JPH06145561A - Coating film having heat-insulation property - Google Patents

Abstract

PURPOSE:To obtain the title film having a coefficient of thermal expansion near to that of the metallic substrate and being usable in a high-temperature region by mixing a specified amount of a ceramic powder mainly consisting of iron oxide powder particles with a binder. CONSTITUTION:A ceramic powder consisting mainly of powder particles of at least one iron oxide selected from among Fed, Fe2O3 and Fe2O3 is mixed with a binder to produce a coating material. This coating material is preapred in a mixing ratio such that the ceramic powder particles account for at least 30 vol. % based on the volume of the coating film obtained by applying the coating material and drying the wet film. This material is then applied to a metallic substrate such as a stainless steel substrate which can with-stand high- temperature service, and the wet film is dried to form an insulation coating film. Because the coefficient of thermal expansion of the coating film can be matched with that of the metallic substrate, the film does not suffer damages, peeling, etc., even in service in a high-temperature region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat insulating coating film. This coating film can be applied to equipment used in a high temperature range such as exhaust system equipment such as an exhaust manifold used in an internal combustion engine.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 58-99180 uses a slurry composed of a mixture of zirconia powder particles, an inorganic binder such as colloidal silica and a frit.
It is disclosed that a slurry film is formed on the inner surface of a metal device such as cast iron that is exposed to high-temperature exhaust gas, and the slurry film is solidified to form a heat-insulating coating film.

Further, conventionally, a liquid paint called red iron oxide, which is a mixture of powder particles of Fe ₂ O ₃ and a binder such as water glass, has been used. The liquid paint is applied to the surface of a steel material and solidified to form a coating film. Is formed to secure the corrosion resistance of the surface of the steel material.

[0004]

By the way, it is preferable that the film used in a high temperature range has a small difference in thermal expansion from the base material. Here, the thermal expansion coefficient of zirconia in the region of 20 to 800 ° C. is 10 × 10 ⁻⁶ , and that of alumina is 9 × 10 ^−6.
Larger than ^-6 , but metal (steel, cast iron: 11 x 10 ^-6
It is small compared to ~ 14 × 10 ^-6 ). Therefore, a difference in thermal expansion between the coating film and the base material is inevitably generated. In this case, the temperature rise,
When cooling is repeated, the coating film is likely to be damaged or peeled off. In particular, in an exhaust system device used in an internal combustion engine, since temperature rising and cooling are repeatedly performed, damage and peeling of the coating film are likely to occur.

Further, the coating film formed of the above-mentioned red iron oxide paint is only used at room temperature. Furthermore, F which is a constituent of a coating film formed from red iron oxide paint
The coefficient of thermal expansion of e ₂ O ₃ is as high as 13 × 10 ^−6, which is close to that of a metal base material, but the volume ratio of Fe ₂ O ₃ powder particles in this coating film is small. The reason is that the powder ratio in the liquid paint is 10 vo
It is kept below 1% to prevent the viscosity of the paint and the curing rate from rising, and the powder ratio is 20 vol% even in the coating film after solidification.
It is the following. FIG. 3 schematically shows the structure of a coating film (powder ratio is 20 vol%) formed of red iron oxide paint. Figure 3
As can be seen from the above, the white particles on the binder are arranged in islands. In addition, in FIG. 3, island-shaped black portions indicate pores.

As described above, since the coating film formed of red iron oxide paint has a small powder ratio, the high thermal expansion property of Fe ₂ O ₃ cannot be expected sufficiently, and the thermal expansion coefficient of the coating film is set to that of the metal base material. It cannot be expected to match the coefficient of thermal expansion. Further, when the coating film is solidified, a large amount of the binder in the coating material shrinks, so that a crack is generated inside the coating film, and when the coating film is used, the crack easily becomes a starting point and peels the coating film.

The present invention has been made in view of the above situation, and an object thereof is to adapt a coefficient of thermal expansion to a metal base material,
An object of the present invention is to provide a coating film having a heat insulating property, which can be used in a high temperature region and which can enhance peeling resistance.

[0008]

The inventor of the present invention has made intensive efforts to achieve the above-mentioned object, and has been developing FeO, Fe ₂ O ₃ and Fe.
₃ O ₄ iron oxide has a small heat transfer coefficient and can be expected to have heat insulating properties of the coating film, and the volume of the coating of ceramic powder containing iron oxide powder particles of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ as the main component. The coating film of the present invention has been completed, paying attention to the fact that if the ratio is increased, the thermal expansion coefficient of the coating film is easily adapted to the thermal expansion coefficient of the metal base material.

The heat-insulating coating film according to the present invention is made of Fe.
A coating film used in a high temperature range, which is composed of a ceramic powder containing iron oxide powder particles of at least one of O, Fe ₂ O ₃ and Fe ₃ O ₄ as a main component, and the remainder substantially a binder. If the volume of the coating film is 100 vol%, the ceramic powder particles are characterized by being 30 vol% or more.

Ceramic powders are FeO, Fe ₂ O ₃
And iron oxide powder particles containing at least one of Fe ₃ O ₄ as a main component. When the volume of the coating film is 100 vol%, the volume ratio of the ceramic powder particles is 3
It is preferably 0 vol% or more, and more preferably 50 vol% or more. Here, just by mixing the ceramic powder particles,
Like the coating film formed from red iron oxide paint, the volume ratio of the ceramic powder particles in the coating film does not exceed 30 vol% and is at most about 20 vol%. Effective means of increasing the volume ratio are, for example, to mix and use ceramic powder particles having a small particle diameter, or to disperse the powder particles by using a dispersant such as a surfactant to prevent the aggregation thereof.

Further, in the present invention, the proportion of iron oxide in the ceramic powder is 10% of the whole ceramic powder particle.
When it is 0 vol%, the volume ratio of the iron oxide powder particles is preferably 20 vol% or more.

[0012]

Since the coating film according to the present invention has a high powder ratio, the bondability of the powder particles in the coating film increases and the thermal expansion coefficient of the coating film approaches that of the metal base material.

[0013]

【Example】

[Test Example 1] (Base material) As a base material, a cast iron test piece (diameter: 30 m)
m, length 20 mm), the surface is roughened by shot blasting to a surface roughness Rz of 70 μ, and the top surface of the test piece is used as the coating surface. The shot blasting treatment was performed using 100 μ alumina grid material.

(Paint) As the ceramic powder, a fine powder of Fe ₂ O ₃ having a particle size of 1 to ₂ μm and a particle size of 20 to 40
μm Fe ₂ O ₃ coarse powder was used. Then, the fine powder: the coarse powder was mixed with a V-type powder mixer in a weight ratio of 30:70 to obtain a raw material aggregate. In addition, Na ₂ O ・ S
water glass solution obtained by dissolving iO ₂ with distilled water (concentration 3
0 wt%) was prepared and used as a binder solution.

Then, the raw aggregate and the binder solution are mixed in a volume ratio of 50:50, and the aggregate weight is 1: 1.
When the amount was 00 wt%, a dispersant was added at a rate of 5 wt%, and the mixture was sufficiently stirred to prepare a slurry-like coating material. The dispersant is a commercially available product having a polycarboxylic acid group (SNOPCO SN Dispersant 5040). This addition, the agglomeration of the aggregate to each other, that Fe ₂ O ₃ powder particles can be prevented, Fe ₂ O ₃ wettability between powder particles and the binder is improved, thereby 50 vol% ones large amount of aggregate, i.e. Fe ₂ It has become possible to produce a slurry raw material having O ₃ powder.

(Coating) This paint was coated with a brush on the top surface of the cast iron test piece described above. After coating, it was dried at room temperature, and after confirming that water on the surface had evaporated, the test piece was put into a drying oven at 200 ° C. and dried for about 2 hours. By this step, the water glass in the binder undergoes a curing reaction and the film is cured. After drying, the film thickness was measured and found to be 100 μm.
Furthermore, the above process was repeated once more, and the film thickness was measured again, and it was found to be 300 μm, so the treatment was completed.

(Firing) The test piece treated as described above was placed in an atmospheric furnace and baked at 500 ° C. for 5 hours to form a coating film. This treatment is intended to complete the reaction of the binder. The coating film is formed by the above processing. (Structure Observation) The coating film produced in Test Example 1 was free from defects such as peeling and cracks from the appearance. Further, the coating film was cut vertically and the cross-sectional structure was observed with an electron microscope, but no crack was observed at the interface between the base material and the coating film.

(Measurement of Volume Ratio of Aggregate in Coating Film) Based on the area ratio of the aggregate in the coating film, the volume ratio of the aggregate in the coating film was obtained. Specifically, an image analysis processor (Nikole Co., Ltd., model Luzex III) was used to measure the ratio of both to a certain area by utilizing the apparent difference in shade between the aggregate and the binder. . Each sample was measured at 5 to 10 points and averaged. As a result, the volume ratio of the aggregate in the coating film, that is, the volume of the coating film in the solidified state is 100 vol%.
, The proportion of Fe ₂ O ₃ powder particles is 65 vol%
Met.

[Form] The base material of the present invention is
A metal material that can withstand use at high temperatures, specifically, iron-based materials such as cast iron, steel and stainless steel, or N
It is a high heat resistant metal material such as Inconel containing i and Co as main components. In the present invention, as described above, in order to match the coefficient of thermal expansion of these metal base materials and the coating film, an aggregate containing iron oxide such as Fe ₂ O ₃ having a large coefficient of thermal expansion as a main component is used. There is something. However, the coefficient of thermal expansion of the above metal material does not always match that of iron oxide such as Fe ₂ O _3, and powder particles of another material are added to the coating film to match the coefficient of thermal expansion between the base material and the coating film. In some cases, it may be more preferable to try. Hereinafter, an example of the form of matching will be described.

That is, Table 1 shows the volume of the coating film as 100 vol.
When the volume ratio of the powder particles is 50% when it is defined as%, it shows a mode in which the thermal expansion coefficient of the coating film is matched with various metal base materials. At this volume ratio of the powder particles, most of the particles are joined and connected in the coating film, and it can be understood that the thermal expansion coefficient of the particles is substantially the thermal expansion coefficient of the coating film. Here, the thermal expansion coefficient of iron oxide is 20 × 800 ° C., and FeO is 13 × 10 ⁻⁶ and Fe ₂ O ₃ is 13 × 1.
0 ^-6, Fe ₃ O ₄ is 16.5 × 10 ^-6, Among them, the most thermal expansion coefficient is large is Fe ₃ O _4.

[0021]

[Table 1]

No. 1 in Table 1 As shown in A, when the base material is cast iron (FC20), the aggregate is made of Fe ₂ O ₃ 100
If it is vol%, matching is achieved. No. As shown in B, when the base material is Ni-resist cast iron, if the aggregate is Fe ₃ O ₄ 100 vol%, matching can be achieved. No. As shown in C, when the base material is ferritic stainless steel (SUS430) having a relatively small coefficient of thermal expansion, the aggregate is made of Fe ₂ O ₃ at 50 vol% and ZrO.
_{If 2} is 50 vol%, matching is achieved. Alternatively, No. As shown in D, when the base material is also ferritic stainless steel (SUS430),
63 vol% Fe ₂ O _{3 and} 37 v Al ₂ O ₃ aggregate
If it is ol%, matching can be achieved. No. As shown in E, the base material is ferritic stainless steel (SUS43
0), Fe ₃ O ₄ is 20 vol.
% And ZrO ₂ is 80 vol%, matching is achieved. No. As shown in F, the base material is a Ni-based alloy (Inc
In the case of oneel600), if Fe ₃ O ₄ is 83 vol% and ZrO ₂ is 17 vol%, matching can be achieved.

The above-mentioned No. C, No. D, No. In E, a case where ferritic stainless steel (SUS430) having a relatively small coefficient of thermal expansion is used as a base material, and in this case, in order to match the coefficient of thermal expansion, ZrO ₂ (coefficient of thermal expansion 10 × 10 ^{− 6} ), Al ₂ O ₃ (coefficient of thermal expansion 9.0 ×
10 ^-6 ) is used. [Test Example 2] By changing the volume ratio of the aggregate in the coating film,
The effect was measured. The same ceramic powder and binder as those used in Test Example 1 were used for the measurement.

The results are shown in Table 2. As shown in Table 2,
In all the test pieces, the volume ratio of the aggregate in the coating film after solidification is higher than the volume ratio of the aggregate in the slurry. The reason is due to evaporation and solidification of water in the binder. Further, the relationship between the proportions of the aggregate before and after the solidification is shown by a circle in FIG. A characteristic line W1 related to the solid line in FIG. 1 shows the relationship when the evaporation component such as water in the slurry is completely evaporated and the coating film is ideally contracted. Figure 1
It is considered that the fact that all of the circles are below the characteristic line W1 in Fig. 6 indicates that the coating film does not completely shrink and pores are generated inside, so that the proportion of the aggregate decreases.

Further, as indicated by the mark ◯ in FIG. 1, the reason why the proportion of the aggregate in the coating film after solidification does not rise to about 66 vol% or more is that even if the compaction of the particles progresses, 3
This is because voids of 0 vol% are inevitably formed. The relationship between the volume ratio of the aggregate and the state of the coating film will be described. That is, as can be understood from Table 2, looking at the relationship between the volume ratio of the aggregate and the state of the coating film, the volume ratio of the aggregate in the slurry was 1
5 vol% or less (aggregate ratio in the coating film after solidification is 25v
ol% or less), cracks are generated inside the coating film.
It is considered that this is because, in this range, the amount of binder is large and the shrinkage amount of the coating film is large. Further, in this range, the pore diameter of the pores contained in the coating film is also large, and there is a high possibility that it will be a starting point of crack generation during use. The volume ratio of the aggregate Fe ₂ O ₃ powder particles in the coating film after solidification was 5
When the content is 0 vol% or more, observation by an electron microscope shows that interparticle bonding has occurred and particles are in contact with each other.
In this case, the thermal expansion coefficient of the Fe ₂ O ₃ powder particles can be regarded as substantially the thermal expansion coefficient of the coating film.

However, when the content is 50 vol% or less, water glass as a binder exists between the particles, and the average value of both materials of the particles and water glass becomes the coefficient of thermal expansion of the coating film. In addition, cracks may occur between the particles and the binder due to the difference in coefficient of thermal expansion between the two materials.
FIG. 2 shows a coating film formed with a volume ratio of Fe ₂ O ₃ powder particles of 50 vol% when the coating film is 100 vol%,
1 schematically shows a structure observed with an electron microscope.
As shown in FIG. 2, in this coating film, the void portions between the coarse powder particles 10 having a relatively large particle diameter are filled with the fine powder particles 12 having a small particle diameter, so that the volume ratio of the powder particles is high. The binder 14 is arranged between them. The black islands are pores 16. As can be understood from FIG. 2, interparticle bonding occurs in this coating film, and as described above, the coefficient of thermal expansion of the Fe ₂ O ₃ powder particles is considered to be substantially the coefficient of thermal expansion of the coating film. You can Figure 4 shows Fe ₂ O ₃
It is an electron micrograph (x1000) which shows the structure of the coating film in which the volume ratio of powder particles is 40 vol%.

From the above results, the volume ratio of the aggregate in the coating film needs to be at least 30 vol% or more after solidification, and more preferably 50 vol% or more. The upper limit of the volume ratio of the aggregate in the coating film is generally 70 vol% which is the limit of the pressure density by the slurry method.
Is.

[0028]

[Table 2]

[Test Example 3] A coating film was formed on a cast iron test piece in the same procedure as in Test Example 1. At that time, those having different film thicknesses were prepared. The performance of the coating film of this test piece was investigated by a durability test by a thermal cycle. The durability test was carried out by heating the vicinity of the coating film with a burner for 20 to 30 seconds to 700 ° C. and then cooling it in water in the normal temperature range as one cycle, and measuring the number of cycles until peeling occurred. went. The results are shown in Table 3.

[0030]

[Table 3]

As shown in Table 3, it can be seen that the durability tends to deteriorate as the film thickness of the coating film increases. As can be understood from Table 3, in the coating film using the Fe ₂ O ₃ powder particles used in Example 1, the target 500 cycles is 500
It can be seen that it can withstand a film thickness of μm. Also, N in Table 3
o. 9-No. As shown in 11, a comparative example having a film thickness of 500 μm using ZrO ₂ powder, Al ₂ O ₃ powder, and cast iron powder as the ceramic powder constituting the aggregate was similarly tested. The results are also shown in Table 3.

As shown in Table 3, No. ₂ with a film thickness of 500 μm using powder particles of Fe ₂ O ₃ as an aggregate. It can be seen that in No. 4, the durability is remarkably improved as compared with the comparative example. It is considered that this is because the coefficient of thermal expansion of the coating film matches the coefficient of thermal expansion of the base material as described above. However, No. 1 using cast iron powder which is a comparative example. In No. 11, although the coefficient of thermal expansion should be similar to that of the base material cast iron, it does not show high durability. It is considered that this is because the cast iron powder, which is an aggregate, was oxidized at a high temperature and thermally expanded, thereby causing cracks in the coating film.

(Other Example) In Test Example 1 described above, the dispersant is added at a rate of 5 wt% when the weight of the aggregate is 100 wt%, but the present invention is not limited to this, and the amount can be increased or decreased as appropriate, for example, 5 It can be 10 wt%. Further, as the dispersant, those having a polycarboxylic acid group are adopted, but not limited to this,
Known ones can be adopted, for example, those having a naphthalene sulfonic acid group may be used. Although water glass is adopted as the inorganic binder in the above-described test examples, the inorganic binder is not limited to this, and silicates such as sodium silicate, potassium silicate, and lithium silicate, monoaluminum phosphate, and monopotassium phosphate. Alternatively, a phosphate such as primary magnesium phosphate, colloidal silica or the like may be adopted.

[0034]

According to the coating film having the heat insulating property of the present invention,
The coefficient of thermal expansion can be made close to that of the metal base material, and the peel resistance can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the content of powder particles in a slurry and the content of powder particles in a coating film after solidification.

FIG. 2 is a structural diagram schematically showing a state in which a particle structure of a coating film having a volume ratio of powder particles of 50 vol% is observed by an electron microscope.

FIG. 3 is a structural diagram in which a particle structure of a structure of a coating film formed of a conventional red iron oxide paint is observed by an electron microscope.

FIG. 4 is a photographic diagram showing a state in which the particle structure of the structure of a coating film in which the volume ratio of powder particles is 50 vol% is observed by an electron microscope.

[Explanation of symbols]

In the figure, 10 is a coarse powder particle, 12 is a fine powder particle, 14 is a binder, and 16 is a pore.

Claims (1)

[Claims] 1. Use in a high temperature range composed of a ceramic powder containing iron oxide powder particles consisting of at least one of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ as a main component, and the remainder being substantially a binder. A coating film having a heat insulating property, characterized in that the ceramic powder particles are 30 vol% or more when the volume of the coating film is 100 vol%.