Preparation method of high-impact high-brightness PS black particles

Abstract

This invention discloses a method for preparing high-impact, high-gloss PS black granules, comprising: S1, raw material pretreatment: electrostatically separating waste household appliance shreds to obtain PS shreds with a purity greater than 99%; S2, multi-source batching and homogenization: mixing the PS shreds with SBS toughening agent and carrier-free black masterbatch in stages according to a predetermined formula ratio; S3, melt extrusion: melt extruding the mixture through a twin-screw extruder with gradient temperature control; S4, cooling and granulation: subjecting the melt strip to multi-stage cooling and pelletizing to obtain PS black granules. This invention solves the problems of unstable performance and low gloss of recycled PS granules in existing technologies by combining high-purity raw material pretreatment, optimized multi-source formulation and homogenization process, refined extrusion process control, and intelligent closed-loop regulation. The resulting PS black granules possess high impact strength, high gloss, and high blackness, achieving high-value utilization of waste PS plastics.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling and modification technology, specifically relating to a method for preparing high-impact, high-brightness PS black particles, and particularly to a waste plastic recycling process based on electrostatic sorting, multi-source batching and mixing, twin-screw melt extrusion, online rheological monitoring and intelligent process control. Background Technology

[0002] With the widespread use of plastic products in home appliances, electronics, packaging, and other fields, the recycling and high-value regeneration of waste polystyrene (PS) materials has become an important way to achieve resource utilization. Polystyrene is widely used in the manufacture of appliance housings and daily necessities due to its good processing performance, dimensional stability, and electrical insulation properties. However, waste PS materials are prone to physical property degradation and appearance deterioration during use and disposal, such as reduced impact strength and dull surface gloss, which limits its scope and value for direct reuse.

[0003] To improve the performance of recycled PS materials, various modification methods have been employed in existing technologies. For example, toughening agents (such as SBS) are introduced through physical blending to enhance impact strength, or equipment such as twin-screw extruders is used to improve mixing effects. In the recycling pretreatment stage, electrostatic sorting technology is also applied to separate and purify different types of plastics to improve raw material purity. These processes, to some extent, restore or enhance the performance of recycled PS materials.

[0004] However, existing technologies still have several technical shortcomings in the preparation of high-impact, high-brightness PS black particles. First, in the raw material pretreatment stage, conventional sorting methods are insufficient to efficiently remove impurities with similar density or dielectric properties to PS, resulting in insufficient purity of the crushed material. Residual non-PS components easily form stress concentration points during subsequent processing, significantly reducing the impact strength of the final particles. Simultaneously, trace amounts of adhering substances or discolored particles in the raw materials can affect the blackness and surface gloss of the product, causing batch-to-batch fluctuations in appearance quality. Second, during the batching and mixing process, toughening agents (such as SBS) and black masterbatch have high viscoelasticity and agglomeration tendencies. Improper mixing can easily lead to uneven dispersion and localized enrichment, thereby weakening the toughening effect and causing a decline in optical performance. Furthermore, although twin-screw extrusion equipment is widely used in the melt extrusion stage, most processes do not perform refined temperature control profiles and screw configuration optimization based on the rheological characteristics of the PS / SBS ​​blend system, resulting in insufficient or excessive shearing action, making it difficult to achieve fine dispersion of the toughening phase. Furthermore, existing technologies lack real-time monitoring methods for changes in melt rheological properties (such as viscosity) during extrusion. They typically rely solely on indirect assessments through die pressure, failing to accurately detect alterations in melt flowability caused by raw material batch fluctuations or microstructural changes, leading to delayed process adjustments. Finally, production processes largely depend on manual experience or open-loop control, lacking real-time monitoring and dynamic feedback adjustment of key process parameters. This makes it impossible to promptly compensate for process deviations caused by raw material fluctuations or environmental changes, resulting in poor product quality stability and difficulty meeting the stringent performance consistency requirements of high-end applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-impact, high-brightness PS black particles, aiming to solve the technical problems in the prior art caused by insufficient purity of raw materials, poor mixing uniformity, and fluctuations in process parameters, resulting in low gloss, unstable impact strength, and inconsistent blackness of the product.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing high-impact, high-brightness PS black particles includes the following steps: S1, raw material pretreatment: electrostatically separating waste household appliance shreds to obtain PS shreds with a purity greater than 99%; S2, multi-source batching and mixing: mixing the PS shreds with a toughening agent and a black masterbatch according to a predetermined formula ratio to obtain a mixture; S3, melt extrusion: melt extruding the mixture through a twin-screw extruder to obtain melt strips; S4, cooling and granulation: cooling and shaping the melt strips and cutting them into pellets to obtain PS black particles.

[0008] Preferably, the waste household appliance shredded material in S1 includes waste refrigerator shredded material and waste air conditioner shredded material. The working voltage of the electrostatic separator is set to 4.5-6.0kV, the drum speed is 80-120rpm, and the feeding speed is controlled within the range of 15-25kg / h.

[0009] Preferably, step S1 further includes color sorting of some of the PS crushed material to remove discolored particles. Specifically, an infrared color sorter is used to perform two screenings to remove discolored particles with a color deviation exceeding ΔE≤1.5.

[0010] Preferably, the predetermined formula in S2 comprises, by mass percentage: 36% of electrostatically sorted refrigerator PS scrap; 36% of electrostatically sorted air conditioner PS scrap; 20% of color-sorted mixed-color PS scrap; 4% of SBS toughening agent; and 4% of carrier-free black masterbatch.

[0011] Preferably, the multi-source batching and homogenization step in S2 specifically involves: putting PS crushed materials from multiple sources into a homogenization tank for a first-stage dry mixing for 1-2 hours; then adding SBS toughening agent and carrier-free black masterbatch for a second-stage stirring for 20 minutes; the homogenization is carried out at a temperature of 35±3℃ to prevent the materials from absorbing moisture and agglomerating.

[0012] Preferably, the twin-screw extruder in S3 has at least nine temperature control zones, and the extrusion temperature is controlled between 200-220°C; the screw assembly of the twin-screw extruder includes a conveying section, a compression section, a shearing section and a homogenizing section, wherein the shearing section is equipped with a kneading disc.

[0013] Preferably, the temperatures of the nine temperature control zones of the twin-screw extruder are set in a gradient of 180→190→200→210→215→220→220→215→210℃.

[0014] Preferably, the cooling and shaping in S4 adopts a counter-flow three-layer cooling water tank, with the water temperature of the first section being 15-20℃, the water temperature of the second section being 25-30℃, and the water temperature of the third section being 35-40℃.

[0015] Preferably, the method further includes an online rheological monitoring step, in which an online rheometer installed behind the extruder die is used to sample and analyze the melt index or apparent viscosity of the melt in real time;

[0016] It also includes a finished product screening step, which uses a double-layer vibrating screen to remove impurities and particles that do not meet the size requirements. The upper screen has a mesh size of 3.0 mm and the lower screen has a mesh size of 1.8 mm.

[0017] Preferably, the method further includes an intelligent process control step, which integrates a PLC controller and a SCADA monitoring platform to collect data in real time, including mixing time, melt temperature, extrusion pressure, current, and melt viscosity data from an online rheometer. When parameter fluctuations exceed preset thresholds, the heating power or feeding speed is automatically adjusted to achieve closed-loop compensation.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Through the synergistic effect of electrostatic sorting and color sorting processes, impurities and discolored particles are effectively removed, and PS raw materials with a purity of more than 99% are obtained. This significantly reduces the adverse effects of the attached substances on the impact strength and surface brightness of the product, ensuring the excellent mechanical properties and appearance quality of the final product from the source.

[0020] (2) The phased and temperature-controlled homogenization strategy effectively solved the problem of SBS toughening agent and black masterbatch and other high-viscosity components agglomerating in the matrix, improved the dispersion uniformity and interfacial bonding of each component in the matrix, and maximized the toughening and coloring effects.

[0021] (3) By using the optimized twin-screw extrusion process, through precise gradient temperature control and strong shear screw configuration, the SBS is promoted to form a fine interpenetrating network structure in the PS matrix, which significantly improves the impact toughness of the composite particles; at the same time, the scientific cooling process ensures the high gloss of the particles.

[0022] (4) By introducing an online rheological monitoring module, real-time perception of the core rheological properties of the melt is realized, and the process control is upgraded from "indirect control based on temperature and pressure" to "direct control based on melt viscosity". It can capture changes in melt flowability caused by batch fluctuations or microstructure changes in raw materials in advance, and make preventive adjustments before significant changes in macroscopic parameters such as die pressure, which greatly improves the intrinsic consistency of product quality and process stability. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow of the preparation method of Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the process flow of the preparation method of Embodiment 2 of the present invention;

[0025] Figure 3 This is a schematic diagram of the process flow of the preparation method of Embodiment 3 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Example 1

[0028] Reference Figure 1 This embodiment provides a method for preparing high-impact, high-brightness PS black particles, the specific steps of which are as follows:

[0029] Step 1: Raw material pretreatment

[0030] Recycled waste refrigerator and air conditioner casing fragments were used as raw materials. First, an electrostatic separator was used to separate the fragments. The operating voltage was set to 5.2kV, the drum speed was controlled at 100rpm, and the feeding speed was maintained at 20kg / h. This step effectively separated PS from other plastic impurities (such as ABS and PP), obtaining electrostatic-filtered refrigerator PS fragments and electrostatic-air conditioner PS fragments with a purity greater than 99%. Simultaneously, the mixed PS fragments were sent to an infrared color sorter for two screenings, removing discolored particles with a color deviation exceeding ΔE≤1.5, resulting in color-sorted mixed-color PS fragments. All raw materials were dried at 80℃ for 2 hours before use to ensure a moisture content below 0.1%.

[0031] Step 2: Mix all ingredients from multiple sources

[0032] The ingredients are prepared according to the following percentages by weight: 36% electrostatic-refrigerator PS crushed material, 36% electrostatic-air conditioner PS crushed material, 20% color sorted PS mixed color crushed material, 4% SBS toughening agent, and 4% carrier-free black masterbatch.

[0033] The three types of PS shredded materials were added to a homogenizing tank equipped with a jacket and a spiral ribbon agitator. Circulating heat transfer oil was introduced into the jacket to maintain the tank temperature at 35±3℃. Stirring was started, and the first stage of dry mixing was performed at 45 rpm for 1.5 hours to achieve a spatially uniform distribution of the PS shredded materials from different sources. Then, 4% SBS toughening agent and 4% carrier-free black masterbatch were added, and low-speed stirring continued for 20 minutes to complete the second stage of mixing, resulting in a homogeneous mixture. This stepwise addition method effectively avoids the premature participation of high-viscosity SBS in the mixing process, preventing the formation of agglomerates. It facilitates the gradual wetting and uniform dispersion of SBS in the continuous PS phase, enhancing interfacial bonding and thus improving the toughness and color stability of the composite material.

[0034] Step 3: Twin-screw melt extrusion

[0035] The mixture is fed into a nine-zone heated twin-screw extruder via a feeding system. The temperatures of each zone of the extruder are set in a gradient: Zone 1 180℃, Zone 2 190℃, Zone 3 200℃, Zone 4 210℃, Zone 5 215℃, Zone 6 220℃, Zone 7 220℃, Zone 8 215℃, and Zone 9 210℃. This ensures that the material undergoes a process of stable plasticization, full melting, efficient shearing, and appropriate cooling. The die head temperature is 210℃. The screw configuration includes a conveying section (30% of the length), a compression section (20%), a shearing section (30%), and a homogenization section (20%). The shearing section is equipped with two sets of staggered toothed kneading discs with a precisely controlled axial clearance of 2 mm. The screw speed is set to 300 rpm. Under high shear stress, the SBS phase is broken down and redistributed, refining its particle size to 0.5-2 μm. The particles are uniformly embedded in the PS matrix, forming a microscale interpenetrating network structure, which significantly improves the impact resistance of the material.

[0036] Step 4: Cooling, pelletizing and screening

[0037] The molten material is extruded into strips through a die and then enters a counter-current three-layer cooling water tank: the first stage has a water temperature of 18℃ for rapid cooling and shaping, the second stage has a water temperature of 28℃ to relieve internal stress, and the third stage has a water temperature of 38℃ for slow-release annealing; the traction rate and extrusion line speed are synchronously controlled at 15m / min. After cooling and shaping, the strips are cut into uniform particles with a length of 3-4mm by a pelletizer. The cut particles are screened by a double-layer circular vibrating screen (the screen body has an adjustable tilt angle of 5-8°, preferably 6.5°, and the vibration frequency is set to 50 times / minute). The upper screen has a mesh size of 3.0mm to intercept oversized particles, and the lower screen has a mesh size of 1.8mm to remove fine powder and debris. After cutting, the particles are transferred to a sealed stainless steel storage silo for packaging through a clean airflow conveying system. The conveying air velocity is controlled at 18-22m / s to avoid particle wear and dust dispersion, and to maintain the cleanliness and flowability of the product to the maximum extent.

[0038] Performance testing

[0039] The performance of the PS black particles prepared in this embodiment was tested, and the results are shown in the table below:

[0040] Notched impact strength of simply supported beam GB / T 1843-2008 ≥ 8 kJ / m² Tensile strength GB / T 1040.2-2022 ≥ 30 MPa Bending strength GB / 178 / T9341 ≥ 42 MPa Darkness (L*) CIE L*a*b* L≤ 30

[0041] Test results show that the PS black particles prepared by this invention have excellent impact strength and surface gloss, pure blackness, and comprehensive performance that meets the requirements of high-end plastic products for high impact and high brightness performance. Moreover, the performance variation coefficient between batches is less than 5%, and the quality stability is high.

[0042] Example 2

[0043] Similar to Example 1, the difference is that the preparation method described above also includes an online rheological monitoring step (such as...) between steps three and four. Figure 2 As shown in the diagram, this step is achieved using an online rheometer installed behind the extruder die. This rheometer has a built-in capillary die and pressure sensor, and can output the apparent viscosity of the melt in real time within a shear rate range of 100-1000 s⁻¹. In this embodiment, during continuous production, two batches of refrigerator scrap (batch A and batch B) with slightly different sources were introduced. Both batches had similar apparent density and purity, but slight differences in molecular weight and melt flowability. During the production of batch B, the intelligent control system did not receive any other abnormal signals (temperature and pressure were stable), but the online rheometer detected that the melt viscosity decreased by 4.5% compared to the average value during batch A production, exceeding the ±3% threshold. As needed, the overall heating temperature of the four rear zones of the extruder was lowered by 2°C, and the feed screw speed was reduced by 6%. Within 30 seconds of adjustment, the online rheometer showed that the viscosity value returned to the target range. Finally, the PS black granules produced by batch B were tested and found to have impact strength and gloss completely consistent with the product of batch A, with a coefficient of variation of less than 4%. In the comparative test where the online rheological monitoring function was disabled, batch B products experienced an 8% decrease in final particle impact strength due to the failure to adjust the process in a timely manner, resulting in defective products. This embodiment demonstrates that the online rheological monitoring module endows the production line with the ability to "sense" and "adapt" to microscopic fluctuations in raw materials, fundamentally improving the batch stability of products.

[0044] Example 3

[0045] Similar to Example 2, but with the addition of step five (as shown in Example 2). Figure 3 (As shown): Intelligent process control: Throughout the entire production process, an intelligent control system integrating PLC and SCADA (monitoring and data acquisition system) collects melt temperature (sampling period ≤1s, accuracy ±1℃), melt pressure (range 0-50MPa), main unit current, and online rheometer data in real time. When a melt temperature fluctuation exceeds ±3℃, a pressure change exceeds 10%, or the melt viscosity deviates from the preset target value by ±3%, the system automatically activates a compensation mechanism: adjusting the power output of the corresponding heating zone by ±5%-10%, or fine-tuning the feed screw speed by ±5%-8%, to achieve dynamic stability of the process window. Simultaneously, the system has a complete process data recording function, automatically generating a process log file for each batch, containing timestamps, formula information, sensor readings (including viscosity curves), and alarm events. This log file is stored on a local server and supports remote access, facilitating quality backtracking, compliance auditing, and continuous process improvement.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing high-impact, high-brightness PS black particles, characterized in that, The process includes the following steps: S1, Raw material pretreatment: Electrostatically separating the waste household appliance shreds to obtain PS shreds with a purity greater than 99%; S2, Multi-source batching and mixing: Mixing the PS shreds with toughening agent and black masterbatch according to a predetermined formula ratio to obtain a mixture; S3, Melt extrusion: Melting the mixture through a twin-screw extruder to obtain melt strips; S4, Cooling and granulation: Cooling and shaping the melt strips and cutting them into pellets to obtain PS black granules.

2. The preparation method according to claim 1, characterized in that: The waste household appliance shredded material in S1 includes waste refrigerator shredded material and waste air conditioner shredded material. The working voltage of the electrostatic separator is set to 4.5-6.0kV, the drum speed is 80-120rpm, and the feeding speed is controlled within the range of 15-25kg / h.

3. The preparation method according to claim 1 or 2, characterized in that: S1 also includes color sorting of some PS crushed material to remove discolored particles. Specifically, an infrared color sorter is used to perform two screenings to remove discolored particles with a color deviation exceeding ΔE≤1.

5.

4. The preparation method according to claim 1, characterized in that: The predetermined formula in S2 comprises, by mass percentage: 36% of electrostatically sorted refrigerator PS scrap; 36% of electrostatically sorted air conditioner PS scrap; 20% of color-sorted mixed-color PS scrap; 4% of SBS toughening agent; and 4% of carrier-free black masterbatch.

5. The preparation method according to claim 1, characterized in that: The multi-source batching and homogenization step in S2 is as follows: PS crushed materials from multiple sources are put into a homogenization tank for the first stage of dry mixing for 1-2 hours; then SBS toughening agent and carrier-free black masterbatch are added, and the second stage of stirring is carried out for 20 minutes; the homogenization is carried out at a temperature of 35±3℃ to prevent the materials from absorbing moisture and agglomerating.

6. The preparation method according to claim 1, characterized in that: The twin-screw extruder in S3 has at least nine temperature control zones, and the extrusion temperature is controlled between 200-220°C. The screw assembly of the twin-screw extruder includes a conveying section, a compression section, a shearing section, and a homogenizing section, wherein the shearing section is equipped with a kneading disc.

7. The preparation method according to claim 6, characterized in that: The temperature of the nine temperature control zones of the twin-screw extruder is set in a gradient of 180→190→200→210→215→220→220→215→210℃.

8. The preparation method according to claim 1, characterized in that: The cooling system in S4 uses a counter-flow three-layer cooling water tank with a water temperature of 15-20℃ in the first section, 25-30℃ in the second section, and 35-40℃ in the third section.

9. The preparation method according to claim 1, characterized in that: The method also includes an online rheological monitoring step, in which an online rheometer installed behind the extruder die is used to sample and analyze the melt index or apparent viscosity of the melt in real time. It also includes a finished product screening step, which uses a double-layer vibrating screen to remove impurities and particles that do not meet the size requirements. The upper screen has a mesh size of 3.0 mm and the lower screen has a mesh size of 1.8 mm.

10. The preparation method according to claim 1, characterized in that: The method also includes an intelligent process control step, which integrates a PLC controller and a SCADA monitoring platform to collect data on mixing time, melt temperature, extrusion pressure, current, and melt viscosity from an online rheometer in real time. When the parameter fluctuations exceed the preset threshold, the heating power or feeding speed is automatically adjusted to achieve closed-loop compensation.

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