High-impact-resistance polypropylene-calcium carbonate composite tray material and preparation method thereof

Abstract

The invention discloses a high-impact-resistance polypropylene-calcium carbonate composite tray material and a preparation method thereof. The preparation method comprises the following steps: (1) fully unbundling chopped glass fibers, stearic acid and ethylene bis stearamide in a closed high-speed stirrer, adding polypropylene wax, heating, dispersing and fusing with the chopped fibers, discharging into a secondary closed cold pot, stirring at a low speed, cooling and solidifying to obtain granular pre-dispersed chopped glass fibers; and (2) uniformly mixing polypropylene, modified calcium carbonate, pre-dispersed chopped glass fibers, precipitated barium sulfate, ethylene propylene diene monomer, basic magnesium sulfate whiskers, polytetrafluoroethylene, an antioxidant 1010, an antioxidant 168 and a pigment, and carrying out mixing, extrusion and granulation through a reciprocating single-screw mixing extruder to obtain the composite tray material. Through pre-dispersion of the chopped glass fibers and granulation in the reciprocating type single-screw mixing extruder, the problem that the glass fibers are difficult to disperse at present is solved, the long fiber length is reserved, the impact resistance and the bending modulus of the material are remarkably improved, and the use requirement of the tray is met.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic modification, and particularly relates to a high-impact polypropylene-calcium carbonate composite pallet material and a preparation method thereof. Background Art

[0002] Plastic pallets are currently widely used in industrial conversion, logistics transportation, warehouse storage, distribution centers, intelligent sorting, freight stations, etc. According to the application scenarios of plastic pallets, they are required to have good strength, impact resistance, high modulus support, wear resistance, weather resistance and anti-aging properties. The pallet surface is not easy to adhere to oil stains, easy to clean, and can be reused.

[0003] Polypropylene (PP) has become a widely used material for plastic pallets due to its excellent performance. Compared with high-density polyethylene (HDPE), polypropylene (PP) has higher strength, higher rigidity, higher hardness, higher toughness, and better resistance to bending fatigue. Therefore, polypropylene (PP) pallets are gradually replacing HDPE pallets.

[0004] However, the shrinkage rate of pallets made of polypropylene is relatively large, the impact resistance is reduced at low temperatures, and warping and deformation are prone to occur after long-term load use. For this reason, the prior art blends calcium carbonate into polypropylene, which not only solves the problem of large shrinkage, but also improves the hardness, toughness and modulus of the material. Usually, when technicians try to add calcium carbonate to polypropylene to prepare pallet materials, when the amount of calcium carbonate added is in the range of 15-20%, the toughness and bending modulus of the blended polypropylene increase to a certain extent, but it is difficult to meet the impact resistance and high modulus requirements of the pallet under high load. When the content of calcium carbonate is further increased, when the amount of calcium carbonate added exceeds 20% and reaches 30%, the impact resistance, bending strength and bending modulus of the material decrease. Obviously, it is difficult to simultaneously meet high impact resistance and high modulus in polypropylene materials with a higher calcium carbonate blending amount, and the pallets used for production are prone to deformation or cracking when subjected to high load impact. Therefore, the prior art alone relies on increasing the amount of calcium carbonate and obviously cannot meet the needs of high-load pallet materials.

[0005] Calcium carbonate is a low-cost, stable-quality filler material that has a significant effect in reducing the cost of pallet materials. We hope to add more calcium carbonate to polypropylene to achieve the goal of reducing costs. How to ensure that the material has good impact resistance and resistance to deformation without being crushed or warped when a high amount of calcium carbonate is added has become a technical problem. Based on this background, we developed a high-impact polypropylene-calcium carbonate composite pallet material with the goal of ensuring the material's excellent impact resistance and high modulus when the calcium carbonate addition reaches 30%, so that the pallet does not deform or crack under high load, and is used to prepare high-quality plastic pallets with a longer service life. Summary of the invention

[0006] In view of the actual problem that the impact resistance, bending strength and bending modulus of the pallet material currently blended with polypropylene with a high calcium carbonate content are reduced, the present invention proposes a high-impact polypropylene-calcium carbonate composite pallet material. In particular, by pre-dispersing and introducing short chopped glass fibers, the impact resistance, bending strength and bending modulus of the material are greatly improved, ensuring that the pallet prepared by the material will not be crushed or deformed and warped when subjected to high load impact. A preparation method of the pallet material is further provided.

[0007] In order to achieve the above technical objectives, the present invention provides the following specific technical solutions.

[0008] A method for preparing a high-impact polypropylene-calcium carbonate composite pallet material, the technical characteristics of which are: the specific preparation method is as follows:

[0009] (1) According to the weight parts, 100 parts of chopped glass fibers, 3-5 parts of stearic acid, and 1-2 parts of ethylene bis stearamide are added to a first-level closed high-speed mixer and stirred at high speed for 5-10 minutes to fully debundle the chopped stripped fibers, and then 15-20 parts of polypropylene wax are added, heated and stirred at high speed to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot, stirred at low speed, cooled and solidified to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin for standby use;

[0010] (2) According to weight parts, 80-90 parts of polypropylene, 60-65 parts of modified calcium carbonate, 35-40 parts of pre-dispersed chopped glass fibers, 3-5 parts of precipitated barium sulfate, 3-5 parts of EPDM rubber, 2-3 parts of basic magnesium sulfate whiskers, 0.5-1 part of polytetrafluoroethylene, 0.2-0.3 parts of antioxidant 1010, 0.1-0.2 parts of antioxidant 168, and 0-3 parts of colorant are added into a high-speed mixer and mixed evenly, and then sent to a reciprocating single-screw compounding extruder for compounding and extrusion, and passed through a porous die, stretched, water-cooled, air-dried, and pelletized. The pelletizing length is adjusted to 8 mm to obtain a high-impact polypropylene-calcium carbonate composite pallet material.

[0011] Preferably, the chopped glass fibers in step (1) are alkali-free chopped glass fibers with a length of 5-6 mm, and the finished chopped glass fibers are fiber bundles composed of hundreds or thousands of single filaments, and more preferably, the single filament diameter is 5-13 μm. The fiber bundles are dispersed into single filaments under high-speed stirring by assisting stearic acid and ethylene bisstearamide to avoid fiber agglomeration and entanglement at the end.

[0012] Preferably, the first-stage closed high-speed mixer in step (1) is fully closed to prevent short fiber dust, and the material is transported from the storage bin through a pipeline, and the ingredients are automatically weighed and mixed; further preferably, the first-stage closed high-speed machine disperses at a high speed of 200-300rpm.

[0013] Preferably, cooling water is designed in the interlayer of the secondary closed cold pot in step (1) to cool the pre-dispersed chopped glass fibers into blocks, and gradually form particles under stirring. In this way, the generation of short fiber dust can be better prevented. Further preferably, the secondary closed cold pot is stirred at a low speed of 60-80 rpm.

[0014] Preferably, the melting point of the polypropylene wax in step (1) is 130-150° C. The heating temperature is controlled to melt the polypropylene wax and fuse it with the dispersed monofilaments, thereby facilitating redispersion and use later.

[0015] Preferably, the modified calcium carbonate in step (2) has a particle size of 3000-5000 mesh and is a modified ultrafine calcium carbonate pretreated with a compatibility aid. Further preferably, the modified calcium carbonate is obtained by surface modification treatment of heavy calcium carbonate with a particle size of 3000-5000 mesh and an aluminate coupling agent in a mass ratio of 100:0.8 by a jet mill.

[0016] Preferably, the polypropylene in step (2) is a compound of homopolymer polypropylene and copolymer polypropylene in a mass ratio of 3: 1. Homopolymer polypropylene has good rigidity and strength, maintaining the rigidity and modulus of the pallet, and copolymer polypropylene has good toughness.

[0017] Further preferably, the polypropylene in step (2) has a melt index of 5-10 g / 10 min. In the prior art, polypropylene with a high melt index is usually used to reduce the extrusion viscosity, achieve dispersion of glass fibers and reduce shearing, thereby reducing the length loss of glass fibers. However, polypropylene with a high melt index has low strength and weak bending resistance. The present invention can well disperse glass fibers in a low melt index polypropylene system by pre-dispersing chopped glass fibers.

[0018] Preferably, the particle size of the precipitated barium sulfate in step (2) is less than 10 um, which is used to improve the injection molding fluidity and surface wear resistance and hardness of the pallet.

[0019] Preferably, the polytetrafluoroethylene particle size in step (2) is less than 10 um, and has self-lubricating and self-cleaning properties, which helps to improve the wear resistance and scratch resistance of the tray and prevents the adhesion of oil, dirt and dust.

[0020] Preferably, the colorant in step (2) is added with color powder or masterbatch according to specific needs. Further preferably, for pallets with antistatic requirements, carbon black is added as the colorant; for blue pallets, high temperature resistant phthalocyanine blue is added.

[0021] Preferably, the reciprocating single-screw mixing extruder in step (2) preferably has a screw diameter of 70 mm and a length-to-diameter ratio of 20:1; the reciprocating single-screw mixing extruder can perform regular axial reciprocating motion while continuously rotating, thereby achieving dispersed mixing and distributed mixing of the materials under low pressure and low shearing, which not only enhances the mixing effect but also prevents the glass fiber from being shortened by excessive shearing.

[0022] Preferably, the operating temperature of the reciprocating single-screw compounding extruder in step (2) is set to: the temperature of zone 1 is 160-180°C, the temperature of zone 2 is 190-200°C, the temperature of zone 3 is 210-220°C, the temperature of zone 4 is 190-200°C, and the temperature of zone 5 is 170-180°C; a vacuum devolatilization port is designed in zone 4, and the vacuum pumping device can remove the gas and some volatile gases generated during the processing.

[0023] Furthermore, the present invention provides a high-impact polypropylene-calcium carbonate composite pallet material prepared by the above method. Traditionally, short-cut glass fibers are used to reinforce polypropylene, mainly by dispersing them under the shear of a co-rotating twin-screw extruder. However, in viscous thermoplastics, it is difficult to disperse the fiber bundles into single filaments, and most of them are aggregated bundles of multiple single filaments. In addition, the fibers are excessively sheared by the twin-screw extruder, resulting in the fiber length being cut short. The length of the fibers is mostly cut to less than 0.5 mm, which is extremely unfavorable for increasing the tensile strength, impact strength, and crack resistance of the material. In particular, when high calcium carbonate is filled in polypropylene, the high filling causes the shear force to increase, and the glass fibers are easily over-cut. Obviously, the prior art is difficult to achieve both shear dispersion of glass fibers and prevention of excessive fiber cutting. In view of the requirement that the pallet material has high bending strength, high modulus and bending deformation resistance, as well as impact crack resistance, the present invention disperses the chopped fibers into monofilaments in advance, fixes them with polypropylene wax to form dispersed chopped glass fiber particles, and uses a reciprocating single-screw mixing extruder to redisperse the glass fibers under low pressure and low shear, which not only enhances the mixing effect, but also prevents the glass fibers from being shortened by excessive shearing. The chopped glass fibers are evenly dispersed in polypropylene as longer monofilaments, which significantly improves the impact resistance and bending modulus of the material.

[0024] At present, the conventional glass fiber reinforced polypropylene is to add short glass fibers to polypropylene during twin-screw extrusion to improve the mechanical properties. The twin-screw extruder needs to be designed with multiple groups of strong shearing and fast meshing to disperse the short glass fibers, but the glass fibers are over-sheared and the reinforcing effect is limited. For example, in Comparative Example 1, when the amount of glass fibers is adjusted to nearly 32%, the tensile strength performance is the best, but the bending modulus and impact strength are low.

[0025] The present invention is significantly different from the prior art in that:

[0026] (1) By pre-dispersing the chopped fibers into monofilaments, and fixing them with polypropylene wax to form chopped glass fiber dispersed particles, it is easy to disperse them in polypropylene, avoiding the current problem of difficult dispersion of glass fibers, and retaining a longer fiber length.

[0027] (2) The present invention adopts a reciprocating single-screw mixing extruder to redisperse the glass fibers under low shearing action, thereby preventing the glass fibers from being shortened by excessive shearing, and significantly improving the impact resistance and bending modulus of the material.

[0028] (3) The present invention uses precipitated barium sulfate and polytetrafluoroethylene as auxiliary materials when adding a high amount of calcium carbonate to improve the injection molding fluidity of the pallet as well as the surface wear resistance, hardness and anti-fouling effect, thereby meeting the long-term use requirements of the pallet.

[0029] (4) The preparation process of the present invention is simple and easy to control, the raw material supply is stable, and it is suitable for large-scale production. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described in combination with the embodiments of the present invention. At the same time, the comparative example is a technical solution in the early stage of research and development. Obviously, the technical effect of the technical solution of the present invention is significantly improved compared with the technical effect of the comparative solution in the early stage of research and development. The described embodiments are part of the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0031] The first-level closed high-speed mixer and the second-level closed cold pot use the complete set of SRL300 / 600 equipment provided by Zhangjiagang Baixiong Kemei Machinery Co., Ltd.

[0032] Modified calcium carbonate is a pre-treated material: heavy calcium carbonate with a particle size of 3000 mesh and an aluminate coupling agent are subjected to surface modification treatment by a jet mill at a mass ratio of 100:0.8.

[0033] Example 1

[0034] (1) According to weight, 100 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um, 3 parts of Indonesian 1801 stearic acid, and 1 part of ethylene bisstearamide are transported from a storage bin through a pipeline, and the ingredients are automatically weighed and added to a first-level closed high-speed machine and stirred at a high speed of 200 rpm for 8 minutes to fully debundle the chopped stripped fibers, and then 15 parts of polypropylene wax are added to maintain the temperature of the first-level closed high-speed mixer at 150° C., and stirred at a speed of 200 rpm for 20 minutes to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot and stirred at a low speed of 60 rpm to cool and solidify to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin 3# for standby use;

[0035] (2) According to the weight, homopolymer polypropylene with a melt index of 5g / 10min and copolymer polypropylene were premixed in a mass ratio of 3:1 and placed in bin 1#, and 85 parts were weighed; modified calcium carbonate was placed in bin 2#, and 60 parts were weighed; 35 parts of pre-dispersed chopped glass fiber, 5 parts of precipitated barium sulfate with a particle size less than 10um, 3 parts of EPDM rubber, 2 parts of basic magnesium sulfate whisker, 1 part of polytetrafluoroethylene with a particle size less than 10um, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material were added to a high-speed mixer and mixed. The mixture was evenly mixed and then sent to a reciprocating single-screw compounding extruder with a diameter of 70 mm and an aspect ratio of 20:1 for compounding. The working temperatures were set as follows: 160°C for zone 1, 190°C for zone 2, 210°C for zone 3, 190°C for zone 4 and 170°C for zone 5. A vacuum devolatilization port was designed in zone 4, and the vacuum device could remove the gas and some volatile gases generated during the processing. After being subjected to a porous die, drawing, water cooling, air drying and pelletizing, the pelletizing length was adjusted to 8 mm to obtain a high-impact polypropylene-calcium carbonate composite pallet material.

[0036] Example 2

[0037] (1) According to weight, 100 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um, 4 parts of Indonesian 1801 stearic acid, and 1 part of ethylene bisstearamide are transported from a storage bin through a pipeline, and the ingredients are automatically weighed and added to a first-level closed high-speed machine and stirred at a high speed of 200 rpm for 10 minutes to fully debundle the chopped stripped fibers, and then 20 parts of polypropylene wax are added to maintain the temperature of the first-level closed high-speed mixer at 150° C., and stirred at a speed of 200 rpm for 20 minutes to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot and stirred at a low speed of 60 rpm to cool and solidify to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin 3# for standby use;

[0038] (2) According to the weight, homopolymer polypropylene with a melt index of 10g / 10min and copolymer polypropylene are premixed in a mass ratio of 3:1 and placed in bin 1#, and 90 parts are weighed; modified calcium carbonate is placed in bin 2#, and 65 parts are weighed; 40 parts of pre-dispersed chopped glass fiber, 3 parts of precipitated barium sulfate with a particle size less than 10um, 4 parts of EPDM rubber, 3 parts of basic magnesium sulfate whisker, 1 part of polytetrafluoroethylene with a particle size less than 10um, 0.2 parts of antioxidant 1010, 0.2 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material are added to the high-speed mixer After mixing evenly, the mixture is sent to a reciprocating single-screw compounding extruder with a diameter of 70 mm and a length-to-diameter ratio of 20:1 for compounding. The working temperatures are set as follows: 180°C for zone 1, 190°C for zone 2, 220°C for zone 3, 200°C for zone 4 and 180°C for zone 5. Vacuum devolatilization is designed in zone 4, and the vacuum device can remove the gas and some volatile gases generated during the processing. After being subjected to a porous die, drawing, water cooling, air drying and pelletizing, the pelletizing length is adjusted to 8 mm to obtain a high-impact polypropylene-calcium carbonate composite pallet material.

[0039] Example 3

[0040] (1) According to weight, 100 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um, 3 parts of Indonesian 1801 stearic acid, and 2 parts of ethylene bis stearamide are transported from a storage bin through a pipeline, and the ingredients are automatically weighed and added to a first-level closed high-speed machine and stirred at 300 rpm for 8 minutes to fully debundle the chopped stripped fibers, and then 18 parts of polypropylene wax are added to maintain the first-level closed high-speed mixer at 150° C. and stirred at 200 rpm for 20 minutes to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot and stirred at a low speed of 80 rpm for cooling and solidification to obtain granular pre-dispersed chopped glass fibers, which are discharged to a closed storage bin 3# for standby use;

[0041] (2) According to the weight, homopolymer polypropylene with a melt index of 5g / 10min and copolymer polypropylene are premixed in a mass ratio of 3:1 and placed in bin 1#, and 80 parts are weighed; modified calcium carbonate is placed in bin 2#, and 60 parts are weighed; 38 parts of pre-dispersed chopped glass fiber, 5 parts of precipitated barium sulfate with a particle size less than 10um, 5 parts of EPDM rubber, 2 parts of basic magnesium sulfate whisker, 0.5 parts of polytetrafluoroethylene with a particle size less than 10um, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material are added to a high-speed mixer. The mixture was mixed evenly and then sent to a reciprocating single-screw compounding extruder with a diameter of 70 mm and a length-to-diameter ratio of 20:1 for compounding. The working temperatures were set as follows: 160°C for zone 1, 190°C for zone 2, 210°C for zone 3, 190°C for zone 4 and 170°C for zone 5. A vacuum devolatilization port was designed in zone 4, and the vacuum device could remove the gas and some volatile gas generated during the processing. After being subjected to a porous die, drawing, water cooling, air drying and pelletizing, the pelletizing length was adjusted to 8 mm to obtain a high-impact polypropylene-calcium carbonate composite pallet material.

[0042] Comparative Example 1

[0043] (1) According to weight, 32 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 μm; homopolymer polypropylene with a melt index of 5 g / 10 min and copolymer polypropylene are premixed in a mass ratio of 3:1 and placed in a No. 1 bin, and 56 parts are weighed; 5 parts of precipitated barium sulfate with a particle size less than 10 μm, 3 parts of EPDM rubber, 2 parts of basic magnesium sulfate whiskers, 1 part of polytetrafluoroethylene with a particle size less than 10 μm, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material are added to a high-speed mixer and mixed evenly, and then sent to a 65-type co-rotating twin-screw extruder for extrusion, and passed through a porous die, stretched, water-cooled, air-dried, and pelletized, and the pelletizing length is adjusted to 8 mm to obtain a composite pallet material.

[0044] Comparative Example 2

[0045] According to the weight proportion, homopolymer polypropylene with a melt index of 5g / 10min and copolymer polypropylene were premixed in a mass ratio of 3:1 and placed in bin 1#, and 85 parts were weighed; modified calcium carbonate was placed in bin 2#, and 60 parts were weighed; 29.5 parts of chopped glass fiber, 5 parts of precipitated barium sulfate with a particle size less than 10um, 3 parts of EPDM rubber, 2 parts of basic magnesium sulfate whisker, 1 part of polytetrafluoroethylene with a particle size less than 10um, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue were added to the high-speed The materials are mixed evenly in a mixer and then sent to a reciprocating single-screw compounding extruder with a diameter of 70 mm and a length-to-diameter ratio of 20:1 for compounding. The working temperatures are set as follows: 160°C for zone 1, 190°C for zone 2, 210°C for zone 3, 190°C for zone 4 and 170°C for zone 5. A vacuum devolatilization port is designed in zone 4, and a vacuum pumping device can remove the gas and some volatile gases generated during the processing. After being subjected to a porous die, strip drawing, water cooling, air drying and pelletizing, the pelletizing length is adjusted to 8 mm to obtain a composite pallet material.

[0046] Comparative Example 3

[0047] (1) According to weight, 100 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um, 3 parts of Indonesian 1801 stearic acid, and 1 part of ethylene bisstearamide are transported from a storage bin through a pipeline, and the ingredients are automatically weighed and added to a first-level closed high-speed machine and stirred at a high speed of 200 rpm for 8 minutes to fully debundle the chopped stripped fibers, and then 15 parts of polypropylene wax are added to maintain the temperature of the first-level closed high-speed mixer at 150° C., and stirred at a speed of 200 rpm for 20 minutes to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot and stirred at a low speed of 60 rpm to cool and solidify to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin 3# for standby use;

[0048] (2) According to the weight proportion, homopolymer polypropylene with a melt index of 5 g / 10 min and copolymer polypropylene are premixed in a mass ratio of 3:1 and placed in bin 1#, and 85 parts are weighed; modified calcium carbonate is placed in bin 2#, and 60 parts are weighed; 35 parts of pre-dispersed chopped glass fiber, 5 parts of precipitated barium sulfate with a particle size less than 10 μm, 3 parts of EPDM rubber, 2 parts of basic magnesium sulfate whisker, 1 part of polytetrafluoroethylene with a particle size less than 10 μm, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material are added to a high-speed mixer and mixed evenly, and then sent to a 65-type co-rotating twin-screw extruder for extrusion, and passed through a porous die, a drawing strip, water cooling, air drying, and pelletizing, and the pelletizing length is adjusted to 8 mm to obtain a composite pallet material.

[0049] Comparative Example 4

[0050] (1) According to weight, 100 parts of chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um, 3 parts of Indonesian 1801 stearic acid, and 1 part of ethylene bisstearamide are transported from a storage bin through a pipeline, and the ingredients are automatically weighed and added to a first-level closed high-speed machine and stirred at a high speed of 200 rpm for 8 minutes to fully debundle the chopped stripped fibers, and then 15 parts of polypropylene wax are added to maintain the temperature of the first-level closed high-speed mixer at 150° C., and stirred at a speed of 200 rpm for 20 minutes to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot and stirred at a low speed of 60 rpm to cool and solidify to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin 3# for standby use;

[0051] (2) According to the weight, homopolymer polypropylene with a melt index of 5g / 10min and copolymer polypropylene were premixed in a mass ratio of 3:1 and placed in bin 1#, and 85 parts were weighed; modified calcium carbonate was placed in bin 2#, and 60 parts were weighed; 35 parts of pre-dispersed chopped glass fiber, 3 parts of EPDM rubber, 2 parts of basic magnesium sulfate whisker, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.03 parts of phthalocyanine blue material were added to a high-speed mixer and mixed evenly, and then sent to a 70mm diameter, aspect ratio The material is mixed by a 20:1 reciprocating single-screw compounding extruder, and the working temperatures are set as follows: the temperature of zone 1 is 160°C, the temperature of zone 2 is 190°C, the temperature of zone 3 is 210°C, the temperature of zone 4 is 190°C, and the temperature of zone 5 is 170°C; a vacuum devolatilization port is designed in zone 4, and the vacuum device can remove the gas and some volatile gases generated in the processing process; after a porous die, drawing, water cooling, air drying, pelletizing, and adjusting the pelletizing length to 8mm, a high-impact polypropylene-calcium carbonate composite pallet material is obtained.

[0052] Performance Testing:

[0053] 1. Mechanical properties test

[0054] The pallet materials of Examples 1-3 and Comparative Examples 1-4 were dried at 60°C for 2h and injection molded into standard specimens. The tensile strength was tested with reference to GB / T1040 (tensile rate was 50mm / min); the flexural strength and flexural modulus were tested with reference to GB / T 9341 (test speed was 2mm / min); the notched impact strength was tested with reference to GB / T 1843 (test condition was 2.75J); the test results are shown in Table 1.

[0055] Table 1:

[0056]

[0057]

[0058] Accordingly, in the present invention, in order to meet the requirements of the composite pallet for the material impact performance and high modulus, the pre-dispersed chopped glass fibers and reciprocating single screw mixing are used to better ensure the excellent impact resistance and bending deformation resistance of the material under high load. However, in Comparative Example 1, chopped glass fibers are directly used for dispersion modification in a twin-screw extruder, and the chopped fibers are cut short and have limited dispersibility, resulting in high cost and low mechanical properties of the obtained pallet material; the chopped glass fibers in Comparative Example 2 are not pre-dispersed, and the impact performance and modulus are greatly reduced; Comparative Example 3 does not use a compound single screw mixing extruder for mixing and extrusion, but uses a twin screw extruder for shearing and dispersion, and due to shear damage to the glass fibers, the mechanical properties are reduced to a certain extent.

[0059] 2. Wear resistance test

[0060] The friction coefficient and wear were tested with reference to ASTM D3702 "Standard Test Method for Friction and Wear Rate and Coefficient of Friction of Materials in Self-lubricating Contact Using a Thrust Washer Tester". Test conditions: pressure 100N, speed 0.5m / s, wear time 2h, and the wear parts were made of 45# steel. The test results are shown in Table 2.

[0061] Table 2:

[0062] Test indicators Friction coefficient / μ Wear amount (mg) Example 1 0.22 3.2 Example 2 0.25 3.5 Example 3 0.27 3.7 Comparative Example 1 0.38 4.5 Comparative Example 2 0.35 4.2 Comparative Example 3 0.33 4.2 Comparative Example 4 0.55 7.1

[0063] The invention maintains the friction coefficient of the material at a reasonable level by precipitating barium sulfate and polytetrafluoroethylene, and at the same time has better wear resistance through synergistic effect.

[0064] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material, characterized in that: include: (1) According to the weight parts, 100 parts of chopped glass fibers, 3-5 parts of stearic acid, and 1-2 parts of ethylene bis stearamide are added to a first-level closed high-speed mixer and stirred at high speed for 5-10 minutes to fully debundle the chopped stripped fibers, and then 15-20 parts of polypropylene wax are added, heated and stirred at high speed to fully disperse and fuse the chopped fibers and the polypropylene wax, and the materials are discharged to a second-level closed cold pot, stirred at low speed, cooled and solidified to obtain granular pre-dispersed chopped glass fibers, and the materials are discharged to a closed storage bin for standby use; (2) According to weight parts, 80-90 parts of polypropylene, 60-65 parts of modified calcium carbonate, 35-40 parts of pre-dispersed chopped glass fibers, 3-5 parts of precipitated barium sulfate, 3-5 parts of EPDM rubber, 2-3 parts of basic magnesium sulfate whiskers, 0.5-1 part of polytetrafluoroethylene, 0.2-0.3 parts of antioxidant 1010, 0.1-0.2 parts of antioxidant 168, and 0-3 parts of colorant are added into a high-speed mixer and mixed evenly, and then sent to a reciprocating single-screw compounding extruder for compounding and extrusion, and passed through a porous die, stretched, water-cooled, air-dried, and pelletized. The pelletizing length is adjusted to 8 mm to obtain a high-impact polypropylene-calcium carbonate composite pallet material.

2. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The chopped glass fibers in step (1) are alkali-free chopped glass fibers with a length of 5-6 mm and a single fiber diameter of 5-13 um.

3. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: In step (1), the first-level closed high-speed mixer disperses at a high speed of 200-300 rpm; and the second-level closed cold pot stirs at a low speed of 60-80 rpm.

4. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The melting point of the polypropylene wax in step (1) is 130-150°C.

5. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The modified calcium carbonate in step (2) is obtained by surface modification treatment of heavy calcium carbonate with a particle size of 3000-5000 mesh and aluminate coupling agent in a mass ratio of 100:0.8 through a jet mill.

6. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The polypropylene in step (2) is a composite of homopolymer polypropylene with a melt index of 5-10 g / 10 min and copolymer polypropylene in a mass ratio of 3:

1.

7. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The particle size of the precipitated barium sulfate in step (2) is less than 10 um; the particle size of the polytetrafluoroethylene is less than 10 um.

8. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The reciprocating single-screw compounding extruder in step (2) has a screw diameter of 70 mm and a length-to-diameter ratio of 20:

1.

9. The method for preparing a high impact resistant polypropylene-calcium carbonate composite pallet material according to claim 1, characterized in that: The working temperature of the reciprocating single-screw compounding extruder in step (2) is set as follows: the temperature of zone 1 is 160-180°C, the temperature of zone 2 is 190-200°C, the temperature of zone 3 is 210-220°C, the temperature of zone 4 is 190-200°C, and the temperature of zone 5 is 170-180°C; a vacuum devolatilization port is designed in zone 4.

10. A high impact resistant polypropylene-calcium carbonate composite pallet material, characterized in that The method is prepared by any one of claims 1 to 9.

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