Magnetic adsorption type replaceable surface synthetic leather and preparation method thereof

Abstract

The present application relates to a kind of magnetic adsorption replaceable surface synthetic leather and its preparation method, belong to synthetic leather technical field.The synthetic leather includes magnetic substrate layer and replaceable magnetic surface layer.Magnetic substrate layer is formed by polymer matrix and magnetic particle with reactive functional group on surface by chemical bonding;Replaceable magnetic surface layer is composed of decorative surface layer and magnetic binding layer containing chemical bonding type magnetic filler.The present application firmly fixes magnetic particle by chemical bonding technology, solves the problem of particle drop-off and magnetic force attenuation caused by traditional physical blending, realizes the lossless, convenient and repeatable replacement between surface layer and substrate layer, and at the same time maintains the soft hand feeling and mechanical properties of material.

Description

Technical Field

[0001] This invention relates to the field of synthetic leather technology, and in particular to a magnetically adsorbed replaceable surface synthetic leather and its preparation method. Background Technology

[0002] Synthetic leather, a polymer composite material widely used in furniture, automotive interiors, bags, and clothing, is increasingly valued for its decorative and functional properties. Traditional synthetic leather products typically have fixed surfaces; changing the texture or color often requires complete replacement, which is costly and environmentally unfriendly. To address this, replaceable decorative films or veneers using adhesives (such as self-adhesive and pressure-sensitive adhesives) have emerged. However, these technologies have significant drawbacks: firstly, adhesives are prone to aging, failure, or residue buildup under long-term use or environmental changes, easily damaging the substrate and difficult to clean during replacement, failing to achieve truly non-destructive and reversible replacement; secondly, repeated pasting leads to a significant decrease in adhesion. Therefore, developing a surface replacement technology that is firmly bonded, easy to separate, and reusable is of great importance.

[0003] Magnetic adsorption offers an ideal approach for achieving non-destructive bonding and separation. Existing technologies have attempted to introduce magnetic materials (such as ferrite and NdFeB powder) into polymer substrates (such as rubber and plastics) through physical blending to prepare a magnetic matrix, which is then bonded to a decorative layer containing ferromagnetic materials via magnetic adsorption. However, this physical blending method has inherent drawbacks: firstly, inorganic magnetic particles have poor compatibility with organic polymer matrices, resulting in weak interfacial bonding. During processing and use, magnetic particles are prone to migration and detachment, leading to magnetic attenuation, surface contamination, and affecting the material's mechanical properties. Secondly, to ensure sufficient adsorption force, a high proportion of magnetic filler is often required, which increases the composite material's hardness and reduces its flexibility, resulting in a loss of the soft touch and flexural strength expected of synthetic leather, making it difficult to meet the comfort requirements of high-end applications. Furthermore, the uniformity and long-term stability of adsorption force in simple physical adsorption structures are also difficult to guarantee.

[0004] Therefore, existing technologies lack an integrated solution that can provide durable and stable magnetic adsorption force, enable convenient and non-destructive replacement, and maintain the excellent mechanical properties and comfortable feel of synthetic leather materials. Fundamentally enhancing the bonding between magnetic particles and the polymer matrix, optimizing the overall material performance while ensuring long-term magnetic functionality, and constructing a reliable, replaceable interface structure have become pressing technical problems to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a magnetically adsorbed replaceable surface synthetic leather and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A magnetically adsorbent replaceable surface synthetic leather includes: a magnetic substrate layer and a replaceable magnetic surface layer.

[0008] Magnetic substrate layer: composed of chemically modified magnetic polymer composite material, which is a polymer matrix in which magnetic particles with reactive functional groups on the surface are composited in situ. The magnetic particles form chemical bonds with the molecular chains of the polymer matrix through the functional groups on their surface.

[0009] Replaceable magnetic surface layer: including a decorative surface layer and a magnetic bonding layer. The magnetic bonding layer is composed of an adhesive containing chemically bonded magnetic fillers. The chemically bonded magnetic fillers are magnetic particles with active groups that can react with the adhesive resin and whose surfaces have been modified by coupling agents.

[0010] Preferably, the polymer matrix is ​​at least one of polyurethane (PU), polyvinyl chloride (PVC), polyacrylate, and rubber elastomer.

[0011] Preferably, the magnetic particles with reactive functional groups on their surface are at least one of the nano (20-100 nm) or micro (1-10 μm) particles of permanent magnet materials such as Fe3O4, γ-Fe2O3, iron-cobalt alloy, or NdFeB; and their surface functional groups are derived from at least one of silane coupling agents (such as KH-550, KH-560, KH-570), titanate coupling agents, and phosphate coupling agents.

[0012] Preferably, the adhesive in the magnetic bonding layer is at least one of reactive polyurethane adhesive, epoxy resin adhesive, acrylate adhesive, or silicone rubber.

[0013] Preferably, the chemically bonded magnetic filler is added in the magnetic polymer composite material or magnetic bonding layer adhesive at an amount of 5-40 wt%.

[0014] A method for preparing magnetically adsorbent replaceable surface synthetic leather includes the following steps:

[0015] S1. Preparation of chemically bonded magnetic fillers: Magnetic particles are added to a 1-3 mol / L dilute hydrochloric acid solution and ultrasonically dispersed at 200-400 W for 30-60 min. Solid-liquid separation is performed using an external magnetic field (electromagnetic separation device). The supernatant is discarded. The magnetic solid is washed alternately with deionized water and ethanol 3-5 times until the washing solution is neutral. The washed magnetic particles are dried in a vacuum oven at 60-80℃ for 6-12 h. A silane coupling agent is added to a mixed solvent of ethanol / water, and the pH is adjusted to 4-5 with acetic acid. The mixture is stirred at 300-500 rpm for 20-40 min. The material is fully pre-hydrolyzed to form silanol. The activated magnetic particles are added to the hydrolysate and stirred at 300-500 rpm for 20-40 min to ensure uniform particle dispersion. The reaction system is heated to 70-85℃ and stirred continuously for 4-8 h under nitrogen protection. After the reaction is completed, the system is cooled to room temperature and solid-liquid separation is performed by applying an external magnetic field. The solid is washed repeatedly with ethanol 4-6 times to remove the physically adsorbed coupling agent and its byproducts. The washed solid product is dried in a vacuum oven at 60-80℃ for 12-24 h and then ground to obtain a chemically bonded magnetic filler.

[0016] S2. Preparation of the magnetic substrate layer: Weigh 100 parts by weight of polyether polyol, 5-40 parts by weight of chemically bonded magnetic filler (Fe3O4 magnetic filler with surface-grafted amino groups, Fe3O4@NH2), 1-4 parts by weight of chain extender (1,4-butanediol), 1-3 parts by weight of foaming agent (water), 0.1-0.5 parts by weight of amine catalyst (A33), 0.01-0.1 parts by weight of tin catalyst (T-9), 0.5-2 parts by weight of foam stabilizer (organosilicon surfactant), and 45-60 parts by weight of isocyanate. Add the polyether polyol, chemically bonded magnetic filler, and chain extender to a reaction vessel. Stir and degas and dehydrate at 800-1500 rpm for 1-2 hours at 60-70℃ and a vacuum of -0.095 MPa to form a uniform, high-viscosity pre-dispersion. During this process, the amino groups on the surface of the magnetic filler begin to bond with the polyol. The trace amounts of moisture or hydroxyl groups in the system undergo initial interactions. The system is cooled to 25-35℃, and foaming agent, catalyst, and foam leveling agent are added sequentially. The mixture is stirred at 300-600 rpm until homogeneous. Then, isocyanate is added and mixed at 2000-5000 rpm for 8-15 seconds. The mixture is immediately poured into a mold preheated to 40-50℃. The material foams and gels freely in the mold. It is cured in a drying tunnel at 100-120℃ for 5-15 minutes. After demolding, it is left at room temperature for 24-72 hours to complete the curing process, resulting in a flexible magnetic polyurethane foam substrate layer. During this process, the amino groups on the surface of the magnetic filler react with the isocyanate components to form strong chemical bonds (urea bonds), chemically anchoring the filler in the PU three-dimensional network. The magnetic substrate layer is obtained after curing through coating, casting, or foaming processes.

[0017] S3. Preparation of a replaceable magnetic surface layer:

[0018] a) Preparation of the decorative surface layer: Weigh 50-70 parts of aliphatic polyester resin (50% solid content), 100 parts of DMF solvent, 0.3-1.0 parts of BYK series wetting and dispersing agent, 0.1-0.5 parts of polyether-modified polysiloxane leveling agent, 0.1-0.5 parts of modified silicone defoamer, and 10-20 parts of rutile titanium dioxide pigment paste (40% pigment solid content). Stir the aliphatic polyester resin and DMF solvent at 800-1000 rpm for 20-30 minutes. Add the wetting and dispersing agent, leveling agent, and defoamer, and stir for 8-12 minutes. Add titanium dioxide powder paste, stir at 1200-1500 rpm for 30-45 minutes, degas in a vacuum degassing machine for 15-30 minutes, filter with a 100-200 mesh filter to remove impurities and gel particles, and make a surface layer paste. Apply the paste to PET release paper with a scraper, and evaporate DMF by gradient heating in an oven to form a patterned PU leather layer with a thickness of about 0.1-0.3 mm. Apply an adhesive layer paste to the leather layer and bond it to the base fabric (non-woven fabric). After solidification, washing, and drying, peel it off from the release paper to obtain a decorative surface layer with a base fabric.

[0019] b) Preparation and lamination of the magnetic bonding layer: Weigh 100 parts epoxy resin (E-51), 20-40 parts chemically bonded magnetic filler (NdFeB@EP with surface-grafted epoxy groups), 5-15 parts diluent (AGE phenyl glycidyl ether), 0.5-1 parts defoamer (modified silicone), 80-120 parts polyamide curing agent 650, and 1-5 parts accelerator DMP-30. Stir the epoxy resin, chemically bonded magnetic filler, diluent, and defoamer at 500-800 rpm for 5-10 minutes for premixing, then increase the temperature to 1200-1500 rpm. Stir at rpm for 30-45 minutes, add polyamide curing agent and accelerator, and stir at 300-500 rpm for 3-5 minutes until homogeneous. Degas under vacuum for 5-10 minutes. Using a scraper, evenly coat the back of the prepared decorative surface layer (i.e., the unpatterned base fabric) with the mixed magnetic adhesive. Control the coating wet weight to 80-150 g / m². 2 The corresponding dry film thickness is about 50-100μm. Place the coated material in an oven at 80-100℃ and cure for 30-60 minutes. During the curing process, the epoxy resin and polyamide curing agent undergo a cross-linking reaction. At the same time, the epoxy groups on the surface of the filler (from KH-560 modification) also participate in the reaction and are chemically bonded to the cross-linking network of the adhesive. After curing, cool to room temperature to obtain a replaceable magnetic surface layer.

[0020] S4. Finished Product Lamination: Cut the prepared magnetic substrate layer and replaceable magnetic surface layer (magnetic bonding layer facing outwards) to the required sizes. Gently contact and align the magnetic bonding layer side of the replaceable surface layer with the magnetic surface of the substrate layer. Due to the magnetic force generated by the chemically bonded magnetic filler inside the materials on both sides, the two will automatically, smoothly and firmly adhere together without additional pressure or glue. Gently press the edges to remove any trapped air. When the surface needs to be replaced, carefully peel it off from one corner to separate. The replaceable surface layer leaves no residue, the substrate layer surface is clean, and a new surface layer can be immediately adsorbed.

[0021] Preferably, the mass ratio of magnetic particles to silane coupling agent in S1 is 20:1-2.

[0022] Preferably, the polyether polyol in S2 is a polyether polyol with a functionality of 2-3 and a hydroxyl value of 50-110 mg KOH / g.

[0023] Preferably, the isocyanate in S2 is a combination of MDI-50 and TDI-80, with a mass ratio of MDI-50:TDI-80 = 0.8-1:0.8-1.

[0024] Preferably, the oven gradient heating process in S3(a) is as follows: the first stage is 75-85℃ for 25-30s, the second stage is 115-125℃ for 40-50s, and the third stage is 95-105℃ for 15-20s.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. Through the "chemically bonded magnetic filler" technology, reactive functional groups (such as -NH2 and epoxy groups) are grafted onto the surface of magnetic particles. During the curing process of the substrate layer and the surface bonding layer, these functional groups undergo in-situ chemical reactions with the isocyanate of polyurethane and the curing agent of epoxy resin, forming covalent bonds (such as urea bonds and ether bonds). This "chemically anchors" the magnetic particles in the three-dimensional polymer network, fundamentally solving the problem of magnetic particle detachment. This ensures the long-term stability and consistency of the magnetic force throughout the product's entire life cycle, laying a solid foundation for the reliability of the "replaceable" function.

[0027] 2. A creative double-layer magnetic adsorption structure of "magnetic substrate layer + replaceable magnetic surface layer" is designed. Both layers contain chemically fixed magnetic fillers, which generate uniform and strong adsorption force through the attraction of opposite poles. No glue is required. It can be automatically adsorbed and flattened with just a light touch after alignment. The construction efficiency is extremely high. When replacing, it can be easily peeled off from one corner. The surface layer is completely peeled off, and the surface of the substrate layer is clean and without residue. The new surface layer can be adsorbed immediately, realizing true non-destructive and reusable replacement.

[0028] 3. By using low-hydroxyl-value polyether polyols and precisely controlling the amount and ratio of chain extenders and isocyanates, flexible polyurethane foam was successfully prepared. The chemically bonded magnetic filler, as part of the crosslinking points, enhances the network strength rather than simply acting as an inert filler. Using polyamide with good flexibility as an epoxy resin curing agent and controlling the amount of magnetic filler added, the final product provides sufficient magnetic adsorption and substrate support while maintaining the soft touch, good resilience and bending resistance of synthetic leather, thus improving user comfort.

[0029] 4. Inside the replaceable surface layer, the decorative surface layer and the magnetic bonding layer are coated and bonded together firmly. Most importantly, the adhesive (epoxy resin, etc.) of the magnetic bonding layer itself forms a three-dimensional chemical cross-linking network with the chemically bonded magnetic filler during curing, making the layer a cohesive and peel-resistant whole. This ensures the durability of the replaceable surface layer itself and makes it less prone to damage from the inside during repeated peeling and re-applying. At the same time, the uniform magnetic adsorption makes the bond between the two layers tight and the stress distribution uniform. Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments, comparative examples and performance test results. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0031] Preparation Example 1: Preparation method of Fe3O4@NH2 magnetic filler:

[0032] 100g of Fe3O4 magnetic particles with an average particle size of 100nm were added to 300ml of 2mol / L dilute hydrochloric acid solution and ultrasonically dispersed at 300W for 45min. After separation by an external magnetic field, the supernatant was discarded, and the particles were washed 4 times alternately with deionized water and ethanol. After vacuum drying at 70℃ for 10h, activated magnetic particles were obtained. 5g of silane coupling agent KH-550 (γ-aminopropyltriethoxysilane) was added to 100g of ethanol / water mixed solvent (volume ratio 9:1). The pH was adjusted to 4.5 with acetic acid, and the particles were pre-hydrolyzed by stirring at 400rpm for 30min. 100g of activated Fe3O4 magnetic particles were added to the hydrolysate (mass ratio 20:1), and dispersed by stirring at 400rpm for 30min. The temperature was raised to 80℃, and the reaction was stirred for 6h under nitrogen protection. After cooling, the particles were separated by an external magnetic field, washed 5 times with ethanol, and vacuum dried at 70℃ for 18h. After grinding, chemically bonded Fe3O4@NH2 magnetic filler with amino groups grafted on the surface was obtained.

[0033] Preparation Example 2: Preparation method of NdFeB@EP packing:

[0034] Take 100g of NdFeB magnetic particles with an average particle size of 10μm, add 500ml of 0.8mol / L dilute hydrochloric acid solution, sonicate at 250W for 30min, separate under an external magnetic field, discard the supernatant, wash 4 times alternately with deionized water and ethanol, and vacuum dry at 60℃ for 8h to obtain activated magnetic particles. Take 5g of silane coupling agent KH-560 (γ-glycidoxypropyltrimethoxysilane), add 100g of ethanol / water mixed solvent (volume ratio 9:1). 1) Adjust the pH to 4.5 with acetic acid, stir at 400 rpm for 30 min for pre-hydrolysis, add 100 g of activated NdFeB magnetic particles to the hydrolysate (mass ratio 20:1), stir at 400 rpm for 30 min for dispersion, heat to 75 °C, stir and react for 6 h under nitrogen protection, cool, separate with an external magnetic field, wash 5 times with ethanol, vacuum dry at 70 °C for 18 h, grind to obtain chemically bonded NdFeB@EP magnetic filler with surface-grafted epoxy groups.

[0035] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 1 is that the mass ratio of Fe3O4 magnetic particles to silane coupling agent KH-550 is 20:0.5 (far lower than the preferred range of 20:1-2).

[0036] Example 1: A method for preparing magnetically adsorbent replaceable surface synthetic leather, comprising the following steps:

[0037] S1. Preparation of chemically bonded magnetic fillers: Fe3O4@NH2 magnetic fillers prepared in Preparation Example 1 were used;

[0038] S2. Preparation of the magnetic substrate layer: Weigh 100 parts of polyether polyol (functionality 3, hydroxyl value 56 mg KOH / g), 5 parts of Fe3O4@NH2 magnetic filler, 2 parts of 1,4-butanediol (chain extender), 1.5 parts of water (foaming agent), 0.2 parts of amine catalyst A33, 0.05 parts of tin catalyst T-9, 1 part of organosilicon foam stabilizer, and isocyanate (MDI-50:TDI-80 = 52 parts of a 1:1 mixture were prepared by adding polyether polyol, magnetic filler, and chain extender to a reactor and stirring at 1200 rpm for 1.5 h at 65 °C and -0.095 MPa. The mixture was then cooled to 30 °C and water, A33, T-9, and foaming agent were added sequentially. The mixture was stirred at 500 rpm for 1 min and then isocyanate was added. The mixture was stirred at 3500 rpm for 10 s and then immediately poured into a 45 °C mold. After free foaming and gelling, the mixture was placed in a 110 °C oven for 10 min to mature. The mixture was then demolded and matured at room temperature for 48 h to obtain a flexible magnetic polyurethane foam substrate layer.

[0039] S3. Preparation of a replaceable magnetic surface layer:

[0040] (a) Preparation of decorative surface layer: Weigh 60 parts of aliphatic polyester resin (50% solid content), 100 parts of DMF, 0.5 parts of wetting and dispersing agent BYK-163, 0.2 parts of leveling agent BYK-333, 0.2 parts of defoamer BYK-025, and 15 parts of titanium dioxide pigment paste (40% solid content). Mix the resin and DMF for 25 min, add the additives and stir for 10 min, add the pigment paste, stir at 1400 rpm for 40 min, vacuum degas for 20 min, filter through a 150-mesh filter, coat it onto PET release paper, and dry it in a three-zone oven (80℃ / 30s, 120℃ / 45s, 100℃ / 18s) to form a 0.15mm thick PU skin layer. Coat it with adhesive layer paste, bond it to non-woven fabric, and peel it off after coagulation bath, washing, drying, and obtaining the decorative surface layer.

[0041] (b) Preparation and lamination of the magnetic bonding layer: Weigh 100 parts of epoxy resin E-51, 20 parts of chemically bonded NdFeB@EP filler (using the NdFeB@EP magnetic filler prepared in Preparation Example 2), 8 parts of diluent AGE, 0.5 parts of defoamer, 90 parts of polyamide curing agent 650, and 2 parts of accelerator DMP-30. Premix the epoxy resin, magnetic filler, diluent, and defoamer at 700 rpm for 8 min, then stir at 1300 rpm for 40 min. Add the curing agent and accelerator, stir at 400 rpm for 4 min until homogeneous, and degas under vacuum for 8 min. Apply the adhesive to the back of the decorative surface layer with a moisture content of 100 g / m². 2 Place it in a 90℃ oven to cure for 45 minutes, and after cooling, you will get a replaceable magnetic surface layer.

[0042] S4. Finished Product Lamination: Cut the magnetic substrate layer and the replaceable magnetic surface layer, align the magnetic surfaces and touch them lightly, they will automatically adhere and bond, and the edges will be gently pressed to release air.

[0043] Example 2: A method for preparing magnetically adsorbent replaceable surface synthetic leather, comprising the following steps:

[0044] S1. Preparation of chemically bonded magnetic fillers: Fe3O4@NH2 magnetic fillers prepared in Preparation Example 1 were used;

[0045] S2. Preparation of the magnetic substrate layer: Weigh 100 parts of polyether polyol (functionality 3, hydroxyl value 56 mg KOH / g), 20 parts of Fe3O4@NH2 magnetic filler, 3 parts of 1,4-butanediol (chain extender), 2 parts of water (foaming agent), 0.3 parts of amine catalyst A33, 0.08 parts of tin catalyst T-9, 1.5 parts of organosilicon foam stabilizer, and isocyanate (MDI-50:TDI-80). =0.9:1) 58 parts, polyether polyol, magnetic filler and chain extender were added to the reactor, and the mixture was stirred at 1200 rpm for 1.5 h at 65℃ and -0.095 MPa. The temperature was then lowered to 30℃, and water, A33, T-9 and foaming agent were added in sequence. The mixture was stirred at 500 rpm for 1 min, and isocyanate was added. The mixture was stirred at 3500 rpm for 10 s. The slurry was immediately poured into a mold at 45℃. After free foaming and gelling, the mixture was placed in a 110℃ oven for 10 min to mature. The mixture was then demolded and matured at room temperature for 48 h to obtain a flexible magnetic polyurethane foam substrate layer.

[0046] S3. Preparation of a replaceable magnetic surface layer:

[0047] (a) Preparation of decorative surface layer: Weigh 60 parts of aliphatic polyester resin (50% solid content), 100 parts of DMF, 0.5 parts of wetting and dispersing agent BYK-163, 0.2 parts of leveling agent BYK-333, 0.2 parts of defoamer BYK-025, and 15 parts of titanium dioxide pigment paste (40% solid content). Mix the resin and DMF for 25 min, add the additives and stir for 10 min, add the pigment paste, stir at 1400 rpm for 40 min, vacuum degas for 20 min, filter through a 150-mesh filter, coat it onto PET release paper, and dry it in a three-zone oven (80℃ / 30s, 120℃ / 45s, 100℃ / 18s) to form a 0.15mm thick PU skin layer. Coat it with adhesive layer paste, bond it to non-woven fabric, and peel it off after coagulation bath, washing, drying, and obtaining the decorative surface layer.

[0048] (b) Preparation and lamination of the magnetic bonding layer: Weigh 100 parts of epoxy resin E-51, 30 parts of chemically bonded NdFeB@EP filler (using the NdFeB@EP magnetic filler prepared in Preparation Example 2), 12 parts of diluent AGE, 0.8 parts of defoamer, 110 parts of polyamide curing agent 650, and 3 parts of accelerator DMP-30. Premix the epoxy resin, magnetic filler, diluent, and defoamer at 700 rpm for 8 min, then stir at 1300 rpm for 40 min. Add the curing agent and accelerator, stir at 400 rpm for 4 min until homogeneous, and degas under vacuum for 8 min. Apply the adhesive to the back of the decorative surface layer with a moisture content of 100 g / m². 2 Place it in a 90℃ oven to cure for 45 minutes, and after cooling, you will get a replaceable magnetic surface layer.

[0049] S4. Finished Product Lamination: Cut the magnetic substrate layer and the replaceable magnetic surface layer, align the magnetic surfaces and touch them lightly, they will automatically adhere and bond, and the edges will be gently pressed to release air.

[0050] Example 3: A method for preparing magnetically adsorbent replaceable surface synthetic leather, comprising the following steps:

[0051] S1. Preparation of chemically bonded magnetic fillers: Fe3O4@NH2 magnetic fillers prepared in Preparation Example 1 were used;

[0052] S2. Preparation of the magnetic substrate layer: Weigh 100 parts of polyether polyol (functionality 3, hydroxyl value 56 mg KOH / g), 40 parts of Fe3O4@NH2 magnetic filler, 4 parts of 1,4-butanediol (chain extender), 2.5 parts of water (foaming agent), 0.5 parts of amine catalyst A33, 0.1 parts of tin catalyst T-9, 1.5 parts of organosilicon foam stabilizer, and isocyanate (MDI-50:TDI-80 = 62 parts of a 1:0.9 mixture were prepared by adding polyether polyol, magnetic filler, and chain extender to a reactor and stirring at 1200 rpm for 1.5 h at 65 °C and -0.095 MPa. The mixture was then cooled to 30 °C, and water, A33, T-9, and foaming agent were added sequentially. The mixture was stirred at 500 rpm for 1 min, and isocyanate was added. The mixture was stirred at 3500 rpm for 10 s. The slurry was immediately poured into a 45 °C mold and allowed to foam and gel freely. The mixture was then placed in a 110 °C oven for 10 min of curing. The mixture was then demolded and cured at room temperature for 48 h to obtain a flexible magnetic polyurethane foam substrate layer.

[0053] S3. Preparation of a replaceable magnetic surface layer:

[0054] (a) Preparation of decorative surface layer: Weigh 60 parts of aliphatic polyester resin (50% solid content), 100 parts of DMF, 0.5 parts of wetting and dispersing agent BYK-163, 0.2 parts of leveling agent BYK-333, 0.2 parts of defoamer BYK-025, and 15 parts of titanium dioxide pigment paste (40% solid content). Mix the resin and DMF for 25 min, add the additives and stir for 10 min, add the pigment paste, stir at 1400 rpm for 40 min, vacuum degas for 20 min, filter through a 150-mesh filter, coat it onto PET release paper, and dry it in a three-zone oven (80℃ / 30s, 120℃ / 45s, 100℃ / 18s) to form a 0.15mm thick PU skin layer. Coat it with adhesive layer paste, bond it to non-woven fabric, and peel it off after coagulation bath, washing, drying, and obtaining the decorative surface layer.

[0055] (b) Preparation and lamination of the magnetic bonding layer: Weigh 100 parts of epoxy resin E-51, 40 parts of chemically bonded NdFeB@EP filler (using the NdFeB@EP magnetic filler prepared in Preparation Example 2), 15 parts of diluent AGE, 1 part of defoamer, 120 parts of polyamide curing agent 650, and 5 parts of accelerator DMP-30. Premix the epoxy resin, magnetic filler, diluent, and defoamer at 700 rpm for 8 min, then stir at 1300 rpm for 40 min. Add the curing agent and accelerator, stir at 400 rpm for 4 min until homogeneous, and degas under vacuum for 8 min. Apply the adhesive to the back of the decorative surface layer with a moisture content of 100 g / m². 2 Place it in a 90℃ oven to cure for 45 minutes, and after cooling, you will get a replaceable magnetic surface layer.

[0056] S4. Finished Product Lamination: Cut the magnetic substrate layer and the replaceable magnetic surface layer, align the magnetic surfaces and touch them lightly, they will automatically adhere and bond, and the edges will be gently pressed to release air.

[0057] Comparative Example 1: Based on Example 2, the difference is that Fe3O4 and NdFeB magnetic particles without silane coupling agent modification were used, otherwise the same as in Example 2.

[0058] Comparative Example 2: Based on Example 2, the difference is that the Fe3O4@NH2 filler from Comparative Preparation Example 1 was used, and the rest is the same as in Example 2.

[0059] Comparative Example 3: Based on Example 2, the difference is that in step S2, NdFeB@EP filler with surface-grafted epoxy groups is used instead of Fe3O4@NH2 filler, and the rest is the same as in Example 2.

[0060] Comparative Example 4: Based on Example 2, the difference is that in step S2, the isocyanate is used in a mass ratio of MDI-50:TDI-80 = 2:1, which is outside the preferred range (0.8-1:0.8-1), and the rest is the same as in Example 2.

[0061] Comparative Example 5: Based on Example 2, the difference is that in step S3, the magnetic bonding layer uses Fe3O4@NH2 filler with surface-grafted amino groups instead of NdFeB@EP filler, and the rest is the same as in Example 2.

[0062] Comparative Example 6: Based on Example 2, the difference is that in step S3(b), after the magnetic bonding layer is coated, the curing conditions are changed to curing at 60°C for 20 minutes, and the rest is the same as in Example 2.

[0063] Performance testing:

[0064] 1. Surface magnetic induction intensity: Using a gaussmeter, 5 points were randomly selected on the surface of the finished product after the substrate layer and the surface layer were bonded together, and the average value was taken. The unit is mT (millitalas), which reflects the magnitude of the initial magnetic adsorption force. The experimental results are shown in Table 1.

[0065] 2. Magnetic retention rate: After soaking the finished product in water at 40℃ for 24 hours, remove it, wipe off the surface moisture, and immediately measure the surface magnetic induction intensity. Calculate its percentage relative to the initial value to evaluate the water resistance / aging resistance of the magnetic force. The experimental results are shown in Table 1.

[0066] 3. Peel strength: In accordance with GB / T 2792-2014 standard, a universal testing machine was used to perform 180° peeling at a speed of 300 mm / min. The average force required to peel the replaceable surface layer from the substrate layer was measured in N / 25 mm to evaluate the strength of the magnetic adsorption bond. The experimental results are shown in Table 1.

[0067] 4. Tensile strength and elongation at break: Tested according to GB / T 6344-2008, dumbbell-shaped specimens. The experimental results are shown in Table 1.

[0068] 5. Replaceability and Interface Cleanliness: Qualitative evaluation, recording whether there is visible filler detachment, adhesive residue or damage on the surface of the substrate layer and the magnetic bonding layer of the surface layer after the first peeling. The experimental results are shown in Table 2.

[0069] 6. Surface layer abrasion resistance: A cotton ball soaked in 95% ethanol was used to wipe the surface 100 times with a pressure of 1 kg weight. The results were observed to see if there was any discoloration, coating damage or magnetic layer exposure. The experimental results are shown in Table 2.

[0070] Table 1. Performance Test Results

[0071]

[0072] Table 2. Performance Test Results

[0073]

[0074] Data Analysis:

[0075] 1. Magnetic stability analysis: The initial surface magnetic induction intensity of Examples 1-3 remained at a high level (44.3-48.2 mT), and after immersion in water at 40°C for 24 hours, the magnetic retention rate was as high as 97% or more. This indicates that anchoring the magnetic filler in the polymer network through chemical bonding technology can effectively prevent the migration, corrosion and detachment of the filler in a humid environment, ensuring the long-term stability of the magnetic force. In contrast, the magnetic retention rate of Comparative Example 1 (unmodified filler) dropped sharply to 85.2%, proving that physical blending cannot solve the filler detachment problem; the retention rate of Comparative Example 2 (insufficient silane content) was also only 90.2%, indicating that sufficient surface modification is crucial for durability.

[0076] 2. Analysis of Interface Bonding Performance and Replaceability: The peel strength of Examples 1-3 ranged from 7.1 to 8.2 N / 25 mm, achieving an ideal balance between "firm adsorption" and "easy peeling". All examples showed a clean interface without residue after peeling, perfectly realizing the core function of non-destructive replacement. In contrast, the peel strength of the comparative examples was significantly lower (1.5-3.9 N / 25 mm), and all were accompanied by varying degrees of interface failure: Comparative Examples 1 and 2 showed filler detachment; Comparative Example 5 (incorrect filler type) showed cohesive failure of the adhesive layer; and Comparative Example 6 (insufficient curing) showed adhesive layer residue. These results fully demonstrate that only when the magnetic filler is firmly anchored in its corresponding polymer matrix through appropriate chemical bonding (such as -NH2 and isocyanate, epoxy group and curing agent) can a stable, reliable and reversible magnetic adsorption interface be formed.

[0077] 3. Analysis of material mechanical properties and overall durability: The tensile strength (210-250 kPa) and elongation at break (200-220%) of Examples 1-3 show that the present invention, while introducing magnetic functionality, effectively maintains the flexibility and mechanical properties of the polyurethane foam substrate. This is due to the chemically bonded filler acting as crosslinking points to enhance the network structure, rather than destroying it like inert fillers. The mechanical properties, especially the elongation at break, of Comparative Example 3 (incorrect filler used in the substrate layer) and Comparative Example 4 (inappropriate isocyanate ratio) deteriorated significantly, indicating that the chemical compatibility of the filler and the substrate molding process are crucial to the user comfort of the final product. The surface layer abrasion resistance test further shows that the magnetic bonding layer of the examples exhibits excellent mechanical strength due to its fully cured three-dimensional crosslinked network.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A magnetically adsorbent replaceable synthetic leather, characterized in that, include: The system comprises a magnetic substrate layer and a replaceable magnetic surface layer. The magnetic substrate layer is composed of a magnetic polymer composite material, in which magnetic particles with reactive functional groups on their surface are in situ composited within a polymer matrix. These magnetic particles form chemical bonds with the molecular chains of the polymer matrix through their reactive functional groups. The replaceable magnetic surface layer includes a decorative surface layer and a magnetic bonding layer. The magnetic bonding layer is composed of an adhesive resin containing chemically bonded magnetic fillers. These chemically bonded magnetic fillers are magnetic particles with surface-modified reactive functional groups capable of reacting with the adhesive resin. The magnetic substrate layer and the replaceable magnetic surface layer are mutually attracted and bonded by the magnetic force generated by the magnetic particles they contain. The magnetic particles are at least one of iron(II,III) oxide, γ-iron(II,III) oxide, iron-cobalt alloy, or neodymium-iron-boron; the reactive functional groups are derived from silane coupling agents; and the mass ratio of the magnetic particles to the silane coupling agent is 20:1-2.

2. The magnetically adsorbent replaceable surface synthetic leather according to claim 1, characterized in that, The polymer matrix is ​​at least one of polyurethane, polyvinyl chloride, polyacrylate, and rubber elastomer.

3. The magnetically adsorbent replaceable surface synthetic leather according to claim 1, characterized in that, The adhesive resin in the magnetic bonding layer is at least one of reactive polyurethane adhesive, epoxy resin adhesive, acrylate adhesive, or silicone rubber.

4. A method for preparing a magnetically adsorbent replaceable surface synthetic leather as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of chemically bonded magnetic filler: Magnetic particles are acid-washed and activated, and then reacted with a pre-hydrolyzed silane coupling agent to graft reactive functional groups onto the surface of the magnetic particles. After washing and drying, chemically bonded magnetic filler is obtained. S2. Preparation of magnetic substrate layer: The polymer matrix raw material is mixed with the chemically bonded magnetic filler obtained in S1, and the mixture is stirred at high speed, foamed, cured and shaped to obtain a flexible magnetic substrate layer. S3. Preparation of a replaceable magnetic surface layer: (a) The surface slurry is coated onto the release paper and dried to form a polyurethane skin. The skin is then bonded to the base fabric through an adhesive layer. After solidification, washing, and drying, the skin is peeled off from the release paper to obtain a decorative surface layer with a base fabric. (b) The adhesive resin, the chemically bonded magnetic filler obtained from S1, and the curing agent are mixed evenly to form a magnetic adhesive, which is then coated on the back of the decorative surface layer. After curing, a magnetic bonding layer is formed, resulting in a replaceable magnetic surface layer. S4. Composite of finished product: The magnetic substrate layer obtained in S2 and the magnetic bonding layer of the replaceable magnetic surface layer obtained in S3 are placed face to face and composited by magnetic adsorption.

5. A method for preparing a magnetically adsorbent replaceable surface synthetic leather according to claim 4, characterized in that, The polymer matrix in S2 is polyurethane, and the raw materials for preparation include polyether polyol, isocyanate, chain extender, foaming agent, catalyst, and foam leveling agent; the polyether polyol is a polyether polyol with a functionality of 2-3 and a hydroxyl value of 50-110 mg KOH / g; the isocyanate is a mixture of MDI-50 and TDI-80 with a mass ratio of 0.8-1:0.8-1.

6. The method for preparing a magnetically adsorbent replaceable surface synthetic leather according to claim 4, characterized in that, The adhesive resin in S3(b) is epoxy resin, and the curing temperature is 80-100℃, and the curing time is 30-60min.

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