothly introduced during multiple absorption processes.

[0031] 3. The present invention further incorporates an array of through-holes, longitudinal flow channels, arc-shaped flow-blocking channels, and an array of micro-blind holes on the liquid core layer. The through-hole array promotes rapid infiltration of menstrual blood, the longitudinal flow channels promote the diffusion of menstrual blood along the length of the core layer, the micro-blind hole array provides local temporary storage space, and the arc-shaped flow-blocking channels reduce the risk of instantaneous concentration and migration of liquid towards the ends. These pore structures work together to allow menstrual blood to quickly enter the core and disperse evenly, thereby reducing the risk of side leakage and end spillage.

[0032] 4. The liquid core layer of the present invention is composed of a continuous polyurethane elastic foam skeleton. Compared with the traditional fluff pulp / superabsorbent polymer composite absorbent core, it is less prone to local swelling, clumping, disintegration or hardening after absorbing liquid. It can still maintain good shape stability and resilience under sitting pressure, walking and bending conditions, thus improving the product's fit comfort and usage stability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a product illustration of the present invention. Detailed Implementation

[0035] The invention will now be described in further detail with reference to specific embodiments, but it should not be construed as limiting the scope of the invention to the following embodiments.

[0036] The raw materials described in this application are partially described; all other raw materials not described are commercially available.

[0037] Polyether triol A was purchased from Jining Fangyu Chemical Co., Ltd., model: 000, with a hydroxyl value of 32-36 mgKOH / g.

[0038] Polyether triol B is polyoxypropylene polyether triol, purchased from Haian Petrochemical Plant in Jiangsu Province, model: GP306.

[0039] Polyether-modified polydimethylsiloxane is a commercially available polyether-modified silicone oil for soft polyurethane open-cell foam, with a viscosity of 800-1800 mPa·s at 25℃ and an active ingredient content of ≥95wt%.

[0040] Sodium 3-chloro-2-hydroxypropanesulfonate, CAS No.: 126-83-0.

[0041] Example 1

[0042] A liquid sanitary napkin, comprising, from top to bottom, a liquid-permeable surface layer, a diversion layer, a liquid core layer, and a leak-proof bottom layer; the liquid-permeable surface layer is a hydrophilic hot-air nonwoven fabric with a basis weight of 22 g / m². 2 The airflow guiding layer is made of three-dimensional crimped ES fiber hot air nonwoven fabric with a basis weight of 35g / m². 2 The leak-proof bottom layer is a breathable polyethylene membrane; the liquid core layer is made of reactive zwitterionic polyurethane foam material.

[0043] The liquid sanitary napkin has a length of 280mm and an unfolded width of 165mm; the liquid core layer has a length of 250mm, a width of 70mm, and a thickness of 3.5mm.

[0044] The preparation method of the reactive zwitterionic conductive polyurethane foam material is as follows:

[0045] S1. Mix 3 parts by weight of polyethylene glycol-600, 1.8 parts by weight of deionized water and 3.5 parts by weight of reactive zwitterionic polyhydroxy chain extender, and stir at 600 rpm for 20 min at 45 °C; add 55 parts by weight of polyether triol A and 25 parts by weight of polyether triol B, and continue stirring at 45 °C for 30 min to obtain a polyol mixture; cool to room temperature, add 1 part by weight of polyether-modified polydimethylsiloxane, 0.08 parts by weight of triethylenediamine catalyst and 0.12 parts by weight of bismuth neodecanoate catalyst, and disperse at 25 °C at 2500 rpm for 90 s to obtain foaming component A;

[0046] S2. Add 42 parts by weight of a mixture of 4,4'-diphenylmethane diisocyanate and carbodiimide-modified MDI to component A above, wherein the NCO content is 30.5 wt% and the isocyanate index is controlled at 0.98-1.02; stir at 5000 rpm for 10 s, and immediately pour into a sheet mold preheated to 45°C for foaming and setting for 5 min, wherein the mold cavity thickness is 3.8 mm; place the set foamed sheet in a 70°C hot air oven for curing for 2 h, and then place the cured sheet in a 4 The foamed sheet was soaked in deionized water at 5℃ for 20 minutes, and then compressed and opened using a double roller. The gap between the double rollers was adjusted to 45% of the initial thickness of the foamed sheet, and the roller speed was 2 m / min. The compression and release were repeated 5 times. After compression and opening, the foamed sheet was rinsed with deionized water 3 times, each time for 5 minutes, until the conductivity of the rinsing solution was lower than 100 μS / cm. The foamed sheet was then placed in a hot air oven at 55℃ and dried for 60 minutes until the moisture content was lower than 1.0 wt%, thus obtaining a reactive zwitterionic conductive polyurethane foam material.

[0047] Preparation of reactive zwitterionic polyhydroxy chain extender: Under nitrogen protection, 119.2 parts by weight of N-methyldiethanolamine, 196.6 parts by weight of organic sodium salt, 300 parts by weight of deionized water and 150 parts by weight of isopropanol were added to a reaction vessel. The pH was controlled at 8.0-8.5, and the reaction was stirred at 75℃ and 300 rpm for 9 h. The reaction solution was cooled to room temperature, and the isopropanol was removed under reduced pressure. Then, desalting was performed using a nanofiltration membrane with a molecular weight cutoff of 100 Da until the conductivity of the permeate was lower than 100 μS / cm. The solution was then concentrated under vacuum at 55℃ and dried under vacuum to obtain the reactive zwitterionic polyhydroxy chain extender. The organic sodium salt was composed of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate in a mass ratio of 3:2. The water content of the obtained reactive zwitterionic polyhydroxy chain extender was lower than 0.5 wt%, and the hydroxyl value was 640 mg KOH / g.

[0048] The processing technology of the liquid core layer is as follows:

[0049] The above-mentioned reactive zwitterionic polyurethane foam sheet was cut into liquid core layers with a length of 250 mm, a width of 70 mm, and a thickness of 3.5 mm.

[0050] A perforated array is fabricated in the rapid infiltration zone in the middle of the liquid core layer. The perforation diameter is 1.1 mm, the center distance between adjacent perforations is 3.8 mm, and the perforation array is elliptical along the length of the sanitary napkin. The perforation array is 115 mm long and 42 mm wide.

[0051] Longitudinal guide grooves are processed on both sides of the through hole array. The longitudinal guide grooves extend along the length of the sanitary napkin, with a length of 105mm, a width of 2.0mm, and a depth of 1.1mm, and the longitudinal guide grooves do not penetrate the liquid core layer.

[0052] Three arc-shaped flow-blocking grooves are machined at the rear end of the through-hole array. The depth of the arc-shaped flow-blocking grooves is 0.8 mm, the width of the grooves is 1.2 mm, and the distance between adjacent arc-shaped flow-blocking grooves is 4 mm.

[0053] Micro-blind hole arrays were fabricated in the front-end inlet area and the rear-end liquid storage and diffusion area, respectively. The micro-blind holes had a diameter of 0.35 mm, a depth of 0.6 mm, and a spacing of 2.5 mm, thus obtaining the liquid core layer.

[0054] The preparation method of the liquid sanitary napkin is as follows: a hydrophilic hot-air nonwoven fabric surface layer, a three-dimensional crimped ES fiber guiding layer, the above-mentioned liquid core layer, and a breathable polyethylene leak-proof bottom layer are sequentially stacked. Structural adhesive is applied to the outer periphery of the liquid core layer, and the periphery is sealed by hot pressing. The hot pressing temperature is 95℃, the pressure is 0.18MPa, and the hot pressing time is 1.5s. Subsequently, the shape is cut, the wings are formed, the backing adhesive is applied, the release paper is laminated, folded, and packaged to obtain the liquid sanitary napkin.

[0055] Example 2

[0056] It is basically the same as Example 1, except that the organic sodium salt is sodium 3-chloro-2-hydroxypropanesulfonate, and the other parameters and conditions are the same as those in Example 1.

[0057] Example 3

[0058] It is basically the same as Example 1, except that the organic sodium salt is sodium chloroacetate, and the other parameters and conditions are the same as in Example 1.

[0059] Comparative Example 1

[0060] This is essentially the same as Example 1, except that a traditional fluff pulp / superabsorbent polymer composite absorbent core is used instead of the liquid core layer in Example 1. In this traditional fluff pulp / superabsorbent polymer composite absorbent core, the mass ratio of fluff pulp to superabsorbent polymer is 7:3, the core length is 250 mm, the width is 70 mm, and the thickness is 3.5 mm. The areal density of this traditional fluff pulp / superabsorbent polymer composite absorbent core is the same as that of the liquid core layer in Example 1.

[0061] Comparative Example 2

[0062] The process is basically the same as in Example 1, except that: when preparing the polyurethane foam material, a reactive zwitterionic polyhydroxy chain extender is not added, but polyethylene glycol-600 with an equivalent amount of active hydrogen is used instead, and the amount of isocyanate added is adjusted so that the isocyanate index is consistent with that in Example 1.

[0063] Comparative Example 3

[0064] The process is basically the same as in Example 1, except that when preparing the polyurethane foam material, 3.5 parts by weight of reactive zwitterionic polyhydroxy chain extender is replaced with 3.5 parts by weight of non-reactive zwitterionic surfactant, and an appropriate amount of polyethylene glycol-600 is added to keep the active hydrogen equivalent and isocyanate index of the system consistent with those in Example 1.

[0065] Comparative Example 4

[0066] The process is basically the same as in Example 1, except that after preparing the reactive zwitterionic polyurethane foam sheet, it is not subjected to double-roller compression and pore opening treatment, but is directly rinsed with deionized water, dried, cut and processed with subsequent pore shapes; the other raw material composition, foaming conditions, liquid core pore shape processing and sanitary napkin composite process are the same as in Example 1.

[0067] Comparative Example 5

[0068] The process is basically the same as in Example 1, except that the liquid core layer uses the same reactive zwitterionic polyurethane foam material as in Example 1 and undergoes the same double-roller compression and opening process, but without processing the through-hole array, longitudinal flow channel, arc-shaped flow blocking channel and micro blind hole array. Instead, the foam sheet is cut into a flat sheet liquid core layer with a length of 250 mm, a width of 70 mm and a thickness of 3.5 mm.

[0069] Test Example 1

[0070] Liquid sanitary napkin samples prepared in Examples 1-3 and Comparative Examples 1-5 were tested after being equilibrated for 24 hours in an environment with a temperature of 23±2℃ and a relative humidity of 50±5%.

[0071] 1. Liquid Penetration Time Test: The liquid penetration time test was conducted according to the principles outlined in GB / T 24218.8-2010 "Textiles - Nonwovens - Test Methods - Part 8: Determination of Liquid Penetration Time (Simulated Urine)," and simulated menstrual blood was used for testing, taking into account the structure of the finished sanitary napkin. The sanitary napkin sample was laid flat on a horizontal test platform. A liquid-adding ring with an inner diameter of 25 mm was placed in the center of the sample. 5 mL of simulated menstrual blood was added to the liquid-adding ring within 5 seconds. The time required for the simulated menstrual blood to completely penetrate the surface layer without a continuously visible liquid film was recorded as the first liquid penetration time.

[0072] After the initial addition of liquid, a 5-minute interval was observed. The second and third additions were then performed in the same manner, with 5 mL of simulated menstrual blood added each time. The liquid penetration time for the third addition was recorded. Five samples were tested in each group, and the average value was taken. The simulated menstrual blood was prepared from 0.9 wt% sodium chloride, 8 wt% glycerol, 0.5 wt% sodium carboxymethyl cellulose, 0.05 wt% red water-soluble dye, and the balance deionized water. Its viscosity was controlled at 8-12 mPa·s at 25°C to simulate the viscous flow characteristics of menstrual blood.

[0073] 2. Surface residual liquid area test: After the third addition of liquid in Test Example 1, let it stand for 30 seconds, take a picture of the central area of ​​the sanitary napkin surface layer under the same lighting conditions, and use image analysis software to count the area of ​​visible red residual liquid on the surface layer, which is recorded as the surface residual liquid area.

[0074] The smaller the surface residual liquid area, the less menstrual blood stays on the surface layer, and the easier it is for the liquid to enter the liquid core layer, resulting in better perceived dryness during use.

[0075] 3. Backflow Test: After the third addition of liquid in Test Example 1 was completed and the mixture was allowed to stand for 1 minute, a pre-weighed stack of filter paper was placed above the central liquid addition area of ​​the sanitary napkin. The size of the filter paper stack was 100mm × 100mm. A pressure of 2.0kPa was applied to the filter paper stack and held for 1 minute. The filter paper stack was then removed and weighed. The weight gain of the filter paper stack was calculated as the backflow amount. The thickness was measured using a thickness gauge with a measuring foot area of ​​2500mm² and a measuring pressure of 0.5kPa. Three points were measured in the central area of ​​each sanitary napkin, and the average value was taken.

[0076] The lower the backflow rate, the better the liquid core layer's ability to introduce, disperse, and temporarily store menstrual blood, and the less likely the surface layer will feel damp.

[0077] 4. Wet thickness retention rate and appearance deformation test: Take sanitary napkin samples prepared in Examples 1-3 and Comparative Examples 1-5, and measure the initial thickness H0 of the central region of the sample. Then, add simulated menstrual blood to the central region of the sample in 3 portions, 5 mL each time, with an interval of 5 min. After the liquid addition is completed, apply a pressure of 5 kPa to the central region of the sample and maintain it for 5 min. After releasing the pressure, let it stand for 3 min, and measure the thickness H1 of the central region of the sample again. Calculate the wet thickness retention rate according to the following formula: Wet thickness retention rate = H1 / H0 × 100%.

[0078] Simultaneously observe whether the sample exhibits core clumping, delamination, localized hardening, significant collapse, displacement, or end-liquid concentration. A higher wet thickness retention rate indicates a stronger ability of the core layer to maintain its original shape after absorbing liquid and being compressed, making it less prone to deformation.

[0079] Table 1 Test results of liquid sanitary napkins

[0080] Example 1 3.0 3.5 0.7 0.04 93.2 The surface layer has very little residual liquid, the diffusion is uniform, the core is flat, and there are no clumps or breaks. Example 2 3.4 4.2 1.1 0.07 91.5 The core is flat with minimal residual liquid on the surface. Example 3 3.8 4.8 1.5 0.09 90.8 The core is basically flat with minimal residual liquid in some areas. Comparative Example 1 8.6 12.3 5.9 0.25 63.4 Localized swelling, clumping, faulting, and hardening may occur. Comparative Example 2 6.5 8.6 4.4 0.18 87.6 The core does not clump together, but the surface feels noticeably damp. Comparative Example 3 4.9 7.3 3.6 0.15 86.2 Initial infiltration was acceptable, but after repeated additions of liquid, the residual liquid on the surface increased. Comparative Example 4 6.2 8.1 4.0 0.17 86.8 Uneven localized liquid absorption, with fluid accumulation in closed pores. Comparative Example 5 5.3 6.7 3.1 0.13 90.1 The core is flat, but the liquid is concentrated in the central area of ​​the filling process, resulting in uneven diffusion.

[0081] The results above show that the liquid sanitary napkin prepared by this invention has the properties of rapid absorption, good dryness, and comfortable use. A comparison of Examples 1-3 shows that Example 1 uses a compound of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate to prepare a reactive zwitterionic polyhydroxy chain extender, while Examples 2 and 3 each use only a single organic sodium salt. The sulfonate-type zwitterionic structure has a strong hydration capacity, which can improve the rapid wetting and introduction of menstrual blood onto the inner wall of the foam pores; the carboxylate-type zwitterionic structure can further improve the affinity between polar components in menstrual blood and the foam pore wall, and reduce the adhesion and blockage of components such as proteins and mucus at the foam pore entrance. The combination of the two forms a more stable hydrophilic and conductive interface, allowing menstrual blood to enter the core layer more quickly and maintain good conductive stability during multiple absorption processes.

[0082] Comparative Example 1 uses a traditional fluff pulp / superabsorbent polymer composite absorbent core instead of the liquid core layer of this invention. Traditional absorbent cores mainly rely on fiber gaps and the expansion of superabsorbent polymers to absorb liquid. After repeated absorption and pressure, they are prone to localized swelling, clumping, discontinuity, or hardening, and the liquid tends to remain on the surface or in localized areas. Example 1 uses a continuous elastic polyurethane foam skeleton as the liquid core layer, which maintains good structural integrity and resilience after liquid absorption, and is less prone to clumping, discontinuity, and localized collapse. Therefore, it can improve the problems of slow absorption, noticeable dampness, and easy deformation after use of traditional cores.

[0083] Comparative Example 2 did not include a reactive zwitterionic polyhydroxy chain extender, but instead used polyethylene glycol-600. Although ordinary polyurethane foam materials have a certain degree of elasticity, their cell walls lack stable zwitterionic hydrophilic groups, resulting in insufficient ability to wet, guide, and prevent adhesion and clogging of menstrual blood. Menstrual blood easily stagnates at the cell inlet or surface area. Example 1 introduced hydrophilic groups such as sulfonic acid groups, carboxylic acid groups, and quaternary ammonium cations into the polyurethane cell framework using a reactive zwitterionic polyhydroxy chain extender, forming a stable flow interface inside the core layer. Therefore, it can significantly improve the rate of menstrual blood penetration and reduce surface residue and backflow.

[0084] Comparative Example 3 uses a non-reactive zwitterionic surfactant instead of a reactive zwitterionic polyhydroxy chain extender. While non-reactive surfactants can improve material wettability in the initial stage, they mainly exist in the cell structure through physical blending and are prone to migration or loss during rinsing, liquid absorption, and pressure treatment, making it difficult to form a durable and stable hydrophilic interface. The reactive zwitterionic polyhydroxy chain extender in Example 1 contains hydroxyl groups that can participate in isocyanate reactions and can be covalently fixed in the polyurethane molecular chains and cell framework during foaming and curing. Therefore, its flow-conducting effect is more stable, and it maintains good dryness even after repeated absorption.

[0085] Comparative Example 4 did not undergo the twin-roll compression opening treatment. After polyurethane foam sheets have cured, some closed or semi-closed cells are unavoidable. Without compression opening treatment, the channels for liquid to enter the core layer are insufficient, easily leading to localized liquid accumulation. Example 1 opened some closed cells through twin-roll compression-release treatment, improving the connectivity between cells and allowing liquid to quickly enter and disperse within the core layer along the three-dimensional channels, thereby further increasing the absorption rate and reducing residual liquid on the surface layer.

[0086] Comparative Example 5, while using the same reactive zwitterionic polyurethane foam material as Example 1 and undergoing the same twin-roll compression and perforation treatment, did not incorporate the through-hole array, longitudinal flow channels, arc-shaped flow-blocking channels, and micro-blind hole array. In this structure, although the liquid can be absorbed by the foamed core, it still tends to concentrate in the central area, resulting in insufficient diffusion uniformity. Example 1 achieves rapid infiltration through the through-hole array, promotes liquid diffusion along the length direction through the longitudinal flow channels, provides local temporary storage space through the micro-blind hole array, and reduces the risk of liquid concentration and migration towards the ends through the arc-shaped flow-blocking channels. Therefore, it can reduce surface residual liquid, reduce backflow, and improve the diffusion uniformity within the core layer.

Claims

1. A liquid sanitary napkin, comprising, from top to bottom, a liquid-permeable surface layer, a diversion layer, a liquid core layer, and a leak-proof bottom layer, characterized in that, The liquid core layer is a reactive zwitterionic polyurethane foam sheet that has undergone double-roll compression and perforation treatment. The foam sheet is obtained by foaming and curing raw materials containing a reactive zwitterionic polyhydroxy chain extender. The reactive zwitterionic polyhydroxy chain extender is obtained by reacting N-methyldiethanolamine with an organic sodium salt, wherein the organic sodium salt contains at least one of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate.

2. The liquid sanitary napkin according to claim 1, characterized in that, The mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium chloroacetate in the organic sodium salt is (1-5):(1-3).

3. The liquid sanitary napkin according to claim 1, characterized in that, The liquid core layer is provided with an array of through holes, longitudinal flow channels, arc-shaped flow obstruction channels, and an array of micro blind holes.

4. The liquid sanitary napkin according to claim 3, characterized in that, The perforation array is elliptical in shape along the length of the sanitary napkin, with a perforation diameter of 0.5-3.0 mm and a center-to-center distance of 2-5 mm between adjacent perforations; the longitudinal flow guide groove is located on both sides of the perforation array, with a length of 80-120 mm, a width of 1-3 mm, and a depth of 0.5-1.5 mm; the arc-shaped flow obstruction groove is located at the rear end of the perforation array, with a depth of 0.5-1.2 mm and a groove width of 1-3 mm; the micro-blind hole array is located in the front inlet area and / or the rear liquid storage and diffusion area, with a pore diameter of 0.2-0.5 mm and a depth of 0.3-0.8 mm.

5. A method for preparing a liquid sanitary napkin according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of reactive zwitterionic polyhydroxy chain extender: N-methyldiethanolamine was reacted with an organic sodium salt in a solvent under nitrogen protection, and then desalted and dried; (2) The polyol, the reactive zwitterionic polyhydroxy chain extender, the foaming agent, the catalyst and the foam leveler are mixed to obtain component A, which is then mixed with isocyanate and foamed and cured to obtain polyurethane foam sheet. (3) The foamed sheet is subjected to double-roller compression and perforation treatment, then rinsed, dried and cut to obtain the liquid core layer; (4) The liquid permeable surface layer, the flow guiding layer, the liquid core layer and the leak-proof bottom layer are stacked and then combined to obtain a liquid sanitary napkin.

6. The preparation method according to claim 5, characterized in that, The organic sodium salt in step (1) is a combination of sodium 3-chloro-2-hydroxypropanesulfonate and sodium chloroacetate, and the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium chloroacetate is 3:2; the reaction conditions are: pH 8.0-8.5, temperature 70-80℃, and time 8-10h.

7. The preparation method according to claim 5, characterized in that, The polyols in step (2) include polyether triols and polyoxypropylene polyether triols; the isocyanate is a mixture of 4,4'-diphenylmethane diisocyanate and carbodiimide-modified MDI; and a post-curing treatment is performed after foaming and curing.

8. The preparation method according to claim 5, characterized in that, The conditions for the double-roller compression opening process in step (3) are as follows: the gap between the two rollers is adjusted to 30%-60% of the initial thickness of the foamed sheet, the roller speed is 1-5m / min, and the continuous compression-release is performed 3-10 times; after compression opening, the sheet is rinsed with deionized water until the conductivity is less than 100μS / cm, and then dried until the moisture content is less than 1.0wt%.

9. The preparation method according to claim 5, characterized in that, In step (3), the liquid core layer obtained by cutting is further processed with a through hole array, a longitudinal flow guide groove, an arc-shaped flow obstruction groove and a micro blind hole array.

10. The preparation method according to claim 9, characterized in that, The through-hole array is elliptical in shape along the length of the sanitary napkin, with a through-hole diameter of 0.5-3.0 mm; the longitudinal guide groove is located on both sides of the through-hole array, with a depth of 0.5-1.5 mm; the arc-shaped flow-blocking groove is located at the rear end of the through-hole array, with a depth of 0.5-1.2 mm; the micro blind hole array is located in the front inlet area and / or the rear liquid storage and diffusion area, with a pore diameter of 0.2-0.5 mm.

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