Flexible film special for handwriting board and preparation method of flexible film

Abstract

The invention relates to the technical field of films, in particular to a flexible film special for a handwriting board and a preparation method of the flexible film. The flexible film is obtained by coating a release film with coating slurry and carrying out thermocuring, wherein the coating slurry contains modified polyurethane, a flatting agent, a defoaming agent and ethyl acetate. According to the modified polyurethane, polycarbonate diol, isophorone diisocyanate and other raw materials are subjected to a reaction, and a nano particle chain extender containing disulfide bonds is added. The nano particle chain extender containing disulfide bonds is prepared by modifying nano silicon dioxide and grafting cystamine dihydrochloride and diamino polyethylene glycol. Through nanoparticle surface modification and dynamic disulfide bond network construction, molecular-level coupling of a rigid reinforced phase and a flexible substrate, inhibition of nanoparticle aggregation and balance of strength and toughness are realized, the dynamic disulfide bond network can self-repair microcracks, and a high-quality special flexible film solution is provided for a high-performance handwriting board.

Description

Technical Field

[0001] The present invention relates to the field of film technology, and in particular to a flexible film dedicated to a handwriting board and a preparation method thereof. Background Art

[0002] With the rapid development of flexible electronic devices, handwriting tablets, as core components of human-computer interaction, have placed higher demands on the performance of their surface flexible films. Ideal flexible films must meet the following requirements: (1) maintain structural integrity under dynamic deformations such as frequent bending and folding; (2) have sufficient surface hardness to resist scratches and wear from the stylus tip; (3) have the ability to self-repair performance degradation caused by microcracks or scratches during long-term use; and (4) have a balance between high tensile strength and moderate elongation at break to adapt to complex stress environments.

[0003] While traditional polyurethane materials offer excellent flexibility and processability, their mechanical strength, scratch resistance, and durability struggle to meet the demands of high-performance tablets. Prior art often enhances material rigidity by adding inorganic nanoparticles (such as nanosilica), but physical blending can easily lead to nanoparticle agglomeration, triggering stress concentration and, in turn, reducing flexibility and interfacial bonding strength. Furthermore, while conventional chemical cross-linking networks can enhance mechanical properties, excessive cross-linking can lead to material embrittlement and irreversible damage during dynamic deformation.

[0004] In recent years, the introduction of dynamic covalent bonds (such as disulfide bonds) has provided new ideas for material self-repair. However, existing research has mostly focused on optimizing the self-repair performance of the bulk, ignoring the system design of the synergistic effect of the nano-reinforced phase and the dynamic network. For example, directly doping disulfide bond compounds may affect the mechanical properties due to uneven cross-linking density; simply using physically modified nanoparticles will make it difficult to achieve a balance between stress transfer efficiency and dynamic bond reversibility. In addition, the contradiction between the special requirements of the surface hardness of the handwriting tablet usage scenario (needing to resist high-frequency friction of the stylus tip) and the flexibility of the material has not yet been effectively resolved. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a flexible film for handwriting tablets and a preparation method thereof, so as to provide a flexible film for handwriting tablets that has high mechanical strength, excellent dynamic flexibility, scratch resistance and self-repairing function.

[0006] Based on the above purpose, the present invention provides a flexible film dedicated to a handwriting tablet, which is obtained by coating a coating slurry on a release film and then thermally curing it.

[0007] Furthermore, the coating slurry comprises the following components in parts by weight: 40-60 parts of modified polyurethane, 0.3-1 parts of leveling agent, 0.1-0.5 parts of defoaming agent and 150-250 parts of ethyl acetate.

[0008] Preferably, the leveling agent is leveling agent BYK-333.

[0009] Preferably, the defoamer is defoamer BYK-055.

[0010] Furthermore, the preparation steps of the modified polyurethane are as follows: after drying the polycarbonate diol, adding isophorone diisocyanate under a nitrogen atmosphere, stirring and reacting for 1-3 hours, cooling to 55-65°C, adding dibutyltin dilaurate and N,N-dimethylacetamide, stirring and reacting for 25-35 minutes, then adding a disulfide bond-containing nanoparticle chain extender, stirring and reacting for 2-4 hours, cooling to room temperature, and rotary evaporation to obtain the modified polyurethane.

[0011] Preferably, the weight average molecular weight of the polycarbonate diol is 1500-2500.

[0012] Preferably, the weight ratio of the polycarbonate diol, isophorone diisocyanate, dibutyltin dilaurate, N,N-dimethylacetamide and disulfide bond-containing nanoparticle chain extender is 15-25:24-40:0.05-0.2:3-10:9.2-27.5.

[0013] Furthermore, the preparation steps of the disulfide bond-containing nanoparticle chain extender are as follows:

[0014] S1: Nano-silica is modified with 3-chloropropyltriethoxysilane to obtain chloride nano-silica;

[0015] S2: Using N,N-dimethylacetamide as solvent and potassium carbonate as acid binding agent, cystamine dihydrochloride and bisamino polyethylene glycol are grafted onto chlorided nano-silica to obtain a nanoparticle chain extender containing disulfide bonds.

[0016] Preferably, the average particle size of the nano-silicon dioxide in step S1 is 20-100 nm.

[0017] Preferably, in step S1, the weight ratio of nano-silica to 3-chloropropyltriethoxysilane is 5-15:0.2-1.

[0018] Preferably, in step S2, the weight ratio of chlorided nano-silica, cystamine dihydrochloride, bisaminopolyethylene glycol, N,N-dimethylacetamide and potassium carbonate is 5-15:1.2-3.5:3-9:50-200:0.2-1.

[0019] Preferably, the weight average molecular weight of the bisamino polyethylene glycol in step S2 is 500-700.

[0020] Furthermore, the steps for preparing the flexible film for handwriting tablet are as follows:

[0021] (1) Adding modified polyurethane, leveling agent and defoaming agent to ethyl acetate and stirring for 8-12 minutes to obtain a coating slurry;

[0022] (2) Fixing the release film on a coating machine, applying the coating slurry on the surface of the release film, and thermally curing it to obtain a flexible film for a handwriting tablet.

[0023] Preferably, the coating gap in step (2) is 0.08-0.12 mm, and the running speed is 8-12 cm / s.

[0024] Preferably, in step (2), the wet film thickness of the coating slurry after being applied to the surface of the release film is 28-32 μm.

[0025] Preferably, the thermal curing in step (2) is: first curing at 38-42°C for 4-6 minutes, and then curing at 78-82°C for 12-18 minutes.

[0026] Beneficial effects of the present invention:

[0027] This invention achieves molecular-level coupling between a rigid reinforcing phase and a flexible matrix through chemical surface modification of nanoparticles and the construction of a dynamic disulfide bond network. The rigid core of the nanoparticles effectively enhances the material's surface hardness and scratch resistance, while the dynamic disulfide bond network dissipates stress through reversible fracture and reformation, significantly improving the material's fatigue resistance under repeated bending and flexing while also imparting excellent self-healing properties.

[0028] This invention uses chloropropylsilane to surface-functionalize the nanoparticles, allowing them to attach to the polyurethane backbone through chemical bonding rather than traditional physical adsorption. This strong interfacial bonding effectively inhibits nanoparticle aggregation, improves stress transfer efficiency, and avoids performance degradation caused by interfacial debonding.

[0029] This invention utilizes a synergistic chain extension strategy involving bisamino polyethylene glycol and cystamine dihydrochloride to construct a dynamic network with a gradient crosslink density. The long-chain polyethylene glycol acts as a flexible spacer, reducing the brittleness caused by excessive crosslinking while promoting the dynamic exchange of disulfide bonds through chain segment motion. The short-chain cystamine provides a high density of crosslinking points, ensuring network stability and achieving a balance between strength and toughness.

[0030] The self-repairing property of the dynamic disulfide bond network provided by the present invention under thermal activation can effectively repair microcracks generated by long-term use and extend the product life.

[0031] Through innovations in molecular structure design and preparation technology, this invention breaks through the technical bottleneck of the single performance of traditional flexible materials, and provides a dedicated flexible film solution for high-performance handwriting tablets that combines the characteristics of "strong surface, dynamic flexibility, and intelligent self-healing". DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0033] In the specific embodiment of the present invention, bisamino polyethylene glycol was purchased from Shanghai Pengshuo Biotechnology Co., Ltd.

[0034] Example 1:

[0035] (1) 5 g of nano-silica (average particle size of 50 nm) was added to 20 g of anhydrous ethanol and 50 g of deionized water, the temperature was raised to 52°C, 0.2 g of 3-chloropropyltriethoxysilane was added, the mixture was stirred for 5 h, centrifuged, washed, and vacuum dried to obtain chlorinated nano-silica;

[0036] (2) 5 g of chlorinated nano-silica, 1.2 g of cystamine dihydrochloride, and 3 g of bisamino polyethylene glycol (weight-average molecular weight of 600) were added to 50 g of N,N-dimethylacetamide, heated to 95°C, and then 0.2 g of potassium carbonate was added. The mixture was stirred for 5 h, centrifuged, washed, and vacuum-dried to obtain a nanoparticle chain extender containing a disulfide bond.

[0037] (3) 15 g of polycarbonate diol (weight-average molecular weight of 2000) was dried at 115 ° C for 3 h, cooled to 78 ° C, and 24 g of isophorone diisocyanate was added under nitrogen atmosphere and stirred for 1 h to obtain an isocyanate-terminated prepolymer. The temperature was lowered to 55 ° C, 0.05 g of dibutyltin dilaurate and 3 g of N, N-dimethylacetamide were added, and the mixture was stirred for 25 min. 9.2 g of a disulfide-containing nanoparticle chain extender was added and the mixture was stirred for 2 h. The temperature was lowered to room temperature, and N, N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0038] (4) Add 40 g of modified polyurethane, 0.3 g of leveling agent BYK-333, and 0.1 g of defoaming agent BYK-055 to 150 g of ethyl acetate and stir for 8 min to obtain a coating slurry;

[0039] (5) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to be 0.08 mm, the running speed was 8 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 28 μm. The film was first cured at 38 ° C for 4 min and then cured at 78 ° C for 12 min to obtain a flexible film for handwriting tablets.

[0040] Example 2:

[0041] (1) 10 g of nano-silica (average particle size of 50 nm) was added to 30 g of anhydrous ethanol and 70 g of deionized water, the temperature was raised to 55°C, 0.5 g of 3-chloropropyltriethoxysilane was added, the mixture was stirred for 6 h, centrifuged, washed, and vacuum dried to obtain chlorinated nano-silica;

[0042] (2) 10 g of chlorided nano-silica, 2.3 g of cystamine dihydrochloride, and 6 g of bisamino polyethylene glycol (weight-average molecular weight of 600) were added to 100 g of N,N-dimethylacetamide, the temperature was raised to 100° C., 0.5 g of potassium carbonate was added, the mixture was stirred for 6 h, centrifuged, washed, and vacuum-dried to obtain a nanoparticle chain extender containing a disulfide bond;

[0043] (3) 20 g of polycarbonate diol (weight-average molecular weight of 2000) was dried at 120 ° C for 4 h, cooled to 80 ° C, and 33.3 g of isophorone diisocyanate was added under nitrogen atmosphere and stirred for 2 h to obtain an isocyanate-terminated prepolymer. The temperature was then cooled to 60 ° C, 0.1 g of dibutyltin dilaurate and 5 g of N, N-dimethylacetamide were added, and the mixture was stirred for 30 min. 18.3 g of a disulfide-containing nanoparticle chain extender was added, and the mixture was stirred for 3 h. The temperature was then cooled to room temperature, and N, N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0044] (4) Add 50 g of modified polyurethane, 0.5 g of leveling agent BYK-333, and 0.3 g of defoaming agent BYK-055 to 200 g of ethyl acetate and stir for 10 min to obtain a coating slurry;

[0045] (5) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to be 0.1 mm, the operating speed was 10 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 30 μm. The film was first cured at 40°C for 5 minutes and then cured at 80°C for 15 minutes to obtain a flexible film for handwriting tablets.

[0046] Example 3:

[0047] (1) 15 g of nano-silica (average particle size of 50 nm) was added to 40 g of anhydrous ethanol and 100 g of deionized water, and the temperature was raised to 57°C. 1 g of 3-chloropropyltriethoxysilane was then added, and the mixture was stirred for 7 h. The mixture was centrifuged, washed, and vacuum dried to obtain chlorinated nano-silica.

[0048] (2) 15 g of chlorided nano-silica, 3.5 g of cystamine dihydrochloride, and 9 g of bisamino polyethylene glycol (weight-average molecular weight of 600) were added to 200 g of N,N-dimethylacetamide, the temperature was raised to 105° C., and 1 g of potassium carbonate was added. The mixture was stirred for 7 h, centrifuged, washed, and vacuum-dried to obtain a nanoparticle chain extender containing a disulfide bond.

[0049] (3) 25 g of polycarbonate diol (weight-average molecular weight of 2000) was dried at 125 ° C for 5 h, cooled to 82 ° C, and 40 g of isophorone diisocyanate was added under nitrogen atmosphere and stirred for 3 h to obtain an isocyanate-terminated prepolymer. The temperature was lowered to 65 ° C, 0.2 g of dibutyltin dilaurate and 10 g of N, N-dimethylacetamide were added, and the mixture was stirred for 35 min. 27.5 g of a disulfide-containing nanoparticle chain extender was added, and the mixture was stirred for 4 h. The temperature was lowered to room temperature, and N, N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0050] (4) Add 60 g of modified polyurethane, 1 g of leveling agent BYK-333, and 0.5 g of defoaming agent BYK-055 to 250 g of ethyl acetate and stir for 12 min to obtain a coating slurry;

[0051] (5) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to be 0.12 mm, the operating speed was 12 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 32 μm. The film was first cured at 42 ° C for 6 min and then cured at 82 ° C for 18 min to obtain a flexible film for handwriting tablets.

[0052] Comparative Example 1:

[0053] The difference between Comparative Example 1 and Example 2 is that the chloride nano-silicon dioxide in step (2) is replaced by nano-silicon dioxide;

[0054] The specific steps are as follows:

[0055] (1) 10 g of nano-silica (average particle size of 50 nm), 2.3 g of cystamine dihydrochloride, and 6 g of bisamino polyethylene glycol (weight-average molecular weight of 600) were added to 100 g of N,N-dimethylacetamide, heated to 100° C., and then 0.5 g of potassium carbonate was added. The mixture was stirred for 6 h, centrifuged, washed, and vacuum-dried to obtain a chain extender.

[0056] (2) 20 g of polycarbonate diol (weight-average molecular weight of 2000) was dried at 120° C. for 4 h, cooled to 80° C., 33.3 g of isophorone diisocyanate was added under nitrogen atmosphere, and stirred for 2 h to obtain an isocyanate-terminated prepolymer. The mixture was cooled to 60° C., 0.1 g of dibutyltin dilaurate and 5 g of N,N-dimethylacetamide were added, and the mixture was stirred for 30 min. 18.3 g of a chain extender was added, and the mixture was stirred for 3 h. The mixture was cooled to room temperature, and N,N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0057] (3) Add 50 g of modified polyurethane, 0.5 g of leveling agent BYK-333, and 0.3 g of defoaming agent BYK-055 to 200 g of ethyl acetate and stir for 10 min to obtain a coating slurry;

[0058] (4) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to 0.1 mm, the operating speed was 10 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 30 μm. The film was first cured at 40°C for 5 min and then cured at 80°C for 15 min to obtain a flexible film.

[0059] Comparative Example 2:

[0060] The difference between Comparative Example 2 and Example 2 is that the bisaminopolyethylene glycol in step (2) is replaced by an equal molar amount of cystamine dihydrochloride;

[0061] The specific steps are as follows:

[0062] (1) 10 g of nano-silica (average particle size of 50 nm) was added to 30 g of anhydrous ethanol and 70 g of deionized water, the temperature was raised to 55°C, 0.5 g of 3-chloropropyltriethoxysilane was added, the mixture was stirred for 6 h, centrifuged, washed, and vacuum dried to obtain chlorinated nano-silica;

[0063] (2) 10 g of chlorided nano-silica and 4.6 g of cystamine dihydrochloride were added to 100 g of N,N-dimethylacetamide, the temperature was raised to 100° C., 0.5 g of potassium carbonate was added, the mixture was stirred for 6 h, centrifuged, washed, and vacuum dried to obtain a nanoparticle chain extender containing a disulfide bond;

[0064] (3) 20 g of polycarbonate diol (weight-average molecular weight of 2000) was dried at 120 ° C for 4 h, cooled to 80 ° C, and 33.3 g of isophorone diisocyanate was added under nitrogen atmosphere and stirred for 2 h to obtain an isocyanate-terminated prepolymer. The temperature was then cooled to 60 ° C, 0.1 g of dibutyltin dilaurate and 5 g of N, N-dimethylacetamide were added, and the mixture was stirred for 30 min. 14.6 g of a disulfide-containing nanoparticle chain extender was added, and the mixture was stirred for 3 h. The temperature was then cooled to room temperature, and N, N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0065] (5) Add 50 g of modified polyurethane, 0.5 g of leveling agent BYK-333, and 0.3 g of defoaming agent BYK-055 to 200 g of ethyl acetate and stir for 10 min to obtain a coating slurry;

[0066] (6) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to 0.1 mm, the operating speed was 10 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 30 μm. The film was first cured at 40°C for 5 min and then cured at 80°C for 15 min to obtain a flexible film.

[0067] Comparative Example 3:

[0068] The difference between Comparative Example 3 and Example 2 is that the 18.3 g of disulfide bond-containing nanoparticle chain extender in step (3) is replaced by 10 g of nano-silica and 8.3 g of ethylenediamine;

[0069] The specific steps are as follows:

[0070] (1) 20 g of polycarbonate diol (weight average molecular weight of 2000) was dried at 120° C. for 4 h, cooled to 80° C., 33.3 g of isophorone diisocyanate was added under nitrogen atmosphere, and stirred for 2 h to obtain an isocyanate-terminated prepolymer. The mixture was cooled to 60° C., 0.1 g of dibutyltin dilaurate and 5 g of N,N-dimethylacetamide were added, and stirred for 30 min. 10 g of nano-silica (average particle size of 50 nm) and 8.3 g of ethylenediamine were added, and stirred for 3 h. The mixture was cooled to room temperature, and N,N-dimethylacetamide was removed by rotary evaporation to obtain a modified polyurethane.

[0071] (2) Add 50 g of modified polyurethane, 0.5 g of leveling agent BYK-333, and 0.3 g of defoaming agent BYK-055 to 200 g of ethyl acetate and stir for 10 min to obtain a coating slurry;

[0072] (3) The release film was fixed on a roll-to-roll coating machine, the coating gap was controlled to be 0.1 mm, the operating speed was 10 cm / s, and the coating slurry was evenly coated on the surface of the release film by micro-gravure coating. The wet film thickness was 30 μm. The film was first cured at 40°C for 5 min and then cured at 80°C for 15 min to obtain a flexible film.

[0073] Performance testing:

[0074] Tensile strength test: According to GB / T 1040.3-2006, the specimens were cut into 150 mm × 10 mm dumbbell-shaped specimens and tested using a universal materials testing machine with a clamping distance set at 50 mm and a tensile rate of 500 mm / min. The maximum load at specimen break and the change in the spacing between markings were recorded. The tensile strength (MPa) and elongation at break (%) were calculated, respectively. Five parallel specimens were tested for each group of specimens, and the average values ​​were taken. The results are shown in Table 1.

[0075] Pencil hardness scratch resistance test: In accordance with GB / T 6739-2006, an electric pencil scratch tester was used, with the specimen fixed on a horizontal test bench. Zhonghua brand 101 drawing pencils (0.5mm lead diameter) were used, with the pencils varying in grade from 6H to 6B. Under a vertical load of 500g, the tester scratched the specimen 50mm in a single direction at a speed of 30mm / s. Each hardness level was repeated three times. The surface was observed under a microscope (100× magnification) for permanent scratches. The highest hardness level without any scratches after three consecutive levels was determined as the scratch resistance level. The results are shown in Table 1.

[0076] Dynamic flexibility test: In accordance with GB / T 13525-1992, using the MIT flexure tester, a 15 mm x 100 mm specimen was clamped between a 1 mm radius bending head. The bending angle was set to 135°, the bending frequency was set to 120 times / min, and the pre-tension was applied to 4.9 N. After 1000 consecutive bends, the specimen was removed and the flexural strength retention rate was determined using the three-point bending method.

[0077] Self-healing performance test: Prepare a specimen with a pre-made scratch (depth of 10 μm), place it in a constant temperature box at 60°C for 2 h, repeat the tensile strength test, and calculate the tensile strength recovery rate.

[0078] Table 1 Performance test results

[0079]

[0080]

[0081] Data Analysis:

[0082] The test data of Examples 1-3 show that the prepared modified polyurethane materials exhibit balanced and excellent comprehensive performance in terms of mechanical strength, surface hardness, dynamic flexibility and self-healing properties. It is speculated that its mechanism may be derived from the synergistic effect of the disulfide-containing nanoparticle chain extender: the surface of nano-silica is chlorinated and modified by 3-chloropropyltriethoxysilane, so that it forms a covalent graft with cystamine dihydrochloride and bisamino polyethylene glycol, and constructs a dynamic disulfide cross-linked network. This network can undergo reversible fracture and recombination under stress, thereby improving the energy dissipation capacity of the material. At the same time, the rigid core of the nanoparticles and the polyurethane soft segment form a microscopic phase separation structure, enhancing the reinforcement effect of the rigid dispersed phase. In addition, the long chain structure of bisamino polyethylene glycol may optimize the dispersion of nanoparticles in the matrix, reduce stress concentration, and thus improve flexibility and self-healing efficiency.

[0083] Compared with Comparative Example 1, Example 2 uses chlorinated nano-silica to replace unmodified nano-silica, and the material properties show significant differences. The data trend shows that chlorination modification may play a role by enhancing the interfacial bonding force between nanoparticles and polyurethane matrix: the introduction of chloropropylsilane causes the surface of nanoparticles to carry active chlorine groups, which can undergo nucleophilic substitution reaction with the amino group of cystamine dihydrochloride to form a more stable chemical bond. This bonding method may reduce the agglomeration tendency of nanoparticles and promote their uniform dispersion in the matrix, thereby improving the stress transfer efficiency. In addition, the dynamic network of chemically grafted disulfide bonds may alleviate local stress concentration through reversible exchange reactions, further improving the flexibility retention rate and self-repair ability of the material. However, the unmodified nano-silica (Comparative Example 1) relies only on physical adsorption, and the interface bonding is weak, resulting in a decrease in mechanical properties and scratch resistance.

[0084] The key difference between Example 2 and Comparative Example 2 is the introduction of bisamino polyethylene glycol. The data show that the addition of bisamino polyethylene glycol may optimize material properties in two ways: First, its long-chain flexible structure can act as a spacer to reduce the disulfide cross-linking density formed by cystamine dihydrochloride, avoid the increase in brittleness caused by excessive cross-linking, and thus balance the tensile strength and elongation at break; Second, the hydrophilicity of the polyethylene glycol segment may promote the dynamic exchange rate of disulfide bonds under thermal activation conditions and enhance the self-repair efficiency. In contrast, Comparative Example 2 relies solely on the short-chain cross-linking of cystamine dihydrochloride, which may form an overly dense network structure, restrict the movement of molecular segments, and cause a significant decrease in flexibility. Although short-chain cross-linking can improve the initial tensile strength, the dynamic performance and self-repair ability are restricted.

[0085] The performance difference between Example 2 and Comparative Example 3 highlights the key role of the disulfide bond-containing nanoparticle chain extender. When Comparative Example 3 directly uses nanosilica as a chain extender, the material performance deteriorates across the board. The reasons for this may include: the unfunctionalized nanosilica exists only as an inert filler and cannot participate in the dynamic bonding process of the polyurethane chain, resulting in low stress transfer efficiency and easy debonding at the interface; while the chain extender of Example 2 integrates the nanoparticles into the polyurethane backbone through disulfide bonds to form a rigid-flexible hybrid network. Under external stress or thermal stimulation, the reversible breakage of the disulfide bonds can effectively dissipate energy, while the nanoparticles provide physical cross-linking points to maintain structural integrity. This design not only retains the enhancement effect of the nanoparticles, but also gives the material self-healing properties through dynamic chemical bonds, while pure physical doping (Comparative Example 3) lacks such a synergistic mechanism.

[0086] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A flexible film for a handwriting tablet, characterized in that: The coating slurry is coated on the release film and then thermally cured to obtain the coating slurry; the coating slurry comprises the following components by weight: 40-60 parts of modified polyurethane, 0.3-1 parts of leveling agent, 0.1-0.5 parts of defoaming agent and 150-250 parts of ethyl acetate; The modified polyurethane is prepared as follows: after drying polycarbonate diol, isophorone diisocyanate is added under a nitrogen atmosphere, stirred for reaction for 1-3 hours, cooled to 55-65° C., dibutyltin dilaurate and N,N-dimethylacetamide are added, stirred for reaction for 25-35 minutes, and a disulfide bond-containing nanoparticle chain extender is added, stirred for reaction for 2-4 hours, cooled to room temperature, and rotary evaporated to obtain the modified polyurethane; The weight ratio of the polycarbonate diol, isophorone diisocyanate, dibutyltin dilaurate, N,N-dimethylacetamide and disulfide bond-containing nanoparticle chain extender is 15-25:24-40:0.05-0.2:3-10:9.2-27.5; The preparation steps of the disulfide bond-containing nanoparticle chain extender are as follows: S1: Nano-silica is modified with 3-chloropropyltriethoxysilane to obtain chloride nano-silica; S2: Using N,N-dimethylacetamide as solvent and potassium carbonate as acid-binding agent, cystamine dihydrochloride and bisamino polyethylene glycol were grafted onto chloride nano-silica to obtain a nanoparticle chain extender containing disulfide bonds; In the step S2, the weight ratio of chlorided nano-silica, cystamine dihydrochloride, bisaminopolyethylene glycol, N,N-dimethylacetamide and potassium carbonate is 5-15:1.2-3.5:3-9:50-200:0.2-1; The weight average molecular weight of the bisamino polyethylene glycol in step S2 is 500-700.

2. The flexible film for handwriting tablet according to claim 1, characterized in that: The leveling agent is BYK-333; the defoaming agent is BYK-055.

3. The flexible film for handwriting tablet according to claim 1, characterized in that: The weight average molecular weight of the polycarbonate diol is 1500-2500.

4. The flexible film for handwriting tablet according to claim 1, characterized in that: The average particle size of the nano-silicon dioxide in step S1 is 20-100 nm.

5. The flexible film for handwriting tablet according to claim 1, characterized in that: In step S1, the weight ratio of nano-silica to 3-chloropropyltriethoxysilane is 5-15:0.2-1.

6. A method for preparing a flexible film for a handwriting tablet according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Adding modified polyurethane, leveling agent and defoaming agent to ethyl acetate and stirring for 8-12 minutes to obtain a coating slurry; (2) Fixing the release film on a coating machine, applying the coating slurry on the surface of the release film, and thermally curing it to obtain a flexible film for a handwriting tablet.

7. The method for preparing a flexible film for a handwriting tablet according to claim 6, wherein: The coating gap in step (2) is 0.08-0.12 mm, and the running speed is 8-12 cm / s.

8. The method for preparing a flexible film for a handwriting tablet according to claim 6, wherein: In the step (2), the wet film thickness of the coating slurry after being coated on the surface of the release film is 28-32 μm.

9. The method for preparing a flexible film for a handwriting tablet according to claim 6, wherein: The thermal curing in step (2) is as follows: first curing at 38-42° C. for 4-6 minutes, and then curing at 78-82° C. for 12-18 minutes.

Images