CN107312230B

CN107312230B - Polyethylene composition, expanded beads, process for producing the same, and expanded bead molded body

Info

Publication number: CN107312230B
Application number: CN201610265206.6A
Authority: CN
Inventors: 郭鹏; 吕明福; 徐耀辉; 张师军; 高达利; 权慧; 吕芸; 张丽英; 董穆; 侴白舸
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petrochemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petrochemical Corp
Priority date: 2016-04-26
Filing date: 2016-04-26
Publication date: 2019-12-20
Anticipated expiration: 2036-04-26
Also published as: CN107312230A

Abstract

The invention relates to the field of polymers, and particularly provides a polyethylene composition, expanded beads, a preparation method of the expanded beads and an expanded bead forming body. The polyethylene composition contains a component A, a component B, a component C and a cell nucleating agent; component A is ethylene/alpha-olefin copolymerized linear low density polyethylene with melt index MI_A0.01-3.5g/10min, density rho_A0.880-0.936g/cm³(ii) a Component B is ethylene/alpha-olefin copolymerized linear low density polyethylene with melt index MI_B3.6-9.9g/10min, density rho_BIs 0.910 to 0.930g/cm³(ii) a Component C is an ethylene/alpha-olefin copolymerized linear low density polyethylene having a melt index MI_CIs 10-80g/10min, density rho_CIs 0.880-0.930g/cm³. The foamed bead made of the polyethylene composition has compact and uniform cells, and the formed body of the foamed bead has high compression strength.

Description

Polyethylene composition, expanded beads, process for producing the same, and expanded bead molded body

Technical Field

The invention relates to a polyethylene composition, a polyethylene expanded bead, a preparation method of the polyethylene expanded bead and a polyethylene expanded bead forming body.

Background

Compared with polypropylene expanded beads, the polyethylene expanded beads have softer surfaces due to light weight, good mechanical properties including low-temperature impact resistance, higher closed cell rate and good rebound resilience, and can be molded to obtain products with special shapes. The polyethylene expanded bead is a polymer expanded material with wide application. The polyethylene expanded bead molded article obtained by molding the polyethylene expanded beads has excellent properties such as chemical resistance, high toughness, high heat resistance, and good compression resilience, as compared with a molded article of polystyrene-series resin expanded beads. However, polyethylene resins are semi-crystalline polymers, generally linear in structure, and when heated to near the melting point, the force between macromolecules is small and there is no temperature range of high elastic state similar to polystyrene and the like. When the resin is melted, the melt strength is low, and therefore, a decomposition product gas of the chemical foaming agent or the physical foaming agent is not easily retained in the resin during foaming, so that the foaming process is difficult to control. Most physical blowing agents have high gas permeability in polyethylene resins, resulting in large, cell-broken and severe cell coalescence of the final foam. To solve this problem, the melt strength of the resin needs to be increased to meet the foaming requirements, and the main approaches include: improving the relative molecular mass, increasing the branching degree, adding a cross-linking agent to form a network structure, widening the relative molecular mass distribution and the like, so that the melt strength can be increased, the crystallinity can be reduced, the foaming performance can be improved, and the broken porosity can be reduced. In addition, in the production process, a method of mixing High Density Polyethylene (HDPE) and Medium Density Polyethylene (MDPE) or Low Density Polyethylene (LDPE) is commonly used to delay crystallization and change the fluidity of the material, so that the aims of keeping certain flexibility and improving the strength of the foam plastic are fulfilled. HDPE is mainly used as a base resin of a low-rate polyethylene foamed sheet, and the application mainly comprises building structure materials, packaging materials and the like. But this reduces the surface softness characteristic of polyethylene expanded bead products.

In addition, the polyethylene foamed products that are currently the largest in industrial scale are generally prepared using an extrusion foaming process. Compared with the extrusion foaming method, the reaction kettle dipping method does not cause the polyethylene melt to be subjected to the high shearing action of screw extrusion, and the entanglement of polymer chains ensures that the melt has enough strength. In the process of cell growth, the bidirectional stretching of the cell wall is not easy to break; meanwhile, polyethylene crystals are not completely melted in the foaming process, and the residual crystals play a role of physical cross-linking points, so that the polyethylene expanded beads (EPE) with high foaming multiplying power and high closed cell rate can be realized more easily. Thus, in the reaction kettle dipping method, the polyethylene does not need to be modified by adding peroxide or a cross-linking agent, and the original melt strength can meet the foaming requirement. Compared with crosslinked foamed polyethylene, the polyethylene foamed beads obtained by adopting the reaction kettle impregnation method have no crosslinked structure, can be recycled and have small side effect on the environment. In addition, the EPE expanded beads obtained by the reaction kettle impregnation method have a plurality of melting peaks, wherein the low-temperature peaks are beneficial to reducing the required steam pressure and temperature in the subsequent compression molding process, thereby reducing the energy consumption of equipment. However, the process is intermittent and complicated, the equipment cost is high, and technical barriers exist, so that the price of the obtained polyethylene expanded beads is high, and the application field of the polyethylene expanded beads is limited.

Disclosure of Invention

The invention aims to provide a novel polyethylene composition, a polyethylene expanded bead, a preparation method of the polyethylene expanded bead and a polyethylene expanded bead forming body. The cells of the polyethylene expanded beads formed from the polyethylene composition are dense and uniform, and the compression strength of the formed polyethylene expanded bead molded body is very high.

Specifically, the invention provides a polyethylene composition comprising component a, component B, component C and a cell nucleating agent; the component A is linear low density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low density polyethylene is at the temperature of 190 ℃ and the load of 2.16kg_A0.01-3.5g/10min, and density of 0.880-0.936g/cm³(ii) a The component B is linear low-density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low-density polyethylene is 190 ℃ at the temperature and 2.16kg under the load_B3.6-9.9g/10min, and density of 0.910-0.930g/cm³(ii) a The component C is ethylene/alpha-olefin copolymerized linear low density polyethylene with a melt index MI of 2.16kg at a temperature of 190 ℃ and a load_C10-80g/10min, and density of 0.880-0.930g/cm³。

The invention also provides polyethylene expanded beads prepared from the polyethylene composition.

In addition, the invention also provides a preparation method of the polyethylene expanded bead, which comprises the steps of granulating the polyethylene composition and expanding the obtained polyethylene particles.

The invention also provides a polyethylene expanded bead molded body obtained by molding the polyethylene expanded bead and/or the polyethylene expanded bead prepared by the method.

After intensive research, the inventors of the present invention found that expanded beads made of a polyethylene composition obtained by using the above-mentioned component a, component B and component C having specific melt index and density in combination with a cell nucleating agent have uniform and dense cells, and that the resulting expanded bead molded body has very high compressive strength, thus having great industrial application prospects.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic diagram of a multiple reactor parallel arrangement for producing polyethylene compositions;

FIG. 2 is a surface electron micrograph of polyethylene expanded beads obtained in example 1;

FIG. 3 is a sectional electron micrograph of the polyethylene expanded beads obtained in example 1;

FIG. 4 is a surface electron micrograph of polyethylene expanded beads obtained in comparative example 1;

FIG. 5 is a sectional electron micrograph of polyethylene expanded beads obtained in comparative example 1.

Description of the reference numerals

1-a first reactor; 2-a second reactor; 3-a third reactor; 4-a solid/liquid (gas) separator; 5-homogenizing stock bin; 6-melting granulation system.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The polyethylene composition provided by the invention contains a component A, a component B, a component C and a foam cell nucleating agent; the component A is linear low density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low density polyethylene is at the temperature of 190 ℃ and the load of 2.16kg_A0.01-3.5g/10min, density rho_A0.880-0.936g/cm³(ii) a The component B is linear low-density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low-density polyethylene is 190 ℃ at the temperature and 2.16kg under the load_B3.6-9.9g/10min, density rho_BIs 0.910 to 0.930g/cm³(ii) a The component C is ethylene/alpha-olefin copolymerized linear low density polyethylene with a melt index MI of 2.16kg at a temperature of 190 ℃ and a load_CIs 10-80g/10min, density rho_CIs 0.880-0.930g/cm³。

The polyethylene composition provided according to the present invention, preferably, the component A has a melt index MI at a temperature of 190 ℃ and a load of 2.16kg_AIs 0.01-3g/10min, and the melt index MI of the component B at the temperature of 190 ℃ and the load of 2.16kg is_BIs 4-8g/10min, and the melt index MI of the component C at the temperature of 190 ℃ and the load of 2.16kg_CIs 10-60g/10 min. More preferably, the component A has a melt index MI at a temperature of 190 ℃ and a load of 2.16kg_AIs 0.01-2g/10min, and the melt index MI of the component B at the temperature of 190 ℃ and the load of 2.16kg is_BIs 4-5g/10min, and the melt index MI of the component C at the temperature of 190 ℃ and the load of 2.16kg_CIs 15-40g/10 min.

In the present invention, the melt index is measured according to the method specified in GB/T3682-2000, wherein the test conditions include a temperature of 190 ℃ and a load of 2.16 kg.

The polyethylene composition provided according to the present invention, preferably the density ρ of component A_AIs 0.910 to 0.930g/cm³Density p of said component B_BIs 0.913-0.928g/cm³Density p of said component C_CIs 0.905-0.928g/cm³. More preferably, the density ρ of the component A_AIs 0.915-0.926g/cm³Density p of said component B_BIs 0.913-0.924g/cm³Density p of said component C_CIs 0.910 to 0.926g/cm³. Particularly preferably, the polyethylene composition has a density ρ of component A, component B and component C_A、ρ_BAnd ρ_CThe relationship between them satisfies-0.04 ≤ rho_A-ρ_BRho is not less than 0.02 and not more than-0.04_A-ρ_C0.02 or less, which enables the polyethylene composition to have a better foaming property, and the polyethylene expanded beads made of the polyethylene composition to have a denser and uniform cell structure, and the resulting polyethylene expanded bead molded body to have a higher compressive strength.

The component A, the component B and the component C are all linear low-density polyethylene copolymerized by ethylene/alpha olefin, wherein the linear structure refers to that a molecular chain only contains a short branched chain structure, but does not contain a long branched chain structure and a crosslinking structure, and is determined by a polymerization monomer and polymerization process conditions, and the components are known by persons skilled in the art and are not described herein in detail.

According to the polyethylene composition provided in the present invention,in order to obtain a polyethylene composition with better foaming properties, preferably, the mass fraction W of component a in the polyethylene composition_A25 to 90 weight portions of the component B, the weight portion W of the component B_B0.1 to 10 parts by weight of the component C, the mass part of the component C, W_C10-75 parts by weight; more preferably, in the polyethylene composition, the mass fraction W of the component A_A30-80 parts by weight of the component B, W_B0.5 to 8 weight portions of the component C, the weight portion W of the component C_C20 to 70 weight portions. Further, the mass fraction W of the component A_AAnd part by mass W of component C_CMelt index MI with component A_APreferably satisfies the relationship of (1) 4.6 XlgMI_A+10.4≥W_A/W_C≥0.18×lgMI_A+0.7, more preferably 1.8 XlgMI_A+4.7≥W_A/W_C≥0.22×lgMI_A+0.9, which enables the polyethylene composition to have better foaming properties, and the polyethylene expanded beads made of the polyethylene composition have a denser and uniform cell structure, and the resulting polyethylene expanded bead molded body has higher compressive strength.

The polyethylene composition provided according to the present invention, particularly preferably, has a melt index at a temperature of 190 ℃ under a load of 2.16kg of from 0.1 to 20g/10min, most preferably from 0.5 to 10g/10 min. When the component a, the component B and the component C having the above-mentioned specific melt index and density are used in combination, the melt index of the entire polyethylene composition is controlled within the above-mentioned range, and the resulting polyethylene composition can have very excellent foaming properties.

The polyethylene composition provided according to the present invention, preferably, the molecular weight distribution index of component a, component B and component C all satisfy M_w/M_n8.0 or less, more preferably 3.5 or less M_w/M_nLess than or equal to 6.0. Specifically, in order to obtain component A, component B and component C having the above molecular weight distribution, the component A, component B and component C are each obtained by polymerization using a Ziegler-Natta catalyst. Wherein the Ziegler-Natta catalyst can be of the typeIt is generally composed of a magnesium/titanium compound and an organoaluminum compound, and optionally an electron donor, as is conventional in the art, and is specifically well known to those skilled in the art and will not be described herein. After intensive research, the inventor of the present invention found that when the component a, the component B and the component C having the above-mentioned melt index and density, which are obtained by polymerization using a ziegler-natta catalyst, are used in combination with a cell nucleating agent, the resulting polyethylene composition has good foaming properties when preparing expanded beads by a reactor impregnation method and the resulting expanded beads have good cell structures, and the molded bodies thereof also have very high compressive strength, and thus are very suitable for home and automobile materials.

The content of the alpha-olefin comonomer in the component a, the component B and the component C is not particularly limited in the present invention, and for example, the molar content of the alpha-olefin comonomer in the component a, the component B and the component C may be each independently 0.2 to 15 mol%, preferably 1.5 to 10 mol%. In the present invention, the molar content of the alpha-olefin comonomer means the ratio of the molar amount of the structural unit formed by polymerization of the alpha-olefin to the molar amount of the total monomer structural unit. In addition, the alpha olefin in the component A, the component B and the component C is independently C₃-C₂₀At least one of olefins. The alpha olefin in the component A, the component B and the component C is preferably propylene, 1-butene, 2-butene, 3-methyl-1-butene, 4-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3-dimethyl-1-pentene, 3, 4-dimethyl-1-pentene, 4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 5-methyl-1-hexene, 1-heptene, 2-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-tetradecene, or the like, from the viewpoint of availability of raw materials, At least one of 1-hexadecene, 1-octadecene and 1-eicosene, more preferably at least one of 1-butene, 1-hexene and 1-octene.

The content of each component in the polyethylene composition is not particularly limited in the present invention, and for example, the content of the foam cell nucleating agent may be 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, more preferably 0.1 to 2 parts by weight, particularly preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the total weight of the component a, the component B and the component C.

The kind of the foam cell nucleating agent may be conventionally selected in the art, and for example, may be at least one of zinc borate, silica, talc, calcium carbonate, borax, and aluminum hydroxide. The foam cell nucleating agent is particularly preferably talc from the viewpoint of easy availability of raw materials.

Considering that the underwater pelletization extrusion step requires a melt pump to increase the melt pressure of a die when the polyethylene composition is formed into polyethylene expanded beads, which indirectly increases energy consumption, it is preferable that the polyethylene composition further contain a lubricant, which can improve the extrusion processability and the drawstring pelletization properties of the polyethylene composition. The type and amount of the lubricant may be conventionally selected in the art, and for example, the lubricant may be selected from at least one of polyethylene glycol (PEG) type lubricant, fluoropolymer type lubricant, silicone type lubricant, fatty alcohol type lubricant, fatty acid ester type lubricant, stearic acid amide type lubricant, fatty acid metal soap type lubricant, alkane and alkane oxide type lubricant, and micro-nano particle type lubricant. Specifically, the PEG-based lubricant may be, for example, PEG molecules with number average molecular weight of 500-50000, which may be subjected to capping, grafting, crosslinking treatment, or other chemical or physical modification. The fluoropolymer lubricant may be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, and the like, or may be another unimodal or multimodal fluoropolymer or a crystalline or semicrystalline fluoropolymer. The organic silicon lubricant can be various compounds which take carbon and silicon atoms as molecular main chains and take oligomers or oligomers of organic groups such as methyl, phenyl, alkoxy, vinyl and the like as side chains. The fatty alcohol-based lubricant may be, for example, at least one of a soft fatty alcohol, a hard fatty alcohol, a tallow fatty alcohol, and the like. The fatty acid based lubricant may be, for example, stearic acid and/or 12-hydroxystearic acid. The fatty acid ester lubricant may be at least one of butyl stearate, monoglyceride stearate, cetyl palmitate, stearyl stearate, and the like. The stearamide-based lubricant may be, for example, at least one of stearamide, oleamide, erucamide, n-Ethylenebisstearamide (EBS), and the like. The fatty acid metal soap lubricant may be at least one of lead stearate, calcium stearate, magnesium stearate, synthetic calcium acetate, and the like. The alkane and the oxidized alkane lubricant may be at least one of liquid paraffin, solid paraffin, polyethylene wax, polypropylene wax, ethylene oxide wax, and the like. The micro-nano particle lubricant can be powder rubber and/or silica gel particles. Further, the lubricant may be contained in an amount of 0.05 to 5 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the total of the component a, the component B and the component C.

When the polyethylene composition is made into polyethylene expanded beads, it is usually necessary to add a blowing agent such as carbon dioxide. In order to increase the impregnation rate and diffusion rate of the blowing agent and increase the uniformity of cells, it is preferable that the polyethylene composition further contains a cell control agent. Examples of the cell control agent include, but are not limited to: glycerol, polyethylene glycol, C₁₂-C₂₃And hydrophilic compounds such as glycerol esters of fatty acids. The polyethylene glycol is a nonionic water-soluble polymer having a structure obtained by polymerization of ethylene glycol, and the number average molecular weight thereof may be 5 ten thousand or less, preferably 500-6000, and more preferably 800-4000. In addition, the C₁₂-C₂₃The glyceride of fatty acid of (a) is preferably at least one of a monoester, a diester, and a triester formed from stearic acid and glycerin. The use of the cell control agent enables easy obtaining of polyethylene expanded beads of high expansion ratio. The cell controlling agent is preferably glycerin and/or polyethylene glycol, and most preferably glycerin, from the viewpoint of obtaining a polyethylene expanded bead having a high expansion ratio with a small amount of addition and having a good degree of fusion of the appearance layer and an excellent appearance when forming an in-mold expanded bead molded body. Further, the cell control agent is preferably used in an amount of 0.1 to 2 parts by weight, more preferably 0.2 to 0.5 part by weight, based on 100 parts by weight of the total of the components A, B and C.

The polyethylene composition may further contain various conventional additives commonly used in polyethylene expanded beads, such as an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a metal deactivator, a pigment, a nucleating agent, a filler, a stabilizer, a reinforcing agent, and the like. The types and the contents of the above-mentioned auxiliaries can be selected conventionally in the art, and those skilled in the art can know the types and the contents, and are not described herein again.

The polyethylene composition may be prepared according to various methods in the prior art, for example, component a, component B and component C may be prepared separately, and then the component a, component B and component C may be mechanically mixed with the cell nucleating agent and optionally other additives in a mechanical mixing device according to the ratio, and then added to a melt blending device for melt blending. The mechanical mixing device may be, for example, a high-speed stirrer, a kneader, or the like. The melt blending equipment may be, for example, a twin screw extruder, a single screw extruder, an open mill, an internal mixer, or the like.

According to a preferred embodiment of the present invention, the polyethylene composition is prepared in a multi-reactor parallel apparatus as shown in fig. 1, which comprises a first reactor 1, a second reactor 2, a third reactor 3, a solid/liquid (gas) separator 4, a homogenization silo 5 and a melt-granulation system 6, wherein the first reactor 1, the second reactor 2 and the third reactor 3 are connected in parallel, the number of the solid/liquid (gas) separators 4 is three, the three solid/liquid (gas) separators are respectively communicated with the first reactor 1, the second reactor 2 and the third reactor 3, a component a prepared from the first reactor 1, a component B prepared from the second reactor 2 and a component C prepared from the third reactor 3 are respectively phase-separated in different solid/liquid (gas) separators 4, and then the phase-separated components a, B, C, The component B and the component C are conveyed into a homogenizing silo 5 in proportion and are uniformly mixed with the foam cell nucleating agent and other optional additives, and then the mixture is sent into a melting granulation system 6 for extrusion granulation. The polymerization in each reactor may be a batch polymerization or a continuous polymerization. When multiple reactors are used in parallel polymerization, W is hereinafter_A、W_BAnd W_CFor the production per unit time of the components in the respective reactor。

The pelletization can be carried out in various ways known in the art, for example, the polyethylene composition can be extruded into strands through one or more dies of a twin-screw or single-screw extruder and cut to obtain polyethylene beads, or an underwater microparticle pelletizing system can be used, the specific operation of which is well known to those skilled in the art. According to a particular embodiment of the invention, the granulation is carried out as follows: the above polyethylene composition is blended with a high-speed mixer, extruded through a twin-screw extruder, hot-cut, and then introduced into water at 75 ℃ or lower, preferably 70 ℃ or lower, more preferably 55 to 65 ℃ to be finely cut so that the length/diameter ratio of each particle is 0.5 to 2.0, preferably 0.8 to 1.3, more preferably 0.9 to 1.1, and the average weight is 0.1 to 20mg, preferably 0.2 to 10mg, more preferably 1 to 3 mg. The length/diameter ratio described herein is an average of 200 randomly selected polyethylene particles.

The foaming can be carried out by various conventional methods, for example, an extrusion foaming method or a reaction kettle immersion foaming method, and the polyethylene expanded beads obtained by the reaction kettle immersion foaming method are preferably in a non-crosslinked structure, so that the polyethylene modified material can be recycled, secondary pollution is avoided, and the requirement of recycling economy is met. According to a specific embodiment of the present invention, the foaming is performed by using a reactor dip foaming method, which specifically comprises the following steps: (1) uniformly mixing polyethylene particles with auxiliary agents such as a dispersion medium, a surfactant, a dispersant, a dispersion enhancer and the like in a high-pressure autoclave; (2) covering the autoclave tightly, discharging residual air in the autoclave by using an air discharging method, namely using a foaming agent, then continuously feeding the foaming agent into the autoclave, starting heating and primarily adjusting the pressure until the foaming agent is stable, then stirring the autoclave at a stirring speed of 50-150rmp, preferably 90-110rmp, and heating the autoclave at a constant speed to a temperature which is 0.1-5 ℃, preferably 0.5-1 ℃ lower than the expansion stability; (3) adjusting the pressure in the autoclave to a pressure required for foaming, the pressure being 1-10MPa, preferably 3-5MPa, raising the temperature to a foaming temperature at an average heating rate of 0.1 ℃/min, the foaming temperature being 0.1-5 ℃, preferably 0.5-1 ℃ lower than the melting temperature of the microparticles, and continuously stirring for 0.1-2 hours, preferably 0.25-0.5 hours under the conditions of foaming temperature and pressure; (4) the discharge port of the autoclave was opened to discharge the contents of the autoclave into a collection tank to obtain polyethylene expanded beads, and carbon dioxide gas was fed while discharging the contents so that the pressure in the autoclave was maintained at about the foaming pressure before all the particles were completely foamed and entered the collection tank.

In the present invention, the pressures are gauge pressures.

The dispersion medium may be any of various existing components capable of dispersing polyethylene particles therein without dissolving the polyethylene particles, and for example, may be at least one of water, ethylene glycol, glycerin, methanol, ethanol, and the like, with water being particularly preferred. Further, the amount of the dispersion medium may be 1 to 5L, preferably 2.5 to 3.5L, relative to 100g of the polyethylene particles.

The surfactant may be any of various conventional components capable of promoting dispersion of polyethylene particles in a dispersion medium, and may be, for example, at least one of stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compound, lecithin, amino acid, betaine, fatty acid glyceride, sorbitan fatty acid, polysorbate, and the like, and sodium dodecylbenzenesulfonate is particularly preferable. Further, the surfactant may be used in an amount of 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 0.5 parts by weight, relative to 100 parts by weight of the polyethylene particles.

The purpose of the dispersant addition is to prevent the polyethylene particles from melt-bonding to each other during foaming. The dispersant may be an organic dispersant or an inorganic dispersant, and is preferably an inorganic dispersant. The inorganic dispersant may be at least one of natural or synthetic clay minerals (e.g., kaolin, mica, magnesium aluminum garnet, clay, etc.), alumina, titanium dioxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, silica, zinc borate, iron oxide, etc., and particularly preferably kaolin. Further, the dispersant may be used in an amount of 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the polyethylene particles.

The purpose of the addition of the dispersion enhancer is to improve the dispersion efficiency of the dispersant, i.e., to reduce the amount of the dispersant while retaining its function of preventing melt-bonding between particles. The dispersion enhancer may be any of various existing inorganic compounds having a solubility of 1mg in 100mL of water at 40 ℃ and providing a divalent or trivalent anion or cation. Examples of the dispersion-enhancing agent include, but are not limited to, at least one of magnesium nitride, magnesium nitrate, aluminum phosphate, magnesium sulfate, aluminum nitride, aluminum nitrate, aluminum sulfate, ferric chloride, ferric sulfate, ferric nitrate, and the like, preferably aluminum sulfate. The use of the dispersion-enhancing agent is advantageous for obtaining polyethylene expanded beads having an apparent density of 100g/L or more. Further, the dispersion enhancer may be used in an amount of 0.0001 to 1 part by weight, preferably 0.01 to 0.2 part by weight, relative to 100 parts by weight of the polyethylene particles.

The foaming agent can be an organic physical foaming agent or an inorganic physical foaming agent. Among them, examples of the organic type physical blowing agent include, but are not limited to, at least one of aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, alicyclic hydrocarbons such as cyclobutane and cyclohexane, and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1, 2-difluoroethane, 1,2,2, 2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, and the like. Examples of the inorganic type physical blowing agent include, but are not limited to, at least one of air, nitrogen, carbon dioxide, oxygen, and water. The blowing agent is preferably carbon dioxide and/or nitrogen, particularly preferably carbon dioxide, in view of stability (uniformity) of the apparent density of the polyethylene expanded beads, low cost and environmental friendliness. In addition, the amount of the blowing agent to be used may be determined depending on the specific kind of the blowing agent, the foaming temperature, and the apparent density of the polyethylene expanded beads to be produced. For example, when nitrogen is used as the blowing agent and water is used as the dispersion medium, the pressure in the closed vessel (i.e., the pressure (gauge pressure) in the upper space in the closed vessel) at the time of depressurization in the foaming apparatus is controlled to 1 to 12 MPa; when carbon dioxide is used as the blowing agent, the gauge pressure is controlled to 1 to 7 MPa. Generally, the desired pressure in the upper space in the closed vessel increases as the apparent density of the polyethylene expanded beads to be obtained decreases.

In the present invention, the molding can be performed in various existing molding machines, and the molding conditions can be selected conventionally in the art, and those skilled in the art can know the molding conditions, and will not be described herein again.

The polyethylene foamed bead and the foamed molded body provided by the invention are suitable for automobile parts, medical equipment materials, household articles, low-temperature cold chain packaging materials, sports equipment, building heat insulation materials, aerospace materials and the like.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples, the properties of the polyethylene were measured according to the following methods:

(1) molecular weight distribution index (Mw/Mn): measuring by using a PL-GPC 220 type gel permeation chromatograph of Polymer Laboratories, UK, combined with an IR5 type infrared detector, wherein the chromatographic columns are 3 series-connected Plgel 10 mu m MIXED-B columns, the solvent and mobile phase are 1,2, 4-trichlorobenzene, the column temperature is 150 ℃, the flow rate is 1.0mL/min, and the general calibration is carried out by adopting EasiCalPS-1 narrow-distribution polystyrene standard sample of PL;

(2) melt Index (MI): the measurement is carried out according to the method specified in GB/T3682-2000, wherein the test temperature is 190 ℃ and the load is 2.16 kg;

(3) density: the measurement was carried out according to the method specified in GB/T1033.2-2010 and by the density gradient column method.

Example 1

This example is for illustrating the polyethylene composition, expanded beads and expanded bead molded body provided by the present invention, and the method for preparing the same.

(1) Preparation of polyethylene composition:

the present example provides a polyethylene composition comprising component a, component B, component C, a foam cell nucleating agent, a lubricant, and a foam cell controlling agent. Wherein, the component A, the component B and the component C are all Linear Low Density Polyethylene (LLDPE) copolymerized by ethylene/alpha olefin, and are all prepared by adopting the same catalyst system (Ziegler-Natta catalyst) and polymerization process, and the difference is that the amount of hydrogen added and the type and molar content of alpha olefin comonomer are different when different components are prepared. The method comprises the following specific steps:

ethylene, alpha-olefin, hydrogen and nitrogen (all of which are polymerization stages and used after water and oxygen removal, the same applies hereinafter) were added to a fluidized bed gas phase reactor, and then a ziegler-natta catalyst system (the ziegler-natta catalyst system was the one prepared in CN101838351A example 1, the same applies hereinafter) was added, followed by polymerization at a temperature of 84 to 88 ℃ and a pressure of 1.8 to 2.0MPa to obtain a component a, a component B and a component C, respectively. Wherein, the control of the melt indexes of the component A, the component B and the component C is realized by adjusting the adding amount of hydrogen, and the control of the density is realized by adjusting the type and the adding amount of alpha olefin. The alpha olefin used in the process for preparing component A is 1-hexene, the alpha olefin used in the process for preparing component B is 1-hexene, and the alpha olefin used in the process for preparing component C is 1-butene.

Through detection, the properties of the component A, the component B and the component C prepared by the method are as follows:

melt index MI of component A_A2.0g/10min, density ρ_A＝0.913g/cm³Molecular weight distribution index M_w/M_n6.4, the molar content of alpha olefin comonomer is 8.9 mol%;

melt index MI of component B_B4.0g/10min, density ρ_B＝0.913g/cm³Molecular weight distribution index M_w/M_n5.7, the molar content of alpha olefin comonomer is 8.9 mol%;

melt index MI of component C_C15g/10min, density ρ_C＝0.905g/cm³Molecular weight distribution index M_w/M_nThe molar content of the alpha olefin comonomer was 10.1 mol% at 4.6.

The foam cell nucleating agent is talcum powder which is produced by Fuji mineral products of Dalian and has the particle size distribution of 20-30 mu m.

The lubricant was a PEG lubricant manufactured by Switzerland, and the number average molecular weight was 10000.

The cell control agent was glycerol manufactured by Beijing Chemicals Inc.

Weighing and mixing the components according to the proportion, wherein the weight part W of the component A_A80 parts by weight of the component B, W_B10 parts by weight of component C, W_CIs 20 parts by weight, W_A/W_C4 (satisfy 4.6 × lgMI)_A+10.4≥W_A/W_C≥0.18×lgMI_A+0.7, also satisfying 1.8 XlgMI_A+4.7≥W_A/W_C≥0.22×lgMI_A+ 0.9); then adding a foam nucleating agent, a lubricant and a foam control agent (the total weight of the component A, the component B and the component C is 100 parts by weight, the adding amount of the foam nucleating agent is 0.3 part by weight, the adding amount of the lubricant is 0.1 part by weight and the adding amount of the foam control agent is 0.2 part by weight), then adding the mixture into a high-speed stirrer for uniform mixing, then adding the mixed material into a feeder of a double-screw extruder manufactured by Nanjing Keplong company, feeding the material into the double screws through the feeder, keeping the temperature of the screws between 160 and 210 ℃ in the processing process, melting and uniformly mixing through the screws, extruding, granulating through an underwater granulating system (manufactured by Germany BKG company, the model is Labline 1000, the same below) and drying to obtain polyethylene composition granules, wherein the melt index MI of the polyethylene composition granules is 3.4g/10 min.

(2) Preparation of polyethylene expanded beads:

uniformly mixing the polyethylene composition granules obtained in the step (1) with a dispersion medium, a surfactant, a dispersing agent and a dispersion reinforcing agent in an autoclave, wherein the dispersion medium is deionized water, the surfactant is sodium dodecyl benzene sulfonate, the dispersing agent is kaolin, the dispersion reinforcing agent is aluminum sulfate, and relative to 100g of polyethylene composition granules, the dosage of the dispersion medium is 2.7L, the dosage of the surfactant is 0.4g, the dosage of the dispersing agent is 5g, and the dosage of the dispersion reinforcing agent is 0.2 g.

The autoclave cover was closed tightly, residual air in the autoclave was purged with carbon dioxide, then carbon dioxide was continuously fed into the autoclave, heating was started and the pressure in the autoclave was preliminarily adjusted until it stabilized, and then the autoclave was stirred at a stirring speed of 100rmp to heat the temperature in the autoclave to 118.5 ℃ at a uniform speed.

The pressure in the autoclave was adjusted to 6MPa and the temperature was raised to 119 ℃ at an average heating rate of 0.1 ℃/min, followed by continuous stirring at the above pressure and temperature for 0.5 hour.

The discharge port of the autoclave was opened to discharge the contents of the autoclave into a collection tank to obtain expanded beads, and carbon dioxide gas was fed while discharging so that the pressure in the autoclave was maintained at about the foaming pressure before all the particles were completely foamed and entered the collection tank.

Collecting the beads, dewatering, drying, and sieving with sieves with pore diameters of 3.35mm and 2.8mm to obtain polyethylene expanded beads with particle diameters of 2.8-3.35mm, wherein the surface electron microscope photograph and the cross-section electron microscope photograph are shown in FIG. 2 and FIG. 3 respectively. As can be seen from the results of fig. 2 and 3, the polyethylene expanded beads obtained from the polyethylene composition provided by the present invention have dense and uniform cells, smooth surface and small cell size.

(3) Preparation of polyethylene expanded bead molded body:

the polyethylene expanded beads obtained in step (2) were molded under a pressure of 0.12MPa using a molding machine (Kurtz T-Line manufactured by Kurtz Ersa, Germany, the same applies hereinafter), and the molded article obtained was aged at a temperature of 65 ℃ under a pressure of standard atmospheric pressure for 24 hours.

Example 2

(1) Preparation of polyethylene composition:

adding ethylene, alpha-olefin, hydrogen and nitrogen into a fluidized bed gas phase reactor, then adding a Ziegler-Natta catalyst system, and then polymerizing under the conditions that the temperature is 84-88 ℃ and the pressure is 1.8-2.0MPa to respectively obtain a component A, a component B and a component C. Wherein, the control of the melt indexes of the component A, the component B and the component C is realized by adjusting the adding amount of hydrogen, and the control of the density is realized by adjusting the type and the adding amount of alpha olefin. The alpha olefin used in the process for preparing component A is 1-butene, the alpha olefin used in the process for preparing component B is 1-butene, and the alpha olefin used in the process for preparing component C is 1-hexene.

melt index MI of component A_A0.01g/10min, density ρ_A＝0.930g/cm³Molecular weight distribution index M_w/M_n5.5, the molar content of alpha olefin comonomer is 2.1 mol%;

melt index MI of component B_BDensity ρ of 9.0g/10min_B＝0.930g/cm³Molecular weight distribution index M_w/M_n4.8, the molar content of alpha olefin comonomer is 2.8 mol%;

melt index MI of component C_C40g/10min, density ρ_C＝0.922g/cm³Molecular weight distribution indexM_w/M_nThe molar content of the alpha olefin comonomer was 4.0 mol% for 4.4.

The cell control agent was glycerol manufactured by Beijing Chemicals Inc.

Weighing and mixing the components according to the proportion, wherein the weight part W of the component A_AIs 55 parts by weight, the mass part W of the component B_BIs 5 parts by weight, the mass part W of the component C_CIs 55 parts by weight, W_A/W_C1 (satisfies 4.6 × lgMI)_A+10.4≥W_A/W_C≥0.18×lgMI_A+0.7, also satisfying 1.8 XlgMI_A+4.7≥W_A/W_C≥0.22×lgMI_A+ 0.9); then adding a foam nucleating agent, a lubricant and a foam control agent (the total weight of the component A, the component B and the component C is 100 parts by weight, the adding amount of the foam nucleating agent is 0.3 part by weight, the adding amount of the lubricant is 0.1 part by weight and the adding amount of the foam control agent is 0.3 part by weight), then adding the mixture into a high-speed stirrer for uniform mixing, then adding the mixed material into a feeder of a double-screw extruder manufactured by Nanjing Keplong company, feeding the material into a double screw through the feeder, keeping the temperature of the screw in the processing process between 180 ℃ and 240 ℃, melting and uniformly mixing through the screw, extruding, granulating through an underwater granulating system and drying to obtain polyethylene composition granules, and detecting the melt index MI of the polyethylene composition granules to be 0.7g/10 min.

(2) Preparation of polyethylene expanded beads:

uniformly mixing the polyethylene composition granules obtained in the step (1) with a dispersion medium, a surfactant, a dispersing agent and a dispersion reinforcing agent in an autoclave, wherein the dispersion medium is deionized water, the surfactant is sodium dodecyl benzene sulfonate, the dispersing agent is kaolin, the dispersion reinforcing agent is aluminum sulfate, and relative to 100g of polyethylene composition granules, the dosage of the dispersion medium is 3.5L, the dosage of the surfactant is 0.35g, the dosage of the dispersing agent is 5.5g, and the dosage of the dispersion reinforcing agent is 0.12 g.

The autoclave cover was closed tightly, residual air in the autoclave was purged with carbon dioxide, then carbon dioxide was continuously fed into the autoclave, heating was started and the pressure in the autoclave was preliminarily adjusted until it stabilized, and then the autoclave was stirred at a stirring speed of 100rmp to heat the temperature in the autoclave to 127.5 ℃ at a uniform speed.

The pressure in the autoclave was adjusted to 4MPa and the temperature was raised to 128 ℃ at an average heating rate of 0.1 ℃/min, followed by continuous stirring at the above pressure and temperature for 0.5 hour.

The beads were collected, dehydrated and dried, and polyethylene expanded beads having a particle size of 2.8 to 3.35mm were sieved using sieves having a pore size of 3.35mm and 2.8 mm.

(3) Preparation of polyethylene expanded bead molded body:

the polyethylene expanded beads obtained in the step (2) were molded at a pressure of 0.18MPa using a molding machine, and the molded article was aged at a temperature of 65 ℃ and a pressure of standard atmospheric pressure for 24 hours.

Example 3

(1) Preparation of polyethylene composition:

the polyethylene composition provided in this example was polymerized by using the multiple reactor parallel apparatus shown in fig. 1, wherein the first reactor 1 was polymerized to produce component a, the second reactor 2 was polymerized to produce component B, and the third reactor 3 was polymerized to produce component C, and the component a, the component B, and the component C were Linear Low Density Polyethylene (LLDPE) copolymerized with ethylene and alpha olefin, and the three components were all prepared by using the same catalyst system (ziegler-natta catalyst) and polymerization process, except that the amount of hydrogen added, the type and molar content of alpha olefin comonomer, and the output per unit time of each reactor were different. The method comprises the following specific steps:

adding alpha olefin, normal hexane and hydrogen into a batch kettle type polymerization reactor, heating the batch kettle type polymerization reactor to a preset polymerization temperature, then simultaneously adding an ethylene monomer and a catalyst system into the batch kettle type polymerization reactor, and polymerizing for 60 minutes under the conditions that the temperature is 240 ℃ and the pressure is 14.8MPa to respectively obtain a component A, a component B and a component C. Wherein, the control of the melt indexes of the component A, the component B and the component C is realized by adjusting the adding amount of hydrogen, and the control of the density is realized by adjusting the type and the adding amount of alpha olefin. The alpha olefin used in the preparation of component A is 1-octene, the alpha olefin used in the preparation of component B is 1-butene, and the alpha olefin used in the preparation of component C is 1-butene.

The production per unit time W of component A in the first reactor 1 during the preparation_AThe yield per unit time W of component B in the second reactor 2_BWith the yield per unit time W of component C in the third reactor 3_CIs maintained at W_A：W_B：W_C75: 2: 35 wherein W_A/W_C2.1 (satisfy 4.6 × lgMI)_A+10.4≥W_A/W_C≥0.18×lgMI_A+0.7, also satisfying 1.8 XlgMI_A+4.7≥W_A/W_C≥0.22×lgMI_A+0.9)。

melt index MI of component A_ADensity p of 0.1g/10min_A＝0.920g/cm³Molecular weight distribution index M_w/M_n5.8, the molar content of alpha olefin comonomer is 2.5 mol%;

melt index MI of component B_BDensity p of 6.0g/10min_B＝0.920g/cm³Molecular weight distribution index M_w/M_n4.5, alpha-olefin co-olefinThe molar content of the comonomer is 5.3 mol%;

melt index MI of component C_C25g/10min, density ρ_C＝0.920g/cm³Molecular weight distribution index M_w/M_nThe molar content of alpha olefin comonomer was 5.7 mol%, 4.2.

The cell control agent was glycerol manufactured by Beijing Chemicals Inc.

The component A, the component B and the component C are respectively conveyed into different solid/liquid (gas) separators 4 according to the output ratio per unit time for phase separation and then conveyed into a homogenizing silo 5 with stirring, and then, the foam cell nucleating agent, the lubricant and the foam cell control agent are added according to the proportion for mixing and homogenizing. Wherein, the total weight of the component A, the component B and the component C is 100 parts by weight, the adding amount of the foam cell nucleating agent is 0.5 part by weight, the adding amount of the lubricant is 0.1 part by weight, and the adding amount of the foam cell controlling agent is 0.2 part by weight. And then adding the mixture homogenized by the homogenizing silo 5 into a feeder of a double-screw extruder manufactured by Nanjing Keplong company, feeding the materials into the double screws through the feeder, keeping the temperature of the screws between 160 ℃ and 210 ℃ in the processing process, melting and uniformly mixing the materials by the screws, extruding the materials, granulating the materials by an underwater granulating system, drying the materials to obtain polyethylene composition granules, and detecting the melt index MI of the polyethylene composition granules to be 0.6g/10 min.

(2) Preparation of polyethylene expanded beads:

uniformly mixing the polyethylene composition granules obtained in the step (1) with a dispersion medium, a surfactant, a dispersing agent and a dispersion reinforcing agent in an autoclave, wherein the dispersion medium is deionized water, the surfactant is sodium dodecyl benzene sulfonate, the dispersing agent is kaolin, the dispersion reinforcing agent is aluminum sulfate, and relative to 100g of polyethylene composition granules, the dosage of the dispersion medium is 3L, the dosage of the surfactant is 0.35g, the dosage of the dispersing agent is 4.8g, and the dosage of the dispersion reinforcing agent is 0.15 g.

The autoclave cover was closed tightly, the residual air in the autoclave was discharged using carbon dioxide, and then carbon dioxide was continuously fed into the autoclave, heating was started and the pressure in the autoclave was preliminarily adjusted until it stabilized, and then the autoclave was stirred at a stirring speed of 100rmp to heat the temperature in the autoclave to 121 ℃ at a uniform speed.

The pressure in the autoclave was adjusted to 5MPa and the temperature was raised to 121.5 ℃ at an average heating rate of 0.1 ℃/min, followed by continuous stirring at the above pressure and temperature for 0.5 hour.

(3) Preparation of polyethylene expanded bead molded body:

Example 4

A polyethylene composition, expanded beads and an expanded bead molding were produced as in example 1, except that the cell nucleating agent was used in an amount of 0.4 part by weight and the molding pressure in step (3) was 0.15MPa, to give a polyethylene composition, polyethylene expanded beads and a polyethylene expanded bead molding.

Example 5

A polyethylene composition, expanded beads and an expanded bead molding were produced as in example 2, except that the cell nucleating agent was used in an amount of 0.2 parts by weight and the molding pressure in step (3) was 0.20MPa, to give a polyethylene composition, polyethylene expanded beads and a polyethylene expanded bead molding.

Example 6

A polyethylene composition, expanded beads and an expanded bead molded body were produced as in example 3, except that the cell nucleating agent was used in an amount of 0.3 part by weight, the blowing agent was nitrogen, and the molding pressure in step (3) was 0.16MPa, to give a polyethylene composition, polyethylene expanded beads and a polyethylene expanded bead molded body.

Comparative example 1

This comparative example is used to illustrate reference polyethylene raw materials, expanded beads and expanded bead molded bodies and methods for producing the same.

(1) Polyethylene raw material:

the film grade linear low density polyethylene produced by the Chinese petrochemical Yanshan petrochemical company used in the comparative example is the No. 7042, the catalyst is a Ziegler-Natta catalyst, the melt index MI is 2.0g/10min, and the density rho is 0.920g/cm³Molecular weight distribution index M_w/M_n＝4.5。

(2) Preparation of polyethylene expanded beads and expanded bead moldings:

polyethylene expanded beads were prepared in the same manner as in example 1, except that the components A, B and C in the polyethylene composition were replaced with the same parts by weight of the polyethylene raw material of step (1), and cell breakage and coalescence, and the beads surface were wrinkled, occurred in all of the several attempts of expansion. Further, neither foam molding nor foamed bead molded article can be obtained by adjusting the molding pressure within the range of 0.1 to 0.2 MPa. In addition, the surface electron micrograph and the cross-sectional electron micrograph of the polyethylene expanded beads obtained in this comparative example are shown in fig. 4 and 5, respectively. As can be seen from the results of fig. 4 and 5, the polyethylene expanded beads obtained from the polyethylene raw material had non-uniform cells, uneven bead surface and lower cell density.

Comparative example 2

This comparative example is for illustrating a polyethylene composition, expanded beads and expanded bead molded bodies of reference and a method of preparing the same.

The polyethylene composition, expanded beads and expanded bead molded bodies were produced in the same manner as in example 1, except that no cell nucleating agent was added during the production of the polyethylene composition, and it was revealed that the resulting expanded beads had large and uneven cell sizes and the expanded bead molded bodies had low compressive strength.

Comparative example 3

A polyethylene composition, expanded beads and an expanded molded body were produced in the same manner as in example 1, except that component C was not added, by the following specific steps:

(1) preparation of polyethylene composition:

the comparative example provides a polyethylene composition comprising component 1, component 2, a foam cell nucleating agent, a lubricant, and a foam cell controlling agent. Wherein component 1 and component 2 are both ethylene/alpha olefin copolymerized Linear Low Density Polyethylene (LLDPE) and are both prepared using the same catalyst system (ziegler-natta catalyst) and polymerization process, except that the amount of hydrogen added and the type and molar content of the alpha olefin comonomer are different when preparing the different components. The method comprises the following specific steps:

adding ethylene, alpha olefin, hydrogen and nitrogen into a fluidized bed gas phase reactor, then adding a catalyst system, and then polymerizing under the conditions that the temperature is 84-88 ℃ and the pressure is 1.8-2.0MPa to respectively obtain a component 1 and a component 2. Wherein, the control of the melt indexes of the component 1 and the component 2 is realized by adjusting the adding amount of hydrogen, and the control of the density is realized by adjusting the type and the adding amount of alpha olefin. The alpha olefins used in the preparation of component 1 and component 2 were 1-hexene.

The properties of the component 1 and the component 2 prepared by the method are detected as follows:

melt index MI of component 1₁2.0g/10min, density ρ₂＝0.913g/cm³Molecular weight distribution index M_w/M_n6.4, the molar content of alpha olefin comonomer is 8.9 mol%;

melt index MI of component 2₂4.0g/10min, density ρ₂＝0.913g/cm³Molecular weight distribution index M_w/M_nThe molar content of the alpha olefin comonomer was 8.9 mol%, 5.7.

The cell control agent was glycerol manufactured by Beijing Chemicals Inc.

Weighing and mixing the component 1 and the component 2 according to the proportion, wherein the component 1 is W in part by mass₁80 parts by weight of the component 2, W₂The production method comprises the following steps of adding 30 parts by weight of a cell nucleating agent, a lubricant and a cell control agent (the total weight of the component 1 and the component 2 is 100 parts by weight, the adding amount of the cell nucleating agent is 0.3 part by weight, the adding amount of the lubricant is 0.1 part by weight and the adding amount of the cell control agent is 0.2 part by weight), adding the mixture into a high-speed stirrer to be uniformly mixed, adding the mixed material into a feeder of a double-screw extruder manufactured by Nanjing Keplong company, feeding the material into a double screw through the feeder, keeping the temperature of the screw in the processing process between 160 and 210 ℃, melting and uniformly mixing through the screw, extruding, and pelletizing and drying through an underwater pelletizing system to obtain polyethylene composition pellets.

(2) Preparation of polyethylene expanded beads and expanded bead moldings:

as a result of preparing polyethylene expanded beads and expanded bead molded articles according to example 1, it was found that the resulting polyethylene expanded beads had nonuniform cell size and suffered breakage, and further, neither expansion molding nor expansion molding could be carried out by adjusting the molding pressure within the range of 0.1 to 0.2MPa, and thus no expanded bead molded article could be obtained.

Comparative example 4

A polyethylene composition, expanded beads and expanded molded articles were produced in the same manner as in example 1, except that component B was not added, by the following specific steps:

(1) preparation of polyethylene composition:

adding ethylene, alpha olefin, hydrogen and nitrogen into a fluidized bed gas phase reactor, then adding a catalyst system, and then polymerizing under the conditions that the temperature is 84-88 ℃ and the pressure is 1.8-2.0MPa to respectively obtain a component 1 and a component 2. Wherein, the control of the melt indexes of the component 1 and the component 2 is realized by adjusting the adding amount of hydrogen, and the control of the density is realized by adjusting the type and the adding amount of alpha olefin. The alpha olefin used in the preparation of component 1 was 1-hexene and the alpha olefin used in the preparation of component 2 was 1-butene.

melt index MI of component 1₁2.0g/10min, density ρ₁＝0.913g/cm³Molecular weight distribution index M_w/M_n6.4, the molar content of alpha olefin comonomer is 8.9 mol%;

melt index MI of component 2₂15g/10min, density ρ₂＝0.905g/cm³Molecular weight distribution index M_w/M_nThe molar content of the alpha olefin comonomer was 10.1 mol% at 4.6.

The cell control agent was glycerol manufactured by Beijing Chemicals Inc.

Weighing and mixing the component 1 and the component 2 according to the proportion, wherein the component 1 is W in part by mass₁80 parts by weight of the component 2, W₂The production method comprises the following steps of adding 30 parts by weight of a cell nucleating agent, a lubricant and a cell control agent (the total weight of the component 1 and the component 2 is 100 parts by weight, the adding amount of the cell nucleating agent is 0.3 part by weight, the adding amount of the lubricant is 0.1 part by weight and the adding amount of the cell control agent is 0.2 part by weight), adding the mixture into a high-speed stirrer to be uniformly mixed, adding the mixed material into a feeder of a double-screw extruder manufactured by Nanjing Keplong company, feeding the material into a double screw through the feeder, keeping the temperature of the screw in the processing process between 160 ℃ and 210 ℃, melting and uniformly mixing through the screw, extruding, pelletizing through an underwater pelletizing system, and drying to obtain polyethylene composition pellets.

(2) Preparation of polyethylene expanded beads and expanded bead moldings:

Test example

Test examples are used to illustrate the tests for the properties of the polyethylene expanded beads and the expanded bead moldings.

(1) Density: the densities of the polyethylene composition pellets and the polyethylene expanded beads were measured using the density accessory of a Satorius balance using the drainage method and according to the method described in ISO 1183-1:2012, and the results are shown in table 1.

The expansion ratio of the polyethylene expanded beads is calculated according to the following formula: where b is an expansion ratio, ρ 1 is a density of the polyethylene composition pellet, and ρ 2 is a density of the polyethylene expanded bead.

(2) Cell density of polyethylene expanded beads: calculated according to the following formula:wherein n is the number of cells in the selected area on the SEM photograph, M is a magnification, and A is the area (unit: cm) of the selected area on the SEM photograph²)，The results are shown in Table 1, which shows the expansion ratio of the polyethylene expanded beads.

(3) Average cell diameter and average cell wall thickness: measured using a scanning electron microscope (available from Hitachi, Inc., model No. S-4700), the results are shown in Table 1.

(4) Compression strength of polyethylene bead compression molded article: the test was carried out according to the method described in ASTM D3575-08 for mechanical properties of closed cell polyolefin flexible foams, wherein the test specimen had a size of 50mm X25 mm, the compression rate was 10mm/min, and the compression strength at 25% of the molded body was as shown in Table 1.

TABLE 1

Note: dense and uniform cells, sparse and uneven cells

From the above results, it can be seen that when a polyethylene composition obtained by using a component a, a component B and a component C having specific melt index and density in combination with a cell nucleating agent is made into expanded beads, the cells of the obtained polyethylene expanded beads are dense and uniform, and expanded beads having a density of 0.04 to 0.15g/L can be obtained by adjusting the foaming pressure and temperature, the cell size is small, and the cell walls are thin, so that the obtained molded body has excellent mechanical properties such as higher compressive strength. From the results of the comparative examples, it can be seen that, compared with the expanded beads obtained from the polyethylene composition of the present invention, whether it is a conventional commercial LLDPE7042 or a polyethylene composition containing only any two of the three components of component A, component B and component C, the expanded beads obtained have uneven cells, uneven bead surface, larger cell diameter, thicker cell wall, and fail to produce a molded body or the resulting molded body has lower compressive strength.

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. A polyethylene composition characterized in that the polyethylene composition comprises component a, component B, component C, and a cell control agent; the component A is linear low density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low density polyethylene is at the temperature of 190 ℃ and the load of 2.16kg_A0.01-3.5g/10min, density rho_A0.880-0.936g/cm³(ii) a The component B is linear low-density polyethylene copolymerized by ethylene/alpha olefin, and the melt index MI of the linear low-density polyethylene is 190 ℃ at the temperature and 2.16kg under the load_B3.6-9.9g/10min, density rho_BIs 0.910 to 0.930g/cm³(ii) a The component C is linear low-density polyethylene copolymerized by ethylene/alpha olefin,having a melt index MI at a temperature of 190 ℃ and a load of 2.16kg_CIs 10-80g/10min, density rho_CIs 0.880-0.930g/cm³，

The polyethylene composition has a density rho of component A, component B and component C_A、ρ_BAnd ρ_CThe relationship between them satisfies-0.04 ≤ rho_A-ρ_BRho is not less than 0.02 and not more than-0.04_A-ρ_C≤0.02；

The content of the foam cell nucleating agent is 0.01 to 10 parts by weight based on 100 parts by weight of the total weight of the component A, the component B and the component C.

2. Polyethylene composition according to claim 1 wherein the component A has a melt index MI at a temperature of 190 ℃ under a load of 2.16kg_AIs 0.01-3g/10min, and the melt index MI of the component B at the temperature of 190 ℃ and the load of 2.16kg is_BIs 4-8g/10min, and the melt index MI of the component C at the temperature of 190 ℃ and the load of 2.16kg_CIs 10-60g/10 min.

3. Polyethylene composition according to claim 1 wherein the component A has a melt index MI at a temperature of 190 ℃ under a load of 2.16kg_AIs 0.01-2g/10min, and the melt index MI of the component B at the temperature of 190 ℃ and the load of 2.16kg is_BIs 4-5g/10min, and the melt index MI of the component C at the temperature of 190 ℃ and the load of 2.16kg_CIs 15-40g/10 min.

4. Polyethylene composition according to claim 1, wherein the component A has a density p_AIs 0.910 to 0.930g/cm³Density p of said component B_BIs 0.913-0.928g/cm³Density p of said component C_CIs 0.905-0.928g/cm³。

5. The polyethylene composition according to claim 4, wherein the component A has a density p_AIs 0.915-0.926g/cm³Density p of said component B_BIs 0.913-0.924g/cm³Density p of said component C_CIs 0.910 to 0.926g/cm³。

6. Polyethylene composition according to any of claims 1 to 5, wherein the mass fraction W of component A in the polyethylene composition_A25 to 90 weight portions of the component B, the weight portion W of the component B_B0.1 to 10 parts by weight of the component C, the mass part of the component C, W_C10 to 75 weight portions.

7. Polyethylene composition according to claim 6, wherein in the polyethylene composition the mass fraction W of component A_A30-80 parts by weight of the component B, W_B0.5 to 8 weight portions of the component C, the weight portion W of the component C_C20 to 70 weight portions.

8. The polyethylene composition according to claim 6, wherein the mass fraction W of component A_AAnd part by mass W of component C_CMelt index MI with component A_ASatisfies the relationship of (1) 4.6 XlgMI_A+10.4≥W_A/W_C≥0.18×lgMI_A+0.7。

9. The polyethylene composition according to claim 8, wherein the mass fraction W of component A_AAnd part by mass W of component C_CMelt index MI with component A_ASatisfies the relationship of 1.8 XlgMI_A+4.7≥W_A/W_C≥0.22×lgMI_A+0.9。

10. The polyethylene composition according to any of claims 1-5 and 8, wherein the polyethylene composition has a melt index at a temperature of 190 ℃ and a load of 2.16kg of from 0.1 to 20g/10 min.

11. The polyethylene composition according to claim 10, wherein the polyethylene composition has a melt index at a temperature of 190 ℃ under a load of 2.16kg of from 0.5 to 10g/10 min.

12. The polyethylene composition according to any of claims 1 to 5, wherein the molecular weight distribution index of component A, component B and component C each satisfy M_w/M_n≤8.0。

13. The polyethylene composition according to claim 12, wherein the molecular weight distribution indices of component a, component B and component C each satisfy 3.5 ≦ M_w/M_n≤6.0。

14. The polyethylene composition of claim 13, wherein component a, component B and component C are polymerized using a ziegler-natta catalyst.

15. The polyethylene composition according to any of claims 1-5, wherein the molar content of alpha olefin comonomer in component A, component B and component C is each independently 0.2-15 mol%.

16. The polyethylene composition according to claim 15, wherein the molar content of alpha olefin comonomer in component a, component B and component C is each independently from 1.5 to 10 mol%.

17. The polyethylene composition according to claim 15, wherein the alpha olefin in component a, component B and component C is each independently C₃-C₂₀At least one of olefins.

18. The polyethylene composition of claim 17 wherein the alpha olefin in component a, component B and component C is each independently propylene, 1-butene, 2-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3-dimethyl-1-pentene, 3, 4-dimethyl-1-pentene, 4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 5-methyl-1-hexene, 1-heptene, 2-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-octene, 1-decene, 1-dodecene, 1-dod, At least one of 1-hexadecene, 1-octadecene and 1-eicosene.

19. The polyethylene composition according to claim 18, wherein the alpha olefin in component a, component B and component C is each independently at least one of 1-butene, 1-hexene and 1-octene.

20. The polyethylene composition according to any of claims 1 to 5, wherein the foam cell nucleating agent is at least one of zinc borate, silica, talc, calcium carbonate, borax and aluminium hydroxide.

21. The polyethylene composition according to any of claims 1 to 5, wherein the polyethylene composition further comprises a lubricant and/or a cell control agent.

22. The polyethylene composition according to claim 21, wherein the lubricant is present in an amount of 0.05 to 5 parts by weight and the cell control agent is present in an amount of 0.1 to 2 parts by weight, based on 100 parts by weight of the total of the components a, B and C.

23. Polyethylene expanded beads prepared from a polyethylene composition according to any of claims 1 to 22.

24. A process for the preparation of polyethylene expanded beads, which comprises pelletizing a polyethylene composition according to any one of claims 1 to 21 and expanding the polyethylene particles obtained.

25. The method of claim 24, wherein the foaming process is a kettle dip foaming process.

26. A molded article of expanded polyethylene beads obtained by molding the expanded polyethylene beads according to claim 23 and/or the expanded polyethylene beads obtained by the method according to claim 24 or 25.