JPS6113505B2 - - Google Patents

Description

[Detailed description of the invention]

The purpose of the present invention is to use silicon as a special surface treatment on aluminum-based metals that has a catalytic effect to suppress the formation of tar-like carbon. The present invention aims to provide a method for forming a coating layer based on an acid-based inorganic paint and a catalyst compound added thereto. Home appliances that generate tar-like carbon and cause problems include, for example, oil, food residue, etc. that scatter, generate strange odors, or become sticky and filthy, and are disliked. Typical products include cooking utensils such as various ovens, and oil-burning appliances that generate hard carbon, resulting in reduced combustion and various safety-related problems. In particular, the places where these tar-like substances are generated are heated parts of the metal surface, and are used because they have good thermal conductivity and excellent corrosion resistance at high temperatures. Aluminum or aluminized metal is often used as the metal. The present inventors have already discovered that as a coating to achieve the above object, on a metal surface, an inorganic paint containing an alkali metal silicate, a metal phosphate, and a pigment is used as a coating based on (A) group A of the periodic table. or A group oxide (B) or a compound containing them, with the formula (M _A ) _x (M _B ) _y
(O) In the compound represented by _z , M _A is a group A or an element of the A group, M B is a group B or an element of the A group, and M _B is a group B or an element of the A group.
A group element, O represents oxygen, and x, y, and z represent integers. It has been found that a coating material containing at least one selected from the above groups (A) and (B) is effective. However, when developing this and applying it to products,
If you try to apply the above coating directly to the surface of an aluminum material, since the paint itself is a strong alkaline (PH: 9-10), the following reaction will occur: 2Al + 2NaOH + 2H ₂ O → 2NaAlO ₂ + 3H ₂ . The hydrogen generated will form a coating film. It blistered and foamed inside, making it extremely difficult to actually form a coating layer on aluminum. The present invention aims to provide a method that can effectively solve this problem. Conventionally, it has been extremely difficult to apply this type of water glass paint itself onto aluminum or aluminum-coated metal due to the above-mentioned bubbling phenomenon. Various developments were attempted, mainly to improve the system, but nothing technically completed was known. In order to improve the paint itself, attempts were made to lower the Na ₂ O / SiO ₂ ratio, add as much curing agent as possible, add fillers to suppress reaction with alkali, and make it porous to suppress foaming. In the former case, there are methods that add surfactants, organic solvents, etc. to effectively release the hydrogen generated by the reaction from the coating film. It certainly has some foaming suppression effect,
Although a certain coating film was formed, there was a problem in terms of adhesion. On the other hand, in the latter case, although a certain level of paint film adhesion was obtained, a large number of pinholes were formed in the paint film, leaving problems with the corrosion resistance of the equipment in practical use. Furthermore, both had the disadvantage that foaming was inevitable when trying to increase the thickness of the coating and stacking the coating layers. When a catalyst that has the ability to decompose and vaporize oils such as salad oil is added to a silicate-based paint,
Most of these types of catalysts increase the viscosity of paints of this type and also act as curing accelerators, so if you try to use the above improved type paints as they are, the viscosity will be very high. This has increased to the point where it is difficult to apply it practically, for example, by air spraying. Furthermore, although many of the additives used to exhibit the catalytic effect are alkaline compounds, the possibility of foaming increases compared to the case where only the paint is used. It depends on the reaction below. 2Al+K ₂ CO ₃ +3H ₂ O →2KAlO ₂ +CO ₂ +3H _2It has been difficult to prevent these problems by simply improving the paint. Examples of the present invention will be described in detail below. In order to search for catalytically active substances that effectively decompose oil, we used a gas chromatograph and a pyrolysis device to pyrolyze salad oil (soybean oil) in the air while it was in contact with various metal oxides. The generated gas was analyzed using a gas chromatograph, and metal oxide systems with particularly excellent thermal decomposition ability were evaluated. Although carbon monoxide and formaldehyde were identified as decomposition gases, they also detected decomposed hydrocarbons that are different from the components contained in salad oil itself. The test conditions were approximately 2mg of metal oxide mixed with 1.0μ of salad oil using a microsyringe, and heated at 300℃ for 10 minutes in a sealed glass container.
After decomposition, the resulting gas was introduced into a gas chromatograph and analyzed. The analysis conditions were as follows: _N2 carrier was used (60
ml/min) With the FID detector ( _H2 flow rate: 60ml/min, air flow rate 0.5/min), the column conditions are 3 mmφ.
Silicon GE.SE−305 with ×3m stainless steel column
% liquid phase (Simalite W carrier) and held at 150°C for 5 minutes, then heated to 250°C at a heating rate of 5°C/min.
Decomposition gas was detected by temperature-rising analysis. 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. Table 1 shows the area integration results for typical metal oxides (values integrated using a digital integrator, sum of 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 (soybean oil) in the presence of air include oxides of metals from groups to groups of the periodic table, especially group A, Examples include oxides of Group A alkali and alkaline earth metals. This is because these substances are known to have a weak partial oxidation ability, and when it comes to thermal decomposition of unsaturated fatty acids, which are the main components of salad oil, they decompose through intermediates of partially oxidized compounds. Although the mechanism is presumed, these catalysts, which are known to have a weak partial oxidation ability, activate this reaction and release the oil before the hydrogen abstraction polymerization reaction that proceeds in parallel. The basic idea of the inventors was that as a result of decomposing and evaporating the oil, it would suppress the oil from turning into tar and exert a so-called self-cleaning effect. It became clear that this was correct.

[Table] In Table 1, the more excellent compounds are:
A compound expressed in the form (M _A ) _x (M _B ) _y (O) _z , where M _A is a group A or group A element, and M _B is a B
It can be seen that group or B group elements are good. In particular, M _A consists of Na, K, Ca, and Mg, and M _B
It turns out that this is the best when using a compound consisting of C, Si, and Al. Based on the catalyst extracted above, this catalyst is added to an inorganic heat-resistant paint consisting of an alkali metal silicate, a hardening agent, a pigment, etc., and the above-mentioned catalytically active substance is added to form a blended paint. It was painted on a treated steel plate and its physical properties and self-cleaning effect were tested.
Aluminized steel sheets were subjected to various treatments, and the paintability and physical properties of the coating films were investigated. A series of tests were conducted using Shikoku Kaken Kogyo Co., Ltd.'s "Ceramitite 'King'" (commercial product) [black type]. The experimental results are shown in Table 2. As shown in Table 2, as a result of conducting comparative tests on various pretreatment methods, it was confirmed that chemical conversion treatment etched the aluminum plating film and was hardly effective as a countermeasure against foaming. On the other hand, a pretreatment method of forming an oxide film on the aluminum surface was extremely effective.

[Table] The film thickness of the oxide film was evaluated for those subjected to boehmite treatment and thermal oxidation treatment. About 5 μ at most, 5
It has been confirmed that if the test is carried out in excess of μ, the coating tends to crack and the color of the oxide film tends to turn gray. Regarding the oxidized film, it is desirable that the thickness is 5μ or less.
On the other hand, alumite was not effective because in reality, almost no alumite layer was formed. Regarding the heat treatment conditions, the results of evaluating the relationship between temperature and time are shown in the figure.
It can be seen that it is effective under conditions of 20 minutes or more at temperatures above ℃. In the figure, ○ indicates effectiveness, and × indicates foaming. Next, as a catalyst, calcium silicate: 1wt
%, alumina cement: 4wt% was added to the previous paint, and at the same time, a similar test was conducted by adding glycerin at a rate of 8ml/100g paint, but it was confirmed that the same results as above were obtained. did. Next, salad oil was added to evaluate the purification ability, and 30 points of oil were removed by 1μ in a 10-minute test period, but all traces disappeared and effective purification ability was maintained. I confirmed that The results of various adhesion evaluation tests were also good, and it was confirmed that the performance was actually improved compared to the case of iron plates. Furthermore, the advantage of this surface treatment method is that there is a concern that aluminum may corrode through pinholes in the paint film if left as is, but this treatment significantly improves corrosion resistance. There are some points where it can be effective. As described above, the present invention provides a surface treatment method that brings about extremely excellent industrial effects.

[Brief explanation of the drawing]

The figure is a diagram of heat treatment conditions.

Claims (1)

[Claims] 1. 5μ by heat treatment on aluminum material
After forming the following oxide film layer, silicate,
The surface of an aluminum material coated with a paint based on an inorganic paint containing a curing agent and a pigment, and containing at least one compound selected from the following groups (A) and (B). Processing method. (A) Oxide of group A or group A of the periodic table. (B) Compounds containing these, having the formula (M _A ) _x (M _B ) _y
(O) A compound represented by _z . However, M _A is an element of group A or group A,
M _B is group B or an element of group B, O is oxygen,
x, y, z represent integers. 2. The method for surface treatment of an aluminum material according to claim 1, wherein an oxide film layer is formed by filter heat treatment at 400° C. or higher for 20 minutes or longer. 3 (A) group: Na ₂ O, K ₂ O, CaO, MgO, (B)
As a group, M _A consists of Na, K, Ca, Mg, and M _B
A method for surface treatment of an aluminum material according to claim 1, using a compound consisting of C, Si, and Al.