JP2009247949A - Water-repellent coating film and liquid transportation piping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-repellent coating film capable of stably holding an air layer over a long period of time in the water-repellent coating film, and to provide a liquid transportation piping. <P>SOLUTION: In the water-repellent coating film, the average pore diameter of pores formed on the film is ≥5 nm and ≤50 nm, the porosity of the film is ≥15 vol.% and ≤50 vol.%, and inorganic particles are included in the film. Also, the liquid transportation piping is for transportation liquid, and the water-repellent coating film is formed on the inner surface of the piping for transporting the liquid by being allowed to pass through the inside. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water-repellent coating film and fluid transport piping for reducing frictional resistance with a fluid.

  Generally, when a fluid is passed through a pipe, a pressure drop, that is, a pressure loss occurs at an inlet and an outlet. This pressure loss increases as the diameter of the pipe decreases and the length of the pipe increases. The pressure loss is an energy loss due to frictional resistance between the fluid and the pipe surface. If this can be reduced, the energy efficiency of the equipment / system will be dramatically improved, and various research and development have been conducted.

  We examined pressure loss when water was passed through the inner surfaces of rectangular and square tubes, and confirmed that when water repellent coating film was formed on the inner surface of the tube, the pressure loss was reduced compared to ordinary tubes. There is a thing (for example, refer nonpatent literature 1). In this case, the rate of pressure loss reduction is about 22% in the case of a square tube, and it is inferred from theoretical analysis that this resistance reduction effect is caused by slippage of the fluid on the pipe surface. However, this phenomenon of pressure loss reduction is observed only in the laminar flow region where the flow velocity is small, and this effect disappears in the turbulent flow region where the flow velocity is high.

  In addition, the same investigation was performed on the friction coefficient of the rotating disk in water, and in this case, when a water-repellent film was formed on the surface, there was confirmed that the friction coefficient was reduced by about 30% (for example, Non-Patent Document 2). In this case as well, the phenomenon of reducing the friction coefficient is observed only in the laminar flow region where the flow velocity is small, and the effect disappears in the turbulent flow region where the flow velocity is high.

  On the other hand, as a result of forming a water-repellent wall on the upper and lower surfaces of the rectangular tube and measuring the pressure loss, there has been confirmed that the flow resistance is reduced by about 4.5% compared to a normal wall (for example, non-patent document) 3). This decrease in resistance greatly depends on the shape of the fine irregularities formed on the water-repellent wall, and on a completely smooth surface, the decrease in resistance is not recognized, and the pressure loss is reduced when a microstructure that easily retains air is formed. It is said that it will be accepted. However, the Reynolds number in this experiment is a laminar flow region of 1300 or less, and measurement at a flow velocity higher than this is not performed.

  These studies show the following. In other words, it is considered possible to reduce the pressure loss by forming a water-repellent film in the fluid flow path, but the pressure loss cannot be reduced with only the water-repellent film, and the water-repellent coating film. It is necessary to hold an air layer, and these pressure loss reduction phenomena can be seen only in a laminar flow region having a small Reynolds number, and no effect is seen in a turbulent flow region having a high flow velocity.

  For this reason, as a method for retaining the air layer in the water-repellent coating film, it has been proposed to form a fine uneven structure on the surface of the water-repellent coating film (see, for example, Patent Document 1). At this time, as a method for artificially forming the concavo-convex structure, mechanical processing such as polishing and grinding, chemical reaction by acid / alkali, electrolysis by electrode, casting by metal, and the like are cited.

  It has also been proposed to reduce the flow resistance between the solid and the liquid by forming irregularities on the solid surface and reducing the surface energy at the solid interface by means of precision cutting, vapor deposition, etching, painting, etc. (For example, refer to Patent Document 2).

  In addition, after forming a resin layer on the surface of the substrate and coating hydrophobic particles on the resin layer, pressing to embed a part of the hydrophobic particles in the resin, It has also been proposed to form a fine uneven surface by projecting onto the resin surface and immobilizing the hydrophobic particles by solidifying the resin (for example, see Patent Document 3).

Furthermore, it is proposed that a specific powder is prepared into a resin and the resulting preparation is applied to the surface of the base material to form irregularities due to the powder on the surface of the coating film to obtain air film retention performance. (For example, refer to Patent Document 4).
Japanese Patent Laid-Open No. 9-279363 JP 2000-87921 A JP-A-9-53612 JP-A-8-26176 Keizo Watanabe, YANUAR, Masaru Okido, Hiroshi Mizunuma, “Study on resistance reduction effect of super water-repellent rectangular tube”, Transactions of the Japan Society of Mechanical Engineers, 62-601, B (1996), p3330-3334 Keizo Watanabe, Satoshi Ogata, “Reduction of Friction Resistance in Newtonian Fluids of Super-Water-Repellent Rotating Discs”, Transactions of the Japan Society of Mechanical Engineers, 63-612, B (1997), p2752-2756 Masato Hasegawa, Masayuki Kakunami, Kosei Kanno, Hisashi Ueno, “Flow characteristics of flow in rectangular pipe with water-repellent microstructure on top and bottom walls”, Proceedings of the 42nd Japan Heat Transfer Symposium, B122, (2005-6 )

  However, in the method of forming irregularities on the water repellent coating film as described above, even if an air layer can be temporarily formed on the film, it is difficult to stably hold the air layer for a long period of time. Alternatively, the air layer is maintained in the low flow velocity region, but there is a problem that the air layer is peeled off in the high flow velocity region.

  An object of the present invention is to provide a water-repellent coating film and a liquid transport pipe that can stably hold an air layer in the water-repellent coating film for a long period of time.

  As a result of intensive research on the water-repellent coating film structure for reducing friction with fluid, the present inventors have formed fine pores having an appropriate pore diameter with an appropriate porosity in the water-repellent coating film. Furthermore, by blending inorganic particles in the water-repellent coating film, the air layer can be stably maintained over a long period of time, and not only in a low flow rate range but also stably in a high flow rate range. The present inventors have found that an air layer can be maintained and completed the present invention.

  That is, the water-repellent coating film according to the present invention has an average pore diameter of 5 nm or more and 50 nm or less of pores formed in the film, and the porosity of the film is 15% by volume or more and 50% by volume or less, And the said film | membrane contains an inorganic particle, It is characterized by the above-mentioned.

  The fluid transport pipe of the present invention is a pipe for transporting a fluid, and the water repellent coating film of the present invention is formed on the inner surface of the pipe for transporting the fluid by passing through the inside thereof. It is what.

  The water-repellent coating film of the present invention has water repellency, and at the same time, fine continuous pores are formed in the water-repellent coating film, and inorganic particles are blended in the film. The layer can be stably held for a long period of time, and the air layer can be stably held not only in the low flow rate region but also in the high flow rate region. Therefore, when this water-repellent coating film is formed on the liquid contact surface, pressure loss due to friction between the liquid and the film can be reduced. For example, the inner surface of the pipeline that transports the fluid, the passage portion of the cooling water, When formed on water turbine parts, ship bottoms, etc., the energy efficiency of the system can be improved.

  In the water-repellent coating film of the present invention, the average pore diameter of pores formed in the film is 5 nm or more and 50 nm or less, and the porosity of the film is 15% by volume or more and 50% by volume or less. It contains inorganic particles. FIG. 1 shows a schematic cross-sectional view when the water-repellent coating film of the present invention is formed on a metal substrate. As shown in FIG. 1, the water repellent coating film 1 is formed on the surface of the metal substrate 2. The water repellent coating film 1 is a film including inorganic particles 4 having water repellency and having fine continuous pores 3 formed therein.

  Here, the water-repellent coating film 1 can be formed of a known material, for example, a silicon oxide main component, an aluminum oxide main component, a zirconium oxide main component, a fluororesin As a main component, a mixture of these may be used. Among these, those mainly composed of a fluororesin are more suitable materials because they exhibit high water repellency and are extremely chemically stable. Furthermore, it is easy to form pores having the above pore diameter and porosity in the water-repellent coating.

In addition, examples of the composition mainly composed of silicon oxide include compositions such as SiO ₂ —ZrO ₂ , and when a film is formed with this composition, it is chemically and thermally stable, It is easy to form pores having the above pore diameter and porosity in the water-repellent film, and at the same time, it is relatively easy to impart a water-repellent group such as a methyl group or a fluorine group.

  The formation of this film may be performed by a normal film forming method, for example, wet coating such as CVD, PVD, spraying, dip coating, spray coating, flow coating, spin coating, roll coating, etc. The film forming method is not limited.

  The pores formed in this film have an average pore diameter of 5 nm or more and 50 nm or less. The smaller the pore diameter in the film, the more the fluid enters the film pores and the more stable the air layer is.

  Here, the reason that the average pore diameter is limited to 50 nm or less is that when the average pore diameter is larger than 50 nm, the ingress of fluid into the pores is not sufficiently suppressed, and the air layer is not stably maintained. On the other hand, the reason why the average pore diameter is limited to 5 nm or more is that when the average pore diameter is smaller than 5 nm, it is difficult to form an air layer, and the pressure loss reduction that is the object of the present invention cannot be realized. Here, the average pore diameter is determined by a method such as a gas adsorption method or a mercury intrusion method.

  Furthermore, this film has a porosity of 15% by volume or more and 50% by volume or less. In order to effectively reduce the pressure loss to the liquid, what is important in the water-repellent coating film is that pores formed in the film are continuously connected to the entire film.

  The reason why the porosity of the film is limited to 15% by volume or more is that when the porosity is smaller than 15% by volume, a part or a substantial part of the pores are closed and a sufficient air layer cannot be formed. It is. Further, the reason why the porosity of the film is limited to 50% or less is that when the porosity is larger than 50% by volume, the strength and durability of the film become insufficient and problems such as peeling occur.

  Here, the porosity indicates the volume ratio of the cavity to the entire coating. In addition, in the cross section in FIG. 1, although it seems that the pore is not connected continuously, it is connected continuously three-dimensionally.

  In addition, the water-repellent coating film 1 of the present invention is formed on the metal substrate 2, but the material that can be used as the substrate is not limited to metal, and forms a water-repellent coating film such as resin or ceramics. If it can do, it will not specifically limit.

  In order to achieve the above-described object, the water-repellent coating film according to the present invention preferably has a contact angle of 90 ° or more between the film and the liquid in contact with the film.

  FIG. 2 is a view for explaining the definition of the contact angle with respect to water. In this figure, the contact angle θ is defined as follows.

θ = 2 tan ⁻¹ (h / r)
In the water-repellent coating film of the present invention, the contact angle with respect to the liquid to be contacted is preferably 90 ° or more. When the contact angle is smaller than 90 °, the slip at the interface with the fluid solid is insufficient. This is because the effect of reducing the pressure loss is reduced.

  The liquid to be contacted is preferably water or a liquid containing water. At this time, it is preferable to use a water repellent coating film having a contact angle of 90 ° or more with respect to those liquids. Here, examples of the water-repellent coating film having a contact angle with water or a liquid containing water of 90 ° or more include, for example, a fluorine resin as a main component, a silicon oxide as a main component, and an aluminum oxide as a main component. And those containing zirconium oxide as a main component, or a mixed system thereof.

  In addition, the water-repellent coating film according to the present invention is preferably water or a liquid containing water as the fluid in contact with the water-repellent coating film, and the water-containing liquid is an inorganic compound or organic compound that is water-soluble or insoluble in water. Examples include water-based liquids containing compounds, and specific examples include seawater, river water, antifreeze liquids (ethylene glycol-based, propylene glycol-based, etc.), water containing rust inhibitors, and the like.

  The water-repellent coating film according to the present invention preferably has a film thickness of 0.1 μm or more and 50 μm or less. The reason for limiting the film thickness of the water-repellent coating film to 0.1 μm or more is that when the film is smaller than 0.1 μm, a part of the film is not formed or the film is not worn due to slight wear. Because it will be lost. Accordingly, sufficient water repellency cannot be maintained, and the object of the present invention cannot be achieved. On the other hand, the reason why the thickness is limited to 50 μm or less is that when the film thickness is greater than 50 μm, the adhesion strength decreases, problems such as peeling occur, and it becomes difficult to apply to an actual machine.

  The inorganic particles of the present invention preferably have an average particle size of 1 nm or more and 300 nm or less. When inorganic particles are blended in a film having continuous pores, a stable air layer can be formed in the vicinity where the inorganic particles are held in the film. Here, the average particle size is limited to 300 nm or less. When the average pore size is larger than 300 nm, the voids formed in the vicinity of the inorganic particles are large, and the entry of fluid into the voids is not sufficiently suppressed, and the air layer This is because is not stably maintained. On the other hand, the reason why the average particle size is limited to 1 nm or more is that when the average particle size is smaller than 1 nm, it is difficult to form an air layer, and it is difficult to reduce the pressure loss, which is the object of the present invention.

  Furthermore, the volume ratio of the inorganic particles is desirably 2% by volume or more and 30% by volume or less of the entire coating excluding the pores. The reason why the volume ratio of the inorganic particles is limited to 2% by volume or more is that when the volume ratio is smaller than 2% by volume, the effect of holding the air layer in the vicinity of the inorganic particles is small, and the volume ratio of the inorganic particles is 30%. The reason why it is limited to not more than volume% is that when the volume ratio is larger than 30 volume%, the inorganic particles fall off and the strength and durability of the film are not sufficient.

  Examples of the inorganic particles according to the present invention include metal compounds such as metal oxides, metal nitrides, metal carbides, metal silicides, and carbon. At this time, crystalline and amorphous are not asked. Specifically, metal oxides such as titanium oxide, zirconium oxide, aluminum oxide, silicon oxide, chromium oxide, yttrium oxide and niobium oxide, metal nitrides such as silicon nitride, titanium nitride, zirconium nitride and chromium nitride, silicon carbide Metal carbides such as titanium carbide, zirconium carbide and chromium carbide, and metal silicides such as molybdenum silicide and tungsten silicide. In particular, carbon itself has water repellency and is chemically stable, and is a highly practical material in terms of environment. Furthermore, since the carbon nanotube has a cavity in the tube and at the same time the particle shape has an aspect ratio, this is very suitable for maintaining the air layer, which is the main point of the present invention.

  In the water-repellent coating film according to the present invention, the inorganic particles to be blended are preferably columnar or needle-like particles having an aspect ratio of 2 or more. The reason is that the inorganic particles have an aspect ratio, so that a stable air layer can be formed in the vicinity of the portion where the inorganic particles are fixed in the film, which is extremely suitable for reducing the pressure loss, which is the object of the present invention. .

  Next, the manufacturing method of the water-repellent coating film of the present invention will be described. In the method for producing a water-repellent coating film of the present invention, first, a water-repellent film composition is prepared by blending a pore-forming substance in a composition capable of forming a water-repellent coating film. The pores can be formed by removing the pore-forming substance from the coating after forming the coating on the surface.

  In addition, the pore-forming substance for forming pores exists in the form of a granular solid or liquid in the process until the film is formed, and only this substance is formed in the process of forming the pores after forming the film. As a result of disappearance of pores, pores are formed in the water-repellent coating film.

  For example, when the water-repellent coating composition is a composition for forming a ceramic, a compound that evaporates or sublimes below the firing temperature can be used, and when the firing operation is not performed, or the firing and heat treatment temperatures are In the case where the temperature is relatively low, a substance that dissolves and elutes in water or a solution can be used by immersing the film in water or a solution after forming a film on the substrate.

  The pore-forming substance is not particularly limited as long as it can be removed by polyethylene glycol, baking during film formation, or elution after film formation. Glycols with a wide range of molecular weights are inexpensive and commercially available, and are low in cost. Since the boiling point is as low as 150 ° C to 200 ° C, they can be lost simultaneously with firing when forming a film with ceramic. Moreover, since it is soluble in water, it can be dissolved and eluted by immersing it in water or an aqueous solution, and it is a suitable compound for forming the water-repellent coating film of the present invention.

  The pores of the water-repellent coating film are formed by the disappearance of the pore-forming substance, and are therefore closely related to the molecular weight of the pore-forming substance, and are determined according to a desired average pore diameter. A pore-forming substance having a molecular weight or the like, that is, a pore-forming substance having a molecular weight close to the average pore diameter to be formed may be selected, whereby the average pore diameter can be controlled. Further, in this preparation step, the porosity can be controlled by the mixing ratio of the pore-forming substance.

  Thus, since the average pore diameter and porosity can be controlled by the molecular weight and blending amount of the pore-forming substance, the optimum average pore diameter and porosity are set for the liquid in contact with the water-repellent coating film. Thus, the water-repellent coating film can be formed by setting the conditions as described above, and the water-repellent coating film capable of achieving a reduction in pressure loss can be efficiently obtained.

  In the case of a composition that is not subjected to a firing operation, after forming a film, the film is immersed in water or a solution to dissolve and elute the pore-forming substance to form pores in the water-repellent coating film. be able to. When dissolving or eluting, ultrasonic treatment may be performed in order to promote these.

  The present invention will be described below with reference to examples and comparative examples. In the present example and the comparative example, as shown in FIG. 1, the inorganic particles 4 are contained in the coating 2 having water repellency on the surface of the metal substrate 1 and formed with fine continuous pores 3. A water-repellent coating film having a structure having

  In addition, as shown in FIG. 3, the performance evaluation of the water-repellent coating film was carried out by measuring the pressure at each of the pump and the inlet and outlet for circulating water through the metal pipe 5 having the water-repellent coating film formed on the inner surface. The pressure gauge 6 and 7 is used to inject water into the pipe 5 in the direction of the arrow by the pump pressure, and the pressure at the inlet and outlet is measured by the pressure gauges 6 and 7. Was evaluated.

Example 1
When polyethylene glycol # 400 (manufactured by Wako Pure Chemical Industries, Ltd.) and carbon powder having a particle size of 100 nm are formed as a film in an aqueous slurry containing a fluororesin, the volume becomes 20% by volume with respect to the entire film portion excluding pores. Thus, a dispersion was prepared. The blending amount of polyethylene glycol at this time was such that a porosity of 45% was formed by elution of polyethylene glycol in the immersion step in water after film formation. This dispersion is applied to the inner surface of an aluminum tube having an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 1 m by dipping. After coating, the coating is dried at room temperature for about 15 hours and heat treated at 120 ° C. for 30 minutes in the atmosphere to form a film. did. Thereafter, the aluminum tube was immersed in water at room temperature and polyethylene glycol was eluted from the film while performing ultrasonic treatment to form pores.

  The film thickness of the coating film at this time was about 1 μm, the average pore diameter of the film was 30 nm, and the contact angle of this film with water was about 100 °. The apparatus configuration shown in FIG. 3 was obtained using the obtained aluminum tube, and the pressure of the aluminum tube was measured by measuring the pressure (static pressure) at the inlet and outlet while passing pure water at room temperature through the pump inside the aluminum tube. Loss was measured. The Reynolds number at this time was 1,000 (laminar flow region). As a result, it was confirmed that the tube with the coating formed was reduced by about 15% in the pressure loss compared to the tube without the coating, and the pressure loss could be reduced effectively. .

(Example 2)
A coating film was formed in exactly the same manner as in Example 1 except that the amount of carbon particles blended in the composition was reduced and the blending amount of carbon was 10% by volume with respect to the entire coating film excluding pores. The pressure loss was measured by the same method. As a result, the pressure loss of the tube with the coating film was recognized by about 12% as compared with the tube without the coating film.

(Example 3)
A coating film was formed in exactly the same manner as in Example 1 except that the amount of carbon particles blended in the composition was reduced and the blending amount of carbon was 5% by volume with respect to the entire coating film excluding pores. The pressure loss was measured by the same method. As a result, the tube with the coating formed was found to have a pressure loss reduction of about 8% compared to the tube without the coating.

(Comparative Example 1)
A coating film was formed in exactly the same manner as in Example 1 except that the amount of carbon particles blended in the composition was reduced and the blending amount of carbon was 1% by volume with respect to the entire coating film excluding pores. The pressure loss was measured by the same method. As a result, the pipe with the coating film did not show a decrease in pressure loss as compared with the pipe without the coating film.

(Comparative Example 2)
The film was formed in exactly the same manner as in Example 1 except that the amount of carbon particles blended in the composition was increased and the blending amount of carbon was 35% by volume with respect to the entire film excluding pores. The pressure loss was measured in the same way as the example. As a result, the tube with the coating was only reduced by about 2% in pressure loss compared to the tube without the coating.

(Comparative Example 3)
A film was formed in exactly the same manner as in Example 1 except that the average particle size of the carbon particles blended in the composition was 400 nm. At this time, the contact angle of the film with water was about 100 °, and the porosity of the film was 45%. With respect to the tube on which this film was formed, the pressure loss was measured by the same method as in the first example. As a result, the tube with the coating was only found to have a pressure loss reduction of about 4% compared to the tube without the coating.

(Comparative Example 4)
A film was formed in exactly the same manner as in Example 1 except that the average particle size of the carbon particles blended in the composition was 0.5 nm. At this time, the contact angle of the film with water was about 100 °, and the porosity of the film was 45%. With respect to the tube on which this film was formed, the pressure loss was measured by the same method as in the first example. As a result, the pipe with the coating film did not show a decrease in pressure loss as compared with the pipe without the coating film.

  As described above, according to the embodiment of the present invention, an air layer can be stably maintained over a long period of time, and the air layer can be stably maintained not only in a low flow rate region but also in a high flow rate region. Therefore, fluid friction resistance can be reduced and energy efficiency can be drastically improved in devices and systems involving fluid.

The schematic cross section at the time of forming the water-repellent coating film of this invention on a metal base material. Explanatory drawing of the contact angle of the liquid in the water-repellent coating film of this invention. The schematic diagram of the apparatus which evaluates the pressure loss of the piping which formed the water-repellent coating film of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Water-repellent coating film, 2 ... Metal base material, 3 ... Pore, 4 ... Inorganic particle,
5 ... Aluminum tube, 6 ... Pressure gauge (for liquid inlet measurement), 7 ... Pressure gauge (for liquid outlet measurement)

Claims (11)

The average pore diameter of pores formed in the film is 5 nm or more and 50 nm or less, the porosity of the film is 15% by volume or more and 50% by volume or less, and the film contains inorganic particles. Water repellent coating film. The water repellent coating film according to claim 1, wherein a contact angle between the film and a liquid in contact with the film is 90 ° or more. The water repellent coating film according to claim 1 or 2, wherein the liquid in contact with the film is water or a liquid containing water. The water-repellent coating film according to any one of claims 1 to 3, wherein the film thickness is 0.1 µm or more and 50 µm or less. The water-repellent coating film according to claim 1, wherein the film is made of a fluororesin. 6. The water-repellent coating film according to claim 1, wherein the inorganic particles have an average particle diameter of 1 nm or more and 300 nm or less. The water-repellent coating film according to any one of claims 1 to 6, wherein the inorganic particles are 2 vol% or more and 30 vol% or less of the entire film. The water repellent coating film according to claim 1, wherein the inorganic particles are made of carbon. The water-repellent coating film according to any one of claims 1 to 8, wherein the inorganic particles are columnar or acicular particles having an aspect ratio of 2 or more. The water-repellent coating film according to any one of claims 1 to 8, wherein the inorganic particles are carbon nanotubes. It is piping which conveys fluid, Comprising: The water-repellent coating film of any one of Claims 1 thru | or 10 was formed in the inner surface of piping which conveys the said fluid by passing the inside. Fluid transport piping.

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