CA1216036A - Low voltage cable with two layers of polyvinyl chloride insulation - Google Patents
Low voltage cable with two layers of polyvinyl chloride insulationInfo
- Publication number
- CA1216036A CA1216036A CA000450191A CA450191A CA1216036A CA 1216036 A CA1216036 A CA 1216036A CA 000450191 A CA000450191 A CA 000450191A CA 450191 A CA450191 A CA 450191A CA 1216036 A CA1216036 A CA 1216036A
- Authority
- CA
- Canada
- Prior art keywords
- parts
- weight
- polyvinyl chloride
- layer
- cross
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229920000915 polyvinyl chloride Polymers 0.000 title claims abstract description 13
- 239000004800 polyvinyl chloride Substances 0.000 title claims abstract description 12
- 238000009413 insulation Methods 0.000 title claims abstract description 11
- 150000001875 compounds Chemical class 0.000 claims abstract description 46
- 239000004020 conductor Substances 0.000 claims abstract description 33
- 239000012764 mineral filler Substances 0.000 claims abstract description 20
- 230000005855 radiation Effects 0.000 claims abstract description 17
- 229920001169 thermoplastic Polymers 0.000 claims abstract description 11
- 239000004416 thermosoftening plastic Substances 0.000 claims abstract description 11
- 238000004132 cross linking Methods 0.000 claims description 10
- MYRTYDVEIRVNKP-UHFFFAOYSA-N 1,2-Divinylbenzene Chemical compound C=CC1=CC=CC=C1C=C MYRTYDVEIRVNKP-UHFFFAOYSA-N 0.000 claims description 6
- 239000003431 cross linking reagent Substances 0.000 claims description 6
- 150000002148 esters Chemical class 0.000 claims description 6
- OKKRPWIIYQTPQF-UHFFFAOYSA-N Trimethylolpropane trimethacrylate Chemical group CC(=C)C(=O)OCC(CC)(COC(=O)C(C)=C)COC(=O)C(C)=C OKKRPWIIYQTPQF-UHFFFAOYSA-N 0.000 claims description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- 239000000654 additive Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910000019 calcium carbonate Inorganic materials 0.000 description 4
- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 description 4
- 239000001095 magnesium carbonate Substances 0.000 description 4
- 229910000021 magnesium carbonate Inorganic materials 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000945 filler Substances 0.000 description 3
- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 description 3
- 230000001902 propagating effect Effects 0.000 description 3
- KEQXNNJHMWSZHK-UHFFFAOYSA-L 1,3,2,4$l^{2}-dioxathiaplumbetane 2,2-dioxide Chemical compound [Pb+2].[O-]S([O-])(=O)=O KEQXNNJHMWSZHK-UHFFFAOYSA-L 0.000 description 2
- 239000004135 Bone phosphate Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 239000003963 antioxidant agent Substances 0.000 description 2
- 235000006708 antioxidants Nutrition 0.000 description 2
- -1 for example Chemical class 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000005995 Aluminium silicate Substances 0.000 description 1
- 241000905957 Channa melasoma Species 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- MQIUGAXCHLFZKX-UHFFFAOYSA-N Di-n-octyl phthalate Natural products CCCCCCCCOC(=O)C1=CC=CC=C1C(=O)OCCCCCCCC MQIUGAXCHLFZKX-UHFFFAOYSA-N 0.000 description 1
- 235000021355 Stearic acid Nutrition 0.000 description 1
- 235000012211 aluminium silicate Nutrition 0.000 description 1
- 230000003078 antioxidant effect Effects 0.000 description 1
- BJQHLKABXJIVAM-UHFFFAOYSA-N bis(2-ethylhexyl) phthalate Chemical compound CCCCC(CC)COC(=O)C1=CC=CC=C1C(=O)OCC(CC)CCCC BJQHLKABXJIVAM-UHFFFAOYSA-N 0.000 description 1
- IISBACLAFKSPIT-UHFFFAOYSA-N bisphenol A Chemical compound C=1C=C(O)C=CC=1C(C)(C)C1=CC=C(O)C=C1 IISBACLAFKSPIT-UHFFFAOYSA-N 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- CZNNQWMLAHSKRA-NVAFIHLTSA-N dTDP 1-ester with 2,6-dideoxy-L-erythro-hexopyranos-3-ulose Chemical compound C1C(=O)[C@@H](O)[C@H](C)O[C@@H]1OP(O)(=O)OP(O)(=O)OC[C@@H]1[C@@H](O)C[C@H](N2C(NC(=O)C(C)=C2)=O)O1 CZNNQWMLAHSKRA-NVAFIHLTSA-N 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 239000008029 phthalate plasticizer Substances 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 239000008117 stearic acid Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
- H01B7/292—Protection against damage caused by extremes of temperature or by flame using material resistant to heat
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
- H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/02—Disposition of insulation
- H01B7/0275—Disposition of insulation comprising one or more extruded layers of insulation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
- H01B7/295—Protection against damage caused by extremes of temperature or by flame using material resistant to flame
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Insulated Conductors (AREA)
- Organic Insulating Materials (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A low voltage electric cable having a conductor with insulation having improved resistance to deformation by heat and to fire propagation, the insulation comprising two layers made of a polyvinyl chloride based compound. One layer, the inner layer, contacts the conductor, is thermoplastic and contains a mineral filler or fillers in an amount at least equal to 60 parts by weight per 100 parts by weight of the polyvinyl chloride, and the outer layer, which surrounds and contacts the inner layer is radiation cross-linked and may contain up to 16 parts by weight of a mineral filler or fillers per 100 parts by weight of polyvinyl chloride.
A low voltage electric cable having a conductor with insulation having improved resistance to deformation by heat and to fire propagation, the insulation comprising two layers made of a polyvinyl chloride based compound. One layer, the inner layer, contacts the conductor, is thermoplastic and contains a mineral filler or fillers in an amount at least equal to 60 parts by weight per 100 parts by weight of the polyvinyl chloride, and the outer layer, which surrounds and contacts the inner layer is radiation cross-linked and may contain up to 16 parts by weight of a mineral filler or fillers per 100 parts by weight of polyvinyl chloride.
Description
3~
I.OW VOLTAGE CABLE WITH TWO LAYERS OF POLYVINYL CHLORID~ INSUL~TI~N
The present invention relates to a low voltage cable which is resistant to heat, and which does not propagate fire and particularly, to an electric cable which is heat-resistant, which does not propagate fire and which is included in the cate-gory of low-voltage cables which are known as "building wires".
The majority of cables which come into said category have conductor coverings formed from a polyvinvl chloride (P.V.C.) based compound. One drawback of these compounds, is that they are thermoplastic and hence, incapable of providing any stabi-lity of form during the action of heat which might be applied tothe conductor covering.
This is a drawback which could cause serious con-sequences. For understanding this fact, it is sufficient to con-sider the risks for the user himself, when, for example, there is overheating resulting from a bad connection of the cables to an energy consuming device, a softening of the conductor coverings results.
Moreover, in the known cables, where the conductor covering is formed from a thermoplastic compound based on P.V.C., it is impossible to have either any significant fire non-propa-gating properties or any optimization of the mechanical and in-sulating properties.
In fact, in order to have such fire non-propating properties, it would be necessary to introduce into the compound itself, very high quanti-ties of mineral fillers, and this is unacceptable since it would reduce the mechanical and insulating properties of the compound and hence, of the conductor covering, to unacceptabie values.
There have been proposed cables having a conductor covering made of a mixture again based on P.V.C., but P-~98 cross-linked through radiation. Ifl in this manner, it was possible to solve the problem of providing stability of form to the conductor coverings of the cable, under the action of heat, the other problems, of not propagating fires and of the o~timization of the mechanical and insulating properties of the cable were not solved.
In fact, for the cross-linking of the compounds forming the conductor covering of a cable, it was necessary to add to the compound an additive selected from divinylbenzene, polyallyl dimethacrylate esters and polyallyl trimethacrylate esters, such as, for example, trimethylolpropane-trimethacrylate.
These additives interact with the mineral fillers of the compound as well as with the P.V.C. during the cross-linking of this latter, and hence, when the quantity of mineral fillers present in the compound is increased, the quantities of the ad-ditives increase.
The cross-linking additives of the p~V.C. have the draw-back of reducing the insulating properties of the compound if, as inevitably occurs in practice, they are still present after the cross-linking of the P.V..~v, and therefore, they reduce the di-electric properties of the conductor coverings of the cable formed out of such a compound.
Accordingly, to limit the quantity of the cross-linking agents present in the compound, the quantity of mineral. fillers is limited, and hence, cables have the property of not propagating fire are not obtained.
One object of the present invention is to provide low-voltage cables in the "building wires" category having a P.V.C.
base covering for the conductor which has an optimum resistance to heat and to propagation of fire in addition to an optimum of both the dielectric characteristics and the mechanical characteristics.
~Z~S03~
In accordance with the present inventlon, low voltage cable comprising a conductor with an extruded covering sur-rounding it has the covering constituted by a primary covering, which is in contact with the conductor, and by a secondary covering surroundina the primary covering. Said coverings are made from a P.V.C. based compound and are characterized by the fact that the primary covering is of a thermoplastic compound, based on P.V.C., containing mineral fillers in quantities which are greater than 60 parts by weight with respect to 100 parts by weight of P.V.C., and that said secondary covering is a compound based on P.V.C. cross-linked through radiation.
Other objects and advantages of the present invention will be apparent from the following detailed description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawing, the single flgure of which is a perspective view, with portions thereof removed,of a length of the cable of the invention.
As can be seen in the drawing, the cable comprises a conductor 1, constituted either by a single wire or by several layed-up wires, which is surrounded by a covering comprising an extruded primary covering 2 which is covered by a secondary covering 3, said coverings being joined together.
The primary covering 2 is made of a thermoplastic compound based on P.V.C., and the secondary coverlng 3 is made of a compound based on P.V.CO cross-linked through radiation and hence, is made of a compound which, prior to being cross-linked, contains the necessary additive for cross-linking. The general characteristics which the P.V.C. based compounds must possess, for forming the primary covering 2 and the secondary covering 3 of a cable according to the present invention,will be set forth hereinafter.
~2~L~iO36 The compounds based on P.V.C., for the formation of the primary covering 2, are thermoplastics and contain mineral fillers in such quantities as to endow it with the dielectric properties and properties of resistance against fire propagation which are desired~ In particular, the mineral fillers in the compound in question, such as calcium carbonate, magnesium carbonate, calcined kaolin and mixtures thereof, are present in an amount which is greater than 60 parts by weight with respect to 100 parts by weight of P.V.C. Preferably, the quantity of mineral fillers present in the compound, is between 60 and 120 parts by weight, with respect to 100 parts by weight of P.V.C. so as to obtain an optimization of the dielectric characteristics for the insulation 2 and a resistance against fire propagation.
For the formation of the secondary covering 3, the compounds based on P.V.C. contain a cross-linking agent selected from among the divinylbenzene, polyallyl-dimethacrylate esters and polyallyl-trimethacrylate esters, such as, for example, the trimethylolpropane-trimethacrylate, in an amount not exceeding 16 parts by weight, with respect to 100 parts by weight o~ P.V.C.
and may contain mineral fillers in quantities not exceeding 10 parts by weight with respect to 100 parts by weight of P.V.C.
Moreover, the mineral fillers, for the compound forming the secondary covering 3, are constituted by calcium carbonate and by magnesium carbonate, and preferably, are of the type obtained through precipitation, i.e. having a high specific surface area. Even mixtures of calcium carbonate and magnesium carbonate, of the types obtained through precipitation, can be utilized as fillers in the compound for the formation of the secondary covering 3.
Set forth hereinafter, solely by way of example, are preferred compositions of a compound for the covering 2 and of a V~
compound for the covering 3 of a cable according to the in-vention.
A preferred compound for the formation of the primary covering 2 of a low voltage cable, according to the invention, may have the following composition, the components being ex-pressed in parts by weight POLYVINYL CHLORIDE (P.V.C.)........... l00 p. bv w.
PHTALATE PLASTICIZER (example:
dioctylphithalate or disodecyl-phthalate~............................ .50 p. by w.
MINE~AL FILLERS (comprises by a mixture of equal parts of calcium carbonate and magnesium carbonate).... .80 p. by w.
TRIBASIC LEAD SULPHATE................ ..5 p. by w.
LUBRICANT (for example: stearic acid or lead-basic stearate)............... .Ø5 p. by w.
ANTI-OXIDANTS (for example: triphenol-A)0.2 p. by w.
A compound for forming the secondary coverin~ 3, of a low voltage cable according to the invention, may have the following composition, the components being expressed in parts by weight.
POLYVINYL CHLORIDE(P.V.C.)............ .l00 p. by w.
PHTHALATE PLASTICIZER (example:
dioctylphthalate or disodecylphthalate 35 p. by w.
MINERAL FILLERS....................... ...5 p. by w.
TRIBASIC LEAD SULPHATE........... ~.................. ...5 p. by w.
LEAD BASIC STEARATE..................... ............ ..Ø5 p. by w.
BISPHENOL-A (anti-oxidant).............. ............ ..Ø2 p. by w.
(cross-linking a~ent)................... ............ ...8 p. by w.
With the particular compounds given above, a low voltage cable, according to the present invention, has been manu~actured, by extruding over the conductor 1, simultaneously or with suc-cessive operations, the primary covering 2 and *he compound for forming, after the cross-linking through radiation, the secondary covering 3.
In particular, the conductor 1 was formed by thirty wires, each one having a diameter of 0.Z5 mm, layed-up together and having a cross~sectional area of 1.5 mm2.
The primary covering 2 had a thickness of 0.7 mm, and the superimposed layer, which, after the cross-linking through radiation, will constitute the secondary covering 3, had a thickness of 0.1 mm and, in any case, the thickness of the covering 3 should not exceed 15~ of the thickness of the primary covering 2.
The conductor l,covered by the extruded layers de-scribed above, underwent radiation treatment by causing it to pass through an apparatus, of a known type, which furnished it with a dose of radiation equal to 10 M rad, so as to cross-link the secondary covering 3 of the cable 1. The speed of pro-duction of the cable was of the same order of magnitude as that of the known cables having a conductor covering constituted entirely of a P.V.C. based thermoplastic compound.
With a cable according to the present invention, ex-perimental tests were carried out, according to the provisions of CEI 20-11, for the purpose of determining, in the conductor covering composed of the assembly of the primary and the secondary coverings:
a) the values of the insulation constant Ki at 20C
expressed in M Qper Km;
b) the resistance to thermo-compression, defined by the crushing force to be exerted upon a flat sample of conductor covering, heated to a temperature of 120C, ~216iO3~
for reducing the thickness to a value equal to 60%
of the initial thickness; and c) the mechanical characteristics of the rupture load and the elongation at rupture.
Moreover, with a cable according to the invention, experimental tests were carried out for determining the capacity of maintaining a sta~ility of its ~orm, at high temperatures, by suspending a cable-length inside a chamber which is heated -to 200C.
In addition, tests were carried out, according to the provisions of CEI 20-22, for checking the resistance against fire propagation. Tests were also carried out for determining the characteristics of the cable according to our invention with respect to the resistance to cable slipping inside a duct. For this latter test, a cable length of 50 m, made according to the invention, was introduced into a rigid P.V.C. hose, shaped in the manner indicated below and having an inner diameter of 30 mm and a length of 10 m.
The shaped hose has a configuration constituted by a broken-line of equal segments and having curved corners, formed by the assembly of hose sections of an S-shape and of an L-shape.
On the extremity of the cable, facing one extremity of the hose, there was applied the force necessary for extracting the cable from the hose, by causing it to slide within it, and the minimum force was determined.
Moreover, for showing the improved properties of a cable according to the invention, due to the simultaneous presence of a primary and a secondary cover having the above-stated characteristics, for comparison purposes in the above-described experimental tests, a conductor having a covering ~ Z~ 36 formed with only the P.V.C. based thermoplastic compound, used for the primary covering 2 of a cable according to our invention, was made.
Identical experimental tests were carried out for a known cable having a conductor covering entirely formed of a P.V.C. based thermoplastic compound and for another known cable having a conductor covering entirely formed out of a P.V.C.
based compound cross-linked through radiation.
The cable for comparison purposes, described previously, and both of the known cables that underwent the e~perimental tests, had conductors identical to the conductor of the cable ac-cording to our invention, and a thickness for the conductor covering that was equal to the sum total of the thicknesses of the primary and the secondary coverings of the cable according to our invention. The results of these experimental tests are set forth in the following table:
CABLE OF CABLE FOR KNOWN CABLE KNOr1N RADIATION
THE C~ARISON WITH THE~- CROSS-LD~
D~NTIO~l PUR OSES PIASTIC SHEATH SH~ C~E
Ki at 20C 2000 M Q 2000 M Q 1000 M Q750 M Q
per Km. per Km. per Km. per Km.
RESISTANCE
TO THERMO-COMERESSION 9N 5N 4.5N 4.5N
RUP~mE LOAD
UNDER TR~.CTION 18 N/mm2 8 N/mm2 15 N/mm2 15N/mm2 ELONGATION AT
RU~ 150% 100% 130% 130 STABILITY OF
XNSULATION-FORM
XNSIDE FURNAOE does not does not does not AT 200C. melt down melt down melts down melt down FIRE-PROPAGATION
BY STAI~RD does not does not spreadsspreads OEI 20/22 TEST spread fire spread fire fire fire DUCT SLIPPING
where Ki is the insulation dielectric constant and N is the force in Newtons.
12~6(~3i~
After examining the results of the tests carried out, the following conclusions can be reached.
First and foremost, it can be seen that the presence of a secondary P.V.C. based covering cross-linked through radiation, did not bring about any reduction in the insulation dielectric constant Ki of a cable, according to the present in-vention, which could have been expected on observin~ the values of the insulation dielectric cons-tant of a known cable having a conductor covering entirely formed out of a P.V.C. based com-pound, cross-linked through radiation.
It is true that, in the cable according to the present invention, the thickness of the secondary covering is extremely reduced, but it would be expected that even such a reduced thick-ness would have had an influence on the value of the insulation dielectric constant of the conductor covering of the cable.
Th~ fact that the dielectric constant has not been reduced, signifies that the secondary-covering 3 of a cable ac-cording to this invention, has, surprisingly, optimum insulation properties in spite of its being formed out of a P.V.C. based compound, cross-linked through radiation.
Moreover, from examining the results of the experi-mental tests that are given in the table, it is found that, with a cable according to the invention, all the previously stated proposed aims are achieved.
Finally, with a cable according to the invention, there can be obtained a good production speed in spite of the need for cross-linking of the secondary covering 3 through radiation.
In fact, the manufacturing speed of a cable according to our invention, expressed in meter/minute, is in the same order of magnitude as that of the "known" cables having a con-ductor covering made of a P.V.C. based thermoplastic compound _g_ ~Z~6~
whereas the manufacturing speed of -the known cables, havin~ a conductor covering of a P.V.C. based compound cross-linked through radiation, is generally slower by 30%.
The reason for this is not due solely to the fact that the thickness of the secondary covering 3, of a cable according to our invention, is small. It is also due to the fact that mineral fillers are absent or are present in minute quantities which allows for keeping to the minimum the quantity of cross-linking agents for the P.V.C. and hence, also permits keeping the dose of radiation energy which has to be furnished, to the minimum.
Although preferred embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention.
I.OW VOLTAGE CABLE WITH TWO LAYERS OF POLYVINYL CHLORID~ INSUL~TI~N
The present invention relates to a low voltage cable which is resistant to heat, and which does not propagate fire and particularly, to an electric cable which is heat-resistant, which does not propagate fire and which is included in the cate-gory of low-voltage cables which are known as "building wires".
The majority of cables which come into said category have conductor coverings formed from a polyvinvl chloride (P.V.C.) based compound. One drawback of these compounds, is that they are thermoplastic and hence, incapable of providing any stabi-lity of form during the action of heat which might be applied tothe conductor covering.
This is a drawback which could cause serious con-sequences. For understanding this fact, it is sufficient to con-sider the risks for the user himself, when, for example, there is overheating resulting from a bad connection of the cables to an energy consuming device, a softening of the conductor coverings results.
Moreover, in the known cables, where the conductor covering is formed from a thermoplastic compound based on P.V.C., it is impossible to have either any significant fire non-propa-gating properties or any optimization of the mechanical and in-sulating properties.
In fact, in order to have such fire non-propating properties, it would be necessary to introduce into the compound itself, very high quanti-ties of mineral fillers, and this is unacceptable since it would reduce the mechanical and insulating properties of the compound and hence, of the conductor covering, to unacceptabie values.
There have been proposed cables having a conductor covering made of a mixture again based on P.V.C., but P-~98 cross-linked through radiation. Ifl in this manner, it was possible to solve the problem of providing stability of form to the conductor coverings of the cable, under the action of heat, the other problems, of not propagating fires and of the o~timization of the mechanical and insulating properties of the cable were not solved.
In fact, for the cross-linking of the compounds forming the conductor covering of a cable, it was necessary to add to the compound an additive selected from divinylbenzene, polyallyl dimethacrylate esters and polyallyl trimethacrylate esters, such as, for example, trimethylolpropane-trimethacrylate.
These additives interact with the mineral fillers of the compound as well as with the P.V.C. during the cross-linking of this latter, and hence, when the quantity of mineral fillers present in the compound is increased, the quantities of the ad-ditives increase.
The cross-linking additives of the p~V.C. have the draw-back of reducing the insulating properties of the compound if, as inevitably occurs in practice, they are still present after the cross-linking of the P.V..~v, and therefore, they reduce the di-electric properties of the conductor coverings of the cable formed out of such a compound.
Accordingly, to limit the quantity of the cross-linking agents present in the compound, the quantity of mineral. fillers is limited, and hence, cables have the property of not propagating fire are not obtained.
One object of the present invention is to provide low-voltage cables in the "building wires" category having a P.V.C.
base covering for the conductor which has an optimum resistance to heat and to propagation of fire in addition to an optimum of both the dielectric characteristics and the mechanical characteristics.
~Z~S03~
In accordance with the present inventlon, low voltage cable comprising a conductor with an extruded covering sur-rounding it has the covering constituted by a primary covering, which is in contact with the conductor, and by a secondary covering surroundina the primary covering. Said coverings are made from a P.V.C. based compound and are characterized by the fact that the primary covering is of a thermoplastic compound, based on P.V.C., containing mineral fillers in quantities which are greater than 60 parts by weight with respect to 100 parts by weight of P.V.C., and that said secondary covering is a compound based on P.V.C. cross-linked through radiation.
Other objects and advantages of the present invention will be apparent from the following detailed description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawing, the single flgure of which is a perspective view, with portions thereof removed,of a length of the cable of the invention.
As can be seen in the drawing, the cable comprises a conductor 1, constituted either by a single wire or by several layed-up wires, which is surrounded by a covering comprising an extruded primary covering 2 which is covered by a secondary covering 3, said coverings being joined together.
The primary covering 2 is made of a thermoplastic compound based on P.V.C., and the secondary coverlng 3 is made of a compound based on P.V.CO cross-linked through radiation and hence, is made of a compound which, prior to being cross-linked, contains the necessary additive for cross-linking. The general characteristics which the P.V.C. based compounds must possess, for forming the primary covering 2 and the secondary covering 3 of a cable according to the present invention,will be set forth hereinafter.
~2~L~iO36 The compounds based on P.V.C., for the formation of the primary covering 2, are thermoplastics and contain mineral fillers in such quantities as to endow it with the dielectric properties and properties of resistance against fire propagation which are desired~ In particular, the mineral fillers in the compound in question, such as calcium carbonate, magnesium carbonate, calcined kaolin and mixtures thereof, are present in an amount which is greater than 60 parts by weight with respect to 100 parts by weight of P.V.C. Preferably, the quantity of mineral fillers present in the compound, is between 60 and 120 parts by weight, with respect to 100 parts by weight of P.V.C. so as to obtain an optimization of the dielectric characteristics for the insulation 2 and a resistance against fire propagation.
For the formation of the secondary covering 3, the compounds based on P.V.C. contain a cross-linking agent selected from among the divinylbenzene, polyallyl-dimethacrylate esters and polyallyl-trimethacrylate esters, such as, for example, the trimethylolpropane-trimethacrylate, in an amount not exceeding 16 parts by weight, with respect to 100 parts by weight o~ P.V.C.
and may contain mineral fillers in quantities not exceeding 10 parts by weight with respect to 100 parts by weight of P.V.C.
Moreover, the mineral fillers, for the compound forming the secondary covering 3, are constituted by calcium carbonate and by magnesium carbonate, and preferably, are of the type obtained through precipitation, i.e. having a high specific surface area. Even mixtures of calcium carbonate and magnesium carbonate, of the types obtained through precipitation, can be utilized as fillers in the compound for the formation of the secondary covering 3.
Set forth hereinafter, solely by way of example, are preferred compositions of a compound for the covering 2 and of a V~
compound for the covering 3 of a cable according to the in-vention.
A preferred compound for the formation of the primary covering 2 of a low voltage cable, according to the invention, may have the following composition, the components being ex-pressed in parts by weight POLYVINYL CHLORIDE (P.V.C.)........... l00 p. bv w.
PHTALATE PLASTICIZER (example:
dioctylphithalate or disodecyl-phthalate~............................ .50 p. by w.
MINE~AL FILLERS (comprises by a mixture of equal parts of calcium carbonate and magnesium carbonate).... .80 p. by w.
TRIBASIC LEAD SULPHATE................ ..5 p. by w.
LUBRICANT (for example: stearic acid or lead-basic stearate)............... .Ø5 p. by w.
ANTI-OXIDANTS (for example: triphenol-A)0.2 p. by w.
A compound for forming the secondary coverin~ 3, of a low voltage cable according to the invention, may have the following composition, the components being expressed in parts by weight.
POLYVINYL CHLORIDE(P.V.C.)............ .l00 p. by w.
PHTHALATE PLASTICIZER (example:
dioctylphthalate or disodecylphthalate 35 p. by w.
MINERAL FILLERS....................... ...5 p. by w.
TRIBASIC LEAD SULPHATE........... ~.................. ...5 p. by w.
LEAD BASIC STEARATE..................... ............ ..Ø5 p. by w.
BISPHENOL-A (anti-oxidant).............. ............ ..Ø2 p. by w.
(cross-linking a~ent)................... ............ ...8 p. by w.
With the particular compounds given above, a low voltage cable, according to the present invention, has been manu~actured, by extruding over the conductor 1, simultaneously or with suc-cessive operations, the primary covering 2 and *he compound for forming, after the cross-linking through radiation, the secondary covering 3.
In particular, the conductor 1 was formed by thirty wires, each one having a diameter of 0.Z5 mm, layed-up together and having a cross~sectional area of 1.5 mm2.
The primary covering 2 had a thickness of 0.7 mm, and the superimposed layer, which, after the cross-linking through radiation, will constitute the secondary covering 3, had a thickness of 0.1 mm and, in any case, the thickness of the covering 3 should not exceed 15~ of the thickness of the primary covering 2.
The conductor l,covered by the extruded layers de-scribed above, underwent radiation treatment by causing it to pass through an apparatus, of a known type, which furnished it with a dose of radiation equal to 10 M rad, so as to cross-link the secondary covering 3 of the cable 1. The speed of pro-duction of the cable was of the same order of magnitude as that of the known cables having a conductor covering constituted entirely of a P.V.C. based thermoplastic compound.
With a cable according to the present invention, ex-perimental tests were carried out, according to the provisions of CEI 20-11, for the purpose of determining, in the conductor covering composed of the assembly of the primary and the secondary coverings:
a) the values of the insulation constant Ki at 20C
expressed in M Qper Km;
b) the resistance to thermo-compression, defined by the crushing force to be exerted upon a flat sample of conductor covering, heated to a temperature of 120C, ~216iO3~
for reducing the thickness to a value equal to 60%
of the initial thickness; and c) the mechanical characteristics of the rupture load and the elongation at rupture.
Moreover, with a cable according to the invention, experimental tests were carried out for determining the capacity of maintaining a sta~ility of its ~orm, at high temperatures, by suspending a cable-length inside a chamber which is heated -to 200C.
In addition, tests were carried out, according to the provisions of CEI 20-22, for checking the resistance against fire propagation. Tests were also carried out for determining the characteristics of the cable according to our invention with respect to the resistance to cable slipping inside a duct. For this latter test, a cable length of 50 m, made according to the invention, was introduced into a rigid P.V.C. hose, shaped in the manner indicated below and having an inner diameter of 30 mm and a length of 10 m.
The shaped hose has a configuration constituted by a broken-line of equal segments and having curved corners, formed by the assembly of hose sections of an S-shape and of an L-shape.
On the extremity of the cable, facing one extremity of the hose, there was applied the force necessary for extracting the cable from the hose, by causing it to slide within it, and the minimum force was determined.
Moreover, for showing the improved properties of a cable according to the invention, due to the simultaneous presence of a primary and a secondary cover having the above-stated characteristics, for comparison purposes in the above-described experimental tests, a conductor having a covering ~ Z~ 36 formed with only the P.V.C. based thermoplastic compound, used for the primary covering 2 of a cable according to our invention, was made.
Identical experimental tests were carried out for a known cable having a conductor covering entirely formed of a P.V.C. based thermoplastic compound and for another known cable having a conductor covering entirely formed out of a P.V.C.
based compound cross-linked through radiation.
The cable for comparison purposes, described previously, and both of the known cables that underwent the e~perimental tests, had conductors identical to the conductor of the cable ac-cording to our invention, and a thickness for the conductor covering that was equal to the sum total of the thicknesses of the primary and the secondary coverings of the cable according to our invention. The results of these experimental tests are set forth in the following table:
CABLE OF CABLE FOR KNOWN CABLE KNOr1N RADIATION
THE C~ARISON WITH THE~- CROSS-LD~
D~NTIO~l PUR OSES PIASTIC SHEATH SH~ C~E
Ki at 20C 2000 M Q 2000 M Q 1000 M Q750 M Q
per Km. per Km. per Km. per Km.
RESISTANCE
TO THERMO-COMERESSION 9N 5N 4.5N 4.5N
RUP~mE LOAD
UNDER TR~.CTION 18 N/mm2 8 N/mm2 15 N/mm2 15N/mm2 ELONGATION AT
RU~ 150% 100% 130% 130 STABILITY OF
XNSULATION-FORM
XNSIDE FURNAOE does not does not does not AT 200C. melt down melt down melts down melt down FIRE-PROPAGATION
BY STAI~RD does not does not spreadsspreads OEI 20/22 TEST spread fire spread fire fire fire DUCT SLIPPING
where Ki is the insulation dielectric constant and N is the force in Newtons.
12~6(~3i~
After examining the results of the tests carried out, the following conclusions can be reached.
First and foremost, it can be seen that the presence of a secondary P.V.C. based covering cross-linked through radiation, did not bring about any reduction in the insulation dielectric constant Ki of a cable, according to the present in-vention, which could have been expected on observin~ the values of the insulation dielectric cons-tant of a known cable having a conductor covering entirely formed out of a P.V.C. based com-pound, cross-linked through radiation.
It is true that, in the cable according to the present invention, the thickness of the secondary covering is extremely reduced, but it would be expected that even such a reduced thick-ness would have had an influence on the value of the insulation dielectric constant of the conductor covering of the cable.
Th~ fact that the dielectric constant has not been reduced, signifies that the secondary-covering 3 of a cable ac-cording to this invention, has, surprisingly, optimum insulation properties in spite of its being formed out of a P.V.C. based compound, cross-linked through radiation.
Moreover, from examining the results of the experi-mental tests that are given in the table, it is found that, with a cable according to the invention, all the previously stated proposed aims are achieved.
Finally, with a cable according to the invention, there can be obtained a good production speed in spite of the need for cross-linking of the secondary covering 3 through radiation.
In fact, the manufacturing speed of a cable according to our invention, expressed in meter/minute, is in the same order of magnitude as that of the "known" cables having a con-ductor covering made of a P.V.C. based thermoplastic compound _g_ ~Z~6~
whereas the manufacturing speed of -the known cables, havin~ a conductor covering of a P.V.C. based compound cross-linked through radiation, is generally slower by 30%.
The reason for this is not due solely to the fact that the thickness of the secondary covering 3, of a cable according to our invention, is small. It is also due to the fact that mineral fillers are absent or are present in minute quantities which allows for keeping to the minimum the quantity of cross-linking agents for the P.V.C. and hence, also permits keeping the dose of radiation energy which has to be furnished, to the minimum.
Although preferred embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention.
Claims (6)
- THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
l. A low voltage cable comprising a conductor with insulation extruded thereover, said insulating comprising:
a first layer of a thermoplastic, polyvinyl chloride based compound surrounding and in contact with said conductor, said compound containing at least one mineral filler which constitutes at least 60 parts by weight for each 100 parts by weight of polyvinyl chloride; and a second layer of a radiation cross-linked polyvinyl chloride based compound surrounding said first layer, the radial thickness of said second layer not exceeding 15 percent of the radial thickness of said first layer and said compound of said second layer, prior to cross-linking, containing cross-linking agents not exceeding 16 parts by weight for each 100 parts by weight of polyvinyl chloride. - 2. A low voltage cable as set forth in claim 1 wherein the mineral fillers are present in the first layer in an amount in the range from about 60 parts to 120 parts by weight for each 100 parts by weight of polyvinyl chloride.
- 3. A low voltage cable as set forth in claim 2 wherein the compound of said second layer contains not more than 10 parts by weight of mineral fillers for each 100 parts by weight of polyvinyl chloride.
- 4. A low voltage cable as set forth in claim 3 wherein the mineral fillers are precipitated mineral fillers.
- 5. A low voltage cable as set forth in claim 1 wherein the compound of said second layer has been cross-linked with a cross-linking agent selected from the group consisting of divinylbenzene, polyallyl dimethacrylate esters and pollyallyl trimethacrylate esters.
- 6. A low voltage cable as set forth in claim 5 wherein the cross-linking agent is trimethylolpropane-trimethacrylate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT20282A/83 | 1983-03-23 | ||
| IT8320282A IT1160761B (en) | 1983-03-25 | 1983-03-25 | LOW VOLTAGE CABLE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1216036A true CA1216036A (en) | 1986-12-30 |
Family
ID=11165409
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000450191A Expired CA1216036A (en) | 1983-03-23 | 1984-03-22 | Low voltage cable with two layers of polyvinyl chloride insulation |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0120382A1 (en) |
| JP (1) | JPS59181414A (en) |
| AU (1) | AU2481084A (en) |
| BR (1) | BR8401320A (en) |
| CA (1) | CA1216036A (en) |
| DK (1) | DK107984A (en) |
| ES (1) | ES278543Y (en) |
| IT (1) | IT1160761B (en) |
| NO (1) | NO841149L (en) |
| NZ (1) | NZ207294A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2280634A (en) * | 1993-08-03 | 1995-02-08 | T & N Technology Ltd | Flame retardant coatings for insulated electrical wires |
| SE506975C2 (en) * | 1996-07-12 | 1998-03-09 | Electrolux Ab | Electrical cable with inner and outer insulating casing layers around conductors |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4008368A (en) * | 1968-05-11 | 1977-02-15 | Kabel-Und Metallwerke Gutehoffnungshutte Aktiengesellschaft | Electrical conductor having inhibited polymer compositions |
| CA1093652A (en) * | 1978-07-11 | 1981-01-13 | John A. Checkland | Electrical conductor with an outer layer of crosslinked insulation |
| JPS6026452B2 (en) * | 1978-09-18 | 1985-06-24 | 株式会社アマダメトレツクス | How to detect machine operating status |
| JPS55121211A (en) * | 1979-03-12 | 1980-09-18 | Toray Industries | Vinyl chloride insulated wire |
| IT1165372B (en) * | 1979-11-15 | 1987-04-22 | Pirelli | LOW VOLTAGE CABLE WITH PERFECTED INSULATOR |
-
1983
- 1983-03-25 IT IT8320282A patent/IT1160761B/en active
-
1984
- 1984-02-22 AU AU24810/84A patent/AU2481084A/en not_active Abandoned
- 1984-02-27 DK DK107984A patent/DK107984A/en not_active Application Discontinuation
- 1984-02-27 NZ NZ207294A patent/NZ207294A/en unknown
- 1984-03-10 EP EP84102638A patent/EP0120382A1/en not_active Withdrawn
- 1984-03-22 CA CA000450191A patent/CA1216036A/en not_active Expired
- 1984-03-22 BR BR8401320A patent/BR8401320A/en not_active IP Right Cessation
- 1984-03-23 NO NO84841149A patent/NO841149L/en unknown
- 1984-03-23 ES ES1984278543U patent/ES278543Y/en not_active Expired
- 1984-03-26 JP JP59058092A patent/JPS59181414A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| BR8401320A (en) | 1984-08-14 |
| DK107984A (en) | 1984-09-26 |
| AU2481084A (en) | 1984-09-27 |
| NO841149L (en) | 1984-09-26 |
| DK107984D0 (en) | 1984-02-27 |
| NZ207294A (en) | 1986-09-10 |
| JPS59181414A (en) | 1984-10-15 |
| IT1160761B (en) | 1987-03-11 |
| EP0120382A1 (en) | 1984-10-03 |
| ES278543Y (en) | 1986-04-16 |
| IT8320282A0 (en) | 1983-03-25 |
| ES278543U (en) | 1985-09-01 |
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