JPH036420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an infrared radiator for application as a thermal radiant heating source, primarily in the field of cooking. It can also be used for heating purposes.

Conventional configurations and their problems In general, radiant heating cookers such as grills require the following properties.

(1) Heat can reach the inside of the food quickly and it can be finished quickly.

(2) The surface of the food should be moderately burnt.

is the point.

When heating a substrate such as metal using electricity or gas as a heat source to form a radiator, its emissivity is low, so a method is used to form a coating on its surface to improve its radiation characteristics.

At that time, there are many unknown points as to what kind of wavelength characteristics the heat (ie, infrared rays) radiator should have from the viewpoint of the above-mentioned cooking and charring. This is because the reflection, transmission, and absorption characteristics of foods for infrared rays are not well understood.

In recent years, use of far-infrared rays as a radiant heat source has begun to be talked about. For example, at wavelengths of 5 to 6 μm or less, the emissivity is 40% or less, and at wavelengths of 8 μm or more, it is 70%.
It is claimed that far-infrared radiators and the like that are larger than the above have characteristics such as high thermal efficiency, no unevenness depending on the color of the heated object, and the ability to uniformly heat the inside of the object. Most organic substances have an absorption band in the far-infrared region. Regarding the interaction between light and matter, it is known that the relationship between the absorption coefficient and the average depth of light penetration (ie, the mean free path of photons) is inversely proportional. That is, the larger the absorption coefficient, the shallower the light penetration depth. Even with visible light, we all know that light penetrates well into a transparent material with a small absorption coefficient, and that the penetration depth becomes shallow in an opaque material with a large absorption coefficient. Among the characteristics of far infrared rays mentioned above, when the object to be heated is the same, it absorbs well and has good thermal efficiency, and it can heat the object evenly to the inside (that is, the heat penetrates quickly to the inside). That is the opposite. That is, for organic substances that have a strong absorption band in the far-infrared region, there is a contradiction between being able to absorb light well and allowing light to penetrate well into the material.

Therefore, when the far-infrared radiator is applied to the cooking field, the far-infrared rays will heat the area near the surface well, but the fire will not penetrate much inside. This will only burn the surface and make it difficult to cook quickly. To this end, it is necessary to carefully evaluate the infrared absorption and transmission characteristics of foods. Therefore, as a result of evaluating the absorption coefficient of water, which is the main component of food, we came up with the idea of making good use of the fact that the absorption coefficient is small at 3 μm or less, and that the absorption coefficient is somewhat small even at 10 μm or more.

Therefore, it is important to skillfully control the wavelength selectivity of infrared radiation. This kind of thinking has never existed before.

The conditions for this are: (1) It must withstand temperatures between 800℃ and 950℃ and has excellent heat resistance.

(2) Excellent instant heating properties.

(3) The base made of metal or the like and the radiation material formed thereon must have high adhesion, and no peeling or cracking will occur, especially when used under cold and hot cycles.

(4) Must be resistant to mechanical shock.

(5) It is easy and inexpensive to manufacture.

On the other hand, conventional infrared radiators include so-called embedded heaters in which an infrared lamp heat-generating line is embedded in a ceramic radiant material, and thermal spray heaters in which the surface of a metal heat radiator is coated with a ceramic radiant material using a thermal spraying method. .

However, although infrared lamps are excellent in heating quickly, they are not only inefficient because they do not emit infrared rays with long wavelengths of 5 μm or more, that is, far infrared rays, but they are also susceptible to mechanical shock and have a short lifespan. It was hot.

In addition, embedded heaters suffer from cracks in the emissive layer when used at temperatures above 500°C, and also have disadvantages such as poor heating speed, vulnerability to mechanical shock, and complicated and expensive manufacturing methods.

In thermal spray heaters, the close contact between the metal substrate and the ceramic radiant material is simply a mechanical bond, so if the pretreatment method and thermal spray conditions are not strictly controlled, the ceramic layer may peel off, cracks may occur, or thermal cycles may In addition to the disadvantage of being inferior, there was also the disadvantage of high cost.

Purpose of the Invention The present invention has been made to eliminate the above-mentioned drawbacks of the conventional technology.
The object of the present invention is to provide an infrared radiator that does not peel or crack even when used in cold or hot conditions, is resistant to mechanical shock, is inexpensive, and has excellent productivity.

Structure of the Invention In order to achieve this object, the present invention provides a cured product of polyborosiloxane resin containing 15% or less of Co/Al oxide and 30% or less of Co/Al oxide by weight.
TiO ₂ and more than 100% ZrO ₂ or ZrSiO ₄
By forming a cured product containing a compound whose main component is
% or more, 50% or less in the vicinity of 3 to 6 μm, and 80% or more in the vicinity of 8 μm or more.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows a conceptual diagram of a cross section of a radiator of the present invention. A radiator coating 2 is formed on a base 1 made of metal or the like. The radiator 2 consists of a cured body 3 of polyborosiloxane resin as a binder and at least three types of radiant materials 4, 5, and 6.

When incorporated into a gas combustor, a surface combustion burner with a honeycomb structure made of ceramic (so-called "shubank" type burner) may be directly coated with a radiator, or it may be formed using wire mesh, lath mesh, or punched metal. A method may also be used in which a radiator is coated on the surface and heated using a separately provided burner.

FIG. 2 shows an embodiment applied to an electric heater system. In FIG. 2, a linear heating element 4 having electrode terminals 3 at both ends is pushed into a base 1 of a pipe made of iron, aluminum or stainless steel,
In a heater having a structure in which a heat-resistant filler 5 such as MgO is filled and both ends are sealed with an airtight material 6, a radiator layer 2 of the present invention is formed on the surface of a base 1.

The radiator 2 in Figs. 1 and 2 uses a cured polyborosiloxane resin as a binder, and the infrared radiator is 80% or more when the diameter is 3 μm or less, and 80% or more when the diameter is around 3 to 6 μm.
It has a radiation characteristic of 50% or less and 80% for 8 μm or more.

Polyborosiloxane resins are, for example, The main component is a polymer with a structure like this. This binder has properties as a "semi-inorganic polymer" and has properties similar to organic polymers at room temperature, and is excellent in terms of operability such as when used as a paint. When heated, the organic matter decomposes into Si,
Ceramic is formed using B and O as the skeleton. Complete ceramicization takes place at 600°C.

Since the thickness of the emissive layer is as thin as 5 to 30 μm, the emissive layer has low thermal resistance and is excellent in rapid heating properties.

Since the coating is formed using a polyborosiloxane resin as a base and is applied using a conventional coating method similar to that used for organic paints, pretreatment of the substrate surface requires only conventional degreasing and no complicated pretreatment is required. Moreover, since the coating can be easily formed by a method such as a spray method, productivity is excellent.

Although the emissive layer is a thin film with a thickness of 5 to 30 μm, its infrared emissivity is approximately 80% or more at 3 μm or less, 50% or less at 3 to 6 μm, and 80% at 8 μm or more.
The above radiation characteristics are shown.

The reason for such radiation characteristics is based on consideration of the optical characteristics of infrared rays for foods. The food is
Although it is complex, consisting of starch, carbohydrates, proteins, and fats, it contains a considerable amount of water, and its optical properties against infrared rays are similar.

When it comes to visible light, foods have unique reflection characteristics depending on their color. Although there is some reflection on the short wavelength side for near-infrared rays of 1 μm to 3 μm, it exhibits excellent transmittance. That is, light of this wavelength penetrates well inside the food. Light of 3 μm to 6 μm is well absorbed by food. However, since this light has a strong energy, it burns the surface a little too much. Light of 6μm to 10μm is similarly well absorbed by food, but light of 3μm to 6μm
Compared to m, the energy is weaker, so it burns just fine.

Light of 10 μm or more can penetrate relatively deep into food, but it is not as penetrating as near-infrared light of 1 μm to 3 μm. Due to the nature of these foods, almost all
80% or more for 3 μm or less, 50% or less for 3 to 6 μm,
When a radiant with a radiation characteristic of 80% or more is used for radiant heating of foods with a diameter of 8 μm or more, the heat penetrates quickly to the inside, allowing for faster cooking, and the surface is nicely charred, resulting in good cooking.

The radiator of the present invention has a film thickness of more than 30 μm.
The radiation layer cracks when subjected to a heat shock placed underwater at a temperature of 850℃.

The temperature of the radiator of the present invention needs to be set to at least 800°C or higher and up to about 950°C.

The emissive layer is formed by dispersing the emissive material in a polyborosiloxane resin binder together with a solvent using a ball mill, etc. to form a paint, and then spraying the paint onto the substrate. Obtained by firing for minutes.

The radiator is a hard ceramic coating with a hardness of 6H, which has excellent heat resistance up to approximately 1000℃ and excellent adhesion to the substrate. In particular, it has good adhesion even under severe heating and cooling cycles of 850 degrees.

A specific example will be shown below.

As a polyborosiloxane resin binder,
The inorganic polymer "SMP-32" from Showa Electric Cable Co., Ltd. was used. This binder turns into a ceramic and stabilizes at 600°C, but due to thermal decomposition during that time, 2/3 of its initial weight is lost and the residue is reduced to 1/3.

In order to increase the emissivity above 8μm, it has the characteristic that the absorption coefficient increases significantly near about 7μm.
ZrO ₂ or ZrSiO ₄ compound is used. By adding these zirconia-based compounds, these compounds become transparent at 7 μm or less, and transparent at 8 μm or more.
It has opaque properties. When these zirconia-based compounds are used alone, the refractive index of these compounds is as high as 2.2, so there is surface reflection of about 15%, and the upper limit of the emissivity is 85%. When used dispersed in a polyborosiloxane resin binder, since the refractive index of the borosiloxane resin is about 1.5, the surface reflection is about 4% and a high-emissivity body can be obtained. In the wavelength range of 8 μm or more, the radiation properties are dominated by specular reflection, and the radiation properties are related to surface reflection.

Next, in order to increase the emissivity in the near-infrared region of 3 μm or less, a material that is relatively transparent in the infrared wavelength region and has a high refractive index is added. TiO ₂ has a high refractive index of 2.8 and satisfies this condition. The particle size of _TiO2 is 0.5~
If the range is 1 μm, scattering in the near-infrared region of 3 μm or less will increase. Even if scattering of 3 μm or less increases, radiation will not increase unless there is absorption. Co/Al oxide is used as an example of a material that absorbs in the near-infrared region.
These are blue compounds with a spinel structure, from 1 to
It has absorption in the near-infrared region of 2 μm. The particle size of these compounds is preferably in the range of 0.1 to 1.5 μm. The blending ratio of these three materials is important from the viewpoint of wavelength selection.

It is desirable to use the Co/Al oxide in an amount of 15 wt% or less based on the cured product of the polyborosiloxane resin.

If it exceeds this value, the emissivity of 3 to 6 μm increases. Similarly, TiO ₂ is preferably 30wt% or less.
This is because if it exceeds this, the emissivity of 3 to 6 μm increases, and the emissivity of 8 μm or more decreases.

Compounds whose main component is ZrO ₂ or ZrSiO ₄ are
Similarly, 100% or more is desirable. If it exceeds 300%, the strength will become weaker.

100 parts by weight of SMP-32, 50 parts by weight of ZrO ₂ ,
A paint was prepared using 5 parts by weight of TiO ₂ , 2.5 parts by weight of CO・Al・Ox, and 150 parts by weight of toluene as a solvent.
Stainless steel plate [SUS 430] with a film thickness of approximately 15μm
It was coated on top and baked at 350°C for 30 minutes and then at 750°C for 30 minutes to obtain a film.

Figure 3 shows the spectral radiation characteristics of this sample at 750°C. In FIG. 3, 7 is the characteristic in the case of a conventional stainless steel plate, and 8 is the characteristic in the case of the above-mentioned radiator.

Next, the paint was applied to the surface of a heater made of stainless steel pipe (100V, 600W, length 480mm, diameter 12mm) to a film thickness of 15μm and fired. A piece of tuna meat was heated from a height of 5 cm, and the heating situation of the meat was compared with that of SUS. In the area directly under the heater, the penetration rate of heat was 5 mm in 10 minutes with stainless steel, but the penetration rate was 11 mm in the same time, which was more than double that, and the surface was also well charred. This proves that it has excellent cooking properties in a short time.

Effects of the Invention As described above, the infrared radiator of the present invention (1) has unique infrared radiation selectivity and is excellent in short-time heating properties of foods.

(2) Because it is a thin film with a thickness of 5 to 30 μm, it has excellent quick heating properties.
Can withstand up to 1000℃.

(3) High adhesion to the substrate, especially excellent cold and heat cycle resistance.

(4) It has a hardness of 6H and is resistant to mechanical shock.

(5) Since it can be applied by spraying, it is highly productive, does not require complicated pretreatment, and is inexpensive.

It has the following effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a radiator according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of a device in which a radiator is formed on the pipe surface of a sheathed heater according to an embodiment of the present invention, and FIG. is an infrared spectral radiation characteristic diagram of a radiator according to an embodiment of the present invention. 2... Radiator, 3... Cured body of polyborosiloxane resin.

Claims (1)

[Claims] 1 Based on the weight ratio of the cured product of polyborosilane resin, 15% or less of Co/Al oxide, 30% or less of TiO ₂ , and 100% or more of ZrO ₂ or
An infrared emitter containing a compound whose main component is _ZrSiO4 .