Detailed Description
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass the range or value in close proximity to the range or value. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The first aspect of the invention provides a polyethylene foam material with a gradient pore structure, wherein the pore diameter of a foam hole of the material is 200-1500 mu m, and the pore diameter of the foam hole has the gradient pore structure;
wherein the material is prepared by foaming a polyethylene composition, and the polyethylene composition comprises: matrix resin, foaming agent and auxiliary foaming agent, wherein the matrix resin comprises polyolefin, cross-linking agent, antioxidant and lubricant;
wherein the shear viscosity of the matrix resin at 0.01Hz is 2500-8500 Pa.s.
According to the invention, preferably, the gradient pore structure means that in the cross section of the material, the cell pore size gradually decreases or increases from one side to the other.
In some embodiments of the invention, as shown in fig. 1, the cell pore size gradually decreases or increases from side to side in the cross section of the polyethylene foam.
In a preferred embodiment, when the polyethylene foam is produced by rotomoulding, the cell size increases gradually from the outside to the inside in the cross section of the polyethylene foam.
In another preferred embodiment, when the polyethylene foam material is produced by pressureless foaming, in the cross section of the polyethylene foam material, the cell pore diameter gradually increases from the one-side cooling direction to the heat retaining direction.
According to the present invention, it is preferable that the cell size of the material is 200 to 800. Mu.m, and the average foaming density of the material is 0.1 to 0.5g/cm 3 Preferably 0.1-0.3g/cm 3 Wherein the cell pore size is measured by a microscopic measurement method and the average foaming density is measured according to GB/T1033.2-2008.
Preferably, the material has a compressive strength of 0.3 to 1.5MPa, preferably 0.5 to 1.2MPa, more preferably 0.8 to 1MPa, wherein the compressive strength is measured according to GB/T8813-2008.
According to the present invention, preferably, the weight ratio of polyolefin, crosslinking agent, antioxidant, lubricant, foaming agent and auxiliary foaming agent is 100:0-0.5:0.1-0.5:0-0.5:1-10:0.1-1; preferably 100:0-0.4:0.1-0.3:0-0.3:1-8:0.1-0.4. The preferable weight ratio is more beneficial to improving the mechanical property of the polyethylene foaming material.
According to a preferred embodiment of the present invention, the foamed polyethylene composition comprises 100 parts by weight of polyolefin, 0 to 0.5 parts by weight of crosslinking agent, 0.1 to 0.5 parts by weight of antioxidant, 0 to 0.5 parts by weight of lubricant, 1 to 10 parts by weight of foaming agent and 0.1 to 1 part by weight of auxiliary foaming agent.
According to a preferred embodiment of the present invention, the foamed polyethylene composition comprises 100 parts by weight of polyolefin, 0 to 0.4 parts by weight of crosslinking agent, 0.1 to 0.3 parts by weight of antioxidant, 0 to 0.3 parts by weight of lubricant, 1 to 8 parts by weight of foaming agent and 0.1 to 0.4 parts by weight of auxiliary foaming agent.
According to the present invention, preferably, the base resin has a shear viscosity of 3000 to 7000 Pa.s at 0.01 Hz. The preferable conditions are adopted, so that the polyethylene foam material is more favorable to have a gradient structure. Specifically, when the shear viscosity is too large, the polyethylene foam material does not foam; when the shear viscosity is too low, the cell size of the polyethylene foam is too large.
In a preferred embodiment of the present invention, a polyolefin, a crosslinking agent, an antioxidant and a lubricant are mixed in a certain weight ratio to obtain a matrix resin having a shear viscosity of 2500 to 8500 Pa.s at 0.01 Hz.
Preferably, the parameters of the polyolefin satisfy: the density is 0.91-0.96g/cm 3 Preferably 0.93-0.94g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The melt index at 190℃and 2.16kg load is 2-30g/10min, preferably 5-10g/10min; wherein the melt index at 190℃and 2.16kg load is measured according to GB/T3682-2000.
In the present invention, the polyolefin has a wide selection range as long as the polyolefin contains polyethylene. Preferably, the polyolefin is selected from polyethylene and/or thermoplastic elastomer, preferably polyethylene.
In some embodiments of the present invention, preferably, the thermoplastic elastomer is a copolymer of ethylene and an α -olefin selected from at least one of butene, hexene and octene, for example, the thermoplastic elastomer may be an ethylene-butene copolymer and/or an ethylene-octene copolymer, but the present invention is not limited thereto.
In the present invention, in order to extrude the particles and then foam, it is preferable that the decomposition temperature of the foaming agent is 30-80 ℃ higher than the melting point temperature of the matrix resin.
In the present invention, the foaming agent is selected from the group consisting of azodicarbonamide, 4-oxo-bis-benzenesulfonyl, N-dinitroso pentamethylene tetra-ammonium, sodium bicarbonate, ammonium bicarbonate and sodium citrate.
Preferably, the crosslinking agent is at least one selected from the group consisting of dicumyl peroxide, benzoyl peroxide, 1, 3-bis (t-butylperoxyisopropyl) benzene and 2, 5-dimethyl-2, 5-bishexane.
Preferably, the co-foaming agent is selected from zinc oxide and/or zinc stearate.
Preferably, the antioxidant is selected from pentaerythritol tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate and/or tris (2, 4-di-tert-butylphenyl) phosphite, wherein pentaerythritol tetrakis [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate is abbreviated as oxidant 1010 and tris (2, 4-di-tert-butylphenyl) phosphite is abbreviated as oxidant 168.
Preferably, the lubricant is selected from calcium stearate and/or white oil.
According to the invention, the polyolefin, the cross-linking agent, the antioxidant, the lubricant, the foaming agent and the auxiliary foaming agent are mixed according to a certain weight ratio, and the shearing viscosity of matrix resin containing the polyolefin, the cross-linking agent, the antioxidant and the lubricant is limited, so that the foaming efficiency of the polyethylene foaming material is improved, and the polyethylene foaming material with a gradient pore structure is obtained.
The second aspect of the present invention provides a method for preparing a polyethylene foam material having a gradient pore structure, the method comprising:
(1) Mixing polyolefin, a cross-linking agent, an antioxidant, a lubricant, a foaming agent and a auxiliary foaming agent to obtain a polyethylene composition;
(2) Granulating and grinding the polyethylene composition to obtain polyethylene resin powder;
(3) And foaming the polyethylene resin powder and cooling the polyethylene resin powder on one side to obtain the polyethylene foam material.
In the present invention, in order to uniformly mix the polyethylene composition, it is preferable that the mixing is performed in a mix; further preferably, the mixing conditions include: the temperature is 15-40deg.C, preferably 15-30deg.C; the time is 1-30min, preferably 2-10min. With the preferred conditions, it is more advantageous to obtain a homogeneous polyethylene composition.
In the present invention, the pelletization means that the polyethylene composition is converted into polyethylene resin pellets, and preferably, the pelletization is performed in an extruder selected from a twin-screw extruder and/or a single-screw extruder. Further preferably, the conditions for granulation include: the extrusion temperature is 120-150 ℃, preferably 125-135 ℃; the screw speed is 80-150rpm, preferably 90-110rpm.
According to a preferred embodiment of the present invention, the polyethylene composition obtained in the step (1) is fed into a twin-screw extruder to be extruded and pelletized, and the polyethylene resin pellets are milled to obtain polyethylene resin powder.
In the present invention, the foaming means that the polyethylene resin powder is subjected to a mold to obtain a polyethylene foam material, and preferably the foaming is selected from rotational molding foaming and/or pressureless foaming.
In some embodiments of the invention, preferably, the foaming conditions include: the temperature is 150-250deg.C, preferably 170-210 deg.C, and the time is 10-30min, preferably 12-20min.
In some embodiments of the invention, preferably, when the foaming is rotomoulding foaming, the means of single-sided cooling is selected from single-sided air cooling and/or single-sided water cooling.
In some embodiments of the invention, preferably, when the foaming is pressureless foaming, the one-sided cooling comprises: and (3) introducing water and/or wind to one side along the thickness direction of the foam for cooling, and preserving heat at the other side, wherein the temperature difference of the two sides is more than 50 ℃.
In the invention, the polyethylene resin powder is subjected to single-side cooling foaming, and the cooling temperature is changed in a gradient manner in the cooling process by controlling the shearing viscosity of the matrix resin containing polyolefin, a cross-linking agent, an antioxidant and a lubricant, so that the pore diameter of the foam holes of the material is changed in a gradient manner, that is, the foam holes on the side with high cooling speed are smaller, the heat preservation time on the side with slower cooling is longer, and the foam holes are larger.
In the present invention, the types and amounts of the polyolefin, the crosslinking agent, the antioxidant, the lubricant, the foaming agent and the auxiliary foaming agent are defined according to the above description, and the present invention is not repeated herein.
The third aspect of the invention provides a polyethylene foam material with a gradient pore structure prepared by the method.
In the invention, the polyethylene foam material has a gradient pore structure and excellent mechanical properties, and can effectively realize the functionalization of the polyethylene foam material.
The fourth aspect of the invention provides an application of the polyethylene foam material with the gradient pore structure in military packaging and heat-insulating products.
The present invention will be described in detail by examples.
Melt index of polyethylene at 190℃and 2.16kg under load was measured according to GB/T3682-2000;
the pore diameter of the foam cells of the polyethylene foam material is measured by a microscopic measuring method;
the average foaming density of the polyethylene foaming material is measured according to GB/T1033.2-2008;
the compression strength of the polyethylene foam material is measured according to GB/T8813-2008;
compression set of the polyethylene foam material is measured according to HG/T1876-2009;
the hardness of the polyethylene foam material was measured according to GB/T531.1-2008.
The conditions for preparing the polyethylene foam materials in examples 1 to 4 and comparative examples 1 to 5 are shown in Table 1, and the performance parameters of the polyethylene foam materials prepared in examples 1 to 4 and comparative examples 1 to 5 are shown in Table 2.
Example 1
(1) Polyethylene (density 0.925 g/cm) 3 Melt index at 190 ℃ and 2.16kg load is 3.5g/10 min), dicumyl peroxide, antioxidant 1010, antioxidant 168, azodicarbonamide and zinc oxide are mixed in a mixer to obtain a polyethylene composition, wherein the mixing conditions comprise: the temperature is 25 ℃ and the time is 3min;
(2) Extruding, granulating and grinding the polyethylene composition in a double-screw extruder to obtain polyethylene resin powder, wherein the double-screw extruding, granulating conditions comprise: the extrusion temperature was 125℃and the screw speed was 100rpm; granulating, drying at 60deg.C for 2 hr, and grinding to obtain granule;
(3) And (3) performing rotational molding foaming on the polyethylene resin powder, and cooling the polyethylene resin powder with air at one side for 25min after the foaming of the material is completed to obtain a polyethylene foam material S1, wherein the rotational molding foaming conditions comprise: the temperature was 220℃and the time was 18min.
As shown in fig. 1, the microscopic photograph of the polyethylene foam material S1 shows that the polyethylene foam material has a gradient pore structure, i.e., in the cross section of the polyethylene foam material S1, the pore size of the cells gradually increases from outside to inside, wherein the outer refers to the bottom of fig. 1, and the inner refers to the top of fig. 1.
Example 2
(1) Polyethylene (density 0.945 g/cm) 3 Melt index at 190℃and 2.16kg of load is 4.1g/10 min), benzoyl peroxide, antioxidant 1010, antioxidant 168, azodicarbonamide and zinc stearate in a mixer to obtain a polyethylene composition, wherein the mixing conditions include: the temperature is 25 ℃ and the time is 3min;
(2) Extruding, granulating and grinding the polyethylene composition in a double-screw extruder to obtain polyethylene resin powder, wherein the double-screw extruding, granulating conditions comprise: the extrusion temperature was 120℃and the screw speed was 100rpm; granulating, drying at 60deg.C for 2 hr, and grinding to obtain granule;
(3) And (3) performing rotational molding foaming on the polyethylene resin powder, and cooling the polyethylene resin powder with air at one side for 25min after the foaming of the material is completed to obtain a polyethylene foaming material S2, wherein the rotational molding foaming conditions comprise: the temperature was 220℃and the time was 18min.
Wherein, the SEM image of the polyethylene foam S2 is similar to FIG. 1.
Example 3
(1) POE (ethylene-butene copolymer, density of 0.915 g/cm) 3 Melt index at 190℃and 2.16kg load of 2.5g/10 min), polyethylene (density 0.945g/cm 3 Melt index at 190 ℃ and under a load of 2.16kg is 4.1g/10 min), antioxidant 1010, azodicarbonamide and zinc stearate are mixed in a mixer to obtain a polyethylene composition, wherein the weight ratio of POE to polyethylene is 3:7, and the mixing conditions comprise: the temperature is 30 ℃ and the time is 3min;
(2) Extruding, granulating and grinding the polyethylene composition in a double-screw extruder to obtain polyethylene resin powder, wherein the double-screw extruding, granulating conditions comprise: the extrusion temperature was 125℃and the screw speed was 100rpm; granulating, drying at 60deg.C for 2 hr, and grinding to obtain granule;
(3) Carrying out pressureless foaming on the polyethylene resin powder, and after the foaming of the material is completed, carrying out unilateral cooling along the thickness direction of the foaming, wherein unilateral cooling comprises that one side is filled with water for cooling, the other side is insulated, the temperature difference of the two sides is 60 ℃, and the polyethylene foaming material S3 is obtained, wherein the pressureless foaming conditions comprise: the temperature was 200℃and the time was 10min.
Wherein the pore diameter of the foam cells of the polyethylene foam material S3 is gradually increased from the one-side cooling direction to the heat preservation direction, and the SEM image of the polyethylene foam material S3 is similar to that of FIG. 1.
Example 4
The procedure of example 1 was followed except that white oil was added in step (1) to obtain a polyethylene foam S4.
Comparative example 1
According to the method of example 1, except that 12 parts by weight of azodicarbonamide was replaced, a polyethylene foam material D1 was obtained, wherein cells of the polyethylene foam material D1 were melted and integrated to obtain a foam material, and the mechanical property test was not performed.
Comparative example 2
The procedure of example 1 was followed except that the weight ratio of polyethylene, dicumyl peroxide, antioxidant 1010 and antioxidant 168 was adjusted so that the base resin had a shear viscosity of 9000 Pa.s at 0.01Hz, to obtain a polyethylene foam D2.
Comparative example 3
The procedure of example 3 was followed except that the weight ratio of polyethylene, dicumyl peroxide, antioxidant 1010 and antioxidant 168 was adjusted so that the shear viscosity of the matrix resin at 0.01Hz was 2000 Pa.s, to obtain a polyethylene foam D3.
Comparative example 4
The procedure of example 2 was followed except that the weight ratio of polyethylene, benzoyl peroxide, antioxidant 1010 and antioxidant 168 was adjusted so that the base resin had a shear viscosity of 12000 Pa.s at 0.01Hz, to obtain a polyethylene foam D4.
Comparative example 5
The procedure of example 1 was followed except that the one-sided air cooling in step (3) was replaced with two-sided air cooling to obtain a polyethylene foam material D5.
TABLE 1
Note that: * -a shear viscosity at 0.01Hz of a matrix resin comprising polyolefin, cross-linker, antioxidant and lubricant;
* Polyolefin: crosslinking agent: an antioxidant: and (3) a lubricant: the weight ratio of the foaming agent to the auxiliary foaming agent.
As can be seen from the data in Table 1, examples 1 to 4 produced polyethylene foam materials having a gradient cell structure by defining a foaming mode of a matrix resin (0.01 Hz shear viscosity of 2500 to 8500 Pa.s) and one-side cooling, as compared with comparative examples 1 to 5. Therefore, the pore diameter of the foam cells of the polyethylene foam material prepared by the method provided by the invention has a gradient structure.
TABLE 2
As can be seen from the data in Table 2, the polyethylene foam material prepared by the method provided by the invention has higher mechanical properties, namely, the polyethylene foam material provided by the invention has higher compressive strength and tensile strength, lower compression set and thermal conductivity through comparing example 1 with comparative examples 2 and 5, example 2 with comparative example 4 and example 3 with comparative example 3, and can be widely applied to military packaging and thermal insulation products.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.