KR20200136643A - Method for thermal spraying using a slurry and a coated material prepared therefrom - Google Patents

Abstract

The present invention relates to a spray coating method using slurry and a coated body manufactured by using the same. According to one aspect of the present invention, the spray coating method comprises: a step of producing a slurry composition by mixing chromic oxide powder having an average particle diameter of 0.1-5 μm, a solvent, and a dispersing agent; and a step of spray coating the slurry composition on a substrate through a plasma device. The present invention can harmoniously realize excellent rigidity, scratch resistance, and adhesion by forming a coating layer having a dense structure.

Description

Spray coating method using a slurry and a coating material manufactured using it {METHOD FOR THERMAL SPRAYING USING A SLURRY AND A COATED MATERIAL PREPARED THEREFROM}

The present invention relates to a thermal spray coating method using a slurry and a coating body manufactured using the same, and more particularly, a slurry thermal spray coating method having a dense coating film and excellent hardness and scratch resistance, and a coating manufactured using the same It is about the sieve.

Thermal spraying involves melting and spraying the powder or wire-shaped ceramic or metal powder as a coating material at a high temperature to coat the thermal spray coating and coating powder. There is a kinetic spray coating method that melts and attaches the powder by converting the impact energy generated during collision into thermal energy by spraying it on the surface of the substrate at high pressure and high speed.

The thermal spray coating method is divided into a gas type and an electric type according to the type of heat source that heats the coating material.The gas type spray includes flame spraying, explosion spraying, and high velocity spraying (High Velocity Oxygen Fuel Spraying, HVOF), and arc spraying for the electric spraying. , Plasma spraying, line width spraying, and laser spraying.

Since the plasma spraying can be miniaturized and can generate ultra-high temperatures of thousands of degrees or more, which is the plasma center temperature, it is essential and almost the only thermal spray coating method for coating metals and ceramics such as chromium, tungsten or molybdenum having a high melting point. Is being used.

The coating technique by plasma spraying is performed by injecting powder into a high-temperature plasma jet, and then spraying the molten powder in the plasma jet onto a substrate at ultra high speed in the form of droplets. The melted and sprayed powder is mainly mechanically bonded by a rapid cooling and solidification method, and is laminated on the surface of the steel sheet.

Such a thermal spray coating can be formed by spraying the thermal spray particles not only in the form of a powder, but also in the form of a slurry including the thermal spray particles. However, when using powder, there is a limitation in implementing excellent compactness and forming a coating layer having an appropriate thickness, and when using a slurry, there may be a problem of sedimentation and precipitation due to gravity.

In particular, the conventional slurry spray coating method has a problem in that it is difficult to uniformly maintain the slurry distribution and pressure in the plasma gas flow, so that the plasma injector (nozzle) is easily closed, and defects such as peeling of the coating layer occur, resulting in poor processability and adhesion. .

Flexography is an eco-friendly high-speed printing method using water-based ink, and printing is performed by transferring a certain amount of ink to a flexographic printing plate by a plurality of cell patterns formed on the surface of an anilox roll. Therefore, as the cell pattern is precise and uniform, and the same amount of ink is carried in each cell, the print quality is improved. Anilox rolls are manufactured by coating the surface of a metal core cylinder with ceramic to improve abrasion resistance, and then generating a cell pattern with a laser. To improve the precision of the pattern, it is necessary to form a high-density coating layer with a dense structure with a low porosity. . In addition, by improving the abrasion resistance of the coating layer, frequent replacement of the anilox roll due to high-speed printing can be prevented.

Accordingly, there is a demand for the development of a slurry spray coating method capable of implementing excellent processability and abrasion resistance while improving the density of the coating layer.

The present invention is to solve the problems of the prior art described above, and an object of the present invention is a slurry spray coating method that can achieve excellent hardness, scratch resistance, and adhesion in a balance by forming a coating layer having a dense structure, and using the same It is to provide the prepared coating.

One aspect of the present invention, (a) preparing a slurry composition by stirring the chromium oxide powder having an average particle diameter of 0.1 ~ 5㎛, a solvent and a dispersant; And (b) thermally spraying the slurry composition on a substrate with a plasma device.

In one embodiment, the content of the chromium oxide powder may be 25 to 35% by weight based on the total weight of the slurry composition.

In one embodiment, the content of the dispersant may be 1 to 3% by weight based on the total weight of the chromium oxide powder.

In one embodiment, the substrate may be pre-treated with sand blast, shot blast, or grit blast.

In one embodiment, the value of R _{a of the} surface of the pretreated substrate may be 1.5 to 3 times that of the pretreatment.

In one embodiment, the plasma injector of the plasma device may have a hole diameter of 0.15 to 0.35 mm and a length of 5 to 15 mm.

In one embodiment, the thermal spray coating may satisfy at least one of the following process parameters (i) to (v): (i) power 55 to 75 kW; (ii) Ar gas flow rate 100 to 200 scfh; (iii) N ₂ gas flow rate 30-100 scfh; (iv) slurry flow rate of 15 to 45 ml/min; (v) Spray distance 25~75㎜.

Another aspect of the present invention is a substrate; And a coating layer formed on at least a portion of the surface of the substrate, wherein the coating layer is formed by the aforementioned slurry spray coating method.

In one embodiment, the coating layer may satisfy at least one of the following conditions (i) to (iii): (i) a thickness of 0.3 mm or less; (ii) 15% or less porosity; (iii) Vickers hardness (HV0.5) 1,000 or more.

In one embodiment, the coating body may be a printing roll.

According to an aspect of the present invention, a slurry composition including chromium oxide powder may be prepared, and the slurry composition may be spray coated on a substrate to form a coating layer capable of achieving excellent hardness, abrasion resistance, and adhesion in a balanced manner.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be deduced from the configuration of the invention described in the detailed description or claims of the present invention.

1 shows a sequence of a slurry spray coating method according to an aspect of the present invention.
2 is a photograph of a peeled surface of a coated specimen prepared according to a comparative example of the present invention.
3 is a photograph of a plasma injector used in an embodiment and a comparative example of the present invention.
4 is _a photograph showing a difference in roughness (R _a ) values according to the presence or absence of pretreatment of specimens used in an embodiment and a comparative example of the present invention.
5 is a photograph taken of the surface of a coating body prepared according to an embodiment and a comparative example of the present invention.
6 shows the results of SEM and EDS analysis of the coating layer of the coating body prepared according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein.

Throughout the specification, when a part is said to be "connected" with another part, this includes not only "directly connected" but also "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, it means that other components may be further provided, rather than excluding other components unless specifically stated to the contrary.

Slurry spray coating method

In the present specification, "spray coating" refers to a method of forming a coating layer on the surface of a substrate by melting and spraying a coating material in the form of a powder using a heat source such as plasma. In addition, "slurry thermal spray coating" refers to a method of thermal spray coating after dissolving a coating material in a powder form in a solvent.

The slurry spray coating method can form a high-density coating layer with a lower porosity compared to the conventional powder spray coating, but has a disadvantage in that uniform spraying is difficult because the slurry distribution and pressure control are difficult compared to the powder spray coating. In addition, due to insufficient heat transfer in the slurry, the coating material is not sufficiently melted, so that the coating surface is poor or the plasma injector is closed.

Plasma thermal spray coating, in which powder is melted and coated using a high-temperature plasma flame, is suitable for coating metal ceramics such as chromium, tungsten or molybdenum having a high melting point.

Thermal spray coating is only advantageous in producing high-functional materials that exhibit the characteristics of abrasion resistance, corrosion resistance, heat and heat barrier, carbide, oxidation resistance, insulation, friction characteristics, heat dissipation, and biological function and radiation resistance by making use of the material properties of the object to be coated. In addition, compared to other coating methods such as chemical vapor deposition or physical vapor deposition, an object of a large area can be coated in a short time.

Conventionally, the powder was formed into a coating layer using a plasma device, but in the present invention, in order to implement a coating layer having excellent density and a high thickness, a spray coating may be performed using a slurry composition instead of powder.

A slurry spray coating method according to an aspect of the present invention includes: (a) preparing a slurry composition by stirring a chromium oxide powder having an average particle diameter of 0.1 to 5 μm, a solvent, and a dispersant; And (b) spray-coating the slurry composition on a substrate with a plasma device.

Compared to other metals, the chromium oxide powder has a high hardness, a beautiful appearance, and may not discolor in air. The chromium oxide powder is one mainly means the Cr ₂ O _3, but are not necessarily limited to the Cr ₂ O _3. That is, the chromium oxide powder may be used as Cr ₅ O ₁₂ , Cr ₃ O ₄ , CrO ₂ , CrO, Cr ₃ O ₂ , and the like, but is not limited thereto.

The chromium oxide powder may have an average particle diameter of 0.1 μm or more, 0.5 μm or more, or 0.9 μm or more, and may be 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1.5 μm or less, or 1.2 μm or less. According to an embodiment of the present invention, a dense and durable coating layer can be formed by performing thermal spray coating using a powder having a small average particle diameter. Powders with a small average particle diameter have low fluidity and agglomeration occurs, so feeding is impossible when applying the conventional powder spray coating method, but the present invention solves this problem by preparing and using a slurry composition by mixing the powder with a solvent. I can.

For example, in the case of thermal spray coating using chromium oxide powder having an average particle diameter of 0.1 to 5 μm in the conventional powder spray coating method, the coating material is attached to the supply path or is supplied to the thermal spray device due to mutual agglomeration between the coating materials. Difficult to form a coating may be deteriorated, and in that the mass of the powder itself is small, a suitable coating layer may not be formed due to scattering by a thermal spraying device or a plasma jet.

That is, in the present invention, by performing the thermal spray coating using the slurry composition, the coating formation ability can be maintained high by preventing the problem of adhesion to the supply path, and the spraying efficiency is increased by supplying in a slurry form without dropping powder. And thermal spray coating can be performed.

The content of the chromium oxide powder may be 25 to 35% by weight based on the total weight of the slurry composition. When the content of the powder satisfies the above range, the uniformity decreases due to the flow of the coating layer, or defects caused by agglomeration of the powder can be easily controlled.

The dispersant refers to a compound capable of improving the dispersion stability of the chromium oxide powder in the slurry composition. Such a dispersant may be, for example, a compound that interacts with the powder to purge the agglomerated powder, or may be a compound that inhibits or inhibits re-aggregation between the peptized powder particles by external force such as stirring.

The dispersant may be appropriately selected and used from an aqueous dispersant and a non-aqueous dispersant. In addition, the kind of such a dispersant is not limited, such as a polymer type dispersant, a surfactant type dispersant (also referred to as a low molecular type dispersant), or an inorganic type dispersant, and may be any of anionic, cationic or nonionic dispersants. That is, in the molecular structure of the dispersant, it may have a functional group of at least one of an anionic group, a cationic group, and a nonionic group.

The content of the dispersant may be 1 to 3% by weight based on the total weight of the chromium oxide powder. When the content of the dispersant satisfies the above range, it is possible to prevent deterioration of properties of the coating layer due to the dispersant and improve dispersibility of the powder.

The slurry composition may be prepared by stirring for 1 to 48 hours at a speed of 5 rpm or more, 25 rpm or more, 50 rpm or more, or 75 rpm or more, 200 rpm or less, 175 rpm or less, 150 rpm or less, 125 rpm or less, or 100 rpm or less. If the agitation speed or time is excessive or insufficient, the agglomerates may not be pulverized or agglomeration between powder particles may occur.

The substrate may be pretreated with sandblast, shot blast or grit blast, and the R _a value of the pretreated substrate surface may be 1.5 times or more, 1.75 times or more or 2 times or more, 3 times or less, 2.75 times or less compared to the pretreatment. Or it may be 2.5 times or less. For example, _a steel plate specimen having an R _a value of 0.651 μm may be subjected to sandblast pretreatment to obtain a R _a value of about 2.25 times 1.464 μm. The pretreatment stabilizes the surface of the substrate to improve corrosion resistance, removes foreign matter, and improves surface roughness, so that the adhesion of the coating layer can be improved.

The sandblast pretreatment may be to spray the abrasive at a pressure of 1 to 10 bar to remove impurities on the surface of the substrate and to improve roughness. For this sandblast pretreatment, it can be performed by borrowing a conventionally known configuration. For example, the sandblasting is performed by using a device consisting of an air compressor, an air tank, a water separator, an abrasive pressure tank, a hose, an abrasive nozzle, a nozzle holder, etc., since the abrasive is sprayed onto the substrate using compressed air. In addition, a vibration suppression device, abrasive material and abrasive material sorting device may be required as auxiliary equipment.

In the present invention, the “abrasive material” is used in the same meaning as the medium, and the abrasive material may be dry sand, and the flow of the abrasive material in the premises of the sprayer is not disturbed, and problems such as shorts do not occur. have. In addition, the abrasive may be white aluminum oxide (Al ₂ O ₃ ) having an average particle diameter of 50 to 250 μm, but is not limited thereto.

The illuminance value R _a means an average value integrated with respect to the center line in a certain measurement section. The illuminance value (R _a ) is different depending on the substrate, but may be, for example, 0.5 to 2.0 μm. If the illuminance value is too small, adhesion of the coating layer may be poor, and if excessively large, rust may occur at the peak of the illuminance not covered by the coating layer.

The plasma injector is also referred to as a plasma nozzle, and refers to a configuration that controls the flow rate and pressure of the slurry supplied to the spray gun. The plasma injector of the plasma device may have a hole diameter of 0.15 to 0.35 mm and a length of 5 to 15 mm. If the hole diameter of the injector satisfies the above range, it is possible to implement a flow rate and pressure suitable for spray coating of the slurry composition, and if the length of the injector satisfies the above range, it is possible to solve the problem that the hole is closed due to heat of plasma. have.

The thermal spray coating may satisfy at least one of the following process parameters (i) to (v): (i) power 55 to 75 kW; (ii) Ar gas flow rate 100 to 200 scfh; (iii) N ₂ gas flow rate 30-100 scfh; (iv) slurry flow rate of 15 to 45 ml/min; (v) Spray distance 25~75㎜. Unlike the powder spray coating method, the slurry spray coating method is difficult to control the distribution and pressure of the slurry during spraying, but if the above process parameters are satisfied, a uniform coating layer can be formed more easily. For example, the thermal spray coating may be performed in a current and voltage range capable of satisfying the power range.

Coating

Coating body according to another aspect of the present invention, the substrate; And a coating layer formed on at least a portion of the surface of the substrate, and the coating layer may be formed by the above-described slurry spray coating method.

The material and shape of the substrate can be appropriately selected and used according to the application.

The coating layer may satisfy at least one of the following conditions (i) to (iii): (i) a thickness of 0.3 mm or less; (ii) 15% or less porosity; (iii) Vickers hardness (HV0.5) 1,000 or more. The thickness, porosity, and Vickers hardness of the coating layer can be measured according to KSD0253, KSD8542 and KSB0811, respectively.

The thickness of the coating layer may be 0.01 mm or more, 0.05 mm or more, or 0.1 mm or more, and may be 0.3 mm or less. If the thickness of the coating layer is out of the above range, the adhesion of the coating layer may decrease or the mechanical strength of the coating may decrease, and formation of a pattern or the like may be difficult.

The porosity of the coating layer may be 2.5% or more, 5% or more, or 7.5% or more, and may be 15% or less, 12.5% or less, or 10% or less. When the porosity of the coating layer satisfies the above range, a more precise pattern can be formed on the surface of the coating.

The Vickers hardness (HV0.5) of the coating layer may be 1,000 or more, 1,250 or more, 1,500 or more, or 1,750 or more, and 3,000 or less, 2,750 or less, 2,500 or less, or 2,250 or less.

The coating body may be a printing roll. The printing roll refers to a roll capable of carrying ink on which an uneven or textured pattern is formed on the surface, and may be, for example, an anilox roll used for flexo printing.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

1.5 kg of chromium oxide powder having an average particle diameter of 1 μm and 3.5 L of H ₂ O were added to the mixing vessel, and 30 cc of a dispersant was added to the container, which is about 2% by weight of the total amount of the powder, followed by stirring at 85 rpm. A used slurry composition was prepared.

Using a white molten alumina abrasive (#220), the carbon steel sheet specimen was subjected to sandblast pretreatment at a pressure of 4 bar. The slurry composition was spray coated on the specimen with a plasma device (Plasma 6600C, PRAXAIR). The optimal process parameters of the thermal spray coating are shown in Table 1 below.

Process variable Condition Power (kW) 55~75 Plasma gas Primary gas Ar (scfh) 105 Secondary gas N ₂ (scfh) 40 Plasma injector Hole diameter (mm) 0.20 Nozzle length (mm) 12.5 Slurry flow rate (ml) 30 Spray distance (mm) 50 Pitch (mm) 3 Density (g/cc) 1.284

Example 2

The thermal spray coating was performed in the same manner as in Example 1, except that the hole diameter of the plasma injector was changed to 0.15 mm, 0.25 mm or 0.35 mm.

Comparative Example 1

Except that the sandblast pretreatment was not performed, the thermal spray coating was performed in the same manner as in Example 1.

Comparative Example 2

2kg of chromium oxide powder, H ₂ O 3L, except that the thermal spray coating was performed using a dispersant 40cc, the thermal spray coating was performed in the same manner as in Example 1, and the results are shown in FIG. 2. Referring to FIG. 2, the slurry composition of 40% by weight of the powder was coated in an unmelted state due to insufficient heat transfer, and as a result, a defect in which the coating layer was peeled occurred.

Comparative Example 3

The spray coating was carried out in the same manner as in Example 1, except that the injector, which is a component of the plasma device, was changed to a hole diameter of 0.35 mm and a nozzle length of 22.5 mm.

Fig. 3 shows an injector having a hole diameter of 0.20 mm and a nozzle length of 12.5 mm, and an injector having a hole diameter of 0.35 mm and a nozzle length of 22.5 mm.

When spray-coating with the slurry composition using the injector having a hole diameter of 0.20 mm of Example 1, a low flow rate and high pressure were realized, so that a constant coating was possible within the spray range.

On the other hand, when the injector having a nozzle length of 22.5 mm in Comparative Example 3 was used, the hole was closed due to the contact of the end of the injector to the plasma flame, but when an injector having a nozzle length of 12.5 mm in Examples 1 or 2 was used This problem has been solved.

Experimental Example 1: Sandblast pretreatment

The surface roughness (R _a ) value before coating of the specimens used in Example 1 and Comparative Example 1 was measured, and the results are shown in FIG. 3 and Table 2 below.

division Example 1 Comparative Example 1 Roughness R _a (㎛) 1.464 0.651

Referring to Table 1, Example 1, in which sandblast pretreatment was performed, had a higher illuminance value than Comparative Example 1. Surface impurities may be removed through the sandblast pretreatment, and adhesion of the coating layer may be improved.

Referring to FIG. 4 comparing the coated specimens of Example 1 and Comparative Example 1, in Example 1, a coating layer having a thickness of about 60 to 70 μm was formed by strongly adhering the coating layer to the rough surface of the specimen. In Comparative Example 1, a coating layer having a thickness of about 30 μm was formed, but the coating was insufficient and peeling occurred.

Experimental Example 2: Measurement of physical properties

The specimen of Example 1 was analyzed with a Vickers hardness tester (HV0.5), and the results are shown in Table 3 below.

division 1 time Episode 2 3rd time 4 times 5 times Vickers hardness 1,982 2,160 1,859 1,912 2,035

The thickness and components of the coating layer of the specimen of Example 1 were analyzed by SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X-ray Spectrometer), and are shown in FIG. 6.

Referring to FIG. 6, it can be seen that the average thickness of the coating layer is 267 μm, and the component of the coating layer is composed of 74 to 76.5% by weight of chromium and 23.5 to 26% by weight of oxygen.

As a result of measuring the porosity of the coating layer according to KSD8542, the porosity of the coating layer was measured to be about 10%.

As a result of testing the adhesion of Example 1 and Comparative Examples 1 to 3 according to KSD0254, the peeling phenomenon did not occur in Example 1, but a part of the coating layer was peeled in the specimens of Comparative Examples 1 to 3.

The above description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims to be described later, and all changes or modified forms derived from the meaning and scope of the claims and the concept of equivalents thereof should be construed as being included in the scope of the present invention.

Claims (10)

(a) preparing a slurry composition by stirring chromium oxide powder having an average particle diameter of 0.1 to 5 μm, a solvent, and a dispersant; And
(b) spray coating the slurry composition with a plasma device on a substrate; containing, a slurry spray coating method. The method of claim 1,
The content of the chromium oxide powder is 25 to 35% by weight based on the total weight of the slurry composition, the slurry spray coating method. The method of claim 1,
The content of the dispersant is 1 to 3% by weight based on the total weight of the chromium oxide powder, the slurry spray coating method. The method of claim 1,
The substrate is sandblast, shot blast or grit blast pre-treated, slurry thermal spray coating method. The method of claim 4,
The R _a value of the surface of the pretreated substrate is 1.5 to 3 times that of the pretreatment before, the slurry spray coating method. The method of claim 1,
The plasma injector of the plasma device has a hole diameter of 0.15 to 0.35 mm and a length of 5 to 15 mm, a slurry spray coating method. The method of claim 1,
The thermal spray coating satisfies at least one of the following process parameters (i) to (v), a slurry thermal spray coating method:
(i) 55-75kW power;
(ii) Ar gas flow rate 100 to 200 scfh;
(iii) N ₂ gas flow rate 30-100 scfh;
(iv) slurry flow rate of 15 to 45 ml/min;
(v) Spray distance 25~75㎜. materials; And
Including; a coating layer formed on at least a portion of the surface of the substrate,
The coating layer is formed by the slurry spray coating method according to any one of claims 1 to 7. The method of claim 8,
The coating layer satisfies at least one of the following conditions (i) to (iii), a coating body:
(i) 0.3 mm or less in thickness;
(ii) 15% or less porosity;
(iii) Vickers hardness (HV0.5) 1,000 or more. The method of claim 8,
The coating body is a printing roll, a coating body.

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