Polypropylene composition and preparation method thereof, shielding material and cable

Abstract

The invention provides a polypropylene composition and a preparation method thereof, a shielding material and a cable, and the polypropylene composition comprises 8-32 wt% of a propylene-alpha-olefin copolymer, 32-48 wt% of a propylene-ethylene-alpha-olefin copolymer and 20-60 wt% of a conductive filler, with the total weight of the polypropylene composition being 100%. The total weight of the propylene-alpha-olefin copolymer is 100%, and the content of o-dichlorobenzene soluble substances is less than or equal to 6 wt%; based on the total weight of the propylene-ethylene-alpha-olefin copolymer being 100%, the total content of ethylene and alpha-olefin is greater than or equal to 20wt%. The cable shielding layer prepared from the polypropylene composition provided by the invention has excellent mechanical properties and electrical properties, and particularly has high surface smoothness, good semiconductor characteristics and good extrusion processing performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a polypropylene composition, a preparation method thereof, a shielding material and a cable, and belongs to the technical field of cable materials. BACKGROUND

[0002] Traditional overhead line transmission is limited by environment and large land occupation, and is difficult to meet the demand of urban power distribution, so power cable transmission is replacing overhead line transmission in more and more fields. At present, extruded insulation cables represented by cross-linked polyethylene (XLPE) cables are widely used in power transmission of various voltage levels. As an important part of power grid architecture, the environmental compatibility, disposal and recycling of cables after retirement have higher requirements. XLPE is a thermosetting material, which can only be buried or incinerated after retirement, causing adverse effects on the environment. Therefore, the development of new environmentally friendly cables to replace XLPE cables has become the focus of attention and research. Using thermoplastic polypropylene material as cable material is an important development direction of new cables, which can realize recycling after the end of product life, simplify the process flow and reduce energy consumption and greenhouse gas emissions in the cable manufacturing process. Therefore, the needs of green, environmentally friendly and sustainable development in various aspects promote the transformation of power cable materials to low-carbon, environmentally friendly and recyclable thermoplastic polypropylene materials.

[0003] Polypropylene (PP) material has excellent insulation performance, does not need to be cross-linked, can be melt-reused, and has excellent insulation and heat resistance comparable to cross-linked polyethylene. Compared with cross-linked polyethylene cables, polypropylene power cables do not need cross-linking and degassing processes, which greatly reduces carbon emissions and has energy-saving advantages; the shielding layer can be recycled after the cable reaches the service life, which has environmental advantages. In addition to the above advantages, polypropylene insulation has high cleanliness and natural water tree resistance, and the upper limit of insulation performance is higher than that of cross-linked polyethylene, which is expected to break through the bottleneck of ultra-high voltage cable technology development.

[0004] The extruded insulated power cable is composed of conductor, conductor shield, insulation, insulation shield and protective material. Among them, the semiconductive shielding layer plays a role of uniformizing the conductor surface electric field or grounding, and is one of the main components affecting the performance of the cable. In order to make the polypropylene-based thermoplastic insulation exhibit the above excellent properties, a corresponding semiconductive shielding material must be matched. The semiconductive shielding material is generally composed of base resin, conductive filler, crosslinking agent, antioxidant and other processing aids, and is made into a semiconductive layer by extrusion molding. Polypropylene material has the disadvantages of poor low-temperature toughness, high hardness at room temperature, and poor processing fluidity, which is not conducive to the dispersion of conductive filler carbon black in it, so that the performance of carbon black after addition is not ideal. The poor dispersion of carbon black not only affects the positive temperature effect (PTC effect) of the volume resistivity of the material, but also causes the protrusion of the shielding layer, which seriously affects the smoothness of the insulation and shielding interface. The protrusions on the surface of the semiconductive shielding layer will cause uneven electric field distribution, local electric field enhancement, and even induce electrical treeing damage.

[0005] To further illustrate the prior art, the applicant further provides the following related literature and makes an explanation.

[0006] CN107108988A discloses an energy cable comprising from the inside out an electrically conductive body, an inner semiconductive layer, an electrically insulating layer made of a thermoplastic material mixed with a dielectric fluid and an outer semiconductive layer, wherein the outer semiconductive layer comprises: (i) 55 wt-90 wt% of a copolymer of ethylene with at least one ester comonomer having ethylenic unsaturation; (ii) 10 wt-45 wt% of a propylene copolymer containing at least one olefin comonomer selected from ethylene and an alpha-olefin other than propylene, said copolymer having a melting point of 145-170°C and a melting enthalpy of 40-80 J / g; (iii) at least one electrically conductive filler; (iv) at least one dielectric fluid; the amounts of (i) and (ii) being expressed with respect to the total weight of the polymer components of said layer. The outer semiconductive layer is cold strippable, has an adhesion to the underlying thermoplastic insulating layer, said adhesion can be adjusted to obtain a suitable balance between strippability without application of heat at temperatures in the range of about 0°C to about 40°C and stable adhesion to said insulating layer during the lifetime of the cable.

[0007] In the prior art, there is still partial delamination of the shielding layer and the possibility of the formation of micro-porosities that can cause the appearance of partial discharge phenomena. CN107108988A wishes to provide a semiconductive layer that is cold strippable, having an adhesion to the underlying thermoplastic insulating layer that can be adjusted to obtain a suitable balance between strippability without the application of heat at temperatures in the range of about 0°C to about 40°C and stable adhesion to the insulating layer during the life of the cable. To this end it uses a specific composition comprising: at least one copolymer of ethylene with at least one ester comonomer having at least one olefinic unsaturation, a copolymer of propylene with at least one olefin comonomer selected from ethylene and an alpha-olefin other than propylene, at least one electrically conductive filler and at least one dielectric fluid. However, there is still the problem of the distribution of the dielectric fluid within the resin, non-uniform distribution and exudation to the surface during long-term use, which can cause charge accumulation and local electric field concentration at the insulating and shielding interface, thus accelerating the ageing of the cable. In addition, there is the problem of poor semiconductive properties caused by the introduction of the dielectric fluid, which has not been taken into account.

[0008] CN116508115A discloses a semiconductive composition, an article comprising the semiconductive composition (preferably a cable having a semiconductive layer comprising the semiconductive composition) and the use of the semiconductive composition as an internal and / or external semiconductive layer of medium voltage cables and high voltage cables, the semiconductive composition comprising: (A) at least 52.0 wt%, based on the total weight of the semiconductive composition, of a heterophasic propylene copolymer having a matrix phase and an elastomeric phase dispersed in the matrix phase; and (B) 5.0 to 40.0 wt%, based on the total weight of the semiconductive composition, of carbon black.

[0009] In the prior art, the shielding layer requires about 40 to 50 wt% of carbon black, but such a large amount of conductor filler has the disadvantage of poor miscibility with the polymer component, which can impair the mechanical properties of the semiconductive composition. CN116508115A wishes to provide a semiconductive composition that exhibits good conductivity as well as good mechanical properties, having a matrix phase and an elastomeric phase dispersed in the matrix phase. To this end, it adjusts the polymer composition of the insulating layer to be a propylene-based composition, rather than an ethylene-based composition, and since the semiconductive layer and the insulating layer have similar polymer compositions, the adhesion between the two layers increases and the electrical properties can be improved. However, the semiconductive composition therein has two or more resin components, and the polarity difference between the elastomeric phase and the matrix phase, the carbon black particles will selectively disperse in the elastomer, resulting in extremely uneven dispersion of carbon black, which can seriously affect the service life and operational reliability of the cable.

[0010] CN108864527A discloses a kind of for high voltage cable polypropylene insulation semiconductive shield layer material, according to weight fraction includes: polypropylene base 20-50 parts, elastomer base 50-80 parts, conductive carbon black 20-55 parts, synergistic antioxidant 0.5-2.5 parts, copper resistance 0.01-3.0 parts and lubricating dispersant 0.5-10 parts;Wherein polypropylene base and elastomer base are 100 parts, polypropylene base is the blend of homopolymer polypropylene and copolymer polypropylene mixed according to the weight ratio of 0-10:1, and the melt index of homopolymer polypropylene is 1.0-5.0g / 10min, the melt index of copolymer polypropylene is 1.0-5.0g / 10min.Its technical effect is: it has good mechanical properties, heat resistance, stable electrical conductivity, good copper resistance, non-crosslinking, fast extrusion line speed, green environmental protection, easy to recycle.

[0011] In the prior art, it is still desirable to obtain a shielding layer that can be in close contact with the insulating layer interface, the interface is smooth and seamless, can uniform electric field and avoid void caused by ionization discharge, effectively ensure the operation safety and cable life.In order to solve the above problems, CN108864527A provides a kind of for high voltage cable polypropylene insulation semiconductive shield layer material preparation method, polypropylene base, elastomer base, conductive carbon black etc.are mixed and then added to continuous mixing machine group and mix, extrusion granulation is obtained for high voltage cable polypropylene insulation semiconductive shield layer material granules.Comparison literature 3 elastomer is selected from at least one of ethylene-octene copolymer, ethylene-butene copolymer, ethylene-propylene rubber and polyethylene and ethylene-propylene rubber blend.However, it uses lubricating dispersant to make carbon black well dispersed and ensure that it does not migrate to the insulating layer, but because it uses two components with large property difference, polypropylene and ethylene copolymer elastomer, as the two-phase structure of the composition, there is still selective dispersion of carbon black in the elastomer phase, which leads to uneven distribution of carbon black, which can seriously affect the service life and operation reliability of the cable.

[0012] Therefore, how to improve the uneven distribution caused by selective dispersion of conductive carbon black in the composition matrix phase and elastomer phase, so as to improve the insulation-shielding interface state and semiconductor properties is still a problem to be solved in the art. SUMMARY

[0013] In order to solve the problems of poor surface state and poor semiconductor properties of the cable shielding layer in the prior art, the purpose of the present application is to provide a polypropylene composition, a preparation method thereof, a shielding material and a cable.The shielding material prepared from the polypropylene composition provided by the present application has excellent mechanical properties and electrical properties when used as a shielding layer material for a cable, especially has high surface smoothness and good semiconductor properties, i.e., a semiconductor shielding material.

[0014] To achieve the above object, in one aspect, the present application provides a polypropylene composition, wherein, based on the total weight of the polypropylene composition being 100%, it comprises 8-32 wt% of a propylene-α-olefin copolymer (matrix phase), 32-48 wt% of a propylene-ethylene-α-olefin copolymer (elastomer phase) and 20-60 wt% of an electrically conductive filler;

[0015] wherein, based on the total weight of the propylene-α-olefin copolymer being 100%, the content of ortho-dichlorobenzene-soluble substance is ≤6 wt%, preferably ≤3 wt%;

[0016] wherein, based on the total weight of the propylene-ethylene-α-olefin copolymer being 100%, the total content of ethylene and α-olefin is ≥20 wt%, preferably ≥20 wt%, and ≤30 wt%.

[0017] Since the polypropylene composition provided by the present application uses the combination of specific matrix phase and elastomer phase, the present application can solve the problem of uneven distribution caused by the selective dispersion of the electrically conductive filler such as conductive carbon black in the matrix phase and elastomer phase, so that when the polypropylene composition is made into a shielding layer of a cable, the insulation-shielding interface state and semiconductor properties can be significantly improved.

[0018] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the content of the electrically conductive filler is 25-50 wt%, preferably 25-40 wt%, and more preferably 25-30 wt%.

[0019] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the electrically conductive filler comprises carbon black and the like.

[0020] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the carbon black comprises one or a combination of several of acetylene black, thermal cracking carbon black, furnace carbon black and channel carbon black and the like.

[0021] In the present application, the electrically conductive filler can be in the form of particles, agglomerates or aggregates, in particular micrometer-sized particles, agglomerates or aggregates and the like, for example having a size of more than 0.1 μm, and preferably more than 0.5 μm. When considering a plurality of particles, agglomerates or aggregates of the electrically conductive filler powder, the term "size" means the number average size of all particles of a given population, which size is determined by customary methods known to the person skilled in the art, for example by microscopic techniques, such as optical microscopy or scanning electron microscopy (SEM) observation or by transmission electron microscopy (TEM).

[0022] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the α-olefin comprises one or a combination of several of C4-C8 olefins and the like.

[0023] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the α-olefin is selected from one or a combination of more than one of 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene and 1-octene, preferably 1-butene.

[0024] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the ratio of the weight content of the α-olefin in the propylene-α-olefin copolymer to the weight content of the α-olefin in the propylene-ethylene-α-olefin copolymer is 0.8-1.2. When the weight content ratio of the α-olefin in the two phases of the matrix phase and the rubber phase is within this range, the refractive index and the polarity of the two phases are further made substantially the same, the two phases are made more uniform, and the conductive filler can be uniformly distributed between the two phases to form a double-channel synergistic optimization of the conductive channel and the percolation structure, and the conductive performance is excellent.

[0025] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the content of the α-olefin is ≥4wt% and ≤5wt% based on the total weight of the propylene-α-olefin copolymer being 100%.

[0026] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the weight content of ethylene / weight content of the α-olefin in the propylene-ethylene-α-olefin copolymer is 1-2.5.

[0027] In the matrix phase and / or the rubber phase of the polypropylene composition of the present application, the comprehensive performance of the polypropylene composition can be further improved by adjusting the content of each structural unit.

[0028] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the molecular weight distribution Mw / Mn of the polypropylene composition is ≥5.5. Within this range of the molecular weight distribution, the cable extrusion processing performance is better.

[0029] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the polypropylene composition further comprises an additive, which comprises one or a combination of more than one of an antioxidant, a voltage stabilizer, a processing aid and a nucleating agent.

[0030] As a specific embodiment of the above-mentioned polypropylene composition of the present application, the content of the antioxidant is 0.01-1wt%, preferably 0.1-0.5wt%, the content of the voltage stabilizer is 0.01-5wt%, preferably 0.1-2wt%, and the content of the nucleating agent is 0.01-5wt%, preferably 0.1-1wt%, based on the total weight of the polypropylene composition being 100%.

[0031] The antioxidant in the polypropylene composition described above can improve the long-term stability of the material, and can be selected from one or more of the following: tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, tris(2,4-di-tert-butylphenyl)phosphite, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, N,N-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, 3,3-thiodipropionic acid octadecyl ester, and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl ester.

[0032] The voltage stabilizer in the polypropylene composition described above can further improve the electrical breakdown resistance and dielectric strength of the material, and can be selected from substituted benzophenone-based voltage stabilizers, wherein the substituent group can be one or a combination of several of the following: alkyl, aryl, alkoxy, and aryloxy; or can be a benzil derivative selected from one or more of the following: 4-methoxybenzil, 4-hydroxybenzil, 4,4'-bis(dioctylamino)benzil, 4,4'-dioctylaminobenzil, p-anisil, 4,4'-dihydroxybenzil, 4,4'-di(dodecyloxy)benzil, and 4,4'-di(undec-10-enyloxy)benzil, 4-hydroxybenzil, 4-dodecyloxybenzil, and 4-undec-10-enyloxybenzil.

[0033] The nucleating agent in the polypropylene composition described above can reduce the grain size in the crystalline phase and further improve the electrical breakdown resistance and dielectric strength of the material, and can be selected from carboxylate-based nucleating agents or phosphate-based nucleating agents; wherein the carboxylate-based nucleating agent can be selected from one or both of sodium benzoate and hydroxyaluminum p-tert-butylbenzoate; and the phosphate-based nucleating agent can be selected from one or both of 2,2'-methylene-bis(4,6-di-tert-butylphenyl) sodium phosphate and bis[2,2'-methylene-bis(4,6-di-tert-butylphenyl)] aluminum phosphate.

[0034] In another aspect, the present application also provides a preparation method of the polypropylene composition described above, wherein the preparation method comprises:

[0035] The catalyst system is pre-contacted and then continuously introduced into the first polymerization reactor to complete the first-stage polymerization reaction, and then propylene and α-olefin are added to the first polymerization reactor and hydrogen is introduced for the second-stage polymerization reaction to obtain a propylene-α-olefin copolymer;

[0036] The product from the first polymerization reactor is fed to a second polymerization reactor, and propylene, ethylene and an alpha-olefin are added to the second polymerization reactor to carry out a third stage polymerization reaction, and the product from the second polymerization reactor is subjected to inactivation and drying treatment to obtain a polymer powder;

[0037] The polymer powder and the conductive filler are mixed, melt-extruded and granulated to obtain the polypropylene composition.

[0038] As a specific embodiment of the above preparation method of the present application, the catalyst system comprises a main catalyst, a cocatalyst and an external electron donor, wherein the main catalyst comprises a Ziegler-Natta catalyst, a metallocene catalyst, an organic metal catalyst or a coordination catalyst, etc., the cocatalyst comprises an organic aluminum, etc., and the external electron donor comprises an organic silicon compound, etc.

[0039] In the above preparation method of the present application, the main catalyst such as a Ziegler-Natta catalyst, a metallocene catalyst, an organic metal catalyst or a coordination catalyst is a conventional substance, which can be selected as required, and can be obtained by commercial purchase or by using a conventional method. Preferably, the main catalyst is a Ziegler-Natta catalyst, more preferably a Ti catalyst supported on MgCl2, and further preferably, the molar ratio of the active solid catalyst component containing titanium in the Ziegler-Natta catalyst to the organic aluminum compound is 10:1-400:1, preferably 25:1-100:1.

[0040] In the above preparation method of the present application, the organic aluminum as the cocatalyst comprises one or a combination of several of trialkylaluminum (such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, trihexylaluminum and trioctylaluminum, etc.), chlorodiethylaluminum, chlorodiisobutylaluminum, chloroethylaluminum and dichloroethylaluminum, etc.

[0041] In the above preparation method of the present application, the organic silicon compound as the external electron donor comprises one or a combination of several of isobutyltriethoxysilane, diisopropyldimethoxysilane, cyclohexylmethyldimethoxysilane, tetramethoxysilane, tetraethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylphenoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyl-tert-butyldimethoxysilane, methylisopropyldimethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, (1,1,1-trifluoro-2-propyl)-2-ethylpiperidyl dimethoxysilane and (1,1,1-trifluoro-2-propyl)-methyldimethoxysilane, etc.

[0042] As a specific embodiment of the above-mentioned preparation method of the present application, the molar ratio of the organoaluminum as the cocatalyst and the organosilicon compound as the external electron donor is 1:1-200:1, preferably 10:1-50:1, in terms of aluminum / silicon.

[0043] As a specific embodiment of the above-mentioned preparation method of the present application, the polymerization temperature of the first-stage polymerization reaction, the second-stage polymerization reaction and the third-stage polymerization reaction is generally 40-100℃, preferably 60-100℃, and the residence time of each stage of polymerization reaction is in the range of 30 min-10 h.

[0044] In the above-mentioned preparation method of the present application, the first polymerization reaction (including the first-stage polymerization reaction and the second-stage polymerization reaction) can be carried out in liquid phase, and the second polymerization reaction (i.e. the third-stage polymerization reaction) can be carried out in gas phase; or both the first polymerization reaction and the second polymerization reaction can be carried out in gas phase. When the polymerization reaction is carried out in liquid phase, the polymerization pressure is preferably in the range of 3.0-4.5 MPa. When the polymerization reaction is carried out in gas phase, the polymerization temperature is preferably 60-90℃, and the polymerization pressure is preferably 1.0-3.0 MPa. When the polymerization reaction is carried out in gas phase, the gas phase reactor used can be a gas phase fluidized bed, a gas phase moving bed or a gas phase stirred bed reactor, etc.

[0045] In the present application, when the polypropylene composition further comprises an additive, the preparation method thereof comprises:

[0046] The polymer powder, the conductive filler and the target additive are mixed, melt-extruded and granulated to obtain the polypropylene composition.

[0047] In another aspect, the present application further provides a shielding material, wherein the shielding material comprises the above-mentioned polypropylene composition.

[0048] In still another aspect, the present application further provides a cable comprising at least one cable core, the cable core comprising a conductor and, in turn, an inner semiconductive shielding layer, an insulation layer and an outer semiconductive shielding layer covering the conductor, wherein the material of the inner semiconductive shielding layer and / or the outer semiconductive shielding layer is the above-mentioned shielding material.

[0049] As a specific embodiment of the above-mentioned cable of the present application, the cable is a power cable, preferably a high-voltage alternating current or direct current power cable for high-voltage power transmission.

[0050] In the above-mentioned cable of the present application, the inner semiconductive shielding layer and / or the outer semiconductive shielding layer is a recyclable layer.

[0051] In the cable according to the application, the inner semiconductive shielding layer and / or the outer semiconductive shielding layer can be an extruded layer, in particular an extruded layer by means of methods well known to the person skilled in the art.

[0052] Compared to the prior art, the application achieves the following advantageous technical effects:

[0053] The polypropylene composition provided by the application has a propylene-α-olefin copolymer as a matrix phase, a propylene-ethylene-α-olefin copolymer as a rubber phase, and the content of the propylene-α-olefin copolymer and the propylene-ethylene-α-olefin copolymer is 8-32 wt% and 32-48 wt%, respectively, based on the total weight of the polypropylene composition being 100%, and the content of ortho-dichlorobenzene-soluble substance is ≤6 wt%, based on the total weight of the propylene-α-olefin copolymer being 100%; and the total content of ethylene and α-olefin is ≥20 wt%, based on the total weight of the propylene-ethylene-α-olefin copolymer being 100%. Under the above component conditions, the refractive index and polarity of the matrix phase and the rubber phase are basically the same, so that the two phases are more uniform, so that the conductive filler can be uniformly distributed between the two phases to form a double-channel synergistic optimization of conductive channels and percolation structures, thereby making the conductive performance more excellent, and finally improving the insulation-shielding interface state and the semiconductor characteristics.

[0054] Meanwhile, under the above component conditions, the cable shielding layer prepared from the polypropylene composition provided by the application has excellent mechanical properties and electrical properties, in particular, has high surface smoothness, good semiconductor characteristics, and good extrusion processing properties.

[0055] In addition, the cable shielding layer prepared from the polypropylene composition provided by the application has a weak PTC effect, solving the common problem of filled semiconductive polymers and improving the safety of cable operation. Moreover, the cable shielding layer prepared from the polypropylene composition provided by the application has an improved tensile strain at break, which can improve the strength and tensile deformation resistance of the insulation layer. DETAILED DESCRIPTION

[0056] It should be noted that the terms "comprising" and any variations thereof in the specification and in the claims are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or apparatus that includes a list of steps or units not necessarily limited to those explicitly listed, but can include other steps or units not expressly listed or inherent to such processes, methods, products or apparatus.

[0057] The ranges disclosed herein are meant to include any and all sub-ranges of the named ranges, including the range endpoints. For instance, a range from 60-120 should be interpreted to include not only 60-120 and 80- 110, but also 60- 80, 80- 100, 100- 120, etc.

[0058] In the present application, unless otherwise stated, the numerical range "a-b" means a shorthand notation for representing any real combination of numbers between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present application, and "0-5" is just a shorthand notation for these numerical combinations.

[0059] In the present application, unless otherwise stated, all embodiments and preferred embodiments mentioned in the present application can be combined with each other to form new technical solutions.

[0060] In the present application, unless otherwise stated, all technical features and preferred features mentioned in the present application can be combined with each other to form new technical solutions.

[0061] In the present application, unless otherwise stated, all steps mentioned herein can be performed in sequence or randomly, but preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method further comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0062] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with tables and examples. The examples described below are part of the examples of the present application, not all examples, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor belong to the scope of protection of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0063] Analysis test method:

[0064] Volume resistivity and PTC strength:

[0065] According to the national standard GB / T 3048.3-2007, the volume resistivity of the target cable shielding material is measured by using a four-electrode system, wherein the experiment is carried out at 30℃, 50℃, 60℃, 70℃, 90℃ and 110℃, and after the experiment, the logarithmic difference between the volume resistivity at 110℃ and the volume resistivity at 30℃ is taken as the PTC strength.

[0066] The volume resistivity of the filled semiconductive polymer increases with the increase of temperature, which is called PTC effect. Severe PTC effect will reduce or even eliminate the effect of the shielding layer, thereby affecting the safe operation of the cable. Therefore, the volume resistivity of the cable shielding material should have high temperature stability, i.e. low PTC strength.

[0067] Surface smoothness:

[0068] The target cable shielding material is extruded into a strip with a thickness of 0.3mm by a single screw extruder equipped with a flat die, i.e. a test strip; then the test strip is maintained under constant mechanical tension by a casting roller at a certain speed, and moved by a winding machine; the strip is advanced to the measurement area of the optical detection system; an online camera connected to a computer records the image of the surface of the extruded strip and performs image analysis; finally, the number of defects or protrusions on the surface of the test strip is counted, and the number of defects or protrusions per m 2 is obtained by classifying the defects according to size and shape.

[0069] Tensile breaking strain: tested according to GB / T 1040.1-2019 standard, the tensile breaking strain meeting the requirements in the present application is greater than 500%.

[0070] Content of ortho-dichlorobenzene-soluble matter:

[0071] The present application analyzes the soluble fraction of the propylene-based heterophasic copolymer by using the crystallization fractionation equipment (such as A-TREF or CEF) of Polymer Char Company, and the experimental process is as follows:

[0072] The polymer is dissolved in ortho-dichlorobenzene at 160℃, after 120 minutes, the temperature is decreased to 95℃ at a rate of 30℃ / min, and then crystallized to 35℃ at a rate of 2℃ / min, while the liquid phase pump pumps the ortho-dichlorobenzene at a speed of 0.05mL / min and slowly rinses the column, after the crystallization is completed, the temperature is increased at a rate of 4℃ / min and a speed of 1mL / min, the ortho-dichlorobenzene is rinsed to 150℃, and the sample information during the rinsing process is recorded by using the IR-5 infrared detector, so as to obtain the crystallization rinsing fractionation curve and the ortho-dichlorobenzene soluble content at room temperature.

[0073] Bending modulus: the product to be tested is injection molded into a sample strip under the temperature condition of 200-220℃, the bending sample is a rectangular sample strip with a size of 80mmx10mmx4mm; then the bending modulus test is carried out according to the method specified in GB / T 9341-2008.

[0074] DC breakdown strength:

[0075] The target shielding material is tested for DC breakdown strength according to the method specified in GB / T 1408-2006, the output alternating voltage is 0-100kV during the test process, the ball-ball copper electrode with a diameter of 10mm is used, the voltage increasing rate is 2kV / s, the film sample has a diameter of 15cm and a thickness of 0.20mm, and the number of data points of each group of samples is not less than 10. The tested sample and the electrode are immersed in silicone oil (which is treated in a vacuum oven at 70℃ for 24h before the test) to prevent surface discharge.

[0076] Molecular weight and distribution: the molecular weight distribution (MWD) in the present application can be expressed as Mw / Mn, that is, the ratio of the weight average molecular weight to the number average molecular weight. The molecular weight and molecular weight distribution of the sample are tested by using the high temperature gel permeation chromatography (GPC) equipped with the Agilent PLgel MIXED-B chromatographic column, the sample to be tested is dissolved in 1,2,4-trichlorobenzene with a concentration of 1.0mg / mL, the test temperature is 150℃, and the solution flow rate is 1.0mL / min. The molecular weight of polystyrene is used as an internal reference to prepare a standard curve, and the molecular weight and molecular weight distribution of the sample to be tested are calculated according to the outflow time.

[0077] Examples 1-11

[0078] Examples 1-11 of the present application provide a series of polypropylene shielding material compositions, which are prepared by using a preparation method comprising the following specific steps:

[0079] I. Preparation of the main catalyst:

[0080] The reactor with a stirrer was replaced with nitrogen, and 2000 mL of ethanol, 60 mL of 2-ethylhexanol, and 40 mL of isopropyl alcohol were added to the reactor, and 2 g of magnesium chloride was added to dissolve it. After stirring, the temperature was raised, and then 30 g of magnesium powder was added sequentially. The reaction was carried out until completion. After the reaction was completed, washing, separation, and drying were performed to obtain a dialkoxymagnesium carrier.

[0081] The dialkoxymagnesium carrier and 500 mL of toluene, 5 mL of di-n-butyl phthalate were prepared into a suspension; in a nitrogen-replaced reactor, 600 mL of toluene and 820 mL of titanium tetrachloride were added, and the temperature was lowered to -5°C, then the suspension was added to the reactor, and the temperature was kept constant for 1.5 hours, then the temperature was slowly raised, and when the temperature rose to 80°C, 5 mL of di-n-butyl phthalate was added, and the temperature was slowly raised to 105°C, and the temperature was kept constant for 1.5 hours, then the liquid was filtered clean; then a mixture of 550 mL of toluene and 750 mL of titanium tetrachloride was added and the temperature was raised to 105°C, and the mixture was stirred for 1 hour, then the liquid was filtered off, the obtained solid was washed with hexane 3 times, the liquid was filtered off and dried, and the main catalyst was obtained.

[0082] II. Preparation of the polypropylene shielding material composition:

[0083] Preparation was carried out according to the formulation shown in Table 1, and the polymerization reaction involved in the preparation process was carried out on a polypropylene device, which mainly included a first loop reactor and a second gas phase reactor.

[0084] The main catalyst prepared in I., a cocatalyst (triethylaluminum), and an external electron donor (isobutyl triethoxysilane) were pre-contacted at 10°C for 30 min and then continuously entered the first loop reactor to complete the first stage of polymerization reaction, and the temperature of the first stage of polymerization reaction in the first loop reactor was 70°C, and the reaction pressure was 4.0 MPa; liquid propylene and α-olefin were added to the first loop reactor, and a certain amount of hydrogen was introduced, and the material was allowed to stay in the first loop reactor (temperature 70°C, pressure 4.0 MPa) for 1 hour to obtain a propylene-α-olefin copolymer.

[0085] The product obtained from the first loop reactor was introduced into the second gas phase reactor, and propylene, ethylene, and α-olefin were introduced into the second gas phase reactor to continue the copolymerization reaction, and the reaction temperature was 75°C, the reaction pressure was 1.5 MPa, and the material stayed in the reactor for 3 hours.

[0086] The reaction product obtained from the second gas phase reactor was dried by wet nitrogen to remove unreacted catalyst and heated to obtain a polymer powder;

[0087] The polymer powder is mixed with a conductive filler, melt extruded and pelletized to obtain a polypropylene shielding material composition.

[0088] Table 1

[0089]

[0090]

[0091] Note: The carbon black used in the examples is all conductive carbon black with model number 250G produced by TIMCAL, Switzerland.

[0092] Comparative Examples 1-7

[0093] To more clearly demonstrate the effects of the present application, the inventors weighed each component according to the proportions listed in Table 2, and prepared the products of Comparative Examples 1-7 in the same manner as Examples 1-11.

[0094] Table 2

[0095]

[0096] Note: The carbon black used in the comparative examples is all conductive carbon black with model number 250G produced by TIMCAL, Switzerland.

[0097] The products obtained in Examples 1-11 and Comparative Examples 1-7 were tested for performance according to the analytical test methods provided above, and the results are shown in Table 3 below.

[0098] Table 3

[0099]

[0100] As can be seen from Table 3, the products provided in Examples 1-11 achieved excellent bending modulus, DC breakdown strength, volume resistivity at 30°C, volume resistivity at 110°C, surface smoothness, tensile strain at break, and PTC strength.

[0101] In contrast, the products provided in Comparative Examples 1-7 performed poorly in many respects. Specifically, compared to Example 2, Comparative Example 1 used a propylene homopolymer instead of a propylene-a-olefin copolymer, and as can be seen from Table 3, the corresponding properties of the product obtained were inferior to those of the product provided in Example 2.

[0102] Comparing to Example 8, the total content of ethylene and α-olefin in the propylene-ethylene-α-olefin copolymer of Comparative Example 2 is only 16 wt% based on the total weight of the propylene-ethylene-α-olefin copolymer being 100%, and the corresponding properties of the product obtained are worse than those of the product provided in Example 8, as can be seen from Table 3.

[0103] Comparing to the Examples, the total content of ethylene and α-olefin in the propylene-ethylene-α-olefin copolymer of Comparative Example 3 and Comparative Example 4 is only 18 wt% and 11 wt% respectively based on the total weight of the propylene-ethylene-α-olefin copolymer being 100%, and the parameters such as the ratio of α-olefin content in copolymer a and copolymer b, the total content of ethylene and α-olefin in copolymer b, and the ratio of ethylene / α-olefin content in copolymer b are not within the more preferred value range of the present application, and the corresponding properties of the product obtained are worse than those of the product provided in the corresponding Examples, as can be seen from Table 3.

[0104] Comparing to the Examples, the content of o-dichlorobenzene-soluble substance in the propylene-α-olefin copolymer of Comparative Example 5 is 7 wt% based on the total weight of the propylene-α-olefin copolymer being 100%, which is not within the value range of ≤6 wt%, and the corresponding properties of the product obtained are worse than those of the product provided in the corresponding Examples, as can be seen from Table 3.

[0105] Comparing to Example 2, the amount of copolymer b in Comparative Example 6 is not within the range of 32-48 wt% claimed by the present application, and the amounts of copolymer a and copolymer b in Comparative Example 7 are not within the ranges of 8-32 wt% and 32-48 wt% respectively claimed by the present application, and the corresponding properties of the product obtained are worse than those of the product provided in Example 2, as can be seen from Table 3.

[0106] In addition, comparing to Examples 1-8, especially Examples 4-5, the content of α-olefin in the propylene-α-olefin copolymer of Example 9 is only 6 wt% based on the total weight of the propylene-α-olefin copolymer being 100%, which is not within the range of ≥4 wt% and ≤5 wt%, and the corresponding properties of the product obtained are worse than those of the product provided in Examples 1-8, especially Examples 4-5, as can be seen from Table 3.

[0107] Comparing to Examples 1-8, especially Example 2, the molecular weight distribution Mw / Mn of the polypropylene composition in Example 10 is only 4.5, which is not within the range of Mw / Mn≥5.5, and the corresponding properties of the product obtained are worse than those of the product provided in Examples 1-8, especially Example 2, as can be seen from Table 3.

[0108] Compared with the examples 1-8, especially examples 4-5, the weight content of ethylene / weight content of α-olefin = 4.2 in only the copolymer b in example 11 is not in the range of 1-2.5, and it can be seen from table 3 that the corresponding performance of the product is poorer than that of the product provided by examples 1-8.

[0109] The above is only a specific embodiment of the present application, which cannot limit the scope of the application. Therefore, the replacement of equivalent components or equivalent changes and modifications made within the scope of the patent protection of the present application should still belong to the scope covered by the present patent. In addition, the technical features in the present application can be freely combined with each other, between technical features, between technical features and technical inventions, and between technical inventions.

Claims

1. A polypropylene composition, characterized in that, The polypropylene composition comprises, by weight 100%, 8-32 wt% of propylene-α-olefin copolymer, 32-48 wt% of propylene-ethylene-α-olefin copolymer and 20-60 wt% of conductive filler. Based on the total weight of the propylene-α-olefin copolymer as 100%, the content of o-dichlorobenzene solubles is ≤6 wt%. Based on the total weight of the propylene-ethylene-α-olefin copolymer as 100%, the total content of ethylene and α-olefin is ≥20wt%.

2. The polypropylene composition according to claim 1, characterized in that, The conductive filler includes particles, clumps, or aggregates with a size greater than 0.1 μm.

3. The polypropylene composition according to claim 1 or 2, characterized in that, The conductive filler includes carbon black.

4. The polypropylene composition according to claim 3, characterized in that, The carbon black includes one or a combination of several of the following: acetylene black, thermal cracking carbon black, furnace black, and channel black.

5. The polypropylene composition according to claim 1, characterized in that, α-olefins include one or more of the C4-C8 olefins.

6. The polypropylene composition according to claim 1 or 5, characterized in that, The weight ratio of α-olefin content in the propylene-α-olefin copolymer to that in the propylene-ethylene-α-olefin copolymer is 0.8-1.

2.

7. The polypropylene composition according to claim 1 or 5, characterized in that, Based on the total weight of the propylene-α-olefin copolymer as 100%, the content of α-olefin is ≥4wt% and ≤5wt%.

8. The polypropylene composition according to claim 1 or 5, characterized in that, In propylene-ethylene-α-olefin copolymers, the weight content of ethylene / weight content of α-olefins = 1-2.

5.

9. The polypropylene composition according to claim 1, characterized in that, The molecular weight distribution of the polypropylene composition is Mw / Mn ≥ 5.

5.

10. The polypropylene composition according to claim 1, characterized in that, The polypropylene composition further comprises additives, which include one or a combination of antioxidants, voltage stabilizers, processing aids and nucleating agents.

11. The polypropylene composition according to claim 10, characterized in that, Based on the total weight of the polypropylene composition (100%), the content of antioxidant is 0.01-1 wt%, the content of voltage stabilizer is 0.01-5 wt%, and the content of nucleating agent is 0.01 to 5 wt%.

12. A method for preparing the polypropylene composition according to any one of claims 1-11, characterized in that, The preparation method includes: After the catalyst system is pre-contaminated, it is continuously fed into the first polymerization reactor to complete the first stage of polymerization. Then, propylene and α-olefin are added to the first polymerization reactor and hydrogen is introduced to carry out the second stage of polymerization to obtain propylene-α-olefin copolymer. The product obtained from the first polymerization reactor is fed into the second polymerization reactor, and propylene, ethylene and α-olefins are added to the second polymerization reactor to carry out the third polymerization reaction. The reactants obtained from the second polymerization reactor are deactivated and dried to obtain polymer powder. The polymer powder and conductive filler are mixed, melt-extruded and granulated to obtain the polypropylene composition.

13. The preparation method according to claim 12, characterized in that, The temperatures for the first, second, and third stages of polymerization are 40-100℃, and the residence time for each stage is 30 min-10 h.

14. A shielding material, characterized in that, The shielding material comprises the polypropylene composition according to any one of claims 1-11.

15. A cable comprising at least one cable core, the cable core comprising a conductor and an inner semiconductor shielding layer, an insulating layer, and an outer semiconductor shielding layer sequentially covering the conductor, characterized in that, The material of the inner semiconductor shielding layer and / or the outer semiconductor shielding layer is the shielding material as described in claim 14.

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