Preparation method of multi-layer composite PVA (Polyvinyl Alcohol) film

Abstract

The invention relates to the technical field of high polymer material processing, in particular to a preparation method of a multi-layer composite PVA (polyvinyl alcohol) film, which comprises the following steps: S1, preparing a basic support layer; s2, preparing a function adjusting layer; s3, preparing an optimization layer; s4, compounding the prepared layers together through a thermocompression bonding method to form a multi-layer composite film structure; s5, soaking the multi-layer composite membrane in a solution containing a swelling agent; s6, carrying out dyeing treatment on the swelled multi-layer composite film; s7, the dyed multi-layer composite film is subjected to two-way stretching in the X direction and the Y direction; and S8, carrying out heat setting treatment on the multilayer composite film subjected to two-way stretching to obtain a final multilayer composite PVA film finished product. According to the invention, by optimizing the combination of different functional layers, the mechanical strength, UV resistance and oxidation resistance of the film are remarkably improved, and meanwhile, an environment-friendly production process is adopted, so that the cost benefit and wide application potential are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material processing, and in particular to a method for preparing a multi-layer composite PVA film. Background Art

[0002] Polyvinyl alcohol (PVA) films are widely used in many fields, including packaging, coating materials and medical uses, due to their excellent chemical stability, biocompatibility and environmental friendliness. However, single-layer PVA films often show performance deficiencies when responding to specific environmental stresses (such as ultraviolet irradiation, oxidative stress, and mechanical loads). Although existing technologies have attempted to enhance the performance of PVA films by introducing different additives or using composite materials structures, these methods often ignore the simplicity of the manufacturing process, cost efficiency, and uniformity and sustainability of the films while improving the overall performance of the films.

[0003] In order to overcome these limitations, the present invention aims to develop a method for preparing a multi-layer composite PVA film, which can significantly improve the mechanical properties, UV resistance and antioxidant capacity of the film without sacrificing environmental friendliness and economic benefits. The preparation methods in the prior art often cannot effectively and stably composite layers of different functions together, resulting in unstable overall performance of the film.

[0004] Therefore, it is particularly important to develop a technology that can ensure good adhesion between the layers of the film and is easy to operate in order to achieve widespread and reliable application in practical applications. Summary of the invention

[0005] Based on the above purpose, the present invention provides a method for preparing a multi-layer composite PVA film.

[0006] A method for preparing a multilayer composite PVA film comprises the following steps: S1: preparing a base support layer, mixing high molecular weight PVA powder with deionized water, heating and stirring until the PVA is completely dissolved to form a PVA solution A; and preparing the PVA solution A into a first layer of PVA film as a base support layer by a casting method; S2: preparing a function regulating layer, dissolving low molecular weight PVA powder, plasticizer and deionized water to form a PVA solution B, then adding a UV absorber and an antioxidant to the PVA solution B, stirring evenly, and preparing a second layer of PVA film as a function regulating layer by a casting method; S3: preparing an optimized layer, mixing the nanoparticles with the prepared PVA solution to form a uniformly dispersed nanocomposite solution, and preparing a third layer of PVA film as the optimized layer by a casting method; S4: Compounding the prepared first PVA film, the second PVA film and the third PVA film together by a heat pressing method to form a multi-layer composite film structure; S5: performing swelling treatment, immersing the multilayer composite film in a solution containing a swelling agent, so that the second layer of PVA film is fully swollen; S6: Select a dye compatible with PVA to dye the swollen multilayer composite film; S7: biaxially stretching the dyed multilayer composite film in the X and Y directions; S8: The multi-layer composite film after biaxial stretching is subjected to heat setting treatment to fix the size and shape of the film to obtain a final multi-layer composite PVA film product.

[0007] Optionally, the molecular weight of the high molecular weight PVA powder is 130,000-170,000; the molecular weight of the low molecular weight PVA powder is 70,000-100,000; the nanoparticles are selected from titanium oxide or zinc oxide; the plasticizer is glycerol or ethylene glycol; the ultraviolet absorber is specifically a hydroxybenzotriazole compound or a benzophenone compound; and the antioxidant is butylated hydroxytoluene or butylated hydroxyanisole.

[0008] Optionally, the S1 specifically includes: S11: adding high molecular weight PVA powder into deionized water in proportion, wherein the weight ratio of the high molecular weight PVA powder to the deionized water is 1:5 to 1:10; S12: heating the mixed solution to 80° C. to 95° C. and continuously stirring for 30 to 60 minutes until the PVA powder is completely dissolved to form a uniform PVA solution A; S13: cooling the obtained PVA solution A to room temperature, and then filtering through a 200 to 400 mesh filter to remove incompletely dissolved solid particles and impurities; S14: The filtered PVA solution A is prepared into a PVA film by a casting method. During the process, the casting temperature is controlled at 50 to 70° C., the casting speed is 5 to 15 m / min, and the obtained film thickness is 50 to 100 μm, which serves as a basic support layer.

[0009] Optionally, the S2 specifically includes: S21: adding low molecular weight PVA powder to deionized water in a proportion, wherein the weight ratio of the low molecular weight PVA powder to deionized water is 1:4 to 1:8, stirring and heating to 70° C. to 90° C., and controlling the stirring speed to 200 to 500 rpm, until the PVA is completely dissolved to form a PVA solution B; S22: adding a plasticizer to the PVA solution B, wherein the amount of the plasticizer added is 5% to 15% of the total weight of the PVA solution B, and continuing stirring for 30 minutes; S23: under stirring, sequentially adding a UV absorber and an antioxidant to the PVA solution B, wherein the amount of the UV absorber added is 0.1% to 1% of the total weight of the PVA solution B, and the amount of the antioxidant added is 0.1% to 1.5% of the total weight of the PVA solution B, and stirring is continued for 30 to 60 minutes after the addition; S24: The uniformly mixed PVA solution B is prepared into a second layer of PVA film by a casting method, specifically the casting temperature is controlled at 40°C to 60°C, the casting speed is 5 to 12 m / min, and the obtained film thickness is 20 to 50 μm, which serves as a functional adjustment layer.

[0010] Optionally, the S3 specifically includes: S31: preparing a preliminary PVA solution, mixing PVA powder having a molecular weight of 40,000 to 100,000 with deionized water in a weight ratio of 1:4 to 1:8, and heating to 70° C. to 90° C., while stirring at a speed of 200 to 500 rpm for 30 to 90 minutes, until the PVA powder is completely dissolved to form a uniform PVA solution; S32: heating the prepared PVA solution to 50° C. to 70° C. and stirring at a rotation speed of 300 to 600 rpm; S33: under continuous stirring, slowly adding nanoparticles into the PVA solution, wherein the amount of the nanoparticles added is 0.5% to 5% of the total weight of the PVA solution, and the particle size of the nanoparticles is 10 nm to 100 nm; S34: continuing to stir at a speed of 300 to 600 rpm for 1 to 2 hours until the nanoparticles are uniformly dispersed in the PVA solution to form a nanocomposite solution; S35: The uniformly dispersed nanocomposite solution is prepared into a third layer of PVA film by a casting method, the casting temperature is controlled at 40°C to 60°C, the casting speed is 3 m / min to 10 m / min, and the obtained film thickness is 10 to 30 μm, as an optimization layer.

[0011] Optionally, the S4 specifically includes: S41: stacking the prepared first layer of PVA film, second layer of PVA film and third layer of PVA film in sequence, ensuring that the surface of each layer of film is flat and wrinkle-free; S42: placing the stacked multi-layer PVA film in a heat press, preheating the upper and lower pressing plates of the heat press to 90° C. to 150° C., and controlling the pressing pressure to 1 MPa to 5 MPa; S43: Pressing the multilayer film in a hot press for 5 to 20 minutes to form an overall composite structure; S44: The laminated multilayer film is taken out from the hot press and placed on a cooling table to be naturally cooled to room temperature.

[0012] Optionally, the S5 specifically includes: S51: preparing a swelling agent solution, mixing deionized water and ethanol in a volume ratio of 7:3 to 7:1 to form a swelling agent solution, and heating the swelling agent solution to 30° C. to 60° C.; S52: completely immersing the prepared multilayer composite membrane in a preheated swelling agent solution; S53: keeping the multilayer composite film immersed in the swelling agent solution for 10 to 60 minutes; S54: The swollen multilayer composite film is taken out from the swelling agent solution, and the excess solution on the surface is removed by rolling, and then the film is hung or laid flat on a drying table to dry naturally to room temperature.

[0013] Optionally, the S6 specifically includes: S61: The dye is an acid dye or a reactive dye, the concentration of the acid dye is 0.1% to 2.0%, and the concentration of the reactive dye is 0.05% to 1.5%; S62: dissolving the selected dye in deionized water in a proportion, wherein the weight ratio of the dye to the deionized water is 1:50 to 1:200, to form a dyeing solution, and controlling the temperature of the dyeing solution to be between 30° C. and 70° C., and adjusting the pH value to be between 4 and 7; S63: completely immersing the swollen multilayer composite film in the dyeing solution for a dyeing time of 20 to 80 minutes, and during this period, the dyeing solution is uniformly stirred at a stirring speed of 100 to 300 rpm; S64: After dyeing is completed, the multilayer composite membrane is taken out from the dyeing solution and immediately rinsed in deionized water to remove excess dye that has not been adsorbed, and the temperature of the rinse water is controlled at 25 to 40°C; S65: Hang the washed multilayer composite film on a drying table and dry it to room temperature.

[0014] Optionally, the S7 specifically includes: S71: Fix the dyed multilayer composite film on the fixture of the biaxial stretching device to ensure that the film is flat and wrinkle-free; S72: firstly stretching the multilayer composite film along the X direction, with a stretching ratio of 2 to 5 times and a stretching speed of 1 to 10 mm / s; S73: After completing the stretching in the X direction, immediately stretching in the Y direction, with a stretching ratio of 2 to 5 times and a stretching speed of 1 to 10 mm / s; S74: After completing the biaxial stretching, the stretched multilayer composite film is kept in the stretched state for cooling to room temperature to fix the size and shape of the stretched film.

[0015] Optionally, the S8 specifically includes: S81: Fixing the biaxially stretched multilayer composite film on the frame of the heat setting device to ensure that the film is flat and wrinkle-free on the frame and remains in a stretched state; S82: placing the fixed multilayer composite film in a heat setting furnace, controlling the heat setting temperature at 100° C. to 160° C. for a setting time of 2 to 15 minutes; S83: After the setting time is over, the multilayer composite film is taken out from the heat setting furnace and immediately placed on a cooling table for rapid cooling, and the cooling temperature is controlled at 25° C. to 40° C.; S84: After cooling is completed, the multi-layer composite film is removed from the frame to obtain a final multi-layer composite PVA film product.

[0016] Beneficial effects of the present invention: The present invention adopts a layered preparation method to specifically optimize the functions of different layers. For example, the antioxidants and UV absorbers in the function adjustment layer significantly improve the stability and service life of the film. In addition, the nanoparticles in the optimization layer enhance the barrier properties and possible conductivity of the film, making the film not only suitable for traditional fields, but also expandable to the fields of electronics and biomedicine.

[0017] The present invention adopts a water-based solution and a simplified hot pressing process, reduces the use of harmful solvents, complies with the principles of green chemistry, and the entire production process is easy to control, has high cost efficiency, and is easy for large-scale industrial production. The multilayer composite PVA film prepared by this method has good comprehensive performance and high cost-effectiveness, and is expected to be widely used in the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 Schematic diagram of a method for preparing a multilayer composite PVA film according to an embodiment of the present invention; Figure 2 Schematic diagram of the composition of a multi-layer composite PVA film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.

[0021] It should be noted that the references to "one embodiment", "embodiment", "exemplary embodiments", "some embodiments" and the like in the specification indicate that the embodiments described may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, when a specific feature, structure or characteristic is described in conjunction with an embodiment, it should be within the knowledge of a person skilled in the art to implement such feature, structure or characteristic in conjunction with other embodiments (whether or not explicitly described).

[0022] In general, a term can be understood, at least in part, from its use in context. For example, depending, at least in part, on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey an exclusive set of factors, but can instead, depending, at least in part, on the context, allow for the presence of other factors that are not necessarily explicitly described.

[0023] Example 1 like Figure 1-Figure 2 As shown, a method for preparing a multilayer composite PVA film comprises the following steps: S1: preparing a base support layer, mixing high molecular weight PVA powder with deionized water, heating and stirring until the PVA is completely dissolved to form a PVA solution A; and preparing the PVA solution A into a first layer of PVA film as a base support layer by a casting method; S2: preparing a function regulating layer, dissolving low molecular weight PVA powder, plasticizer and deionized water to form a PVA solution B, then adding a UV absorber and an antioxidant to the PVA solution B, stirring evenly, and preparing a second layer of PVA film as a function regulating layer by a casting method; S3: preparing an optimized layer, mixing the nanoparticles with the prepared PVA solution to form a uniformly dispersed nanocomposite solution, and preparing a third layer of PVA film as the optimized layer by a casting method; S4: Compounding the prepared first PVA film, the second PVA film and the third PVA film together by a heat pressing method to form a multi-layer composite film structure; S5: performing swelling treatment, immersing the multilayer composite film in a solution containing a swelling agent, so that the second layer of PVA film is fully swollen, so as to facilitate subsequent dyeing and stretching treatment; S6: Select a dye compatible with PVA and dye the swollen multi-layer composite film, so that the dye can evenly penetrate into the second layer of PVA film to achieve the expected dyeing effect; S7: biaxially stretching the dyed multilayer composite film in the X and Y directions to improve the transparency and mechanical properties of the film while ensuring good adhesion between the layers of the film; S8: performing heat setting treatment on the biaxially stretched multilayer composite film to fix the size and shape of the film to obtain a final multilayer composite PVA film product; S9 (optional): The second layer of PVA film can be removed by washing and dissolving as needed to obtain a final multi-layer composite PVA film with specific functions.

[0024] The molecular weight of the high molecular weight PVA powder is 150000; the molecular weight of the low molecular weight PVA powder is 80000; the nanoparticles are selected from titanium oxide or zinc oxide; the plasticizer is glycerol; the ultraviolet absorber is specifically a hydroxybenzotriazole compound; and the antioxidant is butylated hydroxytoluene.

[0025] The preparation of the basic support layer in S1 specifically includes: S11: adding high molecular weight PVA powder into deionized water in proportion, wherein the weight ratio of high molecular weight PVA powder to deionized water is 1:7; S12: heating the mixed solution to 90° C. and continuously stirring for 45 minutes until the PVA powder is completely dissolved to form a uniform PVA solution A; S13: Cooling the obtained PVA solution A to room temperature, and then filtering it through a 300-mesh filter to remove incompletely dissolved solid particles and impurities to ensure the purity of the solution; S14: The filtered PVA solution A is prepared into a PVA film by a casting method. During the process, the casting temperature is controlled at 60° C. and the casting speed is 10 m / min. The obtained film thickness is 80 μm, which serves as a basic support layer.

[0026] The preparation of the function regulating layer in S2 specifically includes: S21: adding low molecular weight PVA powder to deionized water in proportion, wherein the weight ratio of low molecular weight PVA powder to deionized water is 1:6, stirring and heating to 85° C., with the stirring speed controlled at 400 rpm, until the PVA is completely dissolved to form a PVA solution B; S22: adding a plasticizer to the PVA solution B, wherein the amount of the plasticizer added is 10% of the total weight of the PVA solution B, and continuing stirring for 30 minutes to allow the plasticizer to be fully dissolved and evenly distributed in the solution; S23: under stirring, adding a UV absorber and an antioxidant to the PVA solution B in sequence, wherein the amount of the UV absorber added is 0.5% of the total weight of the PVA solution B, and the amount of the antioxidant added is 1% of the total weight of the PVA solution B. After adding, stirring is continued for 45 minutes to ensure that the components are evenly mixed; S24: The uniformly mixed PVA solution B is prepared into a second layer of PVA film by a casting method, specifically the casting temperature is controlled at 50° C., the casting speed is 8 m / min, and the obtained film thickness is 30 μm, which serves as a functional adjustment layer.

[0027] Preparation of the optimization layer in S3 specifically includes: S31: preparing a preliminary PVA solution, mixing PVA powder having a molecular weight of 40,000 to 100,000 with deionized water in a weight ratio of 1:6, and heating to 85° C. while stirring at a speed of 400 rpm for 60 minutes until the PVA powder is completely dissolved to form a uniform PVA solution; S32: heating the prepared PVA solution to 60° C. and stirring at a rotation speed of 500 rpm; S33: under continuous stirring, slowly adding nanoparticles into the PVA solution, the amount of the nanoparticles added is 1% of the total weight of the PVA solution, and the particle size of the nanoparticles is 50 nm; S34: continuing to stir at a speed of 500 rpm for 1.5 hours until the nanoparticles are uniformly dispersed in the PVA solution to form a nanocomposite solution; S35: The uniformly dispersed nanocomposite solution is prepared into a third layer of PVA film by a casting method, the casting temperature is controlled at 50° C., the casting speed is 7 m / min, and the obtained film thickness is 20 μm, which serves as an optimized layer.

[0028] S4 specifically includes: S41: stacking the prepared first layer of PVA film, second layer of PVA film and third layer of PVA film in sequence, ensuring that the surface of each layer of film is flat and wrinkle-free; S42: placing the stacked multi-layer PVA film in a heat press, preheating the upper and lower pressing plates of the heat press to 120° C., and controlling the pressing pressure at 3 MPa; S43: keeping the multi-layer film pressed in a hot press for 15 minutes to ensure that each layer of the film is fully bonded under the action of pressure and temperature to form an overall composite structure; S44: The composite multilayer film is taken out from the hot press and placed on a cooling table to be naturally cooled to room temperature, and the pressure is maintained in the cooling state to prevent the composite film from warping or delamination.

[0029] The swelling treatment in S5 specifically includes: S51: preparing a swelling agent solution, mixing deionized water and ethanol in a volume ratio of 7:2 to form a swelling agent solution, and heating the swelling agent solution to 50° C.; S52: completely immersing the prepared multilayer composite membrane in the preheated swelling agent solution, ensuring that the solution can fully cover every part of the multilayer membrane; S53: keeping the multilayer composite film immersed in the swelling agent solution for 30 minutes, during which the solution is slightly stirred to ensure that the solution is evenly in contact with the film surface, until the second layer of PVA film is fully swollen; S54: The swollen multilayer composite film is taken out from the swelling agent solution, and the excess solution on the surface is removed by rolling, and then the film is hung or laid flat on a drying table to dry naturally to room temperature.

[0030] S6 specifically includes: S61: The dye is an acid dye, and the concentration of the acid dye is 1%; S62: dissolving the selected dye in deionized water in a proportion such that the weight ratio of the dye to the deionized water is 1:100 to form a dyeing solution, and controlling the temperature of the dyeing solution at 60° C. and adjusting the pH value to 5; S63: completely immersing the swollen multilayer composite film in the dyeing solution for 60 minutes, and maintaining uniform stirring of the dyeing solution during this period, with the stirring speed controlled at 200 rpm to ensure that the dye evenly penetrates into the second layer of PVA film; S64: After dyeing is completed, the multilayer composite membrane is taken out from the dyeing solution and immediately rinsed in deionized water to remove excess dye that is not adsorbed, and the temperature of the rinse water is controlled at 35°C; S65: Hang the washed multilayer composite film on a drying table and dry it to room temperature.

[0031] S7 specifically includes: S71: Fix the dyed multilayer composite film on the fixture of the biaxial stretching device to ensure that the film is flat and wrinkle-free; S72: firstly stretching the multilayer composite film along the X direction, with a stretching ratio of 3 times and a stretching speed of 5 mm / s; S73: After completing the stretching in the X direction, immediately stretching is performed in the Y direction, with a stretching ratio of 3 times and a stretching speed of 5 mm / s, to ensure uniform stretching of the film in the Y direction; S74: After completing the biaxial stretching, the stretched multilayer composite film is kept in the stretched state for cooling to room temperature to fix the size and shape of the stretched film.

[0032] The heat setting treatment in S8 specifically includes: S81: Fixing the biaxially stretched multilayer composite film on the frame of the heat setting device to ensure that the film is flat and wrinkle-free on the frame and remains in a stretched state; S82: placing the fixed multilayer composite film in a heat setting furnace, controlling the heat setting temperature at 130° C. for 10 minutes, and ensuring that the film is fully set at this temperature; S83: After the setting time is over, the multilayer composite film is taken out from the heat setting furnace and immediately placed on a cooling table for rapid cooling. The cooling temperature is controlled at 30° C. to ensure that the film size and shape are fixed; S84: After cooling is completed, the multi-layer composite film is removed from the frame to obtain a final multi-layer composite PVA film product.

[0033] Example 2 Step 1: Preparation of the base support layer. First, high molecular weight PVA powder (molecular weight of 130,000) and deionized water were mixed at a weight ratio of 1:5. The mixed solution was then heated to 70°C and stirred for 30 minutes until the PVA was completely dissolved to form a uniform PVA solution A. The solution was filtered through a 200-mesh filter to remove undissolved solids and impurities. After filtration, the PVA solution A was prepared into a film by a casting method at 50°C at a casting speed of 5 m / min to obtain a base support layer with a thickness of 50 μm. Step 2: Preparation of the functional adjustment layer: low molecular weight PVA powder (molecular weight of 70,000) and deionized water were mixed at a weight ratio of 1:4, and heated to 70°C with a stirring speed of 200 rpm until the PVA was completely dissolved. Then, a plasticizer (ethylene glycol) was added, accounting for 5% of the total weight of the PVA solution B, and stirring was continued for 30 minutes. Then, an ultraviolet absorber (benzophenone compound) and an antioxidant (butylated hydroxyanisole) were added in sequence, accounting for 0.1% and 0.1% of the total weight of the PVA solution B respectively, and stirring was continued for 30 minutes. Finally, the uniformly mixed PVA solution B was prepared into a 20 μm thick functional adjustment layer at a casting temperature of 40°C and a casting speed of 5 m / min. Step 3: Preparation of the optimized layer, firstly, PVA powder with a molecular weight of 40,000 was mixed with deionized water in a weight ratio of 1:4, heated to 70°C and stirred at 200 rpm for 30 minutes to form a uniform PVA solution, and zinc oxide nanoparticles (particle size of 10 nm) were slowly added to the uniform PVA solution preheated to 50°C, the nanoparticles accounting for 0.5% of the total weight of the PVA solution, and stirred at 300 rpm for 1 hour to ensure that the nanoparticles were evenly dispersed, after which the nanocomposite solution was prepared into a 10 μm thick optimized layer under casting conditions of 40°C and 3 m / min; Step 4: Composite of multilayer films: stack the prepared first, second and third PVA films in sequence, ensure that the surface of each layer is flat and wrinkle-free, and press them in a hot press at 90°C for 5 minutes with a pressing pressure of 1 MPa to form an overall composite structure; Step 5: Swelling treatment: ethanol and deionized water are mixed in a volume ratio of 7:3 to form a swelling agent solution, and heated to 30°C. The multilayer composite membrane is completely immersed in the preheated solution for 10 minutes and then taken out; Step 6: dyeing treatment, select a reactive dye with a concentration of 0.05%, dissolve it with deionized water at a weight ratio of 1:50 to form a dyeing solution, heat the dyeing solution to 30°C, adjust the pH to 4, completely immerse the swollen multilayer composite membrane, dye for 20 minutes, and stir at a speed of 100 rpm. After dyeing, rinse the multilayer composite membrane in deionized water at 25°C to remove the unabsorbed dye, and hang to dry to room temperature; Step 7: Biaxial stretching: fix the dyed multilayer composite film on the fixture of the biaxial stretching device, first stretch it in the X direction to twice its original length, and the stretching speed is 1 mm / s. After completion, stretch it in the Y direction in the same way. After the stretching is completed, cool it to room temperature to fix the size and shape after stretching; Step 8: Heat setting treatment, fix the biaxially stretched multilayer composite film on the frame of the heat setting device, keep it at 100°C for 2 minutes, and after setting, quickly cool it to 25°C. After cooling, remove it from the frame to obtain the final multilayer composite PVA film product.

[0034] Example 3 Step 1: Preparation of the base support layer. First, high molecular weight PVA powder (molecular weight of 170,000) and deionized water were mixed at a weight ratio of 1:10, and then the mixed solution was heated to 80°C and stirred for 60 minutes until the PVA was completely dissolved to form a uniform PVA solution A. The solution was filtered through a 400-mesh filter to remove undissolved solids and impurities. After filtration, the PVA solution A was prepared into a film by a casting method at 70°C at a casting speed of 15 m / min to obtain a base support layer with a thickness of 100 μm. Step 2: Preparation of the functional adjustment layer: low molecular weight PVA powder (molecular weight of 100,000) and deionized water were mixed at a weight ratio of 1:8, and heated to 90°C with a stirring speed of 500 rpm until the PVA was completely dissolved. Then, a plasticizer (glycerol) was added, accounting for 15% of the total weight of the PVA solution B, and stirring was continued for 30 minutes. Then, an ultraviolet absorber (hydroxybenzotriazole compound) and an antioxidant (butylated hydroxytoluene) were added in sequence, accounting for 1% and 1.5% of the total weight of the PVA solution B respectively, and stirring was continued for 60 minutes. Finally, the uniformly mixed PVA solution B was prepared into a 50 μm thick functional adjustment layer at a casting temperature of 60°C and a casting speed of 12 m / min. Step 3: Preparation of the optimized layer, firstly, PVA powder with a molecular weight of 100,000 was mixed with deionized water in a weight ratio of 1:8, heated to 90°C and stirred at 500 rpm for 90 minutes to form a uniform PVA solution, titanium oxide nanoparticles (particle size of 100 nm) were slowly added to the uniform PVA solution preheated to 70°C, the nanoparticles accounting for 5% of the total weight of the PVA solution, and stirred at 600 rpm for 2 hours to ensure that the nanoparticles were evenly dispersed, after which the nanocomposite solution was prepared into a 30 μm thick optimized layer under casting conditions of 60°C and 10 m / min; Step 4: Composite of multilayer films: stack the prepared first, second and third PVA films in sequence, ensure that the surface of each layer is flat and wrinkle-free, and press them in a hot press at 150°C with a pressing pressure of 5MPa for 20 minutes to form an overall composite structure; Step 5: Swelling treatment: ethanol and deionized water are mixed in a volume ratio of 7:1 to form a swelling agent solution, and heated to 60°C. The multilayer composite membrane is completely immersed in the preheated solution for 60 minutes and then taken out; Step 6: dyeing treatment, select an acid dye with a concentration of 2%, dissolve it with deionized water at a weight ratio of 1:200 to form a dyeing solution, heat the dyeing solution to 70°C, adjust the pH to 7, completely immerse the swollen multilayer composite membrane, dye for 80 minutes, and stir at a speed of 300 rpm. After dyeing, rinse the multilayer composite membrane in deionized water at 40°C to remove the unabsorbed dye, and hang to dry to room temperature; Step 7: Biaxial stretching: fix the dyed multilayer composite film on the fixture of the biaxial stretching device, first stretch it along the X direction to 5 times the original length, and the stretching speed is 10 mm / s. After completion, stretch it along the Y direction in the same way. After the stretching is completed, cool it to room temperature to fix the size and shape after stretching; Step 8: Heat setting treatment, fix the biaxially stretched multilayer composite film on the frame of the heat setting device, keep it at 160°C for 15 minutes, and after setting, quickly cool it to 40°C. After cooling, remove it from the frame to obtain the final multilayer composite PVA film product.

[0035] Table 1 Comparison of finished product parameters and performance As can be seen from Table 1 above, Example 1 shows the best performance in various measurement indicators, including the highest thickness, transparency, tensile strength, elongation at break, UV blocking rate and heat resistance, which makes it the most suitable product for applications requiring high performance. Although Examples 2 and 3 have better performance in some aspects, they fail to surpass Example 1 in all major parameters, showing that Example 1 has obvious advantages in comprehensive performance and adaptability.

[0036] Table 2 Comparison of other parameters It can be seen from Table 2 above that Example 1 continues to lead in comprehensive performance, especially in production cost, production time and environmental impact. This example can achieve efficient production at a lower cost and shorter production time, and has lower CO2 emissions, showing its smaller impact on the environment. In addition, Example 1 also shows the highest performance in dye stability and hydrolysis stability, ensuring the durability and stability of the product during use. In terms of mechanical processing difficulty, Example 1 also shows the best operating convenience, further proving its superiority in production and application.

[0037] The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention. In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details. In addition, in order to avoid unnecessary confusion about the essence of the present invention, well-known methods, processes, procedures, components and circuits are not described in detail.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a multilayer composite PVA film, characterized in that: The following steps are involved: S1: preparing a base support layer, mixing high molecular weight PVA powder with deionized water, heating and stirring until the PVA is completely dissolved to form a PVA solution A; and preparing the PVA solution A into a first layer of PVA film as a base support layer by a casting method; S2: preparing a function regulating layer, dissolving low molecular weight PVA powder, plasticizer and deionized water to form a PVA solution B, then adding a UV absorber and an antioxidant to the PVA solution B, stirring evenly, and preparing a second layer of PVA film as a function regulating layer by a casting method; S3: preparing an optimized layer, mixing the nanoparticles with the prepared PVA solution to form a uniformly dispersed nanocomposite solution, and preparing a third layer of PVA film as the optimized layer by a casting method; S4: Compounding the prepared first PVA film, the second PVA film and the third PVA film together by a heat pressing method to form a multi-layer composite film structure; S5: performing swelling treatment, immersing the multilayer composite film in a solution containing a swelling agent, so that the second layer of PVA film is fully swollen; S6: Select a dye compatible with PVA to dye the swollen multilayer composite film; S7: biaxially stretching the dyed multilayer composite film in the X and Y directions; S8: The multi-layer composite film after biaxial stretching is subjected to heat setting treatment to fix the size and shape of the film to obtain a final multi-layer composite PVA film product.

2. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The molecular weight of the high molecular weight PVA powder is 130,000-170,000; the molecular weight of the low molecular weight PVA powder is 70,000-100,000; the nanoparticles are selected from titanium oxide or zinc oxide; the plasticizer is glycerol or ethylene glycol; the ultraviolet absorber is specifically a hydroxybenzotriazole compound or a benzophenone compound; and the antioxidant is butylated hydroxytoluene or butylated hydroxyanisole.

3. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S1 specifically includes: S11: adding high molecular weight PVA powder into deionized water in proportion, wherein the weight ratio of the high molecular weight PVA powder to the deionized water is 1:5 to 1:10; S12: heating the mixed solution to 80° C. to 95° C. and continuously stirring for 30 to 60 minutes until the PVA powder is completely dissolved to form a uniform PVA solution A; S13: cooling the obtained PVA solution A to room temperature, and then filtering through a 200 to 400 mesh filter to remove incompletely dissolved solid particles and impurities; S14: The filtered PVA solution A is prepared into a PVA film by a casting method. During the process, the casting temperature is controlled at 50 to 70° C., the casting speed is 5 to 15 m / min, and the obtained film thickness is 50 to 100 μm, which serves as a basic support layer.

4. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S2 specifically includes: S21: adding low molecular weight PVA powder to deionized water in a proportion, wherein the weight ratio of the low molecular weight PVA powder to deionized water is 1:4 to 1:8, stirring and heating to 70° C. to 90° C., and controlling the stirring speed to 200 to 500 rpm, until the PVA is completely dissolved to form a PVA solution B; S22: adding a plasticizer to the PVA solution B, wherein the amount of the plasticizer added is 5% to 15% of the total weight of the PVA solution B, and continuing stirring for 30 minutes; S23: under stirring, sequentially adding a UV absorber and an antioxidant to the PVA solution B, wherein the amount of the UV absorber added is 0.1% to 1% of the total weight of the PVA solution B, and the amount of the antioxidant added is 0.1% to 1.5% of the total weight of the PVA solution B, and stirring is continued for 30 to 60 minutes after the addition; S24: The uniformly mixed PVA solution B is prepared into a second layer of PVA film by a casting method, specifically the casting temperature is controlled at 40°C to 60°C, the casting speed is 5 to 12 m / min, and the obtained film thickness is 20 to 50 μm, which serves as a functional adjustment layer.

5. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S3 specifically includes: S31: preparing a preliminary PVA solution, mixing PVA powder having a molecular weight of 40,000 to 100,000 with deionized water in a weight ratio of 1:4 to 1:8, and heating to 70° C. to 90° C., while stirring at a speed of 200 to 500 rpm for 30 to 90 minutes, until the PVA powder is completely dissolved to form a uniform PVA solution; S32: heating the prepared PVA solution to 50° C. to 70° C. and stirring at a rotation speed of 300 to 600 rpm; S33: under continuous stirring, slowly adding nanoparticles into the PVA solution, wherein the amount of the nanoparticles added is 0.5% to 5% of the total weight of the PVA solution, and the particle size of the nanoparticles is 10 nm to 100 nm; S34: continuing to stir at a speed of 300 to 600 rpm for 1 to 2 hours until the nanoparticles are uniformly dispersed in the PVA solution to form a nanocomposite solution; S35: The uniformly dispersed nanocomposite solution is prepared into a third layer of PVA film by a casting method, the casting temperature is controlled at 40°C to 60°C, the casting speed is 3 m / min to 10 m / min, and the obtained film thickness is 10 to 30 μm, as an optimization layer.

6. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S4 specifically includes: S41: stacking the prepared first layer of PVA film, second layer of PVA film and third layer of PVA film in sequence, ensuring that the surface of each layer of film is flat and wrinkle-free; S42: placing the stacked multi-layer PVA film in a heat press, preheating the upper and lower pressing plates of the heat press to 90° C. to 150° C., and controlling the pressing pressure to 1 MPa to 5 MPa; S43: Pressing the multilayer film in a hot press for 5 to 20 minutes to form an overall composite structure; S44: The laminated multilayer film is taken out from the hot press and placed on a cooling table to be naturally cooled to room temperature.

7. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S5 specifically includes: S51: preparing a swelling agent solution, mixing deionized water and ethanol in a volume ratio of 7:3 to 7:1 to form a swelling agent solution, and heating the swelling agent solution to 30° C. to 60° C.; S52: completely immersing the prepared multilayer composite membrane in a preheated swelling agent solution; S53: keeping the multilayer composite film immersed in the swelling agent solution for 10 to 60 minutes; S54: The swollen multilayer composite film is taken out from the swelling agent solution, and the excess solution on the surface is removed by rolling, and then the film is hung or laid flat on a drying table to dry naturally to room temperature.

8. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S6 specifically includes: S61: The dye is an acid dye or a reactive dye, the concentration of the acid dye is 0.1% to 2.0%, and the concentration of the reactive dye is 0.05% to 1.5%; S62: dissolving the selected dye in deionized water in a proportion, wherein the weight ratio of the dye to the deionized water is 1:50 to 1:200, to form a dyeing solution, and controlling the temperature of the dyeing solution to be between 30° C. and 70° C., and adjusting the pH value to be between 4 and 7; S63: completely immersing the swollen multilayer composite film in the dyeing solution for a dyeing time of 20 to 80 minutes, and during this period, the dyeing solution is uniformly stirred at a stirring speed of 100 to 300 rpm; S64: After dyeing is completed, the multilayer composite membrane is taken out from the dyeing solution and immediately rinsed in deionized water to remove excess dye that has not been adsorbed, and the temperature of the rinse water is controlled at 25 to 40°C; S65: Hang the washed multilayer composite film on a drying table and dry it to room temperature.

9. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S7 specifically includes: S71: Fix the dyed multilayer composite film on the fixture of the biaxial stretching device to ensure that the film is flat and wrinkle-free; S72: firstly stretching the multilayer composite film along the X direction, with a stretching ratio of 2 to 5 times and a stretching speed of 1 to 10 mm / s; S73: After completing the stretching in the X direction, immediately stretching in the Y direction, with a stretching ratio of 2 to 5 times and a stretching speed of 1 to 10 mm / s; S74: After completing the biaxial stretching, the stretched multilayer composite film is kept in the stretched state for cooling to room temperature to fix the size and shape of the stretched film.

10. The method for preparing a multi-layer composite PVA film according to claim 1, characterized in that: The S8 specifically includes: S81: Fixing the biaxially stretched multilayer composite film on the frame of the heat setting device to ensure that the film is flat and wrinkle-free on the frame and remains in a stretched state; S82: placing the fixed multilayer composite film in a heat setting furnace, controlling the heat setting temperature at 100° C. to 160° C. for a setting time of 2 to 15 minutes; S83: After the setting time is over, the multilayer composite film is taken out from the heat setting furnace and immediately placed on a cooling table for rapid cooling, and the cooling temperature is controlled at 25° C. to 40° C.; S84: After cooling is completed, the multi-layer composite film is removed from the frame to obtain a final multi-layer composite PVA film product.

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