JPH02236986A - heating element - Google Patents

Abstract

PURPOSE:To form a porous coating layer of large specific surface area on the surface of a tubular armour by providing a large specific surface area porous coating layer formed by partial sintering or by reaction of a large specific surface area powder particle. CONSTITUTION:By partial sintering or by reaction at a number of contacts on a large specific surface area powder particle, without using a bonding agent that is used for the formation of a film, on the surface of a tubular armour of a heating element, a large specific surface area porous coating layer is solidly bonded and formed. Of the infrared rays radiated from the coating layer, far infrared radiation ratio compared to near infrared radiation can be improved. The specific surface area of the large specific surface area porous coating layer is defined as not less than 10m<2>/g. Thickness of the large specific surface area porous coating layer is formed inhomogenously. For the inhomogeneity in the thickness of the coating layer, difference between the maximum value and the minimum value of the film thickness of the large specific surface area porous coating layer is defined as not less than 25mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heating element used for heating, hot water supply, drying, etc.

Conventional technology Conventional heating elements with a tubular exterior body are made by coiling a metal wire such as nichrome wire or Kanthal wire into a metal tube using an insulating material, or a quartz tube, glass tube, ceramic tube, etc. Built-in and configured. In order to improve the far-infrared radiation effect of these heating elements, conventionally a coating layer of a far-infrared radiation material has been formed on the surface of the tubular exterior body by a thermal spraying method, a coating film forming method, or a sol-gel method.

Problems to be Solved by the Invention The conventional heating element having a far-infrared radiation coating layer has the following problems.

Although the coating layer formed by the thermal spraying method is porous, the coating layer is formed by surface bonding by melting and mixing of molten particles, and the specific surface area is small.

The coating layer formed by the coating film forming method is made of a pigment and a binder, and since the voids between the pigments are filled with the binder to form the coating layer, it is not porous and has a very small specific surface area.

As described above, the conventional coating layer has a small surface area, and of the infrared rays emitted from the coating layer, only a low amount of far infrared rays can be obtained.

The coating layer formed by the sol-gel method is very thin.
The coating layer could only be formed in a size of about μm or less, and the far-infrared emissivity was even lower.

The present invention has been made in order to solve the problems of the prior art described above, and provides a heating element having a tubular exterior body having a porous coating layer with a large specific surface area formed on its surface. be.

Means for Solving the Problems The heating element of the present invention is characterized in that the surface of the tubular exterior body is provided with a high specific surface area porous coating layer formed by partial sintering or reaction of high specific surface area powder particles. shall be.

Among the infrared rays used for active heating, near-infrared rays have short wavelengths and high energy, so they penetrate deeply into the human skin and stimulate the pain points. For this reason, the human body feels warmth quickly, but feels pain when exposed to radiation for a long time. On the other hand,... Far-infrared rays have long wavelengths and do not penetrate deeply into the skin, so you do not feel warmth immediately, but even if you are exposed to far-infrared rays for a long time, you will still feel a pleasant warmth, so it is a desirable heating quality.

In the present invention, by partially sintering or reacting high specific surface area powder and granules at multiple contact points, a high specific surface area porous material can be formed on the surface of the tubular exterior body of the heating element without using a binder used in the coating film forming method. By strongly bonding and forming the coating layer, it is possible to improve the ratio of the amount of far infrared rays to the amount of near infrared rays among the infrared rays emitted from the coating layer.

The most porous coating layer formed by conventional thermal spraying is porous from a macroscopic perspective, but from a microscopic perspective, it is a collection of molten particles, so the surface is smooth and has a porous structure. do not. In contrast, the high specific surface area porous coating layer of the present invention has a large number of fine pore structures even when viewed microscopically, and has a very wide convective heat dissipation surface, so the surface temperature is reduced. It is possible to improve the ratio of the amount of far infrared rays radiated compared to the amount of near infrared rays radiated. From this,
The present invention provides a coating with higher infrared radiation ability than conventional coating layers.

The specific surface area of the high specific surface area porous coating layer of the present invention is 10 m
'/g or more is desirable. This is because as the specific surface area of the porous coating layer increases, the ratio of the amount of far infrared rays emitted compared to the amount of near infrared rays emitted increases, but the best far infrared radiation is achieved when the specific surface area is 10 m"/g or more. This is because the infrared radiation ratio can be obtained.

Further, it is desirable to form the high specific surface area porous coating of the present invention with a non-uniform thickness. This is because the unevenness of the coating layer's thickness increases, causing turbulence in the convective air near the coating layer and smoother convective heat dissipation. This is because it is possible to lower the temperature and further increase the far-infrared radiation amount ratio. Desirable non-uniformity of the coating layer thickness is such that the difference between the maximum and minimum thickness of the high specific surface area porous coating layer is 25%.
It is more than μm. This means that the ratio of far infrared radiation to two is 2
This is because it increases up to 5 μm and remains almost constant above 5 μm, resulting in the best far-infrared radiation amount ratio.

The heating element having a tubular exterior body of the present invention is a metal tube using a coiled metal wire such as nichrome wire or Kanthal wire together with an insulating material, or a quartz tube, a glass tube,
Ceramic tubes, such as cordierite tubes, mullite tubes,
It is built into an alumina tube and a zirconia tube.

The high specific surface area coating layer is preferably formed using alumina hydroxide or alumina (V). It is desirable to add barium.

Further, the far-infrared radiation efficiency can be further increased by adding a metal oxide selected from the group of nickel oxide, iron oxide, cobalt oxide, titania, zirconia, magnesia, and chromium oxide to the high specific surface area coating layer.

Furthermore, by containing a catalyst material such as a platinum group metal in the coating layer, it is possible to obtain a heating element that has a far-infrared radiation function and a function of removing harmful gases and odors.

Example Examples of the present invention will be described below.

<Example 1> A quartz tube with an outer diameter of 10 mm, an inner diameter of 9 mm, and a length of 15 cm was obtained by roughening the outer peripheral surface of the inner quartz tube with a blasting device, leaving 25 mm on both sides.

On the other hand, hydroxide alumina 100 with a specific surface area of 210 m2/g
Slurry A was prepared by sufficiently mixing 0 g of the slurry and 1200 g of water using a ball mill.

This slurry A was applied to the roughened portion of the quartz tube by spraying, dried at 100°C for 2 hours, and then heated to 550°C.
The tube was fired for 1 hour to cause a decomposition reaction of alumina hydroxide, thereby preparing a quartz tube having an alumina coating layer. The amount of coating layer is 0.
It is 2g. A heating element of this example (Example A) was prepared by incorporating a 40Ω coiled nichrome wire in this quartz tube and insulating and holding it on both sides of the quartz tube with an insulator.

Similarly, in place of alumina hydroxide in slurry A, the same amount of activated alumina with a specific surface area of 170 m''/g was used to prepare slurry I.
J-B was prepared and applied to the roughened portion of the quartz tube by spraying, dried at 100°C for 2 hours, and then heated at 850°C.
A quartz tube having an alumina coating layer in which the alumina was partially sintered by firing for 1 hour was prepared. The amount of coating layer is 0.2g. A heating element of this example (Example B) was produced in the same manner as Example A using this quartz tube.

For comparison, heating elements A-C were prepared with similar coating layers formed by thermal spraying, coating film formation, and sol-gel methods. Thermal spraying method: A heating element of Comparative Example A was formed in which a 0.2 g coating layer was formed on the surface of a quartz tube in the same manner as in Example A by thermal spraying alumina.

Coating film formation method: Activated alumina 1 with a specific surface area of 170 me/g
Slurry 1 was prepared by thoroughly mixing 100 g of sodium silicate and 1000 g of water using a ball mill.

After applying this to the quartz tube, it was dried at 200° C. for 2 hours to obtain a quartz tube having an alumina coating of 0.2 g, and a heating element of Comparative Example B was prepared in the same manner as in Example A.

Sol-gel method: Using aluminum triethoxide, a 2 mg alumina coating layer was formed by drying and firing to create a heating element of Comparative Example C having the same structure as Example A. In addition, by this method, the coating layer exceeding 2 mg was peeled off.

A power of 500 W was applied to the heating elements of Examples A and B and Comparative Examples A to C prepared above, and the wavelength at that time was 1.
The infrared radiation intensity distribution of 4 to 14 μm is measured, and the amount of far infrared rays (wavelength 3
~14μm) ratio (far-infrared radiation ratio: far-infrared amount/
The amount of near-infrared rays) was calculated. The results are shown in Table 1.

As is clear from Table 1, Example A of the present invention has the highest far-infrared radiation amount ratio compared to the near-infrared radiation amount compared to the conventional comparative example, and has a high and desirable far-infrared radiation ability.

The specific surface areas of the coating layers of Examples A and B and Comparative Examples A to C were 158 and 100.2.3*1, respectively.
．． (L 2. On years old/g.

Table 1 Example 2> By variously changing the firing conditions at 550°C during the preparation process of Example A, the specific surface area of the high specific surface area porous coating layer to be formed was variously changed, and the far-infrared rays at that time were The radiation ratio was measured. The results are shown in Figure 1.

As is clear from Figure 1, as the specific surface area of the porous coating layer increases, the far-infrared radiation ratio increases, but the best amount of far-infrared radiation is obtained when the specific surface area is 10 m"/g or more. The ratio is obtained.

Therefore, the specific surface area of the high specific surface area porous coating layer of the present invention is:
It is desirable that it is 10 m''/g or more.

Example 3 Using the same quartz tube as in Example 1 and slurry A in Example 1, high specific surface area porous coating layers with various coating thickness variations were formed by spraying and roll coating. A heating element having the same configuration as that of Example A was prepared.

The weight of each coating layer was 0.2 g.

Next, in the same manner as in Example 1, 5
A power of 00 W was applied, the infrared radiation intensity distribution at that time was measured, and the ratio of far infrared radiation to the amount of near infrared rays was calculated. Incidentally, the variation in the coating film thickness was measured as the difference between the maximum value and the minimum value of the film thickness of the coating layer (film thickness variation). The results are shown in Figure 2.

As is clear from Fig. 2, by forming the high specific surface area porous coating layer with a non-uniform thickness, the ratio of far-infrared radiation increases, and the film thickness variation increases up to 25 μm.
Above that, it becomes almost constant, and above 25 μm, the best far-infrared radiation and radiation amount ratio can be obtained. Therefore, the desirable non-uniformity of the coating layer thickness is such that the difference between the maximum and minimum thickness of the high specific surface area porous coating, that is, the thickness variation, is 25 μm or more.

<Example 4> Instead of the quartz tube of the tubular exterior tube used in Example A, iron tubes, stainless steel tubes, Vycor glass tubes, cordierite tubes, mullite tubes, alumina tubes, and zirconia tubes were each subjected to blasting treatment to improve their surfaces. A heating element having the same structure as in Example A was prepared by using the crude material.

Next, by energizing these heating elements at room temperature, 5
A heating/cooling cycle was carried out in which the temperature of the high specific surface area porous coating layer was brought to 800°C in 10 minutes, then the electricity was turned off and the temperature was rapidly cooled to room temperature using a blower 1000 times. After this, a coating layer adhesion test was conducted in which each heating element was placed in a vibrator that vibrated 500 times per minute, and the percent weight loss of the coating layer at that time was measured. The calculation method for weight loss percentage is: weight loss percentage (%) = weight loss ff
It was calculated as t/cover layer weight x 100. The results are shown in Table 2.

As is clear from Table 2, when a quartz tube is used, it is preferable that the weight loss rate is the smallest.

Table 2 (Example 5) Using slurry A using a quartz tube without roughening treatment,
A heating element C similar to heating element A was produced.

Regarding this heating element C, a coating layer adhesion test similar to that performed in Example 4 was conducted. The results are shown in Table 3.

As is clear from Table 3, surface roughening treatment is desirable because it can improve the adhesion of the coating layer.

Effects of the Invention As described above, the present invention provides a heating element having a tubular exterior body with a porous coating layer having a large specific surface area formed on its surface, thereby producing a heating element having a coating layer with high far-infrared radiation ability. can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the specific surface area of the high specific surface area porous coating layer of the heating element in the example of the present invention and the far infrared radiation amount ratio, and FIG. It is a figure which shows the relationship between the surface roughness of a specific surface area porous coating layer, and far-infrared radiation amount ratio. Name of agent: Patent attorney Shigetaka Awano One idiot front #(zuV)

Claims (6)

[Claims] (1) A heating element characterized by comprising a high specific surface area porous coating layer formed on the surface of a tubular exterior body by partial sintering or reaction of high specific surface area powder particles. (2) The specific surface area of the high specific surface area porous coating layer is 10 m^
2/g or more. (3) The heating element according to claim 1 or 2, wherein the high specific surface area porous coating layer has a non-uniform thickness. (4) The heating element according to claim 1, 2 or 3, wherein the difference between the maximum and minimum thickness of the high specific surface area porous coating layer is 25 μm or more. (5) The heating element according to claim 1, 2, 3 or 4, wherein the tubular exterior body is a quartz tube. (6) Claims 1 and 2 wherein the surface of the tubular exterior body is roughened.
, 3, 4 or 5.