Positive temperature coefficient heater and production method thereof

Abstract: A positive temperature coefficient heater produced by protecting the form of a definite pattern on an insulator having an aluminum thin film using an etching resist, after etching the portions unprotected with the above-described etching resist using an etching agent, removing the etching resist and the etching agent, and further printing a definite form using a carbon paste to connect electrode terminals to aluminum electrode layer in parallel. In the positive temperature coefficient heater of the present invention, as compared with using a conventional silver paste, there is almost no deviation of temperature, the production cost is greatly reduced, and further the production step is simplified, whereby when the positive temperature coefficient heater is attached to the inside of a side mirror of a motorcar, an excellent effect is shown in the removal of fogging, ice, etc.

Description: 1. BACKGROUND OF THE INVENTION 1.1 Field of the Invention The present invention relates to a positive temperature coefficient heater. More specifically, the invention relates to a self regulating heater using positive temperature coefficient resistive material specifically adapted for use in heating outside rearview mirrors of the vehicles. In still greater particularity, the present invention relates to a positive temperature coefficient heater wherein a definite pattern form is protected on an insulator having an aluminum film using an etching resist, after etching the portions unprotected with the etching resist using an etching agent, the etching resist and the etching agent are removed, and by printing a definite form using a carbon paste, the insulator having the aluminum thin film is constituted to be connected as acting parallel electrodes, and also relates to a production method thereof. 1.2 Description of the Prior Art Hitherto, as positive temperature coefficient heaters utilizing the above-described technique, there are U.S. Patents 3,887,788, 3,790,748, 3,781,526, 3,757,087, 5,446,576, 4,410,790, 4,942,286, 5,015,824, 4,017,715, 4,304,987, 4,330,703, 2,559,077, 2,978,665, 3,243,753, 3,351,882, 3,412,358, 4,034,207, 4,777,351, 4,761,541, 4,857,711, 4,628,187, 5,440,425, 5,155,334, 3,900,654, and 3,848,144 conventionally. Also, as Japanese patent (unexamined) publications and utility model (unexamined) publications similar to those, there are Japanese Patent (unexamined) Publication Nos. 2-162143, 8-64352, 6-176857, 7-99083, 3-261090, and 55-95203, and Utility Model (unexamined) Publication Nos. 61-84063, 59-40417, 3-67904, etc. However, in the above-described techniques, the techniques without having PTC resistor are those of generating heat by flowing a direct current, the patent rights of the almost of these patents have been lapsed, and further because the resistance of the resistors is low and the ampere is high, there is a fault that the temperature control of the heat-generating elements is difficult. Furthermore, direct passing of an electric current to a heat-generating element without using separate electrodes has a fault that the electric conductivity is uneven. Also, in the heat-generating elements each constituted by electrodes and a resistor, the electrode is almost formed by printing a compounded mixture of a metal powder such as silver, etc., and a resin, also the resistor is formed by printing a compounded mixture of a carbon and a resin, and by applying an electric current to the electrodes, heat is generated in the resistor. Such planar heat-generating elements can be classified into a heat-generating element wherein the electrode form is made a comb-like pattern or the resistor is made in a strip form for uniformly transmitting heat and a sheet-form heat-generating element wherein after printing a pattern having a definite band-form space on an insulating substrate with a silver paste, a carbon paste is coated on the surface thereof with a printer such that the portion remained as the space at printing the silver paste and the upper portion of the silver paste are covered by the carbon paste for improving the transfer of heat and the efficiency of heat. However, in the above-described inventions, etc., silver itself has a good electric conductivity as a conductor, but because a paste formed by compounding powdery silver with a resin is used, the electric conductivity becomes weak, the production step becomes complicated, and a large cost is required accompanied thereby. Thus, the development of a new positive temperature coefficient heater different from the conventional ones has been desired. 2. SUMMARY OF THE INVENTON In view of the foregoing circumstances, the present inventor has discovered that the problems as described above can be solved by producing a positive temperature coefficient heater is constituted by protecting a form of a definite pattern using an etching resist on an insulator having an aluminum thin film, and more preferably on a film formed by vapor-depositing aluminum on a PET sheet, after etching the portions unprotected by the above-described etching resist using an etching agent, removing the etching resist and the etching agent, and further printing on the above-described etched portions using a carbon paste, so that the insulator having the aluminum thin film acts as parallel electrodes and the carbon paste layer acts as a resistor, and has accomplished the present invention. 3. BRIEF EXPLANATION OF THE DRAWINGS These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where; Fig. 1 A and Fig. 2 A show plane views of positive temperature coefficient heaters of the present invention each formed, after etching an insulator having a polyethylene layer-laminated aluminum thin film, by printing a definite form on the surface thereof with a carbon paste. Fig. 1 B and 2B show the views of the back surfaces of Fig. 1 A and 2 A. Fig. 3 is a cross-sectional view of the positive temperature coefficient heater of this invention. Fig. 4 A shows the change and transition of the electric current and the surface temperature at -30°C of the Test piece 1 in Test example 2 by a graph, Fig. 4 B shows the change and transition of the electric current and the surface temperature at -40°C of the Test piece 1 by a graph, and Fig. 4 C shows the photograph of change and transition of the state of removing planar frozen ice by surface temperature raising every two minutes after the initiation of passing an electric current at -30°C of the Test piece 1. Fig. 5 A shows the change and transition of the electric current and the surface temperature at -30°C of the Test piece 2 in Test Example 2 by a graph, Fig. 5 B shows the change and transition of the electric current and the surface temperature at room temperature of the Test piece 2 by a graph, and Fig. 5 C shows the photograph of the change and transition of the state of removing planar frozen ice by surface temperature raising every two minutes after the initiation of passing an electric current at -30°C of the Test piece 2. Fig. 6 A shows the change and transition of the electric current and the surface temperature at -30°C of the Test piece 3 in Test Example 2 by a graph, Fig. 6 B shows the change and transition of the electric current and the surface temperature at room temperature of the Test piece 3 by a graph, and Fig. 6 C shows the photograph of the change and transition of the state of removing planar frozen ice by surface temperature raising every two minutes after the initiation of passing an electric current at -30°C of the Test piece 3. 4. DETAILED EXPLANATION OF THE INVENTION The present invention is explained in detail by referring to the accompanying drawings. Fig. 1 A or Fig. 2 A is a plain view of a positive temperature coefficient heater of the present invention. As shown in Fig. 1 A or Fig. 2 A, the positive temperature coefficient heater of this invention is constituted by a insulating substrate, a band-form aluminum thin film pattern formed thereon, a carbon paste, and electric current terminals. Then, the positive temperature coefficient heater of this invention is explained in detail together with the production method thereof. First, an insulator having an aluminum thin film laminated with PET, that is, an insulator having an aluminum thin film prepared by vacuum vapor-depositing aluminum on PET is cut into a definite size, otherwise, cutting is made after producing as it is. After printing a definite pattern on the insulator having the aluminum thin film with an etching resist, for example a heat etching resist or a UV etching resist, such as, X-77, X-65, AS-500, etc., of Daiyo Ink Co., in Korea, the printed pattern is dried by heating or UV. Thereafter, when an acid such as, for example hydrochloric acid is sprayed onto the insulator having the aluminum thin film from a nozzle, the aluminum except the portion protected with the etching resist is corroded and released. The insulator is washed with water. Then, to remove the etching resist, the etching resist is neutralized with an aqueous alkali solution, for example, an aqueous solution of from 1 to 3% sodium hydroxide, and after washing with water, dried, whereby an electrode (aluminum) pattern only remains as shown in Fig. 1 A or Fig. 2 A. Then, a PTC carbon paste is printed on the above-described pattern and dried to produce a positive temperature coefficient heater. The positive temperature coefficient heater thus produced the cross section as shown in Fig. 3. However, the form of the pattern of the positive temperature coefficient heater of this invention can be changed for the sake of the production thereof and is not limited to the pattern shown in any of the accompanying drawings. The above-described carbon paste is explained in brief but there is no particular restriction on carbon used for the carbon paste of this invention if the carbon has a heat conductivity. That is, because amorphous carbon is poor in the heat-conductive property, it is desirable to use commercially available carbons having a good heat-conductive property. The heat conductivity of these carbons is at least 37.7 x 10 -3 deg. cm. sec., and as commercially available carbons. These carbons each has a different heat-conductive property and to control the heat-conductive property, the using amount thereof can be properly determined but the using amount thereof is desirably from 10 to 50 parts by weight to 100 parts by weight of a resin. There is no particular restriction on the resin used for the carbon paste if the resin shows less thermal deformation property, can be easily compounded with carbon, has an adhesive property, and is water-sparingly soluble. As examples thereof, there are polyester, polyacrylate, polyamide, etc., and in these resins, a polyester resin is particularly preferred. Also, the positive temperature coefficient heater of the present invention is a positive temperature coefficient heater comprising electrodes of an aluminum thin film formed by forming a pair of band-form main electrodes opposing each other at an aluminum thin film of an insulating sheet having the aluminum thin film, protecting utilizing an etching resist such that electrodes of a parallel continuous pattern are formed by projecting from these electrodes as engaging each other, etching the unprotected portions using an etching agent, and removing the etching resist and the etching agent; electric source terminals formed to the end portions of the above-described electrodes adjacent and opposing each other; and resistors formed by printing a carbon paste on the electrodes of the aluminum thin film. The construction of the positive temperature coefficient heater thus produced can be used as it is but for the consideration of the distribution and the use of users, by a known method after coating an adhesive on the upper portion of the positive temperature coefficient heater to form an adhesive layer (4), a release paper (5) is attached. Also, the terminals are equipped to the definite portions of the aluminum electrode (2) at the opposite surface through the insulator layer. In this case, the portions of the aluminum electrodes (2) are separated from each other by the carbon paste (3) as shown in Fig. 3 and by equipping the electric current input terminals to the aluminum electrodes (2) separated from each other, electric currents are connected in a parallel state. Furthermore, when the positive temperature coefficient heater is large, 2 pairs of current input terminals may be separately equipped to the electrodes with the longest distance. 5. EXAMPLES The present invention will be described in more detail by way of various examples, which should not be construed to limit the scope of the present invention. 5.1 Example 1 After printing the pattern on a sheet formed by vapor-depositing aluminum on a commercially available PET film (thickness of aluminum layer: 3.0 nm, thickness of the sheet: 150 m) using an etching resist, X-77 (trade name) of Daiyo Ink Co., in Korea, the printed pattern was dried by heating to 60°C for 20 minutes. Thereafter, when an aqueous solution of 5% hydrochloric acid was sprayed, the aluminum layer was corroded and released except the portions protected by the above-described etching resist. The sheet was washed with water and further washed with an aqueous solution of 2% sodium hydroxide. A liquid prepared by dissolving a polyester resin in butyl cellosolve acetate as a solvent at a ratio of 1.4 : 1 was compounded with carbon, at 6 : 5 (by weight ratio) to prepare a carbon paste and the paste was coated by printing on the aluminum sheet obtained by the above-described method at a thickness of 10 nm. By printing as described above, a band-form carbon paste layers (3) and aluminum electrodes (2) shown in Fig. 3 were formed. Furthermore, after coating the above-described carbon paste layers (3), a double coated tape or an adhesive layer was formed thereon. In this case, from the points of the industrial production and the reduction of the cost, it is preferred to coat a hot melt ethylene vinyl acetate. Then, by adhering a release paper and attaching electric current terminals such that they were contacted with the aluminum electrode sites as shown in Fig. 3, the positive temperature coefficient heater of this invention was produced. Because from the positive temperature coefficient heater thus produced, frozen ice, ice, fogging, etc., can be very efficiently removed in a short time, the heat-generating element is useful for side mirrors for motorcars, mirrors in bath room, etc. 5.2 Test Example 1 Using the positive temperature coefficient heater prepared in Example 1, following terms were tested and the results are shown together. 5.2.1. Electric characteristics (1) Related voltage: DC 13.5 V (2) Used voltage: DC 10 to 15 V (3) Largest electric current: AT, -40°C, DC 13.5 V Initial electric current: < 3.5 AMP. After 10 minutes: < 2.2 AMP. (4) Insulation resistance: > 10 M (500 V MEGA) (5) Overvoltage: Even when DC 15 V is applied for 24 hours, the element is neither broken nor burned. 5.2.2. Ice-removing characteristics by the positive temperature coefficient heater of this invention: After wiping the surface of a mirror with aqueous ammonia to remove an oil, etc., the surface was further wiped with distilled water and dried. The mirror was allowed to stand at -18°C for 2 hours. Then, for 1 hour at -40°C, at an atmospheric temperature of 25°C, 65 ± 10%, ice of 0.5 mm was uniformly formed on the surface and after further allowing to stand for 4 hours at -40°C, after allowing stand for 30 minutes at following each temperature, DC 13.5V was applied. The results thereof were as follows. When an electric current was passed for 3.5 minutes at -5°C, 80% of the ice was removed. When an electric current was passed for 6 minutes at -25°C, 80% of the ice was removed. When an electric current was passed for 10 minutes at -25°C, 95% of the ice was removed. When an electric current was passed for 12 minutes at -40°C, 80% of the ice was removed. 5.2.3. Temperature control test of the surface of the mirror: When DC 13.5 V was applied at -30°C, the surface temperature of the mirror became 10°C or higher after 10 minutes. When DC 13.5 V was applied at 25°C, the surface temperature of the mirror became 55°C ± 10°C after 10 minutes. When DC 13.5 V was applied at 45°C, the surface temperature of the mirror became 70°C or lower after 10 minutes. 5.2.4. When a temperature exposure test was carried out by attaching the positive temperature coefficient heater of this invention prepared in Example 1 to a glass, there was nothing wrong with the glass at a temperature of from -30°C to 20°C and also at 115°C, there was nothing wrong with the glass even when an electric current was passed for 1 hour. 5.2.5. The same material as described above was tested in atmosphere for 200 cycles wherein it is set up as one cycle to dip the sample with a 5% NaCl solution for 5 minutes, by applying DC 15V for 10 minutes and then taking off the current source. Further, the same test was carried out using a 5% CaCl 2 solution. As a result, there was nothing wrong with the positive temperature coefficient heater of this invention. 5.2.6. Using the positive temperature coefficient heater of this invention, a surface raising temperature, a low-temperature operating electric current, and a normal-temperature operating electric current were tested and the results were shown in Table 1 to Table 3. (In the tables, LH shows a side mirror at the left side, RH shows a side mirror at the right side, J-95 shows a small-sized car which is a product of one company selected from three motorcar makers in Korea, H-car shows a middle-sized car which is a product of one company selected from three motorcar makers in Korea, and G-car shows a middle-sized car which is a product selected from three motorcar makers in Korea.) 5.2.6. Low-Temperature Operating Current (-30 °C) (unit: A) Model Section Initial 2 min 4 min 6 min 8 min 10 min 12 min 14 min 16 min J-95 LH 1.64 1.53 1.48 1.47 1.46 1.46 1.45 1.45 1.45 RH 1.62 1.52 1.47 1.48 1.45 1.44 1.44 1.43 1.43 H-CAR LH 2.03 1.88 1.81 1.78 1.76 1.76 1.75 1.75 1.75 G-CAR LH 2.10 1.93 1.85 1.82 1.80 1.79 1.79 1.78 1.78 Normal-Temperature Operating Current (at 26°C)(unit: A) Model Section Initial 2 min 4 min 6 min 8 min 10 min 12 min 14 min 16 min J-95 LH 1.27 0.93 0.84 0.80 0.78 0.77 0.77 0.76 0.76 RH 1.25 0.91 0.83 0.79 0.77 0.77 0.76 0.76 0.76 H-CAR LH 1.51 1.03 0.91 0.88 0.83 0.80 0.79 0.78 0.78 G-CAR LH 1.56 1.08 0.97 0.92 0.90 0.89 0.88 0.88 0.88 5.3 Test Example 2 A large-sized positive temperature coefficient heater connected to aluminum in series (a separate resistance heat-generating element was not used) (a product of N company in Europe; hereinafter, is referred to as Test piece 1'), a positive temperature coefficient heater produced by forming electrodes with a paste of a silver powder and forming a resistor with a carbon powder paste according to U.S. Patent 4,857,711 (hereinafter, is referred to as Test piece 2'), and the positive temperature coefficient heater of the present invention (hereinafter, is referred to as Test piece 3') were tested under the following conditions and the results are shown in Fig. 4 to Fig. 6. 5.3.1. First, after cooling the Test piece 1 at -30°C, an electric current of 24 V was passed through it, the change of the initial electric current [A] and the change and transition of the temperature every two minutes were measured, and the results were shown in Fig. 4 A. As shown in the figure, the initial electric current [A] was 2.25 A but at the time of passing 11 minutes, the electric current became 1.94 A, and further after 20 minutes, the electric current was almost same. This shows that there is almost no change of the resistance and because the electric current passes constantly in succession, the temperature control of the positive temperature coefficient heater is very difficult. Also, when the change of the temperature was determined, at the time after passing 11 minutes from the initial temperature of -28°C, the temperature raised to 12.9°C and at the time of passing 20 minutes, the temperature raised to about 20°C. This shows that the temperature control of the positive temperature coefficient heater can not be satisfied as described above. Also, Fig. 4 B showed the result of keeping the Test piece 1 for 30 minutes at 40°C, passing an electric voltage of 24 V at normal temperature, and measuring the change of the initial electric current [A] and the change and transition of the temperature every two minutes. Almost same as Fig. 4 A, the initial electric current [A] was 1.68 A but at the time passing 11 minutes, the electric current became 1.60 A and even after passing 20 minutes, the electric current was almost same. This shows that there is almost no change of the resistance and because the electric current passes constantly in succession, the temperature control of the positive temperature coefficient heater is very difficult. Fig. 4 C showed the figure of the photograph of the state in which water was scattered on the Test piece 1 at -30°C to form ice on the surface of a mirror, after allowing to stand for 30 minutes, an electric current began to pass at a voltage of 24 V, and the planer ice was removed by raising of the surface temperature every two minutes. 5.3.2. Also, after cooling the Test piece 2 at -30°C and keeping for 30 minutes, an electric current of a voltage of 24 V was passed, the change of the initial electric current [A] and the change and transition of the temperature every two minutes were measured, and the results were shown in Fig. 5 A. As shown in the figure, the initial electric current [A] was 4.83 A but at the time of passing 20 minutes, the current became 2.87 A. This shows that when the initial electric current is compared with the electric current after 20 minutes, the electric current after 20 minutes is considerably lower than that of the Test piece 1, and also, the resistance value is increased and the ampere is lowered, whereby the temperature control is easy. Furthermore, from that the temperature raised to 31.9°C after 20 minutes from -27°C, it can be seen that the effect is considerably excellent. Fig. 5 B shows the results of testing the Test piece 2 at normal temperature. In this case, the initial electric current was 3.2 A and after an electric current was passed for 20 minutes, the electric current lowered to 1.70 A and the resistance value is increased. Accordingly, when the temperature is raised, the change of the resistance value is increased and also the electric current becomes low, which prevents the rapid raising of the temperature. Fig. 5 C shows the figure of the photograph of the state of scattering water to the Test piece 2 at -30°C to form ice on the surface of a mirror, after allowing to stand for 30 minutes, initiating passing of an electric current at a voltage of 24 V, and removing the planar ice by surface temperature raising every two minutes. The photograph shows that the results are excellent as compared with Fig. 4 C. 5.3.3. Also, after cooling the Test piece 3 at -30°C and keeping for 30 minutes, an electric current of 24 V was passed, the change of the initial electric current [A] and the change and transition of the temperature every two minutes were measured, and the results were shown in Fig. 6 A. As shown in the figure, the initial electric current [A] was 5.45 A but at the time of passing 20 minutes, the electric current became 2.76 A. As compared with the Test piece 1 and the Test piece 2, when the initial electric current was compared with the electric current after 20 minutes, when the temperature raised after 20 minutes, the change of the resistance value became large and the electric current is lowered, which results in preventing rapid raising of the temperature and making easy the temperature control. Also, from that the temperature raised to 34.8°C after 20 minutes from -27°C, it can be seen that the effect is considerably excellent. Fig. 6 B shows the results of testing the Test piece 3 at normal temperature. In this case also, the initial electric current was 3.30 A, the electric current after 20 minutes passed from the initiation of passing an electric current is lowered to 1.59 A and the resistance value is increased. Accordingly, in the positive temperature coefficient heater of the present invention, when the temperature is raised, the change of the resistance value becomes considerably large and by lowering the electric current, the temperature control becomes easy as compared with the Test piece 1 and the Test piece 2, which are heat-generating elements by conventional techniques. Fig. 6 C shows the figure of the photograph of the state by scattering water to the Test piece 3 at -30°C to form ice on the surface of a mirror, after allowing to stand for 30 minutes, initiating passing of an electric current at a voltage of 24 V, and removing the planer ice by surface temperature raising every two minutes. The photograph shows that the results are excellent as compared with Fig. 4 C and Fig. 5 C. As shown in the examples and the test examples as described above, in the positive temperature coefficient heater of the present invention, the conductivity is uniform and the heat-generating effect is excellent as compared with positive temperature coefficient heaters by conventional techniques, and the positive temperature coefficient heater can be easily produced at a low cost. In the positive temperature coefficient heater of the present invention, there is almost no deviation of temperature, the production cost is greatly reduced, and the production step is simplified as compared with the case of using a silver paste in a conventional technique, and thus by attaching the positive temperature coefficient heater to the inside of a side mirror of a motorcar, an excellent effect is shown for removing frozen ice, fogging, ice, etc.

Claims: A positive temperature co-efficient heater comprising an insulating sheet (1) having an aluminium thin film layer (2) provided thereon, the thin film being arranged to define a pair of side by side main electrodes, said main electrodes being etched to form electrodes of continuous patterns, electric source terminals provided adjacent each respective end of the electrodes, the electrodes having a carbon paste layer (3) provided there over to form a resistor characterised in that the carbon paste comprises a solution, formed by dissolving a polyester resin in butyl cellosolve at a ratio 1.4:1, and carbon at a ratio of 6:5 by weight. A method of forming a temperature co-efficient heater comprising forming a pair of side by side main electrodes on an insulating sheet (1) having a layer of aluminium film (2) thereon, etching said main electrodes to define electrodes of continuous patterns, providing electric source terminals adjacent each end of said electrodes and applying carbon paste (3) to the electrodes to produce a resistor characterised in that the carbon paste comprises a solution, formed by dissolving a polyester resin in butyl cellosolve at a ratio 1.4:1, and carbon at a ratio of 6:5 by weight.

Inventors: KIM GYONGTAE, KIM, GYONGTAE
Applicants: DAEIL P F T CO LTD, DAEIL P.F.T. CO., LTD.
Application year: 1999
Main classification: H05B3
IPC codes: H05B3