阅读说明：本技术 一种轻量化聚合物微孔发泡注塑成型工艺、装置及应用 (Lightweight polymer microcellular foaming injection molding process, device and application ) 是由 董桂伟 赵国群 王桂龙 王召志 于 2021-03-17 设计创作，主要内容包括：本发明涉及聚合物轻量化材料成型技术领域,具体为一种轻量化聚合物微孔发泡注塑成型工艺、装置及应用,包括：合模与型腔反压气体填充、反压填充与保持、反压卸除与开模发泡；所述合模与型腔反压气体填充过程,模具合模后,首先向模具型腔中注入一定量的反压气体,当反压气体压力达到设定值时,停止气体注入,并向注塑机发出允许注射的信号；所述反压卸除与开模发泡过程中,反压作用时间到达后,开启卸压气路,卸除反压的同时沿合模方向打开一定距离的型腔,该工艺能够显著提升微孔发泡注塑制品的泡孔结构、表面质量和轻量化程度。(The invention relates to the technical field of polymer lightweight material forming, in particular to a lightweight polymer microcellular foaming injection molding process, a device and application, wherein the process comprises the following steps: closing the mold, filling the cavity with back pressure gas, filling and maintaining the back pressure, releasing the back pressure, opening the mold and foaming; in the process of die assembly and cavity back-pressure gas filling, after the die is assembled, a certain amount of back-pressure gas is injected into the cavity of the die, when the pressure of the back-pressure gas reaches a set value, the gas injection is stopped, and a signal for allowing injection is sent to an injection molding machine; in the processes of back pressure relief and mold opening foaming, after the back pressure action time is up, the pressure relief gas circuit is opened, and the cavity with a certain distance is opened along the mold closing direction while the back pressure is relieved.)

1. A lightweight polymer microcellular foaming injection molding process is characterized by comprising the following steps: closing the mold, filling the cavity with back pressure gas, filling and maintaining the back pressure, releasing the back pressure, opening the mold and foaming; in the process of die assembly and cavity back-pressure gas filling, after the die is assembled, a certain amount of back-pressure gas is injected into the cavity of the die, when the pressure of the back-pressure gas reaches a set value, the gas injection is stopped, and a signal for allowing injection is sent to an injection molding machine; in the processes of back pressure relief and mold opening foaming, after the back pressure action time is up, the pressure relief gas circuit is opened, and a cavity with a certain distance is opened along the mold closing direction while the back pressure is relieved.

2. The process of claim 1, wherein the process further comprises plasticizing and forming a homogeneous solution of polymer/supercritical fluid: injecting a certain amount of supercritical fluid into the plasticized and melted polymer melt at a certain position of the cylinder, and mixing the polymer melt and the supercritical fluid under the shearing and mixing action of the screw to form a uniform polymer/supercritical fluid homogeneous solution.

3. A lightweight polymer microcellular foaming injection molding process as claimed in claim 1, wherein in the mold closing and cavity back pressure gas filling steps, the cavity back pressure is in the range of 5 to 30MPa, preferably 10 to 20 MPa.

4. The process of claim 1, wherein the back pressure filling and maintaining process comprises: after the injection molding machine receives an injection permission signal, opening the self-locking nozzle, and injecting a polymer/supercritical fluid homogeneous solution into a closed mold cavity; and in the filling process, keeping the back pressure of the cavity at a set value until the set back pressure action time is reached.

5. A light-weight polymer microcellular foam injection molding process according to claim 1, wherein in the counter-pressure filling and maintaining step, the maintaining manner of the cavity counter-pressure in the filling process is a relief valve maintaining manner, the relief pressure of the valve is set to the cavity counter-pressure set value in the mold closing and cavity counter-pressure gas filling steps, so as to relieve the increase of the gas pressure caused by the melt filling compression in real time and maintain the stability of the counter-pressure.

6. The microcellular foam injection molding process for light weight polymers according to claim 1, wherein in the step of counter-pressure filling and maintaining, the counter-pressure acting time ranges from the melt filling time +0 to 5s, preferably from the melt filling time +1 to 3s, so as to ensure uniform and stable pressure distribution after the melt filling is finished;

further, in the steps of back pressure relief and mold opening foaming, the opening distance of the mold cavity for mold opening foaming is 0.5-3 times, preferably 1-2 times of the thickness of the product, so as to ensure that the foaming is fully performed after the melt filling is finished.

7. The microcellular foam injection molding process for a lightweight polymer as claimed in claim 1, further comprising mold cooling and mold opening and taking: and (5) finishing melt foaming, cooling the mold until the product is shaped, and opening the mold to take the product, thereby obtaining the product.

8. A lightweight polymer micropore foaming injection molding device is characterized in that a cavity back pressure control system of the device is connected with a micropore foaming injection mold through a valve pipeline and is connected with a control system of a micropore foaming injection molding machine through an electronic circuit; the supercritical fluid metering control system is connected with a supercritical fluid gas source and a supercritical fluid injector through a high-pressure gas pipeline and is connected with a control system of the microcellular foaming injection molding machine through an electronic circuit; the mold temperature controller is connected with the heating and cooling pipeline of the microcellular foaming injection mold through a pipeline.

9. The light weight polymer microcellular foaming injection molding device according to claim 8, wherein the heating and cooling medium of the mold temperature controller is circulating water, and the mold temperature is controlled within a range of 30 to 100 ℃; further, the microcellular foaming injection molding machine is an electric injection molding machine with a mold opening function after injection; further, the supercritical fluid gas source is nitrogen or carbon dioxide, and the cavity back pressure gas is preferably nitrogen.

10. Use of the process of any one of claims 1 to 7 and/or a light weight polymeric microcellular foam injection molding apparatus of claim 8 or 9 in the preparation of airplanes, automobile parts, sound and heat insulating devices, tissue engineering scaffolds and electromagnetic shielding materials.

Technical Field

The invention relates to the technical field of polymer lightweight material forming, in particular to a lightweight polymer microcellular foaming injection molding process, a device and application.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The development and construction of environment-friendly lightweight polymer products and the reduction of polymer material consumption have important significance for relieving global energy crisis and environmental problems. Polymer foaming is the most direct means for lightening polymer and is an effective way to realize the reduction of the use of polymer materials and the reduction of application cost. In recent years, the microcellular foam injection molding technology is considered to be a method for molding and processing polymer lightweight materials with the most development potential and application prospect due to the advantages of high efficiency, energy saving, no pollution, capability of molding polymer foam products with complex structures at one time and the like, and has received extensive research and attention.

However, since microcellular foaming injection molding is a comprehensive technology integrating microcellular foaming and injection molding of polymers, the process is very complicated, and the foaming of microcellular foaming injection molding melt includes two stages of dynamic foaming during filling and static foaming after filling is finished: the former is influenced by melt filling flowing behavior, and is easy to generate the problems of irregular shape, uneven distribution, surface bubble marks and the like of cells; the latter can form regular and uniform cells, but is limited by the mold cavity and melt pressure, temperature, etc., the foaming space at this stage is small, and the foaming capacity cannot be released. The inherent foaming defects of the microcellular foaming injection molding melt cause the difficulty in forming lightweight polymer microcellular foaming injection molding products with homogeneous inner cells, high surface glossiness and large foaming ratio, and become bottlenecks which restrict the further development of the technology.

In order to solve the problems, researchers at home and abroad carry out active research, and successively provide technologies for auxiliary microcellular foam injection molding, such as segmented injection, cavity back pressure, variable mold temperature, internal gas assistance, accurate mold opening and the like, so that certain effects are achieved in the aspects of improving the surface quality of products, optimizing the cell structure and the like. However, in a comprehensive view, most of the auxiliary technologies are developed aiming at a specific problem of foaming in the filling process of the microcellular foaming injection molding melt or foaming after the filling is finished, and the comprehensive influence of the auxiliary technologies on the whole process of the melt in a two-stage foaming process is not comprehensively examined or solved, so that the bottleneck of the lightweight polymer microcellular foaming injection molding technology with homogeneous inside and high surface gloss is not developed in a breakthrough manner, and the technology is still in a wide exploration stage.

The prior patent discloses a method for improving the surface quality of a foamed plastic part, which utilizes high-pressure gas to be introduced into a closed mold cavity to inhibit the growth and the breakage of bubbles near the surface of the plastic part. However, the inventors believe that: the reverse gas pressure retards the filling of the melt to a certain extent, prolongs the cooling of the melt, has a further adverse effect on the foaming process after the filling of the melt has ended, and no corresponding solution is given in this method.

The prior patent discloses a microcellular foaming injection molding process and a mold with high surface gloss and high bubble density, which avoid dynamic foaming of a melt and promote static foaming of the melt by a series of process operations such as raising the temperature of the mold, introducing high-pressure gas, reserving a foaming space, opening a gas channel, transferring the reserving space, discharging gas in the reserving space, foaming and filling the residual cavity and the like. However, the inventors believe that: obviously, the method needs a plurality of working procedures and has low efficiency, high matching precision requirement among the working procedures and large overall control difficulty.

The prior patent discloses a microcellular foaming and in-mold decoration composite molding method using a physical and chemical mixed foaming agent, which improves the surface quality of products, increases the nucleation efficiency of foam cells and improves the distribution of the foam cells. However, the inventors believe that: the nucleation mechanisms of the physical foaming agent and the chemical foaming agent are different, the method does not distinguish the nucleation mechanisms, and meanwhile, the method for in-mold decoration covers bubble marks on the surface of the product instead of essentially eliminating the bubble marks, so that the method is not suitable for the working condition that the original surface of the product is required to be reserved.

The existing patent discloses a device and a method for controlling the pressure and the temperature of a mold cavity, which utilizes an external gas connecting system, a valve pipeline system, a heat exchange system for controlling the gas temperature of the mold cavity, a high-efficiency self-circulation device for controlling the circulation of heated high-temperature gas and the like to intelligently adjust the air pressure in the mold cavity, the surface temperature of the mold cavity and the surface temperature of resin entering the mold cavity, so as to prepare a foaming product with high surface quality. However, the inventors believe that: the method does not solve the problems that the foaming space is small and the foaming capacity cannot be released after the melt filling is finished, and has defects in the aspect of improving the foaming ratio of the product.

Disclosure of Invention

In order to solve the above problems existing in the prior art, the disclosure provides a lightweight polymer microcellular foaming injection molding process, a device and an application, a novel composite technology of microcellular foaming injection molding is cooperatively applied by cavity back pressure and an opening and closing mold, foaming in a melt filling process is effectively inhibited by utilizing the cavity back pressure, a sufficient foaming space is given to a melt after filling is finished by utilizing the opening and closing mold, foaming capacity of the melt is fully released, and a cellular structure, surface quality and lightweight degree of a microcellular foaming injection molding product are remarkably improved.

Specifically, the technical scheme of the present disclosure is as follows:

in a first aspect of the present disclosure, there is provided a lightweight polymer microcellular foaming injection molding process, comprising: closing the mold, filling the cavity with back pressure gas, filling and maintaining the back pressure, releasing the back pressure, opening the mold and foaming; in the process of die assembly and cavity back-pressure gas filling, after the die is assembled, a certain amount of back-pressure gas is injected into the cavity of the die, when the pressure of the back-pressure gas reaches a set value, the gas injection is stopped, and a signal for allowing injection is sent to an injection molding machine; in the processes of back pressure relief and mold opening foaming, after the back pressure action time is up, the pressure relief gas circuit is opened, and a cavity with a certain distance is opened along the mold closing direction while the back pressure is relieved.

In a second aspect of the disclosure, a lightweight polymer microcellular foaming injection molding device is provided, wherein a cavity back pressure control system of the device is connected with a microcellular foaming injection mold through a valve pipeline and is connected with a control system of a microcellular foaming injection molding machine through an electronic circuit; the supercritical fluid metering control system is connected with a supercritical fluid gas source and a supercritical fluid injector through a high-pressure gas pipeline and is connected with a control system of the microcellular foaming injection molding machine through an electronic circuit; the mold temperature controller is connected with the heating and cooling pipeline of the microcellular foaming injection mold through a pipeline.

In a third aspect of the present disclosure, there is provided a use of a lightweight polymer microcellular foam injection molding process and/or apparatus in the preparation of airplanes, automobile parts, sound and heat insulating devices, tissue engineering scaffolds and electromagnetic shielding materials.

One or more technical schemes in the disclosure have the following beneficial effects:

(1) according to the method, the cavity back pressure and the open-close die are cooperatively applied to the microcellular foaming injection molding process, the cavity back pressure is utilized to inhibit foaming in the filling process of the melt, the open-close die is utilized to endow the melt with sufficient foaming space and release the foaming capacity after filling is finished, and injection molding of a lightweight polymer microcellular foaming product with large foaming multiplying power, regular and uniform inner cells and high surface gloss is realized.

(2) The process designed by the disclosure can effectively and comprehensively regulate and control the specific 'two-stage' foaming process of the microcellular foaming injection molding melt, and can enhance the good effect of static foaming after the filling of the melt while effectively eliminating the adverse effect of dynamic foaming in the melt filling process.

(3) Compared with the conventional microcellular foam injection molding product, the microcellular foam injection molding product formed by the method has the advantages of large foaming ratio, high lightweight degree, good surface quality, no bubble mark, regular shape of internal bubbles and uniform distribution.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

Embodiments of the present disclosure are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic view of the apparatus for microcellular foam injection molding of polymer with homogeneous interior and high surface gloss described in example 1;

wherein, 1 represents a cavity back pressure control system, 2 represents a microcellular foaming injection mold, 3 represents a self-locking nozzle, 4 represents a supercritical fluid injector, 5 represents a pressure release valve, 6 represents a mold temperature machine, 7 represents a supercritical fluid metering control system, 8 represents a supercritical fluid gas source, and 9 represents a microcellular foaming injection molding machine.

FIG. 2 is a flow chart of the internal homogeneous high-gloss polymer microcellular foam injection molding process of example 2;

wherein, I represents the formation of homogeneous solution of plasticizing and polymer/supercritical fluid, II represents the closing and cavity back pressure gas filling, III represents the back pressure filling and maintaining, IV represents the back pressure discharging and opening foaming, and V represents the cooling and opening of the mold to take out the part.

FIG. 3 is a graph showing a comparison of foaming conditions of microcellular foamed injection molding material products prepared in the schemes 2 and 3 of example 2 and a comparative example.

Wherein i represents a conventional microcellular foamed injection molding material product prepared in comparative example, ii represents a microcellular foamed injection molding material product prepared in scheme 2 of example 2, and iii represents a microcellular foamed injection molding material product prepared in scheme 3 of example 2.

FIG. 4 shows the internal cell structure of the microcellular foamed injection-molded product having homogeneous interior and high gloss surface prepared in the embodiment 3 of example 2.

FIG. 5 shows the surface morphology of the microcellular foam injection-molded product with homogeneous interior and high gloss surface prepared in the embodiment 3 of the example 2.

FIG. 6 shows the internal cell structure and surface morphology of a conventional microcellular foamed injection-molded product prepared in a comparative example.

Detailed Description

The disclosure is further illustrated with reference to specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

The reagents or starting materials used in the present invention can be purchased from conventional sources, and unless otherwise specified, the reagents or starting materials used in the present invention can be used in a conventional manner in the art or in accordance with the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only. It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.

At present, the existing method does not solve the problems that the foaming space is small and the foaming capacity can not be released after the melt filling is finished, and has defects in the aspect of improving the foaming ratio of the product. In order to solve the problems, the present disclosure provides a lightweight polymer microcellular foaming injection molding process, device and application.

In one embodiment of the present disclosure, there is provided a lightweight polymer microcellular foam injection molding process, including: closing the mold, filling the cavity with back pressure gas, filling and maintaining the back pressure, releasing the back pressure, opening the mold and foaming; in the process of die assembly and cavity back-pressure gas filling, after the die is assembled, a certain amount of back-pressure gas is injected into the cavity of the die, when the pressure of the back-pressure gas reaches a set value, the gas injection is stopped, and a signal for allowing injection is sent to an injection molding machine; in the processes of back pressure relief and mold opening foaming, after the back pressure action time is up, the pressure relief gas circuit is opened, and a cavity with a certain distance is opened along the mold closing direction while the back pressure is relieved.

The key of realizing injection molding of lightweight polymer microcellular foamed products with homogeneous inner cells, high surface gloss and large foaming multiplying power is considered in the disclosure, and the novel microcellular foaming injection molding technology capable of effectively and comprehensively regulating and controlling the two-stage foaming process of microcellular foaming injection molding melt is researched and developed. To this, this disclosure provides a with die cavity back pressure and open and shut mould novel composite technology of being applied to micropore foaming in coordination and moulding plastics, utilizes the die cavity back pressure effectively to restrain the foaming of fuse-element filling in-process, utilizes the open and shut mould to give the abundant foaming space of fuse-element after the filling, fully releases its foaming ability, is showing the cell structure, surface quality and the lightweight degree that promote micropore foaming injection moulding product.

Wherein, under the action of the gas back pressure of the cavity, the foaming in the filling process of the melt is effectively inhibited, and the cavity is filled with the unfoamed homogeneous solution. Quickly relieving back pressure, opening a cavity with a certain distance along the mold closing direction, providing sufficient foaming space for the melt, fully releasing the foaming capacity of the melt, and foaming the melt after filling;

in one embodiment of the present disclosure, a process for microcellular foam injection molding of a lightweight polymer further comprises plasticizing and forming a homogeneous solution of polymer/supercritical fluid: injecting a certain amount of supercritical fluid into the plasticized and melted polymer melt at a certain position of the cylinder, and mixing the polymer melt and the supercritical fluid under the shearing and mixing action of the screw to form a uniform polymer/supercritical fluid homogeneous solution.

According to a further technical scheme, in the steps of die assembly and cavity back-pressure gas filling, the cavity back-pressure range is 5-30 MPa, preferably 10-20 MPa, so that effective inhibition of foaming in the melt filling process is guaranteed.

As a further technical solution, the process of back pressure filling and maintaining comprises: after the injection molding machine receives an injection permission signal, opening the self-locking nozzle, and injecting a polymer/supercritical fluid homogeneous solution into a closed mold cavity; and in the filling process, keeping the back pressure of the cavity at a set value until the set back pressure action time is reached.

As a further technical scheme, in the step of back pressure filling and maintaining, the mode of maintaining the cavity back pressure in the filling process is that a pressure relief valve is used for maintaining, the pressure relief pressure of the valve is set to be the cavity back pressure set value in the step of die assembly and cavity back pressure gas filling, so that the gas pressure rise caused by melt filling compression is relieved in real time, and the stability of the back pressure is maintained.

According to a further technical scheme, in the step of back pressure filling and maintaining, the range of the back pressure action time is melt filling time + 0-5 s, preferably melt filling time + 1-3 s, so that the uniformity and stability of pressure distribution after melt filling is finished are ensured.

As a further technical scheme, in the steps of back pressure relief and mold opening foaming, the opening distance of a cavity for mold opening foaming is 0.5-3 times, preferably 1-2 times, of the thickness of a product, so as to ensure that foaming is fully performed after melt filling is finished.

As a further technical scheme, the lightweight polymer microcellular foaming injection molding process further comprises the following steps of cooling a mold and opening the mold to take a part: and (5) finishing melt foaming, cooling the mold until the product is shaped, and opening the mold to take the product, thereby obtaining the product.

One of the characteristics of the disclosed technology is as follows: in the processes of die assembly, cavity back pressure gas filling, back pressure filling and maintaining, the cavity back pressure is equivalent to the saturation pressure of a supercritical fluid in a polymer, and the back pressure action time is the whole filling process of a melt or is properly prolonged, so that the foaming in the filling process is comprehensively inhibited, and the defects of inner and surface cells generated by the coupling of foaming and flowing in the filling process are thoroughly eliminated.

The second characteristic of the disclosed technology is: in the processes of back pressure relief and die opening foaming, when the die opening foaming is carried out on the die cavity, the internal gas content of the melt along the length direction is uniformly distributed, a good temperature gradient is formed along the thickness direction, and the die opening endows the melt with a foaming space after the filling is completed, so that the formation of uniform and good cell structures is fully ensured.

In one embodiment of the present disclosure, a lightweight polymer microcellular foaming injection molding device is provided, wherein a cavity back pressure control system of the device is connected with a microcellular foaming injection mold through a valve pipeline and is connected with a control system of a microcellular foaming injection molding machine through an electronic circuit; the supercritical fluid metering control system is connected with a supercritical fluid gas source and a supercritical fluid injector through a high-pressure gas pipeline and is connected with a control system of the microcellular foaming injection molding machine through an electronic circuit; the mold temperature controller is connected with the heating and cooling pipeline of the microcellular foaming injection mold through a pipeline.

As a further technical scheme, the heating and cooling medium of the mold temperature controller is circulating water, and the temperature control range of the mold is 30-100 ℃.

As a further technical scheme, the micropore foaming injection molding machine is an electric injection molding machine with a mold opening function after injection.

As a further technical solution, the supercritical fluid gas source is nitrogen or carbon dioxide, and the cavity back pressure gas is preferably nitrogen.

In one embodiment of the present disclosure, there is provided a use of a lightweight polymer microcellular foam injection molding process and/or apparatus in the preparation of airplanes, automobile parts, sound and heat insulating devices, tissue engineering scaffolds, and electromagnetic shielding materials.

In order to make the technical solutions of the present disclosure more clearly understood by those skilled in the art, the technical solutions of the present disclosure will be described in detail below with reference to specific embodiments.

Example 1

A lightweight polymer microcellular foaming injection molding apparatus, referring to fig. 1, comprising: the device comprises a cavity back pressure control system 1, a microcellular foaming injection mold 2, a self-locking nozzle 3, a supercritical fluid injector 4, a pressure release valve 5, a mold temperature controller 6, a supercritical fluid metering control system 7, a supercritical fluid gas source 8 and a microcellular foaming injection molding machine 9. The cavity back pressure control system 1 is connected with the microcellular foaming injection mold 2 through a valve pipeline and is connected with a control system of a microcellular foaming injection molding machine 9 through an electronic circuit; the supercritical fluid metering control system 7 is connected with a supercritical fluid gas source 8 and a supercritical fluid injector 4 through a high-pressure gas pipeline and is connected with a control system of a microcellular foaming injection molding machine 9 through an electronic circuit; the mold temperature controller 6 is connected with the heating and cooling pipeline of the microcellular foaming injection mold 2 through a pipeline.

Example 2

A lightweight polymer microcellular foam injection molding process is disclosed, referring to FIG. 2, and the process comprises the following steps: plasticizing and forming a polymer/supercritical fluid homogeneous phase solution I, closing a mold, filling a cavity back pressure gas II, filling and maintaining a back pressure III, releasing the mold in a back pressure manner, opening the mold to foam IV, cooling the mold, opening the mold and taking a workpiece V. In the mold closing and cavity back pressure gas filling II, the cavity back pressure range is 5-30 MPa, and preferably 10-20 MPa; in the back pressure filling and maintaining step III, the cavity back pressure is maintained in a manner of maintaining by a pressure relief valve, and the pressure relief pressure of the valve is set to be a cavity back pressure set value in a preferable mold closing and cavity back pressure gas filling step II; in the back pressure filling and maintaining step III, the range of the back pressure action time is the melt filling time plus 0-5 s, preferably the melt filling time plus 1-3 s; in the back pressure relief and mold opening foaming IV, the opening distance of a mold cavity for mold opening foaming is 0.5-3 times, preferably 1-2 times of the thickness of a product.

Example 3

The process method for preparing the lightweight polymer microcellular foam material with homogeneous interior and high surface gloss by using the device in the embodiment 2 comprises the following steps:

(1) plasticization and formation of a polymer/supercritical fluid homogeneous solution: when the microcellular foaming injection molding process is started, the microcellular foaming injection molding machine 9 carries out melting plasticization on polymer solid granules, in the plasticizing process, supercritical fluid is injected into molten polymer melt at a certain position of a charging barrel through the supercritical fluid metering control system 7 and the supercritical fluid injector 4, and the polymer melt and the supercritical fluid are mixed to form uniform polymer/supercritical fluid homogeneous phase solution under the shearing and mixing action of a screw;

(2) closing the mold and filling the cavity with back pressure gas: after the microcellular foaming injection mold 2 is closed, firstly injecting a certain amount of back pressure gas into the mold cavity through the cavity back pressure control system 1, stopping gas injection when the pressure of the back pressure gas reaches a set value, and sending an injection permission signal to the microcellular foaming injection molding machine 9;

(3) back pressure filling and maintaining: after receiving the injection permission signal, the micropore foaming injection molding machine 9 opens the self-locking nozzle 3, injects the polymer/supercritical fluid homogeneous solution into the closed mold cavity, effectively inhibits the foaming in the melt filling process under the action of the cavity gas back pressure, and keeps the unfoamed homogeneous solution state to fill the cavity; in the filling process, the back pressure of the cavity is kept to be a set value by the pressure relief valve 5 until the set back pressure action time is reached;

(4) back pressure relief and mold opening foaming: after the back pressure action time is up, opening a pressure relief gas path to quickly relieve the back pressure, and simultaneously opening a cavity with a certain distance along the mold closing direction of the microcellular foam injection mold 2 to provide sufficient foaming space for the melt and fully release the foaming capacity of the melt, so that the melt is foamed after being filled;

(5) cooling the mold and opening the mold to take out the part: and (5) finishing the foaming of the melt, cooling the mold by the mold temperature controller 6 until the product is shaped, and opening the mold to take the part, thereby obtaining the product.

This example illustrates the preparation of a polymeric microcellular foam material under 3 sets of parameters, wherein: the polymer raw material is polypropylene (PP), the weight of the product is 60g, and the original thickness is 3 mm; the supercritical nitrogen injection amount is 0.8 percent (weight percentage), the rotating speed of melting glue of a screw is 140rpm during plasticizing, and the back pressure of the melting glue is 18 MPa; the melt injection speed is 55mm/s, and the melt filling time under the injection molding parameter condition is 2 s; the mold temperature set value in the filling stage was 90 ℃, the mold circulating cooling water temperature in the cooling stage was 25 ℃, the cooling time was 30s, and the cavity back pressure and mold opening and closing process parameters were set as shown in table 1.

TABLE 1

Comparative example

While the embodiment 2 is carried out, a corresponding polymer microcellular foam injection molding material product is further prepared by utilizing a conventional microcellular foam injection molding process, and the method comprises the following steps:

(1) plasticization and formation of a polymer/supercritical fluid homogeneous solution: the microcellular foaming injection molding machine 9 carries out melting plasticization of polymer solid granules, in the plasticization process, supercritical fluid is injected into melted polymer melt at a certain position of a charging barrel through the supercritical fluid metering control system 7 and the supercritical fluid injector 4, and the polymer melt and the supercritical fluid are mixed to form uniform polymer/supercritical fluid homogeneous solution under the shearing and mixing action of a screw;

(2) mold closing and injection: after the microcellular foaming injection mold 2 is closed, the microcellular foaming injection molding machine 9 opens the self-locking nozzle 5 to inject the monomer solution into the mold cavity until the mold cavity is filled, and the injection is finished.

(3) Cooling and opening the mold to take out the parts: and cooling the mold by the mold temperature machine 6 until the product is shaped, and opening the mold to take the product.

The polymer raw material of the comparative example is polypropylene (PP), the weight of the product is 60g, the thickness is 3mm, the nitrogen injection amount of the supercritical fluid is 0.8%, the rotating speed of molten gel of a screw is 140rpm during plasticizing, and the back pressure of the molten gel is 18 MPa; the melt injection speed is 55mm/s, the melt filling time is 2s, the mold temperature setting value in the filling stage is 90 ℃, the mold circulating cooling water temperature in the cooling stage is 25 ℃, and the cooling time is 30 s.

The foaming conditions, the inner cells and the surface morphology of the polymer microcellular foamed materials obtained in the schemes 1 to 3 and the comparative example of example 3 were observed, and the results are shown in FIGS. 3 to 5 and FIG. 6. As can be seen from the figure: the microcellular foam injection molding material product prepared by the conventional microcellular foam injection molding process has small foaming multiplying power, obvious bubble marks exist on the surface, the size of inner cells is large, deformation is generated in the flow direction, and the cell distribution is not uniform; the product prepared by the microcellular foam injection molding process provided by the invention has the advantages of large foaming multiplying power, no bubble mark on the surface, high glossiness, small size of inner foam holes, regular shape and uniform distribution, and particularly, the microcellular foam injection molding product prepared by the scheme 3 (shown in figure 4) has more uniform and compact inner foam holes, the diameter of the inner foam holes is 10-50 microns, and the density reaches 2.1 multiplied by 10⁸Per cm³。

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.