JPS5949314B2 - How to prevent carbonaceous deposits on surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention can be used to remove cooking device residue or
On surfaces where carbonaceous deposits such as tar, which is a polymerization product of kerosene, are a concern, this method suppresses carbonaceous deposits and further prevents carbonaceous deposits on surfaces that are intended to be decomposed and removed. This is a proposal on how to do this.

A proposal regarding a coated surface for the purpose of catalytically purifying food stains by applying it to the inside of cooking equipment was made by Stiles of DuPont, and has since been based on the same idea. , methods of dispersing oxidation catalysts in glass frit rather than in a water glass binder have been successively proposed and put into practical use.

The gist of these series of proposals is to catalytically oxidize and purify organic compounds such as oils, fatty acids, and proteins.
This is based on the idea that the process should be carried out at a low temperature of about 300°C. The inventors of the present invention have doubts about whether "oxidation catalysts," which have been commonly referred to in the past, are truly effective in preventing surface contamination by cooking contaminants.
Regarding fatty acids that cause particularly bad cooking contaminants, we investigated gasification and decomposition of fatty acids using catalysts from the viewpoint of preventing fatty acid carbonization. As a result, oxides such as alkali metals and alkaline earth metals, calcium silicate, calcium aluminate, and other compound groups, and oxides such as Ti, Fe, Ni, Co, Cr, and Ag have excellent catalytic abilities. I have already suggested that you have a heading.

Among these, "oxidation catalyst" which has been commonly referred to as
Among them, it was found that manganese dioxide, copper oxide, etc. had almost no ability to gasify and decompose fatty acids, but rather inhibited the decomposition. The present invention is completely different from the conventional method using an "oxidation catalyst" or a "gasification decomposition catalyst" and is based on a different purification mechanism. Tar deposits are often a problem on the surfaces of objects where hydrocarbon compounds are vaporized in significant amounts.

In conventional self-cleaning coatings, an "oxidation catalyst" or the like is used to actively oxidize the coating, but the present invention does not rely on that type of reaction. The purification mechanism of the present invention is all about promoting evaporation and vaporization from the object surface. The construction of the surface coating is therefore extremely simple. However, the important point is to suppress active oxidation as much as possible. This point is fundamentally different from conventional self-cleaning coatings. Examples of surface coating in which the method of the present invention is specifically carried out include a plasma spraying method in which a layer of inorganic oxide particles is directly formed on the surface;
Alternatively, methods such as enamel or inorganic coating, in which inorganic oxide particles are dispersed in a suitable binder and coated on the surface, can be used.

Among these methods, a coating method using an inorganic binder is an effective method for obtaining a strong coating layer with excellent productivity in practical terms and relatively easily.

Binders suitable for the practice of this invention include metal phosphates or alkali metal silicates.

In the case of any binder, an extremely strong and stable surface treatment on a metal plate can be obtained by carrying out baking hardening at 200 to 300° C. depending on an effective composition. Paints using these binders, which are commonly commercially available, exhibit heat resistance of 500 to 600°C and surface properties that are similar to those of enamel coatings. The first condition required for the inorganic oxide used in the present invention is that it does not have a positive oxidizing effect on organic substances.

Some metal oxides activate oxidation reactions as oxidation catalysts. As a typical oxidation catalyst, MnO2. Cu
O, Pt, Pd, etc. are known, but such compounds are undesirable. The reason for this is on the vaporized surface of kerosene or on the inside surface of the cooker, and the biggest cause of organic compounds becoming heavy carbonaceous is oxidation and dehydrogenation in the air. Therefore, if a substance with an oxidizing effect is used there, this effect will be amplified and tar formation will be accelerated. The second condition is that it has a certain degree of heat resistance.

Considering the conditions of the surface to which this coating layer is applied, since it is a surface to which temperature is applied, it is undesirable for the coating layer itself to decompose or cause jitter links. Specific compounds that meet the above conditions include M2O3, SlO2
, TiO2, ZnO2, BeO, or a composite thereof.

Furthermore, compounds with high acidity as solid acids are not desirable as inorganic oxides when considering application under high temperatures.

This is because if the organic substance exhibits its ability as a solid acid, there is a concern that the organic substance will undergo radical polymerization and become a heavy carbonaceous substance. Effects of the present invention will be shown below, focusing on examples.
A 10-Aluminium-treated steel plate was used as a test piece, the surface was treated, 100 drops of salad oil made of 1 μt soybean oil was dotted on the surface, and the mixture was placed in a furnace at 250°C and heated for 30 minutes. The purification ability was evaluated based on the weight change. 11}, Sumitomo Chemical's "Sumiceram" was used as the paint base material, and the coating was applied to a film thickness of approximately 100 μm.

``Sumiceram'' is an inorganic paint that uses aluminum phosphate as a binder. First, in the case of Planck, that is, in the case of only aluminized steel sheets, the weight change rate is 6.
It was 0% by weight. Next, when only "Sumi Ceram" was painted, the weight change was 55% by weight, which was a slight decrease. This is probably because the coating film has a somewhat uneven surface, which causes poor oil diffusion and a small evaporation area. Next, alumina α-At2O3 and silica SiO2)
A similar test was conducted by adding 5% by weight of the inorganic oxide and changing the particle size of the inorganic oxide. The test results are shown in the table below. As is clear from the table, inorganic compounds with a particle size of 5 to 10 microns are very good. Conventionally, additives for paints have been used with a particle size of 5 μm or less for dispersibility and other reasons, but in this respect, the present invention uses particles with a slightly larger particle size.

When the particle size becomes even larger, the adhesion of the coating film clearly decreases. When the tape is peeled off in a test, the area around the large particles peels off. The reason why it is preferable to add particles with a particle size of 5 to 10 μm is thought to be that in the case of this particle size, the oil spreads quickly on the surface and evaporation of the oil proceeds effectively. It seems that the surface chemical properties of oil at high temperatures and the particle size in this range exactly match.

Even if alumina is replaced with silica as the inorganic oxide to be added, there is not much difference in effectiveness, so it is thought that the effect is based on the above-mentioned physical factors.

Next, the effect of alumina having a particle size of 5 to 10 μm was evaluated by varying the amount added to the inorganic paint base material.

The test results are shown in the figure. In relation to the physical properties of the coating film, the upper limit of the amount added was 40% by weight. The addition effect is approximately 2
This becomes noticeable when the amount added is ≦weight%, and it tends to become saturated at a level of about 5 to 10% by weight. When particles of this size are included, the surface of the coating layer becomes porous, and some of the dropped oil (2001) remains, but oil stains are not visible due to the way the surface reflects light. It is completely inconspicuous, and especially if it has been blackened using pigment, the difference in condition before and after the test is hardly noticeable.

The method of the present invention is expected to have exactly the same effect even when applied to vaporizing surfaces such as kerosene combustion burners, which have the problem of oil becoming tar due to stagnation.

As described above, the method of the present invention is simple and can be applied very easily to various surfaces where carbonaceous deposition is a problem, and moreover, an effective carbonaceous deposition prevention effect can be obtained.

[Brief explanation of drawings]

The figure shows the relationship between the amount of alumina with a particle size of 5 to 10 microns added to the inorganic paint base material and the weight loss rate due to evaporation and vaporization of the oil deposited on the surface of the coating layer.

Claims (1)

[Claims] 1. On the surface where you want to prevent carbonaceous deposition, apply one or more selected from the group of silica or alumina with a particle size of 5 to 10μ.
A method for preventing carbonaceous deposition on a surface by forming a coating layer made of a metal phosphate or an alkali metal silicate containing 2 to 40 wt% of m.