SK152099A3 - Cable with impact-resistant coating - Google Patents

Abstract

The present invention relates to a coating for cables which is capable of protecting the cable against accidental impacts. By inserting into the structure of a power transmissioncable a suitable coating of expanded polymer material of adequate thickness, preferably in contact with the sheath of outer polymer coating, it is possible to obtain a cable which has a high impact strength. The Applicant has moreover observed that an expanded polymer material used as a coating for cables makes it possible to obtain a higher impact strength for this cable than using a similar coating based on the same polymer which is not expanded. A cable with a coating of this type has various advantages over a conventional cable with metal armor, such as, for example, easier processing, a reduction in the weight and dimensions of the finished cable and a lower environmental impact as regards recycling of the cable once its working cycle is over.

Description

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CABLE PROVIDED WITH SHOCK RESISTANCE

Technical field

The present invention relates to a sheath for cables adapted to protect the cable against accidental or accidental impact.

BACKGROUND OF THE INVENTION

The unforeseen or accidental impact of shocks on power distribution cables, which may occur, for example, during transportation, laying and installation, and the like, may cause or cause a series of damage to the cable structure including deformation of the insulating layer, tearing off the insulating layer from the semiconductive material and so on; the damage may cause changes in the electrical gradient of the insulating layer, resulting in a decrease in the insulating resistance of said insulating layer.

For currently commercially available cables, such as power distribution cables for conducting or distributing medium and low voltage, in order to protect such cables against unwanted damage caused by unforeseen or accidental impact, usually metal reinforcement adapted to withstand such impact is applied to the cables . Said reinforcement may be in the form of strips or wires (typically made of armor steel) or alternatively in the form of a metal sheath (typically made of lead or aluminum); the metal reinforcement is usually coated with an outer protective polymeric sheath. A characteristic example of such a power distribution cable arrangement is described in detail in U.S. Pat. no. 5,153,381.

The Applicant has found that the presence of the aforementioned metal reinforcement in the cable sheath has a number of disadvantages. For example, the application of said metal reinforcement constitutes one or more additional phases that need to be included in the cable manufacturing process. In addition, the presence of metal

332 / B of the cable sheathing significantly increases the total weight of the cable and, in addition, poses environmental pollution problems, since if it is necessary to replace such a cable, this cable becomes very problematic in terms of its disposal.

Japanese patent publication no. JP 07-320 550 (Kokai) discloses a power supply cable for household electrical appliances provided with an impact resistant coating layer located between the insulating coating and the outer protective sheath. This shock-resistant coating layer is formed from an unexpanded polymeric material containing a polyurethane resin as a constituent.

On the other hand, it is also known from the prior art to use expanded polymerization materials in cable design for various purposes.

For example, German patent application DE P no. 15 15 709 discloses the use of an intermediate layer arranged to increase the low temperature resistance of the outer plastic sheath between the outer protective sheath and the inner metal reinforcement of the cable. However, no reference is made in the document to the protection of the internal structural configuration of the intermediate layer cable. Indeed, such an intermediate layer should be adapted to compensate for the elastic stresses generated in the outer plastic sheath due to the effects of low temperatures, which layer may comprise either freely dispersed glass fibers or a material that is either expandable or which includes hollow glass beads .

Another document, German Utility Model DE G no. 81 03 947.6 discloses an electrical cable intended to be used as an installation cable in equipment and machines, exhibiting specific mechanical resistance and flexibility. The cable is specifically designed to be wound onto a pulley and is therefore sufficiently flexible so that when it is unwound, its sheathing substantially returns to its original state. For this reason, this type of cable is specifically aimed at adequately ensuring the resistance to mechanical loads of the static type (i.e., those loads that occur during its winding on the pulley passage),

332 / B wherein the main characteristic of such a cable is its flexibility. It should therefore be readily apparent to those skilled in the art that this type of cable is fundamentally different from a medium and low voltage power cable with metallic reinforcement, which, rather than being flexible, must be able to withstand the dynamic loads caused by impacts, as a result, the sheath of the cable must have a certain impact strength.

In addition, the use of expanded materials for the stripping of metal conductors is known from cable design for the transmission of an electrical signal of the coaxial or to the DT DT of the twisted type. Such coaxial cables are usually intended to transmit high frequency signals and are used, for example, as coaxial cables for television installation (CATV; for frequencies 10 to 100 MHz), satellite coaxial cables (for frequencies up to 2 GHz) or coaxial cables for computing (for frequencies) above 1 MHz); wherein, for comparison, standardly used telephone cables usually transmit electrical signals at frequencies of about 800 Hz.

The purpose of using insulating layers of expanded materials in the cables described is to increase the rate of transmission of electrical signals due to the approximation of the ideal rate of transmission in external metal conductors (which closely approximates the speed of light). The reason for this claim is that, when compared to unexpanded polymerization materials, the expanded materials generally exhibit a lower dielectric constant (K), which, as the degree of expansion of the polymerization material increases, proportionally approaches the dielectric constant air (K = 1).

For example, U.S. Pat. no. No. 4,711,811 discloses an electrical signal cable provided with an expanded fluorinated polymer as an insulating layer (0.05 to 0.76 mm thick), coated with a thin layer of ethylene-tetrafluoroethylene or ethylene-chlorotrifluoroethylene copolymer (thickness of 0.013 to 0.254 mm). As described in this patent, the reason for providing the expanded polymerization material is to strip the conductor, while the reason for providing a thin layer of unexpanded polymerization material that overlaps the expanded polymerization material is to improve mechanical properties.

332 / B properties of the insulating layer, ensuring in particular the delivery of the necessary basic compressive strength in the event that the two insulated conductors twist together to form a so-called " "DT DT".

EP patent no. 0 442 346 discloses an electrical signal transmission cable having an insulating layer based on expanded polymerization material disposed directly on the conductor surface; wherein the expanded polymerization material exhibits an ultramicroporous structure with a pore volume greater than 75% (corresponding to an degree of expansion greater than 300%). The ultra-microporous structure of this polymerization material must be such as to allow 6.89 under load. 10 ⁴ Pa its compression in the range of at least 10% and, after interruption of this load, its return to its original state in the range of at least 50% of the original volume; these values correspond essentially to the characteristic values of the compressive strength which such a material must necessarily exhibit due to its ability to withstand compression under pressure during cable entanglement.

In International Patent Application WO-A. 93/15512, which also relates to an electric signal transmission cable provided with an insulated coating of expanded polymerization material, it is claimed that the required necessary compressive strength is achieved by an insulating coating of expanded material in combination with a layer of unexpanded insulating thermoplastic polymerization material (described for example, in the aforementioned U.S. Patent No. 4,711,811), but unfortunately, the transmission rate of the electrical signal is also reduced. Said patent application WO no. 93/15512 discloses a coaxial cable provided with a double layer of insulating coating, both of which are made of expanded polymerization material and that the inner layer of microporous polytetrafluoroethylene (PTFE) and the outer layer of expanded polymerization material with closed pores, in particular perfluoroethylene (PFA) polymers. An insulating coating based on the expanded polymerization material is obtained by extruding the PFA polymer while applying it to the inner insulating layer of PTFE polymer combined with Freon 113 gas injection as blowing agent. According to the detailed explanation given in the patent specification

332 / B of the application, the use of the thus formed insulating layer of the expanded polymeric material with closed pores maintains a high rate of electrical signal transmission. In addition, the insulating layer in this patent application is defined and characterized as exhibiting pressure resistance, although this is not supported by any data in the description with respect to compressive strength. The description further emphasizes the fact that conductors provided with a double layer of insulating coating can be braided. In addition, according to the teachings of this patent application, increasing the void pore volume in the outer layer of expanded material makes it possible to increase the transmission rate of electrical signals, which in turn provides a source of small load variations in the outer layer to prevent compression of the inner expanded layer.

As can be seen from the above documents, the main reason and purpose of using expanded "open pore" polymeric materials as insulating coating layers in the electrical signal cable design is to increase the electrical signal transmission rate; however, said expanded coating layers have the disadvantage of insufficient compressive strength. However, there are several types of expanded materials, which are characterized as "squeeze-resistant", since they not only ensure a high transmission rate of electrical signals, but also achieve sufficient resistance to the pressure forces that typically occur during the mutual entangling and twisting the two expanded insulating layers of the coated conductors together; in this case, it is also a load of essentially static type.

Thus, while on the one hand it is absolutely necessary that these insulating coating layers, made of expanded polymerization material and intended for electric signal transmission cables, exhibit characteristics suitable for carrying relatively moderate pressure loads (such as pressure loads arising during on the other hand, no mention is made in any patent document known to the applicant or any other publication that the coating layer or sheath of expanded polymerization material is capable of providing

332 / B to achieve any type of impact strength, respectively. impact resistance. In addition, although such expanded insulating coating layers promote the achievement of higher transmission rates of electrical signals, it is considered less suitable as a coating layer or sheath formed from a similar or substantially the same but unexpanded material in terms of compressive strength, as explained in detail. in the aforementioned WO-A-patent application no. 93/15512.

SUMMARY OF THE INVENTION

The Applicant has now found that by inserting into a structural arrangement a power distribution cable of a suitable coating layer of expanded polymerization material of adequate thickness and flexural modulus, preferably positioned in contact with the outer sheath or outer polymerization coating layer, it is possible to create a cable having a high impact strength. which, in effect, makes it possible to omit the use of the protective metal reinforcement mentioned above from the cable structure. In particular, the Applicant has found that the polymerization material must be selected to exhibit a sufficiently high flexural modulus, measured prior to processing by expanding, so that the desired impact resistance properties can be achieved and thereby completely void the possibility of damaging the internal structure of the cable such as due to the undesirable impact of its impact on its outer surface. For the purposes of the present description, the term "shock, shock or shock" is understood to include all types of dynamic loads of a certain energy size capable of causing significant structural damage to standard non-routed cables while having such burdens only negligible effects. An impact force with an impact energy of about 20 to 30 Joules, achieved by the impact of the impact head with a rounded V-shaped working edge with a radius of curvature of 1 mm on the outer sheath of the cable, can be considered as such.

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In addition, the Applicant has surprisingly found that the expanded polymerization material used as part of the power distribution cable construction of the present invention allows to achieve a higher impact resistance than that exhibited by substantially the same coating layer made of a material based on the same polymer but untreated .

A sheathed cable of this type exhibits a number of different advantages over standardly used metal reinforcement cables, such as easier cable manufacture, reduced weight and size of the finished cable, and less environmental hazards associated with replacing the cable after its working life has run out and its liquidation.

According to a first aspect of the present invention, there is provided a power distribution cable comprising:

(a) an electrical conductor,

(b) at least one layer of compact insulating sheathing; and

c) a coating layer formed of an expanded polymerization material, said polymerization material exhibiting predetermined mechanical strength characteristics and a predetermined degree of expansion in order to provide adequate impact resistance properties of the cable.

According to a preferred embodiment of the present invention, the expanded polymeric material coating layer is formed of a polymeric material which, prior to expansion, exhibits a flexural modulus at ambient temperature measured according to ASTM D790 of at least 200 MPa, preferably in the range of 400 to 1 A flexural modulus of between 600 and 1300 MPa is particularly preferred for said purposes.

332 / B

According to a further preferred embodiment of the present invention said polymerization material has an expansion degree in the range of about 20 to about 3000%, preferably in the range of about 30 to about 500%, with an expansion degree in the range of about 10% being particularly preferred. from about 50 to about 200%.

According to a further preferred embodiment of the present invention, the expanded polymerization material coating layer has a thickness of 0.5 mm, preferably in the range of 1 to 6 mm, with a thickness in the range of 2 to 4 mm being particularly preferred for the mentioned purposes.

According to another preferred embodiment of the present invention, said polymerization material is selected from polymerization materials including polyethylene (PE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), and linear low density polyethylene (PE). LLDPE); polypropylene (PP), ethylene-propylene rubber (EPR), ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (polyisobutene), ethylene-vinylene copolymer (EVA) -acrylate copolymer, ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate (EEA) copolymer, ethylene-butylacrylate (EBA) copolymer, ethylene / alpha-olefin copolymer, acrylonitrile-butadiene-styrene (PVC), polyvinyl chloride (ABS) , polyurethane (PUR), polyamides, aromatic polyesters, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) and their copolymers or mechanical mixtures.

According to another preferred embodiment of the present invention, the polymerization material is an olefin polymer or a copolymer based on polyethylene (PE) and / or polypropylene (PP), preferably modified with ethylene-propylene rubber (EPR) in a weight ratio PP / EPR ranging from 90 / 10 to 50/50, preferably in the range of 85/15 to 60/40, with a particularly preferred modified composition being a 70/30 weight ratio composition.

332 / B

According to a further preferred embodiment of the present invention, said olefin polymer or copolymer based on polyethylene (PE) and / or polypropylene (PP) further comprises a predetermined amount of vulcanized rubber in powder form, preferably in the range of 10 to 60% by weight. based on the content of the polymerization material.

According to a further preferred embodiment of the present invention, the power distribution cable is further provided with an outer protective polymeric sheath arranged in contact with a coating layer of expanded polymerization material, the sheath preferably having a thickness greater than 0.5 mm and preferably a thickness within the range. from 1 to 5 mm.

According to a second aspect of the present invention, there is provided a method of providing an impact resistance of a power distribution cable, comprising coating the cable with a coating layer of expanded polymerization material.

According to a preferred embodiment of the present invention, the method of providing an impact resistance of the power distribution cable further comprises coating said expanded polymeric coating layer with an outer protective polymeric sheath.

According to a further aspect of the present invention, it is proposed to use the expanded polymerization material to provide impact resistance of the power distribution cable.

According to a further aspect of the present invention, there is provided a method for assessing the impact resistance of a power distribution cable comprising at least one layer of an insulating coating, comprising:

a) measuring and determining the average peel strength of said insulating coating layer,

b) subjecting the cable to impact energy of a predetermined size;

c) measuring the peel strength of said insulating coating layer at the impact site, and

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(d) checking which of the differences in the average peel strength and peel strength at the impact site is less than a predetermined value for said cable relative to the average peel strength.

According to a preferred embodiment of the present invention, the measurement of said peel adhesion strength is performed between the insulating coating layer and the outer semiconducting coating layer.

The term " degree of expansion of the polymerization material "

G (degree of expansion) = (d ₀ / d _e -1) ° 100, where:

d ₀ represents the density of the unprocessed polymerization material (or, in other words, a polymer with a structure substantially exhibiting no void pore volume); and _e is the relative density of the polymerization material measured in the expanded state.

The term "expanded polymerization material" used in the present invention for the purpose of the description means a polymerization material having a structure having a void pore volume (or, in other words, a certain space not occupied by a polymer but in a polymer enclosed by gas or air). greater than 10% of the total volume of the polymerization material.

The term " adhesive peel strength " of the polymeric material used in the present invention for the purpose of the description is understood to mean the force necessary to separate (tear) the sheath layer from the conductor or another sheath layer; wherein, in the case of separation of the two layers from one another, the layers are typically an insulating layer and an outer semiconducting layer.

332 / B

The insulating layer of power distribution cables typically has a dielectric constant (or permittivity) (K) of a value greater than 2. In addition, unlike electric signal transmission cables where the "electric gradient" parameter is of no significance, distribution cables use electrical gradients from about 0.5 kV / mm for low voltage and electrical gradients up to 10 kV / mm for high voltage; as a consequence, due to the inhomogeneity of the insulating layer of the power distribution cables (for example the above-mentioned pore volume), which could represent a potential source of local variations in dielectric strength and the resulting reduction in insulation resistance, it ensures absolute elimination of the described effects. Accordingly, the insulating material used will typically be a compact polymerization material, and for the purpose of describing the present invention, the term "compact insulating material" will be understood to be an insulating material which, for use in the power distribution cable structure for conducting and distributing medium and low The voltage has a dielectric strength of at least 5 kV / mm, preferably a dielectric strength of greater than 10 kV / mm, and preferably a dielectric strength of greater than 40 kV / mm. In contrast to the expanded polymerization material, this compact material has essentially no pores or pores in its structure. pore volume; typically, the material will have a density of 0.85 g / cm ³ or greater.

The term "low voltage", for the purpose of describing the present invention, shall mean a voltage of up to 1000 V (typically greater than 100 V); the term "medium voltage" shall mean a voltage ranging from 1 to 30 kV and " high voltage " shall mean a voltage above 30 kV for the purpose of the description. The power distribution cables described will typically operate at rated frequencies of 50 or 60 Hz.

Although the use of an expanded polymeric coating in the following description will be explained in detail in connection with power distribution cables where this coating can advantageously replace the metal reinforcement in these cables currently used to provide impact resistance, they must be

332 / B, as is well known in the art, said expanded coating layer can be usefully used in the design of any type of cable that requires adequate mechanical strength and toughness. Specifically, the present interpretation and definition of power distribution cables does not only apply to low and medium voltage cables but also to high voltage cables.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in more detail by way of the following examples of specific embodiments thereof in conjunction with the accompanying drawings, in which:

Fig. 1 shows a power distribution cable of three-core type with metal reinforcement according to the prior art;

Fig. 2 shows a first embodiment of a cable according to the present invention of the three-wire type;

Fig. 3 shows a second embodiment of the cable according to the present invention;

Fig. 4 shows the resulting deformations of the cable according to the present invention a) and a commonly used metal reinforced cable b) after the impact strength test with a falling height of 50 cm;

Fig. 5 shows the resulting deformations of the cable according to the present invention a) and a commonly used metal reinforced cable b) after the impact strength test with a drop height of 20 cm.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 of the accompanying drawings is a schematic cross-sectional illustration of a power distribution cable for conducting a medium voltage three-core metal reinforcement type according to the prior art. This cable comprises three conductors 1, each of which is coated with an inner layer 2 of semiconducting material, an insulating layer 3 of insulating material, an outer layer 4 of semiconducting material and a metal shield 5; for simplicity

332 / B, for the purposes of the present disclosure, this partial structure will be referred to as a " core cable ". The three cable cores thus arranged are coupled together and the star cross-sectional spaces formed therebetween are filled with filler material 9 (which is usually elastomeric blends, polypropylene fiber materials and the like) in order to achieve a cross-section of a circular structural structure that is in turn , as a whole, coated with an inner polymeric sheath 8, a metal reinforcement 7 with wire mesh and a polymeric outer sheath 6.

Fig. 2 is a schematic cross-sectional view of a power distribution cable according to the present invention, which is of the same three-core type and which is also intended to conduct and apply medium voltage. This cable comprises three conductors 1, each of which is coated with an inner layer 2 of semiconducting material, an insulating layer 3, an outer layer 4 of semiconducting material, and a metal shield 5; the star-cross-sectional spaces between the conductors are in this case filled with an impact-resistant expanded polymeric material 10 which is further encapsulated in an outer protective polymerization sheath 6. In the coating layer 10 of the expanded polymeric material is shown in FIG. 2, in close proximity to the outer surface of the interconnected cable cores, a thin circular layer 10a, indicated by a broken line, the thickness of which corresponds to the minimum thickness of the expanded polymeric coating layer.

Fig. 3 of the accompanying drawings represents a schematic cross-sectional view of a power distribution cable according to the present invention, of a single core type for conducting and supplying medium voltage. This cable comprises a centrally arranged conductor 1, which is coated with an inner layer 2 of semiconducting material, an insulating layer 3, an outer layer 4 of semiconducting material, a metal shield 5, a coating layer 10 of expanded polymerization material and an outer protective polymerization sheath 6. shown in FIG. 3, the thin circular layer 10a. shown in FIG. 2 three-core cable, since the cable was live

332 / B has a circular cross-section, coinciding with the coating layer 10 of the expanded polymerization material.

For quite obvious reasons, only a few of the many possible embodiments of the power distribution cable are shown in the accompanying drawings in which the present invention may be advantageously utilized. It will be appreciated that such prior art embodiments may be suitably adapted or varied in a known manner, with such adaptations or variations falling within or within the well-defined claimed scope of the present invention without being limited thereto. For example, referring to FIG. 2, the star-shaped cross-sectional spaces located between the individual cores of the cable may be filled with a commonly used filler material to form a partially completed cross-sectional cable corresponding to an approximately circular cross-section that fills and is surrounded by a thin circular layer 10a; and only thereafter, it is advantageously possible to extrude a coating layer 10 of expanded polymeric material which corresponds approximately to the thickness of the thin circular layer 10a and which is arranged between the surface of the vein structure of the cable and the outer protective layer. Alternatively, the cable cores may be formed with a certain cross-sectional contour (for example, a contour of a partial circular sector) so that, when the individual cores are interconnected to form a unit, a core of approximately circular cross-section is formed without any filler material required. ; and the conductor core of the cable thus formed, consisting of individual cable cores coupled together, is then, by extrusion, provided with a coating layer 10 of an impact-resistant expanded polymeric material and subsequently an outer protective sheath 6.

In the case of low voltage transmission cables, their structural structure will generally comprise only an insulating coating layer placed directly in contact with the conductor, which is then provided first with a coating layer of the expanded polymerization material and then with an outer protective sheath.

332 / B

Other possible solutions will be well known to those skilled in the art, and will be able to perform the most appropriate solutions for the purposes mentioned, for example on the basis of the set-up cost, the type of cable operating location (internal cable installation, external cable installation, cable in the pipeline, laying the cable directly into the ground or subsurface collectors, laying the cable at the bottom of the sea and the like), cable operating temperatures (maximum and minimum cable operating temperature, ambient temperature range) and the like.

The expanded impact resistant polymeric coating layer can be formed from any type of expandable or expandable polymeric material, such as olefin polymers or copolymers, olefin ester copolymers, polyesters, polycarbonates, polysulfones, phenolic resins, urea resins, and mixtures thereof. Examples of suitable polymerization materials useful herein include polyethylene (PE), especially low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), and linear low density polyethylene (LLDPE); polypropylene (PP), ethylene-propylene rubber (EPR), especially ethylene-propylene copolymer (EPM) or ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (polyisobutene), ethylene-vinyl polyethylene (polyvinyl copolymer), acrylate copolymer, especially ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate (EEA) copolymer, ethylene-butyl acrylate (EBA) copolymer, ethylene / alpha-olefin copolymer, acrylonitrile-butadiene-styrene poly (ABS), poly (ABS) ), polyurethane (PUR), polyamides, aromatic polyesters such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) and their copolymers or mechanical mixtures. Preferably olefin polymers or copolymers are used for this purpose, in particular polymers and copolymers based on polyethylene (PE) and / or polypropylene (PP) in a mixture with ethylene-propylene rubbers (EPR). Preferably, polypropylene (PP) modified with ethylene-propylene rubber (EPR) may be used for this purpose, the PP / EPR blend weight ratio being in the range of 90/10 to 50/50, preferably in the range of 85/15 to 60 / 40, wherein a particularly preferred mixture is a 70/30 weight ratio mixture.

332 / B

In addition, in accordance with another aspect of the present invention, the Applicant has found that it is possible to mechanically mix a polymerization material which is subjected to an expanding treatment, particularly when using olefin polymers and, more specifically, polyethylene or polypropylene, with a predetermined amount of rubber in powder form. , for example, vulcanized natural rubber.

Said powdered rubbers are typically formed from particles having a size in the range of 10 to 1000 µm, and preferably in the range of 300 to 600 µm. Advantageously, waste rubber obtained from the manufacture of tires may be used as vulcanized rubber. The percentage of rubber in the powder form contained in the composition and based on the content of the expandable polymerization material may range from 10% to 60% by weight, and preferably from 30% to 50% by weight.

The polymerization material to be expanded, which is used either without further processing, or which is used as a basic expandable component in admixture with powdered rubber, will exhibit a stiffness that, once expanded, will provide a certain, a predetermined value of the impact resistance necessary to protect the internal structure of the cable (or, in other words, the above-mentioned insulating and semiconducting material layers that may be present in the structure) against possible damage that may occur as a result occurring or unforeseen impacts. In particular, the material will exhibit a sufficiently high impact energy absorbing capacity such that the impact energy is transferred to the downstream insulating layer only in a range that ensures that the insulating properties of the downstream coating layers outside the predetermined range will not be affected or modified. value. The reason for this measure is, as will be explained and documented in detail in the following description, the Applicant's finding that the cable subjected to the impact treatment measured differences between the average value of the adhesive peel strength and the value of the peel strength measured at the impact site. and relating to the peeling off of the underlying insulating coating layers; while

332 / B, said adhesive peel strength can preferably be measured between the insulating layer and the outer layer of semiconducting material. The measured difference in said peel strength is proportionally greater the greater the force transmitted to the underlying layers; in the case where the peel adhesion strength is measured between the insulating layer and the outer layer of semiconductive material, the evaluation has determined that the coating layer of the expanded polymerization material provides sufficient protection for the underlying layers when the difference between the peel adhesion strength is the impact area and its average value of less than 25%.

The Applicant has further found that a polymerization material selected from the above group of polymerization materials is particularly suitable and useful for this purpose, and such a material exhibits a flexural modulus at ambient temperature measured according to ASTM D790 prior to processing by expansion, greater than 200 MPa, and preferably at least 400 MPa. In another aspect, regarding too high stiffness of the expanded polymerization material, which may result in difficult handling of the finished product, it is preferred to use a polymerization material that exhibits a flexural modulus at ambient room temperature of less than 2000 MPa. Polymerization materials which are particularly suitable and useful for this purpose are those polymerization materials which exhibit a flexural modulus at ambient temperature ranging from 400 to 1800 MPa prior to their processing by expansion, with a particularly preferred polymerization material for this purpose. the material is a polymerization material having a flexural modulus at ambient temperature ranging from 600 to 1500 MPa.

Said flexural modulus values may be characteristic values of a specific material or may result from mixing two or more materials with different flexural modulus, which are mixed in a bird ratio that will ultimately achieve the desired stiffness of the final material. For example, the stiffness of polypropylene (PP), which exhibits a flexural modulus greater than 1500 MPa, can be correspondingly reduced by its suitably selected

332 / B modification with a suitable and well-defined amount of ethylene-propylene rubber (EPR) having a flexural modulus of about 100 MPa.

Examples of commercially available polymer blends or compounds of this type are:

low density polyethylene: trade name Riblene FL 30 (manufacturer Enichem), high density polyethylene: trade name DGDK 3364 (manufacturer Union Carbide), polypropylene: trade name PF 814 (manufacturer Montell), and polypropylene modified with ethylene-propylene rubber: trade name designation Moplen EP-S 30R, 33R and 81R (manufactured by Montell); Fina-Pro 5660G, 4660G, 2660G and 3660S (manufactured by Fina-Pro).

The degree of expansion of the polymeric material and the thickness of the coating layer must be such that, in combination with the outer polymeric sheath, they are capable of providing adequate resistance to the characteristic impact effects occurring during cable handling, laying and installation.

As mentioned above, said "degree of expansion of the polymerization material" is determined based on the following formula:

G (degree of expansion) = (d ₀ / d _e - 1) ° 100, where:

d ₀ represents the density of the unprocessed polymerization material; and _e represents the relative density of the polymerization material measured in the expanded state.

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The Applicant has further found that where this maintenance of the required impact resistance characteristics explicitly permits, it is advantageous for the same thickness of the expanded layer to use a polymerization material exhibiting a high degree of expansion, mainly because by this measure it is possible to limit the inevitably necessary amount of polymerization material used for this purpose, with distinct advantages in terms of both economic cost and overall reduced weight of the finished product.

The degree of expansion is variable over a wide range, both as a function of the specific polymerization material used and as a function of the intended thickness of the coating layer to be formed; Usually, the degree of expansion can range from 20% to 3000%, preferably from 30% to 500%, with a particularly preferred degree of expansion being from 50% to 200%. The expanded polymerization material exhibits a closed pore structure.

The Applicant has further found that when a certain predetermined degree of expansion is exceeded, the load-bearing capacity of the polymerization coating layer decreases for a given impact strength. In particular, it has been found that the possibility of achieving high degrees of expansion of the polymeric material while maintaining a highly effective impact resistance can necessarily be brought into line with the flexural modulus of the polymeric material to be expanded. The reason for this measure was to find the Applicant that as the degree of expansion of the polymerization material increased, the flexural modulus of the material was reduced, essentially according to the following relationship:

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Ε ₂ / Ε, = (ρ ₂ / ρ,) ^ζ where:

Ε2 represents the flexural modulus of the polymerisation material, measured at a higher degree of expansion,

E1 represents the flexural modulus of the polymerization material measured at a lower degree of expansion, p ₂ represents the relative density of the polymerization material measured at a higher degree of expansion, and

Pi represents the relative density of the polymerization material measured at a lower degree of expansion.

For purposes of illustration, it should be noted that for a polymerization material having a flexural modulus of about 1000 MPa, a change in the degree of expansion in the range of 25% to 100% results in a reduction in the flexural modulus of the material by approximately half. Polymerization materials exhibiting a high flexural modulus may therefore be expanded to a higher degree than polymeric materials exhibiting low flexural modulus values without causing this to adversely affect the capability of the coating to withstand and withstand impact. loading.

Another transformation that affects the impact strength, respectively. cable impact resistance, is the thickness of the coating layer of the expanded polymerization material; the minimum thickness which is still capable of guaranteeing the necessary impact strength expected to be achieved in accordance with the use of such a coating layer will depend mainly on the degree of expansion of the polymerization material and on the flexural modulus of the material. Briefly, the Applicant has found that higher impact strength values can be achieved for one and the same polymerization material and for one and the same degree of expansion of this material by increasing the thickness of the expanded coating. However, due to the desirable use of a limited, at least possible amount of coating polymerization material and the resulting

332 / B reducing the set-up costs and, on the other hand, reducing the dimensional size of the finished product, the thickness of the expanded material must be the minimum possible thickness that is necessary to ensure the required impact strength. Especially in the case of cables of the medium-voltage transmission type, it has been found that an expanded sheath thickness of about 2 mm is usually capable of providing sufficient resistance to the commonly encountered shocks to which a cable of this type is exposed during its functional installation. The thickness of the expanded coating layer may preferably have a value greater than 0.5 mm, in particular a value in the range of about 1 mm to about 6 mm, with a particularly preferred thickness value in the range of 2 mm to 4 mm.

The Applicant has further found that it is possible to sufficiently characterize and define sufficiently closely the relationship between the thickness of the coating layer and the degree of expansion of the polymerization material for materials with different flexural modulus values such that the thickness of the coating layer of the expanded polymerization material is appropriately dimensioned as a function of the degree of expansion and a flexural modulus of the polymerization material, in particular a thickness of the coating layer of the expanded polymerization material ranging from 2 to 4 mm. Such a relationship, respectively. functional verticality can be expressed by the following relation:

The _E ° D> L wherein

V represents the volume of expanded polymerization material per meter of cable length (m ³ / m), which volume refers to the volume of the thin circular layer, precisely defined by the minimum thickness of the expanded polymeric material coating layer corresponding to the thin circular layer 10a of FIG. 2 showing the structural arrangement of the multi-core cable or the polymer coating layer 10 of FIG. 3, in which a single core cable is shown, d _e represents the relative density of the polymerization material measured in the expanded state (kg / m ³ ), and

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N is the result of the product of the two above-mentioned values, which must be greater than or equal to:

0,03 for materials with flexural modulus> 1 000 MPa,

0.04 for materials with a flexural modulus of between 800 and 1 000

MPa,

0,05 for materials with a flexural modulus of between 400 and 800 MPa,

0.06 for materials with flexural modulus <400 MPa.

The parameter V is dependent on the coating thickness (S) of the expanded coating according to the following formula:

V = π ⁰ (2Rj ° S + S ² ),

R 1 represents the inner radius of the thin circular layer 10a,

The parameter d _e is a function of the degree of expansion of the polymerization material according to the above formula:

G = (do / d _e -1) 100 °.

Based on the above relationships, for a coating layer of expanded polymerization material having a thickness of about 2 mm, placed on a circular cross-section of a cable with a diameter of about 22 mm, for various polymerization materials exhibiting different flexural modulus (Mf) at ambient temperature the coating has a minimum relative density of about:

0.40 g / m ³ for LDPE (Mf is about 200 MPa),

0,33 g / m ³ for the PP / EPR mixture in the ratio 70/30 (Mf is about 800 MPa),

0.26 g / m ³ for HDPE (Mf is about 1000 MPa), and

0.20 g / m ³ for PP (Mf is about 1500 MPa).

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The stated relative density values of the expanded polymerization material correspond to the maximum degree of expansion:

130% for LDPE (d ₀ = 0,923 g / m ³ ),

180% for PP / EPR mixture (d ₀ = 0,890 g / m ³ ),

260% for HDPE (d ₀ = 0,945 g / m ³ ), a

350% for PP (d ₀ = 0.900 g / m ³ ).

In a similar manner, the following minimum relative density values were found for a coating layer of expanded polymerization material having a thickness of about 3 mm applied to a core of a cable of identical dimensions:

0,25 g / m ³ for LDPE,

0.21 g / m ³ for PP / EPR mixture

0.26 g / m ³ for HDPE, a

0,20 g / m ³ for PP, corresponding to the maximum degree of expansion:

270% for LDPE,

320% for PP / EPR,

460% for HDPE, and

600% for PP.

The above results indicate that, for the best, resp. In order to make optimal use of the characteristic strength characteristics of the coating layer of the expanded polymerization material of a predetermined thickness in terms of impact strength, both the mechanical strength characteristics of the material (especially the flexural modulus) and the degree of expansion of the material must be taken into account. It should be noted, however, that the values determined on the basis of the above relationships are by no means meant to limit the scope of the present invention. In particular, the maximum degree of expansion of polymerization materials whose flexural moduli are in close proximity to the upper bounds of the intervals defined for the N (or

332 / B (400, 800 and 1 000 MPa), may in fact be even greater than its values calculated on the basis of the above relationships; at this stage, the layer formed from a polypropylene / ethylene / propylene rubber mixture PP / EPR having a thickness of about 2 mm (having a Mf value of about 800 MPa) will still be able to guarantee the required impact resistance even for a degree of expansion of about 200%.

The expansion of the polymerization material is usually carried out during the extrusion processing phase; wherein said extrusion processing may be carried out either chemically, by adding to the polymerization material a suitable "expanding or blowing agent", which is, in short, a means which is capable of causing gas evolution under predetermined temperature and pressure conditions or by physical means by direct injection of high pressure gas into the transfer cylinder.

Examples of suitable &quot; blowing agents &quot; include azodicarboamide or mixtures of organic acids (e.g., citric acid) with carbonates and / or bicarbonates (e.g., sodium carbonate).

Examples of gases useful for injection in a high pressure extruder include nitrogen, carbon dioxide, air, and low boiling hydrocarbons such as propane and butane.

As an outer sheath that overlaps the coating layer of the expanded polymer material, a standard type sheath can be used without difficulty. Materials used to form such an outer sheath include polyethylene (PE), especially medium density polyethylene (MDPE) and high density polyethylene (HDPE), polyvinyl chloride (PVC), elastomer blends and the like. Medium density polyethylene (MDPE) and polyvinyl chloride (PVC) are preferably used for this purpose. The polymeric material of which the outer sheath is formed typically exhibits a flexural modulus of from about 400 MPa to about 1200 MPa, and preferably from about 600 MPa to about 1000 MPa.

332 / B

The Applicant has further found that the presence of an outer protective sheath in the cable sheathing structure, in combination with the characteristics of the coating layer of the expanded polymerization material per se, promotes providing the desired impact strength characteristics of the coating layer. In particular, the Applicant has found that the promotion of overall impact resistance through an outer protective sheath for one and the same layer thickness of the expanded polymerization material increases with increasing the degree of expansion of the polymerization material from which the expanded coating layer is formed. The thickness of the outer sheath is preferably greater than 0.5 mm, preferably in the range of 1 to 5 mm, and preferably in the range of 2 to 4 mm.

The design of the impact-resistant power distribution cable of the present invention will be described below with reference to the schematic representation of the cable shown in FIG. 2 of the accompanying drawing, the star-cross-sectional areas between the interconnected cores of the coating-coated cable are filled with a polymerization material, but not a directly expanded polymerization material, but a commonly used filler material; the expanded polymeric material coating layer 10 is then formed by extruding the polymeric material onto the partially completed cable to form a thin circular layer 10a around said partially completed cable, and the coating layer is then coated with an outer protective polymeric sheath 6. Preparation of the individual cable cores, in short, a structural assembly comprising the conductor 1, the inner layer 2 of semiconducting material, the insulating layer 3, the outer layer 4 of semiconducting material and the metal shielding 5 are carried out in a manner known in the art, for example by extrusion processing technology. The cable cores are then coupled to one another and the thus formed star cross-sectional spaces are filled with a commonly used filler material (for example, a mixture of elastomers, polypropylene fiber material, and the like), typically using a filler material to each other, by pressing the cable until a partially finished circular cross-sectional cable is formed.

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Then, the coating layer 10 of the expanded polymer material is applied to the surface of the filler material layer by extrusion coating. The die head diameter will preferably be slightly less than the final diameter of the cable coated with the expanded polymer material in order to allow the polymerization material to expand at the exit of the extruder.

The Applicant has further found that under identical extrusion conditions (such as the screw spindle rotation speed, progressive extrusion speed, extrusion head die diameter and the like), one of the variables is the extrusion temperature, which exhibits a considerable influence on the degree of expansion. Generally speaking, at extrusion temperatures below 160 ° C, it is very difficult to achieve a sufficient degree of expansion of the polymerization material; wherein the extrusion temperature is preferably at least 180 ° C and in particular about 200 ° C) Increasing the extrusion temperature usually corresponds to a higher degree of expansion.

In addition, the degree of expansion of the polymerization material can be controlled, to some extent, by influencing the cooling rate, since by appropriately decreasing or increasing the cooling rate of the polymerization material from which the respective layer of expanded polymerization material is formed at the extruder die. it is possible to increase or decrease the degree of expansion of the polymerization material.

As mentioned above, the Applicant has found that it is possible to quantitatively determine the impact effects on the sheath of the cable by measuring the adhesive strength of the sheathing of the sheathing of the cable sheath at which they were between the average value of the adhesive tear strength at the tear point. impact, observed differences. Especially for power distribution cables intended for conducting medium voltage and having a structural structure comprising an inner layer of semiconducting material, an insulating layer and an outer layer of semiconducting material, the peel adhesion strength (and, of course, its differences) may advantageously be measured between an outer layer of semiconducting material and an insulating layer.

332 / B

The Applicant has further found that the effects of the mainly combined effect of several shocks at the same time, which may be exposed to a particular cable, in particular a metal-reinforced power cable for medium-voltage conducting, can be determined using a impact toughness test carried out on the French Technical Standard HN 33- S-52, concerning armored high-voltage power distribution cable armor, according to which the cable is subjected to an impact energy of about 72 Joules (J).

Similarly, the peel strength of the respective coating layer can be determined using the facts set forth in the above-mentioned French Technical Standard HN 33-S-52, on the basis of which the force that must be applied in order to separate the outer layer from the semiconducting layer is measured. material from the insulating layer. In this case, the Applicant has found that by continuously measuring this force at the respective impact locations, peak values of said force are measured, which indicate changes in the cohesive force between the two layers. It has been found that these changes are generally associated with a reduction in the insulating resistance of the protective sheathing. These changes will be proportional to the greater the lower the impact resistance of the cable outer sheath (which in this embodiment of the present invention consists of a coating layer of expanded polymeric material) and an outer sheath. The magnitude of the variation of this force, measured at the point of impact, compared to its average value, measured over the entire length of the cable, thus represents an indication of the degree of impact protection achieved by the protective sheath. Generally speaking, variations in peel adhesion strengths of up to 20-25% compared to average values of this force will be considered acceptable for the stated purposes.

The characteristic parameters of the coating layer of the expanded polymerization material (i.e. the material used, the degree of expansion, the thickness) that can be usefully used in conjunction with a suitable external protective polymerization sheath in the structural design of the cable can be appropriately selected depending on the degree of impact resistance desired. which must be ensured in order to adequately protect the downstream cable structure and, moreover, also depending on the characteristics of the specific

332 / B of the material used to form the insulating layer and / or semiconducting layer, for example the hardness of the material, its density and the like.

As can be seen from the foregoing detailed description, the power distribution cable of the present invention is particularly suitable for replacing standardly used metal reinforced power distribution cables, mainly because of the advantageous properties of the coating layer of the expanded polymerization material over metal cable reinforcement. However, the use of the cable of the present invention is not limited to this specific application. In fact, the utility utility cable described herein can be used in all such applications where it is desired to use cables exhibiting increased impact resistance characteristics. The impact-resistant power distribution cable of the present invention can be used to replace, in particular, conventional power distribution cables containing no metal reinforcement in all such applications in which it would be much more advantageous to use metal reinforced power distribution cables, but whose use is impossible in these applications. due to the disadvantage of their metal reinforcement.

In the following description, several exemplary embodiments of the present invention are set forth, describing and explaining the nature thereof in more detail.

Example 1

Preparation of cable with expanded coating

For the purpose of evaluating the impact strength of the coating layer of the expanded polymerization material of the present invention, coating layers of different thicknesses were applied by extrusion of several different polymerization materials with different degrees of expansion, namely a 0.5 mm semiconducting material layer, an insulating layer formed from a mixture 3 mm thick ethylene-propylene rubber (EPR) and another 0.5 mm thick "easy-to-tear" semiconductive material based on ethylene-vinyl 31 332 / B acetate (EVA) copolymer with the addition of soot to the vein of the cable, consisting of several wires and having a diameter of about 14 mm, to form a core of the cable with an overall diameter of about 22 mm, prepared differently different test pieces of the partially completed cable.

Low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polypropylene (PP) modified with ethylene-propylene rubber (EPR) in a weight ratio of PP / EPR 70 were used as polymerization materials to form the expanded coating layer. / 30 and a mixture of low density polyethylene (LDPE) and vulcanized natural rubber, crushed to a fine powder with a particle size in the range of 300 to 600 mm in a weight ratio of LDPE / rubber 70/30 (or PE / rubber powders); said materials are designated by letters A to E for the following description, respectively, and some of their characteristic parameters are listed in Table 1a below.

Table 1a

Used material Trade name, manufacturer Modulus of elasticity (MPa) A Low density PE (LDPE) Riblene FL 30 ;, Enichem 260 B High density PE (HDPE) Union Carbide, DGDK 3364 1000 C Polypropylene (PP) PF 814, Montell 1600 D PP / EPR mixture Fina-Pro 3660S, Finna-Pro 1250 E PE / powdered rubber Riblene FL 30, Enichem

The expansion of the polymerization materials was carried out by chemical means, alternatively using two mutually different blowing agents.

332 / B devices (CE marked), the identification of which is given in Table 1b below:

Table 1b

Blowing agent Commercial designation; manufacturer CE1 azodicarboamide Sarmapor PO; Sarma CE2 Carboxylic acid with bicarbonate Hydrocerol CF 70; Boehringer Ingelheim

The expandable polymerization materials and blowing agents (in the proportions illustrated in Table 2 below) were introduced into a single screw spindle extruder cylinder having the following dimensions: length 80 mm diameter 25 mm (manufactured by Bandera); wherein the screw extruder consists of an extruder head and a cylinder and is provided with a conveying screw spindle whose thread has a depth of 9.6 mm in the end zone of the cylinder. The extruder assembly comprises an internal die adapted to ensure smooth and continuous passage of the cable core to be coated (which generally has a diameter about 0.5 mm greater than the diameter of the cable wire being subjected to), an external die whose diameter is it is chosen to be about 2 mm smaller than the diameter of the cable coated with the expanded polymeric material coating; in this extrusion arrangement, the material to be processed expands not in the interior of the extruder head or in the interior of the extruder cylinder, but at the extruder head outlet. The rate of passage through the coating of the subjected cable core (or progressive extrusion speed) is set as a function of the desired thickness of the expanded material (see Table 2). A cooling system (containing cold water) is provided at a distance of about 500 mm from the extrusion head to complete the expansion and cool the expanded material to ambient temperature. The cable thus formed is then wound onto a drum coil.

332 / B

The composition of the polymerization material to be treated and the blowing agent used and the extrusion conditions (speed, temperature) vary as required and are shown in Table 2 below.

Table 2 Expandable material mixture and extrusion processing conditions

cable sample No .: Polymer + type a bloating content means Speed overload press (Rpm). (1) Temperature Pretl. press (° C) Progress speed Reprinted. (M / min.) 1 A + 2% CE1 6.4 165 3 2 A + 2% CE1 11.8 190-180 2 3 A + 2% CE1 5.5 190-180 2 4 A + 2% CE1 6.8 190-180 2 5 A + 2% CE1 6.4 165 1.5 6 A + 0.8% CE2 5.7 225-200 2 7 C + 0.8% CE2 3.7 200 2 8 C + 0.8% CE2 6.3 200 2 9 E + 0.8% CE2 4.9 225-200 1.8 10 B + 1.2% CE2 8.2 225-200 2 11 D + 0.8% CE2 8 225-200 2

( ¹ ) Extruder temperature refers to cylinder temperature and extruder head temperature.

In the case where only one value is given in Table 2, these temperatures are identical.

In the initial zone of the extruder cylinder, the temperature is about 150 ° C.

332 / B

For cable according to sample no. 1, the expansion of the polymerization material did not occur, probably because the extruder temperature was too low (165 ° C) and the like for the cable of sample no. 5 only limited expansion (only 5%).

The cable coated with the expanded polymeric material was then coated with a commonly used outer protective sheath made of medium density polyethylene MDPE (Trade Mark CE 90, manufactured by Materie Plastische Bresciane) of varying thickness (see Table 3) using commonly known and standard technology techniques. to form appropriate cable samples having the above defined and precisely defined characteristic parameters as shown in Table 3 below; wherein the cable according to sample no. 1, in which the polymerization material has not been subjected to an expanding treatment, is in this case taken as a comparative sample of the coating layer of the unexpanded polymerization material. In addition, Table 3 further provides, for comparison purposes, the characteristics of a cable provided only with an outer sheath that does not contain any filler material (see cable according to Sample No. 0).

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Table 3 Characteristic parameters of the coating layer

cable vz. No .: Degree of expansion filling material (%) Fill thickness have got. (Mm) External thickness Tire (mm) 0 - 0 3 1 0 1 3 2 31 4.3 3 3 61 1 3 4 48 2.5 3 5 5 3 3 6 35 2 2 7 52 2 2 8 29 3 2.2 9 23 2.5 2 10 78 4 2 11 82 4 2

In a similar manner to the process just described above, a further 6 samples were prepared using a coating layer of expanded polymer material having a flexural modulus of about 600 MPa and consisting of ethylene-propylene rubber (EPR) modified polypropylene (PPR) in an amount of about 30% by weight, the characteristics of which are given in Table 4 (these samples are designated as samples 12 to 17 in Table 4); In addition, Table 4 below shows two comparative samples of cables coated with an expanded polymeric material but without an outer sheath (see cables of Samples 16a and 17a).

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Table 4 Characteristic parameters of the coating layer

cable vz. No .: Degree of expansion filling material (%) Fill thickness have got. (Mm) External thickness Tire (mm) 12 71 3 1.9 13 22 2 2 14 167 3 1.8 15 124 2 2 16 56 2 2 16 56 2 - 17 84 2 2 17 84 2 -

Example 2

Testing of impact strength, resp. impact resistance

For the purpose of measuring, detecting and evaluating the impact strength of the cables prepared according to Example 1, these cables were subjected to impact strength test tests followed by impact damage evaluation. The resulting impact effects were evaluated both by visual inspection of the cable and by measuring the change in adhesion strength of the layer of semiconducting material at the impact site. The impact strength test was conducted on the basis of the facts given in French Technical Standard HN 33-S-52, according to which the cable is subjected to an impact energy of about 72 Joules (J) obtained by dropping a 27 kg weight on the cable from a height 27 cm. For the purposes of the test according to the present invention, this impact energy was achieved by dropping a weight of 8 kg

332 / B from a height of 97 cm. The impact acting on the end of this weight is provided with a V-shaped rounded head (radius of curvature 1 mm). For the purposes of the present invention, the impact strength evaluation was performed after the impact of the cable by a single impact. For samples no. 6-12, the cable was subjected to two independent shocks in a test, with the second impact site being 100 mm from the first impact site.

The tear-off adhesion strength measurements were also carried out in accordance with the facts given in French Technical Standard HN 33-S-52, on which the measurement of the force to be applied in order to achieve separation of the outer layer of semiconducting material from the insulating material layers. Peak values are measured by continuously measuring this force at the respective locations of the cable where shock is applied. For each test sample, the "positive" peak values of the specified force corresponding to the increase in force (relative to their mean) required to separate the two layers of cable sheathing and the "negative" peak values (corresponding to the reduced size) of this force relative to the averaged values). The difference between the maximum _(Fmax) and minimum (F _m j _{n) of} the force peaks measured then maximum variation in the peel strength at the point of impact.

Changes in the peel adhesion strength at the impact site are in this state calculated by determining the ratio between the above difference (F _max - F _m j) and the average peel adhesion strength for the measured cable (F <>), expressed as a percentage, of the following relationship:

The percentage change = 100 ° (F max - F _m in) / F o

The magnitude of the variation of said force, measured at the impact site, compared to the average value of this force, measured over the entire length of the cable, is an indication of the degree of impact protection that will be provided by providing a coating layer of the expanded polymerization material. Generally speaking, variations in tear force of up to 20-25% are considered acceptable for the stated purposes. Appropriate values

332 / B tear strength deviations for cables according to samples no. 0 to no. 17a are shown in Table 5.

Table 5 Percentage deviation of peel adhesion strength

Cable vz. no. First test Second test 0 62 78 1 40 - 2 18 - 3 27 - 4 13 - 5 21 - 6 17 23 7 9 12 8 4 5 9 19 15 10 9.8 12.5 11 4.3 2.5 12 7 14 13 16 17 14 14 12 15 10 10 16 16 18 16 30 55 17 15.5 13 17 116 103

332 / B

As can be seen from Table 3, for sample no. 1 (without expanding the polymeric material), the percent change in peel strength is extremely high; this indicates that the unexpanded polymerization material exhibits a significantly lower impact absorbing capacity than a layer made of the same material that is treated by expansion (see Sample 3 with a coating layer expanded to 61%). Sample no. 3 shows a change in peel strength of slightly above 25% of the cut-off value; whereas the limited impact resistance achieved in the embodiment of this sample can be attributed, when compared to the thickness of other samples of 2 to 3 mm, in particular a thickness of only 1 mm, of the coating layer of the expanded polymer material.

Sample no. 5, provided with a 3 mm thick layer of expanded polymerization material, exhibits a high peel adhesion strength value, which is attributed to a low degree of expansion of the polymerization material (5%), indicating that the formation of a low level expanded polymerization material coating. The expansion means providing limited impact strength. Sample no. 4, although it has a thickness of expanded polymerization material less than that of sample no. 5 (2.5 mm vs 3 mm), but shows a higher impact strength, with a change in adhesion strength at a tear strength of 1% compared to a 21% deviation for Sample No. 5. 5, which demonstrates the fact that a higher degree of expansion results in a higher impact strength.

Comparison of sample no. 13 with sample no. 15, it is noticeable how increasing the degree of expansion of the polymeric material (from 22 to 124%) for one and the same thickness of the expanded material coating and the outer protective sheath affects the increase in the impact strength of the sheathing as a whole. 16 to 17% to 10%). This tendency is confirmed by comparing sample no. 16 with sample no. 17. 16a and no. 17a (cable without

332 / B outer protective jacket) with relevant samples no. 16 and no. 17, it can be seen how the provision of the cable with an outer protective sheath promotes an increase in impact resistance as a function of increasing the degree of expansion of the coating layer material.

Example 3

Comparative impact test of a cable according to the invention with a metal reinforcement cable

In this case, the cable according to sample no. 10 together with a standard metal-reinforced power distribution cable, which has been tested to determine the impact strength or impact resistance of their sheathing.

The reinforced cable has the same vein structure as the cable according to sample no. 10 (or a multi-wire conductor with a diameter of about 14 mm coated with a 0.5 mm thick layer of semiconducting material, an insulating layer made of a 3 mm thick ethylene-propylene rubber (EPR) mixture, and another "easy-to-tear" layer of 0.5 mm thick semiconducting material based on ethylene vinyl acetate (EVA) copolymer with the addition of carbon black to form a cable vein with an overall diameter of about 22 mm). Said cable wire is coated, in the direction from the surface of the wire to the outer circumference of the cable:

(a) a layer of rubber-based filling material with a thickness of about 0,6 mm;

(b) a sheath of polyvinyl chloride (PVC) having a thickness of about 0,6 mm;

(c) two reinforcing strips of armor steel, each of which has a thickness of about 0,5 mm, and

(d) an outer sheath of medium density polyethylene (MDPE) having a thickness of about 2 mm.

For the purpose of conducting the comparative test, a dynamic drop test device (CEAST, model 6758) was used. Two sets of test tests were performed using a drop weight

332 / B weighing 11 kg lowered from a height of 50 cm (first set - impact energy about 54 Joules) and from a height of 20 cm (second set - impact energy about 21 Joules); the drop weight is provided at the working end with a hemispherical impact head with a spherical radius of about 10 mm.

The resulting cable deformations found during the test (for falling heights of 50 cm and 20 cm) are shown in FIG. 4 and 5 of the accompanying drawings, in which the cable according to the present invention is marked with a), while the standardly used metal reinforced cable is marked with b).

In order to evaluate the damage to the cable structure caused by the impact, the amount of cable vein deformation was measured. In fact, the greater the deformation of the coating structure of the layers of the semiconducting - insulating semiconducting material, the greater the likelihood that these deformations will cause electrical failure of the insulating properties of the cable. The observed and measured results are shown in Table 6.

Table 6

Percentage reduction of semiconductive layer thickness after impact

standard reinforced cable Cable according to the invention vz. no. 10 Impact toughness test performed at falling altitude weight 50 cm 41% 26.5% Impact toughness test performed at falling altitude weight 20 cm 4.4% 2.9%

332 / B

The results of Table 6 clearly show that the cable of the present invention exhibits a comparable and even substantially better impact resistance than the standard metal-reinforced cable.

332 / B

Claims (28)

1. A power distribution cable comprising: (a) an electrical conductor, b) at least one layer of compact insulating sheath arranged around said conductor; and c) a coating layer formed of expanded polymerization material disposed around said compact insulating sheath, characterized in that said polymerization material exhibits predetermined mechanical strength characteristics and a predetermined degree of expansion to provide corresponding impact resistance properties of the cable. A cable according to claim 1, characterized in that the expanded polymeric material coating layer is formed of a polymeric material which, prior to expansion, exhibits a flexural modulus at ambient temperature measured according to ASTM D790 of at least 200 MPa. The cable according to claim 1, characterized in that said flexural modulus of the polymerization material ranges from 400 MPa to 1800 MPa. The cable of claim 1, wherein said flexural modulus of the polymeric material is in the range of 600 MPa to 1500 MPa. The cable of claim 1, wherein said degree of expansion of the polymerization material is in the range of about 20% to about 3000%. 31,332 / B The cable of claim 1, wherein said degree of expansion of the polymerization material is in the range of about 30% to about 500%. The cable of claim 1, wherein said degree of expansion of the polymerization material is in the range of about 50% to about 200%. The cable according to any one of the preceding claims, characterized in that said coating layer of the expanded polymerization material has a thickness of 0.5 mm. A cable according to any one of the preceding claims 1 to 7, characterized in that said coating layer of expanded polymerization material has a thickness ranging from 1 mm to 6 mm. Cable according to any one of claims 1 to 7, characterized in that said coating layer of expanded polymerization material has a thickness ranging from 2 mm to 4 mm. The cable of claim 1, wherein said expanded polymerization material is selected from the group of polymerization materials including polyethylene (PE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE). ) and linear low density polyethylene (LLDPE), polypropylene (PP), ethylene-propylene rubber (EPR), ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (poly) ethylene-vinyl acetate (EVA) copolymer, polystyrene, ethylene-acrylate copolymer, ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate (EEA) copolymer, ethylene-butyl acrylate (EBA) copolymer, styrene-ethylene / alpha-olefin copolymer ABS) resins, halogenated polymers, polyvinyl chloride (PVC), polyurethane (PUR), polyamides, aromatic polyesters, polyethylene terephthalate (PET) or poly Lybutylene terephthalate (PBT) and their copolymers or mechanical mixtures. 31,332 / B Cable according to claim 1, characterized in that said expanded polymerization material is an olefin polymer or a copolymer based on polyethylene (PE) and / or polypropylene (PP). The cable of claim 1, wherein said expanded polymerization material is an olefin polymer or a copolymer based on polyethylene (PE) and / or polypropylene (PP) modified with ethylene-propylene rubber (EPR). Cable according to claim 13, characterized in that said expanded polymerization material is polypropylene (PP) modified with ethylene-propylene rubber (EPR) in a PP / EPR weight ratio ranging from 90/10 to 50/50. 15. The cable of claim 14 wherein said PP / EPR weight ratio is in the range of 85/15 to 60/40. The cable according to claim 14, wherein said PP / EPR weight ratio is 70/30. The cable according to claim 12, wherein said olefin polymer or copolymer based on polyethylene (PE) and / or polypropylene (PP) further comprises a predetermined amount of vulcanized rubber in powder form. A cable according to claim 17, wherein said predetermined amount of vulcanized rubber in powder form is in the range of 10 to 60% by weight, based on the content of polymerization material. The cable according to any one of the preceding claims 1 to 18, wherein the cable is further provided with an outer protective polymeric sheath. 31,332 / B 20. The cable of claim 19, wherein said outer protective polymerization sheath is arranged in contact with a coating layer of the expanded polymerization material. 21. A cable according to claim 19 or 20 wherein said outer protective polymerization sheath has a thickness greater than 0.5 mm. The cable according to claim 19 or 20, characterized in that said outer protective polymerization sheath has a thickness ranging from 1 to 5 mm. 23. A method of providing an impact resistance of a power distribution cable, comprising coating the cable with a coating layer formed from an expanded polymerization material. 24. The method of claim 23, further comprising coating the coating layer of the expanded polymerization material with an outer protective polymerization sheath. Use of the expanded polymerization material to provide impact resistance of the power distribution cable. 26. A method for assessing the resistance of a power distribution cable comprising at least one impact insulating coating layer, comprising: a) measuring and determining the average peel strength of said layer of insulating coating, b) subjecting the cable to impact energy of a predetermined size; c) measuring the peel strength of said insulating coating layer at the impact site, and 31,332 / B (d) a control which of the differences in mean peel strength and peel strength at the impact site is less than a predetermined value. Method according to claim 26, characterized in that the measurement of the peel strength is performed between the insulating coating layer and the outer layer of the semiconducting coating. The method of claim 27, wherein the difference between the average peel strength and the peel strength measured at the impact site is less than 25%.