1. The utility model provides a component inner wall ALD coating equipment, includes carrier gas device, precursor device, reaction chamber, pressure measurement device and evacuating device, its characterized in that: the reaction cavity is a component inner cavity to be coated, the component inner cavity to be coated forms a closed cavity through a front flange and a rear flange, a two-way joint is arranged on the front flange and is respectively connected with a carrier gas device and a precursor device, so that carrier gas and precursor are mixed and then enter the component inner cavity, and a joint is arranged on the rear flange and is respectively connected with a pressure measuring device and a vacuumizing device.

2. The ALD coating equipment for the inner wall of the component of claim 1, characterized in that: the mounting position and the size of the two-way joint on the front flange ensure that carrier gas cannot form vortex when passing through the front flange through fluid simulation.

3. The ALD coating equipment for the inner wall of the component of claim 1, characterized in that: the size of a joint which is arranged on the rear flange and connected with the pressure measuring device is consistent with that of the double-way joint.

4. The ALD coating equipment for the inner wall of the component of claim 1, characterized in that: the ALD coating equipment further comprises a heating device.

5. The ALD coating equipment for the inner wall of the component of claim 1, characterized in that: and chamfers are arranged at the positions of the flange and the joint drill hole.

6. An ALD coating method for the inner wall of a component is characterized by comprising the following steps:

firstly, reforming ALD equipment and determining an ALD coating process,

A. the ALD device comprises a carrier gas device, a precursor device, a reaction cavity, a pressure measuring device and a vacuumizing device, wherein the reaction cavity is a closed cavity formed by an inner cavity of a component to be coated and front and rear flanges, a bi-pass joint is arranged on the front flange and is respectively connected with the carrier gas device and the precursor device, so that carrier gas and the precursor are mixed and then enter the inner cavity of the component, and a joint is arranged on the rear flange and is respectively connected with the pressure measuring device and the vacuumizing device;

B. the ALD coating process comprises the original outlet pressure, the injection time of a precursor and the time for cleaning the reaction chamber by carrier gas;

b1.1, original outlet pressure, wherein the original outlet pressure is set to ensure that the carrier gas can completely realize stable flow in the reaction cavity;

b1.2, the injection time of the precursor,

according to the shape and the inner surface needing silence in the reaction chamber, the inner surface needing silence can be ensured to be formed uniformly with the thickness of 10^-1A nano-scale film;

b1.3, the time for cleaning the reaction cavity by carrier gas,

determining the time for cleaning the reaction cavity by carrier gas according to the original outlet pressure determined in the step B1.1 and the injection time of the precursor determined in the step B1.2, and determining the time t for cleaning the reaction cavity by carrier gas_zqGuarantee at a certain time t_ΔzqThe outlet pressure of the reaction chamber can be reduced to the original outlet pressure determined in the step B1.1;

secondly, vacuumizing to keep a certain vacuum degree in the reaction cavity;

thirdly, introducing carrier gas into the reaction cavity, and adjusting the introduction amount of the carrier gas through a carrier gas device to enable the outlet pressure measured by the pressure measuring device to meet the requirement range of the original outlet pressure in the first step;

fourthly, ALD coating to the required thickness,

and performing ALD coating for a plurality of times according to the ALD coating process determined in the first step at the coating temperature until the coating meets the design thickness.

7. The ALD coating method for the inner wall of the component of claim 6, wherein: the step a is realized by the following steps,

a1.1, determining the sizes of a front flange and a rear flange according to the structural size of a component to be coated, wherein an inner cavity of the component to be coated forms a closed cavity through the front flange and the rear flange;

a1.2, determining the size of a two-way joint and the installation position on the front flange through fluid simulation according to the size of the front flange determined in the step A1.1, so that a carrier gas cannot form a vortex when passing through the front flange;

and A1.3, determining the size of the joint which is arranged on the rear flange and connected with the pressure measuring device according to the size of the double-way joint determined in the step A1.2.

8. The ALD coating method for the inner wall of the component of claim 6, wherein: the step B1.1 determines the appropriate raw outlet pressure by means of flow simulation, and the step B1.2 determines the appropriate injection time of the precursor by means of experiments.

9. The ALD coating method for the inner wall of the component of claim 6, wherein: step B1.3 time t for carrier gas to clean reaction chamber_zqBy the formula t_zq＝t_Δzq+ Δ t determination, Δ t being the original outlet pressure stabilization time, the recovery pressure time t_ΔzqThe time is that only the carrier gas is injected after the injection of the precursor is stopped, and the outlet pressure of the reaction cavity is reduced to the original outlet pressure.

10. The ALD coating method for the inner wall of the component of claim 6, wherein: the vacuum degree in the reaction cavity in the second step is lower than 20 mtorr.

Background

In industrial application, the inner surfaces of a large number of metal components need to be subjected to surface modification treatment, and particularly, most applied pipe fittings, such as engine cylinders, petroleum industry oil pipelines, chemical pipelines, bearings and other components in the automobile industry, can bear the problems of coking and blockage of fuel oil in a high-temperature process, erosion damage of conveying medium fluid and the like, so that the pipe components fail to cause serious safety accidents; meanwhile, in the military field, especially in the severe environments such as naval gun barrels and torpedo launching tubes configured on naval vessels, engines in the aerospace field and the like, the surface damage of the inner wall of the tubular part is often the main part of the failure of the tubular part, and the common treatment method cannot meet the requirement of strengthening the inner surface of the cavity of the complicated special-shaped tube.

The modification treatment of the inner surface of the workpiece is different from the modification treatment of the outer surface, and the following technical problems mainly exist:

1. the inner surface of the lumen is limited by the shape and size of the inner cavity, and the traditional surface treatment method is difficult to realize, or even the effect of surface modification can not be effectively ensured, particularly for some components with ultra-long aspect ratio, the aspect ratio can be higher than 1000;

2. some processing media (such as common plasma, sputtering target material) are difficult to enter the inside of the tube cavity, or even if the processing media enter, the uniformity of the modified layer is difficult to ensure;

3. the film has poor bonding force with the inner wall due to the shape or size of the inner wall of the member, and the work-making performance is limited.

For solving the problem of coating on the surface of the inner cavity with the ultra-long aspect ratio, the most effective method is to utilize a vapor deposition method to get rid of the limitation of the shape and the size of the component and utilize a gaseous medium to enter the inner cavity. However, although conventional vapor deposition methods such as Chemical Vapor Deposition (CVD) can process various complex-shaped components in a working atmosphere, the required temperature is too high, which may change the original crystal structure of the workpiece and further affect the performance of the workpiece. In addition, due to the limitation of gas source, the CVD method has a few kinds of deposited thin films, the thin film used for the inner surface is mostly Diamond Like Carbon (DLC) or TiN film, and the traditional CVD method is difficult to meet for some members with special requirements on the kind of the thin film.

Atomic Layer Deposition (ALD), also known as atomic layer epitaxy, is a particular chemical vapor deposition technique. The atomic layer deposition process depends on the adsorption of alternate precursors or vapor pulses on the surface of a matrix, and then a nano film is prepared by chemical reaction; in the middle of the alternating pulses, a carrier gas (usually N) is used₂And Ar) cleaning the redundant precursor or vapor of the reaction vacuum chamber.

The advantages of ALD are excellent deposition uniformity and consistency, and very good controllable deposition thickness; various oxides (Al) can be deposited₂O₃、TiO₂Etc.), nitrides (AlN, TiN, etc.) and simple metals (Ru, Pd, etc.). Most processes of ALD can be performed at temperatures below 400 ℃, which can effectively reduce damage to the substrate. Where ALD technology has saturated adsorption characteristics, the self-limiting nature of surface reactions makes possible process automation without requiring precise dose control and constant operator intervention for the deposition process. The films prepared by ALD are, in principle, void-free, uniformly dense, and thus ALD is particularly suitable for the preparation of surface passivation, barrier layers and insulating layers. According to relevant literature, ALD has been applied to a variety of industrial fields including photovoltaics, optics, chemistry, moisture barriers, organic printed electronics, jewelry protection, and the medical industry.

In the ALD process, the limitation of the reaction chamber is usually applied to the preparation of thin films on the surface of some smaller test pieces. Meanwhile, a component or a sample is placed in the reaction cavity, because of the viscous flow characteristic, a region in which some precursors or vapor cannot enter or the residence time is short exists, the film quality of the region is poor, the protection effect of the film on the substrate is influenced, and the influence is particularly prominent on the component with the overlong aspect ratio.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides the ALD coating equipment and the ALD coating method for the inner wall of the component, which ensure the quality of the whole film layer on the inner surface of the component and are not limited by the size of a reaction cavity of the ALD equipment.

The technical solution of the invention is as follows: the utility model provides a component inner wall ALD coating equipment, includes carrier gas device, precursor device, reaction chamber, pressure measurement device and evacuating device, the reaction chamber be the component inner chamber of waiting to coat film, the component inner chamber of waiting to coat film constitutes airtight cavity through front and back flange, install bi-pass joint on the preceding flange, be connected with carrier gas device, precursor device respectively, make carrier gas and precursor get into the component inner chamber after mixing, install the joint on the back flange, be connected with pressure measurement device and evacuating device respectively.

An ALD coating method for the inner wall of a component is realized by the following steps:

firstly, reforming ALD equipment and determining an ALD coating process,

A. the ALD device comprises a carrier gas device, a precursor device, a reaction cavity, a pressure measuring device and a vacuumizing device, wherein the reaction cavity is a closed cavity formed by an inner cavity of a component to be coated and front and rear flanges, a bi-pass joint is arranged on the front flange and is respectively connected with the carrier gas device and the precursor device, so that carrier gas and the precursor are mixed and then enter the inner cavity of the component, and a joint is arranged on the rear flange and is respectively connected with the pressure measuring device and the vacuumizing device;

B. the ALD coating process comprises the original outlet pressure, the injection time of a precursor and the time for cleaning the reaction chamber by carrier gas;

secondly, vacuumizing to keep a certain vacuum degree in the reaction cavity;

thirdly, introducing carrier gas into the reaction cavity, and adjusting the introduction amount of the carrier gas through a carrier gas device to enable the outlet pressure measured by the pressure measuring device to meet the requirement range of the original outlet pressure in the first step;

fourthly, ALD coating to the required thickness,

and performing ALD coating for a plurality of times according to the ALD coating process determined in the first step at the coating temperature until the coating meets the design thickness.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the invention, through equipment modification and process design, uniform plating treatment of the inner surface of the metal part with the complex and fine cavity channel is realized, the technology can be widely applied to the fields of aerospace, machinery, automobiles, microelectronics and the like, and the method has strong popularization and practical significance;

(2) the invention is suitable for preparing passivation films, wear-resistant layers and insulating layer films on the inner surfaces of the complex lumen components;

(3) the invention ensures the quality of the whole film layer on the inner surface of the member and is not limited by the size of the reaction cavity of the ALD device.

Drawings

FIG. 1 is a schematic diagram of an ALD apparatus of the present invention;

FIG. 2 is a flow chart of the present invention;

FIG. 3 shows a member to be coated according to an embodiment;

FIG. 4 is a Scanning Electron Microscope (SEM) topography of an uncoated pre-tube of an example;

FIG. 5 shows TiO of the present invention used in examples₂An SEM (scanning Electron microscope) appearance picture of the coated pipeline;

FIG. 6 shows TiO of the present invention used in examples₂The distribution condition of the pipeline elements after coating (a is Ti element distribution, and b is O element distribution);

FIG. 7 shows TiO of the present invention used in examples₂SEM topography after 800 ℃ thermal shock test of the coated pipeline.

Detailed Description

In view of the defect that the prior ALD process uses the inner surface of a complex component, the ALD equipment is improved, the component is used as a reaction vacuum cavity instead of a reaction cavity in the ALD equipment, and precursors or vapor directly enter the component, so that the precursors or the vapor can flow through all positions of the component, and the quality of the whole film layer on the inner surface of the component is ensured.

In the ALD film growth process, when the carrier gas carries the precursor to pass through the surface of the substrate, the contact part of the carrier gas and the substrate can generate chemical adsorption and physical adsorption with the surface. The precursor needs a certain time from one end to the other end, most of gas molecules collide with the inner wall under the condition that the length L and the diameter d of the pipeline are L > > d, chemical adsorption can be formed on the inner surface of part of reaction gas molecules, and complete supersaturation adsorption on the surface of the inner wall can be realized only if the precursor is introduced excessively and carrier gas flows stably in the pipeline, so that an even film is formed on the inner wall. The stable flow of the precursor gas flow in the inner cavity and the proper introduction amount of the precursor are important process conditions for ensuring the quality of the ALD film on the inner wall of the overlong aspect ratio member.

The invention provides an ALD (atomic layer deposition) coating device for the inner wall of a component, which comprises a carrier gas device, a precursor device, a reaction chamber, a pressure measuring device and a vacuumizing device, wherein the carrier gas device, the precursor device, the pressure measuring device and the vacuumizing device adopt the conventional ALD device, and the reaction chamber is the component to be coated. Two ends of a component to be coated are connected into the conventional ALD equipment through the front flange and the rear flange, and an inner cavity of the component to be coated forms a closed cavity through the front flange and the rear flange. The front flange is provided with a two-way joint which is respectively connected with a carrier gas device and a precursor device, so that the carrier gas and the precursor are mixed and then enter the inner cavity of the component, and the rear flange is provided with a joint which is respectively connected with a pressure measuring device and a vacuum-pumping device. The ALD coating equipment also comprises a heating device which is used for heating the reaction chamber to reach the required process temperature.

The installation position and the size of the two-way joint on the front flange have important influence on whether the precursor gas flow can stably flow in the pipeline. If the selection is not proper, the carrier gas can be caused to form turbulent flow or even eddy current when passing through, so that the precursor stays at the interface for too long time, CVD growth occurs, a powder position is formed, and the quality and uniformity of the ALD thin film are seriously influenced. According to the invention, the installation position and the size of the bi-pass joint on the front flange are determined through fluid simulation, so that a carrier gas cannot form a vortex when passing through the front flange, thus the precursor gas flow can be ensured to stably flow in a pipeline, and the fluid simulation can be carried out by adopting the existing ANSYS fluent software.

The size of a joint which is arranged on the rear flange and connected with the pressure measuring device is consistent with that of the double-way joint. In order to ensure better circulation of gas in the system, chamfers are arranged at the positions of the flange and the joint drill hole, and the chamfers reduce the circulation resistance of the gas. The tightness between the joint and the flange is realized through a VCR gasket, a copper gasket and the like.

The carrier gas device, the precursor device, the pressure measuring device and the vacuumizing device adopt the prior conventional ALD equipment. The carrier gas device provides carrier gas required by the ALD process, and comprises a gas source bottle, a pressure reducing valve, other valves and pipelines, wherein the gas source is generally N₂Or Ar. The precursor device is used for providing precursors and oxygen sources required by the ALD process, and comprises a plurality of precursor sources, a plurality of oxygen sources, various valves and pipelines, and deposited film types comprise a plurality of oxides (Al)₂O₃、TiO₂Etc.), nitrides (AlN, TiN, etc.) and simple metals (Ru, Pd, etc.), etc., and the oxygen source includes O₃、O₂、H₂O、H₂O₂And the like. The vacuumizing device is used for keeping the inner cavity of the component at a corresponding vacuum degree and can be realized by a vacuum pump and other devices. The pressure measuring device is used for measuring the outlet pressure of the inner cavity of the component.

Further, the invention also provides an ALD coating method for the inner wall of the component, which is realized by the following steps:

1. reforming ALD equipment and determining an ALD coating process,

A. the ALD device comprises a carrier gas device, a precursor device, a reaction cavity, a pressure measuring device and a vacuumizing device, wherein the reaction cavity is a closed cavity formed by an inner cavity of a component to be coated and front and rear flanges, a bi-pass joint is arranged on the front flange and is respectively connected with the carrier gas device and the precursor device, so that carrier gas and the precursor are mixed and then enter the inner cavity of the component, and a joint is arranged on the rear flange and is respectively connected with the pressure measuring device and the vacuumizing device;

a1.1, determining the sizes of a front flange and a rear flange according to the structural size of a component to be coated, wherein an inner cavity of the component to be coated forms a closed cavity through the front flange and the rear flange;

a1.2, determining the size of a two-way joint and the installation position on the front flange through fluid simulation according to the size of the front flange determined in the step A1.1, so that a carrier gas cannot form a vortex when passing through the front flange;

a1.3, determining the size of a joint which is arranged on the rear flange and connected with a pressure measuring device according to the size of the double-way joint determined in the step A1.2;

B. the ALD coating process comprises the original outlet pressure, the injection time of a precursor and the time for cleaning the reaction chamber by carrier gas;

b1.1, the original outlet pressure,

the setting ensures that the carrier gas can completely realize stable flow in the reaction cavity, the effective viscous flow of the airflow in the reaction cavity of the ALD system is realized, the specific numerical value can change according to the change of the shape and the volume of the reaction cavity, and the proper preset outlet pressure can be determined in advance through fluid simulation, for example, the current ANSYS Fluent software is adopted.

B1.2, the injection time of the precursor,

according to the shape and the inner surface needing silence in the reaction chamber, the inner surface needing silence can be ensured to be formed uniformly with the thickness of 10^-1Nano-order film;

different injection amounts of the precursor are required according to different inner surfaces and shapes needing silence in the reaction chamber, and the injection amount of the precursor is controlled by the injection time of the precursor. This step can be used to determine the appropriate precursor injection time by specific experimentation.

B1.3, the time for cleaning the reaction cavity by carrier gas,

determining the time for cleaning the reaction cavity by carrier gas according to the original outlet pressure determined in the step B1.1 and the injection time of the precursor determined in the step B1.2, and determining the time t for cleaning the reaction cavity by carrier gas_zqGuarantee at a certain time t_ΔzqThe outlet pressure of the reaction chamber can be reduced to the original outlet pressure determined in the step B1.1;

time t for cleaning reaction chamber by carrier gas_zqBy the formula t_zq＝t_ΔzqDetermining the delta t, wherein the delta t is the original outlet pressure stabilization time, and in order to ensure complete cleaning, the original outlet pressure is stabilized for a period of time, and 5-10 s is selected in general engineering; time to recovery of pressure t_ΔzqThe time is that only the carrier gas is injected after the injection of the precursor is stopped, and the outlet pressure of the reaction cavity is reduced to the original outlet pressure. Precursor injectionWhen the pressure of the outlet of the reaction cavity rises obviously, the pressure is generally more than 1000mtorr, and the time for cleaning the reaction cavity by the carrier gas ensures that the pressure of the outlet of the reaction cavity is recovered to the original pressure.

2. And vacuumizing to keep a certain vacuum degree in the reaction cavity.

In this step, the vacuum pumping is well known in the art and can be accomplished by using a vacuum pump or the like, and the vacuum degree in the reaction chamber is preferably less than 20 mtorr.

3. And (3) introducing carrier gas into the reaction cavity, and adjusting the introduction amount of the carrier gas through a carrier gas device to ensure that the outlet pressure measured by the pressure measuring device meets the requirement range of the original outlet pressure in the step (1).

4. The ALD film is coated to the required thickness,

and (3) performing ALD coating for a plurality of times according to the ALD coating process determined in the step 1 at the coating temperature until the coating film meets the design thickness, wherein the specific operation is the known technology in the field.

Taking the nano film on the inner surface of the complex spiral disk lumen component as an example, as shown in fig. 3, the complex spiral disk lumen component is a cylindrical body with an outer diameter phi 276 x an inner diameter phi 198 x a height 325mm, a spiral channel lumen with a wall thickness of 4mm and a square pore channel cross-sectional dimension of 1 x 1mm exists on the wall surface of the complex spiral disk lumen component, and a film is required to be coated in the spiral channel lumen.

1. And (5) reforming ALD coating equipment.

An inner cavity of a complicated spiral plate pipe cavity member is used as a reaction cavity for atomic layer deposition, and a front flange, a rear flange and a joint are designed to be directly connected with original ALD coating equipment. The schematic diagram of the ALD coating equipment is shown in figure 1, and comprises a front flange, a rear flange, a vacuum chamber component and N₂Gas cylinder, precursor source cylinder 1 (C)₃H₉Al)、3(C₁₂H₂₈O₄Ti)、H₂O₂Source bottle, pressure gauge, vacuum mechanical pump, heating device and various valves and pipelines.

And the bi-pass joint on the front flange is determined as a phi 10 bi-pass joint and an installation position according to simulation, and the joint on the rear flange, which is connected with the pressure gauge, is phi 10.

2. And determining an ALD coating process.

The original outlet pressure is determined to be 400-600 mtorr through fluid simulation, the injection time of each precursor is determined to be 0.5-10 s through experiments, and the time for cleaning the reaction cavity by the carrier gas is 30-60 s.

3. And (4) cleaning.

This step is well known in the art. The method comprises the steps of utilizing a small circulating pump with the lift of 30m to circularly pre-clean a channel inside a spiral coil, enabling a cleaning medium to be absolute alcohol until impurities such as metal fragments do not exist in alcohol, flushing the channel by utilizing high-pressure nitrogen, and sweeping the residual alcohol in the channel.

4. And (3) taking the spiral disc pipe cavity component as a vacuum cavity to be connected into the ALD device, and vacuumizing and maintaining the vacuum state. The vacuum mechanical pump is turned on to make the internal vacuum degree of the spiral coil component lower than 20mtorr, and the vacuum mechanical pump 5 is kept on.

5. The spiral coil was heated using an electric oven to maintain the desired deposition temperature.

Opening the electric heating oven and heating to the desired temperature, e.g. TiO₂Deposition temperature is 150-250 ℃, and Al₂O₃The deposition temperature is between room temperature and 250 ℃, the deposition temperature of the metal ruthenium is between 280 and 350 ℃, and the like.

6. And introducing nitrogen, and regulating the outlet pressure to 400-600 mtorr by controlling the pinhole regulating valve.

7. And carrying out ALD coating according to the determined ALD process.

Different ALD pneumatic valves control different precursors, the specific reference numbers are shown in fig. 1, 1# and 2# control aluminum precursor, 3# control hydrogen peroxide, and 4# and 5# control titanium precursor.

(1) With TiO₂For example, a nanometer film is prepared by opening a No. 4 ALD pneumatic valve for 0.5-10 s at an interval of 0.1-5 s, opening a No. 5 ALD pneumatic valve, and injecting a precursor for 0.5-10 s; flushing with nitrogen for 30-60 s, and recovering to the original outlet pressure; opening 3# ALD pneumatic valve and injecting H₂O₂The source is 0.1-5 s; flushing the gas for 30-60 seconds by using nitrogen, and recovering to the original outlet pressure. The process is circulated for a plurality of times to prepare TiO with the required designed thickness on the inner wall of the spiral channel₂And (3) a nano film.

(2) With Al₂O₃Nano meterFor a thin film as an example, firstly opening a 1# ALD pneumatic valve for 0.1-10 s at an interval of 0.1-5 s, opening a 2# ALD pneumatic valve, and injecting a precursor for 0.5-10 s; flushing with nitrogen for 30-60 s, and recovering to the original pressure; opening 3# ALD pneumatic valve and injecting H₂O₂The source is 0.1-5 s; flushing the mixture for 30-60 seconds by using nitrogen, and recovering the original pressure. The process is circulated for a plurality of times to prepare Al on the inner wall of the spiral channel₂O₃And (3) a nano film.

(3) In addition, the precursor source bottle can be replaced, and other oxides, such as ZnO and HfO, can be prepared₂And rare metal simple substances such as Ru, Pt, Pd and the like can be prepared at the same time. The precursors of choice are generally halides, alkoxides, diketonate compounds or organometallic compounds

8. A sample of 1-2 cm is cut out before the film is coated, the appearance of the inner wall of the stainless steel pipeline is observed as shown in figure 4, the surface roughness of the stainless steel pipeline is large, and obvious microcracks exist. After the circulation is carried out for 2000 times, a sample of 1-2 cm is cut at the source end of the stainless steel pipeline far away from the precursor, the appearance of the inner wall of the stainless steel pipeline is observed as shown in figure 5, the thin film uniformly covers the inner surface of the pipeline, the roughness is greatly improved, and the original microcracks disappear. Meanwhile, the element distribution is observed by using an EDS energy spectrum, and as shown in FIG. 6, Ti and O elements are uniformly covered on the surface of the inner wall.

9. And (3) heating the sample subjected to film coating to 800 ℃ in a box type furnace by using a heat treatment box type furnace, wherein the heating rate is 16 ℃/min, and the temperature is kept for 30 min. And after air cooling to room temperature in the air, putting the film into the box furnace again for heat preservation for 30min, and repeating the thermal vibration test for three times to detect the high temperature resistance of the inner wall film, wherein the appearance of the film is shown in figure 7, the thermal vibration test is repeated for 3 times, the film is kept complete, the high temperature resistance of the film is good, and the bonding force with the inner wall is good.

The invention has not been described in detail and is in part known to those of skill in the art.