Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a multilayer polyethylene rotational molding product, which comprises a surface layer, a middle layer and an inner layer which are sequentially formed, wherein the surface layer is formed by rotational molding of a polyethylene material A, the middle layer is formed by rotational molding of a polyethylene material B, and the inner layer is formed by rotational molding of a polyethylene material C, wherein:
the polyethylene material A is a non-crosslinked and/or low-crosslinked polyethylene material, the shear viscosity eta of the polyethylene material A at the temperature of 200 ℃, the frequency of 1Hz and the strain of 1 percent is 100-8000Pa & s, and the gel content of the surface layer is below 30 weight percent;
the polyethylene material B is a foamed polyethylene material, and the foamed polyethylene material is heated at 180 ℃ under no pressure for 10min and has a foaming density of 0.07-0.25g/cm3The average pore diameter of the obtained cells is 600-;
the polyethylene material C is a cross-linked polyethylene material, the shear viscosity eta of the cross-linked polyethylene material is 10000-70000 Pa.s when the temperature is 200 ℃, the frequency is 1Hz and the strain is 1 percent, and the gel content of the inner layer is more than 40 percent by weight.
According to the invention, the surface layer of the multilayer polyethylene product is an uncrosslinked or low-crosslinked polyethylene layer formed by rotomolding of a polyethylene material A, the middle layer is a foamed polyethylene layer formed by rotomolding of a polyethylene material B, and the inner layer is a crosslinked polyethylene layer formed by rotomolding of a polyethylene material C. When all the polyethylene materials of the invention are controlled to meet the necessary performance requirements, a multilayer polyethylene rotational molding product which has high temperature resistance and environmental stress cracking resistance and can realize component welding can be obtained.
In order to obtain a multilayer polyethylene rotomoulded article with better performance according to the present invention, preferably the polyethylene material a is a non-crosslinked and/or low-crosslinked polyethylene material having a shear viscosity η of 1000-. Preferably, the polyethylene material B is a foamed polyethylene material which is heated at 180 ℃ for 10m without pressureThe in has a foaming density of 0.1-0.2g/cm3(preferably 0.14 to 0.18 g/cm)3) The average pore diameter of the obtained cells is 700-900 μm (preferably 750-850 μm). Preferably, the polyethylene material C is a crosslinked polyethylene material having a shear viscosity η of 20000-65000 Pa.s (preferably 30000-55000 Pa.s) at a temperature of 200 ℃, a frequency of 1Hz and a strain of 1%, and the gel content of the inner layer is from 40 to 80% by weight (preferably from 55 to 70% by weight).
Wherein the shear viscosity eta is the viscosity of the polyethylene material heated into molten fluid at different temperatures under the conditions of 1Hz frequency and 1% strain, and the temperature rise rate is generally 10 ℃/min. The degree of crosslinking can be determined by the gel content of the skin layer, which can be determined by xylene extraction.
According to the invention, the polyethylene material a is required to satisfy the above-mentioned performance conditions, for which reason it is preferred that the polyethylene material a contains a polyethylene matrix a, which is a combination of high density polyethylene and linear low density polyethylene, and optionally a cross-linking agent, preferably in a weight ratio of 100: a combination of 50-800 (preferably 100: 100-500) high density polyethylene and linear low density polyethylene.
In the present invention, the high density polyethylene may be a commercially available product, and preferably, the high density polyethylene has a density of 0.94 to 0.96g/cm3The melt index is 5-20g/10 min.
In the present invention, the linear low density polyethylene is commercially available, and preferably, the linear low density polyethylene has a density of 0.92 to 0.939g/cm3The melt index is 2-20g/10 min.
In the present invention, the Melt Index (MI) was measured at 190 ℃ under a load of 2.16kg at a density of 25 ℃ in accordance with the method of GB/T1033.2-2008.
According to the present invention, the content of the polyethylene matrix a is preferably 99.5 wt% or more and the content of the crosslinking agent is preferably 0.5 wt% or less, based on the total weight of the polyethylene material a. In the case of using a cross-linking agent, it is preferable that the content of the polyethylene matrix a is 99.5 to 99.99% by weight and the content of the cross-linking agent is 0.01 to 0.5% by weight, based on the total weight of the polyethylene material a.
Wherein the cross-linking agent can be selected from a plurality of cross-linking agents, preferably, the cross-linking agents are independently one or more of dicumyl peroxide, benzoyl peroxide, diacetyl peroxide, tert-butyl peroxypivalate, diphenyl oxide peroxydicarbonate, tert-butylcumyl peroxide, 2, 5-dimethyl-2, 5-dihexyl, 2, 5-dimethyl-2, 5-di-tert-butylperoxy-3-hexyne, 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane, 3,5,7, 7-pentamethyl-1, 2, 4-trioxepane and 1, 4-di-tert-butylperoxyisopropyl benzene.
According to the invention, the polyethylene material B is required to satisfy the above performance conditions, and for this reason, in the case of satisfying the above performance conditions, the polyethylene material B preferably contains a polyethylene matrix B and a foaming agent, the polyethylene matrix B is a combination of high density polyethylene and linear low density polyethylene, and the weight ratio is preferably 100: a combination of 50-600 (preferably 100: 100-.
Wherein the high density polyethylene and linear low density polyethylene are selected as described above, but the selection may be the same as or different from that in polyethylene feed a.
According to the invention, the proportions of the individual components of the polyethylene material B can vary within wide limits, preferably the content of the polyethylene matrix B is 93 to 99 wt.% (preferably 96 to 98 wt.%), and the content of the blowing agent is 1 to 7 wt.% (preferably 2 to 4 wt.%), based on the total weight of the polyethylene material B.
According to the present invention, the foaming agent may have a wide selection range, and preferably, the foaming agent is one or more of azodicarbonamide, 4-oxybis-benzenesulfonylhydrazide, tosylsemicarbazide, and 5-phenyltetrazole.
According to the invention, the polyethylene material C is required to satisfy the above performance conditions, and for this purpose, in the case of satisfying the above performance conditions, the polyethylene material C preferably contains a polyethylene matrix C, a crosslinking agent and a crosslinking assistant, the polyethylene matrix C is high-density polyethylene or a combination of the high-density polyethylene and linear low-density polyethylene, wherein, preferably, in the combination of the high-density polyethylene and the linear low-density polyethylene, the weight ratio of the high-density polyethylene to the linear low-density polyethylene is 100: 50-600, preferably 100: 100-400.
Wherein the high density polyethylene and the linear low density polyethylene are selected as described above, but the selection may be the same as or different from that of polyethylene material a or B.
According to the invention, the proportions of the individual components in the polyethylene material C can vary within wide limits, preferably the content of the polyethylene matrix C is 96 to 98 wt.%, the content of the crosslinking agent is 1 to 3 wt.% (preferably 1.5 to 2.5 wt.%), and the content of the crosslinking aid is 1 to 2 wt.%, based on the total weight of the polyethylene material C.
Wherein the cross-linking agent is as described above, the cross-linking agent in the polyethylene material C may be the same as or different from the cross-linking agent in the polyethylene material a.
Preferably, the crosslinking assistant is one or more of triallyl cyanurate, triallyl isocyanurate, trimethylolpropane trimethacrylate and trimethylolpropane triacrylate.
According to the invention, the thicknesses of the surface, intermediate and inner layers can vary within wide limits, preferably the ratio of the thicknesses of the surface, intermediate and inner layers is between 0.2 and 1: 1: 0.1-1.
The thickness of the surface layer can be, for example, 2-5mm, the thickness of the intermediate layer can be, for example, 4-10mm, and the thickness of the inner layer can be, for example, 1-5 mm.
According to the present invention, preferably, the multilayer polyethylene rotomoulded article has a total thickness of 10 to 20 mm.
The invention provides a preparation method of the multilayer polyethylene rotational moulding product, which comprises the following steps:
(1) performing first rotational molding on the polyethylene material A to form a surface layer;
(2) introducing a polyethylene material B for second rotational molding so as to form an intermediate layer in the surface layer;
(3) and introducing a polyethylene material C for third rotational molding so as to form an inner layer in the middle layer.
According to the present invention, the polyethylene material a, the polyethylene material B and the polyethylene material C are as described above, and the present invention is not described herein again.
According to the present invention, before the polyethylene material a, the polyethylene material B and the polyethylene material C are subjected to injection molding, the polyethylene materials may be subjected to extrusion granulation to obtain the master batches of the respective polyethylene materials, and then the injection molding operation is performed, for example, the conditions of the extrusion granulation may include: the extrusion temperature is 125-150 ℃, and the screw rotating speed is 80-150 r/min.
For further convenience of rotational moulding, the above-mentioned master batch may be subjected to a milling treatment to obtain a powder of the respective polyethylene material, for example to a particle size of 50 mesh or less, preferably 30 mesh or less.
According to the invention, the rotational molding can be carried out in a rotational molding machine which is conventional in the field, wherein the polyethylene material A is put into the rotational molding machine to be melted and subjected to first rotational molding to form a surface layer, and the polyethylene material B is put into the rotational molding machine to be heated and melted and subjected to second rotational molding to foam the polyethylene material B in the surface layer to form an intermediate layer; finally, adding the polyethylene material C, heating and melting, and performing third rotational molding to enable the polyethylene material C to be crosslinked in the middle layer to form an inner layer; thus obtaining the rotational molding product which sequentially comprises a surface layer, a middle layer and an inner layer from outside to inside.
Preferably, the conditions of the first rotational moulding comprise: the temperature is 270 ℃ and 280 ℃, and the time is 10-15 min.
Preferably, the conditions of the second rotational moulding comprise: the temperature is 270 ℃ and 280 ℃, and the time is 4-6 min.
Preferably, the conditions of the third rotational moulding comprise: the temperature is 270 ℃ and 280 ℃, and the time is 12-18 min.
Wherein the first rotational molding process melts the polyethylene material A to a temperature of 140-150 ℃. Wherein the second rotational molding process melts the polyethylene material B to a temperature of 130-150 ℃. Wherein the third rotational molding process melts the polyethylene material C to a temperature of 170-200 ℃.
The multilayer polyethylene rotational molding product provided by the invention has the advantages of strong temperature resistance, environmental stress cracking resistance and component welding capability, and is suitable for forming a large-scale corrosion-resistant storage tank.
In a third aspect the invention provides a large corrosion resistant storage tank comprised of the multilayer polyethylene rotomoulded article described above.
The present invention will be described in detail below by way of examples.
In the following examples:
the polyethylene raw material is linear low density polyethylene LLDPE (DFDA-7042 of the commercial Shenhua chemical industry, with a density of 0.92g/cm3MI of 2g/10min), high density polyethylene HDPE (8007, Density of 0.96g/cm, from Shenhua chemical industry)3MI was 8g/10 min).
The density of the polyethylene was determined by GB/T1033.2-2008; the melt index of the polyethylene was determined by GB/T3682.2000 at 190 ℃ under a load of 2.16 kg; the Gel content of the crosslinked polyethylene reflects the degree of crosslinking (Gel) of the crosslinked polyethylene, and the determination is made by measuring the content of xylene insoluble material according to ASTM-D2765.
The shear viscosity eta of the polyethylene material at 200 ℃ and a frequency of 1Hz and a strain of 1% was determined by a rotational rheometer.
The foam density and the average cell diameter of the polyethylene material B were measured by heating at 180 ℃ for 10min without pressure.
The density of the product and the foaming layer is measured at 25 ℃ by measuring the mass and the volume (the surface layer and the foaming layer can be cut apart); the density of the skin layer was measured by GB/T1033.2-2008.
Foaming agent-I is Azodicarbonamide (AC), and foaming agent-II is 4, 4-oxo-bis-benzenesulfonylhydrazide.
The crosslinking agent-I is 2, 5-dimethyl-2, 5-dihexyl, and the crosslinking agent-II is dicumyl peroxide (DCP).
Crosslinking assistant agent: triallyl isocyanurate (national chemical group, chemical Co., Ltd.).
Example 1
This example illustrates the multilayer polyethylene rotomoulded articles of the invention and the process for their preparation.
(1) Polyethylene materials A, B and C (materials with relevant properties shown in table 2) shown in table 1 were each subjected to extrusion granulation under conditions including: the temperature is 125 ℃, the screw rotating speed is 100r/min, and respective master batches are obtained; and (3) respectively grinding the master batches, wherein the grinding temperature is not more than 70 ℃, and a screen is selected to be 30 meshes to obtain powder for later use.
(2) Adding 500 parts by weight of master batch of the polyethylene material A into a mould of an injection molding machine, and carrying out first rotational molding at 275 ℃ for 12min so as to melt the polyethylene material A and enable the temperature to reach 145 ℃ to form a surface layer; then 200 parts by weight of master batch of the polyethylene material B is put into a mould of the injection molding machine, and second rotational molding is carried out for 5min at the rotational molding temperature of 275 ℃, so that the polyethylene material B is melted and the temperature reaches 145 ℃ to form a foaming middle layer; finally, 500 parts by weight of master batch of the polyethylene material C is put into a mould of the injection molding machine, and the third rotational molding is carried out for 15min at the rotational molding temperature of 275 ℃ so that the polyethylene material C is melted and reaches 185 ℃ to form an inner layer; finally cooling by a fan and demoulding to obtain a rotational molding product P1; wherein, the thickness of the surface layer is 2mm, the thickness of the middle layer is 6-8mm, and the thickness of the inner layer is 2 mm.
Examples 2 to 4
This example illustrates the multilayer polyethylene rotomoulded articles of the invention and the process for their preparation.
The process as described in example 1 except that the polyethylene materials A, B and C used had a composition as shown in Table 1 and properties as shown in Table 2; finally obtaining the rotational molding products P2-P4.
Comparative examples 1 to 3
The process as described in example 1 except that the polyethylene materials A, B and C used had a composition as shown in Table 1 and properties as shown in Table 2; finally obtaining the rotational molding products DP1-DP 3.
TABLE 1
Note: the HDPE/LLDPE ratio in the polyethylene matrix is referred to as the weight ratio.
TABLE 2
Test example 1
The measurements of the high temperature tensile elongation of the inner layer, the ESCR (environmental stress crack resistance) of the inner layer, the gel content of the outer layer and the weldability of the article to the component of the rotomoulded article described above are shown in table 3, in which:
high temperature tensile elongation refers to the tensile elongation of the rotomoulded article at 200 ℃.
The inner layer ESCR (environmental stress crack resistance) was determined according to the method specified in GB/T1842-2008.
The process of testing the extent of weldability of the article to the component comprises: the rotational molding product and the plastic flange component are welded at 160 ℃ so as to observe the difficulty degree of welding the product and the component.
TABLE 3
As can be seen from Table 3, the multilayer polyethylene rotational molding product of the invention has strong temperature resistance, environmental stress cracking resistance and component welding capability, and is suitable for forming large-scale corrosion-resistant storage tanks.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.