A polyolefin composite material for rotational molding dumbbell plates and its application

Abstract

The present invention relates to the field of rotational molding plastic products, and particularly to a polyolefin composite material for rotational molding dumbbell sheets and its application. The polyolefin composite material comprises material A and material B; the material A comprises the following raw materials in parts by weight: 65-80 parts of polyolefin, 4.5-6.5 parts of crosslinking initiator, 7-13 parts of co-crosslinking agent, 8-15 parts of adhesion agent, and 0-4.5 parts of antioxidant; the material B comprises the following raw materials in parts by weight: 93-98 parts of polyolefin, 0.25-2.5 parts of demolding agent, and 0-4.5 parts of antioxidant; the size of the material A is smaller than that of the material B. The polyolefin composite material of the present invention can make full use of crosslinking to improve the anti-drop property and minimize the adverse effect of the increase in crosslinking degree on uniformity, thereby endowing the rotational molding dumbbell sheet with better anti-drop performance.

Description

Technical Field

[0001] The present invention relates to the field of rotomolded plastic products, and particularly to a polyolefin composite material for rotomolded dumbbell plates and its application. Background Art

[0002] Dumbbells are auxiliary equipment for weightlifting and fitness exercises. Dumbbell plates are divided into all-rubber bell plates, rubber-coated metal bell plates, electroplated metal bell plates, and painted metal bell plates. Among them, all-rubber bell plates are mainly made by blow molding process. Although the molding cycle is short, there are disadvantages such as rough product surface, stress concentration at the mold joint line, poor toughness and strength of the shell structure, poor anti-drop performance, and easy damage. Currently, in the drop test of dumbbell plates on the market, they often deform after dropping from a height of 2m less than 150 times and can no longer be used.

[0003] Rotomolding is a plastic processing method using a rotating mold. In the processing process, plastic powder or slurry is put into the mold, and the closed mold rotates or sways on the equipment. At the same time, the outside of the mold is heated by an open flame or hot air. The plastic powder or slurry flips and flows inside the mold under the heated state. After the temperature reaches the softening point, it is gradually coated on the inner surface of the mold, melted and solidified. After the mold is cooled in a natural environment or through media such as water, mist, and wind, the mold is removed to take out the product.

[0004] Preparing dumbbell plates by rotomolding process can improve the strength of the product and extend the service life of the product. For example, Patent CN202010625084.3 discloses a method for preparing rotomolded dumbbells or barbell plates, including the following steps: prefabricating a dumbbell or barbell plate shell mold with a filler port on the mold; adding plastic into the mold and then putting it into a rotomolding machine to manufacture the bell plate shell; filling the obtained bell plate shell with a filler and sealing it. Compared with blow molded products, there is no mold joint line in this kind of rotomolded dumbbell plate, so the anti-drop performance is improved, but there are still deficiencies. Summary of the Invention

[0005] In order to solve the technical problem that the existing dumbbell plates have poor anti-drop performance, the present invention provides a polyolefin composite material for rotomolded dumbbell plates and its application. This polyolefin composite material can make full use of crosslinking to improve the anti-drop property and minimize the adverse effect of the increase in crosslinking degree on uniformity as much as possible, so as to endow the rotomolded dumbbell plates with better anti-drop performance.

[0006] The specific technical solution of the present invention is as follows:

[0007] In the first aspect, the present invention provides a polyolefin composite material for rotationally molded dumbbell plates, including material A and material B; the material A includes the following raw materials in parts by weight: 65 to 80 parts of polyolefin, 4.5 to 6.5 parts of cross-linking initiator, 7 to 13 parts of auxiliary cross-linking agent, 8 to 15 parts of adhesive, and 0 to 4.5 parts of antioxidant; the material B includes the following raw materials in parts by weight: 93 to 98 parts of polyolefin, 0.25 to 2.5 parts of release agent, and 0 to 4.5 parts of antioxidant; the size of the material A is smaller than that of the material B.

[0008] The present invention uses polyolefin as the base resin, which can give the roto-molded dumbbell piece good anti-drop performance and make it have a long service life. On this basis, the present invention uses a specific compound of material A and material B to further improve the anti-drop performance of the roto-molded dumbbell piece. Specifically:

[0009] In the process of rotational molding, the smaller size and the presence of the adhesive can make material A easier to adhere to the mold, and the larger size and the presence of the release agent can slow down the mold of material B, so material A preferentially adheres to the mold to form an outer layer, and material B adheres subsequently, and its melt fills the gap in the outer layer formed by material A to form an inner layer, and under the action of the crosslinking initiator and the auxiliary crosslinking agent, the polyolefin in material A undergoes covalent crosslinking to increase its crosslinking degree. Therefore, in the prepared dumbbell sheet, the surface layer is composed of material A and material B, and material A forms a covalent crosslinking network with a large degree of crosslinking therein, and the inner layer is composed of material B with a low degree of crosslinking. The increase in the degree of crosslinking can give the dumbbell sheet better anti-drop performance, but it will also have an adverse effect on the leveling of the melt, thereby affecting the uniformity and limiting the improvement of the anti-drop performance. The present invention utilizes specific A material and B material. When external impact (such as collision with the ground when falling) is applied to the surface of the dumbbell piece, the covalent cross-linked network given by A material in the surface layer can withstand the impact and reduce the impact on the dumbbell piece as a whole. At the same time, the melt of B material with good leveling property fills the gaps in the surface layer and constitutes the inner layer, which can avoid the impact on the overall anti-drop performance of the dumbbell piece due to the poor leveling property of A material. Through the above method, the adverse effect of the increase in the degree of cross-linking on uniformity can be minimized as much as possible, and cross-linking can be fully utilized to improve the anti-drop performance, so that the dumbbell piece as a whole can achieve better anti-drop performance.

[0010] Preferably, the cross-linking initiator comprises a and a cross-linking initiator b in a mass ratio of 1:4.0 to 6.2; the 1-min half-life temperature of the cross-linking initiator a is not higher than the hot-melt extrusion temperature during the preparation of material A; the 1-min half-life temperature of the cross-linking initiator b is higher than the hot-melt extrusion temperature during the preparation of material A, and is not higher than the rotational molding temperature during the preparation of dumbbell pieces from polyolefin composite materials.

[0011] The present invention uses a compound of two crosslinking initiators with different and specific half-lives, which is beneficial to further improve the anti-drop performance of the rotational molding dumbbell sheet. Specifically: The crosslinking initiator a plays a role when preparing material A by hot melt extrusion, causing partial crosslinking to be pre-formed in material A, reducing the contact between the crosslinking initiator and the co-crosslinking agent in material A and their action on material B during rotational molding, and thus triggering the crosslinking of material B, which is beneficial to the flow leveling of material B and filling the voids in the outer layer formed by material A; The crosslinking initiator b plays a role during rotational molding, enabling the melt of material A to flow relatively well before crosslinking is completed, which is beneficial to the connection of the powders of material A after melting and the formation of crosslinking, and further better forming a covalent crosslinking network structure on the surface of the dumbbell sheet.

[0012] Among the two crosslinking initiators, when the relative dosage of a is too large, a large degree of crosslinking occurs in material A during the preparation process, and its melt fluidity drops significantly, which is not conducive to the connection of the melts of material A during rotational molding. Therefore, the coverage area and degree of crosslinking of the formed crosslinking network decrease, which will have an adverse effect on the anti-drop performance of the dumbbell sheet; When the relative dosage of b is too large, it is easy to contact and act on material B during rotational molding, causing a large degree of crosslinking of the polyolefin in material B, which is not conducive to material B fully filling the voids in the outer layer formed by material A, and thus is also not conducive to the improvement of the anti-drop performance of the dumbbell sheet. Based on this, on the basis of using a compound of two crosslinking initiators, the present invention controls their mass ratio to 1:4.0 - 6.2, which can enable the two to cooperate better and improve the anti-drop performance of the dumbbell sheet to a greater extent.

[0013] Further, the 1-minute half-life temperature of the crosslinking initiator a is not higher than 230 °C; the 1-minute half-life temperature of the crosslinking initiator b is 240 - 350 °C.

[0014] Further, the crosslinking initiator a is one or more of dicumyl peroxide (DCP), tert-butyl peroxybenzoate (TBPB), 1,3-bis(tert-butylperoxyisopropyl)benzene (BIBP), di-tert-butyl peroxide (DTBP), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP); the crosslinking initiator b is tert-butyl hydroperoxide (TBHP) and / or t-amyl hydroperoxide (TAHP).

[0015] Preferably, the mass ratio of material A to material B is 1:8 - 11.

[0016] Preferably, material A is a powder with a particle size D95 ≤ 550 μm; material B is a particle with a diameter of 1 - 1.5 mm and a length of 1 - 2 mm.

[0017] Further, the particle size D20 of material A ≥ 150 μm.

[0018] Preferably, the preparation method of the A material comprises the following steps: after mixing all components of the A material, hot melt extrusion granulation is carried out, and then powder grinding is carried out; the process parameters of the hot melt extrusion are as follows: the highest temperature of each zone is 180-230 °C.

[0019] Further, the process parameters of the powder grinding are as follows: the temperature of the grinding disc ≤ 75 °C, and the rotation speed of the grinding disc is 1000-3700 rpm.

[0020] Preferably, the preparation method of the B material comprises the following steps: after mixing all components of the B material, hot melt extrusion granulation is carried out.

[0021] Preferably, the polyolefin includes one or more of polyethylene, polypropylene, polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and polyolefin plastomer.

[0022] Preferably, the adhesion promoter includes one or more of polyethylene wax, polypropylene wax, lignite wax, microcrystalline wax, Fischer-Tropsch wax, ethylene-vinyl acetate copolymer wax, and oxidized polyethylene wax.

[0023] Preferably, the release agent includes one or more of calcium stearate, stearic acid, and ethylene bisoleamide.

[0024] Preferably, the co-crosslinking agent includes one or more of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triallyl cyanurate, and triallyl isocyanurate.

[0025] Preferably, the antioxidant includes a primary antioxidant and a secondary antioxidant with a mass ratio of 1:1.5-4.

[0026] Further, the primary antioxidant is antioxidant 1010 and / or antioxidant 1076; the secondary antioxidant is antioxidant 686 and / or antioxidant 168.

[0027] In the second aspect, the present invention provides the application of the polyolefin composite material in rotational molding dumbbell sheets.

[0028] The polyolefin composite material of the present invention can be used to prepare rotational molding plastic products, such as dumbbell sheets with different specifications of 0.5KG, 1KG, 1.25KG, 1.5KG, 2KG, 2.5KG, 3.75KG, 5KG, 7.5KG, 10KG, etc.

[0029] Preferably, the preparation method of the rotational molding dumbbell sheet comprises the following steps: after mixing the A material and the B material, it is put into a rotational molding mold, rotational molding is carried out, and then it is cooled and demolded to obtain the rotational molding dumbbell sheet.

[0030] Further, the process parameters of the rotational molding are as follows: the rotational molding temperature is 250 - 350 °C, the main shaft speed is 6 - 12 rpm, and the auxiliary shaft speed is 9 - 18 rpm.

[0031] Preferably, the rotational molded dumbbell sheet does not deform after being dropped 500 times from a height of 2 m.

[0032] Through tests, the dumbbell sheet made of the polyolefin composite material of the present invention by the rotational molding process does not deform after being dropped 500 times from a height of 2 m, has good drop resistance, and a long service life.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The polyolefin composite material of the present invention uses specific material A and material B for compounding. Since the material A with a higher degree of crosslinking is only distributed on the surface layer, and the inner layer is the material B with a lower degree of crosslinking, and the melt of the material B can also fill the voids of the surface layer material A, it can make full use of crosslinking to improve the drop resistance, and minimize the adverse effect of the increase in the degree of crosslinking on the uniformity, thereby endowing the rotational molded dumbbell sheet with better drop resistance and a long service life;

[0035] (2) In the polyolefin composite material of the present invention, two crosslinking initiators with different and specific half-lives are compounded in the material A, which is beneficial to the formation of the covalent crosslinking network on the surface layer and the filling of the surface layer voids by the B melt, thus further improving the drop resistance of the rotational molded dumbbell sheet;

[0036] (3) When the polyolefin composite material of the present invention is used to prepare the rotational molded dumbbell sheet, the preparation method is simple, no complex equipment is required, the molding process is simple, and it is easy to realize industrial operation. Specific Embodiments

[0037] The present invention will be further described below in conjunction with embodiments.

[0038] General Embodiment

[0039] A polyolefin composite material for rotational molded dumbbell sheets, comprising material A and material B; the material A comprises the following raw materials in parts by weight: 65 - 80 parts of polyolefin, 4.5 - 6.5 parts of crosslinking initiator, 7 - 13 parts of co-crosslinking agent, 8 - 15 parts of adhesion agent, 0 - 4.5 parts of antioxidant; the material B comprises the following raw materials in parts by weight: 93 - 98 parts of polyolefin, 0.25 - 2.5 parts of mold release agent, 0 - 4.5 parts of antioxidant; the size of the material A is smaller than that of the material B.

[0040] As a specific embodiment, the mass ratio of the material A to the material B is 1:8 - 11.

[0041] As a specific embodiment, the material A is a powder with a D95 particle size of ≤550 μm and a D20 of ≥150 μm; the material B is a particle with a diameter of 1 - 1.5 mm and a length of 1 - 2 mm.

[0042] As a specific embodiment, the preparation method of the material A includes the following steps: after mixing all components of the material A, hot melt extrusion granulation is carried out, and then powder grinding is carried out. The process parameters of the hot melt extrusion are as follows: the highest temperature of each zone is 180 - 230 °C. The process parameters of the powder grinding are as follows: the grinding disc temperature is ≤75 °C, and the grinding disc rotation speed is 1000 - 3700 rpm.

[0043] As a specific embodiment, the preparation method of the material B includes the following steps: after mixing all components of the material B, hot melt extrusion granulation is carried out.

[0044] As a specific embodiment, the crosslinking initiator includes crosslinking initiator a and crosslinking initiator b with a mass ratio of 1:4.0 - 6.2; the 1-minute half-life temperature of the crosslinking initiator a is not higher than the hot melt extrusion temperature during the preparation of the material A; the 1-minute half-life temperature of the crosslinking initiator b is higher than the hot melt extrusion temperature during the preparation of the material A and not higher than the rotational molding temperature during the preparation of dumbbell sheets from the polyolefin composite material.

[0045] As a specific embodiment, the 1-minute half-life temperature of the crosslinking initiator a is not higher than 230 °C; the 1-minute half-life temperature of the crosslinking initiator b is 240 - 350 °C. The crosslinking initiator a can be selected from one or more of dicumyl peroxide (DCP), tert-butyl peroxybenzoate (TBPB), 1,3-bis(tert-butylperoxyisopropyl)benzene (BIBP), di-tert-butyl peroxide (DTBP), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP); the crosslinking initiator b can be selected from tert-butyl hydroperoxide (TBHP) and / or tert-amyl hydroperoxide (TAHP).

[0046] As a specific embodiment, the polyolefin may be selected from one or more of polyethylene, polypropylene, polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and polyolefin plastomer. The adhesion agent may be selected from one or more of polyethylene wax, polypropylene wax, lignite wax, microcrystalline wax, Fischer-Tropsch wax, ethylene-vinyl acetate copolymer wax, and oxidized polyethylene wax. The release agent may be selected from one or more of calcium stearate, stearic acid, and ethylene bisoleamide. The co-crosslinking agent may be selected from one or more of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triallyl cyanurate, and triallyl isocyanurate. The antioxidant includes a primary antioxidant and a secondary antioxidant with a mass ratio of 1:1.5 to 4; the primary antioxidant may be selected from antioxidant 1010 and / or antioxidant 1076; the secondary antioxidant may be selected from antioxidant 686 and / or antioxidant 168.

[0047] Application of the above polyolefin composite material in rotational molding dumbbell sheets.

[0048] As a specific embodiment, the method for preparing the rotational molding dumbbell sheet includes the following steps: After mixing material A and material B, put them into a rotational molding mold, carry out rotational molding, then cool, open the mold, and obtain the rotational molding dumbbell sheet. The process parameters of the rotational molding are as follows: the rotational molding temperature is 250 - 350 °C, the main shaft speed is 6 - 12 rpm, and the auxiliary shaft speed is 9 - 18 rpm.

[0049] Example 1

[0050] Prepare material A through the following steps:

[0051] Weigh polyolefin plastomer (3588FL, ExxonMobil), antioxidant 1010, antioxidant 626, diisopropylbenzene peroxide, tert-butyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam Thai). According to a total mass of 100 parts, the mass ratio of each raw material component is polyolefin plastomer (028, SK): antioxidant 1010: antioxidant 626: diisopropylbenzene peroxide: tert-butyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 79.83%: 0.25%: 0.42%: 0.9%: 3.6%: 7%: 12.5%. Use a high-speed mixer to mix at 230 rpm for 18 min. Set the temperature of each section of the extruder to 70 - 180 °C, the screw speed to 730 rpm, and use a twin-screw extruder to melt and blend to form pellets; with a grinding disc speed of 3200 rpm and liquid nitrogen cryogenic grinding, obtain A-material powder with a particle size distribution of D95 = 510 μm and D20 = 162 μm.

[0052] Prepare material B through the following steps:

[0053] Weigh the polyolefin plastomer (3588FL, ExxonMobil), antioxidant 1010, antioxidant 626, and calcium stearate. According to a total mass of 100 parts, the mass ratio of each raw material component is polyolefin plastomer (028, SK): antioxidant 1010: antioxidant 626: calcium stearate = 98.98%: 0.25%: 0.42%: 0.35%. Use a high-speed mixer to mix at 230 rpm for 18 min. Set the temperature of each section of the extruder to 70 - 180 °C, the screw speed to 730 rpm, and use a twin-screw extruder to melt and blend to produce B-material particles with a diameter of 1 mm and a length of 2 mm.

[0054] Use the A-material and B-material prepared in this example to prepare rotational molding dumbbell sheets through the following steps:

[0055] Weigh the A-material powder and B-material particles, and the weight ratio is A-material powder: B-material particles = 1:10. Use a mixer to mix at 80 rpm for 3 min, put them into a rotational molding mold, set the heating temperature of the mold to 280 °C, the main shaft speed to 10 rpm, and the sub-shaft speed to 15 rpm for rotational molding. Then cool naturally to 40 °C at room temperature, open the mold, and obtain 5KG all-rubber dumbbell sheets.

[0056] Example 2

[0057] Prepare A-material through the following steps:

[0058] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, tert-butyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam, Thailand). According to a total mass of 100 parts, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: 1,3-bis(tert-butylperoxyisopropyl)benzene: tert-butyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 71.65%: 0.13%: 0.32%: 0.9%: 4.5%: 10%: 15%. Use a high-speed mixer to mix at 550 rpm for 10 min. Set the temperature of each section of the extruder to 100 - 230 °C, the screw speed to 530 rpm, and use a twin-screw extruder to melt and blend to produce particles; perform grinding at a grinding disk speed of 2600 rpm and a grinding disk temperature < 65 °C to obtain A-material powder with a particle size distribution of D95 = 498 μm and D20 = 165 μm.

[0059] Prepare B-material through the following steps:

[0060] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, and ethylene bisoleamide. According to a total mass of 100 parts, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: ethylene bisoleamide = 99.3%: 0.13%: 0.32%: 0.25%. Use a high-speed mixer to mix at 550 rpm for 10 min. Set the temperature of each section of the extruder to 100 - 230 °C, the screw speed to 530 rpm, and use a twin-screw extruder to melt and blend to produce B-material particles with a diameter of 1 mm and a length of 1 mm.

[0061] Use the A-material and B-material prepared in this example to prepare a rotational molding dumbbell sheet through the following steps:

[0062] Weigh the A-material powder and B-material particles, and the weight ratio is A-material powder: B-material particles = 1:8. Use a mixer to mix at 80 rpm for 3 min, put it into a rotational molding mold. Set the heating temperature of the mold to 350 °C, the main shaft speed to 6 rpm, and the sub-shaft speed to 9 rpm for rotational molding. Then, naturally cool to 40 °C at room temperature, open the mold, and obtain 5KG all-rubber dumbbell sheets.

[0063] Example 3

[0064] Prepare the A-material through the following steps:

[0065] Weigh ethylene-vinyl acetate copolymer (1010A, Celanese), antioxidant 1076, antioxidant 686, 1,3-bis(tert-butylperoxyisopropyl)benzene, pivalyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam Thai). According to a total mass of 100 parts, the mass ratio of each raw material component is ethylene-vinyl acetate copolymer: antioxidant 1076: antioxidant 686: 1,3-bis(tert-butylperoxyisopropyl)benzene: pivalyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 71.85%: 0.25%: 0.5%: 0.9%: 5.5%: 13%: 8%. Use a high-speed mixer to mix at 600 rpm for 13 min. Set the temperature of each section of the extruder to 60 - 190 °C, the screw speed to 470 rpm, and use a twin-screw extruder to melt and blend to produce particles; use a grinding disc speed of 3000 rpm and liquid nitrogen cryogenic milling to obtain A-material powder with a particle size distribution of D95 = 545 μm and D20 = 175 μm.

[0066] Prepare the B-material through the following steps:

[0067] Weigh ethylene-vinyl acetate copolymer (1010A, Celanese), antioxidant 1076, antioxidant 686, calcium stearate, and ethylene bisoleamide. According to a total mass of 100 parts, the mass ratio of each raw material component is ethylene-vinyl acetate copolymer: antioxidant 1076: antioxidant 686: calcium stearate: ethylene bisoleamide = 98.79%: 0.25%: 0.5%: 0.2%: 0.26%. Use a high-speed mixer to mix at 600 rpm for 13 minutes. The temperature of each section of the extruder is set at 60 - 190 °C, the screw speed is 470 rpm, and a twin-screw extruder is used for melt blending to produce B-material particles with a diameter of 1.5 mm and a length of 2 mm.

[0068] Use the A-material and B-material prepared in this example to prepare a rotational molding dumbbell sheet through the following steps:

[0069] Weigh the A-material powder and B-material particles, and the weight ratio is A-material powder: B-material particles = 1:11. Use a mixer to mix at 80 rpm for 3 minutes, put them into a rotational molding mold. The heating temperature of the mold is set at 300 °C, the main shaft speed is 12 rpm, and the auxiliary shaft speed is 18 rpm for rotational molding. Then, naturally cool to 40 °C at room temperature, open the mold, and obtain 5KG all-rubber dumbbell sheets.

[0070] Example 4

[0071] Prepare the A-material through the following steps:

[0072] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, tert-butyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam, Thailand). According to a total mass of 100 parts, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: tert-butyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 71.65%: 0.13%: 0.32%: 5.4%: 10%: 15%. Use a high-speed mixer to mix at 550 rpm for 10 minutes. The temperature of each section of the extruder is set at 100 - 230 °C, the screw speed is 530 rpm, and a twin-screw extruder is used for melt blending to produce particles; perform grinding at a grinding disk speed of 2600 rpm and a grinding disk temperature < 65 °C to obtain A-material powder with a particle size distribution of D95 = 498 μm and D20 = 165 μm.

[0073] Prepare the B-material through the following steps:

[0074] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, and ethylene bisoleamide. According to a total mass of 100 parts, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: ethylene bisoleamide = 99.3%: 0.13%: 0.32%: 0.25%. Use a high-speed mixer to mix for 10 min at 550 rpm. Set the temperature of each section of the extruder to 100 - 230 °C, the screw speed to 530 rpm, and use a twin-screw extruder to melt and blend to produce B-material particles with a diameter of 1 mm and a length of 1 mm.

[0075] Use the A-material and B-material prepared in this example to prepare a rotational molding dumbbell sheet through the following steps:

[0076] Weigh the A-material powder and B-material particles, with a weight ratio of A-material powder: B-material particles = 1:8. Use a mixer to mix for 3 min at 80 rpm, put them into a rotational molding mold, set the heating temperature of the mold to 350 °C, the main shaft speed to 6 rpm, and the auxiliary shaft speed to 9 rpm for rotational molding. Then, naturally cool to 40 °C at room temperature, open the mold, and obtain 5KG fully plastic dumbbell sheets.

[0077] Example 5

[0078] Prepare A-material through the following steps:

[0079] Weigh polyolefin plastomer (3588FL, ExxonMobil), antioxidant 1010, antioxidant 626, dicumyl peroxide, tert-butyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam, Thailand). According to a total mass of 100 parts, the mass ratio of each raw material component is polyolefin plastomer (028, SK): antioxidant 1010: antioxidant 626: dicumyl peroxide: tert-butyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 79.83%: 0.25%: 0.42%: 2%: 2.5%: 7%: 12.5%. Use a high-speed mixer to mix for 18 min at 230 rpm. Set the temperature of each section of the extruder to 70 - 180 °C, the screw speed to 730 rpm, and use a twin-screw extruder to melt and blend to produce particles; use a grinding disk speed of 3200 rpm and liquid nitrogen cryogenic grinding to obtain A-material powder with a particle size distribution of D95 = 510 μm and D20 = 162 μm.

[0080] Prepare B-material through the following steps:

[0081] Weigh polyolefin plastomer (3588FL, ExxonMobil), antioxidant 1010, antioxidant 626, and calcium stearate. According to a total mass of 100 parts, the mass ratio of each raw material component is polyolefin plastomer (028, SK): antioxidant 1010: antioxidant 626: calcium stearate = 98.98%: 0.25%: 0.42%: 0.35%. Use a high-speed mixer to mix at 230 rpm for 18 min. The temperature of each section of the extruder is set at 70 - 180 °C, the screw speed is 730 rpm, and a twin-screw extruder is used for melt blending to produce B-material pellets with a diameter of 1 mm and a length of 2 mm.

[0082] Use the A-material and B-material prepared in this example to prepare rotational molding dumbbell sheets through the following steps:

[0083] Weigh A-material powder and B-material pellets, with a weight ratio of A-material powder: B-material pellets = 1:10. Use a mixer to mix at 80 rpm for 3 min, then put them into a rotational molding mold. The heating temperature of the mold is set at 280 °C, the main shaft speed is 10 rpm, and the auxiliary shaft speed is 15 rpm for rotational molding. Then, naturally cool to 40 °C at room temperature, open the mold, and obtain 5KG fully rubberized dumbbell sheets.

[0084] Example 6

[0085] Prepare A-material through the following steps:

[0086] Weigh ethylene-vinyl acetate copolymer (1010A, Celanese), antioxidant 1076, antioxidant 686, 1,3-bis(tert-butylperoxyisopropyl)benzene, pivalic acid hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Thai Siam). According to a total mass of 100 parts, the mass ratio of each raw material component is ethylene-vinyl acetate copolymer: antioxidant 1076: antioxidant 686: 1,3-bis(tert-butylperoxyisopropyl)benzene: pivalic acid hydroperoxide: triallyl isocyanurate: polyethylene wax = 71.85%: 0.25%: 0.5%: 0.4%: 6%: 13%: 8%. Use a high-speed mixer to mix at 600 rpm for 13 min. The temperature of each section of the extruder is set at 60 - 190 °C, the screw speed is 470 rpm, and a twin-screw extruder is used for melt blending to produce pellets; use a grinding disc at a speed of 3000 rpm and liquid nitrogen freezing for grinding to obtain A-material powder with a particle size distribution of D95 = 545 μm and D20 = 175 μm.

[0087] Prepare B-material through the following steps:

[0088] Weigh ethylene-vinyl acetate copolymer (1010A, Celanese), antioxidant 1076, antioxidant 686, calcium stearate, and ethylene bisoleamide. According to a total mass of 100 parts, the mass ratio of each raw material component is ethylene-vinyl acetate copolymer: antioxidant 1076: antioxidant 686: calcium stearate: ethylene bisoleamide = 98.79%: 0.25%: 0.5%: 0.2%: 0.26%. Use a high-speed mixer to mix at 600 rpm for 13 minutes. The temperature of each section of the extruder is set at 60 - 190 °C, the screw speed is 470 rpm, and a twin-screw extruder is used for melt blending to produce B-material particles with a diameter of 1.5 mm and a length of 2 mm.

[0089] Use the A-material and B-material prepared in this example to prepare a rotational molding dumbbell sheet through the following steps:

[0090] Weigh the A-material powder and B-material particles, and the weight ratio is A-material powder: B-material particles = 1:11. Use a mixer to mix at 80 rpm for 3 minutes, put them into a rotational molding mold, set the heating temperature of the mold at 300 °C, the main shaft speed at 12 rpm, and the sub-shaft speed at 18 rpm for rotational molding. Then, naturally cool to 40 °C at room temperature, open the mold, and obtain 5KG fully rubber dumbbell sheets.

[0091] Comparative Example 1

[0092] Prepare the A-material through the following steps:

[0093] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, tert-butyl hydroperoxide, triallyl isocyanurate, and polyethylene wax (2040, Siam, Thailand). According to a total mass of 100 parts, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: 1,3-bis(tert-butylperoxyisopropyl)benzene: tert-butyl hydroperoxide: triallyl isocyanurate: polyethylene wax = 71.65%: 0.13%: 0.32%: 0.9%: 4.5%: 10%: 15%. Use a high-speed mixer to mix at 550 rpm for 10 minutes. The temperature of each section of the extruder is set at 100 - 230 °C, the screw speed is 530 rpm, and a twin-screw extruder is used for melt blending to produce particles; perform grinding at a grinding disc speed of 2600 rpm and a grinding disc temperature < 65 °C to obtain A-material powder with a particle size distribution of D95 = 498 μm and D20 = 165 μm.

[0094] Use the A-material prepared in this comparative example to prepare a rotational molding dumbbell sheet through the following steps:

[0095] Put the powder of Material A into the rotational molding mold. Set the heating temperature of the mold at 350 °C, the main shaft speed at 6 rpm, and the auxiliary shaft speed at 9 rpm. Carry out rotational molding, and then naturally cool it to 40 °C at room temperature. Open the mold to obtain 5KG all-rubber dumbbell pieces.

[0096] Comparative Example 2

[0097] Prepare Material B through the following steps:

[0098] Weigh polyethylene (0015XC, ExxonMobil), antioxidant 1010, antioxidant 168, and ethylene bisoleamide. According to a total of 100 parts by mass, the mass ratio of each raw material component is polyethylene: antioxidant 1010: antioxidant 168: ethylene bisoleamide = 99.3%: 0.13%: 0.32%: 0.25%. Use a high-speed mixer to mix for 10 min at 550 rpm. Set the temperature of each section of the extruder at 100 - 230 °C, the screw speed at 530 rpm, and use a twin-screw extruder to melt and blend to produce B-material particles with a diameter of 1 mm and a length of 1 mm.

[0099] Use the B material prepared in this comparative example to prepare rotational molding dumbbell pieces through the following steps:

[0100] Put the B-material particles into the rotational molding mold. Set the heating temperature of the mold at 350 °C, the main shaft speed at 6 rpm, and the auxiliary shaft speed at 9 rpm. Carry out rotational molding, and then naturally cool it to 40 °C at room temperature. Open the mold to obtain 5KG all-rubber dumbbell pieces.

[0101] Test Example

[0102] Conduct a drop resistance test on the dumbbell pieces prepared in Examples 1 - 6 and Comparative Examples 1 - 2. Use the number of times of non-deformation after dropping from a height of 2 m to characterize. Use 5 specimens for the test of each example and comparative example, and take the average value of the results. The test results are shown in Table 1.

[0103] Table 1

[0104] Project Number of times without deformation after dropping from a height of 2m Example 1 803 Example 2 752 Example 3 875 Example 4 649 Example 5 729 Example 6 801 Comparative Example 1 570 Comparative Example 2 466

[0105] It can be seen from the test data in Table 1 that:

[0106] (1) Compared with Comparative Examples 1 and 2, the anti-drop performance of Example 2 is significantly improved. It shows that the compounding of Material A and Material B can improve the anti-drop performance of dumbbell sheets. This is because during rotational molding, Material A molds first before Material B. In the formed dumbbell sheets, Material A with a higher degree of crosslinking is only distributed on the surface layer, and the inner layer is Material B with a lower degree of crosslinking. Moreover, the melt of Material B can also fill the voids in the surface layer of Material A. Therefore, crosslinking can be fully utilized to improve the anti-drop performance, and the adverse effect of the increase in the degree of crosslinking on uniformity can be minimized as much as possible, thereby endowing the rotationally molded dumbbell sheets with better anti-drop performance.

[0107] (2) The anti-drop performance of Example 2 is better than that of Example 4, the anti-drop performance of Example 3 is better than that of Example 6, and the anti-drop performance of Example 1 is better than that of Example 5. It shows that the compounding of crosslinking initiators a and b can improve the anti-drop performance of dumbbell sheets, and an excessive or too small ratio between the two will cause a decrease in the anti-drop performance. This is because crosslinking initiator a plays a role during the hot melt extrusion to prepare Material A, causing partial crosslinking to be pre-formed in Material A, reducing the contact between the crosslinking initiator and co-crosslinking agent in Material A and the action on Material B to initiate the crosslinking of Material B during rotational molding, which is beneficial to the leveling of Material B and filling the voids in the outer layer formed by Material A; crosslinking initiator b plays a role during rotational molding, enabling the melt of Material A to flow relatively well before completing crosslinking, which is beneficial to the connection of molten Material A powders with each other to form crosslinking, and then better forming a covalent crosslinking network structure on the surface of the dumbbell sheets.

[0108] Unless otherwise specified, the raw materials and equipment used in the present invention are all common raw materials and equipment in the art; unless otherwise specified, the methods used in the present invention are all conventional methods in the art.

[0109] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A polyolefin composite material for rotational molding dumbbell pieces, characterized in that, It includes Material A and Material B; Material A includes the following raw materials in parts by weight: 65 - 80 parts of polyolefin, 4.5 - 6.5 parts of crosslinking initiator, 7 - 13 parts of co-crosslinking agent, 8 - 15 parts of adhesion agent, 0 - 4.5 parts of antioxidant; Material B includes the following raw materials in parts by weight: 93 - 98 parts of polyolefin, 0.25 - 2.5 parts of demolding agent, 0 - 4.5 parts of antioxidant; The size of Material A is smaller than that of Material B; The crosslinking initiator includes crosslinking initiator a and crosslinking initiator b with a mass ratio of 1:4.0 - 6.2; The 1-minute half-life temperature of crosslinking initiator a is not higher than the hot melt extrusion temperature during the preparation of Material A; The 1-minute half-life temperature of crosslinking initiator b is higher than the hot melt extrusion temperature during the preparation of Material A and not higher than the rotational molding temperature during the preparation of dumbbell sheets from the polyolefin composite.

2. The polyolefin composite material according to claim 1, wherein The 1-minute half-life temperature of the crosslinking initiator a is not higher than 230°C; The 1-minute half-life temperature of the crosslinking initiator b is 240 - 350°C.

3. The polyolefin composite material according to claim 1, wherein The mass ratio of Material A to Material B is 1:8 - 11.

4. The polyolefin composite material according to claim 1, characterized in that, Material A is a powder with a particle size D95 ≤ 550 μm; Material B is a particle with a diameter of 1 - 1.5 mm and a length of 1 - 2 mm.

5. The polyolefin composite material according to claim 1, wherein The preparation method of Material A includes the following steps: After mixing all components of Material A, hot melt extrusion granulation is carried out, and then grinding is carried out; The process parameters of the hot melt extrusion are as follows: The highest temperature of each zone is 180 - 230°C.

6. The polyolefin composite material according to claim 1, wherein The polyolefin includes one or more of polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and polyolefin plastomer.

7. Application of a polyolefin composite as described in any one of claims 1 - 6 in rotational molding of dumbbell sheets.

8. The application according to claim 7, characterized in that, The preparation method of the rotational molding dumbbell sheets includes the following steps: After mixing Material A and Material B, they are put into a rotational molding mold, rotational molding is carried out, and then cooling and mold opening are carried out to obtain rotational molding dumbbell sheets.

9. The application according to claim 8, characterized in that, The process parameters of the rotational molding are as follows: The rotational molding temperature is 250 - 350°C, the main shaft speed is 6 - 12 rpm, and the sub-shaft speed is 9 - 18 rpm.