Wide-distribution polyethylene resin with low-temperature impact resistance

Abstract

The invention discloses a low-temperature-impact-resistant wide-distribution injection molding grade polyethylene resin, and relates to the field of polyethylene. The polyethylene resin is composed of a high-molecular-weight polyethylene component and a low-molecular-weight polyethylene component, the melt index (MI2.16) of the polyethylene is 0.5-65 g / 10 min, the weight-average molecular weight range is 2 * 10 < 4 >-9 * 10 < 5 > g / mol, the molecular weight distribution is 2.5-50, the comonomer insertion rate is 0-10%, the impact strength at room temperature is 2-75 kJ / m < 2 >, and under the low-temperature condition of-60-0 DEG C, the melt index (MI2.16) of the polyethylene is 0.5-65 g / 10 min. The impact strength retention rate ranges from 70% to 99%. By controlling the blending distribution uniformity of the high-molecular-weight polyethylene component and the low-molecular-weight polyethylene component, the processing performance and the impact performance of the resin are balanced, and under the action of a flow field of an injection molding processing technology, the high-molecular-weight polyethylene component forms a longer-scale extended chain precursor; the low-molecular-weight component is filled in gaps of the high-molecular-weight polyethylene component to form a shish-kebab structure which is larger in size and more regular in structure, so that the aims of improving the impact strength and improving the impact strength retention rate at low temperature are fulfilled.

Description

Technical Field

[0001] The present invention relates to the field of polyethylene, and particularly to a wide-distribution injection molding grade polyethylene resin with low-temperature impact resistance. Background Art

[0002] As a widely used polymer material, polyethylene plays an important role in many industrial fields. During the production process of polyethylene, the molecular weight and its distribution, as well as the content and distribution of comonomers, are key factors affecting its processing performance, mechanical properties, and physical characteristics. Specifically, when the molecular weight of polyethylene is relatively high, the material usually exhibits good mechanical strength and excellent durability. However, at the same time, its melt fluidity is poor, which may lead to difficulties and reduced efficiency during the injection molding process. On the contrary, polyethylene with a relatively low molecular weight has good melt fluidity, which is beneficial for injection molding, but its mechanical properties are relatively poor, especially in terms of impact strength and impact strength at low temperatures.

[0003] To balance the melt fluidity and mechanical properties of polyethylene, traditional solutions are to improve its properties by adding inorganic fillers (such as talc, calcium carbonate, glass fiber, etc.) or using some external substances (such as antioxidants, ultraviolet absorbers, plasticizers, lubricants, etc.). Inorganic fillers can improve the rigidity and wear resistance of polyethylene, but their addition also brings some problems. First, the addition of fillers may reduce the toughness of polyethylene, thereby increasing its brittleness. Second, uneven dispersion of the fillers may affect the overall performance of the material and even lead to deterioration of local properties. In addition, these fillers may also increase the processing difficulty and affect the production efficiency. At the same time, the long-term stability of external additives is usually poor. They may migrate or volatilize during use, thereby having a negative impact on the overall performance and service life of the material. The addition of these external substances sometimes also changes the mechanical properties or other important physical characteristics of polyethylene, thus affecting the quality and use effect of the final product. Therefore, in the process of modifying polyethylene, how to effectively solve these problems and optimize its comprehensive performance has become an important topic in current research and applications.

[0004] Patent CN201310311017.4 discloses a method for preparing wide / bimodal polyethylene in a single reactor. During the reaction process, two catalysts are introduced, where the first catalyst is used to prepare the low molecular weight part of the wide / bimodal polyethylene, and the second catalyst is used to prepare the high molecular weight part of the wide / bimodal polyethylene. Although this method can effectively optimize the molecular weight distribution of polyethylene and improve the comprehensive properties of the material, when the two catalysts coexist in the same reactor, there may be a risk of mutual inhibition or interference. In addition, Patent CN202110522256.9 discloses a method for efficiently preparing a high-performance polyolefin blend by a two-stage process in a single reactor. The molecular weight of the polyolefin component A produced is 1×10 4 ~1×10 7 g / mol, and the molecular weight of the polyolefin component B is 1×10 3 ~5×10 5 g / mol; the branched chain content of the polyolefin component A accounts for 50-96% of the total branched chain content. This method can achieve the effect of uniform mixing of the virgin materials, but the molecular weights of the high and low components of the injection molding grade resin, the proportion of the high and low components, and their corresponding molecular chain structures are not clear.

[0005] Patent CN201711474529.7 discloses a low-temperature impact-resistant polypropylene resin, its preparation method, and a hollow article prepared therefrom. By uniformly mixing 60-95 wt% of a polypropylene resin base material and 5-40 wt% of a polyethylene resin base material and then pelletizing, a low-temperature impact-resistant resin can be obtained, which can improve the strength and heat resistance of the resin. In addition, Patent CN201811171009.3 discloses a rigid-tough balanced highly transparent polypropylene composition, including 100 parts of an ethylene-propylene copolymer and 10-25 parts of a propylene homopolymer, mainly formed by melt-mixing two resins. The rigidity of the propylene-ethylene impact copolymer is adjusted with the propylene homopolymer, ultimately achieving a rigid-tough balance in the composition. However, the above two patents are limited by problems such as blend compatibility and uniform branch distribution, and there are significant limitations in improving the impact resistance and low-temperature retention rate. In summary, the coexistence of high-molecular-weight components and low-molecular-weight components in polyethylene often requires reasonable control to ensure that the material has both sufficient strength and good processing fluidity. Traditional polyethylene often fails to effectively control the balance of different molecular weight components during the polymerization process, making it difficult to obtain polyethylene products with both good processing performance and high strength. In addition, existing technologies usually need to increase the high-molecular-weight components to improve the mechanical properties of polyethylene, but this often leads to poor processing fluidity of the material, making it difficult to meet the requirements of the injection molding process. And blending two materials will have problems such as uneven mixing and high energy consumption. Therefore, by controlling the ratio between high- and low-molecular-weight components, the molecular weights of each component, and regulating the insertion rate of the resin through copolymerization means, the organic coexistence of high-molecular-weight components and low-molecular-weight components can be achieved to improve the mechanical properties and processing performance of injection-grade polyethylene resin. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides an injection-grade polyethylene resin with a wide distribution of high-molecular-weight components and low-molecular-weight components introduced.

[0007] By regulating the molecular weights of different components, the proportions of different components, and the content of comonomers, the present invention can effectively form shish-kebab crystals under an injection molding flow field. Due to the strong molecular chain interweaving characteristics of the shish-kebab crystal structure, this enables a better connection between the crystalline region and the amorphous region of the resin. When subjected to impact, the shish-kebab crystal structure can help the molecular chains to slip and deform, thereby effectively absorbing the impact energy, slowing down the crack propagation, and improving the impact toughness of the material. When the resin with the shish-kebab crystal structure is subjected to impact, cracks usually propagate along the crystal boundaries. The shish-kebab crystal structure changes the arrangement of the crystal boundaries, making the crack propagation path complex, thereby delaying the crack propagation speed and further improving the impact resistance of the material. Moreover, in the broad molecular weight distribution, the long-chain molecules of the high molecular weight component play a strengthening role under impact loads, while the chain segments of the low molecular weight component facilitate the slip and deformation of the molecular chains to reduce the occurrence of stress concentration regions, which helps to improve the impact resistance of polyethylene. In addition, by introducing a uniformly distributed branched chain structure to regulate the crystalline structure of the polyethylene resin, the crystalline region will not show obvious local irregularities due to the aggregation of branched chains, which helps to form a more uniform shish-kebab crystal structure. And the uniform branched chain distribution can make the size and shape of the crystals more uniform, avoiding the stress concentration phenomenon in the crystalline region caused by the non-uniform branched chain distribution and reducing brittle fracture at low temperatures. The present invention simultaneously improves the processing fluidity and impact resistance (low-temperature impact resistance) of the polyethylene resin.

[0008] An embodiment of the present invention provides a broad-distribution injection molding grade polyethylene resin with low-temperature impact resistance, which is composed of a high molecular weight polyethylene component and a low molecular weight polyethylene component. The weight-average molecular weight range of the high molecular weight polyethylene component is 6×10 5 g / mol to 5×10 6 g / mol, and the molecular weight distribution range is 1.5 - 10; the weight-average molecular weight range of the low molecular weight polyethylene component is 5×10 3 g / mol to 5×10 5 g / mol, and the molecular weight distribution range is 1.5 to 20; in the polyethylene resin, the mass percentage of the high molecular weight polyethylene component is 1% - 90%. The melt index of the broad-distribution polyethylene resin with low-temperature impact resistance is in the range of 0.5 - 65 g / 10 min, the weight-average molecular weight range is 2×10 4 g / mol to 9×10 5 g / mol, the molecular weight distribution is in the range of 2.5 - 50, the comonomer insertion rate is 0 - 10%, the impact strength at room temperature (23°C) is in the range of 2 - 75 kJ / m 2 range, and under the low-temperature condition of -60 to 0°C, the impact strength retention rate is in the range of 70% - 99%.

[0009] Preferably, by coupling TREF-GPC-NMR, the low-temperature impact-resistant wide-distribution injection molding grade polyethylene resin is divided into 12 to 20 components with different molecular weights, and the CV value of the comonomer insertion rate of different molecular weight components is tested to be ≤ 3.0%.

[0010] Preferably, the melt index of the polyethylene resin is 2 to 30 g / 10 min, and the impact strength distribution at room temperature (23 °C) is 3 to 50 kJ / m 2 , and the impact performance strength distribution at low temperature (-60 to 0 °C) is 2 to 45 kJ / m 2 , the low-temperature range is -60 °C to 0 °C, and the impact performance at low temperature can retain 70% to 99% of that at room temperature.

[0011] Preferably, the mass ratio range of the high molecular weight polyethylene component to the low molecular weight polyethylene component is preferably 2% to 40%.

[0012] According to the preferred embodiment of the present invention, the high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained by sequential polymerization, and the polymerization includes: first synthesizing the high molecular weight polyethylene component in a polymerization reactor by controlling polymerization conditions, and then switching the polymerization conditions to in-situ polymerize the low molecular weight component in the same polymerization reactor, thereby obtaining the low-temperature impact-resistant wide-distribution injection molding grade polyethylene resin.

[0013] Among them, the method of switching polymerization conditions includes: adding a chain transfer agent to the polymerization reactor, adding a comonomer to the polymerization reactor, changing one or more of the polymerization temperature or polymerization pressure.

[0014] Preferably, the polymerization reactor is a kettle reactor, and when switching polymerization conditions, no polymer is discharged. Preferably, when not switching polymerization conditions, polymerization is carried out under a single polymerization condition until the polymerization ends.

[0015] Typical but not limited, in a further preferred implementation method of the present invention, the polyethylene resin is prepared by the following method:

[0016] 1) Sequentially put a catalyst, a cocatalyst, and an olefin monomer into the reactor. The catalyst is one or more of a metallocene catalyst, a chromium-based catalyst, an FI catalyst, a Ziegler-Natta catalyst, and a late transition metal catalyst; the cocatalyst is one or more of triethylaluminum, triisopropylaluminum, trimethylaluminum, diethylaluminum chloride, dichloroethylaluminum, tributylaluminum, trihexylaluminum, and trioctylaluminum; the olefin monomer is one or several of ethylene, propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene;

[0017] 2) In the first stage of the polymerization process, high-molecular-weight polyethylene is preliminarily synthesized, and in the second stage, low-molecular-weight components are generated by controlling the temperature, pressure, and the content of the comonomer, ensuring that the overall polymer has the property of a high melt index.

[0018] 3) In the first stage of the reaction, high-molecular-weight components with a molecular weight of 6×10 5 g / mol to 5×10 6 g / mol are generated; in the second stage of the reaction, low-molecular-weight components with a molecular weight of 5×10 3 g / mol to 5×10 5 g / mol are generated;

[0019] Among them, according to the requirements of the target product, the different polymerization monomers are introduced or not introduced into the reactor, or after ensuring that the polymerization monomers are initially introduced and then always remain in the reactor, other comonomers are further added to achieve the switching between different homopolymerizations and different copolymerizations.

[0020] In a preferred embodiment of the present invention, the olefin monomer is ethylene, and the comonomer olefin is one or more of α-olefins. Preferably, the comonomer olefin is one or more of propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene.

[0021] In a preferred embodiment of the present invention, the olefin polymerization reactor is a tank reactor.

[0022] In a preferred embodiment of the present invention, the switching point is switched according to the different ratios of high-molecular-weight polyethylene and low-molecular-weight polyethylene components.

[0023] In a preferred embodiment of the present invention, the chain transfer agent for the polymerization reaction is hydrogen and metal alkyl, preferably hydrogen.

[0024] In a preferred embodiment of the present invention, the temperature of the polymerization reaction is -30 to 100 °C, the polymerization pressure is 0.5 to 60 bar, and the reaction time is 0.1 to 10 h.

[0025] Compared with the prior art, the low-temperature impact-resistant wide-distribution polyethylene resin of the present invention is composed of a high-molecular-weight polyethylene component and a low-molecular-weight polyethylene component. The high-molecular-weight component provides more oriented structures for the polyethylene resin. By further introducing the low-molecular-weight component, the overall melt fluidity of the resin can be improved, which helps to enhance the processing performance. And during injection molding, by introducing components with different molecular weights, the high-molecular-weight component forms extended-chain precursors, and under the interaction and guiding effect of the polymer chains, the segments aggregate in a specific direction to form crystalline regions, while the other parts remain amorphous, finally forming a shish-kebab structure. The shish-kebab structure helps to improve rigidity, but due to the existence of more slip and deformation ability between molecular chains in the shish-kebab structure, the impact toughness of the resin can also be improved. Under appropriate conditions, the shish-kebab structure helps the polymer to undergo slip and dispersion of molecular chains when subjected to external force impact, thereby increasing the impact strength. Moreover, with the increase of the extended-chain molecular weight, the molecular chain relaxation ability decreases, the relaxation time becomes longer, and it is not easily affected by temperature to transform into folded chains or amorphous regions, thus achieving the effect of high impact strength retention rate at low temperatures.

[0026] The melt index of the low-temperature impact-resistant wide-distribution polyethylene resin of the present invention is in the range of 0.5-65 g / 10 min, the weight-average molecular weight range is 2×10 4 g / mol - 9×10 5 g / mol, the molecular weight distribution is in the range of 2.5-50, the comonomer insertion rate is 0-10%, the impact strength at room temperature (23°C) is in the range of 2-75 kJ / m 2 range, and under the low-temperature condition of -60 to 0°C, the impact strength retention rate is in the range of 70% - 99%. This resin has both a high melt index and high impact strength (normal temperature / low-temperature impact). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It shows the GPC chart of the injection-grade polyethylene resin prepared in Example 1.

[0028] Figure 2 It shows the low-temperature impact retention rate of the injection-grade polyethylene prepared in Examples 1-6 and Comparative Examples 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0029] Characterization methods for polymer structure and properties:

[0030] (1) Melt index: According to GB / T-3682-83, the melt flow rate in 10 min was measured at 190°C under a load of 2.16 kg.

[0031] (2) Density: Measured according to the method of GB / 1033-1986.

[0032] (3) Impact strength: Determined according to GB / T 1843-2008, where the impact specimens are formed by injection molding, and the low-temperature impact strength is determined after treatment at -40°C for 24 h.

[0033] (4) Weight-average molecular weight, molecular weight distribution, and comonomer distribution: Determined by coupling high-temperature size exclusion chromatography HT-GPC with Fourier transform infrared spectroscopy FTIR.

[0034] (5) Comonomer insertion rate: Determined and calculated according to 13 C-NMR

[0035] Example 1

[0036] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The reactor temperature was adjusted to 40°C, and n-hexane was added as the polymerization solvent. 3 μmol of catalyst (Ziegler-Natta catalyst was selected), 3000 μmol of cocatalyst (triethylaluminum was selected), 5 bar of olefin monomer (ethylene was selected), and 1.0 bar of comonomer (butene was selected) were added in sequence for the preliminary polymerization reaction to prepare high-molecular-weight polyethylene with a weight-average molecular weight of 1×10 6 g / mol, a molecular weight distribution of 6, and a comonomer insertion rate of 1%. Further, the polymerization reaction was carried out by adding 3.5 bar of hydrogen to prepare low-molecular-weight polyethylene with a weight-average molecular weight of 5×10 4 g / mol, a molecular weight distribution of 20, and a comonomer insertion rate of 0.5%. The mass ratio of the high-molecular-weight component to the low-molecular-weight component was 40:60, and finally, an injection-molding grade polyethylene resin was obtained.

[0037] Figure 1 The GPC-IR diagram of the injection-molding grade polyethylene resin prepared in Example 1 of the present invention is shown. The melt index (MI 2.16 ) of the prepared injection-molding grade polyethylene resin is 1 g / 10 min, the weight-average molecular weight is 9×10 5 g / mol, the molecular weight distribution is 50, the butene monomer insertion rate of the resin is 0.7%, the room-temperature impact strength is 75 kJ / m 2 , and the low-temperature impact strength (-40°C) is 74 kJ / m 2 . At low temperature, the impact strength retention rate is 98.7%.

[0038] Example 2

[0039] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The temperature of the reactor was adjusted to 70 °C, and n-heptane was added as the polymerization solvent. 3 μmol of catalyst (a chromium-based catalyst was selected), 3000 μmol of cocatalyst (trimethylaluminum was selected), 2 bar of olefin monomer (ethylene was selected), and 4 bar of comonomer (propylene was selected) were added in sequence for the preliminary polymerization reaction to prepare high-molecular-weight polyethylene with a weight-average molecular weight of 1.2×10 6 g / mol, a molecular weight distribution of 3.5, and a comonomer insertion rate of 15%. Further, 3 bar of ethylene and 2 bar of hydrogen were added for the polymerization reaction to prepare low-molecular-weight polyethylene with a weight-average molecular weight of 5×10 4 g / mol, a molecular weight distribution of 15, and a comonomer insertion rate of 9%. The mass ratio of the high-molecular-weight component to the low-molecular-weight component was 20:80, and finally, injection-molding grade polyethylene resin was obtained.

[0040] The prepared injection-molding grade polyethylene resin had a melt index (MI 2.16 ) of 5 g / 10 min, a weight-average molecular weight of 5×10 5 g / mol, a molecular weight distribution of 22, an insertion rate of propylene monomer of 10%, an impact strength at room temperature of 35 kJ / m 2 , and an impact performance at low temperature (-40 °C) of 33 kJ / m 2 . At low temperature, the impact strength retention rate was 94.3%.

[0041] Example 3

[0042] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The temperature of the reactor was adjusted to 50 °C, and n-hexane was added as the polymerization solvent. 3 μmol of catalyst (a Ziegler-Natta catalyst was selected), 3000 μmol of cocatalyst (triethylaluminum was selected), 3 bar of olefin monomer (ethylene was selected), 50 ml of comonomer (pentene was selected), and 0.2 bar of hydrogen were added in sequence for the preliminary polymerization reaction to prepare high-molecular-weight polyethylene with a weight-average molecular weight of 9×10 5 g / mol, a molecular weight distribution of 5, and a comonomer insertion rate of 9%. Further, 3 bar of ethylene and 3.5 bar of hydrogen were added for the polymerization reaction to prepare low-molecular-weight polyethylene with a weight-average molecular weight of 5×10 3 g / mol, a molecular weight distribution of 1.5, and a comonomer insertion rate of 6%. The mass ratio of the high- and low-molecular-weight components was 30:70. Finally, injection-molding grade polyethylene resin was obtained.

[0043] The prepared injection-molding grade polyethylene resin had a melt index (MI 2.16 ) of 18 g / 10 min, a weight-average molecular weight of 5×104 g / mol, with a molecular weight distribution of 25, the hexene monomer insertion rate of this resin is 7%, and the impact strength at room temperature is 4 kJ / m 2 , and the impact performance at low temperature (-40 °C) is 3.5 kJ / m 2 . At low temperature, the impact strength retention rate is 87.5%.

[0044] Example 4

[0045] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The reactor temperature was adjusted to 60 °C, and n-hexane was added as the polymerization solvent. 3 μmol of catalyst (Ziegler-Natta catalyst was selected), 300 μmol of cocatalyst (triisobutylaluminum was selected), 6 bar of olefin monomer (ethylene was selected), and 1.0 bar of comonomer (butene was selected) were added in sequence for the preliminary polymerization reaction to prepare a high molecular weight component polyethylene with a weight average molecular weight of 5×10 6 g / mol and a molecular weight distribution of 3. Further, the polymerization reaction was carried out by adding 4 bar of hydrogen to prepare a low molecular weight component polyethylene with a weight average molecular weight of 5×10 3 g / mol and a molecular weight distribution of 1.5. The mass ratio of the high and low molecular weight components was 20:80, and finally an injection molding grade polyethylene resin was obtained.

[0046] The melt index (MI 2.16 ) of the prepared injection molding grade polyethylene resin is 65 g / 10 min, the weight average molecular weight is 3×10 7 g / mol, the molecular weight distribution is 50, the butene monomer insertion rate of this resin is 13%, and the impact strength at room temperature is 3.8 kJ / m 2 , and the impact strength at low temperature (-40 °C) is 2.8 kJ / m 2 . At low temperature, the impact strength retention rate is 73.7%.

[0047] Example 5

[0048] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The reactor temperature was adjusted to 85 °C, and n-heptane was added as the polymerization solvent. 3 μmol of catalyst (FI catalyst was selected), 3000 μmol of cocatalyst (triethylaluminum was selected), and 5 bar of olefin monomer (ethylene was selected) were added in sequence for the preliminary polymerization reaction to prepare a high molecular weight component polyethylene with a weight average molecular weight of 6×10 5 g / mol and a molecular weight distribution of 4. Further, the polymerization reaction was carried out by adding 3 bar of hydrogen to prepare a low molecular weight component polyethylene with a weight average molecular weight of 1×10 5 g / mol and a molecular weight distribution of 5. The mass ratio of the high and low molecular weight components was 1:99, and finally an injection molding grade polyethylene resin was obtained.

[0049] The melt index (MI 2.16 ) of the prepared injection-molded polyethylene resin is 3 g / 10 min, the weight-average molecular weight is 1.2×10 5 g / mol, the molecular weight distribution is 8, no comonomer is added to this resin, the impact strength at room temperature is 7 kJ / m 2 , and the impact performance at low temperature (-40 °C) is 6 kJ / m 2 . At low temperature, the retention rate of impact strength is 85.7%.

[0050] Example 6

[0051] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The temperature of the high molecular weight polymerization reactor (Reactor 1) was adjusted to 60 °C, and n-heptane was added as the polymerization solvent. 3 μmol of catalyst (Ziegler-Natta catalyst was selected), 3000 μmol of cocatalyst (triethylaluminum was selected), 10 ml of comonomer olefin (hexene was selected), 5 bar of olefin monomer (ethylene was selected), and 1 bar of hydrogen were added in sequence for preliminary polymerization reaction to prepare a high molecular weight component polyethylene with a weight-average molecular weight of 3×10 5 g / mol, a molecular weight distribution of 4, and a comonomer insertion rate of 9%; the temperature of the low molecular weight polymerization reactor (Reactor 2) was adjusted to 90 °C, and heptane as the polymerization solvent was added. The material still having a catalytic activity in Reactor 1 was separated and introduced into Reactor 2, and 2 ml of comonomer olefin (hexene was selected), 2.5 bar of hydrogen, and 6 bar of olefin monomer (ethylene was selected) were added for polymerization reaction to prepare a low molecular weight component polyethylene with a weight-average molecular weight of 4×10 4 g / mol, a molecular weight distribution of 5, and a comonomer insertion rate of 3%. The mass ratio of the high and low molecular weight components was 35:65, and finally an injection-molded polyethylene resin was obtained.

[0052] The melt index (MI 2.16 ) of the prepared injection-molded polyethylene resin is 7 g / 10 min, the weight-average molecular weight is 9×10 4 g / mol, the molecular weight distribution is 8, the comonomer insertion rate of this resin is 5.2%, the impact strength at room temperature is 8 kJ / m 2 , and the impact performance at low temperature (-40 °C) is 6 kJ / m 2 . At low temperature, the retention rate of impact strength is 75%.

[0053] Comparative Example 1

[0054] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The temperature of the reactor was adjusted to 40 °C, and n-hexane was added as the polymerization solvent. 2 μmol of catalyst (Ziegler-Natta catalyst was selected), 2000 μmol of cocatalyst (triethylaluminum was selected), 6 bar of olefin monomer (ethylene was selected), and 0.1 bar of comonomer (butene was selected) were added in sequence for the preliminary polymerization reaction to prepare high-molecular-weight component polyethylene with a weight-average molecular weight of 3×10 6 g / mol, a molecular weight distribution of 1.5, and a comonomer insertion rate of 0.1%. Further polymerization reaction was carried out by adding 5.0 bar of hydrogen to prepare low-molecular-weight component polyethylene with a weight-average molecular weight of 5×10 3 g / mol, a molecular weight distribution of 20, and a comonomer insertion rate of 0.1%. The mass ratio of the high- and low-molecular-weight components was 1:150, and finally injection-molding grade polyethylene resin was obtained.

[0055] The prepared injection-molding grade polyethylene resin had a melt index (MI 2.16 ) of 70 g / 10 min, a weight-average molecular weight of 7.5×10 3 g / mol, a molecular weight distribution of 25, a butene monomer insertion rate of 0.1% for the resin, a room temperature impact strength of 2.5 kJ / m 2 , and a low-temperature impact performance (-40 °C) of 1.2 kJ / m 2 . At low temperature, the impact strength retention rate was 48%.

[0056] Comparative Example 2

[0057] The reactor was purged with high-purity nitrogen to remove water and oxygen in the autoclave reactor. The temperature of the reactor was adjusted to 70 °C, and n-hexane was added as the polymerization solvent. 2 μmol of catalyst (Ziegler-Natta catalyst was selected), 2000 μmol of cocatalyst (triethylaluminum was selected), 1 bar of olefin monomer (ethylene was selected), and 4 bar of comonomer (propylene was selected) were added in sequence for the preliminary polymerization reaction to prepare high-molecular-weight component polyethylene with a weight-average molecular weight of 2×10 6 g / mol, a molecular weight distribution of 15, and a comonomer insertion rate of 20%. Further polymerization reaction was carried out by adding 0.5 bar of hydrogen to prepare low-molecular-weight component polyethylene with a weight-average molecular weight of 5×10 5 g / mol, a molecular weight distribution of 20, and a comonomer insertion rate of 15%. The mass ratio of the high- and low-molecular-weight components was 95:5, and finally polyethylene resin was obtained.

[0058] The prepared polyethylene resin had a melt index (MI 2.16 ) of 0.4 g / 10 min, a weight-average molecular weight of 1.8×10 6g / mol, molecular weight distribution is 40, the propylene monomer insertion rate of this resin is 20%, and the impact strength at room temperature is 78 kJ / m 2 , and the low-temperature impact performance is 25 kJ / m at (-40°C) 2 . At low temperature, the impact strength retention rate is 34.7%.

[0059] Figure 2 It shows the low-temperature impact retention rate of the injection-molded polyethylene resins prepared in Examples 1-6 and Comparative Examples 1-2. As can be seen from the figure, by controlling the mass percentage range of the high-molecular-weight polyethylene component to be 1% to 90%, and the weight-average molecular weight range of the high-molecular-weight polyethylene component to be 6×10 5 g / mol to 5×10 6 g / mol, the molecular weight distribution range is 1.5 - 10, and the molecular weight range of the low-molecular-weight polyethylene component is controlled to be 5×10 3 g / mol to 5×10 5 g / mol, and the molecular weight distribution range is 1.5 - 20, a polyethylene resin with both high melt index and high impact strength at room temperature / low temperature can be obtained. During injection molding, by introducing different molecular weight components, the high-molecular-weight components form extended-chain precursors, and under the interaction and guiding effect of the polymer chains, the chain segments aggregate in a specific direction to form crystalline regions, while the other parts remain amorphous, finally forming a shish-kebab structure. The shish-kebab structure helps to improve rigidity, but due to the existence of more slippage and deformation ability between molecular chains in the shish-kebab structure, it can also improve the impact toughness of the resin. Under appropriate conditions, the shish-kebab structure helps the polymer to undergo slippage and dispersion of molecular chains when subjected to external force impact, thereby improving the impact strength. Moreover, with the increase of the extended-chain molecular weight, the molecular chain relaxation ability decreases, the relaxation time becomes longer, and it is not easy to transform into folded chains or amorphous regions under the influence of temperature, thus achieving the effect of high impact strength retention rate at low temperature.

[0060] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A low temperature impact resistant broad distribution injection molding grade polyethylene resin, characterized in that: It consists of a high molecular weight polyethylene component and a low molecular weight polyethylene component, wherein the weight average molecular weight of the high molecular weight polyethylene component is in the range of 6×10 5 g / mol to 5×10 6 g / mol, the molecular weight distribution range is 1.5-10; the weight average molecular weight range of the low molecular weight polyethylene component is 5×10 3 g / mol~5×10 5 g / mol, and a molecular weight distribution range of 1.5 to 20; in the polyethylene resin, the mass percentage of the high molecular weight polyethylene component is 1% to 90%; the melt index of the low temperature impact resistant wide distribution polyethylene resin is in the range of 0.5 to 65 g / 10min, and the weight average molecular weight range is 2×10 4 g / mol~9×10 5 g / mol, molecular weight distribution in the range of 2.5-50, comonomer insertion rate of 0-10%, impact strength at room temperature of 2-75 kJ / m 2 Within the range, under low temperature conditions of -60 to 0°C, the impact strength retention rate is within the range of 70% to 99%.

2. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 1, characterized in that: The high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained by sequential polymerization, and the polymerization includes: synthesizing the high molecular weight polyethylene component first by controlling the polymerization conditions, and then switching the polymerization conditions to obtain the low molecular weight component by in-situ polymerization in the same polymerization reactor; or polymerizing in series with multiple reactors to obtain polyethylene components with different molecular weights in different reactors; thereby obtaining the low temperature impact resistant wide distribution injection molding grade polyethylene resin.

3. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 2, characterized in that: The method of switching the polymerization conditions includes: adding a chain transfer agent to the polymerization reactor, adding a comonomer to the polymerization reactor, changing the polymerization reaction temperature or the polymerization reaction pressure or one or more thereof.

4. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 2, characterized in that: The polymerization reactor is a kettle reactor or a tubular reactor, and when the polymerization conditions are switched, no polymer is discharged.

5. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 1, characterized in that: The mass percentage of the high molecular weight polyethylene component in the polyethylene resin is 20%-40%.

6. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to any one of claims 1 to 5, characterized in that: The high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained by ethylene polymerization in the presence of a polyethylene catalyst and a co-catalyst; the polyethylene catalyst is one or more of a metallocene catalyst, a chromium catalyst, an FI catalyst, a Ziegler-Natta catalyst, and a late transition metal catalyst; the co-catalyst is one or more of triethylaluminum, triisopropylaluminum, trimethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, tributylaluminum, trihexylaluminum, and trioctylaluminum.

7. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 6, characterized in that: The solvent used in the polymerization is selected from one or more of C6-C10 alkanes and C7-C10 aromatic hydrocarbons. Preferably, the solvent is one or more of n-hexane, n-heptane, toluene and xylene.

8. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 6, characterized in that: The polymerized olefin monomer is ethylene, and the copolymerized olefin monomer is an α-olefin. Preferably, the copolymerized olefin monomer is one or more of propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene. More preferably, the polyolefin monomer is propylene or 1-butene.

9. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 6, characterized in that: The polymerization reaction is one or more of a slurry process reaction, a gas phase process reaction, and a gas-liquid two-phase process reaction.

10. The low temperature impact resistant broad distribution injection molding grade polyethylene resin according to claim 6, characterized in that: The polymerization reaction temperature is -30°C to 100°C, the polymerization reaction pressure is 0.5 to 60 bar, and the reaction time is 0.1 to 10 hours.

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