High-tensile anti-cracking INS film and gradient plastic uptake forming method thereof

Abstract

The invention discloses a high-tensile anti-cracking INS film and a gradient plastic uptake forming method thereof. The INS film adopts an A / B / A three-layer co-extrusion structure, a skin layer A is composed of basic polycarbonate, interfacial compatible toughening particles, a bifunctional reactive compatilizer and organic modified nano clay, and a core layer B is composed of high impact polystyrene and an acrylonitrile-butadiene-styrene copolymer. The interfacial compatible toughening particles comprise double-scale particle size design and are prepared in situ through reactive extrusion. The bifunctional reactive compatibilizer realizes strong interface bonding between the toughening particles and the PC matrix and between the nano clay and the PC matrix. Through cooperation of material design and process innovation, the tensile elongation at break and the anti-cracking performance of the INS film are remarkably improved, the forming qualification rate of a high-stretching area is greatly improved, and the problems of cracking, stress whitening, interlayer stripping, crystal point defects, uneven stretching and the like in deep stretching forming are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of INS film preparation technology, specifically a high tensile strength and rupture-resistant INS film and its gradient vacuum forming method. Background Technology

[0002] In-mold decoration (INS) technology is an advanced manufacturing process that simultaneously completes the injection molding of pre-printed or surface-treated decorative films, and it is widely used in the automotive interior decoration field. As the core material of this technology, the INS film needs to withstand complex three-dimensional tensile deformation during vacuum forming, while maintaining good dimensional stability and surface quality in subsequent injection molding processes. With automotive interior designs increasingly pursuing complex curved shapes and deep-stretched structures, higher demands are placed on the tensile and tear resistance of the INS film.

[0003] Polycarbonate (PC) is often used as a substrate for INS films due to its excellent transparency, heat resistance, and mechanical strength. However, PC materials have inherent notch sensitivity and low ductility. During deep drawing molding with a high draw ratio (≥2:1), stress whitening or even cracking can easily occur in stress concentration areas, which seriously affects the molding quality and yield of the product.

[0004] To improve the toughness of polycarbonate (PC), current technologies mainly employ the addition of elastomer toughening agents, such as ethylene-acrylic acid copolymer (EBA) and styrene-ethylene-butene-styrene block copolymer (SEBS). However, conventional toughening agents have poor compatibility with PC, resulting in weak interfacial bonding. Under high strain conditions, interfacial debonding easily occurs, limiting the toughening effect and significantly reducing the material's rigidity and heat resistance.

[0005] To improve the dispersion and interfacial bonding of toughening agents, reactive compatibilization methods have been employed, such as using maleic anhydride-grafted polyolefins as compatibilizers. However, single-functional-group compatibilizers can only achieve unidirectional interfacial modification, making it difficult to simultaneously optimize the dispersion morphology of toughening particles in the PC matrix and the synergistic effect with inorganic fillers.

[0006] Adding nanofillers such as nanoclay can improve the stiffness-toughness balance of materials, but nanoclay is prone to agglomeration in polymer matrices, has poor dispersibility, and lacks effective interfacial bridging with PC matrix and toughening phase, making it difficult to fully exert the reinforcing and toughening effect.

[0007] In terms of membrane structure, existing technologies mostly adopt single-layer or simple double-layer co-extrusion structures. Single-layer structures are difficult to balance surface properties and overall mechanical properties; although double-layer structures can achieve functional layering, the layers are prone to delamination under complex tensile deformation, and strain mismatch between different layers can lead to local stress concentration.

[0008] In terms of forming process, traditional vacuum forming typically uses uniform heating, applying the same heating temperature and holding time to the entire film. This process cannot adapt to situations where different areas of the actual product have significantly different stretch ratios: low-stretch areas are prone to overheating, leading to dimensional deformation or sagging, while high-stretch areas suffer from insufficient stretching, stress concentration, or even cracking due to insufficient temperature. Current technical solutions lack gradient temperature control designs based on the material's glass transition temperature.

[0009] In terms of membrane material quality control, poor dispersion of fillers such as nano-clay can lead to crystal point (particle) defects on the membrane surface, severely affecting appearance quality and optical performance. Although existing technologies employ methods such as blending and shear dispersion, they lack systematic pre-composite treatment and multi-stage filtration processes, making it difficult to effectively control crystal point density. Furthermore, traditional uniform heating molding processes result in uneven strain distribution across different stretching ratios. High-stretch areas are prone to overstretching and stress concentration, while low-stretch areas suffer from insufficient deformation and poor stretching uniformity, directly impacting the dimensional accuracy and surface quality of the molded parts.

[0010] Furthermore, existing technologies lack precise control over the size distribution of toughening particles. Toughening particles of a single scale cannot simultaneously meet the requirements of toughness improvement under small deformation and stress dispersion under large deformation, and there is currently a lack of effective technical solutions for how to construct multi-scale toughening particle structures in situ through processing methods. Summary of the Invention

[0011] In view of this, the purpose of this invention is to provide a high-tensile-stretch-resistant INS film and its gradient thermoforming method. By constructing a dual-scale interface compatibility toughening structure, a dual-functional group interface collaborative design, multi-stage filtration crystal point control, and gradient temperature control molding process, this invention solves the technical problems of existing INS films in the deep stretching molding process of complex curved surfaces, such as easy cracking, stress whitening, interlayer delamination, crystal point defects, and uneven stretching, thus meeting the application requirements of deep stretching molding of complex curved surfaces in automotive interiors.

[0012] The present invention solves the above-mentioned technical problems through the following technical means: A high tensile strength and tear-resistant INS film, employing an A / B / A three-layer co-extrusion structure, with a thickness ratio of (10-20):(60-80):(10-20) for the three layers, wherein the INS film comprises: Cortex A is composed of the following components in parts by weight: 5-15 parts of basic polycarbonate (PC) 8-18 parts of interface compatibility toughening particles 3-8 parts of bifunctional reactive compatibilizer 2-6 parts of organic modified nano clay Core layer B is composed of the following components in parts by weight: 30-40 parts of high-impact polystyrene (HIPS) Acrylonitrile-butadiene-styrene copolymer (ABS) 20-30 parts.

[0013] Based on the aforementioned technical methods, a three-layer co-extrusion structure design (A / B / A) is adopted. Layer A uses a PC-based toughening system, providing excellent surface hardness, heat resistance, and transparency. Core layer B uses a HIPS / ABS blend system, providing good overall toughness and processing performance. The thickness ratio of the three layers is controlled at (10-20):(60-80):(10-20), ensuring sufficient strength and wear resistance of the layer while guaranteeing adequate energy absorption capacity of the core layer. This also avoids delamination problems caused by interlayer strain mismatch. In the formulations of layer A and core layer B, the mass fraction represents the relative proportion within each layer. In actual use, the components of layer A and core layer B are prepared according to their mass fraction ratios, and then extruded into a film using a three-layer co-extrusion die at the set thickness ratio.

[0014] By introducing interface-compatible toughening particles into the skin layer A, the toughness of PC can be significantly improved while maintaining its high rigidity. The toughening particles are prepared in situ through reactive extrusion, and a PC-g-SEBS interface compatibility layer is formed between the SEBS dispersed phase and the PC matrix to ensure the interfacial bonding strength. The bifunctional reactive compatibilizer has two terminal epoxy groups that can react with the PC terminal hydroxyl groups, and the middle maleic anhydride segment can react with SEBS to achieve a strong interfacial bond between the toughening particles and the PC matrix. The addition of organic modified nanoclay further improves the rigidity-toughness balance of the material. The synergistic effect of the four components gives the INS film excellent anti-rupture performance when molded at a high stretch ratio (≥2:1).

[0015] Preferably, the interface compatibility toughening particles include primary toughening particles and secondary toughening particles. The number average particle size of the primary toughening particles is 200-600 nm, accounting for 60-80% of the total mass of the toughening particles. Its core is styrene-ethylene-butene-styrene block copolymer (SEBS), and its surface is a PC-g-SEBS grafted compatibility layer. The number average particle size of the secondary toughening particles is 800-2000 nm, accounting for 20-40% of the total mass of the toughening particles. Its core is SEBS, and its surface is a PC-g-SEBS grafted compatibility layer.

[0016] Based on the aforementioned techniques, the toughening particles prepared by exploiting the difference in shear rates in different regions during reactive extrusion exhibit a dual-scale particle size distribution. The primary toughening particles are small in size (200-600 nm) and numerous, effectively terminating crack propagation under low strain conditions and providing basic toughness. The secondary toughening particles are larger in size (800-2000 nm) and can absorb more energy through a voiding mechanism under high strain conditions, preventing stress concentration-induced fracture. The synergistic effect of these two particle sizes gives the material excellent fracture resistance under different stretch ratios. The formation of the PC-g-SEBS graft copolymer in the interfacial region ensures a strong interfacial bond between the toughening particles and the PC matrix, preventing interfacial debonding.

[0017] Preferably, the general structural formula of the bifunctional reactive compatibilizer is as follows: , Wherein X is an epoxy group, selected from glycidyl group, glycidyl oxypropyl group or glycidyl methacrylate group; A is maleic anhydride grafted segment; B is styrene segment; m+n=20-300 and m / (m+n)=0.10-0.40, the number average molecular weight of the compatibilizer is 8,000-60,000 g / mol, and the content of maleic anhydride group is 0.3-1.0wt%.

[0018] Based on the aforementioned technical methods, the bifunctional reactive compatibilizer possesses a symmetrical molecular structure. The epoxy groups at both ends can undergo ring-opening reactions with the terminal hydroxyl groups of the PC molecular chain, while the maleic anhydride segment in the middle can react with the double bonds in SEBS or with other components, achieving interfacial bridging in a multiphase system. The m+n range is 20-300, and the number-average molecular weight is 8,000-60,000 g / mol. This range ensures the compatibilizer has a suitable molecular weight, providing sufficient interfacial bridging capability while maintaining good processing fluidity. The maleic anhydride content is controlled at 0.3-1.0 wt%, ensuring sufficient reaction sites while avoiding excessive cross-linking or degradation. This bidirectional reaction mechanism significantly improves the dispersibility and interfacial bonding strength of the toughening particles, while simultaneously promoting the exfoliation and dispersion of nanoclay.

[0019] Preferably, the bifunctional reactive compatibilizer is pre-composite with the organically modified nanoclay before addition, and the adsorption capacity of the compatibilizer on the clay surface is 0.2-0.8 mg / m². After pre-composite bonding, the interlayer spacing of the clay is... The wavelength ranges from 5.5 to 8.0 nm.

[0020] Based on the aforementioned technical methods, through a pre-composite process, a bifunctional reactive compatibilizer can be intercalated into the interlayer space of nanoclay, expanding the interlayer spacing from the initial approximately 1-2 nm to 5.5-8.0 nm, thus promoting the exfoliation and dispersion of nanoclay in the PC matrix. The appropriate adsorption of the compatibilizer on the clay surface (0.2-0.8 mg / m²) ensures both the intercalation effect and retains sufficient free compatibilizer for interfacial modification of the toughening particles. This pre-composite strategy achieves the dual benefits of the compatibilizer in both nanofiller modification and toughening phase interface optimization, significantly improving the overall mechanical properties of the material.

[0021] This invention also discloses a gradient thermoforming method for a high tensile strength and tear resistance INS film, comprising the following steps: S1: Set up a high-shear mixing zone and a low-shear conveying zone in a twin-screw extruder, add PC and SEBS at a mass ratio of 0.05-0.30:1, add an organic peroxide initiator, and react and extrude at 210-240℃ with a residence time of 60-180 seconds to form dual-scale interface compatibility toughening particles. S2: A pre-composite is obtained by pre-mixing a bifunctional reactive compatibilizer with pre-dried organic modified nanoclay. S3: The components of the skin layer A and the components of the core layer B are fed through two extruders respectively. After they are combined in the three-layer co-extrusion die, they are extruded into a film. The extrusion temperature of the skin layer A is 235-255℃, and the extrusion temperature of the core layer B is 200-230℃. After cooling and shaping, the film is wound up to obtain the INS film. S4: Fix the INS film to the frame of the vacuum forming machine, divide the film into sections according to the product stretch ratio and apply different pretensions. Apply 50-100 N / m to the area with a stretch ratio less than 1.2:1, apply 100-150 N / m to the area with a stretch ratio of 1.2:1-2:1, and apply 150-200 N / m to the area with a stretch ratio greater than or equal to 2:1. S5: At temperature The membrane is heated as a whole at 125-138℃ for 30-60 seconds, and then localized heating is applied to the high-strength areas with a stretch ratio greater than or equal to 2:1 to the specified temperature. The temperature is 158-170℃, and the reheating time is 10-30 seconds; S6: Vacuum forming of the heated film, with a vacuum degree of -0.06 to -0.09 MPa and a forming time of 8-15 seconds; S7: Perform graded cooling on the molded part. The cooling rate is 15-25℃ / s for the high-tension area and 5-10℃ / s for the low-tension area. After cooling, perform contour punching when the temperature of the molded part is 80-110℃ to obtain the INS insert formed by gradient vacuum forming.

[0022] Based on the above technical means, by setting a high-shear mixing zone and a low-shear conveying zone in a twin-screw extruder, dual-scale toughening particles are prepared in situ using the difference in shear rate. The high-shear zone forms small-diameter primary toughening particles, while the low-shear zone forms large-diameter secondary toughening particles, thus avoiding the complex processes of separate preparation and mixing.

[0023] Step S4 applies differentiated pretension based on the stretch ratio of different areas of the product, establishing a stress gradient in the film before molding and reducing stress concentration during the molding process. Step S5 employs a graded heating strategy: first, at a specific temperature... The entire film is heated to 125-138℃ to bring it close to the glass transition temperature of PC (Tg=140-150℃), at which point the material begins to soften but still retains a certain degree of rigidity. Then, localized heating is applied to the high-stretch areas (stretch ratio ≥2:1) to the specified temperature. (158-170℃) This temperature range significantly exceeds the material's tensile strength (Tg), fully softening the material and giving it good ductility, enabling it to withstand large deformations without cracking. The low-tension regions undergo only overall heating, with temperatures close to or slightly below Tg, avoiding dimensional deformation or sagging caused by overheating. This gradient temperature control strategy, based on the material's Tg design, achieves precise temperature matching across different tensile regions.

[0024] Step S7 employs a graded cooling process. A faster cooling rate (15-25℃ / s) is used in the high-tension region to quickly solidify the fully stretched structure and lock in the formed shape. A slower cooling rate (5-10℃ / s) is used in the low-tension region to avoid excessive cooling stress that could lead to warping. The transition region uses a rate of 10-15℃ / s. Contour punching is performed when the formed part temperature is 80-110℃. At this temperature, the material still retains a certain degree of toughness, avoiding cracks that may occur during punching at room temperature.

[0025] Preferably, the organic peroxide initiator in step S1 is selected from one or more of dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP), and the amount added is 0.05-0.5 wt% of the total mass of PC and SEBS.

[0026] According to the above-mentioned technical means, the organic peroxide initiator decomposes during reactive extrusion to generate free radicals, which initiate a grafting reaction between the PC terminal hydroxyl groups and the SEBS molecular chains, forming a PC-g-SEBS copolymer. This copolymer acts as an interfacial compatibilizer, distributed in the interfacial region between the SEBS dispersed phase and the PC matrix, achieving interfacial compatibility. The amount of initiator added is controlled at 0.05-0.5 wt%, which ensures sufficient grafting efficiency while avoiding degradation or cross-linking of the PC backbone caused by excessive initiator. The masterbatch obtained in step S1 is used as a whole component, and its internal components (PC-g-SEBS, SEBS) are not measured separately. In S3, "basic polycarbonate" refers to the pure PC resin added directly, excluding the PC-g-SEBS in the masterbatch.

[0027] Preferably, the high-shear mixing zone in step S1 uses a shear rate of The residence time is 30-90 seconds, forming primary toughening particles; the low-shear transport zone uses a shear rate The residence time is 30-90 seconds, forming secondary toughening particles.

[0028] Based on the aforementioned technical methods, gradient control of toughening particle size was achieved by precisely controlling the shear rate and residence time in different regions. The strong shearing action in the high-shear mixing zone breaks the SEBS dispersed phase into small-diameter particles (200-600 nm), while simultaneously promoting the grafting reaction. Under the mild shear conditions of the low-shear conveying zone, the reduced shear force causes some of the small-diameter particles to aggregate to a certain extent, while retaining some of the insufficiently broken SEBS dispersed phase, forming larger secondary toughening particles (800-2000 nm). Both types of particles are formed in situ during the same extrusion process, resulting in a simple and efficient process.

[0029] Preferably, the organic modified nano-clay in step S2 is dried at 120-150℃ for 2-4 hours before being added; the premixing is carried out by high-speed shearing at a shear rate of 4000-8000 rpm for 10-20 minutes, and the premixed precomposite is filtered through a 200-400 mesh filter.

[0030] According to the above-mentioned technical methods, the organic modifier on the surface of organically modified nanoclay easily adsorbs moisture. The presence of moisture can interfere with the intercalation of the compatibilizer and the subsequent reaction with PC. By drying at 120-150℃ for 2-4 hours, the adsorbed water and interlayer water on the clay surface can be effectively removed, ensuring the pre-composite effect and the performance stability of the final material.

[0031] Preferably, the polycarbonate used in the skin layer A in step S3 has a glass transition temperature of 140-150°C, and the first temperature... Below the glass transition temperature, the second temperature The temperature is higher than the glass transition temperature; a melt filter is installed during the extrusion process, with a filter mesh size of 60-100 mesh, and the filtration temperature is the same as the extrusion temperature.

[0032] Based on the above technical means, by selecting PC with a glass transition temperature of 140-150℃ and designing to meet the requirements... ≤Tg、 The gradient heating temperature (Tg) ensures that the diaphragm is in a state close to or slightly below Tg during the overall heating stage, where the material begins to soften but still retains sufficient shape retention. During the localized reheating stage, the temperature in the high-stretch region exceeds Tg, and the material enters a highly elastic state with excellent ductility, capable of withstanding large deformations without stress whitening or cracking. This Tg-based temperature design is the theoretical basis for achieving gradient molding.

[0033] Preferably, the contour punching in step S7 uses a constant temperature punching tool with the blade temperature controlled at 60-80℃ and the punching speed at 50-150mm / s.

[0034] Based on the above technical methods, a constant-temperature punching tool is used, with the blade temperature controlled at 60-80℃. This maintains a certain local temperature in the material during the punching process, reducing material brittleness and avoiding micro-cracks and burrs that may occur during cold punching. The punching speed is controlled at 50-150mm / s, ensuring both production efficiency and punching quality.

[0035] The present invention, employing the above-described solution, has the following beneficial effects: 1. By constructing an A / B / A three-layer co-extrusion structure and combining it with the synergistic design of dual-scale interface compatibility toughening particles, bifunctional reactive compatibilizers and organically modified nanoclay, the INS film maintains high rigidity and heat resistance while increasing the tensile elongation at break from 105% to 198% and the maximum draw ratio from 1.8:1 to 3.0:1, effectively solving the problems of cracking and stress whitening in deep drawing. 2. The bidirectional reaction mechanism of the bifunctional reactive compatibilizer achieves strong interfacial bonding between toughening particles and PC matrix, and between nanoclay and PC matrix. The interlayer peel strength reaches 19.2 N / mm, which is 54% higher than that of the monofunctional compatibilizer system (12.5 N / mm). The three-layer structure does not produce interlayer peeling under high strain conditions, and the comprehensive mechanical properties of the material are significantly improved. 3. The gradient thermoforming process achieves precise temperature and stress matching in different stretch ratio regions through the coordinated control of differentiated pretension, staged heating and staged cooling. The stress whitening degree (ΔE value) is reduced from 7.5 in the non-gradient process to 2.1. There is no overheating deformation in the low stretching area and the high stretching area is fully extended without cracking. 4. Through the synergistic control of pre-composite high-speed shear dispersion and multi-stage melt filtration processes, the agglomeration of nano-clay was effectively suppressed, and the crystal point density was reduced from 10-15 crystals / m² in conventional processes to 3-8 crystals / m², significantly improving the appearance quality of the membrane. The gradient heating process achieved precise temperature matching in regions with different stretching ratios, and the strain standard deviation σ was reduced from 18.2% in traditional uniform heating processes to 6.5-9.5%, resulting in excellent stretching uniformity and significantly improved dimensional accuracy and surface quality of the molded parts. 5. Dual-scale interface-compatible toughening particles are prepared in situ via reactive extrusion. The process is simple, requiring no separate preparation or mixing of toughening particles, and the particle size distribution is controllable, resulting in stable toughening effect. 6. The INS film and molding process of the present invention can be widely used in complex curved deep-drawn parts of automotive interiors, such as dashboards, door panels, and center consoles, and has good industrial application prospects; Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.

[0037] Polycarbonate (PC): Glass transition temperature 145℃; Bifunctional reactive compatibilizer: prepared by glycidylation modification of styrene-maleic anhydride copolymer (SMA).

[0038] The specific method is as follows: SMA is dissolved in an organic solvent and reacted with a glycidylating agent (such as glycidyl, epichlorohydrin or glycidyl methacrylate) in the presence of a catalyst to graft epoxy groups onto both ends of the SMA, and the target product is obtained by separation and purification.

[0039] By adjusting the reactant ratio and reaction conditions, products of different specifications with epoxy equivalents of 300-700 g / eq and maleic anhydride content of 0.3-1.0 wt% can be obtained.

[0040] Alternatively, commercially available products that meet the above structural requirements may be used.

[0041] The general structural formula of the bifunctional reactive compatibilizer used in this invention is:

[0042] (Where X is an epoxy group, A is a maleic anhydride grafted segment, and B is a styrene segment). All other raw materials were obtained through commercial purchases. Example 1

[0043] S1: A high-shear mixing zone (using a three-lobe kneading block screw assembly) and a low-shear conveying zone (using conveying elements) are set up in a co-rotating twin-screw extruder (screw diameter 35mm, L / D ratio 40:1). 3.6 parts PC and 20 parts SEBS are added at a mass ratio of 0.18:1, along with 0.065 parts DCP (0.275wt% of the total PC and SEBS mass). React extrusion is performed at 225℃ with a total residence time of 120 seconds. The shear rate in the high-shear mixing zone is... Residence time 60 seconds; shear rate in low shear conveying zone The residence time is 60 seconds. The extrudate is cooled and granulated to obtain an interface-compatible toughening particle masterbatch, in which the number average particle size of the primary particles is about 400 nm (70% by mass) and the secondary particles are about 1200 nm (30% by mass). The 3.6 parts of PC in this step are only used to form the PC-g-SEBS interface compatibilizer and are not included in the amount of basic polycarbonate used in the skin layer A formulation.

[0044] S2: The organically modified nano-clay was vacuum dried at 135℃ for 3 hours. After cooling to room temperature, 4 parts of the dried clay and 5.5 parts of a bifunctional reactive compatibilizer (epoxy equivalent 500 g / eq, maleic anhydride content 0.65 wt%, m / (m+n)=0.25) were mixed in a high-speed mixer at a shear rate of 6000 rpm for 15 minutes to obtain 9.5 parts of a pre-composite. The pre-composite was filtered through a 300-mesh filter to remove undispersed large particle agglomerates. The adsorption capacity of the compatibilizer on the clay surface was measured to be 0.5 mg / m². The interlayer spacing of the pre-composite clay was... It is 6.75nm.

[0045] S3: The outer layer A component (10 parts base polycarbonate, 13 parts of the above-mentioned interface-compatible toughening particle masterbatch, and 9.5 parts pre-composite) and the core layer B component (35 parts HIPS and 25 parts ABS) are fed separately through two single-screw extruders (screw diameter 65mm). After converging in a three-layer co-extrusion die, they are extruded into a film. The outer layer A extruder is equipped with an 80-mesh melt filter. The extrusion temperature of the outer layer A is 245℃, and the extrusion temperature of the core layer B is 215℃. The thickness ratio of the three layers is controlled at 15:70:15, and the total film thickness is 0.6mm. After cooling and setting, the film is wound up to obtain the INS film roll for subsequent molding and use.

[0046] S4-S7: Gradient vacuum forming uses an automotive dashboard trim mold (product size 600mm×400mm) as the forming object. CAE analysis was used to determine the stretch ratio of different areas of the film. The stretch ratio of the planar area was less than 1.2:1 (30% of the area), the stretch ratio of the transition area was 1.2:1-2:1 (45% of the area), and the stretch ratio of the deep stretch area was greater than or equal to 2:1 (25% of the area).

[0047] Fix the INS film to the plastic suction machine frame and apply differential pre-tension according to the above-mentioned stretching ratio: 75 N / m for the planar area, 125 N / m for the transition area, and 175 N / m for the deep stretching area. Then carry out hierarchical heating: first heat the whole film at a temperature of 133 °C for 45 seconds (at this time, the Tg of PC is 145 °C, meeting <Tg), so that the film reaches a state close to the glass transition temperature; then locally heat the deep stretching area to a temperature of 162 °C (meeting >Tg), and the heating time is 20 seconds. Infrared heaters are used for supplementary heating (heating power 2.5 kW, 150 mm away from the film surface).

[0048] Immediately carry out vacuum thermoforming after heating is completed. The vacuum degree is -0.075 MPa and the forming time is 12 seconds. After forming, carry out hierarchical cooling on the product: the cooling rate of the deep stretching area is 20 °C / s (using a cold air + cooling water circulation system), the transition area is 12 °C / s, and the planar area is 7.5 °C / s. When the temperature of the formed part drops to 95 °C, carry out contour punching. A constant temperature punching tool is used for punching (the cutting edge temperature is 70 °C, and the punching speed is 100 mm / s) to obtain the finished INS insert after gradient thermoforming. Example 2

[0049] The difference from Example 1 is as follows: S1: The ratio of PC:SEBS is 0.30:1, the reaction temperature is 240 °C, the residence time is 180 seconds, the high shear zone / 90 seconds, the low shear zone / 90 seconds, the DCP addition amount is 0.5 wt%, obtaining primary toughening particles (600 nm, accounting for 80%) and secondary toughening particles (2000 nm, accounting for 20%).

[0050] S2: The epoxy equivalent of the compatibilizer is 700 g / eq, the maleic anhydride content is 1.0 wt%, m / (m + n) = 0.40, the adsorption amount is 0.8 mg / m², the layer spacing is 8.0 nm, and the clay drying conditions are 150 °C / 4 h.

[0051] S3: The formulation of the skin layer A is 15 parts of base PC, 18 parts of interfacial compatibilized toughening particles, 8 parts of compatibilizer, and 6 parts of nano-clay; the formulation of the core layer B is 40 parts of HIPS and 30 parts of ABS; the thickness ratio of the three layers is 20:60:20; the extrusion temperature of the skin layer A is 255 °C, and the extrusion temperature of the core layer B is 230 °C.

[0052] [[ID=​​​The temperature is 170℃ / 30s; the pretension is 100 / 150 / 200 N / m; the vacuum degree is -0.09MPa; the forming time is 15s; the cooling rate is 25℃ / s and 10℃ / s; the punching conditions are 110℃ / 80℃ / 150mm / s.

[0053] Other conditions are the same as in Example 1. Example 3

[0054] The difference from Example 1 is as follows: S1:PC:SEBS ratio of 0.05:1, reaction temperature 210℃, residence time 60 seconds, high shear zone / 30 seconds, low shear zone / 30 seconds, DCP addition amount 0.05wt%, to obtain primary toughening particles (200nm, accounting for 60%) and secondary toughening particles (800nm, accounting for 40%).

[0055] S2: Compatibilizer epoxy equivalent 300g / eq, maleic anhydride content 0.3wt%, m / (m+n)=0.10, adsorption capacity 0.2mg / m², interlayer spacing 5.5nm, clay drying conditions 120℃ / 2h.

[0056] S3: The formulation of the skin layer A is 5 parts of basic PC, 8 parts of interface compatibility toughening particles, 3 parts of compatibilizer, and 2 parts of nano clay; the formulation of the core layer B is 30 parts of HIPS and 20 parts of ABS; the thickness ratio of the three layers is 10:80:10; the extrusion temperature of the skin layer A is 235℃, and the extrusion temperature of the core layer B is 200℃.

[0057] S4-S7: Heating 125℃ / 30s The temperature is 158℃ / 10s; the pretension is 50 / 100 / 150N / m; the vacuum degree is -0.06MPa; the forming time is 8s; the cooling rate is 15℃ / s and 5℃ / s; the punching conditions are 80℃ / 60℃ / 50mm / s.

[0058] Other conditions are the same as in Example 1. Example 4

[0059] The difference from Example 1 is as follows: The initiator used was DTBP, and the amount added was 0.3 wt% of the total mass of PC and SEBS; other conditions were the same as in Example 1.

[0060] Comparative Example 1 The difference from Example 1 is that no interface compatibility toughening particles are added, and the skin layer A contains only 10 parts of basic polycarbonate, 5.5 parts of bifunctional reactive compatibilizer, and 4 parts of organic modified nanoclay, while other conditions are the same as in Example 1.

[0061] Comparative Example 2 The difference from Example 1 is that: a single-scale interface-compatible toughening particle with a number-average particle size of 400 nm is used, and no dual-scale design is performed, while other conditions are the same as in Example 1.

[0062] Comparative Example 3 The difference from Example 1 is that a bifunctional reactive compatibilizer is not used; instead, 5.5 parts of ordinary maleic anhydride-grafted polystyrene (SMA) is used as the compatibilizer, while other conditions are the same as in Example 1.

[0063] Comparative Example 4 The difference from Example 1 is that: the gradient heating process is not used, the entire film is uniformly heated at 145°C for 60 seconds and then directly vacuum-formed without local heating, and other conditions are the same as in Example 1.

[0064] Comparative Example 5 The difference from Example 1 is that a single-layer structure is used, and three-layer co-extrusion is not performed. Only the formulation of skin layer A is used to make a single-layer film with a thickness of 0.6 mm. Other conditions are the same as in Example 1. Performance testing

[0065] The following performance tests were performed on the INS films and molded parts prepared in the above embodiments and comparative examples: (1) Mechanical property testing Tensile strength and elongation at break: Tested according to GB / T 1040.3-2006 standard, with type I dumbbell-shaped specimens cut, tensile speed 50 mm / min, and test temperature 23℃; Notched impact strength: Tested according to GB / T 1043.1-2008 standard, with a sample size of 80mm×10mm×4mm, V-notch, pendulum energy of 5J, and test temperature of 23℃; (2) Molding performance test Maximum tensile ratio: A stepped tensile test was conducted on a standard test mold with grooves of different depths, corresponding to tensile ratios from 1.5:1 to 3.0:1, increasing in increments of 0.1:1. The maximum tensile ratio at which the diaphragm did not break was determined. Stress whitening degree: The ΔE value (color difference) of the deep stretching area (stretch ratio 2:1) before and after molding was measured using a colorimeter (Minolta CM-2600d). ΔE<3 is excellent, 3≤ΔE<5 is good, and ΔE≥5 is poor. Interlayer peel test: The interlayer peel strength is tested according to ASTM D6862 standard. Specimens are cut from the high tensile area of ​​the molded part and the interlayer peel strength is tested using a 90° peel test at a peel speed of 50 mm / min.

[0066] Crystal point density test: Visually inspect the molded film under a standard light source (D65, illuminance 1000 lux) and count the number of visible crystal points with a diameter ≥0.3 mm within a 1 m² area. Use an optical microscope (100x magnification) to randomly select 10 fields of view (each 10 mm × 10 mm) and count the number of tiny crystal points with a diameter of 0.1-0.3 mm.

[0067] (4) Tensile uniformity test: Before molding, a 20mm×20mm grid is printed on the surface of the film. After molding, the grid deformation is measured, the local strain value at each point is calculated, and the strain standard deviation σ is used as the uniformity index. The smaller σ is, the more uniform the stretching.

[0068] Performance Test Comparison Table 1

[0069] Table 2 Test of Crystal Point Density and Tensile Uniformity

[0070] Data Analysis: The performance test results show that the INS films prepared using the technical solution of the present invention in Examples 1-4 all exhibit excellent performance in key indicators such as tensile strength, elongation at break, notched impact strength, maximum stretch ratio, stress whitening control, and interlayer peel strength.

[0071] Among them, Example 1 exhibited the best overall performance, with an elongation at break of 198%, a maximum draw ratio of 3.0:1, a stress whitening ΔE of only 2.1, a tensile strength of 68 MPa, an impact strength of 45 kJ / m², and an interlaminar peel strength of 19.2 N / mm, demonstrating the optimal balance of rigidity and toughness in the median formulation. Example 2, using the upper limit formulation, achieved the highest tensile strength of 70 MPa, an impact strength of 46 kJ / m², and an interlaminar peel strength of 20.2 N / mm, showing outstanding performance in terms of rigidity and interfacial strength. However, its elongation at break (192%) and stress whitening control (ΔE=2.4) were slightly inferior to Example 1, highlighting the importance of a balance between rigidity and toughness. Example 3 verified the lower limit formulation within the scope of the claims, still achieving a maximum draw ratio of 2.5:1, meeting the basic performance requirements. Example 4 verified the applicability of different initiators, achieving an elongation at break of 195%, with performance close to that of Example 1.

[0072] The results of Comparative Examples 1-5 demonstrate the necessity of each technical feature. Comparative Example 1 (without toughening particles): Elongation at break was only 105%, impact strength was 12 kJ / m², and interlaminar peel strength was 13.5 N / mm, far lower than the examples. Comparative Example 2 (single-scale toughening): Maximum tensile ratio was 2.2:1, performance was insufficient. Comparative Example 3 (monofunctional compatibilizer): Interlaminar peel strength was only 12.5 N / mm, interfacial bonding was weak. Comparative Example 4 (without gradient heating): Severe stress whitening (ΔE=7.5), maximum tensile ratio was only 1.9:1, molding quality was poor. Comparative Example 5 (single-layer structure): Overall performance was significantly inferior to the three-layer structure.

[0073] The crystal point density test shows that Examples 1-4 prepared using the method of this invention have a crystal point density of ≤8 points / m², significantly better than Comparative Examples 1 and 3 (12-15 points / m²). Examples 1 and 4, through optimized pre-composite process and melt filtration, reduced their crystal point density to 3 points / m², reaching the superior grade level. Although Comparative Example 4 used a uniform heating process, its film-forming process was the same as Example 1, resulting in a crystal point density of 3 points / m². Comparative Example 5 used a single-layer structure and, although it also employed a filtration process, single-layer extrusion lacked the synergistic dispersion effect of three-layer co-extrusion, resulting in a crystal point density of 6 points / m², still better than the unoptimized comparative example. The tensile uniformity test shows that Examples 1-4 using the gradient heating process had a strain standard deviation σ of ≤9.5%, exhibiting excellent tensile uniformity. In contrast, Comparative Example 4, using the traditional uniform heating process, had a σ as high as 18.2%, indicating overstretching in the high-stretch area and insufficient deformation in the low-stretch area, resulting in poor uniformity. This fully demonstrates the superiority of the gradient heating process.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high tensile strength and tear-resistant INS film, characterized in that, The INS film adopts an A / B / A three-layer co-extrusion structure with a thickness ratio of (10-20):(60-80):(10-20). Cortex A is composed of the following components in parts by weight: 5-15 parts of basic polycarbonate (PC) 8-18 parts of interface compatibility toughening particles 3-8 parts of bifunctional reactive compatibilizer 2-6 parts of organic modified nano clay Core layer B is composed of the following components in parts by weight: 30-40 parts of high-impact polystyrene (HIPS) Acrylonitrile-butadiene-styrene copolymer (ABS) 20-30 parts.

2. The INS film according to claim 1, characterized in that, The interface-compatible toughening particles include primary toughening particles and secondary toughening particles. The number-average particle size of the primary toughening particles is 200-600 nm, accounting for 60-80% of the total mass of the toughening particles. Its main phase is styrene-ethylene-butene-styrene block copolymer (SEBS), and PC-g-SEBS graft copolymer is distributed in the interface region as a compatibilizer. The number-average particle size of the secondary toughening particles is 800-2000 nm, accounting for 20-40% of the total mass of the toughening particles. Its main phase is SEBS, and PC-g-SEBS graft copolymer is distributed in the interface region as a compatibilizer.

3. The INS film according to claim 1, characterized in that, The general structural formula of the bifunctional reactive compatibilizer is as follows: ， Wherein X is an epoxy group, selected from glycidyl group, glycidyl oxypropyl group or glycidyl methacrylate group; A is maleic anhydride grafted segment; B is styrene segment; m+n=20-300 and m / (m+n)=0.10-0.40, the number average molecular weight of the compatibilizer is 8,000-60,000 g / mol, and the content of maleic anhydride group is 0.3-1.0wt%.

4. The INS film according to claim 1, characterized in that, The bifunctional reactive compatibilizer is pre-composite with organically modified nanoclay before addition. The adsorption capacity of the compatibilizer on the clay surface is 0.2-0.8 mg / m². The interlayer spacing of the clay after pre-composite addition is... The wavelength ranges from 5.5 to 8.0 nm.

5. A gradient thermoforming method for a high tensile strength and tear resistance INS film according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Set up a high-shear mixing zone and a low-shear conveying zone in a twin-screw extruder, add PC and SEBS at a mass ratio of 0.05-0.30:1, add an organic peroxide initiator, and react and extrude at 210-240℃ with a residence time of 60-180 seconds to form dual-scale interface compatibility toughening particles. S2: A pre-composite is obtained by pre-mixing a bifunctional reactive compatibilizer with pre-dried organic modified nanoclay. S3: The components of the skin layer A and the components of the core layer B are fed through two extruders respectively. After they are combined in the three-layer co-extrusion die, they are extruded into a film. The extrusion temperature of the skin layer A is 235-255℃, and the extrusion temperature of the core layer B is 200-230℃. After cooling and shaping, the film is wound up to obtain the INS film. S4: Fix the INS film to the frame of the vacuum forming machine, divide the film into sections according to the product stretch ratio and apply different pretensions. Apply 50-100 N / m to the area with a stretch ratio less than 1.2:1, apply 100-150 N / m to the area with a stretch ratio of 1.2:1-2:1, and apply 150-200 N / m to the area with a stretch ratio greater than or equal to 2:

1. S5: At temperature The membrane is heated as a whole at 125-138℃ for 30-60 seconds, and then localized heating is applied to the high-strength areas with a stretch ratio greater than or equal to 2:1 to the specified temperature. The temperature is 158-170℃, and the reheating time is 10-30 seconds; S6: Vacuum forming of the heated film, with a vacuum degree of -0.06 to -0.09 MPa and a forming time of 8-15 seconds; S7: Perform graded cooling on the molded part. The cooling rate is 15-25℃ / s for the high-tension area and 5-10℃ / s for the low-tension area. After cooling, perform contour punching when the temperature of the molded part is 80-110℃ to obtain the INS insert formed by gradient vacuum forming.

6. The method according to claim 5, characterized in that, The organic peroxide initiator mentioned in step S1 is selected from one or more of dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP), and the amount added is 0.05-0.5 wt% of the total mass of PC and SEBS.

7. The method according to claim 5, characterized in that, The high-shear mixing zone in step S1 uses a shear rate The residence time is 30-90 seconds, forming primary toughening particles; the low-shear transport zone uses a shear rate The residence time is 30-90 seconds, forming secondary toughening particles.

8. The method according to claim 5, characterized in that, The organic modified nano-clay mentioned in step S2 is dried at 120-150℃ for 2-4 hours before being added; the premixing is carried out by high-speed shearing, with a shear rate of 4000-8000 rpm and a mixing time of 10-20 minutes; the premixed precomposite is filtered through a 200-400 mesh filter.

9. The method according to claim 5, characterized in that, In step S3, the polycarbonate used in the skin layer A has a glass transition temperature of 140-150°C, a first temperature T1 is lower than the glass transition temperature, and a second temperature T2 is higher than the glass transition temperature; a melt filter device is set in the extrusion process, the filter mesh is 60-100 mesh, and the filtration temperature is the same as the extrusion temperature.

10. The method according to claim 5, characterized in that, The contour punching in step S7 uses a constant temperature punching tool with the blade temperature controlled at 60-80℃ and the punching speed at 50-150mm / s.

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