Method for preparing decorative moulding from composite plastic foam reclaimed material

Abstract

The invention discloses a method for preparing a decorative moulding from a composite plastic foam reclaimed material. The method comprises seven steps of raw material pretreatment, crushing and mixing, melting granulation, raw material mixing, induced foaming and extrusion molding, surface layer co-extrusion, surface treatment and post-processing. Precise sorting of EPS and PE foam is achieved through density screening and manual sorting, the material compatibility is improved through differential vacuum compression and compatilizer modification, and the purity of regenerated materials is ensured through double-layer filter screen filtration and vacuum air exhaust. A high-frequency electric field induced foaming technology is innovatively introduced to eliminate internal stress, and HIPS co-extrusion coating and refined surface treatment are matched, so that the appearance and performance of the product are improved. According to the invention, the problems of poor compatibility, unstable molding, poor surface quality and the like of a composite reclaimed material are effectively solved, the prepared decorative molding is high in impurity removal rate, stable in size and excellent in mechanical property, high-valued utilization of plastic foam renewable resources is realized, and the requirements of environmental protection and industry development are met.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and building decoration materials technology, specifically to a method for preparing decorative moldings from composite recycled plastic foam. Background Technology

[0002] With the increasing demand for environmentally friendly materials in the building decoration industry, the recycling of plastic foam has become an important direction in the field of resource recycling. Currently, most decorative moldings on the market are made from virgin plastics or single-type recycled plastics, while the application of composite recycled plastic foam still faces significant technical bottlenecks. Existing technologies have attempted to mix and recycle different types of plastic foam, but due to the significant differences in density, processing temperature, and chemical properties among various plastics (such as EPS, PE, and PVC), problems such as poor compatibility and unstable molding easily occur during the mixing and recycling process. For example, the density of EPS foam is typically 10-30 kg / m³, while the density of PVC foam is as high as 300-900 kg / m³, a difference of more than 10 times. Furthermore, the processing temperature for PS recycling is approximately 180℃, at which PVC easily decomposes, making effective mixing and recycling impossible. Meanwhile, existing recycling processes suffer from insufficient raw material sorting precision and incomplete impurity removal, resulting in low purity of recycled materials. During melt granulation, residual low-molecular-weight substances and foaming agents are difficult to completely remove, affecting the mechanical properties of subsequent products. The lack of effective internal stress relief methods during molding makes decorative lines prone to warping, cracking, and other defects. Furthermore, the limited surface treatment processes result in products with insufficient flatness and hardness to meet high-end decorative requirements. These issues cause decorative lines made from composite recycled plastic foam to fail to meet market demands in terms of performance stability and appearance quality, thus restricting the high-value utilization of recycled plastic foam resources. Summary of the Invention

[0003] The problem to be solved by the present invention is to provide a method for preparing decorative lines from composite recycled plastic foam, so as to solve the above-mentioned background technical problems.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing decorative moldings from recycled composite plastic foam, the method being as follows: Step 1: Raw material pretreatment EPS and PE foam blocks in compressed or melted state are purchased from waste recycling stations. These blocks undergo sorting, purification, and differentiated vacuum compression to complete the raw material pretreatment. The pretreatment operations at the waste recycling station are as follows: Sorting and Purification: A dual sorting mode of "density screening + manual sorting" is adopted. The density difference between EPS and PE foam is used to achieve initial separation of the two through airflow sorting equipment. Then, manual sorting is used to remove large impurities such as metal, paper scraps, and stones, ensuring the purity of EPS and PE foam after sorting and completely eliminating incompatible materials such as PVC, avoiding subsequent process conflicts caused by material differences. Differential Vacuum Compression: The sorted EPS and PE foams are subjected to vacuum compression treatment separately. EPS foam is placed in the vacuum compression equipment, first sprayed with 0.1-0.2% environmentally friendly antistatic agent, then the chamber door is closed and the vacuum pump is started to achieve a vacuum level of -0.08 to -0.09 MPa, while simultaneously applying a pressure of 5-8 MPa for 15-20 minutes, compressing its volume to 1 / 20-1 / 30 of its original volume. PE foam is first sprayed with 0.1% lubricant, then compressed for 20-25 minutes under a vacuum level of -0.07 to -0.08 MPa and a pressure of 6-9 MPa, compressing its volume to 1 / 15-1 / 25 of its original volume. The negative pressure environment removes residual air and some low-molecular-weight volatiles from the foam, while the pressure densifies the foam structure, initially reducing internal stress and preventing electrostatic adsorption of impurities and foam adhesion to the equipment's inner wall during compression, laying the foundation for subsequent crushing, melting, and granulation processes. Step 2: Crushing and Mixing The vacuum-compressed EPS and PE foam blocks are separately fed into a professional crusher for crushing. The particle size of the crushed EPS foam is controlled at 5-10 mm, and the particle size of the crushed PE foam is controlled at 3-8 mm. After crushing, the crushed EPS and PE materials are fed into a low-temperature mixer for mixing at a mass ratio of 7:3-8:2. During the mixing process, the shear force generated by the rotation ensures that the two materials are evenly dispersed. At the same time, 0.5-1 parts of compatibilizer are added to improve the interfacial compatibility between EPS and PE, providing a guarantee for subsequent melt blending. Step 3: Melt granulation The uniformly mixed crushed material is fed into a twin-screw extruder for melt granulation. The temperatures of each section of the extruder are set as follows: feeding section 140-150℃, compression section 160-170℃, melting section 175-185℃, and die head section 200-220℃; the screw speed is 350-500 r / min; during the melting process, the vacuum pumping system is activated, and the vacuum degree is maintained at -0.09~-0.1MPa to remove residual low-molecular-weight substances, foaming agents, and volatiles; the material is filtered through a filter screen to thoroughly remove fine impurities such as paper scraps, sand, and metal; finally, the material is drawn through the extruder die head and granulated by a pelletizer to obtain uniform and clean composite recycled material granules with a particle size of 3-5 mm. The mass ratio of EPS to PE in the recycled material is maintained at 7:3-8:2 to ensure that the melt index of the granules is stable at 15-25 g / 10min. Step 4: Mixing raw materials The composite recycled material granules and functional additives are fed into a high-speed mixer for mixing. The mixture contains 80-100 parts composite recycled material granules, 5-10 parts HIPS, 0.5-1.2 parts foaming agent, 0.3-0.6 parts antioxidant, 0.5-1 part dispersant, and 3-5 parts toughening agent. During the mixing process, the composite recycled material granules are first added to the high-speed mixer and mixed at 500-600 r / min for 3-5 minutes. Then, HIPS and toughening agent are added sequentially, and the speed is increased to 800 r / min for 3-5 minutes. Finally, the foaming agent, antioxidant, and dispersant are added and mixed at 600 r / min for 3 minutes to ensure that all materials are evenly dispersed and form a stable mixture system. Step 5: Induced foaming and extrusion molding The mixed raw materials are conveyed to an extrusion production line equipped with an induced foaming device. The raw materials first enter the extruder feeding section, where they are initially melted at 145-155℃. After entering the plasticizing section, the temperature rises to 170-180℃, completely plasticizing the raw materials to form a melt. The melt then enters the induced foaming section, where a high-frequency electric field is generated by an electrode induction device, acting on the foaming agent in the melt to uniformly decompose the foaming agent and generate bubble nuclei. Simultaneously, the induction voltage is controlled at 30-50 kV and the frequency at 10-20 kHz to ensure uniform distribution of the bubble nuclei. Subsequently, the melt continues to be heated in the screw, and the bubble nuclei gradually expand. The screw speed is controlled at 80-100 rpm. The screw speed is increased to r / min, and the bubbles are further refined by the shearing action of the screw. Finally, the melt is extruded through the die at an extrusion temperature of 175-180℃. The extruded foam enters the shaping mold and is cooled by forced cooling to quickly cool the product to below the glass transition temperature. It is shaped into a decorative line substrate with the required cross-sectional shape. The tiny bubbles generated during the foaming process can effectively offset the internal stress of the material and prevent warping and cracking after molding. Step 6: Co-extruded surface layer Simultaneously with extrusion molding, a co-extrusion surface layer is applied using an auxiliary machine. This auxiliary machine is a single-screw extruder, which heats the HIPS raw material to 180-190℃ to melt it. The HIPS melt is then uniformly coated onto the surface of the decorative trim substrate through a co-extrusion die, with the coating thickness controlled between 0.5-1.2 mm. During co-extrusion, the extrusion speeds of the main and auxiliary machines are adjusted to ensure a tight bond between the coating layer and the substrate, preventing peeling. This HIPS surface layer coating significantly improves the surface smoothness and hardness of the decorative trim, providing a good foundation for subsequent surface treatment processes. Step 7: Surface treatment and post-processing According to customer requirements, the surface treatment of the co-extruded decorative lines is carried out. First, the decorative lines are fed into a heating device and heated to 80-100℃, held for 3-5 seconds to soften the surface layer for subsequent processing. If the customer requires printing patterns, a roller printing process is used to transfer environmentally friendly ink to the surface of the lines through a printing roller. The printing pressure is controlled at 0.3-0.5 MPa, and the printing speed is consistent with the line conveying speed. If embossing is required, the surface of the lines is embossed using an embossing mold. The mold temperature is 100-110℃, the pressure is 2-3 MPa, and the embossing depth is 0.1-0.3 mm. If both printing and embossing are required, printing is done first, followed by embossing, to ensure clear patterns and uniform embossing texture. After surface treatment, the lines are cut to the length specified by the customer using a high-precision cutting machine. After cutting, they are sent to a sealing device and sealed using a hot air blower to absorb plastic film at a sealing temperature of 60-80℃. Finally, inspection is carried out to remove products with surface defects and out-of-tolerance dimensions. Qualified products are packaged and stored.

[0005] Furthermore, in the vacuum compression process of step 1, before applying pressure, 0.1-0.2% of an environmentally friendly antistatic agent is sprayed into the EPS foam and 0.1% of a lubricant is sprayed into the PE foam to prevent static electricity from adsorbing impurities during compression, while reducing the adhesion between the foam and the inner wall of the equipment, and improving compression uniformity and demolding efficiency.

[0006] Furthermore: In step 2, during the crushing and mixing process, the crusher adopts a shearing structure with a cutter head speed of 500-600 r / min and adjustable blade gap to ensure uniform particle size of the crushed material; during the high-speed mixer mixing process, the internal temperature is controlled at 60-70℃, and the temperature synergistically enhances the dispersion effect of the compatibilizer and silane coupling agent, thereby improving the compatibility between EPS and PE.

[0007] Furthermore, in the melt granulation process of step 3, the filter screen adopts a double-layer structure, with an inner layer of 80-100 mesh stainless steel filter screen and an outer layer of 120-150 mesh stainless steel filter screen. The double-layer filter screen works together to ensure that the impurity removal rate is ≥99.5%. The pelletizer adopts a water-cooled pelletizing method with a cooling water temperature of 20-25℃. The pelletizing speed is matched with the extrusion speed to ensure that the particle size variation coefficient of the recycled material is ≤5%.

[0008] Furthermore: In step 4, the raw material mixing process uses an azo foaming agent and an antioxidant system composed of hindered phenols and phosphate esters; all additives are dried at 100°C for 2 hours to ensure a moisture content of ≤0.2% to avoid adverse effects of moisture on melt molding.

[0009] Furthermore, in step 5, during the induced foaming process, the electrode induction device adopts a parallel plate electrode structure with an electrode spacing of 5-8 mm. The frequency and voltage of the high-frequency electric field can be adjusted in real time according to the melt flowability to ensure uniform generation of bubble nuclei and an internal stress relief rate of ≥90%.

[0010] Furthermore: In the co-extruded surface layer of step 6, the melt index of the HIPS raw material is 18-22 g / 10min, and the color masterbatch is a highly dispersible color masterbatch; the co-extrusion die head adopts a streamlined design, and the die head temperature is 5-10℃ higher than the auxiliary die head temperature, which avoids the HIPS melt from cooling and solidifying in the die head, and ensures that the coating layer is continuous and uniform.

[0011] Furthermore: In the surface treatment of step 7, the printing ink is selected as polyurethane-type environmentally friendly ink with a solid content of ≥50% and an adhesion level of 1; the embossing mold is made by laser engraving process with a texture accuracy of ≤0.01 mm; the sealed product also needs to be cured at constant temperature and humidity for 72 hours to ensure the dimensional stability of the decorative lines, and the warping after curing is ≤0.2mm / m.

[0012] Compared with the prior art, the advantages and positive effects of this invention are: This invention effectively overcomes the industry's technical bottlenecks in preparing decorative moldings from recycled composite plastic foam, achieving breakthroughs in multiple core technologies. Through a dual sorting mode of "density sieving + manual sorting," incompatible materials such as PVC are completely eliminated. Combined with a differentiated vacuum compression process, the purity and density of the raw materials are significantly improved, laying a high-quality foundation for subsequent processing. By adding compatibilizers and using precise temperature-controlled melt granulation, coupled with a double-layer filter and vacuum extraction system, the impurity removal rate of the recycled material is ≥99.5%, and the melt flow index is stabilized at 15-25g / 10min, solving the pain points of poor compatibility and impurity residue among different plastics. The innovative use of high-frequency electric field-induced foaming technology achieves an internal stress relief rate of ≥90%, and with forced cooling and shaping, completely avoids product warping and cracking. The HIPS co-extrusion surface layer and precise surface treatment process significantly improve the product's flatness, hardness, and appearance, achieving Grade 1 printing adhesion and embossing accuracy ≤0.01mm. After 72 hours of constant temperature and humidity curing, the product exhibits a warpage of ≤0.2mm / m, demonstrating excellent dimensional stability. This invention realizes the high-value utilization of recycled plastic foam resources, reducing production costs, practicing environmental protection principles, and ensuring product performance meets high-end decorative needs, thus achieving both economic and social benefits. Attached Figure Description

[0013] Figure 1 This is a flowchart of the present invention; Detailed Implementation

[0014] To better understand the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0015] A method for preparing decorative moldings from recycled composite plastic foam, the method being as follows: Step 1: Raw material pretreatment Sorting and Purification: A dual sorting mode of "density screening + manual sorting" is adopted. The density difference between EPS and PE foam is utilized to achieve initial separation of the two through airflow and photoelectric sorting equipment. Then, manual sorting is used to remove large impurities such as metal, paper scraps, and stones, ensuring the purity of EPS and PE foam after sorting and completely eliminating incompatible materials such as PVC, avoiding subsequent process conflicts caused by material differences. Differential Vacuum Compression: The sorted EPS and PE foams are subjected to vacuum compression treatment separately. EPS foam is placed in the vacuum compression equipment, first sprayed with 0.1-0.2% environmentally friendly antistatic agent, then the chamber door is closed and the vacuum pump is started to achieve a vacuum level of -0.08 to -0.09 MPa, while simultaneously applying a pressure of 5-8 MPa for 15-20 minutes, compressing its volume to 1 / 20-1 / 30 of its original volume. PE foam is first sprayed with 0.1% lubricant, then compressed for 20-25 minutes under a vacuum level of -0.07 to -0.08 MPa and a pressure of 6-9 MPa, compressing its volume to 1 / 15-1 / 25 of its original volume. The negative pressure environment removes residual air and some low-molecular-weight volatiles from the foam, while the pressure densifies the foam structure, initially reducing internal stress and preventing electrostatic adsorption of impurities and foam adhesion to the equipment's inner wall during compression, laying the foundation for subsequent crushing, melting, and granulation processes. Before applying pressure, 0.1-0.2% of environmentally friendly antistatic agent is sprayed into the EPS foam and 0.1% of lubricant is sprayed into the PE foam to prevent static electricity from adsorbing impurities during compression, while reducing the adhesion between the foam and the inner wall of the equipment, and improving compression uniformity and demolding efficiency. Step 2: Crushing and Mixing The vacuum-compressed EPS and PE foam blocks are separately fed into a professional crusher for crushing. The particle size of the crushed EPS foam is controlled at 5-10 mm, and the particle size of the crushed PE foam is controlled at 3-8 mm. After crushing, the crushed EPS and PE materials are fed into a low-temperature mixer for mixing at a mass ratio of 7:3-8:2. During the mixing process, the shear force generated by the rotation ensures that the two materials are evenly dispersed. At the same time, 0.5-1 parts of compatibilizer are added to improve the interfacial compatibility between EPS and PE, providing a guarantee for subsequent melt blending. The crusher adopts a shearing structure with a cutter head speed of 500-600 r / min and adjustable blade gap to ensure uniform particle size of the crushed material. During the high-speed mixer mixing process, the internal temperature is controlled at 60-70℃. Temperature synergy enhances the dispersion effect of compatibilizer and silane coupling agent, thereby improving the compatibility of EPS and PE. Step 3: Melt granulation The uniformly mixed crushed material is fed into a twin-screw extruder for melt granulation. The temperatures of each section of the extruder are set as follows: feeding section 140-150℃, compression section 160-170℃, melting section 175-185℃, and die head section 200-220℃; the screw speed is 350-500 r / min; during the melting process, the vacuum pumping system is activated, and the vacuum degree is maintained at -0.09~-0.1MPa to remove residual low-molecular-weight substances, foaming agents, and volatiles; the material is filtered through a filter screen to thoroughly remove fine impurities such as paper scraps, sand, and metal; finally, the material is drawn through the extruder die head and granulated by a pelletizer to obtain uniform and clean composite recycled material granules with a particle size of 3-5 mm. The mass ratio of EPS to PE in the recycled material is maintained at 7:3-8:2 to ensure that the melt index of the granules is stable at 15-25 g / 10min. The filter screen adopts a double-layer structure, with an inner layer of 80-100 mesh stainless steel filter screen and an outer layer of 120-150 mesh stainless steel filter screen. The double-layer filter screen works together to ensure that the impurity removal rate is ≥99.5%. The pelletizer adopts a water-cooled pelletizing method with a cooling water temperature of 20-25℃. The pelletizing speed is matched with the extrusion speed to ensure that the particle size variation coefficient of the recycled material is ≤5%. Step 4: Mixing raw materials The composite recycled material granules and functional additives are fed into a high-speed mixer for mixing. The mixture contains 80-100 parts composite recycled material granules, 5-10 parts HIPS, 0.5-1.2 parts foaming agent, 0.3-0.6 parts antioxidant, 0.5-1 part dispersant, and 3-5 parts toughening agent. During the mixing process, the composite recycled material granules are first added to the high-speed mixer and mixed at 500-600 r / min for 3-5 minutes. Then, HIPS and toughening agent are added sequentially, and the speed is increased to 800 r / min for 3-5 minutes. Finally, the foaming agent, antioxidant, and dispersant are added and mixed at 600 r / min for 3 minutes to ensure that all materials are evenly dispersed and form a stable mixture system. The foaming agent is an azo foaming agent, and the antioxidant is a mixture of hindered phenols and phosphate esters; all additives are dried at 100℃ for 2 hours to ensure that the moisture content is ≤0.2% to avoid the adverse effects of moisture on melt molding. Step 5: Induced foaming and extrusion molding The mixed raw materials are conveyed to an extrusion production line equipped with an induced foaming device. The raw materials first enter the extruder feeding section, where they are initially melted at 145-155℃. After entering the plasticizing section, the temperature rises to 170-180℃, completely plasticizing the raw materials to form a melt. The melt then enters the induced foaming section, where a high-frequency electric field is generated by an electrode induction device, acting on the foaming agent in the melt to uniformly decompose the foaming agent and generate bubble nuclei. Simultaneously, the induction voltage is controlled at 30-50 kV and the frequency at 10-20 kHz to ensure uniform distribution of the bubble nuclei. Subsequently, the melt continues to be heated in the screw, and the bubble nuclei gradually expand. The screw speed is controlled at 80-100 rpm. The screw speed is increased to r / min, and the bubbles are further refined by the shearing action of the screw. Finally, the melt is extruded through the die at an extrusion temperature of 175-180℃. The extruded foam enters the shaping mold and is cooled by forced cooling to quickly cool the product to below the glass transition temperature. It is shaped into a decorative line substrate with the required cross-sectional shape. The tiny bubbles generated during the foaming process can effectively offset the internal stress of the material and prevent warping and cracking after molding. The electrode induction device adopts a parallel plate electrode structure with an electrode spacing of 5-8 mm. The frequency and voltage of the high-frequency electric field can be adjusted in real time according to the melt flowability to ensure uniform bubble nucleation and internal stress relief rate ≥90%. Step 6: Co-extruded surface layer Simultaneously with extrusion molding, a co-extrusion surface layer is applied using an auxiliary machine. This auxiliary machine is a single-screw extruder, which heats the HIPS raw material to 180-190℃ to melt it. The HIPS melt is then uniformly coated onto the surface of the decorative trim substrate through a co-extrusion die, with the coating thickness controlled between 0.5-1.2 mm. During co-extrusion, the extrusion speeds of the main and auxiliary machines are adjusted to ensure a tight bond between the coating layer and the substrate, preventing peeling. This HIPS surface layer coating significantly improves the surface smoothness and hardness of the decorative trim, providing a good foundation for subsequent surface treatment processes. The melt index of HIPS raw material is 18-22 g / 10min, and highly dispersible masterbatch is selected. The co-extrusion die head adopts a streamlined design, and the die head temperature is 5-10℃ higher than that of the auxiliary die head, which avoids the HIPS melt from cooling and solidifying in the die head and ensures a continuous and uniform coating layer. Step 7: Surface treatment and post-processing According to customer requirements, the surface treatment of the co-extruded decorative lines is carried out. First, the decorative lines are fed into a heating device and heated to 80-100℃, held for 3-5 seconds to soften the surface layer for subsequent processing. If the customer requires printing patterns, a roller printing process is used to transfer environmentally friendly ink to the surface of the lines through a printing roller. The printing pressure is controlled at 0.3-0.5 MPa, and the printing speed is consistent with the line conveying speed. If embossing is required, the surface of the lines is embossed using an embossing mold. The mold temperature is 100-110℃, the pressure is 2-3 MPa, and the embossing depth is 0.1-0.3 mm. If both printing and embossing are required, printing is done first, followed by embossing, to ensure clear patterns and uniform embossing texture. After surface treatment, the lines are cut to the length specified by the customer using a high-precision cutting machine. After cutting, they are sent to a sealing device and sealed using a hot air blower to absorb plastic film at a sealing temperature of 60-80℃. Finally, inspection is carried out to remove products with surface defects and out-of-tolerance dimensions. Qualified products are packaged and stored. The printing ink is a polyurethane-based environmentally friendly ink with a solid content of ≥50% and an adhesion grade of 1. The embossing mold is made using laser engraving technology, with a texture accuracy of ≤0.01 mm. After plastic sealing, the product needs to undergo 72 hours of constant temperature and humidity curing to ensure the dimensional stability of the decorative lines, and the warping after curing is ≤0.2 mm / m.

[0016] I. Core Innovations of this Plan The core innovation of this solution lies in its proposed raw material pretreatment process, which combines a dual sorting mode of "density screening + manual sorting" with differentiated vacuum compression. This solves the problems of insufficient sorting accuracy, incomplete impurity removal, poor compatibility of different materials, and easy adsorption of impurities and adhesion to equipment during compression in the background technology for composite plastic foam recycled materials. Simultaneously, it is the first to combine high-frequency electric field-induced foaming technology with HIPS co-extrusion surface layer coating technology, coupled with a precise temperature-controlled melt granulation system and a multi-step raw material mixing scheme. This achieves a refined control scheme for the entire process of "sorting-compression-crushing-granulation-foaming-coating-post-processing" that has not been disclosed in existing technologies. This effectively overcomes industry technical bottlenecks such as unstable molding, difficulty in eliminating internal stress, and poor surface quality when preparing decorative lines from composite plastic foam recycled materials.

[0017] (I) Innovative Design of Raw Material Pretreatment Stage This innovative approach employs a dual sorting mode of "density sieving + manual sorting." Addressing the density differences between EPS and PE foam, initial separation is achieved using airflow and photoelectric sorting equipment. Manual sorting then thoroughly removes large impurities such as metal, paper scraps, and pebbles, while completely eliminating incompatible materials like PVC. This prevents subsequent process conflicts caused by material differences from the outset, resolving the issues of low raw material sorting accuracy and the impact of incompatible materials on product performance found in existing technologies. This sorting mode overcomes the limitations of single sorting methods, achieving precise separation of different types of plastic foam and laying a purity foundation for subsequent mixing and processing.

[0018] The innovative application of differentiated vacuum compression technology, based on the differences in physical properties of EPS and PE foams, establishes exclusive compression parameters for each: EPS foam, after being sprayed with 0.1-0.2% environmentally friendly antistatic agent, is compressed for 15-20 minutes under vacuum conditions of -0.08~-0.09MPa and pressure of 5-8MPa, reducing its volume to 1 / 20-1 / 30 of the original volume; PE foam, after being sprayed with 0.1% lubricant, is compressed for 20-25 minutes under vacuum conditions of -0.07~-0.08MPa and pressure of 6-9MPa, reducing its volume to 1 / 15-1 / 25 of the original volume. This design not only removes residual air and some low-molecular-weight volatiles from the foam through a negative pressure environment, thus densifying the foam structure and initially reducing internal stress, but also avoids the problems of electrostatic adsorption of impurities and foam adhesion to the inner wall of the equipment during compression. It solves the problems of uneven compression and difficult demolding caused by uniform compression parameters for different foam materials in existing compression processes.

[0019] (II) Innovation and optimization of crushing, mixing and melt granulation processes The precision design of the crushing process addresses the hardness difference between EPS and PE foams, controlling the particle size of crushed EPS foam to 5-10mm and PE foam to 3-8mm. These are then mixed at a mass ratio of 7:3-8:2, with 0.5-1 part compatibilizer added to improve interfacial compatibility. The crusher employs a shearing structure with a cutter head speed of 500-600 r / min and adjustable blade gap to ensure uniform particle size. During the high-speed mixer, the internal temperature is controlled at 60-70℃, which synergistically enhances the dispersion effect of the compatibilizer and silane coupling agent, solving the problems of inconsistent particle size, uneven mixing, and poor compatibility in existing technologies for different plastic foams.

[0020] The melt granulation system features multiple innovations, employing a twin-screw extruder with precisely set temperatures for each section: 140-150℃ for the feeding section, 160-170℃ for the compression section, 175-185℃ for the melting section, and 200-220℃ for the die head section, with a screw speed of 350-500 r / min, ensuring complete melting of the material. It also features a first-ever double-layer filter structure, with an inner 80-100 mesh stainless steel filter and an outer 120-150 mesh stainless steel filter working synergistically to achieve an impurity removal rate of ≥99.5%. Simultaneously, a vacuum extraction system is activated, maintaining a vacuum level of -0.09 to -0.1 MPa to remove residual low-molecular-weight substances, foaming agents, and volatiles. The pelletizer adopts a water-cooled pelletizing method with a cooling water temperature of 20-25℃. The pelletizing speed is matched with the extrusion speed to ensure that the particle size variation coefficient of recycled material is ≤5% and the melt index is stable at 15-25g / 10min. This solves the problems of incomplete impurity removal, low molecular weight residue, and poor particle uniformity in the existing melt granulation process.

[0021] (III) Innovative Breakthroughs in Raw Material Mixing and Induced Foaming This innovative, multi-component raw material mixing process employs a high-speed mixer for staged mixing: first, 80-100 parts of composite recycled material granules are added and mixed at 500-600 rpm for 3-5 minutes; then, 5-10 parts of HIPS and 3-5 parts of toughening agent are added, and the mixing speed is increased to 800 rpm for 3-5 minutes; finally, 0.5-1.2 parts of azo foaming agent, 0.3-0.6 parts of hindered phenolic and phosphate ester compound antioxidant, and 0.5-1 part of dispersant are added, and the mixture is mixed at 600 rpm for 3 minutes. All additives are dried at 100℃ for 2 hours, with a moisture content ≤0.2%. This staged mixing scheme ensures uniform dispersion of each component, forming a stable mixture system, and solves the problems of uneven additive dispersion and moisture affecting melt molding in existing mixing processes.

[0022] The innovative introduction of high-frequency electric field-induced foaming technology employs an electrode induction device with a parallel plate electrode structure and an electrode spacing of 5-8mm. A high-frequency electric field is generated through an induction voltage of 30-50kV and a frequency of 10-20kHz, acting on the foaming agent in the melt to uniformly decompose and generate bubble nuclei. Simultaneously, the electric field frequency and voltage are adjusted in real-time according to the melt's fluidity, and the shearing effect of the screw at 80-100r / min refines the bubbles. Finally, forced cooling rapidly cools the product to below its glass transition temperature for shaping, achieving an internal stress relief rate of ≥90%. This technology overcomes the limitations of traditional foaming processes, such as uneven bubble nucleus distribution and difficulty in eliminating internal stress, solving the key problems of warping and cracking of decorative lines after molding.

[0023] (iv) Innovative design of co-extruded surface layer and post-processing steps This innovative application of HIPS co-extrusion surface coating technology utilizes HIPS raw materials with a melt index of 18-22 g / 10 min. The raw materials are heated to 180-190℃ using a single-screw auxiliary extruder and then uniformly coated onto the substrate surface through a streamlined co-extrusion die (5-10℃ higher than the auxiliary die head). The coating layer thickness is 0.5-1.2 mm. By adjusting the matching of the extrusion speeds of the main and auxiliary extruders, a tight bond between the coating layer and the substrate is ensured without peeling, significantly improving the surface smoothness and hardness of the product and solving the problems of poor surface quality and insufficient hardness in existing products.

[0024] Innovations in refined surface treatment and post-processing solutions offer printing, embossing, or lamination treatments tailored to customer needs: Printing utilizes environmentally friendly polyurethane inks (solid content ≥50%, adhesion grade 1), with roller printing pressure of 0.3-0.5MPa; Embossing employs laser-engraved molds (texture accuracy ≤0.01mm), mold temperature 100-110℃, pressure 2-3MPa, and embossing depth 0.1-0.3mm; After cutting, the product is sealed using a 60-80℃ hot air blower, followed by 72 hours of constant temperature and humidity curing to ensure product warpage ≤0.2mm / m. This post-processing solution achieves precise control over the product's appearance and texture, meeting high-end decorative demands and solving the problems of limited surface treatment processes and low added value in existing products.

[0025] II. Working Principle of this Solution This solution mainly utilizes the synergistic effect of the entire process of "precise pretreatment of raw materials - uniform mixing - efficient melt granulation - controllable induced foaming - dense surface coating - refined post-processing" to transform composite plastic foam recycled materials into high-performance decorative lines by using multidisciplinary technical principles such as physical sorting, vacuum compression, high-temperature melting, electric field induction, and co-extrusion coating.

[0026] In the raw material pretreatment stage, based on the principle of density difference, airflow sorting equipment is used to initially separate EPS and PE foam. Then, manual sorting removes impurities and incompatible materials to ensure raw material purity. Differential vacuum compression, based on the principles of negative pressure degassing and pressure densification, uses different vacuum levels, pressures, and auxiliary agents (antistatic agents, lubricants) to expel internal air and low-molecular-weight volatiles from EPS and PE foam respectively, reducing internal porosity and preventing electrostatic adsorption and equipment adhesion, thus providing dense and pure raw materials for subsequent crushing.

[0027] In the crushing and mixing stage, based on the shear crushing principle, the high-speed rotating blades of the shear crusher break the compressed foam blocks to a set particle size. Then, the rotational shearing force of the low-speed mixer is used to uniformly mix the EPS and PE crushed materials. At the same time, based on the interfacial compatibility principle, a compatibilizer is added and the mixing temperature is controlled to improve the interfacial bonding force between the two plastics, laying the foundation for melt blending.

[0028] The melt granulation process follows the principles of polymer melt rheology. Through zoned temperature control in the twin-screw extruder (gradual heating from the feed section to the die head), the mixture undergoes softening, melting, and plasticization at different stages. Vacuum extraction removes residual low-molecular-weight substances and volatiles during the melting process; a double-layer filter intercepts fine impurities based on filtration; and water-cooled solidification is applied, after the molten material is drawn into strips and cooled with cold water, it is then cut into uniform granules by a pelletizer, ensuring the purity and melt stability of the recycled material.

[0029] During the raw material mixing stage, based on the principle of multi-component dispersion, a high-speed mixer with stepped speed regulation is used to first uniformly disperse the recycled material particles, and then gradually add functional additives such as HIPS, toughening agents, antioxidants, and foaming agents. The shearing and dispersing forces generated by different speeds ensure that each component is evenly distributed in the mixture. At the same time, based on the principle of moisture control, the additives are dried to avoid the formation of air bubbles during the melting process.

[0030] In the induced foaming and extrusion molding process, based on the principle of electric field-induced decomposition, the high-frequency electric field causes the foaming agent molecular chains to break and decompose uniformly, generating a large number of micro bubble nuclei. Utilizing the principle of fluid dynamics, the screw shearing action further refines and evenly distributes the bubble nuclei. Based on the principle of heat conduction, forced cooling rapidly reduces the product temperature, fixing the bubble structure and completing the shaping process. At the same time, the uniform distribution of bubble nuclei can offset the internal stress generated by temperature changes and the molding process, achieving dimensional stability of the product.

[0031] In the co-extrusion surface layer stage, based on the melt coating principle, HIPS melt is uniformly covered on the substrate surface through the co-extrusion die under pressure, and a tight bond is achieved by utilizing the interfacial adhesion between HIPS and the substrate; the streamlined die design reduces melt flow resistance, avoids cooling and solidification, and ensures a continuous and uniform coating layer.

[0032] In the post-processing stage, based on the principle of thermoplastic softening, the decorative lines are heated to 80-100℃ to soften the surface layer, making it easier to print and emboss. Based on the principle of ink transfer, the ink is evenly transferred to the surface of the lines by roller pressure. Based on the principle of thermoforming, the surface is embossed using a high-temperature mold. Based on the principle of dimensional stability, residual stress is eliminated through constant temperature and humidity curing to ensure the final dimensional accuracy and stability of the product.

[0033] III. Technical Effects of Implementing this Plan (i) The raw material processing effect is significant, and the purity and performance of recycled materials are greatly improved. Through a dual sorting process of "density sieving + manual sorting" and double-layer filtration, the impurity removal rate of the composite recycled material is ≥99.5%, completely eliminating incompatible materials such as PVC and effectively avoiding process conflicts caused by material differences. Differential vacuum compression densifies the EPS and PE foam structure, initially reducing internal stress. Combined with compatibilizer modification and precise melt granulation, the mass ratio of EPS to PE in the recycled material is stabilized at 7:3-8:2, the melt index is controlled at 15-25g / 10min, and the particle size variation coefficient is ≤5%. This solves the problems of low purity, poor compatibility, and unstable performance of traditional recycled materials, providing a high-quality raw material foundation for subsequent molding.

[0034] (ii) Molding stability is greatly improved and product defect rate is significantly reduced. The application of high-frequency electric field-induced foaming technology achieves an internal stress relief rate of ≥90%. Combined with forced cooling and shaping process, it completely solves the industry pain point of warping and cracking after decorative molding. After 72 hours of constant temperature and humidity curing, the product exhibits a warping degree of ≤0.2mm / m and excellent dimensional stability. The stepped raw material mixing scheme ensures uniform dispersion of various functional additives, and the bubble nuclei generated by the decomposition of azo foaming agents are evenly distributed. The addition of toughening agents further enhances the toughness of the material, significantly improving the product's mechanical properties. Key indicators such as elongation at break and impact strength meet the requirements of high-end decorative materials, and the defect rate during the molding process is reduced by more than 90%.

[0035] (iii) The surface quality and appearance of the product have been significantly improved. The HIPS co-extruded surface layer coating significantly improves the surface smoothness and hardness of the product. Combined with refined surface treatment processes, the adhesion of printed patterns reaches Level 1, ensuring uniform color and resistance to peeling. Embossing texture precision is ≤0.01mm, resulting in a delicate and realistic texture that can meet the personalized decorative needs of different customers. The use of polyurethane-based environmentally friendly inks and highly dispersible masterbatches ensures the product's environmental friendliness while enhancing the saturation and stability of the colors, solving the problems of rough surfaces, uneven coloring, and poor decorative effects found in traditional recycled material products, thus significantly increasing the product's added value.

[0036] (iv) High resource utilization rate and environmental benefits, achieving high-value utilization. This solution uses recycled EPS and PE foam as the main raw materials, effectively utilizing waste plastic foam resources, reducing white pollution, and aligning with environmental policies and industry development trends. Through full-process optimization, the recycling rate reaches over 95%, reducing production costs by 30%-40% compared to traditional virgin plastic production processes, while maintaining performance indicators no lower than virgin plastic products, achieving high-value utilization by "turning waste into treasure." Furthermore, the process employs environmentally friendly antistatic agents and inks, and a vacuum extraction system effectively collects volatile organic compounds, reducing pollutant emissions and demonstrating significant economic and social benefits.

[0037] (v) It has strong technological adaptability and broad prospects for industrialization. All process parameters in this solution can be flexibly adjusted according to raw material characteristics and product requirements. For example, adjusting the electric field parameters can adapt to melts with different flowability, changing the co-extrusion die structure can achieve different coating thickness requirements, and changing the embossing die can achieve diverse texture designs. The process is highly automated, employing single (twin) screw extruders, high-speed mixers, and precise temperature control systems, enabling large-scale continuous production with a 20%-30% increase in production efficiency compared to traditional processes. The products can be widely used in building decoration, furniture manufacturing, and other fields, with broad market prospects, providing a feasible path for the industrial utilization of recycled plastic foam resources.

[0038] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A method for preparing decorative moldings from recycled composite plastic foam, characterized in that: The method is as follows: Step 1: Raw material pretreatment Sorting and Purification: A dual sorting mode of "density screening + manual sorting" is adopted. The density difference between EPS and PE foam is utilized to achieve initial separation of the two through airflow and photoelectric sorting equipment. Then, manual sorting is used to remove large impurities such as metal, paper scraps, and stones, ensuring the purity of EPS and PE foam after sorting and completely eliminating incompatible materials such as PVC, avoiding subsequent process conflicts caused by material differences. Differential Vacuum Compression: The sorted EPS and PE foams are subjected to vacuum compression treatment separately. EPS foam is placed in the vacuum compression equipment, first sprayed with 0.1-0.2% environmentally friendly antistatic agent, then the chamber door is closed and the vacuum pump is started to achieve a vacuum level of -0.08 to -0.09 MPa, while simultaneously applying a pressure of 5-8 MPa for 15-20 minutes, compressing its volume to 1 / 20-1 / 30 of its original volume. PE foam is first sprayed with 0.1% lubricant, then compressed for 20-25 minutes under a vacuum level of -0.07 to -0.08 MPa and a pressure of 6-9 MPa, compressing its volume to 1 / 15-1 / 25 of its original volume. The negative pressure environment removes residual air and some low-molecular-weight volatiles from the foam, while the pressure densifies the foam structure, initially reducing internal stress and preventing electrostatic adsorption of impurities and foam adhesion to the equipment's inner wall during compression, laying the foundation for subsequent crushing, melting, and granulation processes. Step 2: Crushing and Mixing The vacuum-compressed EPS and PE foam blocks are separately fed into a professional crusher for crushing. The particle size of the crushed EPS foam is controlled at 5-10 mm, and the particle size of the crushed PE foam is controlled at 3-8 mm. After crushing, the crushed EPS and PE materials are fed into a low-temperature mixer for mixing at a mass ratio of 7:3-8:

2. During the mixing process, the shear force generated by the rotation ensures that the two materials are evenly dispersed. At the same time, 0.5-1 parts of compatibilizer are added to improve the interfacial compatibility between EPS and PE, providing a guarantee for subsequent melt blending. Step 3: Melt granulation The uniformly mixed crushed material is fed into a twin-screw extruder for melt granulation. The temperatures of each section of the extruder are set as follows: feeding section 140-150℃, compression section 160-170℃, melting section 175-185℃, and die head section 200-220℃; the screw speed is 350-500 r / min; during the melting process, the vacuum pumping system is activated, and the vacuum degree is maintained at -0.09~-0.1 MPa to remove residual low-molecular-weight substances, foaming agents, and volatiles; the material is filtered through a filter screen to thoroughly remove fine impurities such as paper scraps, sand, and metal; finally, the material is drawn through the extruder die head and granulated by a pelletizer to obtain uniform and clean composite recycled material granules with a particle size of 3-5 mm. The mass ratio of EPS to PE in the recycled material is maintained at 7:3-8:2 to ensure that the melt index of the granules is stable at 15-25 g / 10min. Step 4: Mixing raw materials The composite recycled material granules and functional additives are fed into a high-speed mixer for mixing. The mixture contains 80-100 parts composite recycled material granules, 5-10 parts HIPS, 0.5-1.2 parts foaming agent, 0.3-0.6 parts antioxidant, 0.5-1 part dispersant, and 3-5 parts toughening agent. During the mixing process, the composite recycled material granules are first added to the high-speed mixer and mixed at 500-600 r / min for 3-5 minutes. Then, HIPS and toughening agent are added sequentially, and the speed is increased to 800 r / min for 3-5 minutes. Finally, the foaming agent, antioxidant, and dispersant are added and mixed at 600 r / min for 3 minutes to ensure that all materials are evenly dispersed and form a stable mixture system. Step 5: Induced foaming and extrusion molding The mixed raw materials are conveyed to an extrusion production line equipped with an induced foaming device. The raw materials first enter the extruder feeding section, where they are initially melted at 145-155℃. After entering the plasticizing section, the temperature rises to 170-180℃, completely plasticizing the raw materials to form a melt. The melt then enters the induced foaming section, where a high-frequency electric field is generated by an electrode induction device, acting on the foaming agent in the melt to uniformly decompose the foaming agent and generate bubble nuclei. Simultaneously, the induction voltage is controlled at 30-50 kV and the frequency at 10-20 kHz to ensure uniform distribution of the bubble nuclei. Subsequently, the melt continues to be heated in the screw, and the bubble nuclei gradually expand. The screw speed is controlled at 80-100 rpm. The screw speed is increased to r / min, and the bubbles are further refined by the shearing action of the screw. Finally, the melt is extruded through the die at an extrusion temperature of 175-180℃. The extruded foam enters the shaping mold and is cooled by forced cooling to quickly cool the product to below the glass transition temperature. It is shaped into a decorative line substrate with the required cross-sectional shape. The tiny bubbles generated during the foaming process can effectively offset the internal stress of the material and prevent warping and cracking after molding. Step 6: Co-extruded surface layer Simultaneously with extrusion molding, a co-extrusion surface layer is applied using an auxiliary machine. This auxiliary machine is a single-screw extruder, which heats the HIPS raw material to 180-190℃ to melt it. The HIPS melt is then uniformly coated onto the surface of the decorative strip substrate through a co-extrusion die, with the coating thickness controlled between 0.5-1.2 mm. During co-extrusion, the extrusion speed matching between the main and auxiliary machines is adjusted to ensure a tight bond between the coating layer and the substrate, preventing peeling. The HIPS surface layer significantly improves the surface smoothness and hardness of the decorative strip, providing a good foundation for subsequent surface treatment processes. Step 7: Surface treatment and post-processing According to customer requirements, the surface treatment of the co-extruded decorative lines is carried out. First, the decorative lines are fed into the heating equipment and heated to 80-100℃, and held for 3-5 seconds to soften the surface layer for subsequent processing. If the customer requires printed patterns, roller printing process is used to transfer environmentally friendly ink to the surface of the lines through printing rollers. The printing pressure is controlled at 0.3-0.5MPa, and the printing speed is consistent with the line conveying speed. If embossing is required, the lines are imprinted on the surface using an embossing mold at a temperature of 100-110℃, a pressure of 2-3 MPa, and an embossing depth of 0.1-0.3 mm. If both printing and embossing are required, printing is done first, followed by embossing, ensuring a clear pattern and uniform embossing texture. After surface treatment, the product is cut to the length specified by the customer using a high-precision cutting machine. After cutting, it is sent to a sealing equipment and sealed using a hot air blower to absorb the plastic film at a sealing temperature of 60-80℃. Finally, an inspection is conducted to remove products with surface defects or out-of-tolerance dimensions. Qualified products are packaged and stored.

2. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In the vacuum compression process of step 1, before applying pressure, spray 0.1-0.2% of environmentally friendly antistatic agent into the EPS foam and 0.1% of lubricant into the PE foam to avoid static electricity adsorption of impurities due to friction during compression, while reducing the adhesion between the foam and the inner wall of the equipment, and improving compression uniformity and demolding efficiency.

3. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In step 2, during the crushing and mixing process, the crusher adopts a shearing structure with a cutter head speed of 500-600 r / min and adjustable blade gap to ensure uniform particle size of the crushed material. During the high-speed mixer mixing process, the internal temperature is controlled at 60-70℃. Temperature synergistically enhances the dispersion effect of compatibilizer and silane coupling agent, thereby improving the compatibility between EPS and PE.

4. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In step 3, during melt granulation, the filter screen adopts a double-layer structure, with an inner layer of 80-100 mesh stainless steel filter screen and an outer layer of 120-150 mesh stainless steel filter screen. The double-layer filter screen works together to ensure that the impurity removal rate is ≥99.5%. The pelletizer adopts a water-cooled pelletizing method with a cooling water temperature of 20-25℃. The pelletizing speed is matched with the extrusion speed to ensure that the particle size variation coefficient of the recycled material is ≤5%.

5. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In step 4, the raw material mixing process uses an azo foaming agent and a hindered phenolic and phosphate ester compound antioxidant. All additives are dried at 100°C for 2 hours to ensure a moisture content of ≤0.2% to avoid adverse effects of moisture on melt molding.

6. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In step 5, during the induced foaming process, the electrode induction device adopts a parallel plate electrode structure with an electrode spacing of 5-8 mm. The frequency and voltage of the high-frequency electric field can be adjusted in real time according to the melt flowability to ensure uniform generation of bubble nuclei and an internal stress relief rate of ≥90%.

7. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In the co-extruded surface layer of step 6, the melt index of the HIPS raw material is 18-22 g / 10min, and the color masterbatch is a highly dispersible color masterbatch; the co-extrusion die head adopts a streamlined design, and the die head temperature is 5-10℃ higher than the auxiliary die head temperature to avoid the HIPS melt from cooling and solidifying in the die head, thus ensuring a continuous and uniform coating layer.

8. The method for preparing decorative moldings from recycled composite plastic foam according to claim 1, characterized in that: In step 7, the surface treatment uses polyurethane-type environmentally friendly ink with a solid content of ≥50% and an adhesion level of 1. The embossing mold is made using laser engraving technology with a texture accuracy of ≤0.01 mm. After plastic sealing, the product needs to undergo 72 hours of constant temperature and humidity curing to ensure the dimensional stability of the decorative lines, and the warping after curing is ≤0.2 mm / m.

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