A composite structure sanitary napkin surface layer made of spunlace nonwoven fabric and its preparation method

Abstract

This invention relates to a composite structure sanitary napkin surface layer made of spunlace nonwoven fabric, comprising a first fiber web layer and a second fiber web layer entangled by hydroentanglement. The first fiber web layer is composed of bicomponent fibers with a core-sheath structure, wherein the sheath layer of the bicomponent fibers is modified polypropylene, and the core layer is polypropylene. The second fiber web layer is composed of hydrophilic polyester fibers with a cross-shaped structure. The modified polypropylene is polyether acrylate grafted modified polypropylene, and the hydrophilic polyester is an in-situ polymerized modified copolyester. This invention uses a hydroentanglement process to reinforce the first and second fiber web layers to obtain a sanitary napkin surface layer made of spunlace nonwoven fabric. The significant difference in hydrophilicity and hydrophobicity between the two fiber web layers creates a differential capillary effect, achieving unidirectional hydrophilicity while maintaining softness and skin-friendliness.

Description

Technical Field

[0001] This invention belongs to the field of nonwoven fabrics, specifically relating to a composite structure sanitary napkin surface layer made of spunlace nonwoven fabric and its preparation method. Background Technology

[0002] Sanitary napkins generally consist of three parts: the top layer, the absorbent layer, and the bottom layer. The top layer material requires softness, skin-friendliness, and excellent permeability. It must quickly absorb menstrual blood and transfer it to the absorbent layer, preventing backflow of liquid onto the surface of the sanitary napkin. In other words, the top layer material must possess skin-friendliness and one-way moisture-wicking properties. Spunlace nonwoven fabric, compared to spunbond nonwoven fabric, has a soft feel, good bulkiness, is less prone to pilling, and is non-irritating to the skin, making it widely used in the top layer materials of sanitary napkins. Currently, the top layer material for sanitary napkins using spunlace nonwoven fabric is mostly made of cotton or viscose fiber. While cotton and viscose fibers have good softness and skin-friendliness, their excellent absorbency leads to significant backflow after absorption, making the surface very damp and lacking excellent one-way moisture-wicking properties, resulting in poor comfort. Polypropylene has a regular structure, no polar groups on its surface, and good hydrophobicity. When it is used as the upper and lower layers of composite nonwoven fabric with hydrophilic fibers, it has good unidirectional moisture wicking properties. However, its skin-friendliness and softness are not good, which limits its application in sanitary napkin surface materials.

[0003] Chinese patent CN202211120117.4 discloses a soft, dry spunlace nonwoven fabric and its preparation method, comprising, from the inside out, cotton fiber nonwoven fabric, modified polypropylene nonwoven fabric, and viscose fiber nonwoven fabric. The cotton fiber nonwoven fabric has a certain degree of moisture absorption. Modified phosphazene is introduced into the viscose fiber nonwoven fabric, making the viscose fiber nonwoven fabric more absorbent than the cotton fiber nonwoven fabric, thus giving the spunlace nonwoven fabric moisture-wicking capabilities. While this nonwoven fabric exhibits good unidirectional moisture wicking properties, the introduction of modifiers such as silicon and phosphorus reduces its skin-friendliness.

[0004] Therefore, it is necessary to develop a sanitary napkin surface layer made of spunlace nonwoven fabric that is skin-friendly, soft, and provides rapid one-way moisture wicking. Summary of the Invention

[0005] In view of the shortcomings of existing sanitary napkin surface nonwoven fabrics, which cannot simultaneously achieve rapid unidirectional moisture wicking and skin-friendliness, this invention provides a composite structure sanitary napkin surface layer spunlace nonwoven fabric and its preparation method. This invention uses modified polypropylene and polypropylene (PP) in a core-sheath structure for bicomponent spinning to obtain a soft, skin-friendly, and hydrophobic first fiber web layer; hydrophilic modified polyester is spun through irregularly shaped spinnerets to obtain a hydrophilic second fiber web layer; the first and second fiber web layers are then reinforced by a hydroentangling process to obtain a composite hydroentangled nonwoven fabric for the sanitary napkin surface layer. The significant difference in hydrophilicity and hydrophobicity between the two fiber web layers creates a differential capillary effect, achieving unidirectional water wicking while maintaining skin-friendliness and softness.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A composite sanitary napkin surface layer is made of spunlace nonwoven fabric, comprising a first fiber web layer and a second fiber web layer entangled by hydroentanglement. The first fiber web layer is composed of bicomponent fibers with a core-sheath structure. The sheath of the bicomponent fibers is modified polypropylene, and the core layer is polypropylene. The second fiber web layer is composed of hydrophilic polyester fibers with a cross-shaped structure. The modified polypropylene is polyether acrylate grafted modified polypropylene. The hydrophilic polyester is an in-situ polymerized modified copolyester.

[0008] Furthermore, the areal density of the first and second fiber web layers is independently 8-15 g / m². 2 .

[0009] Furthermore, the fineness of the first fiber is 1.5-2.5 dtex and the length is 30-50 mm, and the fineness of the second fiber is 1.0-1.5 dtex and the length is 30-50 mm.

[0010] In the bicomponent fiber with the core-sheath structure, the mass ratio of modified polypropylene to polypropylene is 10-30:90-70.

[0011] The modified polypropylene is polyether acrylate grafted polypropylene, and the amount of polyether acrylate used is 10-25 wt% of the polypropylene.

[0012] Preferably, the polyether acrylate has a number average molecular weight of 300-800, and for example, at least one of methoxy polyethylene glycol (400) acrylate, methoxy polyethylene glycol (600) acrylate, polyethylene glycol (400) diacrylate, and polyethylene glycol (600) diacrylate. If the grafted molecular chains are too long, it will affect the flowability and strength properties; if the molecular chains are too short, the required flexibility properties will not be achieved.

[0013] Furthermore, the modified polypropylene is prepared by the following steps: dry polypropylene chips, polyether acrylate and initiator are mixed evenly and melt-grafted to obtain modified polypropylene.

[0014] Furthermore, the drying of polypropylene chips and polyether acrylate is carried out in an oven at 60-80℃ for 5-15 hours; the initiator is selected from at least one of ditert-butyl peroxide and dicumyl peroxide, and the amount of initiator is 0.1-0.2 wt% of the polypropylene chips; the melt grafting is carried out in a torque rheometer at a reaction temperature of 200-220℃ and a rotation speed of 70-80 r / min; after the reaction is completed, the product is cooled and granulated.

[0015] The hydrophilic polyester is copolymerized from terephthalic acid, isophthalic acid, ethylene glycol, sodium dimethyl isophthalate-5-sulfonate, and polyethylene glycol under the action of a catalyst and a stabilizer. The amount of isophthalic acid used is 5-10 wt% of terephthalic acid, the amount of sodium dimethyl isophthalate-5-sulfonate used is 5-15 wt% of terephthalic acid, the molecular weight of polyethylene glycol is 1000-2000, and the amount used is 5-10 wt% of terephthalic acid. The catalyst is antimony trioxide or antimony acetate, and the amount used is 0.03-0.04 wt% of terephthalic acid. The stabilizer is trimethyl phosphate, and the amount used is 0.01-0.02 wt% of terephthalic acid.

[0016] The hydrophilic polyester is prepared by the following steps:

[0017] (1) Under stirring, terephthalic acid, ethylene glycol and isophthalic acid are added to the pulping kettle. The molar ratio of ethylene glycol to acid is controlled at 1.2-1.5. Catalyst and stabilizer are added to obtain a uniformly mixed slurry.

[0018] (2) The slurry is introduced into an esterification reactor with stirring and esterification reaction is carried out at 245-255℃. The column top temperature of the fractionation column is controlled not to exceed 110℃. After esterification, sodium dimethyl isophthalate-5-sulfonate and polyethylene glycol are added. When the reactor temperature rises to 230-250℃, it is introduced into a polycondensation reactor with stirring.

[0019] (3) Under the action of a vacuum pump, the pressure inside the polycondensation reactor is kept below 50 Pa for polycondensation reaction, and the reactor temperature is controlled at 270-280℃ for 3-4 hours.

[0020] (4) Stop stirring after the reaction is complete, release the vacuum with high-purity nitrogen, increase the pressure to 0.2-0.5MPa, cast the strip from the casting head, cool it with water and then granulate it into hydrophilic polyester chips using a pelletizer.

[0021] The second objective of this invention is to provide a method for preparing the surface layer of a sanitary napkin with the above-mentioned composite structure using spunlace fabric, comprising the following steps:

[0022] (S1) First fiber web layer: Modified polypropylene chips are fed into an extruder for heating and melting, and then enter the spinning die through a melt filter, melt conveying pipeline, and metering pump. After passing through the spinning die, the chips are evenly distributed to the first spinning assembly. Polypropylene chips are fed into an extruder for heating and melting, filtered, extruded, and then enter the spinning die through a metering pump, where they are evenly distributed to the second spinning assembly. At the outlet, composite spinning is performed, followed by cooling, stretching, winding, and cutting to produce a bicomponent fiber with a core-sheath structure, wherein the sheath layer is modified polypropylene and the core layer is polypropylene. The bicomponent fiber is then opened and combed to form the first fiber web layer.

[0023] (S2) Second fiber web layer: Hydrophilic polyester chips are fed into an extruder for heating and melting, filtered, extruded, and fed into a spinning die by a metering pump, and evenly distributed to a cross-shaped spinning assembly; composite spinning is performed at the outlet, and after cooling, stretching, winding, and cutting, cross-shaped hydrophilic polyester fibers are produced; the cross-shaped hydrophilic polyester fibers are opened and combed to form the second fiber web layer.

[0024] (S3) Spunlace nonwoven fabric: The first fiber web layer and the second fiber web layer are combined, reinforced by spunlace, dried and rolled to obtain the composite spunlace nonwoven fabric for the surface layer of sanitary napkins.

[0025] In step (S3), the composite method is selected from either cross-laying or parallel-laying, and the hydroentanglement pressure is 4-10 MPa, with 3-6 hydroentanglement channels.

[0026] The mechanism of this invention is explained as follows:

[0027] Core-sheath bicomponent fibers are composite fibers with two components arranged in a core-sheath configuration. They are composed of two polymers with different properties or structures, with one component surrounding the other along the fiber axis, combining the characteristics of both types of fibers. Polypropylene has a regular structure, no polar groups on its surface, and good water permeability, but its skin-friendliness and softness are poor. Flexible long molecular chains are grafted onto the polypropylene macromolecular chains through a melt grafting reaction. The introduction of these flexible long molecular chains disrupts the structural regularity of polypropylene, improving softness. However, modified polypropylene fibers are expensive, and the introduction of too many flexible long molecular chains can reduce strength. Modified polypropylene is then composite-spun with polypropylene in a core-sheath structure; polypropylene forms the core layer, providing high tensile strength; modified polypropylene forms the sheath layer, directly contacting the skin, maintaining good hydrophobicity while providing good softness. Simultaneously, due to the difference in heat shrinkage properties between modified and unmodified polypropylene, different degrees of shrinkage occur during spinning, resulting in three-dimensional helical crimp, further improving bulk and softness. In other words, even with the introduction of fewer flexible long molecular chains, the required bulk and softness can be achieved. Therefore, the first fiber web prepared by spinning and laying the core-sheath structure of modified polypropylene / polypropylene has excellent skin-friendliness, hydrophobicity and strength properties, and is highly comfortable when in contact with the skin.

[0028] Polyester possesses good mechanical and chemical resistance properties and is inexpensive, but its high crystallinity and lack of hydrophilic groups result in poor water absorption. In contrast, the cross-shaped fiber structure features numerous longitudinally distributed grooves on its surface, resulting in a large specific surface area. These grooves increase the internal porosity of the fiber, creating capillary action that allows for rapid water absorption and transport. By copolymerizing polyester with monomers containing hydrophilic groups and designing the micropores in the spinneret, fibers with rapid water absorption and transport can be spun, providing excellent hygroscopicity when used as a secondary fiber web.

[0029] By combining the aforementioned first fiber web with good hydrophobicity and skin-friendliness with a second fiber web with good moisture absorption, a composite nonwoven fabric with a hydrophobic layer and a hydrophilic layer is formed. Its differential capillary effect and wetting gradient effect create an additional pressure difference in the thickness direction of the nonwoven fabric, achieving unidirectional water conduction while maintaining good skin-friendliness. More preferably, the first fiber web layer of this invention uses polyether acrylate-modified polypropylene as the skin layer. The polyether acrylate segments have good compatibility with the hydrophilic polyester of the second fiber web layer, and when the two come into contact, it is more conducive to guiding water from the first fiber layer into the second fiber web layer.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The spunlace nonwoven fabric of this invention comprises a first fiber web and a second fiber web. The first fiber web is a modified polypropylene / polypropylene bicomponent fiber with a core-sheath structure. The modified polypropylene sheath provides softness and hydrophobicity, while the polypropylene core provides high tensile strength. When the two fibers are spun in a core-sheath structure, they shrink to different degrees during the spinning process, resulting in a three-dimensional spiral curl, making it fluffy and soft. The resulting first fiber web is both skin-friendly and hydrophobic. The second fiber web is a cross-shaped hydrophilic polyester fiber. Hydrophilic groups are introduced through in-situ polymerization to obtain hydrophilic polyester. Combined with the cross-shaped spinneret design, this gives the first fiber web excellent water absorption and hydrophobicity. The first and second fiber web layers are then reinforced by a spunlace process to obtain the sanitary napkin surface layer of spunlace nonwoven fabric. The large difference in hydrophilicity and hydrophobicity between the two fiber web layers creates a differential capillary effect, achieving unidirectional hydrophoresis while maintaining softness and skin-friendliness. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. The following embodiments are provided to better understand this invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0033] Unless otherwise specified, "parts" in the embodiments of the present invention refers to parts by mass, and "%" refers to percentage by mass unless otherwise specified.

[0034] The polypropylene chips were purchased from Beijing Yanshan Petrochemical Corporation, model S2040, with a melt flow rate of 38±1g / 10min and a density of 0.905±0.01g / cm3.

[0035] Both methoxy polyethylene glycol (400) acrylate and methoxy polyethylene glycol (600) acrylate were purchased from Guangzhou Haoyi New Material Technology Co., Ltd., with models MPEG400A and MPEG600A respectively.

[0036] Sodium dimethyl isophthalate-5-sulfonate was purchased from Shandong Jinsheng New Material Technology Co., Ltd., with an acid value ≤0.6mgKOH / g and a moisture content ≤0.35%.

[0037] Polyethylene glycol PEG-1000, hydroxyl value 102~125mgKOH / g, moisture ≤1.0%.

[0038] Preparation of modified polypropylene

[0039] Preparation example a1

[0040] 100 parts of polypropylene chips and 10 parts of methoxy polyethylene glycol (400) acrylate were dried in a drying oven at 70°C for 5 hours. The dried polypropylene chips, methoxy polyethylene glycol (400) acrylate and 0.1 parts of ditert-butyl peroxide (DTBP) were mixed evenly and then melt-grafted in a torque rheometer at 200°C. The screw speed was 70 rpm. The reaction extrudate was cooled in a cooling water tank and cut into methoxy polyethylene glycol acrylate grafted modified polypropylene chips of a certain shape using a pelletizer.

[0041] Preparation Example a2

[0042] The rest is the same as in Preparation Example 1, except that the raw material components are: 100 parts polypropylene chips, 25 parts methoxy polyethylene glycol (600) acrylate, and 0.2 parts di-tert-butyl peroxide (DTBP).

[0043] Preparation Example a3

[0044] The rest is the same as in Preparation Example 1, except that the amount of methoxy polyethylene glycol (400) acrylate used is 5 parts.

[0045] Preparation Example a4

[0046] The rest is the same as in Preparation Example 1, except that methoxy polyethylene glycol (200) acrylate is used instead of methoxy polyethylene glycol (200) acrylate.

[0047] Comparative preparation example a1

[0048] The rest is the same as in Preparation Example 1, except that 2.47 parts of maleic anhydride are used instead of 10 parts of methoxy polyethylene glycol (400) acrylate. (That is, maleic anhydride is used instead of methoxy polyethylene glycol (400) acrylate in a different molar ratio.)

[0049] Preparation of hydrophilic polyester

[0050] Preparation Example b1

[0051] (1) Under stirring, 100 parts of terephthalic acid, 50 parts of ethylene glycol, 10 parts of isophthalic acid, 0.04 parts of antimony trioxide catalyst and 0.02 parts of trimethyl phosphate stabilizer are added to the pulping kettle and stirred to mix evenly to obtain a slurry.

[0052] (2) The slurry is introduced into an esterification reactor with stirring and esterification reaction is carried out at 250°C. The column top temperature of the fractionation column is controlled at 100-105°C. After esterification, 10 parts of sodium dimethyl isophthalate-5-sulfonate and 6 parts of polyethylene glycol PEG-1000 are added. When the reactor temperature is raised to 240°C, the slurry is introduced into a polycondensation reactor with stirring.

[0053] (3) Under the action of a vacuum pump, the pressure inside the polycondensation reactor is kept below 50 Pa for polycondensation reaction, and the reactor temperature is controlled at 270℃ for 3-4 hours.

[0054] (4) Stop stirring after the reaction is complete, release the vacuum with high-purity nitrogen, increase the pressure to 0.25MPa, cast the strip from the casting head, cool it with water and then granulate it into hydrophilic polyester chips using a pelletizer.

[0055] Preparation Example b2

[0056] The rest is the same as in Preparation Example 1, except for the raw material composition: 100 parts terephthalic acid, 50 parts ethylene glycol, 8 parts isophthalic acid, 0.04 parts antimony trioxide catalyst, 0.02 parts trimethyl phosphate stabilizer, 6 parts sodium dimethyl isophthalate-5-sulfonate, and 10 parts polyethylene glycol PEG-1000.

[0057] Example 1

[0058] (S1) First Fiber Web: 10 parts of the modified polypropylene chips prepared in Preparation Example a1 are fed into an extruder for heating and melting. After passing through a melt filter, melt conveying pipeline, and metering pump, they enter the spinning die and are evenly distributed to the first spinning assembly. 90 parts of polypropylene chips are fed into an extruder for heating and melting. After filtering, extrusion, and metering pump, they enter the spinning die and are evenly distributed to the second spinning assembly. Composite spinning is performed at the outlet. After cooling, stretching, and cutting, modified polypropylene / polypropylene bicomponent fibers with a core-sheath structure of 2.0 dtex and a length of 30 mm are produced. The melt spinning process is as follows: spinning temperature 280℃, setting temperature 150℃, POY spinning speed 2600 m / min, POY draw ratio 2, FDY spinning speed 4200 m / min, FDY draw ratio 3, and winding speed 3000 r / min. The bicomponent fibers are opened and combed to form the first fiber web.

[0059] (S2) Second Fiber Web: The hydrophilic polyester chips obtained in Preparation Example b1 are fed into an extruder for heating and melting. After filtering and extrusion, they are fed into the spinning die via a metering pump and evenly distributed to the cross-shaped spinning assembly. Composite spinning is performed at the outlet. After cooling, stretching, winding, and cutting, cross-shaped hydrophilic polyester fibers with a fineness of 1.5 dtex and a length of 30 mm are produced. The melt spinning process is as follows: spinning temperature 280℃, setting temperature 120℃, POY spinning speed: 2200 m / min, POY draw ratio 2, FDY spinning speed: 3800 m / min, FDY draw ratio 3, and winding speed 3000 r / min. The cross-shaped hydrophilic polyester fibers are opened and combed to form the second fiber web.

[0060] (S3) Spunlace nonwoven fabric: The first fiber web and the second fiber web are combined, reinforced by spunlace, dried and rolled to obtain the composite structure sanitary napkin spunlace nonwoven fabric.

[0061] In step (S3), the composite method is selected as either cross-laying or parallel-laying, and the hydroentanglement pressure is 8MPa with 5 hydroentanglement channels.

[0062] Example 2

[0063] The rest is the same as in Example 1, except that the amount of modified polypropylene used in Preparation Example a1 is 30 parts.

[0064] Example 3

[0065] The rest is the same as in Example 1, except that the modified polypropylene prepared in Preparation Example a2 is used instead of the modified polypropylene prepared in Preparation Example a1.

[0066] Example 4

[0067] The rest is the same as in Example 1, except that the second fiber web uses the hydrophilic polyester chips from Preparation Example b2 instead of the hydrophilic polyester chips obtained in Preparation Example b1.

[0068] Example 5

[0069] The rest is the same as in Example 1, except that the modified polypropylene prepared in Preparation Example a3 is used instead of the modified polypropylene prepared in Preparation Example a1.

[0070] Example 6

[0071] The rest is the same as in Example 1, except that the modified polypropylene prepared in Preparation Example a4 is used instead of the modified polypropylene prepared in Preparation Example a1.

[0072] Comparative Example 1

[0073] The rest is the same as in Example 1, except that the modified polypropylene prepared in Comparative Preparation Example a1 is used instead of the modified polypropylene prepared in Preparation Example a1.

[0074] Comparative Example 2

[0075] The rest is the same as in Example 1, except that the first fiber web layer is made of single-component fibers using only the modified polypropylene of Preparation Example a1, instead of core-sheath bicomponent fibers.

[0076] Comparative Example 3

[0077] The rest is the same as in Example 1, except that the hydrophilic polyester in the second fiber web is spun by a regular circular spinning assembly, that is, not a cross-shaped spinning assembly.

[0078] Application examples

[0079] The spunlace nonwoven fabrics of the above embodiments and comparative examples were subjected to the following performance tests:

[0080] Liquid penetration time: determined according to standard GB / T 24218 Textiles - Nonwovens Test Method.

[0081] Moisture return rate: Determined according to standard GB / T24218 Textiles - Nonwovens Test Methods.

[0082] Softness: Measured according to standard GB-T 8942-2016.

[0083] Table 1

[0084]

[0085]

[0086] As shown in Table 1, the composite structure spunlace nonwoven fabric produced by this invention has a short liquid penetration time, is not prone to backflow, has good unidirectional water permeability, and is soft and skin-friendly.

Claims

1. A composite structure sanitary napkin surface layer made of spunlace nonwoven fabric, comprising a first fiber web layer and a second fiber web layer entangled by spunlace, characterized in that, The first fiber web is composed of bicomponent fibers with a core-sheath structure, wherein the sheath of the bicomponent fibers is modified polypropylene and the core is polypropylene. The second fiber web layer is composed of hydrophilic polyester fibers with a cross-shaped structure. The hydrophilic polyester is copolymerized from terephthalic acid, isophthalic acid, ethylene glycol, sodium dimethyl isophthalate-5-sulfonate, and polyethylene glycol under the action of a catalyst and a stabilizer. The modified polypropylene is polyether acrylate grafted polypropylene; the number average molecular weight of the polyether acrylate is 300-800. The modified polypropylene is prepared by the following steps: polypropylene chips and polyether acrylate are dried, then mixed evenly with an initiator, and melt-grafted to obtain modified polypropylene.

2. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, The areal density of the first and second fiber web layers is independently 8-15 g / m². 2 The fineness of the first fiber is 1.5-2.5 dtex and the length is 30-50 mm; the fineness of the second fiber is 1.0-1.5 dtex and the length is 30-50 mm.

3. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, In the bicomponent fiber with the core-sheath structure, the mass ratio of modified polypropylene to polypropylene is 10-30:90-70.

4. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, In the preparation raw materials for polyether acrylate grafted modified polypropylene, the amount of polyether acrylate is 10-25 wt% of polypropylene.

5. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, The drying process involves drying polypropylene chips and polyether acrylate in a drying oven at 60-80°C for 5-15 hours. The initiator is selected from at least one of ditert-butyl peroxide and dicumyl peroxide, and the amount of initiator used is 0.1-0.2 wt% of the polypropylene chips. The melt grafting is carried out in a torque rheometer at a reaction temperature of 200-220°C and a rotation speed of 70-80 r / min. After the reaction is completed, the product is cooled and granulated.

6. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, The amount of isophthalic acid used is 5-10 wt% of terephthalic acid, the amount of sodium dimethyl isophthalate-5-sulfonate used is 5-15 wt% of terephthalic acid, the molecular weight of polyethylene glycol is 1000-2000, and the amount used is 5-10 wt% of terephthalic acid; the catalyst is antimony trioxide or antimony acetate, and the amount used is 0.03-0.04 wt% of terephthalic acid; the stabilizer is trimethyl phosphate, and the amount used is 0.01-0.02 wt% of terephthalic acid.

7. The sanitary napkin surface layer of the composite structure according to claim 1 is made of spunlace nonwoven fabric, characterized in that, The hydrophilic polyester is prepared by the following steps: (1) Under stirring, terephthalic acid, ethylene glycol and isophthalic acid are added to the pulping kettle. The molar ratio of ethylene glycol to acid is controlled at 1.2-1.

5. Catalyst and stabilizer are added to obtain a uniformly mixed slurry. (2) The slurry is introduced into an esterification reactor with stirring and esterification reaction is carried out at 245-255℃. The column top temperature of the fractionation column is controlled not to exceed 110℃. After esterification, sodium dimethyl isophthalate-5-sulfonate and polyethylene glycol are added. When the reactor temperature rises to 230-250℃, it is introduced into a polycondensation reactor with stirring. (3) Under the action of a vacuum pump, maintain the pressure inside the polycondensation reactor below 50 Pa for the polycondensation reaction, and control the reactor temperature at 270-280℃ for 3-4 hours; (4) Stop stirring after the reaction is complete, release the vacuum with high-purity nitrogen, increase the pressure to 0.2-0.5 MPa, cast the strip from the casting head, cool it with water and then granulate it into hydrophilic polyester chips using a pelletizer.

8. The method for preparing the surface layer of the sanitary napkin with the composite structure according to any one of claims 1-7 using spunlace nonwoven fabric, characterized in that, Includes the following steps: (S1) First fiber web layer: Modified polypropylene chips are fed into an extruder for heating and melting, and then enter the spinning die through a melt filter, melt delivery pipeline, and metering pump. After passing through the spinning die, the chips are evenly distributed to the first spinning assembly. Polypropylene chips are fed into an extruder for heating and melting, filtered, extruded, and then enter the spinning die through a metering pump, where they are evenly distributed to the second spinning assembly. At the outlet, composite spinning is performed, followed by cooling, stretching, winding, and cutting to produce a bicomponent fiber with a core-sheath structure, wherein the sheath layer is modified polypropylene and the core layer is polypropylene. The bicomponent fiber is then opened and combed to form the first fiber web layer. (S2) Second fiber web layer: Hydrophilic polyester chips are fed into an extruder for heating and melting, filtered, extruded, and fed into a spinning die by a metering pump, and evenly distributed to a cross-shaped spinning assembly; composite spinning is performed at the outlet, and after cooling, stretching, winding, and cutting, cross-shaped hydrophilic polyester fibers are produced; the cross-shaped hydrophilic polyester fibers are opened and combed to form the second fiber web layer. (S3) Spunlace nonwoven fabric: The first fiber web layer and the second fiber web layer are combined, reinforced by spunlace, dried and rolled to obtain the composite spunlace nonwoven fabric for the surface layer of sanitary napkins.

9. The method for preparing the surface layer of the sanitary napkin with the composite structure according to claim 8 using spunlace nonwoven fabric, characterized in that, In step (S3), the composite method is selected from either cross-laying or parallel-laying, and the hydroentanglement pressure is 4-10 MPa, with 3-6 hydroentanglement channels.

Images