A process for integrally molding an injection-molded coating on a large-size exterior automotive covering

Abstract

The application discloses a kind of automobile large-size outer covering injection coating integrated forming processes, comprising the following steps: selecting modified polypropylene granules, in-mold injection molding preparation automobile outer covering skeleton;Rotary mould is opened, and the surface modification of skeleton is handled using flame or PP treating agent, and the mould is rotated again, and the temperature of mould is controlled at 50-90 DEG C, and time is 1-30 min;In-mold painting is used to set injection reaction forming polyester paint, and after pressure maintaining, cooling, a layer of soft coating is formed on the surface of outer covering, to realize the in-mold painting of outer covering.The one-step method realizes the injection coating integrated forming of large-size automobile outer covering, reduces the manufacturing process, solves the environmental pollution of traditional paint spraying, realizes the lightweight, customized green manufacturing of automobile outer covering, and meets the high-beat, batch manufacturing requirements of automobile.

Description

Technical Field

[0001] This invention relates to the field of automotive injection molding technology, and in particular to an integrated injection molding and coating process for large-size automotive exterior trim parts. Background Technology

[0002] With the increasing severity of global climate change and environmental problems, governments worldwide are placing greater emphasis on the sustainable development of a low-carbon economy. Achieving energy conservation and emission reduction in the automotive industry is of great significance to both the industry's sustainable development and overall economic development.

[0003] In the transportation equipment manufacturing industry, which is mainly based on automobile manufacturing, the energy consumption of automobile painting workshops accounts for about 70% of the total energy consumption of automobile production. The carbon-based emissions are large, and the task of green transformation is urgent. There is an urgent need to develop new short-process, high-quality and efficient painting technologies.

[0004] Key equipment and process technologies for integrated injection molding and coating not only bring about lightweight improvements in parts and products and reduce manufacturing processes, but also save energy, reduce environmental pollution, and enable high-speed manufacturing, thus becoming a leading trend in the molding and manufacturing of automotive non-metallic parts. However, integrated injection molding and coating technology has not yet achieved mass production and large-scale application, especially the development of complete sets of technologies for large-size automotive exterior body panels is still immature.

[0005] For example, patent CN116533436A discloses an integrated injection molding and painting process for automotive interior parts. This process utilizes ABS injection molding to form a skeleton and trim flash, followed by spraying, injection molding of PPT soft plastic, and secondary spraying to prepare the automotive interior parts. While this process simplifies the process to some extent, it still requires secondary spraying and flash repair, making the process cumbersome and prone to environmental pollution, thus failing to meet the requirements of green manufacturing. Another example is patent CN117774191A, which discloses an in-mold painting molding die and method. This method uses a combination of concave and convex molds and sealing plates to create a sealed cavity for the painted product. After the product is first formed in the mold, paint is injected into the cavity using a micro-opening method, directly painting the parts within the mold. While this method can save energy and reduce environmental pollution to some extent, the micro-opening requires high precision and is difficult to design, potentially leading to defects such as flash and a decline in product quality.

[0006] Therefore, in order to address the problems existing in the current injection molding and coating integrated molding process, achieving integrated molding of complex structures for large-size automotive exterior covering parts is an urgent need for high-speed automotive manufacturing and a trend to promote the automotive industry toward low-carbon, green and sustainable economic development. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an integrated injection molding and coating process for large-size automotive exterior trim parts, which simplifies the process and enables high-speed, batch integrated injection molding and coating.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] The injection molding and painting process for this large-size automotive exterior panel includes the following steps:

[0010] S1. Select modified polypropylene granules and use in-mold injection molding to prepare the skeleton of automotive exterior trim panels;

[0011] S2. Open the mold and rotate the mold. Use flame or PP treatment agent to modify the surface of the skeleton. Then rotate the mold again, close the mold and control the mold temperature at 50-90℃ for 1-30 minutes.

[0012] S3. In-mold painting uses equipment to inject reaction-molded polyester paint. After pressure holding and cooling, a soft coating layer is formed on the surface of the exterior covering, realizing in-mold coating of the exterior parts.

[0013] In step 1, the injection molding method for the exterior trim frame is as follows:

[0014] 1) The injection molding raw material is dried and melted by heating;

[0015] 2) The molten injection molding material is injected into the mold cavity through the injection molding equipment;

[0016] 3) Maintain pressure and cool the mold cavity.

[0017] The injection molding raw material is EPDM, talc, or glass fiber modified polypropylene granules, wherein the glass fiber modified polypropylene granules are 0.2-0.6mm short glass fiber reinforced polypropylene or 5-20mm long glass fiber reinforced polypropylene, with a fiber content of 10-60% and a linear expansion coefficient of less than 35×10. -6 m / (m·K)

[0018] The heating and melting temperature range of the injection molding granules is 180-300℃; the injection pressure is 800-1000 bar; the holding pressure is 300-500 bar; and the cooling time is 10-20 s.

[0019] In step S2, the mold is rotated 90°, and a robotic arm is used to operate a flame gun to flame treat the outer frame of the trim piece. Methane and air mixture is preferred as the combustion source, with an equivalent ratio of 0.9-1.2, a total flow rate of 100-150 L / min, a treatment distance of 75-85 mm, and a flame treatment exposure time of 20-30 ms.

[0020] In step S3, the in-mold painting process is as follows:

[0021] 1) Place the A and B two-component polyester paints into vacuum storage tanks respectively, preferably at a temperature of 40-70℃ and a stirring speed of 500-800 r / min;

[0022] 2) Open the mixing head. Material A and material B are metered into the mixing chamber by the high-pressure pump and mixed evenly. They are then injected into the cavity containing the outer frame of the trim at a certain speed to form a paint surface on the component. After curing, pressure holding and cooling, the in-mold painting is completed.

[0023] 3) Apply clamping force to open the mold and remove the injection-molded and coated integrated product.

[0024] In step S3, component A is isocyanate, and component B is a mixture of polyester polyol or polyether polyol, catalyst, diamine chain extender, additives, and color paste. The preferred ratio of A to B is 1:1 to 1:2.

[0025] In step S3, the pumping pressure of material A and material B is 20-30 MPa, the pumping speed is 80-120 g / s, the curing time is 10-20 s, the curing temperature (i.e., the mold temperature) is 50-70℃, the holding pressure is 200-300 bar, and the cooling time is 10-20 s; the thickness of the in-mold paint film is 300-500 μm.

[0026] The preferred molding process includes the following steps:

[0027] Pretreatment of injection molding substrate: A certain amount of long glass fiber modified polypropylene granules are placed in a drying oven and dried at a temperature of 90-100℃.

[0028] Injection molding of automotive exterior body panel skeleton: Vacuum feeding is used to precisely measure and evenly deliver granules into the injection molding machine hopper. The injection molding machine controller then directs the granules into the injection molding machine barrel. The granules are heated, melted, sheared, and mixed within the machine to form a fluid plastic melt. The injection molding machine barrel has four temperature zones set between 180-300℃. Mold closing and injection filling are performed with a clamping pressure of 500-2000T, a mold temperature of 25-90℃, and an injection pressure of 500-1000 bar. Holding pressure, shrinkage compensation, and cooling are then performed, with a holding pressure of 100-500 bar and a cooling time of 5-40 seconds.

[0029] Surface treatment of automotive exterior trim frame: Open the mold and rotate the mold table 90° counterclockwise. Use a robotic arm to perform flame treatment on the automotive exterior trim frame. The fuel is a mixture of methane and air with an equivalent ratio of 0.5-1.5, a total flow rate of 60-200 L / min, a treatment distance of 60-120 mm, and a flame treatment exposure time of 10-50 ms.

[0030] In-mold painting of automotive exterior trim frame: The mold turntable rotates counterclockwise by 90°, the mold is closed and the mold temperature is controlled at 50-100℃. Material A and material B are metered by a high-pressure pump and then enter the mixing chamber. They are mixed evenly by high-speed collision in the mixing chamber and then quickly injected into the mold cavity to complete the paint filling of the exterior trim frame. The injection pressure is 10-50 MPa, the injection speed is 30-270 g / s, the curing time is 5-60s, the holding pressure is 10-50 MPa, the cooling time is 5-40s, and the resulting paint film thickness is 100-500um.

[0031] Apply the clamping force, open the mold, eject the sample through the ejector pin, and remove it using a robotic arm.

[0032] The injection-molded and coated integrated product has an A-grade surface appearance.

[0033] The automotive exterior coverings include front and rear bumpers, roof, doors, engine hood, or A, B, and C pillar crossbeams.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The design of this large-size automotive exterior panel injection molding and painting integrated molding process is reasonable. It realizes the integrated molding of large-size automotive exterior panel injection molding and painting in one step, which reduces manufacturing processes and solves the environmental pollution of traditional painting. It realizes lightweight, customized and green manufacturing of automotive exterior panel components, and meets the needs of high-speed and mass production of automobiles. Attached Figure Description

[0036] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0037] Figure 1 This is a schematic diagram of the cover structure according to an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the surface treatment of the skeleton in this invention.

[0039] Figure 3 This is a schematic diagram of the in-mold painting system of the present invention.

[0040] Figure 4 This is a schematic diagram of the integrated injection molding and coating process of the present invention.

[0041] In the picture:

[0042] 1. Paint, 2. Panel in injection molded frame, 3. Reinforcing rib structure in injection molded frame,

[0043] 21. Methane gas, 22. Air, 23. Gas flow control valve, 24. Combustion chamber, 25. Flame, 26. Sample

[0044] 31. Slurry A, 32. Slurry B, 33. Mixing head liquid system, 34. Metering pump controller, 35. Paint flow direction, 36. Mixing head. Detailed Implementation

[0045] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and through the description of the examples.

[0046] like Figures 1 to 4 As shown, the in-mold injection molding and painting integrated molding process for this large-size automotive exterior trim panel includes the following steps:

[0047] 1. Modified polypropylene granules were selected and in-mold injection molded to prepare the skeleton of automotive exterior trim panels;

[0048] 2. Open the mold and rotate it counterclockwise by 90°. Use flame or PP treatment agent to modify the surface of the skeleton. Rotate the mold counterclockwise by 90°, close the mold and control the mold temperature at 50-90℃ for 1-30 minutes.

[0049] 3. In-mold coating uses RIM equipment to inject reactive polyester paint. After pressure holding and cooling, a soft coating layer is formed on the surface of the exterior trim, realizing in-mold coating of the exterior trim.

[0050] Preferably, the exterior trim frame in step 1 is injection molded, and the specific method is as follows:

[0051] 1) The injection molding raw material is dried and melted by heating;

[0052] 2) The molten injection molding material is injected into the mold cavity through the injection molding equipment;

[0053] 3) Maintain pressure and cool the mold cavity.

[0054] in,

[0055] The injection molding raw material mentioned in 1) is EPDM, talc, or glass fiber modified polypropylene granules. The glass fiber modified polypropylene granules can be short glass fiber (0.2-0.6 mm) reinforced polypropylene or long glass fiber (5-20 mm) reinforced polypropylene, with a fiber content of 10-60% and a linear expansion coefficient of less than 35 × 10⁻⁶. -6 m / (m·K). To ensure the material's rigidity, strength, and dimensional stability, long fiber reinforced polypropylene granules are preferred, with a fiber content of 20%-30%.

[0056] The heating and melting temperature range of the injection molding granules mentioned in 2) is 180-300℃, preferably 200-280℃;

[0057] 3) The preferred injection pressure is 800-1000 bar, the holding pressure is 300-500 bar, and the cooling time is 10-20 seconds;

[0058] Preferably, the surface treatment of the exterior trim frame in step 2 is specifically as follows: the mold is rotated 90°, and a flame gun is operated by a robotic arm to perform flame treatment on the exterior trim frame sample 26. Preferably, a mixture of methane gas 21 and air 22 is used as the combustion source. The flow rate is controlled by a gas flow control valve 23, and the flame 25 is mixed and controlled in the combustion chamber 24. The equivalent ratio is preferably 0.9-1.2, the total flow rate is preferably 100-150 L / min, the treatment distance is preferably 75-85 mm, and the flame treatment exposure time is 20-30 ms.

[0059] Preferably, the in-mold painting process in step 3 is carried out as follows:

[0060] 1) Place the two-component polyester paint, slurry A31 and slurry B32, into a vacuum storage tank, mix them in the liquid system 33 of the mixing head, control the flow rate through the metering pump controller 34, preferably control the temperature at 40-70℃, and preferably control the stirring speed at 500-800r / min;

[0061] 2) Open the mixing head 36. Material A and material B are metered into the mixing chamber by the high-pressure pump and mixed evenly. According to the paint flow direction 35, they are injected into the cavity containing the outer frame of the component through the mixing head at a certain speed, forming a paint surface on the component. After curing, pressure holding and cooling, the in-mold painting is completed.

[0062] 3) Apply clamping force to open the mold and remove the injection-molded and coated integrated product.

[0063] Preferably, in step 3, component A is mainly isocyanate, and component B is a mixture of polyester polyol or polyether polyol, catalyst, diamine chain extender, additives, color paste, etc. The ratio of A to B is preferably 1:1 to 1:2.

[0064] Preferably, in step 3, 2), the pumping pressure of material A and material B is preferably 20-30 MPa, the pumping speed is preferably 80-120 g / s, the curing time is preferably 10-20 s, the curing temperature (i.e., the mold temperature) is preferably 50-70℃, the holding pressure is preferably 200-300 bar, and the cooling time is preferably 10-20 s.

[0065] Preferably, the thickness of the in-mold paint film in step 3(2) is 300-500 μm.

[0066] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0067] The in-mold injection molding and coating process significantly increases design freedom and meets the diverse functional requirements of parts. By adjusting the injection material and surface modification, the tensile strength of the panel (300-800 MPa), the modal characteristics (25-50 Hz), and the bending stiffness (45-110 N / mm) can be adjusted, while the weight is reduced by 20-50% compared to the raw materials.

[0068] The injection molding and coating integrated molding process can effectively solve the problems of high equipment requirements, complicated processes and environmental pollution in the traditional preparation of exterior parts. It can achieve one-time molding of product structure and painting, smooth outer surface, low warpage, continuous mass production and recyclability. The processing time of a single part is 3-10 minutes, the production cycle efficiency is increased by 30%-60%, and energy consumption is reduced by 30%-50%. It realizes one-step molding of large-size parts in a lightweight and green manner.

[0069] The in-mold injection coating process effectively solves the problems of high energy consumption and high emissions in traditional automotive coating, enabling in-mold painting of large-sized parts with a paint film thickness of 300-500 μm and an A-grade surface appearance.

[0070] Through the combined effects of the above, the manufacturing process of integrally molded lightweight thermoplastic composite automotive exterior parts is significantly shortened, equipment requirements are reduced, and post-bonding is eliminated. The products have high design freedom and strength and can be used to manufacture automotive front and rear bumpers, car roofs, doors, engine hoods, or A, B, and C pillar crossbeams, achieving lightweight and green manufacturing of parts.

[0071] like Figure 4 As shown, the molding process of this invention is as follows: mold closing a-injection molding of the automotive exterior trim frame b-flame modification treatment of the frame surface c-in-mold painting of the frame d-mold opening and part removal e; the corresponding trim structure includes paint 1, panel 2 in the injection molded frame and reinforcing rib structure 3 in the injection molded frame; preferably, it includes the following steps:

[0072] Pretreatment of injection molding substrate: A certain amount of long glass fiber modified polypropylene granules are placed in a drying oven and dried at a temperature of 90-100℃.

[0073] Injection molding of automotive exterior body panel skeleton: Vacuum feeding is used to precisely measure and evenly deliver granules into the injection molding machine hopper. The injection molding machine controller then directs the granules into the injection molding machine barrel. The granules are heated, melted, sheared, and mixed within the machine to form a fluid plastic melt. The injection molding machine barrel has four temperature zones set between 180-300℃. Mold closing and injection filling are performed with a clamping pressure of 500-2000T, a mold temperature of 25-90℃, and an injection pressure of 500-1000 bar. Holding pressure, shrinkage compensation, and cooling are then performed, with a holding pressure of 100-500 bar and a cooling time of 5-40 seconds.

[0074] Surface treatment of automotive exterior trim frame: Open the mold and rotate the mold table 90° counterclockwise. Use a robotic arm to perform flame treatment on the automotive exterior trim frame. The fuel is a mixture of methane and air with an equivalent ratio of 0.5-1.5, a total flow rate of 60-200 L / min, a treatment distance of 60-120 mm, and a flame treatment exposure time of 10-50 ms.

[0075] In-mold painting of automotive exterior trim frame: The mold turntable rotates counterclockwise by 90°, the mold is closed and the mold temperature is controlled at 50-100℃. Material A and material B are metered by a high-pressure pump and then enter the mixing chamber. They are mixed evenly by high-speed collision in the mixing chamber and then quickly injected into the mold cavity to complete the paint filling of the exterior trim frame. The injection pressure is 10-50MPa, the injection speed is 30-270 g / s, the curing time is 5-60s, the holding pressure is 10-50 MPa, the cooling time is 5-40s, and the resulting paint film thickness is 100-500um, which meets the requirements of automotive Class A surface.

[0076] Apply the clamping force, open the mold, eject the sample through the ejector pin, and remove it using a robotic arm.

[0077] A preferred embodiment of the present invention is as follows:

[0078] This invention relates to automotive exterior components, including front and rear bumpers, a roof, doors, engine covers, or A, B, and C pillar crossbeams, etc. This embodiment specifically describes the fabrication of an engine cover for a new energy vehicle, with the following specific steps:

[0079] (1) Pretreatment of injection molding substrate: A certain amount of long glass fiber modified polypropylene granules are placed in a drying oven and dried at a temperature of 90-100℃.

[0080] (2) Injection molding of automotive exterior trim frame: The granules are precisely metered and evenly conveyed into the injection molding machine hopper using a vacuum feeding method. The granules are then conveyed into the injection molding machine barrel via the injection molding machine controller. The granules are heated, melted, sheared, and mixed in the injection molding machine to form a fluid plastic melt. The injection molding machine barrel has four temperature zones set at 180-200℃. Mold closing and injection filling are performed with a clamping pressure of 800-1000T, a mold temperature of 30-50℃, and an injection pressure of 600-800 bar. Pressure holding, shrinkage compensation, and cooling are then performed, with a holding pressure of 150-200 bar and a cooling time of 5-10 seconds.

[0081] (3) Surface treatment of automotive exterior covering skeleton: Open the mold and rotate the mold table counterclockwise by 90°. Use a robotic arm to perform flame treatment on the automotive exterior covering skeleton. The fuel is a mixture of methane and air with an equivalent ratio of 0.5-1.0, a total flow rate of 100 L / min, a treatment distance of 60 mm, and a flame treatment exposure time of 15 ms.

[0082] (4) In-mold painting of automotive exterior trim frame: The mold turntable is rotated 90° counterclockwise, the mold is closed and the mold temperature is controlled at 50-100℃. Material A and material B are circulated separately before mixing. The mixing head is opened and materials A and B are metered by a high-pressure pump and then enter the mixing chamber. They are mixed evenly by high-speed collision in the mixing chamber and quickly injected into the mold cavity to complete the filling of the exterior trim frame paint surface. The injection pressure is 10-50 MPa, the injection speed is 30-270 g / s, the curing time is 5-60s, the holding pressure is 10-50 MPa, the cooling time is 5-40s, and the resulting paint film thickness is 100-500um, which meets the requirements of automotive Class A surface.

[0083] The large-size automotive exterior panel injection molding and coating integrated molding process of this invention achieves controllability of performance parameters such as no shrinkage marks, no warping, tensile strength of 300-800 MPa, component modal characteristics of 25-50 Hz, and bending stiffness of 45-110 N / mm from four aspects: material and structural design, surface treatment, and molding process. Moreover, the weight is reduced by 20-50% compared with raw materials, making it an excellent choice for lightweight and green manufacturing of automotive exterior panels.

[0084] The above description is merely an illustration of preferred embodiments of the present invention, and the above technical features can be arbitrarily combined to form multiple embodiments of the present invention.

[0085] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the concept and technical solution of the present invention, or the direct application of the concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A process for integrated injection molding and coating of large-size automotive exterior trim panels, characterized in that: Includes the following steps: S1. Select modified polypropylene granules and use in-mold injection molding to prepare the skeleton of automotive exterior trim panels; S2. Open the mold and rotate the mold. Use flame or PP treatment agent to modify the surface of the skeleton. Then rotate the mold again, close the mold and control the mold temperature at 50-90℃ for 1-30 minutes. S3. In-mold painting uses equipment injection reaction molding polyester paint. After pressure holding and cooling, a soft coating layer is formed on the surface of the exterior covering, realizing in-mold coating of the exterior parts. in, In step S2, the mold is rotated 90°, and a robotic arm is used to operate a flame gun to flame treat the outer frame of the trim piece. A mixture of methane and air is used as the combustion source, with an equivalent ratio of 0.9-1.2, a total flow rate of 100-150 L / min, a treatment distance of 75-85 mm, and a flame treatment exposure time of 20-30 ms. In step S3, the in-mold painting process is as follows: 1) Place the A and B two-component polyester paints in vacuum storage tanks respectively, control the temperature at 40-70℃, and the stirring speed at 500-800 r / min; 2) Open the mixing head. Material A and material B are metered into the mixing chamber by the high-pressure pump and mixed evenly. They are then injected into the cavity containing the outer frame of the trim at a certain speed to form a paint surface on the component. After curing, pressure holding and cooling, the in-mold painting is completed. 3) Apply clamping force to open the mold and remove the injection-molded and coated integrated product; In step S3, the pumping pressure of material A and material B is 20-30 MPa, the pumping speed is 80-120 g / s, the curing time is 10-20 s, the curing temperature (i.e., the mold temperature) is 50-70℃, the holding pressure is 200-300 bar, and the cooling time is 10-20 s; the thickness of the in-mold paint film is 300-500 μm.

2. The injection molding and painting integrated molding process for large-size automotive exterior trim panels as described in claim 1, characterized in that: In step 1, the injection molding method for the exterior trim frame is as follows: 1) The injection molding raw material is dried and melted by heating; 2) The molten injection molding material is injected into the mold cavity through the injection molding equipment; 3) Maintain pressure and cool the mold cavity.

3. The injection molding and painting integrated molding process for large-size automotive exterior trim panels as described in claim 2, characterized in that: The injection molding raw material is EPDM, talc, or glass fiber modified polypropylene granules, wherein the glass fiber modified polypropylene granules are 0.2-0.6mm short glass fiber reinforced polypropylene or 5-20mm long glass fiber reinforced polypropylene, with a fiber content of 10-60% and a linear expansion coefficient of less than 35×10. -6 m / (m·K) The heating and melting temperature range of the injection molding granules is 180-300℃; the injection pressure is 800-1000 bar; the holding pressure is 300-500 bar; and the cooling time is 10-20 s.

4. The injection molding and painting integrated molding process for large-size automotive exterior trim panels as described in claim 1, characterized in that: In step S3, component A is isocyanate, and component B is polyester polyol or polyether polyol, catalyst, diamine chain extender, additives, and color paste compound. The ratio of A to B is 1:1 to 1:

2.

5. The injection molding and painting integrated molding process for large-size automotive exterior trim panels as described in claim 1, characterized in that: The automotive exterior coverings include front and rear bumpers, roof, doors, engine hood, or A, B, and C pillar crossbeams.

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