Process for the preparation of polyvinyl acetal, polyvinyl acetal film and process and use thereof

Abstract

The disclosure provides a polyvinyl acetal preparation method, a polyvinyl acetal film and a preparation method and application thereof. The polyvinyl acetal preparation method comprises the following steps: adding an acidic catalyst and a first amount of aliphatic aldehyde into a polyvinyl alcohol solution to perform a first-stage reaction at a temperature of 20-30 DEG C, to obtain a first mixture; cooling the first mixture to 5-15 DEG C at a cooling rate of 5 DEG C / min, adding a second amount of aliphatic aldehyde, and performing a second-stage reaction to obtain a second mixture; heating the second mixture to 50-80 DEG C to perform a third-stage reaction, to obtain a third mixture; adjusting the pH value of the third mixture to terminate the reaction, to obtain a polyvinyl acetal with a ratio of meso configuration and racemic configuration of 3.6-6.0, and the mass ratio of the total amount of polyvinyl alcohol, acidic catalyst and aliphatic aldehyde is (10-50):(5-25):(5-15), the total amount of aliphatic aldehyde is the sum of the first amount and the second amount, the first amount accounts for 10-50% of the total amount of aliphatic aldehyde, and the second amount accounts for 50-90% of the total amount of aliphatic aldehyde.

Description

Technical Field

[0001] This disclosure relates to the field of polymer materials technology, and in particular to a method for preparing polyvinyl acetal, a polyvinyl acetal film, the preparation method thereon, and its applications. Background Technology

[0002] Polyvinyl acetal film, due to its excellent impact resistance, adhesion, weather resistance, corrosion resistance, and optical properties, has been widely used in various fields such as interlayers in architectural and automotive safety glass, photovoltaic cells, and multilayer ceramic capacitors. Nevertheless, polyvinyl acetal film still has shortcomings in tensile strength and elongation at break, limiting its potential in specific applications.

[0003] To improve the mechanical properties of polyvinyl acetal films, the main technical approaches currently employed include inorganic nanoparticle blending, multilayer composites with different base films, and chemical grafting modification. While these methods have achieved some success in improving mechanical properties, they also increase production costs and process complexity, hindering large-scale industrial production.

[0004] Therefore, to address the need for improved mechanical properties, especially tensile strength, of polyvinyl acetal films, a simple and economical control method is still required to optimize the performance of polyvinyl acetal films. Summary of the Invention

[0005] In view of the above, the main objective of this disclosure is to provide a method for preparing polyvinyl acetal, a polyvinyl acetal film, the preparation method thereon, and its application, in order to at least partially solve at least one of the aforementioned technical problems.

[0006] To achieve the above objectives, the technical solution disclosed herein is as follows:

[0007] In one aspect of this disclosure, a method for preparing polyvinyl acetal is provided, comprising:

[0008] At a temperature of 20~30℃, an acidic catalyst and a first amount of aliphatic aldehyde are added to a polyvinyl alcohol solution to carry out the first stage reaction, resulting in a first mixed solution.

[0009] The first mixed solution was cooled to 5~15℃ at a cooling rate of 5℃ / min, and a second amount of fatty aldehyde was added to carry out the second stage reaction to obtain the second mixed solution.

[0010] The second mixed solution is heated to 50-80℃ to carry out the third stage reaction, resulting in the third mixed solution.

[0011] The reaction was terminated after adjusting the pH of the third mixed solution to a preset value, yielding polyvinyl acetal. The polyvinyl acetal comprises meso- and racemic polyvinyl acetals, with a ratio of 3.6 to 6.0.

[0012] The mass ratio of polyvinyl alcohol, acidic catalyst and fatty aldehyde added is (10-50):(5-25):(5-15).

[0013] The total amount of fatty aldehyde added is the sum of the first and second additions. The first addition accounts for 10% to 50% of the total amount of fatty aldehyde added, and the second addition accounts for 50% to 90% of the total amount of fatty aldehyde added.

[0014] In another aspect of this disclosure, a method for preparing a polyvinyl acetal film is provided, wherein the polyvinyl acetal prepared by the above method is dissolved in an organic solvent to obtain a mixed solution, wherein the mass ratio of polyvinyl acetal to organic solvent is (5~60):100.

[0015] The mixed solution is poured into a mold and dried to obtain a polyvinyl acetal film.

[0016] In another aspect of this disclosure, a polyvinyl acetal film is provided, which is prepared by the above-described method for preparing a polyvinyl acetal film.

[0017] In another aspect of this disclosure, the application of the above-described polyvinyl acetal film in functional materials is provided.

[0018] According to embodiments of this disclosure, a method for preparing polyvinyl acetal is provided. This method employs segmented feeding and temperature control. By adjusting the addition ratio of polyvinyl alcohol, aliphatic aldehyde, and acidic catalyst, the type of catalyst, and the reaction temperature, as well as optimizing the corresponding parameters, a polyvinyl acetal with a meso-to-racemic configuration ratio between 3.6 and 6.0 is prepared. By controlling the microstructure of polyvinyl acetal, its tensile strength, toughness, and ductility are improved, thereby optimizing the macroscopic mechanical properties of polyvinyl acetal. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of polyvinyl acetal in this disclosure. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0021] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0023] Polyvinyl acetal film plays a crucial role in applications such as safety glass laminates, photovoltaic cells, and multilayer ceramic capacitors in the construction and automotive industries due to its excellent impact resistance, adhesion, weather resistance, corrosion resistance, and superior optical properties. However, limitations in tensile strength and elongation at break affect its performance in applications requiring mechanical loads. Furthermore, currently used modification methods are costly and complex, hindering large-scale industrial production.

[0024] In realizing the concept of this disclosure, it was discovered that the ratio of meso (m) to racemic (r) configurations in polyvinyl acetal at the same degree of acetalization can significantly affect the regularity of the internal sequence structure of the material, thereby controlling its phase structure scale. Specifically, as the ratio of meso to racemic configurations (m / r) increases, the sequence distribution of hydroxyl groups and acetal rings on the polyvinyl acetal molecular chain gradually becomes longer, leading to an increase in the scale of the formed phase separation structure, thereby generating more hydrogen bonds and enhancing the strength of the hydrogen bonds, resulting in higher tensile strength and better tensile properties of polyvinyl acetal. However, when m / r is too high, it leads to excessive intermolecular hydrogen bond content and strength, restricting the mobility of polymer molecular chains, weakening stress dissipation capacity, and thus reducing the toughness and ductility of the material. Therefore, this disclosure uses a staged feeding reaction method, under the action of an acidic catalyst, to cause the hydroxyl groups on the polyvinyl alcohol molecular chain to undergo a condensation reaction with the aldehyde groups of aliphatic aldehydes to form polyvinyl acetal. By controlling the mass ratio of polyvinyl alcohol, aliphatic aldehyde, and acidic catalyst, as well as the type of catalyst and reaction temperature, polyvinyl alcohol acetals with an m / r range of 3.6–6.0 can be prepared. This disclosed preparation method avoids complex physical and chemical modification steps. By controlling the microstructure of polyvinyl alcohol acetal, the macroscopic mechanical properties of polyvinyl alcohol acetal films, especially their tensile properties, are effectively improved. Furthermore, this preparation method effectively reduces production costs and complexity, making it suitable for large-scale industrial production. It provides an economical and efficient solution for improving the tensile properties of polyvinyl alcohol acetal and expanding its application areas.

[0025] Figure 1 This is a flowchart of the preparation method of polyvinyl acetal in this disclosure.

[0026] According to one aspect of the present disclosure, a method for preparing polyvinyl acetal is provided, such as... Figure 1 As shown, it includes the following steps S1~S4:

[0027] Step S1: At a temperature of 20~30℃, an acidic catalyst and a first amount of aliphatic aldehyde are added to the polyvinyl alcohol solution to carry out the first stage reaction, and a first mixed solution is obtained.

[0028] Step S2: Cool the first mixed solution to 5~15℃ at a cooling rate of 5℃ / min, and add the second amount of aliphatic aldehyde to carry out the second stage reaction to obtain the second mixed solution;

[0029] Step S3: Heat the second mixed solution to 50~80℃ to carry out the third stage reaction to obtain the third mixed solution;

[0030] Step S4: Adjust the pH value of the third mixed solution to the preset value and then terminate the reaction to obtain polyvinyl acetal.

[0031] The polyvinyl acetal includes mesopolyvinyl acetal and racemic polyvinyl acetal, with a ratio of 3.6 to 6.0.

[0032] The mass ratio of polyvinyl alcohol, acid catalyst and fatty aldehyde is (10-50):(5-25):(5-15). The total amount of fatty aldehyde is the sum of the first amount and the second amount. The first amount accounts for 10-50% of the total amount of fatty aldehyde, and the second amount accounts for 50%-90% of the total amount of fatty aldehyde.

[0033] According to embodiments of this disclosure, a method for preparing polyvinyl acetal is provided. The method employs segmented feeding and temperature control. By adjusting the addition ratio of polyvinyl alcohol, fatty aldehyde, and acidic catalyst, the type of catalyst, the reaction temperature, and the optimization of parameters, a polyvinyl acetal with a meso-racemic configuration ratio between 3.6 and 6.0 is prepared.

[0034] According to embodiments of this disclosure, the reaction in step S1 is carried out at a temperature of 20-30°C. For example, it can be 20°C, 22°C, 25°C, 28°C, 30°C, etc. By controlling the initial temperature, the catalytic reaction rate is reduced, ensuring that the initial stage of the reaction proceeds at a suitable rate, avoiding agglomeration and cross-linking. The initial addition amount accounts for 10-50% of the total aliphatic aldehyde addition, for example, 10%, 20%, 30%, 40%, 50%, etc. First, the acidic catalyst is added to the polyvinyl alcohol solution and thoroughly mixed with the polyvinyl alcohol, laying the foundation for the subsequent addition of the aliphatic aldehyde, which helps control the degree of cross-linking in the acetal reaction. The aliphatic aldehyde is gradually and slowly added, and the hydroxyl groups on the polyvinyl alcohol molecular chain react with the aliphatic aldehyde to form an initial acetal structure. Because the polyvinyl alcohol molecular chain has a large number of hydroxyl groups, and the molecular chain is in a stretched state in the initial stage of the reaction, it is conducive to the formation of a racemic structure, thereby increasing the ratio of the meso configuration (m) and the racemic configuration (r) in the polyvinyl alcohol acetal.

[0035] According to embodiments of this disclosure, in step S2, the temperature is lowered to 5-15°C for the reaction, for example, 5°C, 7°C, 10°C, 13°C, 15°C, etc. Since the acetal reaction tends to be vigorous at high temperatures, it can cause premature polymer aggregation and cross-linking, leading to agglomeration. Therefore, rapid cooling helps control the reaction rate and selectivity, avoiding side reactions caused by excessively rapid reactions. The second addition amount accounts for 50%-90% of the total aliphatic aldehyde addition, for example, 50%, 60%, 70%, 80%, 90%, etc., continuing to add a larger amount of aliphatic aldehyde to carry out the acetalization reaction and increase the degree of acetalization.

[0036] According to embodiments of this disclosure, in step S3, the temperature is raised to 50-80°C for the reaction, for example, to 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., to continue the heating reaction, accelerating the acetalization reaction of the remaining aliphatic aldehydes with polyvinyl alcohol, ensuring the reaction proceeds completely, and achieving the expected conversion rate and selectivity. An appropriate temperature range can avoid the problem of a slow reaction rate due to excessively low temperatures, while preventing side reactions or over-reactions caused by excessively high temperatures, thereby affecting the purity and yield of the product.

[0037] According to the embodiments of this disclosure, the ratio of mesopolyvinyl acetal to racemic polyvinyl acetal in the prepared polyvinyl acetal is 3.6 to 6.0, for example, it can be 3.6, 3.8, 4.0, 4.5, 5.0, 5.5, 6.0, etc.

[0038] According to embodiments of this disclosure, in step S4, the pH value of the third mixed solution is adjusted to a preset value to terminate the reaction. Specifically, any one or more alkaline solutions selected from sodium hydroxide, potassium hydroxide, and sodium bicarbonate can be used to adjust the pH value. Alkaline solutions neutralize the acidic catalyst, reducing its activity and effectively preventing excessive acetalization of polyvinyl alcohol acetal, thereby ensuring the quality and performance of the product. The preset value ranges from 5 to 8, for example, 5, 6, 6.5, 7, 7.5, 8, etc. By precisely controlling the pH value, byproducts in the process can be neutralized to optimize the performance of the final product. Simultaneously, terminating the reaction facilitates subsequent product processing, such as precipitation, filtration, washing, and drying, to obtain high-purity polyvinyl alcohol acetal.

[0039] According to embodiments of this disclosure, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 5-30 wt%, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc. An appropriate polyvinyl alcohol solution concentration ensures good fluidity of the solution, facilitating stirring and heat transfer, while maintaining sufficient polyvinyl alcohol concentration to promote an effective acetal reaction, avoiding the problem of excessive viscosity of the polyvinyl alcohol solution affecting reaction uniformity. The average degree of polymerization of polyvinyl alcohol is 500-4000, for example, 500, 1000, 2000, 3000, 4000, etc., and the degree of alcoholysis is 80-99%, for example, 80%, 85%, 90%, 95%, 99%, etc. The average degree of polymerization of polyvinyl alcohol can be selected according to different application scenarios. A lower degree of polymerization is beneficial to improving the solubility and processability of polyvinyl alcohol acetal; a higher degree of polymerization helps to improve the mechanical strength and thermal stability of polyvinyl alcohol acetal. Polyvinyl alcohol with a degree of hydrolysis between 85% and 99% contains a large number of hydroxyl groups, which provides sufficient reaction sites for acetal reaction and helps to regulate the degree of acetal reaction and the cross-linking network structure.

[0040] Acidic catalysts include organic acid catalysts and / or inorganic acid catalysts. Organic acid catalysts include any one or two of acetic acid, triacetic acid, and p-toluenesulfonic acid, while inorganic acid catalysts include any one or two of sulfuric acid, hydrochloric acid, and nitric acid. By adjusting the type and amount of acidic catalyst, the catalytic reaction rate can be controlled, thereby affecting the ratio of meso and racemic configurations in the acetalization reaction, achieving precise control over the properties of polyvinyl acetal materials. Furthermore, appropriate acidic catalysts can effectively prevent yellowing and poor stability issues during the synthesis of polyvinyl acetal. By rationally selecting catalyst types and combinations and controlling reaction conditions, the performance of polyvinyl acetal can be optimized to meet the needs of different application scenarios.

[0041] Aliphatic aldehydes include any one or more of acetaldehyde, propionaldehyde, butyraldehyde, pentanaldehyde, hexanal, heptaldehyde, octanaldehyde, and dodecaldehyde. As the carbon chain of aliphatic aldehydes increases, the toughness and elasticity of polyvinyl acetal gradually improve. By controlling the types of aliphatic aldehydes, polyvinyl acetals that meet the needs of different practical applications can be obtained.

[0042] According to embodiments of this disclosure, the reaction time for the first stage is 15-60 min, for example, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc.; the reaction time for the second stage is 0.5-3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.; and the reaction time for the third stage is 1-5 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h, etc. Suitable reaction times ensure that polyvinyl alcohol and aliphatic aldehydes can react fully under the action of an acidic catalyst, allowing the acetal reaction to proceed completely and avoiding incomplete or excessive reactions.

[0043] According to embodiments of this disclosure, the degree of acetalization of polyvinyl alcohol acetal is 78% to 90%, for example, 78%, 80%, 85%, 88%, 90%, etc., and the number-average molecular weight of polyvinyl alcohol acetal is 60,000 to 80,000, for example, 60,000, 65,000, 70,000, 75,000, 80,000, etc. The degree of acetalization refers to the mass percentage of the monomer containing the acetal group in the entire polyvinyl alcohol acetal molecular chain. Through the preparation method of this disclosure, the degree of acetalization and molecular weight of polyvinyl alcohol acetal can be precisely controlled, thereby ensuring that the material possesses excellent chemical stability and mechanical strength.

[0044] According to another aspect of this disclosure, a method for preparing a polyvinyl acetal film is provided, wherein the polyvinyl acetal prepared by the above method is dissolved in an organic solvent to obtain a mixed solution, wherein the mass ratio of polyvinyl acetal to organic solvent is (5~60):100; the mixed solution is poured into a mold and dried to obtain a polyvinyl acetal film.

[0045] According to embodiments of this disclosure, the mass ratio of polyvinyl acetal to organic solvent can be, for example, 5:100, 10:100, 30:100, 50:100, 60:100, etc. An appropriate ratio range ensures the solubility and flowability of polyvinyl acetal in the solvent, thereby facilitating stirring and heat transfer. Simultaneously, it ensures that the concentration of polyvinyl acetal is sufficient to form an effective film thickness, avoiding the inability to form a film due to an excessively dilute mixed solution, or the film's uniformity being affected by an excessively viscous mixed solution.

[0046] According to embodiments of this disclosure, in specific operations, the dissolution reaction temperature is 50~120℃, for example, 50℃, 70℃, 90℃, 100℃, 120℃, etc.; the dissolution time is 1~8h, for example, 1h, 2h, 4h, 6h, 8h, etc.; the stirring speed is 100~400rpm / min, for example, 100rpm / min, 200rpm / min, 250rpm / min, 300rpm / min, 400rpm / min, etc.; the drying temperature is 50~150℃, for example, 50℃, 80℃, 100℃, 130℃, 150℃, etc.; the drying time is 5~24h, for example, 5h, 7h, 10h, 15h, 20h, 24h, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable. By adjusting the reaction parameters, problems such as slow reaction rate and uneven dissolution caused by excessively low temperature, insufficient stirring time, or excessively slow rotation speed are avoided. At the same time, it can prevent oxidation side reactions that may occur when the temperature is too high, the stirring time is too long, or the rotation speed is too high, thereby improving the homogeneity of the mixed solution.

[0047] According to embodiments of this disclosure, the organic solvent includes any one or two of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol. The above-mentioned organic solvents have good solubility for polyvinyl acetal, can dissolve polyvinyl acetal at a lower temperature, and, as volatile solvents, facilitate the subsequent drying process.

[0048] The mold includes either a polytetrafluoroethylene (PTFE) mold or a glass mold. In practice, before film formation, the reaction solution is allowed to stand to eliminate residual air bubbles and prevent film defects. The selected mold has good chemical resistance and high-temperature resistance, can withstand the temperature during the drying process, and is easy to demold, ensuring a smooth and defect-free film surface. Ten minutes before pouring the mixed solution into the mold, the mold is preheated to oven temperature to maintain the temperature of the mixed solution and prevent uneven cooling due to excessively low mold temperature, thus reducing film defects. Before pouring into the mold, any obvious air bubbles in the solution must be removed, and then the solution is placed in an oven for drying to obtain a polyvinyl acetal film.

[0049] The drying temperature is 50~150℃, for example, 50℃, 70℃, 90℃, 130℃, 150℃, etc., and the drying time is 5~24h, for example, 5h, 8h, 10h, 15h, 20h, 24h, etc. The drying temperature and time are adjusted according to the different film thicknesses. An appropriate temperature range can accelerate the evaporation of solvents while avoiding the thermal degradation of polyvinyl acetal caused by excessively high temperatures.

[0050] According to another aspect of this disclosure, a polyvinyl acetal film is provided, which is prepared by the above-described method for preparing a polyvinyl acetal film.

[0051] According to embodiments of this disclosure, polyvinyl acetal films prepared using polyvinyl acetal with an m / r ratio in the range of 3.6 to 6.0 exhibit the following characteristics: as the ratio of meso to racemic configurations (m / r) increases, the sequence distribution of hydroxyl groups and acetal rings on the polyvinyl acetal molecular chain gradually lengthens, leading to an increase in the scale of the formed phase-separated structure, thereby generating more hydrogen bonds and enhancing their strength. Ultimately, this results in the polyvinyl acetal film exhibiting higher tensile strength and better tensile properties under the same strain. However, excessively high m / r values ​​lead to excessive intermolecular hydrogen bond content and strength, restricting the mobility of polymer molecular chains, weakening stress dissipation capacity, and thus reducing the toughness and ductility of the polyvinyl acetal film.

[0052] According to embodiments of this disclosure, the thickness of the polyvinyl acetal film is 80~150μm, for example, 80μm, 90μm, 100μm, 120μm, or 150μm. Appropriate thickness ensures the mechanical strength and tensile properties of the film, while also meeting the needs of different industrial applications.

[0053] According to embodiments of this disclosure, the tensile strength of the polyvinyl acetal film is 6-15 MPa at a strain of 2, exhibiting good mechanical properties. The polyvinyl acetal film remains stable under tensile force and is not easily broken. Simultaneously, appropriate tensile strength also contributes to the flexibility and ductility required during processing and use, enabling it to adapt to different molding and application requirements and preventing brittle fracture during application.

[0054] According to yet another aspect of this disclosure, an application of the above-described polyvinyl acetal film in functional materials is provided.

[0055] According to embodiments of this disclosure, the functional materials include impact-resistant or shock-absorbing materials. Polyvinyl acetal films are suitable for applications requiring the resistance to mechanical loads, such as in the automotive, construction, photovoltaic, and ceramic capacitor industries.

[0056] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Unless otherwise specified, specific techniques or conditions in the embodiments are conventional methods and can be performed according to the techniques or conditions described in the literature in this field or according to the product instructions. It should be noted that, unless otherwise specified, the methods provided in this disclosure are conventional methods, and the reactants and reagents are readily available from publicly available commercial sources.

[0057] Example 1:

[0058] Embodiment 1 of this disclosure provides a polyvinyl acetal film. The preparation steps include:

[0059] Weigh 40 g of polyvinyl alcohol with a degree of polymerization of 1700 and dissolve it in 1 L of pure water. Stir at 80 °C for 6 hours until a clear and transparent polyvinyl alcohol solution is formed.

[0060] At 20°C, 5 ml of hydrochloric acid was added to a polyvinyl alcohol solution, and then 12 ml of butyraldehyde was slowly added dropwise over 30 minutes. After the reaction continued for 1 hour, a first mixed solution was obtained.

[0061] The first mixed solution was rapidly cooled to 10°C at a cooling rate of 5°C / min, and 12 ml of aliphatic aldehyde was added. The mixture was stirred at a constant speed for 3 hours to obtain the second mixed solution.

[0062] The second mixed solution was heated to 80°C and stirred for another 3 hours to obtain the third mixed solution.

[0063] Add 10 ml of 15 wt% sodium hydroxide solution to the third mixed solution to adjust the pH of the third mixed solution to 7, and continue stirring for 10 minutes to terminate the reaction, thus obtaining polyvinyl acetal precipitate.

[0064] The polyvinyl acetal precipitate was separated by filtration and washed repeatedly with pure water to remove residual reactants and byproducts. The obtained polyvinyl acetal precipitate was placed in a 60°C oven and dried by forced air for 12 hours to obtain polyvinyl acetal with an acetal degree of 80% and a meso-to-racemic configuration ratio (m / r) of 5.0.

[0065] Weigh 2g of polyvinyl acetal with an acetal degree of 80% and an m / r of 5.0, add it to 20ml of N,N-dimethylformamide solvent, and stir at 80℃ for 5 hours until completely dissolved to form a clear and transparent mixed solution. After the mixed solution has stood for 5 minutes, slowly pour it into a polytetrafluoroethylene mold preheated to 80℃, place it in a vacuum oven preheated to 80℃, and dry it in the oven under forced air for 12 hours in a non-vacuum state. Then, dry it under vacuum at 120℃ for 3 hours to obtain a polyvinyl acetal film M1 with a thickness of 120μm.

[0066] Example 2:

[0067] Embodiment 2 of this disclosure provides a polyvinyl acetal film.

[0068] The difference from Example 1 is that the first addition of butyraldehyde was 10 ml, and the second addition was 14 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 4.0. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film M2 with a thickness of 120 μm.

[0069] Example 3:

[0070] Embodiment 3 of this disclosure provides a polyvinyl acetal film.

[0071] The difference from Example 1 is that the first addition of butyraldehyde was 13 ml, and the second addition was 11 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 6.0. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film M3 with a thickness of 120 μm.

[0072] Example 4:

[0073] Embodiment 4 of this disclosure provides a polyvinyl acetal film.

[0074] The difference from Example 1 is that the first addition of butyraldehyde was 9 ml, and the second addition was 15 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 3.6. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film M4 with a thickness of 120 μm.

[0075] Comparative Example 1:

[0076] Comparative Example 1 of this disclosure provides a polyvinyl acetal film.

[0077] The difference from Example 1 is that the first addition of butyraldehyde was 4 ml, and the second addition was 20 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 2.5. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film D1 with a thickness of 120 μm.

[0078] Comparative Example 2:

[0079] Comparative Example 2 of this disclosure provides a polyvinyl acetal film.

[0080] The difference from Example 1 is that the first addition of butyraldehyde was 18 ml, and the second addition was 6 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 6.5. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film D2 with a thickness of 120 μm.

[0081] Comparative Example 3:

[0082] Comparative Example 3 of this disclosure provides a polyvinyl acetal film.

[0083] The difference from Example 1 is that the first addition of butyraldehyde was 8 ml, and the second addition was 16 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 3.5. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film D3 with a thickness of 120 μm.

[0084] Comparative Example 4:

[0085] Comparative Example 4 of this disclosure provides a polyvinyl acetal film.

[0086] The difference from Example 1 is that the first addition of butyraldehyde was 15 ml, and the second addition was 9 ml, resulting in a polyvinyl acetal with an acetal degree of 80% and an m / r of 6.2. The above polyvinyl acetal was then used to form a film, resulting in a polyvinyl acetal film D4 with a thickness of 120 μm.

[0087] The tensile strength of the films prepared in Examples 1-4 and Comparative Examples 1-4 was tested, and the test results are recorded in Table 1. Wherein, ○ indicates that the tensile strength of the polyvinyl acetal film is greater than 7 MPa when the strain is 2; △ indicates that the tensile strength of the polyvinyl acetal film is less than 7 MPa when the strain is 2.

[0088] Table 1

[0089]

[0090] As shown in Table 1, when the m / r of polyvinyl acetal is in the range of 3.6 to 6, the tensile strength of polyvinyl acetal film is greater than 7 MPa, exhibiting excellent tensile properties.

[0091] Under the same acetal degree, the higher the m / r value (in the range of 3.6-6.0), the longer the sequence distribution of hydroxyl groups and acetal rings on the polyvinyl acetal molecular chain, the larger the scale of the phase separation structure formed, the more hydrogen bonds formed, and the stronger the hydrogen bonds. Ultimately, this results in the polyvinyl acetal film having greater tensile strength and better tensile properties under the same strain.

[0092] This disclosure discloses a method for controlling the mechanical properties of polyvinyl acetal films and its applications. By adjusting the preparation method, the ratio of meso and racemic configurations of the polyvinyl acetal film can be controlled, thereby achieving the control of the mechanical properties of the polyvinyl acetal film. This method requires minimal changes to the existing polyvinyl acetal film formation process and does not require modification of the processing production line. Furthermore, the obtained polyvinyl acetal phase structure and effective temperature range can be controlled within a wide range, with significant control over tensile strength, giving it good market competitiveness.

[0093] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A polyvinyl acetal film, characterized by, The method for preparing the polyvinyl acetal film includes: dissolving polyvinyl acetal in an organic solvent to obtain a mixed solution, wherein the mass ratio of polyvinyl acetal to organic solvent is (5~60):100; pouring the mixed solution into a mold and drying it to obtain the polyvinyl acetal film, wherein the polyvinyl acetal includes mesopolyvinyl acetal and racemic polyvinyl acetal, and the ratio of mesopolyvinyl acetal to racemic polyvinyl acetal is 4.0~6.

0. The method for preparing the polyvinyl acetal includes: At a temperature of 20~30℃, an acidic catalyst and a first amount of aliphatic aldehyde are added to a polyvinyl alcohol solution to carry out the first stage reaction, resulting in a first mixed solution. The first mixed solution was cooled to 5~15℃ at a cooling rate of 5℃ / min, and a second amount of fatty aldehyde was added to carry out the second stage reaction to obtain the second mixed solution. The second mixed solution is heated to 50-80°C to carry out the third stage reaction, resulting in the third mixed solution. The reaction is terminated after adjusting the pH value of the third mixed solution to a preset value to obtain the polyvinyl acetal, wherein... The mass ratio of the total amount of polyvinyl alcohol, acidic catalyst and fatty aldehyde added is (10-50):(5-25):(5-15). The total amount of fatty aldehyde added is the sum of the first amount and the second amount, wherein the first amount accounts for 10% to 50% of the total amount of fatty aldehyde added, and the second amount accounts for 50% to 90% of the total amount of fatty aldehyde added.

2. The polyvinyl acetal film according to claim 1, characterized in that, The polyvinyl alcohol solution contains 5-30 wt% polyvinyl alcohol. The polyvinyl alcohol has an average degree of polymerization of 500-4000 and a degree of alcoholysis of 80-99%. The acidic catalyst includes any one or two of acetic acid, triacetic acid, p-toluenesulfonic acid, sulfuric acid, hydrochloric acid, and nitric acid. The fatty aldehydes include any one or more of acetaldehyde, propionaldehyde, butyraldehyde, pentanaldehyde, hexanal, heptaldehyde, octanaldehyde, and dodecaldehyde; The preset value ranges from 5 to 8.

3. The polyvinyl acetal film according to claim 1 or 2, characterized in that, The reaction time for the first stage is 15-60 minutes; The reaction time for the second stage is 0.5~3 hours; The reaction time for the third stage is 1 to 5 hours.

4. The polyvinyl acetal film according to claim 1, characterized in that, The degree of acetalization of the polyvinyl alcohol acetal is 78%~90%. The polyvinyl acetal has a number-average molecular weight of 60,000 to 80,000.

5. The polyvinyl acetal film according to claim 1, characterized in that, The organic solvent includes any one or two of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol. The mold includes either a polytetrafluoroethylene mold or a glass mold. The drying temperature is 50~150℃, and the drying time is 5~24h.

6. The polyvinyl acetal film according to claim 1, characterized in that, The polyvinyl acetal film has a thickness of 80 to 150 μm.

7. The polyvinyl acetal film according to claim 6, wherein The polyvinyl acetal film has a tensile strength of 6 to 15 MPa at a strain of 2.

8. Use of the polyvinyl acetal film according to any one of claims 1 to 7 as a functional material.

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