JPS62113377A - Far-infrared heater - 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 Application of the Invention) The present invention relates to a heater that emits long-wavelength infrared rays of 3 to 150 microns by generating heat, and particularly relates to a ceramic heater that has excellent far-infrared radiation efficiency.

(Background of the invention) When heating and drying organic materials such as paints, foods, and fibers,
Hot air, water vapor, infrared rays, etc. are used as heat sources.

Among these, those that use infrared rays do not allow impurities in the environment such as dust and unburned substances to directly mix or come into contact with the heated object, and infrared rays propagate through the air like electromagnetic waves, Because it generates heat by causing molecules to resonate and vibrate, it is not directly affected by conditions such as the temperature and flow rate of the air passing through it, and therefore has the advantage that it can be used outdoors.

Additionally, as shown in Figures 8a, 8b, and 8C,
Since infrared rays can be reflected by metal plates, etc., it is possible to focus the infrared rays with a reflector and efficiently heat the object. In Figure 8a, infrared rays from heat source 1 are reflected by circular reflector 2. Fig. 8b shows a standard parallel reflector that focuses the infrared rays from the heat source 1 on an elliptical reflector 2, and Fig. 8c shows a flat reflector in which the infrared rays from the heat source 1 are reflected. It shows a flat reflector that is focused by plate 2.Furthermore, the use of electricity as the source of infrared rays has the advantage that the structure and control of the device are simpler than those of other systems. ing.

Particularly in recent years, a heater (far-infrared heater D) has been developed that emits infrared rays in the wavelength range of 5.6 to 20 μm, which is easily absorbed by organic materials, as shown in Figure 9.
Compared to a general heater (near infrared heater C) that emits near infrared rays of ~4 μm, the infrared wavelength range emitted by the heater and the absorption wavelength range of the organic material (E in the figure indicates the infrared absorption characteristics of melamine resin) are Because they match, it has excellent thermal efficiency, for example, it saves 30 to 50% in power consumption, and the heat treatment time can be shortened to 115 to 176 cm. Also, because it has the property of penetrating into the inside of organic materials and heating them, , the properties of the heat-treated product are excellent with less heating unevenness.Furthermore, in the case of heating paint, near infrared rays are affected by the absorption characteristics of pigments because their wavelengths are close to that, but far infrared rays have wavelengths that are lower than the absorption wavelength range of pigments. It is attracting attention because it is unaffected due to its long length, and therefore does not cause uneven drying due to paint color.

However, as shown in FIG. 10, the structure of this far-infrared heater is based on far-infrared emitting materials such as Al2O2, ZrO! , N
The method is such that a ceramic 3 such as iO is thermally sprayed onto a heat-resistant metal tube 4, and this is indirectly heated with a metal heating wire 5. In the figure, reference numeral 6 indicates an insulating inorganic powder. Therefore, the structure indirectly heats the far-infrared emitting material, resulting in poor thermal efficiency.
Even if the metal heating wire 5 is made to generate heat up to 1000°C, the surface temperature is 700°C or less, so the emissivity of far infrared rays per unit area is low, and it takes about 10 to 20 minutes to heat up, so there is no immediate heating property. In addition, the thermal expansion coefficient of the far-infrared emitting material 3 is 4~
10 x 10-'/'c) and the heat-resistant metal tube 4 (15 to 20 x 10-'/l),
Cracks due to thermal fatigue are likely to occur in the sprayed layer of the far-infrared radiator t3, resulting in a short service life. Furthermore, when drying a coating, etc., the surface of the heater is contaminated by the adhesion of mist carbon generated by the decomposition of the aqueous solvent that evaporates during drying, reducing the ability to emit far infrared rays.

In contrast to the indirect heating method which has the above-mentioned problems, a method has also been considered in which the far-infrared emitting material is directly energized to generate self-heating. However, no far-infrared emitting material having suitable electrical properties and strength as a heater material for use in this method has been found so far. Conventional far-infrared emitting materials will be classified and explained, for example, in terms of resistivity.

Si, N4. having a resistivity of 102Ω-(up to) or more. Al
2O is superior in the strength of sintered bodies i! ! Because of affinity ii! It does not have self-heating property due to electricity. S i C, Ba C whose resistivity is about 10 to 10 ohms
etc. are semiconductors, so the temperature coefficient of resistance is negative (high resistance at room temperature, low resistance when heating).
It is necessary to control the source conditions, which tends to make the power supply large and complicated, and the resistivity is 10-' to 10-' = Ω.
-cnt ZrBz, TaC, etc. have a low resistance comparable to that of a metal heater, and also have a positive temperature coefficient of resistance, so they do not require a special power source. However, these individual sintered bodies have low strength; for example, a ZrBz hot-pressed sintered body with a theoretical density ratio of 98% requires a bending strength of 2 kg/am'' or more, and for this reason, it is difficult to create a practical heater using these materials. It is difficult to produce.

As a way to solve these problems, S
There is a heater material made by composite sintering of ic, Si: + Na, etc., and ZrBz, 'rac, etc., which are conductive ceramics having a positive temperature coefficient of resistance.

This heater material has a positive temperature coefficient of resistance and a bending strength of 3
It has a relatively high strength of 0 to 49 kg/m''. Therefore, a far-infrared heater using this heater material has excellent characteristics not found in conventional far-infrared heaters. Since it directly generates heat, it has excellent thermal efficiency and can be used in just a few seconds.In addition, since the heat generation temperature can be raised to over 1000℃, the heater has a self-cleaning ability, which allows it to clean mist carbon, etc. It is possible to prevent the decline in far-infrared radiation ability due to the adhesion of metal tubes.Furthermore, since the peak is composed only of far-infrared radiation materials, the difference in thermal expansion between the constituent materials is small, and there is no reduction in the lifespan due to thermal fatigue. It has a longer lifespan than conventional heaters.

Heat generating heaters using composite sintered bodies having the various excellent properties described above also have several drawbacks. In other words, the far-infrared emissivity of the heater is proportional to the surface area of the radiation surface,
Since the heater is made of a brittle hard material, the only way to increase the surface area is to process the surface with a coarse diamond polishing plate, and such processing does not significantly increase the emissivity of the heater. Furthermore, depending on the shape, such processing becomes difficult. For this reason, the above-mentioned far-infrared heater has a problem in that its emissivity is lower than that of conventional far-infrared radiation heaters in which a metal tube is coated with powder of a far-infrared radiation material having a relatively coarse particle size.

(Object of the Invention) An object of the present invention is to provide a far-infrared heater with a high emissivity of far-infrared rays, while eliminating the drawbacks of the above-mentioned prior art.

(Summary of the Invention) In order to achieve this object, the present invention provides that the far infrared ray emitting surface on the outer surface is constituted by a layer containing 50 to 8 Ovol% of a far infrared ray emitting material with a particle size in the range of 30 to 2000 μm. Features.

(Example of the invention) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a far-infrared heater according to the present invention, where 3 is a far-infrared radiation layer, and parts corresponding to those in FIG. 10 are given the same reference numerals.

The far-infrared heater shown in FIG. 1 is a flat plate heater, and the flat plate heater is made of 5i
Mix 1% C64vo and 1% ZrBt36vo,
After hot pressing in vacuum at 100° C. and 300 kg/c+J, cuts 9 are made with a diamond blade to form a serpentine circuit. Both SiC and Z r B z that make up this heater are far-infrared emitting materials, and Zrsz in particular has conductivity, so the metalized lead wires at both ends of the circuit are connected with Kkel leads.
When 8 is energized, it self-heats and emits far-infrared rays. In the figure,
Sasafune 7 is a dense layer.

FIG. 2 shows a far-infrared radiation layer 3 of an infrared heater according to the present invention.
This is a schematic representation of nearby tissues.

The layer 3 that emits far infrared rays to the heated object has an average particle size of 10
0μm SiC coarse particles 10 5Qvo1%, average particle size 2μ
Since the raw material powder is a mixture of 40vol% ZrB and fine particles 11 of
It is more porous and has a larger surface area than the dense layer made of only the raw material powder of No. 1.

There are several methods for manufacturing the far-infrared heater having the structure of the embodiment shown in FIG. 1, such as dry press molding and hot press molding. FIG. 3 shows the molding order in the hot press molding method adopted in this example. According to this molding method, a far-infrared emitting layer 3 containing coarse raw material powder and a dense layer 7 consisting only of fine grains are formed. After forming flexible green sheets 12 and 13, these are laminated and heated in the direction of the arrow using a hot press at a temperature of 210.
Press pressure 300kg/c at 0℃ and 1 hour holding time
It was fired by applying tJ.

A green sheet 12 consisting of the above-mentioned average particle size 100 μm (7) SiC coarse particles 10 and Zr with an average particle size of 2 m and 1 m
The green sheet 13 made of B2 fine grains II was produced by the following method.

1) The purchased raw material powders of SiC and ZrBz are classified using a cyclone-type wind centrifuge and a sieve, and coarse powders with a maximum particle size of 1000 μm or less and an average particle size of 10
0μm powder and maximum particle size 20 as fine powder.
Powder with an average particle size of 2 μm was obtained at less than pm.

2) Coarse grained 3iC64vo1 classified as in 1) above
% and coarse particles of ZrBz36vol.
A fine mixed powder was prepared by mixing vo 1% and fine grain ZrRz36vo 7i%.

3) The raw material powder used for the far-infrared emitting layer 3 is 60 von% of the coarse mixed powder prepared in 2) above, and 4% of the fine mixed powder.
The fine-grained mixed powder was used as it was for the dense layer 7.

4) The raw material powder for each layer was made into a slurry by mixing predetermined parts by weight of the dispersion medium, binder, and reformulation shown in Table 1, respectively.

This was homogenized by stirring in a ball mill for 24 hours.

5) The slurry obtained in 4) above was stretched onto a Mylar sheet (a polyester sheet subjected to mold release treatment with silicone coating) using a blade with a distance of 1.51 m from the sheet surface. FIG. 4 is a schematic diagram illustrating this process, in which 14 is a raw material slurry, 15 is a mylar sheet, 16 is a doctor blade, and 12.13 is a green sheet 12.13 made of the slurry stretched by the doctor blade 16. .

6) The slurry spread on Mylar sheet 15 was dried at room temperature for 10 hours or more. The ventilation speed must be 0.1 m/s or less to prevent cracks from occurring due to rapid drying. The steps 4), 5) and 6) above are shown as a process diagram in FIG. As shown in the figure, the raw material powder is mixed with a binder, a dispersion medium, and a reformulation (organic solvent), formed into a green sheet by a doctor blade method, and then dried.

7) Dry sheet can be hot pressed at 170°C.
It was cut out into a circular shape of φ (see Figure 3). Since the sheet is flexible, any method such as a knife or punching machine can be used to cut it out. Note that the shape of the molded body is not limited to a circular shape as long as hot pressing is possible.

8) The thickness of the sheet is shown in Table 2. Since the dense layer 7 has a thickness of 3.5 mm after firing, the thickness of the layer before firing is 7.5 mm.
It became 21111. Since it is difficult to produce sheets of this thickness, we stacked 6 sheets of 1.2 ms each (
(See Figure 3). In this way, the thickness of each layer can be adjusted by adjusting the thickness of one sheet and the number of sheets laminated.

9) The laminated molded body is pressed using a hot press device at a pressing pressure of 300 kg/cnl, a firing temperature of 2100°C, and a holding time of 1.
It was fired under the conditions of h.

10) The fired body fired in step 9) above was polished and processed using a diamond tool to form the shape shown in FIG. Nickel wires were pressure-welded to both ends of the circuit at 950° C. in a vacuum atmosphere to form lead wires 8 (FIG. 1).

In this example, both the far-infrared emitting layer and the dense layer were formed into green sheets and molded, but the dense layer can also be formed into a powder compact by dry pressing.

In addition, the above sheet manufacturing conditions are greatly affected by the particle size distribution, specific surface area, activity, etc. of the same type of raw material, so it may be necessary to change the conditions somewhat depending on the raw material, as mentioned in m1. The emissivity of far infrared rays is proportional to the surface area of its emitting surface, so in order to improve the emissivity, the larger the diameter of the particles constituting the far infrared emitting layer, the better;
A thickness of 0 μm or more is desirable. However, if the particle size is 2000 μm or more, it will be difficult to mold the powder, so the coarse particle size should be 30 to 200 μm.
A range of 0.011 m is suitable, and in this example, the average particle size is 1.0 m.
Powder with a maximum particle size of 1000 μm or less was used.

If the surface area is made up only of coarse particles, the coarse particles have poor sintering properties, and the bonding force between the particles is weak, causing them to peel off during heat generation, making it unusable. Therefore, it is necessary to mix fine grains with rich sinterability to bond between coarse grains.

In this case, as the mixing ratio of fine particles increases, the bonding force between the coarse particles increases, but if too much fine particles are added, the coarse particles are buried in the fine particles and the surface area becomes smaller. Figure 6 shows the influence of the mixing ratio of fine particles on the intensity and surface area of the far-infrared radiation surface when coarse particles with an average particle size of 100 μm and fine particles with an average particle size of 2 μm are mixed, and the surface area is It is expressed as a ratio of the surface area of a sintered body using only raw material powder with an average particle size of 2 μm. As shown in this graph, increasing the amount of fine grains mixed into coarse grains results in 40V01%.
With the above, the strength increases, but the surface area decreases. As a result, considering the balance between the strength and surface area of the far-infrared emitting layer from a practical point of view, the mixing ratio of fine particles is 20 to 5Qvo.
1%, that is, a coarse particle content in the range of 50 to 80 vol.
! % was optimal. In FIG. 6, S is the stated surface area at each mixing ratio, and So is the stated surface area of the sintered body containing only coarse particles.

The layer below the far-infrared radiation layer preferably has a dense fine grain structure from the viewpoint of increasing the strength of the heater, and it is desirable that the average grain size of the raw material for its constituent material is at least 10 μm or less.

The far-infrared radiation emitting surface of a heater using raw material powder whose particle size has been adjusted as described above is relatively porous, and the surface area is nearly twice as large as that of a heater using raw material powder with only fine particles.
Emissivity increases.

In the present invention, the types and contents of constituent materials are not limited to those in the examples, and include ZrBZ and zrc.

A heater made of one or more conductive far-infrared emitting substances such as TaN, or a mixture of the above-mentioned conductive materials and other insulating or semiconductor far-infrared emitting substances. It can also be applied to Materials that can be used in the present invention are shown in FIG.

Figure 7 shows the improvement in emissivity of the far-infrared heater according to the present invention.
C shows a heater according to the invention. In the radiation efficiency ratio ε/ε0, ε is the emissivity, and eo is the emissivity of a conventional heater using a raw material with an average particle size of 2 μm. As is clear from FIG. 7, if the radiation efficiency ratio of the conventional heater A, which is composed only of fine-grained raw material powder, is 1, then the radiation efficiency ratio of the heater C according to the present invention is improved by about twice. Furthermore, the radiation efficiency ratio is higher than that of heater B, which has improved emissivity through surface processing after firing.

(Effects of the Invention) As explained above, according to the present invention, the intensity of the far-infrared radiation layer is increased, the surface area of the heater is increased, and the emissivity is also increased, thereby eliminating the drawbacks of the above-mentioned prior art. It is possible to provide a far infrared heater with excellent functions.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the far-infrared heater according to the present invention, FIG. 2 is a schematic diagram showing the structure near the far-infrared radiation layer of the far-infrared heater according to the present invention, and FIG. 3 is a far-infrared heater according to the present invention. Fig. 4 is a schematic diagram showing the method for producing a green sheet used for producing a far-infrared heater, and Fig. 5 is a perspective view schematically showing the manufacturing procedure of an infrared heater. Fig. 6 is a characteristic diagram showing the influence of the mixing ratio of fine particles on the intensity and surface area of the far-infrared emitting layer, and Fig. 7 shows the far-infrared heater according to the present invention and the conventional heater. FIG. 8a is a graph showing a comparison of far-infrared emissivity with . Figures 8b and 8C are diagrams showing the usage status of far-infrared heaters, Figure 9 is a comparison diagram showing the radiation characteristics of far-infrared heaters and conventional infrared heaters, and Figure 10 is a diagram of the conventional far-infrared cotton heater. A partial sectional view showing the structure, Fig. 11 is a table showing raw material slurry adjustment conditions during green sheet production, Fig. 12 is a diagram showing conditions for stacking green sheets, and Fig. 13 is a far infrared ray that can be applied to the present invention. It is a diagram listing radioactive substances. 3... Far-infrared emitting material layer, 7... Dense layer. Removal girder Figure 2 Figure 2/I') 3rd rM Figure 6 0 25 5Q 75 100
W top of wandering 1 to string grain (Vo1%) Fig. 7 Fig. 8 Fig. 9 Infrared 1i+ (μm) Fig. 1I Fig. 12

Claims (1)

[Claims] One type or a combination of two or more types of conductive infrared emitting substances such as ZrB_2, ZrC, TaN, TaC, etc. and one type or two or more types of insulating or semiconductor far infrared emitting substances such as SiC, Si_4N_4, Al_2O_3, etc. In the far-infrared heater, which is composed of a composite sintered body, the far-infrared material directly generates heat by itself when energized.
1. A far-infrared heater, wherein the far-infrared radiation surface on the outer surface is constituted by a layer containing 50 to 80 vol% of a far-infrared radiation material having a particle size in the range of 30 to 2000 μm.