High-flow high-gloss modified PP material, preparation method thereof and thin-wall automobile bumper

Abstract

The application provides a high-flow high-gloss modified PP material, a preparation method thereof and a thin-wall automobile bumper, and belongs to the technical field of PP materials. The traditional "high-melt-index PP+POE+talcum powder" thin-wall mold filling is mainly achieved by increasing the melt index or adding POE, which is easy to sacrifice the strength and toughness and cause apparent defects. The application is prepared by reaction extrusion and pre-dynamic exchange network master batch: anhydride-epoxy network building, stearic acid end-capped crosslinking control, Zn promotes exchange to make shear thinning and reduce viscosity, and vacuum exhaust is used to stabilize batches; hollow glass beads with gradient interface are used to replace talcum powder: silanization anchoring and hard shell anti-pressure and anti-crushing, PP-g-MAH compatibilization and outer covering of nucleating agent to refine crystallization; side feeding / low temperature weak shear is used for blending, and antioxidants and calcium stearate are used to stabilize the window; viscosity reduction is used to assist mold filling and inhibit the secondary crushing of microbeads during injection molding, and the network consumes energy to increase toughness after cooling, so that light weight and high strength and toughness are realized.

Description

Technical Field

[0001] This invention belongs to the field of PP material technology, and relates to a high-flow, high-gloss modified PP material, its preparation method, and a thin-walled automotive bumper. Background Technology

[0002] As the automotive industry rapidly develops towards energy conservation, emission reduction, and new energy, "lightweighting" has become a core trend in automotive material research and development, with "thin-wall" design of car bumpers being one of the key approaches. However, thin-wall design places stringent and contradictory demands on material properties: the material must possess a high melt flow rate to meet the requirements of thin-wall molding, while maintaining extremely high rigidity to prevent collapse, and possessing excellent low-temperature toughness to comply with safety regulations.

[0003] Existing technologies mainly use a ternary blend system of "high melt index PP (polypropylene) + POE (polyolefin elastomer) + talc", but it encounters a bottleneck in ultra-thin wall applications: improving the fluidity of the matrix often comes at the cost of strength and toughness, while increasing the content of traditional rubber will increase viscosity and cause appearance defects, making it difficult to balance the inverted contradiction of "fluidity-strength and toughness".

[0004] Furthermore, hollow glass microspheres, introduced to further reduce weight, also face application challenges in existing technologies. Due to their thin walls and high brittleness, hollow glass microspheres are prone to breakage and failure under the high shear fields of extrusion and injection molding. Moreover, the poor interfacial bonding between their polar surfaces and the non-polar PP matrix easily leads to debonding defects, resulting in a significant decrease in the material's impact resistance. Simultaneously, conventional one-pot reactive extrusion makes it difficult to precisely control the degree of crosslinking, easily causing performance fluctuations and appearance problems such as flow marks and pitting. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a high-flow, high-gloss modified PP material, its preparation method, and a thin-walled automotive bumper. Traditional thin-walled molding processes using "high melt flow index PP + POE + talc" often rely on increasing the melt flow index or adding POE, which easily sacrifices strength and toughness and introduces surface defects. This application utilizes reactive extrusion to pre-form a dynamic exchange network masterbatch: anhydride-epoxy network building, stearic acid end-capping to control crosslinking, and Zn-promoting exchange to reduce shear thinning and viscosity, combined with vacuum degassing to stabilize batches; gradient interface hollow glass beads replace talc: silanization anchors and provides a hard shell for compression resistance and breakage prevention; PP-g-MAH (maleic anhydride-grafted polypropylene) compatibilizes and is coated with a nucleating agent to refine crystals. Blending employs side feeding / low-temperature weak shearing with antioxidants and calcium stearate to stabilize the window; during injection molding, viscosity reduction aids molding and inhibits secondary breakage of microspheres; after cooling, the network absorbs energy and increases toughness, achieving a balance between lightweight and high strength and toughness.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a high-flow, high-gloss modified PP material, the method comprising:

[0008] S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA (glycidyl methacrylate grafted polyolefin elastomer) to obtain a first mixture. Zinc acetylacetonate, zinc stearate and compound antioxidant are added to obtain a second mixture. The second mixture is added to a twin-screw extruder for reactive extrusion, water-cooled pelletizing and drying to obtain dynamic exchange network masterbatch.

[0009] S2: The surface-modified microspheres are placed in a vacuum mixer, and the mixture and benzoyl peroxide are sprayed in and pre-wetted under negative pressure to obtain wetted microspheres. The wetted microspheres are dispersed in the modification liquid, stirred and reacted, sieved, washed and dried to obtain hard-shell microspheres. The hard-shell microspheres are placed in a high-speed mixer, PP-g-MAH is added and mixed, and then nucleating agent WBG-II is added and mixed to obtain gradient interface hollow glass microspheres.

[0010] S3: High-crystallinity polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate are mixed to obtain a resin matrix premix. The premix is ​​added from the main feed port of a twin-screw extruder, and gradient interface hollow glass microspheres are added from the side feed port. The mixture is melt-blended, extruded, and granulated to obtain a high-flow, high-gloss modified PP material.

[0011] As a preferred embodiment of the present invention, in S1, the molar ratio of the anhydride group in the dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is (0.8-1.3):1, for example, it can be 0.80:1, 0.85:1, 0.90:1, 0.95:1, 1.00:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1, 1.25:1 or 1.30:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0012] In some optional embodiments, the molar ratio of the carboxyl group in the stearic acid to the epoxy group in POE-g-GMA is (0.1-0.3):1, for example, it can be 0.10:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.20:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1 or 0.30:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0013] In some optional embodiments, the effective zinc content of the zinc acetylacetonate is 300-3000 ppm of POE-g-GMA, for example, it can be 300 ppm, 570 ppm, 840 ppm, 1110 ppm, 1380 ppm, 1650 ppm, 1920 ppm, 2190 ppm, 2460 ppm, 2730 ppm or 3000 ppm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the mass ratio of zinc stearate to POE-g-GMA is (0.05-0.3):100, for example, it can be 0.050:100, 0.075:100, 0.100:100, 0.125:100, 0.150:100, 0.175:100, 0.200:100, 0.225:100, 0.250:100, 0.275:100 or 0.300:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1-2), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the mass ratio of the compound antioxidant to POE-g-GMA is (0.2-0.5):100, for example, it can be 0.20:100, 0.23:100, 0.26:100, 0.29:100, 0.32:100, 0.35:100, 0.38:100, 0.41:100, 0.44:100, 0.47:100 or 0.50:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the front section temperature of the twin-screw extruder is 170-190°C, for example, it can be 170°C, 172°C, 174°C, 176°C, 178°C, 180°C, 182°C, 184°C, 186°C, 188°C or 190°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] In some optional embodiments, the mid-to-rear section temperature of the twin-screw extruder is 190-220°C, for example, it can be 190°C, 193°C, 196°C, 199°C, 202°C, 205°C, 208°C, 211°C, 214°C, 217°C or 220°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some alternative embodiments, the screw speed of the twin-screw extruder is 250-400 rpm, for example, 250 rpm, 265 rpm, 280 rpm, 295 rpm, 310 rpm, 325 rpm, 340 rpm, 355 rpm, 370 rpm, 385 rpm or 400 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the mid-section vacuum exhaust of the twin-screw extruder is -0.06 to -0.08 MPa, for example, it can be -0.080 MPa, -0.078 MPa, -0.076 MPa, -0.074 MPa, -0.072 MPa, -0.070 MPa, -0.068 MPa, -0.066 MPa, -0.064 MPa, -0.062 MPa or -0.060 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] As a preferred technical solution of the present invention, in S2, the preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are added to a mixed solvent for dispersion, wherein the volume ratio of ethanol to deionized water in the mixed solvent is (90-95):(10-5), the mass-volume ratio of hollow glass microspheres to the mixed solvent is (5-10)g:100mL, KH-570 coupling agent is added, the amount of which is 1-3% of the mass of hollow glass microspheres, and the pH is adjusted to 4-5 with glacial acetic acid. The mixture is stirred for 30-60min, filtered, washed, and dried to obtain surface-modified microspheres.

[0022] As a preferred technical solution of the present invention, in step S2, the pre-soaking time is 10-20 min, for example, it can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the mass ratio of styrene to divinylbenzene in the mixture is (5-8):1, for example, it can be 5.0:1, 5.3:1, 5.6:1, 5.9:1, 6.2:1, 6.5:1, 6.8:1, 7.1:1, 7.4:1, 7.7:1 or 8.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] In some optional embodiments, the mass ratio of the mixture to the surface-modified microspheres is (15-30):100, for example, it can be 15.0:100, 16.5:100, 18.0:100, 19.5:100, 21.0:100, 22.5:100, 24.0:100, 25.5:100, 27.0:100, 28.5:100 or 30.0:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the amount of benzoyl peroxide added is 0.5-1.5% of the mass of the mixture, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] In some alternative embodiments, the temperature of the stirring reaction is 75-85°C, for example, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C or 85°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the stirring reaction time is 6-10 h, for example, it can be 6.0 h, 6.4 h, 6.8 h, 7.2 h, 7.6 h, 8.0 h, 8.4 h, 8.8 h, 9.2 h, 9.6 h or 10.0 h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] The main components of the modified liquid are polyvinyl alcohol and xanthan gum.

[0029] In some optional embodiments, the mass fraction of polyvinyl alcohol in the modified liquid is 0.5-2 wt.%, for example, it can be 0.50 wt.%, 0.65 wt.%, 0.80 wt.%, 0.95 wt.%, 1.10 wt.%, 1.25 wt.%, 1.40 wt.%, 1.55 wt.%, 1.70 wt.%, 1.85 wt.%, or 2.00 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the xanthan gum content in the modified solution is 0.05-0.3 wt.%, for example, it can be 0.050 wt.%, 0.075 wt.%, 0.100 wt.%, 0.125 wt.%, 0.150 wt.%, 0.175 wt.%, 0.200 wt.%, 0.225 wt.%, 0.250 wt.%, 0.275 wt.%, or 0.300 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the mass-to-volume ratio of the impregnated microbeads to the modified liquid is 1g:(3-5)mL, for example, it can be 1g:3.0mL, 1g:3.2mL, 1g:3.4mL, 1g:3.6mL, 1g:3.8mL, 1g:4.0mL, 1g:4.2mL, 1g:4.4mL, 1g:4.6mL, 1g:4.8mL or 1g:5.0mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the mixing speed after adding PP-g-MAH is 500-800 rpm, for example, 500 rpm, 530 rpm, 560 rpm, 590 rpm, 620 rpm, 650 rpm, 680 rpm, 710 rpm, 740 rpm, 770 rpm or 800 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the mixing time after adding PP-g-MAH is 3-5 min, for example, it can be 3.0 min, 3.2 min, 3.4 min, 3.6 min, 3.8 min, 4.0 min, 4.2 min, 4.4 min, 4.6 min, 4.8 min or 5.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the mixing speed after adding the nucleating agent WBG-II is 1000-1500 rpm, for example, it can be 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm, 1250 rpm, 1300 rpm, 1350 rpm, 1400 rpm, 1450 rpm or 1500 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In some optional embodiments, the mixing time after adding the nucleating agent WBG-II is 2-4 min, for example, it can be 2.0 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min, 3.0 min, 3.2 min, 3.4 min, 3.6 min, 3.8 min or 4.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the mass ratio of PP-g-MAH to hard-shell microspheres is (0.5-1.5):100, for example, it can be 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1.0:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100 or 1.5:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the mass ratio of the nucleating agent WBG-II to the hard-shell microspheres is (0.2-0.8):100, for example, it can be 0.20:100, 0.26:100, 0.32:100, 0.38:100, 0.44:100, 0.50:100, 0.56:100, 0.62:100, 0.68:100, 0.74:100 or 0.80:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0038] As a preferred embodiment of the present invention, in S3, the mass ratio of the highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate is (70-80):(10-20):(0.2-0.5):(0.05-0.2), for example, it can be (70, 71, 72, 73, 74, 75, 76, 77, 78, 79 or 80):(10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20):(0.20, 0.23, 0.26, 0.29, 0.32, 0.35, 0.38, 0.41, 0.44, 0.47 or 0.50):(0.050, 0.065, 0.080, 0.095, 0.110, 0.125, 0.140, 0.155, 0.170, 0.185 or 0.200), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0039] In some optional embodiments, the mass ratio of the highly crystalline polypropylene to the gradient interface hollow glass microspheres is (70-80):(5-10), for example, it can be (70, 71, 72, 73, 74, 75, 76, 77, 78, 79 or 80):(5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or 10.0), but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] In some optional embodiments, the temperature of the main feed zone of the twin-screw extruder is 190-210°C, for example, it can be 190°C, 192°C, 194°C, 196°C, 198°C, 200°C, 202°C, 204°C, 206°C, 208°C or 210°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] In some optional embodiments, the side feed zone temperature of the twin-screw extruder is 180-200°C, for example, it can be 180°C, 182°C, 184°C, 186°C, 188°C, 190°C, 192°C, 194°C, 196°C, 198°C or 200°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] Secondly, this application provides a high-flow, high-gloss modified PP material prepared by the aforementioned preparation method.

[0043] Thirdly, this application provides a thin-walled car bumper, which is prepared using the high-flow, high-gloss modified PP material: the high-flow, high-gloss modified PP material is dried by blowing air and then added to the hopper of an injection molding machine for injection molding. After holding pressure and cooling demolding, the thin-walled car bumper is obtained.

[0044] As a preferred technical solution of the present invention, the temperature for drying the high-flow, high-gloss modified PP material by blower is 80-90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] In some optional embodiments, the high-flow, high-gloss modified PP material is dried by air for 2-4 hours, for example, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, 3.2h, 3.4h, 3.6h, 3.8h, or 4.0h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0046] In some optional embodiments, the barrel temperature for injection molding is 200-230°C, for example, 200°C, 203°C, 206°C, 209°C, 212°C, 215°C, 218°C, 221°C, 224°C, 227°C or 230°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] In some alternative embodiments, the mold temperature for injection molding is 70-90°C, for example, it can be 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C or 90°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0048] In some optional embodiments, the injection pressure of the injection molding is 60-90 MPa, for example, it can be 60 MPa, 63 MPa, 66 MPa, 69 MPa, 72 MPa, 75 MPa, 78 MPa, 81 MPa, 84 MPa, 87 MPa or 90 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some optional embodiments, the injection speed of the injection molding is 50-80 mm / s, for example, it can be 50 mm / s, 53 mm / s, 56 mm / s, 59 mm / s, 62 mm / s, 65 mm / s, 68 mm / s, 71 mm / s, 74 mm / s, 77 mm / s or 80 mm / s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0050] In some alternative embodiments, the back pressure of the injection molding is 0.3-0.8 MPa, for example, it can be 0.30 MPa, 0.35 MPa, 0.40 MPa, 0.45 MPa, 0.50 MPa, 0.55 MPa, 0.60 MPa, 0.65 MPa, 0.70 MPa, 0.75 MPa or 0.80 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0051] In some alternative embodiments, the screw speed for injection molding is 40-70 rpm, for example, 40 rpm, 43 rpm, 46 rpm, 49 rpm, 52 rpm, 55 rpm, 58 rpm, 61 rpm, 64 rpm, 67 rpm or 70 rpm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In some optional embodiments, the holding time of the injection molding is 10-20s, for example, it can be 10s, 11s, 12s, 13s, 14s, 15s, 16s, 17s, 18s, 19s or 20s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0053] In some alternative embodiments, the wall thickness of the thin-walled car bumper is 1.8-2.0 mm, for example, it can be 1.80 mm, 1.82 mm, 1.84 mm, 1.86 mm, 1.88 mm, 1.90 mm, 1.92 mm, 1.94 mm, 1.96 mm, 1.98 mm or 2.00 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0054] In existing "high melt index PP + POE + talc" systems, improving mold filling is often achieved by increasing the melt index of PP or increasing the POE content. However, the former is prone to weakening strength and toughness due to a decrease in molecular weight, while the latter leads to increased system viscosity and mold filling pressure due to the high viscosity of the rubber phase, and is more prone to appearance defects such as flow marks and pitting. This application prepares a dynamic exchange network masterbatch through reactive extrusion, transforming the rubber phase from a high-viscosity elastomer of simple physical blending into an adjustable network elastomer that can rapidly relax stress in the processing temperature range and maintain network locking in the service temperature range. The ring-opening reaction between dodecenyl succinic anhydride and POE-g-GMA epoxy groups introduces ester bonds and hydroxyl groups into the rubber phase and forms a network structure with a certain gel content. Stearic acid, as a monofunctional regulator, end-capsulates some active sites, limiting the degree of crosslinking and preventing the network from becoming too tight. Zinc acetylacetonate promotes the ester bond-related exchange process in the processing temperature range, making the network exhibit more obvious shear thinning and a decrease in apparent viscosity under high-temperature shear, thereby improving mold filling flowability without significantly increasing the amount of rubber. Zinc stearate, as a co-catalyst and lubricant / interphase stationary component, can reduce catalyst migration and improve processing stability to some extent. Mid-stage vacuum venting is used to remove low-molecular-weight volatiles (such as residual anhydrides, low-boiling-point substances, or byproduct volatiles), thereby reducing odor and bubble risks and helping to stabilize the network state between batches. Through the above reaction process, a dynamic exchange network masterbatch with a certain gel content can be obtained, allowing it to function as a "pre-formed structure" during subsequent blending and injection molding, rather than relying on in-situ reactions during the injection molding stage.

[0055] In existing technologies, talc powder leads to increased weight and a decrease in toughness due to increased rigidity. This application does not rely on a rigid framework of highly filled minerals, but instead establishes support through a combination of a lightweight framework and crystallization control. The gradient interface hollow glass microspheres prepared in this application address the challenges of easy breakage under high shear fields and a sharp decrease in impact due to interface debonding by using a hard shell coating and post-treatment adhesion process: First, the surface of the microspheres is silanized using KH-570 to provide anchoring for the subsequent adhesion of the organic shell layer; then, vacuum pre-wetting is used to preferentially enrich styrene / divinylbenzene monomers on the surface of the microspheres, forming a cross-linked polystyrene hard shell in aqueous suspension polymerization, which acts as a pressure-resistant buffer layer, reducing the probability of breakage of the microspheres under extrusion and injection molding pressure, and ensuring that its lightweight contribution is not lost due to breakage. Subsequently, a small amount of PP-g-MAH is used to form a compatible adhesive layer on the outer layer of the microspheres, making the polypropylene segments compatible with the PP matrix. The polar groups enhance the adhesion of the shell and inorganic surface, thereby strengthening the interfacial bonding between the microspheres and the matrix and reducing the probability of debonding voids and crack initiation. On this basis, post-treatment is used to preferentially distribute the nucleating agent near the outer surface of the microspheres, and it is physically fixed under the action of the adhesive layer. This makes it easier for the nucleating agent to be in the interfacial region in contact with the PP melt and play a nucleating role during melt blending and cooling crystallization, avoiding the "one-pot coating" that would cause the nucleating agent to be completely buried and its efficiency to decrease. This crystallization regulation tends to refine the grains and promote the formation of crystal morphologies that are more conducive to energy dissipation, thereby maintaining impact toughness while providing lightweight skeletal support, achieving a relative balance between weight reduction and strength, rather than exchanging modulus for high-density mineral fillers.

[0056] In the melt blending process, this application reduces the failure risk of hollow microspheres in application through a process pathway. Gradient interface microspheres are added via side feeding, combined with a lower temperature and weak shear conveying in the side feeding zone, reducing the peak shear and compression experienced by the microspheres in the screw's strong kneading section, thus reducing breakage during the process. Simultaneously, the pre-formed dynamic exchange network masterbatch in the resin matrix exhibits shear thinning and accelerated stress relaxation in the processing temperature range, making the overall melt flow more easily under the high shear conditions required for thin-walled molding, reducing the dependence on simply increasing the PP melt index or significantly increasing the POE content, thereby reducing flow marks, pitting, and appearance defects caused by high rubber content. A compounded antioxidant is used to inhibit thermo-oxidative degradation under repeated high-temperature melting and metal catalytic environments, while calcium stearate acts as an acid scavenger to reduce the impact of residual acidic substances on processing stability and odor. Together, they improve the stability of the processing window, indirectly reducing appearance fluctuations caused by viscosity drift.

[0057] During the injection molding stage, the aforementioned pre-fabricated network and gradient microsphere structure exhibit synergistic and complementary effects in both processing and service states. During processing, the dynamic exchange network undergoes topological rearrangement and stress relaxation under catalysis, preventing the rubber phase from significantly increasing melt viscosity as in traditional high-molecular-weight POE. Instead, it tends to reduce apparent viscosity under high shear, thereby improving thin-walled mold filling capacity and reducing flow front instability and surface defects caused by high viscosity. Simultaneously, by controlling injection speed, back pressure, and screw speed, the probability of secondary breakage of microspheres during plasticization and mold filling is reduced, avoiding density rebound or increased interface defects due to breakage. After cooling, the network exchange rate decreases, and the rubber phase maintains a high energy dissipation capacity. Combined with the lightweight support provided by the microsphere hard shell and the optimized crystal morphology resulting from nucleation refinement, this helps to simultaneously maintain the dimensional stability, impact resistance, and appearance consistency of the thin-walled structure, achieving a relative balance between the goals of "high flow, high rigidity and toughness, and lightweight" within the same system.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] Traditional "high melt flow index PP + POE + talc" formulations improve thin-walled molding by increasing the melt flow index or adding POE, but this easily sacrifices strength and toughness and leads to increased viscosity and appearance defects. This application utilizes reactive extrusion to pre-form a dynamic exchange network masterbatch: anhydride-epoxy ring-opening forms a network structure, stearic acid end-capping controls the degree of crosslinking, and Zn catalysis promotes high-temperature exchange to reduce shear thinning and viscosity. Vacuum degassing removes volatiles, thereby achieving stable high flow with less rubber load and avoiding the uncertainties of in-situ reactions during injection molding.

[0060] This application uses gradient interface hollow glass microspheres and crystallization regulation to replace highly filled talc: first, silanize the microspheres to facilitate anchoring, then vacuum pre-impregnate and suspend polymerize to form a cross-linked hard shell to resist pressure and prevent breakage; a small amount of PP-g-MAH on the outer layer compatibilizes and strengthens the interface, reducing debonding and cracking; and a nucleating agent is fixed on the surface to maintain nucleation efficiency, refine grains, and promote crystal morphology that is conducive to energy dissipation. Thus, while providing lightweight support, impact toughness is maintained as much as possible, achieving a balance between weight reduction and strength.

[0061] This application reduces the risk of hollow microspheres breaking due to peak shear and compression during the melt blending stage through a process pathway. Simultaneously, it utilizes the shear thinning and rapid stress relaxation of pre-fabricated dynamic exchange network masterbatch to improve melt flowability, reducing reliance on increasing the PP melt index or POE dosage, thereby reducing appearance defects such as flow marks and pitting. The compounded antioxidant and calcium stearate respectively inhibit thermo-oxidative degradation and capture residual acidic substances, stabilizing the processing window and reducing appearance fluctuations caused by viscosity drift.

[0062] During injection molding, the dynamic exchange network undergoes stress relaxation and topological rearrangement under catalysis. The rubber phase becomes shear-thinned, reducing apparent viscosity and thus improving thin-walled mold filling while reducing flow instability and surface defects. Simultaneously, process parameter control minimizes secondary breakage of microspheres, preventing density rebound and interface defects. After cooling, the network exchange rate decreases, and the rubber phase provides energy dissipation. Combined with the lightweight support of the microsphere hard shell and optimized crystallization through nucleation refinement, this achieves a comprehensive balance of high flowability, high rigidity / toughness, and lightweight design, while maintaining dimensional stability, impact resistance, and consistent appearance. Attached Figure Description

[0063] Figure 1 This is a physical image of the thin-walled car bumper prepared according to Example 1 of this application. Detailed Implementation

[0064] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include any obvious substitutions and modifications made to the embodiments described herein.

[0065] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0066] POE-g-GMA: Lotader AX8840

[0067] PP-g-MAH: Honeywell AC 950

[0068] Example 1

[0069] This embodiment provides a high-flow, high-gloss modified PP material and its preparation method. The preparation method of the high-flow, high-gloss modified PP material specifically includes the following steps:

[0070] S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA to obtain a first mixture, wherein the molar ratio of the anhydride group in dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is 1.1:1, and the molar ratio of the carboxyl group in stearic acid to the epoxy group in POE-g-GMA is 0.25:1. Zinc acetylacetone, zinc stearate, and a compound antioxidant are added to obtain a second mixture, wherein the effective zinc content of zinc acetylacetone is 2000 ppm of POE-g-GMA, and the mass ratio of zinc stearate to POE-g-GMA is... The mass ratio of the compound antioxidant to POE-g-GMA is 0.4:100. The compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 at a mass ratio of 1:1.5. The second mixture is added to a twin-screw extruder for reactive extrusion. The front section temperature of the twin-screw extruder is 185℃, the middle and rear section temperature is 210℃, the screw speed is 350rpm, and the vacuum degree of the middle section vacuum exhaust is -0.075MPa. After water cooling and pelletizing, the dynamic exchange network masterbatch is obtained.

[0071] S2: Surface-modified microspheres were placed in a vacuum mixer, and a mixture and benzoyl peroxide were sprayed in. The mixture was then pre-impregnated under negative pressure for 18 minutes to obtain impregnated microspheres. The mass ratio of styrene to divinylbenzene in the mixture was 7:1, and the mass ratio of the mixture to the surface-modified microspheres was 25:100. The amount of benzoyl peroxide added was 1.2% of the mass of the mixture. The impregnated microspheres were dispersed in a modification solution and stirred at 82℃ for 9 hours. The main components of the modification solution were polyvinyl alcohol and xanthan gum. The mass fraction of polyvinyl alcohol in the modification solution was 1.5 wt.%, and the mass fraction of xanthan gum was... The mass fraction of the modified liquid was 0.2 wt.%, and the mass-volume ratio of the microspheres to the modified liquid after impregnation was 1 g: 4.5 mL. After sieving, washing, and drying, hard-shell microspheres were obtained. The hard-shell microspheres were placed in a high-speed mixer, and PP-g-MAH was added and mixed at 700 rpm for 4 min. Then, nucleating agent WBG-II was added and mixed at 1400 rpm for 3.5 min to obtain gradient interface hollow glass microspheres. The mass ratio of PP-g-MAH to hard-shell microspheres was 1.2:100, and the mass ratio of nucleating agent WBG-II to hard-shell microspheres was 0.6:100.

[0072] S3: A resin matrix premix is ​​prepared by mixing highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate. The premix is ​​fed into the main feed port of a twin-screw extruder. The mass ratio of highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate is 78:18:0.4:0.15. Gradient interface hollow glass microspheres are added from the side feed port. The mass ratio of highly crystalline polypropylene to gradient interface hollow glass microspheres is 75:8. The mixture is melt-blended. The temperature of the main feed zone is 205℃, and the temperature of the side feed zone is 195℃. The mixture is then extruded and granulated to obtain a high-flow, high-gloss modified PP material.

[0073] The preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are dispersed in a mixed solvent, wherein the volume ratio of ethanol to deionized water in the mixed solvent is 90:10, the mass-volume ratio of hollow glass microspheres to mixed solvent is 8g:100mL, KH-570 coupling agent is added, the amount of which is 2% of the mass of hollow glass microspheres, and the pH is adjusted to 5 with glacial acetic acid. The mixture is stirred and reacted for 30min, filtered, washed, and dried to obtain surface-modified microspheres.

[0074] This embodiment also provides a thin-walled automotive bumper and its manufacturing method. The manufacturing method of the thin-walled automotive bumper is as follows:

[0075] After drying the high-flow, high-gloss modified PP material at 88℃ for 3.5 hours, it was added to the hopper of an injection molding machine. Injection molding was carried out under the following process conditions: barrel temperature 220℃, mold temperature 85℃, injection pressure 80MPa, injection speed 70mm / s, back pressure 0.7MPa, and screw speed 60rpm. After holding the pressure for 18s, the material was cooled and demolded to obtain a wall thickness of 1.95mm.

[0076] Example 2

[0077] This embodiment provides a high-flow, high-gloss modified PP material and its preparation method. The preparation method of the high-flow, high-gloss modified PP material specifically includes the following steps:

[0078] S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA to obtain a first mixture, wherein the molar ratio of the anhydride group in dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is 0.8:1, and the molar ratio of the carboxyl group in stearic acid to the epoxy group in POE-g-GMA is 0.1:1. Zinc acetylacetone, zinc stearate, and a compound antioxidant are added to obtain a second mixture, wherein the effective zinc content of zinc acetylacetone is 300 ppm of POE-g-GMA, and the mass ratio of zinc stearate to POE-g-GMA is... The ratio is 0.05:100, the mass ratio of compound antioxidant to POE-g-GMA is 0.2:100, and the compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 at a mass ratio of 1:1.8. The second mixture is added to a twin-screw extruder for reactive extrusion, wherein the front section temperature of the twin-screw extruder is 170℃, the middle and rear section temperature of the twin-screw extruder is 190℃, the screw speed is 250rpm, the vacuum degree of the middle section vacuum exhaust is -0.06MPa, water-cooled pelletizing, and drying are used to obtain dynamic exchange network masterbatch;

[0079] S2: Surface-modified microspheres were placed in a vacuum mixer, and a mixture and benzoyl peroxide were sprayed in. The mixture was then pre-impregnated under negative pressure for 10 minutes to obtain impregnated microspheres. The mass ratio of styrene to divinylbenzene in the mixture was 5:1, and the mass ratio of the mixture to the surface-modified microspheres was 15:100. The amount of benzoyl peroxide added was 0.5% of the mass of the mixture. The impregnated microspheres were dispersed in a modification solution and stirred at 75°C for 6 hours. The main components of the modification solution were polyvinyl alcohol and xanthan gum. The mass fraction of polyvinyl alcohol in the modification solution was 0.5 wt.%, and xanthan gum was 0.5 wt.%. The raw rubber had a mass fraction of 0.05 wt.%, and the mass-to-volume ratio of the microspheres to the modified liquid after impregnation was 1 g: 3 mL. After sieving, washing, and drying, hard-shell microspheres were obtained. The hard-shell microspheres were placed in a high-speed mixer, and PP-g-MAH was added and mixed at 500 rpm for 3 min. Then, nucleating agent WBG-II was added and mixed at 1000 rpm for 2 min to obtain gradient interface hollow glass microspheres. The mass ratio of PP-g-MAH to hard-shell microspheres was 0.5:100, and the mass ratio of nucleating agent WBG-II to hard-shell microspheres was 0.2:100.

[0080] S3: High-crystallinity polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate are mixed to obtain a resin matrix premix, which is added from the main feed port of a twin-screw extruder. The mass ratio of high-crystallinity polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate is 70:10:0.2:0.05. Gradient interface hollow glass microspheres are added from the side feed port. The mass ratio of high-crystallinity polypropylene to gradient interface hollow glass microspheres is 80:5. The mixture is melt-blended. The temperature of the main feed zone is 190℃, and the temperature of the side feed zone is 180℃. The mixture is then extruded and granulated to obtain a high-flow, high-gloss modified PP material.

[0081] The preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are dispersed in a mixed solvent, wherein the volume ratio of ethanol to deionized water in the mixed solvent is 95:5, the mass-volume ratio of hollow glass microspheres to mixed solvent is 9g:100mL, KH-570 coupling agent is added, the amount of which is 3% of the mass of hollow glass microspheres, and the pH is adjusted to 4.5 with glacial acetic acid. The mixture is stirred and reacted for 40min, filtered, washed, and dried to obtain surface-modified microspheres.

[0082] This embodiment also provides a thin-walled automotive bumper and its manufacturing method. The manufacturing method of the thin-walled automotive bumper is as follows:

[0083] After drying the high-flow, high-gloss modified PP material at 80℃ for 2 hours, it was added to the hopper of an injection molding machine. Injection molding was carried out under the following process conditions: barrel temperature 200℃, mold temperature 70℃, injection pressure 60MPa, injection speed 50mm / s, back pressure 0.3MPa, and screw speed 40rpm. After holding the pressure for 10s, the material was cooled and demolded to obtain a wall thickness of 1.8mm.

[0084] Example 3

[0085] This embodiment provides a high-flow, high-gloss modified PP material and its preparation method. The preparation method of the high-flow, high-gloss modified PP material specifically includes the following steps:

[0086] S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA to obtain a first mixture, wherein the molar ratio of the anhydride group in dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is 1.0:1, and the molar ratio of the carboxyl group in stearic acid to the epoxy group in POE-g-GMA is 0.15:1. Zinc acetylacetone, zinc stearate, and a compound antioxidant are added to obtain a second mixture, wherein the effective zinc content of zinc acetylacetone is 1000 ppm of POE-g-GMA, and the molar ratio of zinc stearate to POE-g-GMA is... The mass ratio of the compound antioxidant to POE-g-GMA is 0.3:100. The compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 at a mass ratio of 1:2. The second mixture is added to a twin-screw extruder for reactive extrusion. The front section temperature of the twin-screw extruder is 175℃, the middle and rear section temperature is 200℃, the screw speed is 300rpm, the vacuum degree of the middle section vacuum exhaust is -0.07MPa, water-cooled pelletizing, and drying are used to obtain dynamic exchange network masterbatch.

[0087] S2: Surface-modified microspheres were placed in a vacuum mixer, and a mixture and benzoyl peroxide were sprayed in. The mixture was then pre-impregnated under negative pressure for 12 minutes to obtain impregnated microspheres. The mass ratio of styrene to divinylbenzene in the mixture was 6:1, and the mass ratio of the mixture to the surface-modified microspheres was 20:100. The amount of benzoyl peroxide added was 0.8% of the mass of the mixture. The impregnated microspheres were dispersed in a modification solution and stirred at 78°C for 7 hours. The main components of the modification solution were polyvinyl alcohol and xanthan gum. The mass fraction of polyvinyl alcohol in the modification solution was 1 wt.%, and the mass fraction of xanthan gum was... The mass fraction was 0.1 wt.%, and the mass-to-volume ratio of the microspheres to the modified liquid after impregnation was 1 g: 3.5 mL. After sieving, washing, and drying, hard-shell microspheres were obtained. The hard-shell microspheres were placed in a high-speed mixer, and PP-g-MAH was added and mixed at 600 rpm for 4.5 min. Then, nucleating agent WBG-II was added and mixed at 1100 rpm for 2.5 min to obtain gradient interface hollow glass microspheres. The mass ratio of PP-g-MAH to hard-shell microspheres was 0.8:100, and the mass ratio of nucleating agent WBG-II to hard-shell microspheres was 0.4:100.

[0088] S3: A resin matrix premix is ​​prepared by mixing highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate. The premix is ​​fed into the main feed port of a twin-screw extruder. The mass ratio of highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate is 72:12:0.3:0.1. Gradient interface hollow glass microspheres are added from the side feed port. The mass ratio of highly crystalline polypropylene to gradient interface hollow glass microspheres is 72:7. The mixture is melt-blended. The temperature of the main feed zone is 195℃, and the temperature of the side feed zone is 185℃. The mixture is then extruded and granulated to obtain a high-flow, high-gloss modified PP material.

[0089] The preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are dispersed in a mixed solvent, wherein the volume ratio of ethanol to deionized water in the mixed solvent is 93:7, the mass-volume ratio of hollow glass microspheres to mixed solvent is 5g:100mL, KH-570 coupling agent is added, the amount of which is 1% of the mass of hollow glass microspheres, and the pH is adjusted to 4 with glacial acetic acid. The mixture is stirred and reacted for 50min, filtered, washed, and dried to obtain surface-modified microspheres.

[0090] This embodiment also provides a thin-walled automotive bumper and its manufacturing method. The manufacturing method of the thin-walled automotive bumper is as follows:

[0091] After drying the high-flow, high-gloss modified PP material at 82℃ for 2.5 hours, it was added to the hopper of an injection molding machine. Injection molding was carried out under the following process conditions: barrel temperature 210℃, mold temperature 75℃, injection pressure 70MPa, injection speed 60mm / s, back pressure 0.5MPa, and screw speed 50rpm. After holding the pressure for 12s, the material was cooled and demolded to obtain a wall thickness of 1.85mm.

[0092] Example 4

[0093] This embodiment provides a high-flow, high-gloss modified PP material and its preparation method. The preparation method of the high-flow, high-gloss modified PP material specifically includes the following steps:

[0094] S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA to obtain a first mixture, wherein the molar ratio of the anhydride group in dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is 1.3:1, and the molar ratio of the carboxyl group in stearic acid to the epoxy group in POE-g-GMA is 0.3:1. Zinc acetylacetone, zinc stearate, and a compound antioxidant are added to obtain a second mixture, wherein the effective zinc content of zinc acetylacetone is 3000 ppm of POE-g-GMA, and the molar ratio of the carboxyl group in stearic acid to the epoxy group in POE-g-GMA is... The mass ratio of the compound antioxidant to POE-g-GMA is 0.5:100. The compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The second mixture is added to a twin-screw extruder for reactive extrusion. The front section temperature of the twin-screw extruder is 190℃, the middle and rear section temperature is 220℃, the screw speed is 400rpm, the vacuum degree of the middle section vacuum exhaust is -0.08MPa, water-cooled pelletizing, and drying are used to obtain dynamic exchange network masterbatch.

[0095] S2: Surface-modified microspheres were placed in a vacuum mixer, and a mixture and benzoyl peroxide were sprayed in. The mixture was then pre-impregnated under negative pressure for 20 minutes to obtain impregnated microspheres. The mass ratio of styrene to divinylbenzene in the mixture was 8:1, and the mass ratio of the mixture to the surface-modified microspheres was 30:100. The amount of benzoyl peroxide added was 1.5% of the mass of the mixture. The impregnated microspheres were dispersed in a modification solution and stirred at 85°C for 10 hours. The main components of the modification solution were polyvinyl alcohol and xanthan gum. The mass fraction of polyvinyl alcohol in the modification solution was 2 wt.%, and xanthan gum was 1 wt.%. The raw rubber had a mass fraction of 0.3 wt.%, and the mass-to-volume ratio of the microspheres to the modified liquid after impregnation was 1 g: 5 mL. After sieving, washing, and drying, hard-shell microspheres were obtained. The hard-shell microspheres were placed in a high-speed mixer, and PP-g-MAH was added and mixed at 800 rpm for 5 min. Then, nucleating agent WBG-II was added and mixed at 1500 rpm for 4 min to obtain gradient interface hollow glass microspheres. The mass ratio of PP-g-MAH to hard-shell microspheres was 1.5:100, and the mass ratio of nucleating agent WBG-II to hard-shell microspheres was 0.8:100.

[0096] S3: A resin matrix premix is ​​prepared by mixing highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate. The premix is ​​fed into the main feed port of a twin-screw extruder, where the mass ratio of highly crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate is 80:20:0.5:0.2. Gradient interface hollow glass microspheres are added from the side feed port, where the mass ratio of highly crystalline polypropylene to gradient interface hollow glass microspheres is 70:10. The mixture is melt-blended, with the temperature in the main feed zone being 210℃ and the temperature in the side feed zone being 200℃. The mixture is then extruded and granulated to obtain a high-flow, high-gloss modified PP material.

[0097] The preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are dispersed in a mixed solvent, wherein the volume ratio of ethanol to deionized water in the mixed solvent is 94:6, the mass-volume ratio of hollow glass microspheres to mixed solvent is 10g:100mL, KH-570 coupling agent is added, the amount of which is 2.3% of the mass of hollow glass microspheres, and the pH is adjusted to 4.7 with glacial acetic acid. The mixture is stirred and reacted for 60min, filtered, washed, and dried to obtain the surface-modified microspheres.

[0098] This embodiment also provides a thin-walled automotive bumper and its manufacturing method. The manufacturing method of the thin-walled automotive bumper is as follows:

[0099] After drying the high-flow, high-gloss modified PP material at 90℃ for 4 hours, it was added to the hopper of an injection molding machine. Injection molding was carried out under the following process conditions: barrel temperature 230℃, mold temperature 90℃, injection pressure 90MPa, injection speed 80mm / s, back pressure 0.8MPa, and screw speed 70rpm. After holding the pressure for 20s, the material was cooled and demolded to obtain a wall thickness of 2.0mm.

[0100] Comparative Example 1

[0101] This comparative example provides a high-flow, high-gloss modified PP material and a thin-walled automotive bumper. The difference from Example 1 is that S1 and S3 are omitted, and POE-g-GMA is used to replace the dynamic exchange network masterbatch. Other operating steps and process parameters are exactly the same as in Example 1.

[0102] Comparative Example 2

[0103] This comparative example provides a high-flow, high-gloss modified PP material and a thin-walled automotive bumper. The difference from Example 1 is that zinc acetylacetonate is not added in S1, while the other operating steps and process parameters are exactly the same as in Example 1.

[0104] Comparative Example 3

[0105] This comparative example provides a high-flow, high-gloss modified PP material and a thin-walled car bumper. The difference from Example 1 is that surface-modified microspheres are prepared in S2, and surface-modified microspheres are used to replace gradient interface hollow glass microspheres in S3. Other operation steps and process parameters are exactly the same as in Example 1.

[0106] Comparative Example 4

[0107] This comparative example provides a high-flow, high-gloss modified PP material and a thin-walled automotive bumper. The difference from Example 1 is that PP-g-MAH is not added in S2, while the other operating steps and process parameters are exactly the same as in Example 1.

[0108] Detection method:

[0109] The melt flow rate of high-flow, high-gloss modified PP materials was tested according to GB / T 3682.1-2018.

[0110] Samples were taken from specified locations of the prepared thin-walled automotive bumper to prepare specimens and the following tests were performed:

[0111] The tensile strength of the samples was tested according to GB / T 1040.2-2022;

[0112] The flexural strength of the samples was tested according to GB / T 9341-2008;

[0113] The impact strength of the test sample was determined according to GB / T 1843-2008;

[0114] The density of the test sample was determined according to GB / T 1033.1-2008.

[0115] The specular gloss of the outer surface of the sample was tested according to GB / T 8807-1988.

[0116] The test results are shown in Table 1.

[0117] Table 1 Performance test results of Examples 1-4 and Comparative Examples 1-4

[0118]

[0119] From the test results of Example 1 and Comparative Example 1 in Table 1, it can be seen that, omitting step S1, in S3, POE-g-GMA is used to replace the dynamic exchange network masterbatch. As the rubber phase degenerates from "exchangeable network + rapid stress relaxation" to a conventional physical blend elastomer, the shear thinning and viscosity reduction effects under high shear are insufficient, resulting in poor overall fluidity. The dispersion and interfacial stability of the rubber phase are not as good as the pre-made network system, which easily forms coarser soft phases / local defects, reducing load-bearing continuity and tensile strength. The thickening and unstable morphology of the soft phase will weaken the effectiveness of the bending load-bearing skeleton, resulting in a decrease in bending strength. The lack of a stable energy-dissipating structure brought about by network locking reduces the energy dissipation efficiency during crack propagation and reduces impact toughness. The lightweight filler system remains unchanged, and the density change is not significant. Unstable melt front and increased molding pressure are more likely to cause surface defects such as flow marks / pitting, and reduce mirror gloss.

[0120] As can be seen from the test results of Example 1 and Comparative Example 2 in Table 1, without the addition of zinc acetylacetonate in S1, the exchange / topology rearrangement ability of the dynamic network in the processing temperature zone is limited, the stress relaxation rate decreases, the shear thinning effect weakens, resulting in a decrease in melt mass flow rate; the poor processing fluidity and the increase of micro-defects weaken the material's load-bearing capacity, reducing tensile strength and flexural strength; at the same time, the rubber phase is difficult to achieve sufficient stress rearrangement and energy dissipation under impact load, resulting in a decrease in impact strength; due to the higher apparent viscosity and the less stable flow front, the surface is more prone to defects such as flow marks and pitting, and the specular gloss decreases.

[0121] As can be seen from the test results of Example 1 and Comparative Example 3 in Table 1, surface-modified microspheres can be prepared in S2. In S3, surface-modified microspheres are used to replace the gradient interface hollow glass microspheres. Without the pressure-resistant buffer of the cross-linked hard shell and the synergistic protection of the outer compatible / nucleation structure, the microspheres are more prone to breakage under high shear and high pressure during extrusion and injection molding, introducing fragments and interface defects, which increases the melt flow resistance and decreases the melt mass flow rate. The broken fragments and debonded voids act as stress concentration sources, and the interface transmission capacity is deteriorated, resulting in a decrease in tensile strength and flexural strength. Cracks are more likely to initiate and propagate rapidly from interface defects, resulting in a decrease in impact strength. After the hollow structure breaks, the lightweight contribution fails, and the density of the part increases. At the same time, the increase in fragments / agglomerations and surface defects leads to enhanced scattering and a decrease in specular gloss.

[0122] From the test results of Example 1 and Comparative Example 4 in Table 1, it can be seen that without the addition of PP-g-MAH in S2, the outer layer of the microspheres lacks a bonding bridge compatible with the PP matrix, resulting in poor dispersion stability and interfacial wetting. Local agglomeration and interfacial defects increase, leading to uneven melt flow, increased resistance, and a decrease in melt mass flow rate. Insufficient interfacial adhesion makes it difficult to effectively transfer loads, easily causing microsphere pull-out and interfacial voids, resulting in a decrease in tensile strength and flexural strength. Interfacial debonding weakens the synergistic effect, making cracks more likely to propagate along the interface and reducing impact strength. The hard-shell microspheres remain, and the density of the part does not change much. Due to the increased probability of surface defects and agglomeration caused by interfacial defects and agglomeration, the specular gloss decreases.

[0123] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a high-flow, high-gloss modified PP material, characterized in that, The preparation method includes: S1: Dodecenyl succinic anhydride and stearic acid are added to POE-g-GMA to obtain a first mixture. Zinc acetylacetone, zinc stearate and compound antioxidant are added to obtain a second mixture. The second mixture is added to a twin-screw extruder for reactive extrusion, water-cooled pelletizing and drying to obtain dynamic exchange network masterbatch. S2: The surface-modified microspheres are placed in a vacuum mixer, and the mixture and benzoyl peroxide are sprayed in and pre-wetted under negative pressure to obtain wetted microspheres. The wetted microspheres are dispersed in the modification liquid, stirred and reacted, sieved, washed and dried to obtain hard-shell microspheres. The hard-shell microspheres are placed in a high-speed mixer, PP-g-MAH is added and mixed, and then nucleating agent WBG-II is added and mixed to obtain gradient interface hollow glass microspheres. S3: High crystalline polypropylene, dynamic exchange network masterbatch, compound antioxidant, and calcium stearate are mixed in a mass ratio of (70-80):(10-20):(0.2-0.5):(0.05-0.2) to obtain a resin matrix premix. The premix is ​​added from the main feed port of a twin-screw extruder and gradient interface hollow glass microspheres are added from the side feed port. The mass ratio of high crystalline polypropylene to gradient interface hollow glass microspheres is (70-80):(5-10). The mixture is melt-blended and extruded and granulated to obtain a high-flow, high-gloss modified PP material. The preparation method of the surface-modified microspheres is as follows: hollow glass microspheres are dispersed in a mixed solvent, wherein the volume ratio of ethanol to deionized water in the mixed solvent is (90-95):(10-5), the mass-volume ratio of hollow glass microspheres to mixed solvent is (5-10) g:100 mL, KH-570 coupling agent is added, the amount of which is 1-3% of the mass of hollow glass microspheres, and the pH is adjusted to 4-5 with glacial acetic acid. The mixture is stirred and reacted for 30-60 min, filtered, washed, and dried to obtain surface-modified microspheres. The mass ratio of styrene to divinylbenzene in the mixture is (5-8):1; The main components of the modified liquid are polyvinyl alcohol and xanthan gum; The modified solution contains 0.5-2 wt.% polyvinyl alcohol. The mass fraction of xanthan gum in the modified solution is 0.05-0.3 wt.%.

2. The method for preparing a high-flow, high-gloss modified PP material according to claim 1, characterized in that, In S1: The molar ratio of the anhydride group in the dodecenyl succinic anhydride to the epoxy group in POE-g-GMA is (0.8-1.3):1; The molar ratio of the carboxyl group in the stearic acid to the epoxy group in POE-g-GMA is (0.1-0.3):1; The effective zinc content of the zinc acetylacetonate is 300-3000 ppm of POE-g-GMA.

3. The method for preparing a high-flow, high-gloss modified PP material according to claim 1, characterized in that, In S1: The mass ratio of zinc stearate to POE-g-GMA is (0.05-0.3):100; The compound antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168; The mass ratio of the compound antioxidant to POE-g-GMA is (0.2-0.5):

100.

4. The method for preparing a high-flow, high-gloss modified PP material according to claim 1, characterized in that, In S2: The mass ratio of the mixture to the surface-modified microspheres is (15-30):100; The amount of benzoyl peroxide added is 0.5-1.5% of the mass of the mixture; The mass-to-volume ratio of the impregnated microspheres to the modified liquid is 1 g:(3-5) mL; The mass ratio of PP-g-MAH to hard-shell microspheres is (0.5-1.5):100; The mass ratio of the nucleating agent WBG-II to the hard-shell microspheres is (0.2-0.8):

100.

5. A high-flow, high-gloss modified PP material prepared by the preparation method according to any one of claims 1-4.

6. A thin-walled car bumper, characterized in that, The high-flow, high-gloss modified PP material described in claim 5 is used to prepare a thin-walled car bumper. After the high-flow, high-gloss modified PP material is dried by blowing air, it is added to the hopper of an injection molding machine for injection molding. After holding pressure and cooling demolding, a thin-walled car bumper is obtained.

7. A thin-walled automotive bumper according to claim 6, characterized in that, The high-flow, high-gloss modified PP material is dried at a temperature of 80-90℃. The injection molding parameters are as follows: barrel temperature is 200-230℃; mold temperature is 70-90℃; injection pressure is 60-90MPa.

8. A thin-walled automotive bumper according to claim 6, characterized in that, The injection molding parameters are as follows: injection speed is 50-80 mm / s; back pressure is 0.3-0.8 MPa; screw speed is 40-70 rpm; and the wall thickness of the thin-walled car bumper is 1.8-2.0 mm.

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