Manufacturing process and equipment for light high-brightness plastic product

Abstract

The invention discloses a manufacturing process and equipment for a light high-brightness plastic product, and the process comprises the following steps: firstly, carrying out micro-foaming injection molding by utilizing thermoplastic resin containing supercritical fluid or a chemical foaming agent, and controlling the size and distribution of internal foam holes of a base material by regulating and controlling foaming process parameters, so as to adjust the light transmittance and haze of the base material; performing flame or plasma on-line modification treatment on the surface of the base material by utilizing an automatic surface treatment device in a mold opening or station switching process; finally, a polyurethane reaction system is injected into the surface of the modified base material through a reaction forming technology to form a polyurethane functional layer, and different optical functional areas can be achieved through partition injection or thickness control. Correlation type forming equipment matched with the technology integrates the functions of foaming injection molding, online interface modification and polyurethane reaction forming, in-mold integrated manufacturing of a lightweight foaming base material and a highlight functional surface layer is achieved, and the surface quality, the interface bonding performance and the optical regulation and control capacity of a product can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of polymer material molding and surface functionalization technology, and in particular to a manufacturing process and molding equipment for lightweight high-gloss plastic products. Specifically, it relates to a preparation method based on a combination of micro-foaming injection molding and in-mold polyurethane reaction molding, which can be used to prepare lightweight plastic products with high-gloss surfaces and regionalized optical functional surfaces. Background Technology

[0002] With the rapid development of electrification and intelligence in new energy vehicles, "lightweighting" and "high-quality functional appearance" have become two core demands in the automotive interior and exterior parts manufacturing industry. On the one hand, in order to improve driving range and save energy and reduce emissions, the use of microporous foam injection molding technology to reduce part density and material consumption has become the mainstream trend in the industry. On the other hand, with the popularization of the concept of intelligent cockpit, interior parts are no longer just structural coverings, but are also endowed with optical interactive functions such as ambient lighting and hidden light displays, which places extremely high demands on the light transmittance, haze and surface texture of materials.

[0003] However, due to the surface structure characteristics of microcellular structures, it is usually difficult to achieve a high-gloss surface directly. Therefore, surface quality improvement is typically achieved through surface coatings or films. Among these methods, in-mold polyurethane reaction molding technology can directly form a high-gloss or scratch-resistant surface layer inside the mold, thus avoiding the environmental pollution problems associated with traditional spraying processes.

[0004] In existing technologies, in-mold polyurethane coatings typically form only a surface layer with a uniform structure, primarily serving to enhance the gloss or wear resistance of the product surface. However, with increasing product functional integration, many plastic products not only require a high-gloss appearance but also need to form different optical functional areas on the same part surface, such as light-transmitting areas, light-blocking areas, or light-diffusing areas, to meet application requirements such as hidden displays, ambient lighting, or optical decoration. While traditional spraying or post-processing methods can achieve different functional areas through multiple processing steps, they suffer from complex processes, high costs, and poor interface bonding reliability. Furthermore, existing in-mold coating technologies, due to their simple coating structure, also struggle to achieve complex functional zoning designs.

[0005] Therefore, how to achieve regional or gradient design of surface functional layers on lightweight foamed substrates and complete the construction of multifunctional surface layers in a one-time in-mold molding process has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a manufacturing process and equipment for lightweight, high-gloss plastic products with a short process flow, strong interfacial bonding, and flexible control of light transmittance through molding process parameters.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution, including the following steps: Step 1: Thermoplastic resin melt containing supercritical fluid or chemical foaming agent is injected into the first mold cavity using an injection unit. During this process, the average diameter and distribution density of the cells inside the substrate are precisely controlled by synergistically adjusting process parameters such as injection rate, holding pressure, gas injection pressure, and melt temperature. The optical properties of the substrate are controlled by utilizing the light scattering interface formed by micron-sized bubbles in the polymer matrix. When high-haze, uniformly light-emitting products are required, a high injection rate and high pressure drop process is used to induce high-density nucleation, controlling the average cell diameter within the range of 5μm-50μm, and utilizing the Mie scattering effect to uniformly scatter incident light. When high-shielding products are required, a short-injection foaming process is used to promote cell growth and merging, increasing the average cell diameter, and utilizing the total internal reflection and refraction effects of the gas-solid interface to block light penetration.

[0008] Step 2: After the foamed substrate is formed, the mold is opened for station switching. During this process, an automated modification device emits a high-energy beam (such as a flame or low-temperature plasma) to rapidly scan the substrate surface. This process is completed within the interval between mold opening and closing, introducing polar oxygen-containing functional groups onto the non-polar substrate surface and improving surface bonding performance.

[0009] Step 3: Using a high-precision two-component mixing head, the A and B components of the polyurethane reaction system are dynamically mixed in the mixing chamber, and the mixed reaction system is injected into the mold cavity, so that the polyurethane reacts and cures in situ on the surface of the surface-modified substrate to form a polyurethane functional layer.

[0010] The polyurethane reactive monomers are injected within 1-5 seconds after mixing to ensure that the reaction system has good flowability and interfacial wettability.

[0011] The injection pressure of the polyurethane reaction system is controlled at 5-20MPa, and the injection speed is controlled at 10-80g / s. By controlling the injection path, gate position, or valve needle opening and closing sequence, the polyurethane reaction system can achieve selective filling in different areas of the product.

[0012] During the injection process, by adjusting the local injection volume or controlling the mold cavity gap, the polyurethane functional layer can be formed on the surface of the product with a thickness range of 200-600μm, and a gradient structure with different thicknesses can be formed in different areas.

[0013] After the polyurethane is injected, the reaction and curing are carried out by controlling the mold temperature within the range of 50-120℃ and the curing time is 30-120s, thereby forming a polyurethane functional surface layer with high gloss and high adhesion on the surface of the product.

[0014] Different polyurethane reaction systems with different formulations or injection sequences can be used in different areas to form functional zones such as transparent areas, colored areas or light diffusion areas on the surface of the product, thereby realizing the regional design of the optical functions of the product surface.

[0015] Based on the above process, the present invention also provides a manufacturing equipment for lightweight, high-gloss plastic products, characterized in that it adopts a through-beam layout, comprising: Injection unit: The injection unit is used to plasticize thermoplastic foamed materials and inject them into the mold cavity. It mainly includes: a barrel and heating and temperature control system for heating the thermoplastic resin to a suitable molten state; a plasticizing screw assembly for conveying, compressing and uniformly plasticizing the resin material and fully dispersing the foaming agent in the melt; a foaming agent introduction device for introducing supercritical fluid or chemical foaming agent into the molten resin to form micron-sized bubble structures in the melt; and an injection drive mechanism for driving the screw axially to inject the melt containing the foamed structure into the mold cavity at a set pressure and speed.

[0016] By controlling process parameters such as screw speed, back pressure, barrel temperature and injection speed, a stable micro-foamed structure is formed in the polymer melt during the injection process, thereby obtaining a lightweight foamed substrate.

[0017] Reaction molding unit: The reaction molding unit is used for metering, mixing and injection of polyurethane reaction system. It mainly includes: raw material storage system for storing polyurethane component A and component B raw materials; two-component metering and delivery system for accurately metering the two components and delivering them to the mixing head; and high-precision mixing head for high-speed dynamic mixing of component A and component B in the mixing chamber.

[0018] In a preferred embodiment, the reaction molding unit may also be configured with a multi-gate or multi-valve needle control structure to adjust the injection path and injection sequence of the polyurethane reaction system in the cavity, thereby forming polyurethane functional layers of different areas or thicknesses on the surface of the product.

[0019] Mold and Station Switching System: The mold and station switching system is located between the injection unit and the reaction molding unit to realize the transfer of the substrate between different processing stations. It mainly includes: moving mold assembly and fixed mold assembly, which are used to form the mold cavity structure required for product molding; cavity structure, which is used to complete the injection molding of foamed substrate and the reaction molding of polyurethane functional layer; station conversion mechanism, which is used to carry the substrate to transfer between different injection stations.

[0020] The station conversion mechanism can be a rotary turntable structure or a sliding turntable structure. During the processing, the mold is first located on one side of the injection unit to complete the injection molding of the foamed substrate. Then, the station conversion mechanism transfers the mold cavity containing the substrate to the reaction molding station, where the polyurethane reaction system is injected and cured.

[0021] Online Interface Modification Device: Located within the mold operating space, this device performs online interface modification on the surface of the foamed substrate to improve the interfacial bonding performance between the polyurethane functional layer and the substrate. It mainly includes: a surface treatment unit for generating a flame or plasma beam to activate the substrate surface; a nozzle assembly for spraying the flame or plasma beam onto the substrate surface; a multi-axis motion mechanism for driving the nozzle to move along a trajectory in three-dimensional space, enabling it to scan along the curvature of the substrate surface; and a trajectory control system for adjusting the scanning path and spraying distance according to the surface morphology of the product, thereby achieving uniform interface modification of complex curved surfaces.

[0022] Control system: The equipment also includes a central control system, which coordinates and controls the injection unit, reaction molding unit, mold and station switching system and online interface modification device, so that each process step is executed automatically in the set sequence, thereby realizing continuous production of foamed substrate molding, interface modification and polyurethane reaction molding.

[0023] Compared with the prior art, the present invention has the following significant advantages: Customizable optical properties: This invention innovatively transforms the microfoaming process from a simple "weight reduction method" into an "optical structure manufacturing tool." Without the need for expensive light diffusing agents, by simply adjusting the injection molding process parameters to change the cell structure, products can be flexibly customized from "high light transmittance and uniform light" to "high light blocking," greatly expanding the application of foamed materials in optoelectronic displays, ambient lighting, and other fields.

[0024] High interface bonding strength: By introducing online high-energy beam modification technology, the surface of non-polar substrates is instantly activated under high temperature or residual heat. Through chemical bonding, the industry problem of poor bonding between lightweight materials such as polypropylene (PP), polyethylene (PE), and polycarbonate (PC) and polyurethane (PU) coatings is solved. It also eliminates the traditional offline primer coating process, making it environmentally friendly and pollution-free.

[0025] Lightweight and high quality are achieved simultaneously: the core layer of the product has a microporous foam structure, which can effectively reduce the weight by 10%-30%; the surface layer is a reaction-molded high-gloss polyurethane layer, which perfectly covers the swirling defects caused by foaming and achieves a high-quality curved surface appearance.

[0026] Surface functions can be regionalized: By introducing polyurethane functional layer partition injection or thickness gradient control technology in the in-mold reaction molding stage, different functional layers such as transparent, light-blocking or light-diffusing can be formed on the surface of the product in different areas, realizing the multi-functional integrated design of the same part, breaking through the technical limitations of traditional spraying or coating processes that are difficult to achieve complex functional partitioning.

[0027] High production efficiency: The through-beam equipment layout combined with online processing technology significantly shortens the molding cycle and is suitable for large-scale automated production. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0029] Example 1: High light transmittance functional plastic products Polycarbonate (PC) was selected as the base material, and supercritical carbon dioxide was added as the foaming medium in the injection molding equipment to prepare the foamed substrate through a micro-foaming injection molding process. A high injection rate and a large pressure drop were used during the foaming process to form high-density nuclei in the melt, thereby obtaining a micro-foamed structure with an average cell diameter of approximately 5 μm.

[0030] After the substrate is formed, the mold is opened and the workstation switching stage begins. The surface of the substrate is then subjected to online interface modification treatment by a plasma spray gun installed at the end of the robot arm. This introduces oxygen-containing polar functional groups into the surface of the substrate, thereby improving the interfacial bonding ability between the subsequent coating and the substrate.

[0031] Subsequently, in the reaction molding station, polyurethane component A and component B are dynamically mixed using a high-precision mixing head, and the polyurethane reaction system is injected into the mold cavity to form a polyurethane surface layer with a thickness of approximately 200 μm on the modified substrate surface.

[0032] The resulting products have high light transmittance, with a transmittance of over 80%, and are suitable for transparent decorative parts or light-transmitting display structural parts.

[0033] Example 2: Plastic products with uniform light diffusion function ABS resin was selected as the base material, and supercritical nitrogen was added as a foaming medium during the injection molding process. By controlling the injection rate and holding pressure, a micro-foamed structure with an average diameter of about 30μm was formed inside the base material.

[0034] After the substrate injection molding is completed, the substrate surface is activated online using a flame treatment device set in the mold operating space to improve the surface energy and enhance the interfacial bonding ability of subsequent coatings.

[0035] Subsequently, a polyurethane reaction system is injected into the mold cavity through a reaction molding unit to form a polyurethane functional layer with a thickness of about 400 μm on the surface of the substrate, and the polyurethane system formulation is adjusted to give it light diffusion properties.

[0036] The resulting product allows incident light to be uniformly scattered within the material, achieving a haze of over 70%, making it suitable for lighting covers or decorative parts for ambient lighting.

[0037] Example 3: High-light-shielding plastic products Polypropylene (PP) is selected as the base material. During the injection molding process, a short-injection foaming process is adopted. By reducing the injection pressure and extending the foaming time, the cells grow and merge, thereby forming a cell structure with an average diameter of about 150μm.

[0038] After the substrate is formed, the surface of the substrate is scanned by a low-temperature plasma device to form an activation layer on the substrate surface.

[0039] Subsequently, a colored polyurethane reaction system is injected into the mold cavity through a reaction molding unit to form a polyurethane coating with a thickness of approximately 600 μm on the substrate surface.

[0040] Due to the large bubble structure inside the substrate and the combination with the colored polyurethane surface layer, this product has a low light transmittance of less than 5%, making it suitable for automotive interior sunshades or structural decorative parts.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. For those skilled in the art, various equivalent substitutions or modifications made to the composition of coating materials, process parameters, and implementation methods without departing from the technical concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A process for the manufacture of lightweight, high-gloss plastic articles, characterized in that Includes the following steps: Step 1: Substrate molding and light effect control: Thermoplastic resin melt containing supercritical fluid or chemical foaming agent is injected into the mold cavity using an injection unit. By coordinating the injection rate, holding pressure and melt temperature, the average diameter and distribution density of the cells inside the substrate are controlled. The optical transmittance and haze of the substrate are adjusted by using the light scattering interface formed by micron-sized bubbles in the polymer matrix. Step 2: Online interface modification: When the mold is opened or the work station is switched, the automated modification device linked with the molding equipment emits a high-energy beam to scan the surface of the substrate and introduce polar functional groups on the surface of the substrate. Step 3: Coating Reaction Molding: Using a high-precision mixing head, polyurethane reactive monomers are mixed and injected into the mold cavity, allowing the polyurethane to react and cure on the surface of the modified substrate to form a polyurethane functional layer. The polyurethane functional layer is injected in sections, thickness gradient is controlled, or functional formulation is adjusted according to the functional requirements of different areas of the product, thereby forming a polyurethane surface layer with different optical properties or surface properties on the same product surface.

2. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, In step 1: a high injection rate and high pressure drop process is used to induce high-density nucleation, and the average diameter of the bubble is controlled within the range of 5μm-50μm, so that the incident light is uniformly scattered inside the material; or a short-injection foaming process is used to promote the growth and merging of the bubble, so that the average diameter of the bubble is greater than 100μm, thereby increasing the reflection and scattering of light at the gas-solid interface and reducing the light transmittance.

3. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, The high-energy beam mentioned in step 2 is a flame beam or a low-temperature plasma beam; the scanning process is completed within the gap period of mold opening and closing or during station switching.

4. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, The thermoplastic resin is one or more of polycarbonate, polypropylene, polyethylene or ABS; the foaming medium is supercritical nitrogen, supercritical carbon dioxide or chemical foaming agent.

5. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, In step 3, by controlling the polyurethane injection path or gate position, a functional coating structure with a thickness gradient distribution is formed on the surface of the product using polyurethane.

6. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, In step S3, a transparent polyurethane system, a colored polyurethane system, or a light-diffusing polyurethane system are injected into different areas to form functional zones with light-transmitting, light-shielding, or light-diffusing areas on the surface of the product; or selective injection of the polyurethane reaction system is achieved through a multi-gate, multi-valve needle control method, or the polyurethane functional layer is made to have one or more of the following surface properties by adjusting the polyurethane reaction system formulation or curing conditions: high-gloss surface, scratch-resistant surface, self-healing surface, anti-fingerprint surface, or light-diffusing surface.

7. The manufacturing process of a lightweight, high-gloss plastic product according to claim 1, characterized in that, In step S3, the thickness of the polyurethane functional layer formed is 200μm-600μm.

8. The manufacturing process of a lightweight, high-gloss plastic product according to claims 1-7, characterized in that, The prepared product comprises, from the inside out, a thermoplastic microfoam substrate layer, a modified interface layer, and a polyurethane surface layer; the thermoplastic microfoam substrate layer has a closed-cell or semi-open-cell microfoam structure, and the microfoam structure is configured to have an optical adjustment function that enables the product to have a light transmittance of 5%-85%; the modified interface layer is located between the thermoplastic microfoam substrate layer and the polyurethane surface layer, and is formed by surface activation treatment to form an oxygen-containing polar functional group structure, thereby improving the interfacial bonding strength between the two layers.

9. A manufacturing equipment for lightweight, high-gloss plastic products, characterized in that, The manufacturing process for a lightweight, high-gloss plastic product according to claim 1, employing a through-beam layout, includes: Injection unit: used to plasticize and inject thermoplastic resin material containing foaming medium; Reaction molding unit: arranged opposite to the injection unit or at a specific angle, used to meter, mix polyurethane reactive monomers and inject polyurethane; Mold and station switching system: set between two injection units, including moving mold, fixed mold and rotating or sliding mechanism for carrying the substrate between different injection stations; Online interface modification device: an automated surface treatment system set in the mold operating space, which is equipped with flame nozzle or plasma spray gun and has multi-axis linkage function to follow the surface curvature of the substrate for trajectory scanning.

10. The manufacturing equipment for lightweight, high-gloss plastic products according to claim 9, characterized in that, The online interface modification device is integrated into the end of the picking robot or installed on a separate linear module, and its operation is controlled by the control system in conjunction with the mold opening and closing action.