JPS6052871B2 - Method of manufacturing self-purifying coating layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-purifying coating layer formed on the wall surface of a self-purifying cooking device, and particularly aims to provide a coating layer having excellent catalytic activity against oxidation reactions. .

The coating layer on the wall of this type of self-cleaning cooking device has conventionally been made of enamel using a glass frit as a binder, or coated with a silicate as a binder. A typical example of the former is as shown in Japanese Patent Publication No. 49-33, in which a suitable oxidation catalyst is melt-blended into a vitreous matrix and permanently fixed over the entire enamel coating. It is something that Furthermore, as described in Japanese Patent Publication No. 47-178329, a slip is synthesized by mixing a commercially available oxidation catalyst and a commercially available vitreous frit, and this slip is blown onto an enamel substrate formed on a metal substrate. It is something that has been baked on. On the other hand, in the latter case,
As seen in Publication No. 2812, a catalyst is dispersed and supported on a metal substrate using an alkali metal silicate as a binder. Each of these has advantages and disadvantages, and the former, which uses glass frit as a binder, is baked at 500 to 850°C during the manufacturing process, which limits the type, shape, and thickness of the base material. Furthermore, the fact that the glassy frit does not melt to some extent has the disadvantage that it is not bonded, so the surface area of the coating layer becomes small and the catalytic action is not exhibited. Furthermore, the latter, which uses an alkali metal silicate as a binder, has a weak bonding force and has the disadvantage of peeling off from the substrate due to mechanical impact. A more serious problem is that silicates dissolve in water vapor. As described above, although self-cleaning cooking devices are commercially available, they have been unsatisfactory due to problems in manufacturing costs, catalyst performance, and quality.

The present invention solves the above-mentioned conventional drawbacks, and uses a binder of the general formula MO・XP2O5・YH2O for the self-purifying coating layer.
One of the characteristics is that it is a phosphate represented by (M is a metal, and X and y are real numbers).

Here, M is Ae, Mg, Ca, Fe, Cu, Ba, T
These are metals such as i, Mn, and Zn.

Examples include primary aluminum phosphate, secondary aluminum phosphate, tertiary aluminum phosphate, and magnesium phosphate. The curing mechanism of phosphate is that when heated, it becomes a polymeric condensed phosphate as shown below.
evening.

When this condensed phosphate is heated to a higher temperature, it crystallizes,
harden.

For example, when primary aluminum phosphate is heated, it crystallizes and hardens through the following reaction. In this reaction, when the heating temperature is below 50 degrees, the crystals and amorphous Ae2O3.3p205 and A'203.P2O5 that have completed dehydration, as well as the amorphous intermediate product of the dehydration process, Ae2O3・3P20s-2H20 etc. exist uniformly and will crystallize once, but when left in the air, Ae2O3・3P205・2H20, which is highly hygroscopic, takes in moisture from the air as crystal water and forms Ae2O3・3p2.
0.・6H20 crystals are generated and the volume expands at the same time,
It destroys the initial crystallized structure and turns into powder.

In addition, when heated to 500°C or higher, a stable and strong crystalline Ae2O3.3P20. form. Furthermore, about 1
If the temperature rises by 00℃ or exceeds 600℃, Ae2O3・3p
By causing thermal decomposition of 205→Ae2O, .P2O5+2H20, a stronger heat-resistant product can be obtained. When using a phosphate alone as described above, heating to 500° C. or higher is required.

However, since the base material on which the self-cleaning coating layer is formed is usually made of steel, the temperature cannot be raised above 900C, so it is preferable to heat the base material in the range of 500 to 800C. Furthermore, in the case of primary phosphates, the dissociable H at the terminal can be substituted and blocked by a substance with good water resistance.

Since phosphates exhibit acidity in aqueous solution, a substitution reaction occurs between H in the OH group and the metal. The metals used for this purpose include those that react quite violently with phosphates, such as zinc oxide, and those that are slowly reactive, such as Ae, Si, Ti, and Fe.
, Sn, and other oxides are used.
Curing by phosphate and composite oxide is thought to be due to the synergistic effect of the crosslinking reaction of phosphate groups by the metal accompanied by the formation of metal phosphate by neutralization, and is caused by the synergistic effect of the cross-linking reaction of phosphate groups by the metal, which occurs at relatively low temperatures (12
It hardens at a temperature of 0 to 150°C) and has good water resistance. In addition, MgO, Mg(0H)2, Ca0, Ca(
0H) 2, basic substances such as asbestos, talc, and fly ash can also be used as hardening accelerators.

However, these methods require P (phosphorus) and M (metal)
It is largely controlled by the molar ratio of , and has a large effect on bonding properties, heat resistance, and water resistance.

When using a phosphate alone, the smaller the molar ratio of P and M, the better the water resistance, but if the ratio is less than 1, the adhesion and stability in an aqueous solution will deteriorate. Although this value varies depending on the type of M (metal), it is usually preferably in the range of 1 to 4. In addition, when a complex oxide is used in combination with phosphate, the temperature and water resistance are affected by the molar ratio of P and M, and if the molar ratio of P<5M is greater than 3, high temperatures will not occur. If this ratio is small, water resistance will not be improved, and if this ratio is small, a product with water resistance can be obtained at a relatively low temperature.

However, if the molar ratio of P<15M becomes 0.5 or less, it will rapidly condense at room temperature, so when considering the optimum working temperature, the optimum molar ratio of P and M is 0.5 to 3. . Furthermore, the molar ratio of P and M greatly affects the performance of the self-cleaning coating layer.

There is no effect when the molar ratio of P<5M is small, but P/M
As the ratio increases, the performance of the self-cleaning coating layer decreases. This is because P (phosphorus) becomes a catalyst poison, and the greater the number of moles of P, the greater the effect. In addition, the effect is small until the molar ratio of P and M is 4.0, but
4. @). As the temperature increases, the performance deteriorates significantly. Thus, the molar ratio of P and M is most preferably 0.5 to 4.0 in the present invention. Next, the amount of phosphate added is
It greatly affects the surface hardness of the self-purifying coating layer and its adhesion to the base material.

It must contain at least 5% by weight of phosphate based on the solid content of the catalyst or curing accelerator. That is, if it is less than 5% by weight, the bond between the phosphate and the catalyst is weak and the surface is soft. In addition, the adhesion to the base material is weak and it is easy to peel off. Furthermore, even if a large amount of phosphate is used, the phosphate itself becomes porous when heated, and some synergistic effect between the phosphate and the solid content causes catalytic action or It does not seem to have any effect on surface hardness or adhesion. Therefore, the amount of phosphate should be at least 5% by weight, but since adding a large amount only increases the cost, it is preferably 5 to 5% by weight. As described above, phosphate has good water resistance when used alone or in combination with a curing accelerator.

In addition, a coating layer with excellent adhesion and surface hardness can be obtained, and it also has the characteristics of not affecting the catalytic action. Although phosphate has the above-mentioned characteristics as a binder, there are major problems with self-purifying coating layers in which catalysts are supported using phosphate.

The problem is that phosphates act as catalyst poisons and reduce activity. It is generally said that catalyst poisons exist in catalysts and strongly adsorb to the active sites of the catalyst, rendering the catalyst inactive. Substances that act as catalyst poisons have been widely identified, including P,
Representative examples include Pb, S, Asl and their compounds. Therefore, the dissociated Pq- ions of the phosphate act as catalyst poisons and adhere to the catalyst even after calcination, reducing its activity. The present invention attempts to maintain the activity of this PC8- catalyst poison by treating the catalyst with an alkali in advance.

Alkali treatment of the catalyst is immersing the catalyst in an alkaline solution and coating the catalyst with alkali before mixing with the phosphate solution.

The effect of coating the catalyst with alkali is to prevent the above-mentioned Kt deposition. When an alkali is adsorbed onto the catalyst in advance, it is strongly adsorbed to the active sites, and even if it is left in phosphate afterwards, only a portion of it becomes soluble. If this alkaline treatment is mixed at the same time as the phosphate solution, PO will adhere to the catalyst due to competitive reaction. Therefore, alkaline treatment of the catalyst must be carried out before mixing with the phosphate. Alkali salts used for alkali treatment include Na2CO3, N4HCO3, KHCO3, NaOH,
Selected from the group of K2Cα and KOH.

The characteristics of these alkali salts are that they retain Na2O and K2 even after heating.
It becomes O, K2cO3, and Na2cO3 and remains on the catalyst. Even if the alkali is the same, NH4OH will undergo thermal decomposition after heating, dissipate from the catalyst, and then
Since Pq- is attached, the object of the present invention is not satisfied. Usually, electrolytic manganese dioxide is S in an electrolytic bath.
(Adsorbs Y,- ions, 2.0 to 2.4 wt% S
O: Contains -. In order to remove this Sq-,
Industrially, the pH of electrolytic manganese dioxide is adjusted to 7 or higher by alkali treatment using NH4OH. The alkali treatment in this case is an alkali treatment for dry batteries, and it is preferable that the alkaline treatment be one that easily causes alkali desorption. The feature of the present invention is that the gist is different from the conventional alkali treatment performed with electrolytic manganese dioxide, and in the present invention, as the alkali, NH
Contains no 4OH. In the present invention, alkalis other than these salts can also be used, but the above-mentioned ones are preferred in terms of cost, workability, etc. Among them, carbonate has a high thermal decomposition temperature and can be said to be a preferable material for the present invention. Alkaline treatment is
This is carried out by immersing the above-mentioned salt in a solution of an appropriate concentration for a certain period of time and then drying.

This alkali-treated catalyst plays the following important role in addition to protecting the catalyst active sites. One of them is
This is to adjust the pH of a solution of a phosphate compound. Phosphate compound solutions have a strong acidity with a pH of about 1, and when aluminum is used as a base material, the acid dissolves and generates gas during firing, resulting in strong bonding strength and a beautiful coating layer. The current situation is that it cannot be done. This also applies to the case where a corrosion-resistant layer made of an enamel layer or a heat-resistant paint is provided between the metal surface and the self-cleaning coating layer. The reason is that the above-mentioned corrosion-resistant layer always has pinholes when viewed microscopically, and the phosphate compound solution reaches the metal surface through the pinholes. Therefore, P of the phosphate compound solution
It is preferable that H be as neutral as possible. From this point of view, the alkali-treated catalyst has the effect of partially eluting the alkali in the solution of the phosphate compound and neutralizing the solution. Of course, not all of the alkali attached to the catalyst is eluted, but the alkali is strongly adsorbed to the active sites necessary for catalytic activity. The stable pH range of aluminum is about 4.0 to 8.0, and when an alkali-treated catalyst is mixed into a phosphate solution, the alkali treatment conditions are determined so that the pH falls within this range. Since heat-resistant paints containing phosphates are highly acidic, nearly neutral heat-resistant paints with neutralizing agents added to them are commercially available. Even if a catalyst is mixed therein, Pq- will be adsorbed to the catalyst, which does not satisfy the gist of the present invention. Next, the second feature is that the alkali adsorbed by the alkali treatment remains in the coating layer after firing and exerts a catalytic effect. Alkali metals and alkaline earth metals have long been confirmed to act as decomposition catalysts for fats and oils. The mechanism of action is still debated, but according to the inventors' speculation, the "alkali" adsorbed on the catalyst becomes Na after heating.
It becomes 2O, K2O, K2CO3, and Na2cO3 and absorbs water vapor, and the alkali metal ions become NaOH and KOH. In the presence of an alkali, fats and oils saponify and decompose along with absorbed water to become safer compounds.
This decomposed oil and fat is further oxidized by a nearby catalyst,
It is decomposed into CO2 and H2O. Since the alkali is located near the catalyst rather than uniformly within the coating layer, it is more favorable for complete oxidation. Due to the above mechanism of action, the alkali-treated catalyst of the present invention is believed to be effective in purifying oils and fats. Next, the catalyst used in the present invention will be described. Catalysts that can be used in the present invention are metal oxides or double oxides.

Any metal oxide can be used as long as it has a catalytic action, and oxides of metals such as Mn, Cu, CO, Ni, Fe, and Cr are suitable. These metal oxides are
It may be mixed with a heat-resistant paint as a metal oxide, but it may also be used as a carbonate or hydroxide, which becomes a metal oxide after firing. In the present invention, the above-mentioned compound is treated with an alkali, and this operation changes the thermal properties of the catalyst. The drawing shows the relationship between heat treatment temperature and specific surface area of electrolytic manganese dioxide (γ-MnO2), where curve 1 is for the one subjected to the alkali treatment of the present invention and curve 2 is for the one without the alkali treatment.

The alkali treatment conditions were Na2cO3 2 as alkali.
It was immersed for 2S at 40C using a specified aqueous solution. This sample and one without alkali treatment were heat treated at each temperature for 1 hour, and the specific surface area was measured by the BET method.
As is clear from the figure, the specific surface area of the alkali-treated specimens decreases less at high temperatures than the untreated specimens.

This can be inferred as follows. The alkali adsorbed on the catalyst surface becomes Na2O, K2O,
It is thought that they remain in the form of K2CO3 and Na2CO, and act as inhibitors of sintering of manganese dioxide particles, thereby preventing a decrease in the specific surface area. Therefore, it is presumed that the alkali-treated catalyst contributes to heat resistance and long life. Among the metal oxide catalysts mentioned above, the preferred metal oxide catalyst used in the present invention is particularly manganese dioxide, which is advantageous for the complete oxidation reaction of fats and oils.

Next, a double oxide used in the same manner as the metal oxide will be described.

A double oxide is a higher-order compound consisting of two or more types of oxides, in which the presence of a group ion as an oxygen acid is not recognized in its structure.

The general formula is M(■)M(■)204(M(n) is 2
It is represented by a valent metal (M (■) indicates a trivalent metal) and has a spinel type structure. Particularly effective for the present invention is the one represented by M(■)Fe2O4,
(■) is Mn2+, Fe2+, CO2+, Ni2+, C
It consists of u2+, Zn2+, Ba2+, etc.

A double oxide with such a composition has high heat resistance and 10
Stable up to 00°C. Preferred double oxides for the present invention are:
It contains at least zinc oxide ZnO as one of its components, and ZrlFe2O as spinel.
It contains 4.

This ZnFe2O4 does not need to be added alone;
A mixture of Fe2O4 and MrlF'E2O is preferred. Those containing ZnO as one of the components have particularly excellent heat resistance and are chemically stable. Moreover, MrlF'E2O has an excellent promoter effect when MnO2 is selected as the metal oxide. Others, Ba
Fe2O, COFe2O, etc. are also effective. Next, a method for producing a self-purifying coating layer using the above-mentioned phosphate and catalyst will be explained. The most desirable metal base material for forming the coating layer is an aluminized steel plate coated with aluminum by hot-dip plating. Since this aluminized steel sheet has excellent heat resistance and corrosion resistance, it has the advantage that a self-cleaning coating layer can be formed only on one side. Moreover, the thermal properties of steel sheets depend on the base steel material.
No thermal distortion even when using thin steel plates. Additionally, the process of degreasing the base material can be performed more easily than with enameled steel plates. The catalyst is alkali treated before being mixed with the phosphate compound.

As mentioned above, the alkali treatment step is carried out by immersing the catalyst in an alkaline solution prepared in advance for a certain period of time. The immersion temperature also affects the amount of alkali adsorbed by the catalyst, so it is better to keep it at a constant temperature. After soaking, 12
Dry at a temperature of about 0°C. This catalyst is mixed with a phosphate solution using a ball mill or the like, and then applied to the substrate using a spray gun. The film thickness is an important factor that affects the performance of the self-cleaning coating layer, and the thicker the film thickness, the better the performance, but if it is too thick, the coating layer will crack, so it is desirable to rub 250 μml. After drying, the phosphate is cured by heating at about 300° C. for about 30 minutes. 500 when using phosphate alone
Although heating to a temperature of 300° C. or higher is necessary, curing is accelerated if a metal oxide such as a catalyst is present, and heating at about 300° C. is sufficient. A suitable heating temperature for curing the phosphate and forming the coating layer by heating the paint containing the catalyst and phosphate is 200-500'C. If the temperature is too high, the catalytic ability will decrease. In addition to the catalyst, it is also optional to add various refractory fillers for the purpose of increasing the porosity of the coating layer.

As the refractory filler, SiO. , Al2O3, MgO
, CaO, etc., and minerals containing these as one component are used. In addition, metal powders such as Ae and zn, and alloys thereof can also be used as the refractory filler. Furthermore, natural zeolite, synthetic zeolite, acid clay, activated clay and derivatives thereof, silica alumina, silica magnesia, alumina poria, etc. can also be used.

In addition, lime aluminate, calcium silicate, sodium silicate, titanium oxide, zirconium oxide, colloidal silica, colloidal alumina, or alkaline earth metal compounds are also effective in decomposing fatty acids. These fillers can be used alone or in combination of two or more. Further, the porosity forming agent is not limited to the above-mentioned inorganic fillers, but organic substances that cause thermal decomposition during firing may also be used.

Examples include polyethylene powder, polystyrene, carboxymethylcellulose, polyvinyl alcohol, methylcellulose, and the like. Next, embodiments of the present invention will be described.

Example 1 Ae2O3.3p205.6H as a phosphate compound
A 4% aqueous solution was prepared using monoaluminum phosphate shown by No. 20.

The catalyst contains electrolytic manganese dioxide and ZrlF'E2O,...
Using MnFe2O4, it was immersed in a 1N aqueous solution of Na2cO3 at 4(1)C for 24Tf, dried at 12C for 5 hours, and then mixed in an aqueous solution of monoaluminum phosphate.

Furthermore, a-Ae2O3 was used as a filler. These were blended in the following proportions and mixed in a ball mill to form a paint. Spray this paint to a thickness of 0.6 ugliness and a size of 5 x 1.
Film thickness after firing on 0C1ft aluminized steel plate is 20
After coating to a thickness of 0 μm, and drying at room temperature,
A sample was prepared by heat treating the two powders at 0°C. The performance of this sample was evaluated according to the test items shown below. (1) Performance test 100 m9 of lard oil was scattered on the coating layer at about 100 points, and heated for 30 minutes at each temperature of 200°C, 250°C, and 300°C. Then, the purification rate is calculated from the weight loss before and after heating.

(2) Bend the adhesion strength test piece to 18σC with the coating layer on the outside so that the diameter of the curved surface part is 1i, and depending on the degree of peeling, 0 is not peeled, 0 is partially peeled, and Δ is peeled. Classify as things ×.

(3) Based on corrosion resistance salt spray test method (JISZ-2371), 10
After exposure for one day, if no corrosion is observed, it is expressed as 0. If corrosion is observed, it is expressed as x.

(4) Water resistance The amount of weight loss after boiling for 1 m in a water bath at 95° C. or higher is measured and expressed as the amount of weight loss per 1a11.

(5) Surface Hardness When the surface is rubbed with a metal copper piece, the case where copper remains on the coating is rated as 0, and the case where the coating layer is scraped off is graded as x.

As a result of evaluation according to the above test items, the purification rate in the performance test was 32% at 200℃ and 7 at 25
6%, part% at 3(1)°C.

As a comparative example, a coating layer constructed in the same manner using a catalyst that was not treated with alkali was 11% at 200°C and 250°C at 200°C.
It was 45% at ℃ and 90% at 300C. In addition, the adhesion strength, corrosion resistance, and surface hardness are all O, and the water resistance is 0.5.
mg/Clf.

Example 2 Using a 3% by weight aqueous solution of magnesium phosphate in place of the primary aluminum phosphate aqueous solution of Example 1,
A sample was prepared under the same conditions as in Example 1.

As a result, the purification rate was 30% at 200℃ and 74% at 250C.
%, 30C) C was 96%. In addition, the adhesion strength, corrosion resistance, and surface hardness are all O, and the water resistance is 0.8m9/C.
It was hot. Example 3 Instead of filler a-A'20J in Example 1, A
The purification performance of samples prepared by adding 3 parts of each of e and zn powders was as shown in the following table.

Example 4 411% aqueous solution of monobasic aluminum phosphate
2ri 11th part CUO,
Equivalent mixture of CO3C4 and NiO
5 Heel weight part SiO, powder
8 Liquor section water 3
Weight: A coating material was prepared using the above-mentioned materials, and a coating layer was formed in the same manner as in Example 1.

Note that the catalyst mixture of CUO, CO3O4, and NiO was previously alkali-treated with a 1N aqueous solution of NaHCO3.

The purification rate of the obtained coating layer was 31% at 200'C, 250
It was 73% for C and 97% for 30CfC.

Example 5 In Example 4, when lime aluminate (Ae2O3.CaO-RfI2O) was used instead of SiO2 powder, the purification rate was 35% at 200°C, 76°C at 250°C, and 3% at 250°C.
It was 99% at 00°C.

In addition, the adhesion strength, corrosion resistance and surface hardness are O, and the water resistance is 1.0m9/C7l! It was hot. Example 6 To the coating material of Example 1, 3 parts by weight of polyethylene powder was added as a porosity forming agent.

The purification rate of the obtained coating layer was 36% at 200℃, 250℃.
It was 78% at 300°C and 99% at 300°C. Example 7 In Example 1, the coating layer was formed using a substrate with a enamel corrosion-resistant layer on an aluminized steel plate, and the corrosion resistance was O, and no corrosion occurred even after 30 days had passed. .

Example 8 In Example 1, 3 parts by weight of zeolite (F-9 manufactured by Toyo Soda Co., Ltd.) was added instead of a-Ae2O3.

The purification rate of the obtained coating layer was 33% at 200℃ and 250℃.
and 77% at 300°C. Example 9 Example 1
, the alkali treatment solution for the catalyst was changed to NaHCO3, KH
Using 1N aqueous solutions of CO3, NaOH, KOH, K2CO3, and NH4OH as a comparative example, the solution was heated at 40°C for 24 hours.
! It was immersed for IF and treated with alkali.

The resulting coating layer? ? The conversion rate is shown in Table 2. As is clear from the table, it can be seen that the use of the alkaline treatment liquid of the present invention provides excellent purification performance. Among the alkaline treatment liquids, carbonates are particularly preferred. Example 10 In Example 1, 3 parts by weight of a solid sodium silicate aqueous solution was further added as a hardening accelerator.

The purification rate of the obtained coating layer was 20CfC (%, 250℃
It was heated at 74°C and % at 300C. Furthermore, the adhesion strength, corrosion resistance, and surface hardness were 01, and the water resistance was 0.2 m9/Cll, and the water resistance was particularly excellent compared to others. As is clear from the above examples, the self-purifying coating layer of the present invention provides a high-performance coating layer that cannot be obtained with conventional heat-resistant paints containing phosphates by treating the catalyst with alkali. It is something to do.

This self-purifying coating layer can be used not only on the inner wall of a cooking appliance, but also as a catalyst for purifying exhaust gas by coating a metal surface and installing it in a gas passage. Furthermore, it can also be used as a tar decomposition catalyst in the oil vaporization section of various combustion equipment. As described above, the self-purifying coating layer of the present invention can be applied not only to the decomposition of oils and fats, but also to areas where catalytic oxidation reactions are required, such as the oxidation reactions of carbon monoxide and hydrocarbons. It can be installed as a low-cost catalyst layer.

[Brief explanation of the drawing]

The drawing compares the change in specific surface area of manganese dioxide used as a catalyst, with and without alkali treatment, depending on the heat treatment temperature.

Claims (1)

[Scope of Claims] 1. A method for producing a self-purifying coating layer, which comprises applying a paint containing an alkali-treated catalyst and a phosphate to a coated surface, and then curing the phosphate by heating. 2 Phosphate has the formula MO・xP_2O_5・yH_2O
(However, x, y are real numbers, M is Al, Mg, Ca, Fe
, Cu, Ba, Ti, Mn, and Zn). 3. The method for producing a self-purifying coating layer according to claim 1, wherein the catalyst is selected from the group consisting of metal oxides and double oxides. 4. The method for producing a self-purifying coating layer according to claim 3, wherein the catalyst contains a manganese oxide. 5 Alkali treatment of the catalyst causes Na_2CO_3, NaH
A method for producing a self-purifying coating layer according to claim 1, which is carried out in an aqueous solution of an alkali selected from the group consisting of CO_3, K_2CO_3, KHCO_3, NaOH and KOH. 6. The method for producing a self-purifying coating layer according to claim 1, wherein the heating temperature is 200 to 500°C.