GB2442890A - A method of manufacturing a ceramic heater - Google Patents

Abstract

A method of manufacturing a ceramic heater comprising: a step of applying an electrically conductive paste in a predetermined pattern on the surface of a green ceramic sheet: a step of filling the space between the electrical conductors of the pattern with an insulating material; a step off laminating the green ceramic sheet having the space between the electrical conductors filled with the insulating material on a ceramic compact with the surface whereon the electrically conductive paste has been applied becomes the laminating surface; and a step of firing the stack off green ceramic sheets and the ceramic compact which have been laminated. The filling material may be applied by screen printing or a dispenser.

Description

DESCRIPTION

CERAMIC HEATER, METHOD FOR MANUFACTURING THE SANE,

HEATING APPARATUS AND HAIR IRON

TECHNICAL FIELD

[00011 The present invention relates to a ceramic heater which is used in heating a sensor, particularly a fuel-to-air ratio sensor for automobiles, carburetor, hair iron or soldering iron, and to a heating apparatus and a hair iron that use the ceramic heater.

BACKGROUND ART

2] Alumina ceramic heaters have been widely used, having such a constitution as a heat generating resistive member formed from a metal having high melting point such as W, Re or Mo is embedded in a ceramic member which is constituted from alumina as the main component.

To manufacture a ceramic heater of cylindrical shape, for example, a ceramic compact 12 and a green ceramic sheet 13 shown in Fig. 10 are prepared. A heat generating resistive member 14 constituted from a metal having high melting point such as W, Re or Mo and lead draw-out section are formed on one side of the green ceramic sheet 13, and an electrode pad (not shown) is formed on the other side.

Then the green ceramic sheet is rolled around the ceramic compact 12 with the side having the heat generating resistive member 14 and the lead draw-out section 15 formed thereon facing inward, and is fired. The lead draw-out section 15 and the electrode pad are connected to each other via a through hole 16 formed in the green ceramic sheet 13 (refer to, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-126852) [0003] The ceramic heater of the prior art is manufactured by simultaneously firing the heat generating resistive member 14 in the state of paste, the ceramic compact 12 and the green ceramic sheet 13. The heat generating resistive member of the ceramic heater made in this way has a configuration of running back and forth a plurality of times (refer to Fig. 1 of Japanese Unexamined Patent Publication (Kokai) No. 2001-102156) [0004] Japanese Unexamined Patent Publication (Kokai) No. 2000-232911, Japanese Unexamined Patent Publication (Kokai) No. 2002-291517 and Japanese Unexamined Patent Publication (Kokai) No. 2000-14438 disclose hair irons having such a constitution as a pair of handle members are connected at base portions thereof on a pivot to be capable of opening and closing so that distal ends of the handle members are normally opened by the force of a spring installed in a bearing, and a heater plate is provided on the inside of each of the distal ends of the handle members.

5] The hair iron has such a structure as a nickel chrome wire is rolled around an insulator plate made of ceramics with both surfaces of the insulator plate being covered by other insulator plates to make a heater plate, or heat from the heater plate is transferred to the plate member by pressing with a leaf spring.

DISCLOSURE OF THE INVENTION

[00061 In recent years, ceramic heaters have come to be used at increasingly higher temperatures, thus giving rise to the problem of deteriorating durability. That is, when the ceramic heater is operated at a high temperature with electric power supplied continuously, insulation between adjacent electrical conductors deteriorates leading to lower durability, eventually resulting in sparking or wire breakage.

The heater made by rolling a heating member comprising a nickel chrome wire around an insulator plate has such a problem that repetitive applications of voltage for heating may cause wire breakage, or the heating member reacts with moisture in the atmosphere to form a reaction layer thereby increasing the resistance of the heating member and causing a failure to reach a predetermined temperature under a predetermined voltage, with lower durability.

7] The heater plate comprising a nickel chrome wire has also such a problem that it is difficult to dispose the heating member uniformly over the heater plate, and therefore the plate member cannot be heated to the same temperature throughout the heating surface.

[0O08] Also because the heating surface of the heater plate and the plate-shaped member do not make contact evenly with each other with regard to heat transmission, it is difficult to transmit the heat uniformly from the heater plate to the plate-shaped member, and therefore uniform temperature distribution over the heating surface cannot be achieved.

The present invention has been made to solve the problems described above, and has a first object of providing a ceramic heater having high durability by preventing the insulation from deteriorating at high temperatures.

A second object of the present invention is to provide a heating apparatus and a hair iron which are capable of uniformly heating the heating surface of the plate-shaped member.

9] In order to achieve the first object, the ceramic heater of the present invention is made in such a constitution that comprises a ceramic member which has an external surface and an electrical conductor embedded therein, wherein the electrical conductor has turn-back section of the heat generating resistive member, and void ratio in the ceramic portion interposed between adjacent electrical conductors in the turn- back section is in a range from 0.01 to 50%.

The ceramic portion interposed between adjacent electrical conductors refers to a ceramic portion interposed between electrical conductors in an electrical conductor forming region which is defined as an internal region that has substantially the same thickness as that of the electrical conductor and runs along the external surface.

[00101 A first method for manufacturing a ceramic heater according to the present invention comprises the steps of applying an electrically conductive paste in a predetermined pattern on the surface of a first green ceramic sheet; making a stack of green ceramic sheets by stacking, on the surface of the first green ceramic sheet whereon the electrically conductive paste is applied, a second green ceramic sheet which has the same thickness as the electrically conductor and is more flexible than the first green ceramic sheet; laminating the stack of green ceramic sheets on the ceramic compact; and firing the stack of green ceramic sheets and the ceramic compact which have been laminated.

1] A second method for manufacturing a ceramic heater according to the present invention comprises the steps of applying an electrically conductive paste in a predetermined pattern on the surface of a green ceramic sheet; filling the space between the electrical conductors of the pattern described above with an insulating material; laminating the green ceramic sheet having the space between the electrical conductors filled with the insulating material on the ceramic compact with the surface, whereon the electrically conductive paste has been applied becomes the mating surface; and firing the stack of green ceramic sheets and the ceramic compact which have been laminated.

2] In order to achieve the second object, the heating apparatus of the present invention is made in such a constitution that comprises a heater plate which comprises a plate-shaped ceramic member having the heat generating resistive member embedded therein and has thickness in a range from 0.5 to 5.0 mm, and a plate-shaped member which has first and second surfaces with the heater plate provided on the first surface and the second surface used as a heating surface, and the heating surface consists of a flat surface portion and the surrounding chamfered portions.

3] The hair iron of the present invention is constituted from the ceramic heater of the present invention or the heating apparatus of the present invention.

The effect of the invention [00141 The ceramic heater of the present invention is capable of preventing the insulation from deteriorating at high temperatures since void ratio in the ceramic member interposed between the electrical conductors is in a range from 0.01 to 50%, thus providing the ceramic heater having high durability.

That is, the ceramic heater of the present invention has been completed by finding that the insulation at high temperatures can be prevented from deteriorating by controlling the void ratio in the ceramic portion between the electrical conductors in a particular range.

5] The heating apparatus of the present invention is capable of heating an object to be heated uniformly, since the heat generating resistive member embedded in the plate-shaped ceramic member is not exposed to water vapor so that the heat generating resistive member has high durability and is capable of repeating quick heating operations since the temperature difference across the heating surface can be decreased.

6] The hair iron of the present invention is constituted from the ceramic heater of the present invention or the heating apparatus of the present invention, and therefore the hair iron having high durability is provided.

Also in the hair iron of the present invention provided with the heating apparatus of the present invention, local overheating does not occur in the heating surface, and therefore the hair iron which does not damage the hair through local overheating is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view that is partially cut away showing the constitution of the ceramic heater according to the first embodiment of the present invention.

Fig. 2 is a sectional view of the ceramic heater shown in Fig. 1 taken along lines X-X.

Fig. 3 is an enlarged sectional view of a portion between electrical conductors in the ceramic heater of cylindrical shape according to the first embodiment.

Fig. 4 is an enlarged sectional view of a portion between electrical conductors in the ceramic heater of flat plate shape according to a variation of the first embodiment.

Fig. 5 is a side view that is partially chipped away showing the constitution of a hair iron according to the second embodiment of the present invention.

Fig. 6 is a front view showing the positional relationship between a heater plate and a plate-shaped member used in the hair iron shown in Fig. 5.

Fig. 7 is a sectional view of Fig. 6 taken along lines x-x.

Fig. 8 is a sectional view of a heating apparatus according to a variation of the second embodiment of the present invention.

Fig. 9 is a plan view of a heater plate used in the heating apparatus according to the second embodiment.

Fig. 10 is an exploded view of a ceramic heater of the

prior art.

[Description of Reference Numerals]

8] 1: ceramic heater 2: core ceramic member 3: ceramic sheet 4: heat generating resistive member 5: lead draw-out section 6: through hole 7: electrode pad 8: lead member A: region between electrical conductors in ceramic heater of cylindrical shape B: region between electrical conductors in ceramic heater of flat plate shape 5: heating apparatus 50: handle member 52: pivot 54: coil spring 54: bearing 55: plate-shaped member 55a: heating surface 57: heater plate 58: heat generating resistive member 59: spring 61: lead wire

BEST MODE FOR CARRYING OUT THE INVENTION

9] The present invention will now be described by way of embodiments thereof with reference to the accompanying drawings.

First Embodiment Fig. 1 is a perspective view that is partially cut away showing the constitution of the ceramic heater 1 according to the first embodiment of the present invention, and Fig. 2 is a sectional view of Fig. 1 taken along lines X-X.

0] The ceramic heater 1 according to the first embodiment -10 -comprises a ceramic member consisting of a core ceramic member 2 and a ceramic sheet 3, and a heat generating resistive member 4 embedded therein. The heat generating resistive member 4 is made in such a constitution that comprises a turn-back section of the electrical conductor, and void ratio in the ceramic portion interposed between adjacent electrical conductors in the portion where the heat generating resistive member 4 is formed is in a range from 0.01 to 50%.

1] The ceramic heater 1 is made by a process where a green ceramic sheet (to become the ceramic sheet 3 after being fired) having the heat generating resistive member 4 and a lead draw-out section 5 formed on the surface and an electrode pad 7 formed on the back surface is rolled around a ceramic compact (to become the core ceramic member 2 after being fired) with the side having the heat generating resistive member 4 and the lead draw-out section 5 formed thereon facing inward, and is fired. The lead draw-out section 5 and the electrode pad 7 are connected with each other via through hole 6 which is formed on the ceramic sheet 3.

[00221 The ceramic member comprises the core ceramic member 2 made by firing the ceramic compact and the ceramic sheet 3 -11 -made by firing the green ceramic sheet. Various ceramic materials may be used to form the ceramic member, such as alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics or the like. Among these, ceramic material which contains alumina or silicon nitride as the main component is preferably used, which enables it to make the ceramic heater 1 having capability of quick heating and high durability. In the case of alumina ceramics, for example, it preferably has such a composition that contains 88 to 95% by weight of A1203, 2 to 7% by weight of Si02, 0.5 to 3% by weight of CaO, 0.5 to 3% by weight of MgO and 1 to 3% by weight of Zr02. When the content of Al203 is less than 88% by weight, higher content of glass component may cause significant migration when electric power is supplied. When the content of A1203 exceeds 95% by weight, on the other hand, durability of the ceramic heater 1 may become lower due to insufficient content of glass component which diffuses into the metal layer of the heat generating resistive member 4 which is incorporated in the ceramic heater 1. In the case of silicon nitride ceramics, it is preferable to add oxide of rare earth element in proportion of 3 to 12% by weight and 0.5 to 3% by weight of A1203 as sintering assisting agent in proportion to the main component of silicon nitride, and Si02 in such a quantity as the content of Si02 in the sintered material becomes 1.5 to 5% by weight. The content of Sb2 -12 -here means the sum of Si02 formed from impurity oxygen contained in the stock material of silicon nitride, Si02 contained in other additive agent as impurity and Si02 that is intentionally added. The thermal expansion coefficient of the base material is made proximate to the thermal expansion coefficient of the heat generating resistive member 4 by dispersing MoSi2 or WSi2 in silicon nitride of the base material, thereby making it possible to improve durability of the heat generating resistive member 4.

[00231 The heat generating resistive member 4 is formed from an electrical conductor in a meandering pattern, and is connected to a lead draw-out section 5 which has a resistance about one tenth that of the heat generating resistive member 4. These members are typically formed by printing the heat generating resistive member 4 and the lead draw-out section 5 at the same time on the green ceramic sheet (to become the ceramic sheet 3 after being fired) in order to simplify the process. The turn-back section in the present invention also includes such a shape that is turned back in U shape and a meandering shape formed so as to provide a desired value of resistance.

[0024J Dimensions of the ceramic heater 1 may be 2 to 20 mm in outer diameter or width and 40 to 200 mm in length. When -13 -used for heating a fuel-to-air ratio sensor for automobile, the ceramic heater 1 preferably measure 2 to 4 mm in outer diameter or width and 50 to 65 mm in length. In automobile applications, heating length of the heat generating resistive member 4 is preferably from 3 to 15 mm. When the heating length is less than 3 mm, quick heating is enabled when electric power is supplied but durability of the ceramic heater 1 decreases. When the heating length is more than 15 mm, heating takes longer time and an attempt to increase the speed of heating results in higher power consumption. The heating length refers to the length of the meandering heat generating resistive member 4 shown in Fig. 1 in longitudinal direction. The heating length may be determined at will according to the application.

[00251 Fig. 2 shows a border line between the core ceramic member 2 and the ceramic sheet 3, although the border line often disappears as the green ceramic compact and the green ceramic sheet which have been put together are fired.

6] In the first embodiment, it is preferable to form a primary plating layer on the electrode pad 7 of the ceramic heater 1 after firing. The primary plating layer is provided for the purpose of improving the fluidity of a brazing material and increasing the brazing strength when the lead -14 -member B is brazed on the surface of the electrode pad 7.

The primary plating layer preferably has thickness of 1 to 5 burn, in order to ensure high bonding strength. The primary plating layer is preferably formed from Ni, Cr or a composite material thereof as the main component, and more preferably formed from a material containing Ni which has high heat resistance as the main component.

[00271 In case operation in an atmosphere of high humidity is expected, it is preferable to use a brazing material based on Au or Cu since it makes migration less likely to occur. A brazing material made of a material based on Au, Cu, Au-Cu, Au-Ni, Ag or Ag-Cu is preferably used for the reason of high heat resistance. The Au-Cu brazing material, Au-Ni brazing material and Cu brazing material are particularly preferable for the reason of high durability. It is preferable to form a secondary plating layer, typically made of Ni, on the surface of the brazing material in order to improve durability at high temperatures and protect the brazing material from corrosion.

8] The lead member 8 is preferable made of an alloy based on Ni or on Fe-Ni which has high heat resistance, since the lead member 8 reaches a high temperature due to the heat transferred from the heat generating resistive member 4 when -15 -using.

9] The present invention is characterized in that the ceramic heater 1 has the electrical conductor incorporated therein which has the turn-back section that constitutes the heat generating resistive member 4, and that the void ratio in the ceramic portion interposed between adjacent electrical conductors in the turn-back section is in a range from 0.01 to 50%. The void ratio in the ceramic portion interposed between adjacent electrical conductors in the turn-back section is preferably in a range from 0.1 to 40%, and more preferably from 1 to 20%. When the void ratio is less than 0.01%, heating and expansion of the heat generating resistive member 4 during quick heating and quick cooling may result in concentration of stress in an edge 41 of the heat generating resistive member 4 which leads to crack or wire breakage, since heat cannot be dissipated from the ceramic member surrounding the heat generating resistive member 4 and therefore thermal expansion of the ceramic member does not match the thermal expansion of the heat generating resistive member 4. When the void ratio is higher than 50%, insulation of the ceramic member surrounding the heat generating resistive member 4 deteriorates and results in the degradation of durability, when electrical power is supplied continuously for operation at a high temperature. When the -16 -green ceramic sheet is attached as it is onto the ceramic compact and fired, the void ratio becomes higher than the range described above. In order to keep the void ratio within the range described above, a manufacturing method described later is employed.

0] Fig. 2 is a sectional view (taken along lines X-X in Fig. 1) showing an example of a section perpendicular to the longitudinal direction, where the electrical conductor in the turn-back section (heat generating resistive member 4) is shown to be disposed on the circumferential circle of the core ceramic member 2. That the void ratio in the ceramic portion between the electrical conductors is in a range from 0.01 to 50% means that the proportion of voids in the ceramic member measured in the portion between adjacent electrical conductors (4a and 4b in Fig. 3) as shown in Fig. 3 is in a range from 0.01 to 50%. The portion where the void ratio in the ceramic member is from 0.01 to 50% may be any part of a section perpendicular to the longitudinal direction of the heat generating resistive member 4. The portion between the electrical conductors means, in the case of ceramic heater of cylindrical shape, a region A enclosed by a line which connects the upper side of the electrical conductor 4a and the upper side of 4b which adjoins each other along the circumferential circle of the core ceramic member 2 (that is 17 -the external surface of the ceramic member), a line which connects the lower side of the electrical conductor 4a and the lower side of 4b along the circumferential circle of the core ceramic member 2 and the surfaces of the electrical conductors 4a, 4b. In case the ceramic member has a flat plate shape, the portion between the electrical conductors means a region B enclosed by a line which connects the upper side of the electrical conductor 4c and the upper side of the electrical conductor 4d, a line which connects the lower side of the electrical conductor 4c and the lower side of the electrical conductor 4d and the surfaces of the electrical conductors 4c, 4d.

In this specification, a ring-shaped region interposed by the circumference of the core ceramic member 2 and a circumference separated from the former circumference by the thickness of the conductor is called the electrical conductor forming region in the case of ceramic heater of cylindrical shape, and an internal region interposed by a line which makes contact with the upper side of the electrical conductor and a line which makes contact with the lower side of the electrical conductor is called the electrical conductor forming region in the case of the ceramic member which has a flat plate shape. That is, the portion between the electrical conductors defined as described above means a portion located between the adjacent electrical conductors in -18 -the electrical conductor forming region.

1] In the ceramic heater of the first embodiment, it is also preferable that the length of the void along the external surface in the region between the adjacent electrical conductors is not larger than one half the distance between the adjacent electrical conductors. That is, it is preferable that there exists no void which is longer than one half the length of an arbitrarily chosen line (distance between the electrical conductors) that connects the adjacent electrical conductors along the external surface in the ceramic member between the electrical conductors.

When the length of void is larger than one half the distance between the electrical conductors, insulation of the ceramic member surrounding the heat generating resistive member 4 deteriorates resulting in the degradation of durability, when electrical power is supplied continuously for operation at a high temperature. The phrase "an arbitrarily chosen line" means any line which connects the electrical conductors 4a and 4b which adjoin with each other in the region A, along the external surface. The "arbitrarily chosen line" in this case is an arc line which has center at substantially the same position as the center of a circle formed by the circumference of the section of the ceramic heater of cylindrical shape (circumference of the ceramic member) shown -19 -in Fig. 3. In the case of the ceramic member having a flat plate shape shown in Fig. 4, the "arbitrarily chosen line" is any line which connects the adjacent electrical conductors 4c and 4d in the region B. [0032] According to the present invention, it is preferable that thickness of the electrical conductor pattern, particularly electrical conductor which constitutes the heat generating resistive member 4 is in a range from 5 to 100.tm.

When the thickness of the electrical conductor pattern is less than 5 jm, although voids can be prevented in the region between the electrical conductors, the heat generating resistive member 4 experiences a change in the resistance or wire breakage with lower durability, during high temperature continuous operation durability test and high temperature repetitive cycles durability test. When the thickness of the electrical conductor is larger than 100 j.m, it becomes difficult to control the void ratio in the portion between the adjacent electrical conductors within 50%.

[00331 A method control the void ratio of the ceramic member in the portion between the adjacent electrical conductors within a range from 0.01 to 50% will now be described.

4] For example, such a method may be employed as an -20 -electrical conductor pattern is formed on the surface of a first green ceramic sheet, and a second green ceramic sheet which has substantially the same thickness as that of the electrical conductor pattern and is more flexible than the first green ceramic sheet is stacked on the side of the first green ceramic sheet where the electrical conductor pattern is formed. This method makes it possible to exclude voids from the region between the electrical conductors by filling the gap corresponding to the thickness of the electrical conductor with the flexible second green ceramic sheet. The second green ceramic sheet is required to be more flexible than the first green ceramic sheet. When the second green ceramic sheet is flexible, the first green ceramic sheet where the electrical conductor pattern is formed and the second green ceramic sheet can be put into close contact with each other at least in the mid portion between the electrical conductors, when both green ceramic sheet are laminated.

Hardness of the green ceramic sheet, measured with a digital indicator (manufactured by Mitsutoyo Corporation), is preferably such that a needle measuring 1 mm in diameter can be driven to sink therein to a depth of 200 jim or more in 30 seconds. When the hardness of the green ceramic sheet is such that the depth is less than 200 jim, close contact cannot be achieved between the conductors, thus allowing voids to form. Pressure may be applied by means of a press or the -21 -like thereby to eliminate the gap between the patterns.

5] Alternatively, screen printing of a paste may be employed. This method proceeds as follows. First, the heat generating resistive member 4 and the lead draw-out section 5 are formed on the green ceramic sheet by screen printing.

The paste applied by screen printing is prepared by mixing a powder containing a metal having high melting point (W, Mo, Re, etc.) as the main component, a binder made of an organic resin consisting of an adhesive component, ethyl-cellulose or nitrocellulose, and an organic solvent such as T.P.O.

(terpineol), D.B.P. (dibutyl phthalate), D.O.P. (dioctyl phthalate) or B.C.A. (butyl carbitol acetate) . The paste is printed to a thickness from 5 to 150 jim. The electrical conductor pattern is formed so that while adjusting such factors as the line width, thickness of printing or specific resistance of the paste so that the heat generating resistive member 4 has resistance of about 10 times that of the lead draw-out section 5. Then a paste which contains an insulating material is applied by screen printing so as to fill the gap corresponding to the thickness of the electrical conductor. This paste is prepared by mixing an insulating material having high melting point and the same composition as that of the green ceramic sheet, namely alumina ceramics containing 88 to 95% by weight of A1203, 2 to 7% by weight of -22 -Sb2, 0.5 to 3% by weight of CaO, 0.5 to 3% by weight of MgO and 1 to 3% by weight of Zr02, a binder made of an organic resin consisting of an adhesive component, ethyl cellulose or nitrocellulose, and an organic solvent used as a diluent such as T.P.O. (terpineol), D.B.P. (dibutyl phthalate), D.O.P. (dioctyl phthalate) or B.C.A. (butyl carbitol acetate) used as a

diluent. Besides one having the same composition as that of the green ceramic sheet, the paste may be alumina only or an insulating material having volume specific resistance of 108 C or higher. It is preferable to control the viscosity of paste in a range from 50 to 1000 dPas before printing. When the viscosity is 50 dPas or lower, although it makes it easier to print, density of the green ceramic sheet becomes lower and therefore the paste shrinks significantly when dried so as to cause a step in the portion of upper side of the conductor, thus making voids more likely to be generated after firing. When the viscosity is 1000 dPas or higher, leveling property decreases and voids become more likely to be generated in the coating film. Screen printing is carried out by using a screen having inverted pattern of the heat generating resistive member and the lead draw-out section.

6] Moreover, a filling method by means of a dispenser may also be employed as an alternative method. A paste having -23 -viscosity of 1000 dPas or higher can have higher density before drying so that the paste shrinks less when dried. As a result, although the gap between the electrical conductors can be surely filled up, it is not suited to screen printing and cannot be employed. Therefore, filling method by means of a dispenser is preferably employed for a paste having such a high viscosity.

7] The method of screen printing or using a dispenser is preferable because the insulating material is applied not onto the conductor but to fill in the gap between the conductors.

[00381 While the ceramic member made by firing the green ceramic sheet rolled around the ceramic compact of cylindrical shape is described in this embodiment, the present invention also includes a ceramic member made by firing a ceramic compact of flat plate shape or a green ceramic sheet laminated on a green ceramic sheet having the conductors printed thereon.

[00391 Second Embodiment A heating apparatus 51 according to second embodiment of the present invention will now be described below.

0] -24 -Fig. 5 is a side view that is partially chipped away showing an example of the constitution of a hair iron 100 using the heating apparatus 51 of the second embodiment. In Fig. 5, reference numeral 50 denotes a handle member, 52 denotes a pivot which connects the pair of handle members 50 so as to open and close freely, and 53 denotes a coil spring which is installed in the bearing 54 and exerts urging force to the distal ends of the handle members so as to normally open. Reference numeral 55 denotes plate-shaped members which are fitted in openings 56 formed in the distal ends of the handle members and oppose each other, and 57 denotes a heater plate put into contact with the reverse of the plate-shaped member 55.

1] Fig. 6 is a front view showing the positional relationship between the heater plate 57 and the plate-shaped member 55 taken out of the heating apparatus 51 shown in Fig. 5, and Fig. 7 is a sectional view taken along lines X-X thereof. Heat generated by the heater plate 57 is transferred through one principal surface 57a of the heater plate 57 to one principal surface 55b of the plate-shaped member 55 so as to uniformly heat the heating surface 55a which is the other principal surface of the plate-shaped member 55.

2] -25 -This constitution makes it possible to uniformly heat the plate-shaped member 55 which has the heating surface 55a of wide area, efficiently by using the small heater plate 57 made of ceramics.

[00431 The hair iron shown in Fig. 5 is used by holding the handle members 50 with fingers so as to pinch hair with the plate-shaped member 5, thus making it possible to heat the hair evenly.

4] Specifically, the heating apparatus 51 of the second embodiment comprises the heater plate 57 having the plate-shaped ceramic member and the heat generating resistive member 58 embedded therein and the plate-shaped member 55 which has the heating surface 55a for heating the object to be heated, where one principal surface 55b of the plate-shaped member 55 and one principal surface 57a of the heater plate 57 make contact with each other. According to the present invention, the heating surface 55a consists of a flat surface portion and the surrounding C surfaces or curved chamfered portions, where the heater plate 57 having thickness H in a range from 0.5 to 5 mm. The heater plate 57 has the heat generating resistive member 58 embedded in the plate-shaped ceramic member, so that the heat generating resistive member 58 is shielded from the atmosphere and the -26 -heat generating resistive member 58 is protected from corrosion by moisture contained in the atmosphere. The heat generating resistive member 58 embedded in the plate-shaped ceramic member generates the Joule heat due to the electrical resistance thereof when electrical power is supplied, so as to heat the heater plate 57 to a predetermined temperature.

[00451 Since the heating surface 55a consists of a flat surface portion and the surrounding C surfaces or curved chamfered portions, the object to be heated is less likely to be damaged even when the object to be heated is pushed into the heating surface 55a while sliding. In case the object to be heated is hair, size Wc of the chamfered portion, if it is C surface, is preferably in a range from 0.1 to 5 mm, more preferably from 0.3 to 4 mm and furthermore preferably from 1 to 3 mm, so as not to damage the hair. In case the chamfered portion is curved surface, the curved surface has a section perpendicular to the end face delimited by an arc or a quadratic curve with the width Wr preferably in a range from 0.2 to 5 mm in order to minimize the damage to the object to be heated, and the width Wr is more preferably in a range from 0.3 to 4 mm, and furthermore preferably in a range from 1 to 3 mm.

6] The thickness H of the heater plate 57 is preferably -27 -from 0.5 to 5.0 mm so as to efficiently transfer the heat from the heater plate 57 to the plate-shaped member 55. When thickness H of the heater plate 57 is less than 0.5 mm, since flatness of one principal surface of the plate-shaped member 55 has a large value of 0.02 to 0.2 mm, the heater plate 57 may be broken due to stress generated when the heater plate 57 is installed.

7] When thickness H of the heater plate 57 is larger than 5 mm, one principal surface 57a of the heater plate 57 does not deform even when the heater plate 57 is installed on the plate-shaped member 55, and therefore one principal surface 57a of the heater plate 57 and one principal surface 55b of the plate-shaped member 55 cannot make contact with each other over a wide area, and the heating surface 55a of the plate-shaped member 55 cannot be uniformly heated.

8] The heating surface 55a can be uniformly heated over a wide area thereof by controlling the thickness of the heater plate 5 within a range from 0.5 to 5 mm, since one principal surface 57a of the heater plate 57 and one principal surface 55b of the plate-shaped member 55 deform so as to conform with each other. The thickness of the heater plate 55 is more preferably from 1 to 3 mm.

9] -28 -It is preferable to provide a heat transfer member 63 between one principal surface 57a of the heater plate 57 and one principal surface 55b of the plate-shaped member 55.

Presence of the heat transfer member 63 makes heat transfer easier between one principal surface 57a of the heater plate 57 which has the surface roughness Ra described previously and one principal surface 55b of the plate-shaped member 55, thus making it possible to efficiently transfer the heat of the heater plate 57 to the plate-shaped member 55.

[00501 The heat transfer member 63 is preferably formed from silicone-based resin or a resin having fine metal powder of high heat conductivity mixed therein. The fine metal powder is preferably gold, silver, copper or nickel for the reason of high heat conductivity, and is more preferably silver.

For the resin, silicone resin or fluororesin may be used.

The heat transfer member 63 is capable of eliminating the gap between one principal surface 55a of the plate-shaped member and one principal surface 57a of the heater plate 57, and preventing temperature difference across the heating surface from increasing without changing the heat transfer between the principal surface 55a and the principal surface 57a by the heat transfer member 63 even when the plate-shaped member and the heater plate 57 undergo different amounts of expansion and shrinkage due to the difference in thermal -29 -expansion.

1] In the heating apparatus 51 of the present invention, it is preferable that one principal surface 57a of the heater plate 57 has surface roughness Ra in a range from 1 to 30.

When the surface roughness Ra of one principal surface 57a of the heater plate 57 is less than 1.0, it becomes difficult to uniformly transfer the heat through the contact surface with the plate-shaped member 55, thus increasing temperature difference across the heating surface 55a. When the surface roughness Ra is more than 30, effective contact area with the plate-shaped member 55 may become insufficient to heat the plate-shaped member 55 uniformly because the surface roughness Ra is too large. Surface roughness Ra of one principal surface 57a of the heater plate 57 is more preferably from 3 to 10.

[0052) While the heater plate 57 is held in contact with the plate-shaped member 55 by means of hook 55c of the plate-shaped member 55 in the heating apparatus 51 shown in Figs. 5 and 6 (Fig. 7), one principal surface 55b of the plate-shaped member 55 and one principal surface 57a of the heater plate 57 may also be elastically forced into contact with each other by a spring 59 which is secured onto a hook as shown in Fig. 8. This constitution is preferable since the heater -30 -plate 57 and the principal surface of the plate-shaped member can be put into contact over a wider area by providing a plurality of pressing points of the spring 59. The spring 59 is preferably constituted from leaf spring having a plurality of fulcrums.

[00531 The plate-shaped ceramic member of the present invention is preferably made of ceramics which contains alumina, mullite or silicon nitride as the main component.

Such a ceramic material is preferably used for the reason of relatively high heat conductivity, high durability and high resistance at high temperatures.

4] In case the plate-shaped ceramic member is made of alumina, content of alumina is preferably in a range from 80 to 98% by weight. This is because the plate-shaped ceramic member has high heat conductivity of 16.7 to 25.21 W/(mK), high temperature insulation resistance of iO' Qcm or higher at 300 C and high bending strength of 300 MPa or higher.

When the content of alumina is less than 80% by weight, resistance at high temperatures may become lower due to high proportion of the sintering assisting agent such as Mn, Ca and Si and/or impurity.

[00551 When the content of alumina is more than 99.5% by -31 -weight, low proportion of the sintering assisting agent makes it difficult to sinter into a dense material at a temperature lower than 1700 C, thus resulting in difficulty to manufacture in large volume at a low cost.

6] The plate-shaped member 55 of the present invention is preferably formed from an electrically conductive metal.

Metals have heat conductivity of 200 W/(m.K) or higher and is capable of transferring the heat of the heater plate 7 evenly to the heating surface 55a. The metal is preferably aluminum, iron, or an alloy thereof. The plate-shaped member 5 formed from the metal preferably has thermal expansion coefficient of 8 to 25 x l06/ C or lower, more preferably from 8 to 17 x i06/ C, proximate to that of the plate-shaped ceramic member 57, lest the distance between the principal surface 55b and the principal surface 57a may become uneven due to the difference in thermal expansion of the plate-shaped member 55 and the heater plate 57, thus resulting in uneven temperature distribution. While the object to be heated is put into contact with the heating surface 55a so as to transfer heat from the heating surface 55a to the object to be heated, electrostatic charge may be generated on the heating surface 55a as the object to be heated slides while making contact with the heating surface 5a. The heating surface 55a made of an electrically conductive material is preferable since the -32 -electrostatic charge can be removed.

7] Contact area between the plate-shaped member 55 and the heater plate 57 is preferably in a range from 20 to 80% of the area of the heating surface 55a. When this proportion is less than 20%, it may become impossible to uniformly heat the heating surface 55a of the plate-shaped member 55. When the contact area between the plate-shaped member 55 and the heater plate 57 is more than 80% of the area of the heating surface 55a, the heater plate 57 may become too large and the heating apparatus 51 may become too expensive to be commercially viable. The contact area is more preferably from 30 to 60% of the area of the heating surface 55a.

8] The thickness B of the plate-shaped member 55 is preferably in a range from 0.2 to 10 mm. When the thickness is less than 0.2 mm, the plate-shaped member 55 may deform due to low strength thus resulting in a gap or uneven contact and increase temperature difference across the heating surface 55a, when the plate-shaped member 55 is held together with the heater plate 57 by means of the leaf spring 59.

When the thickness is larger than 10 mm, heat capacity may become too great to raise the temperature of the heating surface 55a of the plate-shaped member 55 quickly when the heater plate 57 is heated. The thickness B is more -33 -preferably in a range from 1 to 3 mm.

9] The thickness of the heater plate 57 may be given by averaging the distance between the principal surface 55b and the principal surface 55a measured at three points.

0] The plate-shaped member 55 is preferably formed from a metal having heat conductivity of 200 W/(mK) or higher, and it is also preferable that the hook 55c is provided on the periphery thereof so as to make surface contact with the heater plate 57 and increase the thickness in the peripheral portion so as to increase the heat capacity and decrease the temperature difference across the heating surface.

1] The method for manufacturing a heating apparatus 51 of the present invention and other constitution will now be described.

2] The heater plate 57 is formed from heat resistant ceramics made by sintering aluminum oxide, mullite or silicon nitride. In case it is made of sintered aluminum oxide, for example, a slurry prepared by mixing aluminum oxide (A1203), silica (Si02), calcia (CaO), magnesia (MgO), etc. with an organic solvent is formed into a sheet by doctor blade method or calendar roll method, thereby making the green ceramic -34 -sheet. The green ceramic sheet is punched out.

[00631 The heat generating resistive member 58 is formed from a metal such as tungsten or molybdenum. A paste to form the heat generating resistive member is prepared by mixing a metal powder such as tungsten and an organic solvent. The heat generating resistive member 8 can be embedded in the plate-shaped ceramic member by applying the paste on the green ceramic sheet which would make the plate-shaped ceramic member by the known method of screen printing. The green ceramic sheet with the heat generating resistive member 58 embedded therein is fired at a high temperature (about 1600 C) to make the heater plate 7. At this time, it is preferable to control the firing temperature and the duration so that crystal grain size in the surface of the heater plate 57 is in a range from 0.5 to 5 tim, in order to achieve the surface roughness described previously.

[00641 Both ends of the heat generating resistive member 58 are drawn out to the end of the heater plate 57, and the ends which are drawn out are exposed from an opening A formed in the plate-shaped member 57 and are connected with lead wires 61 which are brazed by using solder or the like. The opening A where both ends of the heat generating resistive member 58 are exposed provides the area where the heat generating -35 -resistive member 58 and the lead wires 61 are brazed together, and is formed at the end of the heater plate 57 by punching a hole in the green ceramic sheet which would make the plate-shaped ceramic member. The opening A also has a recess 62, of a size that corresponds to the diameter of the lead wire 61, in the side wall thereof. When the heat generating resistive member 58 and the lead wires 61 are brazed together in the opening A, the lead wire 61 can be precisely positioned at the center on the top surface of the heat generating resistive member 58 by inserting the lead wire 61 into the recess 62 which is formed in the side wall of the opening A. Accordingly, the lead wire 61 can be very firmly secured onto the heat generating resistive member 58 by means of the brazing material.

5] The lead wire 61 which is brazed to the heat generating resistive member 58 in the opening A is made of a metal such as nickel. The lead wire 61 connects the heat generating resistive member 58 to an external electrical circuit and carries the electric power required for the heat generating resistive member 58 to generate Joule heat from the external electric circuit.

6] The lead wire 61 can be put into contact precisely at the center on the top surface of the heat generating -36 -resistive member 58 which is exposed by using the recess 62 formed in the side wall of the opening Pt, and is firmly brazed with the heat generating resistive member 58 by means of the brazing material 61 such as solder.

7] Thus in the heating apparatus 51 of the present invention, electric power is supplied via the lead wire 61 to the heat generating resistive member 58, so that the heat generating resistive member 58 generates Joule heat thereby to function as a heat generator to achieve a predetermined temperature.

[00681 The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention.

For example, although the lead wire 61 is connected to the heat generating resistive member 58 which is exposed by using the brazing material such as solder in the second embodiment, the connection may be reinforced by filling the opening A with a resin or glass, or filling the opening A with a heat resistant material and cover it with an insulating sheet.

This reinforcement is preferable since the connection between the heat generating resistive member 58 and the lead wire 61 can be made firmer. While the lead wire 61 is connected to the heat generating resistive member 58 by using the brazing -37 -material such as solder in the embodiment described above, the connection may also be made by putting the lead wire 61 into contact with the heat generating resistive member 58 and securing the contact by filling the opening A with a resin or glass.

9] While the heating apparatus 51 is put into contact with the plate-shaped member 55 made of metal via silicone grease or the like, thickness of the buffer material which also serves as the heat transfer member 63 for the plate-shaped member 55 and the plate-shaped ceramic member 57 is preferably from 5 to 100 m. This is because, since the heater plate made of ceramics 57 of the hair iron and the plate-shaped member 55 make contact with each other, putting the heater plate made of ceramics 57 and the heater plate 55 made of metal into contact with each other leads to warping or deformation due to thermal expansion of the heater plate made of ceramics 57 and the plate-shaped member 55 made of metal, resulting in uneven contact and localized heat transfer which increase the temperature difference across the heating surface 55a. While thickness of the buffer material which serves as the heat transfer member 63 may be minimum, heat transfer between the ceramic heater and the metal plate may decrease when the thickness is too large. Thus thickness of the heat transfer member 63 is preferably from 1 to 100 jim.

-38 -[0070] In the hair iron of the second embodiment described above, the heater plate 57 has the electrical conductor comprising the turn-back section that constitutes the heat generating resistive member 4 as described in the first embodiment, and the void ratio in the ceramic member interposed between adjacent electrical conductors in the turn-back section is preferably in a range from 0.01 to 50% (for example, the heater plate comprising the plate-shaped ceramic heater shown in Fig. 4 of the first embodiment is used) . This improves the durability of the heater plate 57, and therefore the hair iron having high durability can be provided. The void ratio in the ceramic member interposed between adjacent electrical conductors in the turn-back section is more preferably in a range from 0.1 to 40%, and furthermore preferably from 1 to 20%.

Example 1

1] A green ceramic sheet was prepared from a material constituted from A1203 as the main component, containing 10% or less by weight in total of Si02, CaO, MgO and Zr02. A paste comprising W (tungsten) powder, binder and solvent was printed on the green ceramic sheet to form the heat generating resistive member 4 and the lead draw- out section 5.

The electrode pad 7 was printed on the back surface.

-39 -The heat generating resistive member 4 was formed in a meandering pattern running back and forth 4 times with heating length of 5 mm.

Space between the electrical conductors was filled with a paste containing an insulating material by screen printing.

In order to vary the void ratio in the ceramic member between the electrical conductors, samples made without screen printing and samples screen printing applied by changing the viscosity of the paste were prepared.

The through hole 6 was formed at the end of the lead draw-out section 5 made of W, and the through hole 6 was filled with a paste thereby to establish electrical continuity between the electrode pad 7 and the lead draw-out section 5. The through hole 6 was located inside of the brazing area when the brazing was applied.

The green ceramic sheet prepared as described above was rolled tightly around the ceramic compact, and was fired at 1600 C to make the ceramic heater 1.

2] Electric power was supplied to the ceramic heater 1 made as described above so as to heat to 1200 C continuously for 100 hours, then the change in resistance was determined, thereby to evaluate the durability for n=l0 of each lot.

Samples which underwent a change in resistance of 15% or more from the initial resistance were counted as wire -40 -breakage.

Section of the heat generating resistive member 4 after firing was observed under SEM so as to measure the void ratio for samples of n=3 of each lot. The results are shown in

Table 1.

Table 1

Sample Void Void -Heater Pattern Evaluation Decision No. ratio length shape thickness *1 0.005 1/10 Cylinder 10 16 C 2 0.01 1/10 Cylinder 20 13 B 3 0.1 1/10 Cylinder 20 10 B 4 1 1/10 Cylinder 20 8 A 10 1/10 Cylinder 20 6 A 6 20 1/10 Cylinder 20 7 A 7 40 1/10 Cylinder 20 11 B 8 50 1/10 Cylinder 20 14 B *9 60 1/10 Cylinder 20 17 C 10 3/10 Cylinder 20 11 B 11 10 1/2 Cylinder 20 13 B 12 10 1/10 Plate 20 8 A ______ _______ _______ shape __________ __________ _________ 13 10 1/10 Cylinder 3 14 B 14 10 1/10 Cylinder 5 10 B 10 1/10 Cylinder 70 1]. B 16 50 1/10 Cylinder 110 14 B A: Excellent B: Good C: Poor The samples were all made of alumina. Samples marked with * are out of the scope of the present invention.

-41 -[0073] As can be seen from Table 1, in sample No. 9 of which void ratio in the ceramic member between the electrical conductors exceeded 50% and sample No. 1 of which void ratio was 0.005%, wire breakage occurred with the resistance changing by 15% or more. Samples of which void ratio was 50% or less, in contrast, showed satisfactory durability without undergoing wire breakage.

Provided that the void ratio was in the range of the present invention, there was no significant difference in durability regardless of variations in other factors such as the length of void and thickness of ink.

Example 2

4] First, heat generating resistive member made of W was printed on a ceramic sheet prepared from a material constituted from A1203 as the main component, containing 10% or less by weight in total of Si02, CaO, MgO and Zr02 thereby to obtain the heater plate made of ceramics. The opening A where both ends of the heat generating resistive member are exposed provides the area where the heat generating resistive member and the lead wires are brazed together, and is formed at the end of the heater plate by punching a hole in the green ceramic sheet which would make the plate-shaped ceramic member. The opening A also has a recess, of a size that -42 -corresponds to the diameter of the lead wire, in the side wall thereof, for the purpose of brazing the lead-out section of the heat generating resistive member and the lead wires.

Then a coating layer having substantially the same S composition as that of the ceramic sheet was formed on the surface of the heat generating resistive member. After fully drying, an adhesive liquid dispersed ceramics having substantially the same composition as that of the ceramic sheet was applied, and the ceramic sheets prepared in this way were laminated together and fired at 1500 to 1600 C.

5] Then after forming a plating layer from Ni to a thickness of 3 im on the surface of the lead-out section of the heat generating resistive member, the lead wire 61 constituted from Ni as the main component was bonded by means of a brazing material 62 made of Ag at 1030 C in reducing atmosphere, thereby to obtain the heater plate.

[00761 The heater plate obtained as described above and the plate-shaped member were combined to make hair irons while varying the thickness of the heater plate, surface roughness (Ra), presence of spring pressure, presence of heat transfer member and the material used to form thereof.

7] Temperature distribution over the heating surface of -43 -the hair iron made as described above was measured by means of a temperature distribution measuring instrument manufactured by JEOL, Ltd. (TG-6200). Highest temperature and lowest temperature of the heating surface were measured to determine the temperature variation as the difference between the highest temperature and the lowest temperature.

8] The results are shown in Table 2.

-44 -

Table 2

Surface Temperature Heater Heat roughness difference Spring Sample plate transfer of heater across No. thickness pressure member plate heating (mm) (Ra) __________ surface ( C) *1 0.3 None 1 None Broken *2 0. 3 None 10 None Broken 3 0.5 None 2 None 19 4 0.5 None 2 None 19 Silicone 0.5. 0.5 None 16 resin ___________ ________________ Silicone 6 0.5. 1 None 15 resin ____________ ___________ ________________ Silicone 7 0.5. 3 Applied 13 resin ________________ Silicone 8 1. 6 Applied 12 resin __________ ______________ Silicone 9 1. 10 Applied 13 resin ___________ _______________ Silicone 1. 20 None 14 resin Silicone 11 1. 30 None 14 resin ___________ _______________ Silicone 12 3 40 None 16 resin _______________ Fine metal 13 5 3 None 11 particle

S ______________ ______________ ___________________

14 5 None 3 None 19 5 None 3 None 19 *16 7 None 1 None 22 *17 7 None 10 None 24 Evaluation was made under conditions of the plate-shaped member having thickness of 1.5 mm, proportion of the contact area between the plate-shaped member and heater plate of 70% to the heating surface area.

-45 -Samples marked with * are out of the scope of the present invention.

9] As can be seen from Table 2, samples Nos. 3 through 15 where the thickness of the heater plate was in a range from 0.5 to 5 mm showedsatisfactory characteristics with temperature difference across the heating surface not larger than 19 C.

0] In samples Nos. 1 and 2 where the thickness of the heater plate was as small as 0.3 mm, the heater plate broke when mounted. Samples Mos. 16 and 17 where the thickness of the heater plate was 7 mm showed unsatisfactory characteristics with temperature difference across the heating surface being 22 C or larger.

1] Samples Nos. 5 through 13 where the heat transfer member was provided between the plate-shaped member and the heater plate showed satisfactory characteristics with further small temperature difference across the heating surface not larger than 16 C.

[00821 Samples Nos. 6 through 11 where the principal surface of the heater plate showed surface roughness in a range from 1 to 30 m showed satisfactory characteristics with further -46 -small temperature difference across the heating surface not larger than 15 C.

3] In samples Nos. 7 through 9 where one principal surface of the plate-shaped member and one principal surface of the heater plate were pressed by a spring, improvement in the temperature difference was verified with temperature difference across the heating surface not larger than 13 C.

Example 3

4] Ceramic sheets were made while changing the content of A1203 as the main component of the heater plate in a range from 70 to 99.8%, and were used to make the heater plate by the method described in Example 2. High temperature insulation strength and bending strength of the samples having different contents of Al203 were measured at 200 C.

Bending strength was measured on 20 test pieces by the 4-point bending strength test procedure specified in JIS, and the mean value was calculated.

-47 -

Table 3

Sample Alumina High temperature insulation Strength No. content (%) strength 21 70 1 x 10' Qcm or higher 250 MPa 22 75 1 x 10" Qcm or higher 275 MPa 23 80 1 x i' Qcm or higher 300 MPa 24 90 1 x 1013 Qcm or higher 310 MPa 99.5 1 x 10" Qcm or higher 320 MPa 26 99.8 1 x 10" Qcm or higher 328 MPa [0085] As can be seen from Table 3, samples Nos. 23 through 25 having alumina content in a range from 80 to 99.5% showed high temperature insulation resistance of 1 x i0 Qcm or higher, and proved to be usable as hair iron without current leakage from the heater power source. It was also found that the bending strength showed a high value of 300 MPa or more and there was low possibility of breaking due to thermal stress even when the heat generating resistive member was subjected to repetition of quick heating.

6] In samples Nos. 21 and 22 where alumina content was as low as 70% and 75% by weight, respectively, high temperature insulation resistance was 1011 Qcrn or lower and there was a possibility of current leakage through the heater plate.

Sample No. 26 where alumina content was as high as 99.8% had -48 -to be fired at 1700 C or higher so as to sinter, and was difficult to practice for mass production at a low cost.

7] It was found that satisfactory results can be achieved with high bending strength when the alumina content is in a range from 90 to 99.5% as in the cases of samples Nos. 24 and 25.

[00881 Alumina content in the plate-shaped ceramic member was determined by ICP quantitative analysis.

Example 4

[00891 Hair irons were made similarly to Example 2 while changing the length of the heater plate and the ratio of the contact area of the heater plate and the plate-shaped member to the heating surface area with dimensions of the plate-shaped member fixed to 4 mm in thickness, 80 mm in length and mm in width.

[00901 With silicone resin being interposed as the heat transfer member between the heater plate and the plate-shaped member and pressed by means of a spring, a predetermined voltage was applied to the heat generating resistive member.

Time taken to heat the heating surface from the room temperature to the saturation temperature of 200 C in the -49 -hottest portion was determined as the heating surface saturating time.

1] The results are shown in Table 4.

Table 4

Ratio (%) (Contact area between Plate-shaped Heating surface Sample plate-shaped member and member saturating time . heater plate / Heating thickness (mm) (sec) surface area) _______________ _________________ 31 5 2 68 32 10 2 63 33 20 3 60 34 30 3 57 50 0.1 56 36 50 0.2 50 37 50 1 46 38 50 4 46 39 50 10 47 50 12 52 41 60 3 53 42 80 4 60 43 100 4 65 [0092] As can be seen from Table 4, samples Nos. 33 through 42 where the area ratio was in a range from 20 to 80% showed satisfactory characteristic with short heating surface saturating time of 60 seconds or less.

-50 -[00931 Particularly samples Nos. 34 through 41 where the area ratio was from 30 to 60% showed satisfactory characteristic with shorter heating surface saturating time of 57 seconds or less.

[00941 Samples Nos. 31, 32 where the ratio of the contact area of the heater plate 7 and the plate-shaped member 5 to the heating surface area was less than 20% showed long saturating time of 63 second or more.

5] Sample No. 43 where the ratio of contact area exceeded 80% indicated that the heater plate would become too large and expensive to be commercially viable.

6] Samples Nos. 36 through 39 where the thickness of the plate-shaped member was in a range from 0.2 to 10 mm showed satisfactory characteristic with short heating surface saturating time of 50 seconds or less.

-51 -

Claims (3)

1. A method of manufacturing a ceramic heater comprising: a step of applying an electrically conductive paste in a predetermined pattern on the surface of a green ceramic sheet; a step of filling the space between the electrical conductors of the pattern with an insulating material; a step of laminating the green ceramic sheet having the space between the electrical conductors filled with the insulating material on a ceramic compact with the surface whereon the electrically conductive paste has been applied becomes the laminating surface; and a step of firing the stack of green ceramic sheets and the ceramic compact which have been laminated.

2. The method of manufacturing a ceramic heater according to claim 1, wherein a screen printing of a paste is employed in the step of filling with the insulating material.

3. The method of manufacturing a ceramic heater according to claim 1, wherein a filling method by means of a dispenser is employed in the step of filling with the insulating material.

-52 -