JPS5915016B2 - Coating material with catalytic action - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a coating material, which has a catalytic effect to suppress the formation of tar-like carbon on metal surfaces where there is a concern that tar-like carbon may be formed. The purpose of this invention is to provide a covering material that is

Equipment that generates tar-like carbon and causes trouble, such as oil, food residue, etc.
There are various types of open and box-shaped cooking utensils that are disliked because they emit strange odors and get stuck in sticky and unclean conditions, and there are also various types of cooking utensils that generate hard carbon, which reduces the amount of combustion and concerns safety. A typical example of this is oil-burning appliances that cause problems.

Conventionally, the coating surface with such catalytic action is formed by forming an enameled or glassy material on the substrate, but this coating layer is made of oxidized manganese, iron, cobalt, zirconium, chromium copper, or rare earth metals. Catalytic coatings made of vitrified materials, which are mainly composed of metals and the like, are used as self-cleaning enamels and are applied to electrical open circuits, etc. As these conventional catalysts, oxidation catalysts with strong catalytic ability are used. 5.During cooking, oil, protein, fat, and various other organic compounds scattered from cooked foods such as meat and fish are completely oxidized into carbon dioxide gas and water by these oxidation catalysts, and the inner walls of the refrigerator are completely oxidized. The aim is to prevent dirt and keep it clean at all times.

0 The inventors discovered that, for example, when salad oil is in a liquid state,
I had doubts that these oxidation catalysts could be completely oxidized to water and carbon dioxide while in contact with the surface, but they are actually being marketed as self-cleaning enamels. 5 The catalyst coating was pyrolyzed in the air while in contact with salad oil (soybean oil), and the generated gas was analyzed using a gas chromatograph under various conditions (temperature was raised to 350°C for 1 hour). I evaluated it until I left it, but no carbon dioxide was detected.
It wasn't done.

Therefore, it is considered that these oxidation catalysts do not contribute at all to complete oxidation. The process in which oil heated in air turns into tar is partially oxidized to obtain an intermediate such as peroxide pentoxide and polymerized, or hydrogen is extracted to produce olefins, etc. In either process, the effect of a strong oxidation catalyst (which is thought to act as a hydrogen abstraction catalyst at the same time) may act to promote this tar formation, and the process of self-polymerization may occur. The present inventors believe that the catalyst may not be as effective in cleaning applications as the engineers in this field believed, and rather has the ability to decompose reaction intermediates related to tarring. Based on the idea that this would be effective, we searched for a catalyst and discovered a catalyst in a completely new direction compared to conventional methods.

In fact, as oxidation catalysts, manganese dioxide (MnO2) and copper oxide (Cu
As will be described later, it has been found that in the case of O), etc., there is a particularly significant effect of promoting tar formation. These catalysts will be appreciated in practical terms for their ability to force the hydrogen abstraction reaction to occur, and rather to quickly harden the oil and bring it to a dry state. Furthermore, regarding what is conventionally called self-cleaning enamel, when salad oil or the like is dropped onto the surface of a catalyst that has been left in high-temperature air, the salad oil quickly spreads on the surface and under 300℃ conditions, The traces become difficult to see after 20 to 30 minutes, but
On a microscopic scale, it appears that the carbon content has not disappeared, but rather has been deposited in a state that is difficult to see in the porous and thick enamel bottom. Even when evaluated from the weight change before and after the test, there was no significant difference numerically from oil tarred on an ordinary iron plate, supporting the above idea. As described above, conventional self-cleaning enamels are not only insufficient in terms of purification effect, but also have drawbacks in terms of adhesion and abrasiveness because the catalyst layer itself is quite porous. There is.

Unlike conventional catalyst-coated surfaces, the present invention is a heat-resistant paint made of pigments such as alkali metal silicates, acidic metal phosphates, and metal oxides with excellent heat resistance, which have already been widely used as heat-resistant paints. The present invention relates to a catalytic coating system in which a catalytic active substance is added to the catalytic base. From the basic idea of the present invention, an alkali metal silicate and a curing agent for accelerating its curing reaction are essential as a base or binder for adding a catalyst thereto, but a pigment is not necessarily necessary. do not have. Currently, composite metal oxide elements are generally widely used as pigments with excellent heat resistance. In order to obtain a colored coating film, the presence of a pigment is essential, but as mentioned above, the pigment of the complex metal oxide element is added in a state where it can exhibit a certain degree of activity as an oxidation catalyst. However, since this may actually lead to the promotion of tar formation, it is desirable to add the pigment in an inactive state as much as possible, or to use a non-metal oxide pigment that does not cause such concerns. Even if it is unavoidably added, it is desirable to keep it to the minimum necessary amount. Furthermore, although this catalyst exhibits an extremely excellent ability to decompose oil, from a practical standpoint, the contaminant on the coated surface is not necessarily only oil; it also contains various other contaminants. Since contamination may be caused by substances that cannot be completely purified, it is of great practical significance to use a black colored pigment to make it difficult to see the contamination. The present inventors have already discovered and proposed that a catalytic coating based on the above-mentioned heat-resistant paint to which an alkali is added has excellent catalytic activity, but the present invention evaluates catalytically active substances from an even broader perspective. develop,
This is an improved version.

In order to search for catalytically active substances that effectively decompose oil, we used gas chromatography and a pyrolysis device to pyrolyze salad oil (soybean oil) in the air while contacting it with various metal oxides. The resulting gas was analyzed using a gas chromatograph, and metal oxides with particularly excellent thermal decomposition ability were evaluated.

Although carbon monoxide and formaldehyde were identified as gases produced by decomposition, they also detected decomposed hydrocarbons, which are different from the components contained in salad oil itself. The test conditions are approximately 2η
of metal oxide using a microsyringe.
．． The mixture was decomposed in a sealed glass container at 30°C for 10 minutes under conditions in which 0It1 of salad oil was mixed therein, and the resulting gas was introduced into a gas chromatogram and analyzed. The analysis conditions are N
Using 2 carriers (60m1/Min)F. I. At D detector (H2 flow rate: 60 m1/Min, Air flow rate: 0,
51/Min) Column conditions were a 3 mmφ x 3 m stainless steel column with SllcOneGE. SE-30
, using a 5% liquid phase (Shi-Malite W carrier),
After holding the temperature at 150° C. for 5 minutes, the temperature was raised to 250° C. at a heating rate of 5 Wc/Mln, and the decomposed gas was detected.

Under the above conditions, decomposition products were detected at retention time positions of 100, 106, 139, and 173, although they have not yet been identified. Area integration results for typical metal oxides (values integrated using a digital integrator,
Table 1 shows the sum of the counts of the above four decomposition products.
From Table 1, metal oxides or compounds that exhibit good catalytic activity for the decomposition of salad oil (-FU and soybean oil) in the presence of air include oxides of metals from groups 1 to 4 of the periodic table; However, examples include oxides of Group 1 A and Group 2 A alkali and alkaline earth metals.

This is because these substances are known to have a weak partial oxidation ability, and a decomposition mechanism is presumed in which unsaturated fatty acids, which are the main components of salad oil, are decomposed through intermediates of partially oxidized compounds. However, these weak partial oxidation catalysts activate this reaction and decompose and evaporate the oil before the hydrogen abstraction polymerization reaction that proceeds in parallel, resulting in oil tar. The basic idea of the inventors was that it would suppress the chemical reaction and exhibit a so-called self-cleaning effect, and as will be described later, it became clear that this was correct. Regarding this idea, when a similar experiment is conducted in a nitrogen gas replacement atmosphere, almost the same decomposition form is shown, so the catalyst that showed activity in this experiment is more likely to have a mechanism than the one estimated above.
Rather, it is better to think of it as activating the gasification and decomposition reaction. In Table 1, the more excellent compounds are (
It can be seen that in a compound represented by the form MA) x (MB) y (0) z, MA is an element of group IA or group A, and MB is an element of group 1B or group B.

In particular, MA consists of Na, K, Ca, and Mg, and MB consists of C.
, Si, and Al are found to be the best.

Based on the above background, in order to apply the catalytically active substance extracted here as a heat-resistant coating, alkali metal silicates, acidic metal phosphates, and metal oxide-based pigments, which have already been used as heat-resistant paints in this field, were used. The paint consists of
A paint blended with the above-mentioned catalytically active substance was prepared and actually painted on an iron plate to evaluate its self-cleaning effect and physical properties of the paint film.

A series of test paints included Shikoku Kaken Kogyo Co., Ltd.'s Ceramitite: White, which is based on sodium silicate.
It was carried out using "TiO2)".

This paint consists of the following composition. (1) Base O Sodium silicate No. 2 aqueous solution (an example of alkali metal silicate) ...... 1000 parts by weight O titanium oxide (rutile type) ...... 100 parts by weight O silica (
extender pigment) (an example of a pigment with good heat resistance)
...100 parts by weight (2) Hardening agent 0 aluminum phosphate (an example of acidic metal phosphate)
...200 parts by weight O water
・・・・・・300 parts by weight This type of paint is
General formula X2O. y(SiO2) (where X is an alkali metal and y is a positive real number) is a water-based paint made of an alkali metal silicate as a binder and an acidic metal phosphate as a curing agent.

It can be colored with inorganic pigments, and this paint is white because it uses titanium oxide. Since this paint is white, the coloration (blackening) caused by the tar formation of salad oil and the like is sensitively evaluated. Place a test piece (40m77! x 80m1L) on a hot plate set at approximately 250℃.
x0.67n77! t) and 1 mg/~ on top of this.
Approximately 30η of salad oil was added in the form of spots so as to obtain a uniform distribution, and the purification properties of various paint film coatings were observed. Regarding these tests, it is desirable for the catalyst coating layer to be as porous as possible within a range that does not reduce the physical properties of the coating as much as possible. As a result of a series of studies including various additives to make the coating porous, it was found that the addition of glycerin is effective in making the coating film bolus.

The addition of glycerin is effective from about 4 m1/(1009 paints), and is extremely effective up to the order of 20 m1/(1009 paints).

If the addition of glycerin exceeds this order of magnitude, the coating film will become extremely unstable in parts and damage will appear. Table 2 shows data comparing various coating systems regarding their ability to purify salad oil at 250°C.

The purification rate is shown on a black plate (on an untreated iron plate) after correcting the decrease when only salad oil is left.
It is calculated from the weight change before and after the test in minutes.
(The coating film is heat-treated in advance so that it has a constant weight at the same temperature.It is omitted in Table 2, but of course, if no catalytically active substance is added, no purification ability will be obtained at all. At the stage of investigation, a system in which 5 wt% of calcium carbonate was added to the heat-resistant paint was good, but the addition of glycerin and an improved catalytic active material improved the purification ability dramatically. has been done.

In particular, the last system shown in Table 2 (already, 2 wt% potassium carbonate, 1 wt% calcium oxide, 2 wt kg calcium silicate, 2 wt% alumina cement was added to the paint 6 Ceramitide, and an additional 6 m1/(100 g paint ) was the best, with traces completely disappearing within a 30-minute test period. From the ingredients of salad oil,
Palmitic acid, which has a boiling point of 271C, is also included, so the fact that it was 100% purified means that it was thermally decomposed even at 25C by the decomposition ability of the catalytic active substance, and evaporated as a low-Food point substance. It is thought that. Furthermore, a similar test was conducted using lard (pork fat), but the results were exactly the same.

However, the numerical value of the purification rate was larger for lard. Regarding the problem of curing time (pot life), which is a practical problem in terms of paintability, calcium oxide acts as a curing accelerator, and when it is added as much as 10%, problems appear, but the total amount of these catalytically active substances added is It was confirmed that if it is 8% or less, there is almost no practical problem. Furthermore, we conducted a series of tests regarding temperature stability, adhesion, heat shock, corrosion resistance, etc. for these catalyst coatings, and found that when less than 10% of these catalyst active substances were added, the physical properties of conventional coatings were not the same. It was also confirmed that there was almost no damage.

According to these series of test results, the catalyst coating of the present invention exhibited almost the same characteristics as the conventional enameled product. To point out the differences, the catalyst coating of the present invention has better wear resistance, and conversely, the enamel-treated product has better thermal shock resistance. This is because conventional enamel products are porous, emphasizing porosity rather than catalytic effect, but in the case of this coating, the catalytic effect is well exhibited, so it is as good as conventional enamel products. This is thought to be because porosity that sacrifices strength is not necessary. As described above, the catalyst coating of the present invention has discovered a completely new effect completely outside the scope of conventional coatings of this type, and has an extremely excellent self-cleaning effect in practical use. It was also confirmed that the quality of the enamel products was equal to or higher than that of conventional enamel products.

The present invention mainly targets oils such as salad oil,
The effect of suppressing and preventing tar formation has been described, but it is also sufficiently effective for kerosene systems where tar formation is a problem.

Claims (1)

[Claims] 1 an alkali metal silicate, an acidic metal phosphate,
It gasifies and decomposes oil stains in the cooking cabinet, which is made of a heat-resistant pigment and at least one catalyst selected from the group of alkali metal or alkaline earth metal silicates and aluminates. A coating material with catalytic action that has excellent purification ability.