A polyvinyl acetal resin having a high temperature-dependent melt finger and a method for preparing the same

Abstract

The application discloses a polyvinyl acetal resin with high temperature-dependent melt index and a preparation method thereof. According to the key influencing factors of the melt index of the polyvinyl acetal resin at different temperatures, the aggregation state structure of PVA molecules is first considered, the PVA crystallization behavior is controlled, and inorganic salt ions are introduced to control the aggregation degree of PVA molecular chains, the crosslinking reaction between PVA molecular chains in the homogeneous reaction stage and the crosslinking reaction between hydroxyl groups in the heterogeneous stage are simultaneously controlled through optimizing the feeding process, and then the melt index at low temperature is controlled. Secondly, starting from the key parameters affecting the group distribution of the resin, the reaction degree of different chemical environment groups is controlled by increasing the holding temperature and prolonging the holding time, so as to achieve the purpose of controlling the group distribution, and finally realize the melt index control at high temperature. According to the different processing characteristics and application scene requirements of the polyvinyl acetal resin, the temperature dependence of the melt index of the polyvinyl acetal resin can be accurately controlled.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyvinyl alcohol acetal resin with a high temperature-dependent melt index and its preparation method. Background Technology

[0002] Polyvinyl acetal resin is widely used in safety glass, inks, adhesives, coatings, and textiles due to its high transparency, excellent optical properties, good solubility, adhesion, and film-forming processing characteristics. Among these, polyvinyl acetal interlayer films, processed from polyvinyl acetal resin, are widely used in the automotive, construction, and photovoltaic industries due to their good impact resistance, weather resistance, aging resistance, and good adhesion to glass. Polyvinyl acetal interlayer films are mainly prepared by mixing polyvinyl acetal resin with a plasticizer and then extruding it. Therefore, the properties of the polyvinyl acetal resin raw material determine the properties of the final polyvinyl acetal interlayer film. The processability of polyvinyl acetal interlayer films is one of its key evaluation parameters, directly determining its performance quality and production efficiency. The processability of polyvinyl acetal interlayer films is closely related to the melt index of its resin raw material. If the melt index of the polyvinyl acetal resin raw material is too low during the interlayer film processing, it will be detrimental to the smooth extrusion of the interlayer film. Studies have shown that the melt index of polyvinyl acetal resin varies significantly at different temperatures. Based on its processing characteristics and application requirements, polyvinyl acetal resin exhibits a high melt index temperature dependence. Specifically, within the lamination temperature range of laminated glass (120–140°C), excessively high fluidity of the polyvinyl acetal resin is undesirable. However, during the processing of polyvinyl acetal interlayer films, at higher temperatures (150–190°C), good fluidity is desirable for processing. Improving the melt index temperature dependence of polyvinyl acetal resin is key to enhancing product quality and processing efficiency.

[0003] Polyvinyl acetal resin is mainly prepared under acidic conditions through the acetalization reaction of butyraldehyde with the hydroxyl groups in polyvinyl alcohol (PVA). The key to controlling the melt index (MIF) of polyvinyl acetal resin at low temperatures (120℃) lies in controlling the degree of cross-linking in the reaction. This degree of cross-linking involves multiple factors, including the aggregated structure of PVA, the synthesis process, parameters, and formulation. Among these, the aggregated structure of PVA molecules in the homogeneous stage, the uniformity of the acetalization reaction, and the hydroxyl interactions in the heterogeneous stage are crucial in determining the degree of cross-linking. Therefore, effectively controlling the aggregated structure of PVA molecules in the homogeneous stage and the hydroxyl interactions in the heterogeneous stage is of great significance for improving the MIF of polyvinyl acetal resin at low temperatures. The MIF of polyvinyl acetal resin at high temperatures (150℃, 190℃) is closely related to the distribution of functional groups in the resin molecular structure.

[0004] To effectively improve the melt index properties of polyvinyl acetal resin, patent CN103012633B reported the synthesis of highly fluid polyvinyl acetal resin using a hydrochloric acid catalyst at an extremely high proportion (50 wt% of PVA raw material) and an extremely high concentration (30-35 wt%). Undoubtedly, with higher hydrochloric acid dosage and concentration, the reaction system viscosity is lower, the hydroxyl interactions between PVA molecular chains are weaker, and the degree of cross-linking reaction is lower. However, the use of large amounts of hydrochloric acid makes it difficult to control the reaction rate and uniformity, leading to the formation of non-uniform resin and affecting the product yield. Furthermore, a higher proportion and higher concentration of hydrochloric acid catalyst increases production costs and can easily corrode pipelines and damage equipment. In addition, patent CN115677886A reported the use of inorganic salts to inhibit inter-chain cross-linking reactions to increase the degree of reaction. By introducing ions that can disrupt strong hydrogen bond interactions into the PVA raw solution, the degree of PVA cross-linking reaction in the homogeneous reaction stage can be reduced to some extent. However, the addition of ions has limited effect on regulating the aggregated structure of PVA molecules, and by inhibiting the cross-linking reaction, it can only regulate the melt index of polyvinyl acetal resin at low temperatures (120℃), but cannot regulate the melt index at high temperatures (150℃, 190℃) determined by the distribution of functional groups. Furthermore, this patent uses a large amount of inorganic salts and only conducts the reaction at a low temperature of 30℃. To a certain extent, the use of a large amount of inorganic salts may lead to a higher melt index at low temperatures, which is not conducive to the processing and application of the product. On the other hand, the acetalization reaction at low temperatures cannot effectively regulate the distribution of functional groups in polyvinyl acetal resin, resulting in a lower melt index at high temperatures, which is not conducive to downstream film processing. In addition, the use of a large amount of inorganic salts can easily cause difficulties in washing, and the residual trace ions will have an adverse effect on the weather resistance and anti-aging properties of the product. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the main objective of this invention is to propose a polyvinyl acetal resin with high temperature-dependent melt index and its preparation method.

[0006] The industrial production of polyvinyl acetal typically employs a precipitation method, including low-temperature condensation, heating and curing, washing and drying. The processing fluidity of polyvinyl acetal resin, i.e., its melt index, is closely related to the cross-linking and group distribution between polyvinyl acetal resin molecules. At the initial stage of low-temperature condensation, due to the crystallinity of PVA molecules and the presence of numerous hydroxyl groups, strong intramolecular and intermolecular hydrogen bonds easily form, leading to the aggregation of PVA molecular chains. During the acetalization reaction of PVA molecules, the aggregation of PVA molecular chains easily leads to inter-chain acetalization reactions, forming cross-linked polyvinyl acetal molecules, resulting in a lower melt index of polyvinyl acetal resin at low temperatures (120℃).

[0007] From the perspective of controlling the melt index at low temperatures, the degree of intermolecular crosslinking is precisely controlled: 1) By controlling the crystallization behavior of PVA solution during the cooling process, the degree of aggregation of PVA molecules is initially controlled, and the intermolecular crosslinking reaction is weakened; 2) By introducing ions that can destroy the strong interaction between PVA molecular chains, the degree of aggregation of PVA molecules is further weakened; 3) By controlling the amount and time of aldehyde and acid feeding, the reaction rate of the system is controlled, the non-uniformity of the reaction in the homogeneous reaction stage is controlled, and the polyvinyl alcohol resin undergoes a uniform phase transition; after the phase transition, by controlling the timing of aldehyde and acid feeding, the crosslinking reaction of the hydroxyl groups at the interface of unstable polyvinyl alcohol acetal resin is effectively avoided.

[0008] From the perspective of controlling the melt index at high temperatures, based on the kinetics and thermodynamics of PVA acetal reaction, the reaction rate of groups under different chemical environments is controlled by adjusting the temperature process. Under the premise of ensuring reaction stability, the distribution of hydroxyl and acetal groups in the resin molecular structure is regulated, so that the distribution of different groups is more orderly, and the melt index and fluidity are precisely controlled at high temperatures.

[0009] To achieve its objectives, the present invention employs the following technical solution:

[0010] A method for preparing a polyvinyl acetal resin with a high temperature-dependent melt index, characterized by the following steps:

[0011] 1) Dissolve polyvinyl alcohol raw material fully in water at 90℃, cool the polyvinyl alcohol solution at a certain rate, add inorganic salt, and when the system temperature drops to 12-20℃, add part of the aldehyde and part of the acid catalyst to the polyvinyl alcohol solution and stir for 10-60 min; then, heat the reaction system to 20-45℃ and add the remaining aldehyde and acid catalyst during this process; further, heat the reaction system to 60-80℃ at a certain heating rate and keep it warm for aging to finally obtain a resin mixture;

[0012] 2) Cool the resin mixture to below 60°C, then add alkali solution to the system, keep stirring for 5-30 minutes, filter, and obtain solid resin product;

[0013] 3) The solid resin product is first washed with pure water 5 times, then washed with a mixed solution of methanol and water with a volume percentage of 25% methanol 2 times, and finally washed with pure water 5 times to obtain the cleaned product.

[0014] 4) The cleaning product is dried at 40-60°C to obtain polyvinyl alcohol acetal resin.

[0015] The polyvinyl alcohol acetal resin has the following characteristics: hydroxyl value of 18-21 wt%; melt index ≥1.20 g / 10 min at 120℃; melt index ≥15.00 g / 10 min at 150℃; melt index ≥1.60 g / 10 min at 190℃; hydroxyl distribution ≥0.18; average particle size of 100-300 μm; particle size distribution coefficient of 1.0-1.5; bulk density ≥0.120 g / mL; and resin yellowing grade A.

[0016] Further, in step 1), the cations in the inorganic salt include at least one of calcium ions, magnesium ions, lithium ions, and cesium ions, and the anions are at least one of chloride ions and nitrate ions other than sulfate ions, carbonate ions, and acetate ions, such as calcium chloride, magnesium chloride, lithium chloride, cesium chloride, calcium nitrate, and magnesium nitrate.

[0017] Further, in step 1): the amount of aldehyde added in the first step is 10% to 45% of the total content, and the addition time is 10 to 30 minutes; the amount of acid catalyst added in the first step is 30% to 65% of the total content, and the addition time is 15 to 60 minutes, so as to control the uniform phase transformation of polyvinyl acetal resin; the heat preservation and curing time is 30 to 240 minutes.

[0018] Furthermore, in step 1): the crystallinity of the polyvinyl alcohol raw material is 15% to 40%; the cooling rate of the polyvinyl alcohol solution is 20 to 160°C / h.

[0019] Furthermore, in step 1), the inorganic salt is added by dissolving it in distilled water to prepare an inorganic salt solution and then uniformly dripping it in; the inorganic salt solution is added when the PVA solution is cooled to 45-75°C.

[0020] Furthermore, in step 1), the amount of inorganic salt added is 0-5 wt% of the mass of the polyvinyl alcohol raw material (i.e., when added in the form of an inorganic salt solution, the amount of solute in the inorganic salt solution is 0-5 wt% of the mass of the polyvinyl alcohol raw material).

[0021] Furthermore, in step 1), the acidic catalyst includes at least one of the following acidic catalysts: hydrochloric acid, perchloric acid, chloroacetic acid, aminosulfonic acid, benzenesulfonic acid, o-(m)toluenesulfonic acid, ethylbenzenesulfonic acid, and isophenylenedisulfonic acid, but does not include sulfuric acid, carbonic acid, acetic acid, etc.

[0022] Furthermore, in step 1), the aldehyde includes at least one of formaldehyde, acetaldehyde, butyraldehyde, pentanal, isovaleraldehyde, hexanal, heptaldehyde, octanal, nonanal, decanal, benzaldehyde, and phenylacetaldehyde.

[0023] Furthermore, in step 1), the mass ratio of polyvinyl alcohol raw material, acidic catalyst, and aldehyde is 100:(15-35):(54-60).

[0024] Furthermore, in step 3): the time for a single pure water rinse is 20-30 minutes, and the time for a single methanol and water mixed solution rinse is 15-20 minutes, so as to fully wash away the inorganic salt ions encapsulated on the surface and inside of the polyvinyl acetal resin, and prevent the residual inorganic salt ions from causing the polyvinyl acetal resin to yellow and affecting the resin's electrical insulation, transparency, thermal stability, etc.

[0025] The polyvinyl acetal resin prepared by this invention can be directly applied to inks, electronic ceramic adhesives, or made into films for use in photovoltaic encapsulation layers, automotive safety glass, etc.

[0026] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0027] This invention addresses the key factors influencing the melt index (MIF) of polyvinyl acetal resin at different temperatures. First, it addresses the aggregated structure of PVA molecules, controlling the degree of PVA molecular chain aggregation by regulating PVA crystallization behavior and introducing inorganic salt ions. Simultaneously, it optimizes the feeding process to control the cross-linking reactions between PVA molecular chains in the homogeneous reaction stage and the cross-linking reactions between hydroxyl groups in the heterogeneous stage, thereby controlling the MIF at low temperatures. Second, it addresses key parameters affecting resin group distribution by increasing the holding temperature and extending the holding time to control the reaction degree of groups in different chemical environments, thus regulating the group distribution and ultimately achieving MIF control at high temperatures. This method, tailored to the different processing characteristics and application requirements of polyvinyl acetal resin, can precisely control the temperature dependence of its MIF. It effectively meets the needs of polyvinyl acetal resin in various applications and promotes the full reaction of PVA raw materials, butyraldehyde, and acidic catalysts, improving raw material utilization and product yield. This invention also features simple operation, environmental friendliness, low cost, and requires no additional process equipment, giving it strong market competitiveness. Meanwhile, compared with existing production processes, the reaction process of the present invention does not require the addition of emulsifiers or other additives that may affect product performance, and the amount of acidic catalyst used is low. Attached Figure Description

[0028] Figure 1 The yellowing evaluation criteria. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] 1) Dissolve 50g of polyvinyl alcohol with an average degree of polymerization of 1700 and a crystallinity of 35% in 500mL of pure water and stir at 90℃ for 2h to ensure complete dissolution. Then, cool the PVA stock solution to 45℃ at a rate of 30℃ / h and add 10mL of an inorganic salt solution containing 1.5g of calcium chloride solid to the PVA stock solution. Lower the system temperature to 12℃ and add 11.2g of first-step n-butyraldehyde dropwise at a uniform rate over 20min. Then, add 9.0g of first-step hydrochloric acid with a mass concentration of 25% dropwise at a uniform rate over 30min. Stir at this temperature for 15min. Immediately afterward, raise the reaction system to 65℃ at a rate of 25℃ / h. When the temperature reaches 25℃, add 16.8g of second-step n-butyraldehyde and 6.0g of second-step hydrochloric acid dropwise simultaneously, controlling the addition to be completed at a uniform rate over 30min. Then, keep the reaction system at 65℃ and stir for 80min.

[0032] 2) Reduce the temperature of the reaction system to 55℃, add 20mL of 15wt% sodium hydroxide solution to the reaction solution, stir for 10-15min, centrifuge to dehydrate, and obtain solid resin product.

[0033] 3) The solid resin product was washed 5 times with distilled water at 40°C for 30 min each time; then washed 2 times with a mixed solution of methanol and water with a volume percentage of 25% for 15 min each time; finally, it was washed 5 times with distilled water for 30 min each time to obtain the cleaned product.

[0034] 4) Place the cleaned product in a forced-air drying oven and dry it at 60°C for 12 hours to obtain the polyvinyl acetal resin product.

[0035] Example 2 (Changing the amount of n-butyraldehyde and hydrochloric acid fed in the first step)

[0036] Except for step 1), where the amount of n-butyraldehyde added in the first step is changed to 8.4g, the amount of hydrochloric acid added in the first step is changed to 9.75g, the amount of n-butyraldehyde added in the second step is changed to 19.6g, and the amount of hydrochloric acid added in the second step is changed to 5.25g, the remaining steps and conditions are the same as in Example 1.

[0037] Example 3 (Optimization of the addition temperature of aldehyde and acid in the second step)

[0038] Except for step 1), where the temperature is raised to 25°C to add the second step of n-butyraldehyde, and the second step of hydrochloric acid is changed to be added at 30°C, the remaining steps and conditions are the same as in Example 1.

[0039] Example 4 (Extending the heat preservation time at high temperatures)

[0040] Except for step 1), where the heat preservation time is changed from 80 min to 160 min, the other steps and conditions are the same as in Example 1.

[0041] Example 5 (Increasing the high-temperature insulation temperature)

[0042] Except for step 1), where the insulation temperature is changed from 65°C to 70°C, the other steps and conditions are the same as in Example 1.

[0043] Example 6 (Reducing the crystallinity of raw materials and accelerating the cooling rate of the original solution)

[0044] Except for step 1), where the polyvinyl alcohol crystallinity is changed to 30% and the PVA stock solution cooling rate is changed to 60℃ / h, the remaining steps and conditions are the same as in Example 1.

[0045] Example 7 (Increasing the temperature at which the inorganic salt solution is added)

[0046] Except for step 1), where the addition of inorganic salt solution to the PVA stock solution was changed from 45°C to 65°C, the remaining steps and conditions are the same as in Example 1.

[0047] Example 8 (Changing the amount of inorganic salt added)

[0048] Except for step 1), which changes "add 10 mL of inorganic salt solution containing 1.5 g of calcium chloride solid" to "add 10 mL of inorganic salt solution containing 2.5 g of calcium chloride solid", the other steps and conditions are the same as in Example 1.

[0049] Example 9 (Changing the types of inorganic salts added)

[0050] Except for step 1), where the inorganic salt is changed from calcium chloride to magnesium chloride, the other steps and conditions are the same as in Example 1.

[0051] Comparative Example 1 (The feeding process was changed from step-by-step feeding to one-step feeding)

[0052] Except for step 1), when the system temperature drops to 12°C, 28g of n-butyraldehyde (total amount) is added within 20 minutes, followed by the addition of 15g of hydrochloric acid (total amount) within 30 minutes. The remaining steps and conditions are the same as in Example 1.

[0053] Comparative Example 2 (significantly increasing the temperature at which the aldehyde and acid are added in the second step)

[0054] Except for step 1), where the second step of adding n-butyraldehyde is done when the temperature is raised to 25°C, and the second step of adding hydrochloric acid is done when the temperature is raised to 50°C, the remaining steps and conditions are the same as in Example 1.

[0055] Comparative Example 3 (Reducing High-Temperature Insulation Time)

[0056] Except for step 1), where the heat preservation time is changed from 80 min to 40 min, the other steps and conditions are the same as in Example 1.

[0057] Comparative Example 4 (Lowering the High-Temperature Insulation Temperature)

[0058] Except for step 1), where the insulation temperature is changed from 65°C to 50°C, the remaining steps and conditions are the same as in Example 1.

[0059] Comparative Example 5 (Increasing the crystallinity of raw materials and reducing the cooling rate of the original solution)

[0060] Except for step 1), where the polyvinyl alcohol crystallinity is changed to 45% and the PVA stock solution cooling rate is changed to 15℃ / h, the remaining steps and conditions are the same as in Example 1.

[0061] Comparative Example 6 (without added inorganic salts)

[0062] Except for step 1), in which no inorganic salt solution is added to the PVA stock solution, the remaining steps and conditions are the same as in Example 1.

[0063] Comparative Example 7 (Lowering the temperature of inorganic salt addition)

[0064] Except for step 1), where the addition of inorganic salt solution to the PVA stock solution at 45°C is changed to 20°C, the remaining steps and conditions are the same as in Example 1.

[0065] Comparative Example 8 (significantly increased amount of inorganic salts added)

[0066] Except for step 1), which changes "add 10 mL of inorganic salt solution containing 1.5 g of calcium chloride solid" to "add 10 mL of inorganic salt solution containing 5 g of calcium chloride solid", the other steps and conditions are the same as in Example 1.

[0067] Comparative Example 9 (Changing the washing process of the product)

[0068] Except for step 3), which involves washing twice with a methanol-water mixture at a volume percentage of 25%, the remaining steps and conditions are the same as in Example 1.

[0069] The test method for the volatile matter of the polyvinyl acetal resin prepared above is as follows: 1g of the resin to be tested is evenly distributed in a weighing bottle that has been kept at constant weight, and dried in a forced-air drying oven at 105℃ for 2h. The volatile matter can be calculated based on the ratio of the mass reduction of the sample to the original mass of the sample.

[0070] The hydroxyl value of the polyvinyl acetal resin prepared above was tested by chemical titration. The hydroxyl groups in the polyvinyl acetal resin were esterified with acetic anhydride in a pyridine solution, followed by hydrolysis of excess acetic anhydride. Using phenolphthalein as an indicator, the resin was titrated with a standard NaOH solution for neutralization, and the hydroxyl content in the polyvinyl acetal resin was calculated.

[0071] The melt index test method for the polyvinyl alcohol acetal resin prepared above is as follows: 25 wt% of triethylene glycol diisooctanoate is added, and the melt index is determined by passing the resin through a melt indexer at 120℃ and 150℃ with a load of 21.6 kg and at 190℃ with a load of 2.16 kg for 10 min. The melt index is expressed in g / 10 min.

[0072] The method for testing the bulk density of the polyvinyl acetal resin prepared above is as follows: the resin to be tested is poured evenly into a 100mL graduated cylinder, and the mass of 100mL of resin under free stacking is the bulk density, with the unit being g / mL.

[0073] The test method for yellowing of the polyvinyl alcohol acetal resin prepared above is as follows: Take 3.75g of the resin to be tested and mix it evenly with 1.25g of glycol diisooctanoate plasticizer. Pour the mixture into a mold, spread it evenly, and then press the mixed sample with a pressing sheet to ensure that it is uniform and compact. Remove the mold and then place it in a 200℃ forced-air drying oven for aging for 1 hour. Severe yellowing is grade C, slight yellowing is grade B, and transparency is grade A. The specific yellowing evaluation criteria are as follows: Figure 1 As shown.

[0074] The method for testing the block size of the polyvinyl acetal resin prepared above is as follows: 20-30 mg of the resin to be tested is dissolved in 0.5 mL of deuterated DMSO, and the solution is then analyzed by carbon nuclear magnetic resonance (NMR) spectroscopy. 13 The C NMR technique was used to scan 4096 times on a 600 MHz NMR spectrometer. The resulting NMR spectra were integrated using MestReNova software, and the ratio of the mole fraction of carbon in the range of 46-46.9 ppm (connected hydroxyl groups) and 44.1-45.6 ppm (isolated hydroxyl groups) was calculated. This ratio is called the hydroxyl distribution.

[0075] The test method for the average particle size and particle size distribution coefficient of the polyvinyl acetal resin prepared above is as follows: take 3-5g of the resin to be tested and obtain the average particle size and particle size distribution coefficient of the resin by laser particle size analyzer.

[0076] Table 1 Evaluation results of polyvinyl acetal

[0077]

[0078]

[0079] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinyl acetal resin with a high temperature-dependent melt index, characterized in that, Includes the following steps: 1) Polyvinyl alcohol raw material with a crystallinity of 15%~40% is fully dissolved in water at 90℃. The polyvinyl alcohol solution is cooled at a rate of 20~160℃ / h, and inorganic salt is added. When the system temperature drops to 12~20℃, part of the aldehyde and part of the acid catalyst are added to the polyvinyl alcohol solution and stirred for 10~60min. Then, the reaction system is heated to 20~45℃ and the remaining aldehyde and acid catalyst are added during this process. Further, the reaction system is heated to 60~80℃ and kept at this temperature for aging to obtain a resin mixture. The mass ratio of polyvinyl alcohol raw material, acid catalyst, and aldehyde is 100:15~35:54~60. The aldehyde is n-butyraldehyde, and the amount of aldehyde added in the first step is 10% to 45% of the total content, and the addition time is 10 to 30 minutes; the amount of acidic catalyst added in the first step is 30% to 65% of the total content, and the addition time is 15 to 60 minutes; the heat preservation and curing time is 30 to 240 minutes. The cations in the inorganic salt include at least one of calcium ions, magnesium ions, lithium ions, and cesium ions, and the anions include at least one of chloride ions and nitrate ions; the inorganic salt is added by dissolving it in distilled water and then uniformly dripping it in; the inorganic salt is added when the polyvinyl alcohol solution is cooled to 45~75°C; the amount of inorganic salt added is 0~5wt% of the mass of the polyvinyl alcohol raw material, and is not 0; 2) Cool the resin mixture to below 60°C, then add alkali solution to the system, keep stirring for 5-30 minutes, filter, and obtain solid resin product; 3) The solid resin product is first washed with pure water multiple times, then washed with a mixed solution of methanol and water multiple times, and finally washed with pure water multiple times to obtain the cleaned product. The time for a single pure water rinse is 20-30 minutes, and the time for a single methanol and water mixed solution rinse is 15-20 minutes. 4) The cleaning product is dried at 40~60℃ to obtain polyvinyl alcohol acetal resin.

2. A polyvinyl acetal resin with a high temperature-dependent melt index prepared by the preparation method of claim 1.

3. The polyvinyl acetal resin having a high temperature-dependent melt index according to claim 2, characterized by, The polyvinyl alcohol acetal resin has the following characteristics: hydroxyl value of 18~21wt%; melt index at 120℃ ≥1.20g / 10min; melt index at 150℃ ≥15.00g / 10min; melt index at 190℃ ≥1.60g / 10min; hydroxyl distribution ≥0.18; average particle size of 100~300μm; particle size distribution coefficient of 1.0~1.5; and bulk density ≥0.120g / mL.

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