Low-water-absorption polyvinyl acetal film and preparation method thereof

Abstract

The invention relates to the technical field of functional materials for laminated glass, in particular to a low-water-absorption polyvinyl acetal film and a preparation method thereof. The method comprises the following steps: mixing a metal coordination cross-linking agent, a dispersing aid and a first part of low-interference plasticizer to obtain a mixture; carrying out melt blending on the mixture, polyvinyl acetal resin and the residual low-interference plasticizer, so that the metal coordination cross-linking agent and hydroxyl on a polyvinyl acetal molecular chain are subjected to a coordination reaction to obtain a cross-linked melt; and extruding the cross-linked melt to prepare the polyvinyl acetal film with low water absorption. Through the synergistic effect of the metal coordination crosslinking agent, the low-interference plasticizer and the dispersing aid, a uniform and stable dynamic hydrophobic coordination crosslinking network is successfully constructed, so that the contradiction between high crosslinking degree and good processability is successfully overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional materials for laminated glass, in particular to a low water absorption polyvinyl acetal film and a preparation method thereof. BACKGROUND

[0002] Polyvinyl butyral (PVB) film is widely used as a key interlayer material for laminated glass (such as automotive windshield glass and building safety glass) due to its excellent transparency, adhesion and impact resistance. This application scenario requires PVB film to have long-term environmental reliability, among which water resistance is one of the core indicators. Water penetration into the PVB / glass interface will cause adhesion to decrease, bubbles and haze to occur, which not only affects the optical performance, but also brings safety hazards.

[0003] To reduce the water absorption of PVB film, the industry generally adopts the technical idea of improving the crosslinking degree of the material, that is, reducing the number of free hydroxyl groups on the polymer molecular chain to reduce its affinity for water molecules. At present, the mainstream method mainly relies on traditional covalent chemical crosslinking, for example, using epoxy, aldehyde or multi-acid / anhydride crosslinking agents. However, this method has an inherent contradiction: once the covalent crosslinking network is formed, it is irreversible, which will severely limit the movement of molecular chains, resulting in a narrow processing window and a sharp rise in melt viscosity, thereby making subsequent laminated molding difficult. In addition, the auxiliary components introduced in the prior art to improve processability or compatibility, such as certain ether bond-containing plasticizers or co-plasticizers (as disclosed in CN1746220A), or specific functional additives (such as the UV absorber concerned in CN105086307A), are not designed to build a hydrophobic crosslinking network, so they cannot fundamentally solve the problem of high water absorption rate, and may even damage the optical uniformity of the film due to the introduction of polar groups or induced phase separation.

[0004] Therefore, while pursuing high crosslinking degree to reduce water absorption, the existing technology system is difficult to balance the excellent processing fluidity and high optical transparency required by PVB film, and this contradiction has become a key technical bottleneck restricting the further development of the field. SUMMARY

[0005] The purpose of the present application is to solve the problems existing in the prior art, and to provide a low water absorption polyvinyl acetal film and a preparation method thereof. Through the synergistic effect of metal coordination crosslinking agent, low interference plasticizer and dispersing aid, a uniform and stable dynamic hydrophobic coordination crosslinking network is successfully built, thereby successfully overcoming the contradiction between high crosslinking degree and good processability.

[0006] To achieve the above purpose, the present application provides a preparation method of a low water absorption polyvinyl acetal film, comprising the following steps: (1) Mix the metal coordination crosslinking agent, the dispersing agent and the first part of the low-interference plasticizer to obtain a mixture; (2) The mixture, polyvinyl acetal resin and remaining low-interference plasticizer are melt-blended to allow the metal coordination crosslinking agent to coordinate with the hydroxyl groups on the polyvinyl acetal molecular chain to obtain the crosslinked melt; (3) The cross-linked melt is extruded to form a low water absorption polyvinyl acetal film.

[0007] Preferably, in step (1), the metal coordination crosslinking agent is selected from one or two of aluminum acetylacetonate and zirconium acetylacetonate.

[0008] Preferably, the mass ratio of the metal coordination crosslinking agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-5:100.

[0009] Preferably, in step (1), the dispersing agent is selected from one or more of stearic acid, polyethylene wax, oxidized polyethylene wax, hydrophobic fumed silica, and polymeric dispersants.

[0010] Preferably, the mass ratio of the dispersing agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-1:100.

[0011] Preferably, in step (1), the low-interference plasticizer is selected from one or more of dioctyl dicarboxylate, dioctyl sebacate, and trioctyl trimellitate.

[0012] Preferably, the ratio of the total mass of the first part of the low-interference plasticizer in step (1) and the remaining low-interference plasticizer in step (2) to the mass of the polyvinyl acetal resin in step (2) is 20-50:100. The mass ratio of the first part of the low-interference plasticizer in step (1) to the remaining low-interference plasticizer in step (2) is 0.5-1.5:1.5-2.5.

[0013] Preferably, in step (1), the mixing speed is 1500-2000 r / min and the time is 10-15 min.

[0014] Preferably, in step (2), the melt blending is carried out in a twin-screw extruder with a screw speed of 300-400 r / min and a temperature of 155-185℃.

[0015] The present invention also provides a low-water-absorption polyvinyl acetal film, which is prepared according to the preparation method of the low-water-absorption polyvinyl acetal film.

[0016] The beneficial effects of this invention are as follows: This invention successfully constructs a uniform and stable dynamic hydrophobic coordination crosslinking network through the synergistic effect of a metal coordination crosslinking agent, a low-interference plasticizer, and a dispersant, overcoming the contradiction between high crosslinking degree and good processability in traditional technologies. Unlike traditional covalent crosslinking or simple physical blending techniques, the core innovation of this invention lies in constructing a three-in-one synergistic mechanism of "metal coordination crosslinking agent - low-interference plasticizer - dispersant." This mechanism utilizes a specific metal coordination crosslinking agent (such as aluminum acetylacetonate / zirconium) to undergo a dynamic and reversible coordination reaction with the hydroxyl groups on the PVB molecular chain, constructing a hydrophobic three-dimensional network at the molecular level. This network is structurally stable at room temperature, effectively binding free hydroxyl groups and significantly reducing the adsorption of moisture by the material; while at processing temperatures, the coordination bonds reversibly dissociate, giving the network a suitable "fluidity," thus achieving a high degree of crosslinking without sacrificing processing performance. In this process, the low-interference plasticizer avoids competitive coordination with metal ions, ensuring the efficiency and integrity of the crosslinking reaction; the dispersant ensures the uniform distribution of hydrophobic crosslinking centers in the matrix at the nanoscale, preventing optical inhomogeneity and performance fluctuations caused by agglomeration. This systematic approach successfully synergistically optimizes the material's low water absorption, high transparency, and good processability.

[0017] Specifically: 1. This invention innovatively selects hydrophobic aluminum acetylacetonate or zirconium acetylacetonate as the crosslinking center. The unique "high-temperature decoordination and room-temperature inertness" characteristics of this type of crosslinking agent allow the coordination crosslinking reaction to be precisely triggered and controlled within a specific temperature window of melt blending, effectively avoiding the processing performance deterioration caused by uncontrollable reactions, premature or excessive crosslinking, common with traditional crosslinking agents. Simultaneously, this crosslinking agent itself possesses excellent hydrophobicity; when it undergoes an efficient coordination reaction with the hydroxyl groups on the PVB molecular chain to form a stable "metal-hydroxyl" hydrophobic crosslinking network, it does not introduce new hydrophilic groups. This characteristic not only significantly improves the degree of crosslinking of PVB, but more importantly, by effectively reducing the number and activity of free hydroxyl groups, it significantly reduces the film's adsorption capacity for water molecules, giving it excellent water resistance.

[0018] 2. This invention utilizes metal coordination bonds to construct a dynamic reversible crosslinking network. This network significantly reduces water absorption by increasing the degree of crosslinking in PVB, while the coordination bonds exhibit moderate reversibility at processing temperatures, allowing the molecular chains to maintain necessary mobility. This ensures that the PVB melt maintains suitable flowability and viscosity during processing, thus achieving a balance between high crosslinking degree and excellent processing flowability. The material maintains a stable crosslinked structure during use and possesses good formability during processing.

[0019] 3. During the mixing process in step (1), the dispersant, through its unique "bridging" effect, generates an effective steric hindrance effect, preventing the nanoscale aggregation of the crosslinking agent and ensuring that the functional additives are uniformly dispersed at the nanoscale in the PVB matrix. This uniform dispersion system lays a solid foundation for constructing a complete and uniform hydrophobic crosslinking network, ultimately enabling the obtained film to simultaneously possess good optical properties, excellent performance uniformity, and batch stability.

[0020] 4. This invention achieves a synergistic effect by selecting specific crosslinking agents, low-interference plasticizers, and dispersing agents. The low-interference plasticizer ensures efficient crosslinking by minimizing competitive coordination with metal ions; the dispersing agent prevents crosslinking agent aggregation through steric hindrance, ensuring uniform dispersion of all components; and the resulting uniform crosslinking network not only constitutes a highly efficient damping structure, maintaining or even optimizing the film's sound insulation performance, but also ensures high uniformity and excellent batch stability in the final product's optical performance and long-term durability. Detailed Implementation

[0021] This invention provides a method for preparing a low-water-absorption polyvinyl acetal film, comprising the following steps: (1) Mix the metal coordination crosslinking agent, the dispersing agent and the first part of the low-interference plasticizer to obtain a mixture; (2) The mixture, polyvinyl acetal resin and remaining low-interference plasticizer are melt-blended to allow the metal coordination crosslinking agent to coordinate with the hydroxyl groups on the polyvinyl acetal molecular chain to obtain the crosslinked melt; (3) The cross-linked melt is extruded to form a low water absorption polyvinyl acetal film.

[0022] In this invention, in step (1), the metal coordination crosslinking agent is selected from one or two of aluminum acetylacetonate and zirconium acetylacetonate.

[0023] In this invention, when the metal coordination crosslinking agent is aluminum acetylacetonate and zirconium acetylacetonate, the mass ratio of aluminum acetylacetonate to zirconium acetylacetonate is 0.5-1.5:0.5-1.5.

[0024] In this invention, the mass ratio of the metal coordination crosslinking agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-5:100.

[0025] In this invention, in step (1), the dispersing agent is selected from one or more of stearic acid, polyethylene wax, oxidized polyethylene wax, hydrophobic fumed silica, and polymeric dispersant.

[0026] In this invention, the polymeric dispersant is selected from BYK-2150.

[0027] In this invention, the mass ratio of the dispersing agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-1:100.

[0028] In this invention, the low-interference plasticizer used in step (1) is one of the key components for achieving the synergistic effect. It specifically refers to a class of ester compounds whose molecular structure does not contain ether bonds (-O-, but excluding the COC structure in the ester group). This is fundamentally different from the ether-containing plasticizers or co-plasticizers (such as triethylene glycol di-2-ethylhexanoate) commonly used in the prior art to improve compatibility or processability. The low-interference plasticizer selected in this invention avoids ether bonds and other groups that easily coordinate strongly with metal ions due to its molecular structure. This minimizes competition with the metal coordination centers of the PVB chain's hydroxyl groups, thereby ensuring that the metal ions and PVB hydroxyl groups can efficiently and fully form a coordination crosslinking network, constructing a complete and stable hydrophobic crosslinking structure. The redefinition and precise selection of the plasticizer's function in this invention is an important prerequisite for achieving efficient construction of a dynamic hydrophobic crosslinking network.

[0029] In this invention, in step (1), the low-interference plasticizer is selected from one or more of dioctyl dioacetate (DOA), dioctyl sebacate (DOS), and trioctyl trimellitate (TOTM).

[0030] In this invention, the ratio of the total mass of the first part of the low-interference plasticizer in step (1) and the remaining low-interference plasticizer in step (2) to the mass of the polyvinyl acetal resin in step (2) is 20-50:100.

[0031] In this invention, the mass ratio of the first part of the low-interference plasticizer in step (1) to the remaining low-interference plasticizer in step (2) is 0.5-1.5:1.5-2.5.

[0032] In this invention, step (1) involves mixing in a high-speed disperser at a speed of 1500-2000 r / min for 10-15 min. This high-speed pre-dispersion step aims to utilize high shear force to fully deagglomerate the nanoscale metal coordination crosslinking agent particles and stably disperse them in the plasticizer to form a homogeneous slurry. This operation is crucial to preventing the crosslinking agent from agglomerating in the subsequent PVB matrix, laying the necessary foundation for obtaining a film with high uniformity and high optical performance.

[0033] In this invention, in step (2), the polyvinyl acetal resin is a commercially available PVB resin that meets the following specifications: degree of polymerization of 1500-2500 and hydroxyl content of 18-22%.

[0034] Hydroxyl content refers to the percentage by mass of hydroxyl groups (-OH) on the polyvinyl alcohol (PVA) segments that have not participated in the acetalization reaction in the PVB resin molecular chain.

[0035] In this invention, in step (2), melt blending is carried out in a twin-screw extruder with a screw speed of 300-400 r / min and a temperature of 155-185℃.

[0036] In this invention, during the melt blending process in step (2), aluminum acetylacetonate or zirconium acetylacetonate undergoes decoordination under heating conditions. The metal ions at their centers coordinate with the hydroxyl groups on the polyvinyl acetal molecular chain to form a "metal-hydroxyl" coordination crosslinking bond. At the same time, the detached acetylacetonate ligands are converted into gaseous byproducts and discharged from the system through the exhaust port of the twin-screw extruder.

[0037] In this invention, in step (3), the cross-linked melt is extruded through an extruder die and cooled and shaped at 25-30°C. The cooled and shaped material is then granulated and processed by casting or calendering to finally produce a low-water-absorption polyvinyl acetal film.

[0038] In this invention, the casting temperature is 180-190℃.

[0039] In this invention, the gas from the extruder exhaust port in step (2) was analyzed by gas chromatography (GC) to confirm that the content of acetylacetone ligand accounted for more than 95% of the total exhaust gas. Furthermore, the final product of step (3), the low-water-absorbent polyvinyl acetal film, was detected by high performance liquid chromatography (HPLC), and no acetylacetone residue was detected, indicating that there is no risk of residue of the ligand in the system and the process is safe and reliable.

[0040] The present invention also provides a low-water-absorption polyvinyl acetal film, which is prepared according to the preparation method of the low-water-absorption polyvinyl acetal film.

[0041] In this invention, the thickness of the low-absorbency polyvinyl acetal film is 0.3-1.5 mm, preferably 0.5-1.0 mm, and more preferably 0.7-0.8 mm.

[0042] The present invention will be further described below with reference to embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0043] In the following embodiments and comparative examples of the present invention, the polyvinyl acetal resin used is commercially available polyvinyl butyral (PVB) resin: Eastman's Butvar® B-90, with specifications of degree of polymerization 2000 and hydroxyl content 20%.

[0044] Example 1 This embodiment provides a method for preparing a low-water-absorption polyvinyl acetal film, comprising the following steps: Aluminum acetylacetonate, stearic acid, and dioctyl adipate (DOA) were added to a high-speed disperser and dispersed at 1800 r / min for 13 min to obtain a mixture.

[0045] The mixture, polyvinyl acetal resin, and remaining DOA were added to a twin-screw extruder for melt blending. The screw speed was controlled at 350 r / min, and the temperatures of each section of the extruder were: 155℃ for the feeding section, 170℃ for the melting section, 180℃ for the homogenization section, and 185℃ for the die head, to obtain the cross-linked melt.

[0046] The cross-linked melt is extruded through an extruder die and cooled and shaped at 25°C. The cooled and shaped material is then granulated to obtain PVB blend granules. The granules are then formed on a single-screw casting extruder using a casting method (temperature 185°C) to produce a low-water-absorbent polyvinyl acetal film with a thickness of 0.76 mm.

[0047] In this embodiment, the mass ratio of aluminum acetylacetonate, stearic acid, dioctyl adipate (DOA), and polyvinyl acetal resin is 0.5:0.3:35:100, and the mass ratio of the first portion of DOA to the remaining DOA is 1:2.

[0048] Example 2 This embodiment provides a method for preparing a low-water-absorbency polyvinyl acetal film, which differs from Embodiment 1 in that aluminum acetylacetonate is replaced with zirconium acetylacetonate, and the mass ratio of zirconium acetylacetonate, stearic acid, dioctyl adipate (DOA), and polyvinyl acetal resin is modified to 0.3:0.3:35:100.

[0049] Example 3 This embodiment provides a method for preparing a low-water-absorbency polyvinyl acetal film, which differs from Example 1 in that the mass ratio of aluminum acetylacetonate, stearic acid, dioctyl adipate (DOA), and polyvinyl acetal resin is modified to 1:0.3:35:100.

[0050] Comparative Example 1 This comparative example provides a method for preparing a polyvinyl acetal film, which differs from Example 1 in that the addition of aluminum acetylacetonate and stearic acid is omitted.

[0051] Comparative Example 2 This comparative example provides a method for preparing a polyvinyl acetal film, which differs from Example 1 in that dioctyl adipate (DOA) is replaced with triethylene glycol di-2-ethylhexanoate (3GO).

[0052] Comparative Example 3 This comparative example provides a method for preparing a polyvinyl acetal film, which differs from Example 1 in that the addition of stearic acid is omitted.

[0053] Experimental Example 1 The low-absorbency polyvinyl acetal films of Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the test results are recorded in Table 1. The water resistance test was conducted according to ASTM D570 standard, where the film was immersed in deionized water at 23°C for 24 hours, and the water absorption rate was calculated based on the change in mass. The optical performance test was conducted according to ASTM D1003 standard, where the transmittance and haze of the film were measured using a haze meter. The processing performance test was conducted according to ISO 11443 standard, at 180°C for 1000 seconds. -1 At a shear rate of 1 Hz, the apparent viscosity of the PVB blend particles was determined using a capillary rheometer. The sound insulation performance was tested according to ISO 6721-1 standard, using a dynamic mechanical analyzer (DMA) at a frequency of 1 Hz and a temperature of 20 ℃ to measure the loss factor of the film. The value directly characterizes the sound insulation performance of the material, and the higher the value, the better the sound insulation performance is usually.

[0054] Table 1 Test Results

[0055] As shown in Table 1, the water absorption rates of the films in Examples 1-3 of this invention are significantly lower than those in Comparative Examples 1 and 2, demonstrating that the combination of the metal coordination crosslinking network and the low-interference plasticizer plays a crucial role in improving the water resistance of the films. The water absorption rate of Comparative Example 3 is higher than that of the other examples, indicating that the dispersant helps to form a more uniform and complete hydrophobic crosslinking structure, further inhibiting water penetration.

[0056] As shown in Table 1, the optical performance test results indicate that all examples exhibit excellent optical performance with transmittance exceeding 91% and haze below 0.8%. In contrast, Comparative Example 2 (using 3GO) showed a haze increase to 2.5% and a transmittance decrease to 88.1%, indicating that the highly interfering plasticizer (3GO) affected crosslinking uniformity, leading to enhanced light scattering. Comparative Example 3 (without dispersant) also showed high haze, further demonstrating the indispensable role of dispersants in preventing crosslinking agent aggregation and maintaining high transparency.

[0057] The processing performance test results in Table 1 show that the viscosities measured in the examples are between 580-650 Pa·s, which is within the suitable processing range. This indicates that the "dynamic reversible coordination network" constructed in this invention achieves high crosslinking degree without compromising the processing fluidity of the material. Comparative Example 1 has the lowest viscosity, but its water resistance is significantly reduced; Comparative Example 3 has the highest viscosity, reflecting that crosslinking agent agglomeration may cause local over-crosslinking, thereby deteriorating processing performance.

[0058] The sound insulation performance test results in Table 1 show that the loss factor value of the example is the highest, indicating that its sound insulation performance is optimal. This is attributed to the fact that the uniformly distributed dynamic coordination crosslinking points constitute an efficient damping structure, enhancing the sound energy dissipation capability. Comparative Example 2 (using 3GO) has the worst sound insulation performance, indicating that the highly interfering plasticizer hinders the formation of an effective crosslinking network, weakening the damping effect of the material.

[0059] Therefore, the present invention utilizes the above-mentioned low-water-absorbency polyvinyl acetal film and its preparation method, and through the synergistic effect of metal coordination crosslinking agent, low-interference plasticizer and dispersant, successfully constructs a uniform and stable dynamic hydrophobic coordination crosslinking network, thereby successfully overcoming the contradiction between high crosslinking degree and good processability.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a low-water-absorption polyvinyl acetal film, characterized in that, Includes the following steps: (1) Mix the metal coordination crosslinking agent, the dispersing agent and the first part of the low-interference plasticizer to obtain a mixture; (2) The mixture, polyvinyl acetal resin and remaining low-interference plasticizer are melt-blended to allow the metal coordination crosslinking agent to coordinate with the hydroxyl groups on the polyvinyl acetal molecular chain to obtain the crosslinked melt; (3) The cross-linked melt is extruded to form a low water absorption polyvinyl acetal film.

2. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, In step (1), the metal coordination crosslinking agent is selected from one or two of aluminum acetylacetonate and zirconium acetylacetonate.

3. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, The mass ratio of the metal coordination crosslinking agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-5:

100.

4. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, In step (1), the dispersing agent is selected from one or more of stearic acid, polyethylene wax, oxidized polyethylene wax, hydrophobic fumed silica, and polymeric dispersant.

5. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, The mass ratio of the dispersing agent in step (1) to the polyvinyl acetal resin in step (2) is 0.1-1:

100.

6. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, In step (1), the low-interference plasticizer is selected from one or more of dioctyl dicarboxylate, dioctyl sebacate, and trioctyl trimellitate.

7. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, The ratio of the total mass of the first part of the low-interference plasticizer in step (1) and the remaining low-interference plasticizer in step (2) to the mass of the polyvinyl acetal resin in step (2) is 20-50:100; The mass ratio of the first part of the low-interference plasticizer in step (1) to the remaining low-interference plasticizer in step (2) is 0.5-1.5:1.5-2.

5.

8. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, In step (1), the mixing speed is 1500-2000 r / min and the time is 10-15 min.

9. The method for preparing a low-water-absorption polyvinyl acetal film according to claim 1, characterized in that, In step (2), melt blending is carried out in a twin-screw extruder with a screw speed of 300-400 r / min and a temperature of 155-185℃.

10. A low-absorption polyvinyl acetal film, characterized in that, The low-water-absorbency polyvinyl acetal film is prepared according to any one of claims 1-9.

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