PVB film and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a PVB (Polyvinyl Butyral) film and a preparation method thereof. The PVB film provided by the invention is prepared from the following components in parts by mass: 100 parts of PVB resin, 33 to 36 parts of triethylene glycol di-2-ethylhexoate, 7 to 9 parts of integrated anti-radiation toughening filler, 1 to 2 parts of organic montmorillonite, 0.8 to 1.2 parts of composite coupling agent, 0.5 to 1 part of ultraviolet light absorber, 0.6 to 0.8 part of antioxidant and 0.8 to 1 part of heat stabilizer. The integrated anti-radiation toughening filler adopts a core-shell structure, the anti-radiation core is composed of bismuth oxide and tungsten oxide according to the mass ratio of 3: 1, and the elastic coating layer is maleic anhydride grafted modified POE. The preparation method comprises the steps of pre-dispersion treatment, component mixing, melt extrusion, film casting, graded cooling, two-way stretching and the like. Through the core-shell structure design of the integrated anti-radiation toughening filler and the optimized processing technology, the anti-radiation performance and the toughening performance are synergistically improved, and the prepared film has the advantages of excellent anti-radiation effect, high toughness and good transparency.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a PVB film and a preparation method thereof. Background Art

[0002] Polyvinyl butyral (PVB) film, as the interlayer material for safety glass, is widely used in building curtain walls, automotive windshields, bulletproof glass, and other fields. While traditional PVB film meets basic requirements for transparency, adhesion, and safety, the expansion of its application areas has led to higher demands for its functional performance.

[0003] In specialized applications such as the nuclear industry, medical imaging, and aerospace, PVB films require radiation protection to protect personnel. Currently, the most common radiation protection method is to add heavy metal oxides such as lead oxide and tungsten oxide to the PVB matrix. However, this approach presents several challenges: First, traditional radiation-protective fillers have poor dispersion in the polymer matrix and are prone to agglomeration, affecting the film's transparency and mechanical properties. Second, inorganic fillers exhibit poor interfacial compatibility with the organic matrix, leading to interfacial debonding under external forces and reducing the material's toughness. Third, high loadings of inorganic particles significantly increase the material's brittleness, compromising its ability to act as a buffering layer in safety glass.

[0004] Existing methods for improving the toughness of PVB film primarily include adjusting the plasticizer content and adding elastomers, but these methods often compromise the film's transparency and weather resistance. Furthermore, achieving both radiation protection and toughening properties remains a technical challenge. Improving the material's toughness while maintaining radiation protection remains a pressing technical challenge in this field.

[0005] Therefore, developing a PVB film with both excellent radiation protection and high toughness is of great significance for expanding the application of PVB materials in special environments. Summary of the Invention

[0006] The purpose of the present invention is to provide a radiation-proof toughened PVB film and a preparation method thereof. By designing an integrated radiation-proof toughening filler and optimizing the formula composition, the toughness and transparency of the film are significantly improved while ensuring excellent radiation protection performance, thereby meeting the performance requirements of special application environments.

[0007] To achieve the above object, the technical solution adopted by the present invention is: The radiation-proof toughened PVB film of the present invention comprises the following components, measured by weight: 100 parts of PVB resin, 33-36 parts of triethylene glycol diethylhexanoate, 7-9 parts of an integrated radiation-proof toughening filler, 1-2 parts of organic montmorillonite, 0.8-1.2 parts of a composite coupling agent, 0.5-1 parts of an ultraviolet absorber, 0.6-0.8 parts of an antioxidant, and 0.8-1 parts of a thermal stabilizer. The integrated radiation-proof toughening filler comprises a radiation-proof core and an elastic coating layer, wherein the radiation-proof core comprises bismuth oxide and tungsten oxide in a mass ratio of 3:1, with a particle size controlled to be 0.5-3 μm; the elastic coating layer comprises maleic anhydride-grafted modified POE, with a coating thickness of 50-100 nm and a grafting rate of 8-12%.

[0008] in: The integrated radiation-proof toughening filler adopts a core-shell structure, with the radiation-proof core being a composite system of bismuth oxide and tungsten oxide. Bismuth oxide, with its high atomic number (Z=83) and high density (9.196 g / cm³), offers excellent shielding against X-rays and gamma rays. Tungsten oxide (Z=74) not only provides excellent radiation protection but also provides mechanical strength. The two are blended in a 3:1 mass ratio, ensuring effective radiation protection while optimizing cost and processing performance. The particle size is controlled within the 0.5-3 μm range, preventing the impact of coarse particles on transparency and preventing excessive agglomeration of nanoparticles.

[0009] Specifically, the elastic coating layer utilizes polyolefin elastomer (POE) modified with maleic anhydride grafting. POE exhibits excellent elasticity and toughness, and maleic anhydride grafting introduces polar groups, improving compatibility with the PVB matrix. The coating thickness is controlled between 50 and 100 nm, ensuring effective interfacial bonding while minimizing the impact of an excessively thick coating on radiation protection. The optimal grafting ratio is 8-12%. Below 8%, the modification effect is insignificant, while above 12%, the crosslinking density may be excessive, impacting toughness.

[0010] Specifically, the organic montmorillonite is modified with an octadecyl quaternary ammonium salt, with a lamella thickness of 2-5 nm, and is pre-dispersed in a plasticizer to form a stable dispersion. The organic montmorillonite's nanolamellar structure effectively blocks radiation propagation paths, while its layered structure also helps improve the material's toughness. The pre-dispersion treatment ensures uniform distribution of the montmorillonite within the matrix.

[0011] Specifically, the composite coupling agent is composed of γ-glycidyloxypropyltrimethoxysilane and tetrabutyl titanate in a mass ratio of 3:1. The epoxy groups of the silane coupling agent can undergo a ring-opening reaction with the hydroxyl groups on the PVB molecular chain, while the titanate coupling agent has excellent interfacial bonding properties. The combination of the two can significantly improve the interfacial bonding between the filler and the substrate.

[0012] Specifically, the maleic anhydride grafted modified POE is prepared by reactive extrusion: the POE resin is melted at 150-160°C, 0.05-0.1% dicumyl peroxide is added as an initiator, maleic anhydride is added at 8-12% of the mass of POE, and the reaction is extruded in a twin-screw extruder at an extrusion temperature of 160-170°C, a screw speed of 80-120 rpm, and a residence time of 3-5 minutes.

[0013] Specifically, the integrated radiation-proof toughening filler is prepared by a solution coating method: bismuth oxide and tungsten oxide are mixed in a mass ratio of 3:1 and high-energy ball milled for 2-3 hours to obtain a radiation-proof core; maleic anhydride grafted POE is dissolved in toluene to prepare a 5-8% solution; the radiation-proof core powder is added to the POE solution and ultrasonically dispersed at 60-70°C for 1 hour; the solvent is removed by spray drying to obtain a surface-coated integrated radiation-proof toughening filler.

[0014] Specifically, the preparation method of the PVB film includes: S1. Pre-disperse the organic montmorillonite in triethylene glycol diisooctanoate and ultrasonicate for 30 minutes; S2. The integrated radiation-resistant toughening filler and the composite coupling agent are pre-mixed and allowed to stand for 30 minutes; S3. The organic montmorillonite triethylene glycol diethyl octanoate dispersion obtained in step S1, the integrated radiation toughening filler and composite coupling agent premix obtained in step S2, and PVB resin, UV absorber, antioxidant and heat stabilizer are put into a high-speed mixer together and mixed at 2000-2500 rpm for 25-30 minutes to fully disperse the components and form a uniform mixture; S4. The homogeneous mixture obtained in step S3 was melt extruded by a twin-screw extruder, with the temperature zone controlled at 155-170-180°C, the screw speed at 120-140rpm, and the vacuum degree at -0.07 to -0.05MPa; S5. After the cast film is formed, the film is cooled in stages, with the cooling roller in contact at 15-20°C for 12-18 seconds, and then cooled in a cold air circulation system at 5-10°C for 30-40 seconds; S6. Biaxially stretch at 140-150°C, stretching rate 6-8 m / min, heat setting at 55-65°C for 8-12 minutes, film thickness 0.9-1.5 mm, humidity controlled at 0.3-0.4%.

[0015] In the above step S3, triethylene glycol diisooctanoate is used as a common plasticizer, which can form hydrogen bonds with the hydroxyl groups in the PVB molecular chain, thereby effectively lowering the glass transition temperature of PVB, improving its flexibility and processing fluidity, and providing conditions for the subsequent uniform dispersion of fillers.

[0016] Montmorillonite is organically modified with octadecyl quaternary ammonium salt, imparting it with stronger organic affinity. Pre-dispersing it in a plasticizer avoids agglomeration when added directly to a PVB matrix. The modified montmorillonite's layered structure forms a nano-dispersion state within the matrix, enhancing both radiation barrier properties and material toughness.

[0017] Radiation protection core and The composite system is coated with maleic anhydride-grafted POE. The flexible chain segments of POE impart a certain elasticity to the filler, while the polar groups of maleic anhydride can interact with the hydroxyl groups in the PVB molecules, significantly improving the interfacial compatibility between the filler and the matrix, avoiding the degradation of transparency and mechanical properties caused by the agglomeration of traditional inorganic powders. γ-Glycidyloxypropyltrimethoxysilane can chemically bond with the PVB molecular chains, while tetrabutyl titanate can stabilize the hydroxyl groups on the surface of the inorganic filler. When combined, the two form a "molecular bridge" between the inorganic filler and the organic matrix, further enhancing the interfacial bonding strength and ensuring a uniform distribution of the filler in the matrix.

[0018] UV absorbers, antioxidants and heat stabilizers are all added in low doses, and their targets are light stability, thermal oxygen stability and processing stability respectively. They will not react competitively with plasticizers or fillers, so they can function independently and further improve the weather resistance and long-term performance of the film.

[0019] Specifically, the ultraviolet absorber is selected from at least one of UV-326, UV-329, and UV-531, the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168, and the heat stabilizer is a composite heat stabilizer of calcium stearate and aluminum hydroxide in a mass ratio of 2:1.

[0020] The beneficial effects of the present invention are as follows: 1. The core-shell structure design of the integrated radiation-proof and toughening filler achieves a synergistic improvement in radiation protection and toughening properties. The radiation-proof core provides excellent radiation shielding, while the elastic coating improves the interface with the substrate and enhances the material's toughness, avoiding the performance constraints found in traditional methods.

[0021] 2. The maleic anhydride-grafted POE coating significantly improves the compatibility between the inorganic filler and the organic matrix. The grafted maleic anhydride groups can form hydrogen bonds or chemical bonds with the PVB molecular chains, increasing interfacial bonding strength, reducing stress concentration, and improving the material's impact toughness.

[0022] 3. The synergistic effect of organic montmorillonite and the composite coupling agent further optimizes the material's overall performance. The montmorillonite's nanosheet structure provides additional radiation shielding, while its layered structure facilitates stress transfer and energy absorption. The composite coupling agent ensures good interfacial bonding between the components.

[0023] 4. The optimized preparation process ensures uniform dispersion of each component and good processing performance. Step-by-step pretreatment avoids adverse reactions between components, and temperature zone control and graded cooling process ensure the stability of product quality.

[0024] 5. The prepared radiation-proof toughened PVB film has excellent comprehensive properties: lead equivalent ≥1.2mmPb, impact strength ≥25kJ / m², light transmittance ≥85%, which can meet the strict requirements of special application environments. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention encompasses all possible alternatives, improvements, and equivalents within the scope of the claims.

[0026] The grafting rate was determined by acid-base titration: 1.0 g of grafted POE was refluxed with acetone to remove impurities, dissolved in xylene, and the carboxyl groups were neutralized with 0.1 mol / L KOH-ethanol solution, and back-titrated with 0.1 mol / L HCl-isopropanol.

[0027] PVB resin: degree of polymerization 1700-1800, hydroxyl content 18.5-20.5%, purchased from Anhui Xinguang Chemical Co., Ltd.

[0028] Triethylene glycol diisooctanoate (3GO): industrial grade, purchased from Jiangsu Yangzi Petrochemical Co., Ltd.

[0029] Bismuth oxide: purity ≥99.5%, average particle size 1-2 μm, purchased from Beijing Jinyu Jiaye Chemical Co., Ltd.

[0030] Tungsten oxide: purity ≥99.0%, average particle size 0.8-1.5 μm, purchased from Shanghai Maide Chemical Co., Ltd.

[0031] POE elastomer: brand 8150, melt index 0.5 g / 10 min, purchased from The Dow Chemical Company, USA.

[0032] The remaining raw materials are conventional products and are all obtained through commercial channels.

[0033] Example 1:

[0034] A method for preparing a PVB film comprises the following steps: S1. Pre-disperse 1.5 parts of organic montmorillonite in 34 parts of triethylene glycol diisooctanoate and ultrasonicate for 30 minutes; S2. Premix 8 parts of the integrated radiation-proof toughening filler with 1 part of the composite coupling agent and let it stand for 30 minutes; S3, placing the organic montmorillonite triethylene glycol diethyl octanoate dispersion obtained in step S1, the integrated radiation-proof toughening filler and composite coupling agent premix obtained in step S2, 100 parts of PVB resin, 0.8 parts of UV-531, 0.7 parts of antioxidant 1010, and 0.9 parts of thermal stabilizer into a high-speed mixer, and mixing at 2200 rpm for 28 minutes to fully disperse the components and form a uniform mixture; S4, extruding the homogeneous mixture obtained in step S3 through a twin-screw extruder at a temperature zone of 155-170-180° C., a screw speed of 130 rpm, and a vacuum degree of -0.06 MPa; S5. After the film is cast, it is kept in contact with a cooling roller at 15°C for 15 seconds and cooled with cold air at 8°C for 35 seconds; biaxially stretched at 145°C at a stretching rate of 7 m / min and heat-set at 60°C for 10 minutes to obtain a radiation-proof toughened PVB film with a thickness of 1.2 mm.

[0035] The preparation method of the integrated radiation-proof toughening filler includes the following steps: 120g of bismuth oxide and 40g of tungsten oxide are mixed and subjected to high-energy ball milling for 2.5 hours to produce a radiation-proof core. 80g of modified POE is dissolved in 1200ml of toluene to prepare a 6.7% solution. 160g of the radiation-proof core is added to the POE solution, ultrasonically dispersed at 65°C for 1 hour, and then spray-dried to remove the solvent to produce the integrated radiation-proof toughening filler.

[0036] The preparation method of the maleic anhydride grafted modified POE comprises the following steps: melting 1000 g of POE resin at 155° C. in a twin-screw extruder, adding 1 g of dicumyl peroxide, and then adding 100 g of maleic anhydride. The extrusion temperature is 165° C., the screw speed is 100 rpm, and the residence time is 4 minutes to obtain a modified POE with a grafting rate of 10%.

[0037] The composite coupling agent is composed of γ-glycidyloxypropyltrimethoxysilane and tetrabutyl titanate in a mass ratio of 3:1.

[0038] The heat stabilizer is a compound of calcium stearate and aluminum hydroxide in a mass ratio of 2:1.

[0039] Example 2: The only difference between the preparation method of a PVB film and Example 1 is that in step S2, 7 parts of the integrated radiation-proof toughening filler and 1 part of the composite coupling agent are pre-mixed and allowed to stand for 30 minutes.

[0040] The preparation method of the maleic anhydride grafted modified POE comprises the following steps: melting 1000 g of POE resin at 155° C. in a twin-screw extruder, adding 1 g of dicumyl peroxide, and then adding 80 g of maleic anhydride. The extrusion temperature is 165° C., the screw speed is 100 rpm, and the residence time is 4 minutes to obtain a modified POE with a grafting rate of 8%.

[0041] Example 3: A method for preparing a PVB film differs from that of Example 1 only in that step S1: pre-dispersing 1.5 parts of organic montmorillonite in 36 parts of triethylene glycol diisooctanoate and ultrasonicating for 30 minutes; S2. Premix 9 parts of the integrated radiation-proof toughening filler with 1 part of the composite coupling agent and let it stand for 30 minutes.

[0042] The preparation method of the maleic anhydride grafted modified POE comprises the following steps: melting 1000 g of POE resin at 155° C. in a twin-screw extruder, adding 1 g of dicumyl peroxide, and then adding 120 g of maleic anhydride. The extrusion temperature is 165° C., the screw speed is 100 rpm, and the residence time is 4 minutes to obtain a modified POE with a grafting rate of 12%.

[0043] Example 4: A method for preparing a PVB film differs from that of Example 1 only in that step S1: pre-dispersing 1.0 part of organic montmorillonite in 34 parts of triethylene glycol diisooctanoate and ultrasonicating for 30 minutes; S2. Premix 8 parts of the integrated radiation-proof toughening filler with 0.8 parts of the composite coupling agent and let it stand for 30 minutes; S5. After the film is cast, it is kept in contact with a cooling roller at 15°C for 15 seconds and cooled with cold air at 8°C for 35 seconds; biaxially stretched at 145°C with a stretching rate of 7 m / min and heat-set at 60°C for 10 minutes to obtain a radiation-proof toughened PVB film with a thickness of 0.9 mm.

[0044] Example 5: A method for preparing a PVB film differs from that of Example 1 only in that step S1: pre-dispersing 2.0 parts of organic montmorillonite in 34 parts of triethylene glycol diisooctanoate and ultrasonicating for 30 minutes; S2. Premix 8 parts of the integrated radiation-proof toughening filler with 1.2 parts of the composite coupling agent and let it stand for 30 minutes; S5. After the film is cast, it is kept in contact with a cooling roller at 15°C for 15 seconds and cooled with cold air at 8°C for 35 seconds; biaxially stretched at 145°C at a stretching rate of 7 m / min and heat-set at 60°C for 10 minutes to obtain a radiation-proof toughened PVB film with a thickness of 1.5 mm.

[0045] Comparative Example 1 A method for preparing a PVB film differs from Example 1 only in that step S2 is to pre-mix 4 parts of bismuth oxide, 4 parts of oxide, and 1 part of a composite coupling agent, and let it stand for 30 minutes; Comparative Example 2 The only difference between the preparation method of a PVB film and Example 1 is that in step S2, 8 parts of the integrated radiation-proof toughening filler and 1 part of the composite coupling agent are premixed and allowed to stand for 30 minutes.

[0046] The preparation method of the integrated radiation-proof toughening filler comprises the following steps: mixing 120 g of bismuth oxide and 40 g of tungsten oxide, and performing high-energy ball milling for 2.5 hours to obtain a radiation-proof core.

[0047] Comparative Example 3 The only difference between the preparation method of a PVB film and Example 1 is that step S1 is to add 34 parts of triethylene glycol diisooctanoate.

[0048] Comparative Example 4 The only difference between the preparation method of a PVB film and Example 1 is that step S2 is to add 8 parts of integrated radiation-proof toughening filler.

[0049] Comparative Example 5 The only difference between the preparation method of a PVB film and Example 1 is that in step S2, 8 parts of bismuth oxide and 1 part of a composite coupling agent are premixed and allowed to stand for 30 minutes.

[0050] The performance tests of the PVB films prepared in the examples and comparative examples were carried out: (1) Radiation protection performance test: Use an X-ray tube (tube voltage 100kV, tube current 5mA) to measure the lead equivalent value in accordance with GB / T 18871 standard.

[0051] (2) Impact strength test: According to GB / T 1043 standard, a simply supported beam impact test was adopted with a sample size of 80 mm × 10 mm × 4 mm and a pendulum energy of 5.5 J.

[0052] (3) Light transmittance test: A UV-2450 ultraviolet-visible spectrophotometer was used to measure the visible light transmittance (average value within the range of 380-780 nm).

[0053] (4) Tensile strength test: According to GB / T 1040 standard, the specimen is dumbbell-shaped and the tensile rate is 50 mm / min.

[0054] (5) Haze test: According to GB / T 2410 standard, the haze meter is used for measurement.

[0055] The test results are shown in Table 1:

[0056] Table 1 Performance test results According to the data in Table 1, the radiation-proof toughened PVB films prepared in Examples 1-5 have a lead equivalent of ≥1.2 mmPb, an impact strength of ≥25 kJ / m², and a light transmittance of ≥85%. All performance indicators meet the design requirements, indicating that the technical solution of the present invention is significantly effective.

[0057] Comparative Example 1 uses a physically mixed radiation shielding filler, resulting in poor dispersion and a significant decrease in light transmittance and impact strength. Comparative Example 2 lacks an elastic coating layer, resulting in poor interfacial bonding and reduced toughness. Comparative Example 3 lacks the nano-reinforcement effect of montmorillonite. Comparative Example 4 lacks a coupling agent treatment, resulting in poor interfacial bonding. Comparative Example 5 uses only bismuth oxide, resulting in insufficient radiation shielding. These comparative results demonstrate the necessity and synergistic effect of the various technical features of the present invention.

[0058] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A PVB film, characterized in that: Calculated by mass, it includes the following components: PVB resin: 100 parts Triethylene glycol diisooctanoate: 33-36 parts Integrated radiation-proof toughening filler: 7-9 parts Organic montmorillonite: 1-2 parts Composite coupling agent: 0.8-1.2 parts UV absorber: 0.5-1 part Antioxidant: 0.6-0.8 parts Heat stabilizer: 0.8-1 part The integrated radiation-proof toughening filler consists of a radiation-proof core and an elastic coating layer, wherein the radiation-proof core is composed of bismuth oxide and tungsten oxide in a mass ratio of 3:1, and the particle size is controlled at 0.5-3 μm; the elastic coating layer is maleic anhydride grafted modified POE, with a coating thickness of 50-100 nm and a grafting rate of 8-12%.

2. The PVB film according to claim 1, characterized in that: The organic montmorillonite is montmorillonite modified by octadecyl quaternary ammonium salt, has a sheet thickness of 2-5 nm, and is pre-dispersed in a plasticizer to form a stable dispersion.

3. The PVB film according to claim 1, characterized in that: The composite coupling agent is composed of γ-glycidyloxypropyltrimethoxysilane and tetrabutyl titanate in a mass ratio of 3:

1.

4. The PVB film according to claim 1, characterized in that: The preparation method of the maleic anhydride grafted modified POE comprises: melting the POE resin at 150-160° C., adding 0.05-0.1% dicumyl peroxide as an initiator, adding maleic anhydride at 8-12% of the mass of the POE, and reacting and extruding in a twin-screw extruder at an extrusion temperature of 160-170° C., a screw speed of 80-120 rpm, and a residence time of 3-5 minutes.

5. The PVB film according to claim 1, characterized in that: The preparation method of the integrated radiation-proof toughening filler includes: mixing bismuth oxide and tungsten oxide in a mass ratio of 3:1 and high-energy ball milling for 2-3 hours; dissolving maleic anhydride-grafted POE in toluene to prepare a 5-8% solution; adding radiation-proof core powder to the POE solution and ultrasonically dispersing it at 60-70°C for 1 hour; and removing the solvent by spray drying to obtain a surface-coated integrated radiation-proof toughening filler.

6. The PVB film according to claim 1, characterized in that: The ultraviolet absorber is selected from at least one of UV-326, UV-329, and UV-531; the antioxidant is selected from at least one of antioxidant 1010 and antioxidant 168.

7. The PVB film according to claim 1, characterized in that: The heat stabilizer is a composite heat stabilizer of calcium stearate and aluminum hydroxide in a mass ratio of 2:

1.

8. The method for preparing a PVB film according to any one of claims 1 to 7, characterized in that: The steps include: S1. The organic montmorillonite was pre-dispersed in triethylene glycol diethyl octanoate and ultrasonically treated for 30 minutes; S2. The integrated radiation toughening filler and composite coupling agent pre-mixed, let stand for 30 minutes; S3. The components are put into a high-speed mixer according to the ratio, 2000-2500rpm mixing for 25-30 minutes; S4. Melt extrusion through a twin-screw extruder with temperature controlled in zones of 155-170-180°C; S5. After the film is cast, it is cooled in stages, with contact with the cooling roller at 15-20°C for 12-18 seconds, and then cooled with cold air circulation at 5-10°C for 30-40 seconds; S6. Biaxially stretch at 140-150°C, stretching rate 6-8 m / min, heat setting at 55-65°C for 8-12 minutes.

9. The method for preparing a PVB film according to claim 8, characterized in that: In step S4, the screw speed is 120-140 rpm, and the vacuum degree is controlled at -0.07 to -0.05 MPa.

10. The method for preparing a PVB film according to claim 8, characterized in that: In step S6, the film thickness is 0.9-1.5 mm, and the humidity is controlled at 0.3-0.4%.

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