Foaming method of engineering plastic and application thereof

Abstract

The application relates to a foaming method of engineering plastics and application thereof, and belongs to the technical field of foaming. The application provides a foaming method of engineering plastics. In the foaming method, hot air is blown into a mold cavity after a rapid pressure relief stage of a supercritical fluid mold foaming process, the temperature of a material surface is maintained, the temperature difference between the inside and outside of the material is eliminated, the material is kept in a foaming temperature window interval at all times, then the mold cavity is opened, and cell further grows uniformly, so that the problems of wrinkles, warping and cracking of engineering plastic foams are solved, and a shaping step after foaming is not needed.

Description

Technical Field

[0001] This invention relates to a foaming method for engineering plastics and its application, belonging to the field of foaming technology. Background Technology

[0002] Engineering plastics refer to plastic materials that can be used as structural materials to withstand mechanical stress and can be used in a wide temperature range and harsh chemical and physical environments. Compared with conventional foams such as pearl cotton, engineering plastic foam has superior comprehensive properties such as mechanical properties and heat resistance. Therefore, engineering plastic foam is widely used as a structural core material, such as the inner core of wind turbine blades.

[0003] However, currently industrialized engineering plastic foaming technologies mainly include extrusion foaming and autoclaving foaming. Extrusion foaming involves thoroughly mixing the engineering plastic melt with a foaming agent using a twin-screw extruder, then releasing pressure at the die to obtain engineering plastic foam. However, extrusion foaming uses cyclopentane as the foaming agent, posing an explosion hazard during production. Furthermore, the foaming ratio of extruded engineering plastic foam is relatively low (generally not exceeding 20), while the open-cell ratio is relatively high (generally not less than 30%), resulting in poor weight reduction and mechanical properties. Autoclaving foaming, on the other hand, produces engineering plastic foam beads through intermittent water suspension foaming. However, autoclaving foam beads require very high steam pressure (generally above 1.5 MPa) to reach their melting point during later molding, leading to extremely high production costs. Therefore, there is an urgent need to find an engineering plastic foaming technology with low safety risks, high foaming ratio, low open-cell ratio, and low production costs.

[0004] Supercritical fluid compression molding foaming technology is a foaming technology that uses carbon dioxide and nitrogen as foaming agents. It is characterized by being green and environmentally friendly, and the process is non-toxic and harmless. Furthermore, by implementing cell nucleation and growth in separate steps, it significantly reduces the size of high-pressure equipment, lowers the amount of foaming agent used, and reduces the cost of high-pressure equipment. Using supercritical fluid compression molding foaming technology to foam engineering plastics can effectively solve the problems associated with extrusion foaming and autoclaving foaming, offering advantages such as low safety risks, high foaming ratio, low open cell ratio, and low production cost.

[0005] However, in actual production, it has been found that when using supercritical fluid compression molding technology to prepare engineering plastic foam, the high rigidity and high glass transition temperature of engineering plastics mean that the rapid temperature drop during depressurization causes a rapid decrease in surface temperature, leading to a rapid increase in the matrix strength of the material surface. This limits the further growth of cell structures on the material surface, ultimately resulting in wrinkling during the cell growth stage and foaming failure. Furthermore, the preparation of engineering plastic foam using supercritical fluid compression molding technology requires molding the foamed sheets after foaming to prevent warping. For semi-crystalline polymer engineering plastics, temperature drop leads to rapid crystallization; for amorphous polymer engineering plastics, a rapid drop in temperature below the glass transition temperature significantly increases brittleness. Therefore, cracking often occurs during the molding process of engineering plastic foam.

[0006] There is an urgent need to develop a supercritical fluid molding foaming technology that can effectively prevent wrinkles, warping, and cracking of engineering plastics during the supercritical fluid molding foaming process. Summary of the Invention

[0007] To address the aforementioned deficiencies, this invention provides a foaming method for engineering plastics, the foaming method comprising the following steps:

[0008] Dissolution Step: After placing the foamed preform made of engineering plastic into a foaming mold with a cavity temperature of foaming temperature T1, close the cavity and introduce gaseous foaming agent into the cavity until the pressure inside the cavity reaches the foaming pressure P; continue to place the foamed preform in the cavity with a pressure of foaming pressure P and a temperature of foaming temperature T1 until the gaseous foaming agent reaches dissolution equilibrium in the foamed preform;

[0009] Depressurization steps: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate Q; after releasing the pressure to ambient pressure, the mold cavity is kept closed, and hot air at a purging temperature T2 is introduced into the mold cavity for purging; after purging, the mold cavity is opened to allow the foam cells in the foam preform to grow, thus obtaining engineering plastic foam.

[0010] In one embodiment of the present invention, the engineering plastic is a semi-crystalline polymer or an amorphous polymer.

[0011] In one embodiment of the present invention, when the engineering plastic is a semi-crystalline polymer, the foaming temperature T1 = (T m -40)℃~T m ℃; where T m This is the melting temperature of the semi-crystalline polymer.

[0012] In one embodiment of the present invention, when the engineering plastic is an amorphous polymer, the foaming temperature T1 = Tg ℃~(T g +40)℃; where T g This is the glass transition temperature of amorphous polymers.

[0013] In one embodiment of the present invention, when the engineering plastic is a semi-crystalline polymer, the purging temperature T2 = (T m -20)℃~T m ℃; where T m This is the melting temperature of the semi-crystalline polymer.

[0014] In one embodiment of the present invention, when the engineering plastic is an amorphous polymer, the purging temperature T2 = T g ℃~(T g +20)℃; where T is... g This is the glass transition temperature of amorphous polymers.

[0015] In one embodiment of the present invention, the semi-crystalline polymer is one or more of polyethylene terephthalate (PET), polyoxymethylene (POM), polyamide (PA), and liquid crystal polyester (LCP); the amorphous polymer is one or more of polyphenylene ether (PPO) and polycarbonate (PC).

[0016] In one embodiment of the present invention, the purging time is not less than 5 minutes.

[0017] In one embodiment of the present invention, the foaming pressure P = 10-30 MPa.

[0018] In one embodiment of the present invention, the foaming pressure P = 15-25 MPa.

[0019] In one embodiment of the present invention, the depressurization rate Q = 10 to 1000 MPa / s.

[0020] In one embodiment of the present invention, the depressurization rate Q = 100-500 MPa / s.

[0021] In one embodiment of the invention, the gaseous foaming agent comprises carbon dioxide and / or nitrogen.

[0022] In one embodiment of the present invention, the physical foaming agent is carbon dioxide.

[0023] Prior to the dissolution step, the foaming method further includes a molding step; the molding step is: molding the engineering plastic to obtain an engineering plastic foam preform.

[0024] In one embodiment of the present invention, the foamed embryo is plate-shaped, sheet-shaped, columnar, spherical, rolled, or irregular in shape.

[0025] In one embodiment of the present invention, the foamed embryo is plate-shaped.

[0026] In one embodiment of the present invention, the molding is hot pressing, extrusion molding or injection molding.

[0027] The present invention also provides an engineering plastic foam, which is obtained by foaming by the above-described foaming method.

[0028] The present invention also provides an engineering plastic foam, wherein the engineering plastic foam is a foamed board, a foamed sheet, a foamed column, a foamed sphere, a foamed roll, or an irregular foam.

[0029] The present invention also provides the application of the above-described foaming method in the preparation of engineering plastic foam.

[0030] The technical solution of this invention has the following advantages:

[0031] This invention provides a foaming method for engineering plastics. The foaming method comprises: placing a foamed preform of engineering plastic in a foaming mold at a cavity temperature of foaming temperature T1; closing the cavity; introducing a gaseous foaming agent into the cavity until the pressure inside the cavity reaches the foaming pressure P; continuously placing the foamed preform in the cavity at the foaming pressure P and the temperature of foaming temperature T1 until the gaseous foaming agent reaches dissolution equilibrium in the foamed preform; after reaching dissolution equilibrium, releasing the pressure inside the cavity to ambient pressure at a depressurization rate Q; maintaining the closed state of the cavity while introducing hot air at a purging temperature T2 into the cavity for purging; after purging, opening the cavity to allow the cells in the foamed preform to grow, resulting in a smooth engineering plastic foam. The foaming method of the present invention, after the rapid depressurization stage of the supercritical fluid molding foaming process, first introduces hot air into the mold cavity to purge and maintain the temperature of the material surface, eliminate the temperature difference between the inside and outside of the material, and keep it within the deformable temperature window range. Then, the mold cavity is opened to allow the foam cells to grow more uniformly, thereby solving the problems of wrinkles, warping and cracking of engineering plastic foam, and eliminating the need for a shaping step after foaming.

[0032] Furthermore, the engineering plastic is a semi-crystalline polymer or an amorphous polymer; when the engineering plastic is a semi-crystalline polymer, the foaming temperature T1 = (T m -40)℃~T m ℃; where T m The melting temperature of the semi-crystalline polymer is T1; when the engineering plastic is an amorphous polymer, the foaming temperature T1 = T g ℃~(T g +40)℃; where T gThis is the glass transition temperature of the amorphous polymer. When the foaming temperature is below this range, a large amount of crystals still exist in the polymer, resulting in excessively high polymer matrix strength, which restricts cell growth and makes foaming difficult. When the foaming temperature is above this range, the polymer crystals have completely melted, resulting in insufficient polymer matrix strength to support the cells, leading to foaming failure. This foaming temperature range effectively ensures the smooth growth of cells.

[0033] Furthermore, when the engineering plastic is a semi-crystalline polymer, the purging temperature T2 = (T m -20)℃~T m ℃; where T m The purging temperature T2 is the melting temperature of the semi-crystalline polymer; when the engineering plastic is an amorphous polymer, the purging temperature T2 = T g ℃~(T g +20)℃; where T is... g This refers to the glass transition temperature of the amorphous polymer. When the purge temperature is below this range, the surface temperature of the sheet is low, the material strength is high, and the growth of cells is severely restricted after the mold cavity is opened, resulting in severe wrinkling and warping of the sheet. When the purge temperature is above this range, the surface temperature of the sheet is too high, the surface melts, and foaming fails. This purge temperature range effectively ensures the smooth progress of the foaming process.

[0034] Furthermore, the purging time is no less than 5 minutes. If the purging time is too short, the surface temperature of the board will not rise to the foaming temperature range, and wrinkles and warping will still occur. This purging time can effectively ensure that the engineering plastic foam does not wrinkle or warp. Attached Figure Description

[0035] Figure 1 Example 1: A schematic diagram illustrating the principle of the foaming method.

[0036] Figure 2 Photograph of the foamed board prepared in Example 1.

[0037] Figure 3 Photograph of the foamed board prepared in Comparative Example 1.

[0038] Figure 4 Photograph of the foamed board prepared in Comparative Example 2. Detailed Implementation

[0039] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0040] For any experimental steps or conditions not specified in the following examples, the procedures or conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] Example 1: A foaming method for engineering plastics

[0042] This embodiment provides a foaming method for engineering plastics, the steps of which are as follows:

[0043] Molding steps: Use a twin-screw extruder to process polyphenylene ether granules (T... g =160℃, PPO / PS blended particles (purchased from Guangdong Xingshengdi Technology Co., Ltd.) were extruded into foamed boards of 600×1200×7mm;

[0044] Dissolution step: Place the board to be foamed into a foaming mold (900×1800×10.5mm) with a cavity temperature of 180℃ (foaming temperature T1), close the cavity, and introduce carbon dioxide into the cavity through the air channel on the foaming mold until the pressure inside the cavity reaches 15MPa (foaming pressure P); keep the board to be foamed in the cavity with a pressure of 15MPa and a temperature of 180℃ until the carbon dioxide reaches dissolution equilibrium in the board to be foamed (time takes 3.5h);

[0045] Depressurization step: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate of 100MPa / s (depressurization rate Q); after depressurization to ambient pressure, the mold cavity is kept closed, and hot air at a temperature of 170℃ (purge temperature T2) is introduced into the mold cavity for 5 minutes; after purging, the mold cavity is opened to allow the cells in the foamed board to grow, thus obtaining the foamed board.

[0046] Example 2: A foaming method for engineering plastics

[0047] This embodiment provides a foaming method for engineering plastics, the steps of which are as follows:

[0048] Molding steps: Polyethylene terephthalate granules (T...) are produced using a twin-screw extruder. m =252℃, purchased from Shanghai Petrochemical Co., Ltd.) Extruded into 600×1200×7mm foamable sheets;

[0049] Dissolution step: Place the board to be foamed into a foaming mold (900×1800×10.5mm) with a cavity temperature of 250℃ (foaming temperature T1), close the mold cavity, and introduce carbon dioxide into the mold cavity through the air channel on the foaming mold until the pressure inside the mold cavity reaches 20MPa (foaming pressure P); keep the board to be foamed in the mold cavity with a pressure of 20MPa and a temperature of 250℃ until the carbon dioxide reaches dissolution equilibrium in the board to be foamed (time takes 3.5h);

[0050] Depressurization step: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate of 100MPa / s (depressurization rate Q); after depressurization to ambient pressure, the mold cavity is kept closed, and hot air at a temperature of 245℃ (purge temperature T2) is introduced into the mold cavity for 5 minutes; after purging, the mold cavity is opened to allow the cells in the foamed board to grow, thus obtaining the foamed board.

[0051] Example 3: A foaming method for engineering plastics

[0052] This embodiment provides a foaming method for engineering plastics, the steps of which are as follows:

[0053] Molding steps: Use a twin-screw extruder to process polyphenylene ether granules (T... g =160℃, PPO / PS blended particles (purchased from Guangdong Xingshengdi Technology Co., Ltd.) were extruded into a 600×1200×7mm foaming board;

[0054] Dissolution step: Place the board to be foamed into a foaming mold (900×1800×10.5mm) with a cavity temperature of 165℃ (foaming temperature T1), close the cavity, and introduce carbon dioxide into the cavity through the air channel on the foaming mold until the pressure inside the cavity reaches 15MPa (foaming pressure P); keep the board to be foamed in the cavity with a pressure of 15MPa and a temperature of 180℃ until the carbon dioxide reaches dissolution equilibrium in the board to be foamed (time takes 3.5h);

[0055] Depressurization step: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate of 100MPa / s (depressurization rate Q); after depressurization to ambient pressure, the mold cavity is kept closed, and hot air at a temperature of 165℃ (purge temperature T2) is introduced into the mold cavity for 5 minutes; after purging, the mold cavity is opened to allow the cells in the foamed board to grow, thus obtaining the foamed board.

[0056] Example 4: A foaming method for engineering plastics

[0057] This embodiment provides a foaming method for engineering plastics, the steps of which are as follows:

[0058] Molding steps: Use a twin-screw extruder to process polyphenylene ether granules (T... g =160℃, PPO / PS blended particles (purchased from Guangdong Xingshengdi Technology Co., Ltd.) were extruded into a 600×1200×7mm foaming board;

[0059] Dissolution step: Place the board to be foamed into a foaming mold (900×1800×10.5mm) with a cavity temperature of 195℃ (foaming temperature T1), close the cavity, and introduce carbon dioxide into the cavity through the air channel on the foaming mold until the pressure inside the cavity reaches 15MPa (foaming pressure P); keep the board to be foamed in the cavity with a pressure of 15MPa and a temperature of 180℃ until the carbon dioxide reaches dissolution equilibrium in the board to be foamed (time takes 3.5h);

[0060] Depressurization step: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate of 100MPa / s (depressurization rate Q); after depressurization to ambient pressure, the mold cavity is kept closed, and hot air at a temperature of 175℃ (purge temperature T2) is introduced into the mold cavity for 5 minutes; after purging, the mold cavity is opened to allow the cells in the foamed board to grow, thus obtaining the foamed board.

[0061] Comparative Example 1: A foaming method for engineering plastics

[0062] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the depressurization step is modified as follows: after reaching dissolution equilibrium, the pressure in the mold cavity is depressurized to ambient pressure at a depressurization rate of 100 MPa / s (depressurization rate Q); after depressurization to ambient pressure, the mold cavity is opened to allow the cells in the foamed board to grow, thereby obtaining the foamed board.

[0063] Comparative Example 2: A foaming method for engineering plastics

[0064] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the foaming method adjusts the hot air blowing time from 5 minutes to 3 minutes to obtain foamed boards.

[0065] Comparative Example 3: A foaming method for engineering plastics

[0066] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the foaming method adjusts the foaming temperature T1 from 180°C to 150°C to obtain foamed boards.

[0067] Comparative Example 4: A foaming method for engineering plastics

[0068] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the foaming temperature T1 is adjusted from 180°C to 210°C to obtain foamed boards.

[0069] Comparative Example 5: A foaming method for engineering plastics

[0070] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the foaming method adjusts the purging temperature T2 from 170°C to 150°C to obtain foamed boards.

[0071] Comparative Example 6: A foaming method for engineering plastics

[0072] This comparative example provides a foaming method for engineering plastics. Based on Example 1, the foaming method adjusts the purging temperature T2 from 170°C to 190°C to obtain foamed boards.

[0073] Experimental Example 1: Performance Testing of Foamed Boards

[0074] This experimental example provides a performance test for foamed boards. The experimental procedure is as follows:

[0075] The foamed boards prepared in Examples 1-2 and Comparative Examples 1-6 were observed and photographed by the naked eye. The observation and photographic results are shown in the figure. Figures 1-4 And Table 1. The foamed boards obtained in Comparative Example 2 were molded and shaped using a molding machine. The shaping results are shown in Table 1. Figure 3 The foaming ratio of the foamed boards prepared in Examples 1-5 and Comparative Examples 1-5 was tested by the drainage method (see reference: Wan, C., Lu, Y., Liu, T., Zhao, L., & Yuan, W. (2017). Foaming of low density polyethylene with carbon dioxide based on its in situcrystallization behavior characterized by high-pressure rheometer. Industrial & Engineering Chemistry Research, 56(38), 10702-10710.). The test results are shown in Table 1.

[0076] Depend on Figures 1-4As shown in Table 1, all embodiments were able to produce foamed boards with a large expansion ratio and a smooth surface. In Comparative Example 1, hot air purging was not used, resulting in severe wrinkling of the foamed board. In Comparative Example 2, the purging time was insufficient, and the material surface temperature did not reach the foamable temperature range, resulting in warping of the foamed board. Furthermore, after molding, the foamed board cracked. In Comparative Example 3, the foaming temperature was too low, making it difficult for cells to grow, resulting in a low expansion ratio of the foamed board. In Comparative Example 4, the foaming temperature was too high, making it difficult for cells to support themselves, resulting in numerous cracks and collapses, thus resulting in a low expansion ratio of the foamed board. In Comparative Example 5, the purging temperature was too low, and the material surface temperature did not reach the foamable temperature range, resulting in warping of the foamed board. In Comparative Example 6, the purging temperature was too high, causing the material surface to melt, thus reducing the expansion ratio of the foamed board.

[0077] Table 1. Foaming ratio and board condition of foamed boards

[0078] Foamed boards Foaming ratio Board material condition Example 1 15.2 smooth Example 2 31 smooth Example 3 10.2 smooth Example 4 19.91 smooth Comparative Example 1 9.6 folds Comparative Example 2 12.1 Curvy Comparative Example 3 4.2 smooth Comparative Example 4 4.5 smooth Comparative Example 5 13.4 Curvy Comparative Example 6 6.3 smooth

[0079] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for foaming engineering plastics, characterized in that, The foaming method includes the following steps: Dissolution Step: After placing the foamed preform made of engineering plastic into a foaming mold with a cavity temperature of foaming temperature T1, close the cavity and introduce gaseous foaming agent into the cavity until the pressure inside the cavity reaches the foaming pressure P; continue to place the foamed preform in the cavity with a pressure of foaming pressure P and a temperature of foaming temperature T1 until the gaseous foaming agent reaches dissolution equilibrium in the foamed preform; Depressurization step: After reaching dissolution equilibrium, the pressure in the mold cavity is released to ambient pressure at a depressurization rate Q; after releasing the pressure to ambient pressure, the mold cavity is kept closed, and hot air at a purging temperature T2 is introduced into the mold cavity for purging; after purging, the mold cavity is opened to allow the foam cells in the foam preform to grow, thus obtaining engineering plastic foam; The engineering plastic is a semi-crystalline polymer or an amorphous polymer; When the engineering plastic is a semi-crystalline polymer, the purging temperature T2 = (T m -20)℃~T m ℃; where T m This refers to the melting temperature of the semi-crystalline polymer. When the engineering plastic is an amorphous polymer, the purging temperature T2 = T g ℃~(T g +20)℃; where T is... g This refers to the glass transition temperature of amorphous polymers. The purging time shall be no less than 5 minutes.

2. The foaming method as described in claim 1, characterized in that, When the engineering plastic is a semi-crystalline polymer, the foaming temperature T1 = (T m -40)℃~T m ℃; where T m This is the melting temperature of the semi-crystalline polymer.

3. The foaming method as described in claim 1, characterized in that, When the engineering plastic is an amorphous polymer, the foaming temperature T1 = T g ℃~(T g +40)℃; where T g This is the glass transition temperature of amorphous polymers.

4. The foaming method according to any one of claims 1 to 3, characterized in that, The semi-crystalline polymer is one or more of polyethylene terephthalate, polyoxymethylene, polyamide, and liquid crystal polyester; the amorphous polymer is one or more of polyphenylene ether and polycarbonate.

5. An engineering plastic foam, characterized in that, The engineering plastic foam is obtained by foaming according to any one of claims 1 to 4.

6. The application of the foaming method according to any one of claims 1 to 4 in the preparation of engineering plastic foam.

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