SK286369B6 - 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.

Description

Technical field

The present invention relates to a cable sheath adapted to protect the cable against unintended 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 of 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 commercially available cables, such as power distribution cables for conducting or distributing medium and low voltage, to protect such cables against unwanted damage caused by unforeseen or accidental impacts, a metal armor adapted to withstand such impacts is usually 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 said 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 reinforcement in the cable sheath significantly increases the overall weight of the cable, and, in addition, poses environmental pollution problems, since if the cable needs to be replaced, the cable becomes very difficult to dispose of.

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 positioned between the insulating coating and the outer protective sheath. This shock-resistant coating layer is formed from an unexpanded polymerization 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 plastic outer 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 cable provided with the intermediate layer. In fact, 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 which is either expandable or which includes hollow glass bodies.

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 devices and machines having a 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 providing resistance to mechanical loads of the static type (i.e., those loads that occur during its winding through the pulley), the main feature of such a cable being 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 cable sheath 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; at frequencies of 10 to 100 MHz), satellite coaxial cables (at frequencies up to 2 GHz) or coaxial cables for computing (at frequencies). above 1 MHz); wherein, for comparison, standardly used telephone cables usually transmit electrical signals at frequencies of about 800 Hz.

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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 is that, when compared to unexpanded polymerization materials, the expanded materials generally have a lower dielectric constant (K), which, as the degree of expansion of the polymerization material increases, is proportional to the dielectric constant air (K = 1).

For example, U.S. Pat. No. 4,711,811 discloses an electrical signal cable equipped 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 (0.013 to 0.254 mm thick). As described in this specification, 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 the mechanical properties of the insulating layer, mainly providing the necessary basic compressive strength for the case where the two insulated conductors are twisted together to form a so-called " "DT DT".

EP patent no. 0 442 346 discloses an electrical signal transmission cable with an insulating layer based on expanded polymerization material positioned directly on the conductor surface; wherein the expanded polymerization material has 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 essentially correspond to the characteristic values of the compressive strength which such a material must necessarily have 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 electrical signal cable equipped with an insulating coating of expanded polymeric 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 U.S. Pat. No. 4,711,811), but at the same time, the rate of transmission of the electrical signal is 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 perluret (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 specification of the patent application, the use of the thus formed insulating layer of the expanded polymeric material with closed pores allows to maintain a high transmission rate of electrical signals. In addition, the insulating layer in this patent application is defined and characterized as having a resistance to compression, although this is not supported by any data concerning the 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 documents cited, 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. Nevertheless, there are several types of expanded materials which are characterized as 'squeeze-resistant' since they not only ensure the high transmission rate of electrical signals, but also achieve sufficient resistance to the pressure forces that typically occur during the interlocking and twisting the two expanded insulating layers of the coated conductors together; in this case, it is also of a substantially 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, have characteristics suitable for carrying relatively light pressure loads (such as pressure loads generated during on the other hand, no mention is made in any of the applicant's known patent documents or other publications that the coating layer or sheath of expanded polymerization material would be able to ensure that any type of impact strength, respectively, is achieved. 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 patent application WO no. 93/15512.

SUMMARY OF THE INVENTION

The Applicant has now found that by inserting into a structural configuration a power distribution cable of a suitable coating layer of expanded polymerization material of adequate thickness and flexural modulus, preferably located in contact with the outer sheath or outer polymerization coating layer, it is possible to create a cable having high impact strength as a result, it makes it possible to omit the use of the protective metal reinforcement from the cable structure. In particular, the Applicant has found that the polymerization material must be chosen to have 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" means that includes all types of dynamic loads of a certain energy size, capable of causing significant structural damage to standard non-routed cables, while having the structure of standardly used reinforced cables load 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.

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 of substantially the same coating layer made of a material based on the same polymer but not expanded .

A cable equipped with a sheath of this type has a number of different advantages over standardly used metal reinforcement cables, such as easier cable manufacturing, reduced weight and size of the finished cable, and less environmental hazards associated with replacing the cable when its working life has been exhausted 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 expanded polymerization material, said polymerization material having predetermined mechanical strength characteristics and a predetermined degree of expansion in order to provide corresponding 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, has a flexural modulus at ambient temperature, measured according to ASTM D790, of at least 200 MPa, preferably in the range of 400 to 1,500 The flexural modulus of between 600 and 1300 MPa is particularly preferred for the above purposes.

According to a further preferred embodiment of the present invention said polymerization material has an expansion degree of from about 20 to about 3000%, preferably from about 30 to about 500%, with an expansion degree of from about 20% to about 500% being particularly preferred. 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 said 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 (MDPL), high density polyethylene (HDPE), and linear low density polyethylene (HDPE). LLDPE); polypropylene (PP), ethylene-propylene rubber (EPR), ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (polyisobutene), ethylene-vinyl polyethylene (polyvinyl copolymer) -acrylate copolymer, ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate (EEA) copolymer, ethylene-butyl acrylate (EBA) copolymer, ethylene / alpha-olefin copolymer, acrylonitrile-butadiene-styrene poly (ABS), nylon poly (ABS) ), polyurethane (PUR), polyamides, aromatic polyesters, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) and their copolymers or mechanical mixtures.

According to a further 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 PP / EPR weight ratio ranging from 90 / 10 to 50/50, preferably in the range 85/15 to 60/40, with a particularly preferred modified composition being a 70/30 weight ratio composition.

According to a further preferred embodiment of the present invention, said olefinic polymer or copolymer based on polyethylene (PE) and / or polypropylene (PP) further comprises a predetermined amount of vulcanized rubber in powder form, preferably from 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 ranging from 0.5 mm. 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

(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 with respect 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" used in the present invention for the purpose of the description means the expansion of the polymerization material as determined by the following relation:

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

d ₀ represents the density of the unprocessed polymerization material (or, in other words, a polymer with a structure having substantially no void pore volume); and d represents 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 refers to a polymerization material having a pore volume structure (or, in other words, a certain space not occupied by a polymer but in a polymer enclosed by gas or air). 10% of the total volume of the polymerization material.

The term " adhesive peel strength " used in the present invention for the purpose of describing 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.

The insulating layer of power distribution cables typically has a dielectric constant (or permittivity) (K) with a value greater than 2. In addition, unlike electric signal transmission cables where the "electric gradient" parameter is of no importance, power 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 insulation layer of the power distribution cables (for example, the reported pore volume), which could represent a potential source of local variations in dielectric strength and the resulting reduction in insulation resistance, ensures the 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 medium and low voltage lines it 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 substantially no 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 purposes of 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 for the purpose of the description, and the term "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 familiar to those skilled in the art. It will be appreciated by the prior art that said expanded train layer can be usefully used in a structural arrangement 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 the sake of simplicity, for the purposes of the present description, this partial structure will be referred to as a "cable vein". The three cable cores thus arranged are coupled together and the star cross-sectional spaces formed therebetween are filled with filling material 9 (which is usually elastomeric compounds, polypropylene fiber materials and the like) for the purpose of achieving 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; wherein the 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 screen 5, a train layer 10 of expanded polymerization material and an outer protective polymerization sheath 6. The cable shown in FIG. 3, the thin circular layer 10a shown in FIG. 2 of the three-core cable, since the cable core has a circular cross-section, coincides with the coating layer 10 of the expanded polymerization material.

For quite obvious reasons, only a few of the many possible embodiments of a 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 sheath. 6. 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 joined together, the cable core cores are approximately circular in cross-section without requiring any filler material; and the conductor core of the cable thus formed, consisting of individual cable cores interconnected in one piece, is then, by means of extrusion, provided with a coating layer 10 of an impact resistant expanded polymerization 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.

Other possible solutions will be well known to those skilled in the art, and will be able to perform the most suitable solutions by evaluating the above purposes, for example on the basis of the set-up costs, 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 may 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, 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), in particular ethylene-propylene copolymer (EPM) or ethylene-propylene-diene terpolymer (EPDM), natural rubber, butyl rubber (polyisobutene), ethylene-polyvinyl acetate (EVA) ethylene-acrylate copolymer, especially ethylene-methyl acrylate (EMA) copolymer, ethylene-ethylacrylate (EEA) copolymer, ethylene-butyl acrylate (EBA) copolymer, ethylene / alpha-olefin copolymer, acrylonitrile-polyvinyl chloride (ABS) polystyrene (ABS) styrene (styrene) ), 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, in particular polymers and copolymers based on polyethylene (PE) and / or polypropylene (PP) in admixture with ethylene-propylene rubbers (EPR), are used for this purpose. Advantageously, 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 composition is a 70/30 weight ratio composition.

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 tire production may be used as vulcanized rubber. The percentage of rubber in powder form contained in the blend, based on the content of the expandable polymerization material, can 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 have a stiffness that, once expanded, ensures that a certain, a predetermined value of the impact resistance necessary to protect the internal structure of the cable (or, in other words, the insulating layer and layers of semiconducting material that may be present in the structure) against possible damage that may occur as a result occurring or unforeseen impacts. In particular, this material will have a sufficiently high capacity to absorb the impact energy so that it can be used. the transmission of this impact energy to the underlying insulating layer occurred only to an extent that ensures that the insulating properties of the underlying layer layers outside the predetermined value will not be affected or modified. The reason for this measure is, as will be explained and documented in the following description, the Applicant's finding that, for a cable subjected to impact, the differences between the average peel strength and the peel strength measured at the impact site were measured. and relating to the peeling off of the underlying insulating coating layers; wherein said peel adhesion 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 semiconducting material, it has been found, based on the evaluation, that the coating layer of the expanded polymerization material provides sufficient protection of 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 group of polymerization materials is particularly suitable and useful for this purpose, such material having a flexural modulus at ambient temperature, measured on the basis of ASTM D790, greater than prior to processing by expansion. as 200 MPa, and preferably at least 400 MPa. In another aspect, regarding the 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 having 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 have a flexural modulus at ambient temperature of between 400 and 1800 MPa prior to their processing by expansion, with a preferred polymerization 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 the specific material or may result from mixing two or more materials with different flexural modulus, which are mixed in a ratio that will result in the desired stiffness of the final material. For example, the stiffness of a polypropylene (PP) having a flexural modulus of greater than 1500 MPa can be reduced accordingly by suitably selecting 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 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, the 'degree of expansion of the polymerisation material' is determined on the basis of the following formula:

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

d _o represents the density of the unprocessed polymerization material; and _{e e} represents the relative density of the polymerization material measured in the expanded state.

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 having a high degree of expansion, mainly because by this measure it is possible to limit the necessary amount of polymerization material used for this purpose, with distinct advantages in terms of both economical costs 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 has 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 the applicant's finding that as the degree of expansion of the polymerization material increases, the flexural modulus of the material decreases substantially following approximately the following relationship:

E ₂ / E, = (p ₂ / _Pl ) ² , where:

E ₂ represents the flexural modulus of the polymeric material, measured at a higher degree of expansion,

L! represents the flexural modulus of the polymeric material measured at a lower degree of expansion, p ₂ represents the relative density of the polymeric material measured at a higher degree of expansion, and

P! 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 from 25% to 100% results in a reduction in the flexural modulus of this material by approximately half. Polymerization materials having a high flexural modulus can therefore be expanded to a higher degree than polymeric materials that have low flexural modulus values without causing this to adversely affect the ability of the coating to withstand and withstand the impact of 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, because of the desirable use of a limited, at least possible amount of coating polymerization material and the consequent reduction of installation costs and, on the other hand, reduction of the dimensional size of the finished product, the thickness of the expanded material must be the minimum possible thickness necessary to provide the desired impact strength. Especially in the case of cables of the medium-voltage type, it has been found that the thickness of the expanded coating layer of about 2 mm is usually capable of providing sufficient resistance to the commonly occurring 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 ranging from about 1 mm to about 6 mm, with a particularly preferred thickness value ranging from 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 coating layer thickness of the expanded polymerization material ranging from 2 to 4 mm. Such a relationship, respectively. functional verticality can be expressed by the following relation:

V ° d _c > N, where

V represents the volume of expanded polymerization material per meter of cable length (m ³ / m), and this 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 polymeric coating layer 10 of FIG. 3, showing a single core cable, d _e representing the relative density of the polymerization material measured in the expanded state (kg / m ³ ),

N is the result of the product of the two declared 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 modulus of elasticity of bending between 800 and 1 000 MPa,

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

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 (2R ^{1 0} S + S ² ), where

R; represents the inner radius of the thin circular layer 10a.

Parameter d ₆ is a function of the degree of expansion of the polymerization material according to the above formula:

G = (d ₀ / d _e -1) ⁰ 100.

Based on the reported 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 having different flexural moduli (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 PP / EPR mixture 70/30 (Mf is about 800 MPa),

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

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

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.

These results indicate that, for the best, resp. In order to optimally utilize 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 boundaries of the intervals defined for the N variant variants (or given values of 400, 800 and 1000 MPa) may in fact even be greater than its calculated values. based on 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 can 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 a predetermined temperature and pressure condition, or by physical means, by direct injection of high pressure gas into the transfer cylinder.

Examples of suitable &quot; hearing aids &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 into 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 from which the outer protective sheath is formed typically has a flexural modulus ranging from about 400 MPa to about 1200 MPa, and preferably from about 600 MPa to about 1000 MPa.

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, in particular in the range of 1 to 5 mm and preferably in the range of 2 to 4 mm.

The construction of the impact-resistant power distribution cable of the present invention will be further described 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 a cable provided with a coating layer 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 means of extrusion processing technology. The cable cores are then coupled to one another, and the star cross-sectional areas thus formed are filled with a commonly used filler material (e.g., a mixture of elastomers, polypropylene fiber material, and the like), typically using a filler coating technology to one another, by pressing the cable until a partially finished circular cross-sectional cable is formed. 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 of the die will preferably be slightly smaller than the final diameter of the cable provided with the expanded polymer material coating to allow the polymerization material to expand at the die exit.

The Applicant has further found that under identical extrusion conditions (such as the screw spindle rotational speed, progressive extrusion speed, extrusion head die diameter, and the like), one of the variables is the extrusion temperature, which has 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 especially 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 reducing or increasing the cooling rate of the polymerization material from which the respective coating 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 already mentioned, the Applicant has found that it is possible to quantitatively determine the effects of impact on the cable sheath by measuring the peel strength of the sheathing of the cable sheath at which they were between the average peel strength and the peel strength measured at the point of application. the differences observed. 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 mutual differences) can advantageously be measured between the outer a layer of semiconducting material and an insulating layer.

The Applicant has further found that the effects of the mainly combined effect of several shocks simultaneously, which may be exposed to a particular cable, in particular a metal-reinforced power cable for medium-voltage conducting, can be determined using an 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).

Likewise, the peel-off strength of the respective coating layer can be determined using the facts given in the French technical standard HN 33-S-52 mentioned above, on the basis of which the force to be applied in order to separate the outer layer from the semi- conductive 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, the outer cable 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 impact site, 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 strength of up to 20 to 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 outer protective polymerization sheath in the structural design of the cable can be appropriately selected depending on the desired degree of impact resistance This is to be ensured in order to adequately protect the downstream cable structure and furthermore depending on the characteristics of the specific material used to form the insulating layer and / or the semiconductive layer, for example the hardness of the material, its density and the like.

As can be seen from the detailed description, the power distribution cable of the present invention is particularly suitable for replacing the standardly used metal reinforced power distribution cables, mainly because of the advantageous properties of the coating layer of the expanded polymerization material compared to the 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 in which it is desired to use cables having increased impact strength characteristics. The impact-resistant power distribution cable of the present invention can be used to replace, in particular, the previously used power distribution cables containing no metal reinforcement in all such applications where it would be much more convenient 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 acetate (EVA) copolymer with the addition of soot to the vein of the cable, consisting of several wire conductors and having about 14 mm, to form a core of the cable with an overall diameter of about 22 mm, prepared different test specimens 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 the following Table 1a.

Table la

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 said polymerization materials was carried out by chemical means, alternatively using two mutually different blowing agents (labeled CE), the identification of which is given in the following Table 1b:

Table 1b

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

Polymerization materials for expanding and blowing agents (in the proportions shown in Table 2 below) were introduced into a single screw spindle extruder with the following dimensions: length 80 mm - diameter 25 mm (manufactured by Bandera); the screw extruder consisting of an extruder head and a cylinder and is provided with a conveyor screw having a depth of 9.6 mm in the end zone of the cylinder. The extruder assembly consists of an internal die, adapted to ensure a smooth and continuous passage of the cable core to be coated (which generally has a diameter about 0.5 mm larger than the diameter of the subjected cable core coating), 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.

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 and content of blowing agent Speed overload press (rpm) (1) Temp. press (° C) Progressive speed pushes through. (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

(') The extruder temperature refers to the cylinder temperature and the 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.

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 same reasons, with the cable of sample no. 5 only limited expansion (only 5%).

The cable provided with a coating layer of expanded polymer material was then coated with a commonly used outer sheath made of medium density polyethylene MDPE (Trade Mark CE 90, manufactured by Materie Plastischc Bresciane) of varying thickness (see Table 3) using commonly known and standard techniques. to form appropriate cable samples having 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 taken in this case 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 equipped only with an outer protective sheath that does not contain any padding material (see cable of Sample No. 0).

Table 3 Characteristic parameters of the coating layer

cable vz. No .: Expansion rate of filler material (%) Thickness of filling mat. (Mm) Outer sheath thickness (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, 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 provided with a coating layer of expanded polymeric material but without an outer sheath (20 cables according to Samples 16a and 17a).

Table 4 Characteristic parameters of the coating layer

cable vz. No .: Expansion rate of filler material (%) Thickness of filling mat. (Mm) Outer sheath thickness (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 in accordance with Example 1, impact tests were carried out on these cables, followed by impact damage. The resulting impact effects were evaluated both by visual inspection of the cable and by measuring the change in adhesion strength of 30 layers 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 test according to the present invention, this impact energy was achieved by dropping a weight of 8 kg from a height of 97 cm. The impact effect causing the end of this weight is equipped with a bevelled head with a rounded V-shaped edge (radius of curvature 1 mm).

SK 286369-6

The evaluation of the impact strength for the purposes of the present invention was carried out 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, for which a force measurement is necessary for this purpose in order to achieve separation of the outer layer of semiconductive material from the insulating material layers. Peak values are measured by continuously measuring this force at the respective locations of the cable in which the shock is applied. For each test specimen, 'positive' peak values of the specified force, corresponding to the increase in force (relative to their average) required to separate the two layers of cable sheathing and 'negative' peak values (corresponding to reduced size) of this force with respect to the aforementioned average values). The difference between the maximum (F _max ) and the minimum (F _min ) peak value of said force then represents the maximum change in the peel strength at the impact site.

Changes in the tear strength at the impact site are in this state calculated by determining the ratio between the reported difference (F _max - F _nlin ) and the average tear strength for the measured cable (F <>), expressed as a percentage, as follows:

Percentage change = 100 ⁰ (F, _nax - F ^) / F o.

The magnitude of the variation of said force, measured at the impact site, compared to the average value of the 20 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. Corresponding values of the peel strength of the cables according to the 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

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 fact indicates that the unexpanded polymerization material certainly has a lower impact absorbing capacity than a layer made of the same material that is expanded (see Sample 3 with a coating layer expanded to 61%). Sample no. 3 has a change in adhesive peel strength, the value of which is 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 35 thicknesses of other samples of 2-3 mm, in particular a thickness of only 1 mm, of the coating layer of the expanded polymer material.

Sample no. 5, provided with an expanded polymerization material layer of 3 mm thickness, has a high tear-off adhesion value, which is attributed to a low degree of expansion of the 15 polymerization material (5%), indicating that the formation of an expanded polymerization material layer of low The degree of expansion is to provide limited impact strength. Sample no. 4, although it has a thickness of the expanded polymerization material less than the thickness of Sample no. 5 (2.5 mm vs 3 mm), but has a higher impact strength, with a change in adhesion strength at a tear strength of 1% compared to a 21% deviation for Sample # 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 can be seen how increasing the degree of expansion of the polymerization material (from 22 to 124%) for one and the same thickness of the expanded material coating and the outer sheath affects an 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 outer sheath) with relevant samples no. 16 and no. 17, it can be seen how providing the cable with an outer sheath promotes an increase in impact resistance as a function of increasing the degree of expansion of the coating 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 structural design 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 layer of semiconductive material, an insulating layer made of a 3 mm thick ethylene-propylene rubber (EPR) mixture, and another "easy-to-tear" layer of semiconductor material 0.5 mm thick 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 a comparative test, a dynamic drop test device (CEAST, model 6758) was used. Two test kits were performed using a 11 kg drop weight 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 equipped 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 assess the impact of the cable structure caused by the impact, the amount of cable vein deformation was measured. In fact, five, 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 carried out at a falling height of 50 cm 41% 26.5% Impact toughness test carried out at a falling height of 20 cm 4.4% 2.9%

The results shown in Table 6 clearly show that the cable according to the present invention has a comparable and even substantially better impact resistance than the standard metal-reinforced cable.

Claims (30)

Patent claims by providing a modulus of elasticity in polymer bending by providing a modulus of elasticity in polymer bending and by providing a degree of polymer expansion and by providing a degree of polymer expansion CLAIMS 1. A cable comprising an inner structure and a coating layer surrounding the inner structure, characterized in that the coating layer is formed from an expanded polymer material having an expansion degree of from about 20% to about 3000% and a flexural modulus at ambient temperature prior to expansion. polymer, at least 200 MPa. A cable according to claim 1, characterized in that it consists of a power distribution cable comprising an internal structure formed by an electrical conductor and at least one layer of a compact insulating sheath arranged around the conductor. The cable according to claim 1, characterized in that the material is in the range of 400 MPa to 1800 MPa. The cable according to claim 1, characterized in that the material is in the range from 600 MPa to 1500 MPa. The cable of claim 1, wherein the cable is in the range of about 30% to about 500%. The cable of claim 1, wherein the cable is in the range of about 50% to about 200%. A cable according to any one of claims 1 to 6, characterized in that the coating layer of the expanded polymer material has a thickness of 0.5 mm. Cable according to any one of the preceding claims 1 to 6, characterized in that the coating layer of the expanded polymer material has a thickness ranging from 1 mm to 6 mm. The cable according to any one of the preceding claims 1 to 6, characterized in that the coating layer of the expanded polymer material has a thickness ranging from 2 mm to 4 mm. Cable according to claim 1, characterized in that the expanded polymer material is selected from the group of polymeric materials comprising 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 acetate, butyl rubber, poly (ethylene) (EVA) copolymer, polystyrene, ethylene-acrylate copolymer, ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate (EEA) copolymer, ethylene-butyl acrylate (EBA) copolymer, ethylene / alpha-styrene-butadiene acrylonitrile, , halogenated polymers, polyvinyl chloride (PVC), polyurethane (PUR), polyamides, aromatic polyesters, polyethylene terephthalate (PET) or polybutylene terephtha (PBT) and copolymers or mechanical mixtures thereof. Cable according to claim 1, characterized in that the expanded polymer material is an olefin polymer or a copolymer based on polyethylene (PE) and / or polypropylene (PP). A cable according to claim 1, characterized in that the expanded polymer 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 12, characterized in that the expanded polymer material is polypropylene (PP) modified with ethylene-propylene rubber (EPR) in a PP / EPR weight ratio ranging from 90/10 to 50/50. Cable according to claim 13, characterized by a range from 85/15 to 60/40. Cable according to claim 13, characterized in The cable according to claim 12, characterized by a polyethylene (PE) and / or polypropylene (PP) base further comprising a predetermined amount of vulcanized rubber in powder form. A cable according to claim 16, wherein the predetermined amount of vulcanized rubber in powder form is in the range of 10 to 60% by weight, based on the polymer material content. A cable according to any one of claims 1 to 17, characterized in that the cable is further provided with an outer protective polymer sheath. A cable according to claim 18, wherein the outer protective polymer sheath is arranged in contact with the train layer of the expanded polymer material. The cable according to claim 18 or 19, wherein the sheath has a thickness greater than 0.5 mm. The cable of claim 18 or 19, wherein the sheath has a thickness ranging from 1 to 5 mm. by the fact that the weight ratio PP / EPR is in the range weight ratio PP / EPR is 70/30. that the olefin polymer or copolymer is characterized in that the external protective polymer is an external protective polymer17 22. A method of providing an impact resistance of an internal structure of a power distribution cable, comprising the step of locating a coating comprising expanded polymer material around the internal structure. The method of claim 22, wherein the expanded polymer material has an degree of expansion of from about 20% to about 3000% and a flexural modulus at ambient temperature, prior to polymer expansion, of at least 200 MPa. 24. The method of claim 22, wherein the cable is a power distribution cable. 25. The method of claim 22, comprising coating the expanded polymer material coating layer with an outer protective polymeric sheath. 26. The method of claim 22, wherein the internal structure comprises at least two adjacent coating layers having a predetermined average relative surface tension, flexural modulus and degree of expansion of the polymer material such that when the cable is subjected to an impact with an energy of about 72 J, the difference between a given average surface tension and a surface tension measured at the impact site is less than about 25%. Use of an expanded polymer material to provide impact resistance of a power distribution cable. 28. 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 (d) control which of the differences in mean peel strength and peel strength at the impact site is less than the predetermined value. The method of claim 28, wherein the tear strength measurement is performed between the insulating coating layer and the outer semiconducting coating layer. The method of claim 29, wherein the difference between the average peel strength and the peel strength measured at the impact site is less than 25%. 5 drawings