Crosslinked polyethylene rotational molding material and preparation method thereof

Abstract

The invention relates to the technical field of rotational molding processing, and discloses a crosslinked polyethylene rotational molding material and a preparation method thereof, the rotational molding material comprises the following raw materials by mass: 85-95% of high density polyethylene, 5-10% of polyethylene raw powder, 0.05-0.5% of a crosslinking agent, and 0.1-1% of a crosslinking accelerator; the polyethylene raw powder and the high-density polyethylene powder are mixed to prepare the rotational molding material, the cross-linking efficiency of the rotational molding material is remarkably improved through the self-cross-linking effect of the polyethylene raw powder, and the use amount of a cross-linking auxiliary agent in the rotational molding material is reduced, so that the gas production effect of the cross-linking auxiliary agent during rotational molding processing of the rotational molding material is remarkably reduced; round pits cannot be generated on the surface of the manufactured rotational molding part, the quality of the rotational molding part is remarkably improved, the rotational molding machining efficiency is remarkably improved, and the machining cost is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the technical field of roto-molding, in particular to a cross-linked polyethylene roto-molding material and a preparation method thereof. Background Art

[0002] Polyethylene is an important polymer material and is widely used in industry, agriculture and daily life. Polyethylene has poor high temperature resistance, and its mechanical properties and chemical resistance sometimes cannot meet the actual use needs. Because the modification of polyethylene has always been the key to the development and application of polyethylene products, polyethylene cross-linking technology is an important polyethylene modification technology; the high temperature resistance, mechanical properties, environmental stress cracking resistance, chemical corrosion resistance, creep resistance and other properties of cross-linked modified polyethylene can be greatly improved.

[0003] Roto-molding is a hollow molding method for thermoplastic materials. This method is to add plastic powder into the mold, knead it, and then rotate the mold continuously along two vertical axes to heat it, gradually and evenly coat it, melt it and adhere it to the entire surface of the mold cavity, and mold it into the required shape. It is then cooled and shaped into a product. The roto-molding process is suitable for hollow plastic products with large volume and complex structure, and is widely used in engineering machinery, automobiles, medical and military industries, home appliances, amusement and other fields.

[0004] At present, there are many technical problems in applying cross-linked polyethylene to the rotational molding process. For example, a cross-linked polyethylene composition with improved processing performance disclosed in publication number CN104334630B is added with a free radical inhibitor to increase the cross-linking lag time of polyethylene, thereby solving the technical problem of premature cross-linking of the polyethylene composition during the rotational molding process of polyethylene. At present, in order to improve the cross-linking efficiency of rotational molded cross-linked polyethylene, in addition to adding a cross-linking accelerator, the amount of cross-linking agent and cross-linking aid added is generally large. Therefore, whether the cross-linking aid is powder mixed or co-extruded, too much cross-linking aid in the rotational molding cross-linking material will produce by-product gases such as methane, methyl styrene, water, etc. during the high-temperature rotational molding process. These by-products will be excessive, resulting in many large and small round pits on the surface of the cross-linked material after molding, affecting the appearance and quality of the product. It is usually necessary to reprocess it before it can be further used, with high production costs and low production efficiency. Summary of the invention

[0005] The present invention aims to solve the problem of round pits on the surface of roto-molded parts caused by excessive use of cross-linking agent in the prior art, and provides a cross-linked polyethylene roto-molded material and a preparation method thereof. The technical solution mixes polyethylene raw powder into high-density polyethylene powder, and utilizes the self-cross-linking effect of the polyethylene raw powder itself under high temperature of roto-molding to improve the cross-linking efficiency. The self-cross-linking of the polyethylene raw powder does not produce gas. Under the condition of using a small amount of cross-linking auxiliary agent, a roto-molded part with a high degree of cross-linking can be obtained. The surface of the roto-molded part will not have round pits, and the product surface is smooth and the quality is significantly improved.

[0006] The specific technical scheme of the present invention is: A cross-linked polyethylene roto-plastic material, the raw materials comprising, by mass percentage: High-density polyethylene powder 85-95%, Polyethylene powder 5-10%, Crosslinking agent 0.05~0.5%, The cross-linking accelerator is 0.1-1%, the polyethylene content in the polyethylene raw powder is greater than 99.99%, and the high-density polyethylene powder is prepared by blending high-density polyethylene and an auxiliary agent.

[0007] The present invention provides a cross-linked polyethylene roto-plastic material, which uses polyethylene raw powder as a cross-linking aid, improves the cross-linking efficiency of the roto-plastic material through the self-cross-linking effect of polyethylene, and can avoid the problem of round pits on the surface of the roto-molded part caused by gas production of the cross-linking aid during roto-molding due to excessive addition of the cross-linking aid. The polyethylene raw powder is polyethylene with a polyethylene content greater than 99.99% made by using ethylene to polymerize with a catalyst, and does not contain other additives.

[0008] The present invention has found in actual production that circular pits will appear on the surface of rotomolded parts made of high-density polyethylene containing a cross-linking aid as a raw material. The reason for this problem is that the cross-linking aid will have a side reaction and produce gas when promoting the cross-linking reaction. When the amount of gas produced is too much, circular pits will appear on the surface of the rotomolded part, and the amount of gas produced is proportional to the amount of cross-linking aid added. If the amount of cross-linking aid added is too little, the cross-linking efficiency of the polyethylene will be reduced, resulting in the product performance of the polyethylene rotomolded parts failing to meet the production requirements. Therefore, in order to meet the performance requirements and product quality of polyethylene rotomolded parts, it is currently necessary to perform secondary processing on the surface of the rotomolded parts, which leads to a significant increase in production costs.

[0009] In response to the above problems, the present invention finds that the roto-molded material obtained by blending high-density polyethylene, polyethylene raw powder, a cross-linking aid and a cross-linking accelerator as raw materials can significantly reduce the dosage of the cross-linking aid without changing the cross-linking efficiency when producing roto-molded parts, thereby significantly reducing the gas production of the cross-linking aid, so that no round pits will be generated on the surface of the roto-molded product, and polyethylene roto-molded parts with a smooth surface and no secondary processing can be directly produced, which significantly reduces the processing cost and significantly improves the roto-molding processing efficiency.

[0010] Preferably, the density of the high-density polyethylene is 0.940-0.970 g / cm 3 , the melt index is 5-30g / 10min.

[0011] Preferably, the crosslinking agent is one or more of 2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl isopropylbenzene peroxide).

[0012] Preferably, the crosslinking accelerator is one or more of triallyl cyanurate, triallyl isocyanurate and diallyl phthalate.

[0013] Preferably, the auxiliary agent includes one or both of an antioxidant and a light stabilizer.

[0014] Preferably, the antioxidant is one or more of hindered phenol antioxidants and phosphite antioxidants.

[0015] Preferably, the light stabilizer is one or more of benzotriazole, benzophenone and triazine ultraviolet light absorbers.

[0016] Preferably, the mass percentage of the auxiliary agent is 0.1-0.5%.

[0017] A method for preparing the above-mentioned cross-linked polyethylene roto-plastic comprises the following steps: high-density polyethylene, antioxidant, and light stabilizer are mixed evenly, injected into a mixing device for co-extrusion, granulation and grinding to form high-density polyethylene powder, and then the high-density polyethylene powder is mixed with polyethylene raw powder, a cross-linking agent and a cross-linking accelerator to form a cross-linked polyethylene roto-plastic.

[0018] Preferably, the mixing temperature is 50-60° C. and the rotating speed is 100-300 r / min.

[0019] Preferably, the temperature of the hot rolling composite in step 2 is 120-150°C.

[0020] Compared with the prior art, this application has the following technical effects: The present invention uses polyethylene raw powder and high-density polyethylene powder to mix to form roto-plastic material. The self-crosslinking effect of the polyethylene raw powder significantly improves the crosslinking efficiency of the roto-plastic material, reduces the amount of crosslinking auxiliary agent in the roto-plastic material, thereby significantly reducing the gas generation effect of the crosslinking auxiliary agent during roto-molding of the roto-plastic material, so that round pits will not be generated on the surface of the manufactured roto-molded parts, significantly improves the quality of the roto-molded parts, significantly improves the roto-molding processing efficiency, and significantly reduces the processing cost. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the embodiments.

[0022] Embodiment 1: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3 , melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 35:1, and a screw speed of 400r / min for co-extrusion, granulation and grinding to form a high-density polyethylene powder; Step 2: 94% of the high-density polyethylene powder in step 1 and 5% of the polyethylene raw powder (polyethylene The ethylene content is greater than 99.99%), 0.4% of a crosslinking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.6% of a crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 60°C and a rotation speed of 200r / min to form a crosslinked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0023] Embodiment 2: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 2911 (density 0.956g / cm 3, melt index 20g / 10min, Sinopec Zhenhai Refining and Chemical) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 140°C, a length-to-diameter ratio of 40:1, and a screw speed of 500r / min for co-extrusion, granulation and grinding to form a high-density polyethylene powder; Step 2: 95% of the high-density polyethylene powder and 4.85% of the polyethylene raw powder in step 1 (polyethylene content greater than 99.99%), 0.05% cross-linking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.1% cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 80°C and a rotation speed of 300r / min to form a cross-linked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0024] Embodiment 3: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8007 (density 0.964g / cm 3, melt index 9g / 10min, China Energy Group) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 110°C, a length-to-diameter ratio of 30:1, and a screw speed of 300r / min for co-extrusion, granulation and grinding to form high-density polyethylene powder; Step 2: 88.5% of the high-density polyethylene powder and 10% of the polyethylene raw powder in step 1 (polyethylene content greater than 99.99%), 0.5% crosslinking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 1% crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 40°C and a rotation speed of 100r / min to form a crosslinked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0025] Embodiment 4: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3 , melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) were mixed evenly and injected into a twin-screw extruder at a temperature of 130°C, a length-to-diameter ratio of 40:1 and a screw speed of 300r / min for co-extrusion, granulation and grinding to form high-density polyethylene powder; Step 2: Add 90% of the high-density polyethylene powder in step 1, 9.85% of polyethylene raw powder (polyethylene content greater than 99.99%), 0.05% of a crosslinking agent (di-tert-butyl peroxide), and 0.1% of a crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate, and diallyl phthalate in a mass ratio of 1:1:1) into a high-speed mixer and mix them evenly at a temperature of 80°C and a speed of 200 r / min to form a cross-linked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0026] Embodiment 5: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8007 (density 0.964g / cm 3 , melt index 9g / 10min, China Energy Group) and antioxidant (antioxidant 168) and light stabilizer (UV328) were mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 40:1, and a screw speed of 500r / min for co-extrusion, granulation and grinding to form high-density polyethylene powder; Step 2: Add 95% of the high-density polyethylene powder in step 1, 4.45% of polyethylene raw powder (polyethylene content is greater than 99.99%), 0.05% of a crosslinking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne) and 1% of a crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) into a high-speed mixer and mix them evenly at a temperature of 80°C and a speed of 200r / min to form a cross-linked polyethylene roto-plastic; an application of the above cross-linked polyethylene roto-plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0027] Embodiment 6: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3 , melt index 8g / 10min, PetroChina Dushanzi) and antioxidant (2,6-di-tert-butyl-4-methylphenol) and light stabilizer (UV531) are mixed evenly and injected into a twin-screw extruder to be blended, extruded, granulated and ground into high-density polyethylene powder at a temperature of 110-140°C, a length-diameter ratio of 30-40:1 and a screw speed of 300-500r / min; Step 2: Add 94% of the high-density polyethylene powder in step 1, 4.95% of polyethylene raw powder (polyethylene content greater than 99.99%), 0.05% of a crosslinking agent (2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane) and 1% of a crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) into a high-speed mixer and mix them evenly at a temperature of 80°C and a speed of 200r / min to form a crosslinked polyethylene roto-plastic; an application of the above crosslinked polyethylene roto-plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0028] Embodiment 7: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3 , melt index 8g / 10min, PetroChina Dushanzi) and antioxidant (mass ratio of 1:1 2,6-di-tert-butyl-4-methylphenol and antioxidant 168) and light stabilizer (UV1577) are mixed evenly and injected into a twin-screw extruder to mix, extrude, granulate and grind to make high-density polyethylene powder under the conditions of temperature 110-140°C, aspect ratio 30-40:1 and screw speed 300-500r / min; Step 2: Add 90% of the high-density polyethylene powder in step 1, 8.95% of polyethylene raw powder (polyethylene content greater than 99.99%), 0.05% of a cross-linking agent (tert-butyl isopropyl peroxide) and 1% of a cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) into a high-speed mixer and mix them evenly at a temperature of 80° C. and a speed of 200 r / min to form a cross-linked polyethylene roto-plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0029] Embodiment 8: A method for preparing a cross-linked polyethylene roto-plastic comprises the following steps: Step 1: High-density polyethylene 8007 (density 0.964g / cm 3, melt index 9g / 10min, China Energy Group) and antioxidant (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizer (UV1577) were mixed evenly and injected into a twin-screw extruder to be blended, extruded, granulated and ground into high-density polyethylene powder at a temperature of 130°C, a length-diameter ratio of 40:1 and a screw speed of 500r / min; Step 2: Add 95% of the high-density polyethylene powder in step 1, 3.95% of polyethylene raw powder (polyethylene content is greater than 99.99%), 0.05% of a cross-linking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 1% of a cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) into a high-speed mixer and mix them evenly at a temperature of 80°C and a speed of 200 r / min to form a cross-linked polyethylene rolling plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0030] Comparative Example 1: Compared with Example 1, the polyethylene raw powder in Comparative Example 1 is replaced by a cross-linking agent, comprising the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3, melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 35:1, and a screw speed of 400r / min for blending, extrusion, granulation and grinding to form a high-density polyethylene powder; Step 2: 94% of the high-density polyethylene powder in step 1 The raw material, 5.4% of a cross-linking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.6% of a cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 60°C and a rotation speed of 200 r / min to form a cross-linked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold, heated and roto-molded at a speed of 10 r / min for the main shaft and 12.5 r / min for the secondary shaft, and then demoulded at a demoulding temperature of 90°C to obtain the roto-molded part.

[0031] Comparative Example 2: Compared with Example 1, the polyethylene raw powder in Comparative Example 2 contains 10% of a cross-linking agent, and comprises the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3, melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 35:1, and a screw speed of 400r / min for co-extrusion, granulation and grinding to form high-density polyethylene powder; Step 2: 94% of the high-density polyethylene powder and 5% of the polyethylene raw powder in step 1 (containing 10% of a cross-linking agent), 0.4% of a cross-linking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.6% of a cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 60°C and a rotation speed of 200 r / min to form a cross-linked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold, heated and roto-molded at a speed of 10 r / min for the main shaft and 12.5 r / min for the secondary shaft, and then demoulded at a demoulding temperature of 90°C to obtain the roto-molded part.

[0032] Comparative Example 3: Compared with Example 1, the amount of the crosslinking aid in Comparative Example 3 is too large, and the amount of the crosslinking agent is 3%, comprising the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3, melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 35:1, and a screw speed of 400r / min for co-extrusion, granulation and grinding to form high-density polyethylene powder; Step 2: 94% of the high-density polyethylene powder and 2.4% of the polyethylene raw powder in step 1 (polyethylene content greater than 99.99%), 3% crosslinking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.6% crosslinking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 60°C and a rotation speed of 200r / min to form a crosslinked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold, heated and roto-molded at a speed of 10 r / min for the main shaft and 12.5 r / min for the secondary shaft, and then demoulded at a demoulding temperature of 90°C to obtain the roto-molded part.

[0033] Comparative Example 4: Compared with Example 1, Comparative Example 3 does not use polyethylene raw powder, and includes the following steps: Step 1: High-density polyethylene 8008 (density 0.955g / cm 3, melt index 8g / 10min, PetroChina Dushanzi) and antioxidants (2,6-di-tert-butyl-4-methylphenol and antioxidant 168 in a mass ratio of 1:1) and light stabilizers (UV328, UV531 and UV1577 in a mass ratio of 1:1:1) are mixed evenly and injected into a twin-screw extruder at a temperature of 125°C, a length-to-diameter ratio of 35:1, and a screw speed of 400r / min for blending, extrusion, granulation and grinding to form a high-density polyethylene powder; Step 2: 99% of the high-density polyethylene powder in step 1 The raw material, 0.4% cross-linking agent (2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butyl peroxide isopropylbenzene in a mass ratio of 1:1:1) and 0.6% cross-linking accelerator (triallyl cyanurate, triallyl isocyanurate and diallyl phthalate in a mass ratio of 1:1:1) are added into a high-speed mixer and mixed evenly at a temperature of 60°C and a rotation speed of 200r / min to form a cross-linked polyethylene roller plastic; An application of the cross-linked polyethylene rolling plastic comprises the following steps: The cross-linked polyethylene roto-plastic material was injected into the roto-molding mold and heated for roto-molding at a speed of 10 r / min for the main axis and 12.5 r / min for the secondary axis. The roto-molded part was then demoulded at a demoulding temperature of 90°C to obtain a roto-molded part, which was a cube with a side length of 30 cm.

[0034] Test example: The rotomoulded parts prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were tested, and the test items included appearance, crosslinking degree and impact strength; The cross-linking degree is tested in accordance with GB / T 18474-2001 Test method for cross-linking degree of cross-linked polyethylene (PE-X) pipes and fittings; the impact strength is tested in accordance with GB / T 39933-2021 Low temperature impact test for rotational molding; The test results are shown in Table 1.

[0035] Table 1 Test results As shown in Table 1, the surfaces of the rotomolded parts obtained in Examples 1 to 8 have no round pits, a crosslinking degree of 52 to 72%, and an impact strength of 10 to 32 J / mm. The above results indicate that the present application provides rotomolded parts made by rotomolding of cross-linked polyethylene rotomolding plastics, which have no round pits on the surface, are of good quality, have a high degree of crosslinking, and have excellent performance of the rotomolded parts.

[0036] In Comparative Example 1, the polyethylene raw powder was replaced with a cross-linking agent. As a result, it was found that more round pits were produced on the surface of the rotomolded part made in Comparative Example 1. There was no significant difference in the degree of cross-linking and the impact strength between the comparative example and Example 1, but more round pits were produced on the surface of the comparative example 1, and the appearance quality of the product was poor; in Comparative Example 2, the polyethylene raw powder contained 10% of the cross-linking agent. As a result, it was found that more round pits were produced on the surface of the rotomolded part made in Comparative Example 2, which indicates that when the polyethylene raw powder contains a cross-linking agent, more round pits will also be produced on the surface of the rotomolded part; in Comparative Example 3, the amount of polyethylene raw powder was reduced and the amount of cross-linking agent was increased. As a result, it was found that round pits were produced on the surface of the rotomolded part made in Comparative Example 3. The above results indicate that when the amount of cross-linking agent is too much, round pits will appear on the surface of the rotomolded part.

[0037] No polyethylene raw powder was added in Comparative Example 4. As a result, no round pits appeared on the surface of the rotomolded part made in Comparative Example 4, but the degree of crosslinking of Comparative Example 4 was significantly reduced, and the impact strength of the rotomolded part was also significantly reduced. This result shows that reducing the amount of crosslinking agent can prevent round pits from appearing on the surface of the rotomolded part, and polyethylene raw powder can significantly increase the degree of crosslinking of the rotomolding material, so that the rotomolded part surface does not produce round pits while having material properties that meet the requirements.

[0038] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A cross-linked polyethylene plastic, characterized in that: The raw materials include by mass percentage: High density polyethylene powder 85~95%, Polyethylene powder 5~10%, Crosslinking agent 0.05~0.5%, Cross-linking accelerator 0.1~1%, The polyethylene content in the polyethylene raw powder is greater than 99.99%, and the high-density polyethylene powder is prepared by blending high-density polyethylene and an auxiliary agent.

2. The cross-linked polyethylene rotomolding material according to claim 1, characterized in that: The density of the high-density polyethylene is 0.955-0.964 g / cm 3 , the melt index is 8~20 g / 10min.

3. The cross-linked polyethylene rotomolding material according to claim 1, characterized in that: The crosslinking agent is one or more of 2,5-(di-tert-butylperoxy)-2,5-dimethyl-3-hexyne, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and tert-butylperoxide).

4. The cross-linked polyethylene rotoform material according to claim 1, characterized in that: The cross-linking accelerator is one or more of triallyl cyanurate, triallyl isocyanurate and diallyl phthalate.

5. The cross-linked polyethylene rotomolding material according to claim 1, characterized in that: The auxiliary agent includes one or both of an antioxidant and a light stabilizer.

6. The cross-linked polyethylene rotomolding plastic according to claim 5, characterized in that: The antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol and antioxidant 168.

7. The cross-linked polyethylene rotomolding material according to claim 5, characterized in that: The light stabilizer is one or more of UV328, UV531 and UV1577.

8. The cross-linked polyethylene rotoform material according to claim 1 or 5, characterized in that: The mass percentage of the auxiliary agent is 0.1-0.5%.

9. A method for preparing the cross-linked polyethylene rotomolding plastic according to any one of claims 1 to 8, characterized in that: The following steps are involved: The high-density polyethylene, antioxidant and light stabilizer are mixed evenly and injected into a mixing device for blending, extrusion, granulation and grinding to make high-density polyethylene powder, and then the high-density polyethylene powder is mixed with polyethylene raw powder, cross-linking agent and cross-linking accelerator to make cross-linked polyethylene roto-plastic.

10. The preparation method according to claim 9, characterized in that: The mixing temperature is 50-60°C and the rotating speed is 100-300 r / min.

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