SURFACE TYPE HEATING BODY USING CONDUCTIVE MATERIAL Technical Field The present invention relates to a plane heater using a conductive material, and more particularly, to a plane heater using a conductive material comprising an electric heater which is thin and flat, main conducting members secured to the upper surface of the electric insulator, respectively connected to a pair of electrodes and subjected to a surface treatment including silver plating, aluminum plating or etching, a plurality of sub-conducting members diverged from the main conducting members in such a manner that a sub- conducting member diverged from one main conducting member is spaced apart from a sub-conducting member diverged from the other main conducting member by a predetermined gap, a conductive material applied to the upper surface ?- of the electric insulator, the main conducting members and the sub- conducting members, and made of a material, such as PTCR, and an adhesive applied to the upper surface of the conductive material so as to be adhered to the rear surface of an object to be heated.

Background Art In general, as temperature rises, a material's resistance is accordingly increased. In particular, a thermistor, resistance of which drastically increases with temperature in a certain range of temperature, is called a PTC (Positive Temperature Coefficient) thermistor. With this characteristic, the PTC thermistor is used as an electric element or a heater for preventing overheat and over-current. It is mostly materialized of ceramics but recently polymer is used as a material thereof, thereby enabling its wider application.

A polymer PTC thermistor is characterized in that as

ambient temperature rises or its temperature rises because of self-heating, its resistance gradually increases to a certain level and then sharply increases in a certain range of temperature.

Using the above characteristic, when a current less than a predetermined level is applied to the PTC thermister, it can function as a general fixed resistor since a Joule heat generated therefrom and a heat dissipated to the outside are balanced together. When overcurrent more than the predetermined level is applied from the outside to a circuit and flows through the PTC thermistor, however, the thermal equilibrium is broken. Due to self-heating of the PTC thermistor, temperature and resistance of the PTC thermistor simultaneously increase whereby over-current flowing in the circuit is cut off and the circuit and components can be protected from the over-current. Meanwhile, once the cause of over-current is eliminated, a low resistance is formed again and the circuit normally operates.

Using the above characteristics, when the PTC thermistor is used as a heater, it can let lots of currents flowing with a low resistance at a low temperature so that it can apply heat in a short period of time, whereas when temperature increases to a certain level, its resistance drastically increases in a predetermined temperature range so that it can balance a Joule heat supplied thereto and a heat dissipated to the outside in the predetermined range of temperature, resulting in achievement of a positive temperature state.

In another aspect, when the PTC thermistor is used as a heater, there are many cases that it can be used in households or vehicles. Its drastic change in resistance with temperature rather makes over-current flowing at a low temperature, and may cause a problem of exceeding capacity.

According to the inventors'experimental results, the PTC heater used as a general heater showed that its resistance decreases about 30-50% at a temperature of-40°C or so when a reference resistance is defined at a normal temperature of 20°C, so as to prevent over-current from flowing, while its

resistance increases 1000% at a temperature of about 60-70°C, so as to prevent temperature from increasing by a self-current.

The polymer PTC thermistor is of a disk-, rectangular plate-, ring-, rod-, or small chip-shape such that it can be widely applied to a temperature sensor, a circuit protection device, a color TV degaussing element, a PTC heater, a starting motor and so on.

The polymer PTC heater is a kind of film-type plane heater and generates heat due to a Joule heat emitted from a conductive material therein during conduction. It is widely applied to all articles in which a plane heater can be used, for example, a mirror heater of a vehicle, a hot wire in a heating sheet, a heater for a bathroom mirror, a strip type heater in various warmers, a hot wire in a mat, etc.

FIG. 1 is a plan view of a conventional plane heater using a conductive material, and FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1.

Referring to FIGs. 1 and 2, the plane heater comprises: an electric insulator 3 which is thin and flat; main conducting members 1 and 1'secured to the upper surface of the electric insulator 3, connected to a pair of electrodes 6 and 6'and subjected to a surface treatment including silver plating, aluminum plating or etching; a plurality of sub- conducting members 2 and 2'diverged from the main conducting members 1 and 1'in such a manner that a sub-conducting member diverged from one main conducting member is spaced apart from a sub-conducting member diverged from the other main conducting member by a predetermined gap G; a conductive material 4 applied to the upper surface of the electric insulator 3, the main conducting members 1 and 1'and the sub- conducting members 2 and 2', and materialized of PTCR and so on; and an adhesive 5 applied to the upper surface of the conductive material 4 so as to be attached to the rear surface of an object to be heated.

Herein, the adhesive 5 is made of an insulating material, such as acrylic. When the plane heater is applied to a rear- view mirror as shown in FIG. 3, it is adhered to the rear

surface of an interior side of the rear-view mirror 1 by means of the adhesive 5.

In the meantime, the main conducting members 1 and 1' connected to the pair of electrodes 6 and 6'are subjected to a surface treatment including silver plating, aluminum plating, or etching. The main conducting members 1 and 1'are upwardly and downwardly connected to the central portion where the electrodes 6 and 6'are disposed, such that the main conducting members 1 and 1'are respectively distributed at the upper and lower portions along an edge portion of the plane heater.

Further, the plurality of sub-conducting members 2 and 2' are diverged from the main conducting members 1 and 1', which are distributed at the upper and lower peripheral portions of the electric insulator 3, in such a manner that a sub- conducting member is diverged from one main conducting member and extends toward the other main conducting member. The respective sub-conducting members 2 and 2'are spaced apart from each other by a predetermined gap G.

In the meanwhile, the conductive material 4 using PTCR or polymer is uniformly disposed on the upper surface of the conducting members, whereby the conductive material 4 applied in the gaps between the sub-conducting members 2 and 2'acts as a resistor when the electrodes 6 and 6'apply electricity, so as to radiate heat.

On the other hand, in the conventional plane heater, the main conducting members 1 and 1'are connected to the central portion and extend to the upper and lower ends of the plane heater and then extend along the peripheral portions of the plane heater, thereby occupying a considerable area. Since the main conducting members 1 and 1'don't function as a resistor, disadvantageously, heating area is accordingly reduced and heating is unevenly distributed.

Furthermore, the main conducting members 1 and 1'require such a treatment as expensive silver plating, or aluminum or nickel plating, whereby as the area occupied by the main conducting members 1 and 1'is increased, manufacturing costs

of the plane heater is also increased.

Moreover, in the conventional plane heater, the sub- conducting members 2 and 2'are vertically connected in parallel, whereby the length thereof is smaller than the width of the electric insulator 3 and thus a relatively larger number of sub-conducting members 2 and 2'are distributed as a whole. As a result, as the number of the sub-conducting members 2 and 2'becomes larger, the possibility of causing an error in the gap G is increased and therefore heating is apt to be unevenly distributed.

Meantime, in the conventional structure, a conductive paste is first applied, or a metallic material is first applied to or etched on the electric insulator 3 to form the conducting members 1,2 and 2'and then the conductive material 4, i. e., PTCR is applied. When a circuit, namely the conductive material 4, is applied to the conducting members 1, 2 and 2', the thickness of the conductive material 4 applied is apt to be changed depending on the thickness of the conducting members circuit and therefore the conductive material 4 is unevenly applied, leading to uneven distribution of temperature.

Additionally, in the conventional manufacturing process, since the circuit is first formed on the electric insulator 3 and thereafter the conductive material 4, i. e., PTCR is applied, the conductive material 4 as well as the conducting members 1, 2 and 2'should be uniformly applied to the electric insulator 3 to correspond to its relative position to the electric insulator 3. A great attention is required in the conventional manufacturing process and defective proportion is increased.

Besides, in the conventional structure, since the adhesive 5 contacts the conductive material, i. e., heating body, in case that high heat occurs in the conductive material 4, the adhesive 5 may cause a chemical change. In consequence, the expected lifespan of the adhesive 5 is decreased and an abnormal heating may be caused.

In addition, the conventional manufacturing process

usually requires a total of 4 drying processes or more as follows. After the conducting members 1,2 and 2'are applied to the electric insulator 3, a drying process is performed twice to achieve an appropriate resistance in the conducting members circuit. Next, after the conductive material 4, i. e., PTCR is applied to the conducting members 1,2 and 2', a drying process is performed twice again. Because of the large number of drying processes, the manufacturing process takes a long time until products are completed and manufacturing costs are increased.

On the other side, to enhance heating efficiency, it is desirable that the conductive material, i. e., PTCR is multi- applied. However, since the conductive material is applied to the conducting members 1,2 and 2', if another conductive material needs to be applied, both the first and second conductive materials directly contact each other.

There are lots of coating methods. Among them, if a silk screen printing method which is commonly used is adopted, when the second conductive material is applied to the first conductive material, a tool, such as a squeezer, should be used to squeeze a coating solution containing a solvent on the first conductive material. As a consequence, the surface of the first conductive material may be partially melted or damaged, thereby increasing the possibility of making the surface uneven or massed. In the result, the heating efficiency disadvantageously becomes uneven.

Disclosure of Invention Accordingly, the present invention is directed to a plane heater using a conductive material that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a plane heater using a conductive material in which main conducting members requiring a surface treatment, such as silver plating,

aluminum plating or etching, are arranged to extend from the edge portion toward the center or convergently arranged at the central portion and sub-conducting members diverged from the main conducting members are arranged in the form of a contour line extending from the center to the edge portion, thereby significantly improving heating efficiency and reducing manufacturing costs.

Another object of the present invention is to provide a plane heater using a conductive material in which the conductive material is first applied to a substrate which is an electric insulator and dried, and then conducting members are disposed on the dried conductive material, thereby simplifying manufacturing processes and decreasing defective proportion.

Because the arrangement of the conducting members, the area occupied by the main conducting members which require the surface treatment is reduced, manufacturing costs are reduced, heating area is widen, and the unit length of the sub- conducting members which maintain a predetermined gap from each other is elongated and uniformly distributed. Also, the total number of circuits is reduced and thus there can be significantly reduced the possibility of causing an uneven heating distribution due to an error in gap between the main conducting members and the sub-conducting members.

A further object of the present invention is to provide a plane heater using a conductive material in which the conductive material, i. e., PTCR is first widely applied to an electric insulator and thereafter conducting members are formed on the conductive material such that there is no need to correspond a relative position of the conductive material applied each case, thereby considerably simplifying manufacturing processes.

A still further object of the present invention is to provide a plane heater using a conductive material in which an adhesive is not in contact with the conductive material which is a heating body but adjacent to the conductive material with conducting members formed therebetween, whereby the adhesive

is prevented from being overheated when being used, and thus reduction in lifespan or overheat of the plane heater generated due to a chemical change of the adhesive can be prevented.

Yet another object of the present invention is to provide a plane heater using a conductive material in which even in case that the conductive material is formed in a double structure, first and second conductive materials are not in contact with each other but have conducting members therebetween, whereby when the second conductive material is subjected to a silk screen printing by using a squeezer on the first conductive material, the surface of the first conductive material is prevented from being damaged and therefore heating efficiency of the conductive materials becomes more uniform.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Brief Description of the Drawings The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: FIG. 1 is a plan view illustrating a conventional plane heater; FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1 ; FIG. 3 is a perspective view illustrating a rear-view mirror to which the conventional plane heater of FIG. 2 is

applied; FIG. 4 is a cross-sectional view illustrating a plane heater according to one preferred embodiment of the present invention; FIG. 5 is a cross-sectional view illustrating a plan heater according to another preferred embodiment of the present invention; FIG. 6 is a plan view illustrating a first example of the plane heater to which the embodiments of the present invention are applied; FIG. 7 is a plan view illustrating a second example of the plane heater to which the embodiments of the present invention are applied; FIG. 8 is a plan view illustrating a third example of the plane heater to which the embodiments of the present invention are applied; and FIG. 9 is a plan view illustrating a fourth example of the plane heater to which the embodiments of the present invention are applied.

Best Mode for Carrying Out the Invention The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings. For reference, like reference characters designate corresponding parts throughout several views.

FIG. 4 is a cross-sectional view illustrating a plane heater according to one preferred embodiment of the present invention, and FIG. 5 is a cross-sectional view illustrating a plan heater according to another preferred embodiment of the present invention.

Referring to FIGs. 4 and 5, in a plane heater using a conductive material in which conducting members 1,2 and 2' are arranged on the upper surface of an electric insulator 3 which is thin and flat, and a conductive material 4, such as PTCR, is arranged between the conducting members 1, 2 and 2'

such that when the conducting members 1,2 and 2'conduct electricity, the conductive material 4 generates heat, the plane heater is characterized in that the conductive material 4 is first applied to the upper surface of the electric insulator 3, a circuit of the conducting members 1,2 and 2' is formed by applying a conductive paste or applying/etching a metallic material to/on the upper surface of the conductive material 4, and an adhesive 5 is applied to the upper surface of the conducting members 1,2 and 2'which project from the electric insulator 3 so as not to directly contact the conductive material 4.

That is to say, according to the present invention, the conductive material 4, such as PTCR, etc., is first widely applied to the substrate which is the electric insulator 3 whereby the conductive material 4 can be applied over the entire area of the substrate without corresponding to its relative position to the electric insulator. After the conductive material 4 is dried to some extent, the conducting members 1,2 and 2'are just simply applied to the conductive material 4 to correspond to their relative positions to the conductive material 4.

Further, since the adhesive 5 is applied after the conducting members 1,2 and 2'are formed, it is spaced from the conductive material 4 as far apart as the height of the conducting members 1,2 and 2'.

Therefore, if the conducting members 1,2 and 2'conduct electricity and the conductive material 4 generates heat, the heat isn't directly transferred to the adhesive 5, whereby the adhesive's lifespan wouldn't be reduced and the conductive material 4 wouldn't emit overheat due to the adhesive's chemical change.

Meantime, the adhesive 5 is made of such an insulating material as acrylic, and used to make the plane heater adhered to the rear surface of an object to be heated, such as a rear- view mirror.

To be specific, the conductive material, i. e., PTCR is first applied to the upper surface of the flat electric

insulator 3 which is usually in a film form. If an equipment for uniform application or roller coating is used, a mass production can be easily achieved by virtue of automatic operation and thickness can be adjusted by a precision machinery. In consequence, if the plane heater is used as a heater, it can ensure various temperature characteristics and uniform temperature distribution.

In addition, the adhesive 5 is adhered to the conductive material 4 while having the conducting members 1,2 and 2' therebetween, such that there can be reduced effect of the adhesive material on the PTCR heating body. As a result, an abnormal phenomenon of the PTCR heating body due to the adhesive's chemical change at a high temperature can be also reduced.

The manufacturing process of the plane heater according to the present invention will be explained herein below.

In the manufacturing process of the plane heater using the conductive material in which the conducting members 1, 2 and 2'are arranged on the upper surface of the electric insulator 3 which is thin and flat and the conductive material 4, such as PTCR, is arranged between the conducting members 1, 2 and 2'such that when the conducting members 1,2 and 2' conduct electricity, the conductive material 4 generates heat, the manufacturing process comprises the steps of: dissolving the conductive material 4, such as PTCR, in a solvent, and widely applying the dissolved conductive material 4 to the upper surface of the electric insulator 3 by a silk screen printing method or a roller coating method; performing a first heat treatment to remove the solvent contained in the conductive material 4; forming the conducting members 1, 2 and 2'on the solvent-removed conductive material in accordance with reference points so as to be matched with the position of the conductive material 4 while forming a circuit by applying a conductive paste, or applying or etching a metallic material; and performing a second heat treatment to remove the solvent contained in the conducting members 1,2 and 2'and completely drying the conducting members 4 at the same time.

Conditions for the heat treatment to remove the conductive material 4, should be set according to characteristics of individual products. However, at large, when dried for about 1 to 3 minutes at a temperature of 90- 120 (C, higher than the boiling point of an organic solvent used for dissolution of polyolefin, most solvents evaporate and the conductive material 4 is maintained in a film state of 7-15 microns.

Meanwhile, the conducting members 1,2 and 2'should be applied to the position to which the conductive material 4 is applied. In order to protect the surface of the conductive material 4 from being damaged upon application of the conducting members 1, a solvent that doesn't dissolve a base resin of the PTCR is preferably adopted.

The present applicant used a polyolefin resin as a binder of the conductive material 4, i. e., PTCR, and used a polyester polymero chemical and other solvent as a binder of the conducting members 1,2 and 2', so that when the conducting members 1,2 and 2'are applied, the surface of the conductive material 4 can be protected from being damaged and maintained in the existing flat film form.

Further, to keep the resistance of the conducting members 1,2 and 2'in an appropriate range, it is important that the solvent contained in the conducting members should be dried in a given period of time. In this case, it is essential that characteristics of the PTCR material are not affected by drying temperature or time.

To be specific, it is necessary to set drying conditions for obtaining the appropriate resistance of the conducting members without affecting the PTCR material.

The applicant of the present invention performed a drying process for 10-20 minutes or so at a temperature of 100-135 (C with a result of satisfying both the characteristics of the PTCR material and the resistance of the conducting members. In the result, the applicant could reduce the second drying process of the PTCR material.

On the other side, to improve heating efficiency,

conductive materials 4 and 4'can be formed in a double structure as shown in FIG. 5.

The conductive materials 4 and 4'are applied in such a manner that the PTCR material is dissolved in the solvent and applied by a silk screen or a roller type coating method.

According to the present invention, however, the conductive material 4'isn't be directly applied to the upper surface of the conductive material 4, which is applied earlier than the conductive material 4', but applied with the conducting members 1,2 and 2'formed between the conductive material 4 and 4'. Accordingly, even though such a tool as squeezer is used, the conductive material 4'can be applied without damaging the surface of the conductive material 4.

In this manner, the conductive materials 4 and 4'can be applied more thicker and PTCR effect, namely resistance change with temperature rise, can be more increased. Accordingly, there can be achieved a faster heating function at a lower temperature and a more efficient control over temperature rise at a higher temperature.

When the conductive materials 4 and 4'are applied in the double structure, the conducting members 1,2 and 2'are first applied to the conductive material 4 which is first applied and then the conductive material 4'is applied to the conducting members 1,2 and 2'. It should be noted that the surface of the conductive material 4 which is first applied should be protected from being damaged by the solvent contained in the conductive material 4'which is second applied.

The applicant applied the second conductive material 4' and thereafter putted the same into a drying furnace in about 10-20 seconds with a result of a uniform surface of the second conductive material 4'.

In summary, a user can apply the conductive material 4 to the upper surface of the electric insulator 3 only if he or she widely applies the conductive material 4 without a specific reference. Only for the conducting members 1, 2 and 2', he or she should apply them in accordance with their

reference points. As a result, the edge portion of the plane heater can be cut whereby the process control can be accordingly facilitated and a PTCR applying jig can be simplified.

Since the PTCR material can be applied without considering any reference point, a mass application can be carried out by employing a roller type printing method and a roller type coating method as well as a screen printing method using a squeezer. Thus, in the later process of applying the conducting members, an automatic operation is performed when other holes are formed, an electric terminal is connected, and an outer line is formed, thereby considerably enhancing productivity. Since the various application methods can be employed, other PTCR materials different from the PTCR material which is stable at a normal temperature can be used.

Furthermore, in the conventional manufacturing process, after the conducting members 1,2 and 2'are applied and the drying processes are performed twice to attain the appropriate resistance of the conducting members circuit, the conductive material 4, i. e., PTCR is applied to the upper surface of the dried conducting members 1,2 and 2'and the drying processes are carried out twice again, thereby requiring the drying processes four times or more. According to the present invention, however, after the conductive material 4 is applied and the first drying process is performed, the conducting members 1,2 and 2'are applied and the first to second drying processes are performed at the same time, such that the second drying process of the conductive material 4 is not separately carried out. The present invention is accordingly simpler in the manufacturing process than the conventional art.

In this case, the conducting members 1,2 and 2'and the conductive material 4 which actually emits heat are all exposed to the outside air so that a proper drying effect can be obtained, in contrast to the conventional structure.

On the other side, FIG. 6 is a plan view illustrating a first example of the plane heater to which the embodiments of the present invention are applied, FIG. 7 is a plan view

illustrating a second example of the plane heater to which the embodiments of the present invention are applied, FIG. 8 is a plan view illustrating a third example of the plane heater to which the embodiments of the present invention are applied, and FIG. 9 is a plan view illustrating a fourth example of the plane heater to which the embodiments of the present invention are applied.

In the improved plane heater of the type having, the electric insulator 3 which is thin and flat, main conducting members 1 and 1'secured to the upper surface of the electric insulator 3, respectively connected to a pair of electrodes 6 and 6'and subjected to a surface treatment including silver plating, aluminum plating or etching, the plurality of sub- conducting members 2-and 2'respectively diverged from the main conducting members 1 and 1'in such a manner that a sub- conducting member diverged from one main conducting member is spaced apart from a sub-conducting member diverged from the other conducting member by a predetermined gap G, the conductive material 4 applied to the upper surface of the electric insulator 3, the main conducting members 1 and 1'and the sub-conducting members 2 and 2', and made of a material, such as PTCR, and the adhesive 5 applied to the upper surface of the conductive material 4 so as to be adhered to the rear surface of an object to be heated, the improvement comprises: main conducting members 1 and 1'arranged to extend from an edge portion toward the center (see FIGs. 7 and 8) or convergently arranged at a central portion (see FIGs. 6 and 9); and sub-conducting members 2 and 2'diverged from the main conducting members 1 and 1'and arranged in the form of a contour line extending from the center toward the edge portion That is to say, the plurality of sub-conducting members 2 and 2'are alternately arranged from the central portion toward the edge portion, such that each sub-conducting member diverged from one main conducting member extends from the central portion toward the edge portion and returns to the central portion where the other main conducting member is located. As a whole, the sub-conducting members 2 and 2'are

in the contour form.

Meantime, the adhesive 5 is made of such an insulating material as acrylic. When the plane heater is applied to a rear-view mirror 10 as illustrated in FIG. 3, it is adhered to the rear surface of an inner side of the rear-view mirror 10 by means of the adhesive 5.

Additionally, the sub-conducting members 2 and 2' diverged from the main conducting members 1 and 1'are spaced apart from each other by a predetermined gap G, and alternately arranged to face each other.

The operation of the present invention constructed as above will be explained as follows.

If a current flows into the inside of the main conducting members 1 and 1'through the electrodes 6 and 6', the current runs from the edge portion to the central portion through the main conducting members 1 and 1', and flows through the sub- conducting members 2 and 2'.

On the other hand, the sub-conducting members 2 and 2' are spaced apart from each other by the predetermined gap G but the conductive material 4, e. g. PTCR, is coated between the sub-conducting members 2 and 2', whereby when the electrodes 6 and 6'conduct electricity, the conductive material 4 applied between the sub-conducting members 2 and 2' acts as a resistor, so as to generate heat.

By the way, in the plane heater according to the present invention, since the main conducting members 1 and 1'are all arranged to extend from the edge portion to the center or convergently arranged at the central portion, the length of the main conducting members 1 and 1'can be shorter than that of the related art and the area occupied by the main conducting members 1 and 1'can be reduced.

Therefore, the heating area is relatively increased and the heating is uniformly distributed.

Moreover, the main conducting members 1 and 1'require the expensive surface treatment including silver plating, aluminum plating or etching such that as the area occupied by the main conducting members 1 and 1'is reduced, the

manufacturing costs of the plane heater are further reduced.

Also, according to the present invention, the sub- conducting members 2 and 2'are not in a linear form but put around the area ranging from the center to the edge portion and return to the center again, whereby the sub-conducting members 2 and 2'become much elongated in the unit length, as compared with the conventional art, and the number of the sub- conducting members 2 and 2'is accordingly reduced, thereby reducing the possibility of causing an error in the gap G and an uneven heating distribution.

Industrial Applicability As described above, the main conducting members 1 and 1' requiring the surface treatment including silver plating, aluminum plating or etching, are arranged to extend from the edge portion toward the center or convergently arranged at the central portion, and the sub-conducting members 2 and 2' diverged from the main conducting members 1 and 1'are arranged in the contour form extending from the center to the edge portion, thereby significantly improving heating efficiency and reducing manufacturing costs, relative to the conventional art.

Further, the conductive materials 4 and 4'are first applied to the substrate which is the electric insulator 3 and dried, and then the conducting members 1,2 and 2'are arranged on the dried conductive materials 4 and 4', thereby simplifying the manufacturing process and decreasing defective proportion.

That is to say, since the main conducting members 1 and 1'are arranged to extend from the edge portion toward the center or convergently arranged at the central portion so as for the sub-conducting members 2 and 2'to be arranged at the central portion in the contour form, the area occupied by the main conducting members 1 and 1'which require the surface treatment including plating, is reduced, and thus the manufacturing costs are reduced and the heating area is

widened. Further, since the unit length of the sub-conducting members 2 and 2'which maintain the predetermined gap from each other is elongated, the sub-conducting members can be uniformly distributed and the number of the entire circuits is also reduced, thereby significantly decreasing the possibility of causing an uneven heating distribution due to the error in the gap between the main conducting members and the sub- conducting members.

Besides, the conductive material, i. e., PTCR is first widely applied to the upper surface of the electric insulator 3 and then the conducting members 1, 2 and 2'are formed on the upper surface of the conductive material 4, whereby the relative position of the conductive material applied doesn't need to be corresponded, resulting in achievement of a simpler manufacturing process.

Furthermore, the adhesive 5 is not in a direct contact with the conductive material 4 which is a heating body but adjacent to the conductive material 4 by interposing the conducting members 1,2 and 2'between the adhesive 5 and the conductive material 4, whereby the adhesive is prevented from being overheated when being used, thereby not shortening the lifespan of the plane heater and not causing overheat due to a chemical change of the adhesive.

In the event that the conductive materials 4 and 4'are formed in the double structure, the first and second conductive materials are not in a direct contact with each other but have the conducting members 1,2 and 2'formed therebetween, whereby even when the second conductive material is subjected to a silk screen printing on the first conductive material by using a squeezer, the surface of the first conductive material is protected from being damaged, thereby making the heating efficiency of the conductive material uniform.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.