Method for improving tiger wrinkle defect of polypropylene composite material injection molding product

Abstract

The invention discloses a method for improving tiger wrinkle defects of a polypropylene composite material injection molding product. The method comprises the following steps: firstly, melting and plasticizing a blended polypropylene composite material, and then applying a rotation and reciprocating oscillation composite shearing external field on a plasticized blend melt to carry out disentanglement treatment on the plasticized blend melt, the low-entanglement-degree polypropylene composite material is subjected to injection molding to obtain a workpiece with obviously improved tiger skin patterns on the surface. According to the method disclosed by the invention, a shearing external field compounded by rotation and reciprocating oscillation is applied to a blend melt to destroy an entanglement network of a molecular chain, so that not only is the molecular chain effectively disentangled, but also a low-entanglement state is retained in granules, the viscosity of the melt is greatly reduced during subsequent injection molding, and the flowability is remarkably enhanced; and the occurrence of unstable flow in the mold filling process is delayed, so that the tiger skin defect on the surface of a polypropylene composite material injection molding product can be greatly improved on the premise that the good mechanical property of the product can be maintained.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material processing methods, and particularly relates to a method for improving tiger stripe defects in polypropylene composite injection-molded products. Background Art

[0002] Polypropylene, as a thermoplastic, offers advantages such as low price, good mechanical properties, solvent resistance, excellent processing properties, and low processing costs. Composite materials primarily composed of polypropylene, inorganic fillers, and elastomers not only achieve improved impact strength, stiffness, and dimensional stability, but are also suitable for a variety of processing methods, particularly injection molding, which offers excellent dimensional accuracy and production efficiency. Furthermore, the application of these polypropylene composite materials in the automotive industry can meet the demand for lightweight vehicles, reducing the weight of automotive parts by approximately 40%. They are currently widely used in automotive interior and exterior trims such as bumpers, door panels, and pillars. Although these polypropylene composite materials meet lightweighting requirements, they are prone to developing alternating light and dark streaks on the surface of the injection molding process, especially when molding large, thin-walled parts. These streaks are commonly known as "tiger stripes."

[0003] Research has found that tiger stripes typically appear at the end of the injection molding process, perpendicular to the flow direction. They occur due to pressure loss and a thickening of the frozen layer during the polymer melt filling process, leading to unstable flow at the flow front. This causes the flow front to alternately contact the mold surface, resulting in a striped pattern of light and dark stripes. This defect can cause variations in the gloss and texture of the part's surface, seriously affecting the part's appearance. Furthermore, this defect is difficult to conceal with subsequent paint applications, severely impacting the part's appearance. Therefore, reducing or eliminating tiger stripes is crucial.

[0004] Existing methods for improving tiger stripes during injection molding include improving material fluidity, adjusting the injection molding process, and performing polymer structure design. Among them, although selecting small molecule high-flow polypropylene or rubber elastomer to improve the flow properties of polypropylene composites can achieve the effect of improving or removing tiger stripes, material fluidity and material properties are often not taken into account. For example, the method of adding small molecule polypropylene (melt index is 1800g / 10min) to eliminate tiger stripes disclosed in CN102964686A, but the resulting product strength and modulus are often reduced, and it is difficult to apply to large products with high impact requirements. By adjusting the injection molding process (including increasing mold temperature and melt temperature, etc.) to reduce the thickness of the frozen layer at the front of the melt and reduce flow resistance, although it helps to improve the stable flow of the melt to improve tiger stripes, this method has a limited adjustment range, such as CN103434102A. In addition, by adjusting the melt elasticity of the polymer, the intrinsic viscosity of the elastomer and the molecular weight distribution, the generation of tiger stripes can also be suppressed, but because these methods are all based on the structural design of the polymer, they far exceed the actual capabilities of most plastic processing companies. Therefore, without reducing the mechanical properties of injection-molded parts, improving or removing the tiger stripe defects produced on the appearance of product parts through simple and industrial-friendly methods will undoubtedly have important practical significance for the promotion and application of injection molding of polypropylene composite materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving tiger stripe defects of polypropylene composite injection-molded products while maintaining their mechanical properties in response to the problems existing in the prior art.

[0006] Through in-depth research into the causes of tiger stripe defects, the inventors discovered that melt viscosity is a crucial factor influencing the formation of tiger stripe defects. Further research revealed that entanglement of polymer chains is the primary cause of the significant increase in viscosity. Unlike chemical crosslinking, the entanglement network of polymer chains changes dynamically, thus making it possible to reduce viscosity by reducing the degree of entanglement. Therefore, to achieve the aforementioned objectives, the present invention employs a technical solution to disentangle polypropylene composite materials using a composite shear field, effectively improving the tiger stripe defects that occur on the surface of the finished product.

[0007] The technical solutions provided by the present invention are as follows:

[0008] A method for improving tiger stripe defects in polypropylene composite injection-molded products is characterized in that the method comprises first melting a blended polypropylene composite material, then applying a rotational and reciprocating oscillating composite shear field to the blend melt to perform a detangling treatment, thereby obtaining a polypropylene composite material with a low degree of entanglement. The specific process steps and conditions are as follows:

[0009] 1) Add the polypropylene composite material into a screw extruder according to the ratio, and perform melt blending, extrusion and granulation under conventional conditions. The extruder temperature is 10 to 50° C. above the melting point;

[0010] 2) drying the blended polypropylene composite material particles obtained by granulation, and then adding them to the plasticizing system of the disentanglement device for melt plasticization;

[0011] 3) allowing the melted plasticized polypropylene composite material to enter the disentanglement system of the disentanglement device, applying a rotational and reciprocating oscillation composite stress field at 10-30°C above the melting point for shear treatment for 3-10 minutes, and then the melt is extruded into filaments, granulated and dried;

[0012] 4) The detangled pellets are injection molded by an injection molding machine.

[0013] The polypropylene composite material in the above method is composed of the following components by weight: 50-80 parts of copolymerized polypropylene, 10-30 parts of polyolefin elastomer, 10-30 parts of inorganic filler, 0.2-0.3 parts of light stabilizer, 0.1-1 parts of antioxidant and 0.1-0.3 parts of lubricant.

[0014] The polypropylene in the above method is copolymerized polypropylene; the polyolefin elastomer is any one of ethylene-octene copolymer, ethylene-butene copolymer and EPDM rubber; the inorganic filler is any one of talc powder, calcium carbonate, mica powder and wollastonite with a particle size of 600-2000 mesh.

[0015] The light stabilizer, antioxidant, and lubricant described in the above method are all conventional, and their amounts can be adjusted according to actual needs. The light stabilizer is a hindered amine light stabilizer, specifically Tinuvin 770 or UV-5585. The antioxidant is a hindered phenol antioxidant, specifically Irganox 1010 or Irganox 1076, or a phosphite antioxidant, specifically Irganox 168. The lubricant is any of polyethylene, ester, stearic acid, and fatty acid metal salts.

[0016] The disentanglement device described in the above method is a "polymer melt disentanglement device" developed by the inventor in the early stage, with patent number 201911109102.6.

[0017] In the above method, a rotational and reciprocating oscillation composite stress field is applied for shearing, wherein the rotation speed of the rotational shearing is 10-60 rpm, the frequency of the reciprocating oscillation shearing is 2-5 Hz, and the amplitude is 10-30°. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1The following are photos of the polypropylene composite materials obtained in Example 1 and Comparative Examples 1-3 being injection molded under the same injection molding conditions; the glossiness of the injection-molded samples was measured using a gloss meter; among them, (a) corresponds to Comparative Example 1, (b) corresponds to Comparative Example 2, (c) corresponds to Comparative Example 3, and (d) corresponds to Example 1. Figure 2 This is a graph obtained by testing the surface gloss of the injection molded sample along the flow direction using a gloss meter. Figure 3 Graph showing the differences in induced distance, number of stripes, and average glossiness of the injection molded samples prepared in Comparative Examples 1-3 and Example 1 of the present invention. The measurement is recorded starting from the location of the tiger stripe defect on the surface of each injection molded sample ( Figure 2 ), the surface quality of the injection molded parts was evaluated by comparing the induced distance, number of stripes and average gloss difference. The results are shown in Figure 3 As shown. From the tiger stripe evaluation results, it can be seen that the induction distance of the untreated comparative example 1 is 130mm, the number of stripes is 12, and the average unit gloss difference is 1.05% / mm; the sample comparative example 3 treated with a single reciprocating oscillation shearing process is slightly better than the sample comparative example 2 treated with rotary shearing, but the improvement of the tiger stripes is not obvious. Not only is the position of the tiger stripes still relatively forward, but a large number of tiger stripes can still be clearly seen on the surface; but Example 1 with the same material ratio adopts a composite shearing mode treatment, and its induction distance can be extended to 235mm, an increase of 80.7% compared with comparative example 1. At the same time, the number of stripes gradually decreases to 5. Moreover, the average gloss difference is reduced from 1.05% / mm in comparative example 1 to 0.28% / mm in example 1, a decrease of 73.3% (see Table 2). In other words, the attached material can be clearly observed with the naked eye. Figure 1 In samples subjected to composite shear detangling, the appearance of tiger stripes was significantly delayed, the number of tiger stripes on the surface of the part was significantly reduced, and the difference in gloss between light and dark stripes was significantly reduced. This clearly demonstrates that reducing entanglement improves melt fluidity, helps reduce flow resistance, stabilizes fountain flow, and suppresses the occurrence of unstable flow, thereby improving the tiger stripe defect caused by flow marks.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The disentanglement method provided by the present invention can apply a shear field of rotation and reciprocating oscillation to the blend melt, thereby destroying the entanglement network of the molecular chains and effectively disentangling the molecular chains. Therefore, the fluidity of the polypropylene composite material can be significantly improved without adding other components, and the tiger stripe defect on the surface of the polypropylene composite injection-molded product is greatly improved.

[0021] 2. Compared with the existing methods for suppressing the generation of tiger stripe defects, the disentanglement method provided by the present invention can induce disentanglement of molecular chains by utilizing a shear external field in the melt state, thereby avoiding the shortcomings of the dilute solution method and the controlled synthesis method, and is more suitable for the large-scale preparation of disentangled polymers.

[0022] 3. Since the disentanglement method provided by the present invention adopts a composite shear external field for treatment, its disentanglement efficiency is higher than that of single rotational shear and reciprocating oscillation shear, and thus the polypropylene composite material can reach a lower degree of entanglement within the same treatment time.

[0023] 4. The polypropylene composite material treated by the disentanglement method provided by the present invention can not only make the melt viscosity lower and the fluidity stronger during the injection molding process, but also maintain stable fountain flow when the flow resistance decreases during the melt flow process, delaying the occurrence of unstable flow, thereby significantly improving the tiger stripe defect caused by unstable flow.

[0024] 5. Since the method provided by the present invention only physically disentangles the molecular chains in the polypropylene composite material, it does not destroy the chemical structure of the polymer molecular chain or reduce the molecular weight. Therefore, it can greatly improve the tiger skin defects on the surface of the polypropylene composite injection molded product while also enabling the product to maintain good mechanical properties. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to specific embodiments. It is necessary to point out that this embodiment can only be used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-mentioned contents of the present invention, but these non-essential improvements and adjustments still fall within the scope of protection of the present invention.

[0026] Example 1

[0027] 65 parts of copolymerized polypropylene, 25 parts of ethylene-octene copolymer, 10 parts of 2000 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1010 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 110 rpm.

[0028] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0029] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the system inlet to the die are: 180°C, 180°C, 180°C, 180°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 5 minutes, the rotational shear speed is 30 rpm, the reciprocating oscillation shear frequency is 3 Hz, and the amplitude is 30°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0030] Example 2

[0031] 70 parts of copolymerized polypropylene, 20 parts of ethylene-butene copolymer, 10 parts of 1000 mesh calcium carbonate, 0.2 parts of light stabilizer UV-5585, 0.5 parts of antioxidant Irganox1076 and 0.1 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 170°C, 190°C, 200°C, 200°C and 195°C, respectively, and the screw speed was 130 rpm.

[0032] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0033] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 170°C and 160°C in sequence. At the same time, a rotational and reciprocating oscillation composite shear stress field is used for shearing treatment for 7 minutes, the rotational shear speed is 30 rpm, the reciprocating oscillation shear frequency is 3 Hz, and the amplitude is 30°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0034] Example 3

[0035] 65 parts of copolymerized polypropylene, 20 parts of ethylene-octene copolymer, 15 parts of 600 mesh mica powder, 0.3 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1076 and 0.3 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 170°C, 190°C, 200°C, 210°C, 210°C and 205°C, respectively, and the screw speed was 100 rpm.

[0036] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 190°C.

[0037] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 190°C, 190°C, 190°C, 180°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 3 minutes. The rotational shearing speed is 45 rpm, the reciprocating oscillation shearing frequency is 3 Hz, and the amplitude is 30 degrees. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state. The material is injection molded by an injection molding machine.

[0038] Example 4

[0039] 60 parts of copolymerized polypropylene, 30 parts of EPDM rubber, 10 parts of 1200 mesh talc, 0.2 parts of light stabilizer Tinuvin 770, 0.8 parts of antioxidant Irganox 1076 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, and the screw speed was 90 rpm.

[0040] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 190°C.

[0041] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 190°C, 190°C, 190°C, 180°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 4 minutes. The rotational shearing speed is 45 rpm, the reciprocating oscillation shearing frequency is 2 Hz, and the amplitude is 20°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state. The material is injection molded by an injection molding machine.

[0042] Example 5

[0043] 80 parts of copolymerized polypropylene, 10 parts of ethylene-octene copolymer, 10 parts of 800 mesh wollastonite, 0.3 parts of light stabilizer Tinuvin 770, 0.5 parts of antioxidant Irganox 1010 and 0.1 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 170°C, 190°C, 200°C, 200°C and 190°C, respectively, and the screw speed was 130 rpm.

[0044] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0045] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 170°C and 160°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 10 minutes, the rotational shear speed is 30 rpm, the reciprocating oscillation shear frequency is 4 Hz, and the amplitude is 30°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0046] Example 6

[0047] 70 parts of copolymerized polypropylene, 10 parts of ethylene-octene copolymer, 20 parts of 1200 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.3 parts of antioxidant Irganox168 and 0.3 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 90 rpm.

[0048] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 190°C.

[0049] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the inlet to the die of the system are: 190°C, 190°C, 190°C, 190°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 5 minutes, the rotational shear speed is 60 rpm, the reciprocating oscillation shear frequency is 3 Hz, and the amplitude is 30 degrees. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0050] Example 7

[0051] 50 parts of copolymerized polypropylene, 20 parts of ethylene-octene copolymer, 30 parts of 1000 mesh talc, 0.2 parts of light stabilizer Tinuvin 770, 1 part of antioxidant Irganox 1010 and 0.3 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The extruder temperatures were: 170°C, 190°C, 200°C, 210°C, 210°C and 205°C, respectively, and the screw speed was 80 rpm.

[0052] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 200°C.

[0053] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 200°C, 200°C, 200°C, 190°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 3 minutes. The rotational shearing speed is 20 rpm, the reciprocating oscillation shearing frequency is 3 Hz, and the amplitude is 30 degrees. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state. The material is injection molded by an injection molding machine.

[0054] Example 8

[0055] 65 parts of copolymerized polypropylene, 25 parts of ethylene-butene copolymer, 10 parts of 600 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox168 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C, 200°C, and the screw speed was 100 rpm.

[0056] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0057] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the system inlet to the die are: 180°C, 180°C, 180°C, 180°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 5 minutes, the rotational shear speed is 60 rpm, the reciprocating oscillation shear frequency is 3 Hz, and the amplitude is 30 degrees. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0058] Example 9

[0059] 70 parts of copolymerized polypropylene, 20 parts of ethylene-octene copolymer, 10 parts of 1000 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1010 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 170°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 90 rpm.

[0060] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0061] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 180°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 5 minutes, the rotational shear speed is 30 rpm, the reciprocating oscillation shear frequency is 5 Hz, and the amplitude is 10°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0062] Example 10

[0063] 65 parts of copolymerized polypropylene, 20 parts of ethylene-octene copolymer, 15 parts of 1200 mesh talc, 0.2 parts of light stabilizer Tinuvin 770, 0.7 parts of antioxidant Irganox 1076 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 170°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 90 rpm.

[0064] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0065] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device, and the temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 170°C and 170°C in sequence. At the same time, a rotational and reciprocating oscillation composite stress field shearing treatment is adopted for 5 minutes, the rotational shear speed is 10 rpm, the reciprocating oscillation shear frequency is 3 Hz, and the amplitude is 20°. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain a polypropylene composite material in a low entanglement state; and the material is injection molded by an injection molding machine.

[0066] Comparative Example 1

[0067] 65 parts of copolymerized polypropylene, 25 parts of ethylene-octene copolymer, 10 parts of 2000 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1010 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 110 rpm.

[0068] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0069] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 180°C and 170°C in sequence. The inner shaft of the disentanglement system is stationary and the melt is not sheared. The polypropylene composite material is extruded from the disentanglement system in the form of filaments, granulated and dried to obtain the polypropylene composite material; and the material is injection molded by an injection molding machine.

[0070] Comparative Example 2

[0071] 65 parts of copolymerized polypropylene, 25 parts of ethylene-octene copolymer, 10 parts of 2000 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1010 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 110 rpm.

[0072] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0073] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 180°C and 170°C, respectively. At the same time, a rotary shear stress field is used for treatment for 5 minutes. The rotary shear speed is 30 rpm. After being extruded from the disentanglement system in the form of filaments, it is granulated and dried to obtain a polypropylene composite material in a low entanglement state. The material is injection molded by an injection molding machine.

[0074] Comparative Example 3

[0075] 65 parts of copolymerized polypropylene, 25 parts of ethylene-octene copolymer, 10 parts of 2000 mesh talc, 0.2 parts of light stabilizer UV-5585, 0.7 parts of antioxidant Irganox1010 and 0.2 parts of lubricant calcium stearate were fully mixed and added to a screw extruder for melt blending, extrusion and granulation. The temperatures of the extruder were: 160°C, 180°C, 200°C, 210°C, 210°C and 200°C, respectively, and the screw speed was 110 rpm.

[0076] The blended polypropylene composite material particles obtained by granulation are first dried and then added into the plasticizing system of the single-screw extruder of the disentanglement device for melt plasticization at a temperature of 180°C.

[0077] The molten plasticized polypropylene composite material is allowed to enter the disentanglement system of the disentanglement device. The temperatures from the inlet to the die of the system are: 180°C, 180°C, 180°C, 180°C and 170°C, respectively. At the same time, a reciprocating oscillating shear stress field is used for treatment for 5 minutes. The reciprocating oscillating shear frequency is 3Hz and the amplitude is 30°. After being extruded from the disentanglement system in the form of filaments, granulated and dried, a polypropylene composite material in a low entanglement state is obtained. The material is injection molded by an injection molding machine.

[0078] The present invention conducted the following relevant performance tests on the polypropylene composite materials obtained in the above examples and comparative examples:

[0079] 1. Melt index was determined according to ISO 1133-2011 Thermoplastics — Determination of melt mass-flow rate (MFR) and melt volume-flow rate (MVR) — Part 1. The test conditions were 230°C / 2.16 kg. The results are shown in Table 1.

[0080] 2. Mechanical properties The tensile strength was measured in accordance with ISO 527.2-2012, Test method for tensile properties of plastics, at a tensile rate of 50 mm / min. The notched impact strength was measured in accordance with ISO 180-2013, Test method for impact strength of plastics, using Type I specimens. The results are shown in Table 1.

[0081] 3. Tiger stripe test The tiger stripe test is performed by injection molding annular thin strips with a width of 25 mm, a thickness of 2.5 mm, and a flow of 350 mm. The results are shown in the attached figure and Table 2.

[0082] Table 1

[0083]

[0084] 1) As can be seen from the tensile strength and notched Izod impact strength results in Table 1, the disentanglement treatment has little effect on the mechanical properties of the polypropylene composite. After treatment using different shear modes, the mechanical properties of the examples and comparative examples with similar proportions are similar. 2) As can be seen from the melt index results, the disentanglement treatment reduces the viscosity of the composite and improves its fluidity. Compared with a single rotational or reciprocating oscillating shear mode, the combined shear mode has a better disentanglement effect, significantly reducing the degree of molecular chain entanglement within the same treatment time, i.e., the melt index of the composite increases significantly.

[0085] Table 2

[0086] Test items Induction distance Number of stripes Average unit gloss difference unit mm strip % / mm Example 1 235 5 0.28 Example 2 255 4 0.21 Example 3 230 5 0.31 Example 4 220 5 0.39 Example 5 295 2 0.13 Example 6 280 2 0.15 Example 7 215 5 0.42 Example 8 250 4 0.25 Example 9 255 4 0.23 Example 10 230 5 0.36 Comparative Example 1 130 12 1.05 Comparative Example 2 165 9 0.73 Comparative Example 3 175 8 0.61

[0087] Note: Induction distance refers to the distance between the location where the tiger skin defect first appears on the surface of the part and the gate; the number of tiger skin stripes is related to the induction distance. The shorter the induction distance, the earlier the tiger skin defect appears and the more tiger skin stripes there are on the part surface; the average unit gloss difference refers to the average value of the unit gloss difference between the light stripe and the dark stripe.

[0088] As can be seen from the accompanying figures and Table 2: 1) Under the same material ratio, the induced distance of the sample treated with the composite stress field shearing treatment was extended to 235 mm (Example 1), an increase of 80.7% compared to Comparative Example 1. At the same time, the number of streaks gradually decreased to 5. 2) The average gloss difference decreased from 1.05% / mm in Comparative Example 1 to 0.28% / mm in Example 1, a decrease of 73.3%. 3) The attached Figure 1 After shear disentanglement in the composite stress field, the appearance of tiger stripes is significantly delayed, the number of tiger stripes on the surface of the part is significantly reduced, and the difference in gloss between light and dark stripes is significantly reduced. This indicates that the reduction in molecular chain entanglement improves the fluidity of the melt, which helps reduce flow resistance, stabilize fountain flow, and inhibit the occurrence of unstable flow, thereby improving the tiger stripe defect caused by flow marks.

Claims

1. A method for improving tiger stripe defects in polypropylene composite injection molded products, characterized in that The method comprises first melting the blended polypropylene composite material, and then applying a rotational and reciprocating oscillation composite shear field to the blend melt to disentangle it, thereby obtaining a polypropylene composite material with a low degree of entanglement. The specific process steps and conditions are as follows: 1) Add the polypropylene composite material into a screw extruder according to the ratio, and perform melt blending, extrusion, and granulation under conventional conditions. The extruder temperature is 10-50°C above the melting point; 2) drying the blended polypropylene composite material particles obtained by granulation, and then adding them to the plasticizing system of the disentanglement device for melt plasticization; 3) allowing the melted plasticized polypropylene composite material to enter the disentanglement system of the disentanglement device, applying a rotational and reciprocating oscillation composite stress field for shear treatment for 3-10 minutes at 10-30°C above the melting point, and then extruding the melt into filaments, pelletizing and drying; 4) The detangled pellets are injection molded by an injection molding machine.

2. The method for improving tiger stripe defects of polypropylene composite injection molded products according to claim 1, characterized in that The polypropylene composite material in the method is composed of the following components by weight: 50-80 parts of copolymerized polypropylene, 10-30 parts of polyolefin elastomer, 10-30 parts of inorganic filler, 0.2-0.3 parts of light stabilizer, 0.1-1 parts of antioxidant and 0.1-0.3 parts of lubricant.

3. The method for improving tiger stripe defects of polypropylene composite injection molded products according to claim 2, characterized in that The polypropylene described in the method is copolymerized polypropylene.

4. The method for improving tiger stripe defects of polypropylene composite injection molded products according to claim 2, characterized in that The polyolefin elastomer in the method is any one of ethylene-octene copolymer, ethylene-butene copolymer and ethylene propylene diene monomer rubber.

5. The method for improving tiger stripe defects of polypropylene composite injection molded products according to claim 2, characterized in that The inorganic filler in the method is any one of talc powder, calcium carbonate, mica powder and wollastonite with a particle size of 600-2000 meshes.

6. The method for improving tiger stripe defects in a polypropylene composite injection molded product according to any one of claims 1 to 5, characterized in that In the method, the rotation speed of the rotational shearing is 10-60 rpm, the frequency of the reciprocating oscillating shearing is 2-5 Hz, and the amplitude is 10-30 degrees.

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