JPS5914545B2 - Articles with self-cleaning coating layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-purifying coating layer that has the effect of using a catalyst to decompose and purify oil that scatters and becomes dirt on the inner wall of a cooking appliance during cooking.

10 In recent years, with the spread of various types of cooking appliances, appliances with a coating layer that has a self-purifying effect have become commercially available.

These coating layers can be broadly classified into those using glass frit as a binder and those using silicate as a binder.
A typical example of the former method, as disclosed in Japanese Patent Publication No. 4915-33088, is a method in which a catalyst is supported on a metal substrate using a molten mixture with a glassy material as a component of a frit. The disadvantages of this method are that the catalyst is a glass component, so it cannot fully demonstrate its effect;
If the temperature is higher than that, it may become inactive. As a means to improve this, JP-A-52-135
As seen in No. 325 and JP-A-52-127913-5, there is a baking method in which the frit and the catalyst are separated and at a low temperature that does not make the catalyst inactive.

A disadvantage of this approach is the use of sodium silicate as a mill additive when using low softening point frits. K0 Sodium silicate poisons the catalyst and reduces the activity of the catalyst. This can also be seen in the self-purifying coating layer shown in Japanese Patent Publication No. 49-28120, which uses sodium silicate as a binder. The decrease in catalytic ability due to sodium silicate is particularly noticeable at relatively low temperatures, where the degree of use of fluorine is below 250°C.
Therefore, in order to fully exhibit the catalytic ability, it is desirable to form the coating layer without using sodium monosilicate.

However, as a practical matter, when using low softening point glass, it is difficult to form without it from the viewpoints of slip stability, adhesion strength with metal as an enamel layer, surface hardness, etc. Very difficult. The present invention improves the drawbacks of the conventional self-purifying coating layer using sodium silicate as a mill additive as described in Section 7. It improves the purifying performance at low temperatures and also provides sufficient adhesion strength and surface hardness. It is something.

The self-purifying coating layer of the present invention contains a glassy frit, a catalyst, and a phosphoric acid compound as essential components. The present inventors previously proposed a self-cleaning coating layer using a phosphate binder. When compared with conventional self-purifying coating layers, this material certainly has superior performance, but L was not always satisfactory from the viewpoints of adhesion strength and surface hardness. In the present invention, by coexisting this phosphate-based binder with a glassy frit, the present invention achieves a
The present invention provides a self-purifying coating layer that has excellent cleaning performance and excellent physical properties as a enamel. The glassy frit desirably used in the present invention has a softening temperature of 600° C. or less, which is suitable for aluminum or an aluminized steel plate coated with aluminum.

Materials with a softening temperature of 600° C. or higher cannot be used because the aluminum will melt during firing. Conventionally, it is already known to use sodium silicate as a mill additive for aluminum enamel.

The reason for using this sodium silicate is as follows.
The vitreous frit melts a little during slip manufacturing and P
Shows alkalinity with H of about 11 to 12. When applied on aluminum in this state, the stable range of aluminum, that is, the pH range where aluminum does not melt, is 4 to 9.
As a result, aluminum dissolves, hydrogen is generated, and pinholes are created. Therefore, close contact between the frit layer and the metal cannot be obtained. The effect of adding sodium silicate plays a major role as an inhibitor against the dissolution reaction between aluminum and slip. That is, it is generally said that Na+ ions in sodium silicate are adsorbed to metal aluminum and inhibit the dissolution reaction. Due to this effect, even if the pH of the slip is 9 or higher, it is possible to perform enameling on aluminum without generating hydrogen. In addition to the above-mentioned reasons, the addition of sodium silicate has a great effect in improving surface hardness and adhesion strength. This is true for both the undercoat layer that comes into direct contact with the aluminum metal and the topcoat layer formed thereon. usually,
The overcoat layer has an undercoat layer that separates it from the metal, so it seems that no dissolution reaction occurs, but since there are many minute pinholes in the undercoat layer, a dissolution reaction occurs as well. It is. As mentioned above, the softening temperature is 6
The use of sodium silicate is an essential condition for enameling aluminum or aluminized steel sheets using a frit of 00'C or less.

However, as mentioned above, this sodium silicate is undesirable from the viewpoint of the catalytic performance of the self-purifying coating layer.The present invention uses phosphoric acid instead of this sodium silicate. The phosphoric acid compound has the general formula MO, XP2O5・Y
It is indicated by H2O. In this formula, M is A
t, Mg, Ca, Fe, Cu, Ba, Ti, Mn and Zn. Generally, the cheapest and most easily available materials include aluminum compounds such as monoaluminum phosphate and dibasic aluminum phosphate, and tribasic magnesium phosphate. When heated, these phosphoric acid compounds turn into the following polymeric condensed phosphates. When heated to a higher temperature, for example, primary aluminum phosphate crystallizes and hardens through the following reaction.

A4O3・3P205・XH2O In this reaction, when the heating temperature is 500℃ or less, At2O3・3p205 and At2O3 are completely dehydrated.
・Crystalline and amorphous P2O5, and amorphous At2O33P2O5・2H2, which is an intermediate product of the dehydration process.
A4O3, 3P205, 2H2, which are uniformly present and crystallize once, but are highly hygroscopic when left in the air.
0 takes in moisture from the air as crystal water and forms A4O3.
Crystals of 3P205 and 6H20 are formed, and at the same time, their volume expands, and for the first time, the crystallized structure is destroyed and they become powder-like.

Moreover, when heated to 500° C. or higher, stable and strong crystalline At2O3.3p205 is formed. 100 more
When the temperature is below 0℃, A4O3・3P205 → At2O3
・By causing thermal decomposition of P2O5+2H20, a product with stronger heat resistance can be obtained.

As described above, phosphates can be obtained stably at temperatures of 500 DEG C. or higher, and the frit baking temperature is 500 DEG to 600 DEG C., so it can be said to be preferable.

Furthermore, there is a reason why this phosphoric acid compound is advantageous for the present invention. That is, phosphoric acid compounds exhibit acidity in aqueous solutions. This acidity has the function of neutralizing the alkaline content of the dissolved components of the frit. Therefore, slip is neutralized and dissolution reaction with aluminum or aluminum alloy is suppressed. However, if the amount added to the frit is too large or the amount of glass components eluted from the frit is too large, gelation will occur, so it is important to select an appropriate amount. Next, regarding the glass frit, the frit preferred for the present invention has a softening temperature of 600
℃ or below.

Usually, such low softening point glass contains lead oxide or cadmium as a component, but if possible, it is preferable to use Japanese Patent Application Laid-Open No. 52-1353, which does not contain the above-mentioned pollutants.
The following composition shown in Publication No. 25 is preferable. Glass produced within this composition has a small amount of elution in water, is a preferable glass frit for the present invention, and has a softening temperature of 500 to 500.
It is within 580℃.

The properties of frit are not only useful as a binder, but also play an important role in self-purification performance. The coefficient of thermal expansion of the frit is also important in determining the bonding strength with the metal and the amount of catalyst added, and the preferable range is 100 to 130 x 10
-7Degl. Firing conditions are important factors in satisfying self-purifying performance and physical characteristics required for enamel, and it is necessary to have a softening point within 600°C. The metal base material to which the present invention can be applied is a steel plate coated with aluminum or an aluminum alloy, preferably an aluminum hot-dip plated steel plate (aluminized steel plate).

Aluminized steel plate has 90% At and Si on the steel plate.
This is a steel plate plated with a layer composed of about 8 to 9% of At-Si by a hot-dip plating method, and has an At-Si layer of about 10 to 30 μm. This aluminized steel sheet is made of ordinary pure A
Although it has higher heat resistance than t, it is still up to 600°C. When the temperature exceeds 600°C, an alloying reaction occurs between At in the surface layer and Fe in the steel, forming an alloy layer made of At-SiFe.

Therefore, a frit that can be fired at 600° C. or lower is required. Next, the catalyst will be explained in detail.

Catalysts that can be used in the present invention are metal oxides, double oxides, solid acid catalysts, and solid base catalysts.

The metal oxide is an oxide of a metal selected from Mn, Cu, Fe, Ni, Cr, CO, etc. Particularly preferred is Mn, Cu, Fe, Ni, Cr, CO, etc.
It is an oxide of n, Cu, and Fe. A double oxide is a higher-order compound consisting of two or more types of oxides, in which the presence of a base ion as an oxygen acid is not recognized in its structure. The general formula is M[[)M[1
1204 (Mll), M represents divalent and trivalent metal ions, respectively), and has a spinel structure. Particularly effective for the present invention are MlI)Fe2O4
MIl) is a divalent metal ion, Mn2+,
It consists of F +, CO2+, Ni2+, Zn2+, Ba2+, etc. Solid acid catalysts and base catalysts have been attracting attention in recent years, and are catalysts having acidic sites and basic sites on a solid according to the definition of acid-base by Bronsted or Lewis.

Typical solid acid catalysts are silica, alumina,
Examples include silica, magnesia, and zeolite. In addition, basic ones include CaO, MgO, Na2cO3, K2c
Examples include O3, BacO3, and lime aluminate. These acid-base catalysts have excellent decomposition performance in reaction with fats and oils. 7. When the catalyst mentioned above coexists with sodium silicate, which is a conventional mill additive, it becomes a catalyst poison and reduces performance, but when it coexists with phosphoric acid compounds, the performance decreases. I can't stand it.

The reason for this is thought to be as follows. The alkali ions present in the slip will be adsorbed to the active sites of the catalyst, but in the case of phosphoric acid compounds, the alkali ions are thought to form salts. Furthermore, even if an excess of the phosphoric acid compound is present, taking the primary phosphate as an example, it is possible to replace and block the dissociated H at the terminal with a highly water-resistant compound. Metal oxides used for this purpose include those that react quite violently, such as zinc oxide, and those that react slowly, such as At, Si, Ti, Fe, and Sn. These are convenient in the present invention because they are one of the components of the catalyst mentioned above, and are added as porosity forming agents and mat forming substances. A mat forming agent is added for the purpose of providing porosity to the self-cleaning coating layer, and is used for fire-resistant base aggregates such as AbO.
3. Oxides such as SlO2, TiO2, MgO, and CaO, and various minerals containing these as one component.

In addition to these inorganic substances, there are also organic substances that impart porosity through thermal decomposition during firing. For example, polyethylene powder,
carboxymethylcellulose, polyvinyl alcohol,
Examples include polytetrafluoroethylene and polystyrene. The present invention is a self-purifying coating layer composed of the above-mentioned elements, and can be applied to the inner wall surfaces of various cooking appliances.
It can be applied to any wall surface that requires catalytic action, regardless of its purpose. As an example, tin on the walls of combustion equipment,
It is also effective for cleaning tar. Examples of the present invention will be described below.

Example 1 As a base material, size 10 x 10 cm, thickness 0.

A 4 mm aluminized steel plate with an undercoat and enamel was used.

The frit constituting the self-cleaning coating layer was shown in Table 2, and had a coefficient of thermal expansion of 127 x 10-7Deg-1 (measured with DL-1500 manufactured by Sadaku Riko) and a softening vorticity of 535°C. This frit was made into a particle size that would pass through a 100 mesh sieve, and this was mixed with a catalyst, a phosphoric acid compound, a mat forming agent, and a mill additive so as to have the composition shown in Table 3, and ground in a ball mill for 1 hour. I made a slip.

This slip was applied to the base material described in Section 7 using a spray gun to a thickness of 200 μm.

After drying, the sample was baked at 550°C for 5 minutes. This sample was tested for the test items shown below. (1)
Purification ability test lard 100η was divided into 6 points and dropped, 2000C12
Heating was performed at 50°C and 300°C for 30 minutes each, and the purification rate was calculated from the weight loss before and after.

(2) Adhesion test The substrate was bent 186' to a diameter of 10 mm with the coating layer on the outside, and peeling between the substrate and the coating layer was observed.

If it is adhered, it is represented by ○, if it is peeled off, it is represented by ×, and if it is partially adhered, it is represented by △. (3) Surface hardness test, test thickness 1.0 mm (1) Copper piece (Cll specified by JIS)
The case where the copper is scratched off due to OOP) is indicated by ○, and the opposite case is indicated by X.

(4) Water resistance test 1 Boil in boiling water at 95°C or higher for 10 hours, calculate weight loss,
It is expressed as the amount of decrease per unit area of 6D.

The results of the test were as shown below. (1) Purification capacity 200'C: 35% 250'C: 720t) 3000C: 96% (2) Tight enclosure...○ (3) Surface hardness...○ (4) Water resistance・・・・・・098ヮ/C7n2 Example
A sample was prepared in the same manner as in Example 1, except that the following phosphoric acid compound was used instead of monobasic aluminum phosphate.

The test results are shown in Table 4. Example 3 A sample was prepared and tested under the same conditions as in Example 1, except that the catalyst in the slip composition was changed.

The results are shown in Table 5. In the table, parts by weight of catalyst are values based on 100 parts by weight of frit. (manufactured by Low Co., Ltd.),
The composition of the slip was the same as in Example 1, and the firing conditions were 52.
A sample was obtained at 0°C for 5 minutes.

This product has a ○ in both adhesion and surface hardness, and a water resistance of 1.
2η/CTn2. Example 5 In Example 1, the amount of primary aluminum phosphate was 3, 5, 10, 20, 30, 4 with respect to 100 parts by weight of frit.
When slips were prepared by changing the amount to 0.50 parts by weight, gelation occurred when the amount exceeded 30 parts by weight, making it difficult to apply.

Therefore, the amount of phosphoric acid compound added is 100 frits.
The amount should be within 30 parts by weight based on the heavy weight. Example 6 In Example 1, the matte forming material was SiO2 and T.
The purification ability of the sample made with iO2 is 38% at 200℃, 63% at 250℃, and 9% at 300℃ in the case of SiO2.
4%, and in the case of TiO2, it is 32%, 60%, and 60%, respectively.
It was 90%.

Example 7 Added a mat forming agent to the slip composition of Example 1? The purification ability of the sample prepared under the same conditions with the addition of 5 parts by weight of polyethylene powder (UF-20 manufactured by Tetsutsu Kagaku Co., Ltd.) was 42% at 200°C, 74 (fl) at 250°C,
It was 98% at 300°C.

Claims (1)

[Scope of Claims] 1. An article having a self-purifying coating layer comprising a vitreous frit, a catalyst, and a phosphoric acid compound. 2 The phosphoric acid compound has the general formula MO・xP_2O_5・
yH_2O (M is Al, Mg, Ca, Fe, C
At least one selected from the group consisting of u, Ba, Ti, Mn and Zn. ) An article having a self-cleaning coating layer according to claim 1, which is a compound represented by: 3 The catalyst is a metal oxide,
Claim 1 is at least one selected from the group consisting of a double oxide, a solid acid catalyst, and a solid base catalyst.
An article having a self-purifying coating layer as described in 1. 4. An article having a self-cleaning coating layer according to claim 1, wherein the vitreous frit has a softening point of 600° C. or lower. 5. An article having a self-purifying coating layer according to claim 2, wherein the phosphoric acid compound is a primary phosphate.