WO2019139497A1

WO2019139497A1 - Thin film electric heater

Info

Publication number: WO2019139497A1
Application number: PCT/RU2018/000007
Authority: WO
Inventors: Борис Григорьевич ПОЛЕВОЙ; Олег Иванович ФИЛАТОВ
Original assignee: Борис Григорьевич ПОЛЕВОЙ; Олег Иванович ФИЛАТОВ
Priority date: 2018-01-15
Filing date: 2018-01-15
Publication date: 2019-07-18

Abstract

The invention relates to flat radiator-type electric heaters, particularly to thin film heaters intended for heating low-volume spaces. The present thin film electric heater comprises a resistance element that is disposed between two heat resistant, electrically insulating films and that is made of a polymer film having a conductive covering in the form of a nano layer, and contacts are disposed along the full width of said nano layer along two opposing edges, said contacts being made of a material that adheres to the conductive covering, the latter having conductors and outlets for connecting to an electrical power grid, and the contacts are in the form of a flat figure that is bounded on two sides by periodic waveform lines.

Description

Thin-film electric heater

The invention relates to flat electric heaters of a radiating type, in particular to thin-film electric heaters intended for heating small spaces: cars, various inhabited vehicles - aircraft, space, underwater, medical, for heating spacesuits and clothes, and also as a basis for creating industrial heating systems and residential premises, heating systems for young animals and birds, drying coatings.

State of the art

Known patent for the invention of Russia b 2379857, published January 20, 2010. A thin-film electric heater consists of two sheets of flexible heat-resistant electrical insulation films, between which, by their size, a resistive element is obtained obtained by depositing a conductive layer 3 - 25 μm thick onto a heat-resistant polymer film by vacuum ion-plasma spraying through a mask. The resistive element has a zigzag (meander) shape and is equipped with down conductors soldered to copper-coated areas, which are made by ion-plasma spraying through a mask.

A disadvantage of the known thin-film electric heater is the low reliability of the resistive element, since with a zigzag shape of the resistive element, any defect thereof, comparable in size to the meander bandwidth, leads to the destruction of the conductive layer, i.e. to reduce reliability, in addition, a coating with a thickness of 3 μm or more, necessary to obtain the required power of the electric heater, is unstable to bending deformation, which also leads to a decrease in its reliability.

The patent of Russia for utility model N ° 100353, published on December 10, 2010, is known. The film heater contains two external heat-resistant electrical insulation films, between which there is an internal heat-resistant electrical insulation film with a nanoscale layer of a resistive material deposited on its entire surface - nichrome thickness, determined by the specific power of the electric heater and its length. The conclusions for connecting to the electric network are connected to flat contacts made of copper foil and adjacent to the surface of the resistive material layer.

A disadvantage of the known device is the low reliability of the system for supplying electric current to a layer of resistive material. The current, following the path of least resistance, passes from flat contacts from the foil to the resistive layer in a narrow region of the contact edge, which leads to an increase in current density in the transition region, overheating and destruction of the resistive layer.

Another disadvantage is the formation of air cavities in the place of loose contact of the foil to the layer of resistive material, which leads to the appearance of electric arcs and to the destruction of the layer of resistive material.

The closest analogue, selected as a prototype, is the Russian patent for utility model Ns 113624, published on 02.20.2012.

A thin-film electric heater contains a resistive element located between two heat-resistant electrical insulating films, and a polymer film with a conductive coating in the form of a nanoscale layer is used as a resistive element. Across the entire width of the nanoscale layer, along two edges of the resistive element, opposite each other, contacts are made in the form of a comb made of a material having adhesion to the conductive coating. The current leads to which the terminals of the connection to the electric network are connected are made in the form of a foil tape (from a material with low electrical resistance) along the entire length of the contacts and are pressed to the contacts by two heat-resistant electrical insulating films. The implementation of contacts in the form of a comb is designed to increase the length of the line of transition of the current from the contact material into the nanoscale conductive layer of the resistive element, in order to reduce the current density in the transition region. The disadvantages of this thin-film electric heater are contacts made in the form of a comb, consisting of rectangular teeth. With a sufficiently close arrangement of the teeth, due to screening (by each other's teeth), the current passes into the nanoscale conductive layer only from the top of the teeth, the effective length of the current transition line decreases and tends to the contact length as the frequency of the teeth increases. Moreover, the applicant experimentally proved that the maximum potential gradient and, therefore, the maximum current density occur at the upper corners of the teeth. When a breaking stress is applied, the destruction of the nanoscale layer begins precisely at these points.

Disclosure of invention

The technical task of the present invention is to increase the reliability of the film heater by optimizing the shape of the contacts by maximizing the use of the entire length of the contact edge as a line of electric current from the contact material to the nanoscale layer by eliminating areas with an increased potential gradient from the contact form.

The technical result is achieved by the fact that in a thin-film electric heater containing a resistive element made of a polymer film with a conductive coating located between two heat-resistant electrical insulating films in the form of a nanoscale layer, along the entire width of which, on two edges opposite each other, contacts made of material are placed, having adhesion to a conductive coating, with current leads and leads for connection to an electric network, and current leads for connecting to an electric network made of a material with low electrical resistance in the form of a continuous foil strip along the entire length of the contacts pressed against the contacts, according to the invention, the contacts are made in the form of a flat figure bounded on both sides by periodic wavy lines, while the height of the line maxima is determined by the specific power of the heater and is in the range of 1 - 50 mm, the height of the maxima does not exceed the distance between adjacent maxima, and the current leads for connecting to the electric network is additionally glued to the contacts by means of a conductive compound.

Due to the fact that in a thin-film electric heater the contacts are made in the form of a flat figure bounded on two sides by periodic wavy lines, the height of the line maxima is determined by the specific power of the heater and is in the range of 1 - 50 mm, the height of the maxima does not exceed the distance between adjacent maxima, and current leads for connecting to the electric network are additionally glued to the contacts by means of a conductive compound, the reliability of the film heater is increased, due to optimization contact form, by maximizing the use of the entire length of the contact edge as a line of electric current transition from the contact material to the nanoscale layer by excluding from the contact form sections with an increased potential gradient.

The inventive thin-film electric heater has a novelty in comparison with the prototype, differs from it by the above features and ensures the achievement of the technical result perceived by the applicant.

The set of essential features of the claimed thin-film electric heater does not follow explicitly from the studied prior art, i.e. meets the criteria of "novelty" and "inventive step".

The inventive thin-film electric heater will find wide application, i.e. is industrially applicable.

Brief Description of the Drawings

The essence of the proposed thin-film electric heater is illustrated by drawings, which show:

In FIG. 1 - general view of the device;

In FIG. 2 - the same section AA;

In FIG. 3 - the same, a top view of the contact;

In FIG. 4 - the same, the region of transition of the current from the contact to the resistive layer. The thin-film electric heater contains a resistive element 1 of a polymer film 2 with a conductive coating in the form of a nanoscale layer 3, along the entire width of which, on two edges, opposite each other, are placed contacts 4 made of a conductive material having adhesion to the conductive coating in the form of a nanoscale layer 3, and the resistive element 1 is located between two heat-resistant electrical insulating films 5, and is equipped with current leads 6 for connecting contacts 4 to the electrical network, and current leads 6 for The connections to the electric network are made of material with low electrical resistance in the form of a rectangular foil tape along the length of the contacts 4 and are connected to the contacts 4 (Fig. 1, Fig. 2).

Contacts 4 are made in the form of a flat figure bounded on two sides by periodic wavy lines, while the height of the maxima N is determined by the specific power of the heater and is in the range of 1 - 50 mm, the height of the maxima does not exceed the distance between adjacent maxima (Fig.Z).

The purpose and implementation of the details of the claimed device is as follows. As the resistive element 1, a polymer film 2 is used with a conductive coating layer deposited on its entire surface in the form of a nanoscale layer 3 made, for example, of nichrome, titanium, stainless steel, indium tin oxide, titanium nitride, and other materials.

The conductive coating in the form of a nanoscale layer 3 is applied to the polymer film 2 by magnetron sputtering in vacuum. During magnetron sputtering, the resulting coating has high adhesion, since the deposited metal atoms reach the substrate in the form of ions. The method of magnetron sputtering allows the conductive coating to be applied without significant heating of the polymer film 2 (up to 80 ° C), precisely controlling the thickness of the deposited nanoscale layer. When this conductive coating has the same thickness over the entire surface of the resistive element 1. The process of applying a conductive coating is carried out on the installation of magnetron sputtering WU-700. The thickness of the conductive coating is determined depending on the specified specific power and the length of the thin-film electric heater.

As the material for the contacts 4, any material from the following can be selected - copper, gold, silver, nickel, aluminum, conductive pastes. Contacts 4 can be applied by any of the following methods: spraying in a vacuum; electroplating; tribogalvanics; conductive paste from a material having adhesion to the conductive coating in the form of a nanoscale layer 3 by silk screen printing.

The applicant experimentally established the optimal shape of the contacts 4, in the form of a flat figure bounded on two sides by periodic wavy lines, while the height of the maxima is determined by the specific power of the heater and is in the range of 1 - 50 mm, the height of the maxima does not exceed the distance between adjacent maxima, which allows maximum effectively use the entire envelope to transfer the current to the nanoscale layer 3, depending on the specific power of the heater.

The current leads 6 are designed to transfer electric current to the contacts 4 and equalize the potential along the entire length of the contact 4, which is especially important for the contacts 4, applied conductive paste. The current leads 6, made in the form of a rectangular strip of copper or brass foil, are glued to the contacts 4, excluding the conductive coating in the form of a nanoscale layer 3, by means of a conductive compound along the entire length and additionally pressed with an insulating film 5.

The supply wires 7 are connected to the current leads 6 by soldering or conductive tape.

Contact 4 to the conductive coating in the form of a nanoscale layer 3, deposited by the conductive compound, has a thickness of 5-25 μm.

The conductive coating in the form of a nanoscale layer 3 is 0.03-0.5 μm. When the electric current passes from a macroscopic contact into a conductive coating in the form of a nanoscale layer 3, the current flows along the path of the smallest resistance and passes into a conductive coating in the form of a nanoscale layer 3 in a narrow region 8 of the current transition Dc at the end of contact 4. (Fig. 4).

The current density in the j transition region is determined by:

j = sDf / Dc where:

Df / Dc - potential gradient,

Dc is the width of the current transition region

s - electrical conductivity in the field of current transition

Mathematical modeling shows that the current is transferred from the bulk of the contact material to the nanoscale layer in the contact region with a width Dc comparable with the thickness of the nanoscale layer. The current density in the transition region reaches much higher values than the nanoscale layer far from the contact and is determined by the potential difference Df and the width of the region Dc, which leads to the destruction of the conductive layer at the contact boundary.

The total current I flowing through the heater is determined by Ohm's law:

1 = U / R, where:

U is the voltage between the contacts of the electric heater;

R is the impedance of the heater.

The linear current density j defined as the current passing through a unit of length of the current transition line:

j _L = I / L,

where L is the length of the current transition line.

In order to reduce the current density j ^, (determined by the law of conservation of charge j is the same current I and goes through sections of a conductor of different cross-sections (Fig. 4), it is necessary to increase the length of the line L.

In the patent selected for the prototype, a comb-shaped contact form consisting of rectangular teeth was used for this purpose, the length of the envelope L of the comb being no less than three times the contact length. However, when the teeth are quite close due to screening (by each other's teeth), the current passes into the nanoscale conductive layer only from the top of the teeth, the effective length of the transition line decreases and tends to the contact length as the frequency of the teeth increases. Moreover, the applicant experimentally and mathematically proved that the maximum potential gradient and, therefore, the maximum current density occurs at the upper corners of the teeth. When a breaking stress is applied, the destruction of the nanoscale layer begins precisely at these points. In turn, a minimal potential gradient is observed in the lower parts of the comb.

To increase the reliability of a thin-film electric heater, it is necessary to work the entire transition line with a fairly uniform current density.

In the claimed technical solution, the contacts 4 are made in the form of a flat figure, bounded on both sides by periodic wavy lines that exclude any angles, and aligning the potential along the length of the heater and the height of the contact 4.

Industrial applicability

In the inventive thin-film electric heater, the reliability of the film heater is improved by optimizing the shape of the contacts by maximizing the use of the entire length of the contact edge as the line of transition of electric current from the contact material to the nanoscale layer by eliminating areas with an increased potential gradient from the contact form due to the fact that in the thin-film the electric heater contacts are made in the form of a flat figure, bounded on both sides by periodic wavy lines, while the height the maximum of the lines is determined by the specific power of the heater and is in the range of 1 - 50 mm, the height of the maximum does not exceed the distance between adjacent maxima, and the current leads for connecting to the electric network are additionally glued to the contacts by means of a conductive compound. ·

Claims

Claim

1. A thin-film electric heater containing, located between two heat-resistant electrical insulating films, a resistive element made of a polymer film with a conductive coating in the form of a nanoscale layer, along the entire width of which, on two edges, opposite each other, contacts made of a material with adhesion to conductive coating, with current leads and terminals for connection to the electric network, and the current leads for connecting to the electric network are made of material with low electrical m resistance in the form of a continuous foil tape along the entire length of the contacts pressed against the contacts, according to the invention, the contacts are made in the form of a flat figure bounded on both sides by periodic wavy lines, while the height of the line maxima is determined by the specific power of the heater and is in the range 1 - 50 mm, the height of the maxima does not exceed the distance between adjacent maxima, and the current leads for connecting to the electric network are additionally glued to the contacts by means of a conductive compound.