JPS6215109B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a self-cleaning paint that is applied to the wall surface of an oven in a cooking device to form a self-cleaning coating layer. The inner walls of cooking devices such as ovens are contaminated with substances scattered from food, giving off unpleasant odors and discoloring due to oxidation, giving an unpleasant feeling. Furthermore, when heated, oils and fats adhering to the inner wall surface of the oven undergo oxidative discoloration and turn into polymers, forming a solidified film with strong adhesion that is extremely difficult to remove and clean. Recently, there is a cooking device in which a porous film containing an oxidation catalyst is applied to the inner wall surface of the oven, and the porous film is decomposed and removed by the oxidation catalyst effect. However, when actually cooking in an electric oven, the internal wall temperature is 200℃.
Because the temperature rarely exceeds 100°F, it often does not reach the temperature at which the catalytic action is active (around 250°C in the case of MnO ₂ ), and the oils and fats that adhere to the self-purifying coating layer will polymerize over time. , a polymer film of oils and fats may cover the catalyst and reduce catalyst performance,
When these processes are repeated, the catalytic action eventually disappears, and the fats and oils enter the pores of the porous layer and solidify, making it even more difficult to remove them. The present invention relates to a self-cleaning paint for reducing wall surface contamination caused by such a polymerized film of oils and fats. It is characterized by finishing a porous rough surface layer with a membrane composition. When animal and vegetable oils and fats that adhere to walls are heated, phenomena such as evaporation, polymerization, and carbonization occur. This phenomenon is related to temperature, time, temperature rise, speed, etc. Below 200℃, there is little evaporation, carbonization, and decomposition, and polymerization becomes more intense. At temperatures above 250°C, evaporation, carbonization, decomposition, and polymerization occur simultaneously, and the polymerized oils and fats are carbonized and sintered. The wall temperature of an electric oven or oven range is
Temperatures rarely reach 300°C or higher, and even if they do, they are localized. In any case, if the temperature is below 300°C, a large amount of polymerized and charred substances of oils and fats will be produced, causing contamination. In particular, oils and fats adhering to a film containing only an oxidation catalyst undergo polymerization at temperatures below 200°C, producing a large amount of polymerized film, making removal work difficult. Focusing on these points, we conducted the following experiments to develop paints and self-cleaning films that are ideal for the oven walls of cooking equipment and have good self-cleaning effects even at relatively low temperatures. Ingredients were selected. [Experiment method] Mixed oil (10% butter, 20% corn oil, 10% fish oil)
%, beef fat 20%, rapeseed oil 20%, soybean oil 20%)
6 parts by weight and the substance to be sorted (previously 500 parts by weight)
℃, 1 hour heat treatment)) Mix together 4 parts by weight and apply to the surface of heat-resistant glass using an applicator for 30 minutes.
After spreading to a micron thickness and heating at 200℃ for 20 minutes, the surface condition was determined, and then heated to 250℃.
After heating for 1 hour, the surface condition was determined again. [Judgment Criteria] A. Check the evaporation rate of the mixed oil after heating at 250℃ for 1 hour. Evaporation rate = weight decreased / weight of mixed oil used × 100 If the evaporation rate exceeds 100%, it is because oxygen, etc. of the substance to be sorted has dispersed. A small value of evaporation rate means that the mixed oil did not evaporate much. (b) Observe the surface condition of the experimental material and judge what kind of effect it has using the standard table in Table 1 below.
Rank each experimental material as A, B, C, or D.

〔Experimental result〕

As a result of experiments on various substances based on the above experimental method and criteria, data as shown in Table 2 was obtained.

【table】

[Table] Based on the data in Table 2, the effects are classified as follows. (a) Substances that have oxidative decomposition effects: manganese oxide, nickel oxide, platinum, palladium, and others; (b) Substances that inhibit polymerization: antimony oxide, aluminum hydroxide, phosphoric acid frits, antimony powder, and others (c) Substances that promote polymerization. ...Lead oxide, zinc oxide, lead glass, cobalt oxide, and other substances that do not have any of the following effects...silica powder, titanium oxide, calcium carbonate, mica powder, etc. In Table 2, substances that have a low evaporation rate and have a polymerization inhibiting effect The substance shown has the effect of inhibiting the polymerization of oils and fats at low temperatures. Among these, aluminum hydroxide, antimony oxide, phosphoric acid frit, or a mixture thereof are most suitable as polymerization inhibitors as components of self-cleaning paints, considering cost, adhesion of the paint film, porosity formation effect, etc. be. Further, as the oxidation catalyst contained in the self-cleaning paint, noble metals such as platinum and palladium, or metal oxides such as manganese oxide and nickel oxide are effective, and they can be used alone or in combination. The following points were found from the above experimental results. When oils and fats come into contact with substances that have a polymerization-promoting effect, so-called polymerization solidification catalysts, they form a solidified film quickly at low temperatures, significantly reducing the evaporation and decomposition of oils and fats, so they should not be used in self-purifying coating layers. . On the contrary, it has become clear that by dispersing a substance that has a polymerization inhibiting effect in a porous layer, it can inhibit the normal thermal polymerization of oils and fats, and also act as a catalyst poison for the polymerization catalyst, suppressing the formation of a solidified film. . If the polymerization of oils and fats is inhibited by using a substance that has a polymerization inhibiting effect in combination with an oxidation catalyst, the evaporation effect in which part of the mixed oil is reduced to low molecular weight becomes active, and a large amount of the mixed oil can be gasified in a short time. This also made it possible to evaporate at low temperatures (around 50℃). Conditions that further assist evaporation by inhibiting polymerization include the surface area of the porous rough surface and the substance having a polymerization inhibiting effect, and the state and distance of contact with the oil and fat. The most effective condition is that a substance that has an effect must exist within a radius of 15 microns, which is the distance at which oils and fats are affected. This requires the presence of oils on the surface that penetrate into the film, or both at the same time. In order to speed up the penetration and lateral spread of oils and fats, the film should have a porous and rough finish that is dotted, linear, or dotted and linear at the same time. It can be expanded. What guides fats and oils are the overlapping particles and pores formed by protrusions, and the protrusions formed on the walls of these pores. Furthermore, in order for the polymerization inhibiting action to be effective, the surface of the substance having the polymerization inhibiting action must be exposed and in contact with the oils and fats. Next, a method for manufacturing a porous rough surface coating layer forming a self-cleaning film using the coating material of the present invention will be described with reference to an example. First, manganese oxide and nickel oxide, which have an oxidizing effect, are ground into particles of 50 microns or less using a ball mill, and polygonal plate-shaped crystals of aluminum hydroxide, which has a polymerization-inhibiting effect, a phosphoric acid frit, and polygonal particles of 50 microns or less are produced. The silica powder, which has an uneven surface, is dispersed in a xylene solution of the initial polymerization of epoxy-modified silicone resin using a stirrer, and the viscosity is adjusted to a thixotropic state using thinner to form a paint (referred to as a self-cleaning paint). This paint is placed in a pressure tank with an agitator and a pressure of 0.5 to 1.5 kg/cm ² is applied, and a spray gun with a diameter of 1 mm or more is used to atomize it with air pressure of 2 to 4 kg/cm ² and applied to the object to be painted. . The coated film is applied multiple times until the dry film is 150 microns or more and 300 microns or less, left at room temperature for 10 minutes, and then heated at 200°C for 5 minutes to completely volatilize the organic solvent. , further at 530℃
After baking for 10 minutes, it is cooled and the coating is completed.
The components of the paints used in the examples are shown in Table 3.

[Table] The particle size, shape, and surface roughness of the oxidation catalyst, polymerization inhibitor, and auxiliary agent used in the above examples are shown in electron micrographs (a, b, c, d, e, f, g, h, i,
The cross section of the cured film is as shown in Figure 2, an electron micrograph, and is made by bonding silica powder, aluminum hydroxide, phosphate frits, and coarse particles of manganese oxide with a decomposed product of silicone resin. It has a bone core with membranous composition and constitutes pores and rough surfaces. The walls of this hole are also uneven and play a role in spreading oils and fats. The faster the rate of penetration of oils and fats into these pores, the better. On surfaces that are less susceptible to polymerization inhibiting effects, an oil film of 15 microns in thickness is the limit at which polymerization inhibiting effects occur, and beyond this, a polymerized and solidified film is formed by heating. The penetration rate of oils and fats into the coating film can be determined by dropping 4 to 5 mg of salad oil onto the coating surface.
If it takes less than 15 minutes for the luster caused by oil to disappear in an atmosphere of 25°C, a polymeric film will not form on the surface even if heated. In order to confirm the evaporative decomposition effect of oils and fats in the porous coating layer forming the self-cleaning film obtained in the example, a thermobalance is used to perform measurement. The porous layer piece bonded to the material is finished into a circular piece with a diameter of 7 mm, placed face up in a platinum container of a thermobalance, and 5 mg of salad oil is added dropwise to start heating within 1 minute. Here, the results of measuring the weight loss of oil at each temperature when the temperature was raised from room temperature to 300°C at a rate of 20°C/min are shown in Figure 5a. According to this, the lower the starting temperature for weight loss, the more effective it is.
It shall be SC. ) starts to lose weight at around 200°C, while the film of the present invention starts to lose weight at around 50°C, demonstrating its excellent performance at low temperatures. Figures b and c in Figure 5 show the loss of salad oil when the temperature of the thermobalance is kept at 200℃ and 250℃.At 200℃, there is almost no difference between the aluminum plate and the existing SC. It doesn't have that effect. Compared to aluminum plate, even at 250℃
Although the effect of SC is confirmed, it is clear that it does not reach the weight loss exhibited by the coating according to the present invention at any temperature. Furthermore, when comparing wall contamination with actual heating equipment, etc., the difference becomes the subject of further expanded evaluation. Although the binder used in the examples is a silicone resin, the effect remains the same even if it is a phosphate or hollow frit. like,
The catalyst must be dissolved in the enamel, and the porosity must be rough and the particle surface must not be smooth. The present invention uses the above-mentioned oxidation catalyst in combination with a polymerization inhibitor to form a unique film formed by the overlap of the particle size and shape of particles having the effect, expanded powder particles, or mixed particles and their surface roughness. The aluminum hydroxide, silica powder, phosphoric acid frits, and The roughness of the particle surface and the surface area of the unevenness created by the adhesion of fine particles of oxidation catalysts such as nickel oxide and manganese oxide help the spread of oils and fats. It must be possible to increase the contact area and at the same time increase the evaporation surface. In order to clarify whether the loss of salad oil due to the film caused by the coating of the present invention was due to decomposition or evaporation, the gas generated in the furnace was analyzed by gas chromatography. As a result, water,
Components such as carbon dioxide gas were confirmed. It became clear that most of the weight loss below 250 was due to evaporation of fats and oils. However, the components that evaporated from the aluminum plate and the components that evaporated from the film formed by the paint of the present invention are different, and most of them are decomposed into low boiling point substances and evaporated. Also, when the slight tar-like substance remaining in the film formed by the paint of the present invention was heated again at 300℃,
Large amounts of water and carbon dioxide gas were generated. This indicates that oils and fats are not polymerized in the film formed by the paint of the present invention. Furthermore, when the film obtained by the paint of the present invention is used in a cooking device such as an electric oven, fats and oils adhering to the wall surface will be effectively removed not only during cooking but also while the wall surface naturally cools down after cooking is completed. is demonstrated. As explained above, the inventive paint uses an oxidation catalyst and a polymerization inhibitor in combination to form a porous, rough self-cleaning film on the wall surface, thereby preventing the evaporation and decomposition of oils and fats at relatively low temperatures. It can be done efficiently. In other words, the polymerization reaction of the oils and fats is inhibited by the polymerization inhibitor and the oils and fats exhibit fluidity for a long time, so the oils and fats spread on the oxidation catalyst particle surface and convection occurs, making the whole particle susceptible to the influence of the catalyst. This increases the evaporation effect, including some of the substances that become low in molecular weight, allowing large amounts of fats and oils to evaporate into the atmosphere at low temperatures and quickly from the rough surface. Furthermore, even if a small amount of polymeric film is formed, the film is thin and located at a position where the oxidation catalyst effect is active and can be easily decomposed. Such a porous rough surface using a combination of an oxidation catalyst and a polymerization inhibitor is optimal if used on the wall surface of a cooking device where fats and oils are generated, especially on the top surface and exhaust duct.

[Brief explanation of the drawing]

Figures 1a and b are views showing the surface condition of aluminum hydroxide dispersed in the self-cleaning film of the present invention at magnifications of 40x and 900x, Figures 1c and d
Similarly, Figure 1 e and f are diagrams showing the surface condition of silica powder at 300 and 4000 times magnification, Figure 1 g , h are diagrams showing the surface state of nickel oxide at 100x and 1700x magnification, and Figures i and j are diagrams showing the surface state of manganese oxide at 100x and 220x magnification. FIG. 2 is a diagram showing the cross-sectional particle arrangement of the film of the present invention at a magnification of 700 times. Figures 3a, b, and c are diagrams showing the surface conditions of various conventional self-cleaning films at magnifications of 100x, 300x, and 2600x. Figures 4a, b, and c show the state of the surface of the self-cleaning film according to the present invention at a magnification of 100.
The figures are magnified by magnification, 600x, and 2700x. Figure 5a is a diagram showing the loss of salad oil with respect to temperature rise.
Figure b is a graph showing the time change in the weight loss of salad oil at 200°C, and Figure 5c is a view showing the time change in the weight loss of salad oil at 250°C. However, ●--● are examples of the present invention, ×--× are existing S/C, and 〇-〇 are the characteristics of the aluminum plate.

Claims (1)

[Claims] 1. A self-cleaning paint comprising a heat-resistant film-forming composition containing a metal or metal oxide having an oxidation catalytic action, or a mixture thereof, which is selected from aluminum hydroxide, antimony oxide, phosphoric acid frit, or a mixture thereof. A self-cleaning paint containing a polymerization inhibitor.