JPS61230286A - Heat generating body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heating element in which a heating element is integrally embedded in an electrically insulating hollow layer, and relates to a heater.

Used in cooking equipment, drying equipment, etc.

BACKGROUND OF THE INVENTION Recently, a heating element has been proposed in which a hollow layer is formed on a metal substrate, and a heating element is further coated and adhered to the hollow surface of the hollow layer, so-called a heating element sandwiched between the hollow layers. There is. The configuration of this heating element is shown in FIG. 16. 1 is a metal substrate for hollow holes, and has hollow layers 2 and 3 on both sides thereof. 6 is a heating element, 6a is a terminal, 4
is a hollow layer covering the heating element.

This heating element has a hollow layer with excellent heat resistance and excellent electrical insulation properties, so it is suitable for use in medium to high temperature ranges of about 10 to 300 degrees Celsius, and is also thin and can be expected to have a long life. Has characteristics.

Problems to be Solved by the Invention However, when a heating element having the above-mentioned configuration is formed and the heating element 5 is energized to raise the surface temperature of the hollow to about 360°C, the hollow layer 4 is peeled off and the hollow surface is damaged. It was found that cracks were formed.

This is because the metal substrate 1 is easily deformed due to the non-uniform distribution of surface temperature of the hollow metal when energized, and the hollow metal cannot withstand such deformation. As a solution to this problem, it is possible to prevent the metal substrate 1 from deforming due to heat by pressing the metal substrate 1 in steps or increasing the thickness of the metal substrate 1.

When a heating element is formed using this method, the temperature is 350'C to 400°C.
Although it is possible to improve the heat resistance at
There was no durability in a thermal shock test in which water droplets were dropped at 00°C. This is due to the hollow layer 2 as shown in FIG.
This is because 4 has a three-layer structure, so the film thickness is thick and delamination is likely to occur. One way to counter this is to reduce the thickness of the hollow layer on which the water droplets are dripped, but if only one side is made thinner, it will cause more wrinkles after firing.
Moreover, peeling occurred.

Means for Solving the Problems As described above, the heating element having the structure shown in FIG. 16 is prone to cracking after firing and to peeling when energized. This occurs because the metal substrate 1 deforms when heated. Therefore, in the present invention, the metal substrate 1 is made to protrude on the side opposite to the side where the heating element is buried.

Function: By forming the heating element in the above-described shape, the bulge toward the heating element side that occurs during normal energization can be reduced by making the metal substrate 1 protrude toward the opposite side. It acts to cancel out the heat generation, making it possible to prevent warping of the heating element and peeling of the hollow layer.

Example (1) Stamping and pretreatment of metal substrate The metal substrate 1 shown in FIG. 1 includes aluminum, aluminum die-cast, cast iron,
Aluminized steel, low carbon steel, hollow steel plate, or stainless steel plate is used.

After this metal substrate 1 is made to protrude by pressing one side, bending, etc., it is subjected to pretreatments such as degreasing, cleaning, pickling, cleaning, and nickel treatment. Hollow processing 2 on metal substrate 1
When performing step 4, baking is performed at 800°C to 850°C, so
The metal expands, making it more likely to warp or distort. Further, the heating element in which the heating element 6 is embedded in the hollow layer 4 has the heating element 6 buried in the hollow layer 4.
When electricity is applied to the metal, the polymetal at high temperature expands and becomes easily distorted.
If you repeat this process, the hollow layer 4 will also peel off.
It becomes easier to push. From this, it is also necessary to match the thermal expansion coefficients of the hollow layers 2 to 4 and the metal substrate 1,
It is also necessary to perform step stamping or bending on the metal substrate 1 so that it protrudes to one side so that deformation does not occur as much as possible even in a hot atmosphere.

(2) Heating element The heating element 6 is basically a thin strip-like element as shown in FIG. 16, and its thickness is suitably 10 to 200 μm, preferably in the range of 30 to 100 μm.

Note that 6 is a terminal.

Various electric heating materials can be used as the material for the heating element 6, but one must have appropriate values for specific resistance and coefficient of thermal expansion, as well as excellent adhesion to the hollow layer 4 and workability. things are selected. From these points of view, ferritic stainless steel is most preferred.

(3) Hollow layer The electrical properties (insulation resistance and dielectric strength) of the glass thrift used in the hollow layers 2 and 3.4 shown in FIG. 1 are important. In addition to the film thicknesses of the hollow layers 2 to 4, important factors that determine electrical properties, such as insulation resistance, include the volume resistivity of the glass. The thickness of the hollow layer is determined from the viewpoint of the adhesion of the hollow, and is at most 100~S.
From this point of view, in order to improve the electrical characteristics of the hollow layers 2 to 4, it is necessary to form the hollow layers 2 to 4 with glass frit having excellent volume resistivity.

The volume resistivity of glass frit is 1 in the frit composition.
It is determined by the amount of the alkali component (Li20.Na2o, Ni20), and the smaller the amount of the alkali component, the higher the volume resistivity becomes. For this reason, in this example, a glass frit containing a small amount of monovalent alkali components was used. The composition is shown in Table 1.0 Table 1 (4) Manufacturing method of heating element 6 The metal substrate 1 was made of a steel plate for hollow holes. This steel plate for hollow holes was pretreated to a size of 300 x 300 mm, and the shape of the base material was made to protrude from the side opposite to the side where the heating element 5 was buried as shown in FIG. 1B.

The first hollow layer 2 uses the insulating frit shown in Table 1, and the second
．． For the third hollow layers 3 and 4, the milky white slits shown in Table 1 were used. The mill compositions of these hollow layers 2 to 4 were prepared as shown in Table 2, and milled in a ball mill for 2 hours to obtain hollow slips.

150 μm of the slip resistance shown in Table 2 on both sides of the metal substrate 1.
Coat and bake, and then apply the slip (3) in Table 2 on top.
) was applied to a thickness of 160 μm and fired. Furthermore, after applying a thin layer of slip (4) in Table 2 on this hollow substrate,
The heating element 6 was installed while the surface was still wet, and slip ←) was further applied thereon and fired. At this time, the cover coat slip (4) was not applied to the surface on which the heating element 6 was not set. The configuration diagram at this time is shown in the first part.

In this way, the thickness of the hollow layer on the side where the heating element 6 is not buried is made thinner to form the heating element.

The conventional heating element shown in Fig. 16 has approximately the same film thickness on both sides,
It is 400 to 450 μm. After firing, this heating element has a warp so that the center part bulges toward the heating element 5 side, and when electricity is applied to raise the temperature of the hollow surface to 400'l:, peeling and cracks occur on the protrusions and hollow surface. occurred. Peeling and cracking occur because the substrate is not easily deformed by heat and also because the hollow layer is thick. Reducing the thickness of the hollow layer has the advantage of improving heat resistance, thermal shock resistance, and mechanical shock resistance. Although reducing the thickness of the hollow layer in this way has many advantages, reducing the thickness of the hollow layer 4 in which the heating element 6 is buried causes a problem in that the electrical insulation deteriorates. From this, the thickness of the hollow layer on the side of the heating element S is set to about 400 to 450 μm as before, and the thickness of the hollow layer on the opposite side is made thinner to form the heating element. It is also considered to have excellent heat resistance. However, the structure described above using the metal substrate 1 shown in FIG.
After firing, warps that bulge toward the heating element 6 are likely to occur, so by using a downwardly convex metal substrate 1 as shown in FIG. 1, it is possible to reduce warps after firing. it is conceivable that.

Based on these ideas, we conducted experiments such as specific examples.

(Specific Example 1) As shown in FIG. 2B and FIGS. 3 to 6, a metal substrate 1
The heat resistance was investigated when the metal substrate 1 was processed downward into a trapezoidal or convex shape and the hollow layer was formed into a three-layer structure on both sides of the metal substrate 1. This standard resistance evaluation method is to energize the heating element 6 so that the temperature of the hollow surface on the side where the heating element 5 is not buried becomes 4cc℃, hold it for 16 minutes, and then bury the heating element 6. A schematic diagram of this is shown in Figure 14, which was performed by dropping 5 cc of water onto the untreated hollow surface.

This was regarded as one cycle and was repeated until the hollow surface peeled off or cracked. When dropping water from the second time onwards, do so after the surface temperature reaches 400°C. The results are shown in Table 3. 0 Nαα of Table 3 On Figure 2, the shape of the metal substrate 1 is processed as shown in Figure 2 (B), and a first hollow layer 2 is formed on the inner surface of the metal substrate 1. , second hollow layer 3,
It is coated with a cover coat layer 4. An enlarged cross-sectional view of the structure at that time is shown in the equation of FIG. Note that N(L) in Table 3
It is assumed that FIGS. 3 to 5 also have the same hollow layer structure as in FIG. 1.

For F = 2tran in Figure 2B shown in Table 3,
When electricity was applied to the heating element 5 and the surface temperature reached 400° C., cracks occurred.

The one in Figure 3 with F = 5 m has a surface temperature of 4 when energized.
Although no abnormality was observed even when the temperature was increased to cc°C, peeling occurred after one cycle of a water drop test.

In the case of F=2 and H=s in FIG. 4, peeling occurred after three cycles of the water drop test.

In the case of F=5 and H=5 in FIG. 5, peeling occurred after 4 cycles of the water drop test.

As described above, when a metal substrate was pressed into a trapezoidal or convex shape to form a three-layer heating element, it was possible to obtain a heating element with better heat resistance than the conventional one.

The conventional one had a large amount of warpage after firing, but as shown in Figure 2~
There were very few items in Figure 5. This is metal substrate 1
This is because by making the shape into a trapezoidal or convex protruding shape, it was possible to prevent warping toward the heating element 5 side when electricity is applied, and this shape is considered to be resistant to thermal deformation.

However, none of the shapes showed excellent durability in the water drop thermal shock test. Therefore, next, a test similar to that in (Specific Example 1) was conducted by reducing the film thickness of the hollow layer on the side where the heating element 5 was not buried. (Specific Example 2) Shape of the metal substrate 1 The one shown in Fig. 5 is used, and the heating element S
The hollow layer on the side has a three-layer structure or a two-layer structure, and the heating element 6 is embedded, so that the first side has a two-layer structure or a one-layer structure. The configuration is shown in FIG. 6, and the results are shown in Table 4.

GA is the thickness of the hollow layer on the side where the heating element 6 is buried;
GB is the film thickness of the four layers on the side where the heating element 5 is not buried.

The above table supplements the embodiments of claims 1) to (4).

1IJQ, 4 in Table 4 is shown in FIG. 6 and has the same thickness of the hollow layer on the heating element 5 side and on the side where the heating element 6 is not buried. In this heating element, peeling occurred in the hollow layer after 4 cycles of the water drop test.

A cross-sectional view of the structure of Table 4 Nα5 is shown in FIG. Heat generating element 5
The side structure is based on the slip composition in Table 2, the first hollow layer 2 is 150 μm thick, the second hollow layer 3 is 150 μm thick,
The cover coat layer 4 has a thickness of 150 μm. Further, in the configuration on the side where the heating element 6 is not buried, the first hollow layer 2 has a thickness of 150 μm.

The second hollow layer 3 is 150μm and the GB/GA ratio is %
It is. When this heating element was energized to a surface temperature of 400° C., no abnormality was observed, but when a water drop test was performed, peeling occurred after 6 cycles.

The structure of K4 table NIIL6 is shown in FIG. The configuration on the heating element S side is the same as that of N015. In the configuration on the side where the heating element 5 is not embedded, the first hollow layer 2 has a thickness of 1 ω μm, and the GBZGA ratio is small. This heating element developed cracks after 8 cycles of the water drop test.

The configuration of Table 4 N (L7 is shown in FIG. 8. The configuration on the heating element side is the same as Nα5. In the configuration on the side where the heating element is not embedded, the first hollow layer 2 is 90 μm thick, GBZ
GA ratio is shoes. This heating element showed no abnormality even after 10 cycles of the water drop test. The configuration of Table 4 Nα8 is shown in FIG. The configuration on the heating element side is that the first hollow layer 2 has a thickness of 300 μm, and the cover coat layer 3 has a thickness of 300 μm.
In the configuration on the side where the heating element 6 is not embedded, the first hollow layer 2 has a thickness of 150 μm, and the thickness of the first hollow layer 2 is 30 μm.
/GA ratio is %0 This heating element cracked after 8 cycles of the water drop test.0 Table 4 shows Nα9. Nα10 in Figures 10 and 11, respectively.
As shown in the figure, the configuration of N(L9, N1100 heating element 6 side is the same as N[L8. No, s + No, 1
The configuration on the side where the heating element 5 of o is not embedded is the first note. - The layer 3 has a thickness of 150 μm, the first hollow layer 2 has a thickness of 90 μm, and the GB/GA ratio is approximately 150 μm. No abnormality was observed in these heating elements even after 10 cycles of a water drop test.

If the G2/G1 ratio is less than pure, that is, the thickness of the hollow layer on the side where the heating element 5 is not buried is less than 80 μm, the metal substrate 1 will not be exposed and rust will easily occur, so it cannot be used as a heating element. It is unsuitable for use.

From Table 4, although the GB film thickness of the heating element No. 5 is the same as that of Nα8, the reason for its poor heat resistance is that it is composed of two layers of glass with different expansion coefficients. Reeds and delamination are likely to occur.

From the above, the heat resistance is improved by setting the ratio GB/GA of the film thickness on the side of the heating element 5 to that on the side where the heating element 6 is not embedded to %. Furthermore, it has been found that heat resistance is further improved when there is only one hollow layer on the side where the heating element 6 is not embedded.

Nl111 in Table 4 is shown in FIG. The first hollow layer 2 on the heating element 6 side has a thickness of 460 μm, and the first hollow layer 2 on the opposite side has a thickness of 90 μm.

Further, the magnet 12 is shown in FIG. The structure on the side of the heating element 5 is that the hollow layer 3 has a thickness of 450 μm, and the hollow layer 3 on the opposite side has a thickness of 450 μm.
is 90 μm. The dielectric strength of these heating elements was o, e KV, o, s KV, respectively, and showed extremely poor values. In Nα11, since the expansion coefficients of the heating element 5 and the hollow layer 2 do not match, the heating element 6 cannot be covered with the hollow layer 2, and most of the heating element 5 is exposed. It seems that the dielectric strength has deteriorated. Further, since the expansion coefficients of the heating element 5 and the hollow layer 3 of NO,12 match, the matching with the heating element 6 is extremely excellent. However, since the hollow layer 3 is made of glass with a low volume resistivity, it is difficult to form a heating element with excellent insulation using only this glass.

Generally speaking, the higher the electrical insulation properties of glass, the more
Since the coefficient of expansion tends to be low, it is difficult to form a heating element with excellent electrical insulation and excellent compatibility with the heating element 6 using only one hollow layer.

From the above, at least the hollow layer on the side where the heating element 6 is embedded needs to have a two-layer structure or more.Advantages of the Invention According to the structure of the heating element of the present invention, heat resistance can be greatly improved. It is also possible to form a heating element with excellent dimensional accuracy and less warpage and deformation. The present invention can also be applied to open microwave ovens, open toasters, etc. as heating elements for cookers.

[Brief explanation of the drawing]

The first part is a cross-sectional view showing the configuration of the heating element according to an embodiment of the present invention, and the shape of the attached substrate. Figures 6 to 13 are cross-sectional views showing the configuration of the heating element. Figure 14 is a cross-sectional view showing the configuration of the heating element. FIG. 16 is a schematic diagram, and FIG. 16 is a plan view showing a pattern of a heating element. FIG. 16 (C) is a sectional view showing the structure of a conventional heating element. 1... Metal substrate, 2... Hollow layer, 3
- Old: hollow layer, 4: cover coat (hollow layer), 5: heating element, 5a: terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person3-
11 1 Ro 1 4-1-Horo Layer 5-11 Brother Moshuzi Ting 111 skin 1 child @m's48 Figure 2 Figure 6 Figure 10 Figure 14! (MMM V Figure 16

Claims (4)

[Claims] (1) A heating element in which a heating element is provided by covering one surface of a metal substrate with a hollow layer, and the metal substrate is made to protrude on the side opposite to the side on which the heating element is embedded. (2) Hollow layers are formed on both sides of the metal substrate, and the thickness of the first hollow layer on the side where the heating element is embedded is (G_A), and the thickness of the second hollow layer formed on the opposite side. The heating element according to claim 1, wherein (G_B) is thinner than (G_A). (3) Film thickness ratio (G_B)/(G_A) is 1/5 to 2/
3. The heating element according to claim 2, set forth in claim 3. (4) The heating element according to claim 1 or 2, wherein the first hollow layer has a two-layer structure or more.