阅读说明：本技术 一种包含第一烯烃聚合物和第二烯烃聚合物的可交联的聚烯烃组合物 (Crosslinkable polyolefin composition comprising a first olefin polymer and a second olefin polymer ) 是由 O·普列托 D·亚拉洛夫 M·莫里 C·穆勒 A·彼得森 于 2019-05-23 设计创作，主要内容包括：本发明涉及一种可交联的聚烯烃组合物,其包括：包含含有环氧基团的第一共聚单体的第一烯烃聚合物(A),以及包含含有羧酸基团和/或其前驱体的第二共聚单体的第二烯烃聚合物(B)。(The present invention relates to a crosslinkable polyolefin composition comprising: a first olefin polymer (a) comprising a first comonomer comprising epoxy groups, and a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof.)

1. A crosslinkable polyolefin composition comprising:

a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups and/or precursors thereof.

2. The crosslinkable polyolefin composition according to claim 1, wherein the amount of the first olefin polymer (a) is from 20 to 95 wt. -%, based on the total amount of the polyolefin composition.

3. Crosslinkable polyolefin composition according to any one of the preceding claims wherein the amount of the second olefin polymer (B) is from 5 to 60 wt. -%, based on the total amount of the polyolefin composition.

4. The crosslinkable polyolefin composition according to any of the preceding claims, wherein the first comonomer comprising epoxy groups is an aliphatic glycidyl methacrylate comonomer.

5. Crosslinkable polyolefin composition according to any one of the preceding claims wherein the amount of the first comonomer is at least 0.1 wt. -%, more preferably at least 0.5 wt. -%, more preferably at least 1 wt. -%, based on the amount of the first olefin polymer (a).

6. Crosslinkable polyolefin composition according to any one of the preceding claims wherein the amount of the first comonomer is 20 wt% or less, preferably 15 wt%, more preferably 10 wt% or less, most preferably 5 wt% or less based on the amount of the first olefin polymer (a).

7. The crosslinkable polyolefin composition according to any of the preceding claims wherein the second comonomer comprising carboxylic acid groups is an acrylic comonomer.

8. The crosslinkable polyolefin composition according to any one of the preceding claims, wherein the amount of the second comonomer is from 0.1 to 20 wt. -%, based on the amount of the second olefin polymer (B).

9. Crosslinkable polyolefin composition according to any of the preceding claims wherein the crosslinkable polyolefin composition further comprises a third olefin polymer (C).

10. The crosslinkable polyolefin composition according to any of the preceding claims, wherein the polyolefin composition is crosslinked.

11. The crosslinkable polyolefin composition according to claim 10, wherein the crosslinked polyolefin composition has a hot set elongation of less than 175% as determined according to IEC 60811-2-1.

12. Crosslinkable polyolefin composition according to any of the preceding claims wherein the crosslinkable polyolefin composition is substantially free of curing agents.

13. A process for the manufacture of a crosslinkable polyolefin composition comprising the steps of:

(1) providing a first olefin polymer (a) comprising a first comonomer comprising epoxy groups;

(2) providing a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups;

(3) mixing said first olefin polymer (A) and said second olefin polymer (B), thereby obtaining said crosslinkable polyolefin composition.

14. The method of claim 13, wherein the mixing step (3) is an extrusion step.

15. The method according to claim 13 or 14, wherein the method further comprises the step of:

(4) crosslinking said crosslinkable polyolefin composition.

16. A cable comprising at least one layer comprising the crosslinkable polyolefin composition according to any one of claims 1-12.

17. Cable according to claim 16, comprising at least one layer comprising a crosslinkable polyolefin composition comprising:

20 to 95 wt%, based on the total amount of the polyolefin composition, of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

5 to 60 wt%, based on the total amount of the polyolefin composition, of a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof;

wherein the crosslinkable polyolefin composition is substantially free of curing agents.

18. A polyolefin composition comprising:

20 to 95 wt%, based on the total amount of the polyolefin composition, of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

5 to 60 wt%, based on the total amount of the polyolefin composition, of a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof;

wherein the crosslinked polyolefin composition is substantially free of curing agents;

the polyolefin composition has been crosslinked.

19. The crosslinked polyolefin composition according to claim 18, wherein the polyolefin composition has a gel content of at least 50%, more preferably at least 60%, most preferably at least 70%.

20. A method comprising providing a polyolefin composition comprising:

20 to 95 wt%, based on the total amount of the polyolefin composition, of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

5 to 60 wt%, based on the total amount of the polyolefin composition, of a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof;

wherein the crosslinked polyolefin composition is substantially free of curing agents; and

crosslinking the composition, for example by heating to a temperature of at least 150 ℃.

Technical Field

The present invention relates to a crosslinkable polyolefin composition comprising: a first olefin polymer (a) comprising a first comonomer comprising epoxy groups and a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups, to a cable comprising at least one layer comprising such a polyolefin composition, and to a process for the manufacture of such a polyolefin composition.

Background

Polyethylene produced in High Pressure (HP) processes is widely used in demanding polymer applications where the polymer must meet high mechanical and/or electrical requirements. For example, in W & C applications, such as power cable applications, like Low Voltage (LV), Medium Voltage (MV), High Voltage (HV) and Extra High Voltage (EHV) applications, the mechanical and electrical properties of polyethylene and polymer compositions comprising polyethylene are of great importance.

Moreover, the electrical properties of interest may differ in different cable applications, as is the case between AC and DC cable applications.

Furthermore, it is well known that crosslinking of polymers (such as polyethylene) greatly contributes to the improvement of the heat and deformation resistance, mechanical strength, chemical resistance and abrasion resistance of the polymer. Thus, crosslinked polymers are widely used in different end-use applications, such as the W & C applications mentioned above.

Furthermore, in cable applications, the electrical conductor is usually first coated with an inner semiconductive layer, followed by an insulation layer and an outer semiconductive layer. For these layers, one or more further layers may also be added, for example one or more screens and/or one or more auxiliary barrier layers, such as one or more waterproof layers and one or more sheath layers.

Due to the advantages mentioned herein that can be achieved by crosslinking, the insulating and semiconductive layers in cable applications are typically manufactured using crosslinkable polymer compositions. The polymer composition in the formed layered cable application is then crosslinked.

Moreover, such crosslinkable polymer compositions including Low Density Polyethylene (LDPE) are one of the main cable insulation materials used today for power cables.

Crosslinking may be performed using a crosslinking agent, in which the crosslinking agent decomposes to generate radicals. Such crosslinking agents (e.g. peroxides) are typically added to the polymer material before or during extrusion of the cable. The crosslinking agent should preferably remain stable during the extrusion step. The extrusion step should preferably be carried out at a temperature such that: low enough to minimize premature decomposition of the crosslinking agent, but high enough to achieve proper melting and homogenization of the polymer composition. If a large amount of crosslinking agent, such as peroxide, has decomposed in the extruder and thus initiates premature crosslinking, so-called "scorching", i.e.inhomogeneities, surface irregularities and possible discoloration, will result in the different layers of the resulting cable. Therefore, any substantial decomposition of the crosslinking agent (i.e. the free radical former) should be avoided during extrusion. Rather, the crosslinking agent should ideally decompose only at elevated temperatures in the subsequent crosslinking step. The increased temperature will increase the rate of decomposition of the crosslinking agent, thereby increasing the rate of crosslinking, and the desired degree of crosslinking, i.e., the target degree of crosslinking, can be achieved more quickly.

Furthermore, when the polymer composition, e.g. in a cable, is crosslinked, the decomposition of the crosslinking agent (e.g. peroxide) during crosslinking will also further lead to the formation of peroxide decomposition products. Part of the peroxide decomposition products are volatile, and if the type of peroxide typically used for crosslinking involving e.g. cables is used, the main component of the peroxide decomposition products is methane. After crosslinking, the peroxide decomposition products are mostly trapped within the polymer composition, e.g. cable. This may lead to some problems, for example, with respect to the cable manufacturing process and with respect to the quality of the final cable.

In particular, MV, HV and EHV power cables must have high quality layers to improve the safety of the cables during installation and in end use. For example, in installation, it is important to avoid combustion of trapped decomposition products (such as flammable methane) when, for example, the end cap is removed. In operation, volatile peroxide decomposition products formed in the cable during the crosslinking step can cause gas pressure, leading to defects in the shielding and in the joint. For example, when the cable core is equipped with metal barriers, then the gas products can exert pressure, particularly on the splice and the end, whereby system failures may occur. Thus, the level of these volatile peroxide decomposition products needs to be reduced to a sufficiently low level before the subsequent cable production steps can be carried out.

The sufficiently low level of volatile peroxide decomposition products makes the use of the LDPE-containing polymer composition safe for use in installations, such as cable installations, and with fittings, such as cable fittings. Therefore, today a so-called degassing step is required in the cable production process to reduce the level of volatile peroxide decomposition products. The degassing step is time and labor consuming and therefore an expensive operation in the cable manufacturing process. Degassing requires a large heating chamber which must be well ventilated to avoid accumulation of e.g. flammable methane. The cable core (i.e., layers and conductors) is typically wound onto a cable drum and is typically maintained at an elevated temperature in the range of 50 c-80 c (e.g., 60 c-70 c) for an extended period of time during the degassing step. When exposed to the required temperatures, the insulation can thermally expand and soften and lead to unwanted deformation of the formed cable layer, directly leading to failure of the cable. Therefore, the degassing of HV and EHV cables with high cable weight usually needs to be performed at reduced temperatures, which further prolongs the degassing time.

Furthermore, the crosslinking of the polymer composition comprised in, for example, a cable contributes greatly to the improvement of the heat and deformation resistance, the mechanical strength, the chemical resistance and the abrasion resistance of the polymer composition and of the cable comprising the polymer composition.

See US5539075 in this connection, which relates to a process for producing unsaturated copolymers of ethylene and at least one monomer, wherein the monomer is a polyunsaturated compound and is copolymerizable with ethylene.

See also EP2318210, which relates to a polymer composition comprising an unsaturated LDPE copolymer of ethylene with one or more polyunsaturated comonomers and suitable for use in crosslinked polymer applications. The polymer composition has a melt flow rate MFR of at least 2.8g/10min under a load of 2.16kg₂And contains carbon-carbon double bonds in an amount of at least 0.40 carbon-carbon double bonds/1000 carbon atoms.

WO2017/000121 describes the crosslinking of epoxy-functional copolymers and carboxylic acid-functional based copolymers in the presence of peroxide initiators.

To avoid volatile byproducts and thus eliminate the need for a degassing step, click chemistry type curing of polyethylene can be used, for example, crosslinking of epoxy-functionalized resins using a variety of difunctional curing agents such as aromatic and aliphatic diamines, dicarboxylic acids, and diphenols.

WO2013/091575 describes the crosslinking of epoxy-functional copolymers and carboxylic acid-functional copolymers based in the presence of curing agents.

However, the above-mentioned curing agents also present their own drawbacks, in particular in terms of toxicity, manner of handling, storage, moisture resistance and cost. In addition, it has been found that crosslinking using the above curing agents results in discoloration of the final product, taking on a yellow to orange color, rather than a colorless color. Furthermore, any unreacted curing agent or lewis acid remaining after the crosslinking step will negatively affect the electrical properties.

Therefore, there is a need to find new solutions to overcome the problems of the current state of the art.

In view of the above, it is an object of the present invention to provide a crosslinkable polyolefin composition which can be crosslinked without a curing agent which may generate a by-product.

Furthermore, it is an object of the present invention to provide a polyolefin composition, in particular an insulation layer for power cables, which is crosslinked at mild temperatures and in a short time at high cable line speeds.

Disclosure of Invention

Accordingly, the present invention provides a crosslinkable polyolefin composition comprising: a first olefin polymer (a) comprising a first comonomer comprising epoxy groups, and a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof. In one embodiment, the polyolefin composition consists of the first olefin polymer (a) and a second olefin polymer (B).

In one embodiment, the present invention provides a cable comprising at least one layer comprising a crosslinkable polyolefin composition comprising:

20 to 95 wt%, based on the total amount of the polyolefin composition, of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

5 to 60 wt%, based on the total amount of the polyolefin composition, of a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof;

wherein the crosslinkable polyolefin composition is substantially free of curing agents.

In one embodiment, the instant invention provides a polyolefin composition comprising:

20 to 95 wt%, based on the total amount of the polyolefin composition, of a first olefin polymer (A) comprising a first comonomer comprising epoxy groups, and

5 to 60 wt%, based on the total amount of the polyolefin composition, of a second olefin polymer (B) comprising a second comonomer comprising a carboxylic acid group and/or a precursor thereof;

wherein the crosslinked polyolefin composition is substantially free of curing agents;

the polyolefin composition has been crosslinked.

The term "precursor" refers to a chemical moiety or functional group that can be converted to another moiety or functional group, in this case a carboxylic acid. Precursors of carboxylic acids are described in more detail below.

According to the present invention, the second olefin polymer (B) is used as a curing agent for crosslinking with the first olefin polymer (A). It has been demonstrated that the second olefin polymer (B) bearing carboxylic acid groups and/or precursors thereof can be effectively used to cure the first olefin polymer (a) bearing epoxide groups, rapidly forming networks at reasonably low temperatures, producing covalent crosslinks between the epoxide functional groups, and without the formation of volatile by-products. The concept of using two olefin-based copolymers with compatible organofunctional groups that can react with each other upon heating without releasing any undesired or volatile by-products could be a breakthrough development in the power cable insulation industry: the absence of undesirable organic molecules throughout the mixing, extrusion and crosslinking processes makes such chemical processes safe in an industrial environment and also economically and technically attractive for the curing of insulation materials during cable extrusion.

As mentioned above, it is an object of the present invention to provide a crosslinkable polyolefin composition which can be crosslinked without the need for (external) curing agents which may generate by-products. Thus, in one embodiment, the polyolefin composition is substantially free of curing agents. The term "substantially free" as used herein means that the total amount of curing agent in the polyolefin composition is less than 0.01 wt%, based on the total amount of the polyolefin composition. Desirably, the polyolefin composition is free of curing agents. In the absence of an external curing agent, the curing which occurs in the present invention is solely through the reaction of the second olefin polymer (B) with the first olefin polymer (A).

The term "curing agent" as used herein shall be taken to mean any species that promotes or participates in the curing reaction between the first and second olefin polymers (except for the second olefin polymer (B) or the first olefin polymer (a) itself). Curing agents include, but are not limited to, nucleophilic catalysts, tertiary amines, amine complexes, urea derivatives, imidazoles, substituted imidazoles, lewis bases having catalytic curing capabilities, and mixtures thereof. The curing agent may be a crosslinking catalyst, such as a catalyst compound containing amine, phosphine, heterocyclic nitrogen, ammonium, phosphorus, arsenic, sulfur moieties, or any combination thereof. For example, the curing agent may be ethyl triphenyl phosphine; benzyl trimethyl ammonium chloride; nitrogen-containing heterocyclic catalysts as described in U.S. Pat. No. 4,925,901; imidazole; triethylamine; or any combination thereof. For example, the curing agent may be selected from the group consisting of tertiary amines, 1-substituted imidazoles, organic phosphines, and acid salts. The curing agent may be a tertiary amine such as triethylamine, tripropylamine, tributylamine, 1-methylimidazole, benzyldimethylamine and mixtures thereof.

In one embodiment, the curing agent includes difunctional curing agents such as aromatic and aliphatic diamines, dicarboxylic acids, and diphenols. The curing agent may be 1-methylimidazole. An example of a commercially available curing agent is available from BASF765 which is a mixture of bis (l,2,2,6, 6-pentamethyl-4-piperidinyl) sebacate (70-90 wt%) and methyl 1,2,2,6, 6-pentamethyl-4-piperidinyl sebacate (15-30 wt%) (CAS No.: 41556-26-7; 8291-37-7).

The term "curing agent" as used herein also includes cross-linking agents, for example free radical initiators such as azides or peroxides. Thus, in one embodiment, the polyolefin composition is substantially free of free radical initiators, such as azides or peroxides.

For the first olefin polymer (a) containing epoxy groups, this expression refers to an olefin polymer into which epoxy group-containing units are introduced. This unit is referred to herein as an "epoxy-containing monomeric unit" and is represented by an epoxy-containing unsaturated compound, preferably a vinyl-containing compound with epoxy groups. As is well known in the polymer art, such compounds may be used as comonomers for copolymerizing epoxy-containing monomer units to the first olefin polymer (a), or may be grafted to the first olefin polymer (a). The grafting and copolymerization of monomeric units comprising epoxy groups can be carried out according to methods described in the literature or similar. Olefin polymers (a) containing epoxide groups and monomeric units containing epoxide groups are well known (e.g. as mentioned in JP06-116362 of Nippon Petrochem co. ltd and WO2010040964 of Arkema France) and are commercially available. As preferred examples of monomeric units containing an epoxy group, mention may be made, for example, of aliphatic esters and glycidyl ethers such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate or itaconate, glycidyl (meth) acrylate, and cycloaliphatic esters and glycidyl ethers such as 2-cyclohexene-1-glycidyl ether, cyclohexene-4, 5-diglycidylcarboxylate, cyclohexene-4-glycidylcarboxylate, 5-norbornene-2-methyl-2-glycidylcarboxylate and endo-cis-bicyclo (2,2,1) -5-heptene-2, 3-diglycidyldicarboxylate.

In the present invention, it is preferred to introduce an epoxy-containing monomer unit as a comonomer, i.e., by copolymerization of an olefin monomer with a vinyl-containing comonomer bearing an epoxy group (═ epoxy group-containing monomer unit).

Most preferably, the monomeric unit comprising an epoxy group is a glycidyl methacrylate comonomer unit.

Preferably, the amount of monomeric units comprising an epoxy group is at least 0.1 wt%, more preferably at least 0.5 wt%, more preferably at least 1 wt%, based on the amount of the first olefin polymer (a).

The content of the epoxy group-containing monomer unit is preferably 20% by weight or less, preferably 15% by weight, more preferably 10% by weight or less, and most preferably 5% by weight or less, based on the amount of the first olefin polymer (A).

Suitable first olefin polymers (a) may be homopolymers or copolymers of olefins in which monomeric units comprising epoxy groups are grafted as defined above, or copolymers of olefins with at least monomeric units comprising epoxy groups as defined above. Preferred first olefin polymers (a) are copolymers of an olefin with at least epoxy group-containing monomeric units as defined above, more preferably copolymers of an olefin with at least glycidyl methacrylate comonomer units.

The first olefin polymer (a) may further comprise one or more comonomers different from the monomeric unit comprising an epoxy group, and if present, preferably one or more other polar comonomers different from the monomeric unit comprising an epoxy group. In case the first olefin polymer (a) contains further polar comonomer(s), then the further polar comonomer(s) is/are present in an amount of preferably at least 5.0 wt. -%, more preferably at least 8 wt. -%, more preferably at least 12 wt. -%, based on the amount of the first olefin polymer (a). In case the first olefin polymer (a) comprises a polar comonomer, then, preferably, the polar group-containing monomer units are present in an amount of not more than 50 wt. -%, more preferably not more than 45 wt. -%, even more preferably not more than 40 wt. -%, even more preferably not more than 35 wt. -%, even more preferably not more than 25 wt. -% and most preferably not more than 20 wt. -%, based on the amount of the first olefin polymer (a).

Preferably, the polar group-containing monomer units are selected from acrylate or acetate comonomer units, preferably from alkyl (meth) acrylate or vinyl acetate comonomer units, preferably alkyl (meth) acrylate comonomer units.

In the present invention, the term "alkyl (meth) acrylate comonomer units" includes alkyl acrylate comonomer units and/or alkyl methacrylate comonomer units.

The alkyl portion of the alkyl (meth) acrylate comonomer units may be selected from C1 to C8-hydrocarbyl groups, which may be branched or straight chain. In particular, the alkyl moiety is a C3 or C4 hydrocarbyl group, wherein the C3 or C4 hydrocarbyl group may be linear or branched.

According to the present invention, the first olefin polymer (a) may be a polyethylene containing epoxy group-containing monomer units, more preferably a copolymer of ethylene and at least epoxy group-containing monomer units as defined above, more preferably a copolymer of ethylene and at least glycidyl methacrylate comonomer units.

The copolymer of ethylene with monomer units comprising at least an epoxy group as the first olefin polymer (a) is also referred to herein simply as an ethylene/epoxy copolymer.

As noted above, the ethylene/epoxy copolymer may further comprise other comonomer units.

Thus, the first olefin polymer (a) may be a copolymer of ethylene with at least a comonomer comprising epoxy groups and one or more further comonomers different from the monomer units comprising epoxy groups, the further comonomers preferably being polar comonomers different from the monomer units comprising epoxy groups, more preferably comonomer units comprising acrylate or acetate groups.

In the case of the present invention, the first polymer (a) comprising a comonomer with epoxy groups may be a blend of at least two polymers, each polymer comprising a comonomer unit with epoxy functional groups. The epoxy functional groups in each polymer that is part of the first polymer (a) may be the same or different.

In particular, the first olefin polymer (a) may be selected from ethylene copolymers with glycidyl methacrylate comonomer units, or ethylene copolymers with glycidyl methacrylate comonomer units and a polar comonomer selected from alkyl (meth) acrylate or vinyl acetate comonomer units. The polar comonomer units may be selected from methyl acrylate, ethyl acrylate, butyl acrylate.

The first olefin polymer (A) may have a melt flow rate MFR of at least 0.1g/10min, more preferably at least 0.5g/10min, determined according to ISO 1133 under a load of 2.16kg and a temperature of 190 ℃₂. Further, the first olefin polymer (A) may have a melt flow rate MFR of 75g/10min or less, more preferably 60g/10min or less, even more preferably 55g/10min or less, determined according to ISO 1133 under a load of 2.16kg and a temperature of 190 ℃₂。

The first olefin polymer (A) may have a molecular weight of from 860kg/m³To 960kg/m³Preferably not higher than 955kg/m³The density of (c).

In case the epoxy group containing monomer units are grafted to a homopolymer or copolymer of ethylene after production of the ethylene polymer as olefin polymer (a), and in case the epoxy group containing monomer units are copolymerized with ethylene and optionally further comonomer(s), the first olefin polymer (a) may be a low density ethylene polymer (LDPE) produced in a High Pressure (HP) process in a tubular reactor or an autoclave reactor or any combination thereof. Thus, in the case of the introduction of monomeric units comprising epoxy groups by grafting, the polymer before grafting can likewise be produced by this process. High Pressure (HP) polymerization has been widely described in the literature and process conditions can be adjusted within the knowledge of one of ordinary skill in the art to further tailor other properties of the polyolefin depending on the desired end use application.

In a tubular reactor, the polymerization is carried out at a temperature generally up to 400 ℃, preferably from 80 ℃ to 350 ℃ and at a pressure of from 70MPa, preferably from 100MPa to 400MPa, more preferably from 100MPa to 350 MPa. The pressure may be measured after at least the compression stage and/or after the tubular reactor. The temperature can be measured at several points along the reactor. More details of the production of ethylene (co) polymers by High-pressure free-radical polymerization are available in Encyclopedia of Polymer Science and Engineering, Vol.6(1986), pp 383- & 410 and Encyclopedia of Materials: Science and Technology,2001Elsevier Science Ltd. "Polyethylene: High-pressure, R.Klimch, D.Littmann and F. -O.pp.7181-7184.

The autoclave process may be carried out, for example, in a stirred autoclave reactor. The stirred autoclave reactor is generally divided into separate zones. The main flow pattern is from one or more top zones to one or more bottom zones, but back-mixing is permissible and sometimes desirable. The agitator is preferably designed to produce efficient mixing and flow patterns at suitable rotational speeds selected by one of ordinary skill in the art. The compressed mixture is typically cooled and fed to one or more reactor zones. The free radical initiator may also be injected at one or more zones along the reactor. Any compound or mixture thereof that decomposes to free radicals at elevated temperatures may be used as the free radical initiator. Useful free radical initiators are commercially available. The polymerization pressure is usually from 20MPa to 300MPa, for example from 20MPa to 250 MPa. The polymerization reaction is exothermic and the exothermic heat generated after start-up (the first free radical is generated at elevated temperatures, e.g., from 80 ℃ to 150 ℃) maintains the reaction. The temperature in each zone is controlled by the cooled feed mixture. Suitable temperatures range from 80 ℃ to 300 ℃. This process is well known to the person skilled in the art and is described, for example, on page 11, lines 23 to 32 and on page 12, lines 1 to 8 in WO2010040964 to Arkema France or can be produced analogously to the description, for example, in FR2498609, FR2569411 and FR 2569412. This autoclave polymerization is preferred when ethylene is copolymerized with an epoxy group containing monomer as defined above, preferably with a glycidyl methacrylate comonomer, and optionally preferably with one or more other comonomers, preferably with a polar comonomer as defined above, more preferably an alkyl (meth) acrylate comonomer, more preferably a methyl acrylate comonomer.

According to the present invention, the amount of the first olefin polymer (a) may be at least 20 wt%, preferably at least 30 wt%, more preferably at least 40 wt%, based on the amount of the polyolefin composition. According to the present invention, the amount of the first olefin polymer (a) may be less than 95 wt%, preferably less than 75 wt%, most preferably less than 60 wt%, based on the amount of the polyolefin composition.

The second olefin polymer (B) according to the invention is an olefin polymer comprising a second comonomer comprising carboxylic acid groups and/or precursors thereof.

In the context of the present invention, the carboxylic acid group and the group which is a precursor of the carboxylic acid will be referred to hereinafter as "group bearing a carboxyl function".

According to the invention, the second olefin polymer (B) may thus be a copolymer comprising a second comonomer comprising carboxylic acid groups.

Alternatively, the second olefin polymer (B) may be an olefin polymer comprising comonomer units containing functional groups as precursors of carboxylic acid groups, such as a tert-butyl acrylate copolymer. This second polymer (B) can be extruded at elevated temperature (for example 190 ℃) without any pre-crosslinking and then undergoes a transition to carboxylic acid functions in the vulcanization tube, immediately crosslinking with epoxide groups. Among other possible carboxylic acid precursors, mention may be made of anhydrides, such as maleic anhydride.

Finally, the second olefin polymer (B) may be a terpolymer comprising comonomer units containing carboxylic acid groups and comonomer units containing functional groups as precursors of the carboxylic acid groups. The precursor of this carboxylic acid may be, for example, an ester group. In this case, the crosslinking temperature should be high enough to promote hydrolysis of the ester and to convert all ester groups to carboxylic acid functions. An example of such a terpolymer which can be used as second polymer (B) in the context of the present invention is, for example, a terpolymer comprising tert-butyl acrylate and acrylic acid comonomer units.

The second olefin polymer (B) may comprise other comonomer(s) than the monomer units comprising the carboxylic acid groups and/or carboxylic acid precursors. If present, other polar comonomer or comonomers are preferred. In case the second olefin polymer (B) comprises further polar comonomer(s), then the further polar comonomer(s) is/are preferably present in an amount of at least 5.0 wt. -%, more preferably at least 8 wt. -%, more preferably at least 12 wt. -%, based on the amount of the second olefin polymer (B). In case the second olefin polymer (B) comprises a polar comonomer, then, preferably, the polar group-containing monomer units are present in an amount of not more than 50 wt. -%, more preferably not more than 45 wt. -%, even more preferably not more than 40 wt. -%, even more preferably not more than 35 wt. -%, even more preferably not more than 25 wt. -% and most preferably not more than 20 wt. -%, based on the amount of the second olefin polymer (B).

Preferably, the polar group-containing monomer units are selected from acrylate or acetate comonomer units, preferably from alkyl (meth) acrylate or vinyl acetate comonomer units, preferably alkyl (meth) acrylate comonomer units.

In the present invention, the term "alkyl (meth) acrylate comonomer units" includes alkyl acrylate comonomer units and/or alkyl methacrylate comonomer units.

The alkyl portion of the alkyl (meth) acrylate comonomer units may be selected from C1 to C8-hydrocarbyl groups, which may be branched or straight chain. In particular, the alkyl moiety is a C3 or C4 hydrocarbyl group, wherein the C3 or C4 hydrocarbyl group may be linear or branched.

In the context of the present invention, the second polymer (B) comprising a comonomer bearing a carboxylic acid group or a functional group as a precursor of a carboxylic acid group may be a blend of at least two polymers, each polymer comprising a comonomer unit bearing a carboxylic acid group or a functional group as a precursor of a carboxylic acid group. The carboxylic acid groups in each polymer as part of the second polymer (B) or the functional groups as precursors of the carboxylic acid groups may be the same or different.

Like above, the comonomer units of the second olefin polymer (B) may be copolymerized or grafted into the olefin polymer.

In the present invention, the carboxyl functional monomer units are preferably incorporated as comonomers, i.e. by copolymerization of olefin monomers with vinyl containing carboxyl functional comonomers.

Most preferably, the second comonomer used in the second olefin polymer (B) comprises carboxylic acid groups, especially acrylic acid groups.

The amount of carboxyl functional monomer units may be at least 0.1 wt%, more preferably at least 0.5 wt%, more preferably at least 1 wt%, based on the amount of the second olefin polymer (B).

The content of monomer units bearing a carboxyl function may be less than 20% by weight, preferably less than 15% by weight, more preferably less than 10% by weight, based on the amount of the second olefin polymer (B).

According to the invention, the second olefin polymer (B) may be a polyethylene comprising monomer units bearing a carboxyl function, more preferably a copolymer of ethylene and acrylic acid.

The second olefin polymer (B) may have a melt flow rate MFR of at least 0.1g/10min, more preferably at least 0.5g/10min, determined according to ISO 1133 at a load of 2.16kg and a temperature of 190 ℃₂. Further, the second olefin polymer (B) may have a melt flow rate MFR of 75g/10min or less, more preferably 60g/10min or less, even more preferably 55g/10min or less, determined according to ISO 1133 at a load of 2.16kg and a temperature of 190 ℃₂。

The second olefin polymer (B) may have a molecular weight of from 860kg/m³To 960kg/m³Preferably not higher than 955kg/m³The density of (c).

In the case of grafting the monomer units bearing a carboxyl function to a homopolymer or copolymer of ethylene after the production of the ethylene polymer as olefin polymer (B), and in the case of copolymerizing the monomer units bearing a carboxyl function with ethylene, the second olefin polymer (B) may be a low density ethylene polymer (LDPE) produced in a tubular reactor or autoclave reactor or any combination thereof under a High Pressure (HP) process. High Pressure (HP) polymerization has been widely described in the literature and process conditions can be adjusted within the knowledge of one of ordinary skill in the art to further tailor other properties of the polyolefin depending on the desired end use application.

In a tubular reactor, the polymerization is carried out at a temperature generally up to 400 ℃, preferably from 80 ℃ to 350 ℃ and at a pressure of from 70MPa, preferably from 100MPa to 400MPa, more preferably from 100MPa to 350 MPa. The pressure may be measured after at least the compression stage and/or after the tubular reactor. The temperature can be measured at several points along the reactor. More details of the production of ethylene (co) polymers by High-pressure free-radical polymerization are available in Encyclopedia of Polymer Science and Engineering, Vol.6(1986), pp 383- & 410 and Encyclopedia of Materials: Science and Technology,2001Elsevier Science Ltd. "Polyethylene: High-pressure, R.Klimch, D.Littmann and F. -O.pp.7181- "7184.

The autoclave process may be carried out, for example, in a stirred autoclave reactor. The stirred autoclave reactor is generally divided into separate zones. The main flow pattern is from one or more top zones to one or more bottom zones, but back-mixing is permissible and sometimes desirable. The agitator is preferably designed to produce efficient mixing and flow patterns at suitable rotational speeds selected by one of ordinary skill in the art. The compressed mixture is typically cooled and fed to one or more reactor zones. The free radical initiator may also be injected at one or more zones along the reactor. Any compound or mixture thereof that decomposes to free radicals at elevated temperatures may be used as the free radical initiator. Useful free radical initiators are commercially available. The polymerization pressure is usually from 20MPa to 300MPa, for example from 20MPa to 250 MPa. The polymerization reaction is exothermic and the exothermic heat generated after start-up (the first free radical is generated at elevated temperatures, e.g., from 80 ℃ to 150 ℃) maintains the reaction. The temperature in each zone is controlled by the cooled feed mixture. Suitable temperatures range from 80 ℃ to 300 ℃. This process is well known to the person skilled in the art and is described, for example, on page 11, lines 23 to 32 and on page 12, lines 1 to 8 in WO2010040964 to Arkema France or can be produced analogously to the description, for example, in FR2498609, FR2569411 and FR 2569412.

According to the present invention, the amount of the second olefin polymer (B) may be at least 5 wt%, preferably at least 10 wt%, more preferably at least 15 wt%, even more preferably at least 20 wt%, based on the total amount of the olefin polymer composition. According to the present invention, the amount of the second olefin polymer (B) may be less than 60 wt%, preferably less than 50 wt%, most preferably less than 40 wt%, based on the total amount of the olefin polymer composition.

The crosslinkable polyolefin composition according to the present invention may further comprise a third olefin polymer (C). The third olefin polymer (C) may be LDPE, HDPE or may be a polyethylene copolymer. The third olefin polymer (C) may participate in the crosslinking reaction or may be inert.

Furthermore, the crosslinkable polyolefin composition according to the present invention may be crosslinked, in particular when used as a layer in a cable.

After crosslinking, the composition can have a hot set elongation of 175% or less, more preferably 100% or less, and most preferably 90% or less, when tested as described below under "test methods" herein.

After crosslinking, the polyolefin composition of the invention may have a gel content of at least 50%, more preferably at least 60%, most preferably at least 70%, when tested according to the "gel content" described below under "test method".

The present invention further relates to a process for the manufacture of a crosslinkable olefin polymer composition comprising the steps of:

(1) providing a first olefin polymer (a) comprising a first comonomer comprising epoxy groups;

(2) providing a second olefin polymer (B) comprising a second comonomer comprising carboxylic acid groups;

(3) mixing said first olefin polymer (A) and said second olefin polymer (B), thereby obtaining said crosslinkable olefin polymer composition.

The mixing step (3) may be an extrusion step. Alternatively, the method according to the present invention may comprise the step of (3a) micronizing said crosslinkable olefin polymer composition. If this step is present, extrusion will be carried out in the subsequent step (3 b). The method of the present invention may further comprise the step of (4) crosslinking the crosslinkable olefin polymer composition.

The crosslinking step may be carried out at a temperature of at least 150 ℃, more preferably at a temperature of at least 180 ℃.

The crosslinking step may be carried out at a temperature below 360 deg.c, more preferably below 320 deg.c.

The crosslinking process may be carried out at atmospheric pressure. Furthermore, the crosslinking process may be carried out at elevated pressure, for example at a pressure of at least 5 bar. Typically, the pressure is not higher than 25 bar.

The crosslinkable polyolefin composition according to the present invention is very suitable for W & C applications, for example in cables which are crosslinkable and comprise one or more layers, wherein at least one layer is obtained from the crosslinkable polyolefin composition as described herein. The cable may be a power cable, such as an AC power cable or a DC power cable. The cable layer obtained from the crosslinkable polyolefin composition may be an insulation layer.

Furthermore, the cable of the invention may for example be a power cable comprising at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer in the given order, wherein at least the insulation layer is obtained from a crosslinkable polyolefin composition as described herein.

By "power cable" is meant herein a cable that operates to transmit energy at any voltage. The voltage applied to the power cable may be AC, DC or transient (pulsed). The multilayer article may be a power cable operating at a voltage higher than 6 kV.

The invention further relates to a method for producing an article, such as a cable, wherein the method may for example comprise at least the following steps:

a₀) Melt-mixing a crosslinkable polyolefin composition as described herein, optionally together with one or more further components, and

a) forming a cable obtained from the polymer composition as described herein.

"melt mixing" is a well-known blending process in which one or more polymeric components are mixed at an elevated temperature, typically above the melting or softening point of the one or more polymeric components, e.g., at least 20 ℃ to 25 ℃ above.

The step a) may be the following steps: applying a crosslinkable polyolefin composition as described herein on a conductor to form at least one of the layers surrounding the conductor.

The crosslinkable polyolefin composition as described herein may be introduced into step a of the process, e.g. in the form of pellets₀) And mixing, i.e., melt mixing, is carried out at an elevated temperature that melts (or softens) the polymeric material to enable it to be processed.

Furthermore, step a) may be (co) extrusion. The term "(co) extruded" means herein that in the case of two or more layers, the layers may be extruded in separate steps, as is well known in the art, or at least two or all of the layers may be co-extruded in the same extrusion step.

Step a₀) The melt mixing of the crosslinkable polyolefin composition of (a) may be carried out in a mixer or an extruder or any combination thereof at an elevated temperature below the crosslinking temperature. a is₀) After melt mixing (e.g. in the extruder), the resulting melt mixed layer material, e.g. a), is then (co) extruded on a conductor in a manner well known in the art. Mixers and extruders, such as single-screw extruders or twin-screw extruders, which are commonly used in cable manufacture, are suitable for use in the process of the present invention.

The method for producing the article (e.g. power cable) may further comprise step b): crosslinking at least one cable layer comprising the crosslinkable polyolefin composition obtained from step a).

It is understood and well known that other cable layers and their materials, if present, may also be cross-linked simultaneously if desired.

In one embodiment, the method does not involve the use of any curing agent, such as a peroxide. Unlike peroxide crosslinking, no or only small amounts of volatile by-products are formed during crosslinking. Thus, safety is improved, and a production cycle time is reduced since an additional process step, such as a degassing step, can be shortened or avoided.

Finally, the problems of storage stability and discoloration are avoided.

The invention also relates to a cable comprising a conductor surrounded by one or more layers, wherein at least one layer comprises or consists of a polyolefin composition according to any of the above embodiments. Preferably, at least one layer of said cable comprising or consisting of the composition of the invention is selected from the group consisting of an insulating layer, a semiconductive layer or a jacketing layer, preferably from the group consisting of an insulating layer or a semiconductive layer.

The term "surrounding" includes layers that are directly connected to the conductor, as well as one or more additional layers that are present between the layers and the conductor.

The term "conductor" as used herein refers to a wire of conductive material, such as metal for conducting electricity, and such as fiberglass for conducting information, i.e., one or more wires may be used for any purpose, and may be, for example, an optical wire, a communications wire, or an electrical wire. The conductor may comprise one or more wires. Further, the cable may include one or more such conductors.

In a preferred embodiment, the cable is an electrical power cable, i.e. the conductor is an electrical conductor and comprises one or more metal wires.

If the semiconductive layer comprises the polyolefin composition of the invention, the composition further comprises a conductive filler, preferably carbon black.

The amount of conductive filler is at least that amount which results in a semiconductive polyolefin composition. The amount of conductive filler can vary depending on the type of carbon black used, the conductivity of the composition, and the desired end use.

Preferably, the conductive filler (preferably carbon black) is present in an amount of at least 10 wt%, preferably at least 15 wt%, even preferably at least 20 wt%, further preferably at least 30 wt%, most preferably at least 35 wt%, based on the total amount of the semiconductive polyolefin composition.

The conductive filler (preferably carbon black) is preferably present in an amount of 50 wt% or less, more preferably 45 wt% or less, most preferably 40 wt% or less, based on the total amount of the semiconductive polyolefin composition.

The polyolefin composition may further comprise one or more other additives. As suitable further additives, mention may be made of colorants, antioxidants, scorch retardants, crosslinking inhibitors, stabilizers, processing aids, lubricants, compatibilizers, mold release agents, antiblocking agents, flame retardants, acid scavengers, inorganic fillers, voltage stabilizers, additives for improving water tree resistance or mixtures thereof. It is noted that any additives should preferably not function as curing agents.

Detailed Description

1. Material

The materials used in the composition of the present invention are described below. In particular, polymers (P1-P10) are classified as polymer (a) (i.e. a polymer bearing epoxy groups), polymer (B) (i.e. a polymer bearing carboxylic acid functional groups or precursors thereof) or polymer (C).

1.1 P1(A)

P1 is a polymer of ethylene-glycidyl methacrylate having a glycidyl methacrylate content of 8% by weight and an MFR₂(2.16kg/190 ℃) at 5g/10min and a density of 940kg/m³Melting point 106 ℃ and is commercially available from Arkema.

1.2 P2(B)

P2 is an ethylene-methacrylic acid copolymer resin having 7 wt% of a methacrylic acid comonomer and a density of 0.93g/cm³，MFR₂(190 ℃/2.16kg) 8g/10min, commercially available from Dow.

1.3 P3(C)

P3 is an LDPE homopolymer, MFR₂(190 ℃/2.16kg) is 1.9g/10min, and the density is 0.923g/cm³。

1.4 P4(A)

P4 is a copolymer of ethylene and glycidyl methacrylate produced from a tubular reactor with 2 wt% GMA, MFR₂(190 ℃/2.16kg) was 1.9g/10 min.

1.5 P5(B)

P5 is a terpolymer of ethylene, t-butyl methacrylate and acrylic acid produced from a tubular reactor having 5.8 wt% TBMA and 5.8 wt% EAA, MFR₂(190 ℃/2.16kg) was 1.5g/10 min.

1.6 P6(A)

P6 is an ethylene/glycidyl methacrylate/butyl acrylate terpolymer produced from a tubular reactor having 1.8 wt% GMA, 18 wt% BA, MFR₂(190 ℃/2.16kg) was 6.6g/10 min.

1.7 P8(A)

P8 is a polymer of ethylene-glycidyl methacrylate, which polymerHas a glycidyl methacrylate content of 4.5 wt.%, MFR₂(2.16kg/190 ℃) 2g/10min, and a density 930kg/m³Commercially available from Arkema.

1.8 P9(C)

P9 is HDPE with density 962kg/m³，MFR₂(2.16kg/190 ℃) was 12g/10 min.

1.9 P10(B)

P10 is an ethylene-methacrylic acid copolymer resin having a methacrylic acid comonomer of 3.1 wt%, MFR₂(190 ℃/2.16kg) is 10.6g/10min, commercially available from Dow.

1.10 Ad1

Ad1 is 1, 8-octanediamine, CAS number 373-44-4, commercially available from Sigma Aldrich.

1.11 Ad2

Ad2 is trimethylolpropane tris [ poly (propylene glycol) amino-terminated ] ether, CAS number 39423-51-3, commercially available from Sigma Aldrich.

1.12 Ad3

Ad3 is 2, 2-bis (4-hydroxy-3-methylphenyl) propane, CAS number 79-97-0, commercially available from Sigma Aldrich.

1.13 Ti1

Ti1 is tetraisooctyl titanate, CAS number 1070-10-6, with an Mw of 564g/mol, commercially available from Dorf Ketal.

2. Test method

Unless stated otherwise in the specification or claims, the following methods were used to test the properties defined throughout the specification and claims. Unless otherwise stated, samples were prepared according to the given standards.

2.1 melt flow Rate

The Melt Flow Rate (MFR) of the ethylene copolymers was tested according to ISO 1133 at 190 ℃ under a load of 2.16kg₂)。

2.2 Density

The density was tested according to ISO 1183-2. Sample preparation (compression moulding) was carried out according to ISO 1872-2, Table 3Q.

2.3 comonomer content

The determination of the comonomer content was carried out using the procedure described on page 19, line 40 to page 20, line 29 of EP 2444980A 1.

2.4 elongation at Heat set and permanent set

The dumbbells prepared according to ISO-527-2-5A were subjected to hot set elongation and permanent set testing. Dumbbells were taken from crosslinked compressed plates prepared as described below.

The hot set elongation was tested on the dumbbell specimens prepared as described above according to IEC 60811-2-1. The properties of the sample have been specified in the context. In the hot set test, the dumbbell configuration of the material to be tested corresponds to 20N/cm²The weight of (2). The sample was placed in an oven at 200 ℃ and tested for elongation after 5 minutes. The test specimen with the weight was then left in the oven for an additional 10min while monitoring the elongation. Subsequently, the weight was removed and the sample was left in the oven for an additional 5min to recover before being removed. The sample was then removed from the oven and cooled to room temperature. The permanent set is measured.

2.5 gel content

The gel content of the crosslinked samples was measured gravimetrically using solvent extraction techniques. The sample (. about.150 mg) was placed in a pre-weighed 100 mesh stainless steel basket at 1.1dm³The refluxed decalin was extracted for 6 h. To this solvent was added 10g of Irganox 1076 from Ciba-Geigy as an antioxidant to prevent degradation. Then, the solvent was mixed with 0.9dm³The additive-free, preheated decalin was exchanged and extraction continued under reflux for 1 h. Finally, the samples were first dried overnight at ambient conditions and then dried overnight under vacuum at 50 ℃. After this period, the insoluble fraction remaining in the basket reached a constant weight, which was used to calculate the gel content.

2.6 mixing and crosslinking

The copolymer/crosslinker formulation was mixed by melt mixing at 120 ℃ for 10 minutes using a Haake Minilab mini-mixer and extruded into ribbons. The ribbons were used to prepare plaques for cross-linking (plaque) by first melting the ribbons in a preheated first press at 140 ℃ and above 5bar for 5 minutes to transform the plaques. The formed plaque was then removed from the first press and placed in a second press of the same size, where the second press had been preheated to the desired crosslinking temperature (see table below). Subsequently, the plaques were crosslinked at the desired temperature and 25bar for the desired time (see table below) to form crosslinked plaques 1.25mm thick. The crosslinked plaque is then removed from the second press at the desired crosslinking temperature and placed in a water/ice bath to ensure rapid cooling of the crosslinked plaque.

2.7 Tan. delta. and conductivity

At 10^-2Hz to 10⁷Measurements were performed in the frequency range of Hz, at different temperatures (error. + -. 0.1 ℃ C.) in the range of 20-130 ℃ C., under atmospheric pressure and under a nitrogen atmosphere using a Novocontrol Alpha spectrometer. The sample chamber consisted of two stainless steel electrodes of 40mm diameter and a sample of 0.1mm thickness. Each set of measurements was taken 6 times and averaged. The complex conductivity σ ═ σ' + i σ ", used herein for analysis is the real part thereof, where σ ═ i ω ∈ can be deduced from the complex permittivity ∈₀ε, wherein ∈₀Is the free space dielectric constant. Both the dielectric constant and the conductivity can be directly measured by an instrument. The DC conductivity is taken from the real part σ' of the conductivity at the limit of very low frequencies. For this analysis, only temperature is considered, and a flat part (plateau), i.e. a frequency independent σ', is observed in the spectrum.

The dielectric loss tan (δ) can be derived from the ratio of the real part and the imaginary part of the dielectric constant according to the relation tan (δ) ═ ε "/ε'. The dielectric loss values used in this work were obtained at 56 Hz.

3. Results

In order to show the effects provided by the present invention, a reference composition (RE1-RE7) and a composition according to the invention (IE1-IE12) were prepared using the following materials and conditions. The results are summarized in tables 1-4 and will be discussed in detail.

First, a series of compositions according to the invention were prepared to evaluate the crosslinking performance and visual appearance of the final crosslinked samples. The results are summarized in Table 1. The composition of RE1 comprises a first polymer (a) P1 containing epoxy groups, a titanate and a curing agent (bisphenol derivative, Ad 3). Plaque samples prepared from the composition of RE1 had satisfactory crosslinking properties, namely < 100% elongation and > 75% gel content within 5min at a crosslinking temperature of 180-220 ℃. However, the color of these samples is deep yellow (strong yellows), even orange, and may be unacceptable in some applications. Furthermore, the composition of RE1 requires the presence of catalysts and additives, which makes the system more expensive and complex, and requires special storage and handling conditions to avoid hydrolysis of the additives.

On the other hand, the composition system of IE1-IE4 is simpler, involving only 2 (IE1) or 3 (IE2-IE4) components in pellet form. The composition of the invention comprises a first olefin polymer (A) P1 containing epoxy groups and a second olefin polymer (B) P2 containing methacrylic acid. As can be seen from table 1, the crosslinking performance of the compositions of IE1-IE4 was improved, as indicated by the hot set elongation of the inventive compositions compared to the composition of RE 1. Furthermore, the crosslinked samples made from the compositions of the present invention were colorless.

IE14 and IE15 show that an increase in polarity of the first olefin polymer (a) improves the crosslinking characteristics.

TABLE 1

Next, the crosslinking characteristics and dielectric loss of the composition according to the present invention were examined. The results are shown in Table 2.

As can be seen from Table 2, the peroxide-free compositions containing a certain degree of polarity can achieve excellent tan delta values (RE2-RE5) by crosslinking of the epoxy rings by means of a click chemistry type reaction in the presence of different curing agents. The crosslinked composition exhibits an increased tan delta value compared to the thermoplastic. This means that after crosslinking the polarity is locked and fixed in the polymer structure, increasing the tan delta value.

The composition of IE5 was an ethylene polymer composition comprising a first polymer (a) produced in an autoclave reactor and a second polymer (B) comprising acrylic acid. Both IE6 and IE7 included a first polymer (a) which was a composition produced in a tubular reactor. In IE6, the second polymer (B) contained acrylic functionality, while in IE7, the second polymer (B) was a terpolymer containing acrylic acid and t-butyl acrylate.

Plaques were prepared from the composition of IE5-IE7 as described above and crosslinked at 200 ℃ for 10min to a gel content of at least 80%. The Tan delta values were measured at several temperatures as described above. The compositions of IE5-IE7 exhibited excellent tan δ values, particularly at high temperatures, while also exhibiting excellent crosslinking properties. Furthermore, the composition of IE6 based on epoxy containing polymer (a) and a second polymer (B) comprising only acrylic units produced in a tubular reactor showed excellent tan δ values at 90 ℃, indicating that the first polymer (a) produced in a tubular reactor is preferred.

The tan delta values reported above, especially for IE6, are lower. Without wishing to be bound by theory, it is thought that the absence of curing agent helps to reduce tan δ. The curing agent may typically contain metals or highly polar materials, which have a negative impact on the electrical properties of the material.

TABLE 3

Further, the influence of the production method of the first olefin polymer (a) on the crosslinking performance of the ethylene polymer composition was investigated. The results are summarized in Table 3. The ethylene polymer composition of IE5 comprises the first olefin polymer (a) produced in an autoclave. From the composition of IE5, the tapes were extruded at 150 ℃. Extrusion temperatures in excess of 150 ℃ result in pre-crosslinking during extrusion. Pre-crosslinking was assessed by visual plaque. If pits, spots, bumps, or other surface defects are observed, the sample is considered pre-crosslinked. Plaques were formed by compression molding from the extruded tapes without pre-crosslinking and crosslinked according to the conditions specified in table 3.

The ethylene polymer composition of IE12 comprises the first olefin polymer (a) produced in an autoclave. Although the gel content of the crosslinked IE12 composition was higher than IE5, indicating better crosslinking performance, the IE12 composition showed pre-crosslinking during extrusion at temperatures exceeding 150 ℃.

IE6 and IE7 comprise ethylene polymer compositions containing a first olefin polymer (a) produced in a tubular reactor. At temperatures above 150 ℃, pre-crosslinking was not observed in either case during tape extrusion, and both compositions exhibited good crosslinking performance, as indicated by gel contents of 72% and 77%, respectively. Without wishing to be bound by any theory, the larger bulk nature of the first olefin polymer (A) produced in the tubular reactor slows down the rate of crosslinking, thus leading to the disappearance of pre-crosslinking.

Finally, studies were carried out to investigate the DC conductivity of the polymer compositions according to the invention. The results are shown in Table 4.

TABLE 4

As can be seen from table 4, the composition of IE5-IE7 showed lower DC conductivity relative to the composition of RE 7. In particular the composition of IE7, in which the polymer produced in the tubular reactor was used, showed the lowest DC conductivity values.

While the invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made thereto without departing from the scope of the invention. It is intended that the specific embodiments be considered as illustrative and that the appended claims, including all equivalents, be interpreted as limiting the scope of the invention.