A method for preparing polyvinyl alcohol acetal resin

Abstract

This invention discloses a method for preparing polyvinyl alcohol acetal resin. It utilizes the kinetic differences of different stereoisomers of hydroxyl groups during the acetalization reaction to accurately control the reactivity advantages of different stereoisomers. By introducing an alcohol solvent, a swelling effect is achieved on the heterogeneous polyvinyl alcohol acetal resin particles, thereby increasing the penetration of aldehydes and acids into the heterogeneous polyvinyl alcohol acetal resin particles. This releases unreacted m-OH groups encapsulated within the heterogeneous polyvinyl alcohol acetal resin particles, promotes the reaction of the embedded m-OH groups, and ensures that the m-OH groups maintain their reactivity advantage over r-OH groups throughout the reaction, thus increasing the m / r value of the final product. The process of this invention is simple and low-cost, and compared to existing production processes, it eliminates the need for any dispersants or surfactants or other additives that may affect product performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a method for preparing polyvinyl alcohol acetal resin. Background Technology

[0002] Polyvinyl acetal interlayers are widely used in the manufacture of laminated safety glass due to their high light transmittance, excellent cold resistance, impact resistance, and good adhesion to inorganic materials. Polyvinyl acetal resin, as the primary raw material for polyvinyl acetal interlayers, determines the final performance of the interlayer through its structural properties.

[0003] Polyvinyl acetal comprises three structural units: vinyl acetal, vinyl alcohol, and vinyl acetate. The vinyl acetal unit provides impact resistance. This is because PVA resin raw materials contain different stereoisomers of hydroxyl groups, such as isotactic hydroxyl groups (m-OH) and meta-isotactic hydroxyl groups (r-OH). Figure 1 Therefore, the vinyl alcohol acetals generated during acetalization mainly include two acetal isomers: meso (m) and racemic (r). Figure 1 Furthermore, the relative ratio (m / r) of these two isomers is closely related to the impact resistance of polyvinyl acetal resin used in the interlayer of laminated safety glass. Generally speaking, at the same degree of acetalization, the higher the proportion of the meso acetal isomer, the greater the rigidity and the better the impact resistance of the interlayer processed from polyvinyl acetal resin. However, as described in patent CN100384887C, during the acetalization process of polyvinyl acetal resin, the relative ratio of its meso (m) and racemic (r) acetal isomers decreases linearly with the increase of the degree of acetalization (acetalization degree). Therefore, under normal conditions, it is not possible to effectively guarantee that polyvinyl acetal resin maintains a high m / r value at a high degree of acetalization.

[0004] Furthermore, reports indicate that introducing surfactants during the polyvinyl acetal resin reaction can improve the m / r value. However, the introduction of surfactants creates significant difficulties for subsequent washing processes. If residual surfactants cannot be effectively removed, the weather resistance and adhesion of the polyvinyl acetal laminated safety glass will be greatly affected, easily leading to defects such as bubbles during use. To effectively meet the high impact strength requirements of automotive-grade polyvinyl acetal interlayer films, it is urgent to control the relative proportions of meso (m) and racemic (r) acetal isomers in PVB resin by adjusting the reaction rates of different stereoisomers of hydroxyl groups under current conventional process conditions, based on the reaction kinetics of different stereoisomers of hydroxyl groups in PVA resin raw materials. US Patent 2345946 discloses a method of adding alcohol to promote the reaction, but it adds a dispersant during the reaction process, and all alcohols are added to the PVA solution. It does not address the reaction kinetics of meso (m-OH) and racemic (r-OH) hydroxyl groups, making it impossible to precisely control the m / r value. Furthermore, Chinese patent CN103319635B discloses a method in which, after the complete precipitation of polyvinyl acetal resin, a large amount of organic solvent is added to thoroughly dissolve the polyvinyl acetal resin, thus transforming the acetalization reaction from heterogeneous to homogeneous. This method, combining heterogeneous and homogeneous phases, can improve the reaction degree of polyvinyl acetal resin to some extent. However, the homogeneous reaction is costly, requires a large amount of water resources to precipitate the polyvinyl acetal resin, and poses significant difficulties for the subsequent water washing process, failing to achieve precise control over the molecular structure of the polyvinyl acetal resin. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the main objective of this invention is to provide a method for preparing polyvinyl alcohol acetal resin, aiming to precisely control the m / r value of the polyvinyl alcohol acetal resin by adding different amounts of alcohol and at different times. Furthermore, the addition of alcohol effectively dissolves residual hydrochloric acid and aldehyde reagents from the reaction, effectively avoiding the hassle of thoroughly removing residual substances such as hydrochloric acid and butyraldehyde under harsh conditions such as high temperature and prolonged washing in the water washing process, thus greatly saving costs and resources.

[0006] To achieve its objectives, the present invention employs the following technical solution:

[0007] A method for preparing polyvinyl alcohol acetal resin is characterized by: utilizing the kinetic differences of different stereoisomers of hydroxyl groups during the acetalization reaction to accurately control the reactivity advantages of different stereoisomers of hydroxyl groups; introducing an alcohol solvent to achieve swelling of heterogeneous polyvinyl alcohol acetal resin particles, thereby increasing the penetration of aldehyde and acid materials into the heterogeneous polyvinyl alcohol acetal resin particles; releasing unreacted m-OH groups encapsulated within the heterogeneous polyvinyl alcohol acetal resin particles; promoting the reaction of the encapsulated m-OH groups; ensuring that m-OH groups maintain their reactivity advantage over r-OH groups throughout the reaction; and increasing the m / r value of the final product. Specifically, the method includes the following steps:

[0008] 1) Polyvinyl alcohol (PVA) is fully dissolved in pure water at 90°C to obtain a PVA solution. The PVA solution is cooled to 5-20°C, and an acidic catalyst and aldehyde are added to the PVA solution to precipitate a white powder, resulting in a white solid suspension.

[0009] 2) The white solid suspension was reacted at a low temperature of 5-20℃ for 0-2 hours, and then the temperature was raised to 40-60℃ within 0.5-3 hours and kept at that temperature for 0.5-4 hours. The alcohol solvent was added at a certain point in the reaction process (including the low temperature reaction and the high temperature reaction); the mixed solution A was obtained after the reaction was completed.

[0010] 3) Add sodium hydroxide solution to mixed solution A to terminate the reaction, and obtain a suspension containing polyvinyl acetal resin powder;

[0011] 4) The obtained suspension is separated into solid and liquid by a filtration device, and the liquid is recovered by a pressure reducing device; the solid is washed and dried to obtain polyvinyl alcohol acetal resin.

[0012] In step 2), the alcohol solvent is added when the degree of acetalization is between 30 wt% and 70 wt%, i.e., when the degree of acetalization of the polyvinyl alcohol acetal resin is between 30 and 70%. More preferably, the degree of acetalization is between 35 wt% and 60 wt%, and particularly preferably, the degree of acetalization is between 35 wt% and 50 wt%.

[0013] Further, the alcohol solvent mentioned in step 2) includes at least one of the following alcohol reagents: methanol, ethanol, n-butanol, isobutanol, n-propanol, isopropanol, n-pentanol, benzyl alcohol, methoxypropanol, ethoxypropanol, diacetone alcohol, and propylene glycol.

[0014] Furthermore, in step 2), the amount of alcohol solvent added accounts for 1% to 50% of the mass of pure water in step 1), and the alcohol solvent is added dropwise at a uniform rate over 10 to 30 minutes.

[0015] Further, in step 1), the mass ratio of PVA, pure water, acidic catalyst and aldehyde is 100:(700-1200):(20-60):(50-70).

[0016] Further, in step 1), the aldehyde includes at least one of formaldehyde, acetaldehyde, butyraldehyde, pentanaldehyde, isovaleraldehyde, hexanal, heptaldehyde, octanaldehyde, nonanaldehyde, decanaldehyde, benzaldehyde, and phenylacetaldehyde.

[0017] Further, in step 1), the acidic catalyst includes at least one of the following acidic catalysts: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrobromic acid, hydroiodic acid, perchloric acid, chloroacetic acid, aminosulfonic acid, benzenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid, ethylbenzenesulfonic acid, and isophenylenedisulfonic acid.

[0018] Furthermore, in step 4), the water washing temperature is 20-50℃ (preferably 30℃, more preferably 20℃), the number of water washings is 3-8 times, and the time for each water washing is 5-30 minutes.

[0019] The polyvinyl alcohol acetal resin obtained by this invention has an acetal degree ≥78.0wt% and m / r ≥3.50.

[0020] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0021] The process of this invention is simple and low-cost. Compared with existing production processes, the reaction process of this invention does not require the addition of any dispersants or surfactants or other additives that may affect product performance. By adding different amounts of alcohol and controlling the timing of addition, the m / r value of polyvinyl acetal resin can be precisely controlled, while promoting the cleaning of reaction residues, reducing the water washing process steps, and lowering energy consumption. This invention also has the advantages of simple operation and no need for additional process equipment, giving it good market competitiveness. Attached Figure Description

[0022] Figure 1 The structural diagrams of isotactic hydroxyl (m-OH) and metaisotactic hydroxyl (r-OH) of PVA resin raw materials and the corresponding meso (m) and racemic (r) acetal isomers of polyvinyl alcohol acetal resin are shown.

[0023] Figure 2 The image shows the 1H NMR spectrum of the polyvinyl acetal resin prepared in Example 1. Detailed Implementation

[0024] 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] In this embodiment, polyvinyl acetal resin is prepared according to the following steps:

[0027] (1) Add 50g of polyvinyl alcohol with an average degree of polymerization of 1700 to 500mL of pure water and stir at 90℃ for 2h to dissolve it completely to obtain polyvinyl alcohol stock solution; cool down to 15℃, add 16g of hydrochloric acid with a mass concentration of 36% to 38% and stir thoroughly; when the temperature drops to 10℃, add 28.5g of n-butyraldehyde dropwise to precipitate white powder and obtain white solid suspension.

[0028] (2) Starting from the end of the addition of n-butyraldehyde (at which point the degree of acetalization reaction is between 35wt% and 45wt%), 150mL of methanol is added uniformly over 10min; at the same time, the white solid suspension is kept at 10℃ and stirred for 1.5h, and then the temperature is raised to 60℃ and stirred for 2h over 3h. The reaction ends to obtain mixed solution A.

[0029] (3) Add 15 mL of 15 wt% sodium hydroxide solution to mixed solution A and stir for 30 min to obtain a suspension containing polyvinyl acetal resin powder.

[0030] (4) Filter the suspension to separate the solid and liquid. Wash the solid PVB with water 8 times at 20°C, with each wash lasting 15 minutes. Centrifuge to remove water and dry at 50°C for 12 hours to obtain polyvinyl alcohol acetal resin.

[0031] Example 2

[0032] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 150 mL of methanol was added after the temperature was maintained at 10°C for 0.5 h (at which point the degree of acetalization reaction was between 45 wt% and 50 wt%).

[0033] Example 3

[0034] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 150 mL of methanol was added after the temperature was maintained at 10°C for 1.5 h (at which point the degree of acetalization reaction was between 50 wt% and 60 wt%).

[0035] Example 4

[0036] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 150 mL of methanol was added at the beginning of the heating process to 55°C (where the degree of acetalization reaction is between 60 wt% and 70 wt%).

[0037] Example 5

[0038] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 50 mL of propanol was added instead of 150 mL of methanol.

[0039] Example 6

[0040] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 70 mL of propanol was added instead of 150 mL of methanol.

[0041] Example 7

[0042] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 150 mL of ethanol was added instead of 150 mL of methanol.

[0043] Example 8

[0044] This embodiment was prepared using the same method and conditions as in Example 1, except that in step 2), 150 mL of isopropanol was added instead of 150 mL of methanol.

[0045] Comparative Example 1

[0046] This comparative example was prepared using the same method and conditions as in Example 1, except that 150 mL of distilled water was added in step (2) to replace 150 mL of methanol.

[0047] Comparative Example 2

[0048] This comparative example was prepared using the same method and conditions as in Example 3, except that 150 mL of distilled water was added in step (2) to replace 150 mL of methanol.

[0049] Comparative Example 3

[0050] This comparative example was prepared using the same method and conditions as in Example 4, except that 150 mL of distilled water was added in step (2) to replace 150 mL of methanol.

[0051] The degree of acetalization and the ratio of meso to racemic acetal isomers (m / r) of the polyvinyl alcohol acetal resin prepared above were determined by proton nuclear magnetic resonance spectroscopy (NMR). 1 HNMR or carbon nuclear magnetic resonance (NMR) 13The NMR spectrum was determined using any one or two techniques from C1NMR. When characterizing polyvinyl butyral (PVB) using 1H NMR spectroscopy, 1–2 mg of PVB was thoroughly dissolved in 0.6 mL of DMSO-d6, and the spectrum was scanned at least 16 times on a 600 MHz NMR spectrometer. The resulting NMR spectrum was integrated using MestReNova software, and the ratio of the mole fraction of hydrogen in the ranges of 4.40–4.65 ppm (meta-acetal, m) and 4.65–4.75 ppm (racemic, r) was calculated. This ratio is called the meta-to-racemic acetal isomer ratio (m / r). Figure 2 The polyvinyl acetal resin prepared in Example 1 of this invention was used to calculate the 1H NMR spectrum of m / r.

[0052] It should be noted that the degree of acetalization is the mass percentage of the monomer containing the acetal group in the entire polyvinyl alcohol acetal molecular chain. Similarly, the degree of acetalization can also be calculated using 1H NMR spectroscopy, specifically as follows:

[0053] Acetal degree (mole fraction) VB m =2 / ((3*A) CH2 / A CH3 )-6).

[0054] Where A CH2 and A CH3 The integral areas are methylene (-CH2) at 1.0-1.9 ppm and methyl (-CH3) at 0.755-0.9 ppm, respectively.

[0055] Among them, acetal degree VB m This is a relative mole fraction. To better reflect actual industrial processing, this relative mole fraction needs to be converted to a relative mass fraction (VB). w The specific method is as follows:

[0056] Acetal degree (mass fraction): VB w =142*VB m / (142*VB m +(1-VB m )*44).

[0057] Table 1. Test results of acetal degree and m / r of polyvinyl alcohol acetal resin.

[0058] Example 1 79.5％ 3.72 Example 2 78.8％ 3.70 Example 3 78.4％ 3.69 Example 4 78.0％ 3.57 Example 5 78.4％ 3.65 Example 6 79.3％ 3.73 Example 7 79.5％ 3.52 Example 8 78.4％ 3.52 Comparative Example 1 77.6％ 3.42 Comparative Example 2 78.4％ 3.37 Comparative Example 3 79.1％ 3.24

[0059] 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 scope of protection of the present invention.

Claims

1. A method for preparing polyvinyl acetal resin, characterized in that, Includes the following steps: 1) PVA is fully dissolved in pure water at 90℃ to obtain a PVA solution. The PVA solution is cooled to 5~20℃, and an acidic catalyst and aldehyde are added to precipitate a white powder, resulting in a white solid suspension. 2) The white solid suspension is reacted at a low temperature of 5~20℃ for 0~2h, and then the temperature is raised to 40~60℃ within 0.5~3h, and the reaction is maintained at this temperature for 0.5~4h. The alcohol solvent is added at a certain point in the reaction process. The reaction is completed to obtain mixed solution A. The alcohol solvent is added when the degree of acetalization reaction is 30wt%~70wt%. 3) Add sodium hydroxide solution to mixed solution A to terminate the reaction, and obtain a suspension containing polyvinyl acetal resin powder; 4) The obtained suspension is separated into solid and liquid by a filtration device, and the liquid is recovered by a pressure reducing device; the solid is washed and dried to obtain polyvinyl alcohol acetal resin, wherein the degree of acetalization of the polyvinyl alcohol acetal resin is ≥78.0wt%, and m / r is ≥3.50, wherein m / r is the relative ratio of the two acetal isomers, meso m and racemic r.

2. The preparation method according to claim 1, characterized in that: The alcohol solvent mentioned in step 2) is added when the degree of acetalization reaction is between 35wt% and 60wt%.

3. The preparation method according to claim 1, characterized in that: Step 2) The alcohol solvent is added when the degree of acetalization reaction is 35wt%~50wt%.

4. The preparation method according to claim 1, characterized in that: The alcohol solvent mentioned in step 2) includes at least one of methanol, ethanol, n-butanol, isobutanol, n-propanol, isopropanol, n-pentanol, benzyl alcohol, methoxypropanol, ethoxypropanol, diacetone alcohol, and propylene glycol.

5. The preparation method according to claim 1, characterized in that: The amount of alcohol solvent added in step 2) is 1% to 50% of the mass of pure water in step 1), and the alcohol solvent is added dropwise at a uniform rate over 10 to 30 minutes.

6. The preparation method according to claim 1, characterized in that: In step 1), the mass ratio of PVA, pure water, acidic catalyst and aldehyde is 100:700~1200:20~60:50~70.

7. The preparation method according to claim 1, characterized in that: In step 1), the aldehyde includes at least one of formaldehyde, acetaldehyde, butyraldehyde, pentanal, isovaleraldehyde, hexanal, heptanal, octanal, nonanal, decanal, benzaldehyde, and phenylacetaldehyde, and the acidic catalyst includes at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrobromic acid, hydroiodic acid, perchloric acid, chloroacetic acid, aminosulfonic acid, benzenesulfonic acid, o-toluenesulfonic acid, m-toluenesulfonic acid, ethylbenzenesulfonic acid, and isophenylenedisulfonic acid.

8. The preparation method according to claim 1, characterized in that: In step 4), the water washing temperature is 20~50℃, the number of water washings is 3~8 times, and the time for each water washing is 5~30 minutes.

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