JPH0611294A - Corrosionproofing method for heat exchanging medium in contact with hard urethane foam - Google Patents

Abstract

PURPOSE:To prevent overall corrosion, partial corrosion such as pitting corrosion of a heat exchanging medium and to prevent leakage of refrigerant gas, etc., by using the medium having a corrosionproofing layer at least at a part of the medium. CONSTITUTION:A corrosionproofing layer 7 having a thickness of about 8mum is provided by coating a surface of an aluminum pipe 5 with epoxy series paint by a coating method and curing it. Corrosion of the pipe 5 can be prevented by the layer 7. Hard urethane foam 4 is manufactured by polyol, isocyanate, water, HCFC-22 foaming agent, etc., as materials. Foams are formed mostly by independent foaming and uniformly distributed thereby to eliminate a defect such as a froth void, etc. Thus, it has large mechanical strength, excellent flame retardance, dimensional stability, sound insulation, electric characteristics, chemical resistance, etc., high heat insulation at a low temperature to be desirably used as a heat insulator for a refrigerator, a freezer, an ice box, a container for frozen food, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing corrosion of a heat exchange element which comes into contact with a rigid urethane foam. More specifically, since it contains hydrogen atoms in its molecule, it has a short life in the atmosphere, so there are few problems with depletion of the ozone layer in the stratosphere and global warming, such as chlorodifluoromethane (CHClF ₂ and HCFC-22) (C
Corrosion of _{H 3 CClF 2, HCFC-142b} ) including a heat exchanger in direct contact with the rigid urethane foam having excellent thermal insulation properties, which is produced using as the blowing agent (such as refrigerant tubes) moiety such as pitting The present invention relates to an anticorrosion method capable of preventing corrosion.

[0002]

2. Description of the Related Art Polyol, isocyanate, water, trichlorofluoromethane (CCl ₃ F, hereinafter CFC-11)
Hard urethane foam manufactured using foaming agents as raw materials is mostly closed cells, has high mechanical strength, good heat insulation, and other dimensional stability, sound insulation, electrical characteristics, chemical resistance, etc. It is also excellent for refrigerators, freezers, freezer cars, ice boxes, frozen food containers,
It is widely used for heat insulating materials such as tanks of LPG tankers, panel insulating materials such as curtain walls, roofs of frozen warehouses, building materials such as eaves, and various automobile parts.

In 1974, by Roland (University of California), specified Freon [CFC-11, dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113), dichlorotetrafluoroethane (CFC-114) and chloro. Five types of pentafluoroethane (CFC-115)] have been discovered. Depletion of the ozone layer has a large effect on biological systems, such as a decrease in grain production and an increase in skin cancer. Moreover, it is said that specific CFCs exist in the environment for about 100 years without being decomposed and infrared absorption. Therefore, the contribution to the greenhouse effect is high, and the movement of regulations on specific CFCs is becoming active internationally. 19 in Japan
Regulations on the production and use of specific CFCs were started in July 1989, and the direction to completely abolish the production and use of CFCs was clearly stated. Therefore, in order to maintain the modern society, the production and use of alternatives to specific CFCs have become important.

CFC-11 which is such a specific CFC
Is used as a foaming agent, and since it has a hydrogen atom in the molecule and thus has a short life in the atmosphere, a foaming agent composed mainly of HCFC-22, which has less problems of depletion of the stratospheric ozone layer and global warming, was used. Rigid urethane foam is being developed.
However, HCFC-22 dissolves 0.30% by weight in water at a temperature of 25 ° C. under normal pressure and is relatively stable.
It is known that when it coexists with a metal or the like for a long period of time, it gradually hydrolyzes to generate an acidic substance, which causes corrosion of the metal. Since water is used as a foaming agent together with HCFC-22 foaming agent, carbon dioxide gas, etc., it may exist in the foam cells of rigid urethane foam. In addition, it may be exchanged with a heat exchanger by a heat cycle of continuous operation such as a freezer or a refrigerator. Water may intrude through a slight gap between the rigid urethane foam and the rigid urethane foam to absorb water. Therefore, the existence of water, which causes corrosion of metal, cannot be avoided. Therefore, even if a causative substance such as water is substantially present, it prevents corrosion of the heat exchanger such as the refrigerant pipe that is in direct contact with the hard urethane foam of the freezer or the refrigerator to prevent trouble such as refrigerant gas leakage. Therefore, there is a strong demand to prevent such problems and ensure stable operation over a long period of time.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention General corrosion of heat exchangers (refrigerant pipes, etc.) in direct contact with rigid urethane foam produced by using a blowing agent mainly composed of HCFC-22,
We will develop a corrosion protection method for heat exchangers that prevents partial corrosion such as pitting corrosion, prevents problems such as refrigerant gas leaks, and enables stable operation of freezers and refrigerators for a long period of time.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the problems of the prior art, the inventors of the present invention can solve the above problems by using a heat exchange element provided with an anticorrosion layer. The inventors have found what can be done and have completed the present invention.

The invention according to claim 1 of the present invention is HCFC-2.
In a method of anticorrosion of a heat exchanger contacting a hard urethane foam made by using a foaming agent containing 2 as a main component, a heat exchanger having an anticorrosion layer is used in at least a part of the heat exchanger. It is a method of preventing corrosion of the heat exchanger.

A method of preventing corrosion of the heat exchanger of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows a cross-sectional view of a refrigerating (freezing) stocker made by using the anticorrosion method for a heat exchanger of the present invention, and FIG. 2 shows an area around an aluminum pipe 5 of an evaporator of the refrigerating (freezing) stocker of FIG. The expanded sectional view is shown. 1 is a compressor, 2 is an inner box, 3 is an outer box, 4 is a rigid urethane foam, 5 is an aluminum pipe, 6 is a condenser, and 7 is an anticorrosion layer. The surface of the aluminum pipe 5 is provided with an anticorrosion layer 7 having a thickness of about 8 μ, which is obtained by applying an epoxy-based paint by a coating method and curing it. The anticorrosion layer 7 can prevent corrosion of the aluminum pipe 5.

The rigid urethane foam 4 referred to in the present invention is a rigid urethane foam produced from polyol, isocyanate, water, HCFC-22 foaming agent, etc. as raw materials, and most of the cells are closed cells and are evenly distributed. Since it has no defects such as floss voids, it has high mechanical strength, flame retardancy, dimensional stability, sound insulation, electrical characteristics, chemical resistance, etc., and has good heat insulation at low temperatures.
It can be suitably used as a heat insulating material for refrigerators, freezers, freezer cars, ice boxes, containers for frozen foods, etc. for business or home use. In the rigid urethane foam used in the present invention, an organic filler, an inorganic filler, an antioxidant, a lubricant, an organic or inorganic pigment, an ultraviolet inhibitor, a dispersant, a neutralizer, a plasticizer, depending on the purpose of use.
A nucleating agent or the like may be added.

The foaming agent which can be used together with HCFC-22 in the present invention includes known foaming agents such as water, carbon dioxide gas, nitrogen gas, air, and HCFC-142b and HFC-1.
34a, HFC-134, HFC-152a, and other hydrogen-containing CFCs.

Although the aluminum pipe (refrigerant pipe) 5 of the evaporator is mentioned as an example of the heat exchange element used in the present invention, the shape is not limited to a pipe shape, but a hollow plate shape or a hollow bar shape. , Hollow horns, etc. are not particularly limited. These heat exchangers may have a heat exchange rate improved by a known method or means, for example, may have fins or have an uneven surface. As an example of a hollow plate-shaped heat exchanger having an uneven surface,
An aluminum roll bond evaporator can be mentioned. Examples of the material of the heat exchanger include those having good thermal conductivity, such as copper and its alloys, and aluminum and its alloys, but are not particularly limited.

In the present invention, at least a part of the outer surface of the heat exchange element which is in direct contact with the above-mentioned rigid urethane foam, for example, a heat exchange element having an anticorrosion layer on a portion where corrosion is likely to occur is used, or It is important to use a heat exchanger having an anticorrosion layer over the entire surface. In the present invention, corrosion occurs for the same reason as the heat exchanger,
Alternatively, the outer box 3 and the inner box 2 which may be corroded may be provided with the anticorrosion layer according to the present invention.

As the above-mentioned anticorrosion layer, a protective film by a chemical or electrochemical means, an oxide film or a passivation film, and a coating of thermoplastic or thermosetting plastic which can be applied by a known method (coating method) Examples include extrusion coating, spray coating, plastic tube coating, powder coating, electrodeposition coating, dip coating, etc.), or coatings such as paint, insulating oil, grease, etc., baked, cured, etc. Examples thereof include, but are not limited to, an anticorrosion layer that can prevent corrosion of the heat exchanger.

The thickness of the anticorrosion layer is from 0.1 μm to
Although it is about 1.0 mm, it cannot be unconditionally determined because it also depends on the size and design of the refrigerator or refrigerator. The thickness of the anticorrosion layer may be such that corrosion of the heat exchanger can be prevented, and it can be appropriately determined.

[0015]

The following table (Table 1) shows the degree of hydrolysis of HCFC-22 for various substance systems.

[Table 1] It is known that when air coexists, metal corrosion is further promoted.

Since aluminum and its alloys are often used in near-neutral water where the passive state is stable, it is thought that local corrosion, that is, pitting corrosion under passive state occurs even if general corrosion is small. Certain anions present in water, such as SO ₄ ²⁻ , SiO ₃ ²⁻ ,
There are CrO ₄ ²⁻ , PO ₄ ³⁻ and Cl ⁻ , and dissolved oxygen in water, chlorine gas, and oxidizing agents such as peroxides are added to cause pitting corrosion. Corrosion of copper and its alloys and others is thought to proceed in the same way as in the case of aluminum. Even if the HCFC-22 gradually hydrolyzes to generate an acidic substance as described above, if a heat exchanger having a surface anticorrosion layer is used as the heat exchanger in contact with the rigid urethane foam, a freezer or It is possible to prevent water from entering through a slight gap between the heat exchanger and the rigid urethane foam by a cooling / heating cycle in a continuous operation of a refrigerator or the like, and in particular, since the direct contact with the above acidic substance and water is avoided, the heat exchanger It is thought that the corrosion of the can be prevented. In this way, even if water or an acidic substance is substantially present, it prevents the heat exchanger from corroding, preventing problems such as refrigerant gas leaks,
It enables stable operation for a long period of time.

[0017]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.
A refrigerator (50 cm) having the rigid urethane foam 4 shown in FIG. 1 is prepared by using the foaming machine equipped with a large mixing head for the component A and the isocyanate component B in which a polyol, a foaming agent, a catalyst and a silicon dispersant are mixed according to the following formulation. ×
50 cm) was made. The physical properties of the rigid urethane foam 4 were measured and are shown in Table 2.

[0018]

[Table 2] (Unit: parts by weight)Rigid urethane foam 1 2 3 Component A Polyol 100 100 100 Blowing Agent HCFC-22 10 6 HCFC-142b 4 CFC-11 16 Catalyst 0.64 0.64 0.64 Silicone Dispersant 0.64 0.64 0.64 Water 1 1 1 Component B Isocyanate 140 140 140Physical properties of foam Density (kg / m³ ) 34 34 34 34 closed cell (%) 95 95 95 tensile strength (Kg / cm² ) 2.4 2.4 2.4Flame retardant self-extinguishing self-extinguishing

As the evaporator 5, an aluminum pipe and a copper pipe (outer diameter 8 mm) were used. After degreasing, these pipes are spray coated with a commercially available epoxy paint (electrostatic coating), heated and baked in the air for about 15 minutes, dried, and provided with an anticorrosion layer with a film thickness of about 10 μ. Used in the example. (Operating conditions) Temperature: -15 to -20 ° C Period: 1 month (40 days operation), operation started in September 1991. 3 months (80 days operation) 6 months (180 days operation) Atmosphere: normal temperature and humidity atmosphere. A continuous operation test was conducted under operating conditions that match actual operating conditions.

(Comparative Example) With respect to the one using the hard urethane foams 1 to 3, after continuously operating for 1, 3 and 6 months, it was examined what kind of influence (corrosion) the aluminum pipe and the copper pipe had. In the comparative example, an aluminum pipe and a copper pipe without the anticorrosion layer were used. The results are shown in Table 3.

[0021]

[Table 3]

Copper pipe ・ By observation with a stereoscopic microscope, there was no significant difference between the one month object and the three month object. There were many black spots of corrosion on the surface, but the depth was shallow and there was no problem. Aluminum pipe ・ By observation with a stereomicroscope, five months after one month, corrosion, which is thought to be pitting corrosion, was found. The pH of the water absorbed in the urethane foam by the universal pH test paper was pH≈7.・ According to SEM / EPMA analysis, Na and C are present in the corroded parts.
1, O, K, S, Ca were detected. N in the normal part
a, Cl was detected.

(Examples) With respect to the ones using the hard urethane foams 1 to 3, after being continuously operated for 1, 3 and 6 months, the aluminum pipe and the copper pipe provided with the anticorrosion layer are affected by what (corrosion). I looked up. After continuous operation for 1, 3 and 6 months, the aluminum pipe and the copper pipe provided with the anticorrosion layer were examined, but no corrosion was observed at all. The example using the rigid urethane foam 3 is an example of the conventional method.
Since 11 is used, there are problems of ozone layer depletion and global warming.

[0024]

INDUSTRIAL APPLICABILITY Since the present invention contains hydrogen atoms in its molecule and thus has a short life in the atmosphere, HCFC-22 or HFC-2 having less problems of depletion of the stratospheric ozone layer and global warming can be obtained.
The present invention provides a method for corrosion protection of a heat exchange element which is in direct contact with a rigid urethane foam produced by using CFC-142b or the like as a foaming agent, and a heat exchange element having an anticorrosion layer on at least a part of the heat exchange element. By using, HC
Even if acidic substances and water produced by hydrolysis of FC-22 are substantially present, corrosion of the heat exchanger is prevented, problems such as refrigerant gas leaks are prevented, and refrigerators and freezers are stable for a long time. I can drive.

[Brief description of drawings]

FIG. 1 shows a sectional view of a refrigerating stocker.

FIG. 2 shows an enlarged cross-sectional view of the periphery of an aluminum pipe 5 of an evaporator of a refrigerating (freezing) stocker.

[Explanation of symbols]

 1 Compressor 2 Inner box 3 Outer box 4 Hard urethane foam 5 Aluminum pipe 6 Condenser 7 Anticorrosion layer

Claims (1)

[Claims] 1. A method for anticorrosion of a heat exchange body, which is in contact with a rigid urethane foam produced by using a foaming agent containing HCFC-22 as a main component, wherein the heat exchange body has an anticorrosion layer on at least a part thereof. A method for preventing corrosion of a heat exchanger, which comprises using a body.