A lactone-modified polyvinyl acetal resin, a method for preparing the same, and an application thereof

Abstract

The present application relates to the technical field of high polymer material modification, and particularly relates to a lactone modified polyvinyl acetal resin and a preparation method and application thereof. The lactone modified polyvinyl acetal resin comprises the following raw materials in parts by weight: 80-85 parts by weight of polyvinyl acetal resin, 15-20 parts by weight of lactone monomer, 0.1-0.3 parts by weight of rare earth alkoxide catalyst, 0.1-0.2 parts by weight of antioxidant, and 0-2.0 parts by weight of regulator; wherein the lactone monomer is at least one selected from carboxyl-containing lactone and non-carboxyl-containing lactone. Through the organic combination of "monomer precise selection-high-efficiency catalytic system-green process route", a series of lactone modified polyvinyl acetal resins with excellent performance and customization are successfully prepared, and breakthrough progress is achieved in grafting efficiency, performance balance, durability, environmental protection and production feasibility.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and in particular to a lactone-modified polyvinyl acetal resin, its preparation method, and its application. Background Technology

[0002] Polyvinyl acetal resins, such as polyvinyl butyral (PVB) and polyvinyl formal (PVF), have been widely used in coatings, adhesives, and ceramic binders due to their excellent film-forming properties, adhesion, and weather resistance. However, unmodified polyvinyl acetal resins generally suffer from insufficient flexibility, poor water-based dispersibility, low curing reactivity, and poor compatibility with polar substrates, which limits their use in high-end applications.

[0003] To improve the aforementioned properties, existing technologies typically employ transesterification modification of polyvinyl acetal resin with acrylic polyols. However, this method has significant drawbacks: First, the transesterification reaction is reversible, resulting in low grafting efficiency, usually only 10-15%. Most of the acrylic polyol exists only in a physically blended form, making it prone to phase separation, leading to a cloudy resin appearance and reduced gloss. Second, this method fails to introduce effective hydrophilic groups, making it impossible to achieve aqueous dispersion of the resin and still requiring organic solvents, resulting in poor environmental friendliness. Third, relying solely on the resin's own hydroxyl groups for curing activity makes the curing reaction conditions harsh and time-consuming. Finally, the resulting modified resin has limited crosslinking density, leading to insufficient improvement in its water resistance, solvent resistance, and abrasion resistance, making it difficult to meet the performance requirements of high-end applications.

[0004] Lactone monomers, through ring-opening grafting, modify polymer materials with potential advantages such as irreversible reactions, high grafting efficiency, and precise introduction of functional segments, and are considered a direction for high-performance resin modification. However, a mature and systematic technical solution for lactone-modified polyvinyl acetal resins has not yet been developed. Specifically, existing technologies lack systematic comparative studies on the modification characteristics and applicable scenarios of different types of lactones (e.g., carboxyl-containing and non-carboxyl-containing lactones); dedicated catalyst systems that are highly compatible with the ring-opening reaction of lactones have not been developed; and existing modification processes mostly employ solution methods, which suffer from problems such as the need for large amounts of organic solvents in the production process, high costs, significant environmental pollution risks, and difficulty in continuous industrial production. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a lactone-modified polyvinyl acetal resin, its preparation method, and its application. Through the organic combination of "precise monomer selection, high-efficiency catalytic system, and green process route", a series of high-performance and customizable lactone-modified polyvinyl acetal resins have been successfully prepared, achieving breakthrough progress in grafting efficiency, performance balance, durability, environmental friendliness, and production feasibility.

[0006] To achieve the above objectives, the present invention provides a lactone-modified polyvinyl acetal resin, comprising the following raw materials in parts by weight: The composition includes 80-85 parts by weight of polyvinyl acetal resin, 15-20 parts by weight of lactone monomer, 0.1-0.3 parts by weight of rare earth alkoxide catalyst, 0.1-0.2 parts by weight of antioxidant, and 0-2.0 parts by weight of regulator. The lactone monomer is selected from at least one of carboxyl lactones and non-carboxyl lactones.

[0007] Preferably, the carboxyl-containing lactone is selected from at least one of γ-carboxybutyric acid lactone and δ-carboxyvalerol lactone; the non-carboxyl-containing lactone is selected from at least one of ε-caprolactone and γ-butyric acid lactone.

[0008] Preferably, the rare earth alkoxide catalyst is selected from yttrium isopropoxide or lanthanum isopropoxide.

[0009] Preferably, the polyvinyl acetal resin is selected from polyvinyl butyral resin; the hydroxyl content of polyvinyl butyral is 18-22 mol%, and the molecular weight is 20,000-80,000.

[0010] Preferably, the antioxidant is selected from antioxidant 1076.

[0011] Preferably, the regulator is selected from diethylene glycol.

[0012] The present invention also provides a method for preparing the lactone-modified polyvinyl acetal resin, comprising the following steps: The raw materials are mixed and subjected to a melt grafting reaction to obtain the lactone-modified polyvinyl acetal resin.

[0013] Preferably, the melt grafting reaction is carried out in a twin-screw extruder; the reaction section temperature of the twin-screw extruder is 165-175℃, the screw speed is 280-320rpm, and the vacuum degree is 0.095-0.098MPa.

[0014] Preferably, prior to the melt grafting reaction, the process further includes drying the polyvinyl acetal resin and purifying the lactone monomer.

[0015] The present invention also provides the application of the lactone-modified polyvinyl acetal resin or the lactone-modified polyvinyl acetal resin prepared according to the preparation method described herein in water-based anti-corrosion coatings, medical bio-adhesives, ion exchange membrane substrates or ink resins.

[0016] The beneficial effects of this invention are as follows: This invention has successfully prepared a series of high-performance, customizable lactone-modified polyvinyl acetal resins by organically combining "precise monomer selection, high-efficiency catalytic system, and green process route". It has achieved breakthrough progress in grafting efficiency, performance balance, durability, environmental protection, and production feasibility.

[0017] (1) By selecting lactone monomers and employing a rare earth alkoxide catalytic system, and utilizing the irreversible nature of the lactone ring-opening reaction, highly efficient covalent grafting with the hydroxyl groups of polyvinyl acetal resin was achieved. Examples show that the grafting rate can reach 20-30%, far exceeding the 10-15% of traditional acrylic polyol transesterification modification. This covalent grafting method fundamentally avoids the phase separation problem caused by physical blending, resulting in excellent product uniformity, a colorless and transparent appearance, and high gloss (≥92%), ensuring the stability and reliability of the material properties.

[0018] (2) By selecting different types of lactone monomers, differentiated and precise design of modified resin properties can be achieved. Using non-carboxyl lactones can significantly improve the flexibility and thermoplasticity of the resin, meeting the needs of high-end solvent-based coatings and adhesives; using carboxyl lactones can improve flexibility while introducing hydrophilic carboxyl groups, thereby giving the resin excellent water-based dispersibility, higher curing activity and good compatibility with polar substrates, perfectly adapting to environmentally friendly and high-performance applications such as water-based anti-corrosion coatings and medical adhesives. The two lactones can also be compounded in proportion to achieve performance balance and further expand the application range.

[0019] (3) The high grafting rate and covalent cross-linked network structure comprehensively enhance the mechanical properties and media resistance of the modified resin. Examples show that the elongation at break of the modified resin is significantly improved, and its flexibility is good; its gel fraction is as high as 65-80%, more than three times that of the comparative example (20-25%), indicating a high cross-linking density. The direct effect of this is that its water resistance (72h weight gain ≤1.8%), solvent resistance (48h swelling rate ≤4.5%), and abrasion resistance (1000 rpm abrasion loss ≤12mg) are far superior to traditional modified products, meeting more stringent environmental requirements.

[0020] (4) The carboxyl lactone-modified resin introduces dual active sites of carboxyl and hydroxyl groups, exhibiting high activity when reacting with curing agents such as epoxy resin, significantly shortening the curing time (≤28min), and greatly improving efficiency compared to traditional modification methods (≥50min). At the same time, the presence of carboxyl groups enhances the interaction force with polar substrates such as metals, enabling the paint film to achieve the optimal 0-level adhesion to aluminum foil, thus enhancing its application value in coating and bonding fields.

[0021] (5) This invention abandons the traditional solution modification process and innovatively adopts twin-screw extrusion melt grafting technology. This process eliminates VOC emissions to the greatest extent, making it environmentally friendly. At the same time, the twin-screw extruder can realize continuous material conveying, melting, reaction, devolatilization and granulation. The process flow is short and efficient, and the daily production capacity can reach the ton level, which greatly reduces energy consumption and production costs. It solves the bottleneck problem that existing technologies cannot achieve large-scale clean production and has good prospects for industrial application. Detailed Implementation

[0022] This invention provides a lactone-modified polyvinyl acetal resin, comprising the following raw materials in parts by weight: The composition includes 80-85 parts by weight of polyvinyl acetal resin, 15-20 parts by weight of lactone monomer, 0.1-0.3 parts by weight of rare earth alkoxide catalyst, 0.1-0.2 parts by weight of antioxidant, and 0-2.0 parts by weight of regulator. The lactone monomer is selected from at least one of carboxyl lactones and non-carboxyl lactones.

[0023] In this invention, the lactone monomer is selected according to the target performance requirements, specifically including the following types: (1) Contains carboxyl lactones, selected from at least one of γ-carboxybutyric acid lactone and δ-carboxypentyl lactone. After ring opening, this type of lactone monomer can simultaneously introduce flexible segments and polar carboxyl groups, thereby effectively improving the water-based dispersibility, curing activity and polar substrate compatibility of the resin. It is especially suitable for water-based anti-corrosion coatings, medical bio-adhesives and other application scenarios that require water-based and high polar compatibility.

[0024] in: The carboxyl group content of γ-carboxybutyric acid lactone is ≥12.5wt%. Its synthesis process is as follows: Starting with maleic anhydride, it is first esterified with methanol at room temperature and pressure under concentrated sulfuric acid catalysis for 4-6 hours to produce dimethyl maleate (esterification rate ≥95%). Then, it is placed in a high-pressure reactor and selectively hydrogenated using palladium on carbon as a catalyst at a hydrogen pressure of 3-5 MPa and a temperature of 80-100℃ to obtain dimethyl γ-hydroxybutyrate (hydrogenation conversion rate ≥98%). Finally, excess hydrogen is added... Sodium oxide aqueous solution was refluxed for 2-3 hours for hydrolysis. After acidification to pH 2-3, γ-hydroxybutyric acid was precipitated. Finally, γ-hydroxybutyric acid was dissolved in toluene, p-toluenesulfonic acid was added as a catalyst, and the mixture was refluxed at 110-120℃ for dehydration and cyclization. Water generated was separated by a water separator. After the reaction was completed, the mixture was purified by vacuum distillation (vacuum degree 0.09-0.095MPa, temperature 130-140℃) to obtain γ-carboxybutyric acid lactone with a purity ≥99% and a carboxyl content ≥12.5wt%.

[0025] The carboxyl content of δ-carboxyvalerol is ≥10.8wt%. The synthesis process is as follows: Adipic acid is reacted with ethanol at a molar ratio of 1.0-1.2:1 under concentrated sulfuric acid catalysis at 70-80℃ for 3-4 hours to produce monoethyl adipic acid (the product has a purity ≥96% after washing and drying). Then, it is dissolved in tetrahydrofuran, and a tetrahydrofuran solution of sodium borohydride is slowly added dropwise under an ice bath. After the addition is complete, the temperature is raised to room temperature and reacted for 4-5 hours to reduce it to 5-hydroxyvalerate (reduction yield ≥92%). Then, 5-hydroxyvalerate is dissolved in xylene, and phosphoric acid solution is added as a catalyst. Under inert gas protection, it is refluxed at 130-140℃ for dehydration and cyclization for 6-8 hours, while the water generated is separated by a water separator. After the reaction, xylene is removed by distillation, and the product is purified by vacuum distillation (vacuum degree 0.092-0.096MPa, temperature 145-155℃) to obtain δ-carboxyvalerate with a purity ≥98.5% and a carboxyl content ≥10.8wt%.

[0026] (2) Non-carboxyl lactones, selected from at least one of ε-caprolactone and γ-butyrolactone. These lactone monomers have high reactivity, and the polyester segments formed after ring opening have excellent flexibility, which can significantly improve the flexibility, thermoplasticity and solubility of the resin in organic solvents. They are suitable for high-end solvent-based coatings, structural adhesives and other applications where water-based dispersibility is not mandatory. (3) Mixed lactones, that is, mixing carboxyl lactones and non-carboxyl lactones at a mass ratio of (0.5-2):1. This mixing method can maintain the good flexibility of the resin while taking into account its water dispersibility, thereby further expanding the application range of modified resins.

[0027] In this invention, the rare earth alkoxide catalyst is selected from yttrium isopropoxide (CAS No.: 2172-12-5) or lanthanum isopropoxide (CAS No.: 68959-87-5).

[0028] In this invention, the polyvinyl acetal resin is selected from polyvinyl butyral (PVB) resin; the hydroxyl content of polyvinyl butyral is 18-22 mol%, and the molecular weight is 20,000-80,000.

[0029] In this invention, the antioxidant is selected from antioxidant 1076.

[0030] In this invention, the regulator is selected from diethylene glycol.

[0031] The present invention also provides a method for preparing the lactone-modified polyvinyl acetal resin, comprising the following steps: The raw materials are mixed and subjected to a melt grafting reaction to obtain the lactone-modified polyvinyl acetal resin.

[0032] In this invention, the melt grafting reaction is carried out in a twin-screw extruder; the twin-screw extruder has a diameter of 35-65 mm and an aspect ratio of 40-48; the reaction zone temperature of the twin-screw extruder is 165-175℃, the screw speed is 280-320 rpm, and the vacuum degree is 0.095-0.098 MPa.

[0033] In this invention, the melt grafting reaction process is controlled sequentially by equipment section as follows: First, the catalyst and regulator are pre-mixed to prepare a mother liquor for later use. Polyvinyl acetal resin and antioxidant are added to the extruder through the feeding section, where the temperature is controlled at 80-100℃, the screw speed at 180-200 rpm, and the material residence time at 1-1.5 min. No vacuum is applied during this stage; a low-speed melting method is used to prevent material agglomeration. After the material enters the melting section, the temperature rises to 140-160℃, the screw speed increases to 200-230 rpm, and the residence time is 1-1.5 min, still without vacuum. Once the material is completely melted and uniformly mixed, the lactone monomer and the aforementioned mother liquor are precisely metered and injected through the side feed port. Then, the material enters the reaction section, where the temperature is further increased to 165-175℃, and the screw speed is increased to 280-320 rpm to create a high-shear environment to promote the ring-opening and grafting reactions of the lactone monomer. The material residence time is 2.5-3 min, and the vacuum system is activated simultaneously, controlling the vacuum level at 0.095-0.098 MPa. This stage requires strict temperature control to prevent excessive cross-linking of the material. After reaction, the material enters the homogenization section, where the temperature is appropriately reduced to 155-165℃, the screw speed is adjusted back to 220-250 rpm, the residence time is 1-1.5 minutes, and a high vacuum of 0.095-0.098 MPa is maintained to remove residual small molecules and stabilize the product structure. Finally, the material is extruded through an extrusion die, with the die temperature controlled at 145-155℃. The extruded strip material is immediately cooled by air cooling and pelletized (particle size controlled at 3-4 mm). This air cooling method avoids the hydrolysis of carboxyl groups in the carboxyl lactone-modified resin caused by water cooling, thus ensuring the stability of the product performance.

[0034] In this invention, before the melt grafting reaction, the steps of drying the polyvinyl acetal resin and purifying the lactone monomer are also included.

[0035] In this invention, the drying temperature is 105-110℃ and the drying time is 4-6 hours; after drying, the moisture content of the polyvinyl acetal resin is ≤0.3%.

[0036] In this invention, the lactone monomers require targeted purification treatment according to their type before use to remove impurities that may inhibit catalyst activity. When the lactone monomer is a carboxyl-containing lactone, the purification operation is carried out by vacuum distillation at 45-55°C to effectively remove trace amounts of acidic impurities. When the lactone monomer is a non-carboxyl-containing lactone, purification is carried out by preheating and filtration, typically at 35-45°C, to remove any mechanical impurities that may be present. This differentiated pretreatment step provides qualified and pure raw materials for the subsequent efficient melt grafting reaction.

[0037] In this invention, if the lactone monomer used is a carboxyl-containing lactone, the resin particles after pelleting need to undergo surface neutralization treatment. Specifically, this involves spraying with a 0.05-0.15% sodium bicarbonate aqueous solution to neutralize residual carboxyl groups on the particle surface and prevent moisture absorption and clumping during storage. Subsequently, all particles undergo secondary drying, typically hot air drying at 65-75°C for 2.5-3.5 hours, to ensure the final product has a moisture content ≤0.5%. Finally, the product is sealed and packaged to obtain the finished product: lactone-modified polyvinyl acetal resin.

[0038] The present invention also provides the application of the lactone-modified polyvinyl acetal resin or the lactone-modified polyvinyl acetal resin prepared according to the preparation method described herein in water-based anti-corrosion coatings, medical bio-adhesives, ion exchange membrane substrates or ink resins.

[0039] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0040] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] Example 1 This embodiment provides a method for preparing lactone-modified polyvinyl acetal resin, comprising the following steps: Prepare the following raw materials by weight: 82 parts of polyvinyl butyral (PVB) resin (hydroxyl content 21 mol%, molecular weight 40000); 18 parts of ε-caprolactone; 0.27 parts of yttrium isopropoxide; 0.15 parts of antioxidant 1076; and 1.58 parts of diethylene glycol.

[0042] PVB resin was vacuum dried at 110℃ for 6 hours, with the moisture content controlled at 0.25%; ε-caprolactone was preheated at 40℃ and then filtered to remove mechanical impurities; under nitrogen protection, yttrium isopropoxide was mixed with diethylene glycol to prepare a mother liquor.

[0043] The melt grafting reaction was carried out using a twin-screw extruder with a diameter of 45 mm and an aspect ratio of 44. PVB resin and antioxidant 1076 were added to the extruder through the feeding section, where the temperature was controlled at 95°C, the screw speed at 190 rpm, and the material residence time at 1.5 min. No vacuum was applied during this stage. After the material entered the melting section, the temperature was raised to 150°C, the screw speed was increased to 220 rpm, and the residence time was again 1.5 min, without applying a vacuum. Once the material was completely melted and uniformly mixed, the lactone monomer and the aforementioned mother liquor were precisely metered and injected through the side feed port. Subsequently, the material entered the reaction section, where the temperature was further increased to 175°C, the screw speed was increased to 300 rpm, and the material residence time was 2.5 min. Simultaneously, the vacuum system was activated, and the vacuum level was controlled at 0.096 MPa. After the reaction, the material enters the homogenization section, where the temperature is appropriately reduced to 165℃, the screw speed is adjusted back to 230 rpm, the residence time is 1 minute, and a high vacuum of 0.098 MPa is maintained. Finally, the material is extruded through an extrusion die, with the die temperature controlled at 155℃. The extruded strip material is immediately cooled by air cooling and pelletized (particle size controlled at 3.5 mm).

[0044] The granules were dried with hot air at 70°C for 3 hours to reduce the moisture content to 0.4%, and then sealed and packaged to obtain lactone-modified polyvinyl acetal resin.

[0045] Example 2 This embodiment provides a method for preparing lactone-modified polyvinyl acetal resin, comprising the following steps: Starting with maleic anhydride, it was mixed with methanol at a molar ratio of 1:2.2, and a 98% sulfuric acid solution was added as a catalyst (the catalyst amount was 1 wt% of the total mass of maleic anhydride and methanol). Esterification was carried out at room temperature and pressure for 5 hours to produce dimethyl maleate (esterification rate ≥95%). Subsequently, it was placed in a high-pressure reactor and selectively hydrogenated at a hydrogen pressure of 4 MPa and a temperature of 90 °C using palladium on carbon as a catalyst to obtain dimethyl γ-hydroxybutyrate (hydrogenation conversion rate ≥95%). (≥98%) Then, excess sodium hydroxide aqueous solution was added and refluxed for 2 hours for hydrolysis. After acidification to pH=2, γ-hydroxybutyric acid was precipitated. Finally, γ-hydroxybutyric acid was dissolved in toluene, p-toluenesulfonic acid was added as a catalyst, and dehydration and cyclization were carried out by reflux at 115℃. At the same time, the generated water was separated by a water separator. After the reaction was completed, it was purified by vacuum distillation (vacuum degree 0.092MPa, temperature 135℃) to obtain γ-carboxybutyric acid lactone with a purity ≥99% and a carboxyl content of 12.8wt%.

[0046] Prepare the following raw materials by weight: 82 parts of polyvinyl butyral (PVB) resin (hydroxyl content 21 mol%, molecular weight 40000); 16 parts of γ-carboxybutyric acid lactone (carboxyl content 12.8 wt%); 0.25 parts of yttrium isopropoxide; 0.15 parts of antioxidant 1076; and 1.6 parts of diethylene glycol.

[0047] PVB resin was vacuum dried at 110℃ for 6 hours, with the moisture content controlled at 0.25%; γ-carboxybutyric acid lactone was subjected to vacuum distillation at 50℃ to remove acidic impurities; under nitrogen protection, yttrium isopropoxide was mixed with diethylene glycol to prepare the mother liquor.

[0048] The melt grafting reaction was carried out using a twin-screw extruder with a diameter of 45 mm and an aspect ratio of 44. PVB resin and antioxidant 1076 were added to the extruder through the feeding section, where the temperature was controlled at 95°C, the screw speed at 190 rpm, and the material residence time at 1.5 min. No vacuum was applied during this stage. After the material entered the melting section, the temperature was raised to 150°C, the screw speed was increased to 220 rpm, and the residence time was again 1.5 min, without applying a vacuum. Once the material was completely melted and uniformly mixed, the lactone monomer and the aforementioned mother liquor were precisely metered and injected through the side feed port. Subsequently, the material entered the reaction section, where the temperature was further increased to 170°C, the screw speed was increased to 300 rpm, and the material residence time was 2.5 min. Simultaneously, the vacuum system was activated, and the vacuum level was controlled at 0.096 MPa. After the reaction, the material enters the homogenization section, where the temperature is appropriately reduced to 160℃, the screw speed is adjusted back to 230 rpm, the residence time is 1 minute, and a high vacuum of 0.098 MPa is maintained. Finally, the material is extruded through an extrusion die, with the die temperature controlled at 150℃. The extruded strip material is immediately cooled by air cooling and pelletized (particle size controlled at 3.5 mm).

[0049] The granules were sprayed with a 0.1% sodium bicarbonate aqueous solution (30s), then dried with hot air at 70°C for 3 hours to reduce the moisture content to 0.4%. Finally, they were sealed and packaged to obtain lactone-modified polyvinyl acetal resin.

[0050] Example 3 This embodiment provides a method for preparing lactone-modified polyvinyl acetal resin, comprising the following steps: Prepare the following raw materials by weight: 82 parts of polyvinyl butyral (PVB) resin (hydroxyl content 20 mol%, molecular weight 35000); 15 parts of ε-caprolactone; 0.225 parts of yttrium isopropoxide; 0.15 parts of antioxidant 1076; and 1.625 parts of diethylene glycol.

[0051] PVB resin was vacuum dried at 108℃ for 5 hours, with the moisture content controlled at 0.28%; ε-caprolactone was preheated at 42℃ and then filtered to remove mechanical impurities; under nitrogen protection, yttrium isopropoxide was mixed with diethylene glycol to prepare a mother liquor.

[0052] The melt grafting reaction was carried out using a twin-screw extruder with a diameter of 45 mm and an aspect ratio of 44. PVB resin and antioxidant 1076 were added to the extruder through the feeding section, where the temperature was controlled at 92°C, the screw speed at 185 rpm, and the material residence time at 1.5 min. No vacuum was applied during this stage. After the material entered the melting section, the temperature rose to 145°C, the screw speed increased to 210 rpm, and the residence time was 1.2 min, still without vacuum. Once the material was completely melted and uniformly mixed, the lactone monomer and the aforementioned mother liquor were precisely metered and injected through the side feed port. Subsequently, the material entered the reaction section, where the temperature was further increased to 172°C, the screw speed increased to 290 rpm, and the material residence time was 2.5 min. Simultaneously, the vacuum system was activated, and the vacuum level was controlled at 0.095 MPa. After the reaction, the material enters the homogenization section, where the temperature is appropriately reduced to 162℃, the screw speed is adjusted back to 225 rpm, the residence time is 1 minute, and a high vacuum of 0.098 MPa is maintained. Finally, the material is extruded through an extrusion die, with the die temperature controlled at 152℃. The extruded strip material is immediately cooled by air cooling and pelletized (particle size controlled at 3 mm).

[0053] The granules were dried with hot air at 75°C for 2.5 hours to reduce the moisture content to 0.45%, and then sealed and packaged to obtain lactone-modified polyvinyl acetal resin.

[0054] Example 4 This embodiment provides a method for preparing lactone-modified polyvinyl acetal resin, comprising the following steps: Adipic acid was mixed with ethanol at a molar ratio of 1.1:1, and a 98% sulfuric acid solution was added as a catalyst (the amount of catalyst was 1 wt% of the total mass of adipic acid and ethanol). The mixture was reacted at 75°C for 3.5 h to produce monoethyl adipic acid. The product was washed three times with deionized water (each time using water equal to the product mass), and dried under vacuum at 60°C for 4 h, with a purity ≥96%. Subsequently, the dried monoethyl adipic acid was dissolved in tetrahydrofuran (solid-liquid mass ratio 1:5), and placed in an ice bath environment (0°C). A 1 mol / L tetrahydrofuran solution of sodium borohydride (molar ratio of sodium borohydride to monoethyl adipic acid was 1.2:1) was slowly added dropwise at a rate of 1 drop per second. After the addition was complete, the temperature was raised to room temperature (25°C) and the reaction was carried out for 4.5 h to reduce 5-hydroxyvalerate (reduction yield ≥92%). 5-Hydroxyvalerate was then dissolved in xylene (solid-liquid mass ratio 1:4), and an 85% phosphoric acid solution was added as a catalyst (catalyst amount was 0.8wt% of the mass of 5-hydroxyvalerate). The mixture was refluxed at 135℃ for 7 hours under nitrogen protection to dehydrate and cyclize, while water was separated by a water separator. After the reaction was completed, xylene was removed by distillation, and the mixture was purified by vacuum distillation (vacuum degree 0.094MPa, temperature 150℃) to obtain δ-carboxyvalerate with a purity ≥98.5% and a carboxyl content of 10.8wt%.

[0055] Prepare the following raw materials by weight: 82 parts of polyvinyl butyral (PVB) resin (hydroxyl content 22 mol%, molecular weight 45000); 19 parts of δ-carboxyvalerol (carboxyl content 10.8 wt%); 0.285 parts of yttrium isopropoxide; 0.15 parts of antioxidant 1076; and 1.565 parts of diethylene glycol.

[0056] PVB resin was vacuum dried at 110℃ for 6 hours, with the moisture content controlled at 0.22%; δ-carboxypentolone was subjected to vacuum distillation at 55℃ to remove acidic impurities; under nitrogen protection, yttrium isopropoxide was mixed with diethylene glycol to prepare the mother liquor.

[0057] The melt grafting reaction was carried out using a twin-screw extruder with a diameter of 45 mm and an aspect ratio of 44. PVB resin and antioxidant 1076 were added to the extruder through the feeding section, where the temperature was controlled at 98°C, the screw speed at 195 rpm, and the material residence time at 1.5 min. No vacuum was applied during this stage. After the material entered the melting section, the temperature rose to 155°C, the screw speed increased to 225 rpm, and the residence time remained at 1.5 min, still without vacuum. Once the material was completely melted and uniformly mixed, the lactone monomer and the aforementioned mother liquor were precisely metered and injected through the side feed port. Subsequently, the material entered the reaction section, where the temperature was further increased to 168°C, the screw speed increased to 310 rpm, and the material residence time was 2.8 min. Simultaneously, the vacuum system was activated, and the vacuum level was controlled at 0.097 MPa. After the reaction, the material enters the homogenization section, where the temperature is appropriately reduced to 158℃, the screw speed is adjusted back to 235 rpm, the residence time is 1 minute, and a high vacuum of 0.098 MPa is maintained. Finally, the material is extruded through an extrusion die, with the die temperature controlled at 148℃. The extruded strip material is immediately cooled by air cooling and pelletized (particle size controlled at 3.8 mm).

[0058] The granules were sprayed with a 0.1% sodium bicarbonate aqueous solution (30s), then dried with hot air at 68°C for 3.5h to reduce the moisture content to 0.38%, and finally sealed and packaged to obtain lactone-modified polyvinyl acetal resin.

[0059] Comparative Example 1 This comparative example provides a method for preparing hydroxyl-containing acrylic polyol-modified polyvinyl acetal resin, comprising the following steps: Prepare the following raw materials by weight: 82 parts of polyvinyl butyral (PVB) resin (hydroxyl content 21 mol%, molecular weight 40000); 16 parts of hydroxyl-containing acrylic polyol (hydroxyl value 135 mg KOH / g, Tg=25℃, solid content 100%); 0.25 parts of yttrium isopropoxide; 0.15 parts of antioxidant 1076; and 1.6 parts of diethylene glycol.

[0060] PVB resin was vacuum dried at 110℃ for 6 hours, with the moisture content controlled at 0.28%; hydroxyl-containing acrylic polyol was vacuum dried at 80℃ for 4 hours, with the moisture content controlled at 0.18%; under nitrogen protection, yttrium isopropoxide was mixed with diethylene glycol to prepare a mother liquor.

[0061] The melt grafting reaction was carried out using a twin-screw extruder with a diameter of 45 mm and an aspect ratio of 44. The melt grafting reaction process was basically the same as in Example 1, except that the following modifications were made: the melting zone temperature was 160°C, the reaction zone temperature was 185°C, the homogenization zone temperature was 175°C, and the die temperature was 165°C.

[0062] The granules were dried with hot air at 70°C for 3 hours to reduce the moisture content to 0.4%, and then sealed and packaged to obtain hydroxyl-containing acrylic polyol modified polyvinyl alcohol acetal resin.

[0063] Experimental Example 1 The modified polyvinyl acetal resins prepared in Examples 1-4 and Comparative Example 1 were characterized for their properties. The specific test items, methods, and conditions are as follows: The appearance is evaluated directly by visual inspection, observing the color, transparency, and presence of impurities or lumps in the resin particles under natural light.

[0064] The gloss was measured according to GB / T 9754-2007 standard. After the resin was made into a 50μm thick paint film, its surface gloss was measured using an incident angle of 60°.

[0065] The water resistance test was conducted in accordance with the GB / T 1733-1993 standard. The sample was immersed in distilled water at room temperature for 72 hours. The weight gain rate was calculated by measuring the change in mass before and after immersion, and the presence of blistering, whitening, or other phenomena in the paint film was observed.

[0066] Solvent resistance was assessed by solvent immersion method, in which the sample was immersed in a mixed solvent of ethanol and toluene in a volume ratio of 1:1 for 48 hours, the swelling rate was calculated by mass change, and the integrity of the paint film was observed.

[0067] The gel fraction was determined by Soxhlet extraction, with acetone as the solvent and reflux extraction for 24 hours. The percentage of insoluble matter after extraction relative to the initial mass of the sample was then calculated.

[0068] Abrasion resistance was tested according to GB / T 1768-2006 standard using a Taber abrasion tester. The specific conditions were: applying a 500g load, using a CS-10 grinding wheel, setting the grinding speed to 1000 revolutions, and evaluating the mass loss of the sample before and after grinding.

[0069] The grafting rate was quantitatively analyzed using infrared spectroscopy. Infrared spectra of the samples were acquired, and characteristic absorption peaks were integrated and calculated. The example sample was analyzed at 1710 cm⁻¹. -1 The characteristic peaks of the carboxyl and carbonyl groups were used as the basis for quantitative analysis, while the comparative example used the peak at 1730 cm⁻¹. -1 The characteristic peak of the carbonyl group of acrylate at the location is used as the basis for quantitative analysis.

[0070] The water dispersibility was evaluated using the static observation method. The resin was prepared into an aqueous dispersion with a solid content of 30%, and allowed to stand at room temperature for 72 hours to observe whether stratification or precipitation occurred.

[0071] The curing time was determined by the gel time method. After the modified resin and E-51 epoxy resin were mixed evenly, they were placed in a constant temperature environment of 80°C, and the time from the start of mixing to the formation of a non-flowing gel was recorded.

[0072] Adhesion was tested according to GB / T 9286 standard, using the cross-cut test to determine the adhesion level of the coating film formed by the modified resin on the aluminum foil substrate.

[0073] The test results are recorded in Table 1.

[0074] Table 1 Test Results

[0075] As can be seen from Table 1, the modified resins provided in Examples 1-4 of the present invention are superior to Comparative Example 1 in many key performance aspects, as detailed below: (1) Appearance and gloss: All products of Examples (1-4) were colorless, transparent, and regular particles, and the gloss of the paint film was not less than 92%. This is mainly due to the irreversible covalent reaction of the lactone ring-opening graft, which formed a product with uniform molecular structure and phase. After film formation, the molecular chains were arranged regularly, and the surface was smooth. Among them, Example 3 had a lower amount of ε-caprolactone, resulting in fewer flexible segments and a slightly lower gloss than Example 1. Example 4 had a slightly lower effective carboxyl content of δ-carboxypentyl lactone than γ-carboxybutyric acid lactone in Example 2, resulting in slightly less uniform polarity of the resin surface and a slightly lower gloss. In contrast, the comparative example used a reversible transesterification reaction, and the modified monomers mainly existed in the form of physical blending. The poor compatibility of the components resulted in the product particles being translucent milky white with local slight turbidity. The micro-phase separation made the paint film surface rough, and the gloss was only 70-75%.

[0076] (2) Grafting rate and structural characteristics: The grafting rates of Examples 1-4 were between 20-30%, which was much higher than the 10-15% of the comparative examples. This fundamental difference stems from the irreversibility and high efficiency of the lactone ring-opening reaction. Among them, Example 3 had the lowest grafting rate due to the lowest amount of ε-caprolactone; Example 4 had a slightly lower grafting rate than Example 2 due to the slightly lower reactivity of δ-carboxypentolactone. The comparative examples, limited by the reversible transesterification reaction, had low grafting efficiency, and a large amount of acrylic polyols remained unreacted.

[0077] (3) Resistance to media: The high grafting rate and covalent cross-linked network directly result in excellent resistance to media. The water resistance (72h weight gain ≤1.8%) and solvent resistance (48h swelling rate ≤4.5%) of Examples 1-4 are significantly better than those of the comparative examples (water resistance weight gain ≥8.5%, solvent resistance swelling rate ≥25%). In particular, Examples 2 and 4, which contain carboxyl groups, can form complexes with rare earth ions in the system, further strengthening the network structure and reducing water absorption. Among them, Example 2, with a higher effective carboxyl group content, performs best (water absorption ≤1.2%). In contrast, the physical blend structure of the comparative examples has interfacial defects and the hydroxyl groups are hydrophilic, resulting in a serious decrease in water resistance and solvent resistance, and the paint film exhibits blistering, whitening, swelling, and stickiness.

[0078] (4) Crosslinking density and abrasion resistance: The high crosslinking properties of the products in the examples are reflected in the gel fraction (65-80%) and abrasion resistance (weight loss ≤12mg at 1000 revolutions), which are significantly higher than those in the comparative examples (gel fraction 20-25%, weight loss ≥35mg). This is also attributed to the dense covalent crosslinking network. Examples 2 and 4, which have dual active crosslinking sites of carboxyl and hydroxyl groups, have better gel fractions and abrasion resistance than Examples 1 and 3, which rely solely on hydroxyl crosslinking. The comparative examples, due to their extremely low crosslinking density and reversible depolymerization, have poor material toughness and are easily worn.

[0079] (5) Aqueous dispersibility: Examples 2 and 4, which only contain carboxyl lactone modification, were able to prepare stable aqueous dispersions (30% solids content) that did not separate after 72 hours of storage, thanks to the effective hydrophilic groups provided by the grafted carboxyl groups. Examples 1 and 3, and the comparative examples, which do not contain carboxyl lactone modification, could not achieve aqueous dispersion due to the lack of hydrophilic groups and could only be dissolved in organic solvents.

[0080] (6) Curing behavior and adhesion: In the curing reaction with epoxy resin at 80°C, Examples 2 and 4, which contain carboxyl groups, have the shortest curing time (≤28 min) due to the presence of both carboxyl and hydroxyl active sites, and achieve the best adhesion to aluminum foil at grade 0. This is due to the strong coordination bond that can be formed between the carboxyl groups and the metal substrate. Examples 1 and 3, which contain only hydroxyl groups, have a longer curing time (≤38 min) and an adhesion grade of 1. The comparative examples rely only on a single active site of hydroxyl groups, and the reaction is reversible, resulting in the longest curing time (≥50 min), weak bonding with the substrate, and an adhesion grade of only 2-3.

[0081] Therefore, this invention, by selecting different types of lactone monomers and combining them with a specific catalytic system and twin-screw extrusion process, successfully achieved precise and efficient modification of the properties of polyvinyl acetal resin. The resulting product comprehensively surpasses traditional acrylic polyol modification routes in key performance indicators such as grafting efficiency, phase uniformity, media resistance, crosslinking density, abrasion resistance, water-based adaptability, curing speed, and adhesion, fully meeting the differentiated needs of various high-end application scenarios.

[0082] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A lactone-modified polyvinyl acetal resin, characterized in that, The preparation materials include the following parts by weight: The composition includes 80-85 parts by weight of polyvinyl acetal resin, 15-20 parts by weight of lactone monomer, 0.1-0.3 parts by weight of rare earth alkoxide catalyst, 0.1-0.2 parts by weight of antioxidant, and 0-2.0 parts by weight of regulator. The lactone monomer is selected from at least one of carboxyl lactones and non-carboxyl lactones.

2. The lactone-modified polyvinyl acetal resin according to claim 1, characterized in that, Carboxyl-containing lactones are selected from at least one of γ-carboxybutyric acid lactone and δ-carboxyvalerol lactone; non-carboxyl-containing lactones are selected from at least one of ε-caprolactone and γ-butyric acid lactone.

3. The lactone-modified polyvinyl acetal resin according to claim 1, characterized in that, The rare earth alkoxide catalyst is selected from yttrium isopropoxide or lanthanum isopropoxide.

4. The lactone-modified polyvinyl acetal resin according to claim 1, characterized in that, Polyvinyl alcohol acetal resin is selected from polyvinyl alcohol butyral resin; the hydroxyl content of polyvinyl alcohol butyral is 18-22 mol%, and the molecular weight is 20,000-80,000.

5. The lactone-modified polyvinyl acetal resin according to claim 1, characterized in that, The antioxidant is selected from antioxidant 1076.

6. The lactone-modified polyvinyl acetal resin according to claim 1, characterized in that, The regulator is selected from diethylene glycol.

7. The method for preparing the lactone-modified polyvinyl acetal resin according to any one of claims 1-6, characterized in that, Includes the following steps: The raw materials are mixed and subjected to a melt grafting reaction to obtain the lactone-modified polyvinyl acetal resin.

8. The preparation method according to claim 7, characterized in that, The melt grafting reaction is carried out in a twin-screw extruder; the reaction section temperature of the twin-screw extruder is 165-175℃, the screw speed is 280-320rpm, and the vacuum degree is 0.095-0.098MPa.

9. The preparation method according to claim 7, characterized in that, Prior to the melt grafting reaction, the process also includes drying the polyvinyl acetal resin and purifying the lactone monomer.

10. The application of the lactone-modified polyvinyl acetal resin according to any one of claims 1-6 or the lactone-modified polyvinyl acetal resin prepared by the preparation method according to any one of claims 7-9 in water-based anti-corrosion coatings, medical bio-adhesives, ion exchange membrane substrates or ink resins.

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