JP2023016540A - Heat insulating film and heat insulating component - Google Patents

Abstract

To provide a heat insulating film which, despite being provided with an inorganic compound layer, overcomes various problems that arise due to the occurrence of voids or microcracks in the inorganic compound layer.SOLUTION: A heat insulating film 10 formed on at least a portion of the surface of a component 2 to be heat-insulated is formed from: an inorganic compound layer 20 in which scaly inorganic particles 22 are dispersed in an inorganic compound 21 formed from an alkoxide; and a top coat 30 that is formed on the inorganic compound layer 20, has a thickness of 0.5-30 μm, and is formed with an organic-inorganic hybrid material comprising a mixture of a metal alkoxide and a resin. By the formation of the top coat 30, voids 23 or microcracks in the inorganic compound layer 20 are filled with the organic/inorganic hybrid material, and the surface of the inorganic compound layer 20 is covered, so that the heat insulating performance of the heat insulating film 10 is enhanced, and fuel efficiency of an engine is improved by forming the heat insulating film 10 on piston top surfaces of the engine.SELECTED DRAWING: Figure 1

Description

The present invention relates to a heat shield film and a part (hereinafter referred to as "heat shield part") insulated by the formation of the heat shield film, for example, a heat shield film formed on the top surface of an engine piston , and a heat shielding component such as a piston on which the heat shielding film is formed.

In order to reduce the heat loss caused by the heat generated in the combustion chamber of the engine being released through the piston, etc., for the purpose of improving fuel efficiency, etc., a heat insulating film is formed on the top surface of the piston to improve thermal efficiency. Improvements are being made.

As such a heat insulating film, as shown in FIG. A configuration has been proposed in which the thermal barrier film 70 is formed of inorganic coating layers 72 (72a, 72b) made of an inorganic material such as silica, zirconia, alumina, and ceria containing hollow particles 80a, 80b. (See FIG. 4 of Patent Document 1).

In addition, in the resin heat insulating layer 71 provided in the heat insulating film described in Patent Document 1 and the inorganic coating layers 72 (72a, 72b) containing the hollow particles 80a, 80b, the high temperature such as the combustion chamber of the engine In view of the fact that the heat resistance in the environment is insufficient and the inorganic coating layer 72 (72a, 72b) is easily peeled off due to cracks, etc., as shown in FIG. , the heat insulating layer formed on the top surface of the piston 102 is formed by the alumite layer 241, and on this heat insulating layer (alumite layer) 241, scale-like inorganic particles are dispersed in an inorganic compound formed from alkoxide as a protective layer. It is proposed to form an inorganic compound layer 243 composed of a reference).

Japanese Patent No. 6067712 Japanese Patent No. 6339118

In the heat shield film 240 described in Patent Document 2 above, the heat insulating layer 71 formed by the resin and the hollow particles 80 in Patent Document 1 is changed to an alumite layer 241, and in Patent Document 1, the hollow particles 80a and 80b By replacing the inorganic coating layers 72 (72a, 72b) formed of an inorganic material with an inorganic compound layer (protective layer) 243 in which scale-like inorganic particles are dispersed in an inorganic compound formed from an alkoxide, This overcomes the weak point of the heat shield film 70 described in Patent Document 1, namely low heat resistance.

However, the inorganic compound layer 243 formed of alkoxide provided on the heat shield film 240 described in Patent Document 2 mentioned above is a liquid paint (a metal alkoxide solution containing inorganic particles) that becomes the inorganic compound layer 243 is applied to the piston 102. After coating the parts to be heat-shielded, such as the heat shielding target parts, the chemical reaction is caused by baking. Destruction such as cracks occurs.

Further, such destruction such as microcracks may occur not only when the inorganic compound layer 243 is baked, but also when heating and cooling are repeated due to use in a high-temperature environment after film formation.

The occurrence of voids and microcracks generated in the inorganic compound layer 243 in this manner serves as a starting point for peeling of the inorganic compound layer 243 or the like.

In addition, if the surface of the inorganic compound layer 243 becomes uneven due to the occurrence of microcracks and the surface area increases, the heat receiving area increases and the amount of heat transfer increases. function deteriorates.

In particular, in the configuration in which the heat shield film 240 of Patent Document 2 is provided on the top surface of the engine piston 102, if holes or microcracks occur in the inorganic compound layer 243, part of the fuel injected into the combustion chamber becomes empty. It soaks into the pores and microcracks and is retained in the pores and microcracks.

In addition, since the scaly inorganic particles dispersed in the inorganic compound layer 243 have liquid absorption properties, the fuel that has penetrated into the microcracks further penetrates into the scaly inorganic particles and is retained in the inorganic particles. .

In this way, the fuel held in pores, microcracks, scale-like inorganic particles, etc. is not burned even in the combustion process of the engine, and is discharged outside the aircraft as unburned fuel together with the exhaust gas. (Hereinafter, the fuel loss associated with the discharge of unburned fuel is referred to as "unburned loss".) increases.

In addition, the formation of the inorganic compound layer 243 on the top surface of the piston 102, which has an uneven surface due to the occurrence of microcracks, not only reduces the heat insulating properties of the heat insulating film 240 as described above, but also Abnormal explosion (knocking) is likely to occur on the top surface.

As a result, in an "actual engine test" in which the piston 102 with the heat shield film 240 described in Patent Document 2 was mounted on the engine, the heat loss was reduced by forming the heat shield film 240. In spite of this, a sufficient improvement in fuel efficiency could not be obtained.

As described above, the heat shielding film 240 of Patent Document 2, which includes the inorganic compound layer 243, has high heat shielding properties and heat resistance. I haven't been able to.

Therefore, the present invention has been made to solve the above-mentioned drawbacks of the prior art. It is an object of the present invention to provide a heat insulating film and a heat insulating component on which the heat insulating film is formed, which solves the various problems caused by cracks.

Means for solving the problems are described below together with the symbols used in the mode for carrying out the invention. This code is for clarifying the correspondence between the description of the claims and the description of the mode for carrying out the invention, and needless to say, it is used restrictively to interpret the technical scope of the present invention. It is not something that can be done.

In order to achieve the above object, the heat shield film 10 of the present invention is
In the heat shield film 10 formed on at least part of the surface of the heat shield target component 2,
an inorganic compound layer 20 in which scaly inorganic particles 22 are dispersed in an inorganic compound 21 formed from an alkoxide;
It is characterized by comprising a top coat 30 formed on the inorganic compound layer 20 and having a thickness of 0.5 to 30 μm and made of an organic-inorganic hybrid material composed of a mixture of metal alkoxide and resin. (Claim 1).

The surface of the top coat 30 preferably has a surface arithmetic mean height Sa defined in ISO 25178 of 0.1 to 1.5 μm, or an interface development area ratio Sdr of 0.01 to 1.5 (claim Item 2).

An anodized layer 40 can be further provided under the inorganic compound layer 20 (claim 3).

In addition, the heat shield part 1 of the present invention is formed by covering at least a part of the surface of the heat shield target part 2 with the heat shield film 10,
The heat shield film 10 is
an inorganic compound layer 20 in which scaly inorganic particles 22 are dispersed in an inorganic compound 21 formed from an alkoxide;
A top coat 30 formed on the inorganic compound layer 20 and having a thickness of 0.5 to 30 μm and made of an organic-inorganic hybrid material composed of a mixture of a metal alkoxide and a resin is provided. (Claim 4).

In the heat shielding component 1 having the above configuration, the surface of the top coat 30 has a surface arithmetic mean height Sa defined in ISO25178 of 0.1 to 1.5 μm, or an interface developed area ratio Sdr of 0.01 to 1. 0.5 (claim 5).

Further, an anodized film layer 40 can be further provided under the inorganic compound layer 20 (claim 6).

The part 2 to be heat-insulated may be an engine piston, preferably an engine piston made of an aluminum alloy (Claim 7).

With the configuration of the present invention described above, the heat shielding film 10 of the present invention and the heat shielding component 1 on which the heat shielding film 10 is formed have the following remarkable effects.

A top coat 30 made of an organic-inorganic hybrid material, which is a mixture of a metal alkoxide and a resin, is applied to a thickness of 0.5 to 30 μm on the inorganic compound layer 20 in which pores 23 and microcracks are generated during film formation. By providing a film thickness of , the inorganic compound layer 20 could be covered with the topcoat 30 in a state in which the organic-inorganic hybrid material was impregnated in the pores 23 and microcracks generated in the inorganic compound layer 20.

The top coat 30 is an organic-inorganic mixture of metal alkoxides, such as silicon alkoxide, zirconium alkoxide, and titanium alkoxide, which are inorganic components, and resins, which are organic components such as alkylsilicate resins, silicone resins, and fluorine-based resins. Because it is made of a hybrid material, it has both the high hardness and high heat resistance of the metal alkoxide, which is an inorganic component, and the flexibility of the resin, which is an organic component. Breakage such as microcracks is less likely to occur even when used in .

As a result, even when the heat shielding component 1 provided with the heat shielding film 10 of the present invention is used in a high-temperature environment, peeling of the topcoat 30 is difficult to occur, and the voids 23 and microcracks occur in the inorganic structure. The compound layer 20 is covered with the topcoat 30, and the organic-inorganic hybrid material constituting the topcoat 30 penetrates into the microcracks and the pores 23 and hardens, so that the pores 23 and the microcracks are used as starting points. It was possible to make it difficult to cause peeling of the inorganic compound layer 20 formed on the substrate.

In addition, since the surface of the heat shield film 10 is smoothed by the formation of the top coat 30, the surface area becomes smaller than when the surface is uneven, resulting in heat exchange on the surface of the heat shield film 10. is less likely to occur, and the heat shielding properties of the heat shield film 10 can be improved.

In particular, when the heat shield film 10 of the present invention is formed on the top surface of the piston of the engine, the surface of the inorganic compound layer 20 is covered with the top coat 30, so that part of the fuel injected into the combustion chamber becomes inorganic. Since the compound layer 20 does not soak into the pores 23, microcracks, and scaly inorganic particles 22 and is not retained, the unburned loss can be reduced.

In addition, by forming the top coat 30, the top surface of the piston becomes a smooth surface, thereby suppressing the occurrence of abnormal explosion (knocking) on the top surface of the piston.

As a result, by forming the heat shield film 10 of the present invention on the top surface of the piston of the engine, the fuel efficiency of the engine equipped with the piston could be improved.

BRIEF DESCRIPTION OF THE DRAWINGS Cross-sectional explanatory drawing which shows one structural example of the thermal insulation film of this invention. FIG. 4 is a cross-sectional explanatory view showing another configuration example of the heat shield film of the present invention. A laser microscope image (×50) of the surface of the heat shield film of Example 1. FIG. A laser microscope image (×50) of the surface of the heat shield film of Example 2. FIG. A laser microscope image (×50) of the surface of the heat shield film of Comparative Example 1. FIG. A surface image of the heat shield film of Comparative Example 2 (digital camera image obtained by a microscope) (×50). A laser microscope image (×50) of the surface of the heat shield film of Comparative Example 3. FIG. A cross-sectional SEM image (×2000) of the heat shield film of Example 1. FIG. A cross-sectional SEM image (×2000) of the heat shield film of Comparative Example 1. FIG. Cross-sectional explanatory drawing of the conventional thermal insulation film (corresponding to FIG. 4 of Patent Document 1). Cross-sectional explanatory drawing of the conventional thermal insulation film (corresponding to FIG. 10 of Patent Document 2).

Next, embodiments of the present invention will be described below with reference to the accompanying drawings.

In the following explanation, an example will be described in which the part 2 to be heat-insulated is the piston of the engine, and the heat-insulating film 10 of the present invention is formed on the top surface of the piston to form the heat-insulating part 1 of the present invention. The heat shielding film 10 of the present invention can be formed not only on engine pistons, but also on various articles requiring heat shielding, such as various machine parts used in high temperature environments.

[Overall structure of heat shield parts and heat shield film]
As shown in FIGS. 1 and 2, the heat shielding component 1 of the present invention includes a heat shielding target component 2, which is a metal part such as an engine piston, and at least a portion of the surface of the heat shielding target component 2, such as In the piston described above, it is constituted by a heat insulating film 10 formed on the top surface.

As shown in FIGS. 1 and 2, the heat shield film 10 is a film formed on the surface of the heat shield part 2 in order to block heat conduction to the heat shield part 2, and is made of alkoxide. It includes at least an inorganic compound layer 20 in which scaly inorganic particles 22 are dispersed in an inorganic compound 21 and a topcoat 30 formed from an organic-inorganic hybrid material that is a mixture of a metal alkoxide and a resin.

The heat shield film 10 in FIG. 1 is a two-layer structure heat shield film 10 formed of the inorganic compound layer 20 and the topcoat 30 described above, and FIG. , and an anodized film layer 40 formed under the inorganic compound layer 20. The thermal barrier film 10 has a three-layer structure.

As shown in FIG. 2, when the anodized film layer 40 is provided on the lower layer of the inorganic compound layer 20, the part 2 to be heat-insulated is made of aluminum or an aluminum alloy, and the part 2 to be heat-insulated is subjected to anodization treatment in advance. An anodized film layer (alumite layer) 40 may be formed in advance, and the inorganic compound layer 20 and the topcoat 30 may be formed on the anodized film layer (alumite layer) 40 .

Such an alumite layer 40 can be formed by anodic oxidation of aluminum using an acidic aqueous solution of sulfuric acid, oxalic acid, phosphoric acid, etc., and its film thickness ranges from 10 to 100 μm.

By providing the alumite layer 40 under the inorganic compound layer 20 in this way, the adhesion between the inorganic compound layer 20 and the base material of the aluminum alloy piston can be improved.

The heat shield film 10 of the present invention is not limited to the structure shown in FIGS. 1 and 2. In the heat shield film 10 having the structure shown in FIG. A configuration in which a known heat insulating layer such as a heat insulating layer made of an inorganic material is provided, and a known heat insulating layer such as a heat insulating layer made of an inorganic material in which the hollow particles are dispersed are provided between the alumite layer 40 and the inorganic compound layer 20 in FIG. A configuration in which a heat insulating layer is provided may be employed, and various configurations can be employed as long as the configuration comprises at least the inorganic compound layer 20 and the topcoat 30 described above.

[Inorganic compound layer]
Among the layers constituting the heat shield film 10 of the present invention, the inorganic compound layer 20 has a structure in which scale-like inorganic particles 22 are dispersed in an inorganic compound 21 formed from an alkoxide, as described above. As shown in FIGS. 1 and 2, scale-like inorganic particles 22 arranged in parallel with the surface of the heat shielding target part 2 in the longitudinal direction are formed from an alkoxide with an inorganic compound 21 as a binder. It has a combined structure.

The inorganic compound 21 forming the inorganic compound layer 20 is composed of a metal oxide formed from an alkoxide such as silicon alkoxide, zirconium alkoxide, aluminum alkoxide and cerium alkoxide.

In particular, zirconium alkoxide is preferable because it has toughness and can easily follow the elongation of the heat-insulated part 2, which is a piston made of an aluminum alloy.

Thus, since the inorganic compound 21 of the inorganic compound layer 20 is composed of a metal oxide formed from an alkoxide, water and alcohol are generated as by-products when the alkoxide is treated, but these can be easily removed by heat treatment. It is possible to

As a result, it is possible to prevent foreign matter from remaining, so that it is possible to improve the heat resistance.

A binder having an amino group (—NH ₂ ) is dispersed in the inorganic compound 21, and examples of such a binder include aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and aminopropylmethyldimethoxysilane. An amino-based coupling agent such as can be used.

Such an amino coupling agent is added in an amount of 0.1 mass % to 10 mass % with respect to 100 mass % of paint (not including scale-like inorganic particles) which is a metal alkoxide solution.

The thickness of the inorganic compound layer 20 constructed as described above is 10 to 500 μm, preferably 10 to 200 μm.

Examples of the scale-like inorganic particles 22 dispersed in the inorganic compound 21 include mica, talc, and wollastonite. Any one of these may be used alone, or any of them may be used. It is also possible to use a mixture of two or all three types.

Mica, talc, and wollastonite do not melt even at high temperatures of about 1000° C. and have sufficient heat resistance.

Here, scale-like refers to a shape with a thickness that is sufficiently small relative to the length, and in addition to plate-like and flake-like shapes, if the thickness is sufficiently small relative to the length, fibrous and needle-like shapes are also included in the scaly form here.

The size of the scale-like inorganic particles 22 dispersed in the inorganic compound layer 20 is preferably about 0.1 to 100 μm, more preferably about 1 to 20 μm in average particle size.

Such scale-like inorganic particles 22 are dispersed in the inorganic compound 21 so that 35 to 75 vol % of the inorganic compound layer 20 becomes the inorganic particles 22 .

By adding such scale-like inorganic particles, it is possible to suppress peeling of the inorganic compound layer 20, and it is possible to ensure high heat shielding properties even in a high-temperature environment.

[top coat]
The topcoat 30 formed on the inorganic compound layer 20 is a mixture of a metal alkoxide such as silicon alkoxide, zirconium alkoxide, and titanium alkoxide, and a resin having excellent heat resistance such as alkylsilicate resin, silicone resin, and fluorine resin. It is formed from an organic-inorganic hybrid material consisting of

By forming the top coat 30 in a thickness range of 0.5 to 30 μm, the organic-inorganic hybrid material is impregnated into the pores 23 and microcracks generated in the inorganic compound layer 20. You can cover the top.

This makes it possible to reinforce the inorganic compound layer 20 in which the pores 23 and microcracks are generated, and to flatten the surface of the heat shield film 10, thereby improving the heat shielding property of the heat shield film 10. .

In addition, when the heat shield film 10 having such a top coat 30 is formed on the top surface of the piston, the fuel penetrates into the pores 23 and cracks of the inorganic compound layer 20 and the scale-like inorganic particles 22. In addition, by making the surface of the heat shield film 10 smooth, it is possible to prevent abnormal fuel combustion (knocking) from occurring on the top surface of the piston.

The thinner the film thickness of the top coat 30 is, the lower the effect of fuel penetration into the inorganic compound layer 20 is. It becomes difficult to maintain 30 in good condition.

Therefore, the film thickness of the topcoat is preferably 0.5-30 μm, more preferably 0.5-10 μm.

As described above, the formation of the top coat 30 smoothes the surface of the heat shield film 10, which improves the heat shield performance due to the reduction in the surface area and prevents the occurrence of abnormal combustion (knocking) on the top surface of the piston. By preventing this, the fuel efficiency of the engine is improved.

From this point of view, the surface roughness of the top coat 30 is 0.1 to 1.5 μm in terms of surface arithmetic mean height Sa defined by ISO 25178, or 0.01 to 1.5 μm in terms of interface development area ratio Sdr. It is preferable to

[Parts subject to heat insulation]
The heat shield film 10 of the present invention described above uses the piston of the engine as a heat shield target component as described above, and by forming it on the top surface of this piston, as with the conventional heat shield film, It is possible to reduce the unburned loss while maintaining the effect of suppressing the heat release in the combustion chamber, and the formation of the heat shield film 10 with a smooth surface is due to the unevenness of the surface. Compared to the conventional heat shield film, which has a large surface area and facilitates heat exchange (thus, the heat shielding performance is low), the heat shielding performance can be improved, and abnormal combustion (knocking) on the top surface of the piston can be prevented. can be suppressed to improve fuel efficiency.

Thus, the heat shield film 10 of the present invention is suitable for forming on the top surface of an engine piston, particularly a piston made of an aluminum alloy with good thermal conductivity.

However, the part (part to be heat-insulated) 2 for which heat is shielded by forming the heat-insulating film 10 of the present invention is not limited to the piston of the engine, but may be a mechanical part used in a high-temperature environment, such as an exhaust manifold. It can be applied to various mechanical parts that require heat insulation, such as exhaust system parts and EGR (exhaust gas recirculation).

1. Evaluation Test The evaluation test results for the heat shield film of the present invention are described below.
[Evaluation target]
Samples in which the heat insulating film of the present invention was formed on a test piece made of SUS304 (Examples 1 and 2) and samples in which the heat insulating film of the comparative example was formed (Comparative Examples 1 to 3: However, Comparative Example 1 Only aluminum alloy specimens were used) were tested and evaluated.

The thermal barrier films formed on the samples of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1 below.

[Test/observation method]
(1) Oil absorption test After forming the heat shield film, each sample in the state as it is and each sample after applying thermal shock were subjected to the test.

As the thermal shock described above, each sample was held in a heated state of 350° C. for 10 minutes, and then cooled by being immersed in room temperature water.

For the evaluation of oil absorption, drop n-hexadecane (low-viscosity oil similar to fuel) on the surface of the heat shield film and leave it for 3 minutes, then wipe it off with a paper cloth. After dropping and wiping off with a waste cloth, the weight change of each sample was measured as "oil absorption (mg)".

The value (×100) obtained by dividing the measured oil absorption by the weight of the heat shield film before the oil was dripped was obtained as the “oil absorption (%)”.

(2) Observation of surface and cross section After applying thermal shock, the surface of the heat shield film of each sample of Examples 1 and 2 and Comparative Examples 1 to 3 was observed. Observed the cross section of

Surface observation was performed with a laser microscope using an objective lens with a magnification of 50 times.

Cross-sectional observation was performed using a scanning electron microscope (SEM) at a magnification of 2000 times.

(3) Measurement of Surface Roughness The surface roughness of the samples of Examples 1 and 2 and Comparative Examples 1 to 3 was measured after the heat shield film was formed and before the thermal shock was applied.

The measurement was performed using a laser microscope (objective lens with a magnification of 50 times), and the surface arithmetic mean height Sa defined by ISO25178 and the developed area ratio Sdr of the interface were measured as roughness parameters.

[Test/observation results]
Table 2 below shows the results of the oil absorption test, surface/cross-section observation, and surface roughness measurement described above.

3 to 7 show the state of the heat shield film surface of each sample of Examples 1 and 2 and Comparative Examples 1 to 3, and cross-sectional SEM images of Example 1 and Comparative Example 1 are shown in FIGS. each shown.

[Discussion]
In the samples of Examples 1 and 2, the oil absorption rate was low in any state before and after the thermal shock was applied, and the occurrence of cracks could not be confirmed. Both the ratios Sdr were significantly below 1.5.

Further, as shown in FIG. 8, as a result of cross-sectional observation by SEM, it was confirmed that the pores in the inorganic compound layer were filled by the permeation of the organic-inorganic hybrid material.

FIG. 8 is a cross-sectional SEM image of the sample of Example 1, and although the cross-sectional SEM image of the sample of Example 2 is omitted, similar results were confirmed.

On the other hand, in the heat shield film of Comparative Example 1, in which the inorganic compound layer was directly exposed on the surface without the topcoat, the oil absorption was 17.9% before the thermal shock and 19.5% after the thermal shock. As a result of observation of the surface and cross section, the occurrence of microcracks in the inorganic compound layer (see Figure 5) and the occurrence of many holes (see Figure 9) were confirmed, and the surface roughness The surface arithmetic average height Sa was 1.64 μm, and the developed area ratio Sdr of the interface was 4.26, which were rough.

From the above results, the superiority of the heat shielding film of the present invention in which the topcoat is provided on the inorganic compound layer was confirmed.

In addition, in Comparative Example 2, as in Examples 1 and 2, a top coat formed of an organic-inorganic hybrid material was provided, and the oil absorption rate before thermal shock was 0.3%, which was higher than that of Examples 1 and 2. It is lower than that of the hot film, and the surface roughness is 0.12 in surface arithmetic average height Sa, and 0.03 in surface expansion area ratio Sdr, confirming that a smooth surface is obtained. rice field.

However, with the thermal barrier film provided on the sample of Comparative Example 2, the topcoat peeled off when subjected to thermal shock (see Fig. 6), and it was confirmed that the film could not withstand use in a high-temperature environment. rice field.

The film thickness of the top coat formed on the thermal barrier film of Comparative Example 2 was 50 μm, which is thicker than the film thickness of the top coats of Examples 1 and 2 (3 μm in Example 1 and 30 μm in Example 2). Therefore, it is considered that the residual stress in the film was increased by increasing the film thickness of the topcoat, and as a result, the film delaminated due to the thermal shock.

From the above results, it was confirmed that the thickness of the top coat in the heat shield film of the present invention is 30 μm or less.

The thermal barrier film of Comparative Example 3 has a topcoat thickness of 5 μm, which is within the thickness range of the topcoat of the present invention, but the topcoat is formed only of an inorganic alkoxide metal (Zr alkoxide). It is different from the structure of the heat shield film of the present invention in that

In this configuration, the oil absorption rate before the thermal shock was already as high as 16.2%, and the surface roughness was 1.30 μm in surface arithmetic mean height Sa, but the developed area ratio Sdr of the interface was 4.07. The top coat was peeled off by applying high and further thermal shock.

From the above results, the superiority of the thermal barrier film of the present invention, which employs an organic-inorganic hybrid material as the topcoat material, was confirmed.

2. Confirmation of the lower limit of the film thickness of the top coat In order to determine the lower limit of the film thickness of the top coat, the film thickness of less than 3 µm (Example 1), which is the minimum value of the film thickness of the top coat in the above-mentioned test examples, was 0.00. The film thickness of the top coat was changed in the range of 5 to 2 μm, and the changes in the appearance and oil absorption of the formed heat shield film were measured.

Measurements are performed on both the sample before applying heat load and the sample after heat load. When no cracks were observed, the evaluation was given as "○", when the cracks were observed under a microscope but not observed with the naked eye, "△", and when the cracks were observed with the naked eye, "X".

The film thickness of the top coat was determined based on cross-sectional observation.

The test results are shown in Table 3 below.

As a result, cracks did not occur even when the film thickness of the top coat was in the range of 0.5 μm to 2 μm, and a heat insulating film with a low oil absorption rate was obtained. As such, it was confirmed that even a relatively thin film thickness of 0.5 μm is effective.

1 Heat shield part 2 Heat shield target part (piston)
REFERENCE SIGNS LIST 10 heat shield film 20 inorganic compound layer 21 inorganic compound 22 scaly inorganic particles 23 pores 30 top coat 40 anodized layer (alumite layer)
70 heat insulating film 71 heat insulating layer 72 (72a, 72b) inorganic coating layer 80, 80a, 80b hollow particles 102 piston 240 heat insulating film 241 heat insulating layer (alumite layer)
243 inorganic compound layer (protective layer)

Claims (7)

In the heat shield film formed on at least part of the surface of the part to be heat shielded,
an inorganic compound layer in which scaly inorganic particles are dispersed in an inorganic compound formed from an alkoxide;
A shield characterized by comprising a top coat formed on the inorganic compound layer and having a thickness of 0.5 to 30 μm and made of an organic-inorganic hybrid material composed of a mixture of a metal alkoxide and a resin. hot film. 2. The method according to claim 1, wherein the surface of the topcoat has an area arithmetic mean height Sa defined in ISO25178 of 0.1 to 1.5 μm, or an interface developed area ratio Sdr of 0.01 to 1.5. Thermal insulation film. 3. The thermal barrier film according to claim 1, further comprising an anodized film layer under the inorganic compound layer. In a heat shielding part that covers at least part of the surface of the part to be heat shielded with a heat shielding film,
The heat shield film is
an inorganic compound layer in which scaly inorganic particles are dispersed in an inorganic compound formed from an alkoxide;
A heat shield characterized by comprising a top coat formed on the inorganic compound layer and having a thickness of 0.5 to 30 μm and made of an organic-inorganic hybrid material composed of a mixture of metal alkoxide and resin. parts. 5. The surface of the topcoat according to claim 4, wherein the surface arithmetic mean height Sa defined in ISO 25178 is 0.1 to 1.5 μm, or the interface development area ratio Sdr is 0.01 to 1.5. Heat insulation parts. 6. The heat shielding component according to claim 4, further comprising an anodized film layer under the inorganic compound layer. The heat shielding part according to any one of claims 4 to 6, wherein the heat shielding target part is an engine piston.

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