JPS63199274A - Aqueous coating composition for heat exchanger and heat exchanger coated with said composition - Google Patents

Abstract

PURPOSE:To provide the titled composition outstanding in water wettability, and performance persistency when applied on the aluminum fin of heat exchangers, effective in suppressing frost deposition on the heat exchangers, comprising each specific cation exchange resin, film-forming resin emulsion and surfactant in specified proportion. CONSTITUTION:The objective composition comprising (A) 5-40wt.% of a cation exchange resin in which >=30(pref. >=50)% of the ion exchange group has been ionically exchanged by lithium (pref., with the total exchange capacity >=1.5mg eq./g dry resin and a particle size 0.5-10mu), (B) 94-40wt.% of a film-forming resin emulsion free from cationic surfactant, and (C) 1-20wt.% of either anionic or nonionic surfactant (pref., nonionic one; e.g., polyethylene glycol monolaurate), and furthermore, pref. (D) a non-neutral type water-soluble resin. All of the amounts mentioned above are on a solid basis.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a water-based coating composition for heat exchangers, and more specifically, it is applied to the heat transfer surface of a heat exchanger, and has excellent water wettability and frost formation control for a long period of time. The present invention relates to an aqueous coating composition capable of providing an effective coating and to a heat exchanger having a heat transfer surface coated with the composition.

BACKGROUND ART In recent years, the proportion of air-source heat pump type air conditioners (hereinafter simply referred to as heat pumps) in air conditioners has been rapidly increasing, and they now account for more than half of household room air conditioners, commercial air conditioners, and the like. Furthermore, most of the heat exchangers used in these heat pumps are fin-tube heat exchangers that are composed of aluminum fins and refrigerant pipes orthogonal to the aluminum fins.

On the other hand, during cooling, moisture condenses on the fin surfaces of the indoor heat exchanger, but if the fin surfaces are water-repellent, water droplets may adhere between adjacent fin surfaces or form bridges between the fin surfaces. . This increases the ventilation resistance of the heat exchanger, leading to a decrease in the amount of ventilation in the heat exchanger, which in turn causes a decrease in cooling capacity.

On the other hand, during heating, a phenomenon similar to that which occurs in the indoor exchanger during cooling occurs in the outdoor heat exchanger as described above. Furthermore, during heating, depending on the outside air temperature, frost may form on the outdoor heat exchanger. When frost forms on a heat exchanger, ventilation resistance increases, leading to a decrease in the amount of air passing through the heat exchanger, which causes a decrease in heating capacity, just as moisture condensation occurs. As the vessel becomes more and more clogged, the decrease in the passing air volume does not stay at a certain level, but gradually decreases over time. For this reason, the outdoor heat exchanger is generally defrosted according to certain determination conditions. Hot gas defrost is the best defrosting method, but heating operation is temporarily suspended during this time. This causes the indoor temperature to drop, resulting in discomfort.

Further, if the fin surface is water-repellent during defrosting, water from melting frost becomes water droplets between adjacent fins or remains in the heat exchanger in a bridged state. As a result, when heating operation is restarted, the initial air volume decreases, and residual moisture freezes between the fins, which promotes frost formation and accelerates clogging of the heat exchanger, resulting in heating capacity. The decline will become even more severe. This increases the frequency of defrosting, which increases discomfort and significantly reduces operating efficiency.

As described above, in conventional heat pumps, various problems occur unless the aluminum fin surfaces are made hydrophilic, so several treatment methods have been proposed for making the fin surfaces hydrophilic. For example, Japanese Patent Application Laid-open No. 50-38645 describes a method of forming a porous inorganic film on the fin surface.
JP-A No. 54-148034 describes a method of attaching an organic film and hydrolyzing only the surface to obtain water wettability, and a method of specializing the shape of the fins to improve drainage and water wettability. Proposed. However, all of these methods mainly aim to maintain heat exchange characteristics by improving water wettability, eliminating bridges between fins, and suppressing increases in ventilation resistance, and prevent frost formation. is completely powerless.

In addition, in the technology of improving water wettability using surfactants, Japanese Patent Application Laid-Open No. 58-16192 taught the formation of a film consisting of a surfactant and a higher fatty acid in order to reduce durability due to dissolution of the surfactant. No. 1, but this technology does not take into account frost prevention at all.

On the other hand, as a means to prevent frost formation, the Japanese Patent Publication No. 53-161
No. 38 proposes that a melting point depressing substance be periodically injected into a pressurized container, but this is mainly a means of preventing frost formation inside a refrigerator, and the outdoor heat exchanger of a heat pump with a large number of fins has a uniform temperature. It is difficult to spray properly, and the provision of a pressure vessel increases the size of the device, which is undesirable. In addition, as another method, a method of forming a hydrophobic film on the fin surface is disclosed in JP-A-54-139159, but although it has the possibility of suppressing frost formation, it has the problem of water droplet bridge formation during defrosting. Yes, undesirable.

Furthermore, JP-A No. 60-102978 discloses a method of imparting hydrophilicity by forming a film on the surface of the object to be coated by fixing ion-exchange resin powder with an adhesive. The method is limited to improving the workability and water wettability of the fin material.

As described above, no technology has been found that can simultaneously solve the problems of water wettability and sustainability and the suppression of frost formation, and there has been a strong desire in the market for the development of an effective means. On the other hand, it is clear that water-based coating compositions meet market needs in terms of fire prevention in coating lines, worker health, and resource conservation.

In view of the problems to be solved by the invention, it is an object of the present invention to provide an aqueous coating composition that has excellent water wettability and durability when applied to aluminum fins of a heat exchanger, and is effective in suppressing frost formation. is the object of the present invention. It is further an object of the invention to provide a heat exchanger having a heat transfer surface coated with such a composition.

Means for Solving the Problems According to the present invention, the above objects are achieved by: (a) a cation exchange resin in which 30% or more of the ion exchange groups are ion-exchanged with lithium (in terms of solid content) 5 to 40% by weight (b ) A film-forming resin emulsion that does not contain a cationic surfactant (in terms of solid content) 94 to 40% by weight (e) Anionic or nonionic surfactant (in terms of solid content) 1 to 20% by weight as the main component This can be achieved by applying a water-based coating composition for a heat exchanger and the composition to the heat transfer surface of the heat exchanger.

The inventors of the present invention have conducted research into the formation and growth mechanisms of frost formation, and have found that the frost formation and growth process involves first condensing water droplets when the fin surface is below the dew point, and then freezing the water droplets or water film. It was confirmed that so-called ice crystallization occurs, frost nuclei are formed on the ice, and then moisture in the air adheres to the nuclei through sublimation, causing frost growth. Moreover, once frost kernels have formed and their growth begins, the only way to control the frost height is by controlling external factors such as wind speed, temperature, humidity, fin shape, etc., and the aluminum fins of the heat exchanger. If lowering the height of the frost above is due to factors other than these external factors, it is necessary to take some measures before the water film turns into ice crystals, and in the process of the water film turning into ice crystals. When the crystal structure of the ice crystal film was examined using a reflective polarizing microscope, it was found that the crystal structure differs depending on the substrate. Therefore, as a result of various studies on the relationship between the base paint composition, frost formation, and frost height, we found that only a system with a specific surfactant and an ion exchange resin adsorbing a specific cation has a long-lasting adhesion. The present invention was completed based on the discovery that it has a frost suppressing effect, particularly an effect of suppressing frost height to a low level.

That is, the aqueous coating composition of the present invention uses a cation exchange resin in which 30% or more of the ion exchange groups have been ion exchanged with lithium. Various types of such cation exchange resins are commercially available, including strongly acidic cation exchange resins of the polystyrene sulfonic acid type, and any of them can be suitably used in the present invention, but those with a total exchange capacity of 1.5 mg equivalent /g DRY R or higher is preferred. These ion exchange resins are available as H-type or sodium-neutralized type, but in the present invention, they are first converted into H-type by a conventional method, and then 30% or more, preferably 50% or more of the ion exchange groups are is ion-exchanged with lithium. In addition, since the ion exchange resin is used in coating compositions, its average particle size is about 0.1 to 20 μm, more preferably 0.1 to 20 μm.
．． It is preferable to use the particles in the form of particles of about 5 to 10 μm, and they are used after being pulverized and classified by a conventional method.

In the present invention, an anionic or nonionic surfactant is used in combination with the above cation exchange resin. These surfactants are of the usual type; for example, anionic types include alkylbenzene sulfonates, lauryl sulfate salts, and sulfosuccinic acid octyl ester salts; nonionic types include nonylphenols, lauryl alcohols, and polyethylene glycol monolaurates. etc. are given as representative examples, but of course the invention is not limited to these. Particularly preferred surfactants are nonionic surfactants.

The present inventors found that when both the above-mentioned lithium-containing cation exchange resin and nonionic or anionic surfactant are present in the coated surface, the frost height is low even if frost forms, and therefore the heat exchanger can be used for a long time. We have discovered that scales can be used to form a coating that can withstand driving. This effect of suppressing frost height to a low level is specific to the combination of the above-mentioned ion exchange resin and surfactant, for example, only one of them, or other alkali metal ion-containing cation exchange resin and surfactant. This effect cannot be achieved depending on the combination of , and the effect cannot be obtained when the lithium content is less than 30%. As to whether or not only the combination of a cation exchange resin in which 30% or more of the ion exchange groups are ion-exchanged with lithium and a nonionic or anionic surfactant can suppress frost height to a low level even if frost forms for any reason. It has not been fully elucidated to date.

It is generally known that ice grows perpendicular to the surface of the ice crystal nucleus, so it is assumed that the generation and growth of frost nuclei is the same phenomenon, and that frost also grows perpendicular to the surface of the frost nucleus. The inventors found that the higher the number of crystals per unit area in the ice crystal film, the lower the frost height, and in the case of the above-mentioned combination of cation exchange resin and surfactant, It has also been confirmed that the number of crystals in the ice crystal film is greater than in other cases. A large number of crystals in the ice crystal film indicates a large number of frost nuclei generated on it, and as a result, when the same amount of water vapor is carried, frost grows by sublimation on the heat exchanger surface. However, it is easy to understand that the amount of frost per frost kernel decreases as the number of frost kernels increases, and as a result, the frost height becomes lower. Therefore, in the case of the combination of the above cation exchange resin and surfactant, the present inventors
Compared to simple ion exchange resins, metal powders, freezing point depressants, or combinations of other ion exchange resins and surfactants, it has the effect of significantly increasing the number of crystal nuclei in the ice crystal film. We believe that this is effective in generating a large number of frost kernels and suppressing frost height.

Since the present invention provides a coating composition for coating aluminum fins of heat exchangers, etc., a film-forming component is additionally required, but a water-based coating is preferable for resource saving and other reasons. The film-forming component is contained as a resin emulsion. Therefore, another essential component of the present invention is a film-forming resin emulsion that does not contain a cationic surfactant. As such emulsions, ordinary acrylic emulsions, silicone emulsions, epoxy emulsions, urethane emulsions, vinyl acetate emulsions, etc. are used, but acrylic emulsions, silicone emulsions, or blends thereof are preferred from the viewpoint of the durability of the coating.

Resin emulsions are produced by conventional methods, but surfactants or emulsifiers are usually used for emulsification, and if these are cationic, coagulation of the system is observed due to interaction with lithium, the cation exchange resin, etc. must not contain cationic surfactants.

In the present invention, in terms of solid content, 5 to 40% by weight of a cation exchange resin in which 30% or more of the above-mentioned ion exchange groups are ion-exchanged with lithium, 1 to 20% by weight of an anionic or nonionic surfactant, and a cationic type surfactant. There is provided an aqueous coating composition containing as an essential component a film-forming resin emulsion that does not contain a surfactant. If the amount of the above-mentioned cation exchange resin is less than 5% by weight, the frost height suppression effect aimed at by the present invention will not be sufficient, and if it exceeds 40% by weight, the film-forming properties of the composition will be lost, and the surface activity will be reduced. The dosage is 1
If it is less than 2% by weight, the purpose and effect of the invention will not be achieved.
This is because if it exceeds 0% by weight, the physical properties of the film such as water resistance will deteriorate.

However, when an anionic or nonionic surfactant is used in the production of a resin emulsion, the above amount of surfactant should be selected within a predetermined range, including the amount of surfactant contained in the glazing emulsion. It should be done.

In addition to the above-mentioned essential components, the present inventors have developed water-soluble resins that exclude non-neutralized water-soluble resins, that is, those obtained by neutralizing acid groups with alkalis, etc., such as polyvinyl alcohol and ethylene oxide. Improved water wettability by adding water-soluble resin, methyl cellulose, etc.
It has also been found that a coating film having good durability and film properties can be obtained.

The composition of the present invention may also contain conventional paint additives such as coloring pigments, extender pigments, solvents for dyes, and surface conditioners, if desired.

The water-based paint composition of the present invention is applied onto the aluminum fins of the heat exchanger by a conventional coating method, spraying, etc., and an excellent surface coating film is formed by drying, but if the coating film is too thin, it will not be effective. If the thickness is too small or too thick, it will affect the thermal conductivity, so it is usually preferable to apply the thickness in the range of 1 to 50μ. The coating thus obtained exhibits good water wettability and durability, and is extremely effective in inhibiting frost formation and frost height, and the composition of the present invention is extremely useful as a coating for heat exchangers.

The present invention will be explained below with reference to Examples. Parts and percentages are by weight unless otherwise specified.

Production Example 1: Production of lithium-containing ion exchange resin Duolite C-20 (Na type cation exchange resin, manufactured by Sumima Kagaku Co., Ltd., registered trademark) with 2.0 equivalents/A of ion exchange groups was converted to H type by treatment with hydrochloric acid. After that, it was treated with a lithium hydroxide aqueous solution to form an ion exchange resin with a lithium ion adsorption degree of 70%, and dispersed in water to form an ion exchange resin dispersion with a nonvolatile content of 30% (
A) was obtained. For comparison, Duolite C-20 was directly treated with lithium hydroxide solution to obtain a lithium ion adsorption rate of 20%.
Make an ion exchange resin and disperse it with water to reduce the non-volatile content to 30%.
An ion exchange resin dispersion (B) was obtained. Furthermore, for comparison, Duolite C-20 was dispersed in water to obtain a dispersion (C) with a nonvolatile content of 30%.

Example 1 Tocryl 1lCX-1 in a 500-stainless steel beaker
007 (acrylic emulsion, manufactured by Toyo Ink Co., Ltd., non-volatile content 45%) was charged, 50 parts of ion exchange resin dispersion (A) was added with stirring, and Unitika Bobal 0F-100 (manufactured by Unitika Kasei Co., Ltd., nonionic) was added with stirring. type surfactant, polyvinyl alcohol registered trademark name, non-volatile content 10
0%) and 90 parts of water were gradually added and stirred to obtain a homogeneous composition.

Example 2 A composition having the following composition was obtained in the same manner as in Example 1.

Ion exchange resin dispersion (A) 100 parts Lithium carbonate 3 parts Comparative Example 1 The same method as in Example 1 was carried out except that the following composition was prepared using fF.

)-Resi'): Fn5E-1980 200 parts Ion exchange resin dispersion (B) 50 parts Unitika Bobal uF-1 Oolo part water
90 parts Comparative Example 2 A composition was prepared in the same manner as in Example 1, but with the following composition.

Tori IJ tIy IcX-1007 200 parts Ion exchange resin dispersion (A) 15 parts Adekanol 0H-420 40 parts Comparative Example 3 A composition was prepared in the same manner as in Example 1, but with the following composition.

Toray Silicone 5E-1980 200 parts Ion exchange resin dispersion (C) 100 parts Adekanol 0H-4
2040 parts of each composition of Examples 1-2 and Comparative Examples 1-3 was placed on an aluminum plate (
10CIIX 20CIIIX 1 am) with a bar coater to a dry film thickness of 10μ, and coated at 140℃ for 2
A test piece was prepared by drying for 0 minutes. Further, an untreated aluminum plate (10 cm x 20 cm x 1 mm) was used as Comparative Example 4. Using these, the following water wettability and durability tests were conducted, and the results are shown in Table 1.

Test "1" L Water wettability: Using Wider #71 (manufactured by Iwakuni Painting Machinery Co., Ltd.), pure water was sprayed once on the test piece in a mist-like manner, and the spread of water droplets was observed.

Sustainability of water wettability: The test piece was immersed in pure water at 20°C for 8 hours, then pulled out and
One cycle is air drying at 0℃ for 16 hours, and 5
Water wettability after cycling was determined using the water wettability test method described above.

Frost height: The above test piece was brought into close contact with the cooling plate of the device shown in the reference diagram.

Air temperature (DB) 20℃ air temperature (
WB) 14.5℃ Average wind speed inside the duct
0.5m/s Sample surface temperature
The entire −10°C apparatus is installed in a thermostatic chamber where temperature and humidity can be controlled. The average wind speed in the duct is calculated from the value obtained from the nozzle differential pressure type airflow meter, and is maintained at a predetermined value by controlling the rotation speed of the fan.

The surface temperature of the test piece is kept at a predetermined value by controlling the temperature of the brine sent to the cooling plate.

For frost height evaluation, move perpendicular to the cooling plate,
They devised a device that could read the distance and measured the height of the frost surface 60 minutes later. For the frost height, the average value of the measurement results at multiple points was used.

The above test results are shown in Table 1.

(Left below) Example 3 Using a roll coater, the coating composition obtained in Example 1 was applied to a rolled fin material for an aluminum heat exchanger that had been previously degreased to a dry film thickness of 10 μm. ,
Drying treatment was performed at 140°C for 20 minutes. The heat exchanger obtained by assembling the fins treated in this way was used as an outdoor heat exchanger during heating operation of a heat pump type air conditioner, and was operated under conditions where frost formation occurred. Examine the relationship between elapsed time and heating capacity, elapsed time and air volume,
The results are shown as A in FIGS. 1 and 2 of the attached drawings. It showed superior heat exchange properties compared to the untreated material.

Comparative Example 5 Using the same heat pump air conditioner as that used in Example 3, but without applying the above coating composition to the fin material of the outdoor heat exchanger, heating operation was performed in the same manner as in Example 3. The relationship between time, heating capacity, and air volume over time was investigated, and the results are shown as B in Figures 1 and 2 of the attached drawings.

[Brief explanation of the drawing]

Figure 1 shows the elapsed time during heating operation with a top pump air conditioner using a heat exchanger (A) coated with the coating composition of the present invention and a heat exchanger (B) without the coating. The diagram of the relationship between heating capacity and Figure 2 is also a diagram of the relationship between elapsed time and air volume, and the reference diagram is a diagram of the equipment used in the frosting test of the painted test board. In addition, in the reference diagram, 1 is an air flow, 2 is a duct, 3 is a hot wire anemometer sensor, 4 is a hot wire anemometer, 5 is a cooling plate, 6 is a test piece, 7 is a frost height measuring device, 8 is a heat insulating material, 9 is a brine cooling tank, 10 is a pump, 11 is a chamber, 12 is a nozzle differential pressure airflow meter, and 13 is a fan. patent application agent

Claims (4)

[Claims] (1) (a) Cation exchange resin in which 30% or more of the ion exchange groups are ion-exchanged with lithium (solid content) 5 to 40% by weight (b) Film-forming resin emulsion containing no cationic surfactant (in terms of solid content) 94 to 40% by weight (c) An aqueous coating composition for heat exchangers containing as a main component 1 to 20% by weight of an anionic or nonionic surfactant (in terms of solid content). (2) A water-based coating composition further containing a non-neutralized water-soluble resin. (3) The composition according to claim 1, wherein the film-forming resin emulsion is an acrylic resin or a silicone resin emulsion. (4) (a) Cation exchange resin in which 30% or more of the ion exchange groups are ion-exchanged with lithium (solid content) 5 to 40% by weight (b) Film-forming resin emulsion containing no cationic surfactant (solid content equivalent) 94 to 40% by weight (c) Anionic or nonionic surfactant (solid content equivalent) 1 to 20% by weight A heat transfer surface coated with an aqueous coating composition containing as a main component 1 to 20% by weight exchanger.