Gas counter-pressure microcellular foam injection compression molding injection molding process

Abstract

This invention relates to a gas-backpressure microcellular foaming injection compression molding process, comprising the following steps: placing the moving mold and stationary mold of the injection mold in a partially locked, sealed mold-closing state; opening the gas backpressure device communicating with the cavity, allowing backpressure gas to fill the cavity and maintaining a predetermined backpressure gas pressure within the cavity; starting the injection molding machine and a supercritical fluid delivery device to generate injection melt containing foaming gas; the predetermined volume of injection melt entering the cavity under the action of the backpressure gas, pushing the moving mold to compress the injection melt within the cavity; the compressed injection melt expelling part of the backpressure gas from the cavity; leaving a foaming space between the injection melt and the compressed cavity; and releasing the backpressure gas from the cavity when the injection melt cools to the foaming temperature, allowing the injection melt to begin foaming until it fills the entire cavity. This invention employs an injection molding process combining gas backpressure, injection compression molding, and microcellular foaming, resulting in high surface quality of the plastic parts and improved foaming quality.

Description

Technical Field

[0001] This invention relates to a microporous foaming injection molding process, and more particularly to a gas backpressure microporous foaming injection compression molding process, belonging to the field of microporous foaming. Background Technology

[0002] Microcellular foaming technology is an advanced process used in plastic parts processing to reduce product weight. Currently, for energy conservation and emission reduction purposes, lightweight plastic parts are highly emphasized and applied in the automotive parts manufacturing industry. Automotive parts contain a large number of plastic components, and lightweighting these components can significantly reduce their weight, thus reducing the overall weight of the vehicle and demonstrating significant energy-saving and environmental protection effects. Microcellular foaming involves mixing gas with the fluid in the plastic part and then injection molding. The gases used are typically nitrogen and carbon dioxide. However, under normal conditions, the solubility of nitrogen and carbon dioxide in polymer materials is very low, insufficient for foaming. Therefore, a supercritical method is used to fully mix the gas with the fluid in the plastic part. In the supercritical state, the solubility and diffusion rate of the gas increase significantly, thereby achieving the microcellular foaming effect. Supercritical microcellular foaming injection molding offers advantages such as reduced manufacturing costs, weight reduction, lower material and mold temperatures, shorter molding cycles, improved part quality, and flexible design.

[0003] During injection molding, gas within the fluid escapes to the surface of the material flow due to pressure, leaving pores and surface cracks. This results in poor surface finish in microcellular foamed injection molded parts, making them prone to defects such as eddy marks, silver streaks, surface microbubbles, and surface openings. These surface defects significantly affect the appearance quality of the parts. Furthermore, foamed parts produced using only injection molding exhibit uneven bubble morphology and contain numerous large bubbles, which may impact the overall strength of the part. Therefore, it is necessary to improve current microcellular foaming injection molding processes. Summary of the Invention

[0004] This invention discloses a new solution for gas back pressure microporous foaming injection compression molding process. It adopts an injection molding process that combines gas back pressure process, injection compression molding process and microporous foaming process, which improves the surface quality of plastic parts and the uniformity of foam morphology, reduces the size of foam, and significantly improves foaming quality. It solves the problems of poor surface quality and low foaming quality of plastic parts in existing similar processes.

[0005] The gas backpressure microporous foaming injection compression molding process of this invention includes the following steps:

[0006] The moving mold and stationary mold of the injection mold are placed in a partially locked, sealed mold-closing state. The gas back pressure device connected to the cavity is opened, allowing back pressure gas to fill the cavity and maintaining a predetermined back pressure in the cavity. The injection molding machine and supercritical fluid delivery device are turned on to generate injection melt containing foaming gas. The injection melt of a predetermined volume enters the cavity under the action of back pressure gas, pushing the moving mold to squeeze the injection melt in the cavity. The compressed injection melt discharges part of the back pressure gas in the cavity. A foaming space is left between the injection melt and the compressed cavity. When the injection melt cools to the foaming temperature, the back pressure gas in the cavity is released, and the injection melt cooled to the foaming temperature begins to foam until it fills the entire cavity.

[0007] Furthermore, the base material of the injection melt in this solution is ABS, and the injection melt also includes graphene nanomaterial additives, with the mass percentage of graphene nanomaterial additives in the injection melt not exceeding 7%.

[0008] Furthermore, the graphene nanomaterial additive in this solution has a mass percentage of 2% or 3% in the injection molding melt.

[0009] Furthermore, this solution preheats the core portion of the injection mold, and then performs the injection molding operation once the core portion reaches the predetermined temperature.

[0010] Furthermore, the gas back pressure device of this solution includes a nitrogen generator, a gas compression pump, and a gas supply pipeline. The gas supply pipeline includes a main gas supply pipeline and multiple branch gas supply pipelines. The nitrogen generator is connected to the gas compression pump, the gas compression pump is connected to the main gas supply pipeline, and the main gas supply pipeline is connected to the branch gas supply pipelines. The outlet of the branch gas supply pipeline is located on the side wall at the end of the feed stroke of the cavity.

[0011] Furthermore, in this solution, at least one of the multiple gas supply branch pipes has its outlet located on the central part of the moving mold on one side of the cavity. This pushes the moving mold to squeeze the injection melt in the cavity, causing the injection melt to diffuse to the surrounding area of ​​the cavity. The back pressure gas from the surrounding area is then sequentially forced into the cavity through the outlet of the gas supply branch pipe located on the side wall of the feeding stroke end of the cavity, the gas supply branch pipe, and the outlet of the gas supply branch pipe located on the central part of the moving mold on one side of the cavity. The gas forced into the cavity forms a foaming depression in the central part of the injection melt.

[0012] Furthermore, the gas back pressure device in this solution also includes a pressure regulating device, which includes a booster valve, a stabilizing valve, a pressure relief valve, and a pressure regulating control unit. The booster valve is used to increase the pressure of the back pressure gas, the stabilizing valve is used to maintain the pressure of the back pressure gas, and the pressure relief valve is used to decrease the pressure of the back pressure gas. The pressure regulating control unit controls the booster valve, the stabilizing valve, and the pressure relief valve to complete the boosting, stabilizing, and depressurizing operations based on the signal sent by the pressure sensor installed in the injection mold.

[0013] Furthermore, the moving mold of this design is provided with a sealing bushing at the mold closing end, and several elastic high-temperature resistant sealing rings are provided between the sealing bushing and the stationary mold after mold closing.

[0014] Furthermore, the back pressure gas in this scheme is nitrogen and / or carbon dioxide.

[0015] Furthermore, the foaming gas in this scheme is nitrogen.

[0016] This invention relates to a gas backpressure microporous foaming injection compression molding process that combines gas backpressure, injection compression molding, and microporous foaming processes. This process improves the surface quality and uniformity of the foam morphology of the plastic parts, reduces the size of the foam, and significantly improves the foaming quality. It overcomes the problems of poor surface quality and low foaming quality in existing similar processes, and features high surface quality and improved foaming quality. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the gas backpressure microporous foaming injection compression molding process.

[0018] Figure 2 This is a schematic diagram of the axial section of an injection mold.

[0019] in,

[0020] 100 is the moving mold, and 101 is the sealing bushing.

[0021] 200 is a static model.

[0022] 300 is the injection melt.

[0023] 410 is the main gas supply pipe, and 421 is the branch gas supply pipe.

[0024] 501 is the foaming space, and 502 is the foaming recess.

[0025] 601 is an elastic, high-temperature resistant sealing ring. Detailed Implementation

[0026] The following is a detailed explanation with reference to the attached diagram.

[0027] like Figure 1 , 2As shown, the gas backpressure microporous foaming injection compression molding process of the present invention includes the following steps: placing the moving mold 100 and the stationary mold 200 of the injection mold in a partially locked sealed mold-closing state, opening the gas backpressure device communicating with the cavity, so that the cavity is filled with backpressure gas, maintaining a predetermined backpressure gas pressure in the cavity, starting the injection molding machine and the supercritical fluid conveying device to generate injection melt 300 containing foaming gas, the predetermined volume of injection melt 300 enters the cavity under the action of backpressure gas, pushing the moving mold 100 to squeeze the injection melt 300 in the cavity, the compressed injection melt 300 discharges part of the backpressure gas in the cavity, leaving a foaming space 501 between the injection melt 300 and the compressed cavity, and when the injection melt 300 cools to the foaming temperature, the backpressure gas in the cavity is released, and the injection melt 300 cooled to the foaming temperature begins to foam until it fills the entire cavity. Figure 1 As shown, the supercritical fluid delivery device is used to generate a supercritical foaming agent, the injection molding machine is used to mix the foaming agent with the injection plastic and input the injection melt into the injection mold, the injection mold is used to mold the plastic part, the gas back pressure device is used to provide back pressure gas and control the change of back pressure gas during the injection stage, and the push mold device is used to push the moving mold to extrude the injection melt in the cavity.

[0028] The above-mentioned solution employs an injection molding process that combines gas backpressure, injection compression molding, and microcellular foaming. This improves the surface quality and uniformity of the foam morphology of the plastic parts, reduces the size of the foam, and significantly improves the foaming quality. The injection mold is designed according to the expansion coefficient of the microcellular foamed injection molded parts. A flow channel structure is incorporated into the mold to facilitate the filling of the foaming material, reducing resistance during the filling process. Backpressure gas, such as nitrogen or carbon dioxide, is pre-injected into the mold. The properties of the gas in the microcellular foam are similar to those of the backpressure gas, which helps to ensure uniform gas distribution within the foaming material and form a uniform pore structure. Furthermore, the backpressure gas acts directly on the surface of the foaming fluid, inhibiting the flow and dissipation of the foaming gas to the fluid surface, effectively improving the surface quality of the microcellular foamed plastic parts. Experimental results show that using a foaming injection compression process results in a more uniform foam morphology. Combining both processes produces foamed products with a more uniform bubble structure and smaller bubble size, especially near the gate. Compared to parts without injection compression, the foam morphology is more uniform and the bubble size is smaller. Furthermore, the results demonstrate that by synergistically controlling mold temperature and cavity gas back pressure, the surface bubble morphology and internal cell structure of microporous foamed injection molded products can be well controlled. Therefore, this solution overcomes the problems of poor surface quality and low foaming quality found in existing similar processes, offering advantages such as high surface quality and improved foaming quality.

[0029] Based on the above scheme, in order to further improve the foaming morphology and make the bubble size more uniform, this scheme adds an additive to the injection molding compound. Specifically, the base material of the injection melt 300 is ABS, and the injection melt 300 also includes graphene nanomaterial additives. The mass percentage of the graphene nanomaterial additives in the injection melt 300 is no more than 7%. Furthermore, the mass percentage of the graphene nanomaterial additives in the injection melt 300 in this scheme is 2% or 3%.

[0030] This scheme establishes a method for preparing composite materials with different proportions of graphene content, such as 1, 2, 3, 5, and 7 wt%, using ABS as the base material and graphene nanomaterials as additives, through a microporous foaming injection molding process. Experiments were conducted on the foaming morphology of ABS / GP nanocomposites. The results show that the foaming injection compression process can make the foaming morphology more uniform, and increasing the amount of graphene added can improve the foaming morphology and make the bubble size more uniform. Transmission electron microscopy can be observed that when the amount of graphene added is 2 wt%, there is less agglomeration, and the thickness of the graphene with an added amount of 2 wt% is thinner than that with an added amount of 3 wt%, indicating better dispersion. Cone-shaped thermal analysis, limiting oxygen index, and UL-94 flame retardancy test results show that graphene nanocomposites significantly improve the flame retardancy of the material. A 3 wt% graphene addition reduces the heat release rate by 30.4%. Compared to pure PC / ABS samples, the graphene composite exhibits less dripping in the UL-94 test. TGA experiments show that the addition of graphene enhances the thermal stability and combustion residue yield of the nanocomposites. In foaming and injection molding experiments of ABS / GP nanocomposites with different graphene additions (0, 3, 5, and 7 wt%), it was found that after using the injection compression process, samples with the same graphene addition amount show smaller bubble size and increased bubble density. The bubble size does not necessarily change steadily with the addition of graphene; a 3 wt% graphene addition increases bubble size, but the bubble size is relatively uniform. Therefore, this method improves the quality of microporous foaming by introducing ABS / GP nanocomposites, i.e., ABS with graphene additives.

[0031] To improve injection molding quality, this solution preheats the core of the injection mold. Injection is then performed once the core reaches a predetermined temperature. The mold core is heated before injection, and an electric heating element raises it to the preheated temperature. A heat insulation layer can be installed between the core and the mold base structure to prevent the preheated heat from diffusing into the base structure. Because microporous foam materials contain supercritical foaming gases and have high fluid temperatures, preheating the mold extends the fluid flow distance and improves filling efficiency. However, heating the entire mold results in a large volume, high heat consumption, and significant heat loss. Therefore, localized heating of the core improves heating efficiency, reduces heat consumption, and the heat insulation layer provides insulation, further reducing heat loss and improving thermal efficiency.

[0032] To achieve the function of the gas backpressure device and improve the pressure balance within the mold cavity, such as... Figure 2 As shown, the gas backpressure device in this solution includes a nitrogen generator, a gas compression pump, and a gas supply pipeline. The gas supply pipeline includes a main gas supply pipeline 410 and multiple branch gas supply pipelines 421. The nitrogen generator is connected to the gas compression pump, the gas compression pump is connected to the main gas supply pipeline 410, and the main gas supply pipeline 410 is connected to the branch gas supply pipelines 421. The outlet of the branch gas supply pipelines 421 is located on the side wall at the end of the feed stroke of the mold cavity. This arrangement of the branch gas supply pipeline outlets ensures the uniformity of gas pressure within the mold cavity, avoids uneven pressure distribution in different parts of the injection melt entering the mold cavity, and ensures the surface quality of the plastic part.

[0033] Based on the above solution, in order to create a suitable foaming space for the injection molten metal in the mold cavity, this solution will return the gas discharged during the extrusion of the injection molten metal to an appropriate location within the mold cavity through a suitable pipeline design, so as to meet the requirement of uniform foaming of the injection molten metal. Figure 2 As shown, at least one of the aforementioned gas supply branch pipes 421 has its outlet located on the central part of the moving mold 100 on one side of the cavity. This pushes the moving mold 100 to extrude the injection melt 300 within the cavity. The injection melt 300 diffuses outwards from the cavity, sequentially forcing the surrounding back pressure gas into the cavity through the outlet of the gas supply branch pipe 421 located on the side wall surrounding the end of the feed stroke of the cavity, the gas supply branch pipe 421, and the outlet of the gas supply branch pipe 421 located on the central part of the moving mold 100 on one side of the cavity. The gas forced into the cavity forms a foaming recess 502 in the central part of the injection melt 300. For example... Figure 2 As shown, the injection melt 300 has a disc-shaped structure, with foaming spaces 501 and foaming recesses 502 provided around its four edges and in the center, thus meeting the foaming requirements.

[0034] To control the back pressure gas and meet the need for real-time pressure changes within the pipeline, this gas back pressure device also includes a pressure regulating device. This device comprises a booster valve, a stabilizing valve, a pressure relief valve, and a pressure regulating control unit. The booster valve increases the back pressure gas pressure, the stabilizing valve maintains the pressure, and the pressure relief valve decreases the pressure. The pressure regulating control unit controls the booster valve, stabilizing valve, and pressure relief valve based on signals from a pressure sensor located within the injection mold to perform boosting, stabilizing, and depressurizing operations. The pressure regulating device has the capability to boost, maintain, and reduce pressure. Through the pressure regulating control unit, the coordinated working process is cyclical, improving automation efficiency. Furthermore, it features stable operation and long operating time, which contributes to quality control during the process.

[0035] To improve the airtightness of the mold and prevent air pressure leakage, such as Figure 2 As shown, the moving mold 100 of this design has a sealing bushing 101 at its closing end, and several elastic high-temperature resistant sealing rings 601 are provided between the sealing bushing 101 and the stationary mold 200 after mold closing. The elastic high-temperature resistant sealing rings 601 can preferably be made of fluororubber, which has the characteristics of good stability, high temperature resistance, aging resistance, good vacuum performance, and excellent mechanical properties.

[0036] The back pressure gas in this scheme is nitrogen and / or carbon dioxide, and the foaming gas is nitrogen.

[0037] Unless otherwise specified, the structures, mechanisms, and components disclosed in this solution can all be implemented using common and conventional methods known in the art. The gas-backpressure microporous foaming injection compression molding process of this solution is not limited to the content disclosed in the specific embodiments. The technical solutions appearing in the embodiments can be extended based on the understanding of those skilled in the art, and simple substitutions made by those skilled in the art based on this solution and common knowledge also fall within the scope of this solution.

Claims

1. Gas backpressure microporous foaming injection compression molding process, characterized by: Includes the following steps: The moving mold and stationary mold of the injection mold are placed in a partially locked sealed mold-closing state. The gas back pressure device connected to the cavity is opened, so that the cavity is filled with back pressure gas. The predetermined back pressure gas pressure in the cavity is maintained. The injection molding machine and supercritical fluid delivery device are turned on to generate injection melt containing foaming gas. The injection melt of the predetermined volume enters the cavity under the action of back pressure gas, pushing the moving mold to squeeze the injection melt in the cavity. The compressed injection melt discharges part of the back pressure gas in the cavity. A foaming space is left between the injection melt and the compressed cavity. When the injection melt cools to the foaming temperature, the back pressure gas in the cavity is released. The injection melt cooled to the foaming temperature begins to foam until it fills the entire cavity. The substrate of the injection melt is ABS, and the injection melt also includes graphene nanomaterial additives, wherein the mass percentage of the graphene nanomaterial additives in the injection melt is 2% or 3%. The core of the injection mold is preheated, and the injection molding operation is performed when the core reaches the predetermined temperature.

2. The gas backpressure microporous foaming injection compression molding process according to claim 1, characterized in that... The gas back pressure device includes a nitrogen generator, a gas compression pump, and a gas supply pipeline. The gas supply pipeline includes a main gas supply pipeline and multiple branch gas supply pipelines. The nitrogen generator is connected to the gas compression pump, the gas compression pump is connected to the main gas supply pipeline, and the main gas supply pipeline is connected to the branch gas supply pipelines. The outlet of each branch gas supply pipeline is located on the side wall at the end of the feed stroke of the cavity.

3. The gas backpressure microporous foaming injection compression molding process according to claim 2, characterized in that... At least one of the multiple gas supply branch pipes has its outlet located at the center of the moving mold on one side of the cavity. This pushes the moving mold to squeeze the injection melt inside the cavity. The injection melt diffuses to the periphery of the cavity, and the back pressure gas from the periphery is sequentially forced into the cavity through the gas supply branch pipe outlet located on the side wall of the feeding stroke end of the cavity, the gas supply branch pipe, and the gas supply branch pipe outlet located at the center of the moving mold on one side of the cavity. The gas forced into the cavity forms a foaming depression in the center of the injection melt.

4. The gas backpressure microporous foaming injection compression molding process according to claim 2, characterized in that... The gas back pressure device also includes a pressure regulating device, which includes a booster valve, a stabilizing valve, a pressure relief valve, and a pressure regulating control unit. The booster valve is used to increase the pressure of the back pressure gas, the stabilizing valve is used to maintain the pressure of the back pressure gas, and the pressure relief valve is used to decrease the pressure of the back pressure gas. The pressure regulating control unit controls the booster valve, the stabilizing valve, and the pressure relief valve to complete the boosting, stabilizing, and depressurizing operations based on the signal sent by the pressure sensor installed in the injection mold.

5. The gas-backpressure microporous foaming injection compression molding process according to claim 1, characterized in that... The moving mold is provided with a sealing bushing at the mold closing end, and a number of elastic high-temperature resistant sealing rings are provided between the sealing bushing and the stationary mold after the mold is closed.

6. The gas backpressure microporous foaming injection compression molding process according to claim 1, characterized in that... The backpressure gas is nitrogen and / or carbon dioxide.

7. The gas backpressure microporous foaming injection compression molding process according to claim 1, characterized in that... The foaming gas is nitrogen.

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