JPH0696847A - Surface heating unit and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a surface heating unit of excellent electric insulation, heat resistance, and durability. CONSTITUTION:A surface heating unit comprises a metal base 1, a crystalline glass layer 2 formed on the surface of the metal base 1, and an electric heating element 3, which is coated and bonded to the surface of the glass layer 2 with a glass layer 4. Since the crystalline glass layer 2 is used, foams in the glass layer 2 do not grow, and the dielectric strength shows a very high value because of this. This crystalline glass layer 2 is of almost the same value as the coefficient of thermal expansion of the metal base 1, which means excellent heat resistance. The volume specific resistance of the glass is high, and, since the glass grains are covered watertight with catephoresis electrodeposition, the surface heating unit of excellent insulation can thus be formed even when the total thickness of enamel is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar heating element used in various heaters and cooking appliances which use electric energy as a heat source.

[0002]

2. Description of the Related Art Conventionally, a sheet heating element having an electric heating element body sandwiched between resin films has been widely used.
Since the heat resistance of the resin film is low, it cannot be used above 200 ° C.

Therefore, after forming an insulating holo layer on a holo steel sheet as disclosed in Japanese Patent Application Laid-Open No. 61-128487, a foil-shaped electric heating element is integrally embedded in the holo layer. A planar heating element has been proposed.

The structure of this sheet heating element is shown in FIG. The surface of the metal substrate 1 is covered with an insulating holo layer 11. A holo layer 12 made of titanium opal glass is formed thereon. The electric heating element 3 is placed on the surface of the holo layer 12, and a slip for forming the holo layer 13 is applied and fired to form the holo layer 13. In this way, the sheet heating element covered with the holo layer 13 and integrally bonded to the metal substrate 1 is obtained. Since this sheet heating element is relatively excellent in electrical insulation, it is suitable for use in the medium to high temperature range of 150 ° C. to 300 ° C., and is thin and expected to have a long life.

[0005]

By the way, according to the standards for electrical appliances, the insulation resistance is 1 MΩ or more when used, and the dielectric strength is 1 kV.
It is stipulated as above. Therefore, the biggest problem of the holo-type sheet heating element is the stabilization of the above characteristics.

That is, the insulation resistance of the sheet heating element is expressed by the following equation.

[0007]

## EQU1 ## R = ρ _t × (d / A) where R is the insulation resistance of the planar heating element, ρ _t is the volume resistivity of the holo layer, A is the area of the electric heating element, and d is the film of the holo layer. Indicates the thickness.

Here, the thickness of the holo layer is determined from the viewpoint of holo adhesion, and is at most 100 to 300 μm.
It is about m. In order to improve the insulation resistance of the sheet heating element, the insulating holo layer may be formed of glass frit having an excellent volume resistivity. The volume resistivity of the glass frit is the alkaline component (Na ₂ O, K ₂ O, Li ₂ O) in the glass.
Is greatly affected by. Stabilization of insulation resistance can be achieved by selecting a glass frit with a small amount of alkali components.

However, the dielectric strength is not as clear as that of the above-mentioned insulation resistance, and the characteristics thereof remarkably change depending on the type of glass frit used, the film thickness, the firing conditions and the like. The inventors of the present invention disclosed in JP-A-61-12848
As shown in Japanese Patent Publication No. 7, the inventors have found that if titanium opal frit is used for the holo layer 12 in FIG. 5, improvement in dielectric strength can be achieved. However, this method alone does not completely stabilize the dielectric strength. In particular, when the heat cycle test (400 ° C. to rapid cooling in water) is performed, cracks are generated in the holo layer 12, so that the insulation resistance and the dielectric strength still remain a problem.

The present invention has been made in consideration of the problems of the conventional sheet heating element, and an object thereof is to provide a sheet heating element having no problem in insulation resistance and dielectric strength and a method for manufacturing the sheet heating element. .

[0011]

The sheet heating element of the present invention comprises:
It has a metal base, a crystallized glass layer formed on the surface of the metal base, and an electric heating element coated on and bonded to the surface of the crystallized glass layer by the glass layer.

[0012]

Operation: For example, alkaline components (Li ₂ O, Na ₂ O, K
_When an alkali-free crystallized glass containing no ₂ O) is used, the electric insulating property is dramatically improved. In addition, since this glass deposits innumerable fine crystals when baked on a metal substrate, it is similar to ceramics and its heat resistance (about 900 ° C.) is greatly improved. On the other hand, the glass that is usually used is amorphous and has a low heat resistance temperature (about 600 ° C.). For example, when the electric heating element is formed at 700 ° C., the amorphous glass is softened and flows above the heat resistant temperature, so that small bubbles in the glass grow and become large bubbles. As a result, the large bubbles cause a decrease in dielectric strength. On the other hand, since the alkali-free crystallized glass has improved heat resistance due to the precipitation of crystals, even if the electric heating element is baked at 800 ° C., the crystallized glass layer does not soften and flow, and Bubbles do not grow large. Therefore, the dielectric strength also shows a high value.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (1) Metal Substrate The metal substrate used in the present invention includes various alloy materials such as holo steel, stainless steel, silicon steel, nickel-chromium-iron, nickel-iron, kovar, invar, and clad materials thereof. Is selected. In particular, since the metal material used in the present invention needs to match the expansion coefficient with the glass layer, the expansion coefficient is 100 to 140 × 10 ⁻⁷ /
C. stainless steel is preferred.

Once the material of the metal substrate is determined, the desired shape processing, hole processing, etc. can be carried out by ordinary mechanical processing, etching processing,
It is applied by laser processing or the like.

For the purpose of improving the adhesiveness of the glass layer, these metal substrates are degreased on the surface and then plated with various kinds of nickel, cobalt or the like, or an oxide coating layer is formed by thermal oxidation treatment.

(2) Glass Layer In the glass layer used in the present invention, from the viewpoint of electrical insulation and heat resistance, alkali-free crystallized glass (by firing,
For example, it is preferable that the MgO-based crystal phase is deposited). Its glass composition is, in particular, 16 to 50% by weight of MgO, 7 to 30% by weight of SiO ₂ , 5 to 34% by weight of B ₂ O ₃ , and 0 to 50% of BaO.
% By weight, 0-40% by weight of La ₂ O ₃ , 0-20% by weight of CaO, 0 of P ₂ O ₅
More preferably, it is -5 wt% and MO ₂ is 0-5 wt% (however, M is at least one element of Zr, Ti, and Sn).

As described above, one of the reasons for selecting the crystallized glass material is that the heat resistant temperature of the glass layer becomes high. That is, when the electric heating element is formed on the glass layer, the glass layer is fired at a high temperature (800 ° C. or higher), so that the glass layer must have a heat resistant temperature of at least 900 ° C. By crystallizing the glass, the heat-resistant temperature is 900 ° C or higher (the glass does not flow even at 900 ° C, so even if an electric heating element is formed at 800 ° C, bubbles in the glass layer do not grow large. It does not deteriorate). On the other hand, general amorphous glass does not crystallize even if it is reheated, so it has heat resistance (because the glass flows at about 600 ° C or more, if an electric heating element is formed at 800 ° C or more, bubbles in the glass layer , But causes a decrease in dielectric strength) and does not improve.

Another reason for selecting the crystallized glass material is to strengthen the adhesion between the metal substrate and the glass layer. In particular, the glass having the above composition has very strong adhesion.

As a method for coating the above-mentioned crystallized glass layer on a metal substrate, there are a usual spray method, a powder electrostatic coating method, an electrophoretic electrodeposition method and the like. The electrophoretic electrodeposition method is the most preferable from the viewpoints of the denseness of the coating film, the electrical insulating property, and the like.

The slurry used in this method contains glass, alcohol and a small amount of water in a ball mill.
It is prepared by crushing, mixing for 20 hours. The average particle size of the glass in the slurry of the present invention is about 1 to 5 μm. The obtained slurry is put in an electrolytic cell and the liquid is circulated. Then, the metal substrate is immersed in this slurry and negatively polarized at 100 to 400 V to deposit glass particles on the surface of the metal substrate. After this is dried, it is baked at 850 to 900 ° C. for 10 minutes to 1 hour. As a result, the glass fine particles are melted, and the glass component and the metal material interdiffuse, so that strong adhesion between the glass layer and the metal substrate can be obtained.

[0021] In the firing, if the temperature is gradually raised from room temperature to reach the above temperature, innumerable fine needle-like crystals are precipitated and the heat resistance is further improved.

(3) Electric heating element The electric heating element used in the present invention is basically an electric heating material such as ribbon-shaped or lath-mesh-shaped Fe-Ni, Fe-Ni-Cr, stainless steel, etc., or printed. Resistors such as ruthenium oxide-glass, Ag-Pd-glass, and carbon formed by the method are preferable.

As a method of forming the electric heating element in the planar heating element of the present invention, the transfer method and printing method described below are preferable.

(4) Method for forming electric heating element layer When an electric heating element is formed by the transfer method, Ni-Cr alloy foil or stainless steel foil is preferable as the material of the element.
FIG. 2 shows the structure of a transfer paper containing an electric heating element. A glass powder layer 4 and an overcoat layer 7 for forming a holo layer are formed on the surface of the transfer mount 5 via a water-soluble glue layer 6. The glass powder layer containing the electric heating element 3 is composed of two layers 4a and 4b. Next, details of this transfer paper will be described.

(A) Transfer Mount 5 The transfer mount 5 is preferably water resistant and has a thickness of about 100 to 600 μm. The thickness of the mount and the rigidity of the mount are adjusted according to the components laminated on the mount. Need to be adjusted.

(B) Adhesive Layer 6 The adhesive layer 6 formed on the mount 5 is preferably a re-wettable adhesive, which is a water-soluble polymer such as casein, dextrin, starch,
Glue, polyvinyl alcohol, polyacetyl acid salt, polyvinylpyrrolidone and the like are used, and among them, dextrin is most preferable.

(C) Glass Layer 4 The glass used here is preferably a titanium opal glass which has good wettability with the electric heating element 3 and has a low softening point. Its composition is as follows.

[0028]

[Table 1]

(D) Overcoat layer 7 The role of the resin film as the overcoat layer 7 is extremely important. When the transfer paper is immersed in water before use, the rewetting glue layer absorbs water and swells, and separates into a mount and a transfer part. At this time, it is necessary to transfer the transfer portion to the substrate and maintain the flexibility and mechanical strength of the transfer portion until the substrate and the transfer portion are joined together. In addition, when it is bonded to the substrate, it is necessary to have a function of oxidatively burning during burning to eliminate ash without leaving it. Vinyl chloride resin, acrylic resin, and the like are used to achieve this purpose, and acrylic resin is particularly excellent. The acrylic resin is adjusted in viscosity with an appropriate solvent, and an overcoat layer is formed by spraying or printing.

Next, a case of forming by a printing method will be described.

When the electric heating element is formed by the printing method,
A paste containing ruthenium oxide and glass frit as a main component, a paste containing Ag-Pd and glass frit as a main component, and the like are printed on the crystallized glass layer, and then baked. The components of these pastes may be ruthenium oxide, Ag-Pd, glass frit (borosilicate glass, etc.) as main components, as well as filler (ZrO ₂ etc.), bismuth oxide, ethyl cellulose, butyl carbitol acetate (terpineol). ) Etc. are included. Also,
These pastes may be used alone or in combination. That is, Ag-Pd alone may be used as an electric heating element, or ruthenium oxide may be used in combination as a resistor and Ag-Pd as an electrode for taking out a lead.

Next, a more specific embodiment will be described.

(Example 1) SUS430 substrate (100 mm x 100 mm x
(0.5 mm) surface, a crystallized glass layer having a composition shown in (Table 2) to (Table 6) is electrophoretically deposited to a thickness of 100 μm, and the temperature is 10 ° C. at 880 ° C.
After baking for a minute, various properties such as surface roughness, waviness and heat resistance of the sample were examined. The results are shown in Table 2 together with the composition.
It is shown in (Table 6).

The surface roughness was measured by a Talysurf surface roughness meter and indicated by the surface center line average roughness Ra, and the waviness was expressed by the difference Rmax between the peak and the valley obtained by the Talysurf surface roughness meter.

The heat resistance was measured by placing the sample in an electric furnace at 850 ° C.
A spalling test was repeated in which the sample was put in for 0 minutes and taken out of the furnace for 30 minutes, and spontaneous cooling was repeated to examine the state of cracking and peeling of the sample. Incidentally, the crack is immersed in the red ink, then the surface is wiped off, and by visual observation,
The presence or absence thereof was investigated. ○, △, × in the table, ○ indicates that no abnormality is observed even after 10 cycles or more, △ is 5-9
What occurred in the cycle, x shows what occurred in 4 cycles or less.

The adhesion was evaluated by conducting a bending test on the substrate, and X indicating that the metal part was exposed by peeling off the glass layer, Δ indicating that the metal part was partially exposed, and Δ indicating that the metal part was not exposed. ○

Based on the above evaluations, a comprehensive evaluation was performed, and the results are shown by ◯, Δ, and x. Nos. 1 to 8 are those in which SiO ₂ and B ₂ O ₃ are changed while other components are constant, and Nos. 9 to 15 are S
iO ₂ / B ₂ O ₃ was kept almost constant and the amount of MgO was changed, No1
Similarly, 6 to 19 are the ones in which the amount of CaO was changed. No20 ~ 24
Is the same as the BaO amount. No. 25 to 29 are the ones with the same La ₂ O ₃ content. No30 to 42 are ZrO
₂ shows the effects of ₂ , TiO ₂ , SnO ₂ , P ₂ O ₅ , and ZnO.

As is clear from these tables, when SiO ₂ is increased, the heat resistance is improved, but the surface property and the adhesion are deteriorated. On the contrary, when the amount of B ₂ O ₃ is increased, the surface property and the adhesion are improved, but the heat resistance is decreased. Therefore, in the present invention, the range of 7-30 wt% SiO _{2 and} 5-34 wt% B ₂ O ₃ is preferable.

The amount of MgO has a correlation with the crystallinity, and if it is 16% by weight or less, the precipitation of crystals is insufficient and the heat resistance is poor. On the other hand, if it is 50% by weight or more, crystals tend to precipitate, it is difficult to crystallize when the glass melts, it is difficult to obtain a homogeneous glass, and the surface roughness becomes large.

If the CaO content is 20% by weight or more, the surface property is deteriorated, which is not preferable.

When the amount of BaO is 50% by weight or more, heat resistance and adhesion are deteriorated, which is not preferable.

When La ₂ O ₃ is 40% by weight or more, heat resistance is deteriorated, which is not preferable.

Other components that can be added are ZrO ₂ , TiO ₂ and Sn.
O ₂ , P ₂ O ₅ , ZnO and the like can be mentioned, but up to 5% by weight can be added.

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

(Embodiment 2) A planar heating element having an electric heating element formed by a transfer method will be described with reference to FIG.

The metal substrate 1 of 200 mm × 200 mm is degreased / washed / pickled / washed / nickel plated / washed to pretreat the substrate, and then it is composed of No. 7 glass particles having the composition of (Table 2). By immersing in the slurry and applying a DC voltage between the counter electrode and the metal substrate, 100 glass particles are deposited on the metal substrate.
μm coating and heating from room temperature to 880 ℃ for 4 hours,
Further, the crystallized glass layer 2 was formed by carrying out firing at this temperature for 10 minutes. Next, using the glass having the composition shown in (Table 1), a transfer paper having the structure shown in FIG. 2 was produced. Next, this transfer paper is immersed in water, the glass layer supported by the overcoat layer and the electric heating element are peeled from the mount, placed on the surface of the crystallized glass layer 2, dried sufficiently, and then at 800 ° C. It was fired to form a sheet heating element.

(Embodiment 3) A planar heating element having an electric heating element formed by a printing method will be described with reference to FIG.

Metal substrate 1 having an outer shape of 200 mm × 200 mm
After degreasing, washing with water, pickling, washing with water, nickel plating, washing with water and pretreatment, dip it in a slurry consisting of No. 7 glass particles with the composition of (Table 2), and place it between the counter electrode and the metal substrate. Applying DC voltage, 100μ of glass particles on the metal substrate
m, the temperature was raised from room temperature to 880 ° C. over 4 hours, and the temperature was kept at this temperature for 10 minutes for firing to form a crystallized glass layer 2. Next, Ag on the surface of the crystallized glass layer 2
-Pd paste pattern printing by screen printing, 85
The electrode 8 was baked at 0 ° C. Further, Ru on this electrode 8
The O ₂ paste was similarly printed and fired at 830 ° C. to form the electric heating element 9, which was used as a planar heating element.

Comparative Example 1 As a comparative example, Japanese Patent Laid-Open No. 61-
A conventional sheet heating element disclosed in Japanese Patent No. 128487 was produced. Degreasing, washing with water, pickling, washing with water, nickel plating of the metal substrate 1 with an outer shape of 200 mm × 200 mm shown in FIG.
After washing with water and pretreatment, SiO ₂ : 43.5, B ₂ O
₃ : 21.0, Na ₂ O: 0.8, K ₂ O: 2.2, Li ₂
O: 1.0, CaO: 11.3, BaO: 6.0, Mg
O: 2.9, ZnO: 5.5, Al ₂ O ₃ : 3.1, Zr
O _2: 2.7 Glass composition (low alkali amorphous glass) particles and _{Al 2 O 3, SiO 2,} F-10, was coated a Horo slip comprising water to a thickness of about 150 [mu] m, dried 850 The first holo layer 11 was formed by firing at 10 ° C. for 10 minutes. Next, in the same manner, a glass holo-slip composed of glass (titanium opal glass) having the composition (Table 1), clay, sodium nitrite, and water was deposited on the first holo layer 11 to a thickness of 150 μm.
The coating was applied to about 10 minutes, dried, and baked at 810 ° C. for 10 minutes to form the second holo layer 12. On top of that, the same glass and clay as the second holo layer, sodium nitrite, 2MgO
A holo-slip consisting of SiO ₂ and water was applied on the second holo layer 12, and the electric heating element 3 of FIG. 4 was installed while the surface was wet. Further, the same slip was applied thereon, dried, and baked at 800 ° C. for 10 minutes to form a planar heating element.

(Comparative Example 2) External shape 200 mm shown in FIG.
Degreasing, washing with water, pickling, washing with water
After nickel-plating and washing with water to pretreat the substrate, S
_{iO 2: 43.5, B 2 O} 3: 21.0, Na 2 O: 0.
8, K ₂ O: 2.2, Li ₂ O: 1.0, CaO: 11.
3, BaO: 6.0, MgO: 2.9, ZnO: 5.
5, Al ₂ O ₃ : 3.1, ZrO ₂ : 2.7 was immersed in a slurry composed of glass particles, and a DC voltage was applied between the counter electrode and the metal substrate to coat it on the metal substrate. Then, the temperature is raised from room temperature to 850 ° C over 4 hours, and at this temperature 10
The glass layer 14 was formed by firing for holding for a minute. Next, the electric heating element 3 was formed on the surface of the glass layer 14 in the same manner as in Example 1 to obtain a planar heating element.

With respect to the sheet heating elements of Examples 2 and 3 and Comparative Examples 1 and 2, the insulation resistance and the dielectric strength between the metal substrate and the electric heating element were measured. The insulation resistance was measured when a voltage of 500 V was applied. The dielectric strength was shown by the voltage when a short circuit was made by using a withstanding voltage insulation automatic tester manufactured by Kuniyo Denki Co., setting a breaking current at 10 mA, and applying a voltage for 1 minute. In addition, the above-mentioned sheet heating element is heated to 400 ° C.
After holding it for a minute, a heat shock test of putting it in water was performed for 20 cycles. The insulation resistance and dielectric strength after 20 cycles were also measured. The above results are shown in (Table 7).

[0056]

[Table 7]

As described above, the sheet heating element of the present invention is 400
It can be seen that the insulation resistance and the dielectric strength do not deteriorate even when the rapid cooling test at ℃ to water is performed. On the other hand, in the comparative example, both the insulation resistance and the dielectric strength are significantly deteriorated after the heat shock test. The reason for this is that the difference in the coefficient of thermal expansion between the metal substrate and the glass is greatly different. Especially in the comparative example, it is considered that the total holo layer was thick because of the three-layer structure, cracks were more likely to occur, and deterioration was more severe.

As described above, in the sheet heating element of the present invention, since the glass layer made of the crystallized glass material is used, bubbles in the glass layer do not grow largely. Therefore, the dielectric strength also shows a very high value.

In the case where the crystallized glass used in the present invention shows a value substantially equal to the coefficient of thermal expansion of the metal substrate,
Even when the heat cycle resistance test is performed, the holo layer does not peel off or crack. This glass has a high volume resistivity, and since the glass particles are densely coated by electrophoretic electrodeposition, it is necessary to form a planar heating element with excellent insulation even if the total holo thickness is reduced. Is possible. As a result, even if the high temperature heat cycle test is performed, peeling of the holo does not occur.

The crystallized glass of the present invention is not necessarily alkali-free.

[0061]

As is apparent from the above description,
Since the present invention utilizes the crystallized glass layer formed on the surface of the metal substrate, it is possible to realize a planar heating element having no problem in insulation resistance or insulation force.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a planar heating element formed by a transfer method according to an embodiment of the present invention.

FIG. 2 is a sectional view of a transfer sheet according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a planar heating element formed by a printing method according to an embodiment of the present invention.

FIG. 4 is a plan view of an electric heating element according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a planar heating element in a first conventional comparative example.

FIG. 6 is a cross-sectional view of a planar heating element in a second conventional comparative example.

[Explanation of symbols]

 1 Metal Substrate 2 Crystallized Glass Layer 3 Electric Heating Element 4 Overcoat Layer 5 Transfer Mount 6 Paste Layer 7 Transfer Overcoat Layer 8 Electrode 9 Resistor (Electric Heating Element) 10 Overcoat Layer 11, 14 First Hollow Layer 12 Second holo layer 13 Overcoat layer

Claims (4)

[Claims] 1. A metal substrate, a crystallized glass layer formed on the surface of the metal substrate, and an electric heating element covered and bonded to the surface of the crystallized glass layer by a glass layer. Sheet heating element to be. 2. The composition of the crystallized glass material is such that MgO is 16-5.
0% by weight, SiO ₂ 7-30% by weight, B ₂ O ₃ 5-34% by weight, BaO 0-50% by weight,
La ₂ O ₃ is 0-40% by weight, CaO is 0-20% by weight, P ₂ O ₅ is 0-5% by weight, and MO ₂ is 0-5% by weight (where M is Zr, Ti, or Sn. The sheet heating element according to claim 1, which contains at least one element. 3. A step of coating and baking glass particles on a metal substrate by an electrophoretic electrodeposition method to obtain a crystallized glass layer, and forming a transfer sheet in which an electric heating element is laminated on a transfer mount via the glass layer. A method of manufacturing a planar heating element, comprising: a step; and a step of attaching the transfer sheet onto the crystallized glass layer, firing and integrating the sheet. 4. A step of coating a metal substrate with glass particles by an electrophoretic electrodeposition method, followed by firing to obtain a crystallized glass layer, and a paste containing a resistance component is printed on the crystallized glass layer. Post-baking to form an electric heating element,
And a step of printing a glass paste on the electric heating element to form a protective layer.