JP7061297B2 - Carbon fiber-containing paint and method for forming a coating film of carbon fiber-containing paint - Google Patents

Description

The present invention relates to a carbon fiber-containing paint applied to a heat exchanger and a heat exchanger coated with the carbon fiber-containing paint, and more specifically, protects a tube or fin made of metal. It also relates to carbon fiber-containing paints and the like that are designed to improve thermal conductivity.

Generally, a heat exchanger is configured to include a tube through which a fluid to be exchanged heat is passed, and a plurality of fins provided so as to intersect the tube. Then, a fluid to be heated is passed through this tube, and heat is exchanged between the fluid and the fluid flowing outside the fins.

Such heat exchangers are used in a wide variety of fields, but for example, when water is heated using the exhaust gas of a boiler using heavy oil, the following problems occur.

That is, when heavy oil containing sulfur is burned to heat water, it is generally said that the heat exchange efficiency increases by 1% every time the temperature of the exhaust gas drops by 10 ° C. However, when the exhaust gas temperature becomes 120 ° C. or lower, the sulfur content contained in the exhaust gas is extracted from the surface of the tube or fin and becomes sulfuric acid, which corrodes the tube or fin. For this reason, in the past, the temperature of the exhaust gas was raised to 200 ° C., but in this way, not only is sulfur released into the atmosphere and it causes acid rain, but also heat exchange efficiency. Will also fall.

On the other hand, fins and the like are made of matrix resin. In addition, a heat exchanger in which carbon fibers are contained therein has also been proposed.

For example, Patent Document 1 below proposes a heat exchanger using a resin in which carbon fibers are arranged in a direction orthogonal to the longitudinal direction of a tube. In such a heat exchanger, the metal is not corroded by sulfur content, and heat can be transferred to the fins by the carbon fiber in the direction orthogonal to the tube, so that the carbon fiber having high thermal conductivity is used instead of the metal. It becomes possible to exchange heat using.

Japanese Unexamined Patent Publication No. 2017-219214

However, in such a configuration, a resin having carbon fibers arranged in a grid pattern must be molded in advance, which not only increases the manufacturing cost but also heats the gaps between the carbon fibers in a grid pattern. Cannot be transmitted. In addition, existing heat exchangers cannot be made to adopt such a configuration later. Further, since the boundary portion between the tube and the fin is bent, it becomes difficult to bend the carbon fiber along such an aspect, a gap is formed, and the thermal conductivity is lowered.

Therefore, the present invention has been made by paying attention to the above-mentioned problems, and is a carbon fiber-containing paint capable of improving the thermal conductivity efficiency even in the configuration of an existing heat exchanger made of metal or the like. Further, it is an object of the present invention to provide a heat exchanger coated with this carbon fiber-containing paint.

That is, in order to solve the above problems, the present invention is a carbon fiber-containing paint applied to the outer surface of a heat exchanger, in which coarsely pulverized carbon having an average fiber length of 5 μm to 100 μm and an average fiber diameter of 5 μm to 15 μm. Carbon fiber in which fibers and finely pulverized carbon fibers having an average fiber length of 0.5 μm to 5 μm and an average fiber diameter of 0.3 to 1.0 μm are blended in a weight ratio of 20:80 to 10:90, respectively. It is composed of a powder and a matrix resin containing the carbon fiber powder.

With this configuration, crushed carbon fiber powder can be attached by simply applying such a paint to an existing metal heat exchanger, and heat is transferred to the tubes and fins for heat exchange. You will be able to make it. Further, since the fins and the like can be coated with a paint, the metal does not corrode even if sulfur content adheres, and the need for maintenance can be reduced. This makes it possible to lower the temperature of the exhaust gas and improve the heat exchange efficiency. In addition, it is possible to increase the contact area between carbon fibers to improve thermal conductivity, suppress the aggregation of carbon fiber powder during firing, and prevent obstacles such as pinhole generation and peeling. become able to.

Further, in such an invention, the carbon fiber powder is blended in a ratio of 5 to 35 parts by weight with respect to the matrix resin .

By doing so, the contact property between the tube or fin and the carbon fiber can be enhanced, and heat can be exchanged between the carbon fiber and the carbon fiber exposed on the surface of the coating film. Further, if the content of the carbon fiber is too large, cracks will be formed in the coating film, but in the case of this ratio, cracks will not be formed. Further, if the content of the carbon fiber is made too small, the heat exchange efficiency is lowered, but with such a content, the heat exchange efficiency can be improved.

According to the present invention, crushed carbon fiber powder can be attached by simply applying such a paint to an existing metal heat exchanger, and heat is transferred from a tube or fin to exchange heat. You will be able to make it. Further, since the fins and the like can be coated with a paint, the metal does not corrode even if sulfur content adheres, and the need for maintenance can be reduced. This makes it possible to lower the temperature of the exhaust gas and improve the heat exchange efficiency. In addition, it is possible to increase the contact area between carbon fibers to improve thermal conductivity, suppress the aggregation of carbon fiber powder during firing, and prevent obstacles such as pinhole generation and peeling. become able to.

Heat exchanger to which the carbon fiber-containing paint according to the embodiment of the present invention is applied.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The heat exchanger 1 to which the carbon fiber matrix resin of this embodiment is applied is designed to heat water by utilizing waste heat from the boiler, and as shown in FIG. 1, it is from the boiler. A heat exchange chamber 2 in which exhaust gas is placed, a tube 3 provided so as to meander in the heat exchange chamber 2, and a plurality of parallel fins 4 arranged so as to be orthogonal to the tube 3 are provided. It is composed. Then, cold water is passed through the tube 3, and high-temperature exhaust gas is allowed to flow into the heat exchange chamber 2 to exchange heat with the water in the tube 3 via the fins 4 to heat the water. And, characteristically, the heat exchanger 1 was coated with a matrix resin containing crushed carbon fibers, thereby preventing metal corrosion due to sulfur content and improving heat exchange efficiency. It is a thing. Hereinafter, an embodiment of the present invention will be described in detail.

First, an outline of the heat exchanger 1 to which the carbon fiber-containing paint is applied will be briefly described.

First, the heat exchange chamber 2 constituting the heat exchanger 1 is for passing a fluid such as high-temperature exhaust gas, and as shown in FIG. 1, the input port 21 is on one side and the discharge port 22 is on the other side. Is provided. Then, the high-temperature first fluid flowing into the inlet 21 is passed through the gap between the fins and discharged from the outlet 22. In FIG. 1, the input port 21 is provided in a direction orthogonal to the fin 4 (normal direction), but the first fluid is put in the direction parallel to the fin 4 and the exhaust gas is passed through the gap of the fin 4. You may try to make it easier.

On the other hand, the tube 3 is provided so as to meander from side to side, and allows a second fluid to be heat exchange to pass through the inside. Here, cold water is used as the second fluid, and the cold water is heated and discharged as hot water. Here, the tube 3 is meandered, but a header (not shown) for meandering the second fluid in the tube 3 is provided at both left and right ends, and the linear tube 3 is connected to this header to meander. You may do it.

Further, the fins 4 provided so as to intersect with the tube 3 are designed to exchange heat between the second fluid in the tube 3 and the first fluid in the heat exchange chamber 2, and are welded to the tube 3. Is provided. Then, the first fluid, which is an exhaust gas, is passed through this gap to allow the fins 4 to absorb heat, and the heat is transferred to the second fluid in the tube 3.

In such a configuration, if exhaust gas obtained by burning heavy oil is used as the first fluid, the sulfur content in the heavy oil adheres to the inner wall of the heat exchange chamber, the tubes 3, the fins 4, etc., and the metal thereof. It reacts with and corrodes. Further, in the past, a method of opening a gap between the fins 4 and the fins 4 was adopted in order to dissolve the adhered dirt with a solution and periodically remove the dirt, but this would increase the size of the device. Not only that, it was necessary to use expensive metals such as titanium and SUS316L to prevent corrosion. Therefore, in this embodiment, in a conventional metal heat exchanger, a matrix resin containing carbon fibers is applied to coat the metal surface with a coating film to prevent corrosion and to prevent corrosion. Instead of dissolving the dirt with a solution and removing it, the dirt can be easily removed.

Such a carbon fiber-containing paint is configured to contain carbon fibers and a matrix resin.

When such carbon fibers are used, if the fiber length of the carbon fibers is too long, the carbon fibers are formed along the connecting portion between the tube 3 and the fin 4, the bent portion and the outer peripheral portion of the tube 3, the end portion of the fin 4, and the like. I can't attach it well. Further, if the fiber length is too short, not only the connection with each carbon fiber is reduced, but also aggregation occurs when the fiber is mixed with the matrix resin. Therefore, preferably, the carbon fibers are pulverized in a range where the average fiber length is 100 μm or less so as to be in close contact with the end portion of the fin 4 or the bent portion of the tube 3. At this time, the coarsely pulverized carbon fibers have an average fiber length of 5 to 100 μm and an average fiber diameter of 5 to 15 μm. Further, with only such coarsely pulverized carbon fibers, the contact area between the carbon fibers becomes small, and the heat conduction efficiency deteriorates. Therefore, in the present embodiment, carbon fibers having a fiber length of 5 μm or less (preferably an average fiber length of 0.5 to 5 μm) and an average fiber diameter of 0.3 to 1 μm are contained as the finely pulverized carbon fibers. .. By containing such fine particles of carbon fibers, it is possible to prevent carbon fibers from agglomerating in the matrix resin, and also prevent reaggregation during firing of the matrix resin, generation of pinholes, peeling, and the like. You will be able to. The ratio of the coarsely pulverized carbon fiber to the finely pulverized carbon fiber shall be in the range of 20:80 to 10:90 by weight.

As such a carbon fiber, a new or recycled carbon fiber or the like can be used, and the type of the carbon fiber may be a PAN type or a pitch type. When such carbon fibers are pulverized into particles, they can be pulverized by a known method, and for example, airflow pulverization, a ball mill, a crusher mill, or the like can be used.

On the other hand, the matrix resin contains carbon fibers and is made to adhere to metals such as tubes 3 and fins 4, and here, varnish-based resin, silicon-based resin, acrylic resin, vinyl acetate-based resin. A resin or the like can be used, and if necessary, a copolymerized product can also be used. Here, a polyimide varnish is used, and one diluted with the solvent porolidone is used. Since this varnish-based resin is a polyamic acid solution that is a precursor of polyimide, the solvent is removed and the imidization reaction proceeds by applying it to the surface of the heat exchanger 1 and baking it at a high temperature. Therefore, it becomes a polyimide coating film having excellent insoluble and infusible properties, heat resistance, chemical properties, and electrical insulation properties. Then, a dispersant is appropriately added to this matrix resin so that the carbon fibers are dispersed in the solution.

The operation when this varnish-based matrix resin is used will be described.

When forming a polyimide coating film, the polyamic acid contained in the varnish-based resin is imidized (closed) so that the coating film is formed on the metal surface. At this time, in order to adjust the polyamic acid. , Generally, a diamine component or a tetracarboxylic acid dianhydride component is used. However, this diamine component or tetracarboxylic acid dianhydride component is greatly affected by the dispersant of carbon fibers, and in particular, pyrrolidone in imidizing the varnish-based resin at the time of initial firing at 100 to 120 ° C. The residual content of the solvent such as the above drops to around 10 ppm, and when the temperature exceeds 180 ° C, the aqueous dispersant used to disperse the carbon fiber powder begins to vaporize, and the carbon particles that have lost the steric disorder melt. Reaggregation occurs in the matrix resin that is thermally cured from the state, and the air passage in the matrix resin is widened to become a foamed state. Therefore, it is impossible to use a dispersant with a large number of hydrophilic groups, which has a small lipophilic group and is easily adsorbed on the surface of carbon particles, which has been used to disperse carbon fibers, because it falls into the above-mentioned situation by molding a polyimide resin. Will be. Therefore, a phosphate-free fatty acid-based dispersant having adsorption suitable for a non-polar surface is used, and 1 to 3 parts by weight thereof is blended with respect to the total amount. As a result, the reaggregation of carbon fibers due to the vaporization and movement of water molecules is reduced from the time when the temperature exceeds 200 ° C to the time when the water molecules are decomposed at a high temperature, and the generation of pinholes can be prevented.

When carbon fibers are contained in such a matrix resin, if the proportion of carbon fibers is small, the carbon fibers do not continue between the tube 3 or fin 4 and the outside of the coating film, and heat exchange cannot be performed. On the other hand, if the proportion of carbon fiber is too large, cracks and peeling from the metal will occur. Therefore, the carbon fiber is preferably blended in a proportion of 5 to 35 parts by weight, and preferably within the range of 10 to 20 parts by weight in consideration of peeling prevention and crack prevention after the coating film is cured.

When the carbon fiber-containing paint thus blended is applied to the heat exchanger 1, various methods can be used. , A coating method using a defoaming roller, a dipping coating method, a brush coating, or the like can be used. At this time, if the dipping coating method is used, the coating film can be uniformly formed, the exposed portion of the metal is eliminated, the thickness is made uniform, and the carbon fibers are continuously contacted between the metal and the surface of the coating film. It will be possible to exchange heat.

In such a configuration, first, when producing a carbon fiber-containing paint, PAN-based or pitch-based carbon fibers are coarsely crushed to generate chipped fibers, and the chipped fibers are put into an air flow crusher or the like. Then, crude carbon fiber powder having an average fiber length of 5 to 100 μm and an average fiber diameter of 5 to 15 μm is produced. Then, the crude carbon fiber powder is taken out, and a part of the carbon fiber powder is put into the crusher again, and this time, fine carbon having an average fiber length of 0.5 to 5 μm and an average fiber diameter of 0.3 to 1 μm is finely pulverized. Fiber powder is produced, and the coarsely crushed carbon fiber powder and the finely crushed carbon fiber powder are mixed in a weight ratio of 20:80 to 10:90.

On the other hand, in order to form a matrix resin at the same time, a dispersant is added to the varnish-based resin, and the mixed carbon fiber powder is added at a ratio of 5 to 35 parts by weight and mixed.

At this time, if the charged carbon fiber powder is only finely crushed carbon fiber powder, aggregation will occur, but the coarsely crushed carbon fiber and the finely crushed carbon fiber are mixed, so that the carbon fiber powder is mixed. Aggregation can be prevented, and the contact area between the carbon fibers can be increased to ensure thermal conductivity. Then, the matrix resin containing the carbon fibers is stirred in this way to disperse the carbon fibers in the solution.

Next, the matrix resin thus produced is applied to the tubes 3 and fins 4 of the heat exchanger 1. In this coating step, when applying to the existing heat exchanger 1, it is difficult to apply between the fins 4 and 4, so a matrix resin is put in a bathtub and the heat exchanger 1 is placed therein. Dipping (pickling). Then, after that, the heat exchanger 1 is taken out, dried, and then heat-treated in the firing chamber.

In this heat treatment step, the solvent is removed by the high temperature, and the imidization reaction proceeds to produce a polyimide coating film having excellent insolubility, heat resistance, chemical resistance and the like. In addition, by using a fatty acid-based dispersant that does not contain phosphate as the dispersant, reaggregation of carbon fibers due to vaporization and movement of water molecules is reduced even during high-temperature heating, and the occurrence of pinholes is prevented. can do.

As described above, according to the above embodiment, in the carbon fiber-containing paint applied to the outer surface of the heat exchanger 1, the coarsely pulverized carbon fiber having an average fiber length of 5 μm to 100 μm and an average fiber diameter of 5 μm to 15 μm is used. , Finely crushed carbon fibers having an average fiber length of 0.5 μm to 5 μm and an average fiber diameter of 0.3 to 1.0 μm, and a carbon fiber powder blended in a weight ratio of 20:80 to 10:90, respectively. Since the matrix resin containing the carbon fiber powder is provided, the crushed carbon fiber powder can be attached only by applying such a paint to the existing metal heat exchanger 1. , The heat of the tube 3 and the fin 4 can be transferred and exchanged. Further, since the fins 4 and the like can be coated with a paint, the metal does not corrode even if sulfur content adheres, and the need for maintenance can be reduced. This makes it possible to lower the temperature of the exhaust gas and improve the heat exchange efficiency. In addition, it is possible to increase the contact area between carbon fibers to improve thermal conductivity, suppress the aggregation of carbon fiber powder during firing, and prevent obstacles such as pinhole generation and peeling. become able to.

Further, since the carbon fiber powder is blended in a ratio of 5 to 35 parts by weight with respect to the matrix resin, the contact between the tube 3 and the fins 4 and the carbon fiber can be improved, and the carbon fiber can be combined with the carbon fiber. It becomes possible to exchange heat with the carbon fibers exposed on the surface of the coating film. Further, if the content of the carbon fiber is too large, cracks will be formed in the coating film, but in the case of this ratio, cracks will not be formed. Further, if the content of the carbon fiber is made too small, the heat exchange efficiency is lowered, but with such a content, the heat exchange efficiency can be improved.

The present invention is not limited to the above embodiment and can be carried out in various embodiments.

For example, in the above embodiment , the heat exchanger 1 is made to generate a coating film containing carbon fiber powder, but the resin may disappear and the coating film may become thin due to use. Even in such a case, only the carbon fiber remains, but the thermal conductivity can be ensured by forming a coating film on the carbon fiber in the same manner.

1 ... Heat exchanger 2 ... Exchange chamber 21 ... Input port 22 ... Discharge port 3 ... Tube 4 ... Fins

Claims (3)

In the carbon fiber-containing paint applied to the outer surface of the heat exchanger
Coarse crushed carbon fiber with an average fiber length of 5 μm to 100 μm and an average fiber diameter of 5 μm to 15 μm and finely crushed carbon fiber with an average fiber length of 0.5 μm to 5 μm and an average fiber diameter of 0.3 to 1.0 μm. Carbon fiber powder containing fibers in a weight ratio of 20:80 to 10:90, respectively .
A matrix resin containing the carbon fiber powder and
A carbon fiber-containing paint characterized by the provision of. The carbon fiber-containing paint according to claim 1 , wherein the carbon fiber powder is blended with the matrix resin in a ratio of 5 to 35 parts by weight. Coarse crushed carbon fiber with an average fiber length of 5 μm to 100 μm and an average fiber diameter of 5 μm to 15 μm and finely crushed carbon fiber with an average fiber length of 0.5 μm to 5 μm and an average fiber diameter of 0.3 to 1.0 μm. A step of dispersing carbon fiber powder in which fibers are mixed at a weight ratio of 20:80 to 10:90 in a matrix resin, and
The process of applying a carbon fiber-containing paint made of a matrix resin in which the carbon fiber powder is dispersed to the outer surface of the heat exchanger, and
After applying the carbon fiber-containing paint, the process of drying the carbon fiber-containing paint and
The step of heating and firing the coating film formed by the dried carbon fiber-containing paint, and
A method for forming a coating film of a carbon fiber-containing paint of a heat exchanger.

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