High-temperature-resistant and dimensionally stable acrylic sheet material and preparation and shaping process thereof

Abstract

This invention relates to the field of polymer molding technology, specifically to a high-temperature resistant, dimensionally stable acrylic sheet and its preparation and shaping process, comprising the following components: 80-95 parts by weight of polymethyl methacrylate matrix resin, 5-20 parts by weight of isoborneol methacrylate, 2-6 parts by weight of nano-silica, 0.4-1.2 parts by weight of silane coupling agent, 0.2-0.6 parts by weight of initiator, 0.5-1.5 parts by weight of crosslinking agent, 0.1-0.4 parts by weight of antioxidant, 0.1-0.3 parts by weight of light stabilizer, and 0.05-0.2 parts by weight of release agent. By introducing isoborneol methacrylate as a comonomer into the polymethyl methacrylate matrix, the glass transition temperature of the polymer is significantly increased by utilizing the cyclic rigid groups in its molecular structure. Combined with the reinforcing effect of nano-silica, the high-temperature resistance of the acrylic sheet is significantly improved, with a heat distortion temperature and Vicat softening temperature significantly higher than those of ordinary acrylic sheets.

Description

Technical Field

[0001] This invention relates to the field of polymer material molding technology, specifically to a high-temperature resistant, dimensionally stable acrylic sheet and its preparation and shaping process. Background Technology

[0002] In the automotive industry, acrylic sheets are widely used in automotive light covers (such as taillights and interior ambient lighting), dashboard panels, and window triangles due to their excellent light transmittance, lightweight properties, and design flexibility. With the development of intelligent and lightweight vehicles, as well as the increasing requirements for interior texture and optical performance, the application scenarios for transparent plastic automotive components are expanding.

[0003] However, the glass transition temperature of traditional acrylic sheets is typically between 100-105℃, and their heat distortion temperature is relatively low, generally between 80-95℃. This deficiency leads to severe challenges under specific automotive conditions: for example, in the heat of a closed car interior during summer exposure, the temperature can reach over 70℃, while the temperature near the engine compartment or inside the headlights can exceed 100℃; during winter defrosting or prolonged operation of lights, localized areas also experience rapid temperature increases. Under such high-temperature environments, traditional acrylic sheets are prone to softening, deformation, and dimensional instability, which may lead to decreased optical performance of automotive lights, light distortion, or warping of interior panels and changes in assembly gaps, seriously affecting product reliability, safety, and aesthetics. Therefore, the shortcomings of traditional acrylic sheets, such as insufficient heat resistance and poor dimensional stability, limit their application in heat-resistant scenarios, especially restricting their further promotion and application in the field of high-end, high-performance automotive parts. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a high-temperature resistant, dimensionally stable acrylic sheet and its preparation and shaping process. The sheet's formulation design significantly enhances heat resistance through rigid-flexible monomer copolymerization, nanoparticle composites, and synergistic effects of multiple additives. Meanwhile, the accompanying process, through precise control of steps such as graded polymerization, symmetrical cooling, and stress relaxation, effectively prevents sheet warping, resulting in excellent surface flatness and dimensional stability.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A high-temperature resistant, dimensionally stable acrylic sheet, the raw materials of which include the following components by weight: 80-95 parts of polymethyl methacrylate (PMMA) matrix resin; Isobornyl methacrylate (IBOMA) 5-20 parts; 2-6 parts of nano-silica; 0.4–1.2 parts of silane coupling agent; Initiator 0.2–0.6 parts; Crosslinking agent 0.5–1.5 parts; Antioxidant 0.1–0.4 parts; Light stabilizer 0.1–0.3 parts; 0.05 to 0.2 parts of release agent.

[0006] The preferred particle size of the nano-silica is 30 nm, and it is surface modified using the silane coupling agent.

[0007] Preferably, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane (KH-570); the crosslinking agent is ethylene glycol dimethacrylate (EGDMA); and the initiator is azobisisobutyronitrile (AIBN).

[0008] Preferably, the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the light stabilizer is hindered amine light stabilizer 770; and the release agent is pentaerythritol tetrastearate (PETS).

[0009] The further preferred weight components are: 88 parts PMMA matrix resin, 12 parts IBOMA, 4 parts nano silica, 0.8 parts KH-570 coupling agent, 0.4 parts AIBN initiator, 1.0 part EGDMA crosslinking agent, 0.25 parts 1010 / 168 compound antioxidant, 0.2 parts light stabilizer 770, and 0.12 parts PETS release agent.

[0010] The preparation and shaping process of the above-mentioned sheet material is characterized by including the following steps: S1: Nanoparticle surface modification: Modified nano-silica was prepared by drying nano-silica at 110°C for 3 hours, cooling it, and then stirring it at high speed at 80-90°C for 45 minutes with silane coupling agent KH-570.

[0011] S2: Preparation of prepolymer slurry: Under a nitrogen atmosphere, PMMA matrix resin and IBOMA monomer were heated to 80–90°C and stirred until dissolved. The modified nano-silica, EGDMA crosslinking agent, antioxidant, light stabilizer, and release agent were added. The mixture was first ultrasonically dispersed at 500W for 15 minutes, then stirred at 2000 rpm for 30 minutes until homogeneous. Finally, AIBN initiator was added, and a prepolymerization reaction was carried out at 75–85°C until the system viscosity reached approximately 1200 mPa•s. The mixture was then cooled to approximately 30°C to obtain the prepolymerized slurry.

[0012] S3: Casting and defoaming: The prepolymer slurry was degassed under a vacuum of -0.1 MPa for 20 minutes, then filtered through a 300-mesh filter, and subsequently poured into a symmetrical stainless steel molding mold preheated to 50°C. The casting thickness was controlled to be 1.02 times the target finished product thickness to allow space for subsequent curing shrinkage.

[0013] S4: Programmed temperature curing: The mold is placed in a curing oven for staged temperature curing: First stage: Increase the temperature from room temperature to 50℃ at a rate of 2℃ / h, and cure at a constant temperature for 12 hours; Second stage: Increase the temperature to 70℃ at a rate of 1℃ / h and cure at a constant temperature for 8 hours; Third stage: Increase the temperature to 80-90℃ at a rate of 1℃ / h, and cure at a constant temperature for 4 hours.

[0014] S5: Controlled symmetrical cooling: After curing, the mold is transferred to a controlled cooling device. A symmetrical heat transfer oil circulation system is used for cooling, with an initial oil temperature of 80–90°C, slowly decreasing to 50°C at a rate of 2°C / h. During this process, the temperature difference between the upper and lower surfaces of the sheet is monitored and controlled to be ≤2°C. After maintaining a constant temperature of 50°C for 3 hours, natural air cooling is switched on, decreasing to room temperature at a rate of 5°C / h. Throughout the entire cooling process, the mold maintains physical constraint on the sheet.

[0015] S6: Stress relaxation and post-treatment: After demolding, the board is placed in an oven at 70-80℃ for 4 hours to eliminate residual stress. Finally, the finished board is obtained after trimming, polishing, and cleaning.

[0016] Further preferred, the cooling control device in step S5 is a double-roller cooling and shaping mechanism, which can ensure the tight contact between the surface of the board and the cooling roller by adjusting the air bladder to 0.3MPa air pressure, thereby achieving efficient and uniform heat transfer.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the high-temperature resistant dimensionally stable acrylic sheet and its preparation and shaping process, isobornyl methacrylate is introduced as a comonomer into the polymethyl methacrylate matrix. The cyclic rigid groups in its molecular structure significantly increase the glass transition temperature of the polymer. Combined with the reinforcement effect of nano-silica, the high-temperature resistance of the acrylic sheet is significantly improved, and the heat distortion temperature and Vicat softening temperature are significantly higher than those of ordinary acrylic sheets.

[0018] 2. In this high-temperature resistant, dimensionally stable acrylic sheet and its preparation and shaping process, a slow, step-by-step temperature-controlled curing process avoids uneven polymerization and defects caused by localized intense heat release. The subsequent symmetrical, slow, and forced-bonding controlled cooling process effectively suppresses warping and residual stress caused by temperature gradients and uneven shrinkage. Finally, a specialized stress relaxation heat treatment further releases the orientation energy of the microscopic molecular chains. This entire process is essential to ensure that the finished sheet has high flatness (e.g., <0.5mm / m) and low thickness tolerance (e.g., <±0.05mm). It uses 30nm nano-silica modified with KH-570 and optimizes the ultrasonic / high-speed stirring dispersion process to ensure uniform dispersion within the polymer matrix. This ensures excellent reinforcement and heat resistance while maintaining a light transmittance higher than 91% (e.g., 91.8% in Example 3), meeting regulatory requirements for light transmittance and the optical purity requirements of high-end automotive products.

[0019] 3. In this high-temperature resistant, dimensionally stable acrylic sheet and its preparation and shaping process, the slow, step-by-step temperature-controlled curing process avoids uneven polymerization and defects caused by localized intense heat release. The subsequent symmetrical, slow, and forced-bonding controlled cooling process (especially the double-roller constraint and temperature difference <2℃) effectively suppresses warping and residual stress caused by temperature gradients and uneven shrinkage. Finally, a specialized stress relaxation heat treatment further releases the orientation energy of the microscopic molecular chains. This entire process is essential to ensure that the finished sheet has high flatness (e.g., <0.5mm / m) and low thickness tolerance (e.g., <±0.05mm). Attached Figure Description

[0020] Figure 1 This is the formulation table of the composition of the present invention; Figure 2 This is the performance test table for this invention. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. However, it should be noted that the embodiments do not constitute a limitation on the scope of protection of the present invention.

[0022] A high-temperature resistant, dimensionally stable acrylic sheet comprises the following components: 80-95 parts by weight of polymethyl methacrylate matrix resin, 5-20 parts by weight of isoborneol methacrylate, with isoborneol methacrylate as a comonomer, the cyclic groups in its molecular structure can significantly increase the glass transition temperature of the polymer and improve the high-temperature resistance of the sheet; 2-6 parts by weight of nano-silica, 0.4-1.2 parts by weight of silane coupling agent, 0.2-0.6 parts by weight of initiator, 0.5-1.5 parts by weight of crosslinking agent, 0.1-0.4 parts by weight of antioxidant, 0.1-0.3 parts by weight of light stabilizer, and 0.05-0.2 parts by weight of release agent.

[0023] The preferred components are as follows: 88 parts by weight of polymethyl methacrylate matrix resin, 12 parts by weight of isoborneol methacrylate, 4 parts by weight of nano silica, 0.8 parts by weight of silane coupling agent, 0.4 parts by weight of initiator, 1.0 part by weight of crosslinking agent, 0.25 parts by weight of antioxidant, 0.2 parts by weight of light stabilizer, and 0.12 parts by weight of release agent.

[0024] The antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a 1:1 mass ratio; the light stabilizer is hindered amine light stabilizer 770; antioxidant 1010, as the main antioxidant, can capture free radicals generated by polymer oxidative degradation and terminate the chain reaction; antioxidant 168, as the auxiliary antioxidant, can decompose hydrogen peroxide. The synergistic use of the two produces a significant anti-thermal and oxygen aging effect. On this basis, the addition of light stabilizer 770 can effectively quench singlet oxygen and capture free radicals generated by ultraviolet rays, thereby comprehensively resisting the aging and damage of heat, oxygen and light to the material during high-temperature processing and long-term outdoor use, and greatly extending the service life of the board.

[0025] The release agent is pentaerythritol tetrastearate; pentaerythritol tetrastearate has good thermal stability and chemical inertness, and will not decompose or change color during high-temperature curing. The long-chain alkyl in its molecular structure can form a uniform lubricating film at the interface between the mold and the sheet, which significantly reduces the interfacial adhesion force and allows it to be smoothly removed from the stainless steel mold, avoiding sheet tearing, warping or surface scratches caused by difficult demolding, and greatly improving the yield and production efficiency.

[0026] The particle size of nano-silica is 30 nm. Silica with a particle size that is too small (<10 nm) is prone to agglomeration and is costly; while particle sizes that are too large (>100 nm) weaken the nano-effect, making it more like a conventional filler and prone to forming defects at the interface, thus reducing performance. Selecting a particle size of 30 nm for nano-silica achieves a good balance. The 30 nm nano-silica is surface-modified with a silane coupling agent, namely γ-methacryloyloxypropyltrimethoxysilane. γ-methacryloyloxypropyltrimethoxysilane is a... This amphiphilic molecule has one end that can bind to inorganic substances and the other end that can bind to or react with organic substances. In water or under heating conditions, it hydrolyzes to generate silanol groups. These active silanol groups can undergo dehydration condensation reactions with hydroxyl groups on the surface of nano-silica to form strong covalent bonds. Through chemical bonding, it constructs molecular bridges between 30nm inorganic particles and organic polymer matrices, fundamentally solving the problem of nanomaterial aggregation in polymer matrices and achieving efficient transfer of interfacial stress. This lays the structural foundation for the material's high heat resistance and high dimensional stability.

[0027] The crosslinking agent is ethylene glycol dimethacrylate; the initiator is azobisisobutyronitrile.

[0028] The above-mentioned preparation and shaping process of a high-temperature resistant dimensionally stable acrylic sheet includes the following steps: S1. Modified nano-silica is prepared by the following steps: Nano-silica is dried in an oven at 110°C for 3 hours, cooled to room temperature, mixed with a silane coupling agent, and stirred in a high-speed mixer at 80-90°C for 45 minutes for later use; After drying, the modified nano-silica is stirred with a silane coupling agent at 80-90°C to improve its dispersibility in the organic matrix.

[0029] S2. Add polymethyl methacrylate matrix resin and isobornyl methacrylate to a reactor, purge the air with nitrogen three times, heat to 80-90°C, and stir until completely dissolved to form a comonomer system. Then add the modified nano-silica obtained in step S1, as well as crosslinking agent, antioxidant, light stabilizer, and release agent to the comonomer system. After ultrasonic dispersion for 15 minutes, stir at high speed for 30 minutes to form a homogeneous mixture. Then add an initiator to the mixture and prepolymerize at a constant temperature of 85°C. When the system viscosity reaches 1200 mPa·s, stop heating and quickly cool to 30°C to obtain a prepolymer slurry. After the comonomer is dissolved, add the modified nano-silica and additives, ultrasonically disperse, and prepolymerize to the specified viscosity to ensure the uniformity and moldability of the slurry. S3. The prepolymer slurry obtained in step S2 is vacuum degassed for 20 minutes, filtered, and then injected into a preheated mold at 50°C. The mold is a double-sided symmetrical stainless steel template with sealing strips and positioning pins on the edges. The pouring thickness is controlled to be 1.02 times the target thickness. After vacuum degasing, the slurry is injected into the preheated mold, and the pouring allowance is controlled to leave space for curing shrinkage. S4. Place the mold filled with prepolymer slurry into the curing oven and perform the following graded curing procedure: First stage: Heat from room temperature to 50℃ at a rate of 2℃ / h, and cure at a constant temperature for 12h; Second stage: Heat to 70℃ at a rate of 1℃ / h, and cure at a constant temperature for 8 hours; The third stage: heating to 80-90℃ at a rate of 1℃ / h, and curing at a constant temperature for 4 hours; adopting a graded procedure of slow heating at low temperature, followed by medium temperature constant temperature, and finally high temperature curing to reduce internal stress caused by concentrated heat release from the polymerization reaction. S5. After curing, the mold is transferred to a controlled cooling device, using symmetrical upper and lower heat transfer oil circulation cooling. The cooling medium is heat transfer oil. The initial temperature is 80-90℃, and the temperature is reduced to 50℃ at a rate of 2℃ / h. During this period, the temperature of the upper and lower surfaces of the board is monitored in real time by the temperature sensor built into the mold. The temperature difference is controlled within ≤2℃. After maintaining a constant temperature of 50℃ for 3 hours, air cooling is switched to reduce the temperature to room temperature at a rate of 5℃ / h. The positioning constraint of the mold is maintained throughout the process to prevent the board from warping. The use of symmetrical cooling with heat transfer oil on both sides, strict control of the temperature difference between the upper and lower surfaces, combined with the positioning constraint, prevents warping caused by uneven cooling shrinkage. S6. After demolding, the sheet is placed in a stress relaxation furnace and kept at 70°C for 4 hours to eliminate internal residual stress. Then the sheet is trimmed, polished and cleaned to obtain the finished high-temperature resistant dimensionally stable acrylic sheet.

[0030] Among them, the ultrasonic dispersion power in S2 is 500W; the modified nano-silica aggregates are opened by utilizing the local high temperature and high pressure and strong shock wave generated by ultrasonic cavitation effect, so that they are initially uniformly dispersed in the viscous resin system. The high-speed stirring speed is 2000 r / min. High-speed stirring maintains and consolidates the dispersion effect and prevents secondary agglomeration of particles. In step S3, the vacuum degree of vacuum degassing is -0.1 MPa. Oxygen is an inhibitor of free radical polymerization. Through deep degassing at -0.1 MPa, dissolved oxygen is removed to the maximum extent, avoiding the consumption of initiators or termination of chain growth by oxygen during the curing process. This ensures that the polymerization reaction is complete and the designed molecular weight and crosslinking density are achieved. A 300-mesh filter is used for filtration. The choice of 300 mesh instead of a finer filter (such as 500 mesh) is based on a comprehensive consideration of the viscosity of the prepolymer slurry at 30°C. Too high a mesh number will lead to filtration difficulties, excessive time, and may even damage the formed prepolymer structure due to excessive shear force. 300 mesh is the best balance point for effective impurity removal while ensuring the smooth passage of the slurry.

[0031] In step S5, the cooling device uses a double-roller cooling and shaping mechanism. When the board is cooled from 80-90°C to room temperature, the polymer chains tend to curl up, resulting in volume shrinkage. If the shrinkage is not restrained, the board will warp and deform. The double-roller symmetrical structure applies mechanical restraint to the board from both the top and bottom directions, forcing it to shrink isotropically in the thickness direction, thereby ensuring the flatness of the board.

[0032] The air pressure of the airbag is adjusted to regulate the adhesion of the board. The air pressure is controlled at 0.3MPa. The board surface and the cooling roller are not perfectly fitted, and there are tiny air gaps. This will form contact thermal resistance and greatly reduce cooling efficiency. By applying air pressure of 0.3MPa through the airbag, the board is pressed tightly onto the cooling roller, which can effectively squeeze out the gap air, so that the board surface and the roller surface can be tightly fitted, greatly improving the heat conduction efficiency and ensuring precise and controllable cooling rate.

[0033] To illustrate the advantages of the present invention, the following description uses a comparison between Examples 1-4 and Comparative Examples 1-3, specifically as follows: Figure 1 As shown; The acrylic sheets prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests respectively: S1: Heat distortion temperature test method: Cut the finished plates prepared in each embodiment and comparative example into standard specimens of 80mm×10mm×4mm, apply a stress of 1.82MPa, heat up at a rate of 2℃ / min, and record the temperature at which the specimen undergoes the specified deformation, which is the heat distortion temperature.

[0034] S2: Vicat softening temperature test method: Cut the sample into standard size, apply a heat load of 10N, and heat up at a rate of 50℃ / h. Monitor the pressure on the sample surface in real time. When the surface deformation reaches 1mm, record the temperature at this time, which is the Vicat softening temperature.

[0035] S3: Linear expansion coefficient test method: Using a thermomechanical analyzer, the sample is cut into a suitable size, and the test temperature range is controlled between 25 and 80℃ (simulating the common temperature range in actual use). The length change of the sample within this temperature range is recorded, and the linear expansion coefficient is calculated.

[0036] S4: Transmittance test method: The finished boards of each embodiment and comparative example are processed into standard samples with a thickness of 4mm. The transmittance of the samples is measured in the visible light band of 400-700nm using a spectrophotometer. Five different test points are selected for each sample, and the average value is taken as the final transmittance data.

[0037] S5: Thickness tolerance test method: Use a high-precision thickness gauge to measure the thickness of each finished board at multiple points (no less than 10 test points, evenly distributed on the surface of the board), record the thickness value of each test point, calculate the difference between the maximum thickness and the minimum thickness, and determine the thickness tolerance range.

[0038] S6: Flatness test method: Using a precision plate and a dial indicator, place the finished board material stably on the precision plate, slowly move the dial indicator, measure the gap between each point on the board surface and the plate, and record the maximum gap value, which is the flatness of the board material (unit: mm / m).

[0039] Test results for each performance indicator are as follows Figure 2 As shown; The performance comparison between Examples 1-4 and Comparative Examples 1-3 shows that the present invention, through specific formula modification and shaping process, can significantly improve the high temperature resistance, dimensional stability and flatness of acrylic sheets while ensuring high light transmittance.

[0040] For example, optical-grade covers for automotive interiors (such as continuous light strip covers), ambient lighting panels, and large-size window / sunroof triangular area panels have extremely high requirements for the flatness, thickness tolerance, and dimensional stability of components, even at the millimeter or micrometer level. Any warping or shrinkage marks caused by thermal expansion / contraction due to temperature changes or release of internal stress will disrupt the tight fit of the assembly, causing abnormal noises or a cheap appearance.

[0041] By employing a precise and controllable symmetrical gradient curing and cooling process (temperature difference ≤2°C, physical constraints of the mold), the flatness of the sheet material is controlled at an extremely low level (e.g., 0.35 mm / m in Example 3), which is far superior to the warping deformation of traditional processes (flatness of 5.60 mm / m in Comparative Example 3), ensuring that the components maintain excellent flatness even after severe thermal cycling.

[0042] Low expansion and high stability: Through the synergistic effect of rigid monomer (IBOMA) and modified nanofiller, the coefficient of linear expansion is reduced to approximately 58 × 10⁻ 6 / °C, significantly better than pure PMMA's approximately 155×10⁻ 6 / °C ensures the dimensional stability of the components in a wide temperature range (such as -30°C to 85°C), avoiding stress concentration or jamming problems caused by the difference in thermal expansion and contraction between the components and the metal frame.

[0043] As mobile assets used outdoors for extended periods, automobiles require their exposed components (lamp covers, trim strips) to withstand the corrosive effects of ultraviolet radiation and humidity, while interior components must also resist photothermal aging. Furthermore, both lamps and translucent trim pieces have strict requirements for light transmittance, haze, and gloss, directly impacting visual quality and brand premium.

[0044] Effect correlation: By using a specially formulated system of hindered phenol / phosphite antioxidants and hindered amine light stabilizers, the aging and degradation of materials caused by heat, oxygen and ultraviolet radiation are significantly slowed down, effectively preventing yellowing and strength reduction of the board after many years of use, and extending the service life of the components.

[0045] High light transmittance: 30nm nano-silica modified with KH-570 is used, and the ultrasonic / high-speed stirring dispersion process is optimized to make it uniformly dispersed in the polymer matrix. While ensuring excellent reinforcement and heat resistance, the light transmittance of the board is kept higher than 91% (91.8% in Example 3), which meets the light transmittance requirements of regulations and the optical purity requirements of high-end cars.

[0046] Comparative Example 1 used only 100 parts of ordinary polymethyl methacrylate resin, without adding isoborneol methacrylate, nano silica, crosslinking agent, or any other additives, retaining only pure polymethyl methacrylate resin as raw material; Comparative Example 1 uses a traditional single casting and curing process instead of the shaping process of this invention. The specific steps are as follows: pure polymethyl methacrylate resin is heated to 90°C and stirred to dissolve, then directly cast into an ordinary stainless steel mold, cured at 80°C for 24 hours, and after curing, it is naturally cooled to room temperature. After demolding, the edges are trimmed directly without stress relaxation treatment to obtain the finished product. Comparative Example 1, without formula modification and sizing process, compared with Examples 1-4 of the present invention, clearly shows the core defects of traditional acrylic sheets, such as poor heat resistance, poor dimensional stability, and poor flatness. This contrasts sharply with the embodiments of the present invention, highlighting the synergistic improvement effect of the formula and process of the present invention.

[0047] The formulation of Comparative Example 2 is exactly the same as that of Example 2, except that the surface of the nano-silica was not modified in the shaping process, and the rest of the shaping process is the same. Comparative Example 2 only contained unmodified nano-silica. Compared with Example 2, the performance data showed that the unmodified nano-silica was prone to agglomeration due to the mismatch between its surface polarity and the organic matrix, resulting in a significant decrease in heat resistance, dimensional stability, and light transmittance. This clearly demonstrates that surface modification of nano-silica with silane coupling agent is one of the key technologies for achieving high heat resistance, high light transmittance, and high dimensional stability in this invention.

[0048] Comparative Example 3 has the same formulation as Example 2, except that it does not use S4, S5, and S6 of the process of this invention, but instead uses a traditional single curing and natural air cooling process. The specific steps are as follows: Comparative Example 3 uses the same S1 process as Example 2; Comparative Example 3 uses the same S2 process as Example 2; Comparative Example 3 differs from the S3 process in Example 2; instead, the mold with the cast slurry is directly placed into the curing oven, rapidly heated to 85°C (heating rate 5°C / h, no gradient heating process), and cured at a constant temperature for 24 hours. During the curing process, the heating rate is not controlled, and no segmented constant temperature is set to ensure that the curing reaction proceeds in a concentrated manner.

[0049] Comparative Example 3 differs from Example 2 in its S4 process; instead, after curing, the mold was removed from the curing oven and placed directly in a room temperature environment (25°C) to cool naturally to room temperature. Comparative Example 3 differs from Example 2 in its S5 process; it does not employ any cooling control measures, does not use double-sided symmetrical heat transfer oil circulation cooling, does not control the temperature difference between the upper and lower surfaces of the plate during the cooling process (the temperature difference between the upper and lower surfaces can reach 5-8°C under natural cooling conditions), and does not maintain mold positioning constraints, allowing the mold to shrink freely.

[0050] The process of Comparative Example 3 differs from that of Example 2 in that it was directly demolded after cooling to room temperature without undergoing a 75°C constant temperature stress relaxation treatment. After demolding, only simple trimming, polishing, and cleaning were performed. The residual stress generated during curing and cooling was not eliminated through constant temperature treatment, and the final product was obtained.

[0051] Comparative Example 1 (pure PMMA + traditional process): The heat distortion temperature is the lowest (about 88°C), and the linear expansion coefficient is the highest, indicating that the traditional pure acrylic sheet has the worst heat resistance and dimensional stability; the flatness is extremely poor (3.20mm / m), proving that its warping deformation is serious, which confirms the problems in the background technology.

[0052] Comparative Example 2 (same formulation, but without silane coupling agent modification of nano-silica): Compared with Example 2 with the same formulation, all key properties were significantly deteriorated, and the transmittance dropped sharply to 76.8%, far lower than 91.5% in Example 2. This fully demonstrates that surface modification treatment with silane coupling agent (KH-570) is a key technical means to solve the problem of nanoparticle agglomeration, improve interfacial bonding, and ensure the synergy of high transmittance and high strength.

[0053] Comparative Example 3 (same formulation, but using a simple curing and natural cooling process): Although its formulation is exactly the same as Example 2, its flatness deteriorated to 5.60 mm / m because it did not use the stepped temperature-programmed curing and symmetrical controlled cooling process described in this invention, which is much higher than that of Example 2 (0.38 mm / m). This directly and powerfully demonstrates the decisive role of the patented process of this invention (steps S4, S5, and S6) in overcoming internal stress, preventing warping, and achieving high flatness.

[0054] Example 3 (preferred formulation combination): The overall performance is the most balanced and superior, with a heat distortion temperature as high as 135.2°C, while maintaining high light transmittance (91.8%) and excellent flatness (0.35mm / m), clearly demonstrating the best synergistic effect of the formulation and process.

[0055] This invention, through precise collaboration across the entire process from formulation design to molding technology, produces high-temperature resistant, dimensionally stable acrylic sheets that specifically address the four core performance requirements of the automotive industry: high-temperature durability, high dimensional accuracy, excellent light transmittance, and long-term weather resistance. It is not a general modification, but rather a product of deep customization and optimization tailored to the specific scenario of "demanding automotive applications," significantly expanding the application boundaries of acrylic sheets in high-end, intelligent, and high-performance automotive interior and exterior components and lighting fixtures, possessing clear commercial application prospects and market competitiveness.

[0056] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A high-temperature resistant, dimensionally stable acrylic sheet, characterized in that: Composed of the following raw materials in parts by weight: 80-95 parts of polymethyl methacrylate matrix resin; 5-20 parts of isobornyl methacrylate; 2-6 parts of nano-silica; 0.4–1.2 parts of silane coupling agent; Initiator 0.2–0.6 parts; Crosslinking agent 0.5–1.5 parts; Antioxidant 0.1–0.4 parts; Light stabilizer 0.1–0.3 parts; 0.05 to 0.2 parts of release agent.

2. The high-temperature resistant, dimensionally stable acrylic sheet according to claim 1, characterized in that: The nano-silica consists of particles with a diameter of 30 nm, and its surface is modified by the silane coupling agent.

3. The high-temperature resistant, dimensionally stable acrylic sheet according to claim 1, characterized in that: The silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; the crosslinking agent is ethylene glycol dimethacrylate; and the initiator is azobisisobutyronitrile.

4. The high-temperature resistant, dimensionally stable acrylic sheet according to claim 1, characterized in that: The antioxidant is a compound of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the light stabilizer is hindered amine light stabilizer 770; and the release agent is pentaerythritol tetrastearate.

5. The high-temperature resistant, dimensionally stable acrylic sheet according to claim 4, characterized in that: The polymethyl methacrylate matrix resin comprises 88 parts by weight, the isoborneol methacrylate comprises 12 parts by weight, the nano silica comprises 4 parts by weight, the silane coupling agent comprises 0.8 parts by weight, the initiator comprises 0.4 parts by weight, the crosslinking agent comprises 1.0 part by weight, the antioxidant comprises 0.25 parts by weight, the light stabilizer comprises 0.2 parts by weight, and the release agent comprises 0.12 parts by weight.

6. A process for preparing and shaping high-temperature resistant dimensionally stable acrylic sheets as described in any one of claims 1-5, characterized in that: Includes the following steps: S1: The nano-silica is dried and mixed with the silane coupling agent to obtain modified nano-silica; S2: After dissolving the polymethyl methacrylate matrix resin and the isoborneol methacrylate, add the modified nano silica obtained in step S1, the crosslinking agent, antioxidant, light stabilizer and release agent, and after dispersing and mixing evenly, add an initiator to prepolymerize to obtain a prepolymer slurry. S3: After degassing and filtering, the prepolymer slurry is injected into a preheated mold; S4: Place the mold in a curing oven and execute the program to heat and cure; S5: After curing, the mold is transferred to a controlled cooling device and a symmetrical circulating cooling method is used for temperature control and cooling, maintaining the mold's positioning constraint on the board throughout the process; S6: After demolding, the obtained sheet material is subjected to stress relaxation treatment to obtain the final product.

7. The preparation and shaping process of a high-temperature resistant, dimensionally stable acrylic sheet according to claim 6, characterized in that, Step S1 specifically involves drying nano-silica at 110°C for 3 hours, cooling it to room temperature, and then stirring it with a silane coupling agent at 80-90°C for 45 minutes at high speed. Step S2 is as follows: Mix polymethyl methacrylate matrix resin and isobornyl methacrylate, heat to 80-90°C under nitrogen protection and stir to dissolve, then add the modified nano silica, crosslinking agent, antioxidant, light stabilizer and release agent, first ultrasonically disperse at 500W power for 15 minutes, then stir at 2000r / min speed for 30 minutes, finally add initiator, and prepolymerize at a constant temperature of 75-85°C. When the viscosity of the system reaches 1200mPa·s, stop heating and cool down to 30°C.

8. The preparation and shaping process of a high-temperature resistant, dimensionally stable acrylic sheet according to claim 6, characterized in that, Step S3 specifically involves: degassing the prepolymer slurry under a vacuum of -0.1MPa for 20 minutes, filtering it through a 300-mesh filter, and then injecting it into a preheated mold at 50°C. The mold is a double-sided symmetrical stainless steel template with sealing strips and positioning pins on the edges. The pouring thickness is controlled to be 1.02 times the thickness of the target board.

9. The preparation and shaping process of a high-temperature resistant, dimensionally stable acrylic sheet according to claim 6, characterized in that, The programmed temperature rise curing described in step S4 specifically involves: First stage: Increase the temperature from room temperature to 50°C at a rate of 2°C / h, and then keep it at the same temperature for 12 hours to cure. Second stage: Heat to 70℃ at a rate of 1℃ / h and keep at the temperature for 8 hours to cure; The third stage: heat the product to 80-90℃ at a rate of 1℃ / h and then keep it at that temperature for 4 hours to cure.

10. The preparation and shaping process of a high-temperature resistant, dimensionally stable acrylic sheet according to claim 6, characterized in that, The temperature control cooling described in step S5 is as follows: symmetrical heat transfer oil circulation cooling is adopted, with an initial oil temperature of 80-90℃, and the temperature is reduced to 50℃ at a rate of 2℃ / h. During this period, the temperature difference between the upper and lower surfaces of the board is monitored and controlled to be ≤2℃. After maintaining a constant temperature of 50℃ for 3 hours, the system is switched to air cooling and the temperature is reduced to room temperature at a rate of 5℃ / h. Furthermore, in step S5, the cooling control device adopts a double-roller cooling and shaping mechanism, which uses an airbag to adjust the fit between the plate and the cooling roller with an air pressure of 0.3MPa.

Images