JPH02242580A - Plane-like heater - Google Patents

Abstract

PURPOSE:To improve the thermal shock resistance of a plane-like heater as well as the insulating property at the time of having high humidity by having glass phases contained in an insulating layer, in the plane-like heater prepared through the process of applying the flame coating of a resistor onto the insulating layer for forming a heating resistance layer. CONSTITUTION:An insulating layer is formed in such a condition that a glass phase-containing layer (a glass layer) and a layer (a crystallized layer) made substantially of a crystalline member only may be laminated together. In such a case as laminating the glass layer and the crystallized layer respectively, it is intended for the glass layer to be positioned inside or it is intended for the crystallized layer to be positioned on each of the two sides of the glass layer because the mutual adhesion of the glass layer and a heating resistance layer comparatively is not good. Furthermore, part or all of glass phases in the glass layer constituting the insulating layer are heat-treated to be crystallized. Thus, a film of structural denseness is formed for making it hard to be cracked while improving the insulating property of the film at the time of having high humidity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a planar heater having a heating resistance layer formed by thermal spraying, and is particularly suitable for heaters for cooking appliances, far-infrared radiation, and the like.

[Prior art] Conventionally, sheet heaters have been made by wrapping a metal heating element around a mica plate and sandwiching it between insulating materials, or by coiling a heating wire between two metal plates or inside a tubular metal body. Alternatively, there are known methods in which a pattern is installed and the pattern is insulated with ceramic powder, and a metal heating resistor is embedded in the ceramic.

For example, in JP-A No. 62-143386, a porous layer mainly composed of glass frit and mica powder is provided on a substrate with an enamel layer on the surface, and a mesh metal foil is formed on top of the porous layer. A surface heater coated with a heater element is disclosed. However, when the heater element 1~ is coated on the substrate via a porous layer containing glass frit, although the porous layer of the sheet heater has good airtightness,
Because it has low thermal conductivity and lacks impact resistance, it is susceptible to thermal shock caused by rapid heating and cooling, making it susceptible to cracks and resulting in a reduction in insulation performance at high temperatures.

[Problem to be Solved by the Invention 1] Also, recently, a heater has been known in which an insulator is thermally sprayed on a metal surface and a heating resistor is thermally sprayed on top of the insulator (Japanese Unexamined Patent Publication No. 62-85280). Public bulletin).

However, in conventional heaters in which a heating resistor is thermally sprayed on a metal surface through an insulating layer, the insulation layer formed on the metal surface is minute and contains racks and voids, resulting in a significant drop in insulation performance at high temperatures. There is a risk that it will happen.

On the other hand, in order to impart solvent resistance to a coating sprayed onto a metal surface, it is known that Rada silicone dissolved in a solvent is applied to the coating and cured (Japanese Patent Laid-Open No. 1983-1999-1).
138064), in a heat roll in which a bonding layer, an insulating layer, and a heating layer are sequentially provided on the surface of a cylindrical body, insulation is A method of impregnating minute gaps between layers with a resin is also known (Japanese Unexamined Patent Publication No. 132974/1983).

However, even if we try to apply the above-mentioned technology of covering the insulating layer with ladder silicone or impregnating the insulating layer with resin to sheet heaters used in cookers, etc., these resins cannot be heated at temperatures above 500°C. It deteriorates and becomes hard, or it sublimates.

As a result, the thermal shock resistance and the insulation properties at high humidity deteriorate, making it impossible to obtain the desired effect.

In order to realize a planar heater that can be used above the medium humidity range of about 500 to 600°C, the inventors of the present invention conducted extensive research to see if it was possible to improve the thermal shock resistance of the insulating layer and the insulation properties at high temperatures. Since the insulating layer in conventional planar heaters is made by laminating only crystal grains of insulating material, it is assumed that the insulating layer is not dense and cannot achieve thermal shock resistance or insulation properties at high humidity. did.

Therefore, the present invention provides a planar heater in which an insulating layer and a heat-generating resistor layer are provided on a metal substrate 1 by thermal spraying, and by improving the insulating layer, the insulating layer is resistant to thermal shock (and has good insulation properties at high humidity). Aim to be excellent.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention provides an insulating layer on a metal substrate by thermal spraying, and a heat-generating resistor layer formed by thermally spraying a resistor on the insulating layer. The heater is characterized in that the insulating layer contains a glass phase.

In the present invention, a layer containing a vitreous phase is a microscopic mixture of vitreous phase particles and particles made of a crystalline material, or a mixture of particles of a vitreous phase and a crystalline phase and particles made of a crystalline material. It is possible that there is a microscopic mixture. In the present invention, such a layered structure is sometimes referred to as a microscopically laminated layer.

Further, in the planar heater of the present invention, the insulating layer may be formed by laminating a layer containing a glass phase (glass layer) and a layer consisting essentially only of crystalline material (crystalline layer). When laminating a glass layer and a crystal layer in this way, the adhesion between the glass layer and the heating resistor layer is relatively poor. It is preferable to Further, in the present invention, a part or all of the glass phase in the glass layer constituting the insulating layer may be crystallized by heat treatment. - This is because the density remains unchanged even if the glass phase is crystallized in a high-temperature atmosphere after obtaining the glass phase. Insulating layers with significantly different densities can be constructed.

Usually, in the present invention, the insulating layer is made of Si, Al, Mg, Z
r.

A composition containing one or more of the oxides of Mn, Tj, and Cr is used, but in particular, a composition containing one or more of the oxides of Mn, Tj, and Cr, and especially the oxides of Si, Al, and Mg.
, Zr, Mn, Ti, and Cr in combination with one or more of the following oxides, since some of them tend to become a glass phase during thermal spraying. Further, as the heating resistor layer, a known heating resistor can be used, but in particular, F
When e-Cr-Al alloy is used, it is convenient to adjust the temperature coefficient of the resistor from positive to negative. In other words, for Fe-Cr-Al alloys, for example, the resistivity and temperature coefficient have the relationship shown in Table 1 depending on the composition, so it is possible to select an arbitrary temperature coefficient by changing the composition. It is.

Further, in the present invention, by providing a bonding layer between the insulating layer and the substrate, the bonding between both layers can be further strengthened.

Stainless steel is preferably used as the substrate material due to its mechanical properties at high temperatures, oxidation resistance, etc. Among these, mardensite stainless steel or ferritic stainless steel is a preferable substrate material because it has a coefficient of thermal expansion α close to that of the insulating layer and the heating resistance layer. For example, these coefficients of thermal expansion have the following relationship.

Resistance layer Fe-Cr-Ala = 11~13X
10-' // Ni-Cr 17
X 16-6 insulating layer MgO-3t02io~], 2
XlO-'// Al□037.5x 10-6
Substrate Alz03-3iO□ 5X 10-
6 stainless steel lOx 10-6 Furthermore, in the present invention, as mentioned above, the insulating layer is
A plurality of layers containing a glass phase and a layer made of a crystalline material may be laminated, and a bonding layer may be interposed between the insulating layer and the substrate, but if both adjacent layers are made of at least one of the same metal, In the case of containing an element, the same oxide or the like is shared in the boundary region of both layers, so it is thought that the bonding property is better.

Furthermore, if a far-infrared generating film such as ZrO□-3i02 paint or MgO□-3, i02 sprayed film is provided on the surface of the heater, it is possible to realize a heater with even better radiation efficiency. .

Note that electrical appliances are normally required to have properties of insulation resistance IMΩ or more and dielectric strength voltage IKV or more, so the present invention also aims to have similar insulation properties. Further, although the planar heater of the present invention is mainly intended for use in a medium temperature range of about 500 to 600°C, it is not necessarily limited to this temperature range.

[Function] In the planar heater of the present invention having the above means, when forming the insulating layer by thermal spraying, the glass phase forming component fills the gaps between the crystal phase particles and spreads, so that a dense film is formed. Guessed. It is thought that this denseness makes it difficult for cracks to occur (and improves insulation properties at high temperatures).

[Examples] Hereinafter, the present invention will be described in more detail based on Examples.

(Example 1) 100 x 100 Xi mm s u as a metal substrate
A bonding layer was formed by plasma spraying Ni-Al onto a S410 plate. Next, insulating materials having various material compositions shown in Table 2 were thermally sprayed to form insulating layers. Note that in Table 2, the insulator raw material powders with a blending ratio of each oxide less than 100 wt% are due to the use of raw materials containing a small amount of impurities. Furthermore, in the three comparative examples, insulating layers were thermally sprayed using only a crystalline material or a material containing only a small amount of a glass phase-forming component as the insulating material powder.

The equipment for spraying insulating material is METCO-INC.

I used the company's 7MG system and the company's 9MB gun. Thermal spraying conditions were: Ar injection amount: 4017 minutes, hydrogen injection amount: 8 minutes.
1/min, applied voltage of 65 to 70 V, and current of 500 A, and the moving device of the thermal spray gun was controlled so that the thickness of the insulating layer was 0.4 mm on average.

Whether or not the obtained insulating layer contained a glass phase was detected by X-ray analysis. In this analysis, if the appearance of sharp peaks characteristic of crystal formation has decreased and a wide range of peaks can be seen, it is considered to contain a vitreous phase. The content of the glass phase was evaluated relative to three levels: strong, medium, and weak.

Figures 1 to 4 show examples of X-ray analysis results. For example, as shown in Figures 1 and 3, a sharp peak value A is observed in the relationship between X-ray intensity and diffraction angle. is the crystalline phase. On the other hand, as shown in FIGS. 2 and 4, the glass phase has a lower sharp peak and a higher base B. FIG. 1 is an X-ray analysis chart of the PC-SP raw material powder, which is mostly crystalline. Figure 2 is an X-ray analysis chart of an insulating layer obtained by thermal spraying the PC8P powder, and a peak unique to crystals is clearly observed, indicating that the crystal phase is the main component and a small amount of glass phase is present. It can be seen that this is about the same level. In contrast, Fig. 3 shows the PC-
This is an X-ray analysis of the M2S powder before thermal spraying, and although it is mostly crystalline, as shown in Figure 4, the insulating layer obtained by thermal spraying the M2S powder is As is clear from the above, the peak characteristic of crystals disappears and the base rises, indicating that the glass phase is the main component.

The vertical axis (X-ray intensity) in Figure 4 is 5 on the vertical axis in Figure 3.
Although the image was enlarged twice, the sharp peaks characteristic of crystals were still not observed.

The insulation properties of each insulation layer were measured at 30° C. and 85% humidity and are shown in Table 1. Note that the measurement of insulation resistance and dielectric strength voltage was performed using Ni-A with an area of 50 x 50 mm inside the insulation layer.
1 alloy was thermally sprayed to a thickness of 30 to 150 μm, and the insulation performance between the layer and the substrate was measured and shown.

As can be seen from Table 2, the examples of the present invention containing a glass phase have significantly improved insulation performance. Further, after heating the above insulating layer in the atmosphere at 900°C for 11 hours,
When X-ray analysis was performed, a sharp peak characteristic of the glass phase appeared, but the insulation properties were at almost the same level in both cases. From this, it is thought that once a dense insulating layer containing a glass phase is formed, the density remains unchanged even if the glass layer is crystallized thereafter.

FIGS. 5 and 6 are photographs of the metal structure for explaining the denseness of the sheet heater of the present invention.

Figure 5 shows the structure of the MgO5i02 sprayed film of this example, where the gray part is almost a vitreous phase, the black part is pores, and the areas where dark gray dots are gathered are crystals, and the whole is dense. It turns out that there is. Figure 6 shows Al of comparative example.
□03-The structure of the sprayed film of MgG is shown. The parts with many dark gray dots are crystals, and the black parts are pores.
It can be seen that there is no precision.

(Example 2) A bonding layer and an insulating layer were formed on a metal substrate by thermal spraying in the same manner as in Example 1, except that the composition and structure of the insulating layer were changed as shown in Table 3, and then the insulating layer was SOX 50 on top of
A heating resistance layer with a thickness of approximately (Llmm) was formed by gas spraying Fe-25Cr-8Al in the range of Sample 3.4 had only an insulating layer.The thickness of the insulating layer of Sample 1.2 was 0.2 mm.
Sample 3.4 was formed by thermal spraying with a target thickness of 0-4 mm. Since film peeling (lifting) of each heating resistor layer mainly occurs at the end of thermal spraying, the peeling situation of each heating resistor layer immediately after thermal spraying was visually observed and shown in Table 3. Also,
After repeating the process of raising the temperature from room temperature to 550° C. in 3 minutes and cooling it 100 times, the insulation resistance and dielectric strength voltage of the insulating layer were measured. The results are also shown in Table 3.

According to Table 3, it is clear that by providing an insulating layer containing only crystals on an insulating layer containing a glass phase, the adhesion performance between the insulating layer and the heating resistance layer is improved. It is thought that because the insulating layer containing a phase, the insulating layer consisting only of crystals, and the heat-generating resistance layer all contain at least one metal element, the bonding performance at the boundary between them could be improved. In addition, the insulation properties of each insulation layer were sufficiently desirable for a planar heater.

(Example 3) Using a metal substrate on which a bonding layer was thermally sprayed in the same manner as in Example 1, the insulating layers shown in Samples 5 to 8 in Table 4 were thermally sprayed on the metal substrate under the same conditions as in Example 1. It was formed by Sample 5.6 had a crystalline material layer sandwiched between two insulating layers containing a glass phase, and was thermally sprayed with a target thickness of approximately 0.15 mm for each layer. Sample 7.8 had a layer containing a glass phase on top of the crystalline material layer, and was thermally sprayed to a thickness of 0.2 mm for each layer. Obtained sample 5
The insulation resistance and dielectric strength voltage of the insulating layers No. 8 to 8 were measured and shown in Table 4. From Table 4, it can be seen that the insulating properties of each insulating layer are good and are suitable for a planar heater.

In addition, in order to improve the bond between the insulating layer containing the glass phase and the heat generating resistor layer, the first layer may be a layer containing the glass phase and the second layer may be a crystal layer, or the layer containing the glass phase may be combined with the heat generating resistor layer. A layer containing only crystals may be sandwiched between the two layers.

(Example 4) A substrate made of martenzite stainless steel SUS 403 or ferritic stainless steel SUS 430 was coated with an insulating film having a thickness of about 0.4 mm as shown in Table 5 by the same method as in Example 1. A heating resistor layer having a thickness of about 0.1 mm as shown in Table 5 was formed thereon by thermal spraying to prepare a planar heater.

In Table 5, Al2O35I02 represents Al20377%, 5
L0222%, Al□03-310□ powder and Cl7
The ratio of 203 powder is 7:3, the Nj-Cr composition is bal Ni
-20Cr, Fe-Cr-Al composition is balFe-2
5Cr-8Al, the ratio of Fe-Cr-Al and Ni-Cr is 1:1.

Each sheet heater shown in Table 5 can be used from room temperature to 500℃.
The process of raising the temperature for minutes and allowing it to cool was repeated 1000 times, but no change was observed in the heating state in any case, and the sample had sufficient thermal shock resistance.

This is because the thermal expansion coefficient of martenzite or ferritic stainless steel, which is the substrate material, is 1. Ox to-6
This is probably due to the fact that the MgO-3jO□ alloy forming the insulating layer has a thermal expansion coefficient of 0.8 to I-2Xl0-6, and the thermal expansion coefficients of both are close to each other.

Therefore, the planar heaters of Samples 9 to 14 can be used even at 1000°C.

In addition, Fe-0r-Al alloy is used for the heating resistance layer, and Al203-3iO:+ is used for the insulating layer, so
Both types contain the same metal element, which may be advantageous for bonding.

(Example 5) A commercially available far-infrared emitting paint (CRC600 manufactured by Nippan Research Institute Co., Ltd.) was applied to a thickness of 30 μm on the opposite side of the substrate of the planar heater obtained in Samples 1 and 2 of Example 2. did. When the planar heater thus prepared was heated to 500°C and the radiation efficiency at a wavelength of 3 μm μm was measured using a spectral emissivity measuring device, a value of 0.8 or more was obtained. In addition, it was 0.3 in the case where no coating was applied.

[Effects of the Invention] In the sheet heater of the present invention, the insulating layer includes a dense glass phase, so the insulating properties are improved, and the bondability with the heating resistance layer and the substrate is also improved, making it difficult to peel off. It is also resistant to thermal shock caused by rapid heating and cooling. In addition, by selecting the substrate material, insulating material, and heat generating resistor material, we can make the thermal expansion coefficients close to each other, and by making them contain the same metal element, we can improve the bonding property, and the thermal shock caused by rapid heating and cooling can be improved. performance can be further improved.

As a result of the above, it is possible to obtain a planar heater that is excellent in instant heating properties and easy to assemble, such as a heater for a cooking machine, a far-infrared radiation heater, a heater for a heating furnace, a heat retention heater, and a heating heater for thermal fixing and thermal transfer.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams showing the X-ray analysis results of the raw material powder before thermal spraying and the insulating layer created using it, respectively, and Figures 5.6 are photographs of the metallographic structure of the insulating layer of the present example and comparative example, respectively. It is.

Claims (10)

[Claims] (1) A planar heater in which an insulating layer is provided on a metal substrate by thermal spraying and a resistor is thermally sprayed on the insulating layer to form a heating resistance layer, in which the insulating layer contains a glass phase. shaped heater. (2) In a planar heater in which an insulating layer is provided on a metal substrate by thermal spraying and a resistor is thermally sprayed on the insulating layer to form a heating resistance layer, the insulating layer is made of a layer containing a glass layer and a crystal material. A planar heater characterized by microscopically laminated layers. (3) In a planar heater in which an insulating layer is provided on a metal substrate by thermal spraying and a resistor is thermally sprayed on the insulating layer to form a heating resistance layer, the insulating layer consists of only a layer containing a glass phase and a crystalline material. A planar heater characterized by being laminated with two layers. (4) The insulating layer is made of Si oxide, Al, Mg, Zr,
4. The planar heater according to claim 1, further comprising at least one of Mn, Ti, and Cr oxides. (5) The insulating layer is characterized in that a plurality of layers containing a glass phase and a layer made of a crystalline material are laminated, and both adjacent layers contain at least one same metal element.
The planar heater described in . (6) In a planar heater in which an insulating layer is provided on a metal substrate by thermal spraying and a resistor is thermally sprayed on the insulating layer to form a heating resistance layer, part or all of the glass phase constituting the insulating layer is heat-treated. 6. The planar heater according to claim 1, wherein the sheet heater is crystallized. (7) The planar heater according to any one of claims 1 to 6, further comprising a bonding layer provided between the metal substrate and the insulating layer. (8) The planar heater according to any one of claims 1 to 7, wherein the heating resistance layer is made of a Fe-Cr-Al alloy. (9) The metal substrate is made of martensitic or ferritic stainless steel, and the thermal expansion coefficient of the insulating layer is 0.8 to 1.
．． 9. The planar heater according to claim 1, wherein the area is 2×10^-^6. (10) The planar heater according to any one of claims 1 to 9, characterized in that a far-infrared ray generating film is provided on the surface of the heater.