Patent Description:
In general, a cooking appliance refers to a device for heating and cooking food using gas or electricity. Various products such as a microwave oven using microwaves, an oven using a heater, a gas stove using gas, an electric stove using electricity, or a cooktop including a gas stove or an electric stove have come into widespread use.

The gas stove directly generates flame using gas as a heating source, while the electric stove heats a container and food placed on a top plate thereof using electricity.

In the gas stove, heat loss caused by flame is large and contaminants are discharged due to incomplete combustion, thereby polluting room air. Therefore, recently, electric stoves are attracting attention.

Electric stoves may be classified into an inductive electric stove which directly heats a container in which a magnetic field is generated by a magnetic induction method, and a resistive electric stove which heats a top surface made of ceramic using a hot wire.

The inductive electric stove has a short cooking time at a high temperature and must use a dedicated magnetic container. The resistive electric stove may use an existing container but has a relatively long cooking time.

Even if an existing resistive electric stove uses a heating element made of a nichrome wire, an electric heater using a plane heating element is being developed in order to reduce the thickness of the heating element.

In addition, in order to shorten the cooking time, a resistive electric stove using an electric heater capable of heating a limited area at a high temperature is being developed.

As an example of such an electric heater, <CIT>) discloses a plane heating element including a substrate including a surface made of an electrically insulating material, a heating element attached to the surface of the substrate and having a predetermined shape, and a power supply for supplying electricity to the heating element.

In the electric heater, the temperature distribution of an object to be heated may be changed according to the shape (that is, the pattern) of the plane heating element, and the plane heating element may be formed in a shape capable of heating the object to be heated as uniformly as possible.

The plane heating element of the electric heater includes a plurality of tracks having a straight-line shape or an arc shape and adjacent tracks of the plurality of tracks may be connected through a bridge (or a track).

As another example of the heater, European Patent Publication No. <CIT>) discloses a temperature sensitive device. Such a device is configured by printing a heater track made of a conductive material and a plurality of electrodes on a ceramic coating layer. As current is supplied through the electrodes, radiant heat is generated in the heater track.

However, the existing plane heating element includes a heating unit in which a single hot wire is formed within a limited area in a predetermined pattern shape, and the heating unit is designed to have a high resistance in order to generate heat at a high temperature of <NUM> or higher.

However, the required power required for each size of the cooking appliance differs, and there is a limit in configuring the pattern portion with only one hot wire in order to heat up to a high temperature step by step according to the user's need.

Therefore, it is possible to constitute a plane heating element having a plurality of pattern portions, and the necessary power is distributed for each pattern portion, the limited area is divided into each zone in proportional to the required power of each pattern portion, and then each pattern portion corresponding to each zone is formed.

However, the pattern portion located at the outermost side of the limited area is more likely to deprive heat by the surroundings than the other pattern portions, and it is difficult to maintain a heating temperature similar to other pattern portions due to high heat loss.

In addition, in a case where the pattern portion located at the outermost side of the limited area is designed with a relatively large required power among the total required power, the heat loss becomes larger, so that the heating value cannot be realized by the total required power.

<CIT> discloses an electric liquid vessel comprising a heater having three track sections forming heating areas. <CIT> discloses a thick film electric heater comprising at least two distinct sections connected by a bridge of lower resistance. <CIT> discloses an electric heater having a plurality of heating elements, at least one of heating connection portions connecting the heating elements, and non-heating connection portions connecting the heating elements.

The present invention has been made in order to solve the above problems of the related art, and an object of the present invention is to provide an electric heater including a plane heating element capable of ensuring a heating temperature and a heating value of a pattern portion located at an outermost side of a limited area.

The present invention is defined by the appended independent claim. An electric heater according to an embodiment of the present invention, which does not fall within the scope of the independent claim, includes a substrate <NUM> (an insulating material capable of forming a conductor pattern on a surface of an insulating substrate); and a plane heating element <NUM>, <NUM> and <NUM> configured to be formed on one surface of the substrate; wherein the plane heating element <NUM>, <NUM>, <NUM> includes: a first pattern portion <NUM> configured to connect a start point and an end point, and a third pattern portion <NUM> configured to surround at least a portion of the first pattern portion <NUM> and to connect a start point and an end point thereof, which are located at the outermost side, wherein the first pattern portion <NUM> includes: a plurality of first tracks <NUM> having an arc shape, configured to be spaced apart from each other and to be formed to have a length increasing from the center to the outside, wherein the third pattern portion <NUM> includes: a plurality of third tracks <NUM> having an arc shape, configured to be spaced apart from each other on the outside of the first track <NUM> and to be formed to have a length increasing from the inside to the outside, and wherein the width W3 of the third track <NUM> is configured to be longer than a width W1 of the first track <NUM>.

In addition, the plane heating element <NUM>, <NUM> and <NUM> further includes: a second pattern portion <NUM> configured to be located between the first pattern portion <NUM> and the third pattern portion <NUM> and to connect a start point and an end point thereof, which are located at the innermost side, and wherein the second pattern portion <NUM> includes: a plurality of second tracks <NUM> having an arc shape, configured to be spaced apart from each other between the first tracks <NUM> and the third tracks <NUM> and to be formed to have a length increasing from the inside to the outside.

In addition, the width W3 of the third track <NUM> is configured to be longer than a width W2 of the second track <NUM>.

In addition, the gap G3 between the third tracks <NUM> adjacent to each other is configured to be longer than the gap G1 between first tracks <NUM> adjacent to each other.

In addition, the gap G3 between the third tracks <NUM> adjacent to each other is configured to be longer than the gap G2 between second tracks <NUM> adjacent to each other.

In addition, the first pattern portion <NUM> includes a plurality of first bridges <NUM> connecting the first tracks <NUM> in series, and wherein the third pattern portion <NUM> includes a plurality of third bridges <NUM> connecting said third tracks <NUM> in series.

In addition, the length L3 of the third bridge <NUM> is configured to be longer than the length L1 of the first bridge <NUM>.

In addition, the second pattern portion <NUM> includes a plurality of second bridges <NUM> connecting the second tracks <NUM> in series.

In addition, the length L3 of the third bridge <NUM> is configured to be longer than the length L2 of the second bridge <NUM>.

In addition, the first, second, and third bridges <NUM>, <NUM> and <NUM> are configured with an arc shape having a predetermined width.

In addition, the radius of curvature R3 of the third bridge <NUM> is configured to be longer than the radius of curvature R1 of the first bridge <NUM>.

In addition, the radius of curvature R3 of the third bridge <NUM> is configured to be longer than the radius of curvature R2 of the second bridge <NUM>.

In addition, the number N3 of the third bridges <NUM> is configured to be smaller than the number N1 of the first bridges <NUM> and the number N2 of the second bridges <NUM>.

In addition, the plane heating element <NUM>, <NUM> and <NUM> includes: a pair of first electrodes <NUM> and <NUM> connected to the start point and the end point of the first pattern portion, a pair of second electrodes <NUM> and <NUM> connected to the start point and the end point of the second pattern portion, and a pair of third electrodes <NUM> and <NUM> connected to the start point and the end point of the third pattern portion, and wherein the third electrodes <NUM> and <NUM> are disposed in a direction opposite to the first and second electrodes.

In addition, the required power of the third pattern portion <NUM> is distributed by <NUM>% or more with respect to the power required for the entirety of the first, second, and third pattern portions <NUM>, <NUM> and <NUM>.

In the electric heater according to the present invention, the width of the track of the pattern portion located on the outermost side of the limited area is configured to be wider than that of the track of the other pattern portion, so that the heating value in the outermost zone of the limited area can be increased.

Therefore, since the heating temperature can be kept high in the outermost zone of the limited area, the entire limited area can be heated to a uniform heating temperature.

In addition, even if heat loss occurs in the outermost zone of the limited area, the heating value can be realized by the required power, so that the heating performance can be improved.

Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings.

<FIG> is a perspective view illustrating an electric stove, to which an electric heater according to an embodiment of the present invention is applied, and <FIG> is a control block diagram of an electric stove, to which an electric heater according to an embodiment of the present invention is applied.

The electric stove may include a cabinet <NUM> forming an outer appearance. The electric heater <NUM> of the present invention may configure a portion of an electric stove such as a cooktop.

The electric heater <NUM> may be provided on the cabinet <NUM>. The upper surface of the cabinet <NUM> may be opened and the electric heater <NUM> may be provided on the upper surface of the cabinet <NUM>.

The electric stove may include an input unit <NUM> for manipulating the electric stove and a display <NUM> for displaying a variety of information such as information on the electric stove. In addition, the electric stove may further include a power supply <NUM> connected to the electric heater <NUM> to apply current to the electric heater <NUM>. The electric stove may further include a controller <NUM> for controlling the power supply <NUM> and the display <NUM> according to input of the input unit <NUM>.

The electric heater <NUM> may be provided on the cabinet <NUM> such that the upper surface thereof is exposed to the outside. An object to be heated by the electric stove may be placed on the upper surface of the electric heater <NUM>, and the upper surface of the electric heater <NUM> may be a surface in which the object to be heated is seated.

<FIG> is a cross-sectional view illustrating an electric heater according to an embodiment of the present invention.

The electric heater <NUM> includes a substrate <NUM> and a plurality of plane heating elements <NUM>, <NUM>, and <NUM> formed on one surface of the substrate <NUM>.

The substrate <NUM> may be an insulating substrate having a conductor pattern formed on a surface thereof. The upper surface of the substrate <NUM> may be a surface <NUM> in which the object to be heated is seated. The lower surface of the substrate <NUM> may be a surface <NUM> in which the plane heating elements <NUM>, <NUM>, and <NUM> are formed.

The substrate <NUM> may include only a base <NUM> formed of an insulating material or may include a base <NUM> formed of an insulating material or a non-insulating material and an insulating layer <NUM> formed on one surface of the base <NUM>.

The base <NUM> may be glass and the insulating layer <NUM> may be formed on the lower surface of the glass using a coating or a printing method.

The plane heating elements <NUM>, <NUM>, and <NUM> may be directly formed on one surface of the base <NUM> formed of an insulating material or may be formed on the insulating layer <NUM>.

The base <NUM> may be formed in a shape of a plate on which the object to be heated is placed or in a shape of a container in which the object to be heated is received.

The insulating layer <NUM> may be formed on the lower surface of the base <NUM>. The insulating layer <NUM> may be formed on the entire lower surface of the base <NUM> or may be formed on a portion of the lower surface of the base <NUM>. The insulating layer <NUM> may be formed only in a zone in which the plane heating elements <NUM>, <NUM>, and <NUM> will be formed. The insulating layer <NUM> may configure the entire lower surface of the substrate <NUM> or a portion of the lower surface of the substrate <NUM>.

The plane heating elements <NUM>, <NUM>, and <NUM> may be formed on the lower surface <NUM> of the insulating layer <NUM>. The plane heating elements <NUM>, <NUM>, and <NUM> may have a size smaller than the substrate <NUM> and the lower surface of the substrate <NUM> may have a heated zone H, in which the plane heating elements <NUM> and <NUM> is formed, and an unheated zone UH located around the heated zone H.

The heater <NUM> may further include a coating layer <NUM> surrounding the plane heating elements <NUM>, <NUM>, and <NUM>. The coating layer <NUM> may be formed of an electrically insulating material to protect the plane heating elements <NUM>, <NUM>, and <NUM>. The substrate <NUM> of the present embodiment may be formed of a flexible material, such as a flexible insulating film. In this case, the electric heater <NUM> may be a flexible planar heater. Such a flexible planar heater may be attached to a member, on which the object to be heated is placed, to heat the object to be heated, like the upper plate of the electric stove.

<FIG> is a plan view illustrating a triple-type plane heating element according to an embodiment of the present invention.

As illustrated in <FIG>, the triple-type plane heating element according to an embodiment of the present invention includes a first plane heating element <NUM>, a second plane heating element <NUM>, and a third plane heating element <NUM> formed on the same plane, the first plane heating element <NUM> is located at the center, the second plane heating element <NUM> is located to surround the first plane heating element <NUM>, and the third plane heating element <NUM> is located so as to surround the second plane heating element <NUM>.

The first plane heating element <NUM> includes a first pattern portion <NUM> in which a hot wire is arranged in a predetermined shape in a circular first zone and a pair of first electrodes <NUM> and <NUM> connected to the first pattern portion <NUM>.

The first pattern portion <NUM> is a heating unit which generates heat at <NUM> or more, a hot wire constituting the first pattern portion <NUM> connects between the start point and the end point, which are located at the outermost side of the first zone, along various paths, and the first pattern portion <NUM> is configured in a symmetrical shape in the lateral direction with respect to a reference line passing through the center of the first pattern portion <NUM>.

According to an embodiment, the first pattern portion <NUM> may include a plurality of first tracks <NUM> having an arc shape increasing in size from the center to the outside and a first bridge <NUM> connecting the first tracks <NUM> in series.

The area on which the first pattern portion <NUM> is formed and the length of the hot wire which constitutes the first pattern portion <NUM> may be set in proportion to the required power.

For example, in order to realize a required power of 515W in a <NUM>-inch size, the first pattern portion <NUM> may be arranged such that a hot wire having a width of <NUM> and a length of <NUM> in a circular zone having a diameter of <NUM> is maintained at an gap of <NUM> to <NUM>, and the number N1 of the first bridges <NUM> connecting the first tracks <NUM> having an arc shape, which are symmetrical with each other about the reference line in the lateral direction is <NUM>, but is not limited thereto.

The first electrodes <NUM> and <NUM> are unheated units which generate heat at <NUM> or less or are hardly heated and include the first positive electrodes <NUM> to which current is input and the first negative electrodes <NUM> from which current is output.

The first positive electrode <NUM> and the first negative electrode <NUM> are unheated units and are preferably located horizontally outside the second and third pattern portions <NUM> and <NUM>, which are heating units to be described below, with a predetermined gap.

The first positive electrode <NUM> extends at a start point of the first pattern portion <NUM> and the first negative electrode <NUM> extends from an end point of the first pattern portion <NUM>.

However, the resistance of the first electrodes <NUM> and <NUM> is configured to be small in order to more greatly reduce the heating temperature than that of the first pattern portion <NUM>, and the thickness of the first electrodes <NUM> and <NUM> can be configured to be thicker than that of the first pattern portion <NUM>.

When current is supplied to the first plane heating element having the above configuration, current flows sequentially along the first positive electrode <NUM>, the first pattern portion <NUM>, and the first negative electrode <NUM>.

The second plane heating element <NUM> includes a second pattern portion <NUM> in which a hot wire is arranged in a predetermined shape in a second ring-shaped zone surrounding the first pattern portion <NUM>, and a pair of second electrodes <NUM> and <NUM> connected to the second pattern portion <NUM>.

The second pattern portion <NUM> is also a heating unit which generates heat at <NUM> or more like the first pattern portion <NUM>, the hot wire constituting the second pattern portion <NUM> connects between the start point and the end point, which are located at the second zone, along various paths, and the second pattern portion is configured with a symmetrical shape in the lateral direction about the reference line.

According to an embodiment, the second pattern portion <NUM> may also include a plurality of second tracks <NUM> and a plurality of second bridges <NUM> in a symmetrical shape like the first pattern portion <NUM>.

In order to keep the potential difference between the first and second pattern portions <NUM> and <NUM> low, it is preferable that the start point and the end point of the second pattern portion <NUM> is located at the innermost side of the second zone so as to be close to the start point and the end point of the first pattern portion <NUM>.

The area on which the second pattern portion <NUM> is formed and the length of the hot wire constituting the second pattern portion <NUM> may be set in proportion to the required power.

For example, in order to realize a required power of 500W in a size of <NUM> inches, the second pattern portion <NUM> may be arranged such that a hot wire having a width of <NUM> and a length of <NUM> in a ring-shaped zone having a diameter of <NUM> to <NUM> is maintained at an gap of <NUM> to <NUM> and the number N2 of the second bridges <NUM> connecting the second tracks <NUM> having an arc shape which is symmetrical about the reference line in the lateral direction may be four but is not limited thereto.

The second electrodes <NUM> and <NUM> are also unheated units which generate heat at <NUM> or less or hardly generates heat and include a second positive electrode <NUM> and a second negative electrode <NUM>.

It is preferable that the second positive electrode <NUM> and the second negative electrode <NUM> are also unheated units and are horizontally located outside the second pattern portion <NUM> at a predetermined gap.

The second positive electrode <NUM> extends from the start point of the second pattern portion <NUM> and the second negative electrode <NUM> extends from the end point of the second pattern portion <NUM>.

However, the resistance of the second electrodes <NUM> and <NUM> is also configured to be small in order to more greatly reduce the heating temperature than that of the second pattern portion <NUM>, and the thickness of the second electrodes <NUM> and <NUM> can be configured to be thicker than that of the second pattern portion <NUM>.

The first and second electrodes <NUM>, <NUM>, <NUM> and <NUM> are located in the same direction as the start point and the end point of the first and second pattern portions <NUM> and <NUM> are located adjacent to each other, current may be supplied to the first positive electrode <NUM> and the second positive electrode <NUM> by one power supply.

In order to keep the potential difference between the first and second electrodes <NUM>, <NUM>, <NUM> and <NUM> low, it is preferable that the first and second positive electrodes <NUM> and <NUM> are located adjacent to each other and the first and second negative electrodes <NUM> and <NUM> are located adjacent to each other.

When current is supplied to the second plane heating element <NUM> constructed as described above, current flows sequentially through the second positive electrode <NUM>, the second pattern portion <NUM>, and the second negative electrode <NUM>.

The third plane heating element <NUM> includes a third pattern portion <NUM> in which a hot wire is arranged in a predetermined shape in a third ring-shaped zone surrounding the second pattern portion <NUM>, and a pair of third electrodes <NUM> and <NUM> connected to the third pattern portion <NUM>.

The third pattern portion <NUM> is a heating unit which generates heat at <NUM> or more like the first pattern portion <NUM>, the hot wire constituting the third pattern portion <NUM> connects between the start point and the end point, which are located at the third zone, along various paths, and the third pattern portion is configured with a symmetrical shape about the reference line in the lateral direction.

According to an embodiment, the third pattern portion <NUM> may also include a plurality of third tracks <NUM> and a plurality of third bridges <NUM> in a symmetrical shape in the lateral direction like the first pattern portion <NUM>.

When the start point and the end point of the second pattern portion <NUM> are located at the innermost side of the second zone, it is difficult for the start point and the end point of the third pattern portion <NUM> to be located so as to be close to the start point and the end point of the second pattern portion <NUM>.

Accordingly, in order to reduce the potential difference between the second and third pattern portions <NUM> and <NUM>, it is preferable that the start point and the end point of the third pattern portion <NUM> are located at the outermost side of the third zone so as to be farther from the start point and the end point of the second pattern unit <NUM>.

The area on which the third pattern portion <NUM> is formed and the length of the hot wire constituting the third pattern portion <NUM> may be set in proportion to the required power.

For example, in order to realize the required power of 1085W in the <NUM> inch size, the third pattern portion <NUM> may be arranged such that a hot wire having a width of <NUM> and a length of <NUM> in a ring-shaped zone having a diameter of <NUM> to <NUM> may be arranged so as to maintained at an gap of <NUM>, and the number N3 of the third bridges <NUM> connecting the third tracks <NUM> having an arc shape symmetrical about the reference line in the lateral direction may be two but is not limited thereto.

It is preferable that the third electrodes <NUM> and <NUM> are also unheated units which generate heat at <NUM> or less or hardly generates heat, include a third positive electrode <NUM> and a third negative electrode <NUM>, and is horizontally located at a predetermined gap outside the third pattern portion <NUM>.

The third positive electrode <NUM> extends from the start point of the third pattern portion <NUM> and the third negative electrode <NUM> extends from the end point of the third pattern portion <NUM>, and the third electrodes <NUM> and <NUM> may be configured to be thicker than the third pattern portion <NUM> in order to significantly reduce the heating temperature.

The third electrodes <NUM> and <NUM> are located in opposite directions to the first and second electrodes <NUM>, <NUM>, <NUM>, and <NUM>, and current can be supplied to the third positive electrode <NUM> by a power supply different from the power supply connected to the first and second electrodes <NUM>, <NUM>, <NUM>, and <NUM>.

When a current is supplied to the third plane heating element <NUM> configured as described above, current flows sequentially along the third positive electrode <NUM>, the third pattern portion <NUM>, and the third negative electrode <NUM>.

When a current is supplied to the first, second, and third plane heating elements <NUM>, <NUM>, and <NUM> configured as described above, the difference in current density flowing along the inside/outside of the first, second, and third bridges <NUM>, <NUM>, and <NUM> are large and thus heating occurs locally, but the resistances of the first, second, and third bridges <NUM>, <NUM> and <NUM> are configured to be smaller to prevent local heating.

Accordingly, the total heating value of the first, second, and third pattern portions <NUM>, <NUM>, and <NUM> is determined by the first, second, and third tracks <NUM>, <NUM>, and <NUM> rather than the first, second, and third bridges <NUM>, <NUM>, and <NUM>.

If all of the first, second, and third pattern portions <NUM>, <NUM>, and <NUM> generate heat, since the first and second pattern portions <NUM> and <NUM> are surrounded by the third pattern portion <NUM>, that is, the heating zone, the heat loss of the first and second pattern portions <NUM> and <NUM> is relatively small, but since the third pattern portions <NUM> are surrounded by the non-heated zone, the heat loss of the third pattern portion <NUM> is generated to be relatively large.

In addition, the total required power is distributed by the first, second, and third pattern portions <NUM>, <NUM>, and <NUM>, and in a case where the required power of the third pattern portion <NUM> is relatively large or in a case where the required power of the third pattern portion <NUM> is designed to be <NUM>% or more of the total required power, the heat loss due to the third pattern portion <NUM> located at the outermost side of the limited area can be greatly generated.

Therefore, it is preferable that the third pattern portion <NUM> is designed to improve the heating temperature and the heating value than those of the first and second pattern portions <NUM>.

<FIG> is a partially enlarged view of <FIG>.

According to an embodiment of the present invention, it is preferable that the third track is provided in the outermost zone of the limited area, and in order to increase the heating value of the third track <NUM>, that is, the heating area by the third track <NUM>, the width W3 of the third track <NUM> is designed to be longer than the width W1 of the first track <NUM> and the width W2 of the second track <NUM>.

At this time, as the width W3 of the third track <NUM> becomes wider, the heating value can be maintained even if the third gap G3, which is an gap between the adjacent third tracks <NUM>, is configured to be wider.

Therefore, the third gap G3 is designed to be longer than the first gap G1, which is an gap between the adjacent first tracks <NUM>, or the second gap G2, which is an gap between the adjacent second tracks <NUM>.

In the present invention, since the bridge connects two tracks spaced apart at a predetermined gap in series, the longer the gap between the two tracks is, the longer the length of the bridge is, and the same can be applied even if the bridge has an arc shape or a straight line shape.

Therefore, it is preferable that the length L3 of the third bridge is designed to be longer than the length L1 of the first bridge or the length L2 of the second bridge.

In the present invention, in a case where the bridge has an arc shape, the radius of curvature of the bridge connecting the two tracks also increases as the gap between the two tracks increases.

Therefore, it is preferable that the curvature radius R3 of the third bridge is designed to be longer than the curvature radius R1 of the first bridge or the curvature radius R2 of the second bridge.

However, since the third track <NUM> is formed in the ring-shaped zone located on the outermost side of the limited area, the third track <NUM> is formed into an arc shape longer than the first and second tracks <NUM> and <NUM>.

Of course, even if the required power is considered, the number of the relatively long third tracks <NUM> should be smaller than the number of the first tracks <NUM> or the second tracks <NUM>, which has a relatively short length.

Accordingly, it is preferable that the number N3 of the third bridges connecting the third tracks <NUM> is provided to be smaller than the number N1 of the first bridges connecting the first tracks <NUM> in series or the number N2 of the second bridges connecting the second tracks <NUM> in series.

The present invention relates to an electric heater having a plurality of plane heating elements, and may be configured in various ways, such as the number and shape of the plane heating elements, and is not limited thereto.

The foregoing description is merely illustrative of the technical idea of the present invention and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the technical idea of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments.

Claim 1:
An electric heater comprising:
a substrate (<NUM>); and
a plane heating element (<NUM>, <NUM> and <NUM>) formed on one surface of the substrate;
wherein the plane heating element (<NUM>, <NUM>, <NUM>) includes:
a first pattern portion (<NUM>) connecting a start point and an end point thereof,
a third pattern portion (<NUM>) surrounding at least a portion of the first pattern portion (<NUM>) and connecting a start point and an end point thereof, and
a second pattern portion (<NUM>) located between the first pattern portion (<NUM>) and the third pattern portion (<NUM>) and connecting a start point and an end point thereof, which are located at the innermost side of the second pattern portion (<NUM>),
wherein the first pattern portion (<NUM>) includes:
a plurality of first tracks (<NUM>) having an arc shape, spaced apart from each other and having a length increasing from the center to the outside,
wherein the third pattern portion (<NUM>) includes:
a plurality of third tracks (<NUM>) having an arc shape, spaced apart from each other on the outside of the first track (<NUM>) and having a length increasing from the inside to the outside, and
wherein the second pattern portion (<NUM>) includes:
a plurality of second tracks (<NUM>) having an arc shape, spaced apart from each other between the first tracks (<NUM>) and the third tracks (<NUM>) and having a length increasing from the inside to the outside,
wherein a width (W3) of the third track (<NUM>) is longer than a width (W1) of the first track (<NUM>),
characterized in that the start point and the end point of the third pattern portion (<NUM>) are located at the outermost side of the third pattern portion (<NUM>),
wherein the plane heating element (<NUM>, <NUM> and <NUM> includes):
a pair of first electrodes (<NUM> and <NUM>) connected to the start point and the end point of the first pattern portion (<NUM>),
a pair of second electrodes (<NUM> and <NUM>) connected to the start point and the end point of the second pattern portion (<NUM>), and
a pair of third electrodes (<NUM> and <NUM>) connected to the start point and the end point of the third pattern portion (<NUM>), and
wherein the third electrodes (<NUM> and <NUM>) are disposed in a direction opposite to the first and second electrodes.