Heat exchanger

Abstract

A surface polyaniline layer comprising a polyaniline and/or a derivative thereof capable of generating active oxygen or hydrogen peroxide upon the reaction with the water component in external air that comes in contact therewith, is formed on at least a portion of the outermost surface of a base body constituting tubes and/or fins, wherein a benzenoid/quinoid ratio in the surface polyaniline layer (defined as a ratio of an absorbancy of the benzenoid structure to an absorbancy of the quinoid structure in the polyaniline and/or the derivative thereof) is in a range of about 0.5 to about 3.0.

Description

TECHNICAL FIELD

The present invention relates to a heat exchanger. More specifically, the invention relates to a novel heat exchanger having tubes equipped with heat-exchanging members, of an air conditioner such as a vehicle air conditioner and the like, with resistance to water and chemicals, as well as functions for decomposing and deodorizing malodorous substances and sterilizing harmful microorganisms adhered to heat-exchanging members, such as fins and plates and surfaces of the tubes. According to the heat exchanger of the present invention, a polyaniline is used on the surfaces of the heat-exchanging members, such as tubes, fins, plates and the like to efficiently generate hydrogen peroxide and active oxygen that remove orders or to effect sterilization.

BACKGROUND ART

It has been known that hydrogen peroxide generates active oxygen, such as —OH due to its own effect or by bringing it into contact with iron ions. As its effect can be reliably expected along with chlorine, ozone, ultraviolet rays, a photo catalyst and the like, hydrogen peroxide has been used for sterilization or disinfection in a variety of fields.

As a method of generating hydrogen peroxide, it has been known to bring polyaniline into contact therewith. For example, Japanese Unexamined Patent Publication No. 9-175801 (JP-A-9-175801) discloses an active oxygen-generating agent containing a polyaniline capable of generating active oxygen useful for sterilizing microorganisms living in water, and a method of generating active oxygen by using the same. JP-A-10-99863 discloses a method of utilizing a superoxide for sterilization, which is generated by arranging in a city's water supply an anode and a cathode having polyaniline on the surface thereof, and causing a current to flow between the two electrodes, to sterilize water such as drinking water and cooling water, and a water treating apparatus used for the method of sterilization. JP-A-10-316403 discloses generating superoxide anion radicals by coating the surface of an electrically conductive substance with an electrically conductive composition composed of a powder of an electrically conductive material and/or fibers, a binder and a polyaniline, and causing a current to flow using the coating as a cathode to generate active oxygen in water.

Further, an apparatus for generating active oxygen is disclosed in JP-A-11-79708. The apparatus for generating active oxygen is characterized by including an anode and a cathode supporting a redox polymer, such as polyaniline or a derivative thereof which has the ability to generate active oxygen, and having between the two electrodes a spacer of a thickness in a range of 0.005 to 5 mm which is liquid-permeable or liquid-penetrating. JP-A-11-158675 discloses an apparatus for generating active oxygen which is characterized by having an electrode and particles on the surfaces thereof a redox polymer, such as polyaniline or a derivative thereof which has the ability to generate active oxygen.

In addition, JP-A-8-500700 discloses a method of producing a metallic material protected from corrosion and a material obtained by the method. More specifically, JP-A-8-500700 teaches a method of producing a metallic material, comprising the steps of (a) forming a layer of an intrinsically conductive polymer capable of absorbing water, preferably a polyaniline, in a non-electrochemical manner on a metallic material, such as a metallic material treated with phosphate, a metallic material such as a steel, stainless steel, copper, aluminum, bronze or any other alloy that has corroded, (b) contacting the metallic material coated according to step (a) with a passivating medium comprising oxygen-containing water for a period of at least 30 seconds, (c) as required, conducting a secondary passivation treatment, (d) as required, removing the layer of the electrically conductive polymer, and (e) providing the metallic material with a corrosion-protection covering. The ultimate object of the invention is to attain protection from the corrosion by forming a passivation film on the surface of the metallic material. The layer of the water-absorbing polymer, or preferably, a polyaniline formed according to step (a) can be also removed according to step (d).

SUMMARY OF INVENTIONS

An object of the present invention is to provide a novel heat exchanger having tubes and fins like an air conditioner such as a vehicle air conditioner, which guarantees durability, and has functions for decomposing and deodorizing malodorous substances deposited on the surfaces of the tubes and fins, sterilizing harmful microorganisms, as well as maintaining fundamental performance without decreasing the decomposing and deodorizing, and sterilizing functions.

The inventors of the present invention noted that the above-described polyaniline is capable of generating hydrogen peroxide when moisture or other water component has come in contact therewith, and have conducted extensive studies in an attempt to develop a method of efficiently maintaining the capability of the polyaniline for generating hydrogen peroxide for extended periods of time, and an apparatus that utilizes the above method. As a result, the inventors have discovered that, after a large amount of active oxygen stemming from hydrogen peroxide has been generated from the polyaniline, the ability to generate active oxygen, and then conceived of the present invention based on the above discovery.

The present invention is intended to enhance the ability to generate active oxygen by selecting the structure of the polyaniline that easily generates active oxygen. Generally, it is considered that polyaniline has a high capability to generate active oxygen when a benzenoid structure and a quinoid structure are present at a ratio of 1:1 in the polyaniline molecules. However, it has been discovered that when an electric current is caused to flow using the polyaniline as the cathode at an accelerated test, the ratio of the quinoid structure increases, and the ability to generate active oxygen decreases. In order to permanently generate active oxygen, the ratio of the benzenoid structure to the quinoid structure must be controlled. The ratio is ideally 1:1, but active oxygen can be sufficiently generated at a ratio of 1:2. Therefore, in order to permanently generate active oxygen from the polyaniline, the present invention provides a method of generating active oxygen wherein the structure of the polyaniline is controlled relying upon the absorbancy ratio thereof when the film is being formed or when deterioration of the film is discovered, and a heat exchanger having a function for generating active oxygen.

The present invention is concerned with a heat exchanger equipped with at least one tube having at least one fin, wherein:

at least one tube and/or at least one fin are composed of at least a base body and a surface film formed on at least a portion of an uppermost surface of the base body,

the surface film is a surface polyaniline layer composed of a polyaniline and/or a derivative thereof capable of generating active oxygen or hydrogen peroxide by reacting with a water component in external air that comes in contact therewith, and

a ratio of benzenoid to quinoid in the surface polyaniline layer is in a range of about 0.5 to about 3.0, which is defined as a ratio of an absorbancy of a benzenoid structure to an absorbancy of a quinoid structure in the polyaniline and/or in the derivative thereof.

In another aspect, the heat exchanger of the present invention further comprises a means for bringing the benzenoid/quinoid ratio back into a preset range of about 0.5 to about 3.0, when the benzenoid/quinoid ratio has fallen outside the preset range in the surface polyaniline layer. The means for bringing the benzenoid/quinoid ratio back is preferably a structure-converting means for converting the benzenoid structure constituting the polyaniline and/or the derivative thereof into the quinoid structure, or for converting the quinoid structure into the benzenoid structure.

As a result of employing the above-mentioned constitution for the heat exchanger of the invention, the malodorous components or bacteria are decomposed or sterilized at a normal temperature due to the oxidizing action of active oxygen generated by the polyaniline and/or the derivative thereof which has been firmly coated on the heat exchanger having large contact areas. It is, therefore, possible to prevent malodorous components or bacteria from becoming a generating source of malodor or a source of bacteria for extended periods of time without hindering water-wetting performance of the heat exchanger.

According to the heat exchanger including tubes having heat-exchanging members such as fins and plates of the present invention, as understood from the following detailed description, not only durability can be obtained, such as resistance to water and chemicals, but also the structural ratio of benzenoid to quinoid can be maintained in the surface polyaniline layer to suppress adhered malodors and to maintain fundamental performance of the heat exchanger, without lowering the ability to generate active oxygen of the polyaniline, after the film has been formed or has been used. Therefore, the present invention can be advantageously utilized for a vehicle air conditioner mounted to a vehicle, air conditioner, radiator and any other heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view schematically illustrating an evaporator for a car using a heat exchanger according to the present invention.

FIG. 2 shows a partial sectional view illustrating a preferred embodiment of a heat exchanger of the present invention.

FIG. 3 shows a partially enlarged sectional view illustrating a portion of a fin of the heat exchanger shown in FIG. 2.

FIG. 4 shows a partially enlarged sectional view illustrating another preferred embodiment of a fin of a heat exchanger of the present invention.

FIG. 5 shows a partially enlarged sectional view illustrating a further preferred embodiment of a fin of a heat exchanger of the present invention.

FIG. 6 shows partially enlarged sectional view illustrating a still further preferred embodiment of a fin of a heat exchanger of the present invention.

FIG. 7 shows a partially enlarged sectional view illustrating yet further preferred embodiment of a fin of a heat exchanger of the present invention.

FIG. 8 shows a graph plotting a relationship between a benzenoid/quinoid ratio and a concentration of generated hydrogen peroxide in a surface polyaniline layer of the present invention.

FIG. 9 shows a graph illustrating changes in a benzenoid structure and in a quinoid structure as changes in absorbency thereof when an electric potential is applied to a polyaniline.

FIG. 10 shows a chemical formula representing a change from a quinoid structure to a benzenoid structure when an electric potential is applied to the polyaniline.

FIG. 11 shows a graph illustrating a change in a benzenoid structure and in a quinoid structure as a change in an absorbancy when an opposite electric potential is applied to a polyaniline.

FIG. 12 shows a chemical formula representing a change from a benzenoid structure to a quinoid structure of when an opposite electric potential is applied to a polyaniline.

FIG. 13 shows a graph plotting changes in a benzenoid/quinoid ratio and in an active oxygen generating capability when an electric potential and an opposite electric potential are successively applied to a polyaniline.

DETAILED DESCRIPTION

The present invention relates to a heat exchanger, and particularly, a heat exchanger of an oxygen peroxide-generating type, and can be advantageously put into practice in various forms. The heat exchanger of the present invention is not limited to the forms that are described below.

The heat exchanger of the invention is equipped with tubes which have at least one heat-exchanging member, such as a fin(s) (vanes), a plate(s), etc. (hereinafter referred to as “a fin(s)”), and forms thereof can encompass various forms. In other words, the heat-exchanging members used for improving the heat-exchanging efficiency of the heat exchanger include various forms such as fins, plates, etc., and are desirably configured with members having large surface areas. As described later concerning the base body, the heat-exchanging members are preferably configured with a light metallic material. The size of the fin can be arbitrarily varied depending upon the desired effect.

The tubes having fins can also encompass various forms. For example, the tubes may have a circular shape, a rectangular shape or a flat shape, such as a crushed circular shape, in cross section. To modify the heat exchanger to be small and light weight, it is desirable that the tubes have a flat shape in cross section, and the tubes be made of a light metallic material in the same manner as fins. The size of the tube can be arbitrarily varied depending upon the desired effect in the same manner as fins, as a matter of course.

The tube with at least one fin can be variously arranged in the heat exchanger, and there is no particular limitation on the arrangement and the structure thereof. For example, a long tube with a plurality of fins may be folded a plurality of times to constitute a heat exchanger having a predetermined shape, or a tube member composed of a plurality of tubes and a plurality of fin members in a shape being adapted to the tube member, and the tube member and fin members joined together to constitute the heat exchanger.

Typical examples of the heat exchanger include an evaporator and a condenser used for an air conditioner for a vehicle, i.e., a car air conditioner. In addition to the car air conditioner, examples of the heat exchanger include an air conditioner, radiator and the like, without limitation thereto.

FIG. 1 schematically illustrates a use of the heat exchanger in a car air conditioner, i.e. use as an evaporator. Slightly hot air (indicated by arrow A) is sent from a blower 21 to a car air conditioner 22. The hot air further passes through a filter 23 and arrives at a heat exchanger 10 where heat is exchanged. The air (cold air) cooled through the exchange of heat is exhausted in a direction indicated by arrow B through a duct 24 attached to the car air conditioner 22.

As described above, the heat exchanger 10 can have various forms. FIG. 2 is a sectional view schematically illustrating a potion of the heat exchanger 10. The heat exchanger 10 is obtained by joining fin members 17 to a tube member 15. A surface polyaniline layer 2 is provided on all of the uppermost surfaces of both members that are joined together. If necessary, the surface polyaniline layer 2 may be partially omitted. The tube member 15 has a base body 1 made of an aluminum alloy of which the exposed portions are covered with the surface polyaniline layer 2. A coolant 16 flows inside the tube member 15. The coolant 16 is, for example, a fluorine-containing hydrocarbon-based coolant such as 1,1,1,2-tetrafluoroethane (hydrofluorocarbon (HFC) such as HFC 134a). Herein, fin members 17 having a rugged pattern in cross section in order to increase heat-exchange efficiency are attached by brazing (not shown) onto one side of the surface of the tube member 15. Like the tube member 15, each of the fin members 17 has a base body 1 made of an aluminum alloy, the exposed portions of which are covered with the surface polyaniline layer 2. The drawing show the fin members 17 having a rugged shape in cross section. It is, however, also possible to use fin members 17 having a recurring triangular sectional pattern like bellows or fin members 17 having any other sectional pattern instead of a rugged cross-section pattern.

Concretely, FIG. 3 is a sectional view illustrating the fin portion in the heat exchanger shown in FIG. 2 by further enlarging it. In the heat exchanger of this invention as shown, the fin 17 consists of a base body 1 and the surface polyaniline layer 2 formed on the uppermost surface thereof. Although no other layers are shown in FIG. 3, an interlayered intermediate layer may be provided, or any other layer may be provided between the base body 1 and the surface polyaniline layer 2, as described below. Further, the base body 1 and the surface polyaniline layer 2 may be subjected to any treatment in order to improve the junction therebetween. Further, the surface polyaniline layer 2 may be additionally subjected to arbitrary treatment on its surface.

On the fins and the tube provided therewith, the base body can be formed by using various materials. However, a metallic material, and a particularly light metal, such as a metallic material containing aluminum (aluminum alloy or aluminum mixture) can be advantageously used. This is because, the aluminum-containing metallic material is light in weight, efficiently exchanges heat and has excellent durability and corrosion resistance. Typical aluminum-containing metals are Al—Mn alloys and the like. As a material useful for constituting the base body, other than the aluminum-containing metal, there can be exemplified copper and a resin material.

The fins and the tubes provided therewith can be advantageously formed by molding the aluminum-containing metallic material or any other metallic material which is the base body material. As a suitable method of molding, there can be exemplified extrusion molding and press working. If necessary, these members may be produced by, for example, forging or cutting instead of molding.

The fins and the tubes may be produced separately or may be integrated together through a subsequent step. The fins and tubes may also be simultaneously or nearly simultaneously formed integrally together. Generally, it is desirable that the fins and the tubes are formed by molding using the same metallic material. Any junction means can be used when the fins and the tubes are to be integrally formed together through a subsequent step like in the former method. As a suitable junction means, brazing can be exemplified. When brazing is used, the brazing agent is washed and removed with an acid or an alkali after the junction has been completed.

The surface polyaniline layer may be provided on the entire uppermost surface of the base body that constitutes fins and tubes or may be partially provided on the uppermost surface of the base body. As required, the surface polyaniline layer may be provided on the entire uppermost surfaces of the fins or tubes only or may be selectively provided on only portions of the uppermost surfaces of the fins or the tubes. FIG. 2 illustrates an embodiment in which the surface polyaniline layer 2 is provided on the entire uppermost surfaces (uppermost surfaces of the base body 1) that are the exposed tube member 15 and the fin members 17 of the heat exchanger 10.

It is desirable that the surface polyaniline layer is formed on the entire uppermost surfaces of the base body 1, but may be selectively formed on the required portions as required. The surface polyaniline layer can be formed by using a polyaniline having a benzenoid structure and a quinoid structure as represented by the following general formula and/or a derivative thereof. The compound which is hereinafter simply referred to as “polyaniline-based compound” undergoes reaction with a water component in external air that is brought into contact therewith and generates hydrogen peroxide or active oxygen. The “water component” referred to here includes moisture, water and any other form of water contained in external air or in an external atmosphere.

The polyaniline-based compound represented by the above formula is commercially available from Aldrich Co., under the trade name “Polyaniline Emeraldine Base”. As derivatives of polyaniline, though not limited thereto, there can be exemplified sulfonated polyaniline and the like.

In the heat exchanger of the present invention, the ratio of the benzenoid structure to the quinoid structure in the surface polyaniline layer plays an important role. The ratio of the two structures, i.e. the benzenoid/quinoid ratio can be defined as a ratio of an absorbancy of the benzenoid structure to an absorbancy of the quinoid structure in the polyaniline and/or in the derivative thereof, and is preferably in a range of about 0.5 to about 3.0 and, more preferably, in a range of about 1.0 to about 2.0. The absorbancy can be measured by using, for example, an absorbancy meter “UV-2500PC” (trade name) manufactured by Shimazu Mfg. Co. or “U-4100” (trade name) manufactured by Hitachi High Techologies Co.

The surface polyaniline layer can be formed in various thicknesses, from about 0.1 to about 10 μm, preferably from about 0.1 to 1 μm, and more preferably from about 0.1 to about 0.5 μm. If the thickness of the surface polyaniline layer is less than 0.1 μm, the desired action and effect cannot be expected. If the thickness thereof exceeds 10 μm, on the other hand, there is a problem that it becomes difficult to form a film.

Various compositions and film-forming methods can be used for forming the surface polyaniline layer. For example, the surface polyaniline layer can be advantageously formed by using a solution, such as a polyaniline-containing solution which is preferred for forming the surface polyaniline layer, and has for example, the following composition:

Polyaniline          about 1 to about 5% by wt.
Binder (carbodiimide about 1 to about 20% by wt.
compound)
Solvent (water)      about 80 to about 98% by wt.

The above composition can be arbitrarily varied, as a matter of course. As a binder, for example, a polymer, a silane coupling agent and the like which have a sulfuric acid group or a phosphoric acid group can be advantageously used. As the solvent, alcohols such as methanol or ethanol can be used instead of water in nearly the same amount as water.

Various film-forming methods can be used for forming the surface polyaniline layer. Advantageously, however, there is usually a dipping method used for dipping a precursor of the heat exchanger in the polyaniline-containing solution, or an application method for applying the polyaniline-containing solution. For example, the dipping method can be advantageously carried out by dipping the precursor of the heat exchanger in the polyaniline-containing solution at a temperature of about 4 to about 30° C. for about one minute.

In the heat exchanger of the present invention, the surface polyaniline layer constituting the uppermost layer can be improved in a variety of ways.

For example, in the fin 17 for the heat exchanger shown in FIG. 4, the surface polyaniline layer 2 formed on the base body 1 may further have hydrophilic functional groups (abbreviated here as FG) on the surface portion thereof. The hydrophilic functional groups FG may be various functional groups having hydrophilic property, and are preferably selected from a primary amino group, a secondary amino group, a tertiary amino group, an ammonium group, a nitric acid group, a carboxyl group, a sulfonic acid group and hydroxyl group. One kind of these functional groups may be solely introduced or two or more kinds of these functional groups may be introduced in combination. The presence of the hydrophilic functional groups FG is useful particularly for improving the water-wetting property of the heat exchanger.

The hydrophilic functional group described above can be preferably introduced into a binder used for the polyaniline compound during forming the surface polyaniline layer from the polyaniline compound. More preferably, the hydrophilic functional group may be introduced in advance into the binder. Desired binders may include a carbodiimide group, a carboxyl group and the like, but are not limited thereto. For example, due to the work of the binder, the hydrophilic functional groups can be easily added to amino groups in the polyaniline-based compounds, and can be uniformly distributed over the surface of the formed surface polyaniline layer.

The fins and tubes are usually formed by using the base body that is referred to in the present invention. The base body for these members is formed by molding any metallic material, such the light metallic material as described earlier, however the fins and tubes may be made of the same metallic material or different metallic materials.

As the metallic material, there can be exemplified a metallic material containing aluminum, i.e. an aluminum-containing metallic material. Herein, the aluminum-containing metallic material is generally an aluminum alloy containing aluminum at an arbitrarily given ratio, however, the aluminum-containing metal may be a metallic material containing aluminum in any other form. A typical aluminum-containing metal is an Al—Mn based alloy as described above.

The fins and tubes are usually formed from a single layered or a single metallic material. As required, they may consist of a composite body of at least two metallic material layers. In the metal composite body, it is desirable that the amount of the metallic material having a higher oxidation-reduction potential is increasing from the upper metallic material layer toward the lower metallic material layer. This is because, upon introducing an inclined oxidation-reduction potential into the metallic material that constitutes the base body, it is possible to prevent the occurrence of undesired oxidation of the base body while the heat exchanger is being used. When the metal composite body of a three-layered structure is employed, the third metallic material layer arranged in contact with the surface polyaniline layer is allowed to have any oxidation-reduction potential in a range from the highest value or a value lower than it, and to a value higher than the lowest value, compared to the oxidation-reduction potentials of the first and second metallic material layers under the third metallic material layer.

FIG. 5 is an example in which the base body 1 for the fin 17 has been constituted by a composite body of two metallic material layers. As shown there, the base body 1 is constituted by a lower metallic material layer 11 and an upper metallic material layer 12. This is an example of the base body 1 for the fin 17. However, this is not limited to this example only, the same also holds for the other fins 17. Similarly, the base body for the tube may also be constituted by the lower metallic material layer 11 and the upper metallic material layer 12.

In the metallic material composite body shown in FIG. 5, the lower metallic material layer preferably consists of an aluminum (Al) alloy and the upper metallic material layer preferably consists of a zinc (Zn)-containing metallic material. Further, the lower metallic material layer preferably consists of an Al—Mn alloy, and the upper metallic material layer preferably consists of a metallic material which contains silicon (Si) in addition to zinc. In particular, the upper metallic material layer preferably consists of an aluminum alloy, which contains aluminum (Al) and negligible amounts of impurities in addition to zinc and silicon.

As schematically illustrated in FIG. 6, the surface polyaniline layer 2 may further contain a dopant 18 dispersed therein. When used in the present invention, the dopant exhibits a bonding action for bonding the polyaniline to the underlying base body and can, therefore be referred to as a “binder”. Preferably, the dopant is deposited on the polyaniline and/or the derivative thereof due to the electrostatic interaction. If described with reference to the general formula of the polyaniline described above, the dopant generally deposits on a nitrogen atom of an —NH— group among the adjacent benzene rings or on a nitrogen atom between the benzene ring and the polyaniline ring adjacent each other.

When the surface polyaniline layer is provided according to the present invention, an interlayered intermediate layer may be further provided between the surface polyaniline layer and the underlying base body. FIG. 7 is a partially enlarged sectional view illustrating the above heat exchanger, wherein, as shown, the fin 17 further has an interlayered intermediate layer 3 between the surface polyaniline layer 2 and the underlying base body 1. The interlayered intermediate layer usually works to enhance the adhering force of the surface polyaniline layer to the base body, and prevent electrons from being robbed by the polyaniline (prevention of rust).

The interlayered intermediate layer can be formed by using various materials, and preferably, comprises a non-metallic material. Preferred examples of the interlayered intermediate layer include an insulating film, an antioxidizing film, a nonmetallic material having an oxidation-reduction potential which is higher than in the polyaniline compound, and the like. More concretely, for example, a chromate film or a polyamide film can be used. The interlayered intermediate layer is usually a single layer. However, as required, two or more interlayered intermediate layers may be used in combination. There is no particular limitation of the thickness of the interlayered intermediate layer.

In the present invention as already described above, the ratio of the benzenoid structure to the quinoid structure in the surface polyaniline layer, i.e. the benzenoid/quinoid ratio, is usually in a range of about 0.5 to about 3.0 and, more preferably, in a range of about 1.0 to about 2.0. This is because, as shown in FIG. 8, if the benzenoid/quinoid ratio becomes less than 0.5, the concentration of the generated hydrogen peroxide, in other words, the capability of generating the active oxygen decreases. In a portion that is hatched in FIG. 8, as a more important matter, a malfunction such as peeling of the surface polyaniline layer from the base body or dissolution of the surface polyaniline layer occurs in a subsequent step. Further, if the benzenoid/quinoid ratio exceeds 3.0, the concentration of the generated hydrogen peroxide sharply decreases at a nearly constant rate.

Thus, in the present invention, it is important to maintain the benzenoid/quinoid ratio constant in the range of about 0.5 to about 3.0. In other words, in case the benzenoid/quinoid ratio in the surface polyaniline layer deviates from the range of 0.5 to 3.0, the means for bringing the benzenoid/quinoid ratio back in the preset range can be further provided. In the case of the present invention, this means is one for converting the benzenoid structure constituting the polyaniline compound into the quinoid structure, or one for converting the quinoid structure into the benzenoid structure, and therefore, can be referred to as “structure conversion means”.

Here, the benzenoid/quinoid ratio and the structure conversion means for its adjustment will be described in further detail.

FIG. 9 shows a change in the structure of the polyaniline due to the application of a voltage, which was observed as a change in the absorbancy from the absorbancy spectra, the benzenoid structure in the polyaniline can be detected near the wavelength of about 350 nm, and the quinoid structure can be detected near the wavelength of about 650 nm. Further, the benzenoid/quinoid ratio can be easily calculated from the ratio of the absorbancies.

When voltage is applied, on the other hand, the benzenoid structure (i.e. absorbancy thereof) increases while the quinoid structure (i.e. absorbancy thereof) decreases, in the polyaniline. In the present invention, the anode of the sample was connected to a power source (+), the sample was dipped in 50 ml of pure water, and thereafter, a voltage of 2 volts was applied for different periods of time period (0 hour, 24 hours and 96 hours) by stirring with a stirrer. The eluates were measured for their absorbancy spectra for their respective time periods, and the results were plotted as shown in FIG. 9. From these results, it was presumed that a change in the structure occurred in the polyaniline as shown in FIG. 10.

Even when the structure has changed in the polyaniline as described above, the quinoid structure can increase and the active oxygen generating capability can be restored in the present invention, by applying a potential opposite to the voltage applied to the same sample, i.e. by applying an opposite potential. However, if the opposite potential is applied for extended periods of time, the quinoid structure increases to a degree more than expected and other portions are oxidized, causing the polyaniline to become soluble in water, and may elute out into water from the electrode plate. Thus, it is desirable that the opposite potential is correctly applied for a short period of time. The time for applying the opposite potential is usually within about 2 hours, preferably within about one hour, and more preferably in a range of about 30 minutes to about 60 minutes.

FIG. 11 shows a plot of results obtained by measuring the absorbancy spectra of the eluates according to the same manner as described in FIG. 10, but changing into the opposite potential. In other words, in this case, the electrode connected to the power source (+) was changed from the anode into the cathode, the sample was dipped in 50 ml of pure water, and then a voltage of 2 volts was applied for different periods of time (0 minute, 30 minutes and 60 minutes) by stirring with a stirrer. The eluates were measured for their absorbancy spectra for their respective time periods, and the results were plotted as shown in FIG. 11. From these results, it was presumed that a change in the structure occurred in the polyaniline as shown in FIG. 12.

Further, based on the measured results of FIGS. 9 and 11, the benzenoid/quinoid ratios and the active oxygen generating capabilities (ppm) were plotted as a function of time, and to obtain a graph as shown in FIG. 13. As understood from this graph, the benzenoid/quinoid ratio can be restored to the initial state by applying the opposite potential for only a short period of time. Accompanying this restoration, the active oxygen generating ability can also be restored near the initial state.

The above results cannot be achieved, if the surface polyaniline film has fine defects such as pinholes or has not been perfectly formed. If the solution used in the subsequent steps directly infiltrates into the base body of the heat exchanger, the surface polyaniline film may peel off or its properties may be deteriorated. Therefore, a film evaluation step is necessary for evaluating whether, after formed, the surface polyaniline film has defects or has not been perfectly formed. After this step, the surface polyaniline film can be removed if it has defects or has not been perfectly formed. As a method of detecting pinholes, for example, a predetermined measuring point is observed by using an optical microscope, the image is taken in as electronic data, turned into a binary form (white: aluminum substrate and pinholes, black: polyaniline) by using an image processing software, and the white portions are detected to easily discover the pinholes in a short period of time. In times other than during production, a metal having an oxidation-reduction potential higher than the chromate or the polyaniline is formed as an underlying film, and thereafter, the polyaniline film is formed to prevent pitting caused by the occurrence of pinholes, i.e. to decrease the problem of corrosion.

For instance, when a water-absorbing polymer film or preferably, a thin polyaniline film is formed on the surface of a metallic material such as aluminum, iron or zinc according to a method disclosed in JP-A-8-500700 referred to earlier, there is no problem if the film is perfect. However, if the polyaniline film is partially damaged and the underlying passivated metallic material is exposed, electrons are robbed from the metallic material of the exposed region, and corrosion occurs in a concentrated manner from the exposed portion. If corrosion occurs in the tubes of the heat exchanger, coolant may leak or scatter through openings (pinholes) in the corroded portion decreasing the function of the heat exchanger.

As described above, the structure conversion means advantageously acts to adjust the benzenoid/quinoid ratio and the active oxygen generating capability. The structure conversion means can assume various constitutions, but is desirably, the voltage applying means as described above. For instance, an opposite electrode composed of another base member is arranged for the heat exchanger, and current is caused to flow by the voltage applying means across the heat exchanger and the opposite electrode to rob electrons from the surface polyaniline layer, thereby achieve the desired object.

According to another preferred embodiment, the structure conversion means may be a voltage applying means with means for switching the current-flowing direction. By using this structure conversion means, in case the benzenoid/quinoid ratio has exceeded the preset range of 0.5 to 3.0, the current can be flowed in the opposite direction across the heat exchanger and the opposite electrode.

It is further desirable that the structure conversion means is equipped with a timer means. Use of the timer means makes it possible to control flow time of the reverse current of the means for switching the current-flowing direction.

It is further allowable to provide an absorbancy ratio detector means instead of the timer means, which makes it possible to quickly and correctly detect the benzenoid/quinoid ratio in the surface polyaniline layer.

In flowing the current across the heat exchanger and the opposite electrode, it is further desirable to control the current relying upon the amount of current flowing or the amount of electric charge. For example, it is recommended to further provide a means for measuring the amount of current flowing or the amount of electric charge to control the time for flowing the electric current.

The heat exchanger of the invention can be produced according to various manners, and described below is one example.

First, the aluminum material is molded to fabricate heat-exchanging members such as tube members, fins and plates. These members are brazed at a high temperature of not lower than 600° C. to produce a precursor for the heat exchanger in a desired shape. Next, the brazing agent used for joining the members is removed by washing the precursor by using an acid or an alkali, and further washed with water followed by draining the water off and drying. Drying is conducted, for example, at 140° C. for 15 minutes.

Next, the polyaniline film is formed on the surface of the precursor of the heat exchanger. In the step of forming the film, the precursor of the heat exchanger is dipped in a solution containing the polyaniline for about 60 seconds, followed by draining the water off and drying. The polyaniline-containing solution used here may have a composition, for example, as described below:

Polyaniline          about 1 to about 5% by weight
Binder (carbodiimide about 1 to about 20% by weight
compound)
Solvent (water)      about 80 to about 98% by weight

Here, the drying step is conducted, for example, at 140° C. for 15 minutes. If drying of the precursor is not sufficient, the polyaniline film may peel off in a subsequent step, therefore, it is desirable to make sure during this step that the precursor has sufficiently dried, and after drying, the polyaniline film is formed having a thickness of about 0.5 μm.

It is further desirable to execute a film forming-state evaluation step to evaluate whether the polyaniline film has completely formed, so that the solution used in the subsequent steps will not directly infiltrate into the heat exchanger. The film forming-evaluation state can be executed easily and in a short period of time, for example, by observing a predetermined measuring point by using an optical microscope, taking a picture thereof, converting the picture into a binary form (white: aluminum substrate and pinholes, black: polyaniline) by using picture processing software, and detecting the white portion. After the above step, the polyaniline film is removed if it is determined that the polyaniline film has not been perfectly formed (pinholes have occurred). To prevent pitting due to pinholes, a metal film having an oxidation-reduction potential which is higher than the chromate or the polyaniline is formed as an underlying film, and thereafter, the polyaniline film is formed to decrease corrosion.

In a heat exchanger equipped with the tube having fins composed of the aluminum member and the surface polyaniline layer covering the aluminum member, a particular electrode structure is provided to vary the structure ratio of the polyaniline. The electrode structure is constituted by, for example, a power source, an anode and a cathode connected thereto. The surfaces of the electrodes are coated with a material having an oxidation-reduction potential which is higher than the polyaniline. Voltage is applied to the electrode structure from the power source. In the case of the present invention, it is desirable to provide a mechanism for applying a voltage to the electrode structure before and after use, in which voltage is opposite to that of during use, and a timer for controlling the time of application to be constant, in order to apply the potential and opposite potential.

According to the present invention, the aim of providing the mechanism for controlling the applied voltage is to return the polyaniline, of which the structure has changed, back to the structure before being used, as easily understood from the foregoing description with reference to FIGS. 9 to 13. As illustrated in FIGS. 11 and 12, the aim is to return the benzenoid structure, of which the ratio has increased, back to the quinoid structure. However, if the opposite potential is continuously applied for an extended period of time, the quinoid structure increases to a degree more than expected and other portions are oxidized, causing the polyaniline to become soluble in water and elute out into water from the electrode plate. It is, therefore, desirable that the application of the opposite potential be measured by using a timer in order to discontinue the application. Further, a method for correctly measuring the time is to measure the absorbancy in the structure in which light transmits through a part of the electrode. In this case, a peak in the quinoid structure is observed near to 650 nm, and a peak in the benzenoid structure is observed near to 350 nm. Thereby, application of the opposite potential may be discontinued by setting the peak ratio.

EXAMPLES

The invention will be further described with reference to Examples thereof. However, it should be noted that the invention is in no way limited to these Examples only.

Fabrication of a Tube with Fins

An aluminum alloy (AlMn alloy) was molded to produce a tube and fins as partly shown in FIG. 2. The brazing temperature was about 600° C. After having confirmed the junction between the tube and fins, the brazing agent after use was dissolved with diluted sulfuric acid and removed, followed by washing with water to a sufficient degree. After the water was drained off, the obtained precursor was dried at 140° C. for 15 minutes.

Next, the polyaniline film was formed on the surface of the precursor after drying. The polyaniline-containing solution possessed the following composition:

Polyaniline          about 1 to about 5% by weight
Binder (carbodiimide about 1 to about 20% by weight
compound)
Solvent (water)      about 80 to about 98% by weight

Thereafter, the precursor was dipped in the above polyaniline-containing solution (liquid temperature: about 20° C.) for about 60 seconds, followed by draining and drying. The drying step was conducted, for example, at 140° C. for 15 minutes. Tubes were obtained with fins coated on the whole surfaces thereof with a surface polyaniline film having a thickness of about 0.5 μm.

Use in the Heat Exchanger

The tube with fins obtained above were used in a car heat exchanger as shown in FIG. 1 to examine performance. As a result, the tube with fins exhibited excellent durability exhibiting functions for decomposing malodorous substances deposited on the surfaces of the tube and fins, and sterilizing harmful microorganisms. It was further confirmed that not only the functions for decomposing and deodorizing malodorous substances and sterilizing organic microorganisms could be efficiently exhibited, but also the ratio of the benzenoid structure to the quinoid structure could be maintained in the polyaniline to suppress malodors without lowering the active oxygen generating capability of the polyaniline after it was formed and was used, and the basic performance of the heat exchanger could be maintained.

Testing for Evaluation

The obtained tube with fins was put through the following testing in order to evaluate the benzenoid/quinoid ratio in the surface polyaniline layer and a change in the active oxygen generating capability with the passage of time.

(1) Preparation of Samples

Samples were prepared by attaching an anode and a cathode to the surface polyaniline layer of the tube with fins to apply an electric potential and opposite potential of 2 volts. The anode and cathode were constituted by using a titanium based material and a carbon based material. A power source was provided as a voltage applying means for applying voltage to these electrodes to flow an electric current.

(2) Application of Electric Potential

The anode of the sample was connected to the power source (+), the sample was dipped in 50 ml of pure water, and thereafter, a voltage of 2 volts was applied for different periods of time (0 hour, 24 hours and 96 hours) by stirring with a stirrer. The eluates were measured for their absorbancy spectra for their respective times by using an absorbancy meter “UV-2500PC” (a trade name) manufactured by Shimazu Mfg. Co., and the results were plotted as shown in FIG. 9. From these results, it was presumed that a change in the structure occurred in the polyaniline as shown in FIG. 10.

(3) Application of Opposite Potential

Following the above step, the cathode of the sample was connected to the power source (+), and the sample was dipped in 50 ml of pure water. A voltage of 2 volts was applied for different periods of time (0 minute, 30 minutes and 60 minutes) by stirring with a stirrer. The eluates were measured for their absorbancy spectra for their respective times by using the absorbancy meter (described above), and the results were plotted as shown in FIG. 11. From these results, it was presumed that a change in the structure occurred in the polyaniline as shown in FIG. 12. In other words, due to the application of the opposite potential, the quinoid structure increased, and the active oxygen generating capability was restored.

(4) Conclusion

Based on the measured results of FIGS. 9 and 11, the benzenoid/quinoid ratios and the active oxygen generating capabilities (ppm) were plotted as a function of time to obtain a graph as shown in FIG. 13. As understood from this graph, the benzenoid/quinoid ratio could be restored to the initial state by applying the opposite potential for only a short period of time. Accompanying this restoration, the active oxygen generating capability could also be restored near to the initial state.

Claims

1. A heat exchanger equipped with at least one tube having at least one fin, wherein:

said at least one tube and/or said at least one fin being composed of at least a base body and a surface film formed on at least a portion of an uppermost surface of the base body,

the surface film is a surface polyaniline layer composed of a polyaniline and/or a derivative thereof capable of generating active oxygen or hydrogen peroxide by reacting with a water component in external air that comes in contact therewith, and

a ratio of benzenoid to quinoid in the surface polyaniline layer is in a range of 0.5 to 3.0, which is defined as a ratio of an absorbancy of a benzenoid structure to an absorbency of a quinoid structure in the polyaniline and/or in the derivative thereof.

2. The heat exchanger according to claim 1, wherein the ratio of benzenoid to quinoid is in a range of 1.0 to 2.0.

3. The heat exchanger according to claim 1, wherein the surface polyaniline layer is formed on the entire uppermost surface of the base body.

4. The heat exchanger according to claim 1, wherein the surface polyaniline layer further has at least one kind of hydrophilic functional group introduced therein.

5. The heat exchanger according to claim 4, wherein said at least one kind of hydrophilic functional group is selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, an ammonium group, a nitric acid group, a carboxyl group, a sulfonic acid group and a hydroxyl group.

6. The heat exchanger according to claim 4, wherein said at least one kind of hydrophilic functional group is one that stems from a binder used for forming the surface polyaniline layer from the polyaniline and/or the derivative thereof.

7. The heat exchanger according to claim 6, wherein said at least one kind of hydrophilic functional group is one that has been introduced in the binder in advance.

8. The heat exchanger according to claim 1, wherein the base bodies of said at least one tube and/or said at least one fin are the ones which have been formed by molding a metallic material.

9. The heat exchanger according to claim 8, wherein the metallic material is composed of a metallic material containing aluminum.

10. The heat exchanger according to claim 1, wherein the base bodies of said at least one tube and/or said at least one fin are composed of a composite body of at least two layers of metallic materials, wherein an amount of a metallic material having a higher oxidation-reduction potential increases from an upper metallic material layer toward a lower metallic material layer.

11. The heat exchanger according to claim 10, wherein the base bodies of said at least one tube and/or said at least one fin are composed of a composite body of two layers of metallic materials, wherein a lower metallic material layer of the composite body is composed of an aluminum (Al) alloy, and an upper metallic material layer of the composite body is composed of a zinc (Zn)-containing metallic material.

12. The heat exchanger according to claim 11, wherein the lower metallic material layer is composed of an Al—Mn based alloy, and the upper metallic material layer is composed of a metallic material containing silicon (Si) in addition to zinc.

13. The heat exchanger according to claim 12, wherein the upper metallic material is composed of an aluminum alloy containing aluminum (Al) and impurities, in addition to zinc and silicon.

14. The heat exchanger according to claim 1, wherein the surface polyaniline layer further contains a dopant.

15. The heat exchanger according to claim 14, wherein the dopant is adhered to the polyaniline and/or the derivative thereof due to an electrostatic interaction.

16. The heat exchanger according to claim 1, wherein said at least one tube and/or said at least one fin further have at least one interlayered intermediate layer between the base body thereof and the surface polyaniline layer.

17. The heat exchanger according to claim 16, wherein said at least one interlayered intermediate layer is composed of a nonmetallic material.

18. The heat exchanger according to claim 16, wherein said at least one interlayered intermediate layer is selected from the group consisting of an insulating film, an antioxidizing film, and a film composed of a nonmetallic material having a higher oxidation-reduction potential than that of the polyailine and/or the derivative thereof.

19. The heat exchanger according to claim 1, further comprising structure-converting means for converting the benzenoid structure constituting the polyaniline and/or the derivative thereof into the quinoid structure, or for converting the quinoid structure into the benzenoid structure, in order to bring the ratio of benzenoid to quinoid back into a preset range of 0.5 to 3.0, when the ratio of benzenoid to quinoid has fallen outside the preset range in the surface polyaniline layer.

20. The heat exchanger according to claim 19, wherein the structure-converting means is voltage-applying means, wherein electrons are removed from the surface polyaniline layer, by arranging an opposite electrode composed of another substrate to the heat exchanger, and flowing a current between the heat exchanger and the opposite electrode via the voltage-applying means.

21. The heat exchanger according to claim 20, wherein the structure-converting means is the voltage applying means with a means for changing the direction of current, and a current is flowed between the heat exchanger and the opposite electrode by reversing the direction of current, when the ratio of benzenoid to quinoid has become greater than the preset range of 0.5 to 3.0.

22. The heat exchanger according to claim 19, further comprising timer means for controlling a time period in which the current is reversely flowed by the means for changing the direction of current.

23. The heat exchanger according to claim 19, further comprising absorbancy-ratio detecting means for detecting the ratio of benzenoid to quinoid in the surface polyaniline layer.

24. The heat exchanger according to claim 20, wherein when a current is flowed between the heat exchanger and the opposite electrode, the flow of current is controlled depending upon an amount of electric current that flows or upon an amount of electric charge.

25. The heat exchanger according to claim 20, further comprising means for measuring the amount of current flow or the amount of electric charge thereby to control the time period for flowing the electric current.

26. The heat exchanger according to claim 1, wherein the surface polyaniline layer is further formed also on the uppermost surface of said at least one tube.

27. The heat exchanger according to claim 1, which is used for a vehicle air conditioner.