Polyamide foamed material and crystallization molding process thereof

Abstract

The application discloses a kind of polyamide foamed material and crystallization forming process, belong to polyamide foamed material technical field, by polyamide matrix resin, nucleating agent and chain extender composition raw material system cooperate supercritical physical foaming process is prepared, the supercritical physical foaming process uses supercritical CO2, N2, cyclopentane, n-butane one or more as foaming agent, the polyamide foamed material is prepared by extrusion foaming after segmented gradient airtight physical cooling and shaping process is obtained.The application is directly sent into segmented gradient airtight cooling and shaping device after extrusion foaming, sets precooling section, main setting section, constant temperature curing section three independent temperature control units, and is matched with closed loop circulating air duct and all domain air distribution structure, strictly controls blank axial, circumferential temperature deviation, effectively locks bubble hole morphology, uniform cooling rate, substantially improves bubble hole aperture uniformity, simultaneously standardizes polyamide molecular crystallization behavior, stabilizes material crystallinity and porosity.

Description

Technical Field

[0001] This invention relates to the field of polyamide foam materials technology, and more specifically, to a polyamide foam material and its crystallization molding process. Background Technology

[0002] Polyamide foam materials combine the excellent mechanical, temperature resistance, and abrasion resistance properties of the polyamide matrix with the advantages of lightweight, cushioning, heat insulation, and sound insulation properties of foam materials, leading to their continuous expansion in applications across numerous fields such as the automotive industry, cushioning packaging, and rail transportation. Supercritical carbon dioxide and nitrogen, due to their environmental friendliness and stable foaming effect, have become the mainstream physical foaming agents for preparing polyamide foam materials, with the industry widely employing melt extrusion foaming processes for large-scale production. In the entire preparation process, the cooling and shaping process after extrusion foaming directly affects the cell morphology, porosity, and matrix crystallinity, making it a core step determining the overall quality of the finished product.

[0003] In existing conventional polyamide foaming extrusion production processes, most adopt conventional open cooling methods without designing segmented temperature control systems or closed uniform temperature cooling structures for the foamed preform. After extrusion, the foamed preform is directly exposed to the external environment, making it susceptible to local temperature differences caused by ambient temperature and natural airflow. Furthermore, the use of uniform cooling conditions throughout the process cannot adapt to the temperature and cooling rate requirements of different molding stages of the preform, leading to problems such as cell deformation, uneven pore size distribution, and low porosity. At the same time, it hinders the orderly arrangement of polyamide molecular chains, resulting in insufficient material crystallinity, poor structural stability, and significant performance differences between product batches, failing to meet the requirements of high-end fields for consistent polyamide foam material quality.

[0004] Based on this, the present invention designs a polyamide foam material and its crystallization molding process to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a polyamide foam material and its crystallization molding process to solve the problems mentioned in the background art.

[0006] A polyamide foam material is prepared by a raw material system consisting of a polyamide matrix resin, a nucleating agent, and a chain extender, combined with a supercritical physical foaming process. The supercritical physical foaming process uses one or more of supercritical CO2, N2, cyclopentane, and n-butane as foaming agents. The polyamide foam material is prepared by a segmented gradient closed-loop physical cooling and shaping process after extrusion foaming. The polyamide foam material has a pore size uniformity of ≥95%, a porosity of 40% to 70%, and a crystallinity of 28% to 35%.

[0007] Preferably, the polyamide matrix resin is any one or more of PA6, PA66, PA1010, and PA56, and the number-average molecular weight of the polyamide matrix resin is 15,000 to 30,000.

[0008] Preferably, the nucleating agent is selected from one or more of talc, montmorillonite, and organobentonite, and the amount of nucleating agent added is 0.1 to 1.0% of the mass of the polyamide matrix resin. The chain extender is selected from one or more of epoxy and isocyanate chain extenders, and the amount of chain extender added is 0.2 to 0.8% of the mass of the polyamide matrix resin.

[0009] A crystallization molding process for a polyamide foam material includes the following steps: S1. Raw material blending: The polyamide matrix resin, nucleating agent and chain extender are uniformly mixed to obtain blended raw materials; S2, Supercritical melt extrusion foaming: After the blended raw materials are melt-plasticized and homogenized, one or more physical foaming agents selected from supercritical CO2, N2, cyclopentane, and n-butane are injected into the extruded melt. After the melt and foaming agent are homogenized and fused, they are extruded through the foaming die head to obtain the initial polyamide foamed preform. S3. Segmented gradient closed cooling and shaping: After the initial polyamide foam preform is extruded from the foaming machine head, it is directly fed into the cooling and shaping device without a natural settling process. The cooling and shaping device is set with an independently temperature-controlled pre-cooling section, a main shaping section, and a constant temperature curing section in sequence along the conveying direction of the initial polyamide foam preform, so as to perform segmented gradient physical cooling on the initial polyamide foam preform. S4. Post-processing: The initial polyamide foam preform after cooling and shaping is drawn, leveled, trimmed and cut into blocks to obtain polyamide foam material.

[0010] Preferably, the temperature of the precooling section is 80-120℃ and the cooling rate is 2-5℃ / s, the temperature of the main shaping section is 40-80℃ and the cooling rate is 1-3℃ / s, and the temperature of the constant temperature curing section is 30-40℃ and the curing time is 3-10s.

[0011] Preferably, the cooling and shaping device has a built-in closed-loop circulating cooling air duct and a uniform air distribution structure. The uniform air distribution structure includes a diversion air duct, a pressure stabilizing chamber, an air distribution grid, and a flow guide grid, so that the circumferential temperature deviation and axial temperature deviation of the initial polyamide foam preform are ≤±2℃.

[0012] Preferably, the extrusion melt plasticizing temperature is 220–320℃, the foaming die head pressure is 8–15MPa, the extrusion line speed is 1–20m / min, the supercritical physical foaming agent injection pressure is 10–100MPa, and the injection temperature is 35–55℃.

[0013] Preferably, in step S3, the initial polyamide foam preform undergoes gradient cooling and shaping entirely within a sealed temperature-controlled cavity.

[0014] Compared with the prior art, the advantages of this invention are: 1. This invention directly feeds the extruded foamed material into a segmented gradient closed cooling and shaping device. It is equipped with three independent temperature control units: a pre-cooling section, a main shaping section, and a constant temperature curing section. Combined with a closed-loop circulating air duct and a uniform airflow structure, it strictly controls the axial and circumferential temperature deviation of the preform, effectively locks the cell morphology and uniform cooling rate, significantly improves the uniformity of cell diameter, and standardizes the crystallization behavior of polyamide molecules, stabilizing the crystallinity and porosity of the material.

[0015] 2. This invention abandons the traditional natural air cooling and single-stage constant temperature cooling methods, and adopts a fully enclosed, segmented gradient differentiated cooling process. Combined with a matching cooling rate and constant temperature curing process, it avoids defects such as cell merging, collapse, and inconsistent size in the foamed preform, and significantly improves the product molding consistency and overall performance. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the crystallization molding process of a polyamide foam material proposed in this invention. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 S1. In this embodiment, the polyamide matrix resin used is PA6 with a number average molecular weight of 15,000; the nucleating agent is talc powder, and the added mass is 0.1% of the mass of the polyamide matrix resin; the chain extender is an epoxy chain extender, and the added mass is 0.2% of the mass of the polyamide matrix resin; the above components are uniformly mixed to obtain a blended raw material.

[0019] S2. The blended raw materials are fed into an extrusion device for melt plasticization and homogenization. The melt plasticization temperature is set to 220℃. One or more physical foaming agents selected from supercritical CO2, N2, cyclopentane, and n-butane are injected into the extrusion melt cavity. The foaming agent injection pressure is 10MPa and the injection temperature is 35℃. After the foaming agent and polymer melt are homogenized and fused, the initial polyamide foamed preform is prepared by pressure release extrusion under the conditions of foaming die head pressure of 8MPa and extrusion line speed of 1m / min.

[0020] S3. The initial polyamide foamed preform is directly fed into the cooling and shaping device after being extruded from the foaming die head, without a natural settling process. The cooling and shaping device adopts a closed temperature-controlled cavity structure with a built-in closed-loop circulating cooling air duct and a uniform air distribution structure consisting of a diversion air duct, a pressure stabilizing chamber, an air distribution grid, and a flow guide grid, controlling the circumferential and axial temperature deviation of the preform to ≤±2℃. Among them, the pre-cooling section temperature is 80℃ and the cooling rate is 2℃ / s, the main shaping section temperature is 40℃ and the cooling rate is 1℃ / s, and the constant temperature curing section temperature is 30℃ and the curing time is 3s.

[0021] S4. The initial polyamide foam preform that has completed segmented gradient cooling and shaping is sequentially subjected to traction, leveling, trimming and cutting to obtain the finished polyamide foam material.

[0022] Example 2 S1. In this embodiment, PA6 and PA56 are used as the polyamide matrix resin with a number average molecular weight of 22,500. Montmorillonite is selected as the nucleating agent and is added at 0.5% of the mass of the polyamide matrix resin. The epoxy chain extender and isocyanate chain extender are selected as the chain extender and are added at 0.5% of the mass of the polyamide matrix resin. The above components are mixed evenly to obtain the blended raw material.

[0023] S2. The blended raw materials are fed into an extrusion device for melt plasticization and homogenization. The melt plasticization temperature is set to 270℃. One or more physical foaming agents selected from supercritical CO2, N2, cyclopentane, and n-butane are injected into the extrusion melt cavity. The foaming agent injection pressure is 55MPa and the injection temperature is 45℃. After the foaming agent and polymer melt are homogenized and fused, the initial polyamide foamed preform is prepared by pressure relief extrusion under the conditions of foaming die head pressure of 11MPa and extrusion line speed of 10m / min.

[0024] S3. The initial polyamide foam preform is directly fed into the cooling and shaping device after being extruded from the foaming die head, without a natural settling process. The cooling and shaping device adopts a closed temperature-controlled cavity structure with a built-in closed-loop circulating cooling air duct and a uniform air distribution structure consisting of a diversion air duct, a pressure stabilizing chamber, an air distribution grid, and a flow guide grid, controlling the circumferential and axial temperature deviation of the preform to ≤±2℃. Among them, the pre-cooling section temperature is 100℃ and the cooling rate is 3.5℃ / s, the main shaping section temperature is 60℃ and the cooling rate is 2℃ / s, and the constant temperature curing section temperature is 35℃ and the curing time is 6s.

[0025] S4. The initial polyamide foam preform that has completed segmented gradient cooling and shaping is sequentially subjected to traction, leveling, trimming and cutting to obtain the finished polyamide foam material.

[0026] Example 3 S1. In this embodiment, PA66 and PA1010 are used as the polyamide matrix resin with a number average molecular weight of 30,000. The nucleating agent is organic bentonite, which is added at 1.0% of the mass of the polyamide matrix resin. The chain extender is an isocyanate chain extender, which is added at 0.8% of the mass of the polyamide matrix resin. The above components are mixed evenly to obtain the blended raw material.

[0027] S2. The blended raw materials are fed into an extrusion device for melt plasticization and homogenization. The melt plasticization temperature is set to 320℃. One or more physical foaming agents selected from supercritical CO2, N2, cyclopentane, and n-butane are injected into the extrusion melt cavity. The foaming agent injection pressure is 100MPa and the injection temperature is 55℃. After the foaming agent is homogenized and fused with the polymer melt, the pressure is released and extruded under the conditions of 15MPa at the foaming die head and 20m / min at the extrusion line speed to prepare the initial polyamide foamed preform.

[0028] S3. The initial polyamide foamed preform is directly fed into the cooling and shaping device after being extruded from the foaming die head, without a natural settling process. The cooling and shaping device adopts a closed temperature-controlled cavity structure with a built-in closed-loop circulating cooling air duct and a uniform air distribution structure consisting of a diversion air duct, a pressure stabilizing chamber, an air distribution grid, and a flow guide grid, controlling the circumferential and axial temperature deviation of the preform to ≤±2℃. Among them, the pre-cooling section temperature is 120℃ and the cooling rate is 5℃ / s, the main shaping section temperature is 80℃ and the cooling rate is 3℃ / s, and the constant temperature curing section temperature is 40℃ and the curing time is 10s.

[0029] S4. The initial polyamide foam preform that has completed segmented gradient cooling and shaping is sequentially subjected to traction, leveling, trimming and cutting to obtain the finished polyamide foam material.

[0030] Comparative Example 1 This comparative example uses a natural air-cooling shaping process, without a sealed temperature control cavity, closed-loop circulating cooling air duct, or uniform air distribution structure, and without a segmented independent temperature control structure; the other raw material component parameters, supercritical extrusion foaming process parameters, and post-processing parameters are completely consistent with those of Example 2.

[0031] Comparative Example 2 This comparative example uses a single-stage constant temperature cooling process, eliminating the three-stage gradient temperature control structure of pre-cooling section, main shaping section, and constant temperature curing section, and setting the cooling temperature to a uniform 50℃; the remaining raw material component parameters, supercritical extrusion foaming process parameters, equipment structure, and post-processing parameters are completely consistent with those of Example 2.

[0032] Product performance testing methods, procedures, and test results All embodiments and comparative samples of this invention use the same testing standards, equipment and procedures. Before testing, all samples are placed at room temperature and normal pressure for 24 hours to balance and eliminate the influence of processing internal stress on the test data.

[0033] Foam pore size uniformity test Testing equipment: Scanning electron microscope; Testing steps: Select a flat cross-section of the foam material to be tested and perform surface gold spraying for conductivity; Randomly select 5 different test areas of the sample, and independently select 100 complete closed cells in each area, and measure the cell diameter of each cell; Statistically analyze all cell diameter data, calculate the average and standard deviation of the cell diameter, and calculate the cell diameter uniformity using "1 - standard deviation of cell diameter / average cell diameter".

[0034] Porosity testing Testing equipment: electronic analytical balance, vernier calipers; Testing steps: Cut regular block-shaped samples to be tested, measure the length, width and height of the samples with vernier calipers, and calculate the apparent volume of the samples; weigh the actual mass of the samples using an electronic analytical balance and calculate the apparent density of the samples; based on the dense solid density of the polyamide matrix resin, calculate the porosity of the material according to the formula: porosity = (1 - apparent density of the sample / dense density of the matrix) × 100%.

[0035] Crystallinity testing Testing equipment: X-ray diffractometer; Testing steps: Press the sample to be tested into a flat specimen and fix it at the testing station. Set the scanning angle to 5°~40° and the scanning rate to 2° / min. Continuously acquire the X-ray diffraction pattern of the sample. Perform baseline correction and peak fitting on the diffraction pattern to separate the crystalline diffraction peaks and the amorphous diffuse peaks. Calculate the total area of ​​the crystalline diffraction peaks and the total area of ​​the total diffraction peaks. Use the ratio of the two as the crystallinity of the sample.

[0036] Comparison of test results and technical effects The samples from each experimental group were tested using the aforementioned unified testing method. The specific performance data and comparative differences are as follows: Examples 1, 2, and 3 were prepared using the segmented gradient closed cooling and shaping process and dedicated equipment structure of the present invention. The uniformity of the bubble pore size was 95.2%, 97.1%, and 96.5%, respectively; the porosity was 42%, 55%, and 68%, respectively; and the crystallinity was 29.2%, 32.6%, and 34.1%, respectively. The bubble pore structure of the samples was regular and the molding consistency was high.

[0037] Comparative Example 1 used a natural air-cooling shaping process without employing segmented gradient temperature control and a closed uniform air cooling structure. The prepared sample had a pore size uniformity of only 82.3%, a porosity of 33.5%, and a crystallinity of 24.8%. Compared with the embodiments of the present invention, it has obvious problems such as uneven pore size, local pore collapse, low matrix crystallinity, and loose structure.

[0038] Comparative Example 2 used a single-stage isothermal cooling process instead of a three-stage gradient differential cooling and shaping structure. The prepared sample had a cell diameter uniformity of 88.6%, a porosity of 36.2%, and a crystallinity of 26.1%. Compared with the embodiment of the present invention, the cell regularity, porosity, and crystallinity were significantly deteriorated, and stable and controllable cell forming and crystallization shaping effects could not be achieved.

[0039] In summary, compared with conventional processes such as natural cooling and single-stage constant temperature cooling, the present invention, through its core technical solutions of independent segmented gradient closed cooling and shaping and uniform airflow temperature control throughout the entire area, can effectively stabilize the cell structure of supercritical polyamide foam preform, improve cell uniformity and material crystal regularity, and achieve precise and controllable preparation of polyamide foam material structure and performance.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyamide foam material, characterized in that, The polyamide foam material is prepared by a raw material system consisting of polyamide matrix resin, nucleating agent and chain extender, combined with a supercritical physical foaming process. The supercritical physical foaming process uses one or more of supercritical CO2, N2, cyclopentane and n-butane as foaming agents. The polyamide foam material is prepared by a segmented gradient closed physical cooling and shaping process after extrusion foaming. The polyamide foam material has a cell size uniformity ≥95%, a porosity of 40% to 70%, and a crystallinity of 28% to 35%.

2. The polyamide foam material according to claim 1, characterized in that, The polyamide matrix resin is any one or more of PA6, PA66, PA1010, and PA56, and the number-average molecular weight of the polyamide matrix resin is 15,000 to 30,000.

3. The polyamide foam material according to claim 1, characterized in that, The nucleating agent is selected from one or more of talc, montmorillonite, and organobentonite, and the amount of nucleating agent added is 0.1 to 1.0% of the mass of the polyamide matrix resin. The chain extender is selected from one or more of epoxy and isocyanate chain extenders, and the amount of chain extender added is 0.2 to 0.8% of the mass of the polyamide matrix resin.

4. A crystallization molding process for polyamide foam material according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Raw material blending: The polyamide matrix resin, nucleating agent and chain extender are uniformly mixed to obtain blended raw materials; S2, Supercritical melt extrusion foaming: After the blended raw materials are melt-plasticized and homogenized, one or more physical foaming agents selected from supercritical CO2, N2, cyclopentane, and n-butane are injected into the extruded melt. After the melt and foaming agent are homogenized and fused, they are extruded through the foaming die head to obtain the initial polyamide foamed preform. S3. Segmented gradient closed cooling and shaping: After the initial polyamide foam preform is extruded from the foaming machine head, it is directly fed into the cooling and shaping device without a natural settling process. The cooling and shaping device is set with an independently temperature-controlled pre-cooling section, a main shaping section, and a constant temperature curing section in sequence along the conveying direction of the initial polyamide foam preform, so as to perform segmented gradient physical cooling on the initial polyamide foam preform. S4. Post-processing: The initial polyamide foam preform after cooling and shaping is drawn, leveled, trimmed and cut into blocks to obtain polyamide foam material.

5. The crystallization molding process of a polyamide foam material according to claim 4, characterized in that, The temperature of the precooling section is 80-120℃, and the cooling rate is 2-5℃ / s. The temperature of the main shaping section is 40-80℃, and the cooling rate is 1-3℃ / s. The temperature of the constant temperature curing section is 30-40℃, and the curing time is 3-10s.

6. The crystallization molding process of a polyamide foam material according to claim 4, characterized in that, The cooling and shaping device has a built-in closed-loop circulating cooling air duct and a uniform air distribution structure. The uniform air distribution structure includes a diversion air duct, a pressure stabilizing chamber, an air distribution grid, and a flow guide grid, so that the circumferential temperature deviation and axial temperature deviation of the initial polyamide foam preform are ≤±2℃.

7. The crystallization molding process of a polyamide foam material according to claim 4, characterized in that, The extrusion melt plasticizing temperature is 220–320℃, the foaming die head pressure is 8–15MPa, the extrusion line speed is 1–20m / min, the supercritical physical foaming agent injection pressure is 10–100MPa, and the injection temperature is 35–55℃.

8. The crystallization molding process of a polyamide foam material according to claim 4, characterized in that, In step S3, the initial polyamide foam preform undergoes gradient cooling and shaping within a sealed temperature-controlled cavity throughout the entire process.

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