High-acetalization-rate environment-friendly PVB resin, preparation method and application thereof

Abstract

This invention relates to the field of polyvinyl butyral synthesis technology, and particularly to a high-acetal-rate environmentally friendly PVB resin, its preparation method, and its applications. Addressing the technical pain points of homogeneous methods (uneven acetal group distribution, severe product coloring, and difficulty in solvent recovery), precipitation methods (low acetal yield and easy agglomeration), one-step methods (high catalyst residue and unstable performance), and poor environmental performance of traditional processes), this invention achieves precise control of the acetal rate at 75-80%, hydroxyl content at 17-19%, solvent recovery rate ≥95%, and product bulk density of 0.25-0.3 g / cm³ through an integrated technical solution of "composite solvent + staged catalytic system + directional separation and recovery + precise reaction control + post-treatment modification." 3 The catalyst residue is ≤0.01%. Furthermore, the high acetal rate environmentally friendly PVB resin provided by this invention exhibits excellent optical transparency, thermal stability, and aging resistance.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl butyral (PVB) synthesis technology, and in particular to an environmentally friendly PVB resin with high acetal content, its preparation method, and its applications. Background Technology

[0002] PVB resin, as an important polymer adhesive material, plays an irreplaceable role in high-end fields such as photovoltaic energy, automobile manufacturing, and optical instruments due to its excellent light transmittance, bonding strength, impact resistance, and weather resistance. With the rapid development of the global photovoltaic industry and the continuous improvement of automotive safety standards, the market's performance requirements for PVB resin are becoming increasingly stringent. These requirements not only demand higher acetal ratios and more uniform acetal group distributions, but also higher standards for optical purity, thermal stability, and aging resistance. At the same time, tightening environmental policies also require low emissions and high resource utilization in the manufacturing process.

[0003] However, existing synthesis methods for PVB resins, such as homogeneous synthesis, precipitation synthesis, and one-step synthesis, still have many insurmountable technical defects that limit their application in high-end fields.

[0004] Regarding the homogeneous method: This method typically uses a single solvent, such as dimethyl sulfoxide (DMSO) or ethanol, to carry out an acetal reaction between polyvinyl alcohol (PVA) and n-butyraldehyde in a homogeneous system. However, during the reaction, as PVB resin is formed, the system easily transitions from homogeneous to heterogeneous, resulting in uneven distribution of acetal groups on the molecular chain. This leads to yellowing and discoloration of the product (Gardner color intensity is typically ≥5), and poor thermal stability (weight loss ≥3% after 1000 hours of thermal aging). Furthermore, the separation and purification of the single solvent is difficult, with a solvent recovery rate of only 60-70%, resulting in high recovery costs and generating large amounts of high chemical oxygen demand (COD) wastewater, posing significant environmental pressure. For example, Chinese patent CN108640715A discloses a homogeneous method for preparing PVB resin using DMSO as a single solvent. Although the acetal rate can reach 80-84%, the product has high color intensity, and the solvent recovery rate is only 75%, making it difficult to meet the needs of high-end applications.

[0005] Regarding the precipitation method: To address the environmental concerns of homogeneous methods, the precipitation method was developed. This method uses water as the dispersion medium and induces the reaction of PVA with n-butyraldehyde through a catalyst to precipitate PVB resin. However, the acetalization rate of the precipitation method is relatively low, generally between 70% and 76%, and intermolecular cross-linking easily occurs during the reaction, leading to severe product agglomeration, poor particle uniformity, and uneven distribution of acetal groups, limiting its application in high-transmittance and high-bonding-strength scenarios. For example, Chinese patent CN109705642A uses the precipitation method to prepare PVB resin, but the acetalization rate is only 78% to 80%, and the product bulk density fluctuates greatly (0.18~0.22 g / cm³). 3This makes it unsuitable for the packaging requirements of high-end photovoltaic glass.

[0006] One-step method: The one-step method can achieve a high acetal yield (82~85%) by optimizing reaction conditions, but it suffers from catalyst encapsulation problems. The PVB particles generated in the reaction easily encapsulate the acid catalyst inside, resulting in a high catalyst residue (usually ≥0.05%). This leads to decreased product aging resistance, with a transmittance retention rate ≤80% after 1000 hours of UV aging, and poor performance stability with large batch-to-batch fluctuations. For example, US Patent 6232316B1 uses a one-step method to prepare PVB resin, but the catalyst residue reaches 0.06~0.08%, resulting in insufficient thermal stability and a glass transition temperature of only 58~62℃, which is difficult to meet the high-temperature requirements for automotive safety glass.

[0007] In addition to the specific defects mentioned above, existing methods also suffer from the common problem of an imperfect solvent recovery system. Solvent recovery often employs simple distillation, resulting in a purity of only 95-98%, which can easily affect product performance during recycling.

[0008] Therefore, developing a high-acetal-rate, environmentally friendly PVB resin that can simultaneously solve core problems such as low acetal rate, uneven distribution of acetal groups, high catalyst residue, and poor environmental performance, while maintaining stable product performance, has become an urgent need for the industry. Summary of the Invention

[0009] In view of this, the present invention provides a high acetal rate environmentally friendly PVB resin, its preparation method and application. The high acetal rate environmentally friendly PVB resin provided by the present invention has a high acetal rate, uniform acetal group distribution, low catalyst residue, good environmental performance and stable performance.

[0010] This invention provides a method for preparing a high acetal content environmentally friendly PVB resin, comprising the following steps: 1) A composite solvent, PVA, n-butyraldehyde, and a graded catalytic system are mixed and subjected to an acetal reaction to obtain crude PVB; the composite solvent includes dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (NMP); the degree of polymerization of the PVA is 1700~2000, and the degree of alcoholysis is 98~99%; 2) The crude PVB product and the hindered phenolic antioxidant are mixed to obtain the high acetal rate environmentally friendly PVB resin.

[0011] Preferably, the dimethyl sulfoxide accounts for 90-95 wt% of the composite solvent.

[0012] Preferably, the staged catalytic system includes a main catalyst, a rate regulator, and a complexing agent; the main catalyst is hydrochloric acid, the rate regulator is an organophosphonic acid, and the complexing agent is disodium ethylenediaminetetraacetate.

[0013] Preferably, the acetal reaction is a staged acetal reaction, comprising a first stage reaction, a second stage reaction, and a third stage reaction carried out sequentially; the temperature of the first stage reaction is 45~50℃, the holding time is 1.8~2.2 hours, and the first stage reaction is carried out under stirring conditions at a stirring speed of 100~150 rpm; the temperature of the second stage reaction is 50~55℃, the holding time is 1.8~2.2 hours, and the second stage reaction is carried out under stirring conditions at a stirring speed of 200~250 rpm; the temperature of the third stage reaction is 48~50℃, the holding time is 0.9~1.1 hours, and the third stage reaction is carried out under stirring conditions at a stirring speed of 100 rpm; the total time of the acetal reaction is 5 hours.

[0014] Preferably, after the first stage reaction and before the second stage reaction, the system is further heated at a rate of 2-3 °C / min; after the second stage reaction and before the third stage reaction, the system is further cooled at a rate of 1-2 °C / min.

[0015] Preferably, the acetal reaction further includes sequentially cooling, allowing to stand, and separating the solvent from the obtained product, collecting the solvent, and obtaining a solid product.

[0016] Preferably, after collecting the solvent, the process further includes distilling and purifying the obtained solvent, collecting the fraction with a top temperature of 189~202℃ to obtain a recovered solvent mother liquor with a purity of ≥99.5%; the solid product further includes post-treatment, which includes washing the solid product with water, centrifuging, collecting the solid and the washing liquid, concentrating the washing liquid or drying the solid.

[0017] Preferably, the hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0018] The present invention also provides a high acetal rate environmentally friendly PVB resin obtained by the preparation method described above, with an acetal rate of 75~80%, a glass transition temperature ≥60℃, a weight loss rate ≤2.0% after 1000 hours of heat aging at 120℃, and a catalyst residue of ≤0.01%.

[0019] This invention also provides the application of the high acetal rate environmentally friendly PVB resin described above in the fields of photovoltaic glass, automotive safety glass, or optical device adhesives.

[0020] Compared with the prior art, the present invention has achieved the following beneficial effects: Addressing the technical challenges of homogeneous acetal production (uneven acetal group distribution, severe product coloring, and difficult solvent recovery), precipitation-based acetal production (low acetal yield and easy agglomeration), one-step acetal production (high catalyst residue and unstable performance), and poor environmental friendliness of traditional processes, this invention employs an integrated technical solution combining "composite solvent + staged catalytic system + targeted separation and recovery + precise reaction control + post-treatment modification." This achieves precise control of the acetal yield at 75-80%, hydroxyl content at 17-19%, solvent recovery rate ≥95%, and product bulk density of 0.25-0.3 g / cm³. 3 The catalyst residue is ≤0.01%. Furthermore, the high acetal rate environmentally friendly PVB resin provided by this invention exhibits excellent optical transparency, thermal stability, and aging resistance. Specifically, this invention has the following significant and verifiable core advantages: 1) Excellent performance indicators: The uniformity of acetal group distribution is significantly improved, the product color (Gardner) is ≤1, and the optical transparency is excellent; the catalyst residue is ≤0.01%, the weight loss rate after 1000 hours of heat aging is ≤2.0%, the light transmittance retention rate after 1000 hours of UV aging is ≥88%, and the ash content is ≤0.1%. All performance indicators meet the requirements of high-end photovoltaic glass, automotive safety glass, and optical device adhesives. It is especially suitable for high-end photovoltaic glass encapsulation, automotive safety glass interlayer, and high-precision optical device bonding, which have stringent requirements for material performance and environmental protection.

[0021] 2) Outstanding environmental performance: The combination of "gradient cooling crystallization + vacuum distillation + distillation purification" is used to replace the traditional water washing and centrifugation method. The solvent recovery rate is ≥95% and the recovery cost is reduced by more than 40%. Both the washing liquid and the solid product are effectively treated. There is no wastewater or waste gas emission in the whole process, which meets the needs of green chemical development and has broad prospects for industrial application.

[0022] 3) Strong process stability and repeatability: Key specifications such as the degree of polymerization, purity, and moisture content of raw materials are clearly defined, and parameters such as reaction temperature, stirring speed, and heating / cooling rate are precisely controlled. The process steps are standardized, and the performance fluctuation between product batches is ≤2%, which solves the problem of poor reaction repeatability of existing methods and facilitates industrial scale-up production. Detailed Implementation

[0023] This invention provides a method for preparing a high acetal content environmentally friendly PVB resin, comprising the following steps: 1) A composite solvent, PVA, n-butyraldehyde, and a graded catalytic system are mixed to carry out an acetal reaction to obtain crude PVB; the composite solvent includes dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (NMP). 2) The crude PVB product and the hindered phenolic antioxidant are mixed to obtain the high acetal rate environmentally friendly PVB resin.

[0024] This invention involves mixing a composite solvent, PVA, n-butyraldehyde, and a staged catalytic system (referred to as the first mixture, yielding the reaction system) to perform an acetal reaction, yielding crude PVB. In this invention, the purity of the dimethyl sulfoxide is preferably ≥99.8%, and the moisture content is preferably ≤0.1%.

[0025] In this invention, the purity of the N-methylpyrrolidone is preferably ≥99.5%, and the moisture content is preferably ≤0.2%.

[0026] In this invention, the mass ratio of dimethyl sulfoxide to the composite solvent is preferably 90-95 wt%, more preferably 92-93 wt%. The composite solvent in this invention uses dimethyl sulfoxide as the main solvent and N-methylpyrrolidone as a co-solvent. The main solvent accounts for 90-95% of the total mass of the composite solvent, and the co-solvent accounts for 5-10%.

[0027] This invention employs the above-mentioned specifications of main solvent to avoid the influence of moisture on the acetal reaction rate. It also employs the above-mentioned specifications of co-solvent to ensure compatibility with the main solvent and its regulatory effect on the reaction. This invention uses a composite solvent system of DMSO and NMP. The polarity of NMP is similar to that of DMSO, which can significantly enhance the compatibility between PVA and n-butyraldehyde, inhibit premature precipitation of PVB during the reaction, maintain system homogeneity for ≥4.5 hours, guide intramolecular acetal reaction preferentially, and reduce intermolecular crosslinking and aggregation.

[0028] In this invention, the composite solvent preferably further includes a recycled solvent mother liquor; the recycled solvent mother liquor is a mixed solvent of dimethyl sulfoxide and N-methylpyrrolidone obtained by distillation purification in the preceding process; the purity of the recycled solvent mother liquor is preferably ≥99.5%; the mass ratio of the recycled solvent mother liquor to the composite solvent is preferably 1~2wt%. This invention uses the above-mentioned recycled solvent mother liquor to ensure reaction stability during recycling, improving solvent recycling rate and reducing production costs without affecting reaction stability.

[0029] In this invention, the degree of polymerization of the PVA is preferably 1700-2000, and the degree of alcoholysis is preferably 98-99%. This invention uses PVA of the above specifications to ensure its reactivity with n-butyraldehyde and the bonding performance of the product.

[0030] In this invention, the purity of the n-butyraldehyde is preferably ≥99.0%, and the moisture content is preferably ≤0.1%. Using n-butyraldehyde of the above specifications reduces the occurrence of side reactions.

[0031] In this invention, the preferred mass ratio of PVA to n-butyraldehyde is 1:0.75~0.8, more preferably 1:0.77~0.78. By using the above-mentioned ratio of PVA to n-butyraldehyde, this invention ensures the complete reaction of the hydroxyl groups in PVA while avoiding waste caused by excessive n-butyraldehyde.

[0032] In this invention, the staged catalytic system preferably includes a main catalyst, a rate regulator, and a complexing agent.

[0033] In this invention, the main catalyst is preferably hydrochloric acid; the HCl in the hydrochloric acid is preferably analytical grade; and the mass concentration of the hydrochloric acid is preferably 36-38 wt%. This invention uses a main catalyst of the above specifications to ensure the reaction rate.

[0034] In this invention, the main catalyst accounts for 1.5 to 2 wt% of the reaction system by mass, more preferably 1.6 to 1.8 wt%.

[0035] In this invention, the rate regulator is preferably an organophosphonic acid; the organophosphonic acid is preferably triethyl phosphite; the purity of the organophosphonic acid is preferably ≥98.5%, and the moisture content is preferably ≤0.1%.

[0036] In this invention, the rate regulator preferably accounts for 0.05~0.1 wt% of the reaction system, more preferably 0.06~0.09 wt%, and even more preferably 0.07~0.08 wt%. This invention uses the above-mentioned specifications and amounts of rate regulator to precisely control the reaction process.

[0037] In this invention, the complexing agent is preferably disodium ethylenediaminetetraacetate (EDTA-2Na); the purity of the complexing agent is preferably analytical grade.

[0038] In this invention, the complexing agent preferably accounts for 0.03~0.05 wt% of the reaction system, more preferably 0.04 wt%. Using the complexing agent of the above specifications and dosage, this invention can efficiently chelate metal impurities.

[0039] In this invention, the mass ratio of the staged catalytic system to the reaction system is preferably 1.58~2.15wt%, more preferably 1.7~2wt%.

[0040] The staged catalytic system in this invention adopts a ternary system of "main catalyst + rate regulator + complexing agent": the main catalyst provides sufficient protons to ensure the acetal reaction rate; the rate regulator slows down the reaction process through weak interaction with the main catalyst, avoids excessive local acetalization, and improves the uniformity of acetal group distribution; the complexing agent chelates trace metal impurities such as iron and calcium in the system, avoids the inhibition of catalyst activity, and at the same time reduces metal residue in the product, solving the problem of catalyst encapsulation in one-step process, so that the catalyst residue is ≤0.01%.

[0041] In this invention, the first mixing preferably includes the following steps: adding PVA to a composite solvent, stirring and dispersing for 30-40 minutes to obtain a premix, and then sequentially adding n-butyraldehyde and a graded catalytic system to the premix.

[0042] In this invention, the acetal reaction is preferably a staged acetal reaction, comprising a first stage reaction, a second stage reaction, and a third stage reaction carried out sequentially.

[0043] In this invention, the temperature of the first stage reaction is preferably 45~50℃, more preferably 47~48℃, and the holding time is preferably 1.8~2.2 hours, more preferably 2 hours; the first stage reaction is preferably carried out under stirring conditions; the stirring speed of the stirring conditions is preferably 100~150 rpm, more preferably 120 rpm.

[0044] In this invention, after the first stage reaction and before the second stage reaction, it is preferable to further heat the system; the heating rate is preferably 2~3℃ / min.

[0045] In this invention, the temperature of the second stage reaction is preferably 50~55℃, more preferably 52~53℃, and the holding time is preferably 1.8~2.2 hours, more preferably 2 hours; the second stage reaction is preferably carried out under stirring conditions; the stirring speed of the stirring conditions is preferably 200~250 rpm, more preferably 220 rpm.

[0046] In this invention, after the second stage reaction and before the third stage reaction, it is preferable to further cool the system; the cooling rate is preferably 1~2℃ / min.

[0047] In this invention, the temperature of the third-stage reaction is preferably 48~50℃, more preferably 49℃, and the holding time is preferably 0.9~1.1 hours, more preferably 1 hour; the third-stage reaction is preferably carried out under stirring conditions; the stirring speed of the stirring conditions is preferably 100 rpm.

[0048] In this invention, the total time for the acetal reaction is preferably 5 hours. This invention employs a segmented temperature-controlled acetal reaction, maintaining system homogeneity for at least 4.5 hours during the reaction.

[0049] This invention employs a segmented temperature-controlled reaction to achieve precise regulation of reaction parameters: initial activation of raw materials, mid-stage acceleration of the reaction, and final stage supplementation to improve the stability of the acetal ratio; furthermore, different stirring conditions are used at different stages: foaming is avoided in the initial stage, homogeneity is ensured in the mid-stage, and crystal formation is assisted in the final stage. Through the above regulation methods, the acetal ratio is precisely controlled at 75-80%.

[0050] In this invention, the acetal reaction preferably further includes cooling, settling and separating the solvent from the obtained product in sequence, collecting the solvent and obtaining a solid product.

[0051] In this invention, the cooling rate is preferably 2°C / min, and the final temperature is preferably 30°C.

[0052] In this invention, the preferred temperature for the static setting is 30°C, and the preferred holding time is 1 hour.

[0053] In this invention, the method for separating the solvent is preferably vacuum distillation; the temperature of the vacuum distillation is preferably 80~90℃, more preferably 85℃, the vacuum degree is preferably -0.09MPa, and the holding time is preferably 2~3 hours, more preferably 2.5 hours.

[0054] In this invention, after collecting the solvent, it is preferable to further purify the obtained solvent by distillation, collect the fraction with a top temperature of 189~202℃, and obtain a recovered solvent mother liquor with a purity of ≥99.5%.

[0055] In this invention, the theoretical number of trays in the distillation column used for the distillation purification is preferably 15-20, more preferably 18, and the reflux ratio is preferably 1.5-2.0, more preferably 1.7-1.8. DMSO has a boiling point of approximately 189°C, and NMP has a boiling point of approximately 202°C. Under the above ratio and reflux ratio, azeotropic or near-boiling point fractions can be effectively separated and purified, with a solvent recovery rate ≥95%. The recovered solvent mother liquor has a heavy component impurity content ≤0.5%, which can be recycled for use in composite solvents.

[0056] In this invention, the solid product preferably further includes post-processing, which preferably includes sequentially washing the solid product with water, centrifuging, collecting the solid and the washing liquid, concentrating the washing liquid or drying the solid.

[0057] In this invention, the water used for washing is preferably deionized water; the mass ratio of the deionized water to the solid product is preferably 3:1; the washing time for a single wash is preferably 15 to 20 minutes, more preferably 18 minutes; and the number of washes is preferably 2 or more.

[0058] In this invention, the centrifugation speed is preferably 3000 rpm, and the time is preferably 15-20 minutes, more preferably 17-18 minutes.

[0059] In this invention, the concentration is preferably vacuum concentration; the vacuum degree of the vacuum concentration is preferably -0.08 to -0.09 MPa; the concentration temperature is preferably 60 to 70°C, more preferably 64 to 68°C, and the holding time is preferably based on a solid content ≥30%. After concentration, the washing liquid undergoes the same subsequent treatment as the collected solvent, including distillation purification, collecting the fraction with a top temperature of 189 to 202°C to obtain a recovered solvent mother liquor with a purity ≥99.5%, which is then recycled.

[0060] In this invention, the drying is preferably vacuum drying; the vacuum degree of the vacuum drying is preferably -0.08 to -0.09 MPa; the drying temperature is preferably 50 to 60°C, more preferably 55°C, and the holding time is preferably 4 to 6 hours, more preferably 5 hours; during the drying process, the volatile matter is controlled to be less than 3 wt%.

[0061] This invention employs a directional separation and solvent recovery method combining gradient cooling crystallization, vacuum distillation, and distillation purification. Gradient cooling allows PVB resin to precipitate slowly, preventing particle agglomeration; vacuum distillation reduces energy consumption by more than 15% compared to conventional distillation; and distillation purification ensures solvent purity ≥99.5% and recovery rate ≥95%. The solid product is washed with water and centrifuged to obtain coarse powder. The washing liquid is concentrated under vacuum and incorporated into the solvent recovery system, achieving zero wastewater discharge throughout the entire process. This invention removes residual solvent through drying, controlling the volatile content to less than 3 wt%.

[0062] After obtaining crude PVB, the present invention mixes the crude PVB with a hindered phenolic antioxidant (denoted as the second mixture) to obtain the high acetal content environmentally friendly PVB resin. In the present invention, the hindered phenolic antioxidant is preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. In a specific embodiment of the present invention, it is specifically antioxidant 1010.

[0063] In this invention, the purity of the hindered phenolic antioxidant is preferably ≥99.0%, and the particle size is preferably ≤10μm.

[0064] In this invention, the mass ratio of crude PVB to hindered phenolic antioxidant is preferably 100:0.1~0.2, more preferably 100:0.15. This invention uses hindered phenolic antioxidants of the above specifications and dosage to ensure uniform coating without affecting the product's light transmittance.

[0065] In this invention, the second mixing is preferably agitated mixing, and the stirring speed is preferably 1500 rpm; the second mixing time is preferably 15-20 minutes, more preferably 18 minutes; the temperature of the second mixing is preferably ≤40℃. This invention achieves high-speed mixing and coating of hindered phenolic antioxidants, controls the system temperature, avoids the decomposition of hindered phenolic antioxidants, improves the thermal stability of the product, and achieves a glass transition temperature ≥60℃.

[0066] The present invention also provides a high acetal rate environmentally friendly PVB resin obtained by the preparation method described above, with an acetal rate of 75~80%, a glass transition temperature ≥60℃, a weight loss rate ≤2.0% after 1000 hours of heat aging at 120℃, and a catalyst residue of ≤0.01%.

[0067] In this invention, the high acetal rate environmentally friendly PVB resin is subjected to 1000 hours of ultraviolet aging (wavelength 340nm, irradiation intensity 0.68W / m). 2 After processing, the light transmittance retention rate is ≥88%, the ash content is ≤0.1%, and the bulk density is 0.25~0.3g / cm³. 3 , coloring degree (Gardner) ≤ 1.

[0068] This invention also provides the application of the high acetal rate environmentally friendly PVB resin described above in the fields of photovoltaic glass, automotive safety glass, or optical device adhesives.

[0069] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments thereof.

[0070] Example 1: Preparation of composite solvent: Take 90 kg of DMSO (purity 99.8%, water content 0.08%) and mix with 10 kg of NMP (purity 99.5%, water content 0.15%), add 1 kg of recovered solvent mother liquor (purity 99.6%, heavy component content 0.4%), stir for 30 minutes to obtain composite solvent; Raw material mixing and reaction system construction: 100 kg of PVA (degree of polymerization 1700, degree of alcoholysis 98%) was added to the above composite solvent and stirred at 120 rpm for 35 minutes to disperse evenly. Then, 75 kg of n-butyraldehyde (purity 99.2%, water content 0.07%) was added. Subsequently, 1.5 wt% hydrochloric acid catalyst (analytical grade, diluted with 37 wt% hydrochloric acid), 0.05 kg of triethyl phosphite (purity 98.6%, water content 0.08%), and 0.03 kg of EDTA-2Na (analytical grade) were added and stirred for 10 minutes to obtain a homogeneous reaction system. The reaction was carried out in stages with controlled temperature: the total reaction time was 5 hours. First, the temperature was maintained at 45℃ for 2 hours with a stirring speed of 100 rpm; then the temperature was increased to 50℃ at a rate of 2℃ / min and maintained for 2 hours with a stirring speed of 200 rpm; then the temperature was decreased to 48℃ at a rate of 1℃ / min and maintained for 1 hour with a stirring speed of 100 rpm; the homogeneity of the system was maintained for 4.8 hours during the reaction. Targeted separation and solvent recovery: After the reaction, the temperature was lowered from 55℃ to 30℃ at a rate of 2℃ / min, and held at this temperature for 1 hour. Subsequently, the solvent was separated by vacuum distillation at 80℃ and -0.09MPa for 2.5 hours. The recovered composite solvent was purified by a distillation column with 15 theoretical plates and a reflux ratio of 1.5. The fraction at 189~202℃ at the top of the column was collected to obtain a mother liquor of recovered solvent with a purity of 99.6%. The solid product was washed twice with deionized water at a mass ratio of 3:1 (water to solid product) for 15 minutes each time, and centrifuged at 3000rpm for 15 minutes to obtain crude PVB powder. The washing liquid was concentrated under vacuum at -0.085MPa to a solid content of 32% and then incorporated into the solvent recovery system. Post-treatment modification: PVB coarse powder was vacuum dried at 55℃ and -0.08MPa for 5 hours, and the volatile content was controlled at 2.5%; 0.1kg antioxidant 1010 (purity 99.2%, particle size 8μm) was added to the dried PVB coarse powder, and the mixture was mixed at 1500rpm for 15 minutes, while the system temperature was controlled at 35℃, to obtain environmentally friendly PVB resin with high acetal rate.

[0071] Example 2: Preparation of composite solvent: Take 95 kg of DMSO (purity 99.9%, water content 0.05%) and 5 kg of NMP (purity 99.6%, water content 0.1%), mix them, add 2 kg of recovered solvent mother liquor (purity 99.7%, heavy component content 0.3%), stir for 30 minutes to get a uniform composite solvent; Raw material mixing and reaction system construction: 100 kg of PVA (degree of polymerization 2000, degree of alcoholysis 99%) was added to the above composite solvent and stirred at 150 rpm for 30 minutes to disperse evenly. Then, 80 kg of n-butyraldehyde (purity 99.5%, water content 0.05%) was added. Subsequently, 2 wt% hydrochloric acid catalyst (analytical grade, diluted with 38% hydrochloric acid), 0.1 kg of triethyl phosphite (purity 98.8%, water content 0.05%), and 0.05 kg of EDTA-2Na (analytical grade) were added and stirred for 10 minutes to obtain a homogeneous reaction system. Segmented temperature-controlled reaction: The total reaction time was 5 hours. First, the temperature was maintained at 50°C for 2 hours with a stirring speed of 150 rpm; then the temperature was increased to 55°C at a rate of 3°C / min and maintained for 2 hours with a stirring speed of 250 rpm; then the temperature was decreased to 50°C at a rate of 2°C / min and maintained for 1 hour with a stirring speed of 100 rpm; the homogeneity of the system was maintained for 5.0 hours during the reaction. Targeted separation and solvent recovery: After the reaction, the temperature was lowered from 55℃ to 30℃ at a rate of 2℃ / min, and held at this temperature for 1 hour. Subsequently, the solvent was separated by vacuum distillation at 90℃ and -0.09MPa for 2 hours. The recovered mixed solvent was purified by a distillation column with 20 theoretical plates and a reflux ratio of 2.0. The fraction at 189~202℃ at the top of the column was collected to obtain a recovered solvent with a purity of 99.8%. The solid product was washed twice with deionized water at a mass ratio of 3:1, each time for 20 minutes, and centrifuged at 3000rpm for 20 minutes to obtain crude PVB powder. The washing liquid was concentrated under vacuum at -0.09MPa to a solid content of 35% and then incorporated into the solvent recovery system. Post-treatment modification: PVB coarse powder was vacuum dried at 60℃ and -0.09MPa for 4 hours, and the volatile content was controlled at 2.0%; 0.2kg of antioxidant 1010 (purity 99.5%, particle size 5μm) was added to the dried PVB coarse powder, and the mixture was mixed at 1500rpm for 20 minutes, and the system temperature was controlled at 38℃ to obtain environmentally friendly PVB resin with high acetal rate.

[0072] Comparative Example 1: This comparative example uses a traditional homogeneous method with a single DMSO solvent. The specific steps are as follows: Solvent preparation: Take 100 kg of DMSO (purity 99.8%, water content 0.08%), without recovering the mother liquor; Raw material mixing and reaction system setup: Take 100 kg of PVA (degree of polymerization 1700, degree of alcoholysis 98%) and add it to the above solvent. After stirring at 120 rpm for 35 minutes to disperse it evenly, add 75 kg of n-butyraldehyde (purity 99.2%, moisture 0.07%). Then add 1.5 wt% hydrochloric acid catalyst, without rate regulators or complexing agents. Reaction: The reaction was carried out at a constant temperature of 60℃ for 5 hours with a stirring speed of 200 rpm. During the reaction, the system became heterogeneous after 2.0 hours. Separation and recovery: After the reaction, the temperature was rapidly reduced to 30℃ and centrifuged at 3000 rpm to obtain coarse powder; the solvent was recovered by distillation with a purity of 97.2% and a recovery rate of 72%; the coarse powder was washed with water to remove the catalyst, generating a large amount of wastewater; Post-treatment: The coarse powder was dried in a forced-air dryer at 60°C for 6 hours without antioxidant modification to obtain PVB resin.

[0073] Comparative Example 2: This comparative example uses the traditional sedimentation method with water as the dispersion medium. The specific steps are as follows: Dispersion medium: Take 300 kg of deionized water; Raw material mixing and reaction system setup: Take 100 kg of PVA (degree of polymerization 1700, degree of alcoholysis 98%) and add it to water. Heat to 80℃ to dissolve and then cool to 40℃. Add 75 kg of n-butyraldehyde (purity 99.2%, water content 0.07%), followed by 5 wt% hydrochloric acid catalyst. Reaction: The reaction was carried out at a constant temperature of 40℃ for 6 hours with a stirring speed of 150 rpm. A large amount of precipitate agglomerates were generated during the reaction. Separation: After the reaction is completed, the mixture is centrifuged at 3000 rpm to obtain coarse powder, which is then washed with water to remove the catalyst, resulting in a large amount of wastewater. Post-processing: The coarse powder was dried in a forced-air dryer at 60°C for 6 hours to obtain PVB resin.

[0074] Test Example 1: The performance of the high acetal rate environmentally friendly PVB resins prepared in Examples 1-2 and the PVB resins prepared in Comparative Examples 1-2 was tested, as follows: Acetalization rate determination: GB / T 12010.14-2019 "Plastic Polyvinyl Alcohol Materials Part 14: Determination of Acetalization".

[0075] Bulk density determination: GB / T 16913.3-2008 "Test methods for physical properties of dust - Part 3: Determination of bulk density" was adopted.

[0076] Hydroxyl content determination: Hydrogen nuclear magnetic resonance (HNMR) spectroscopy was used. 1 H-NMR, using deuterated dimethyl sulfoxide as solvent, was calculated by integrating characteristic peaks.

[0077] Colorimetric determination: Gardner colorimetric standard was adopted, referring to ASTM D1544-2018 "Standard test method for color of transparent liquids (Gardner color scale)".

[0078] Glass transition temperature (T) g Determination: Differential scanning calorimetry (DSC) was used, with a heating rate of 10℃ / min and a test range of 30~100℃, in accordance with ISO 11357-2:2013 "Plastics - Differential scanning calorimetry (DSC) - Part 2: Determination of glass transition temperature".

[0079] Determination of weight loss due to thermal aging: The sample was placed in an oven at 120℃ for 1000 hours and the weight loss was determined in accordance with GB / T 11353-2008 "Test Method for Thermal Aging of Plastics".

[0080] UV aging transmittance retention rate determination: A UV aging test chamber was used with a wavelength of 340 nm and an irradiation intensity of 0.68 W / m². 2 After aging for 1000 hours, the light transmittance was measured in accordance with GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics", and the retention rate was calculated.

[0081] Catalyst residue determination: Ion chromatography was used to determine the chloride ion content according to GB / T 30902-2014 "Determination of Anions in Inorganic Chemical Products by Ion Chromatography" and converted it into catalyst residue.

[0082] Ash content determination: Refer to GB / T 9345.1-2008 "Determination of ash content in plastics - Part 1: General method".

[0083] Volatile content determination: Refer to GB / T 6284-2014 "Determination of Moisture Content in Chemical Products - Loss on Drying Method". The test results are shown in Table 1.

[0084] Table 1 Performance test results of Test Example 1:

[0085] As shown in Table 1, regarding acetalization rate and structural properties, the acetalization rates of the high-acetalization-rate environmentally friendly PVB resins in Examples 1 and 2 were 80.0% and 79.6%, respectively, significantly higher than those of Comparative Example 1 (77.3%) and Comparative Example 2 (74.7%). Furthermore, the hydroxyl content was controlled at 17-19%, indicating that the composite solvent system and segmented temperature-controlled reaction of this invention can promote the full reaction between PVA and n-butyraldehyde. The bulk density of Examples 1 and 2 was 0.25-0.30 g / cm³. 3 The result was higher than that of comparative examples 1-2, indicating that the product particles had good uniformity and no obvious agglomeration. This is due to the intramolecular acetal reaction guided by NMP cosolvent and the gradient cooling crystallization process.

[0086] In terms of optical performance: the colorimetric properties of the high acetal rate environmentally friendly PVB resins in Examples 1-2 are much lower than those in Comparative Examples 1 and 2, and the UV aging transmittance retention rate (89-91%) is significantly higher than that in Comparative Examples 1-2 (78-82%). This is because the graded catalytic system of the present invention reduces yellowing caused by local excessive acetalization, EDTA-2Na chelates metal impurities to avoid coloring, and hindered phenolic antioxidants improve UV aging resistance.

[0087] Regarding stability and purity: The glass transition temperature (62-64℃) of the high acetal rate environmentally friendly PVB resins in Examples 1-2 is higher than that in Comparative Examples 1-2 (55-56℃), the thermal aging weight loss rate (1.5-1.8%) is lower than that in Comparative Examples 1-2 (3.2-3.5%), the catalyst residue (0.005-0.01%) is much lower than that in Comparative Examples 1-2 (0.03-0.04%), and the ash and volatile matter are also lower. This demonstrates that the graded catalytic system, directional separation, and post-treatment modification effectively improve the thermal stability, purity, and performance stability of the high acetal rate environmentally friendly PVB resins.

[0088] In terms of environmental protection and economy: the solvent recovery rate of Examples 1-2 (95.2-96.5%) is much higher than that of Comparative Example 1 (72.0%). Comparative Example 2 has no solvent recovery process and generates a large amount of wastewater. The preparation method of the present invention has no wastewater discharge throughout the entire process, has a high solvent recovery rate, significantly improves environmental protection and reduces production costs.

[0089] Regarding process stability: the homogeneous maintenance time of the systems in Examples 1 and 2 (4.8 to 5.0 hours) was longer than that of Comparative Example 1 (2.0 hours), ensuring the uniformity and repeatability of the reaction. The performance fluctuation between product batches was ≤2%, while the batch fluctuations of Comparative Example 1 and Comparative Example 2 were 5% and 8%, respectively. This indicates that the present invention effectively improves process stability by precisely controlling process parameters and limiting raw material specifications.

[0090] As can be seen from the above embodiments, the high acetal rate environmentally friendly PVB resin prepared by the present invention through controlling the composite solvent, the graded catalytic system, the directional separation and the reaction parameters is significantly superior to the existing methods in terms of acetal rate, optical properties, stability and environmental protection, and fully meets the application requirements of high-end fields.

[0091] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A method for preparing a high acetal content environmentally friendly PVB resin, characterized in that, Includes the following steps: 1) A composite solvent, PVA, n-butyraldehyde, and a graded catalytic system are mixed to carry out an acetal reaction to obtain crude PVB; The composite solvent includes dimethyl sulfoxide and N-methylpyrrolidone; The degree of polymerization of the PVA is 1700~2000, and the degree of alcoholysis is 98~99%. 2) The crude PVB product and the hindered phenolic antioxidant are mixed to obtain the high acetal rate environmentally friendly PVB resin.

2. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 1, characterized in that, The dimethyl sulfoxide accounts for 90-95 wt% of the composite solvent.

3. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 1, characterized in that, The staged catalytic system includes a main catalyst, a rate regulator, and a complexing agent; the main catalyst is hydrochloric acid, the rate regulator is an organophosphonic acid, and the complexing agent is disodium ethylenediaminetetraacetate.

4. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 1, characterized in that, The acetal reaction is a segmented acetal reaction, which includes a first-stage reaction, a second-stage reaction, and a third-stage reaction carried out sequentially. The temperature of the first stage reaction is 45~50℃, the holding time is 1.8~2.2 hours, and the first stage reaction is carried out under stirring conditions, the stirring speed of which is 100~150 rpm. The temperature of the second stage reaction is 50~55℃, the holding time is 1.8~2.2 hours, and the second stage reaction is carried out under stirring conditions, the stirring speed of which is 200~250 rpm. The temperature of the third stage reaction is 48~50℃, the holding time is 0.9~1.1 hours, and the third stage reaction is carried out under stirring conditions with a stirring speed of 100 rpm. The total time for the acetal reaction is 5 hours.

5. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 4, characterized in that, The process includes heating the system after the first stage reaction and before the second stage reaction, with a heating rate of 2~3℃ / min. The process includes cooling the system after the second stage reaction and before the third stage reaction, with a cooling rate of 1~2℃ / min.

6. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 1, characterized in that, The acetal reaction further includes sequentially cooling, allowing the product to stand, separating the solvent, collecting the solvent, and obtaining a solid product.

7. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 6, characterized in that, The process of collecting the solvent further includes distilling and purifying the obtained solvent, collecting the fraction with a top temperature of 189~202℃, and obtaining a recovered solvent mother liquor with a purity of ≥99.5%. The solid product further includes post-processing, which includes sequentially washing the solid product with water, centrifuging, collecting the solid and the washing liquid, concentrating the washing liquid or drying the solid.

8. The method for preparing the high acetal rate environmentally friendly PVB resin according to claim 1, characterized in that, The hindered phenolic antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

9. A high acetal content environmentally friendly PVB resin, characterized in that, The high acetal rate environmentally friendly PVB resin was prepared by any one of claims 1 to 8, with an acetal rate of 75-80%, a glass transition temperature ≥60℃, a weight loss of ≤2.0% after 1000 hours of heat aging at 120℃, and a catalyst residue of ≤0.01%.

10. The application of a high acetal content environmentally friendly PVB resin in the fields of photovoltaic glass, automotive safety glass, or optical device adhesives, characterized in that... The high acetal rate environmentally friendly PVB resin is the high acetal rate environmentally friendly PVB resin described in claim 9.

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