JPS6412307B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an inorganic coating composition for forming a coating film having a catalytic action. More specifically,
The present invention relates to an inorganic coating composition for forming a coating film that uses acidic aluminum phosphate as a binder and has a catalytic action with excellent alkali resistance, water resistance, water vapor resistance, and adhesion. The inner surface of the oven becomes contaminated with oil, protein, fat, etc. that splatter from the food such as meat and oil during cooking. This contamination is a problem not only from an appearance standpoint but also from a practical standpoint, such as the transfer of odor. Conventionally, strong alkaline cleaning agents have been used to remove this oil and fat. Recently, ovens with a so-called self-cleaning coating layer on the inner surface, which uses various heat-resistant paints and enamel frit as a binder and contains a catalyst to decompose oils and fats, have become popular, and the inconvenience caused by oil and fat stains has been considerably reduced. has been done. However, the coating layer is usually not applied to the entire surface, and the areas not coated with the coating agent are contaminated. Furthermore, if a large amount of oil or fat adheres at once, the stains will become noticeable even if the coating layer is applied. In such cases, the method of removing stains is generally to spray a strongly alkaline oven cleaning agent onto the stained area and decompose the stain, but due to the alkaline nature of the cleaning agent, acidic phosphoric acid is used as a binder. A significant disadvantage of using aluminum is that the binder dissolves and the self-cleaning coating layer becomes disintegrated. In addition, stainless steel has traditionally been used as the inner wall material for ovens, but in order to reduce costs, the use of aluminum-treated steel sheets coated with heat-resistant paint is being considered; however, this aluminum-treated steel sheet has poor alkali resistance. Therefore, a paint with improved alkali resistance is desired. An object of the present invention is to overcome the above-mentioned problems of an inorganic coating composition for forming a coating film having a catalytic action using acidic aluminum phosphate as a binder, and based on this viewpoint, the present invention has been developed. As a result of intensive research, the inventors found that by using acidic aluminum phosphate as a binder and adding alkaline earth metal phosphates that had been specially heat-treated, a product with excellent alkali resistance, adhesion, and
The present inventors have discovered that an inorganic coating composition for forming a coating film that has excellent water resistance and water vapor resistance and has a catalytic action can be obtained, and has completed the present invention. That is, the present invention comprises acidic aluminum phosphate as a binder, a calcined alkaline earth metal phosphate, and an oxidation catalyst, and optionally contains a curing agent, a pigment, a filler, an auxiliary agent, etc. Can be cleaned with strong alkaline cleaning agents,
Another object of the present invention is to provide an inorganic coating composition for forming a coating film, which has excellent catalytic properties such as adhesion, water resistance, and water vapor resistance. Acidic aluminum phosphate is used as the binder, which is one of the components constituting the inorganic coating composition for forming a coating film having a catalytic action according to the present invention. As a binder for phosphate-based paints, acidic phosphates of alkaline earth metals such as magnesium and calcium and transition metals such as copper and iron are also used, but in the present invention, acidic aluminum phosphate is the best. It is preferably used because it exhibits excellent water resistance, water vapor resistance, and adhesion. A coating film using an acidic phosphate of an alkaline earth metal as a binder has superior alkali resistance compared to aluminum phosphate, but is inferior in water resistance and water vapor resistance. In the inorganic coating composition for forming a coating film having a catalytic action according to the present invention, each constituent component is appropriately mixed to obtain excellent physical properties, applied, and further baked and cured. The proportion of each component depends on the desired workability, physical properties,
Although it is selected depending on the surface condition, etc., the proportion of acidic aluminum phosphate is preferably 7% by weight or more on a dry basis in the entire coating composition, and if it is less than 7% by weight, adhesion may deteriorate. It becomes easier. The calcined alkaline earth metal phosphate, which is one of the components constituting the inorganic paint composition for forming a catalytic film according to the present invention, improves the alkali resistance of paints containing acidic aluminum phosphate as a binder. The purpose is to obtain an inorganic coating composition for forming a coating film having a catalytic action with excellent alkali resistance, water resistance, water vapor resistance, and adhesion. Calcined alkaline earth metal phosphate refers to alkaline earth metal phosphate heated at a temperature of usually about 350°C or higher, preferably about 600°C.
It is fired at ~1300℃, and the firing temperature is 350℃.
If the temperature is lower than ℃, the reactivity with the binder acidic aluminum phosphate increases, resulting in shorter pot life, lower adhesion, easier cracking, and poor water resistance and water vapor resistance. However, if an attempt is made to avoid the above-mentioned drawbacks by reducing the amount added, the effect of imparting alkali resistance will be reduced. The upper limit is not particularly limited, but it is difficult to crush the sintered material at high temperatures, the composition may change due to volatilization of phosphoric acid, energy costs increase, etc. Usually fired at below 1300℃. Such alkaline earth metal phosphates include tertiary phosphates of calcium, magnesium, strontium, and barium and/or phosphates with a higher proportion of alkaline earth metal than tertiary phosphates, that is, MO/ One type of alkaline earth metal phosphate expressed as P ₂ O ₅ (M represents an alkaline earth metal) and having a molar ratio of 3 or more, a mixture of two or more types, and double salts can be mentioned. . Especially _Ca3
Calcium phosphates such as (PO ₄ ) and Ca ₅ (PO ₄ ) ₃ OH are preferably used. Generally, the higher the proportion of calcined alkaline earth metal phosphate, the better the alkali resistance.
The alkaline earth metal phosphate also has the ability to act as a hardening agent for acidic metal phosphates, so if too large a quantity is added, adhesion may deteriorate and the coating film is likely to crack. This may cause other inconveniences. Therefore, the mixture of calcined alkaline earth metal phosphate to acidic aluminum phosphate is based on 100 parts by weight of aluminum phosphate on a dry basis.
10 to 150 parts by weight are preferred, especially 20 to 100 parts by weight.
If it is less than 10 parts by weight, it will be difficult to obtain the desired alkali resistance, and if it exceeds 150 parts by weight, the coating film will tend to crack or its adhesion will decrease. The oxidation catalyst, which is a constituent of the inorganic coating composition for forming a coating film having a catalytic action according to the present invention, is blended to decompose oils and fats. Such catalysts include those already known for forming self-purifying coatings, such as transition metal oxides such as manganese dioxide, copper oxide, nickel oxide, and iron oxide, such metal oxides, activated alumina, Examples include those in which a noble metal catalyst is supported on a carrier such as silica, and further examples include silica/alumina, zeolite, antimony oxide, etc. alone or in a mixture of two or more thereof. The amount of the oxidation catalyst to be blended is approximately 5 to 70% by weight based on the total coating composition. In addition to acidic aluminum phosphate and calcined alkaline earth metal phosphate, the inorganic coating composition for forming a coating film having a catalytic action of the present invention is formulated into a coating material to improve workability and film-forming properties. Pigments, fillers, and other auxiliary agents are mixed as necessary to improve the quality of the coating. It can be arbitrarily selected as long as it is added to the paint. For example, as pigments, compounds relatively stable against phosphoric acid such as red iron oxide, titanium oxide, chromium oxide, manganese dioxide, various spinel or reverse spinel type complex oxide ferrite compounds, and/or graphite are used. . As the filler, a refractory filler powder stable to phosphoric acid, such as quartz, alumina, mullite, zirconia, zircon, glass powder, silicon carbide, etc., is used. Other adjuvants include clay compounds such as bentonite as viscosity modifiers for paints and anti-settling agents for fillers, glycerin and ethylene glycol as drying retardants for paint films, and various organic emulsions for controlling surface conditions. Used as a modifier. Since the alkaline earth metal phosphate plays a role as a hardening agent, it is not particularly necessary to add a hardening agent, but a commonly known hardening agent used for acidic metal phosphates may be added. When applying the coating composition to a substrate, the coating composition of the present invention is first mixed and dispersed, and then applied to the substrate, but there are no particular limitations on the mixing and coating methods. Instead, commonly known processes and means are used, and dilution with water is also possible. The coated base material is further heat-cured, and generally a method of heat-curing at a temperature of 250°C or higher is adopted. As described in detail above, the inorganic coating composition for forming a coating film having a catalytic action, which uses the acidic aluminum phosphate of the present invention as a binder and contains a calcined alkaline earth metal phosphate, is different from the conventional acidic metal phosphate. It has the remarkable effect of improving alkali resistance, water resistance, and water vapor resistance, which are disadvantages of inorganic coating compositions for forming coating films that have a catalytic action using phosphate as a binder. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. Note that the physical properties were measured by the following method. Adhesion: Scotch tape was rubbed on the paint film and the state of peeling of the paint film was observed when it was strongly peeled off. Normal water resistance: Place the coated plate in boiling water,
Changes in appearance and adhesion after boiling for 1 hour were examined. Alkali resistance: The coated plate was immersed for 2 hours in an alkaline oven cleaning agent containing approximately 1% by weight NaOH aqueous solution as a solvent, and then washed with water. This was placed in the gas phase section of a pressure cooker, heated for 1 hour, and brought into contact with water vapor. This coating film was dried and examined for changes in appearance and adhesion. Ability to decompose salad oil: Salad oil was dropped onto the coating film at a concentration of approximately 2 mg/cm ² and the relationship between temperature and weight loss was investigated using a thermobalance. Table 1 shows the weight loss up to 300°C. Example 1 The composition shown in Table 1 and water were mixed in a ball mill to prepare a coating composition for forming a self-cleaning coating film having a clay content of about 2000 cp. Spray this paint onto an aluminized steel plate and apply 300
A coating sample having a coating film of approximately 150μ was obtained by heat curing for approximately 30 minutes at °C. The physical property measurement results for this sample were as shown in Table 1.

[Table] ◎ No abnormality ○ Slight discoloration △ Slight decrease in adhesion × Collapse and deterioration of the coating film From Table 1, when the product does not contain alkaline earth metal phosphates ( Example 1), when a phosphate other than acidic aluminum phosphate was used as a binder (Experiment Example 7), the boiling water resistance and alkali resistance were poor, and when an unfired alkaline earth metal phosphate was used. It is clear that a coating film having both adhesion and alkali resistance cannot be obtained in (Experimental Example 8). When acidic aluminum phosphate according to the method of the present invention is used as a binder and calcinable alkaline earth metal phosphate is added (experimental rows 2, 3, 4, 5).
and 6) exhibit excellent adhesion, water resistance, and alkali resistance, and it is clear that the self-purification ability does not deteriorate even with the addition of calcinable alkaline earth metal phosphate. Example 2 In the composition of Experimental Example 2 in Table 1, the catalyst
Even when MnO ₂ was replaced with a catalyst consisting of 40% by weight MnO ₂ , 10% by weight Ni, and 50% by weight activated alumina (carrier), the same excellent adhesion, boiling water resistance, alkali resistance, and salad properties as in Experimental Example 2 were obtained. It showed oil decomposition ability.

Claims (1)

[Claims] 1. Contains acidic aluminum phosphate as a binder, a calcined alkaline earth metal phosphate, and an oxidation catalyst, and optionally contains a curing agent, a pigment, a filler, and an auxiliary agent. An inorganic coating composition for forming a coating film having a catalytic action, comprising: 2 The calcined alkaline earth metal phosphate is approximately
The inorganic coating composition for forming a coating film having a catalytic action according to claim 1, which is an alkaline earth metal phosphate calcined at 350° C. or higher. 3 The calcined alkaline earth metal phosphate is approximately
Claim 1, characterized in that it is an alkaline earth metal phosphate calcined at 600 to 1300°C.
Alternatively, the inorganic coating composition for forming a coating film having a catalytic action according to item 2. 4 Alkaline earth metal phosphate with MO/P ₂ O ₅ (M
is an alkaline earth metal) and has a molar ratio of 3 or more;
An inorganic coating composition for forming a coating film having a catalytic action according to item 2 or 3. 5 Claim 1, characterized in that the alkaline earth metal phosphate is calcium phosphate.
An inorganic coating composition for forming a coating film having a catalytic action according to item 1, 2, 3 or 4.