JP7231331B2 - Thermal insulation film - Google Patents

Description

The present disclosure relates to thermal barrier films.

A technique for forming a heat shield film on a base material such as fire glass is known. Patent Literature 1 describes a heat shielding film having a three-layer film structure.

Japanese Patent No. 4284694

The heat shield film needs to have high heat shielding properties. Also, the heat shield film needs to have good adhesion to the base material. It has been difficult for conventional heat shield films to achieve both heat shielding properties and adhesion. An object of one aspect of the present disclosure is to provide a heat shielding film that has high heat shielding properties and good adhesion to a substrate.

One aspect of the present disclosure is a heat shield film formed on a base material, the heat shield film contains glass and inorganic fibers, and is porous and has continuous pores penetrating the heat shield film in the thickness direction. It is a heat shield film consisting of a body.

A heat shielding film, which is one aspect of the present disclosure, is composed of a porous material containing glass and inorganic fibers, and has low thermal conductivity and excellent heat shielding properties. Therefore, the heat shield film, which is one aspect of the present disclosure, can suppress heat conduction to the base material.

When forming the heat shield film, the heat shield film is generally heated and then cooled. When heated, the thermal barrier film is pulled by the substrate and expands. After that, when the heat shield film is cooled, the amount of shrinkage of the heat shield film is generally smaller than that of the base material, so stress is generated at the interface between the heat shield film and the base material. If the heat shield film cracks due to the stress, the heat shield film will peel off from the substrate.

The heat shield film, which is one aspect of the present disclosure, is not easily peeled off from the base material even after being heated and then cooled. The reason is presumed as follows. The heat shield film is composed of a porous body and contains pores. When stress is applied to the heat shield film during cooling, the pores are crushed and the heat shield film can be shrunk. Therefore, the heat shield film is difficult to crack and peel off from the substrate during cooling. In addition, since the heat shielding film contains inorganic fibers, stress at the interface is easily transmitted to a portion of the heat shielding film distant from the interface. Therefore, since stress is less likely to concentrate near the interface, the thermal barrier film is less likely to crack or peel off from the substrate during cooling.

A heat shield film that is one aspect of the present disclosure has continuous pores penetrating in the thickness direction of the heat shield film. Therefore, the heat shield film, which is one aspect of the present disclosure, can moderately conduct heat to the substrate through the continuous pores.

It is explanatory drawing showing the manufacturing method of a thermal insulation film. It is a photograph showing the cross section of a thermal insulation film. FIG. 4 is an explanatory diagram showing a method of measuring the thermal conductivity of a heat shield film;

Exemplary embodiments of the disclosure are described.
1. Structure of heat shield film

The thermal barrier film of the present disclosure is formed on a substrate. Examples of the base material include metal base materials. The metal forming the substrate may be a pure metal or an alloy. Examples of pure metals include Fe, Ti, and Al. Examples of alloys include Fe alloys, Ti alloys, Al—Si alloys, and the like.

The heat shield film may be provided on a part of the surface of the substrate, or may be provided on the entire surface of the substrate. The heat shield film is made of a porous material containing glass and inorganic fibers. The porous body is, for example, a porous body mainly composed of a skeleton of glass and inorganic fibers. Since the heat shielding film is composed of a porous material, it has a low thermal conductivity and a high heat shielding property. The heat shield film has, for example, a lower thermal conductivity than the base material.

The heat shield film of the present disclosure is not easily peeled off from the substrate even when heated and then cooled. The reason is as described above.
The heat shield film may or may not contain components other than glass and inorganic fibers. The heat shield film has, for example, a structure in which inorganic fibers are entangled with each other. Glass, for example, is bonded with inorganic fibers. At least part of the glass is bonded to, for example, contact points between intertwined inorganic fibers.

Pores in the heat insulating film are, for example, spaces that are not occupied by glass or inorganic fibers. The heat shield film has continuous pores penetrating the heat shield film in the thickness direction. The heat shield film of the present disclosure can moderately conduct heat to the substrate through the continuous pores. The heat insulating film may further have closed pores in addition to continuous pores.

The glass can be appropriately selected from known glasses. The glass preferably contains at least one of Te and Bi. A glass containing at least one of Te and Bi has a larger coefficient of thermal expansion than a glass not containing them. Therefore, when the glass contains at least one of Te and Bi, the thermal expansion coefficient of the heat shield film is even greater, and the difference between the thermal expansion coefficient of the heat shield film and the thermal expansion coefficient of the substrate is even smaller. As a result, when the glass contains at least one of Te and Bi, the adhesion between the heat shield film and the substrate is even better.

The glass includes, for example, (a) at least one of P ₂ O ₅ and B ₂ O ₃ and (b) R ₂ O and R'O, and with respect to the total number of moles of (a) and (b), A glass in which the molar ratio of (b) (hereinafter referred to as the RR' ratio) is 40 to 60%. R is one or more selected from the group consisting of Li, Na, and K, and R' is one or more selected from the group consisting of Mg, Ca, and Cu. When the glass is the glass described above, the coefficient of thermal expansion of the heat shield film is even greater, and the difference between the coefficient of thermal expansion of the heat shield film and the coefficient of thermal expansion of the substrate is even smaller. As a result, the adhesion between the heat shield film and the substrate is even better.

Inorganic fibers can be appropriately selected from known inorganic fibers. Examples of inorganic fibers include ceramic fibers and metal fibers. Specific examples of _inorganic fibers include _Al2O3 fibers, SiO2 fibers, _ZrO2 fibers, BN fibers, SiC fibers, _TiO2 fibers, CNF _fibers , glass wool, and the like. The inorganic fibers preferably include one or more selected from the group consisting of Al ₂ O ₃ fibers, SiO ₂ fibers and ZrO ₂ fibers. When the inorganic fibers include one or more selected from the group consisting of Al ₂ O ₃ fibers, SiO ₂ fibers, and ZrO ₂ fibers, it is easy to control the state of the porous body constituting the heat shield film. . In addition, the strength of the heat insulating film is high.

Examples of inorganic fibers include crystalline oxide fibers. Examples of crystalline oxide fibers include α-alumina fibers, γ-alumina fibers, mullite fibers and the like. When the inorganic fibers are crystalline oxide fibers, the heat shielding film is less likely to break even when a thermal shock is applied to the heat shielding film.

In the cross section of the heat insulating film, the ratio of the area of the inorganic fibers to the total area of the glass and the inorganic fibers (hereinafter referred to as the fiber area ratio) is preferably 20 to 60%. When the fiber area ratio is 20 to 60%, it is easy to control the state of the porous body that constitutes the heat insulating film. In addition, the strength of the heat insulating film is high. When the inorganic fibers are crystalline oxide fibers and the fiber area ratio is 20 to 60%, the thermal barrier film is less likely to break even if the thermal shock is applied to the thermal barrier film.

The method for measuring the fiber area ratio is as follows. Cut the heat shield film to form a cross section. A 200 μm×100 μm range of the cross section is subjected to composition analysis using EPMA to identify the glass portion and the inorganic fiber portion. The area of the glass portion is measured and the measured value is defined as S1. The area of the inorganic fiber portion is measured, and the measured value is defined as S2. Let Sf represented by the following formula (1) be a fiber area ratio (%).

Formula (1) Sf=(S2/(S1+S2))×100
The average aspect ratio of inorganic fibers is preferably 10 or more. When the average aspect ratio is 10 or more, the inorganic fibers tend to entangle with each other in the heat insulating film. Therefore, the strength of the heat insulating film is high.

The method for measuring the average aspect ratio is as follows. Cut the heat shield film to form a cross section. Aspect ratios are measured for all inorganic fibers present in a 200 μm×200 μm region of the cross section. Aspect ratio is the ratio of the length of an inorganic fiber to the diameter of the inorganic fiber. The diameter used for calculating the aspect ratio is the value of the smallest diameter portion of one inorganic fiber. Length is the length measured along the shape of the inorganic fiber. Let the average value of the aspect-ratio in all the inorganic fibers which exist in the area|region of 200 micrometers x 200 micrometers be an average aspect-ratio.

The average thickness of the heat shield film is preferably 80 to 400 μm. When the average thickness of the heat shielding film is 80 μm or more, the heat conduction to the substrate can be further suppressed by the heat shielding film. When the average thickness of the heat shield film is 400 μm or less, cracks are less likely to occur in the heat shield film, and the heat shield film is less likely to peel off from the substrate.

The method for measuring the average thickness of the heat shield film is as follows. Cut the heat shield film to form a cross section. The thickness of the heat shield film is measured at a plurality of locations within a 500 μm length range of the cross section. All of the multiple locations where the thickness of the heat shield film is measured are locations other than the end portions of the heat shield film. The average value of the thickness of the heat shield film at a plurality of locations is taken as the average thickness of the heat shield film.

It is preferable that the difference between the maximum value and the minimum value of the thickness of the heat shielding film (hereinafter referred to as the thickness difference) in the range of 0.5 mm in width in the cross section of the heat shielding film is 70 μm or less. When the thickness difference is 70 μm or less, the heat insulating film is less likely to be damaged even if a thermal shock is applied to the heat insulating film.

The heat insulating film preferably has an average porosity of 25 to 50%. When the average porosity is 25% or more, the heat transfer to the substrate can be further suppressed by the heat shield film. When the heat shielding film has an average porosity of 50% or less, the heat shielding film is less likely to crack and peel off from the base material.

The method for measuring the average porosity of the heat shield film is as follows. Cut the heat shield film to form a cross section. A backscattered electron image of the cross section is obtained using an SEM. In each of the 10 fields of view in the backscattered electron image, the glass portion, the inorganic fiber portion, and the pore portion are identified, respectively. Each field of view has a size of 200 μm×50 μm. In the backscattered electron image, the glass portion, the inorganic fiber portion, and the pore portion can be distinguished by contrast density.

The area of the glass portion included in 10 fields of view is measured, and the measured value is defined as S1. Also, the area of the inorganic fiber portion included in the 10 visual fields is measured, and the measured value is defined as S2. Also, the area of the pore portion included in the 10 visual fields is measured, and the measured value is defined as S3. Let Sp represented by the following formula (2) be the average porosity (%).

Formula (2) Sp=(S3/(S1+S2+S3))×100
2. Method for Producing Thermal Insulating Film The thermal insulating film of the present disclosure can be produced, for example, as follows. A slurry containing glass powder, inorganic fibers, and water is prepared. The slurry may or may not contain other ingredients.

Next, as shown in STEP 1 of FIG. 1, slurry is applied to the surface of the substrate 1 to form the coating layer 3 .
Next, in STEP 2, the coating layer 3 is dried by holding at a temperature of 60 to 120° C. for 1 to 2 hours, and the heat shield film 5 is formed. Next, in STEP 3, the temperature of 400 to 600° C. is maintained for 0.5 to 2 hours to bake the heat shield film 5 . The heat insulating film 5 is completed through the above steps.

FIG. 2 shows a cross section of the heat shield film. A heat insulating film is formed on the surface of the base material. The heat shield film is composed of a porous material containing glass and inorganic fibers. The heat shield film has continuous pores penetrating the heat shield film in the thickness direction.

3. Examples (3-1) Manufacture of Heat Shielding Films Heat shielding films of Examples 1 to 23 and Comparative Example 1 were produced as follows. A slurry containing glass powder, inorganic fibers, and water was prepared. The composition of the glass powder is described in the "Glass composition" column in Table 1 below. The types of inorganic fibers are those described in the "type" column of "inorganic fibers" in Table 1. The blending ratio of the glass powder and the inorganic fibers in the slurry is a blending ratio at which the fiber area ratio is the value described in the "fiber area ratio" column in Table 1.

次に、基材の表面にスラリーを塗布し、塗布層を形成した。基材の材質は、上記表１における「基材の材質」の列に記載したものである。次に、５０～１００℃の温度で３０分間～６時間保持して塗布層を乾燥させ、遮熱膜を形成した。次に、３５０～５００℃の温度で５分間～２時間保持し、遮熱膜を焼き付けた。以上の工程により、遮熱膜が完成した。

Next, the slurry was applied to the surface of the substrate to form a coating layer. The material of the base material is described in the column of "Material of base material" in Table 1 above. Next, the coating layer was dried by holding at a temperature of 50 to 100° C. for 30 minutes to 6 hours to form a heat shield film. Next, the temperature was kept at 350 to 500° C. for 5 minutes to 2 hours to bake the heat shield film. Through the steps described above, the heat insulating film was completed.

(3-2) Evaluation of Heat Shielding Films The heat shielding films of Examples 1 to 23 and Comparative Example 1 were evaluated as follows.
The average aspect ratio of the inorganic fibers, the average thickness of the heat shield film, and the average porosity of the heat shield film were measured. The measuring method is the method described above. The measurement results of the average aspect ratio of the inorganic fibers are shown in the "average aspect ratio" column of the "inorganic fibers" in Table 1 above. The measurement results of the average thickness of the heat shield film are shown in the "thickness" column in Table 1 above. The measurement results of the average porosity of the heat insulating film are shown in the column of "Porosity" in Table 1 above.
Image analysis of the three-dimensional modeling created by X-ray CT was performed to confirm whether or not the heat shield film had continuous pores. It should be noted that a mercury intrusion method may be used to confirm whether or not the heat insulating film has continuous pores. A continuous pore is a pore that penetrates the heat insulating film in the thickness direction. When the heat shield film has continuous pores, it is marked with "◯" in the column "Presence or absence of continuous pores" in Table 1 above, and when it does not have continuous pores, it is marked with "x".

The bonding strength between the base material and the heat shield film was measured by the following method. A sample including a substrate and a heat shield film formed on the substrate was prepared. The sample is placed in water, the water pressure is increased to a predetermined value, and held for 10 minutes. After that, it is confirmed whether or not the heat shield film is peeled off from the base material. This process is repeated while gradually increasing the predetermined value until the heat shield film is peeled off from the substrate. The above predetermined value when the heat shield film is peeled off from the base material is defined as the bond strength. The measurement results of the bonding strength are shown in the "bonding evaluation" column of the "evaluation" in Table 1 above.

The thermal conductivity of the heat shield film was measured by the following method. As shown in FIG. 3, a sample 7 including a substrate 1 and a heat shield film 5 formed on one surface of the substrate 1 was prepared. Of the base material 1 constituting the sample 7, the surface 9 opposite to the heat shield film 5 was heated with infrared rays. At this time, the thermocouple 11 was used to continuously measure the temperature of the heat shield film 5 to acquire the transition of the temperature. Similarly, for a comparative sample consisting of only the base material 1 without the heat shield film 5, one surface of the base material 1 was heated by infrared rays and the opposite surface was continuously subjected to temperature measurement. , the transition of temperature was obtained. The thermal conductivity of the heat shield film 5 was calculated by simulation based on the temperature transition of the heat shield film 5 in Sample 7 and the temperature transition in the comparative sample. Thermal conductivity was evaluated by applying the calculated thermal conductivity to the following criteria. The evaluation results are shown in the "heat conduction" column of the "evaluation" in Table 1 above.

A: The thermal conductivity is 0.3 W/(m·k) or less.
◯: The thermal conductivity exceeds 0.3 W/(m·k) and is 0.6 W/(m·k) or less.
x: Thermal conductivity exceeds 0.6 W/(m·k).

In the heat shield films of Examples 1 to 23, the bonding strength between the substrate and the heat shield film was high, and the heat shield properties of the heat shield film were good. The heat shielding film of Comparative Example 1 had poor heat shielding properties.
4. Other Embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made.

(1) A function of one component in each of the above embodiments may be assigned to a plurality of components, or a function of a plurality of components may be performed by one component. Also, part of the configuration of each of the above embodiments may be omitted. Also, at least part of the configuration of each of the above embodiments may be added, replaced, etc. with respect to the configuration of the other above embodiments. It should be noted that all aspects included in the technical idea specified by the wording in the claims are embodiments of the present disclosure.

(2) In addition to the heat shielding film described above, the present disclosure can also be realized in various forms such as a system having the heat shielding film as a component, a method for manufacturing the heat shielding film, and the like.

DESCRIPTION OF SYMBOLS 1... Base material, 3... Coating layer, 5... Thermal insulation film, 9... Opposite surface, 11... Thermocouple

Claims (5)

A heat shielding film formed on a substrate,
The heat shield film contains glass and inorganic fibers and is made of a porous body having continuous pores penetrating the heat shield film in the thickness direction ,
The heat shielding film, wherein the ratio of the area of the inorganic fiber to the total area of the area of the glass and the area of the inorganic fiber in the cross section of the heat shielding film is 15% or more. The heat shield film according to claim 1,
The glass is a heat insulating film containing at least one of Te and Bi. The heat shield film according to claim 1 or 2,
The inorganic fibers include one or more selected from the group consisting of Al ₂ O ₃ fibers, SiO ₂ fibers, and ZrO ₂ fibers,
The heat shielding film, wherein the ratio of the area of the inorganic fiber to the total area of the area of the glass and the area of the inorganic fiber in the cross section of the heat shielding film is 20 to 60%. The heat shield film according to any one of claims 1 to 3,
The heat insulating film, wherein the inorganic fibers have an average aspect ratio of 10 or more. The heat shield film according to any one of claims 1 to 4,
The heat shield film has an average thickness of 80 to 400 μm,
The heat shield film having an average porosity of 25 to 50%.

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