Patent Application
20190011200
The present invention generally relates to a fin material for use in a heat exchanger and to a heat exchanger that uses the same.
Fin-tube-type heat exchangers are used in, for example, indoor units and outdoor units of air conditioners. Such heat exchangers typically comprise metal tubes, through which a coolant flows, and numerous fins made of aluminum, through which the metal tubes pass. A hydrophilic-coating material or a water-repellent coating material is precoated on both sides of the fins, such that the fins have a coating film on both surfaces thereof.
Various contaminants, such as dust, soot, and tobacco tar, adhere to the surfaces of the fins of a heat exchanger during operation. To deal with this problem, a method that prevents the adhesion of such contaminants and a method that facilitates the removal of adhered contaminants are known. Specifically, a method is known that prevents the adhesion of hydrophilic contaminants, such as dust, due to static electricity by, for example, coating an antistatic agent on the fin surfaces. In addition, a method is known that makes it easy to remove lipophilic contaminants, such as soot, by coating an oil-repellent fluororesin on the fin surfaces. However, there is a need in the art for further improvement in adhesion-prevention effects against positively charged contaminants, such as dust.
For example, in Patent Document 1, a technique is described that prevents the adhesion of tar components of tobacco by setting the absolute value of the amount of triboelectric charge of a surface-coating film of an electrically insulating substrate to 0-200 V. In addition, a fin having a hydrophilic blended film, which includes hydrophobic particles, formed thereon is described, for example, in Patent Document 2.
Patent Document 1
PCT International Publication No. WO 2006/134808
Patent Document 2
Japanese Laid-open Patent Publication 2009-229040
However, in Patent Document 1, electric charge on a metal substrate that is generated by friction is easily dissipated. In addition, in Patent Document 2, although an attempt was made to inhibit the adhesion of hydrophobic and hydrophilic contaminants by using a blended film that includes a hydrophilic component and a hydrophobic component, there was a problem in that hydrophobic contaminants tend to adhere to the hydrophobic component, and hydrophilic contaminants tend to stick to the hydrophilic component. In particular, there is a tendency for positively charged contaminants, such as dust, to adhere to the fins of a heat exchanger. In addition, uncharged contaminants also tend to adhere. Consequently, there is a need in the art for improvement in the adhesion inhibition and removability of such contaminants.
In view of one or more of these circumstances, aspects of the present teachings concern a heat-exchanger fin material that excels in adhesion-inhibiting effects and removability of contaminants, such as dust, and a heat exchanger that uses the same.
In one aspect of the present teachings, a heat-exchanger fin material preferably comprises:
a substrate composed of aluminum; and
a coating film formed on at least one surface of the substrate, the coating film being composed of a coating having one layer or two or more layers;
wherein an outermost surface of the coating film is a positively-chargeable coating;
the positively-chargeable coating is essentially composed of only one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins; and
the surface roughness Ra of the coating film is 100 nm or less.
In another aspect of the present teachings, a heat exchanger comprises a fin composed of the above-described heat-exchanger fin material.
The above-described heat-exchanger fin material (hereinbelow, called “fin material” where appropriate) has, on its outermost surface, the positively-chargeable coating essentially composed of the resins described above. A positively-chargeable coating composed only of such specified resins tends to become positively charged upon contact (by friction) with air. Furthermore, because the above-mentioned resins that constitute the coating of the outermost surface are electrically insulating, they hold charge well. Consequently, if a positively charged contaminant, such as dust, approaches the surface of the coating film (which has the positively-chargeable coating on the outermost surface thereof), a repulsive force acts between the positively charged coating-film surface and the positively charged contaminant, and therefore the contaminant tends not to adhere.
In addition, owing to the fact that the surface roughness Ra of the coating film is 100 nm or less and the coating film excels in surface smoothness, contaminants tend not to adhere for this reason as well. Consequently, not only do positively charged contaminants tend not to adhere, but also uncharged contaminants tend not to adhere. Furthermore, even if a contaminant adheres, the contaminant is easily washed away by condensed water or the like that adheres to the coating-film surface of the fin material, for example, during operation of the heat exchanger when the condensed water flows off the fin. In this regard, it is noted that, if condensed water adheres to the coating-film surface of the fin material, then the amount of charge on the surface temporarily decreases and becomes zero. However, even though it becomes easier for contaminants to adhere to the wetted surface, adhered contaminants are easily washed away in the manner described above. Furthermore, when the coating-film surface dries, the positively-chargeable coating will then carry positive charges once again, such that the adhesion-inhibiting effects against contaminants, such as dust, are exhibited once again.
In addition, a positively-chargeable coating composed only of the resins described above excels not only in hydrophilic properties but also in hydrophilicity durability. Consequently, condensed water easily penetrates between the coating and any contaminants adhered thereto, such that contaminants adhered to the surface are easily washed away.
As was mentioned above, in a heat exchanger comprising the fins composed of the above-mentioned fin materials, the fins can exhibit excellent adhesion-inhibiting effects and removability of contaminants. Furthermore, they also excel in hydrophilic properties and hydrophilicity durability.
Embodiments of a fin material and a heat exchanger using the same will now be explained. The fin material comprises a substrate composed of aluminum. In the present specification, “aluminum” is a general term for a metal or an alloy in which aluminum is the principal constituent and is a general concept that includes pure aluminum and aluminum alloys.
A coating film formed on the substrate includes a coating having one layer or two or more layers. A coating formed by a single application of one coating material is one layer; furthermore, a coating that is formed by multiple applications of a coating material in which the composition is the same for each application is also one layer. The coating film has a positively-chargeable coating on its outermost surface.
Examples of resins that form the positively-chargeable coating are cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. At least one of these can be used. These resins have a carboxy group or a hydroxy group as the functional group.
The positively-chargeable coating is essentially composed only of the resins described above; it does not contain, for example, silica-based or titanium-based inorganic particles, water-soluble resins, or the like; it may contain unavoidable impurities, such as a resin cross-linking agent (e.g., a metal compound such as a Zr compound). As described above, the positively-chargeable coating is essentially composed of at least one resin selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. The content of these resins in the positively-chargeable coating is preferably 99 mass % or more and more preferably 99.5 mass % or more.
The surface of the positively-chargeable coating will positively charge upon contact (by friction) with air. The surface electrical potential of the positively-chargeable coating varies depending on the type of resin in the positively-chargeable coating, the composition, the film thickness, the surface roughness, and the like and is within a range of, for example, +0.01 V to +10 V. In addition, the absolute value of the surface electrical potential varies not only in accordance with the coating but also with the external environment, such as the temperature and the humidity of the air.
The thickness of the positively-chargeable coating is preferably 0.1-6 μm. In this case, the positive charge on the positively-chargeable coating is more readily retained, and surface smoothness is more easily increased. From the same viewpoint, the thickness of the positively-chargeable coating is preferably 0.3-3 μm and more preferably 0.5-1.5 μm.
The coating film may have another coating in addition to the positively-chargeable coating. An example of such a coating is a corrosion-resistant coating composed of, for example, a urethane-based resin, an epoxy-based resin, or the like. Even if the coating film has another coating, the coating of the outermost surface is the positively-chargeable coating described above.
In addition, a primer layer may be formed between the coating film and the substrate. Thereby, adhesion between the substrate and the coating film can be further improved. The primer layer can be formed of at least one type selected from the group consisting of a urethane-based primer, an acrylic-based primer, and an epoxy-based primer.
In addition, a chemical-conversion coating may be formed between the coating film and the substrate or between the primer layer and the substrate. Adhesion between the coating film and the substrate or adhesion between the primer layer and the substrate can be improved by the chemical-conversion coating. The chemical-conversion coating can be formed by subjecting the aluminum substrate to a phosphate-chromate treatment, a phosphate-zirconium treatment, a boehmite treatment, or the like.
The surface roughness Ra of the coating film on the fin material is preferably 100 nm or less. If the surface roughness Ra is more than 100 nm, then uncharged contaminants and the like tend to adhere and, furthermore, adhered contaminants tend not to come off. The surface roughness Ra of the coating film is preferably 50 nm or less and more preferably 20 nm or less. The surface roughness of the coating film is an arithmetic-mean roughness Ra as stipulated in JIS B0601-2001. The surface roughness Ra of the coating film can be controlled by adjusting the thickness of the coating film, the surface roughness of the substrate, and the like.
The contact angle of water on the surface of the coating film is preferably 40° or less. In this case, the surfaces of the fin material can sufficiently exhibit excellent hydrophilic properties. In addition, both immediately after the manufacture of a fin material, as well as after the repeated immersion in water and drying according to the aging procedure described below, the water-contact angle on the coating-film surface is, as described above, preferably 40° or less and more preferably 30° or less.
Fin materials are used in the manufacture of the heat exchanger as, for example, described below. Specifically, first, a coil-shaped fin material is cut to prescribed dimensions, and thereby a plurality of sheet-shaped fins is obtained. Subsequently, the fins are subject to slit (hole) formation, louver molding, and collar formation using a press. Next, the fins are arranged such that they are stacked in the state in which they are spaced apart from one another by a prescribed spacing while metal tubes, which are disposed at prescribed locations, are passed through holes provided in the fins. Subsequently, tube-expanding plugs are inserted into the metal tubes to enlarge the outer diameter of the metal tubes, and thereby the metal tubes and the fins are caused to closely contact each other. Thus, the heat exchanger can be obtained. The heat exchanger can be used in, for example, an indoor unit or an outdoor unit of an air conditioner.
In the present example, multiple fin materials (specifically, sample E1 to sample E13 and sample C1 to sample C7) pertaining to working examples and comparative examples were prepared, and their characteristics were compared and evaluated. As shown in
The fin materials 1 of the samples were manufactured by applying coating materials, which contained the resin components of the compositions shown in Table 1 (discussed below), onto the substrates, thereby forming the coating films 3. Each coating film 3, i.e., the positively-chargeable coating 31, in the present example was formed directly on the substrate 2. In the manufacture of sample C7, a coating material containing a resin component and silica particles was used (refer to Table 1). It is noted that, in Table 1, CMC indicates carboxymethyl cellulose, PAA indicates polyacrylic acid, PAM indicates polyacrylamide, PVA indicates polyvinyl alcohol, PES indicates polyester, EPO indicates polyepoxy, PU indicates polyurethane, and PEG indicates polyethylene glycol.
As the surface roughness Ra of the coating film 3 for each of the samples, the arithmetic-mean roughness Ra according to JIS B0601-2001 was measured using a probe-type, surface-roughness measuring instrument (specifically, the scanning probe microscope JSPM-5200 made by JEOL® Ltd.) compliant with JIS B0651-2001. The visual field during measurement was 25 μm×25 μm. For each sample, arbitrary visual fields were selected at ten locations, the measurement described above was performed at each location, and the arithmetic mean of these ten locations was taken as the surface roughness Ra.
Next, the surface electrical potential of the coating film of each sample in the dry state was measured as follows, and the results are shown in Table 1. The measurements were performed using the scanning probe microscope (i.e., SPM) JSPM-5200 made by JEOL® Ltd. Specifically, a bias voltage was applied between the probe of the scanning probe microscope and an arbitrary location of the coating-film surface, and the surface electrical potential was calculated based on the change in frequency when the bias voltage was changed. The measuring method, the calculating method, and the like were in accordance with the manual of the JSPM-5200 made by JEOL® Ltd. For each sample, the surface electrical potential was measured at ten locations, and the arithmetic-mean value thereof is shown in Table 1. It is noted that the surface electrical potentials shown in the table are representative values, and it was confirmed that, even for the same sample, variations arise in the measurement values due to external factors and the like, such as temperature and humidity. However, inversion of positive or negative in the charged state of the surface did not occur.
For each sample, evaluations of the hydrophilic properties, the contamination-adhesion properties, the contamination-removing properties, corrosion resistance, and moisture resistance were performed as below. The results thereof are shown in Table 2.
(1) Hydrophilic Properties
After the manufacture of each sample, the initial water-contact angle was measured. Specifically, as shown in
(2) Contamination-Adhesion Properties
The contamination-adhesion properties were evaluated by assessing the adhesion of electrically charged dust and electrically conductive dust to the coating-film surface of each sample. Specifically, the electrically charged dust and the electrically conductive dust were each blown against the surface of the coating film of each sample via air. Subsequently, the amount of the electrically charged dust and the amount of the electrically conductive dust adhered to the coating-film surface were each measured. The measurements of the adhered amounts were performed by measuring the weight of each sample before and after the dust was blown against each sample, calculating the amount of adhered dust of each sample based on the weight difference, and then converting the weight difference into the amount of adhered dust per unit of area. If the adhered amount of the electrically charged dust was less than 0.2 g/m2, then the sample was evaluated as “excellent”; if the adhered amount of the electrically charged dust was 0.2 g/m2 or more and 0.5 g/m2 or less, then the sample was evaluated as “satisfactory”; and if the adhered amount of the electrically charged dust was more than 0.5 g/m2, then the sample was evaluated as “unsatisfactory.” The evaluation of the adhered amount of the electrically conductive dust was also performed in the same manner. It is noted that Kanto loam dust, which is a powder stipulated in JIS Z8901-2006, was used as the electrically charged dust, and carbon black, which is a powder stipulated in JIS Z8901-2006, was used as the electrically conductive dust.
(3) Contamination Removability
Contamination removability was evaluated by assessing removability of electrically charged dust and electrically conductive dust from the coating-film surface of each sample. Specifically, as in the evaluation of contamination-adhesion properties described above, samples were prepared by adhering electrically charged dust and electrically conductive dust to the coating-film surfaces. Next, each sample was cooled to a prescribed temperature by cooling the surface on the opposite side that the dust is adhered to, thereby causing condensed water to form on the surface having the adhered dust. Then, the state in which condensed water formed and flowed off was maintained for a prescribed period of time. Subsequently, the surfaces of each sample were sufficiently dried, after which the amount of the remaining dust that was not removed by the condensed water was measured in the same manner as the evaluation of the adhesion properties described above. If the residual amount of each dust was less than 0.1 g/m2, then the sample was evaluated as “excellent”; if the residual amount of each dust was 0.1 g/m2 or more and less than 0.5 g/m2, then the sample was evaluated as “satisfactory”; and if the residual amount of each dust was 0.5 g/m2 or more, then the sample was evaluated as “unsatisfactory.”
(4) Corrosion Resistance
Using each sample, the salt spray test stipulated in JIS Z2371 was performed for 500 hours, and post-test corrosion resistance was evaluated. Observation was performed visually; after the test, if the surface of the coating film did not whiten, then the sample was evaluated as “excellent”; if part of the surface whitened, then the sample was evaluated as “satisfactory”; and if the entire surface whitened, then the sample was evaluated as “unsatisfactory.”
(5) Moisture Resistance
Using each sample, the moisture-resistance test stipulated in JIS H4001 was performed for 960 hours, and post-test moisture resistance was evaluated. Observation was performed visually; after the test, if the surface of the coating film did not whiten, then the sample was evaluated as “excellent”; if part of the surface whitened, then the sample was evaluated as “satisfactory”; and if the entire surface whitened, then the sample was evaluated as “unsatisfactory.”
As can be understood from Table 1 and Table 2, each fin material having the positively-chargeable coating on its outermost surface, which, as in sample E1 to sample E13, is essentially composed only of one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins, excels in the contamination-adhesion-inhibition effect. This is because, as shown in
The surface of each positively-chargeable coating 31 in sample E1 to sample E13 is positively charged upon contact (by friction) with air, as described above. If condensed water or the like adheres to the positively-chargeable coating 31, then the surface electrical potential decreases and becomes zero, but it carries a positive charge once again upon drying and contact with air. Charging by this drying and the charge dissipation by the condensed water are reversible and performed repeatedly.
In addition, the sample E1 to sample E13 also excel in hydrophilic properties and in post-aging hydrophilic properties (i.e., hydrophilicity durability). Furthermore, they also excel in post-contamination hydrophilic properties. In addition, they also excel in corrosion resistance and moisture resistance.
In contrast, the surface of the sample C1, which has a coating composed of an epoxy resin as the coating film, the surface of the sample C2, which has a coating that contains both carboxymethyl cellulose and polyurethane as the coating film, and the surface of the sample C6, which has a coating composed of polyurethane as the coating film, are negatively charged by contact with air. Consequently, the adhesion properties with respect to contaminants, such as dust, the removability of contaminants, and the like were insufficient. In particular, the adhesion properties and removability of positively charged electrically charged dust were poor. In addition, the hydrophilic properties—particularly the post-aging hydrophilicity durability and the post-contamination hydrophilicity durability—of sample C1 to sample C6 were also insufficient. The post-contamination hydrophilicity durability was also insufficient for sample C2.
In addition, with regard to sample C3 and sample C4, in which the surface roughness Ra of the coating film was large and the smoothness was insufficient, the adhesion properties, the removability, etc. of contaminants, such as electrically conductive dust, were insufficient. In addition, with regard to sample C5, which contains a water-soluble resin, such as PEG, in the coating, the removability of electrically charged dust and the like were insufficient. Furthermore, the post-contamination hydrophilicity durability was also insufficient. In addition, the post-contamination hydrophilicity durability of sample C7, which has silica particles in the coating, was insufficient. Furthermore, the surface roughness of sample C7, which has the silica particles, became large and, as in sample 3 and sample 4, the adhesion properties, the removability, etc. of contaminants, such as electrically conductive dust, were insufficient.
In the present example, although a fin material was described in which the coating film 3, which comprises the positively-chargeable coating 31, was formed directly on the substrate 2, as shown in
Working example 2 is a heat exchanger comprising fins composed of the fin materials of working example 1. As shown in
Each of the heat exchangers 5 was prepared as follows. First, assembly holes (not shown), each having a fin-collar part with a height of 1-4 mm for inserting the metal tubes 7 therethrough and fixing such, were formed by press working the fins 6, each composed of the fin material 1. After stacking the plate fins 6, the separately prepared metal tubes 7 were inserted through the assembly holes. A copper tube having a groove formed on its inner surface by rolling or the like was cut to a standard length and hairpin bent, to form the metal tubes 7. Next, by inserting tube-expanding plugs into one end of the metal tubes 7 and widening the outer diameter of the metal tubes 7, the metal tubes 7 were secured to the plate fins 6. After the tube-expanding plugs were removed, U-bent tubes were joined, by braising, to the metal tubes 7, and thereby each of the heat exchangers 5 was obtained.
By using samples E1-E13 according to working example 1 as the fin materials 1, contaminants, such as dust, tend not to adhere to the fins 6 of the heat exchanger 5 and, even if these contaminants adhere, they are easily removed by condensed water or the like. Furthermore, the fins 6 also excel in hydrophilic properties, hydrophilicity durability, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-033395 | Feb 2016 | JP | national |
This application is the US national stage of International Patent Application No. PCT/JP2017/005971 filed on Feb. 17, 2017, which claims priority to Japanese Patent Application 2016-033395 filed on Feb. 24, 2016.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/005971 | 2/17/2017 | WO | 00 |
