JP3265359B2 - Coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method. More specifically, the invention of this application relates to a new coating method that can achieve high functionality, high performance, and long life by modifying the material surface.

[0002]

2. Description of the Related Art Conventionally, by coating a surface of a material such as a metal with an isomer material, a new function is imparted, or performance such as corrosion resistance, abrasion resistance, and heat resistance is improved. Is known to be effective. Of these coating methods, the so-called dry process includes thin film manufacturing methods such as PVD and CVD,
There are thick film manufacturing methods such as thermal spraying. Both are well-known methods.

[0003] In the case of the former thin film manufacturing method, although the obtained film is dense and high purity, the basic problem is that the film formation rate is low and the cost is high because a vacuum apparatus is required. There is. On the other hand, the thermal spraying method is characterized in that the film forming speed is high and the economic efficiency is excellent. However, this method of producing a thick film by thermal spraying has problems in controllability of the film structure and stability of performance. This is probably because the powder used in the thermal spraying method generally has a particle size of 10 microns or more and has a wide particle distribution. This results in speed and position variations when injected into a heat source such as a plasma jet, which is a major cause of the variation in the melting state and speed of the powder particles, and the unmelted particles are contained inside the formed coating. It is considered that the dispersion of the structure such as the inclusion of the like occurs, which impairs the performance such as the corrosion resistance of the coating and the reproducibility thereof.

[0004] In order to solve such a problem, it is naturally considered that the particle size of the coating material powder used in the thermal spraying method is reduced and the particle size distribution is narrowed. However, in the thermal spraying method, if the particle size is reduced to 10 microns or less, it becomes difficult to handle the powder by the method and the apparatus, and there arises a problem that coating by thermal spraying is actually difficult.

Therefore, the invention of this application solves the above-mentioned problems of the prior art, makes use of the economical characteristics of the thermal spraying method, and improves the uniformity of the structure and performance of the coating. It is an object of the present invention to provide a new coating method capable of improving the re-workability.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention of the present application is, first, to form droplets composed of a suspension of a coating material fine powder in substantially straight lines at substantially regular intervals. Coating characterized by generating a series of droplets of uniform diameter, throwing the series of droplets into the heating zone to evaporate the liquid medium, sintering or melting the coating raw material powder, and depositing them on the substrate. Provide a way.

[0007] Secondly, the invention of this application also provides the above-mentioned coating method in which the coating raw material powder is brought into contact with a reactive gas at the time of charging into a heating zone.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention of this application has the above-mentioned features, and has already established a high degree of controllability and stability as an office printer by solving the problems of the conventional spraying technique. This problem is solved by using a mechanism such as an ink jet or bubble jet printer to precisely and stably feed the coating material into the heating area.

An embodiment of the present invention will be described below. In the coating method of the present invention, for example, as schematically shown in FIG. 1, in a droplet generator, droplets composed of a suspension of a coating material fine powder are linearly and uniformly spaced at a uniform diameter. The droplet train is generated as a train of droplets, and the train of droplets is put into a heating area by a heating device to evaporate the liquid medium, and at the same time, sinter or melt the coating raw material powder to deposit on the substrate.

[0010] If desired, the fine powder of the coating material is brought into contact with a reactive gas at the time of introduction into the heating zone. For example, an inkjet or a bubble jet can be used as a droplet generator for obtaining fine droplets. This ink jet or bubble jet is known as a printer nozzle, and is an ink generating device for printing. This ink generator is
Since high precision printing is the purpose, the generation of ink is highly controlled as shown below, and such a highly controlled ink generation mechanism is important for the present invention. . That is, it is important in that the diameter of the generated droplet can be strictly controlled. For example, in the bubble jet method, the generation of droplets using these nozzles is as follows. First, an aqueous solution is instantaneously heated to about 300 ° C. by a heater in the nozzle to foam the aqueous solution. Further, the operation of discharging the bubbles is performed simultaneously with the growth of the bubbles in the nozzle. These series of operations can generate droplets of the same diameter.

The desired droplet can be obtained by using any of the nozzles. However, the ink jet type nozzle has a feature that it is relatively inexpensive, while the bubble jet type nozzle has no clogging and is stable. Thus, there is an advantage that droplets of the same size can be discharged. Therefore, inkjet or bubble jet can be selected in consideration of these advantages and features. In addition,
Since the size of the nozzle depends on the diameter of the droplet, the size of the nozzle may be selected according to the target diameter of the droplet.

For example, the droplets of the present invention ejected from the above nozzles are constituted by a suspension in which fine powder of a coating material is dispersed in a liquid medium. The powder of the coating material is not particularly limited in its degree,
Various kinds of alloys, inorganic substances, and organic substances may be used, and may be appropriately selected according to the intended use and function of the film. For example, when a wear-resistant and heat-resistant film is formed by thermal spraying, an inorganic powder such as zirconia or alumina can be used. When a corrosion-resistant film is formed by thermal spraying, a powder such as a Ni-based alloy can be used.

The liquid medium for dispersing the coating material powder into a suspension is selected from those which do not react with the coating material powder. For example, it is selected from various organic solvents such as water, alcohols, esters, amides, sulfoxides, nitriles, ethers, and hydrocarbons. And, of course,
As these liquid media, those which have no danger of burning or explosion at the time of heating are used.

In the method of the present invention, as described above, a liquid serving as a coating material is formed into droplets by using a nozzle of an ink jet printer or a bubble jet printer. The droplets are obtained by stabilizing fine ceramic or metal powder as a suspension. Since a suspension is used, it is necessary that sufficiently fine powder is uniformly dispersed at an appropriate concentration in order to stably form droplets without clogging the nozzle. And this droplet is
And are ejected at substantially equal intervals on a straight line. This ejection is characterized in that the diameter of the droplet and the flight speed are constant.

The nozzle diameter, the concentration of the suspension, the diameter of the coating raw material powder, and the like are appropriately selected in consideration of the above. For example, but not limited to, 10
In order to generate a droplet having a size of about 0 micron, the nozzle diameter is about 50 to 70 microns, but the diameter of the raw material powder is 5 microns or less, further 1 micron or less,
It is contemplated that the suspension may have up to 10% by volume, or even 5% by volume.

Next, in the method of the present invention, the row of generated droplets is put into a heat source, the dispersion medium of the suspension is evaporated, and the dispersed fine powder is sintered or melted and deposited on the substrate. Let it. At this time, a coating covering the entire surface of the substrate can be obtained by providing an appropriate moving mechanism to the nozzle or the substrate, or a pattern can be formed only on a necessary portion.

On the substrate, molten particles of the coating material fine powder are deposited to obtain a coating such as a film having a dense structure. It is also possible that a deposit of sintered aggregate particles is formed. Which one to use is controlled by the type of the raw material powder and the heating temperature, the type of the substrate, the flight distance of the raw material powder to the substrate, and the like. Various devices are also considered as devices for heating the heating zone. For example, plasma jet,
Laser light, infrared light, high temperature gas flow, and the like.

The substrate may be selected from various types according to the purpose. For example, various construction objects such as metals, alloys, and ceramics may be used. In the heating zone, by contact with reactive gas or plasma,
Compounds such as oxides and nitrides can also be generated.
Therefore, the present invention will be described in more detail with reference to the following examples. Of course, the invention of this application is not limited to the following examples.

[0019]

EXAMPLE A zirconia fine powder (average particle size 0.1
μm) was uniformly dispersed by adding a surfactant at a ratio of 2% by volume to butyl acetate and used as a coating material. The raw material was supplied to the inkjet nozzle, and the diameter of a droplet obtained by vibrating at a predetermined frequency was about 100 microns, and the flight speed was about 20 m / s. This was put into a plasma jet generated by a DC plasma torch, butyl acetate as a solvent was evaporated, and zirconia powder was heated and deposited on a stainless steel substrate. At this time, in order to avoid the influence of the turbulent flow of the plasma jet, a pipe was provided on the way along which the droplets flow.

The substrate is set at a distance of 60 to 80 mm from the outlet of the plasma torch because particles are cooled and solidified if the substrate is too far away from the plasma. The state of the particles deposited on the substrate was investigated by changing the input power to the plasma. When the plasma current was 500 A or less, the raw ceramic fine powder was deposited almost as it was. With increasing current, the percentage of fused ceramic particles increases,
At 1.3 kA, most of the particles captured on the substrate were molten particles having a diameter of 10 microns or less. This is about 1/10 of the particle size obtained by the conventional plasma spraying method, and it is confirmed that the denseness is considerably high.

[0021]

As described in detail above, according to the invention of this application, it is possible to improve the uniformity of the structure and performance of the film and realize a dense structure with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the invention of this application.

Claims (2)

(57) [Claims] A liquid droplet comprising a suspension of a coating material fine powder is generated as a liquid droplet array having a uniform diameter at substantially regular intervals in a straight line, and the liquid droplet array is introduced into a heating zone to form a liquid medium. And evaporating and sintering or melting the coating material fine powder and depositing it on a substrate. 2. The coating method according to claim 1, wherein the fine powder of the coating raw material is brought into contact with a reactive gas when charged into the heating zone.