A low internal stress high toughness micro-foamed PC-ABS alloy material and a preparation method thereof

Abstract

The present application relates to a kind of low internal stress high toughness micro-foaming PC-ABS alloy material and its preparation method, belong to the technical field of polymer composite preparation.The preparation method of the present application, PC resin and ABS resin are mixed according to mass ratio (55-65):(35-45) First, then be transferred to twin-screw extruder and melt plasticization;By precisely injecting 0.3-0.8wt% supercritical CO2 at the end of twin-screw extrusion melting section, and control die head pressure relief rate 5-15MPa / s, make the material inside form 0.3-3 μm uniform closed cell structure, to obtain the PC-ABS alloy material with uniform closed cell microcell structure.The microcell can be used as internal stress release channel, reduce molecular chain orientation freezing;And PC phase around microcell can induce diffuse crazing when impacting, efficiently dissipate energy, rather than initiate crack propagation, so as to achieve the effect of microcell stress buffer-multiple crazing synergistic toughening.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer composite materials, and more specifically, relates to a low-internal-stress, high-toughness micro-foamed PC-ABS alloy material and its preparation method. Background Technology

[0002] Polycarbonate (PC) composites have become core materials in the electronics, automotive, and construction industries due to their high impact strength, excellent heat resistance, dimensional stability, and ease of processing. Among them, PC-ABS alloys, which combine the rigidity of PC with the processing fluidity of ABS, are widely used in the electronics and automotive sectors.

[0003] However, existing PC-ABS alloys suffer from three major industry pain points: Internal stress concentration leads to cracking: high shear and rapid cooling during melt blending cause the molecular chain orientation to freeze, making the product prone to stress cracking during assembly or use; The processing-performance contradiction is prominent: to improve fluidity, the processing temperature needs to be increased (≥260℃), which exacerbates PC hydrolysis and ABS thermal degradation, resulting in excessive VOC emissions. Microfoaming technology application failure: Although microfoaming can reduce internal stress and reduce weight, when microfoaming technology is applied to PC-ABS, residual decomposition products of chemical foaming agents (such as AC) cause yellowing and strong odor; micropores are prone to become stress concentration points, and the impact strength is generally reduced.

[0004] Therefore, the industry urgently needs a new process that is low-cost, easy to mass-produce, and can synergistically optimize internal stress, toughness, and environmental friendliness. Summary of the Invention

[0005] The purpose of this invention is to provide a micro-foamed PC-ABS alloy material with low internal stress and high toughness, and its preparation method, which has the characteristics of low internal stress and high toughness.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a low-internal-stress, high-toughness micro-foamed PC-ABS alloy material includes the following steps: S1. Mix PC resin and ABS resin at a mass ratio of (55–65):(35–45) to obtain a mixture. S2. Transfer the mixture to a twin-screw extruder for melt plasticization; S3. Inject supercritical CO2 at the end of the molten section. The injection amount is 0.3–0.8 wt% of the total mass of the mixture, the injection pressure is 8–12 MPa, and the temperature at the injection point is 40–60 °C to obtain a melt containing CO2. S4. The CO2-containing melt is extruded through a die, and the pressure relief rate is controlled at 5–15 MPa / s to form a PC-ABS alloy material with a microporous structure.

[0007] Furthermore, the PC resin is bisphenol A type polycarbonate with a weight-average molecular weight of 25,000–35,000; the acrylonitrile content in the ABS resin is 20–30 wt%.

[0008] The mass ratio of PC resin to ABS resin is controlled at (55–65):(35–45) to avoid a decrease in heat resistance when the proportion of PC resin is too small, or a decrease in fluidity and difficulty in micropore nucleation when the proportion of PC resin is too large.

[0009] Furthermore, in step S1, an antioxidant and a lubricant are added at a ratio of 0.1–0.5% of the total mass of the mixture.

[0010] Further, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168; the lubricant is selected from at least one of calcium stearate, zinc stearate, erucamide, oleamide, polyethylene wax, and oxidized polyethylene wax. Preferably, the antioxidant is selected from a compound of antioxidant 1010 and 168; more preferably, antioxidant 1010 and 168 are compounded in a mass ratio of 1:1.

[0011] The twin-screw extruder has a temperature setting range of 220–260℃ to ensure that the PC resin and ABS resin are fully melted and to avoid thermal degradation.

[0012] Furthermore, the temperature settings for each zone of the twin-screw extruder are as follows: Zone 1 215-225℃, Zone 2 225-235℃, Zone 3 235-245℃, Zone 4 245-255℃, Zone 5 245-255℃, Zone 6 240-250℃, Zone 7 235-245℃, and Die Head 245-255℃, wherein the supercritical CO2 injection point is located in Zone 5.

[0013] Furthermore, in step S3, the end of the melting section is located at 60%–75% of the total length of the twin-screw extruder. The CO2 injection point is chosen at 60%–75% of the total screw length to avoid premature injection leading to CO2 escape, or premature injection leading to uneven dissolution and coarsening of micropores.

[0014] The critical point of the PC resin and ABS resin system is approximately 7.4 MPa and 31 ± 1 °C. By limiting the injection pressure and temperature of supercritical CO2, the supercritical state of CO2 in the delivery pipeline is ensured. The injection point temperature refers to the preheating temperature of CO2 after being pressurized by the high-pressure pump and before being injected into the extruder, preventing phase change in the injection pipeline. After injection, CO2 quickly reaches thermal equilibrium with the high-temperature melt, and its injection point temperature does not affect the bulk melt temperature in the twin-screw extruder. Furthermore, the supercritical CO2 injection amount is controlled at 0.3–0.8 wt% to avoid insufficient injection leading to insufficient micropores and weak effect, or excessive injection causing cell coalescence and a sharp drop in strength.

[0015] More preferably, the supercritical CO2 injection amount is 0.4–0.7 wt%, and the depressurization rate is 8–12 MPa / s.

[0016] The pressure relief rate is controlled at 5–15 MPa / s to avoid excessively slow pressure relief leading to excessively large micropore growth, or excessively fast pressure relief leading to overly dense nucleation and uneven pore size.

[0017] Furthermore, in step S4, the average pore size of the microporous structure is 0.3–3 μm, and the porosity is 5%–15%. The average pore size of the microporous structure is controlled within 0.3–3 μm to avoid either excessively small pores leading to weak stress buffering or excessively large pores becoming crack initiation points.

[0018] Further, the specific operation steps of step S4 are as follows: the CO2-containing melt is extruded through a die, the pressure relief rate is controlled at 5–15 MPa / s, forming a strip with a microporous structure. The extruded strip is introduced into a water-cooling tank within 5 seconds, and after water-cooling solidification, it is dried to obtain a PC-ABS alloy material with a microporous structure. The temperature of the water-cooling tank is 20–30°C; the drying temperature is 75–85°C, and the drying time is 1.5–2.5 hours. Preferably, the extruded strip is introduced into the water-cooling tank within 3 seconds.

[0019] Furthermore, the moisture content of the dried PC-ABS alloy material is ≤0.02wt%.

[0020] A microcellular PC-ABS alloy material is prepared by the method described above. The density of the microcellular PC-ABS alloy material prepared by this technical solution is 1.00–1.15 g / cm³. 3 .

[0021] Furthermore, the melt flow rate of the micro-foamed PC-ABS alloy material under conditions of 260°C and 5kg load is 15–25 g / 10 min.

[0022] An article is made of the aforementioned micro-foamed PC-ABS alloy material.

[0023] Furthermore, the product is a car center console panel, a dashboard frame, a laptop casing, or a smartphone frame.

[0024] Furthermore, the wall thickness of the automotive center console panel is 1.2–2.0 mm.

[0025] The above methods are used in the preparation of low-stress electronic and electrical structural components and reliable automotive interior parts.

[0026] The beneficial effects of this invention are: In the micro-foamed PC-ABS alloy material preparation process of this invention, 0.3–0.8 wt% supercritical CO2 is precisely injected at the end of the melting section of a twin-screw extruder, and the die depressurization rate is controlled at 5–15 MPa / s. This results in a uniform closed-cell structure of 0.3–3 μm within the material. These micropores serve as channels for releasing internal stress, reducing molecular chain orientation freezing. Furthermore, the PC phase surrounding the micropores can induce diffuse crazing upon impact, efficiently dissipating energy rather than initiating crack propagation, thus achieving a synergistic toughening effect of micropore stress buffering and multiple crazing. In addition, this invention lowers the effective processing temperature and inhibits degradation through CO2 plasticization. The CO2 carrying effect promotes the escape of small molecules, eliminating the need for nanofillers or modifiers, significantly improving stress cracking problems, and making it suitable for high-reliability applications such as automotive center console panels and laptop casings. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to specific embodiments, but the scope of protection of this invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or according to the manufacturer's recommendations. Unless otherwise specified, all reagents and materials used are commercially available.

[0028] Example 1 A method for preparing a low-internal-stress, high-toughness micro-foamed PC-ABS alloy material includes the following steps: S1. Mix 60 parts by weight of PC resin (bisphenol A type polycarbonate, Mw≈30000), 40 parts by weight of ABS resin (acrylonitrile content 25wt%), 0.2 parts by weight of antioxidant (antioxidant 1010) and 0.3 parts by weight of lubricant (calcium stearate) at 600±100 rpm for 5 minutes until the material is a uniform and loose powder to obtain the mixture.

[0029] S2. Transfer the mixture to a twin-screw extruder for melt plasticization; set the temperatures of zones one to seven and the die head in the twin-screw extruder (L / D=40) as follows: 220℃→230℃→240℃→250℃→250℃ (injection point)→245℃→240℃→die head 250℃.

[0030] S3. In the fifth zone, supercritical CO2 is injected through a high-pressure injection pump. The injection pressure is 10±1MPa, the injection point temperature is 50±1℃, and the injection amount is 0.5wt% of the total mass of the mixture. The mixture is further mixed by the reverse screw and kneading block in the twin-screw extruder to ensure uniform dissolution of CO2 and obtain a CO2-containing melt.

[0031] S4. The CO2-containing melt is extruded through a die. A quick-release valve is connected to the die outlet to control the pressure release rate at 10MPa / s. After the melt is extruded, micropores instantly nucleate and grow, forming strips with a uniform closed-pore microporous structure. The extruded strips are introduced into a circulating water cooling tank with a water temperature of 25±2℃ (cooling length ≥2m) within 3 seconds to quickly solidify the microporous structure. After water cooling and solidification, PC-ABS strips with a microporous structure are obtained.

[0032] S5. Part of the water-cooled and cured PC-ABS strips are cut into Φ3×3mm cylindrical particles by a rotary pelletizer, dehydrated by a vibrating screen, and then dried in an 80℃ hot air dryer for 2 hours to obtain PC-ABS dried particles with microporous structure and a moisture content ≤0.02wt%.

[0033] Example 2 Compared with Example 1, the difference in this example is that in step S1, the mass parts of PC resin and ABS resin are 55 parts by mass and 45 parts by mass, respectively, and the added antioxidant is a complex of antioxidant 1010 and 168 (mass ratio of 1:1), with a mass part of 0.3 parts; in step S3, the amount of supercritical CO2 injected is 0.3 wt% of the total mass of the mixture; in step S4, the pressure relief rate is controlled at 5 MPa / s. The remaining components, preparation steps, and parameters are the same.

[0034] Example 3 Compared with Example 1, the difference in this example is that in step S1, the mass fractions of PC resin and ABS resin are 65 parts by mass and 35 parts by mass, respectively, and the added lubricant is polyethylene wax; in step S3, the amount of supercritical CO2 injected is 0.8 wt% of the total mass of the mixture; and in step S4, the pressure relief rate is controlled at 15 MPa / s. All other components, preparation steps, and parameters are the same.

[0035] Comparative Example 1 Compared with Example 1, the difference in this comparative example is that in step S3 of this comparative example, the amount of supercritical CO2 injected is 0.1 wt% of the total mass of the mixture. The remaining components, preparation steps and parameters are the same.

[0036] Comparative Example 2 Compared with Example 1, this comparative example differs in that, in step S3 of this comparative example, the amount of supercritical CO2 injected is 1.5 wt% of the total mass of the mixture. The remaining components, preparation steps, and parameters are the same.

[0037] Comparative Example 3 Compared with Example 1, the difference in this comparative example is that in step S4, the pressure relief rate is controlled at 25 MPa / s. All other components, preparation steps, and parameters are the same.

[0038] Comparative Example 4 Compared with Example 1, this comparative example differs in that it omits step S3, meaning it does not inject supercritical CO2, and in step S2, the temperature of the nozzle is set to 260°C. All other components, preparation steps, and parameters remain the same.

[0039] Comparative Example 5 Compared with Example 1, this comparative example differs in that it uses AC foaming agent to prepare micro-foamed PC-ABS alloy material. The specific steps are as follows: S1. Mix 60 parts by weight of PC resin, 40 parts by weight of ABS resin, 0.2 parts by weight of antioxidant (antioxidant 1010) and 0.3 parts by weight of lubricant (calcium stearate) at 300 rpm for 4 minutes under jacket cooling water temperature control (material temperature ≤35℃); then add 0.5 parts by weight of azodicarbonamide (AC foaming agent), reduce the speed to 150 rpm, and continue mixing for 1-2 minutes to obtain the mixture.

[0040] S2. Transfer the mixture to a twin-screw extruder for melt plasticization; set the temperatures of zones one to seven and the die head in the twin-screw extruder (L / D=40) as follows: 180℃→190℃→200℃→205℃→205℃→200℃→195℃→200℃ at the die head (the temperature is below the complete decomposition temperature of AC throughout the process, ensuring that the gas is decomposed by shear heat at the die head outlet).

[0041] S3. The melt is extruded through the die. Irregular bubbles are visible on the surface of the extruded strip, and the cross-section is spongy (SEM confirms that the porosity is >40%). Within 3 seconds after extrusion, it is introduced into a circulating water cooling tank with a water temperature of 25±2℃ (cooling length ≥2m). After water cooling, PC-ABS strip is obtained.

[0042] S4. Part of the water-cooled PC-ABS strips are cut into Φ3×3mm cylindrical particles by a rotary pelletizer, dehydrated by a vibrating screen, and then dried in an 80℃ hot air dryer for 2 hours to obtain dried PC-ABS particles.

[0043] The performance testing method is as follows: (1) Density test Referring to GB / T 1033.1, the water-cooled PC-ABS strip sample was cut into standard strips of 20×20×2mm. The dry weight (m1) was weighed using an electronic balance, and then the strips were immersed in distilled water at 23℃ and weighed again for wet weight (m2). The density was calculated using the formula ρ=m1 / (m1-m2)×ρ0 (where ρ0 is the density of distilled water at 23℃, approximately 1g / cm³). 3 ).

[0044] (2) Notch impact test Following ISO 180:2000, water-cooled PC-ABS strip samples were used to prepare standard specimens with A50 notches (depth 2.0±0.1mm, included angle 45°), measuring 80×10×4mm. Impact tests were conducted at 23℃ and -30℃ using a pendulum impact testing machine with a 15J pendulum energy. Before testing at -30℃, the specimens were pre-conditioned in a cryogenic chamber for 3 hours. Ten specimens were tested in each group, and the results of each impact were recorded.

[0045] (3) Internal stress test Following ASTM D 4093, water-cooled PC-ABS strip samples were cut into standard strips of 50×50×2mm. A polarimeter was set to orthogonal field mode, and photographs were taken of the central 20×20mm area of ​​each strip. The number of bright and dark fringes in the photographs was analyzed using ImageJ software. The fringe density was calculated as: total number of fringes / observed area (fringes / cm²). 2 ), take the average value of 3 different regions.

[0046] (4) VOC content test Following VDA 278, 1.0 ± 0.1 g of dried PC-ABS particles were placed in a 20 mL headspace vial, and 10 μL of internal standard solution (4-bromofluorobenzene, 100 μg / mL) was added. The vial was sealed and heated at 120 °C for 60 minutes. Subsequently, the headspace gas was introduced into the thermal desorption system via an autosampler, and the total TVOC (μg / g) was determined.

[0047] (5) Melt Flow Rate (MFR) Test Referring to ISO 1133, 4.0±0.2g of dried PC-ABS particles (moisture content ≤0.02wt%) were loaded into the melt flow rate (MFR) meter barrel and preheated at 260±0.5℃ with a load of 5.0±0.01kg for 300±5s. After preheating, a segment of extrudate was cut every 30±0.5s using a standard cutter; the first two segments were discarded, and the third–5 segments of extrudate were weighed using an analytical balance; the MFR was calculated using the formula: MFR=(600×m) / t (g / 10min), where m is the average mass of the cut segment (g) and t is the cutting time (s); the average value of three valid tests was taken.

[0048] The MFR (Mean Flow Rate) test value of microcellular materials reflects their effective processing flowability at high injection molding temperatures. The complete collapse of the microporous structure at 260℃ during the test is a normal physical phenomenon; however, the melt composition after collapse is consistent with that of conventional PC-ABS. Therefore, the measured MFR can be directly used for injection molding process parameter design.

[0049] The test results are shown in Table 1.

[0050] Table 1

[0051] As shown in Table 1, the test results indicate that Examples 1-3 exhibit superior overall performance compared to Comparative Examples 1-5. Specifically, in Comparative Example 1, the insufficient supercritical CO2 injection amount resulted in the failure to form effective micropores, leading to reduced notch impact resistance. In Comparative Example 2, the high supercritical CO2 injection amount resulted in coarsened pores and a high open-cell ratio. Although the high porosity reduced the density, the open-cell structure caused water infiltration during the immersion test, resulting in a density higher than the theoretical value. The large pores became channels for rapid propagation of low-temperature cracks, significantly degrading the impact strength. In Comparative Example 3, the excessively rapid decompression rate led to overly dense micropore nucleation but insufficient growth, resulting in low porosity and a density close to the conventional level. The excessively small micropores failed to effectively induce crazing and instead weakened the stress buffering capacity. In Comparative Example 4, no supercritical CO2 was injected, meaning no micropores were formed, resulting in deterioration of impact strength and stress. In Comparative Example 5, the foaming agent decomposed to produce a N2 / CO / CO2 mixed gas, leading to uncontrollable nucleation. The gas diffusion rate exceeded the polymer melt strength growth rate, causing cell merging and increased pore size. Larger pores weaken the matrix continuity, resulting in reduced notched impact resistance. Furthermore, the decomposition byproducts of the foaming agent resulted in excessive VOC content, failing to meet environmental protection requirements. In summary, this invention achieves an optimal balance between lightweight and toughness by synergistically controlling the CO2 injection amount and depressurization rate to construct uniform closed pores at the 0.3–3 μm scale.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a low-internal-stress, high-toughness micro-foamed PC-ABS alloy material, comprising the following steps: S1. Mix PC resin and ABS resin at a mass ratio of (55–65):(35–45) to obtain a mixture. S2. Transfer the mixture to a twin-screw extruder for melt plasticization; S3. Inject supercritical CO2 at the end of the molten section. The injection amount is 0.3–0.8 wt% of the total mass of the mixture, the injection pressure is 8–12 MPa, and the temperature at the injection point is 40–60 °C to obtain a melt containing CO2. S4. The CO2-containing melt is extruded through a die, and the pressure relief rate is controlled at 5–15 MPa / s to form a PC-ABS alloy material with a microporous structure.

2. The preparation method according to claim 1, characterized in that, The PC resin is bisphenol A type polycarbonate with a weight-average molecular weight of 25,000–35,000; the acrylonitrile content in the ABS resin is 20–30 wt%.

3. The preparation method according to claim 1, characterized in that, In step S1, an antioxidant and a lubricant are added at a ratio of 0.1–0.5% of the total mass of the mixture.

4. The preparation method according to claim 1, characterized in that, The temperature settings for each zone of the twin-screw extruder are as follows: Zone 1 215-225℃, Zone 2 225-235℃, Zone 3 235-245℃, Zone 4 245-255℃, Zone 5 245-255℃, Zone 6 240-250℃, Zone 7 235-245℃, and Die Head 245-255℃, with the supercritical CO2 injection point located in Zone 5.

5. The preparation method according to claim 1, characterized in that, In step S3, the end of the melt section is located at 60%–75% of the total length of the twin-screw extruder.

6. The preparation method according to claim 1, characterized in that, In step S4, the average pore size of the microporous structure is 0.3–3 μm, and the porosity is 5%–15%.

7. The preparation method according to claim 1, characterized in that, The specific operation steps of step S4 are as follows: the CO2-containing melt is extruded through a die, the pressure relief rate is controlled at 5–15 MPa / s, and a strip with a microporous structure is formed. The extruded strip is introduced into a water-cooling tank, and after water-cooling solidification, it is dried to obtain a PC-ABS alloy material with a microporous structure.

8. A micro-foamed PC-ABS alloy material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. An article, characterized in that, The product is made using the micro-foamed PC-ABS alloy material as described in claim 8, and is used as a car center console panel, dashboard frame, laptop shell, or smartphone frame.

10. The application of the preparation method according to any one of claims 1-8 in the preparation of low internal stress electronic and electrical structural parts and reliable automotive interior parts.

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