WO2006001571A1

WO2006001571A1 - Positive temperature coefficient(ptc) composition comprising electro graphite powder and method for preparing ptc heating unit by use of the ptc composition

Info

Publication number: WO2006001571A1
Application number: PCT/KR2005/000753
Authority: WO
Inventors: Moon-Woo Jeong
Original assignee: Moon-Woo Jeong
Priority date: 2004-03-16
Filing date: 2005-03-16
Publication date: 2006-01-05
Also published as: KR20050092566A

Abstract

Disclosed is a PTC (Positive Temperature Coefficient) composition, including electro graphite powder and silica sand mixed at a ratio suitable for a surface control temperature of a heating body, and a phenol resin is included therein as a uniting material at a suitable mass ratio for the mixture. Also disclosed is a method for preparing a PTC heating unit by use of an electro graphite powder, which includes stirring electro graphite powder and silica sand at a ratio suitable for a surface control temperature of a heating body; mixing a phenol resin as a uniting material to the stirred mixture at a suitable ratio; adjusting a density of the mixture at curing by adding methyl alcohol to the mixture; putting the mixture in a mold at a normal temperature for shaping; and hardening the shaped material.

Description

POSITIVE TEMPERATURE COEFFICIENT(PTC)

COMPOSITION COMPRISING ELECTRO GRAPHITE

POWDER AND METHOD FOR PREPARING PTC HEATING

UNIT BY USE OF THE PTC COMPOSITION Technical Field [1] The present invention relates to a PTC (Positive Temperature Coefficient) composition using an electro graphite powder and a method for preparing a PTC heating unit by use of the PTC composition, and more particularly to a PTC composition including electro graphite powder and silica sand mixed at a suitable ratio for a control temperature and also including a phenol resin as a uniting material at a suitable mass ratio of the mixture, and a method for preparing a PTC heating unit by use of the PTC composition. Background Art [2] A PTC heating unit is a repeatedly usable element, differently from a general fuse. The PTC heating unit is also called a poly switch and has a positive temperature co¬ efficient characteristic. A PTC element is a resistance element utilizing the feature that a resistance value is abruptly increased when reaching a specific temperature. If the PTC element is connected to a circuit, the increase of current flowing through the circuit makes the temperature of the PTC element increased. If the current is increased beyond an allowable value, the temperature of the PTC element reaches the specific temperature to increase resistance abruptly, thereby interrupting the flow of current. This feature is widely used for protecting an electronic device by preventing an excessive current from flowing through the device. [3] Generally, a PTC using BaTiCβ ceramic or polymer is well known in the art. The ceramic PTC has disadvantages in the points that a peculiar resistance has a lower limit in a normal state due to its properties by nature and it has a limited persistence to high voltage or high current. In addition, the ceramic PTC has a limitation since it is not easily processed. [4] Thus, consumption of the polymer PTC element is rapidly increased. When using the polymer PTC, it is possible to make a protection element for various circuits from high current at a low resistance to high voltage. It addition, the polymer PTC element is effective in preventing excessive current or overheating at a region that was not covered in the conventional ceramic PTC. Though the polymer PTC has a short history rather than the BaTiCβ ceramic PTC thermistor, it has many possibilities in application to be developed. Thus, there are many possibilities to develop the polymer PTC. However, the polymer PTC has disadvantages such as a low temperature range for usage, a low heat transfer rate, and low stability due to increase of a resistance value after soldering. Disclosure of Invention Technical Problem [5] Thus, the present invention is designed to overcome the disadvantages of the con¬ ventional PTC heating unit, and an object of the invention is to provide a self current control resistance heating material for supplying a heating unit that enables stable and efficient automatic temperature control in various usages owing to a large resistance range, a large temperature range for usage, and a large usable current range. Technical Solution [6] In one aspect of the present invention, there is provided a PTC (Positive Temperature Coefficient) composition, wherein the PTC composition comprises electro graphite powder and silica sand mixed at a ratio suitable for a surface control temperature of a heating body, and wherein a phenol resin is included therein as a uniting material at a suitable mass ratio for the mixture. [7] In one embodiment, the PTC composition according to the present invention is composed of a mixture of graphite and silica sand (medium-sized sand) so that a temperature range for usage is about 40 to 400⁰C. At this time, the mixing ratio of the electro graphite powder and the silica sand suitable for the surface control temperature of the heating body is 100:500 to 100:700 on the basis of mass. In addition, when the mixed graphite and silica sand is coated on a wall of a building for example, the content of the phenol resin is mixed by about 18 to 30% with respect to the total mass of the electro graphite powder and the silica sand so that the graphite as well as the sane may be converted from the negative (-) characteristic to the positive (+) char¬ acteristic with keeping a uniting force. [8] Here, the reason of mixing the silica sand is that the graphite having a positive (+) characteristic at about 400 to 600⁰C may have a positive (+) characteristic even at a low temperature of about 40 to 400 ⁰C. [9] As another aspect of the present invention, there is also provided a method for preparing a PTC heating unit by use of an electro graphite powder, which includes stirring electro graphite powder and silica sand at a ratio suitable for a surface control temperature of a heating body; mixing a phenol resin as a uniting material to the stirred mixture at a suitable ratio; adjusting a density of the mixture at curing by adding methyl alcohol to the mixture; putting the mixture in a mold at a normal temperature for shaping; and hardening the shaped material. [10] In one embodiment, in the case that the surface control temperature is about 40 to 400⁰C, the mixing ratio of the electro graphite powder and the silica sand suitable for the surface control temperature of the heating body is 100:500 to 100:700. In addition, the content of the phenol resin is preferably about 18 to 30% with respect to the total mass of the electro graphite powder and the silica sand at this time. In a specific embodiment, in the case that the surface control temperature is 250⁰C, the mixing ratio of the electro graphite powder and the silica sand is preferably 1:5, and the content of the phenol resin is preferably 25% with respect to the total mass of the electro graphite powder and the silica sand. [11] In another embodiment, in the case that it is intended to increase the surface control temperature higher than 250⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled lower, while, in the case that it is intended to decrease the surface control temperature lower than 250⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled higher. During the control, the mixing ratio is preferably controlled to increase or decrease the silica sand by 25% and the phenol resin by 2% with respect to the graphite. [12] In still another embodiment, the content of the methyl alcohol added for controlling density of the composition is corresponding to 50 to 80% of the total mass of the composition, and the methyl alcohol is evaporated in the following shaping step. [13] In another embodiment, the shaping step is executed by injecting the composition into a mode whose width with respect to the section is fixed according to electric resistance. The shaping size and form may be controlled depending on place, structure and size for usage. Yellow soil, material wood or gems placed on its surface may enhance its effects. The heating unit may be utilized in a fixed type for a floor, a ceiling or a wall of a building or in a movable type for a partition, a hot air blower, an iron or a hair drier. [14] In still another embodiment, the hardening step of the composition preferably employs the thermosetting procedure, preferably hardening the composition rapidly at 280 to 350 ⁰C. The hardening step is completed when the surface temperature reaches 150 to 180 °C. [15] Seeing the properties of the electro graphite powder that composes the PTC composition of the present invention, the electro graphite powder has an apparent density of 1.5 to 1.6 g/6, an apparent porosity rate of 20 to 30%, a bending strength of 19.6 Gpa, a bending rate of 4.9 to 11.7 Gpa, an electric resistance of 5 to 12 μΩm, a thermal conductivity of 104.5 to 242.4 W/mk, and a thermal expansion coefficient of 1 to 3.5x10 / ⁰C. In addition, graphite has a moment of resistance of 8.0 (Ω.m), which is far greater than 1.7241x10 (Ω.m) of copper. Thus, it is apparent that the complex inorganic PTC of the present invention has much more excellent thermal resistance moment than a conventional PTC using copper. [16] The PTC heating unit of the present invention using the electro graphite powder is an inorganic electric heating unit using an economic and efficient sensor method in which a thermal capacity is increased when it is cold and the thermal capacity is decreased again when an internal temperature is increased since a resistance value is responsive to an environmental temperature. According to the automatic temperature controlling action, it shows an automatic protection function against overheating or excessive current, does not cause oxidization reaction with oxygen in the air, and does not generate oxidization gas that is a factor of the air pollution. [17] Though it is not intended to theoretically limit the operating principle, the electro graphite powder PTC heating unit of the present invention is operated in such a way that, when this heating unit is heated to a certain temperature (250 to 300 ⁰C), a resistance is slowly increased and a current is decreased below an initial current due to thermal expansion, so the surface of the heating body is kept constantly. Advantageous Effects [18] The electro graphite powder PTC heating unit of the present invention has the following advantages. [19] (1) Bio functions - generation of far infrared rays, generation of anions, de- odorization, dehumidification, no electronic wave, no water vain [20] (2) Electric functions - self current control, absorption of electric leakage, self temperature control, low power density of about 0.03 to 0.12 (a common wattage density is 0.5 W/cm³ to 25 W/cm³ ) [21] (3) Electronic functions - electronic wave shielding [22] (4) Functions as a component - adjustable size according to place, structure and size, enhanced effect according to yellow soil, material wood and gems loaded on its surface, applicable both in a fixed type (a floor, a ceiling and a wall) and in a movable type (a partition and a hot air blower) [23] (5) Convenience in constructing - no need of an auxiliary device for heating, easy installation according to specifications without special building or electric knowledge [24] (6) Product stability - improved efficiency per an installation area owing to a low surface temperature of 40 to 250 ⁰C [25] (7) Product durability - as durable as a building since it is composed of inorganic material [26] (8) Product efficiency - maximized thermal efficiency and minimized heating time since far infrared ray radiation is used in natural convection [27] (9) Energy reduction - no use of fossil fuel (petroleum or gas) for heating, excellent heating efficiency per a unit area as much as about 90% as a boiler in comparison to an internal combustion engine whose heating efficiency is 30 to 40%. Brief Description of the Drawings [28] Fig. 1 shows a PTC heating unit using an electro graphite powder in a block shape according to one embodiment of the present invention; [29] Fig. 2 is a graph showing a thermal expansion feature according to a temperature change of the PTC heating unit including an electro graphite powder according to the present invention; [30] Fig. 3 is a graph showing a specific thermal expansion of an artificial graphite as a comparative group, in comparison to silica and magnesia; and [31] Fig. 4 is a graph showing the change of current as time goes according to the present invention. Mode for the Invention [32] Example 1 [33] Preparing PTC heating Unit 1 including Electro Graphite Powder [34] Electro graphte powder and silica san(sand of medium-sized particles)were mixed at a ratio of 100:500, and then a phenol resin was mixed therto by 25% of the total mass of the electro graphite powder and the silica sand. Methyl alcohol was also added to the mixture by 50% of the total mass of the mixture. The mixture sufficiently stirred was put into a mold of 80mm*380mm*10mm in length/width/heiht, and then heated at temperature of 280 for shaping and harding. As a result, a PTC heating unit having a block shape, which may be utilized as a heating unit for a hot air blower, was obtained.(see Fig. 1) [35] [36] Example 2 [37] Preparing of the PTC heating Unit including Electro Graphite Powder prepared according to the First Embodiment [38] when a current of 0.75A to 1.5A was applied to the electro graphite powder PTC obtained in the first embodiment under the natural convection condition, it was shown that a resistance range is between 10OmW and 30OmW. A surface temperature reaches 250⁰C after 12 minutes, and this temperature was maintained(see Fig. 2) After that a current change as time goes was measured to check an automatic control tuntion of the surface temperature, and it was found that the current was lowered to 0.7 A about 21 minutes later as shown in Fig. 4, and then a current is reapplied. Such reapplying ofcurrent was shorted at about 30 minutes, and then there might be found a stable surface temperature automatic control capability. Peculiar heat expansion features of artifical graphite, silica and magesia according to a temperature change were suggested in Fig. 3 as comparative groups. [39] When such an electro graphite powder PTC heating unit according to the present invention was used for a hot air blower, a heating characteistic of an assembly in which tree or eight nits are assembled was measure under to forced convection. Its result is shown in the following table 1. [40] Table 1 [41]

[42] In addition in order to prove the performance of the electric hot air blower using the electro graphite powder PTC, the performance was compared with a performance of a product, as a cmparation group, manufactured by Donwootech Ltd. that supplies heating units for a hot and cold air blower of Samsung Electronic. As a result, it was found that the electric hot air blower of the present invetion showed better performance in view of energy consumption and life cycle, though a heating capability was shown similar. In partcular, the product of the present invention migth give a metabolism promoting function and deodorizing effect owing to radiation of far infrared rays(see Table 2). [43] Table 2 [44]

[45] Example 3 [46] Preparing PTC heating Unit 2 including Electro Graphite Powder [47] Electro graphte powder and silica san(sand of medium-sized particles)were mixed at a ratio of 100:500, and then a phenol resin was mixed therto by 18% of the total mass of the electro graphite powder and the silica sand. Methyl alcohol was also added to the mixture by 50% of the total mass of the mixture and the stirred for the purpose of density control at curing of the mixture. The mixture sufficiently stirred was put into a mold of 80mm*380mm*10mm in length/width/heiht, and then heated at temperature of 280 for shaping and harding. As a result, a PTC heating unit having a block shape, which may be utilized as a heating unit for a hot air blower, was obtained. [48] A current was applied to the heating unit for a heater, and then after operation for 1 hour thermal efficiency was measured. As a rsult, the thermal efficiency was measured to be 84.4% under the following conditions. [49] Input voltage : 220V [50] Input current : 17.2A [51] Air volume (volume flix) : 0.0457 m³/s [52] Air volume (mass flix) : 0.0457 m³/s 1.1774 kg/m³3600 s/hr 194 kg/hr [53] Air inlet temperature : 15.4 ⁰C [54] Air outlet temperature : 74.4 ⁰C [55] Input heat capacity : wattage (P) = voltage (V) * currnt (I) [56] 220V * 17.2A = 3784kW = 3254 kcal/hr [57] Output heat capacity : Q = mass flux specific heat temperature differnce [58] 194 kg/hr * 0.24 kcal/kg°C(74.4 * 15.4)°C = 2747 kcal/hr [59] * thermal efficiency : h output heat capaity / input heat capacity [60] [2747 (kcal/hr) / 3254 (kcal/hr)] * 100 = 84.4% [61] [62] Example 4 [63] Preparing PTC heating Unit 3 including Electro Graphite Powder [64] Electro graphte powder and silica san(sand of medium-sized particles)were mixed at a ratio of 100:700, and then a phenol resin was mixed therto by 30% of the total mass of the electro graphite powder and the silica sand. Methyl alcohol was also added to the mixture by 50% of the total mass of the mixture and the stirred for the purpose of density control at curing of the mixture. The mixture sufficiently stirred was put into a mold of 130cm*60cm*0.8cm in length/width/heiht, and then heated at temperature of 280 for shaping and harding. As a result, a PTC heating unit having a block shape, which may be utilized as a heating unit for a hot air blower, was obtained, and it was mesured that a control temperature was 40⁰C and a heat capacity was 61 kcal, as a result of experiment in which a current was applied at 110V of a regular voltage and 73Wh og a regular capacity under the natural convection. [65] When synthetically comparing the performance of various electro graphite powder PTC with that of a conventional ceramic or polmer PTC of the present invention is various in the temperature range for usage, the current range for usage, and applicable outer sizes and also showed a small differenc in the positive features of current, so it is a heating unit that may be safely used in varius fields. [66] [67] Table 3 [68] Difference between the Electro Graphite Powder PTC and the ceramic or polymer PTC [69]

Industrial Applicability [70] The electro graphite powder PTC heating unit prepared as above according to the present invention may keep a surface temperature of a heating body constantly since increase of temperature up to a certain level makes a resistance increased, thereby lowering the current below an initial current. In addition, the heating unit may sig¬ nificantly decrease a heat loss of a heated body by radiation heat since a surface power density is decreased and a heating surface area is increased. Moreover, a heating temperature per a unit volume may be uniformly kept since a complex inorganic material containing graphite that has large peculiar resistance, contact resistance and thermal expansion coefficient is used. Furthermore, since an emitting amount of far infrared rays is maximized by means of graphite, it is possible to give a temperature amplifying action by means of resonance absorption. In addition, though a con¬ ventional alloyed PTC shows a great width of the positive/negative regions (about 2 times or more), the PTC of the present invention shows a very small width of the positive/negative regions, thereby consuming a very small amount of energy. Ac¬ cordingly, a product according to the present invention has at least 5 year life though a conventional alloyed PTC has just 2 or 3 year life. [71]

Claims

Claims [1] A PTC (Positive Temperature Coefficient) composition, wherein the PTC composition comprises electro graphite powder and silica sand mixed at a ratio suitable for a surface control temperature of a heating body, and wherein a phenol resin is included therein as a uniting material at a suitable mass ratio for the mixture. [2] The PTC composition according to claim 1, wherein, in the case that the surface control temperature is about 40 to 400⁰C, the mixing ratio of the electro graphite powder and the silica sand suitable for the surface control temperature of the heating body is 100:500 to 100:700, and at this time the content of the phenol resin is about 18 to 30% with respect to the total mass of the electro graphite powder and the silica sand. [3] The PTC composition according to claim 1 or 2, wherein, in the case that the surface control temperature is 250 ⁰C, the mixing ratio of the electro graphite powder and the silica sand is 100:500, and the content of the phenol resin is 25% with respect to the total mass of the electro graphite powder and the silica sand. [4] The PTC composition according to claim 2, wherein, in the case that the surface control temperature is higher than 250⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled lower. [5] The PTC composition according to claim 2, wherein, in the case that the surface control temperature is lower than 250 ⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled higher. [6] A method for preparing a PTC (Positive Temperature Coefficient) heating unit by use of an electro graphite powder, comprising; stirring electro graphite powder and silica sand at a ratio suitable for a surface control temperature of a heating body; mixing a phenol resin as a uniting material to the stirred mixture at a suitable ratio; adjusting a density of the mixture at curing by adding methyl alcohol to the mixture; putting the mixture in a mold at a normal temperature for shaping; and hardening the shaped material. [7] The method for preparing a PTC heating unit by use of an electro graphite powder according to claim 6, wherein, in the case that the surface control temperature is about 40 to 400⁰C, the mixing ratio of the electro graphite powder and the silica sand suitable for the surface control temperature of the heating body is 100:500 to 100:700, and at this time the content of the phenol resin is about 18 to 30% with respect to the total mass of the electro graphite powder and the silica sand. [8] The method for preparing a PTC heating unit by use of an electro graphite powder according to claim 7, wherein, in the case that the surface control temperature is 250⁰C, the mixing ratio of the electro graphite powder and the silica sand suitable for the surface control temperature of the heating body is 100:500, and at this time the content of the phenol resin is 25% with respect to the total mass of the electro graphite powder and the silica sand. [9] The method for preparing a PTC heating unit by use of an electro graphite powder according to claim 7, wherein, in the case that the surface control temperature is higher than 250⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled lower. [10] The method for preparing a PTC heating unit by use of an electro graphite powder according to claim 7, wherein, in the case that the surface control temperature is lower than 250⁰C, a mixing ratio of the silica sand and the phenol sand with respect to the electro graphite powder is controlled higher.