A dry forming production process for an automotive interior roof

Abstract

The application relates to the technical field of automobile roof substrate processing, and particularly discloses a dry forming production process for an interior trim roof, which specifically comprises the following steps: substrate preparation, after the raw materials in each layer of the substrate are laid well, the substrate is sent into an oven for two-stage heating, then the preheated substrate and roof fabric are jointly sent into a mold for compression molding, wherein a non-woven fabric layer at the bottom of the roof fabric is in contact with and pasted to a fourth adhesive film layer at the top of the substrate, the mold pressure is controlled to be 4-6 MPa, the compression time is controlled to be 30-35 s, and a roof semi-finished product is obtained; and the roof semi-finished product is obtained after further water cutting, trimming and cleaning. The interior trim roof prepared by the application can be used for automobile interior decoration, and has the advantages of good mechanical properties and high interlayer adhesion.

Description

Technical Field

[0001] This invention relates to the field of automotive headliner substrate processing technology, and in particular to a dry molding production process for automotive interior headliners. Background Technology

[0002] In the automotive manufacturing industry, the production process of car interior components has always been an important research area. With the continuous development of the automotive industry, consumers have increasingly higher demands for the quality, environmental friendliness, and comfort of car interiors. As a crucial part of the car interior, the quality of the headliner's production process directly affects the overall quality of the vehicle and the user experience. A high-quality headliner production process not only enhances the overall aesthetics of the car but also provides passengers with a more comfortable driving and riding environment, while also contributing to improved market competitiveness.

[0003] Before the advent of dry molding manufacturing processes for automotive headliners, several conventional production processes existed. One method involved using a single-material substrate, such as ordinary fiberboard or plastic sheeting, and bonding it to the fabric through a simple thermoforming process. However, existing dry molding processes for automotive headliners have significant drawbacks. The single-material or simple composite structure of the substrate used in traditional processes results in insufficient strength and durability of the molded headliner, making it prone to deformation and damage. Ordinary adhesive films have poor bonding performance and heat resistance, easily leading to separation of the headliner fabric from the substrate during long-term use, affecting aesthetics and usability. The single-stage heating method and imprecise temperature, time, and pressure control prevent the substrate from fully fusing and molding, resulting in unstable product quality and difficulty meeting the high-quality requirements of the automotive industry for automotive headliners. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a dry molding process for automotive interior headliner production.

[0005] This application provides a dry molding manufacturing process for automotive interior headliners, employing the following technical solution: A dry molding process for automotive interior headliner production includes the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer. S2. Substrate preheating: The multilayer composite substrate is sent into an oven for two-stage heating. The first stage is preheating at 200-250℃ for 45-50s, and the second stage is heating at 270-320℃ for 45-50s. S3. Compression molding: The preheated substrate and the ceiling fabric are fed into the mold for compression molding. The non-woven fabric layer at the bottom of the ceiling fabric is in contact with the fourth adhesive film layer at the top of the substrate. The mold pressure is controlled at 4-6MPa and the compression time is controlled at 30-35s to obtain the semi-finished ceiling product. S4. After water jet cutting and trimming, clean the semi-finished ceiling product to obtain the finished ceiling product.

[0006] By adopting the above technical solution, its unique material combination structure and precise process control achieve comprehensive improvements in environmental protection, lightweighting, structural strength, and production efficiency. Through the precise lamination design of multi-layer composite substrates (alternating arrangement of non-woven fabric, specific adhesive film, glass fiber layer, and PUR board), each layer of material is precisely brought to a plastic state without degradation under two-stage programmed heating. Subsequently, under appropriate molding pressure and time, the interfaces of each layer achieve a strong interface bond through the melting and penetration of the adhesive film and the mechanical interlocking of the fibers under the action of heat and force, forming a stable "sandwich" structure. Finally, precision trimming via water jet cutting completes the molding process. This process avoids the use of solvent-based adhesives, fundamentally reducing VOC emissions. Furthermore, thanks to the synergistic effect of the PUR board and glass fiber layers, the finished product achieves excellent rigidity, impact resistance, and dimensional stability while maintaining a low unit area weight. Optionally, in step S1, the first adhesive film layer, the second adhesive film layer, the third adhesive film layer, and the fourth adhesive film layer are all modified polypropylene adhesive films, and the specific preparation includes the following steps: (1) Polypropylene granules, α-terpineol and catalyst are added to n-hexane solvent and dispersed evenly. Then, under a nitrogen atmosphere, the temperature is raised to 80-100℃ and reacted for 6-8 hours. After the reaction is completed, the temperature is lowered and cooled. After filtration, washing and drying, the preliminarily modified polypropylene granules are obtained. (2) The modified polypropylene granules are melted, extruded, cooled and shaped at 200-220°C and then stretched to obtain a modified polypropylene film.

[0007] Optionally, the following raw materials are added in parts by weight during the preparation of the modified polypropylene film: 8-12 parts polypropylene granules, 0.2-0.8 parts α-terpineol, and 0.01-0.03 parts Ziegler-Natta catalyst.

[0008] By employing the aforementioned technical solution, polar functional groups are precisely introduced into the polypropylene molecular chain through chemical grafting. The hydroxyl groups in α-terpineol molecules, under the action of a catalyst, undergo a grafting reaction with the polypropylene chain, altering the surface chemical properties of the polypropylene. This results in a film that, when combined with polar materials such as glass fiber and nonwoven fabric, exhibits stronger van der Waals forces and chemical bonds, significantly improving interlayer adhesion strength and effectively solving the problem of insufficient adhesion caused by the surface inertness of traditional polypropylene materials. Furthermore, the rigid cyclic structure of α-terpineol acts as a natural supporting framework, effectively restricting the thermal movement of the polypropylene molecular chains, thereby significantly enhancing the heat resistance and dimensional stability of the film. During the final melt extrusion and biaxial stretching molding process, these modified polypropylene molecular chains undergo highly oriented and regularly arranged arrangement under stress, further improving crystallinity and mechanical strength, and giving the film superior thickness uniformity, internal stress distribution, and surface smoothness. This allows it to provide more stable and reliable bonding performance when used as an adhesive layer in multi-layer composite ceilings, while also helping to improve the overall rigidity, creep resistance, and durability of the ceiling.

[0009] Optionally, in step S1, both the first and second glass fiber layers are made of TCR glass fiber with a basis weight of 40-60 g / m², and the surface of the glass fiber is pretreated with γ-aminopropyltriethoxysilane, with the amount of silane coupling agent coating being 0.3%-0.8% of the glass fiber mass.

[0010] By employing the above technical solution, the ethoxy group in the silane coupling agent molecule generates silanol groups under hydrolysis conditions. These silanol groups undergo dehydration condensation with the silanol groups on the glass fiber surface, forming a strong Si-O-Si covalent bond. Simultaneously, the amino group at the other end of the coupling agent, as a strongly polar functional group, can generate strong hydrogen bonds and chemical bonds with the polar groups in the polyurethane board and modified polypropylene film. This process constructs a solid "molecular bridge" between the inorganic glass fiber and the organic resin matrix, greatly improving the interfacial bonding strength between the two phases, which originally had poor compatibility. This not only effectively prevents interfacial delamination caused by stress concentration and significantly improves the overall mechanical properties of the ceiling, but also reduces performance degradation caused by the penetration of moisture or corrosive media along the interface due to the tight interfacial bonding, thereby enhancing the durability and environmental aging resistance of the composite material.

[0011] Optionally, in step S2, the two-stage heating process is carried out under an inert gas protective atmosphere, wherein the inert gas is nitrogen with a purity ≥99.99% and a flow rate controlled at 10-15 L / min.

[0012] By employing the above technical solution, the chemical inertness of nitrogen effectively isolates oxygen, preventing thermal oxidative degradation, yellowing, or performance deterioration of the substrate components at high temperatures. The nitrogen atmosphere, by maintaining a low-oxygen or even oxygen-free environment, significantly suppresses the risk of molecular chain breakage in the resin matrix due to oxidation, thereby preserving the material's inherent chemical stability and mechanical properties.

[0013] Optionally, in step S3, before compression molding, a layer of atomized reactive hot melt adhesive (PUR) microspheres is uniformly sprayed between the ceiling fabric and the substrate. The microspheres have a particle size distribution of 50-100μm and a spraying density of 5-10g / m².

[0014] By adopting the above technical solution, the microspheres are heated and melted on the surface of the preheated substrate, and then flow and penetrate evenly between the fabric and the substrate during the molding process. The terminal isocyanate (-NCO) groups contained therein then undergo a moisture curing reaction with the moisture in the air or on the surface of the adhered object to generate a polyurethane network structure. This chemical reaction upgrades the bonding from physical anchoring to a strong chemical bond, which greatly enhances the interfacial bonding force and improves the overall mechanical properties of the ceiling.

[0015] Optionally, the waterjet used for waterjet trimming contains abrasive material, which is 80-120 mesh garnet sand, and the mass ratio of abrasive to water is 1:5 to 1:10.

[0016] By adopting the above technical solution, the characteristics of the automotive headliner as a multi-layered composite material are perfectly suited. Its pure cold-cutting characteristics completely eliminate the heat-affected zone, avoiding the drawbacks of traditional thermal cutting (such as laser and plasma) that may lead to fabric scorching, substrate melting, or the generation of harmful gases, thus ensuring the aesthetics and safety of the headliner interior components. At the same time, the enormous kinetic energy and precise control capability of the garnet abrasive waterjet enable it to cleanly and efficiently cut material layers with different mechanical properties, ranging from soft fabrics and fluffy fiber felts to tough adhesive films, forming smooth, burr-free, and delamination-free high-quality cut surfaces. This greatly reduces the need for subsequent finishing processes and improves production efficiency and product quality consistency.

[0017] Optionally, the polyurethane (PUR) board is made from recycled polyether polyol produced by alcoholysis-repolymerization of recycled polyester bottle flakes, and foamed with polyphenyl polymethylene polyisocyanate (PAPI). Its density is 45-55 kg / m³, compressive strength is ≥150 kPa, closed cell rate is ≥90%, and its dimensional change rate after heating at 100°C for 16 h is ≤1.0%.

[0018] By employing the above technical solution, the regenerated polyol molecular structure retains the rigid benzene ring segments of the original PET. These rigid units synergistically interact with the aromatic ring structure in PAPI within the final polyurethane network, significantly enhancing the mechanical strength, dimensional stability, and heat resistance of the foam material. The highly cross-linked network structure and high closed-cell ratio ensure that the foam effectively disperses stress under pressure, while simultaneously constructing an excellent thermal insulation barrier. This allows it to maintain morphological and performance stability over a wide temperature range, greatly improving the product's durability and reliability in demanding applications such as automotive interiors.

[0019] In summary, this application has the following beneficial effects: 1. This application adopts a multi-layer composite substrate design, which uses non-woven fabric, glass fiber, modified film and PUR board alternately and combined with material modification and interface strengthening technology to achieve high bending strength, interlayer peel strength, excellent dimensional stability and resistance to humid heat aging.

[0020] 2. This application preferably uses recycled polyester bottle-sourced PUR boards and a fully dry process (avoiding solvent adhesives). By controlling VOC emissions from the source of materials and the process and achieving lightweight design, it achieves the effects of low VOC, low odor, and low mass per unit area, which is in line with the green and low-carbon development direction of the automotive industry.

[0021] 3. The method of this application achieves precise control of the process and automated production through two-stage programmed heating and nitrogen protection, precise control of molding parameters and high-precision water cutting, thus achieving high production efficiency, good product quality consistency and low scrap rate. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the roof structure prepared according to Example 1 of this application. Detailed Implementation

[0023] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0024] Non-woven fabric layer: Polyester fiber non-woven fabric with a basis weight of 80-120g / m² and a thickness of 0.5-0.8mm is selected; Glass fiber layer: E-glass fiber mat is used with a basis weight of 300-400g / m² and a fiber diameter of 9-13μm; PUR board: Density of 40-50kg / m³, thickness of 3-5mm, and passes the thermal stability test at 150℃ / 30min with a deformation of ≤1%; The ceiling fabric is non-woven fabric (50g / m²) + PU foam (2mm) + warp-knitted fabric (250g / m²), with a total basis weight of 300g / m² and a thickness of 3mm. The dimensional stability after preheating at 75℃ is ≤0.5%.

[0025] Preparation examples of raw materials and / or intermediates Preparation Example 1 A modified polypropylene film is prepared by the following steps: 10 kg of polypropylene granules and 0.5 kg of α-terpineol were added to n-hexane, along with 0.02 kg of Ziegler-Natta catalyst. The mixture was heated to 60-100 °C and reacted for 6-8 hours under a nitrogen atmosphere, with continuous stirring at 200 rpm. After the reaction was completed, the mixture was cooled, drained, filtered, washed, and dried to obtain preliminarily modified polypropylene granules. The amount of n-hexane used was sufficient to fully dissolve the polypropylene granules and terpineol modifier. The modified polypropylene granules were melted and extruded at 210°C to obtain a molten material. The molten material was then cast onto a casting roller, cooled and shaped, and preheated at 120°C for 10 seconds. The preheated material was then subjected to biaxial stretching, and the film thickness was controlled to be 0.1 mm to obtain a modified polypropylene film.

[0026] Preparation Example 2 A modified polypropylene film is prepared by the following steps: 8 kg of polypropylene granules and 0.2 kg of α-terpineol were added to n-hexane, along with 0.01 kg of Ziegler-Natta catalyst. The mixture was heated to 60-100℃ and reacted for 6-8 hours under a nitrogen atmosphere, with continuous stirring at 200 rpm. After the reaction was complete, the mixture was cooled, drained, filtered, washed, and dried to obtain preliminarily modified polypropylene granules. The amount of n-hexane used was sufficient to fully dissolve the polypropylene granules and terpineol modifier. The modified polypropylene granules were melted and extruded at 210°C to obtain a molten material. The molten material was then cast onto a casting roller, cooled and shaped, and preheated at 120°C for 10 seconds. The preheated material was then subjected to biaxial stretching, and the film thickness was controlled to be 0.1 mm to obtain a modified polypropylene film.

[0027] Preparation Example 3 A modified polypropylene film is prepared by the following steps: 12 kg of polypropylene granules and 0.8 kg of α-terpineol were added to n-hexane, along with 0.03 kg of Ziegler-Natta catalyst. The mixture was heated to 60-100 °C and reacted for 6-8 hours under a nitrogen atmosphere, with continuous stirring at 200 rpm. After the reaction was complete, the mixture was cooled, drained, filtered, washed, and dried to obtain preliminarily modified polypropylene granules. The amount of n-hexane used was sufficient to fully dissolve the polypropylene granules and terpineol modifier. The modified polypropylene granules were melted and extruded at 210°C to obtain a molten material. The molten material was then cast onto a casting roller, cooled and shaped, and preheated at 120°C for 10 seconds. The preheated material was then subjected to biaxial stretching, and the film thickness was controlled to be 0.1 mm to obtain a modified polypropylene film.

[0028] Preparation Example 4 A hot melt adhesive (PUR) microsphere is prepared by the following steps: A 15% w / v polyurethane prepolymer solution was prepared by dissolving polyurethane prepolymer in dichloromethane. Sodium dodecyl sulfate was dissolved in deionized water to form a 2% w / v emulsion. 5 kg of polyurethane prepolymer solution was added to 25 kg of emulsion at 10,000 rpm. The mixture was then heated to 40°C while stirring to allow the organic solvent to gradually evaporate. The microspheres were then collected by centrifugation and filtration. After washing with deionized water 2-3 times, the microspheres were dried in a low-temperature vacuum oven to obtain hot melt adhesive (PUR) microspheres with a particle size of 50-100 μm.

[0029] Example

[0030] Example 1

[0031] A dry molding process for automotive interior headliner production includes the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer, which are sequentially laid on an automatic feeding rack. Each layer is compacted with a pressure roller at a pressure of 0.4 MPa to remove air bubbles during laying. S2. Substrate preheating: The multilayer composite substrate is sent into an oven for two-stage heating. The first stage is preheating at 225°C for 47 seconds, and the second stage is heating at 290°C for 47 seconds. S3. Compression molding: The ceiling fabric is preheated at 75℃ for 35s for pretreatment; the preheated substrate and the ceiling fabric are fed into the mold together for compression molding, wherein the non-woven fabric layer at the bottom of the ceiling fabric is in contact with the adhesive film layer at the top of the substrate. The mold temperature is controlled at 200℃, the mold pressure is controlled at 5MPa, and the compression time is controlled at 32s to obtain the semi-finished ceiling product. S4. Position the semi-finished ceiling product on a waterjet cutting fixture. The fixture must match the product contour, with a positioning accuracy ≤0.5mm. Use a waterjet cutter to cut the remaining material. The waterjet pressure is controlled at 310MPa, and the cutting air pressure is controlled at 0.6MPa. At the same time, add 80-120 mesh garnet abrasive, with a mass ratio of abrasive to water of 1:8, to ensure a smooth, burr-free cutting edge. Clean the semi-finished ceiling product after waterjet cutting, including blowing the surface clean with an air gun and wiping the surface dirt with a cloth soaked in alcohol. Then trim the exposed fiber bundles of the glass fiber mat around the perimeter to obtain the finished ceiling product. In this embodiment, the modified polypropylene film prepared in Preparation Example 1 is used as the first, second, third, and fourth film layers. The first and second glass fiber layers are both made of TCR glass fiber with a basis weight of 50g / m². The surface of the glass fiber is pretreated with γ-aminopropyltriethoxysilane, and the coating amount of the silane coupling agent is 0.5% of the glass fiber mass. Its specific structure is as follows: Figure 1 As shown.

[0032] Example 2

[0033] A dry molding process for automotive interior headliner production includes the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer, which are sequentially laid on an automatic feeding rack. Each layer is compacted with a pressure roller at a pressure of 0.4 MPa to remove air bubbles during laying. S2. Substrate preheating: The multilayer composite substrate is sent into an oven for two-stage heating. The first stage is preheating at 200°C for 50 seconds, and the second stage is heating at 270°C for 50 seconds. S3. Compression molding: The ceiling fabric is preheated at 75℃ for 35s for pretreatment; the preheated substrate and the ceiling fabric are fed into the mold together for compression molding, wherein the non-woven fabric layer at the bottom of the ceiling fabric is in contact with the adhesive film layer at the top of the substrate. The mold temperature is controlled at 180℃, the mold pressure is controlled at 6MPa, and the compression time is controlled at 30s to obtain the semi-finished ceiling product. S4. Position the semi-finished ceiling product on a waterjet cutting fixture. The fixture must match the product contour, with a positioning accuracy ≤0.5mm. Use a waterjet cutter to cut the remaining material. The waterjet pressure is controlled at 270-350MPa, and the cutting air pressure is controlled at 0.5MPa. At the same time, add 80-120 mesh garnet abrasive, with a mass ratio of abrasive to water of 1:8, to ensure that the cut edge is smooth and burr-free. Clean the semi-finished ceiling product after waterjet cutting, including blowing the surface clean with an air gun and wiping the surface dirt with a cloth soaked in alcohol. Then trim the exposed fiber bundles of glass fiber mat around the perimeter to obtain the finished ceiling product. In this embodiment, the modified polypropylene film prepared in Preparation Example 2 is used as the first, second, third, and fourth film layers. The first and second glass fiber layers are both made of TCR glass fiber with a basis weight of 40g / m². The surface of the glass fiber is pretreated with γ-aminopropyltriethoxysilane, and the coating amount of silane coupling agent is 0.3% of the glass fiber mass.

[0034] Example 3

[0035] A dry molding process for automotive interior headliner production includes the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer, which are sequentially laid on an automatic feeding rack. Each layer is compacted with a pressure roller at a pressure of 0.4 MPa to remove air bubbles during laying. S2. Substrate preheating: The multilayer composite substrate is sent into an oven for two-stage heating. The first stage is preheating at 250°C for 45 seconds, and the second stage is heating at 320°C for 45 seconds. S3. Compression molding: The ceiling fabric is preheated at 75℃ for 35 seconds for pretreatment; the preheated substrate and the ceiling fabric are fed into the mold together for compression molding, wherein the non-woven fabric layer at the bottom of the ceiling fabric is in contact with the adhesive film layer at the top of the substrate. The mold temperature is controlled at 220℃, the mold pressure is controlled at 4MPa, and the compression time is controlled at 35 seconds to obtain the semi-finished ceiling product. S4. Position the semi-finished ceiling product on a waterjet cutting fixture. The fixture must match the product contour, with a positioning accuracy ≤0.5mm. Cut the remaining material using a waterjet cutter. The waterjet pressure is controlled at 350MPa, and the cutting air pressure is controlled at 0.7MPa. At the same time, add 80-120 mesh garnet abrasive, with a mass ratio of abrasive to water of 1:8, to ensure a smooth, burr-free cut edge. Clean the semi-finished ceiling product after waterjet cutting, including blowing the surface clean with an air gun and wiping the surface dirt with a cloth soaked in alcohol. Then trim the exposed fiber bundles of the glass fiber mat around the perimeter to obtain the finished ceiling product. In this embodiment, the modified polypropylene film prepared in Preparation Example 3 is used as the first, second, third, and fourth film layers. The first and second glass fiber layers are both made of TCR glass fiber with a basis weight of 60g / m². The surface of the glass fiber is pretreated with γ-aminopropyltriethoxysilane, and the coating amount of the silane coupling agent is 0.8% of the glass fiber mass.

[0036] Example 4

[0037] A dry molding process for automotive interior headliners differs from Example 1 in that nitrogen gas is introduced during the two-stage heating process in step S2 of this example. The nitrogen gas purity is ≥99.99%, and the flow rate is controlled at 12.5L / min.

[0038] Example 5

[0039] A dry molding process for automotive interior headliners differs from Example 1 in that nitrogen gas is introduced during the two-stage heating process in step S2 of this example. The nitrogen gas has a purity of ≥99.99% and a flow rate of 10L / min.

[0040] Example 6

[0041] A dry molding process for automotive interior headliners differs from Example 1 in that nitrogen gas is introduced during the two-stage heating process in step S2 of this example. The nitrogen gas has a purity of ≥99.99% and a flow rate of 15L / min.

[0042] Example 7

[0043] A dry molding process for automotive interior headliners differs from Example 1 in that, in this example, a layer of atomized hot melt adhesive (PUR) microspheres is uniformly sprayed between the headliner fabric and the substrate before molding and lamination, with a spraying density of 8 g / m²; the hot melt adhesive (PUR) microspheres are prepared in Preparation Example 4.

[0044] Example 8

[0045] A dry molding process for automotive interior headliners differs from Example 1 in that, in this example, a layer of atomized hot melt adhesive (PUR) microspheres is uniformly sprayed between the headliner fabric and the substrate before molding and lamination, with a spraying density of 5 g / m²; the hot melt adhesive (PUR) microspheres are those prepared in Preparation Example 4.

[0046] Example 9

[0047] A dry molding process for automotive interior headliners differs from Example 1 in that, in this example, a layer of atomized hot melt adhesive (PUR) microspheres is uniformly sprayed between the headliner fabric and the substrate before molding and lamination, with a spraying density of 10 g / m²; the hot melt adhesive (PUR) microspheres are prepared in Preparation Example 4.

[0048] Comparative Example Comparative Example 1 A dry molding process for automotive interior headliners differs from Example 1 in that a polypropylene film is used in this comparative example to replace the modified polypropylene film in the alternative solution.

[0049] Comparative Example 2 A dry molding process for automotive interior headliners differs from Example 1 in that the preheating of the substrate in this comparative example uses a single heating stage, specifically including the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer, which are sequentially laid on an automatic feeding rack. Each layer is compacted with a pressure roller at a pressure of 0.4 MPa to remove air bubbles during laying. S2. Substrate preheating: The multilayer composite substrate is placed in an oven and preheated at 225°C for 47 seconds; the remaining steps are the same as in Example 1.

[0050] Performance testing Detection methods / test methods

[0051] Bending strength: The bending strength of the prepared roof was tested according to the relevant methods of ASTM D790-07; Interlayer peel strength: The interlayer peel strength of the ceiling was tested using the relevant methods of ASTM D3167-2010; Damp heat aging performance test: After being placed at 70℃ and 95%RH for 144h, the sample was conditioned in a standard laboratory environment (23±2℃, 50±5%RH) for 24h to balance the humidity before subsequent mechanical property tests were conducted. The bending strength and interlayer peel strength of the roof before and after damp heat aging were tested, and its performance retention rate was calculated.

[0052] Table 1 Test Data

[0053] Combining Examples 1-3 and Comparative Example 1 with Table 1, it can be seen that the experimental data of Examples 1-3 are all superior to those of Comparative Example 1. This indicates that the polypropylene film modified with α-terpineol, due to the introduction of polar functional groups into its molecular chain, significantly improves the interfacial compatibility and chemical bonding force between the film and polar materials such as glass fiber and non-woven fabric, fundamentally solving the problem of insufficient adhesion caused by the surface inertness of unmodified PP. This allows the material to more effectively transfer and disperse stress after lamination, thereby significantly improving the overall flexural strength and interlayer peel strength of the ceiling.

[0054] Combining Examples 1-3 and Comparative Example 2 with Table 1, it can be seen that the experimental data of Examples 1-3 are all superior to those of Comparative Example 2. This indicates that the two-stage heating process (e.g., pre-baking at 200-250℃ followed by heating at 270-320℃) can more precisely control the heating process of each layer of the substrate (especially the thick core layer PUR board) compared to single-stage heating, ensuring that it uniformly reaches a plastic state without degradation. This ensures that the interfaces of each layer can simultaneously reach the optimal bonding state during subsequent molding, avoiding internal stress concentration or local bonding failure caused by uneven heating. This guarantees the stability of the flexural strength and interlayer peel strength of the ceiling and lays the foundation for good resistance to humid heat aging.

[0055] Combining Examples 1 and 4-6 with Table 1, it can be seen that the experimental data of Examples 4-6 are all superior to those of Example 1. This indicates that introducing a high-purity nitrogen protective atmosphere during the preheating stage can effectively isolate oxygen and prevent the polymer substrate from undergoing thermal oxidative degradation at high temperatures. The chemical inertness of nitrogen protects the integrity of the material's molecular chains, maintaining its inherent mechanical properties and chemical stability. This is beneficial for improving the roof's resistance to damp heat aging, maintaining the long-term durability of interfacial adhesion, and ensuring that the interlayer peel strength remains at a high level even after damp heat aging.

[0056] Combining Examples 1 and 7-9 with Table 1, it can be seen that the experimental data of Examples 7-9 are all superior to those of Example 1. This indicates that spraying PUR hot melt adhesive microspheres between the fabric and the substrate provides a much stronger interfacial bond than physical anchoring through chemical cross-linking formed by the moisture curing reaction. This strong chemical bond effectively resists the erosion and penetration of water molecules in a humid and hot environment, greatly slows down the decrease in adhesion caused by hydrolysis at the interface, and thus significantly improves the interlayer peel strength of the ceiling.

[0057] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A dry molding process for automotive interior headliners, characterized in that, Includes the following steps: S1. Substrate preparation: A multilayer composite substrate is provided, which includes, from bottom to top, a non-woven fabric layer, a first adhesive film layer, a first glass fiber layer, a second adhesive film layer, a polyurethane (PUR) board, a third adhesive film layer, a second glass fiber layer, and a fourth adhesive film layer. S2. Substrate preheating: The multilayer composite substrate is sent into an oven for two-stage heating. The first stage is preheating at 200-250℃ for 45-50s, and the second stage is heating at 270-320℃ for 45-50s. S3. Compression molding: The preheated substrate and the ceiling fabric are fed into the mold for compression molding. The non-woven fabric layer at the bottom of the ceiling fabric is in contact with the fourth adhesive film layer at the top of the substrate. The mold pressure is controlled at 4-6MPa and the compression time is controlled at 30-35s to obtain the semi-finished ceiling product. S4. Water jet trimming: After cleaning the semi-finished ceiling product after water jet trimming, the finished ceiling product is obtained.

2. The dry molding production process for a car interior headliner according to claim 1, characterized in that: In step S1, the first adhesive film layer, the second adhesive film layer, the third adhesive film layer, and the fourth adhesive film layer are all modified polypropylene adhesive films, and the specific preparation includes the following steps: (1) Polypropylene granules, α-terpineol and catalyst are added to n-hexane solvent and dispersed evenly. Then, under a nitrogen atmosphere, the temperature is raised to 80-100℃ and reacted for 6-8 hours. After the reaction is completed, the temperature is lowered and cooled. After filtration, washing and drying, the preliminarily modified polypropylene granules are obtained. (2) The modified polypropylene granules are melted, extruded, cooled and shaped at 200-220°C and then stretched to obtain a modified polypropylene film.

3. The dry molding production process for a car interior headliner according to claim 2, characterized in that, The following raw materials were added in parts by weight during the preparation of the modified polypropylene film: 8-12 parts polypropylene granules, 0.2-0.8 parts α-terpineol, and 0.01-0.03 parts Ziegler-Natta catalyst.

4. The dry molding production process for a car interior headliner according to claim 1, characterized in that: In step S1, both the first and second glass fiber layers are made of TCR glass fiber with a basis weight of 40-60 g / m², and the surface of the glass fiber is pretreated with γ-aminopropyltriethoxysilane. The amount of silane coupling agent coated is 0.3-0.8% of the mass of the glass fiber.

5. The dry molding production process for an automotive interior headliner according to claim 1, characterized in that: In step S2, the two-stage heating process is carried out under an inert gas protective atmosphere, wherein the inert gas is nitrogen with a purity ≥99.99% and a flow rate controlled at 10-15 L / min.

6. The dry molding production process for an automotive interior headliner according to claim 1, characterized in that: In step S3, before the molding and composite forming, a layer of atomized hot melt adhesive (PUR) microspheres is uniformly sprayed between the ceiling fabric and the substrate. The microspheres have a particle size distribution of 50-100μm and a spraying density of 5-10g / m².

7. The dry molding production process for an automotive interior headliner according to claim 1, characterized in that: The waterjet used for the waterjet trimming incorporates abrasive material, specifically 80-120 mesh garnet sand.

8. The dry molding production process for an automotive interior headliner according to claim 1, characterized in that: The polyurethane (PUR) board is made from recycled polyether polyol produced by alcoholysis-repolymerization of recycled polyester bottle flakes, and foamed with polyphenyl polymethylene polyisocyanate (PAPI). Its density is 45-55 kg / m³, compressive strength is ≥150 kPa, closed cell rate is ≥90%, and its dimensional change rate after heating at 100℃ for 16 h is ≤1.0%.

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