阅读说明：本技术 形成有防污覆盖膜的热交换器 (Heat exchanger with antifouling coating film ) 是由 小中洋辅 久保次雄 于 2017-08-02 设计创作，主要内容包括：本发明的热交换器在作为防污对象的表面形成有防污覆盖膜,上述防污覆盖膜至少由纳米颗粒构成,上述防污覆盖膜的表面具有算术平均粗糙度Ra在2.5～100nm的范围内的凹凸。由此,能够提供至少能够有效地抑制或防止干性污垢的附着的热交换器。(The heat exchanger of the present invention has an antifouling coating film formed on a surface of an object to be antifouling, the antifouling coating film being composed of at least nanoparticles, and the surface of the antifouling coating film having irregularities with an arithmetic average roughness Ra of 2.5 to 100 nm. This can provide a heat exchanger capable of effectively suppressing or preventing adhesion of dry fouling at least.)

1. A heat exchanger having an antifouling coating film formed on a surface to be antifouling, the heat exchanger characterized in that:

The antifouling coating film is composed of at least nanoparticles, and the surface of the antifouling coating film has irregularities having an arithmetic average roughness Ra in the range of 2.5 to 100 nm.

2. The heat exchanger of claim 1, wherein:

The average particle size of the nanoparticles is within the range of 5-100 nm.

3. The heat exchanger of claim 1 or 2, wherein:

The nanoparticles are at least one selected from the group consisting of metal nanoparticles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, inorganic chalcogenide nanoparticles, (meth) acrylic resin nanoparticles, and fluororesin nanoparticles.

4. The heat exchanger of any one of claims 1 to 3, wherein:

The film thickness of the antifouling coating film is 500nm or less.

5. The heat exchanger of any one of claims 1 to 4, wherein:

The antifouling coating film contains a binder component composed of at least a material having affinity with the nanoparticles, in addition to the nanoparticles.

6. The heat exchanger of any one of claims 1 to 5, wherein:

The method comprises scattering and shaking mixed simulated dust formed by mixing organic simulated dust and inorganic simulated dust, performing binarization processing on the image photographed by optical microscope, calculating the area ratio of the residual mixed simulated dust as dust adhesion area,

When the dust attachment ratio is defined as the ratio of the dust attachment area on the antifouling coating film to the dust attachment area on the surface on which the antifouling coating film is not formed,

The antifouling coating film has a dust adhesion rate of 15% or less.

7. The heat exchanger of any one of claims 1 to 6, wherein:

The surface resistivity of the antifouling coating film is 10¹³Omega/□ or less.

Technical Field

The present invention relates to a heat exchanger having an antifouling coating film formed thereon. In particular, the present invention relates to a heat exchanger capable of effectively suppressing or preventing adhesion of dry fouling.

Background

The refrigeration cycle is widely used in the field of various refrigerators such as an air conditioner (air conditioner), a refrigerator, a freezer showcase, and an automatic vending machine. The refrigeration cycle includes a heat exchanger for absorbing heat from a low-temperature heat source and discharging heat to a high-temperature heat source. Various substances tend to adhere to the heat exchanger as "fouls".

For example, in order for an air conditioning apparatus to exchange heat with air sucked by a heat exchanger, various substances contained in the air tend to adhere to the heat exchanger as "dirt". If such dirt adheres to the heat exchanger, not only the performance of the heat exchanger is degraded, but also a sanitary problem may occur due to the propagation of microorganisms such as mold and bacteria.

Thus, for example, patent document 1 discloses a coating composition containing ultrafine silica particles having an average particle diameter of 15nm or less and fluororesin particles, which are blended at a predetermined mass ratio, in order to prevent both hydrophilic fouling and lipophilic (hydrophobic) fouling from adhering to a heat exchanger of an air conditioner.

Disclosure of Invention

As shown in patent document 1, there are hydrophilic dirt (wet dirt) and lipophilic dirt (oil dirt) as dirt adhering to an article. These are "wet" soils in which "liquid" such as water or oil is used as a medium (such as a solvent or a dispersant). The dirt adhering to the article has not only such "wet" dirt but also "dry" dirt such as dust. In the technique disclosed in patent document 1, inhibition of adhesion of dirt to articles is studied based on only the "wet" aspect, and it is therefore difficult to sufficiently prevent or inhibit adhesion of dry dirt.

As a result of intensive studies, the inventors of the present invention preferably consider "dry" dirt as two types of dirt, i.e., hard dirt having a relatively high specific gravity and soft dirt having a relatively low specific gravity. For the sake of convenience of explanation, the former "dry" dirt is referred to as "hard straight type with large specific gravity", and the latter "dry" dirt is referred to as "soft type with small specific gravity". Both carbon as an oleophilic soil and dust as a hydrophilic soil are "high specific gravity hard straight" soils when considered as "dry" soils.

Here, in patent document 1, oil smoke, tobacco tar seeds, carbon, and the like are exemplified as lipophilic (hydrophobic) dirt, and dust is exemplified as hydrophilic dirt. In the examples of patent document 1, examples of "dust" of the "hydrophilic dirt" include kunto loam dust and carbon black, and the adhesion of the dust to the coating film was evaluated by blowing the dust with air. That is, in patent document 1, the adhesion of the "dry" dirt of the "high specific gravity hard straight type" is evaluated as the "hydrophilic dirt", and therefore, it can be judged that the "dry" dirt of the "high specific gravity hard straight type" is not sufficiently evaluated in patent document 1.

On the other hand, examples of the "low specific gravity soft type" dirt include fiber-based dust such as thread waste and cotton dust, and food powder-based dust such as wheat flour and raw starch. In patent document 1, there is no evaluation of such "dry" dirt of the "soft type with small specific gravity". Therefore, in the coating composition disclosed in patent document 1, prevention of "dry" fouling is not sufficiently studied.

The present invention has been made to solve the above problems, and an object thereof is to provide a heat exchanger capable of effectively suppressing or preventing adhesion of dry fouling at least.

In order to solve the above problems, the present invention provides a heat exchanger having an antifouling coating film formed on a surface of an object to be antifouling, the antifouling coating film being composed of at least nanoparticles, the surface of the antifouling coating film having irregularities with an arithmetic average roughness Ra in a range of 2.5 to 100 nm.

According to the above configuration, the antifouling coating film having fine surface irregularities and made of nanoparticles is formed on the surface of the antifouling object of the heat exchanger. This can effectively suppress or prevent dry fouling from adhering to the surface of the heat exchanger.

In the present invention, the above configuration provides an effect of providing a heat exchanger capable of effectively suppressing or preventing adhesion of dry fouling at least.

Drawings

Fig. 1 is a schematic cross-sectional view showing a structure of a fin-tube type heat exchanger as an example of a heat exchanger according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing a structure of a plate-stacked heat exchanger as an example of a heat exchanger according to an embodiment of the present invention.

Detailed Description

The heat exchanger of the present invention has an antifouling coating film formed on a surface of an object to be antifouling, the antifouling coating film is composed of at least nanoparticles, and the surface of the antifouling coating film has irregularities having an arithmetic average roughness Ra in a range of 2.5 to 100 nm.

According to the above configuration, the antifouling coating film having fine surface irregularities and made of nanoparticles is formed on the surface of the antifouling object of the heat exchanger. This can effectively suppress or prevent dry fouling from adhering to the surface of the heat exchanger.

In the heat exchanger having the above-described structure, the average particle diameter of the nanoparticles may be in the range of 5 to 100 nm.

According to the above structure, when the average particle diameter of the nanoparticles is within the above range, fine surface irregularities can be more favorably realized.

In the heat exchanger having the above-described structure, the nanoparticles may be at least one selected from the group consisting of metal nanoparticles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, inorganic chalcogenide nanoparticles, (meth) acrylic resin nanoparticles, and fluororesin nanoparticles.

According to the above configuration, the nanoparticles are particles made of at least one material of the above group, and a good antifouling coating film can be formed.

in the heat exchanger having the above-described structure, the film thickness of the antifouling coating film may be 500nm or less.

according to the above configuration, the electrification of the antifouling coating film can be favorably reduced, and the adhesion of dry dirt can be favorably suppressed or prevented.

In the heat exchanger having the above-described configuration, the antifouling coating film may contain, in addition to the nanoparticles, a binder component made of a material having an affinity with the nanoparticles.

According to the above configuration, the strength or durability of the antifouling coating film can be improved, fine irregularities on the surface can be easily maintained, and the effect of suppressing or preventing adhesion of dry dirt can be improved.

In the heat exchanger having the above-described configuration, when a mixed pseudo dust obtained by mixing an organic pseudo dust and an inorganic pseudo dust is scattered and shaken off, an image photographed by an optical microscope is subjected to binarization processing, an area ratio of the mixed pseudo dust remaining calculated by the binarization processing is taken as a dust adhesion area, and a ratio of the dust adhesion area on the antifouling coating film to the dust adhesion area on the surface on which the antifouling coating film is not formed is taken as a dust adhesion ratio, the dust adhesion ratio of the antifouling coating film may be 15% or less.

According to the above configuration, the dust adhesion rate of the antifouling coating film is 15% or less, and therefore adhesion of dry dirt can be particularly favorably suppressed or avoided.

In the heat exchanger having the above-described structure, the surface resistivity of the antifouling coating film may be 10¹³Omega/□ or less.

According to the above configuration, the electrification of the antifouling coating film can be favorably reduced, and the adhesion of dry dirt can be favorably suppressed or prevented.

Hereinafter, typical configuration examples of the present invention will be specifically described.

[ antifouling coating film ]

The antifouling coating film formed on the heat exchanger of the present invention is a film comprising at least nanoparticles and having irregularities, the arithmetic average roughness Ra of the surface of which is in the range of 2.5 to 100 nm. The nanoparticles constituting the antifouling coating film are not particularly limited, but typically include metal nanoparticles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, inorganic chalcogenide nanoparticles (excluding inorganic oxide nanoparticles), (meth) acrylic resin nanoparticles, fluororesin nanoparticles, and the like.

specifically, examples of the metal nanoparticles include elements of group 11 of the periodic table such as gold (Au), silver (Ag), copper (Cu), and iron platinum (FePt), and alloys thereof; and metal elements for plating other than the group 11 elements of the periodic table, such as nickel (Ni, a group 10 element) and tin (Sn, a group 14 element). Examples of the inorganic oxide nanoparticles include silica (silicon oxide, SiO)₂) Yttrium oxide (Y)₂O₃) Barium titanate (BaTiO)₃) Antimony doped tin oxide (ATO), titanium oxide (TiO)₂) Indium oxide (In)₂O₃) And the like. Examples of the inorganic nitride nanoparticles include gallium nitride (GaN). Examples of the inorganic chalcogenide nanoparticles include cadmium selenide (CdSe). Examples of the (meth) acrylic resin nanoparticles include polymethyl methacrylate (PMMA). Examples of the fluororesin nanoparticles include Polytetrafluoroethylene (PTFE).

The above nanoparticles constitute the antifouling coating film substantially only by one kind, but can also constitute the antifouling coating film by a plurality of combinations. Among the above, silica nanoparticles are particularly preferably used in view of versatility, cost, ease of adjustment of average particle diameter, and the like. The antifouling coating film is basically composed of only nanoparticles, but may contain components other than nanoparticles as long as the antifouling performance of the antifouling coating film is not hindered. For example, the antifouling coating film contains a charge preventing agent in addition to the nanoparticles.

The particle size of the nanoparticles is not particularly limited, and is preferably 100nm or less, and more preferably in the range of 5 to 100 nm. Further, a more preferable range of the average particle diameter is a range of more than 15nm and less than 100nm, or a range of 20nm to 100 nm.

When the particle diameter of the nanoparticles is 100nm or less, a nanoscale uneven structure is easily formed on the surface of the antifouling coating film. In addition, depending on the specific structure of the antifouling coating film, when the particle diameter of the nanoparticles is in the range of 5 to 100nm, the nanoscale uneven structure can be easily adjusted to a more suitable range. In addition, when the antifouling coating film contains an adhesive component as described later, the nano-scale uneven structure can be easily adjusted to a more suitable range by setting the particle size of the nanoparticles to a range of more than 15nm and less than 100nm, or to a range of 20 to 100 nm.

Further, the particle size of the nanoparticles tends to be too small depending on various conditions such as the specific components of the antifouling coating film, the method of forming the antifouling coating film, and the surface state of the heat exchanger as the object to be coated. When the particle diameter of the nanoparticles is too small, the nanoparticles tend to agglomerate and coarsen. Thus, the obtained antifouling coating film had surface irregularities greatly exceeding the range of the predetermined arithmetic average roughness Ra. In this case, the dry dirt is likely to be caught by large irregularities on the surface, and as a result, the dry dirt is likely to adhere.

The arithmetic average roughness Ra of the surface of the antifouling coating film is within the range of 2.5 to 100 nm. If the arithmetic average roughness Ra is within this range, the formation of such an antifouling coating film on the heat exchanger as the object to be coated can effectively suppress or prevent the adhesion of dry fouling at least.

The antifouling coating film is composed of at least nanoparticles as described above, and the arithmetic average roughness Ra of the surface may be within the above range, and the specific structure other than the above is not particularly limited. For example, the film thickness of the antifouling coating film is not particularly limited, but generally may be less than 1 μm (1, 000nm), preferably 500nm or less, and more preferably in the range of 20 to 500 nm.

When the film thickness of the antifouling coating film is smaller than 1 μm, that is, on the order of nanometers, the film thickness is relatively small (thin), so that the charging property of the antifouling coating film can be favorably reduced, adhesion of dry dirt can be favorably suppressed or prevented, and the transparency of the antifouling coating film can be improved. In addition, although depending on various conditions, when the film thickness is 500nm or less, the electrification property of the antifouling coating film can be further favorably reduced and the transparency can be further improved. Further, depending on various conditions, when the film thickness is in the range of 20 to 500nm, the transparency can be improved and the charging property can be further reduced, and the adhesion of dry dirt can be further favorably suppressed or prevented.

In particular, when the film thickness is 500nm or less (or in the range of 20 to 500 nm), the heat exchanger as the object of coating is basically made of metal, and therefore even if the antifouling coating film is charged, grounding can be achieved by the conductivity of the heat exchanger. Therefore, substantial charging can be avoided. This can further effectively suppress or prevent adhesion of dry dirt. In addition, although the antifouling coating film is likely to cause cracks due to the nanoparticles as the main component when the film thickness of the antifouling coating film is large (thick), the generation of cracks can be substantially avoided when the film thickness is 500nm or less.

The surface properties of the antifouling coating film are not particularly limited, but the surface resistivity is 10¹³Omega/□ or less. This can reduce the electrification of the antifouling coating film, and thus can suppress or prevent the adhesion of dry dirt. The water contact angle of the antifouling coating film may be less than 15 °, and may be 10 ° or less depending on various conditions. As described above, when the water contact angle of the antifouling coating film is small, the hydrophilicity of the surface is increased. Therefore, even if dry dirt is deposited on the surface of the antifouling coating film, the deposited dry dirt can be easily removed by washing with water.

The method for measuring the particle diameter of the nanoparticles is not particularly limited, and a known method (diffusion method, inertia method, sedimentation method, microscopy, light scattering diffraction method, or the like) can be suitably used. In the evaluation of the present embodiment, the particle diameter measured by a known method may be in the order of nanometers. The method for measuring (evaluating) the arithmetic average roughness Ra of the antifouling coating film is not particularly limited, and for example, the arithmetic average roughness Ra may be measured (evaluated) by using a laser microscope or an Atomic Force Microscope (AFM), and calculated according to JIS B0601. In the present embodiment, as described in the examples described later, the coating cross section is observed with an electron microscope, and an average value of the film thicknesses measured from a plurality of observation images is calculated. The method for measuring (evaluating) the water contact angle of the antifouling coating film is not particularly limited, and for example, a contact angle meter manufactured by synechia interface science corporation, a product name: DMo-501, the measurement (evaluation) is carried out.

The specific method for forming the antifouling coating film (production method) is not particularly limited, and various known methods can be used when fine irregularities formed by nanoparticles can be formed. Typical forming methods include a known coating method of preparing and coating a coating liquid (coating agent) containing nanoparticles, a sol-gel method, nanoimprinting, transfer using an anodic oxidation mold, a sand blast method, self-organization of ceramics, and the like.

The antifouling coating film may be composed of at least nanoparticles as described above, but may contain a binder component composed of at least a material having affinity for the nanoparticles. The function of the adhesive component may be a function of adhering nanoparticles to each other and a function of adhering nanoparticles to the surface of the heat exchanger as the object to be coated. Therefore, a material having affinity for at least the nanoparticles may be used as the main component.

the antifouling coating film contains a binder component, and the strength or durability of the antifouling coating film made of nanoparticles can be improved. Further, since the nanoparticles are well maintained by the surface of the antifouling coating film, fine irregularities on the surface are easily maintained, and the effect of suppressing or preventing adhesion of dry dirt can be improved.

the specific composition of the binder component is not particularly limited as long as it has affinity for the nanoparticles. For example, if the nanoparticles are silica nanoparticles, a material having affinity with silica can be used as the bonding component. Examples of the material having affinity for silica include silane compounds such as tetramethoxysilane and tetraethoxysilane, acrylic resins, and fluorine resins. The adhesive composition may contain known additives in addition to the above materials. Therefore, in the heat exchanger of the present invention, the antifouling coating film may be composed of at least nanoparticles, but may be a structure containing a binder component in addition to the nanoparticles, or may be a structure containing a known additive in addition to the nanoparticles and the binder component.

When the antifouling coating film contains the adhesive component, the content (content ratio) is not particularly limited, and for example, when the total weight of the antifouling coating film is 100 wt%, a preferable range is 5 to 60 wt%, and a more preferable range is 10 to 50 wt%. Although depending on various conditions, when the amount of the binding component exceeds 60% by weight, the amount of the binding component is too large relative to the nanoparticles, and there is a problem that the arithmetic average roughness Ra of the surface of the antifouling coating film deviates from a prescribed range. In addition, when the content of the bonding component is less than 5% by weight, there is a problem that effects such as improvement in strength or durability corresponding to the content of the bonding component cannot be sufficiently obtained.

[ dust adhesion percentage of antifouling coating film ]

The dirt-repellent coating film having the above-described structure has a dust adhesion rate of 15% or less. Here, the dust adhesion rate of the present invention is calculated as the adhesion amount of the pseudo dust on the surface of the heat exchanger (the coated surface formed of the antifouling coating film) on which the antifouling coating film is formed relative to the adhesion amount of the pseudo dust on the surface (the coated front surface) of the heat exchanger (the coated object) on which the antifouling coating film is not formed.

As described above, the "dry" soil includes a "large specific gravity hard straight type" soil having a relatively large specific gravity and being hard and a "small specific gravity soft type" soil having a relatively small specific gravity and being soft. In the present invention, the simulated dust used for calculating the dust adhesion rate is preferably a mixed simulated dust obtained by mixing a simulated dust of a "high specific gravity hard straight type" and a simulated dust of a "low specific gravity soft type". In general, the pseudo dust of the "large specific gravity hard straight type" is dust made of an inorganic material, and the pseudo dust of the "small specific gravity soft type" is dust made of an organic material.

The specific types of the "large specific gravity hard straight type" dust simulant and the "small specific gravity soft type" dust simulant are not particularly limited, and a material corresponding to the "large specific gravity hard straight type" or the "small specific gravity soft type" among the test powders and the like prescribed in various standards such as JIS (japanese industrial standards) can be appropriately selected and used. The "large specific gravity hard straight type" dust simulant and the "small specific gravity soft type" dust simulant are both one type, but two or more types are preferably used in combination.

In the present invention, as shown in examples described later, 2 types of silica sand as inorganic materials were used as the "high specific gravity hard straight type" dust simulant, and cotton linter and corn starch as organic materials were used as the "low specific gravity soft type" dust simulant. As specific silica sand, one kind of silica sand and 2 kinds of 3 kinds of silica sand specified in JIS Z8901 can be used.

As the cotton linters, those sold by Japan Air Cleaning Association (JACA), a public good society, as one of the powders for testing, can be used. Corn starch is a commercially available material. Silica sand was used for evaluation of adhesion of "high specific gravity hard straight type", cotton linter was used for evaluation of adhesion of fiber-like dust in "low specific gravity soft type", and corn starch was used for evaluation of adhesion of food powder-like dust in "low specific gravity soft type". Therefore, as a suitable example of the mixed dust of the "large-specific gravity hard straight type" pseudo dust and the "small-specific gravity soft type" pseudo dust, a mixed pseudo dust in which an organic pseudo dust and an inorganic pseudo dust are mixed can be cited.

In the examples and comparative examples of patent document 1, the adhesion (antifouling performance) of dust was evaluated by using kanto soil dust or carbon black as a pseudo dust alone. However, since various kinds of dust are generally present in a mixture of dust present in a living space, sufficient evaluation results cannot be obtained even when adhesion (antifouling performance) is evaluated using separate types of dust, as in the aspect of evaluating antifouling performance of dry fouling. Further, although the Kanto loam dust is used for evaluation of hydrophilic soil and the carbon black is used for evaluation of lipophilic soil, they are both "dry" soil of "hard straight type with large specific gravity". In patent document 1, there is no evaluation of "dry" dirt of "soft type with small specific gravity, such as fiber-based dust or food powder-based dust.

In contrast, in the present invention, as the dry dirt, a mixed pseudo dust in which a pseudo dust of "hard straight type with a large specific gravity" and a pseudo dust of "soft type with a small specific gravity" are mixed is used by modeling an actual dust existing in a living space without using a single pseudo dust. Therefore, the antifouling performance of dry fouling can be evaluated well. In addition, the powdery dust as the dry dirt includes hydrophilic dust such as Kanto loam dust, but in the mixed pseudo dust of the present invention, in addition to cotton linters as the fiber-based pseudo dust, corn starch having hydrophilicity is used as the pseudo dust of the food powder. Corn starch acts as a dry soil in the dry state, but absorbs water and acts as a hydrophilic soil when moisture is present. The corn starch having such characteristics was used as a pseudo dust, and the antifouling performance against actual dust was evaluated well.

The dust adhesion rate is defined as a ratio of the amount of adhesion of the mixed pseudo dust on the coating surface of the antifouling coating film to the amount of adhesion of the mixed pseudo dust on the coating front surface of the antifouling coating film in the heat exchanger, as described above. In the present invention, the amount of adhesion of the mixed pseudo dust on the coating front surface or in the coating surface is calculated as the area ratio of the remaining mixed pseudo dust calculated by binarizing the image captured by the optical microscope. The area ratio was defined as the dust attachment area. Let the dust-attaching area of the front surface be A₀The dust-attaching area of the coating surface is A₁Dust adhesion rate A_RCan be calculated by the following equation (1).

[ formula 1]

The dust adhesion rate of the antifouling coating film may be 15% or less, but is preferably 10% or less, more preferably 5% or less, and particularly preferably 2% or less. When the dust adhesion rate is 15% or less, the adhesion of dust is not noticeable visually, and therefore it can be judged that sufficient antifouling performance is obtained.

In calculating the dust adhesion rate, for example, an antifouling coating film is formed on a part of the surface of the heat exchanger or a part of the heat exchanger that is fragmented, and this can be used as a sample for evaluation. In the sample for evaluation, when the surface on which the antifouling coating film is formed is referred to as "coating surface", the mixed pseudo dust is attached to the coating surface, but before the mixed pseudo dust is attached, the sample for evaluation is preferably subjected to static elimination.

The method of adhering the mixed dust mimic to the sample for evaluation and the method of shaking off the adhered mixed dust mimic are also not particularly limited, and various methods can be suitably used. For example, in the examples described later, the mixed pseudo dust was deposited on the coating surface by a predetermined amount, and the evaluation sample was vertically dropped obliquely, whereby the mixed pseudo dust was shaken off. The image pickup of the coated surface of the optical microscope is not particularly limited, and a plurality of images may be picked up at a magnification at which the mixture of the pseudo dust can be observed. The binarization processing of the captured image is not particularly limited, and known image processing software or the like may be used.

[ Heat exchanger ]

The heat exchanger of the present invention may be such that the antifouling coating film having the above-described structure is formed on the surface of the object to be antifouling. Here, the surface to be subjected to stain prevention may be a part of the surface of the heat exchanger, may be a plurality of parts of the surface of the heat exchanger, or may be the entire surface of the heat exchanger.

The structure of the heat exchanger of the present invention, that is, the specific structure of the heat exchanger as the object to be coated with the antifouling coating film is not particularly limited, and any structure may be used as long as it can be used in a refrigeration cycle or the like. Specifically, for example, there can be mentioned a configuration used in an air conditioner (air conditioner), a refrigerator, a freezer showcase, an automatic vending machine, and the like.

In the present embodiment, a heat exchanger used in an air-conditioning apparatus will be described as a typical heat exchanger. The specific structure of the heat exchanger used in the air-conditioning apparatus is not particularly limited, and a known structure may be employed, and typically, a fin-tube type heat exchanger 10A schematically shown in fig. 1, a plate-stacked type heat exchanger 10B schematically shown in fig. 2, and the like can be cited.

As shown in fig. 1, a fin-tube type heat exchanger 10A typically has a structure in which a plurality of flat plate-like fins 11 are stacked, and a plurality of refrigerant tubes 12 having folded portions are provided so as to penetrate the fins 11. The refrigerant tubes 12 form refrigerant flow paths, and for example, as indicated by block arrows in the drawing, the refrigerant flows through the refrigerant tubes 12, and the refrigerant and the outside air exchange heat via the refrigerant tubes 12 and the fins 11.

As shown in fig. 2, the plate-laminated heat exchanger 10B typically has a structure in which a plurality of rectangular heat transfer plates 13 are laminated to form a substantially rectangular parallelepiped (quadrangular prism) plate laminated structure 14, and refrigerant tanks 15 are provided at both ends of the plate laminated structure 14. The refrigerant tank 15 communicates with the inside of the respective heat transfer plates 13 constituting the plate lamination structure 14. In each heat transfer plate 13, for example, as indicated by block arrows in the figure, the refrigerant flows from one refrigerant tank 15 to the other refrigerant tank 15, and thereby the refrigerant and the outside air exchange heat via the heat transfer plate 13.

The heat exchanger of the present invention is a fin-tube type or a plate-stacked type, and the antifouling coating film having the above-described structure is formed on at least a part of the surface thereof. Thus, even if the surface of the heat exchanger (particularly the surface of the fin or the surface of the heat transfer plate) comes into contact with dry dirt (dust or the like), the adhesion of the dry dirt to the surface due to the fine irregularities on the surface of the antifouling coating film can be effectively suppressed or prevented.

In particular, since the surface resistivity can be relatively lowered by limiting the film thickness of the antifouling coating film, adhesion of dry dirt can be more effectively suppressed or prevented by the synergistic effect of fine irregularities on the surface. Furthermore, if hydrophilic particles such as silica particles are used as the nanoparticles, the deposited dry fouling can be easily removed by washing the heat exchanger with water.

As described above, the heat exchanger of the present invention is constituted by at least nanoparticles, and the antifouling coating film having irregularities with an arithmetic average roughness Ra of the surface in the range of 2.5 to 100nm is formed on the surface of the object to be antifouling. This can effectively suppress or prevent dry fouling from adhering to the surface of the heat exchanger.

(examples)

The present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited thereto. Those skilled in the art can make various changes, modifications and alterations without departing from the scope of the present invention.

(Mixed simulated dust)

As the simulated dust of the "high specific gravity hard straight type", 1 kind of silica sand and 3 kinds of silica sand prescribed in JIS Z8901 were used, and as the simulated dust of the "low specific gravity soft type", cotton linters sold as test powder by Japan Air Cleaning Association (JACA) of the public good community law and commercially available corn starch were used. The 4 types of pseudo dust were weighed to be equal in weight and sufficiently mixed to form mixed pseudo dust.

(arithmetic average roughness Ra of antifouling coating film)

The arithmetic average roughness Ra was measured using a scanning probe microscope (product name: AFM5300, manufactured by Hitachi ハ イ テ ク サ イ エ ン ス, K.K.) and calculated in accordance with JIS B0601.

(evaluation of dust attachment ratio)

After the evaluation sample was electrically removed, the mixed powder was scattered and shaken on the evaluation sample, and then the surface of the evaluation sample was photographed with an optical microscope, and the photographed image was subjected to binarization processing to measure the dust adhesion area on the surface. When the surface of the sample for evaluation on which the antifouling coating film was not formed was taken as a reference surface and the surface on which the antifouling coating film was formed was taken as an evaluation surface, the dust adhesion ratio was determined as the ratio of the dust adhesion area on the evaluation surface to the dust adhesion area on the reference surface. When the dust adhesion area was 5% or less, the dust adhesion rate was evaluated as "very good", when it exceeded 5% and 15% or less, it was evaluated as "good", and when it exceeded 15%, it was evaluated as "poor".

(example 1)

An aluminum metal plate was prepared as a part of the heat exchanger, which was fragmented. A coating liquid in which silica particles having an average particle size of 20nm were sufficiently dispersed in ethanol as a dispersant by pH adjustment was prepared by a known method, and the coating liquid was applied to approximately half of the surface of an aluminum metal plate and dried, thereby preparing an evaluation sample having an antifouling film formed in example 1. In this sample for evaluation, an antifouling coating film was formed on one half of the surface, and no antifouling coating film was formed on the remaining half. The surface of the formed antifouling coating film had irregularities with an arithmetic average roughness Ra of 10nm with respect to the sample for evaluation. The dust adhesion rate of the evaluation sample was ". circleincircle".

(example 2)

The evaluation sample of example 2, in which the antifouling coating film was formed, was prepared in the same manner as in example 1, using particles having an average particle diameter of 100nm as the silica particles. The surface of the formed antifouling coating film had irregularities with an arithmetic average roughness Ra of 40nm with respect to the sample for evaluation. The dust adhesion rate of the evaluation sample was "o".

Comparative example 1

A sample for evaluation having an antifouling film formed thereon according to comparative example 1 was prepared in the same manner as in example 1, except that particles having an average particle diameter of 100nm were used as the silica particles, and the coating liquid was prepared without sufficiently dispersing the silica particles. The surface of the formed antifouling coating film had irregularities with an arithmetic average roughness Ra of 140nm with respect to the sample for evaluation. The dust adhesion rate of the evaluation sample was "x".

Comparative example 2

A sample for evaluation having an antifouling film formed in comparative example 2 was prepared in the same manner as in example 1, except that particles having an average particle diameter of 250nm were used as the silica particles, and the coating liquid was prepared without sufficiently dispersing the silica particles. The surface of the formed antifouling coating film had irregularities with an arithmetic average roughness Ra of 130nm with respect to the sample for evaluation. The dust adhesion rate of the evaluation sample was "x".

(comparison of examples and comparative examples)

from the results of examples 1 and 2, it is clear that the antifouling coating film is composed of nanoparticles, and when the antifouling coating film has irregularities having an arithmetic average roughness Ra of the surface in the range of 2.5 to 100nm, the rate of dust adhesion can be suppressed to 15% or less, and the adhesion of dry fouling can be favorably suppressed in a heat exchanger. On the other hand, it is found that, as in the embodiment of comparative example 1 or 2, the antifouling coating film is composed of nanoparticles, and when the unevenness of the surface of the antifouling coating film exceeds the upper limit 100nm of the arithmetic average roughness Ra, the dust adhesion rate exceeds 15%, and the adhesion of dry dirt cannot be satisfactorily suppressed.

The present invention is not limited to the description of the above embodiments, and various modifications are possible within the scope of the claims, and embodiments obtained by appropriately combining the technical means of the respective inventions in different embodiments or in a plurality of modifications are also included in the technical scope of the present invention.

industrial applicability of the invention

The present invention can be widely applied to the field of heat exchangers in which prevention of adhesion of dry fouling is particularly desired.

Description of the reference numerals

10A Fin tube type heat exchanger (Heat exchanger)

10B plate laminated heat exchanger (Heat exchanger)

11 Fin

12 refrigerant pipe

13 heat transfer plate

14-plate laminating structure

15 refrigerant tank.