JP3193818B2 - Waterproof ceramic heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to household appliances ceramic heater where the product is used, the ceramic heater data that are especially necessary waterproof.

[0002]

2. Description of the Related Art Generally, silicon carbide-based porous conductive ceramic substrates used as heaters are mainly used for industrial purposes, and include siliconitk (trade name manufactured by siliconitk industrial) and Elema (trade name manufactured by Tokai High Heat Corporation). (Trade name) and Tecorundum (trade name made by Toshiba Ceramics). Recently, the applicant of the present invention has proposed a silicon carbide ceramic heater used for home appliances (Japanese Patent Laid-Open No. 4-65360).
Has been made.

[0003]

However, since each of these ceramic heaters is a structure made of porous conductive ceramics, for example, a heater such as a defrost heater in a refrigerator or a heater for drying a bathroom may be in contact with water. When used in any place, there is a problem in that when water permeates into the heater, and when the heater comes into contact with cold air and freezes, the ceramic base material is destroyed due to expansion of the ice, that is, there is a problem of so-called frost damage.

[0004] Further, when used in a heater for a cooker, moisture in food permeates into the ceramic base material, and bacteria are generated inside the substrate, causing food contamination, and there is a hygiene problem. Further, even in a ceramic heater in which a metal film is formed on the heater surface by thermal spraying, since the metal film is porous, there is a problem that water penetrates, particularly when water containing salt in foods penetrates, causing metal corrosion. Was.

[0005] The present invention has been made in view of the above problems, a ceramic heater motor having a waterproof function to prevent penetration of water into
The purpose is to provide.

[0006]

Means for Solving the Problems According to the present invention, there is provided a method for filling and covering a pore and a surface of a porous conductive ceramic substrate with a water-resistant material composed of an inorganic polymer having a siloxane bond as a skeleton. Thus, the ceramic heater has good waterproof properties. Further, when a metal film is formed by thermal spraying as an electrode, an electrode having good corrosion resistance can be provided by coating the electrode with a similar water-resistant material.

As the porous conductive ceramic heater, a general silicon carbide ceramic heater may be used.
In a ceramic heater mainly composed of silicon nitride and silicon carbide generated by a nitridation reaction of metallic silicon, particularly when the pore diameter is reduced to 1 μm or less, the filling state of the water-resistant material is improved, and the waterproof effect is increased. .

Next, as a waterproofing method for the ceramic heater, a porous conductive ceramic substrate or a porous conductive ceramic substrate on which an electrode of a sprayed metal film is formed in advance is formed on the surface and inside pores of the porous conductive ceramic substrate. Impregnated and coated with a methylhydrogenpolysiloxane-based silicone oil or alkoxysilane-based solution,
Thereafter, heat treatment is performed.

The heating conditions are as follows.
The temperature is suitably from 0 to 400 ° C., whereby a continuous, strong and water-resistant polysiloxane-bonded amorphous film is formed on the surface and inside of the porous ceramic substrate. 150
If the temperature is lower than 400 ° C., the film cannot be formed due to insufficient cross-linking reaction. For the latter water-resistant material, a temperature between room temperature (15 ° C.) and 400 ° C. is appropriate, whereby a continuous, strong and water-resistant polysiloxane-bonded amorphous film similar to the above is formed. At a temperature of 400 ° C. or higher, crystallization occurs, resulting in a discontinuous film and poor water resistance. As for the heat resistance of the water-resistant film, the former is better. The latter has the advantage that the film can be formed even at room temperature and the workability is easy.

As a method for impregnating and coating the surface and the inside of the porous conductive ceramic substrate, a dipping method is suitable. Further, in order to efficiently impregnate the inside of the ceramic base material, the liquid is preferably subjected to ultrasonic vibration. Then, it is preferable that the dripping remaining on the surface when the ceramic substrate is taken out of the liquid is removed by air blowing. That is,
This is because if the heat treatment is performed in an excessively thick film state, defects such as cracks are likely to occur during film formation.

[0011]

In the above-mentioned means for solving the above problems, a porous conductive ceramic substrate used as a ceramic heater is impregnated with a methylhydrogenpolysiloxane-based silicone oil or an alkoxysilane-based solution in the surface and inside pores thereof. By coating, the pores on the surface and inside of the ceramic substrate are coated and filled with a water-resistant material of an inorganic polymer having a siloxane bond as a skeleton, and have complete impermeability to liquids such as water. As a result, water does not permeate into the ceramic substrate, and freezing damage and food contamination can be prevented.

Further, when a sprayed metal film as an electrode is previously formed on the ceramic base material, the inside of the pores in the metal film is filled with a waterproof material to prevent corrosion of the metal film due to water or the like. Can be.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a ceramic heater according to the present embodiment fills the pores on the surface and inside of a silicon carbide-based porous ceramic base material 1 with a waterproof material made of an inorganic polymer having a siloxane bond as a skeleton. The silicon carbide particles 2 are coated with water-resistant material 3 at the grain boundaries, and the same outermost surface is coated with the same water-resistant material 3. For this reason, even if water adheres to the surface of the conductive ceramic substrate 1, the water does not penetrate into the ceramic substrate, and the ceramic substrate 1 is prevented from being broken by frost damage.

FIG. 2 shows another ceramic heater.
As described above, the water-resistant material 3 is filled and coated on the surface and inside pores of the silicon carbide-based ceramic base material 1 on which the metal coating 4 is formed on the surface by thermal spraying as an electrode in advance. For this reason, the porous metal film 4 is also filled and covered with the water-resistant material 3, and even if water contacts the ceramic heater,
Since it is difficult for water to directly contact the metal film 4, corrosion can be prevented. When used as a ceramic heater, a lead wire or a lead plate for supplying power is usually joined to the electrode by brazing or the like. By immersion treatment in an empolysiloxane-based silicone oil or an alkoxysilane-based solution, the effect of preventing corrosion of the joint can be exerted. Note that aluminum or nickel is suitable as a material used for the metal film 4.

FIG. 3 shows a molecular model of a water-resistant material of an inorganic polymer having a siloxane bond as a skeleton. R in this figure
Is an alkyl group. When a methylhydrogenpolysiloxane-based silicone oil is used, R is a methyl group, and when an alkoxysilane-based silicone oil is used,
R becomes various alkyl groups depending on the type. Examples of the alkoxysilane include tetramethoxysilane, methyltrimethoxysilane, dimethylmethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane , Isobutyltrimethoxysilane, decyltrimethoxysilane and the like. Among them, those having a methyl group, such as methyltriethoxysilane, are particularly excellent in water impermeability after crosslinking and curing because the film surface has water repellency.

As the porous conductive ceramic heater, a general silicon carbide ceramic heater may be used.
By using a ceramic base material containing silicon nitride and silicon carbide generated by the nitridation reaction of metallic silicon as main components, the pore diameter is particularly reduced to 1 μm or less, and the filling state of the waterproof material is improved.

Next, a method of manufacturing a ceramic heater containing silicon nitride and silicon carbide as main components will be described. The silicon carbide used here usually has a purity of 99% by weight or more, and
It has an average particle size of 10 to 10 μm, especially 2 to 7 μm
Having an average particle size of If it exceeds 10 μm, there is a problem in the production of abrasion of the molding machine, and abrasion powder is mixed into the raw material, which adversely affects the physical properties and electrical properties of the sintered product. On the other hand, if the thickness is less than 1 μm, it is difficult to achieve high purity, the moldability is deteriorated, and the variation in electrical characteristics is increased. The silicon carbide particles can be produced by treating silicon carbide having an average particle size of 1 to 10 μm with an aqueous acid solution containing hydrofluoric acid. Further, silicon nitride is a substance that binds silicon carbide particles in a porous manner, and mixes metal silicon powder having an average particle diameter of 1 to 10 μm with silicon carbide particles, nitrifies the metal silicon powder, and mixes silicon carbide particles with each other. Bind over.

A raw material consisting of 60 to 90 parts by weight of the silicon carbide powder and 10 to 40 parts by weight of the metal silicon powder is mixed with a molding aid such as an organic resin binder and a surfactant and water, and mixed. After sintering, it is heated and sintered in a nitrogen atmosphere.

Here, if the amount of the silicon carbide powder is less than 60 parts by weight, the specific resistance of the ceramic heater becomes too large,
If it exceeds 90 parts by weight, the toughness is reduced. Therefore, 65 to 75 parts by weight is particularly preferable. If the amount of the metal silicon powder is less than 10 parts by weight, the toughness is reduced, and
Exceeding the parts by weight increases the specific resistance. Therefore, 25 to 35 parts by weight is particularly preferable.

In the heat sintering, the dried mixture is heated in a nitrogen atmosphere, for example, at 400 to 600 ° C. for 2 to 6 hours to remove a gas generating substance such as a molding aid, and then again heated in a nitrogen atmosphere for 1300 hours. The temperature is raised to １４1450 ° C. and reaction sintering is performed for 2 to 24 hours. Then, the ceramic heater is completed by processing into a predetermined size. The ceramic heater thus obtained has a specific resistance of 10 ^-1 to 10 ² Ω · cm.

Next, a method of waterproofing the ceramic heater will be described. A porous conductive ceramic substrate is immersed in a methylhydrogenpolysiloxane-based silicone oil or an alkoxysilane-based solution.
The liquid is ultrasonically vibrated. As a result, the surface and inside pores of the ceramic substrate are impregnated with and coated with a methylhydrogenpolysiloxane-based silicone oil or an alkoxysilane-based solution. Then, the ceramic base material is removed from the liquid, and the dripping remaining on the surface is removed by air blowing. After that, heat treatment is performed.

The heating conditions are 15
The temperature is suitably from 0 to 400 ° C., whereby a continuous, strong and water-resistant polysiloxane-bonded amorphous film is formed on the surface and inside of the porous ceramic substrate. Also,
For the latter water-resistant material, a temperature between room temperature (15 ° C.) and 400 ° C. is appropriate, whereby a continuous, strong and water-resistant polysiloxane-bonded amorphous film similar to the above is formed. The former has better heat resistance as the water-resistant film. In the latter case, since film formation is possible even at room temperature drying,
Workability is easy.

Table 1 shows that a porous conductive ceramic base material containing silicon nitride and silicon carbide produced by the nitridation reaction of metallic silicon as main components is provided with a methylhydrogenpolysiloxane-based silicone oil and a methyltriethoxysilane-based silicone oil. Shows the water absorption of the sample waterproofed with the solution of Example 1. Water absorption is the initial value immediately after waterproofing, 300
It shows the water absorption after the heat resistance test for 10 hours, 100 hours, and 1000 hours at 400C and 400C. As is clear from these results, no deterioration of any of the water resistant materials is observed at 300 ° C. At 400 ° C., it can be seen that the methylhydrogenpolysiloxane-based silicone oil is less deteriorated. Table 2 shows the material properties of the porous conductive ceramics used in this test.

[0024]

[Table 1]

[0025]

[Table 2]

Next, an embodiment in which the ceramic heater of the present invention is applied to a defrost heater for a refrigerator will be described. FIG. 4 shows the appearance of a ceramic heater H of the present invention, in which electrode portions 5 made of a metal film are formed on the upper surfaces of both ends of a flat ceramic base material 1 by thermal spraying. An electrode terminal 6 is soldered to each electrode section 5, and a lead wire 7 is connected to each electrode terminal 6 by caulking. By applying a voltage between the two lead wires 7 and causing a current to flow through the ceramic heater H, the ceramic heater H generates heat.

In the refrigerator, as shown in FIG. 5, an evaporator 11 is mounted on a refrigerator main body 10, a thermostat 12 is arranged near an upper portion of the evaporator 11, and an angle gutter 13 is arranged below the entire bottom surface of the evaporator 10. ing. The upper part of the angle gutter 13 is bent at a right angle to form an eave 14, and the lower part is bent into a substantially U-shape to form a drain receiver 15.
A drain hose 16 is connected to the drain receiver 15. Further, the ceramic heater H is provided with a pair of right and left holders 17 protrudingly formed on the angle gutter 13 so that the eaves 1 are formed.
4 is supported immediately below. The eaves 14 are attached to prevent water (drain) dripping from the evaporator 11 from directly flowing to the ceramic heater H during the defrosting operation.

In the above configuration, when the defrosting operation of the refrigerator is started, power is supplied to the ceramic heater H, and the ceramic heater H generates heat and melts the frost attached to the evaporator 11. Then, the dripped water flows into the drain receiver 15 of the angle gutter 13 and is drained through a drain hose 16 to a drain pan (not shown) installed outside the refrigerator.
When the temperature detected by the thermostat 12 becomes equal to or higher than a predetermined temperature, the defrosting operation mode ends, and the ceramic heater H
Is turned off. Here, the ceramic heater H
Is exposed to a humidified atmosphere during defrosting, and comes into contact with water due to the rebound of drain water from the angle gutter 13. At this time, since the ceramic heater H of the present invention is waterproofed, water does not permeate into the ceramic base 1 and the electrode portion 5 and the ceramic base 1 caused by frost damage during cooling.
And corrosion of the electrode portion 5 can be completely prevented.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention. In the present embodiment, the ceramic heater is applied to the refrigerator, but may be applied to a bathroom drying heater and a cooker heater.

[0030]

As is apparent from the above description, according to the present invention, the porous and conductive ceramic substrate is filled and coated with a water-resistant material of an inorganic polymer having a siloxane bond as a skeleton in the pores on the surface and inside. Accordingly, it is possible to prevent moisture from entering the inside of the ceramic base material, and it is possible to provide a ceramic heater having good waterproof properties. Even when a porous metal film electrode is formed by thermal spraying, the electrode is simultaneously filled and coated with a water-resistant material, thereby improving the corrosion resistance of the electrode. A high ceramic heater can be provided. Here, silicone oil is used as a water-resistant material
And, because of the effect of water repellency, this waterproof treatment
Ceramic heaters are used in humid environments in refrigerators
Suitable for defrost heaters.

In a ceramic heater containing silicon nitride as a main component generated by a nitriding reaction of metallic silicon, the pore size is particularly reduced to 1 μm or less, so that the water-resistant material is filled well and the waterproof effect can be further enhanced. it can.

The porous conductive ceramic base material and
Metal coating previously formed by spraying on the surface of
Siloxane bonds on the surface and inside pores of the electrode
Impregnated and coated with a solution of an inorganic polymer serving as a skeleton, for example, a methylhydrogenpolysiloxane-based silicone oil, and heat-treated at 150 to 400 ° C., or impregnated and coated with an alkoxysilane-based solution, The inorganic polymer having good water resistance can be formed on the surface and inside pores of the porous conductive ceramic substrate and the electrode by a simple method such as drying or heat treatment at a temperature of ° C. At this time, perform ultrasonic vibration
Impregnates the solution up to the pores inside the substrate and electrode
Can be done. Also, when taken out of the liquid
Blow to remove dripping, water resistant material is thick film
And the occurrence of cracks during film formation can be prevented. Therefore, it is possible to provide a ceramic heater having not only the water resistance of the ceramic base material but also the corrosion prevention of the electrode.

[Brief description of the drawings]

FIG. 1 is a state diagram when a water-resistant material is filled and covered in pores on the surface and inside of a silicon carbide-based porous ceramic substrate.

FIG. 2 is a diagram showing a state where a water-resistant material is filled and covered in pores on the surface and inside of a silicon carbide-based ceramic substrate having a metal film electrode formed on the surface.

FIG. 3 is a molecular model diagram of a water-resistant material of an inorganic polymer having a siloxane bond as a skeleton.

FIG. 4 is a perspective view of a ceramic heater applied to a defrost heater of a refrigerator.

FIG. 5 is a perspective view of a rear part of a refrigerator equipped with a ceramic heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic base material 2 Silicon carbide particles 3 Waterproof material 4 Metal film 5 Electrode part 6 Electrode terminal 7 Lead wire 11 Evaporator 12 Thermostat 13 Angle gutter 14 Eave 15 Drain receiver 17 Holder H Ceramic heater

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-341787 (JP, A) JP-A-2-311348 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 3/04 C04B 41/83 C09K 3/18 H05B 3/14

Claims (4)

(57) [Claims] 1. A porous conductive ceramic heater having a waterproof function for preventing water from seeping into the inside thereof, wherein a ceramic base material constituting the ceramic heater is formed of silicon carbide powder and metal silicon powder. The mixing ratio is such that the amount of silicon carbide powder is not less than 60 parts by weight and not more than 90 parts by weight;
The ceramic heater is characterized in that the amount of metallic silicon is 10 parts by weight or more, and the waterproof function is provided by filling a water-resistant material into internal pores. 2. The waterproofing function comprises forming a metal film electrode on the surface of the ceramic base material by spraying in advance, then immersing the electrode in an inorganic polymer solution having a siloxane bond as a skeleton, and ultrasonically vibrating the solution. 2. The ceramic heater according to claim 1, wherein the solution is impregnated into pores inside the ceramic substrate and the electrode, coated on the surface, and subjected to heat treatment. 3. The waterproofing function is such that after forming an electrode of a metal film on the surface of the ceramic base material by spraying in advance, the waterproofing function is immersed in a methylhydrogenpolysiloxane-based silicone oil and subjected to ultrasonic vibration. Impregnated and coated on the surface and inside pores of the ceramic base material, blow off the silicone oil dripping remaining on the surface after removing the ceramic base material,
The ceramic heater according to claim 1, wherein the ceramic heater is applied by performing a heat treatment at 150 to 400C. 4. The waterproofing function is such that after forming an electrode of a metal film on the surface of the ceramic base material by spraying in advance, the metal base material is immersed in an alkoxylan-based solution and ultrasonically vibrated. By impregnating and coating the pores inside, removing the dripping of the alkoxylan-based solution remaining on the surface after taking out the ceramic base material, and removing the ceramic base material by performing heat treatment at room temperature to 400 ° C. The ceramic heater according to claim 1, wherein