Recycled material modified anti-shrinkage injection molding material and its molding method

Abstract

This invention discloses a recycled material modified anti-shrinkage injection molding material and its molding method. By weight, the raw materials for preparing the injection molding material include: 50-75 parts recycled polypropylene base material; 10-25 parts virgin high-crystallinity polypropylene; 10-20 parts anti-shrinkage modified filler system; 2-6 parts compatibilizer; and 0.2-0.8 parts antioxidant. The anti-shrinkage modified filler system is composed of surface-block treated wollastonite microneedles and microporous vitrified microspheres. In the molten state, the two form a three-dimensional interlocking anti-shrinkage network of "rigid skeleton-micro-airbag" in the polypropylene matrix. The shrinkage rate of the molded product along the flow direction can be reduced to about 0.45%, and the shrinkage rate perpendicular to the flow direction is about 0.52%. The difference between longitudinal and transverse shrinkage is small, basically eliminating defects such as warping and shrinkage marks. The dimensional stability reaches or even exceeds the level of new ABS engineering plastics.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification and resource recycling technology, specifically to recycled material modified anti-shrinkage injection molding materials and their molding methods. Background Technology

[0002] With the development of the plastics industry, the recycling and reuse of waste plastics (especially polypropylene (PP) packaging materials, appliance casings, etc.) has become an important way to protect the environment and reduce costs. However, after undergoing multiple heat processing and photo-oxidative aging processes, the molecular chains of recycled polypropylene (rPP) break, cross-link, and branch, resulting in an extremely uneven molecular weight distribution. This material deterioration directly leads to a very troublesome problem in industrial production: the molding shrinkage rate is extremely unstable and difficult to predict.

[0003] In actual injection molding production, the shrinkage rate of pure recycled PP products typically fluctuates between 1.5% and 2.5%, and is often accompanied by severe anisotropy (i.e., shrinkage is inconsistent in the flow direction and perpendicular to the flow direction), leading to serious appearance and assembly defects such as warping, deformation, and shrinkage marks. To reduce the shrinkage rate, the conventional practice is to fill the recycled material with large amounts of inexpensive inorganic powders (such as calcium carbonate and talc).

[0004] However, traditional filler modification has inherent contradictions that are difficult to overcome: A sharp decline in mechanical properties: The addition of a large number of inorganic rigid particles (usually >30%) reduces shrinkage, but it severely disrupts the continuity of the matrix, causing the material to become brittle and its impact strength to drop significantly, often failing to meet product requirements.

[0005] Poor processing fluidity: High filler content will drastically increase melt viscosity, which can easily cause insufficient injection molding or obvious flow marks on the surface.

[0006] Limitations of passive shrinkage resistance: Fillers such as talc only "passively" reduce the absolute amount of plastic shrinkage by occupying volume, and cannot "actively" compensate for the sharp volume reduction of plastic during the cooling and crystallization process.

[0007] Therefore, this paper proposes a recycled material modified anti-shrinkage injection molding material and its molding method. Summary of the Invention

[0008] The purpose of this invention is to provide a recycled material modified anti-shrinkage injection molding material and its molding method. This aims to solve one of the problems existing in the prior art.

[0009] Firstly, to solve the aforementioned technical problems, one technical solution adopted in this application is: a recycled material modified anti-shrinkage injection molding material, wherein, by weight, the raw materials for preparing the injection molding material include: 50-75 parts of recycled polypropylene base material; 10-25 parts of raw, highly crystalline polypropylene; 10-20 parts of anti-shrinkage modified filler system; 2-6 parts compatibilizer; Antioxidant 0.2-0.8 parts; The anti-shrinkage modified filler system consists of surface-block treated wollastonite microneedles and microporous vitrified microspheres, which form a three-dimensional interlocking anti-shrinkage network of "rigid skeleton-micro-bag" in the polypropylene matrix in the molten state.

[0010] Due to molecular chain defects, recycled PP crystallizes extremely slowly and incompletely. This invention utilizes 10-25 parts of virgin, highly crystalline PP. During the initial stage of melt cooling, this portion of highly crystalline PP crystallizes first, forming an initial rigid crystalline framework at the microscopic level. This pre-formed framework can largely resist the inward shrinkage stress generated during the subsequent slow crystallization of recycled PP.

[0011] The anti-shrinkage modified filler system is not a single powder, but a mixture of wollastonite microneedles with an aspect ratio greater than 15 and microporous vitrified microspheres with a closed pore rate greater than 80% (weight ratio of 2~4:1).

[0012] Wollastonite microneedles: like "steel bars" in the microscopic world, they become oriented when the melt flows and resist the shrinkage of the matrix when cooled by their high modulus.

[0013] Microporous vitrified microspheres (micro-airbags): Vitrified microspheres have a closed microporous structure containing a small amount of gas. Under the high temperature and pressure of the injection molding machine, the microspheres are compressed. When the melt is injected into the mold cavity and begins to cool and shrink, due to the special pressure holding process adopted in this invention, the compressed gas inside the microspheres begins to expand in the opposite direction (i.e., volume self-compensation effect).

[0014] The synergistic effect of the rigid tension of microneedles and the elastic expansion of microbeads completely breaks the limitation of traditional powders that can only passively occupy space, and achieves active anti-shrinkage.

[0015] To address the issue of material embrittlement caused by the addition of inorganic fillers, this invention employs a special "soft coating" treatment on wollastonite and vitrified microspheres before adding them to the PP matrix. First, the surface of the inorganic material is treated with a silane coupling agent containing double bonds, followed by a grafting reaction with a polyolefin elastomer. This results in each rigid inorganic particle being coated with an extremely thin elastomeric buffer layer. When the material is impacted, this elastomer layer effectively absorbs energy, triggering crazing in the matrix to dissipate the impact energy, achieving a perfect balance between "shrinkage reduction" and "toughness preservation."

[0016] In one possible implementation, the melt flow rate of the recycled polypropylene base material is 10-25 g / 10min; the isotacticity of the virgin highly crystalline polypropylene is greater than 95%, and its melt flow rate is 2-8 g / 10min.

[0017] In one possible implementation, the weight ratio of the wollastonite microneedles to the microporous vitrified microspheres is (2~4):1; The wollastonite microneedles have an aspect ratio greater than 15 and an average length of 20-60 μm; the microporous vitrified microspheres have an average particle size of 10-30 μm and a closed-pore rate greater than 80%.

[0018] In one possible implementation, the surface-block-treated wollastonite microneedles and microporous vitrified microspheres are coated with polyolefin elastomer grafts. The polyolefin elastomer graft is grafted onto the surface of the inorganic filler using a silane coupling agent containing double bonds.

[0019] In one possible implementation, the compatibilizer is maleic anhydride-grafted polypropylene, with a grafting rate controlled at 0.8%-1.2%.

[0020] Secondly, to solve the above-mentioned technical problems, another technical solution adopted in this application is: a molding method for recycled material modified anti-shrinkage injection molding material, comprising the following steps: The molding method includes two steps: stepped mixing and granulation, and variable pressure micro-foaming and pressure-holding injection molding. Step 1: Add the recycled polypropylene base material, virgin high-crystallinity polypropylene, compatibilizer and antioxidant to the main feed port of the twin-screw extruder. After melting and plasticizing, add the anti-shrinkage modified filler system to the side feed port of the middle and rear section of the extruder; extrude and granulate to obtain modified granules. Step 2: Add the modified particles to the injection molding machine. After the injection filling is completed, implement segmented pressure control to compensate for the volume shrinkage caused by the cooling and crystallization of polypropylene by utilizing the volume expansion effect of the microporous vitrified microspheres under heat and pressure conditions.

[0021] In one possible implementation, in step one, the temperature settings of the twin-screw extruder are saddle-shaped, with the feed section temperature at 170-185℃, the melt mixing section temperature at 200-220℃, and the temperature dropping to 180-195℃ from the side feeding section to the die head; the screw speed is 300-450 rpm.

[0022] In one possible implementation, in step two, the segmented pressure holding control specifically refers to: First holding pressure stage: The holding pressure is 70-80% of the injection pressure, and the holding time is 2-4 seconds, so that the melt in the mold cavity is compacted; Second pressure holding stage: The pressure holding pressure suddenly drops to 20-30% of the injection pressure, and the pressure holding time is 3-6 seconds, triggering the microporous vitrified microspheres in the compressed state to undergo secondary volume expansion; The third pressure holding stage: the pressure is raised back to 40-50% of the injection pressure, the pressure holding time is 2-5 seconds, and the surface is shaped and cooled.

[0023] This invention abandons the traditional constant pressure holding mode and pioneers a segmented variable pressure holding process: High-pressure compaction (shrinkage compensation) – instantaneous pressure reduction (stimulating microsphere expansion) – medium-pressure shaping (surface cooling).

[0024] The second stage of instantaneous pressure reduction is specifically designed for vitrified microspheres. By suddenly reducing the holding pressure before the melt is completely frozen, the external constraints on the microspheres are released, and the high-pressure gas inside the microspheres forces them to expand slightly.

[0025] The volume increase caused by this expansion precisely offsets the volume reduction caused by PP crystallization. The core physical mechanism by which this method absorbs the shrinkage of the plastic through the expansion of tiny pores is the key to controlling the shrinkage rate to an extremely low level.

[0026] In one possible implementation, during the variable pressure microfoaming and pressure-holding injection molding process, the temperature of the moving mold platen side is set 10-15°C lower than that of the fixed mold platen side, so as to guide the release of shrinkage stress to the non-surface surface.

[0027] Thirdly, in order to solve the above-mentioned technical problems, another technical solution adopted in this application is: an injection molded product made of recycled material modified anti-shrinkage injection molding material, or manufactured by the molding method described above.

[0028] Fourthly, to solve the above-mentioned technical problems, another technical solution adopted in this application is: an electronic device, including a processor, a memory and a communication interface, wherein the memory stores a computer program, and when the processor executes the computer program, it implements the steps of the above-mentioned molding method.

[0029] Fifth aspect: To solve the above-mentioned technical problems, another technical solution adopted in this application is: a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the steps of any of the molding methods described above.

[0030] The present invention has the following beneficial effects: 1. The shrinkage rate of the molded product along the flow direction can be reduced to about 0.45%, and the shrinkage rate perpendicular to the flow direction is about 0.52%. The difference between longitudinal and transverse shrinkage is small, basically eliminating defects such as warping and shrinkage marks. The dimensional stability reaches or even exceeds the level of new ABS engineering plastics. 2. With only 10-20% inorganic filler added, the notched impact strength of the cantilever beam of the product can reach 11.5kJ / m², which is higher than that of pure recycled PP. This completely solves the problem of material brittleness caused by traditional high-filler modification and achieves a balance between rigidity and toughness. 3. No need for large amounts of inorganic fillers, excellent melt flow, avoiding defects such as insufficient glue and flow marks in injection molding, simple molding process, compatible with existing injection molding equipment, and easy to promote industrialization; 4. Using recycled PP as the main raw material, we can realize the resource utilization of waste plastics, reduce raw material costs, and reduce plastic waste pollution, thus achieving both environmental value and economic benefits. 5. It can be used in recycled plastic products with high requirements for dimensional accuracy and mechanical properties, such as automotive interiors, precision electrical brackets, and office supplies, with significant industrial conversion value. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic flowchart of the molding method of the present invention; Figure 2 This is a schematic diagram of the structure of the electronic device of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Figure 1 This is a schematic flowchart of the molding method according to an embodiment of the present invention. It should be noted that if substantially the same result is achieved, the method of this application is not necessarily identical. Figure 1 The sequence of processes shown is limited.

[0035] Preparation of experimental materials; Recycled polypropylene base material: derived from granulation of waste washing machine inner drums, melt flow rate 15 g / 10min (230℃, 2.16kg); Natural high-crystallinity PP: isotacticity 97%, melt flow rate 4 g / 10min (230℃, 2.16kg); Wollastonite microneedles: aspect ratio 20, average length 40 μm; Microporous vitrified microspheres: average particle size 20 μm, closed-cell rate 85%; Compatibilizer: PP-g-MAH, grafting rate 1.0%; Antioxidant: 1010 and 168 are mixed in a 1:2 ratio; Silane coupling agent: A-171 (containing vinyl double bonds); POE elastomers have a high melt flow rate, which facilitates grafting and coating. Initiator: Dicumyl peroxide (DCP); Talc: average particle size 10 μm (used for Comparative Example 1).

[0036] Preparation of anti-shrinkage modified filler system; Prepare the elastic-coated anti-shrinkage system according to the following steps: 1. Coupling activation: Weigh 800g of wollastonite microneedles and 200g of microporous vitrified microspheres, put them into a high-speed kneader with a heating jacket, heat to 110℃ at low speed (300 rpm), and hold for 15 minutes; dilute 25g of A-171 silane coupling agent with a small amount of ethanol, spray it into the kneader, increase the speed to 1500 rpm, and knead at high speed for 10 minutes to complete the coupling activation; 2. POE grafting coating: Cool the activated mixed filler to 80℃, add 150g POE powder and 1.5g DCP initiator, start high-speed kneading (1200 rpm), rely on frictional heat generation to raise the material temperature to about 140℃, continue kneading for 15 minutes, cool down and discharge to obtain an elastic coating anti-shrinkage system. Example

[0037] 1. Formula (by weight): 65 parts recycled PP, 15 parts natural high-crystallinity PP, 15 parts elastic coating anti-shrinkage system, 4 parts PP-g-MAH, 0.5 parts antioxidant; 2. Stepped compounding and granulation: A co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1 is used. The barrel temperature is set as follows: Zone 1 175℃, Zone 2 210℃, Zone 3 215℃, Zone 4 210℃, Zone 5 210℃, Zone 6 200℃, Zone 7 190℃, Zone 8 185℃, and the die head 185℃; the screw speed is 350 rpm; recycled PP, high-crystallinity PP, compatibilizer and antioxidant are added to the main feed port, and an elastic coating anti-shrinkage system is added to the side feed port in Zone 6. The extruded strip is water-cooled, pelletized and dried to obtain modified granules. 3. Variable pressure micro-foaming injection molding: A 120-ton injection molding machine is used, with a melt temperature of 200℃ and a mold temperature of 40℃ (35℃ on the moving mold platen side and 50℃ on the fixed mold platen side); the injection pressure is 100 MPa, with segmented pressure holding settings: the first pressure holding segment is 80 MPa for 3.0s, the second pressure holding segment is 25 MPa for 4.0s, and the third pressure holding segment is 45 MPa for 3.0s; the injection molded sample size is 150×100×3mm, and it is left to stand for 48 hours after molding for later use.

[0038] Comparative Example 1: 1. Formulation (by weight): 65 parts recycled PP, 30 parts talc, 4 parts PP-g-MAH, 0.5 parts antioxidant; no surface coating treatment was applied to the talc. 2. Mixing and granulation: Same as in Example 1, but all raw materials are added from the main feed port; 3. Injection molding process: Conventional constant pressure holding, holding pressure 60 MPa, total holding time 10s, other parameters are the same as in Example 1; injection molded sample size and placement time are the same as in Example 1.

[0039] Comparative Example 2 1. The formulation and mixing / granulation process are exactly the same as in Example 1; 2. Injection molding process: Conventional constant pressure holding, holding pressure 60 MPa, total holding time 10s, without performing segmented pressure release steps, other parameters are the same as in Example 1; injection molded sample size and placement time are the same as in Example 1.

[0040] Benchmark group: Only recycled PP was used for injection molding, and the injection molding process was the same as that of Comparative Example 1, which served as the performance benchmark.

[0041] Performance testing and results analysis: The injection molded samples of Example 1, Comparative Example 1, Comparative Example 2, and the baseline group were subjected to performance tests after being left to stand for 48 hours. The test items included molding shrinkage (along the flow direction and perpendicular to the flow direction), cantilever beam notched impact strength, flexural modulus, and surface quality. The test results are shown in the table below:

[0042] The shrinkage rate of Example 1 (0.45%–0.52%) was significantly lower than that of the baseline group (1.60%–1.85%) and Comparative Examples 1 and 2, with minimal difference in longitudinal and transverse shrinkage. This indicates that the "rigid skeleton-micro-airbag" structure of the present invention, combined with the segmented variable pressure holding process, effectively suppresses shrinkage and eliminates anisotropy. Although Comparative Example 2 used the material formulation of the present invention, it did not employ the segmented variable pressure holding process. As a result, the microspheres could not achieve volume expansion compensation, and the shrinkage rate only decreased to 0.68%–0.80%, proving that the molding process is the key to achieving ultra-low shrinkage. Comparative Example 1 used a traditional high-filling scheme, and even with a filling amount of 30%, the shrinkage rate was still higher than that of Example 1, with significant anisotropy and a substantial decrease in mechanical properties.

[0043] Although the flexural modulus of Comparative Example 1 is higher than that of Example 1, its impact strength is only 4.2 kJ / m², and the material is severely brittle and cannot be used practically. The impact strength of Example 1 (11.5 kJ / m²) is higher than that of the benchmark group (8.5 kJ / m²), and its flexural modulus (1850 MPa) also meets the requirements for precision products. This indicates that the POE elastic coating layer on the filler surface effectively solves the embrittlement problem caused by rigid fillers and achieves a balance between rigidity and toughness. The impact strength of Comparative Example 2 is close to that of Example 1, proving that the material formulation is the basis for ensuring mechanical properties, and the molding process has little impact on mechanical properties.

[0044] The sample in Example 1 had no shrinkage marks, a smooth surface, and no warping or deformation, meeting the appearance requirements of high-precision products. Comparative Example 1 had slight shrinkage marks and warping, and Comparative Example 2 had slight edge deformation. The surface defects of the benchmark group were serious, further proving that the synergistic effect of the materials and processes of the present invention can effectively improve the surface quality of the products.

[0045] Experimental results show that this invention successfully solves the technical problems of high shrinkage and poor mechanical properties in recycled PP injection molding by reshaping the material's microstructure (a three-dimensional interlocking network of "rigid skeleton-micro-airbags" and POE elastic coating) and controlling stress during the molding process (segmented variable pressure holding). The technical solution of this invention is not a simple mixing of raw materials, but a close coupling of material formulation and molding process, possessing outstanding substantive characteristics and significant progress. The process is simple, cost-controllable, and easy to promote industrially, providing a new technical path for the recycling of waste plastics.

[0046] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system-type embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. Example

[0047] like Figure 2 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present disclosure. It illustrates a structural schematic diagram suitable for implementing the electronic device in the embodiment of the present disclosure. Figure 2 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of the embodiments disclosed herein.

[0048] like Figure 2 As shown, the electronic device includes a processor, a memory, and a communication interface. The memory stores a computer program, and when the processor executes the computer program, it implements the molding methods of the aforementioned embodiments of this disclosure. The electronic device can exchange data with other devices or systems through the communication interface, enabling real-time updates and sharing of data information.

[0049] The processor in the aforementioned electronic device serves as its core, responsible for executing the computer program stored in the memory to implement various functions of the molding method. The processor can employ a high-performance multi-core CPU or a dedicated chip to meet the demands of complex calculations and real-time processing. The memory stores the operating system, applications, data, and computer programs. In this embodiment, the memory stores the computer program implementing the molding method. The memory can be RAM, ROM, Flash memory, or other types of non-volatile memory. The communication interface connects the electronic device to other devices or networks, enabling data transmission and exchange. In this embodiment, the communication interface supports various communication protocols and interface standards, such as Wi-Fi, Bluetooth, USB, and Ethernet, to meet communication needs in different scenarios.

[0050] For a detailed description of this embodiment, please refer to the corresponding descriptions in the foregoing embodiments, which will not be repeated here. Example

[0051] According to embodiments of the present disclosure, a computer-readable storage medium stores a computer program, which, when executed by a processor, implements the various functions of the molding methods described in the foregoing embodiments of the present disclosure.

[0052] The aforementioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or portable hard drive), media with built-in rewritable non-volatile memory (e.g., memory card), and media with built-in ROM (e.g., ROM cartridge).

[0053] For a detailed description of this embodiment, please refer to the corresponding descriptions in the foregoing embodiments, which will not be repeated here.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A recycled material modified anti-shrinkage injection molding material, characterized in that, The raw materials for preparing the injection molding material, by weight, include: Recycle 50-75 parts of polypropylene base material; 10-25 parts of raw, highly crystalline polypropylene; 10-20 parts of anti-shrinkage modified filler system; 2-6 parts compatibilizer; Antioxidant 0.2~0.8 parts; The anti-shrinkage modified filler system consists of surface-block treated wollastonite microneedles and microporous vitrified microspheres.

2. The recycled material modified anti-shrinkage injection molding material according to claim 1, characterized in that, The melt flow rate of the recycled polypropylene base material is 10~25 g / 10min; the isotacticity of the original high-crystallinity polypropylene is greater than 95%, and its melt flow rate is 2~8 g / 10min.

3. The recycled material modified anti-shrinkage injection molding material according to claim 1, characterized in that, The weight ratio of the wollastonite microneedles to the microporous vitrified microspheres is (2~4):1; The wollastonite microneedles have an aspect ratio greater than 15 and an average length of 20-60 μm; the microporous vitrified microspheres have an average particle size of 10-30 μm and a closed-pore rate greater than 80%.

4. The recycled material modified anti-shrinkage injection molding material according to claim 1 or 3, characterized in that, The surface-block treated wollastonite microneedles and microporous vitrified microspheres are coated with polyolefin elastomer grafts. The polyolefin elastomer graft is grafted onto the surface of the inorganic filler using a silane coupling agent containing double bonds.

5. The recycled material modified anti-shrinkage injection molding material according to claim 1, characterized in that, The compatibilizer is maleic anhydride-grafted polypropylene, and its grafting rate is controlled at 0.8%~1.2%.

6. A molding method for a recycled material modified anti-shrinkage injection molding material as described in any one of claims 1-5, characterized in that, The process includes two steps: stepped compounding and granulation, and variable pressure micro-foaming and pressure-holding injection molding. Step 1: Add the recycled polypropylene base material, virgin high-crystallinity polypropylene, compatibilizer and antioxidant to the main feed port of the twin-screw extruder. After melting and plasticizing, add the anti-shrinkage modified filler system to the side feed port of the middle and rear section of the extruder; extrude and granulate to obtain modified granules. Step 2: Add the modified particles to the injection molding machine. After the injection filling is completed, implement segmented pressure control to compensate for the volume shrinkage caused by the cooling and crystallization of polypropylene by utilizing the volume expansion effect of the microporous vitrified microspheres under heat and pressure conditions.

7. The molding method according to claim 6, characterized in that, In step one, the temperature settings of the twin-screw extruder are saddle-shaped, with the feed section temperature at 170~185℃, the melt mixing section temperature at 200~220℃, and the temperature dropping to 180~195℃ after the side feeding section and down to the die head; the screw speed is 300~450 rpm.

8. The molding method according to claim 6, characterized in that, In step two, the segmented pressure holding control specifically includes: First holding pressure stage: The holding pressure is 70-80% of the injection pressure, and the holding time is 2-4 seconds to compact the melt in the mold cavity; Second pressure holding stage: The pressure holding pressure suddenly drops to 20-30% of the injection pressure, and the pressure holding time is 3-6 seconds, triggering the microporous vitrified microspheres in the compressed state to undergo secondary volume expansion; The third pressure holding stage: the pressure is raised back to 40-50% of the injection pressure, the pressure holding time is 2-5 seconds, and the surface is shaped and cooled.

9. The molding method according to claim 6, characterized in that, During the variable pressure micro-foaming and pressure-holding injection molding process, the temperature setting on the moving mold platen side is 10~15℃ lower than that on the fixed mold platen side.

10. An injection-molded product, characterized in that, It is manufactured using the recycled material modified anti-shrinkage injection molding material according to any one of claims 1-5, or using the molding method according to any one of claims 6-9.

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