FR2464006A1 - HEATER WITH POSITIVE TEMPERATURE COEFFICIENT - Google Patents

Abstract

THE INVENTION RELATES TO SELF-REGULATING BAND-SHAPED HEATING ORGANS CONTAINING CTP 3 CONDUCTIVE POLYMERS. ACCORDING TO THE INVENTION, THE BAND-SHAPED HEATING UNIT IS SURROUNDED BY A SHELL 5 AND 6 OF A CONDUCTIVE MATERIAL. HIGH THERMAL, FOR EXAMPLE INTERCAL BETWEEN SHEETS OF ALUMINUM. THIS MAKES POSSIBLE TO USE A BAND HEATING UNIT HAVING HIGHER PASSIVE POWER AND RESULTS IN A UNIT WITH HIGHER ACTIVE OUTPUT POWER.

Description

The present invention relates to organs

heating system with self-regulating strip

of a conductive polymer with positive temperature coefficient (PTC), two (or more) parallel electrodes in electrical contact (and optionally also physical

que) with the strip, and an electrically insulating sheath.

  Such heating devices are known and are described, for example, in American patents NO 3,793,716; 3,823,217; 3861.029; 4,177,376 and 4. 188,276 and in the Thermal Design Guide published by the Chemelex Division of

  Raychem Corporation (H 50190 505 B5 1/78).

To define such heating devices, we

often refers to their "passive output power

  ve "and their" active output power ". The" power-

this passive output "of a heater is the value of the term V / R, where R is the resistance of a unit length (usually 1 meter) of the heater to 210C and V is the voltage of the electrical energy source connected to the heating device,

  usually 120 or 240 volts AC. The "then-

active output "of a heater is the measured output power of a unit length of the heater (usually 1 meter) when connected to the source of electrical power, with a main surface of the heating element in contact

  with a metal substrate which is held at a certain

  temperature related to the intended use of the gold

  heating gane, for example 7 to 650C, such as 100C for heaters designed to prevent freezing of pipes. Conventional strip heaters have two or more electrodes in the form of wires embedded in a conductive polymer element with a positive temperature coefficient (cTP)

  and have a sensitive passive output power-

less than 165 watts per meter at their nominal operating voltage; the use of such heating devices having higher passive output powers has been avoided since they give little or no useful increase in active output power and have major drawbacks, in particular

shorter longevity.

  It has been found that if a heating organ

fage in conductive polymer with temperature coefficient

  positive ture is surrounded by a metal envelope or

other material with thermal conductivity satisfies

  health, it is possible to make use of the organ of

  heating at voltages at which its output power

  passive tie is greater than 165 watts per meter without having the drawbacks previously associated with such use, and that a very significant increase

  active output power can thus be obtained.

For example, the addition of such an envelope surprisingly makes it possible to use, at a voltage of 240 volts, a heater with a positive temperature coefficient which has a passive output power at 120 volts less than 165 watts / meter and 240 volts greater than 165 watts / meter, although such

heating element, in the absence of the envelope, poss-

  from an unacceptable short longevity to 240 volts.

  According to one of its aspects, the invention proposes a heating method which includes circulation

a current through a self-regulating heater

  A lation comprising (a) a PTC positive temperature coefficient heating element which comprises (i) an elongated strip of a composition

  conductive polymer having a

PTC support, (ii) two parallel elongated electrodes in electrical contact with said strip, and (iii) an electrically insulating sheath which

  surrounds said strip and said elect

  trodes; and (b) an envelope which surrounds said PTC heating member and which is made of a material having a thermal conductivity of at least 0.1 Cal / cm dry OC, preferably at least 0.3 Cal / cm C dry.,

  the current being supplied by an electric power source

stick having a voltage V and the heating member a-

  having an active output power at said voltage V of at least 165 watts / meter, preferably at least

230 watts / meter.

  The heater can be used to heat a solid substrate, in which case the casing is preferably shaped to match the substrate; or it can be used as a space heater, in which case the assembly is preferably in the form of a coil, with a space between the turns in view

  air or other liquid circulation.

According to another aspect, the invention provides a self-regulating heating member comprising a

  heating element with temperature coefficient for

CTP and an envelope as defined above

sus, the heater having a power output

  passive tie at 120 volts of at least 165 watts / meter.

  The PTC heater includes pre-

ference two (or more) electrodes in the form of wires which are embedded in and in physical contact with the PTC strip. However, the invention encompasses

  other types of PTC heaters, e.g.

  ple those in which one or more of the electrodes is separated from the PTC strip by a strip from another

conductive material, for example a composition po-

  conductive lymer exhibiting a coef-

  zero temperature, and those which include a laminar PTC element and two or more laminar electrodes. The passive output power of the heater depends on the resistivity of the PTC composition and the size and shape of the electrodes

and the CTP element. For an ordinary heating strip

nary, for example tele as described in the example above

  below, the passive output power is preferably

rence from 165 to 655 watts / meter, preferably 230 to

  655 watts / meter. For all the heating organs

fage within the scope of the invention, the range

  r preferred passive output power is better ex-

  awarded by an expression that includes the width of the CTP element on which the heat is produced. Thus the passive output power of the heating elements according to the invention is preferably from 2170 D to 862 D,

  particularly 302 D to 862 D watts / meter, in the-

  which D is the maximum transverse dimension (in cent

meter) of the PTC strip which is located between the elect

trodes. The active output power of an organ

de-chauffage CTP is significantly increased by the presen-

ce of the enclosure, and preferred heaters have an active output power at 100C which is at least 1.5 times the active output power at 101C

  the PTC heating element without the envelope.

The envelope is preferably constituted by a pair of elongated sheets, the heating member

being interposed between them, the leaves coming into contact

tact of each other on either side of the heating member. The sheets preferably have 0.025 to

  1.3 mm, for example 0.075 to 0.2 mm thick and com-

  laid with a material having thermal conductivity

  than at least 0.3, for example aluminum. They can be fixed to each other and / or to the heating element by means of an adhesive, for example a

epoxy glue.

  It is important that the casing and the PTC heating element are in intimate thermal contact, and the casing is preferably in contact (either directly or via an adhesive) at least in the areas of the insulating sheath adjacent to those parts of the heater in which heat is generated. Preferably, there is no

voids between the casing and the heater.

  It is preferable that the envelope extends towards the ex-

inside of the PTC heating element in the form of fins, so that the exposed surface area of the envelope is at least 1.5 times, for example

  at least 2 times, the surface area of the sheath i-

  solante of the PTC heating element, in particular at least twice. The envelope can also be used to limit access of oxygen to the CTP composition as taught by the French patent application

No 79/29556.

The heating elements may include two or more PTC heating elements. The heating elements can be spaced from each other and joined by an envelope which surrounds each of them, for example a set of heating elements in the form of parallel strips inserted between a pair of

metal sheets.

The invention is illustrated in the drawings

attached.

  Figure lest isometric view, in section

  partial, of a heating device according to the invention.

  Figure 2 is a graph showing the re-

  relationship between the electric current and the temperature of the substrate in the tests described in the example;

We now refer to Figure 1 which

  presents a PTC heating element comprising elec

trodes 1 and 2 embedded in a strip 3 of a composition

conductive polymer CTP which is surrounded by a gai-

  insulating 4. The heating element is interposed between a pair of aluminum sheets 5 and 6 which are

  attached to each other and to the heater at the mo-

  yen of an adhesive (not shown).

  The invention is further illustrated by e-

next example.

EXAMPLE

The PTC heater used was a length of 61 cm of a shaped heater

  CTP tape as shown in Figure 1. The elect

trodes were copper wire 1.3 mm in diameter

  be, with a spacing between the axes of 7.6 mm. The-

  CTP element was 10mm wide and 1.8mm thick

  and consisted of a composition comprising a dis-

  carbon black persion in a polyethylene blend

lene and an ethylene / ethyl acrylate copolymer. The insulating sheath was made of polyurethane and was about 0.25 mm thick. The heater had a passive output power of approximately 250,275 watts / meter. The active output power of this heater, alone or as part of an assembly

  heater, was measured by fixing the heater

  ge or the whole to a 1.25 x aluminum plate

, 25 x 61 cm, by connecting the heating element to a supply

  120 volts AC and leaving the system

  me reach his balance while maintaining the plate at a desired temperature. During the tests, the heating element alone (Sample A) or the heating element interposed between two identical aluminum sheets, 61 cm long and 0.03 cm thick, and having widths of 11, 4; 6.3; 3.8 and 1.9 cm (BsC samples, 24640b06

D and E) was used. Figure 2 shows the relationship between-

  be the temperature of the plate and the current passing through the heating element. The table below shows the calculated active output power (current x applied voltage) of the heater when the plate is

found at 10OC.

BOARD

Sample A B C D

E

Metal shell width (cm) none 11.4 6.3 3.8 1.9 Active power

at 10 C

(watts / meter).

Claims (9)

  1) Heating process, which includes the circulation   tion of a current through a self-regulating member comprising a PTC positive temperature coefficient heating element which comprises (i) an elongated strip (3) of a composition   conductive polymer with un.compor-   CTP, (ii) two elongated parallel electrodes (1 and 2) in electrical contact with said strip, and (iii) an electrically insulating sheath (4) which surrounds said strip and said electrodes; characterized in that the heating element (a) is surrounded by an envelope which is made of a material having a thermal conductivity of at least 0.1 Cal / cm 0C dry, and (b) has a power of passive output at supply voltage of at least watts / meter.   2) Method according to claim i, characterized in that said PTC heating member has a passive output power of 217 D to 862 D in which D is the maximum transverse dimension (in   centimeter) of the PTC band between the electrodes.   - 3) - Method according to claim 1 or 2, characterized in that said PTC member is interposed between a pair of elongated sheets (5 and 6) which are in contact with each other on either side of the heater and which are made of a material having a thermal conductivity of at least 0.3 Cal / cm. C sec.   4) Method according to claim 3, characterized in that the exposed surface area of said sheets is at least 1.5 times the surface area of the insulating sheath of the PTC heating element.   5) Method according to one of claims   previous, characterized in that the heater has an active output power at 100C which is at least 1.5 times the active output power at 100C of the PTC heater without the jacket.   6) Method according to one of claims   above, characterized in that the supply voltage   tation is 120 or 240 volts AC.   7) Self-regulating heating assembly   as a PTC heating element which comprises (i) an elongated strip (3) of a composition conductive polymer having a   CTP, (ii) two elongated parallel electrodes (1 and 2) in electrical contact with said strip, and (iii) an electrically insulating sheath (4) which surrounds said strip and said electrodes; characterized in that said PTC heater (a) has a passive output power at 120 volts of 165 to 655 watts / meter, and (b) is surrounded by an envelope which is made of a material having a   thermal conductivity of at least 0.1 Cal / cm.C sec.   8) Heating assembly according to claim 7, characterized in that said PTC member is interposed between a pair of elongated sheets (5 and 6) which come into contact with each other on either side of the heating element and which are made of a material having a thermal conductivity of at least 0.3 Cal / cm 0C sec.   2464oo6 9) A heating assembly according to claim 8, characterized in that the exposed surface area of said sheets is at least 1.5 times the surface area of the insulating sheath of the PTC heating member.   ) Heating assembly according to one of the res-   dications 7 to 9, characterized in that the heating device has an active output power at 10 ° C which is at least 1.5 times the active output power at 10 C from the PTC heating device without the enclosure.