A wedge-shaped polyvinyl butyral interlayer and a method for preparing and using the same

Abstract

This invention relates to the field of interlayer film technology in laminated glass, and particularly to a wedge-shaped polyvinyl butyral interlayer film, its preparation method, and its application. The method includes the following steps: under stirring conditions, a portion of a polyvinyl alcohol aqueous solution and a portion of butyral are first added, and preliminary condensation is carried out under acid catalyst A; then, the temperature is gradually reduced, while the remaining polyvinyl alcohol aqueous solution and remaining butyral are added, and the reaction is maintained at a constant temperature to precipitate resin particles; the resin particles are heated and acid catalyst B is added for a curing reaction to obtain polyvinyl butyral resin; the polyvinyl butyral resin, plasticizer, and additives are mixed, melted, and then extruded through an extrusion die with an adjustable die opening. This invention solves the technical problem in the prior art where the wedge angle profile deteriorates due to self-adhesion during storage and transportation of wedge-shaped interlayer films, thereby achieving the dual goals of simultaneously meeting the requirements of a low absolute wedge angle change rate in the head-up display area and high wedge angle accuracy retention after storage and transportation.

Description

Technical Field

[0001] This invention relates to the field of interlayer film technology in laminated glass, and in particular to a wedge-shaped polyvinyl butyral interlayer film, its preparation method, and its application. Background Technology

[0002] Head-up display (HUD) systems project driving information onto the windshield, allowing drivers to access information without looking down. To eliminate ghosting caused by light reflection from the inner and outer surfaces of the glass, a wedge-shaped polyvinyl butyral (PVB) interlayer is typically used to create a small angle between the inner and outer glass panels. Currently, numerous patent studies have been conducted both domestically and internationally on the processing, dimensional inspection, and heat insulation modification of wedge-shaped PVB interlayers. For example, Chinese patent CN116533612A discloses a heat-insulating PVB wedge film for vehicle head-up displays and its preparation method; CN119348095A discloses a method for manufacturing multi-angle wedge-shaped PVB interlayers; CN119261155A discloses a method and system for controlling the thickness of wedge-shaped PVB interlayers; and CN222069640U discloses a device for measuring the generalized wedge angle of HUD wedge-shaped PVB interlayers. US Patent US2023 / 0288699A1 discloses a sandwich with enhanced optical performance and points out that “dynamic ghosting” occurs when the wedge angle changes too much in the HUD area. It proposes to control the absolute wedge angle change rate below 3.0 μrad / mm to suppress dynamic ghosting, but only limits the wedge angle change index and does not pay attention to the surface self-adhesion defects of PVB film during the winding and storage stage.

[0003] PVB interlayer film rolls are prone to surface self-adhesion after being compressed during warehousing and long-distance container transportation. The stress generated by unwinding and peeling can cause local plastic deformation of the film, damaging the pre-made precision wedge angle profile, and ultimately leading to the degradation of the finished glass HUD imaging. Existing solutions for improving PVB self-adhesion focus on controlling the three-dimensional structure of the resin. Japanese patent JPA1990123103 discloses a method to improve self-adhesion by controlling the stereoregularity of hydroxyl groups in PVB resin (6-12 mol% heteroregular triunits and 3-5 mol% syndiotactic triunits). Chinese patent CN1675258A also involves the control of PVB resin stereoisomerism. However, the research objects of the above literature are all conventional flat PVB films, which are not adapted to the wedge-shaped interlayer film for HUDs. They have not established the correlation between resin stereoregularity, film self-adhesion, and wedge angle accuracy after storage and transportation, nor have they proposed a quantitative evaluation standard for the degradation of the wedge angle profile after storage and transportation.

[0004] In summary, existing technologies cannot simultaneously meet the dual requirements of low in-situ wedge angle change rate and long-term stability of wedge angle profile after storage and transportation. There is an urgent need for a wedge-shaped PVB interlayer film solution that can suppress storage and transportation deformation and adapt to HUD optical requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a wedge-shaped polyvinyl butyral interlayer film, its preparation method, and its application. By directional control, polyvinyl butyral resin with a specific stereoregularity is prepared, and then mixed with a plasticizer and extruded to obtain a wedge-shaped interlayer film. This solves the technical problem in the prior art where the wedge angle profile deteriorates due to self-adhesion during storage and transportation of the wedge-shaped interlayer film, thereby achieving the dual goals of simultaneously satisfying the low absolute wedge angle change rate in the head-up display area and the high wedge angle accuracy retention after storage and transportation.

[0006] To achieve the above objectives, the present invention provides a wedge-shaped polyvinyl butyral interlayer film, its preparation method, and its application, comprising the following steps: S1. Under stirring conditions, a portion of polyvinyl alcohol aqueous solution and a portion of butyraldehyde are first added, and preliminary condensation is carried out under acid catalyst A; then the temperature is gradually reduced, and the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde are added, and the reaction is kept at the temperature to precipitate resin particles. S2. The resin particles from S1 are heated and acid catalyst B is added to carry out a aging reaction to regulate the stereoregularity of the resin and obtain polyvinyl butyral resin. S3. Mix the polyvinyl butyral resin, plasticizer, and additives from S2 to obtain a plasticized mixture; S4. After the plasticized mixture of S3 is melted, it is extruded through an extrusion die with adjustable die opening to obtain a wedge-shaped polyvinyl butyral intermediate film.

[0007] Preferably, in S1, the mass ratio of the total amount of polyvinyl alcohol, the total amount of butyraldehyde, and the acid catalyst A in the polyvinyl alcohol aqueous solution is 300~360:170~200:180~220.

[0008] Preferably, in S1, during the initial condensation, the amount of polyvinyl alcohol aqueous solution added is 70-85 wt% of the total amount of polyvinyl alcohol aqueous solution, the amount of butyraldehyde added is 70-80 wt% of the total amount of butyraldehyde, the initial condensation reaction temperature is 15-20℃, the reaction time is 40-50 min, and the acid catalyst A is hydrochloric acid with a mass concentration of 0.2 wt%. The step-by-step cooling process involves first cooling to 5-10°C, then adding the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde, and finally cooling to 0-5°C.

[0009] Preferably, in S2, the temperature is raised to 60~95℃, the acid catalyst B is 3wt% hydrochloric acid, the amount of acid catalyst B added is 0.5~2wt% of the resin particles, and the ripening reaction time is 1~3h.

[0010] Preferably, in S2, the polyvinyl butyral resin has a butyralization degree of 65-75 mol%, the residual hydroxyl group has a chain length of more than 3 hydroxyl groups, the heterodioretic triunit content is 6-12 mol%, and the syndioretic triunit content is 3-5 mol%.

[0011] Preferably, in S3, the weight parts of polyvinyl butyral resin, plasticizer, and additive are 100 parts of polyvinyl butyral resin, 25-50 parts of plasticizer, and 0.1-0.5 parts of additive.

[0012] Preferably, in S3, the plasticizer is selected from one of triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutyrate, tetraethylene glycol di-n-heptanoate, diethylene glycol dibenzoate, triethylene glycol dipropionate, diethyl adipate, and triethylene glycol diisobutyrate; the additives include ultraviolet absorbers and antioxidants.

[0013] Preferably, in S4, the melting temperature is 180~220℃, the extrusion die temperature is 190~210℃, the die lip opening of the extrusion die is 0.3~1.0mm, and the die lip opening changes linearly along the vertical section of the film extrusion direction, with the rate of change corresponding to the target wedge angle.

[0014] The present invention also provides a wedge-shaped polyvinyl butyral intermediate film, which is prepared by the above-mentioned method for preparing a wedge-shaped polyvinyl butyral intermediate film. The wedge-shaped polyvinyl butyral intermediate film has a head-up display area, and the absolute wedge angle change rate of the wedge-shaped polyvinyl butyral intermediate film in the head-up display area is less than 3.0 μrad / mm.

[0015] The present invention also provides an application of the above-mentioned wedge-shaped polyvinyl butyral interlayer film, which is used to prepare laminated glass for head-up displays. The laminated glass includes a first glass plate, a second glass plate, and a wedge-shaped polyvinyl butyral interlayer film, wherein the wedge-shaped polyvinyl butyral interlayer film is disposed between the first glass plate and the second glass plate.

[0016] Therefore, the present invention, employing the above-mentioned wedge-shaped polyvinyl butyral interlayer film, its preparation method, and its application, has the following beneficial effects: (1) This invention employs segmented temperature-controlled precipitation polymerization and stepwise feeding to precisely control the stereoregularity of residual hydroxyl groups in polyvinyl butyral resin, thereby controlling the content of heterodioretic triunits to 6-12 mol% and the content of syndioretic triunits to 3-5 mol%. Compared with resins synthesized by conventional one-step methods, the interlayer film prepared by polyvinyl butyral resin in this invention exhibits significantly reduced self-adhesion (T-peel force below 350 g / cm), effectively avoiding peeling deformation caused by adhesion during winding and storage, and ensuring that the wedge angle profile change (ΔROC) after storage and transportation is less than 0.5 μrad / mm.

[0017] (2) The wedge-shaped polyvinyl butyral interlayer film prepared by the present invention has an increment ΔROC of the maximum absolute wedge angle change rate in the HUD area of ​​no more than 0.5 μrad / mm, and an increment ΔDev of the deviation between the maximum actual vertical wedge angle and the target vertical wedge angle of no more than 0.03 mrad, which ensures that the interlayer film can maintain a precise wedge angle profile after storage and transportation, thereby ensuring the head-up display optical performance of the final laminated glass.

[0018] (3) The polyvinyl butyral intermediate membrane provided by the present invention can withstand the addition of ≤20% recycled material and maintains excellent performance after being stored at 40℃ and 75%RH for 90 days, and has good long-term stability and industrial applicability.

[0019] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0020] 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.

[0021] A method for preparing a wedge-shaped polyvinyl butyral interlayer film includes the following steps: S1. Under stirring conditions, a portion of polyvinyl alcohol aqueous solution and a portion of butyraldehyde are first added, and preliminary condensation is carried out under acid catalyst A; then the temperature is lowered step by step, and the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde are added at the same time, and the reaction is kept at the temperature to precipitate resin particles. S2. The resin particles from S1 are heated and acid catalyst B is added to carry out a aging reaction to regulate the stereoregularity of the resin and obtain polyvinyl butyral resin. S3. Mix the polyvinyl butyral resin, plasticizer, and additives from S2 to obtain a plasticized mixture; S4. After the plasticized mixture of S3 is melted, it is extruded through an extrusion die with adjustable die opening to obtain a wedge-shaped polyvinyl butyral intermediate film.

[0022] This invention prepares PVB resin with specific stereoregularity (6-12% heteroregular and 3-5% syndiotactic) through segmented temperature-controlled precipitation polymerization and stepwise feeding. This results in a wedge-shaped interlayer film with an absolute wedge angle change rate of less than 3.0 μrad / mm within the head-up display area. Furthermore, the increment of the maximum absolute wedge angle change rate ΔROC after storage and transportation is ≤0.5 μrad / mm, and the increment of the deviation between the maximum actual vertical wedge angle and the target vertical wedge angle ΔDev is ≤0.03 mrad. This effectively eliminates dynamic ghosting, significantly reduces self-adhesion, and improves storage and transportation stability, demonstrating good industrial applicability and economic benefits.

[0023] In this invention, the "head-up display area" refers to the continuous vertical section corresponding to the head-up display projection area when the intermediate film is installed on the windshield of a vehicle; this section typically starts 100-200mm above the lower edge of the windshield and extends 200-400mm, depending on the vehicle model, but does not exceed 70% of the total height of the intermediate film. Those skilled in the art can determine this area based on the target vehicle model.

[0024] The absolute wedge angle variation rate is defined as the absolute value of the linear regression slope of the wedge angle within a 50mm span along the vertical direction in the head-up display area. The deviation between the actual vertical wedge angle and the target vertical wedge angle refers to the absolute value of the difference between the wedge angle value measured at the same vertical position and the design target value.

[0025] Preferably, in S1, the mass ratio of the total amount of polyvinyl alcohol, the total amount of butyraldehyde, and the acid catalyst A in the polyvinyl alcohol aqueous solution is 300~360:170~200:180~220.

[0026] Preferably, in S1, during the initial condensation, the amount of polyvinyl alcohol aqueous solution added is 70-85 wt% of the total amount of polyvinyl alcohol aqueous solution, the amount of butyraldehyde added is 70-80 wt% of the total amount of butyraldehyde, the initial condensation reaction temperature is 15-20℃, the reaction time is 40-50 min, and the acid catalyst A is hydrochloric acid with a mass concentration of 0.2 wt%. The step-by-step cooling process involves first cooling to 5-10°C, then adding the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde, and finally cooling to 0-5°C.

[0027] This invention controls the local monomer concentration in the reaction system by adding polyvinyl alcohol aqueous solution and butyraldehyde in stages, which helps to form more uniform primary polymer chains.

[0028] In an even better configuration, in S1, the stirring speed is controlled at 80~120 rpm.

[0029] Preferably, in S2, the temperature is raised to 60~95℃, the acid catalyst B is 3wt% hydrochloric acid, the amount of acid catalyst B added is 0.5~2wt% of the resin particles, and the ripening reaction time is 1~3h.

[0030] This invention precisely controls the stereoregularity of residual hydroxyl groups in the resin to a target range by controlling the temperature and time of the curing reaction. During the curing stage, supplementing with acid catalyst B and providing suitable heat energy promotes the further acetalization of unreacted hydroxyl groups on the polyvinyl alcohol chain with butyraldehyde, driving molecular chain rearrangement. By precisely controlling the temperature, time, and catalyst dosage of this curing reaction, the reaction can be preferentially guided towards the formation of specific stereoconfigurations (heterodactyl and syndiodactyl triunits), thereby precisely controlling the stereoregularity of the final resin. This specific stereoregularity is key to imparting low self-adhesion and high dimensional stability to the interlayer.

[0031] Preferably, in S2, the polyvinyl butyral resin has a butyralization degree of 65-75 mol%, and among the residual hydroxyl groups with a chain length of 3 or more, the heterodioretic triunit content is 6-12 mol% and the syndioretic triunit content is 3-5 mol%.

[0032] More preferably, the average degree of polymerization of the polyvinyl butyral resin is 1000~2500.

[0033] Preferably, in S3, the weight parts of polyvinyl butyral resin, plasticizer, and additive are 100 parts of polyvinyl butyral resin, 25-50 parts of plasticizer, and 0.1-0.5 parts of additive.

[0034] Preferably, in S3, the plasticizer is selected from one of triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutyrate, tetraethylene glycol di-n-heptanoate, diethylene glycol dibenzoate, triethylene glycol dipropionate, diethyl adipate, and triethylene glycol diisobutyrate; the additives include ultraviolet absorbers and antioxidants.

[0035] More preferably, the ultraviolet absorber includes one or more of 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol and 2-hydroxy-4-n-octyloxybenzophenone, and the antioxidant includes one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite.

[0036] Preferably, in S4, the melting temperature is 180~220℃, the extrusion die temperature is 190~210℃, the die lip opening of the extrusion die is 0.3~1.0mm, and the die lip opening changes linearly along the vertical section of the film extrusion direction, with the rate of change corresponding to the target wedge angle. The accuracy of the die lip opening and its linear change directly determines the thickness distribution and wedge angle profile accuracy of the wedge-shaped intermediate film.

[0037] This invention controls the extrusion molding parameters within the aforementioned range, resulting in a wedge-shaped polyvinyl butyral intermediate film with an absolute wedge angle variation rate of less than 3.0 μrad / mm within the head-up display area and uniform thickness distribution. The aforementioned melt and die temperature range ensures good flowability and melt strength of the plasticized mixture, facilitating stable extrusion of the material from the die lip. Precise control and linear adjustment of the die lip opening is a direct means of achieving continuous, linear film thickness variation (i.e., forming a precise wedge angle). The combination of stable temperature and precise die lip opening control guarantees the uniformity of the extruded film thickness and the accuracy of the wedge profile, thereby controlling the absolute wedge angle variation rate to a low level from a physical molding perspective.

[0038] In a further preferred embodiment, the wedge-shaped polyvinyl butyral interlayer is annealed at a temperature of 40–60°C for 12–24 hours. Annealing eliminates residual stress in the wedge-shaped polyvinyl butyral interlayer, further improving dimensional stability and wedge profile retention.

[0039] The present invention also provides a wedge-shaped polyvinyl butyral intermediate film, which is prepared by the above-mentioned method for preparing a wedge-shaped polyvinyl butyral intermediate film. The wedge-shaped polyvinyl butyral intermediate film has a head-up display area, and the absolute wedge angle change rate of the wedge-shaped polyvinyl butyral intermediate film in the head-up display area is less than 3.0 μrad / mm.

[0040] Preferably, after undergoing simulated storage and transportation conditions, the wedge-shaped polyvinyl butyral interlayer membrane exhibits an increment ΔROC of the maximum absolute wedge angle change rate within its head-up display area that does not exceed 0.5 μrad / mm, and an increment ΔDev of the deviation between the maximum actual vertical wedge angle and the target vertical wedge angle that does not exceed 0.03 mrad.

[0041] The present invention also provides an application of a wedge-shaped polyvinyl butyral interlayer film for preparing laminated glass for head-up displays. The laminated glass includes a first glass plate, a second glass plate, and a wedge-shaped polyvinyl butyral interlayer film disposed between the first glass plate and the second glass plate.

[0042] Preferably, the laminated glass is prepared by conventional autoclave lamination process, with lamination temperature of 130~150℃, pressure of 1.0~1.5MPa, and time of 30~60min. After lamination, the change rate of the wedge angle in the head-up display area is no more than 0.3μrad / mm compared with that before lamination.

[0043] Example 1 This invention provides a wedge-shaped polyvinyl butyral interlayer membrane, the preparation method of which includes the following steps: S1. Disperse 330g of polyvinyl alcohol (PVA) with an average degree of polymerization of 1700 and a saponification degree of 99.2 mol% in 2885g of distilled water. Heat to 95℃ with stirring until completely dissolved, then cool to 18℃ to obtain an aqueous PVA solution. Under stirring at 100 rpm, first add 80wt% PVA aqueous solution, 139.5g of butyraldehyde (total butyraldehyde amount is 186g, accounting for 75% of the total butyraldehyde content), and 200g of 0.2wt% hydrochloric acid. Perform a preliminary condensation reaction at 18℃ for 45min. Then cool to 8℃, add the remaining PVA aqueous solution and butyraldehyde, continue the reaction for 30min, then cool to 2℃ and maintain the temperature for 1h to precipitate resin particles.

[0044] S2. Maintaining a rotation speed of 100 rpm, heat the resin particles from S1 to 90°C and add 50 g of 3 wt% hydrochloric acid (approximately 0.9 wt% of the resin particle mass). Allow the reaction to mature for 90 min, adjusting the resin's stereoregularity. Neutralize with a 10 wt% sodium carbonate aqueous solution to pH 6.5-7.0, then wash with deionized water until the conductivity of the wash water is <10. Finally, dry in a vacuum drying oven at 60°C until the water content is <0.5 wt%, obtaining polyvinyl butyral resin A1. 1 H-NMR analysis showed that the degree of butyralization was 71 mol, the content of heterodioretic triunits was 8.5 mol, and the content of syndioretic triunits was 4.0 mol.

[0045] S3. Mix 100 parts of polyvinyl butyral resin A1 from S2, 38 parts of triethylene glycol di-2-ethylhexanoate (3GO), 0.3 parts of ultraviolet absorber (2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol) and 0.1 parts of antioxidant (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester) to obtain a plasticized mixture.

[0046] S4. The plasticized mixture from S3 is premixed in a high-speed mixer for 5 minutes, then melted and extruded through an adjustable die head. The screw speed of the high-speed mixer is 200 rpm, and the temperatures of each zone (from the feed section to the die head) are as follows: feed zone: 170℃; melting zone: 200℃; metering zone: 210℃; die head temperature: 200℃; the die lip opening changes linearly from 0.38 mm to 0.82 mm, the extrusion rate is controlled at 50 kg / h, and the traction speed is 1.8 m / min; a wedge-shaped polyvinyl butyral intermediate film with a thickness of 0.76 mm is obtained. Wedge profile achievement: The die lip opening is automatically adjusted in the vertical direction by a servo-controlled variable die lip extrusion die head to form the target wedge angle (0.30 mrad) of the film material.

[0047] After the extruded wedge-shaped polyvinyl butyral intermediate film is cooled and shaped, it is immediately sent to an annealing oven at 50°C and placed horizontally for 18 hours to completely eliminate residual stress.

[0048] Example 2 The difference from Example 1 is that polyvinyl alcohol with an average degree of polymerization of 2300 was used in S1; in S2, the temperature was raised to 85°C and the curing reaction was carried out for 100 min to obtain polyvinyl butyral resin A2. 1 ¹H-NMR analysis showed that the degree of butyralization was 70 mol%, the content of heterodioretic triunits was 7.8 mol%, and the content of syndioretic triunits was 4.2 mol%. All other parameters were the same as in Example 1.

[0049] Example 3 The difference from Example 1 is that in S2, the temperature was raised to 70°C and the curing reaction was carried out for 60 minutes to obtain polyvinyl butyral resin A3. After... 1 ¹H-NMR analysis showed that the degree of butyralization was 68 mol%, the content of heterodioretic triunits was 6.5 mol%, and the content of syndioretic triunits was 3.2 mol%. All other parameters were the same as in Example 1.

[0050] Example 4 The difference from Example 1 is that in S2, the temperature was raised to 95°C, and the curing reaction was carried out for 120 minutes to obtain polyvinyl butyral resin A4. After... 1 ¹H-NMR analysis showed that the degree of butyralization was 73 mol%, the content of heterodioretic triunits was 11.5 mol%, and the content of syndioretic triunits was 4.8 mol%. All other parameters were the same as in Example 1.

[0051] Example 5 The difference from Example 1 is that the plasticizer in S3 is tetraethylene glycol di-n-heptyl ester, while the rest is the same as in Example 1.

[0052] Example 6 The difference from Example 1 is that the amount of the plasticizer triethylene glycol di-2-ethylhexanoate in S3 is 25 parts, while the rest is the same as in Example 1.

[0053] Example 7 The difference from Example 1 is that in S4, the traction speed is 3.6 m / min; a wedge-shaped polyvinyl butyral interlayer with a thickness of 0.38 mm is obtained, and the rest is the same as in Example 1.

[0054] Example 8 The difference from Example 1 is that in S4, the die head temperature is 195°C, the die lip opening changes linearly from 0.40mm to 0.85mm, and the traction speed is adjusted to 2.5m / min. All other aspects are the same as in Example 1.

[0055] Comparative Example 1 The difference from Example 1 is that in S1, under stirring at 100 rpm, the polyvinyl alcohol aqueous solution and 186 g of butyraldehyde were added all at once, followed by 200 g of 3.6 wt% hydrochloric acid. The reaction was carried out for 6 hours, without proceeding to S2, resulting in polyvinyl butyral resin B1. 1 ¹H-NMR analysis showed that the degree of butyralization was 70 mol%, the content of heterodioretic triunits was 13.5 mol%, and the content of syndioretic triunits was 6.5 mol%. All other parameters were the same as in Example 1.

[0056] Comparative Example 2 The difference from Example 1 is that in S2, the temperature was raised to 80°C and the curing reaction was carried out for 30 minutes to obtain polyvinyl butyral resin B2. 1 ¹H-NMR analysis showed that the degree of butyralization was 69 mol%, the content of heterodiuronic triunits was 9.0 mol%, and the content of syndiuronic triunits was 5.8 mol%. All other parameters were the same as in Example 1.

[0057] Comparative Example 3 The difference from Example 1 is that in S2, the temperature was raised to 98°C, and 5g of butyraldehyde and 50g of hydrochloric acid with a mass concentration of 3.6wt% were added. The reaction was allowed to mature for 150 minutes to obtain polyvinyl butyral resin B3. 1 ¹H-NMR analysis showed that the degree of butyralization was 74 mol%, the content of heterodioretic triunits was 13.0 mol%, and the content of syndioretic triunits was 4.2 mol%. All other parameters were the same as in Example 1.

[0058] Comparative Example 4 The difference from Example 1 is that in S2, the temperature was raised to 65°C, and the curing reaction was carried out for 45 minutes to obtain polyvinyl butyral resin A5. After... 1 ¹H-NMR analysis showed that the degree of butyralization was 66 mol%, the content of heterodiuronic triunits was 5.8 mol%, and the content of syndiuronic triunits was 2.9 mol%. All other parameters were the same as in Example 1.

[0059] Comparative Example 5 The difference from Example 1 is that in S2, the temperature was raised to 98°C, and the curing reaction was carried out for 150 minutes to obtain polyvinyl butyral resin A6. After... 1 ¹H-NMR analysis showed that the degree of butyralization was 74 mol%, the content of heterodioretic triunits was 12.3 mol%, and the content of syndioretic triunits was 5.1 mol%. All other parameters were the same as in Example 1.

[0060] The wedge-shaped polyvinyl butyral interlayer films prepared in Examples 1-8 and Comparative Examples 1-5 were subjected to performance tests. The test methods are as follows: Wedge Angle Profile Measurement: Using a Möller-Wedel electronic autocollimator (He-Ne laser light source, measurement spot diameter approximately 1 mm), the local wedge angle of the laminated glass was measured at 1 mm intervals along the vertical direction of the interlayer. The wedge angle α was calculated using the following formula: α = Θ / n, where Θ is the measured reflection separation angle and n is the sample refractive index (1.48). The maximum absolute wedge angle change rate ROC (based on the linear regression slope over a 50 mm span) and the maximum actual-target wedge angle deviation Dev were calculated within the entire HUD area. Each sample was measured 5 times, and the mean ± standard deviation was taken; in the examples, the standard deviation was less than 5% of the measured value. The results are shown in Table 1.

[0061] Table 1. Wedge angle profiles of different intermediate films

[0062] Self-adhesive strength (T-peel strength) determination: Following ASTM D1876, the interlayer film was cut into 30mm wide and 100mm long pieces. Two pieces were overlapped and placed under a 6kg load at 20℃ for 48 hours. A 90° T-peel test was then performed using a tensile testing machine at a speed of 500mm / min. The average peel strength (g / cm) was recorded. The test was repeated three times, and the average value was taken. The results are shown in Table 2.

[0063] Table 2 Self-adhesiveness of different intermediate films

[0064] Table 2 shows that the T-peel forces of the intermediate films prepared in Examples 1-8 of this invention are significantly lower than those in Comparative Examples 1-5. This indicates that controlling the stereoregularity of the resin (6-12% heteroregular, 3-5% synregular) using the method of this invention can effectively reduce the self-adhesion of the intermediate film. Comparative Examples 1 (one-step method), 3, and 5 (stereoregularity exceeding the range) have the highest self-adhesion, while Comparative Examples 2 and 4, whose stereoregularity is not optimal, also have higher self-adhesion than the examples of this invention. Low self-adhesion helps to prevent the roll material from sticking together during storage and transportation, and the resulting damage to the wedge-shaped profile.

[0065] Evaluation of wedge profile retention: (1) Simulated storage and transportation conditions: In accordance with the pressure loading principle of ISO 22391-2:2019, the intermediate film was cut into 300mm×300mm samples, 10 samples were stacked on top of each other, and a flat steel plate was placed on each side. A uniform pressure of 0.05MPa was applied (achieved by weights or a press) and placed in a constant temperature chamber at 40℃ for 72h. After removal, the samples were horizontally separated along the plane at a speed of 300mm / min. It was verified that the correlation between this condition and the degree of wedge profile deterioration in actual storage and transportation (7 days of summer container transportation) was R. 2>0.92. (2) The wedge angle profile of the HUD area of ​​the same batch of intermediate film before and after simulated storage and transportation treatment was measured respectively, and the increment of the maximum absolute wedge angle change rate (ΔROC) and the increment of the maximum actual-target wedge angle deviation (ΔDev) before and after treatment were calculated. The results are shown in Table 3.

[0066] Dynamic ghosting evaluation: A windshield sample was fabricated by laminating the intermediate film after simulated storage and transportation treatment between two 2.1 mm thick glass plates. A grid pattern was projected using a HUD projection unit with a virtual image distance of 6 meters. A Baslerac A1300-200μm CCD camera (resolution 1280×1024, lens focal length 50mm, aperture f / 8) was used to capture the projected image at the center of the eye box. The ghosting angle (angular separation between the primary and secondary images) was calculated using the Canny edge detection algorithm (threshold 0.3) in the Matlab image processing toolbox. A ghosting angle less than 0.5 arcmin was considered "no dynamic ghosting", 0.5~1.0 arcmin was "partially visible", and greater than 1.0 arcmin was "clearly visible". The results were confirmed by three observers, and the consistency between the observer evaluation and the CCD results was ≥95%. The results are shown in Table 3.

[0067] Table 3. Wedge Angle Profile Retention of Different Intermediate Films

[0068] Note: In Example 6, the ROC before treatment was 3.2 μrad / mm (exceeding the 3.0 limit of this invention), but the ΔROC after treatment was still 0.2. Although the ΔROC of this sample met the requirements, the local dynamic ghosting occurred due to the excessive initial ROC, proving that an initial ROC < 3.0 is a necessary characteristic.

[0069] As shown in Table 3, after simulated storage and transportation treatment, the increment of the maximum absolute wedge angle change rate (ΔROC) in all embodiments of the present invention (1-5, 7-8) did not exceed 0.5 μrad / mm, and the increment of the maximum actual-target wedge angle deviation (ΔDev) did not exceed 0.03 mrad. Furthermore, the dynamic ghosting evaluation was mostly "none". This fully demonstrates that the present invention, by controlling the three-dimensional regularity of the resin to impart low self-adhesion to the intermediate film, can effectively resist plastic deformation caused by storage and transportation pressure, thus maintaining a high-precision wedge angle profile after storage and transportation. In contrast, the ΔROC and ΔDev values ​​of all comparative examples (1-5) significantly exceeded the standard, and the dynamic ghosting was "obviously visible," indicating that their wedge angle profiles deteriorated significantly after storage and transportation. Example 4, due to its initial ROC being close to the upper limit, had slightly weaker resistance to deformation, and the dynamic ghosting evaluation was "partially visible." In Example 6, because the initial ROC was already exceeded, even though the change after storage and transportation was small (ΔROC=0.2), "locally visible" ghosting still appeared in the end. This strongly proves from the opposite perspective that strictly controlling the initial ROC below 3.0 μrad / mm is a prerequisite for achieving no dynamic ghosting, and also highlights the dual advantages of the present invention in simultaneously optimizing the initial profile (low ROC) and profile preservation (low ΔROC).

[0070] Long-term aging test: The intermediate film prepared in Example 1 was wound onto a paper core (300 mm in diameter and about 0.04 MPa in radial pressure) and stored at 40°C and 75% RH for 90 days (simulating 3 months of summer storage). The self-adhesive force and wedge angle profile changes were then measured as described above to evaluate long-term stability.

[0071] After 90 days of storage at 40°C, 75%RH, and under winding pressure, the intermediate film prepared in Example 1 showed an increase in T-type peel strength to 355 g / cm, ΔROC to 0.3 μrad / mm, ΔDev to 0.02 mrad, and no dynamic ghosting, indicating that the intermediate film of the present invention has excellent long-term storage stability.

[0072] Experiment on the effect of recycled materials: The intermediate film of Example 1 was crushed and mixed with virgin material (polyvinyl butyral resin A1) at a ratio of 20 wt%. Steps S3-S4 were repeated to obtain a wedge-shaped polyvinyl butyral intermediate film made of recycled materials. The self-adhesion test was carried out, and the T-type peel force was measured to be 345 g / cm, ΔROC was 0.3 μrad / mm, ΔDev was 0.03 mrad, and dynamic ghosting was still "none". This shows that the intermediate film of the present invention can withstand the addition of ≤20% recycled materials without significant deterioration of performance.

[0073] The intermediate film prepared in Example 1 was placed between the first glass plate and the second glass plate and laminated using an autoclave process (lamination temperature of 140°C, pressure of 1.2 MPa, and time of 45 min). After lamination, the wedge angle change rate in the HUD area changed from 2.0 μrad / mm before the treatment to 2.1 μrad / mm, a change of 0.1 μrad / mm, which is much lower than 0.3 μrad / mm. This indicates that the intermediate film of the present invention can maintain the wedge angle accuracy well under conventional lamination conditions.

[0074] Therefore, the present invention employs the above-mentioned wedge-shaped polyvinyl butyral interlayer film, its preparation method and application, with an absolute wedge angle change rate of less than 3.0 μrad / mm in the HUD area to eliminate dynamic ghosting; after experiencing storage and transportation conditions, the degree of deterioration of the wedge angle profile is significantly reduced, thereby ensuring the stability of the HUD optical performance of the final product.

[0075] 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 wedge-shaped polyvinyl butyral interlayer film, characterized in that: Includes the following steps: S1. Under stirring conditions, a portion of polyvinyl alcohol aqueous solution and a portion of butyraldehyde are first added, and preliminary condensation is carried out under acid catalyst A; then the temperature is lowered step by step, and the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde are added at the same time, and the reaction is kept at the temperature to precipitate resin particles. S2. The resin particles from S1 are heated and acid catalyst B is added to carry out a aging reaction to regulate the stereoregularity of the resin and obtain polyvinyl butyral resin. S3. Mix the polyvinyl butyral resin, plasticizer, and additives from S2 to obtain a plasticized mixture; S4. After the plasticized mixture of S3 is melted, it is extruded through an extrusion die with adjustable die opening to obtain a wedge-shaped polyvinyl butyral intermediate film.

2. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S1, the mass ratio of the total amount of polyvinyl alcohol, the total amount of butyraldehyde, and the acid catalyst A in the polyvinyl alcohol aqueous solution is 300~360:170~200:180~220.

3. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S1, during the initial condensation, the amount of polyvinyl alcohol aqueous solution added is 70-85 wt% of the total amount of polyvinyl alcohol aqueous solution, the amount of butyraldehyde added is 70-80 wt% of the total amount of butyraldehyde, the initial condensation reaction temperature is 15-20℃, the reaction time is 40-50 min, and the acid catalyst A is hydrochloric acid with a mass concentration of 0.2 wt%. The step-by-step cooling process involves first cooling to 5-10°C, then adding the remaining polyvinyl alcohol aqueous solution and the remaining butyraldehyde, and finally cooling to 0-5°C.

4. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S2, the temperature is raised to 60~95℃, the acid catalyst B is 3wt% hydrochloric acid, the amount of acid catalyst B added is 0.5~2wt% of the resin particles, and the ripening reaction time is 1~3h.

5. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S2, the polyvinyl butyral resin has a butyralization degree of 65-75 mol%, the residual hydroxyl groups have a chain length of more than 3 hydroxyl groups, the heterodioretic triunit content is 6-12 mol%, and the syndioretic triunit content is 3-5 mol%.

6. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S3, the weight proportions of polyvinyl butyral resin, plasticizer, and additives are 100 parts of polyvinyl butyral resin, 25-50 parts of plasticizer, and 0.1-0.5 parts of additives.

7. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S3, the plasticizer is selected from one of the following: triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutyrate, tetraethylene glycol di-n-heptanoate, diethylene glycol dibenzoate, triethylene glycol dipropionate, diethyl adipate, and triethylene glycol diisobutyrate; the additives include ultraviolet absorbers and antioxidants.

8. The method for preparing a wedge-shaped polyvinyl butyral interlayer according to claim 1, characterized in that: In S4, the melting temperature is 180~220℃, the extrusion die temperature is 190~210℃, the die lip opening of the extrusion die is 0.3~1.0mm, and the die lip opening changes linearly along the vertical section of the film extrusion direction, with the rate of change corresponding to the target wedge angle.

9. A wedge-shaped polyvinyl butyral interlayer membrane, characterized in that: The wedge-shaped polyvinyl butyral intermediate film is prepared by the preparation method of any one of claims 1-8. The wedge-shaped polyvinyl butyral intermediate film has a head-up display area, and the absolute wedge angle change rate of the wedge-shaped polyvinyl butyral intermediate film in the head-up display area is less than 3.0 μrad / mm.

10. The application of the wedge-shaped polyvinyl butyral interlayer as described in claim 9, characterized in that: This invention is used to manufacture laminated glass for head-up displays. The laminated glass includes a first glass plate, a second glass plate, and a wedge-shaped polyvinyl butyral interlayer, wherein the wedge-shaped polyvinyl butyral interlayer is disposed between the first glass plate and the second glass plate.

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