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EP0258139A1 - Self-regulating heating element and manufacturing process - Google Patents

Self-regulating heating element and manufacturing process Download PDF

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Publication number
EP0258139A1
EP0258139A1 EP87401902A EP87401902A EP0258139A1 EP 0258139 A1 EP0258139 A1 EP 0258139A1 EP 87401902 A EP87401902 A EP 87401902A EP 87401902 A EP87401902 A EP 87401902A EP 0258139 A1 EP0258139 A1 EP 0258139A1
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EP
European Patent Office
Prior art keywords
copolymer
weight
self
vinyl acetate
heating element
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Granted
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EP87401902A
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German (de)
French (fr)
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EP0258139B1 (en
Inventor
Bernard Michel Dalle
Claude Caillot
François Legros
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Electricite de France SA
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Electricite de France SA
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Priority to AT87401902T priority Critical patent/ATE73257T1/en
Publication of EP0258139A1 publication Critical patent/EP0258139A1/en
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01CRESISTORS
    • H01C7/00Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H01C7/027Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient consisting of conducting or semi-conducting material dispersed in a non-conductive organic material
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00Ohmic-resistance heating
    • H05B3/10Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H05B3/146Conductive polymers, e.g. polyethylene, thermoplastics

Definitions

  • the invention relates to a self-regulating heating element.
  • self-regulating heating elements structures, in particular of the cable or strip type, established in a synthetic polymer material which is given, by incorporation of conductive fillers, in particular carbon black, a resistivity which increases from the ambient temperature - it then has a value called ⁇ amb-- up to a so-called "switching" temperature from which it increases very quickly to a maximum value called ⁇ max.
  • the self-regulating heating elements in question are said to have a positive temperature coefficient, by abbreviation CTP.
  • the switching temperature is not very far from the melting temperature of the polymer and experience has shown that, for temperatures above the melting temperature, certain polymers have a negative temperature coefficient, by abbreviation CTN, corresponding to a rapid decrease in resistivity.
  • the properties of the self-regulating heating elements derive from the PTC and the switching temperature.
  • the heat energy dissipated by Joule effect within the element will depend on the temperature at which it is and, in any case, will decrease as this temperature increases; this decrease becomes faster when the switching temperature is exceeded.
  • the temperature of the heating element increases, by Joule effect, up to a temperature from which very little electric current flows through the element; it cools, its resistivity decreases, more current flows, the temperature rises and so on.
  • the invention relates more particularly to self-regulating heating elements based on copolymers with a melting temperature Tf1, obtained from an olefin, in particular ethylene, and a comonomer consisting by vinyl acetate, said copolymers comprising conductive fillers consisting in particular of carbon black, the heating elements in question being prepared, according to the prior art, by a process comprising several stages, namely essentially: a step consisting in establishing an intimate mixture of the copolymer and of the conductive filler, a step consisting in forming, in particular, by extrusion the conductive element of the cable or strip type, with the positioning at the time of the extrusion of two parallel metallic wires intended to be connected to the source of potential, a step consisting in sheathing the above-mentioned element with a second polymer of melting temperature Tf2 higher than Tf1, an annealing step at a temperature T R between Tf1 and Tf2 and a step consisting in
  • the resistivity of the elements in question does not increase suddenly from a given temperature; it simply increases faster from a certain temperature range including the switching temperature.
  • the self-regulating heating element in accordance with the invention comprises a crosslinked copolymer based on ethylene and vinyl acetate in which the proportion of vinyl acetate is less than 10% and more than 2% in weight, more particularly from 9 to 2% by weight and, in practice, from 9 to 5% by weight, said copolymer comprising from 13 to 30% by weight of carbon black chosen from those of which .
  • the specific surface is between 40 and 270, .
  • the structure index is between 100 and 270, . volatile content is less than 2%, .
  • the particle size is between 10 and 40 nm.
  • the process according to the invention for manufacturing the above self-regulating heating element is characterized in that it successively comprises: a step of preparing an ethylene-vinyl acetate copolymer of less than 10% and more than 2% by weight of vinyl acetate, a step of mixing said copolymer and from 13 to 30% of carbon black chosen from those of which .
  • the specific surface is between 40 and 270, .
  • the structure index is between 100 and 270, . volatile content is less than 2%, .
  • the particle size is between 10 and 40 nm, a step of extruding the copolymer thus loaded with carbon black, in particular in the form of a ribbon or cable, with the placing of two parallel metallic wires embedded in the copolymer lengthwise, a step of crosslinking the copolymer, in particular by irradiation.
  • the invention also relates to other provisions which preferably apply at the same time and which will be more explicitly discussed below.
  • Figures 1 and 2 of the drawing show respectively in plan and in section along II-II fig. 1, a heating element established in accordance with the invention.
  • the proportion of vinyl acetate is preferably from 9 to 2% and, in practice, from 9 to 5%.
  • the above-mentioned copolymer and 13 are mixed intimately, at a temperature of 110-130 ° C. and for 2 hours and 30 minutes. at 30% by weight of carbon black selected from those of which .
  • the specific surface is between 40 and 270, .
  • the structure index is between 100 and 270, . volatile content is less than 2%, .
  • the particle size is between 10 and 40 nm, being reminded that - the specific surface, which is measured by nitrogen absorption, is expressed in m2 / g and provides information on the microporosity and on the size of the basic aggregate of carbon black, - the structure index, which is measured by absorption of dibutylphthalate, is expressed and cm3 / 100 g and provides information on the number of elementary particles in the aggregate as well as on the form thereof, - the volatile content, expressed in%, reflects the chemistry of surface and provides information on chemisorption and the formation of complexes on the surface of the aggregate.
  • the proportion with which these carbon blacks are dispersed in the copolymer is preferably from 23 to 27% by weight and in particular from 25% by weight.
  • antioxidant based on 4,4 ⁇ -thiobis- (6-tert.-butyl-3-methylphenol) known under the trademark SANTONOX is mentioned.
  • the intimate mixture once obtained is extruded in a manner known per se in the form of a cable or a ribbon in which are embedded in the longitudinal direction and substantially parallel to each other, two conductive wires for example made of copper, tinned copper or nickel-plated copper.
  • the ribbon is generally represented at 1 and the wires at 2a and 2b.
  • the two wires are connected to the terminals of an electrical outlet 3.
  • the copolymer constituting the ribbon once extruded and provided with its wires, is crosslinked by irradiation; the conductive charges distributed in the copolymer are shown in 1b.
  • Irradiation can be carried out by bombardment electronic ( ⁇ radiation) with a dose of 15 Mrads.
  • the ribbon 1 may be advantageous to cover the ribbon 1 with a sheath 4 in a polymer or mixture of polymers with a melting temperature higher than that of the constituent copolymer of the ribbon 1, the latter being 105 ° C, 102 ° C and 98 ° C for vinyl acetate proportions of 5%, 7.5% and 9% respectively.
  • the range within which the switching temperatures are for the copolymers having a proportion of 5 to 9% of vinyl acetate is from 61 to 80 ° C.
  • the elements in accordance with the invention have a resistivity of 104 to 105 ⁇ -cm, which results in the fact that the inequality 2 x (carbon black concentration) + 5 log ⁇ ⁇ 70 is satisfied.
  • this ratio is greater than 104 for all the heating elements of the type in question in accordance with the invention, which translates the frank and abrupt character of the increase in resistivity above the switching temperature, frank character that do not have heating elements of the kind in question according to the prior art.
  • the stability of the self-regulating heating elements according to the invention is remarkable; it is reported that the decrease in the peak ratio is very small after 100 cycles between 70 and 130 ° C.
  • the elements in question do not have a negative temperature coefficient between the melting temperature of the copolymer and 120 ° C.
  • constituent copolymer of the self-regulating heating elements in accordance with the invention does not flow according to the NFC 32020 standard.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Ceramic Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Dispersion Chemistry (AREA)
  • Resistance Heating (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
  • Apparatuses And Processes For Manufacturing Resistors (AREA)
  • Thermistors And Varistors (AREA)
  • Surface Heating Bodies (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Formation Of Insulating Films (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)

Abstract

Self-regulating heating element (1) comprising a crosslinked copolymer based on ethylene and on a comonomer consisting of vinyl acetate, in which the proportion of vinyl acetate is less than 10% and greater than 2% by weight, more particularly from 9 to 2% by weight and, in practice, from 9 to 5% by weight, said copolymer containing from 13 to 30% by weight of carbon black and having a rho max DIVIDED rho amb ratio greater than 10<4>. <IMAGE>

Description

L'invention a pour objet un élément chauffant autorégulant.The invention relates to a self-regulating heating element.

Elle vise également le procédé de préparation dudit élément.It also relates to the process for preparing said element.

Il est rappelé que, par éléments chauffants auto­régulants, on désigne des structures, notamment du type câble ou bande, établies en un matériau synthétique poly­mère auquel on confère, par incorporation de charges con­ductrices, notamment du noir de carbone, une résistivité qui croît depuis la température ambiante --elle présente alors une valeur appeléeρamb-- jusqu'à une température dite "de commutation" à partir de laquelle elle augmente très rapidement jusqu'à une valeur maximum appelée ρmax.It is recalled that, by self-regulating heating elements, is meant structures, in particular of the cable or strip type, established in a synthetic polymer material which is given, by incorporation of conductive fillers, in particular carbon black, a resistivity which increases from the ambient temperature - it then has a value called ρ amb-- up to a so-called "switching" temperature from which it increases very quickly to a maximum value called ρ max.

On dit que les éléments chauffants autorégulants en question présentent un coefficient de température posi­tif, par abréviation CTP.The self-regulating heating elements in question are said to have a positive temperature coefficient, by abbreviation CTP.

Dans la pratique, la température de commutation n'est pas très éloignée de la température de fusion du polymère et l'expérience a montré que, pour des températu­res supérieures à la température de fusion, certains poly­mères présentaient un coefficient de tempérture négatif, par abréviation CTN, correspondant à une diminution rapide de la résistivité.In practice, the switching temperature is not very far from the melting temperature of the polymer and experience has shown that, for temperatures above the melting temperature, certain polymers have a negative temperature coefficient, by abbreviation CTN, corresponding to a rapid decrease in resistivity.

Il est connu d'éliminer le CTN par réticulation du polymère.It is known to remove the CTN by crosslinking the polymer.

Les propriétés des éléments chauffants autorégu­lants découlent du CTP et de la température de commuta­tion.The properties of the self-regulating heating elements derive from the PTC and the switching temperature.

Ainsi, en appliquant une tension donnée, par exem­ple celle du réseau, à deux points d'un élément du genre en question, l'énergie calorifique dissipée par effet Joule au sein de l'élément dépendra de la température à laquelle celui-ci se trouve et, en tout cas, diminuera au fur et à mesure que cette température augmente ; cette diminution devient plus rapide lorsqu'est dépassée la température de commutation.Thus, by applying a given voltage, for example that of the network, to two points of an element of the kind in question, the heat energy dissipated by Joule effect within the element will depend on the temperature at which it is and, in any case, will decrease as this temperature increases; this decrease becomes faster when the switching temperature is exceeded.

Ce comportement est mis à profit dans les appli­cations des éléments chauffants autorégulants, applica­tions dont on rappellera, pour fixer les idées, par exem­ple celle consistant à mettre les éléments en question en oeuvre dans le gainage de canalisations devant être maintenues à une température donnée, ou celle consistant à avoir recours auxdits éléments pour des articles du type couverture chauffante ; l'élément chauffant autorégulant maintiendra, si l'on prend l'exemple du gainage des cana­lisations, les canalisations "gainées" à une température constante.This behavior is taken advantage of in the applications of self-regulating heating elements, applications which will be recalled, to fix ideas, for example that of putting the elements in question into use in the cladding of pipes to be maintained at a given temperature, or that of having recourse to said elements for articles of the heating blanket type; the self-regulating heating element will maintain, if we take the example of the sheathing of the pipes, the "sheathed" pipes at a constant temperature.

En effet, par application de la tension dont il a été question plus haut, la température de l'élément chauf­fant augmente, par effet Joule, jusqu'à une température à partir de laquelle il passe très peu de courant électrique dans l'élément ; celui-ci se refroidit, sa résistivité di­minue, davantage de courant passe, la température remonte et ainsi de suite.In fact, by applying the voltage mentioned above, the temperature of the heating element increases, by Joule effect, up to a temperature from which very little electric current flows through the element; it cools, its resistivity decreases, more current flows, the temperature rises and so on.

Il apparaît donc clairement que, pour une appli­cation donnée, nécessitant le maintien d'une température donnée, il importe de disposer d'un élément chauffant autorégulant ayant une température de commutation donnée.It therefore clearly appears that, for a given application, requiring the maintenance of a given temperature, it is important to have a self-regulating heating element having a given switching temperature.

Ces généralités étant rappelées, il est précisé que l'invention concerne plus particulièrement les élé­ments chauffants autorégulants à base de copolymères d'une température de fusion Tf₁, obtenus à partir d'une oléfine, notamment l'éthylène, et d'un comonomère constitué par l'acétate de vinyle, lesdits copolymères comportant des charges conductrices constituées par notamment du noir de carbone, les éléments chauffants en question étant prépa­rés, selon l'art antérieur, par un procédé comportant plusieurs étapes, à savoir essentiellement :
    - une étape consistant à établir un mélange intime du copolymère et de la charge conductrice,
    - une étape consistant à former par, notamment, extru­sion l'élément conducteur du type cable ou bande, avec mise en place au moment de l'extrusion de deux fils métalliques parallèles destinés à être raccor­dés à la source de potentiel,
    - une étape consistant à gainer le susdit élément par un deuxième polymère de température de fusion Tf₂ plus élevée que Tf₁,
    - une étape de recuit à une température TR comprise entre Tf₁ et Tf₂ et
    - une étape consistant à réticuler l'élément notamment par irradiation.
These generalities being recalled, it is specified that the invention relates more particularly to self-regulating heating elements based on copolymers with a melting temperature Tf₁, obtained from an olefin, in particular ethylene, and a comonomer consisting by vinyl acetate, said copolymers comprising conductive fillers consisting in particular of carbon black, the heating elements in question being prepared, according to the prior art, by a process comprising several stages, namely essentially:
a step consisting in establishing an intimate mixture of the copolymer and of the conductive filler,
a step consisting in forming, in particular, by extrusion the conductive element of the cable or strip type, with the positioning at the time of the extrusion of two parallel metallic wires intended to be connected to the source of potential,
a step consisting in sheathing the above-mentioned element with a second polymer of melting temperature Tf₂ higher than Tf₁,
an annealing step at a temperature T R between Tf₁ and Tf₂ and
a step consisting in crosslinking the element in particular by irradiation.

Des éléments de ce genre à base d'éthylène et d'acétate de vinyle sont décrits dans le brevet français no 77 37496 et contiennent au moins 10% d'acétate de vi­nyle.Elements of this kind based on ethylene and vinyl acetate are described in French Patent No. 77 37496 and contain at least 10% vinyl acetate.

L'inconvénient majeur qu'ils présentent réside dans le fait que la température de commutation n'est pas bien définie.The major drawback they present lies in the fact that the switching temperature is not well defined.

En d'autres termes, la résistivité des éléments en question n'augmente pas brutalement à partir d'une tempé­rature donnée ; elle augmente simplement plus vite à partir d'un certain domaine de température englobant la température de commutation.In other words, the resistivity of the elements in question does not increase suddenly from a given temperature; it simply increases faster from a certain temperature range including the switching temperature.

C'est à cet inconvénient que les Inventeurs se sont appliqués à remédier.It is to this drawback that the Inventors have applied themselves to remedy.

Et ils ont eu le mérite de trouver, à l'issue de recherches approfondies, qu'il était possible de conférer aux éléments chauffants autorégulants du genre en ques­tion, une température de commutation plus franche à partir de laquelle la résistivité augment si rapidement --cette augmentation est de l'ordre de 10²- 10³ Ω-cm pour 30°C-- qu'il ne passe pratiquement plus de courant dans l'élé­ment, dès lors que la proportion d'acétate de vinyle dans le copolymère constitutif desdits éléments est abaissée en dessous de 10 %.And they had the merit of finding, after extensive research, that it was possible to give self-regulating heating elements of the kind in question, a more frank switching temperature from which the resistivity increases so rapidly - this increase is of the order of 10² - 10³ Ω-cm for 30 ° C - that practically no more current flows through the element, as soon as the proportion of vinyl acetate in the constituent copolymer of said elements is lowered below 10%.

Il s'ensuit que l'élément chauffant autorégulant conforme à l'invention comprend un copolymère réticulé à base d'éthylène et d'acétate de vinyle dans lequel la pro­portion d'acétate de vinyle est inférieure à 10% et supé­rieure à 2% en poids, plus particulièrement de 9 à 2% en poids et, dans la pratique, de 9 à 5% en poids, ledit copolymère comportant de 13 à 30% en poids de noir de carbone choisi parmi ceux dont
    . la surface spécifique est comprise entre 40 et 270,
    . l'indice de structure est compris entre 100 et 270,
    . le contenu volatil est inférieur à 2 %,
    . la granulométrie est comprise entre 10 et 40 nm.
It follows that the self-regulating heating element in accordance with the invention comprises a crosslinked copolymer based on ethylene and vinyl acetate in which the proportion of vinyl acetate is less than 10% and more than 2% in weight, more particularly from 9 to 2% by weight and, in practice, from 9 to 5% by weight, said copolymer comprising from 13 to 30% by weight of carbon black chosen from those of which
. the specific surface is between 40 and 270,
. the structure index is between 100 and 270,
. volatile content is less than 2%,
. the particle size is between 10 and 40 nm.

Le procédé conforme à l'invention pour la fabrica­tion du susdit élément chauffant autorégulant est caracté­risé par le fait qu'il comprend successivement :
- une étape de préparation d'un copolymère éthylène-acé­tate de vinyle à moins de 10% et plus de 2% en poids d'acétate de vinyle,
- une étape de mélange dudit copolymère et de 13 à 30% de noir de carbone choisi parmi ceux dont
    . la surface spécifique est comprise entre 40 et 270,
    . l'indice de structure est compris entre 100 et 270,
    . le contenu volatil est inférieur à 2 %,
    . la granulométrie est comprise entre 10 et 40 nm,
- une étape d'extrusion du copolymère ainsi chargé en noir de carbone, notamment sous forme de ruban ou de cable, avec mise en place dans le sens de la longueur de deux fils métalliques parallèles noyés au sein du copolymère,
- une étape de réticulation du copolymère, notamment par irradiation.
The process according to the invention for manufacturing the above self-regulating heating element is characterized in that it successively comprises:
a step of preparing an ethylene-vinyl acetate copolymer of less than 10% and more than 2% by weight of vinyl acetate,
a step of mixing said copolymer and from 13 to 30% of carbon black chosen from those of which
. the specific surface is between 40 and 270,
. the structure index is between 100 and 270,
. volatile content is less than 2%,
. the particle size is between 10 and 40 nm,
a step of extruding the copolymer thus loaded with carbon black, in particular in the form of a ribbon or cable, with the placing of two parallel metallic wires embedded in the copolymer lengthwise,
a step of crosslinking the copolymer, in particular by irradiation.

L'invention vise encore d'autres dispositions qui s'appliquent de préférence en même temps et dont il sera plus explicitement question ci-après.The invention also relates to other provisions which preferably apply at the same time and which will be more explicitly discussed below.

Et elle pourra, de toute façon, être bien comprise à l'aide du complément de description qui suit et du dessin, relatifs à des modes avantageux de réalisation de l'invention.And it can, in any case, be well understood with the aid of the additional description which follows and of the drawing, relating to advantageous embodiments of the invention.

Les figures 1 et 2 du dessin montrent respective­ment en plan et en coupe selon II-II fig. 1, un élément chauffant établi conformément à l'invention.Figures 1 and 2 of the drawing show respectively in plan and in section along II-II fig. 1, a heating element established in accordance with the invention.

Se proposant donc d'établir un élément chauffant autorégulant du genre en question, conformément à l'inven­tion on s'y prend comme suit ou de façon équivalente.Therefore proposing to establish a self-regulating heating element of the kind in question, in accordance with the invention, this is done as follows or in an equivalent manner.

On prépare tout d'abord et cela d'une manière en elle-même connue, un copolymère d'éthylène et d'acétate de vinyle comportant moins de 10% et plus de 2% en poids d'acétate de vinyle.First of all, in a manner known per se, a copolymer of ethylene and vinyl acetate comprising less than 10% and more than 2% by weight of vinyl acetate is prepared.

La proportion d'acétate de vinyle est de préfé­rence de 9 à 2% et, dans la pratique, de 9 à 5%.The proportion of vinyl acetate is preferably from 9 to 2% and, in practice, from 9 to 5%.

Dans un malaxeur monovis constitué par exemple par celui connu sous la marque Ko-Malaxeur PR 46 commercialisé par la Société Buss, on mélange intimement, à une tempéra­ture de 110-130°C et pendant 2 heures et 30 minutes, le susdit copolymère et 13 à 30% en poids de noir de carbone sélectionné parmi ceux dont
    . la surface spécifique est comprise entre 40 et 270,
    . l'indice de structure est compris entre 100 et 270,
    . le contenu volatil est inférieur à 2 %,
    . la granulométrie est comprise entre 10 et 40 nm,
étant rappelé que
- la surface spécifique, qui est mesurée par absorption d'azote, s'exprime en m²/g et renseigne sur la micro­porosité et sur la taille de l'agrégat de base du noir de carbone,
- l'indice de structure, qui est mesuré par absorption de dibutylphtalate, s'exprime et cm³/100 g et renseigne sur le nombre de particules élémentaires dans l'agrégat ainsi que sur la forme de celui-ci,
- le contenu volatil, exprimé en %, traduit la chimie de surface et renseigne sur la chimisorption et la forma­tion de complexes en surface de l'agrégat.
In a single-screw mixer constituted for example by that known under the brand Ko-Mixer PR 46 sold by the company Buss, the above-mentioned copolymer and 13 are mixed intimately, at a temperature of 110-130 ° C. and for 2 hours and 30 minutes. at 30% by weight of carbon black selected from those of which
. the specific surface is between 40 and 270,
. the structure index is between 100 and 270,
. volatile content is less than 2%,
. the particle size is between 10 and 40 nm,
being reminded that
- the specific surface, which is measured by nitrogen absorption, is expressed in m² / g and provides information on the microporosity and on the size of the basic aggregate of carbon black,
- the structure index, which is measured by absorption of dibutylphthalate, is expressed and cm³ / 100 g and provides information on the number of elementary particles in the aggregate as well as on the form thereof,
- the volatile content, expressed in%, reflects the chemistry of surface and provides information on chemisorption and the formation of complexes on the surface of the aggregate.

L'expérience a montré que l'augmentation de la surface spécifique et de l'indice de structure entraîne la diminution de la résistivité alors que celle-ci s'accroît avec l'augmentation du contenu volatil.Experience has shown that the increase in the specific surface area and in the structure index leads to a decrease in the resistivity while this increases with the increase in the volatile content.

Les susdits critères de sélection conduisent à re­tenir, parmi les noirs de carbone actuellement disponibles dans le commerce, par exemple ceux commercialisés sous les marques
    - VULCAN P (commercialisé par la Société Cabot)
    - VULCAN XC 72 (commercialisé par la Société Cabot).
The above selection criteria lead to choosing, among the carbon blacks currently commercially available, for example those marketed under the brands
- VULCAN P (marketed by the Cabot Company)
- VULCAN XC 72 (marketed by the Cabot Company).

La proportion avec laquelle ces noirs de carbone sont dispersés dans le copolymère est de préférence de 23 à 27% en poids et notamment de 25% en poids.The proportion with which these carbon blacks are dispersed in the copolymer is preferably from 23 to 27% by weight and in particular from 25% by weight.

Il peut également être utile d'ajouter au mélange en question d'autres additifs, notamment pour stabiliser les compositions contre l'oxydation.It may also be useful to add other additives to the mixture in question, in particular to stabilize the compositions against oxidation.

A titre d'exemple, on signale l'agent antioxydant à base de 4,4ʹ-thiobis-(6-tert.-butyl-3-méthylphénol) connu sous la marque SANTONOX.By way of example, the antioxidant based on 4,4ʹ-thiobis- (6-tert.-butyl-3-methylphenol) known under the trademark SANTONOX is mentioned.

Le mélange intime une fois obtenu est extrudé d'une manière en soi connue sous forme d'un câble ou d'un ruban dans lequel sont noyés dans le sens longitudinal et sensiblement parallèles l'un à l'autre, deux fils conduc­teurs par exemple en cuivre, cuivre étamé ou cuivre nickelé.The intimate mixture once obtained is extruded in a manner known per se in the form of a cable or a ribbon in which are embedded in the longitudinal direction and substantially parallel to each other, two conductive wires for example made of copper, tinned copper or nickel-plated copper.

Sur les figures 1 et 2, on a représenté le ruban globalement en 1 et les fils en 2a et 2b.In FIGS. 1 and 2, the ribbon is generally represented at 1 and the wires at 2a and 2b.

Comme montré, les deux fils sont connectés aux bornes d'une prise électrique 3.As shown, the two wires are connected to the terminals of an electrical outlet 3.

Le copolymère la constitutif du ruban une fois extrudé et muni de ses fils est réticulé par irradiation ; les charges conductrices réparties dans le copolymère sont représentées en 1b.The copolymer constituting the ribbon, once extruded and provided with its wires, is crosslinked by irradiation; the conductive charges distributed in the copolymer are shown in 1b.

L'irradiation peut être réalisée par bombardement électronique (rayonnement β) avec une dose de 15 Mrads.Irradiation can be carried out by bombardment electronic (β radiation) with a dose of 15 Mrads.

Il peut être avantageux de recouvrir le ruban 1 d'une gaine 4 en un polymère ou mélange de polymères de température de fusion supérieure à celle du copolymère constitutif du ruban 1, cette dernière étant de 105°C, 102°C et 98°C pour des proportions d'acétate de vinyle respectivement de 5%, 7,5% et 9%.It may be advantageous to cover the ribbon 1 with a sheath 4 in a polymer or mixture of polymers with a melting temperature higher than that of the constituent copolymer of the ribbon 1, the latter being 105 ° C, 102 ° C and 98 ° C for vinyl acetate proportions of 5%, 7.5% and 9% respectively.

La température de commutation Tc [qui correspond à l'intersection des segments (quasi linéaires pour les co­polymères utilisés conformément à l'invention) rencontrés sur la partie ascendante de la courbe
    Logρ = f(T)
(le premier segment étant celui compris entre la tempéra­ture ambiante et la température de commutation, alors que le second est celui traduisant l'augmentation --brutale dans le cas des copolymères utilisés conformément à l'in­vention-- de la résistivité au-dessus de la température de commutation)] est déterminée avec une imprécision de seu­lement ±5°C.
The switching temperature Tc [which corresponds to the intersection of the segments (almost linear for the copolymers used in accordance with the invention) encountered on the ascending part of the curve
Logρ = f (T)
(the first segment being that between ambient temperature and the switching temperature, while the second is that reflecting the - brutal increase in the case of the copolymers used according to the invention - of the resistivity above switching temperature)] is determined with an inaccuracy of only ± 5 ° C.

Etant donné que les températures Tc mesurées pour les copolymères à 5, 7,5 et 9% d'acétate de vinyle sont respectivement de 75°C, 72°C et 66°C, la plage dans la­quelle se situent les températures de commutation pour les copolymères ayant une proportion de 5 à 9% d'acétate de vinyle, est de 61 à 80°C.Since the temperatures Tc measured for the 5, 7.5 and 9% vinyl acetate copolymers are 75 ° C, 72 ° C and 66 ° C respectively, the range within which the switching temperatures are for the copolymers having a proportion of 5 to 9% of vinyl acetate, is from 61 to 80 ° C.

A la température ambiante et pour une proportion de noir de carbone d'environ 25%, les éléments conformes à l'invention ont une résistivité de 10⁴ à 10⁵ Ω-cm, ce qui se traduit par le fait que l'inégalité
2 x (concentration en noir de carbone) + 5 log ρ ≧ 70
est satisfaite.
At room temperature and for a proportion of carbon black of approximately 25%, the elements in accordance with the invention have a resistivity of 10⁴ to 10⁵ Ω-cm, which results in the fact that the inequality
2 x (carbon black concentration) + 5 log ρ ≧ 70
is satisfied.

La valeur de la résistivité ρmax (exprimée en Ω-cm) à la température de pic étant d'environ 10⁹ alors qu'elle est de 5.10⁴ à la température ambiante dans le cas de l'élément conforme à l'invention constitué par un copo­lymère comportant 9% en poids d'acétate de vinyle et dans lequel 25 % en poids de noir de carbone ont été dispersés, le rapport

Figure imgb0001
est d'environ 2.10⁴.The value of the resistivity ρ max (expressed in Ω-cm) at the peak temperature being around 10⁹ whereas it is 5.10⁴ at room temperature in the case of the element according to the invention constituted by a copolymer comprising 9% by weight of vinyl acetate and in which 25% by weight of carbon black have been dispersed, the ratio
Figure imgb0001
is about 2.10⁴.

Plus généralement ce rapport est supérieur à 10⁴ pour tous les éléments chauffants du genre en question conformes à l'invention, ce qui traduit le caractère franc et brutal de l'augmentation de la résistivité au-dessus de la température de commutation, caractère franc que ne pré­sentent pas les éléments chauffants du genre en question selon l'art antérieur.More generally, this ratio is greater than 10⁴ for all the heating elements of the type in question in accordance with the invention, which translates the frank and abrupt character of the increase in resistivity above the switching temperature, frank character that do not have heating elements of the kind in question according to the prior art.

De plus, la stabilité des éléments chauffants autorégulants conformes à l'invention est remarquable ; on signale que la diminution du rapport de pic est très fai­ble après 100 cycles entre 70 et 130°C.In addition, the stability of the self-regulating heating elements according to the invention is remarkable; it is reported that the decrease in the peak ratio is very small after 100 cycles between 70 and 130 ° C.

Grâce à la réticulation du copolymère, les élé­ments en question ne présentent pas de coefficient de température négatif entre la température de fusion du copolymère et 120°C.Thanks to the crosslinking of the copolymer, the elements in question do not have a negative temperature coefficient between the melting temperature of the copolymer and 120 ° C.

Enfin, le copolymère constitutif des éléments chauffants autorégulants conformes à l'invention ne flue pas selon la norme NFC 32020.Finally, the constituent copolymer of the self-regulating heating elements in accordance with the invention does not flow according to the NFC 32020 standard.

Pour être complet, on signale que si, dans la pra­tique, on n'a pas recours à des proportions d'acétate de vinyle dans le copolymère inférieures à 5% --bien que de telles proportions très faibles seraient avantageuses du point de vue de l'augmentation de

Figure imgb0002
-- c'est en raison du fait que la cristallinité du copolymère augmente alors dans des proportions telles que les qualités mécaniques de l'élément en souffrent.For completeness, it is pointed out that if, in practice, vinyl acetate proportions in the copolymer are less than 5% - although such very low proportions would be advantageous from the point of view of the increase of
Figure imgb0002
- This is due to the fact that the crystallinity of the copolymer then increases in proportions such that the mechanical qualities of the element suffer from it.

En suite de quoi et quel que soit le mode de réa­lisation adopté, on dispose ainsi d'un élément chauffant autorégulant dont les caractéristiques résultent suffisam­ment de ce qui précède pour qu'il soit inutile d'insister à leur sujet et qui présentent, par rapport aux éléments chauffants du genre en question qui existent déjà, de nombreux avantages dont notamment celui de présenter une température de commutation particulèrement franche.Following what and whatever the embodiment adopted, there is thus a self-regulating heating element whose characteristics result sufficiently from the above so that it is unnecessary to insist on them and which have, in relation to heating elements of the kind in question which already exist, many advantages including in particular that of having a particularly frank switching temperature.

Claims (3)

1. Elément chauffant autorégulant caractérisé par le fait qu'il comprend un copolymère réticulé, à base d'éthylène et d'un comonomère constitué par l'acétate de vinyle, dans lequel la proportion d'acétate de vinyle est inférieure à 10% et supérieure à 2% en poids, plus parti­culièrement de 9 à 2% en poids et, dans la pratique, de 9 à 5% en poids, ledit copolymère comportant de 13 à 30% en poids de noir de carbone choisi parmi ceux dont
      . la surface spécifique est comprise entre 40 et 270,
      . l'indice de structure est compris entre 100 et 270,
      . le contenu volatil est inférieur à 2 %,
      . la granulométrie est comprise entre 10 et 40 nm.
1. Self-regulating heating element characterized in that it comprises a crosslinked copolymer, based on ethylene and of a comonomer constituted by vinyl acetate, in which the proportion of vinyl acetate is less than 10% and greater than 2% by weight, more particularly from 9 to 2% by weight and, in practice, from 9 to 5% by weight, said copolymer comprising from 13 to 30% by weight of carbon black chosen from those of which
. the specific surface is between 40 and 270,
. the structure index is between 100 and 270,
. volatile content is less than 2%,
. the particle size is between 10 and 40 nm.
2. Elément chauffant autorégulant selon la reven­dication 1, caractérisé par le fait qu'il présente un rapport
Figure imgb0003
ce grâce à quoi sa résistivité augmente brutalement, d'en­viron 10²-10³ Ω-cm pour 30°C, au-delà de la température de commutation.
2. Self-regulating heating element according to claim 1, characterized in that it has a ratio
Figure imgb0003
thanks to which its resistivity increases suddenly, by around 10²-10³ Ω-cm for 30 ° C, beyond the switching temperature.
3. Procédé de fabrication de l'élément chauffant autorégulant selon les revendications 1 et 2, caractérisé par le fait qu'il comprend successivement :
- une étape de préparation d'un copolymère à partir d'éthylène et d'un comonomère constitué par l'acétate de vinyle, la proportion de ce dernier dans le copoly­mère final étant de moins de 10% et de plus de 2% en poids,
- une étape de mélange dudit copolymère et de 13 à 30% de noir de carbone choisi parmi ceux dont
      . la surface spécifique est comprise entre 40 et 270,
      . l'indice de structure est compris entre 100 et 270,
      . le contenu volatil est inférieur à 2 %,
      . la granulométrie est comprise entre 10 et 40 nm,
- une étape d'extrusion du copolymère ainsi chargé en noir de carbone, notamment sous forme de ruban ou de cable, avec mise en place dans le sens de la longueur de deux fils métalliques sensiblement parallèles noyés au sein du copolymère,
- une étape de réticulation du copolymère notamment par irradiation.
3. Method for manufacturing the self-regulating heating element according to claims 1 and 2, characterized in that it successively comprises:
a step for preparing a copolymer from ethylene and a comonomer constituted by vinyl acetate, the proportion of the latter in the final copolymer being less than 10% and more than 2% by weight ,
a step of mixing said copolymer and from 13 to 30% of carbon black chosen from those of which
. the specific surface is between 40 and 270,
. the structure index is between 100 and 270,
. volatile content is less than 2%,
. the particle size is between 10 and 40 nm,
a step of extruding the copolymer thus loaded with carbon black, in particular in the form of a ribbon or cable, with the placing of two substantially parallel metal wires embedded in the lengthwise direction embedded in the copolymer,
a step of crosslinking the copolymer, in particular by irradiation.
EP87401902A 1986-08-21 1987-08-19 Self-regulating heating element and manufacturing process Expired - Lifetime EP0258139B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT87401902T ATE73257T1 (en) 1986-08-21 1987-08-19 SELF-REGULATING HEATING ELEMENT AND PROCESS FOR ITS MANUFACTURE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8611945 1986-08-21
FR8611945A FR2603133B1 (en) 1986-08-21 1986-08-21 SELF-REGULATING HEATING ELEMENT AND ITS PREPARATION METHOD

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EP0258139B1 EP0258139B1 (en) 1992-03-04

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EP (1) EP0258139B1 (en)
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AT (1) ATE73257T1 (en)
AU (1) AU610514B2 (en)
CA (1) CA1332280C (en)
DE (1) DE3777016D1 (en)
ES (1) ES2029280T3 (en)
FR (1) FR2603133B1 (en)
GR (1) GR3003975T3 (en)

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WO2015104218A1 (en) * 2014-01-08 2015-07-16 Voss Automotive Gmbh Prefabricated heatable media line and a method for the production of same

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US5122641A (en) * 1990-05-23 1992-06-16 Furon Company Self-regulating heating cable compositions therefor, and method
US5113058A (en) * 1990-06-01 1992-05-12 Specialty Cable Corp. PCT heater cable composition and method for making same
US5517003A (en) * 1993-06-29 1996-05-14 Metagal Industria E Comercio Ltd. Self-regulating heater including a polymeric semiconductor substrate containing porous conductive lampblack
FR2733637B1 (en) * 1995-04-26 1997-05-30 Gec Alsthom T & D Sa SULFUR HEXAFLUORIDE INSULATED APPARATUS
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EP0008235A2 (en) * 1978-08-10 1980-02-20 Eaton Corporation Semi-conductive polymeric compositions suitable for use in electrical heating devices; flexible heating cables made by using said compositions and method for making the like cables

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WO2015104217A1 (en) * 2014-01-08 2015-07-16 Voss Automotive Gmbh Heatable media line, method for the production thereof, and circuit assembly for a heatable media line
WO2015104218A1 (en) * 2014-01-08 2015-07-16 Voss Automotive Gmbh Prefabricated heatable media line and a method for the production of same

Also Published As

Publication number Publication date
JPS63126203A (en) 1988-05-30
DE3777016D1 (en) 1992-04-09
ATE73257T1 (en) 1992-03-15
ES2029280T3 (en) 1992-08-01
EP0258139B1 (en) 1992-03-04
FR2603133B1 (en) 1990-04-06
GR3003975T3 (en) 1993-03-16
AU610514B2 (en) 1991-05-23
US4908156A (en) 1990-03-13
AU7731487A (en) 1988-02-25
FR2603133A1 (en) 1988-02-26
CA1332280C (en) 1994-10-11

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