Method for coating the inner surface of a metal tubing and a metal tubing with its inner surface electroplated.

Abstract

To provide an inexpensive and versatile metal tubing with an inner surface that has excellent corrosion resistance. [Solution] A method for coating the inner surface of a metal tube, characterized by applying a DC voltage while supplying electrodeposition paint to a metal tube filled with electrodeposition paint, thereby electrodepositing the inner surface of the metal tube, and a metal tube characterized by having its inner surface electrodeposited.

Description

Technical Field

[0001] The present invention relates to a method for coating the inner surface of a thin metal tube, and a thin metal tube having an inner surface formed by electrophoretic coating.

Background Art

[0002] Piping for transporting etching gas, which is a thin metal tube used in semiconductor manufacturing apparatuses, is required to be evaluated in a shape processed according to the application, and its inner surface must not be corroded by the gas transported through the tube, and elution of metal ions must be prevented.

[0003] Conventionally, as surface treatment for the inner surface of a thin metal tube, there are a method of coating the inner surface of the tube with Teflon resin, and a method of forming an oxide film or a nitride film by discharge treatment. However, when the inner diameter of the metal tube is small and the shape is complicated due to welding or bending, the prior art has a problem that it is difficult to reliably perform surface treatment on the inner surface of the tube (Patent Document 1).

[0004] There is also a method of coating the inner surface of the tube with glass coating, but since the film thickness is as thin as 0.3 to 1 μm, the corrosion resistance is insufficient.

[0005] In order to solve this problem, as a conventional technique, there is a measure of manufacturing the thin metal tube using a high-nickel alloy such as Hastelloy. However, this measure still has a problem from the viewpoint of the running cost of the thin metal tube.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0007] The object of the present invention is to provide a metal tube having an inner surface with excellent corrosion resistance by surface-treating the inner surface of the metal tube. As a result of diligent research, the inventors have found that by filling a metal tube with electrodeposition paint and electrodepositing the paint while moving it by liquid transport, it is possible to manufacture an inexpensive and versatile metal tube with excellent corrosion resistance on its inner surface, thus completing the present invention. [Means for solving the problem]

[0008] The present invention is a method for coating the inner surface of a metal tube, characterized by applying a DC voltage while supplying electrodeposited paint to a metal tube filled with electrodeposited paint, thereby electrodepositing the inner surface of the metal tube.

[0009] The present invention is characterized by continuously supplying electrodeposition paint at a flow rate of no more than 10 times the internal volume of the metal tube used for electrodeposition painting, per minute.

[0010] The present invention is characterized in that the metal tubular tube has an inner diameter of 15 mm or less.

[0011] Furthermore, the present invention relates to a metal tube characterized in that the inner surface of the metal tube is electrodeposited.

[0012] The present invention is characterized in that the metal tube is a stainless steel tube with an inner diameter of 2 to 15 mm, and the metal tube has an electrodeposited coating film with a thickness of 5 to 100 μm formed from an amide-imide electrodeposited coating on its inner surface. [Effects of the Invention]

[0013] According to the present invention, by forming a dense and corrosion-resistant electrodeposited coating on the inner surface of a metal tube, it is possible to manufacture a metal tube with significantly improved corrosion resistance compared to general stainless steel piping.

[0014] Furthermore, since a highly corrosion-resistant electrodeposited coating can be stably formed on the inner surface of a metal tube regardless of the number of bends, a highly corrosion-resistant coating can be formed on the inner surface of even tubes with complex shapes.

[0015] Furthermore, when metal tubing is used as piping for etching gases in semiconductor manufacturing equipment, it is possible to use inexpensive SUS316 tubing because it does not corrode internally, resulting in significant cost reductions. In addition, since the liquid flow is controlled based on the internal volume of the metal tubing, manufacturing control is easy. [Modes for carrying out the invention]

[0016] The present invention is a method for coating a metal tube by filling the metal tube with electrodeposition paint, moving the electrodeposition paint inside the tube by liquid transfer, and applying a DC voltage between the metal tube and an electrode to electrodeposit the inner surface of the metal tube.

[0017] In the present invention, the reasons for obtaining the above-mentioned effects are presumed to be that by sending the electrodeposition paint into the pipe, air stagnating in the pipe and electrolytic gases generated during electrodeposition painting are discharged to the outside of the pipe, the concentration of the paint resin components is kept uniform, and the occurrence of unpainted areas due to the gases is suppressed.

[0018] The metal tubes are not particularly limited as long as they are electrically conductive, but examples include single metals such as iron, silver, copper, aluminum, anodized aluminum, zinc, nickel, and titanium, as well as electrically conductive alloys such as stainless steel, Hastelloy, duralumin, bronze, cupronickel, and brass.

[0019] When metal capillaries are used as piping for transporting etching gases in semiconductor manufacturing equipment, it is desirable that they do not contain metal elements with a low ion exchange tendency (especially precious metals). Therefore, anodized aluminum, titanium, stainless steel (SUS), Hastelloy, and duralumin are preferred as metal capillaries, with SUS316 being particularly preferred among these.

[0020] The metal thin tube is not particularly limited as long as it has a tubular structure, but any tube within the range generally referred to as a thin tube can be suitably used in the present invention (hereinafter sometimes simply referred to as a thin tube). As an example, those having an inner diameter of 2 to 15 mm, preferably 3 to 10 mm, and particularly preferably 4 to 8 mm may be mentioned. However, the method of the present invention is not limited to thin tubes with inner diameters within these ranges, and even for thin tubes with inner diameters exceeding the aforementioned ranges, an electrodeposition coating film can be formed on the inner surface thereof by adjusting the feed rate of the electrodeposition paint.

[0021] In the present invention, since the inner surface of the thin tube is coated, the thickness of the thin tube is not limited, but as an example, those having a thickness of 0.2 to 2.0 mm, preferably 0.5 to 1.5 mm, and particularly preferably 1.0 to 1.2 mm may be mentioned.

[0022] Further, the inner diameter of the metal thin tube to be subjected to electrodeposition coating does not need to be uniform in the length direction, and the thin tube may have various different inner diameters, that is, thin tubes of different thicknesses are also acceptable.

[0023] Furthermore, the metal thin tube may be not only a straight tube, but also a shape having bent portions, arc portions, curved portions, etc., such as an L-shape, U-shape, S-shape, or multi-branched shape, or a complex shape including a plurality or a large number of these shapes.

[0024] Considering the adhesion of the electrodeposition coating film to the inner surface, etc., the inner surface of the metal thin tube is preferably as smooth and clean as possible, so the inner surface of the metal thin tube may be subjected to pretreatment such as degreasing, pickling, electrolytic polishing, and chemical conversion treatment.

[0025] In the present invention, as the electrodeposition paint, for example, known cationic electrodeposition paints containing modified epoxy resin, acrylic resin, urethane resin, polyester resin, amide-imide resin, etc. as main components and containing a neutralizing agent, organic solvent, flexibility reinforcing material, curing agent, etc., and known anionic electrodeposition paints containing modified epoxy resin, acrylic resin, alkyd resin, amide-imide resin, melamine-based resin, etc. as main components and containing a neutralizing agent, organic solvent, flexibility reinforcing material, curing agent, etc. can be suitably used.

[0026] Among these, electrodeposition paints containing aromatic polyimide or amidoimide resins are preferred, as they are characterized by excellent heat resistance, corrosion resistance, and insulating properties. They also exhibit good solubility in water, and thus have excellent properties in terms of safety and environmental friendliness due to the reduced usage of organic solvents, making electrodeposition paints containing such resins the most preferred.

[0027] Examples of such known cationic electrodeposition paints include Elecoat IE (manufactured by Shimizu Co., Ltd.), Elecoat PI-ew (manufactured by Shimizu Co., Ltd.), Elecoat FEW (manufactured by Shimizu Co., Ltd.), Elecoat TFY (manufactured by Shimizu Co., Ltd.), and Elecoat PAI (manufactured by Shimizu Co., Ltd.).

[0028] Examples of known anionic electrodeposition paints include Elecoat AMG (manufactured by Shimizu Co., Ltd.), Elecoat Nicelon (manufactured by Shimizu Co., Ltd.), Elecoat AM-1 (manufactured by Shimizu Co., Ltd.), and Elecoat AP (manufactured by Shimizu Co., Ltd.).

[0029] In the present invention, the method for filling the electrodeposition paint into the thin metal tube is not particularly limited, as long as the electrodeposition paint is filled to adhere to the entire inner surface of the inner region of the thin tube where the electrodeposition coating film is to be formed. Examples of the filling method include injecting the electrodeposition paint into the thin metal tube, and immersing the thin metal tube in an electrodeposition paint bath. A cationic electrodeposition paint or an anionic electrodeposition paint may be selected as the electrodeposition paint to be filled according to the target electrodeposition coating film.

[0030] As the counter electrode, those commonly used in electrodeposition coating can be used, and examples thereof include aluminum, platinum, titanium, tantalum, and stainless steel. When the thin metal tube is used as a piping for transporting etching gas in a semiconductor manufacturing apparatus, it is desirable that the electrode does not contain metal elements (particularly noble metals) with a high ion exchange tendency, so aluminum, titanium, tantalum, stainless steel and the like are preferred as the electrode, and among these, stainless steel is particularly preferred.

[0031] Of the above, when the metal tubing is used as piping for transporting etching gases in semiconductor manufacturing equipment, aluminum is preferred.

[0032] Furthermore, the electrodes may be placed in the electrodeposition coating bath, as in known electrodeposition coating, or placed inside a metal tube, or even placed in the electrodeposition coating bath and then inserted into the tube as an auxiliary electrode. In this case, the electrodeposition coating efficiency inside the tube can be improved. As an auxiliary electrode, one of the aforementioned electrodes molded to fit the inner diameter of a metal tube can be suitably used.

[0033] In the present invention, "delivering the electrodeposited paint" means that the electrodeposited paint in contact with the inner surface of a metal tube is delivered to the inner surface at a constant speed or with varying speeds, continuously or intermittently at constant or different time intervals.

[0034] The supply of the electrodeposition coating should be carried out at a rate that supplies the coating resin components consumed by electrolysis during electrodeposition coating, and that adequately discharges the air remaining in the pipe and the hydrogen or oxygen gas generated during electrolysis to the outside of the pipe; there are no particular restrictions on this.

[0035] The liquid delivery rate can be adjusted by any means, but for example, it can be controlled based on the ratio of the flow rate of the electrodeposition paint to the volume of the tube in which the electrodeposition coating is performed, using the internal volume of the tube as a reference.

[0036] When controlling the liquid delivery rate based on the ratio of the flow rate of electrodeposition paint to the internal volume of a capillary tube, the internal volume of the tube to be coated can be easily determined by sealing one end of the metal capillary tube, filling the tube with water or the like, and measuring the amount up to the other end. This makes it easy to control the liquid delivery regardless of the shape of the metal capillary tube. In the following, the ratio of the flow rate of electrodeposition paint per minute to the internal volume of the tube, i.e., (flow rate of electrodeposition paint per minute) / (internal volume of the metal capillary tube), may be referred to as the liquid delivery ratio.

[0037] Specifically, the liquid transfer method uses a liquid transfer device consisting of a liquid transfer pump, liquid transfer piping, and a power supply for driving the pump. The liquid transfer pump can be a diaphragm pump or a rotary pump, and the liquid transfer piping may be made of polypropylene, or a flexible resin hose that is easy to arrange to match the shape of a metal tubing can be used. Examples include braided hoses with reinforced materials, fluorine hoses with excellent chemical resistance, or oil-resistant hoses.

[0038] When controlling the liquid delivery rate based on the liquid delivery ratio, the liquid delivery ratio, i.e., the amount of electrodeposition paint delivered per minute, should be adjusted to be 1 to 10 times, preferably 2 to 5 times, the internal volume of the tube. The electrodeposition paint may be delivered continuously or intermittently. In either case, this can be done by appropriately adjusting the liquid delivery ratio as described above.

[0039] If the liquid-to-water ratio is too high, the pump may draw in air along with the paint, resulting in areas where the electrodeposition coating is not applied. Conversely, if the liquid-to-water ratio is too low, the exhaust of air and electrolytic gases will be insufficient, which may also result in areas where the coating is not applied inside the pipe.

[0040] Furthermore, electrodeposition coating can be easily carried out according to known methods, with a bath temperature (electrodeposition paint temperature) of approximately 25-50°C, an applied voltage of approximately 10-350V, and a voltage application time of approximately 1-60 minutes.

[0041] Electrodeposition coating can be performed by placing electrodes in an electrodeposition paint bath and immersing a metal tube in the electrodeposition paint bath, or it can be performed in a closed system by connecting the metal tube to a liquid delivery pipe. When performing electrodeposition coating by immersion in an electrodeposition paint bath, the electrodeposition paint should be delivered within the electrodeposition paint bath. In this case, it is preferable to first coat the outer surface of the metal tube with a non-conductive protective film, or to electrodeposit only the outer surface and then paint the inner surface. When performing electrodeposition coating in a closed system, electrodes can be inserted into the metal tube and the liquid delivered by a liquid delivery pump or the like, allowing the electrodeposition coating to form only on the inner surface of the metal tube.

[0042] In the case of cationic electrodeposition coating, a cationic electrodeposition paint is used, and a negative voltage is applied to the tube and a positive voltage to the electrode. In the case of anionic electrodeposition coating, a positive voltage is applied to the tube, and an anionic electrodeposition paint is used, with a negative voltage applied to the electrode.

[0043] The electrodeposited tubes are removed from the energizing tank, rinsed with water, drained, and then baked. The baking process includes pre-drying and curing heat, with curing heat performed after pre-drying. Pre-drying is carried out at a temperature of approximately 60-140°C for 3-30 minutes, and curing heat is carried out at a temperature of approximately 150-250°C for 10-60 minutes.

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to such examples.

[0045] As the electrodeposition coatings, Examples 1-5 and Comparative Examples 1-2 used cationic electrodeposition coating (Elecoat PAI), Example 6 used anionic electrodeposition coating (Elecoat AP), and Comparative Example 3 used anionic electrodeposition coating (Elecoat AMG). <Elecoat PAI resin composition> Epoxy-modified amide-imide resin: 30% Trioctyl trimellitate: 30% Amine-modified epoxy resin: 40% <Elecoat AP Resin Composition> Urethane-modified amide-imide resin: 60% Trioctyl trimellitate: 10% Carboxylic acid-modified epoxy resin: 30% <Elecoat AMG Resin Composition> Melamine resin component: 40% Epoxy acrylate resin: 20% Carboxyl group-containing acrylic resin: 40%

[0046] <Evaluation Method for Electrodeposited Coatings> To determine if the internal coating was present, 1 liter of test solution containing 10 g of ethanol, 1 g of sodium chloride, and 10 drops of phenolphthalein indicator was filled into a pipe with an internal coating. A stainless steel wire was inserted into the pipe opening, the pipe was connected to the negative terminal and the stainless steel wire to the positive terminal, and a DC voltage of 12 V was applied between the electrodes for 1 minute. The current value during application was read, and then the test solution was removed from the pipe to check for any color change in the test solution. ○: Indicates that the current value is 0 and the test solution is a colorless, transparent liquid. ×: Indicates that the current value is displayed numerically, or that the test solution is a red liquid.

[0047] The film thickness of the electrodeposited coating was measured by cutting a metal tube after internal coating and using a digital microscope (VHX-2000, Keyence Corporation). Film thickness was measured at five locations, and the average value was calculated.

[0048] Corrosion resistance was tested by exposing a metal tubular tube, after internal coating, to the gas phase of a test container containing a 35% hydrochloric acid aqueous solution at a test temperature of 25°C for 24 hours. After the test, the metal tubular tube with internal coating was cut lengthwise with a band saw and observed using a digital microscope (VHX-2000, Keyence Corporation) to check the coating condition, corrosion, and presence or absence of coating blistering. ○: Indicates that there are no signs of corrosion or blistering on the electrodeposited coating surface. ×: Indicates rust marks due to corrosion and blistering of the paint film.

[0049] <Example 1> A U-shaped metal tube with a cylindrical cross-section made of SUS316, having an inner diameter of 5 mm and a total length of 450 mm, was immersed in an electrodeposition paint bath to fill the inside of the metal tube with electrodeposition paint.

[0050] Next, while maintaining the temperature at 45°C, the electrocoating paint, Elecoat PAI, was supplied at a flow rate of 10 ml / min, and a DC voltage of 250 V was applied for 60 minutes to perform the electrocoating process.

[0051] Subsequently, the metal tubes were thoroughly washed with deionized water, dried by air blowing, pre-dried in a 110°C forced-air constant-temperature oven for 10 minutes, and then baked at 240°C for 30 minutes.

[0052] The electrodeposited coating on the inner surface of the obtained metal tubes was evaluated. The results are shown in Table 1, and an electrodeposited coating with excellent corrosion resistance was formed on the inner surface of the entire metal tube.

[0053] <Example 2> Electrodeposition coating was performed in the same manner as in Example 1, except that a SUS316 tubular tube with an inner diameter of 10 mm was used, the flow rate of the electrodeposition coating was set to 70 ml / min, and the energizing time was changed to 5 minutes. The electrodeposition coating on the inner surface of the obtained SUS316 tubular tube was evaluated. The results are shown in Table 1, and an electrodeposition coating with excellent corrosion resistance was formed on the inner surface of the entire metal tubular tube.

[0054] <Example 3> Electrodeposition coating was performed in the same manner as in Example 1, except that a SUS316 tubular tube with an inner diameter of 10 mm was used, the liquid flow rate was set to 150 ml / min, and the energizing time was changed to 5 minutes. The electrodeposited coating on the inner surface of the obtained SUS316 tubular tube was evaluated. The results are shown in Table 1, and an electrodeposited coating with excellent corrosion resistance was formed on the inner surface of the entire metal tubular tube.

[0055] <Example 4> Electrodeposition coating was performed in the same manner as in Example 1, except that a SUS316 tubular tube with an inner diameter of 10 mm was used, the liquid flow rate was set to 150 ml / min, and the energizing time was changed to 30 minutes. The electrodeposited coating on the inner surface of the obtained SUS316 tubular tube was evaluated. The results are shown in Table 1, and an electrodeposited coating with excellent corrosion resistance was formed on the inner surface of the entire metal tubular tube.

[0056] <Example 5> Electrodeposition coating was performed in the same manner as in Example 1, except that a SUS316 tubular tube with an inner diameter of 15 mm was used and the flow rate of the electrodeposition coating was set to 800 ml / min. The electrodeposition coating on the inner surface of the obtained SUS316 tubular tube was evaluated. The results are shown in Table 1, and an electrodeposition coating with excellent corrosion resistance was formed on the inner surface of the entire metal tubular tube.

[0057] <Example 6> Using a 5mm inner diameter SUS316 tubing, electrodeposition coating was performed for 60 minutes while maintaining the paint temperature at 50°C, supplying the liquid at a flow rate of 10 ml / min, and applying a DC voltage of 150 V.

[0058] Subsequently, the metal tubes were thoroughly washed with deionized water, dried by air blowing, and then pre-dried in a 110°C constant-temperature oven with forced air for 10 minutes, followed by baking at 210°C for 30 minutes. The electrodeposited coating on the inner surface of the resulting SUS316 tubes was evaluated. The results are shown in Table 1, and an electrodeposited coating with excellent corrosion resistance was formed on the inner surface of the entire metal tube.

[0059] <Comparative Example 1> Electrodeposition coating was performed in the same manner as in Example 1, except that a 5mm inner diameter SUS316 tubular capillary was used and the liquid flow rate was set to 5ml / min. The electrodeposited coating on the inner surface of the obtained SUS316 tubular capillary was evaluated. The results are shown in Table 1, and pinhole marks were observed in the electrodeposited coating on the inner surface. In the corrosion resistance test, rust corrosion was observed at the pinhole marks, indicating insufficient corrosion resistance. This is thought to be due to a low liquid flow rate and insufficient removal of air and electrolytic gases.

[0060] <Comparative Example 2> Electrodeposition coating was performed in the same manner as in Example 1, except that a SUS316 tubular tube with an inner diameter of 10 mm was used and the flow rate of the liquid was set to 450 ml / min. The electrodeposited coating on the inner surface of the obtained SUS316 tubular tube was evaluated. The results are shown in Table 1, and it was found that the electrodeposited coating was not formed on the inner surface of the entire metal tubular tube, and areas with thin film thickness were observed. In the corrosion resistance test, blistering of the coating occurred in the areas with thin film thickness, indicating insufficient corrosion resistance. It is thought that excessive liquid flow caused air to be drawn in along with the paint, preventing the formation of a coating with sufficient thickness.

[0061] <Comparative Example 3> Using a 5mm inner diameter SUS316 tubing, electrodeposition coating was performed for 60 minutes while maintaining the paint temperature at 25°C, supplying the liquid at a flow rate of 70 ml / min, and applying a DC voltage of 150 V. Afterward, the metal tubing was thoroughly washed with deionized water, dried by air blowing, and then pre-dried in a 110°C constant-temperature oven with forced air for 10 minutes, followed by baking at 180°C for 30 minutes. The electrodeposited coating on the inner surface of the resulting SUS316 tubing was evaluated. The results are shown in Table 1. While the inner surface coating properties were acceptable, blistering of the coating occurred during the corrosion resistance test, indicating insufficient corrosion resistance. It is considered that the acrylic melamine resin failed to meet the required corrosion resistance standards.

[0062] [Table 1]

[0063] As shown in Table 1, when the fluid supply ratio is set to 1 to 10, a corrosion-resistant electrodeposited coating is formed on the inner surface of the metal tube regardless of the inner diameter of the metal tube. However, when the fluid supply ratio is outside this range, it was confirmed that the formed electrodeposited coating has corrosion resistance issues.

[0064] <Example 7> A U-shaped SUS316 tubular tube with an inner diameter of 4 mm, a total length of 450 mm, and an internal volume of 5.6 ml was filled with cationic electrodeposition coating Elecoat PAI (manufactured by Shimizu Corporation).

[0065] Next, the electrodeposition coating was performed for 30 minutes by applying a DC voltage of 300V while the electrodeposition paint was supplied into a metal tube at a rate of 30 ml per minute.

[0066] Subsequently, the metal tubes were thoroughly washed with deionized water, dried by air blowing, pre-dried in a 110°C forced-air constant-temperature oven for 10 minutes, and then baked in a 240°C forced-air constant-temperature oven for 30 minutes.

[0067] An electrodeposited coating film mainly composed of amide-imide resin with an average thickness of 45 μm was formed inside the obtained metal tubular tubes, and no corrosion marks or blistering were observed on the electrodeposited coating surface.

Claims

1. A method for coating the inner surface of a metal tube, characterized by applying a DC voltage while supplying electrodeposition paint to a metal tube filled with electrodeposition paint, thereby electrodepositing the inner surface of the metal tube.

2. The painting method according to claim 1, characterized in that the electrodeposition paint is continuously supplied at a flow rate of 10 times or less the internal volume of the metal tube used for electrodeposition painting, per minute.

3. The method according to claim 1 or 2, characterized in that the metal tubular tube has an inner diameter of 15 mm or less.

4. A metal tube characterized by having its inner surface electroplated.

5. The metal tube according to claim 4, wherein the metal tube is a stainless steel tube with an inner diameter of 2 to 15 mm, and the metal tube has an electrodeposited coating film with a thickness of 5 to 100 μm formed on its inner surface from an electrodeposited coating containing an amide-imide resin.

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