Compound additive for chromium polyethylene

Abstract

The invention discloses a compound additive for chromium polyethylene. The compound additive comprises the following components in percentage by weight: 30-40% of a main antioxidant, 30-40% of an auxiliary antioxidant and 30-40% of a stabilizer. The compound additive for the chromium-based polyethylene can avoid great fluctuation generated by production load of a polymerization unit and avoid the problem that performance indexes of materials are reduced due to residual chromium-based catalysts, and the obtained chromium-based polyethylene product is good in stability and especially suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the field of plastic additives, and more specifically, particularly relates to a compound additive for chromium-based polyethylene. Background Art

[0002] At present, the commonly used catalysts for synthesizing low-density polyethylene include chromium catalysts, molybdenum catalysts, palladium-nickel catalysts, etc. Chromium catalysts are an important industrial polyethylene catalyst, producing 40-50% of the world's total high-density polyethylene and a small amount of linear low-density polyethylene. They have high polymerization activity and wide product distribution. Chromium polyethylene products are superior to other catalyst products in tensile strength, tear strength, environmental stress cracking resistance, low temperature resistance, heat resistance and puncture resistance. Moreover, among the above catalysts, chromium catalysts have the lowest price and are currently the most widely used polyethylene catalysts. However, the main disadvantage of using chromium catalysts is that the production load of the polymerization unit is prone to large fluctuations during the production of polyethylene, and the residual catalyst is prone to change the physical properties and chemical stability of the product. Therefore, for chromium polyethylene products, it is crucial to further improve product stability and find a suitable antioxidant system. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a compound additive suitable for chromium-based polyethylene.

[0004] The object of the present invention is achieved in the following ways:

[0005] A compound additive for chromium-based polyethylene, the compound additive is made of the following components in percentage by weight:

[0006] Main antioxidant 30~40%

[0007] Auxiliary antioxidant 30~40%

[0008] Stabilizer 30-40%.

[0009] Preferably, the above-mentioned compound additive for chromium-based polyethylene is made of the following components in percentage by weight:

[0010] Main antioxidant 30.33~36.33%

[0011] Auxiliary antioxidant 30.33~36.33%

[0012] Stabilizer 30.34~36.34%.

[0013] Preferably, the primary antioxidant is antioxidant 168.

[0014] Preferably, the secondary antioxidant is antioxidant 1010.

[0015] Preferably, the stabilizer is a mixture of zinc stearate and calcium stearate.

[0016] The most preferred weight ratio of zinc stearate to calcium stearate is 2:1.

[0017] The method for preparing the above-mentioned chromium-based polyethylene compound additive comprises the following steps:

[0018] 1) Premix all components and disperse them roughly;

[0019] 2) Use a ball mill to further refine and disperse all the components; control the speed to 120-150 revolutions per minute;

[0020] 3) Use a granulator to further enhance the dispersion of all components during extrusion granulation.

[0021] Preferably, the additive is used in an amount of 5-6‰ of the mass of the chromium polyethylene, preferably 5.4‰; it can be added in a continuous manner.

[0022] The method of using the above-mentioned compound additive for chromium-based polyethylene is as follows:

[0023] The chromium polyethylene granules or powders are added to the target product chromium polyethylene through a feeding hopper, mixed with the raw materials, and then melted and granulated by an extruder. In the extrusion granulation process of chromium polyethylene, the compound additive for chromium polyethylene of the present invention can avoid the degradation of polymer molecular chains and avoid the large fluctuation of the production load of the polymerization unit.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention obtains a suitable antioxidant system for chromium-based polyethylene products by screening, thereby avoiding large fluctuations in the production load of polymerization units, avoiding the problem of decreased material performance indicators due to residual chromium-based catalysts, and inhibiting free radical reactions caused by light, heat, oxygen, shearing, etc. during the use or processing of polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a test diagram of the melt mass flow rate of the DGDB6097 product in Example 2.

[0027] Figure 2 This is a density detection diagram of the DGDX6095 product pellets in Example 1. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] A chromium-based polyethylene compound additive is prepared from the following components in percentage by weight:

[0031]

[0032] Preparation method:

[0033] 1) Premix all components and disperse them roughly;

[0034] 2) Using a horizontal ball mill to further refine and disperse all the components; controlling the speed to 120-150 revolutions per minute, the temperature to 40-60° C., and the time to 40 minutes.

[0035] 3) The granulator is used to further enhance the dispersion of all components during extrusion granulation. The granulation is carried out using a twin-screw granulator with an internal temperature of 120-130°C and a discharge temperature of 40-60°C.

[0036] Example 2

[0037] A compound additive for chromium-based polyethylene, made from the following components in percentage by weight

[0038]

[0039] Preparation method: Same as Example 1.

[0040] Example 1-2 Additive Quality Index

[0041]

[0042]

[0043] Comparative Example 1

[0044] A compound additive for chromium-based polyethylene, made from the following components in percentage by weight

[0045]

[0046] Preparation method: Same as Example 1.

[0047] Comparative Example 2

[0048] formula:

[0049] Antioxidants 168 30.5%;

[0050] Antioxidant 1010 30.5%;

[0051] Zinc stearate 39%.

[0052] Preparation method: Same as Example 1.

[0053] Comparative Example 3

[0054] formula:

[0055]

[0056] Preparation method: Same as Example 1.

[0057] Comparative Examples 1-3 Additive Quality Index

[0058]

[0059]

[0060] Test example

[0061] The quality of chromium-based polyethylene (Lanzhou Petrochemical) DGDB6096, DGDB6097 and DGDX6095 products prepared using the additives of the present invention and the comparative example additives is shown in Table 1. The added mass in the chromium-based polyethylene is 5.4‰.

[0062] Table 1

[0063]

[0064] During the trial of the additive of the present invention, the production load of the polymerization unit did not fluctuate significantly, and the key parameters such as reaction temperature, total reaction pressure, ethylene partial pressure, butene-ethylene ratio, RO / C2H4, etc. were all in a stable state, which can avoid the production fluctuation of the polymerization unit from affecting the test results. Therefore, the chromium-based polyethylene product produced by using the additive of the present invention as an auxiliary agent has good stability and can significantly reduce the cost of raw materials.

Claims

1. A compound additive for chromium-based polyethylene, characterized in that The compound additive is made of the following components in percentage by weight: Main antioxidant 30~40% Auxiliary antioxidant 30~40% Stabilizer 30-40%.

2. The chromium-based polyethylene compound additive according to claim 1, characterized in that Made of the following components in percentage by weight: Main antioxidant 30.33~36.33% Auxiliary antioxidant 30.33~36.33% Stabilizer 30.34~36.34%.

3. The chromium-based polyethylene compound additive according to claim 1 or 2, characterized in that The main antioxidant is antioxidant 168.

4. The chromium-based polyethylene compound additive according to claim 1 or 2, characterized in that The secondary antioxidant 1010.

5. The chromium-based polyethylene compound additive according to claim 1 or 2, characterized in that The stabilizer is a mixture of zinc stearate and calcium stearate.

6. The chromium-based polyethylene compound additive according to claim 5, characterized in that The weight ratio of the zinc stearate to the calcium stearate is 2:

1.

7. A method for preparing the composite additive for chromium-based polyethylene according to claim 1 or 2, characterized in that The method comprises the following steps: 1) Premix all components and disperse them roughly; 2) Use a ball mill to further refine and disperse all the components; control the speed to 120-150 revolutions per minute; 3) Use a granulator to further enhance the dispersion of all components during extrusion granulation.

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