Preparation method of polyvinyl acetal, polyvinyl acetal film, and preparation method and application of polyvinyl acetal film

Abstract

The invention provides a preparation method of polyvinyl acetal, a polyvinyl acetal film and a preparation method and application of the polyvinyl acetal film. The preparation method of polyvinyl acetal comprises the following steps: at the temperature of 20-30 DEG C, adding an acid catalyst and fatty aldehyde with a first addition amount into a polyvinyl alcohol solution, and carrying out a first-stage reaction to obtain a first mixed solution; cooling the first mixed solution to 5-15 DEG C at a cooling rate of 5 DEG C / min, adding a second dosage of fatty aldehyde, and carrying out a second-stage reaction to obtain a second mixed solution; heating the second mixed solution to 50-80 DEG C, and carrying out a third-stage reaction to obtain a third mixed solution; the reaction is stopped after the pH value of the third mixed solution is adjusted, the polyvinyl acetal with the meso-racemic configuration and racemic configuration ratio of 3.6-6.0 is obtained, the mass ratio of the polyvinyl alcohol to the acid catalyst to the total addition amount of the fatty aldehyde is (10-50): (5-25): (5-15), the total addition amount of the fatty aldehyde is the sum of the first addition amount and the second addition amount, the first addition amount accounts for 10-50% of the total addition amount of the fatty aldehyde, the second addition amount accounts for 10-50% of the total addition amount of the fatty aldehyde, and the third addition amount accounts for 10-50% of the total addition amount of the fatty aldehyde. The second addition amount accounts for 50-90% of the total addition amount of the fatty aldehyde.

Description

Technical Field

[0001] The present disclosure relates to the technical field of polymer materials, and in particular to a method for preparing polyvinyl acetal, a polyvinyl acetal film, and a preparation method and application thereof. Background Art

[0002] Polyvinyl acetal film has been widely used in many fields such as interlayer film of architectural and automotive safety glass, photovoltaic cells and multi-layer ceramic capacitors due to its good impact resistance, adhesion, weather resistance, corrosion resistance and optical properties. However, polyvinyl acetal film still has shortcomings in tensile strength and elongation at break, which limits its potential in specific application scenarios.

[0003] In order to improve the mechanical properties of polyvinyl acetal film, the main technical means currently adopted include inorganic nanoparticle blending film, multi-layer composite of different base films and chemical grafting modification. Although these methods have achieved certain results in improving mechanical properties, they also increase production costs and process complexity, which is not conducive to large-scale industrial production.

[0004] Therefore, in order to meet the demand for improving the mechanical properties of polyvinyl acetal films, especially the tensile strength, it is still necessary to study a simple and economical regulation method to achieve the optimization of the performance of polyvinyl acetal films. Summary of the invention

[0005] In view of this, the main purpose of the present disclosure is to provide a method for preparing polyvinyl acetal, a polyvinyl acetal film, and a preparation method and application thereof, in order to at least partially solve at least one of the above-mentioned technical problems.

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

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

[0008] At a temperature of 20-30° C., adding an acidic catalyst and a first dosage of aliphatic aldehyde to a polyvinyl alcohol solution to carry out a first stage reaction to obtain a first mixed solution;

[0009] The first mixed solution is cooled to 5-15°C at a cooling rate of 5°C / min, and a second amount of fatty aldehyde is added to perform a second stage reaction to obtain a second mixed solution;

[0010] The second mixed solution is heated to 50-80° C., and a third stage reaction is performed to obtain a third mixed solution;

[0011] The pH value of the third mixed solution is adjusted to a preset value, and then the reaction is terminated to obtain polyvinyl acetal, wherein the polyvinyl acetal includes meso-configuration polyvinyl acetal and racemic-configuration polyvinyl acetal, and the ratio of meso-configuration polyvinyl acetal to racemic-configuration polyvinyl acetal is 3.6-6.0, wherein,

[0012] The mass ratio of the total amount of polyvinyl alcohol, acid 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 amount and the second amount, 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.

[0014] In another aspect of the present disclosure, a method for preparing a polyvinyl acetal film is provided, wherein the polyvinyl acetal prepared by the above preparation method is dissolved in an organic solvent to obtain a mixed solution, wherein the mass ratio of the polyvinyl acetal to the 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 yet another aspect of the present disclosure, a polyvinyl acetal film is provided, which is prepared by the above-mentioned method for preparing the polyvinyl acetal film.

[0017] In yet another aspect of the present disclosure, there is provided a use of the polyvinyl acetal film in a functional material.

[0018] According to an embodiment of the present disclosure, a method for preparing polyvinyl acetal is provided, which adopts a staged feeding and temperature control method, and adjusts the addition ratio of polyvinyl alcohol, aliphatic aldehyde and an acidic catalyst, the type of catalyst and the reaction temperature, and optimizes the corresponding parameters to prepare a polyvinyl acetal with a meso configuration and a racemic configuration ratio between 3.6 and 6.0. By adjusting the microscopic configuration of polyvinyl acetal, the tensile strength, toughness and ductility of polyvinyl acetal are improved, and the macroscopic mechanical properties of polyvinyl acetal are optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the preparation method of polyvinyl acetal in the present disclosure. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below 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 these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this disclosure.

[0022] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0023] Polyvinyl acetal film plays an important role in safety glass interlayers, photovoltaic cells, and multilayer ceramic capacitors in the construction and automotive fields due to its excellent impact resistance, bonding ability, weather resistance, corrosion resistance, and excellent optical properties. However, the limitations of the film in terms of tensile strength and elongation at break affect its performance in application scenarios that require mechanical loads. In addition, the commonly used modification and regulation methods have high production costs and complex processes, which are not conducive to large-scale industrial production.

[0024] In the process of realizing the concept of the present disclosure, it is found that the ratio of the meso configuration (m) and the racemic configuration (r) in the polyvinyl alcohol acetal under the same acetalization degree can significantly affect the regularity of the sequence structure inside the material, thereby controlling its phase structure scale. Specifically, with the increase of the ratio of the meso configuration and the racemic configuration (m / r), the sequence distribution of the hydroxyl group and the acetal ring on the polyvinyl alcohol acetal molecular chain gradually becomes longer, resulting in an increase in the scale of the formed phase separation structure, thereby generating more hydrogen bonds, enhancing the strength of the hydrogen bonds, and making the polyvinyl alcohol acetal exhibit higher tensile strength and better tensile properties. When m / r is too high, the content and strength of the intermolecular hydrogen bonds will be too large, which will limit the mobility of the polymer molecular chain and weaken the stress dissipation capacity, thereby reducing the toughness and ductility of the material. Therefore, the present disclosure uses a segmented feeding reaction to cause the hydroxyl group on the polyvinyl alcohol molecular chain to undergo a condensation reaction with the aldehyde group of the fatty aldehyde under the action of an acidic catalyst to form polyvinyl alcohol acetal. By regulating the mass ratio of polyvinyl alcohol, fatty aldehyde and acidic catalyst, the type of catalyst and the reaction temperature, polyvinyl acetal with m / r in the range of 3.6 to 6.0 is prepared. The preparation method disclosed in the present invention avoids complicated physical and chemical modification steps, and effectively improves the macroscopic mechanical properties, especially the tensile properties, of the polyvinyl acetal film by regulating the microscopic configuration of the polyvinyl acetal. In addition, the preparation method disclosed in the present invention can effectively reduce production costs and production complexity, is suitable for large-scale industrial production, and provides an economical and efficient solution for improving the tensile properties of polyvinyl acetal and expanding its application field.

[0025] Figure 1 It is a flow chart of the preparation method of polyvinyl acetal in the present disclosure.

[0026] According to an embodiment of one aspect of the present disclosure, a method for preparing polyvinyl acetal is provided, such as Figure 1 As shown, the following steps S1 to S4 are included:

[0027] Step S1: adding an acidic catalyst and a first dosage of aliphatic aldehyde to a polyvinyl alcohol solution at a temperature of 20-30° C. to carry out a first stage reaction to obtain a first mixed solution;

[0028] Step S2: cooling the first mixed solution to 5-15°C at a cooling rate of 5°C / min, adding a second amount of fatty aldehyde, and performing a second stage reaction to obtain a second mixed solution;

[0029] Step S3: heating the second mixed solution to 50-80° C. and performing a third stage reaction to obtain a third mixed solution;

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

[0031] Wherein, the polyvinyl acetal includes meso-configuration polyvinyl acetal and racemic-configuration polyvinyl acetal, and the ratio of meso-configuration polyvinyl acetal to racemic-configuration polyvinyl acetal is 3.6-6.0, wherein,

[0032] The mass ratio of the total amount of polyvinyl alcohol, acid 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 addition amount and the second addition amount, the first addition amount accounts for 10% to 50% of the total amount of fatty aldehyde added, and the second addition amount accounts for 50% to 90% of the total amount of fatty aldehyde added.

[0033] According to an embodiment of the present disclosure, a method for preparing polyvinyl acetal is provided, which adopts a staged feeding and temperature control method, and adjusts the addition ratio of polyvinyl alcohol, fatty aldehyde and acidic catalyst, the type of catalyst and the reaction temperature, as well as the optimization of parameters to prepare polyvinyl acetal with a ratio of meso configuration to racemic configuration between 3.6 and 6.0.

[0034] According to an embodiment of the present disclosure, the reaction is carried out at a temperature of 20 to 30°C in step S1. 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 is carried out at an appropriate rate to avoid agglomeration and cross-linking. The first dosage accounts for 10 to 50% of the total amount of fatty aldehyde added, for example, it can be 10%, 20%, 30%, 40%, 50%, etc. First, an acidic catalyst is added to the polyvinyl alcohol solution and fully mixed with the polyvinyl alcohol to lay the foundation for the subsequent addition of fatty aldehyde, which helps to control the degree of cross-linking of the acetal reaction. Fatty aldehyde is gradually and slowly added, and the hydroxyl groups on the polyvinyl alcohol molecular chain react with the fatty aldehyde to form an initial acetal structure. Since the polyvinyl alcohol molecular chain has a large number of hydroxyl groups, and the molecular chain is in a stretched state at the initial stage of the reaction, it is conducive to the formation of a meso structure, thereby increasing the ratio of the meso configuration (m) and the racemic configuration (r) in the polyvinyl alcohol acetal.

[0035] According to an embodiment of the present disclosure, the temperature in step S2 is lowered to 5-15°C for reaction, for example, 5°C, 7°C, 10°C, 13°C, 15°C, etc. Since the acetalization reaction tends to react violently under high temperature conditions, the polymer is prematurely agglomerated and cross-linked, resulting in agglomeration. Therefore, rapid cooling helps to control the reaction rate and selectivity and avoid side reactions caused by too fast a reaction. The second dosage accounts for 50% to 90% of the total amount of fatty aldehyde added, for example, 50%, 60%, 70%, 80%, 90%, etc., and a larger amount of fatty aldehyde is continued to be added for acetalization reaction to increase the acetalization degree.

[0036] According to an embodiment of the present disclosure, the temperature in step S3 is raised to 50-80°C for reaction, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the temperature is continued to rise to accelerate the acetalization reaction of the remaining fatty aldehyde and polyvinyl alcohol, ensure that the reaction is completely carried out, and achieve the expected conversion rate and selectivity. The appropriate temperature range can avoid the problem of too slow reaction rate due to too low temperature, and can prevent side reactions or overreactions caused by too high temperature, thereby affecting the purity and yield of the product.

[0037] According to the embodiments of the present disclosure, the ratio of meso-configuration polyvinyl acetal to racemic-configuration polyvinyl acetal in the prepared polyvinyl acetal is 3.6-6.0, for example, 3.6, 3.8, 4.0, 4.5, 5.0, 5.5, 6.0, etc.

[0038] According to an embodiment of the present disclosure, the pH value of the third mixed solution is adjusted to a preset value in step S4 to terminate the reaction. In specific operations, any one or more alkaline solutions of sodium hydroxide, potassium hydroxide, and sodium bicarbonate can be used to adjust the pH value. The alkaline solution can neutralize the acidic catalyst, reduce its activity, and effectively prevent the excessive acetalization of polyvinyl acetal, thereby ensuring the quality and performance of the product. The preset value ranges from 5 to 8, for example, it can be 5, 6, 6.5, 7, 7.5, 8, etc. By accurately controlling the pH value, the by-products in the neutralization process can be optimized to optimize the performance of the final product. At the same time, after the reaction is terminated, it is easier to carry out subsequent product processing, such as precipitation, filtration, washing and drying, to obtain high-purity polyvinyl acetal.

[0039] According to an embodiment of the present disclosure, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 5-30 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc. The appropriate concentration of polyvinyl alcohol solution ensures that the solution has good fluidity, is convenient for stirring and heat transfer, and maintains sufficient polyvinyl alcohol concentration to promote effective acetal reaction, avoiding the problem of excessive viscosity of polyvinyl alcohol solution affecting the uniformity of reaction. The average degree of polymerization of polyvinyl alcohol is 500-4000, for example, it can be 500, 1000, 2000, 3000, 4000, etc., and the degree of alcoholysis is 80-99%, for example, it can be 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 conducive 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 an alcoholysis degree between 85% and 99% contains more hydroxyl groups, which provides sufficient reaction sites for the acetal reaction and helps to regulate the degree of acetal reaction and the cross-linking network structure.

[0040] The acidic catalyst includes an organic acid catalyst and / or an inorganic acid catalyst. The organic acid catalyst includes: any one or two of acetic acid, triacetic acid, and p-toluenesulfonic acid. The inorganic acid catalyst includes: any one or two of sulfuric acid, hydrochloric acid, and nitric acid. By adjusting the type and amount of the acidic catalyst, the catalytic reaction rate can be controlled, thereby affecting the change in the ratio of the meso configuration and the racemic configuration in the acetalization reaction, and realizing the fine regulation of the performance of the polyvinyl acetal material. In addition, a suitable acidic catalyst can effectively avoid the problems of yellowing and poor stability of polyvinyl acetal during the synthesis process. By reasonably selecting the catalyst type and combination and controlling the reaction conditions, the performance of polyvinyl acetal can be optimized to meet the needs of different application scenarios.

[0041] Fatty aldehydes include any one or more of acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, heptanal, octanal and dodecanal. As the carbon chain of the fatty aldehyde increases, the toughness and elasticity of the polyvinyl acetal gradually increase. By adjusting the type of fatty aldehyde, polyvinyl acetal that meets different practical application requirements can be obtained.

[0042] According to the embodiments of the present disclosure, the reaction time of the first stage reaction is 15 to 60 minutes, for example, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc.; the reaction time of the second stage reaction is 0.5 to 3 hours, for example, 0.5 hours, 1 hours, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc.; the reaction time of the third stage reaction is 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc. The appropriate reaction time ensures that the polyvinyl alcohol and the fatty aldehyde can fully react under the action of the acidic catalyst, so that the acetal reaction is completely carried out, and incomplete or excessive reaction is avoided.

[0043] According to the embodiments of the present disclosure, the acetal degree of polyvinyl acetal is 78% to 90%, for example, 78%, 80%, 85%, 88%, 90%, etc., and the number average molecular weight of polyvinyl acetal is 60000 to 80000, for example, 60000, 65000, 70000, 75000, 80000, etc. The acetal degree refers to the mass percentage of the monomer where the acetal group is located in the entire polyvinyl acetal molecular chain. Through the preparation method disclosed in the present disclosure, the acetal degree and molecular weight of polyvinyl acetal can be accurately controlled, thereby ensuring that the material has excellent chemical stability and mechanical strength.

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

[0045] According to an embodiment of the present 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. The appropriate ratio range can ensure the solubility and fluidity of polyvinyl acetal in the solvent, thereby facilitating stirring and heat transfer. At the same time, it is ensured that the concentration of polyvinyl acetal can form an effective film thickness, avoiding the inability to form a film due to the mixed solution being too dilute, or affecting the uniformity of the film due to the excessive viscosity of the mixed solution.

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

[0047] According to an embodiment of the present disclosure, the organic solvent includes: any one or two of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol. The above organic solvents have good solubility for polyvinyl acetal and can dissolve polyvinyl acetal at a lower temperature. At the same time, as a volatile solvent, they help the subsequent drying process.

[0048] The mold includes: any one of a polytetrafluoroethylene mold and a glass mold. In the specific operation, before film formation, the reaction solution is allowed to stand to eliminate residual bubbles and prevent defects in the film. 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 that the surface of the film is smooth and defect-free. Within 10 minutes before the mixed solution is poured into the mold, the mold is preheated to the oven temperature to maintain the temperature of the mixed solution to prevent uneven cooling of the solution due to the low mold temperature and reduce film defects. Before pouring into the mold, it is necessary to pick out obvious bubbles in the solution, and then send it into the oven for drying to obtain a polyvinyl acetal film.

[0049] The drying temperature is 50-150°C, for example, 50°C, 70°C, 90°C, 130°C, 150°C, etc. 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 thickness of the film. The appropriate temperature range can accelerate the volatilization of the solvent and avoid thermal degradation of the polyvinyl acetal caused by excessively high temperature.

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

[0051] According to the embodiments of the present disclosure, the polyvinyl acetal film prepared by using polyvinyl acetal with m / r in the range of 3.6 to 6.0, as the ratio of meso configuration to racemic configuration (m / r) increases, the sequence distribution of hydroxyl groups and acetal rings on the polyvinyl acetal molecular chain gradually becomes longer, resulting in an increase in the scale of the formed phase separation structure, thereby generating more hydrogen bonds and enhancing the strength of the hydrogen bonds. Ultimately, the polyvinyl acetal film exhibits higher tensile strength and better tensile properties under the same strain. However, too high an m / r value will lead to excessive content and strength of intermolecular hydrogen bonds, limit the mobility of the polymer molecular chain, weaken the stress dissipation capacity, and thus reduce the toughness and ductility of the polyvinyl acetal film.

[0052] According to an embodiment of the present disclosure, the thickness of the polyvinyl acetal film is 80-150 μm, for example, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm. Appropriate thickness ensures the mechanical strength and tensile properties of the film, while meeting the requirements of different industrial applications.

[0053] According to the embodiments of the present disclosure, when the strain is 2, the tensile strength of the polyvinyl acetal film is 6-15 Mpa, which has good mechanical properties. The polyvinyl acetal film can remain stable when subjected to tensile force and is not easy to break. At the same time, appropriate tensile strength also helps the film to have the flexibility and ductility required during processing and use, so that it can adapt to different molding and application requirements and avoid brittle fracture during application.

[0054] According to an embodiment of yet another aspect of the present disclosure, there is provided a use of the above-mentioned polyvinyl acetal film in a functional material.

[0055] According to an embodiment of the present disclosure, the functional material includes an impact-resistant or shock-absorbing material. The polyvinyl acetal film can be applied to application scenarios that need to withstand mechanical loads, such as automobiles, construction, photovoltaics, and ceramic capacitors.

[0056] In order to make the purpose, technical scheme and advantages of the present disclosure clearer, the present disclosure is further described in detail below in conjunction with specific examples and drawings. Specific techniques or conditions not specified in the examples are all conventional methods, which can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. It should be noted that the methods provided in the present disclosure are all conventional methods unless otherwise specified, and the reactants and reagents can be obtained from public commercial channels unless otherwise specified.

[0057] Embodiment 1:

[0058] Embodiment 1 of the present 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 a temperature of 20° C., 5 ml of hydrochloric acid was added to the polyvinyl alcohol solution, and then a first dosage of 12 ml of butyraldehyde was slowly added dropwise within 30 minutes. After the reaction was 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 a second dosage of 12 ml of fatty aldehyde was added, and the mixture was stirred at a constant speed for 3 hours to obtain a second mixed solution;

[0062] The second mixed solution was heated to 80° C. and the reaction was continued under stirring for 3 h to obtain a third mixed solution.

[0063] 10 ml of a 15 wt % sodium hydroxide solution was added to the third mixed solution, the pH value of the third mixed solution was adjusted to 7, and stirring was continued for 10 minutes to terminate the reaction to obtain polyvinyl acetal precipitate.

[0064] The polyvinyl acetal precipitate was filtered and separated, and washed with pure water for multiple times to remove the residual reactants and by-products. The obtained polyvinyl acetal precipitate was placed in an oven at 60°C and air-dried for 12 hours to obtain a polyvinyl acetal with an acetal degree of 80% and a ratio (m / r) of meso and racemic configurations of 5.0.

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

[0066] Embodiment 2:

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

[0068] The difference compared with Example 1 is that the first dosage of butyraldehyde is 10 ml, and the second dosage of butyraldehyde is 14 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 4.0 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film M2 with a thickness of 120 μm.

[0069] Embodiment 3:

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

[0071] The difference compared with Example 1 is that the first dosage of butyraldehyde is 13 ml, and the second dosage of butyraldehyde is 11 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 6.0 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film M3 with a thickness of 120 μm.

[0072] Embodiment 4:

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

[0074] The difference compared with Example 1 is that the first dosage of butyraldehyde is 9 ml, and the second dosage of butyraldehyde is 15 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 3.6 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film M4 with a thickness of 120 μm.

[0075] Comparative Example 1:

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

[0077] The difference compared with Example 1 is that the first dosage of butyraldehyde is 4 ml, and the second dosage of butyraldehyde is 20 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 2.5 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film D1 with a thickness of 120 μm.

[0078] Comparative Example 2:

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

[0080] The difference compared with Example 1 is that the first dosage of butyraldehyde is 18 ml, and the second dosage of butyraldehyde is 6 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 6.5 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film D2 with a thickness of 120 μm.

[0081] Comparative Example 3:

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

[0083] The difference compared with Example 1 is that the first dosage of butyraldehyde is 8 ml, and the second dosage of butyraldehyde is 16 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 3.5 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film D3 with a thickness of 120 μm.

[0084] Comparative Example 4:

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

[0086] The difference compared with Example 1 is that the first dosage of butyraldehyde is 15 ml, and the second dosage of butyraldehyde is 9 ml, and a polyvinyl acetal with an acetal degree of 80% and m / r of 6.2 is obtained. The polyvinyl acetal is formed into a film to obtain a polyvinyl acetal film D4 with a thickness of 120 μm.

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

[0088] Table 1

[0089]

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

[0091] Under the same acetalization degree conditions, 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 will be, the larger the scale of the phase separation structure formed, the more hydrogen bonds formed, and the greater the strength, which ultimately leads to the polyvinyl acetal film having greater tensile strength and better tensile properties under the same strain.

[0092] The present disclosure provides a method for regulating the mechanical properties of polyvinyl acetal films and its application. By regulating the preparation method, the ratio of the meso configuration and the racemic configuration of the polyvinyl acetal film can be controlled, so that the mechanical properties of the polyvinyl acetal film can be regulated. The original polyvinyl acetal film forming process is slightly changed, and there is no need to change the processing production line. In addition, the obtained polyvinyl acetal phase structure and effective temperature range have a wide range of regulation, and the regulation effect on stretching is significant, which has good market competitiveness.

[0093] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A method for preparing polyvinyl acetal, comprising: At a temperature of 20-30° C., adding an acidic catalyst and a first dosage of aliphatic aldehyde to a polyvinyl alcohol solution to carry out a first stage reaction to obtain a first mixed solution; The first mixed solution is cooled to 5-15°C at a cooling rate of 5°C / min, and a second amount of fatty aldehyde is added to perform a second stage reaction to obtain a second mixed solution; The second mixed solution is heated to 50-80° C., and a third stage reaction is performed to obtain a third mixed solution; The pH value of the third mixed solution is adjusted to a preset value, and then the reaction is terminated to obtain polyvinyl acetal, wherein the polyvinyl acetal includes meso-configuration polyvinyl acetal and racemic-configuration polyvinyl acetal, and the ratio of the meso-configuration polyvinyl acetal to the racemic-configuration polyvinyl acetal is 3.6-6.0, wherein, The mass ratio of the total amount of polyvinyl alcohol, acid 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, 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 preparation method according to claim 1, characterized in that: The mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 5-30 wt %. The average polymerization degree of the polyvinyl alcohol is 500-4000, and the alcoholysis degree is 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, valeraldehyde, hexanal, heptaldehyde, octanal and dodecanal; The preset value ranges from 5 to 8.

3. The preparation method according to claim 1 or 2, characterized in that: The reaction time of the first stage reaction is 15 to 60 minutes; The reaction time of the second stage reaction is 0.5~3h; The reaction time of the third stage reaction is 1 to 5 hours.

4. The preparation method according to claim 1, characterized in that: The acetal degree of the polyvinyl acetal is 78% to 90%, The number average molecular weight of the polyvinyl acetal is 60,000-80,000.

5. A method for preparing a polyvinyl acetal film, characterized in that: The polyvinyl acetal prepared by any one of the preparation methods of claims 1 to 4 is dissolved in an organic solvent to obtain a mixed solution, wherein the mass ratio of the polyvinyl acetal to the organic solvent is (5-60):100; The mixed solution is poured into a mold and dried to obtain the polyvinyl acetal film.

6. The preparation method according to claim 5, characterized in that: The organic solvent includes: any one or two of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol; The mold includes: any one of a polytetrafluoroethylene mold and a glass mold; The drying temperature is 50-150° C., and the drying time is 5-24 hours.

7. A polyvinyl acetal film, characterized in that: The compound is prepared by the preparation method described in claim 5 or 6.

8. The film according to claim 7, characterized in that The thickness of the polyvinyl acetal film is 80-150 μm.

9. The film according to claim 8, characterized in that When the strain is 2, the tensile strength of the polyvinyl acetal film is 6-15 Mpa.

10. Use of the polyvinyl acetal film according to any one of claims 7 to 9 in functional materials.

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