PVB interlayer with anisotropic creep properties and method of making and use thereof

Abstract

The present application relates to the technical field of PVB interlayer, and particularly relates to a PVB interlayer with anisotropic creep characteristics, a preparation method and application thereof, raw materials are mixed to obtain a mixture; the mixture is sent into an extruder, and after being melt plasticized in the extruder, the mixture is filtered through a melt filter, and finally extruded through a T-shaped flat die head to form a melt sheet; the melt sheet is subjected to longitudinal stretching and transverse relaxation treatment, and finally cooled and shaped through a cooling roller group to obtain the PVB interlayer. The PVB interlayer with anisotropic creep characteristics, the preparation method and application thereof adopt the above steps, through synergistic regulation of special plasticizers and longitudinal stretching orientation, the PVB interlayer is differentiated in terms of creep compliance in the extrusion direction and perpendicular to the extrusion direction, can flow along the curved direction during lamination, reduces the optical failure rate, and simultaneously has the advantages of stable migration resistance, reworkability, easy direction identification and the like.

Description

Technical Field

[0001] This invention relates to the field of PVB interlayer technology, and in particular to PVB interlayers with anisotropic creep properties, their preparation methods, and applications. Background Technology

[0002] Polyvinyl butyral (PVB) interlayers are widely used in laminated glass due to their excellent adhesion, transparency, and impact resistance. With the rapid development of the automotive industry, the demand for curved laminated glass (such as panoramic sunroofs and windshields) is increasing, while also placing higher demands on the optical quality of curved laminated glass.

[0003] In the fabrication of curved laminated glass, a PVB interlayer is typically laminated with two curved glass sheets under high temperature (approximately 130℃-140℃) and high pressure (approximately 1.0MPa-1.3MPa). Traditional PVB interlayers exhibit isotropic rheological properties in the plane, meaning their creep compliance is essentially the same in the extrusion direction (MD direction) and perpendicular to the extrusion direction (TD direction). When this isotropic PVB film is used for curved lamination, the PVB film cannot preferentially flow along the curvature direction of the surface under pressure, leading to defects such as stress concentration, localized thickness unevenness, optical distortion, and even interlayer delamination at glass edges or in areas of drastic curvature change.

[0004] To address the aforementioned issues, existing research has attempted improvements through two main approaches. One is to add inorganic particles (such as silica and alumina) to the PVB film to adjust its rheological properties. However, the addition of inorganic particles often leads to increased film haze, decreased light transmittance, or discoloration during long-term use. The second approach is to adjust the flowability of the PVB film by changing the type of plasticizer. However, traditional plasticizer systems struggle to achieve differentiated flow in different directions within a plane. Furthermore, existing PVB films lack directional identification methods in curved surface lamination, making them prone to poor adhesion due to incorrect laying direction. Moreover, most products lack reworkability; once lamination fails, the entire film is scrapped, increasing production costs.

[0005] Therefore, developing a PVB interlayer with controllable anisotropic creep characteristics in a plane without the need for adding inorganic particles, enabling it to preferentially flow along the bending direction during curved surface lamination while maintaining excellent optical transparency and degassing properties, and possessing orientation identification markings and reworkability, has significant industrial application value. Summary of the Invention

[0006] The purpose of this invention is to provide a PVB interlayer with anisotropic creep characteristics, its preparation method and application. By combining a special plasticizer and synergistically controlling the longitudinal stretching orientation, the creep flexibility of the PVB interlayer is differentiated in the extrusion direction and perpendicular to the extrusion direction. During lamination, it can flow in a directional manner along the bending direction of the curved surface, reducing the optical defect rate. At the same time, it has the advantages of stable migration resistance, reworkability and easy orientation identification.

[0007] To achieve the above objectives, the present invention provides a method for preparing a PVB interlayer film with anisotropic creep properties, comprising the following steps: S1. Raw material mixing: PVB resin, plasticizer and additives are mixed evenly in a mixer to obtain a mixture. S2, Melt Extrusion: The mixture obtained in S1 is fed into an extruder, melted and plasticized in the extruder, filtered through a melt filter, and finally extruded through a T-shaped flat die to form a molten sheet; S3, Longitudinal stretching orientation: The molten sheet obtained in S2 is stretched longitudinally with a stretching ratio of 1.5-3.5 times to obtain the stretched sheet; S4. Casting and Cooling: The sheet stretched in S3 is subjected to transverse relaxation treatment with a relaxation rate of 0.90-0.98. Finally, it is cooled and shaped by a cooling roller group to obtain the PVB interlayer film.

[0008] Preferably, in S1, the plasticizer is a mixture of triethylene glycol bis(2-ethylhexanoate) (3GO) and polyoxypropylene glycerol ether (PPG-1000), and the mass ratio of triethylene glycol bis(2-ethylhexanoate) to polyoxypropylene glycerol ether is 1:0.3-1:1.2.

[0009] Preferably, in S1, the mixing is carried out at a temperature of 40-60℃ and a rotation speed of 200-400rpm for 10-20 minutes.

[0010] Preferably, in S2, the temperatures of each section of the extruder are set as follows: Zone 1 180℃-190℃, Zone 2 200℃-210℃, Zone 3 215℃-220℃, Zone 4 215℃-220℃, and the die head temperature 205℃-215℃; the melt filter is a 200-300 mesh melt filter.

[0011] Preferably, in S3, the longitudinal stretching is completed at a temperature of 100℃-150℃ by the cooperation of a heating roller and a stretching roller.

[0012] Preferably, in S4, the lateral relaxation process is carried out in a lateral relaxation device, and the temperature of the lateral relaxation process is 80-120°C.

[0013] Preferably, in S4, the cooling roller group includes a first cooling roller, a second cooling roller, and a third cooling roller connected in series. The temperature of the first cooling roller is 40℃-50℃, the temperature of the second cooling roller is 25℃-35℃, and the temperature of the third cooling roller is 20℃-30℃.

[0014] The present invention also provides a PVB interlayer with anisotropic creep characteristics, which is prepared by the above preparation method. The PVB interlayer has a first direction and a second direction in the plane. The first direction is along the extrusion direction and the second direction is perpendicular to the extrusion direction. At a temperature of 90°C, the creep compliance of the first direction to the creep compliance of the second direction is 1.5-5.0.

[0015] Preferably, at a temperature of 90°C, the creep compliance in the first direction is 8.0 × 10⁻⁶. -5 -5.0×10 -4 Pa -1 The creep compliance in the second direction is 2.0 × 10⁻⁶. -5 -2.5×10 -4 Pa -1 .

[0016] The present invention also provides an application of a PVB interlayer with anisotropic creep properties. The aforementioned PVB interlayer with anisotropic creep properties is used to prepare curved laminated glass, which includes a first curved glass plate and a second curved glass plate, with the PVB interlayer sandwiched between the first curved glass plate and the second curved glass plate.

[0017] Therefore, the present invention, by employing the above-mentioned PVB interlayer film with anisotropic creep properties, its preparation method, and its application, has the following beneficial effects: (1) The PVB interlayer of the present invention has anisotropic creep characteristics. Through the synergistic effect of longitudinal stretching orientation treatment and a specific plasticizer system (3GO and PPG-1000 compound), the PVB film has a high creep compliance at 90°C along the extrusion direction and a low creep compliance at 90°C perpendicular to the extrusion direction. The ratio of the two can reach 1.5 to 5.0. When used for laminating curved laminated glass, the extrusion direction is placed along the curvature direction of the curved glass. The PVB interlayer can preferentially flow along the curvature direction, effectively filling the curvature difference of the curved glass and significantly reducing stress concentration and optical distortion.

[0018] (2) The PVB interlayer of the present invention has high surface bonding accuracy. The thickness deviation between the edge and the center of the curved laminated glass prepared by the PVB interlayer of the present invention can be controlled to less than 50 μm and the optical distortion can be controlled to less than 1.5 points, which is far superior to the products using traditional isotropic PVB interlayer (thickness deviation is usually greater than 100 μm and optical distortion is greater than 2.5 points).

[0019] (3) The PVB interlayer film of the present invention has a wide process window and strong robustness. It can maintain a creep compliance ratio greater than 1.5 in the extrusion direction to the creep compliance perpendicular to the extrusion direction within a wide temperature range of 70℃-110℃, and can obtain qualified curved surface bonding effect within a pressure range of 0.8MPa-1.6MPa. At the same time, the present invention has verified a low plasticizer migration rate (less than 2.0%) through a high temperature storage test at 80℃ for 7 days, ensuring long-term stability.

[0020] (4) The PVB interlayer of the present invention is reworkable. After the PVB interlayer is laminated once, after reheating and separation, the ratio of creep compliance in the extrusion direction to creep compliance perpendicular to the extrusion direction can be retained at more than 80%. After secondary lamination, it can still meet the quality requirements of curved laminated glass, which significantly reduces production losses.

[0021] (5) The present invention sets a direction identification mark on the edge of the PVB interlayer film in the MD direction, which avoids the operation error of reversing the direction when laying on the production line and improves the production reliability.

[0022] (6) This invention does not rely on inorganic particles such as silicon dioxide and graphene to achieve functionality, and completely avoids the problems of increased haze, discoloration or decreased transparency of PVB interlayer caused by the addition of inorganic particles, thus ensuring the excellent optical quality of laminated glass.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the method for preparing a PVB interlayer with anisotropic creep characteristics according to Embodiment 1 of the present invention. Detailed Implementation

[0025] This invention provides a method for preparing a PVB interlayer with anisotropic creep properties, comprising the following steps: S1. Raw material mixing: PVB resin, plasticizer and additives are mixed evenly in a mixer to obtain a mixture. S2, Melt Extrusion: The mixture obtained in S1 is fed into an extruder, melted and plasticized in the extruder, filtered through a melt filter, and finally extruded through a T-shaped flat die to form a molten sheet; S3, Longitudinal stretching orientation: The molten sheet obtained in S2 is stretched longitudinally with a stretching ratio of 1.5-3.5 times to obtain the stretched sheet; S4. Casting and Cooling: The sheet stretched in S3 is subjected to transverse relaxation treatment with a relaxation rate of 0.90-0.98. Finally, it is cooled and shaped by a cooling roller group to obtain the PVB interlayer film.

[0026] Preferably, in S1, the plasticizer is a mixture of triethylene glycol bis(2-ethylhexanoate) (3GO) and polyoxypropylene glycerol ether (PPG-1000), and the mass ratio of triethylene glycol bis(2-ethylhexanoate) to polyoxypropylene glycerol ether is 1:0.3-1:1.2.

[0027] This invention utilizes a longitudinal stretching and orientation treatment after melt extrusion to orient PVB molecular chains along the extrusion direction, establishing an anisotropic structural basis. Simultaneously, a plasticizer system combining 3GO and PPG-1000 is employed. This system leverages the synergistic effect of small-molecule plasticizers preferentially plasticizing the orientation region to enhance chain segment mobility in the extrusion direction, while large-molecule plasticizers, due to their low migration rate, maintain a low creep compliance perpendicular to the extrusion direction. This effectively amplifies the anisotropy imparted by stretching and achieves a wide adjustable range (extrusion direction / 90°C creep compliance ratio: 1.5–5.0). This ratio range strikes the optimal balance between providing sufficient directional flow advantage and retaining the necessary deformation capacity perpendicular to the extrusion direction. This allows the PVB film to select a matching extrusion direction / 90°C creep compliance ratio based on the radius of curvature during curved surface lamination, achieving directional stress release, thickness uniformity, and minimized optical distortion.

[0028] In this invention, when 3GO plasticizer is used alone, the creep flexibility of the PVB interlayer after longitudinal stretching is limited, and the creep flexibility ratio of the extrusion direction to 90°C perpendicular to the extrusion direction is usually no more than 1.5. When PPG-1000 is used alone, the overall creep flexibility of the PVB interlayer is low, resulting in insufficient flowability during lamination. This invention combines 3GO and PPG-1000, allowing the small molecule 3GO to preferentially enter the orientation region of the PVB molecular chain, significantly enhancing the chain segment mobility in the extrusion direction and amplifying the high creep compliance imparted by the stretching treatment in the extrusion direction. On the other hand, the large molecule PPG-1000, due to its low mobility and large steric hindrance, mainly plays a filling and diluting role in the non-oriented region, having little impact on the entanglement network perpendicular to the extrusion direction, thus maintaining a low level of creep compliance perpendicular to the extrusion direction. The synergistic effect of the two significantly amplifies the anisotropy factor imparted by the stretching orientation, widening the ratio of creep compliance in the extrusion direction to 90°C perpendicular to the extrusion direction from 1.2-1.5 in the stretching treatment itself to 1.5-5.0.

[0029] This invention enables precise control of the creep compliance at 90°C in the extrusion direction / perpendicular to the extrusion direction by independently adjusting the compounding ratio of 3GO / PPG-1000 (adjusting the degree of plasticization in the extrusion direction) and the longitudinal stretching ratio (adjusting the degree of orientation). This invention allows for precise control of the creep compliance at 90°C in the extrusion direction / perpendicular to the extrusion direction within a wide range of 1.5 to 5.0.

[0030] Preferably, in S1, the mixing is carried out at a temperature of 40-60℃ and a rotation speed of 200-400rpm for 10-20 minutes.

[0031] In a further preferred embodiment, in S1, the mass fractions of each raw material are: 100 parts of PVB resin, 30-50 parts of plasticizer, and 0.1-0.5 parts of additives, wherein the additives are selected from one of ultraviolet absorbers, antioxidants, and light stabilizers; and the hydroxyl content of the PVB resin is 25-35 mol.

[0032] Preferably, in S2, the temperatures of each section of the extruder are set as follows: Zone 1 180℃-190℃, Zone 2 200℃-210℃, Zone 3 215℃-220℃, Zone 4 215℃-220℃, and the die head temperature 205℃-215℃; the melt filter is a 200-300 mesh melt filter.

[0033] Preferably, in step S3, the longitudinal stretching is performed at a temperature of 100℃-150℃ by the cooperation of a heating roller and a stretching roller. Longitudinal stretching causes the PVB molecular chains to align in the extrusion direction, thereby imparting anisotropic creep properties to the membrane material.

[0034] Preferably, in S4, the lateral relaxation process is carried out in a lateral relaxation device, and the temperature of the lateral relaxation process is 80-120°C.

[0035] Preferably, in S4, the cooling roller group includes a first cooling roller, a second cooling roller, and a third cooling roller connected in series. The temperature of the first cooling roller is 40℃-50℃, the temperature of the second cooling roller is 25℃-35℃, and the temperature of the third cooling roller is 20℃-30℃.

[0036] In a more preferred embodiment, in step S4, a PVB interlayer with a thickness of 0.3-1.2 mm is obtained after cooling and shaping.

[0037] In a further preferred embodiment, after the casting and cooling process, the following steps are also included: S5. Thickness Measurement and Feedback Control: The thickness of the PVB intermediate film obtained in S4 is continuously measured by an online beta-ray thickness gauge or an infrared thickness gauge, and the thickness signal is fed back to the die bolt heating controller and the speed controller of the stretching roller of the extruder. By automatically adjusting the die opening and stretching speed, the film thickness tolerance is controlled within ±15μm.

[0038] S6, Orientation Marking: Apply orientation identification marks to the edge of the PVB intermediate film extrusion direction after S5 measurement. The orientation identification marks are applied by inkjet printing, hot pressing micro-embossing or mechanical cutting. The spacing between two adjacent orientation identification marks is 200-500mm.

[0039] S7. Trimming and winding: Trim 20-40mm off each side edge of the PVB interlayer film marked in S6 to remove uneven edge thickness. Then remove foreign matter from the surface using a dust removal device. Finally, the film is wound up by a winding machine at a speed of 5-15m / min under a winding tension of 150-250N.

[0040] More preferably, in S6, the orientation identification mark is one of printed stripes, micro-embossing, or edge cuts. The orientation identification mark is used to indicate that the extrusion direction should be placed along the curvature of the curved glass during the lamination of curved laminated glass, so as to avoid incorrect laying direction.

[0041] The present invention also provides a PVB interlayer with anisotropic creep characteristics, which is prepared by the above preparation method. The PVB interlayer has a first direction and a second direction in the plane. The first direction is along the extrusion direction and the second direction is perpendicular to the extrusion direction. At a temperature of 90°C, the creep compliance of the first direction to the creep compliance of the second direction is 1.5-5.0.

[0042] The ratio of creep compliance in the first direction to creep compliance in the second direction of this invention falls precisely within the optimal balance range between "providing sufficient directional flow advantage" and "retaining the necessary deformation capacity perpendicular to the extrusion direction." Within this range, during curved surface lamination, the extrusion direction provides tensile flow along the bending direction to accommodate arc length differences, while sufficient compressive flow perpendicular to the extrusion direction is retained to absorb excess material in the circumferential direction. The two work together to achieve directional stress release, thickness uniformity, and minimization of optical distortion.

[0043] Preferably, at a temperature of 90°C, the creep compliance in the first direction is 8.0 × 10⁻⁶. -5 -5.0×10 -4 Pa -1 The creep compliance in the second direction is 2.0 × 10⁻⁶. -5 -2.5×10 -4 Pa -1 .

[0044] More preferably, the creep compliance at 90°C in the first direction is 1.3 × 10⁻⁶. -4 -4.0×10 -4 Pa -1 The creep compliance at 90°C in the second direction is 4.0 × 10⁻⁶. -5 -2.5×10 -4 Pa -1 .

[0045] The present invention also provides an application of a PVB interlayer with anisotropic creep properties. The aforementioned PVB interlayer with anisotropic creep properties is used to prepare curved laminated glass, which includes a first curved glass plate and a second curved glass plate, with the PVB interlayer sandwiched between the first curved glass plate and the second curved glass plate.

[0046] Preferably, the radii of curvature of both the first and second curved glass plates are 500-5000 mm. During lamination, a PVB interlayer film with a corresponding extrusion direction / creep compliance ratio perpendicular to the extrusion direction at 90° is selected according to the radii of curvature of the first and second curved glass plates, and the extrusion direction of the PVB interlayer film (identified by a direction identification mark) is placed along the curvature direction of the curved glass.

[0047] More preferably, when the curvature radius of the first curved glass plate and the second curved glass plate is 500-1500mm, a PVB interlayer film with a creep compliance ratio of 3.0-5.0 at 90°C perpendicular to the extrusion direction is selected; when the curvature radius of the first curved glass plate and the second curved glass plate is greater than 1500mm but not more than 5000mm, a PVB interlayer film with a creep compliance ratio of 1.5-3.0 at 90°C perpendicular to the extrusion direction is selected.

[0048] Furthermore, curved laminated glass is used in the manufacture of automotive sunroofs, automotive windshields, or architectural curved glass.

[0049] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled 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.

[0050] Raw materials used in the embodiments and comparative examples of this invention: PVB resin with a hydroxyl content of 30.9 mol% was obtained by reacting 150 g of polyvinyl alcohol A (average degree of polymerization 1700, degree of saponification 99 mol%) and 50 g of polyvinyl alcohol B (average degree of polymerization 800, degree of saponification 99 mol%) with n-butyraldehyde under acid catalysis, followed by aging, neutralization, washing with water, and drying. The resin has a hydroxyl content of 30.9 mol%, a degree of acetylation of 0.99 mol%, a degree of acetalization of 68.1 mol%, and a weight-average molecular weight of 245,000.

[0051] PVB resin with 25.2 mol% hydroxyl content: Prepared by adjusting the ratio of PVA degree of polymerization to n-butyraldehyde using the above method (this is existing technology and is not subject to many restrictions), and the hydroxyl content was determined to be 25.2 mol% by titration.

[0052] PVB resin with 34.8 mol% hydroxyl content: Prepared by adjusting the ratio of PVA degree of polymerization to n-butyraldehyde using the above method, and the hydroxyl content was determined to be 34.8 mol% by titration.

[0053] Triethylene glycol bis(2-ethylhexanoate) (abbreviated as 3GO): molecular formula is C 22 H 42 O6, with a molecular weight of 402, is produced by Sekisui Chemicals Co., Ltd.

[0054] Polyoxypropylene glycerol ether (PPG-1000): Molecular formula C3H5(OC3H6) n OH, with a number average molecular weight of 1000, is produced by Nippon Oil Co., Ltd.

[0055] UV absorber: Tinuvin 326 (2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole), manufactured by BASF.

[0056] Example 1 This invention provides a PVB interlayer with anisotropic creep properties, and its preparation method is as follows: Figure 1 As shown, it includes the following steps: S1. Raw material mixing: Add 100 parts of PVB resin (hydroxyl content 30.9 mol%), 30 parts of 3GO plasticizer, 10 parts of PPG-1000 plasticizer and 0.2 parts of ultraviolet absorber (Tinuvin 326) to a high-speed mixer and mix for 15 minutes at 50°C and 300 rpm to obtain a mixture.

[0057] S2. Melt Extrusion: The mixture obtained in S1 is fed into an extruder (65 mm in diameter, L / D ratio 36). The temperatures of each section of the extruder are set as follows: Zone 1 185℃, Zone 2 205℃, Zone 3 220℃, Zone 4 220℃, and the die head temperature 210℃. After the material is melted and plasticized in the extruder, it is filtered through a 200-mesh melt filter and then extruded through a T-shaped flat die (1500 mm wide) to form a molten sheet.

[0058] S3, Longitudinal Stretching Orientation: The molten sheet obtained in S2 is introduced into the longitudinal stretching unit, which consists of four heating rollers and two stretching rollers. The heating roller temperature is set to 120℃, and the stretching roller temperature is also set to 120℃. The stretching ratio (the ratio of the stretching roller linear speed to the heating roller linear speed) is set to 2.5 times. The stretched sheet is then obtained. S4. Casting and Cooling: The sheet stretched in S3 undergoes transverse relaxation in a transverse relaxation device at a temperature of 100℃, with a relaxation rate of 0.95 (i.e., 5% shrinkage in the film width direction). It then passes sequentially through a first cooling roller, a second cooling roller, and a third cooling roller connected in series. The first cooling roller is at 40℃, the second cooling roller at 25℃, and the third cooling roller at 25℃. After cooling and setting, a PVB interlayer film with a thickness of 0.76mm is obtained.

[0059] S5. Thickness Measurement and Feedback Control: The thickness of the PVB intermediate film obtained in S4 is continuously measured using an online beta-ray thickness gauge (ScanAb), and the thickness signal is fed back to the die bolt heating controller and the stretching roller speed controller of the extruder. By automatically adjusting the die opening and stretching speed, the film thickness tolerance is controlled within ±15μm.

[0060] S6, Direction Marking: Use an inkjet printer to print light blue direction indicator stripes with a width of 2mm at 300mm intervals along the extrusion direction edge of the PVB intermediate film after measurement in S5.

[0061] S7. Trimming and winding: Trim 30mm off each side edge of the PVB interlayer film marked in S6, remove foreign matter from the surface using a dust removal device, and finally wind it up by a winding machine at a speed of 10m / min under a winding tension of 200N.

[0062] Example 2 The difference from Example 1 is that in S1, the amount of 3GO plasticizer is 20 parts and the amount of PPG-1000 plasticizer is 20 parts; in S3, the temperature of the hot roller is set to 110°C, the temperature of the stretching roller is set to 110°C, the stretching ratio is 3.5 times, and the rest are the same as in Example 1.

[0063] Example 3 The difference from Example 1 is that in S1, the amount of 3GO plasticizer is 25 parts and the amount of PPG-1000 plasticizer is 15 parts; in S3, the temperature of the hot roller is set to 140°C, the temperature of the stretching roller is set to 140°C, the stretching ratio is 1.5 times, and the rest are the same as in Example 1.

[0064] Example 4 The difference from Example 1 is that in S1, the amount of 3GO plasticizer is 28 parts and the amount of PPG-1000 plasticizer is 12 parts; in S3, the temperature of the hot roller is set to 130°C, the temperature of the stretching roller is set to 130°C, the stretching ratio is 2.0 times, and the rest are the same as in Example 1.

[0065] Example 5 The difference from Example 1 is that in S1, the hydroxyl content of PVB resin is 25.2 mol%, the amount of 3GO plasticizer is 32 parts, and the amount of PPG-1000 plasticizer is 8 parts; in S3, the temperature of the hot roller is set to 125°C, the temperature of the stretching roller is set to 125°C, the stretching ratio is 2.2 times, and the rest are the same as in Example 1.

[0066] Example 6 The difference from Example 1 is that in S1, the hydroxyl content of PVB resin is 34.8 mol%, the amount of 3GO plasticizer is 24 parts, and the amount of PPG-1000 plasticizer is 16 parts; in S3, the temperature of the hot roller is set to 115°C, the temperature of the stretching roller is set to 115°C, the stretching ratio is 2.8 times, and the rest are the same as in Example 1.

[0067] Example 7 The PVB interlayer film obtained in Example 1 was sandwiched between a first curved glass plate and a second curved glass plate, and curved laminated glass (curvature radius 2000 mm) was prepared according to the existing lamination process. After one lamination, the laminated glass was reheated to 120°C, and the first curved glass plate, the second curved glass plate and the PVB interlayer film were separated.

[0068] Comparative Example 1 A PVB interlayer film, the preparation method of which includes the following steps: S1 differs from Example 1 in that only 40 parts of 3GO plasticizer were added, and PPG-1000 plasticizer was not added. All other aspects are the same as S1 in Example 1.

[0069] S2 is the same as S2 in Example 1.

[0070] S3 differs from Example 1 in that the stretching ratio is 1.0 (i.e., no longitudinal stretching is performed), while the rest are the same as S3 in Example 1. S4-S7 are the same as in Example 1.

[0071] Comparative Example 2 A PVB interlayer film, the preparation method of which includes the following steps: S1 differs from Example 1 in that the hydroxyl content of the PVB resin is 31.5 mol%, the weight average molecular weight is 267,000, the amount of 3GO plasticizer is 25 parts, the amount of PPG-1000 plasticizer is 15 parts, and the rest are the same as S1 in Example 1.

[0072] S2 is the same as S2 in Example 1.

[0073] S3 differs from Example 1 in that the heating roller temperature is set to 130°C, the stretching roller temperature is set to 130°C, and the stretching ratio is 2.0 times. All other aspects are the same as S3 in Example 1. S4-S7 are the same as in Example 1.

[0074] Comparative Example 3 A PVB interlayer film, the preparation method of which includes the following steps: S1. The difference from Example 1 is that the amount of 3GO plasticizer is 38 parts and the amount of PPG-1000 plasticizer is 2 parts, while the rest is the same as S1 in Example 1.

[0075] S2 is the same as S2 in Example 1.

[0076] S3 differs from Example 1 in that the heating roller temperature is set to 130°C, the stretching roller temperature is set to 130°C, and the stretching ratio is 1.2 times. All other aspects are the same as S3 in Example 1. S4-S7 are the same as in Example 1.

[0077] Comparative Example 4 A PVB interlayer film, the preparation method of which includes the following steps: S1. The difference from Example 1 is that the amount of 3GO plasticizer is 15 parts and the amount of PPG-1000 plasticizer is 25 parts, while the rest is the same as S1 in Example 1.

[0078] S2 is the same as S2 in Example 1.

[0079] S3 differs from Example 1 in that the heating roller temperature is set to 130°C, the stretching roller temperature is set to 105°C, and the stretching ratio is 4.0 times. All other aspects are the same as S3 in Example 1. S4-S7 are the same as in Example 1.

[0080] The performance of the PVB interlayers prepared in Examples 1-7 and Comparative Examples 1-4 was tested using the following methods: (1) Determination of creep compliance: The dynamic viscoelasticity measurement system MCR702eMultiDrive manufactured by Anton Paar was used. Circular samples with a diameter of 8 mm were cut from the PVB interlayer along the MD and TD directions, respectively. The sample thickness was 0.76 mm (if the film thickness was less than 0.76 mm, the actual thickness was used for measurement). The samples were placed in the measuring device, and a shear stress of 400 Pa was applied at the measurement temperatures of 70℃, 90℃, and 110℃ for 15 minutes. The creep compliance J(t) change curve over time was recorded. The J(t) value at 10 minutes was taken as the creep compliance in that direction. Each sample was measured three times, and the arithmetic mean was taken. The results are shown in Table 1-2.

[0081] Table 1. Creep compliance test results of PVB interlayer film prepared in Example 1 at different temperatures.

[0082] Note: In the table, MD refers to the extrusion direction, and TD refers to the direction perpendicular to the extrusion direction.

[0083] As shown in Table 1, with the temperature increasing from 70℃ to 110℃, the MD creep compliance, TD creep compliance, and MD / TD creep compliance ratio of Example 1 all increased significantly. This indicates that the PVB interlayer of the present invention has good temperature adaptability in terms of anisotropic properties. As the temperature increases, the mobility of molecular chain segments is enhanced, and the absolute value of creep compliance increases. However, the increase in the extrusion direction is significantly greater than that perpendicular to the extrusion direction, causing the MD / TD creep compliance ratio to increase with increasing temperature. This characteristic results in the PVB interlayer having a moderate MD / TD creep compliance ratio in the typical temperature range of curved lamination (around 90℃), with more significant anisotropy at higher temperatures, which is beneficial for directional flow during the lamination process.

[0084] Table 2. Creep compliance test results of PVB interlayers prepared in Examples 2-6 and Comparative Examples 1-4

[0085] Note: In the table, MD refers to the extrusion direction, and TD refers to the direction perpendicular to the extrusion direction.

[0086] As shown in Table 2, Example 2 has the highest MD / TD creep compliance ratio at 90℃ (4.75), because the high proportion of PPG-1000 suppresses creep compliance in the TD direction and the high stretch ratio improves the orientation in the MD direction; Example 3 has the lowest MD / TD creep compliance ratio at 90℃ (1.65), because the low stretch ratio limits the orientation, but it is still significantly greater than 1.5, proving the effectiveness of the compound plasticizer system; Examples 4-6 have ratios between 2.40 and 3.44, confirming the adjustability of the process.

[0087] Examples 5-6 verified the feasibility of the hydroxyl content boundary conditions. The creep compliance in the MD direction was higher at low hydroxyl content (25.2 mol%), while at high hydroxyl content (34.8 mol%), a higher stretch ratio and more PPG-1000 were required to balance the anisotropy. Both obtained acceptable ratios.

[0088] Comparative Example 1 has an isotropic MD / TD creep compliance ratio of 1.00 at 90℃; Comparative Example 3 has insufficient anisotropy due to low PPG-1000 and low stretch ratio; Comparative Example 4 has lost its deformation capacity in the TD direction due to high PPG-1000 and high stretch ratio; Although Comparative Example 2 is at the boundary value, the resin parameters deviate, and the surface bonding effect is still not up to standard.

[0089] (2) Determination of creep recovery rate: The PVB interlayer film prepared in Example 1 was subjected to a shear stress of 400 Pa at 90°C for 15 minutes, and the stress was removed. The strain recovery was recorded for another 15 minutes. The creep recovery rate was calculated using the following formula: Creep recovery rate (%) = (strain at the end of loading - strain at the end of recovery) / strain at the end of loading × 100%.

[0090] The creep recovery rate of the PVB interlayer film prepared in Example 1 was 68% in the extrusion direction and 72% perpendicular to the extrusion direction. This indicates that the creep recovery rate in the MD direction is slightly lower than that in the TD direction. This is because the molecular chains in the MD direction are more regularly aligned along the orientation direction after longitudinal stretching, resulting in greater deentanglement and slippage of the chain segments under shear stress. After stress removal, the contribution of some irreversible viscous flow is significant. In contrast, the molecular chains in the TD direction maintain a more entangled network structure, leading to more complete elastic recovery after stress removal. The moderate creep recovery rate (68%) in the MD direction indicates that this direction has good stress release capability. During curved surface lamination, it can achieve sufficient irreversible flow to conform to the curved shape while retaining some elasticity to cope with thermal stress, thus possessing both fluidity and dimensional stability.

[0091] (3) Preparation and evaluation of curved laminated glass: Preparation of curved laminated glass: Float glass with dimensions of 300mm (length) × 300mm (width) × 3mm (thickness) was used. Convex glass plates with radii of curvature of 500mm, 1500mm, 2000mm, 3000mm, and 5000mm were used according to testing requirements. These plates were cleaned and dried before use. The extrusion direction of the PVB interlayer was confirmed using orientation identification marks, and the interlayer was placed along the curvature direction of the curved glass, stacked in the order of "first curved glass plate / PVB interlayer / second curved glass plate". The stacked components were placed in a vacuum bag and degassed for 5 minutes at 90℃ and 4kPa. Then, at the same temperature, the pressure was increased to 100kPa at a rate of 2kPa / s, and held at 90℃ and 100kPa for 3 minutes for pre-compression. Finally, the curved laminated glass sample was subjected to autoclave treatment at 140℃ and 1.3MPa for 20 minutes to obtain the sample.

[0092] b. Evaluation indicators: Thickness deviation (ΔX): The thickness of the PVB film in curved laminated glass was measured at the edge and center using the OptiGauge multilayer film thickness measuring instrument manufactured by Lumetrics, USA. The absolute difference between the two was calculated. Three different locations were measured for each sample, and the maximum difference was taken as the thickness deviation ΔX.

[0093] Optical distortion: Measured using an NDH-7000 optical distortion meter manufactured by Nippon Denshoku Co., Ltd. The curved laminated glass sample was placed between the light source and the observation screen, and the distortion angle of the image formed through the glass was measured in arcminutes. The acceptable standard is a distortion angle not exceeding 1.5 arcminutes.

[0094] Visual inspection: In a light box with an illumination of 1000 lux and a black background, visually inspect the curved laminated glass samples for bubbles, delamination, ripples, wrinkles, or cracks. Three trained inspectors independently evaluate the samples, and records are made if the results are consistent. Results are shown in Table 3-5.

[0095] Table 3 Test data of curved laminated glass prepared in Examples 1-6 and Comparative Examples 1-4 (radius of curvature 2000 mm).

[0096] Table 4 Comparison of thickness deviation ΔX under different radii of curvature (unit: μm)

[0097] Table 5 Thickness deviation ΔX under different lamination pressures (Example 1, radius of curvature 2000 mm)

[0098] As shown in Tables 3 to 5, the curved laminated glass prepared using the PVB interlayer film of the present invention can have its thickness deviation between the edge and the center controlled to be less than 50 μm and its optical distortion controlled to be less than 1.5 points (Examples 1-6), which is far superior to products using traditional isotropic PVB films (thickness deviation is usually greater than 100 μm and optical distortion is greater than 2.5 points, Comparative Example 1).

[0099] Curved lamination requires the extrusion direction to provide tensile flow along the curvature to accommodate differences in arc length, while retaining necessary compressive flow perpendicular to the extrusion direction to absorb excess circumferential material. This invention, through comparisons of Examples 1-3 and Comparative Example 1 at different radii of curvature, establishes a clear matching strategy: when the radius of curvature is 500mm to 1500mm, a PVB interlayer film with an extrusion direction / perpendicular direction ratio of 3.0-5.0 is selected (Example 2, ΔX≤35μm); when the radius of curvature is greater than 1500mm but not exceeding 5000mm, a PVB interlayer film with an extrusion direction / perpendicular direction ratio of 1.5-3.0 is selected (Examples 1 and 3, ΔX≤52μm). This invention achieves satisfactory curved lamination results across a wide pressure range of 0.8MPa to 1.6MPa (Table 5, ΔX≤46μm), indicating that the anisotropic design reduces the lamination process's sensitivity to pressure fluctuations. Meanwhile, the PPG-1000 macromolecular plasticizer forms hydrogen bonds with the residual hydroxyl groups of PVB through its polyether segments, and combined with the steric hindrance effect of the macromolecular segments, effectively inhibits the migration and precipitation of the plasticizer at high temperatures.

[0100] (4) Plasticizer migration test: The PVB interlayer film samples (100mm × 100mm × 0.76mm) of Example 1 and Comparative Example 1 were placed in an 80℃ constant temperature oven and stored for 7 days. The mass change before and after storage was measured, and the plasticizer migration rate was calculated according to the following formula: Plasticizer migration rate (%) = (initial mass - mass after 7 days) / initial mass × 100%.

[0101] The transmittance before and after storage was measured using a haze meter (Nippon Denshoku NDH-7000). The results are shown in Table 6.

[0102] Table 6 Comparison of plasticizer migration and optical properties of PVB interlayer films prepared in Example 1 and Comparative Example 1 (80℃ / 7 days)

[0103] As shown in Table 6, the high-temperature storage test at 80℃ for 7 days confirms that the plasticizer migration rate of the present invention is only 1.8%, and the light transmittance decreases by only 0.7 percentage points, which is far superior to Comparative Example 1 (which uses only 3GO, with a migration rate of 5.6% and a light transmittance decrease of 3.8 percentage points), ensuring long-term stability.

[0104] (5) Reworkability test: The PVB interlayer film separated in Example 7 was re-stacked between two new curved glass plates in the same direction, and a second lamination was performed under the same lamination conditions. The creep compliance of the PVB interlayer film and the thickness deviation and optical distortion of the curved laminated glass were measured after the first lamination and the second lamination, respectively. The results are shown in Table 7.

[0105] Table 7 Results of PVB Interlayer Reworkability Test

[0106] Note: In the table, MD refers to the extrusion direction, and TD refers to the direction perpendicular to the extrusion direction. As shown in Table 7, after the first lamination, the orientation structure of the PVB molecular chains undergoes partial relaxation (entropy elastic recovery) at the lamination temperature of 140℃. However, the physical entanglement network between the PVB molecular chains reforms upon cooling. Furthermore, the hydrogen bonding between PPG-1000 and the PVB hydroxyl groups delays the complete relaxation of the molecular chains, allowing residual orientation to be retained. Reworkability tests show that after the second lamination, the ratio of extrusion direction to perpendicular to the extrusion direction is retained at 79.6% (decreasing from 2.89 to 2.30), with a thickness deviation of 39 μm and optical distortion of 1.0 point, still meeting the quality requirements for curved laminated glass and significantly reducing production losses.

[0107] 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 PVB interlayer with anisotropic creep properties, characterized in that: Includes the following steps: S1. Raw material mixing: PVB resin, plasticizer and additives are mixed evenly in a mixer to obtain a mixture. S2, Melt Extrusion: The mixture obtained in S1 is fed into an extruder, melted and plasticized in the extruder, filtered through a melt filter, and finally extruded through a T-shaped flat die to form a molten sheet; S3, Longitudinal stretching orientation: The molten sheet obtained in S2 is stretched longitudinally with a stretching ratio of 1.5-3.5 times to obtain the stretched sheet; S4. Casting and Cooling: The sheet stretched in S3 is subjected to transverse relaxation treatment with a relaxation rate of 0.90-0.

98. Finally, it is cooled and shaped by a cooling roller group to obtain the PVB interlayer film.

2. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S1, the plasticizer is a mixture of triethylene glycol bis(2-ethylhexanoate) and polyoxypropylene glycerol ether, with a mass ratio of triethylene glycol bis(2-ethylhexanoate) to polyoxypropylene glycerol ether of 1:0.3-1:1.

2.

3. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S1, mixing is carried out at a temperature of 40-60℃ and a rotation speed of 200-400rpm for 10-20 minutes.

4. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S2, the temperatures of each section of the extruder are set as follows: Zone 1 180℃-190℃, Zone 2 200℃-210℃, Zone 3 215℃-220℃, Zone 4 215℃-220℃, and the die head temperature 205℃-215℃; the melt filter is a 200-300 mesh melt filter.

5. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S3, longitudinal stretching is accomplished at a temperature of 100℃-150℃ by the cooperation of a heating roller and a stretching roller.

6. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S4, the transverse relaxation process is carried out in a transverse relaxation device at a temperature of 80-120℃.

7. The method for preparing a PVB interlayer with anisotropic creep properties according to claim 1, characterized in that: In S4, the cooling roller group includes a first cooling roller, a second cooling roller, and a third cooling roller connected in series. The temperature of the first cooling roller is 40℃-50℃, the temperature of the second cooling roller is 25℃-35℃, and the temperature of the third cooling roller is 20℃-30℃.

8. A PVB interlayer with anisotropic creep properties, characterized in that: The PVB interlayer film prepared by the preparation method according to any one of claims 1-7 has a first direction and a second direction in the plane, the first direction being along the extrusion direction and the second direction being perpendicular to the extrusion direction, and at a temperature of 90°C, the ratio of the creep compliance of the first direction to the creep compliance of the second direction is 1.5-5.

0.

9. A PVB interlayer with anisotropic creep properties according to claim 8, characterized in that: At 90℃, the creep compliance in the first direction is 8.0 × 10⁻⁶. -5 -5.0×10 -4 Pa -1 The creep compliance in the second direction is 2.0 × 10⁻⁶. -5 -2.5×10 -4 Pa -1 .

10. An application of a PVB interlayer with anisotropic creep properties, characterized in that: A PVB interlayer with anisotropic creep properties as described in any one of claims 8-9 is used to prepare curved laminated glass, the curved laminated glass comprising a first curved glass plate and a second curved glass plate, the PVB interlayer being sandwiched between the first curved glass plate and the second curved glass plate.

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