JP2001107204A - Copper tube excellent in discoloring resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper tube excellent in discoloring resistance, in which the discoloring of a copper tube coil can be suppressed. SOLUTION: In a phosphorous deoxidized copper tube or an oxygen-free copper tube subjected to annealing treatment at a high temperature of >=550 deg.C such as bright annealing and whose crystal grain size after the annealing is >=0.030 mm, the oxidation current value of the outer surface of the copper tube after the annealing is controlled to <=6.0 μA.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper tube having excellent resistance to discoloration after annealing.

[0002]

2. Description of the Related Art As is well known, copper pipes are widely used as heat transfer pipes for coolers, air conditioners, fan coil units, air handling units and the like, and refrigeration air conditioning pipes such as refrigerant pipes. I have.

[0003] The surface of copper or copper alloy, which is the material of the copper tube,
Usually, it is covered with an extremely thin oxide film. This oxide film has high protection, and copper itself is a noble metal. For this reason,
Copper pipe is a material that is relatively resistant to corrosion and discoloration due to corrosion, which is also the reason that it is widely used for the above-mentioned applications.

[0004] However, depending on the manufacturing process, transportation or storage of the copper tube, and the conditions of use, oxidation (corrosion) proceeds under the influence of temperature, humidity, corrosive substances, etc., and the surface of the copper tube may be discolored. There is.

Here, a general manufacturing process of a copper tube coil product will be described. Copper pipes are usually made from copper and copper alloy ingots (billets) by hot extrusion or the like, and the pipes are drawn to a predetermined diameter, length or shape by cold working such as drawing or a reducer. After being made into a copper tube (straight tube etc.) or a copper tube coil (LWC: Level wound coil) wound in a line, bright annealing treatment is performed to obtain a copper tube product. Among them, the bright annealing treatment is performed at a predetermined temperature and a predetermined time according to the required characteristics of the copper tube product by using a reducing DX gas containing a reducing substance such as H ₂ and CO.

[0006] Of the copper tube products manufactured in such a process, the copper tube coil, in particular, is unwound from the coil and cut, brazed, etc. in the process of processing into the aforementioned refrigeration / air-conditioning pipe. Piping.

[0007] During the bright annealing, tight (dense)
At high temperatures, the copper tubes of the copper tube coil wound around the tube may stick together. In order to prevent the joining of the copper tubes during the bright annealing, silicone oil is sometimes applied as a release agent when the copper tubes are coiled (after drawing) before the bright annealing. The application of silicone oil when the copper tube is coiled after the cold working is significantly more efficient in process than the application to the coiled copper tube.

On the premise of the above-described copper tube manufacturing process, the discoloration that occurs in the copper tube, which is a problem of the present invention, is a typical and characteristic discoloration of the copper tube inside the copper tube coil after the bright annealing treatment. This is oxidative discoloration that occurs on the outer surface of the copper tube (anko portion) in a long band in the longitudinal direction. This discoloration is usually called anko discoloration, and it is said that dew condensation accompanying changes in temperature and humidity promotes oxidation. This discoloration of the bean paste (hereinafter simply referred to as discoloration) impairs the commercial value of the copper tube in appearance,
Depending on the application, it also leads to impairing the performance of the copper tube such as an increase in frictional resistance during processing.

Various techniques have been conventionally proposed to prevent the discoloration of the copper tube. The typical one is
This is the surface treatment of copper tubes. A typical surface treatment is to apply a benzotriazole (BTA) -based discoloration inhibitor, which is used as an aqueous solution by mixing with another hexylene glycol or an amine compound. These discoloration inhibitors are applied to the copper tube before the bright annealing at the time of coiling (drawing) or to the coil after the bright annealing.

[0010] Further, a compound or light oil is mixed with silicone oil, which is widely used as the release agent, to modify it so as to have a function as a rust preventive oil, and applied to a copper tube before and after the bright annealing. A technique for preventing discoloration has been proposed in Japanese Patent Publication No. 8-954 and the like.

Various techniques for modifying the surface side of a copper tube have also been proposed. For example, Japanese Unexamined Patent Publication No. Hei 6-49620 discloses that an oxide film on the surface of a copper tube is harder to oxidize.
(For example, cupric oxide) is disclosed.

In Japanese Patent Application Laid-Open No. Hei 1-287258, among the discoloration of the copper tube, the drawing lubricating oil remaining on the surface of the copper tube is carbonized during annealing, and the discoloration due to the carbonized lubricating oil is prevented. Therefore, it is disclosed that annealing is performed after removing the lubricating oil.

[0013]

However, first, regarding the surface treatment of copper tubes, it is widely known that a BTA-based or other discoloration preventing coating agent is effective in preventing discoloration of copper tubes due to oxidation. However, these coating agents
Basically, it has a property of being applied to a copper tube after bright annealing to prevent discoloration of a product copper tube. For this reason,
Originally without heat resistance, when applied to copper tube before bright annealing,
For example, the copper tube is decomposed or deteriorated during bright annealing at a high temperature of 550 ° C. or higher. As a result, a residue harmful to the discoloration of the copper tube may be left on the surface of the copper tube to cause or promote discoloration. In addition, the joining (sticking) of the copper tubes of the copper tube coil at a high temperature during bright annealing cannot be suppressed.

Further, these BTA-based and other discoloration-preventing coating agents may have an adverse effect on the processing steps for the refrigeration / air-conditioning piping and on the quality of the piping. This adverse effect is, for example, a decrease in wettability when brazing a copper tube. Even when these BTA-based or other anti-tarnish coating agents are applied to annealed copper tubes, especially in the case of copper tube coils, they are applied to the bean that is subject to discoloration because they are tightly wound. It is difficult.

Next, as described later, the silicone oil applied to the copper tube before the bright annealing as a mold release agent is also transformed during the bright annealing depending on the conditions of the bright annealing, and on the contrary, the discoloration of the copper tube coil is changed. The result is to promote. The same applies to the case where a compound, light oil, or the like is mixed with silicone oil to modify the rust-preventive oil.

In the method of removing the lubricating oil for drawing in advance before annealing as disclosed in JP-A-1-287258, the discoloration itself due to the carbonization of the lubricating oil can be prevented.
However, after the drawing, the lubricating oil was removed and then applied to (coated with) silicone oil as a mold release agent, and also to the copper tube from which the lubricating oil was removed and the mold release agent was not applied. still,
The discoloration in question in the present invention has occurred. Therefore, the mere removal of the drawing lubricating oil does not provide a solution to the oxidative discoloration of the copper tube coil, which is a problem of the present invention.

Furthermore, the technology for modifying the surface side of the copper tube and the technology for improving the atmosphere side of the copper tube also require a copper tube coil which is a problem in the present invention when compared with the required cost such as capital investment. There is a problem that the effect of improving discoloration is extremely small.

The present invention has been made in view of such circumstances, and an object thereof is to provide a copper tube excellent in discoloration resistance, which can fundamentally suppress discoloration of a copper tube coil. Is what you do.

[0019]

In order to achieve this object, the gist of the copper tube excellent in discoloration resistance of the present invention is that the crystal tube after annealing is subjected to a high-temperature annealing treatment at 550 ° C. or more such as bright annealing. In a phosphorus deoxidized copper tube or an oxygen-free copper tube having a particle size of 0.030 mm or more, the oxidation current value on the outer surface of the copper tube after the annealing is 6.0 μA or less (claim 1).

In a preferred embodiment, in order to prevent the joining of the copper tubes during the high-temperature annealing, before the annealing,
That is, a copper tube coated with a release agent is provided (claim 2).

Further, as a preferred embodiment, the present invention is directed to a copper tube coil in which a copper tube is wound in a coil shape, in which discoloration due to oxidation is particularly likely to occur (claim 3).

The present inventors have studied the causes of the discoloration of the copper tube coil. As a result, the conditions of bright annealing, silicon oil commonly used as the release agent, and the external surface treatment adhering to the surface of the copper tube have been studied. It was found that residues such as oil were deeply involved in the generation of discoloration.

As described above, for the copper tube or copper tube coil, conditions such as the temperature and time of bright annealing are selected in accordance with the composition of the copper alloy and the required characteristics. Of these, in recent years, in order to improve the workability, etc., which becomes more severe for copper tubes, it is called soft annealing, and it is based on the temperature of JIS O material (complete annealing) and OL material (annealing) (500-550 ° C). Also above 550 ℃ 65
Higher temperature bright annealing up to 0 ° C (the actual temperature of the copper tube) is commonly used. In this high-temperature bright annealing, the O
The crystal grain size of copper tubes of materials and OL materials is 0.030 mm or less, 0.030 to 0.
The crystal grain size of the copper tube is 0.040 mm or more compared to 040 mm.

However, when the high-temperature bright annealing is performed, and particularly when the crystal grain size of the copper tube is set to 0.040 mm or more, the silicon oil applied after drawing and adhering to the surface of the copper tube is decomposed to form the copper tube. On the other hand, it was found that the substance had changed to a compound that promoted oxidative discoloration. Incidentally, regarding the scope of the present invention,
As will be described later, not only copper tubes having a crystal grain size (after annealing) of 0.040 mm or more, in which this phenomenon is particularly remarkable, but also copper tubes having a crystal grain size of 0.030 mm or more in which this phenomenon can occur.

That is, in bright annealing at a normal low temperature, the decomposition or alteration of the silicon oil does not easily occur, so that the discoloration of the copper tube due to the decomposition or alteration of the silicon oil does not easily occur. However, bright annealing at a higher temperature of 550 ° C. or higher particularly remarkably decomposes or degrades silicon oil, and tends to generate oxidation promoting substances for copper tubes. More specifically, in the high-temperature bright annealing, the silicon oil is oxidized by the DX gas in the atmosphere and a very small amount of oxygen gas, and organic groups (hydrophobic groups) such as CH ₃ in the silicon oil are lost. The hydrophobicity of the oil decreases, and it changes to a component having a higher affinity for water. Further, a part of the silicon oil is decomposed to generate oxidizing gases or compounds such as formaldehyde and formic acid. The presence of the silicon oil or oxidizing gas or compound having reduced hydrophobicity on the outer surface of the copper tube acts as a compound that promotes oxidative discoloration of the copper tube, thereby preventing oxidation of the outer surface of the copper tube. It was found that it accelerated and resulted in discoloration.

In order to prevent the discoloration of the copper tube coil based on the cause of the discoloration, a mold release agent such as silicone oil which causes the discoloration is not used. It is conceivable to apply later. However, as described above, in the case of a copper tube processed by coil form, in order to prevent joining of the copper tubes during bright annealing,
It is often necessary to apply a release agent. Further, when applying the release agent to the coiled copper tube after bright annealing, in order to uniformly apply the surface of the copper tube relatively densely coiled, the coil form must be rewound once. There are only methods such as loosening the winding or immersing each coil in a mold release agent, all of which result in significantly impairing the productivity of the copper tube coil. In addition, there is a concern that the copper tube is hardened by unwinding.

[0027] Therefore, in order not to hinder the productivity of the copper tube coil, the present inventors apply (release) a release agent to the copper tube and perform the high-temperature bright annealing before the bright annealing. Based on the premise, we studied how to prevent discoloration of the copper tube coil. Then, instead of the silicon oil, the basic characteristics and physical properties of a release agent that does not generate an oxidation-promoting substance for a copper tube even by bright annealing at a high temperature were examined.

As a result, it has been found that there is a correlation between the degree of deterioration of the silicon oil after the bright annealing at a high temperature, which promotes the oxidation of the outer surface of the copper tube, and the value of the oxidation current on the surface of the copper tube. On the other hand, the value of the oxidation current also indicates the susceptibility of the copper tube surface to corrosion.Using the oxidation current value, the copper tube subjected to high-temperature bright annealing without applying a release agent is used. Also found that the discoloration of the copper tube surface can be quantified easily.

In high-temperature bright annealing, when a release agent such as silicon oil is applied, as described above, the silicon oil on the surface of the copper tube is denatured to oxidize the outer surface of the copper tube with an oxidizing gas or a compound. The substance which promotes is produced. When this fact is viewed from the side of the applied release agent, the oxidation current value is
This indicates the ease of oxidation (decomposition) of the release agent after bright annealing, or the stability (degradability) of the release agent during bright annealing. Also, when viewed from the copper tube side, it is a measure of the susceptibility of the copper tube surface to oxidation, regardless of the presence of the release agent on the surface.

On the other hand, the oxidation current of the surface of a metal or the like is known as an anode current as a measure for measuring the ease of oxidation or corrosion of the surface of a metal or the like. In this regard, the oxidation current value of the copper tube surface (copper tube and oxide film) after high-temperature bright annealing, and when a mold release agent is applied, the oxidation current value of the copper tube surface including the mold release agent is The present invention was made based on the finding that the surface of the tube is easily oxidized, that is, it is well-corresponding to the discoloration resistance. Therefore, the oxidation current value defined in the present invention can be said to be an index indicating the discoloration of the outer surface of the copper tube.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The significance of each requirement in the present invention will be described below.

(Oxidation current) First, the oxidation current referred to in the present invention is, as described above, an anode current known as a measure for measuring the easiness of oxidation or corrosion of a substance such as a metal. . However, even with a known anode current, the measurement conditions are determined according to the type of specific oxidation or corrosion of the specific metal or the like, and the specific metal or specific It varies depending on the type of typical oxidation or corrosion. In other words, depending on the selection of the conditions for measuring the anode current, it may happen that the anode current does not correlate with the actual oxidation or corrosion behavior.

In this respect, the discoloration itself of the copper tube targeted in the present invention is only slight oxidation of only the surface of the copper tube, and therefore, the corresponding measurement condition of the anode current (hereinafter referred to as oxidation current). However, relatively loose measurement (current) conditions need to be met.

More specifically, the measurement conditions of the oxidation current specified in the present invention are as follows: in order to prevent measurement errors and to provide reproducibility of the measured values, the temperature is room temperature (25 ° C.);
(M) in a KCl aqueous solution, the copper tube sample (0.2
A measurement area (5 cm ² , 0.5 cm × 0.5 cm) is immersed in a measurement area, and the measured value is an oxidation current (μA) measured at 0 V (saturated calomel electrode: SCE) after 1000 seconds.

The oxidation current of the copper tube is determined by a three-electrode method using a saturated calomel electrode as a reference electrode.
The current value of the electrode copper tube (sample) by constant potential electrolysis (constant potential) is measured with a potentiostat. Therefore, in the present invention, copper on the outer surface of the copper tube, a copper oxide film, and a release agent
This means that the oxidation current on the outer surface of the copper tube, including (when applied), was measured. In other words, the overall influence of various factors affecting the anode current characteristics on the outer surface of the copper tube is evaluated.

In the present invention, the measured value (μm) of the oxidation current of the copper tube having the release agent after the bright annealing on the surface or the copper tube having no release agent after the bright annealing under the above-mentioned measurement conditions (μ)
A) is specified to be 6.0 μA or less, and a mold release agent having such a value is applied to the copper tube before bright annealing, and / or an oxide film on the surface of the copper tube is adjusted.

When the measured value of the oxidation current (μA / cm ² ) exceeds 6.0 μA, when the release agent is used, the release agent layer applied before the bright annealing is altered by the high-temperature bright annealing. do it,
Or, even if it is not deteriorated, it is a release agent layer that is corrosive to the copper tube (surface). For this reason, depending on the subsequent manufacturing process, transportation or storage of the copper tube, and furthermore, depending on the situation of use, oxidation proceeds under the influence of temperature, humidity, corrosive substances, and the like, and this causes the discoloration of the bean paste targeted in the present invention.

Further, even when a release agent is not used,
When the measured oxidation current (μA) exceeds 6.0 μA, the copper tube surface is susceptible to corrosion due to high-temperature bright annealing. Therefore, as described above, the temperature, humidity,
Oxidation proceeds due to the influence of corrosive substances and the like, and leads to discoloration of the bean paste, which is the object of the present invention. The measurement of the main oxidation current may be appropriately performed after the annealing.

(Target copper tube) In the present invention,
The target copper tube was a phosphorus deoxidized copper tube or an oxygen-free copper tube having a crystal grain size of 0.030 mm or more after annealing, because the low-temperature bright annealing and the crystal grain size after annealing were less than 0.030 mm. This is because, in the alloy copper tube, the problem of discoloration targeted by the present invention, that is, the problem of discoloration due to deterioration of the release agent such as the silicone oil and the problem of discoloration without the release agent do not occur. Therefore, the discoloration targeted in the present invention is a phosphor deoxidized copper tube or an oxygen-free copper tube having a crystal grain size of 0.030 mm or more after annealing,
For example, it can be said that this is a problem that occurs remarkably for the first time in a phosphor deoxidized copper tube or an oxygen-free copper tube brightly annealed at a high temperature of 550 ° C. or higher. Therefore, it has not been possible to find the cause of the discoloration problem in such high-temperature bright annealing and to have a quantitative measure (index) with reproducibility.
Incidentally, the measurement of the crystal grain size referred to in the present invention is based on a comparison method defined by JIS H0501 (measurement of the crystal grain size by comparing a microscope image of a test piece with a standard crystal grain size photograph).

(Release Agent) The release agent used in the present invention includes:
In high-temperature annealing where the crystal grain size after annealing is 0.030 mm or more, and the quality of the release agent is deteriorated,
It is necessary to use a release agent such that the measured value (μA) of the oxidation current of the copper tube having the coating layer after the annealing under the above measurement conditions is 6.0 μA or less (corresponding to claim 2).
. In other words, in the present invention, a release agent that does not deteriorate so as to have an oxidation-promoting property on the copper tube (surface) is required even in the case of bright annealing at the high temperature. In addition to these basic properties, processing into refrigeration and air-conditioning piping, such as releasability, which is the original required property of the release agent (application purpose), and other factors that do not reduce the wettability during brazing, etc. It is necessary to have characteristics that do not adversely affect the process and piping quality.

Release agents satisfying these characteristics include:
Naphthenic mineral oils, lubricating oils composed of synthetic hydrocarbons such as polyolefins, oleic acid, methyl oleate, oleyl alcohol, and the like, release agents having excellent stability even at high temperatures such as the above-described bright annealing, are preferred embodiments. As an example.

On the other hand, the benzotriazole (BT
A) system discoloration inhibitor, water-insoluble polyalkylene glycol, silicone oil commonly used as a release agent, or a rust-preventive oil mixed with a compound or light oil, etc., at a high temperature such as the bright annealing described above. Measured oxidation current (μA) 6.0 μ
It is likely to exceed A, and it is likely to be a release agent layer having oxidation promoting properties on the copper tube (surface) even if it is modified or not transformed by high-temperature bright annealing.

However, even with the preferred release agent,
Depending on the type of copper tube (alloy, shape), bright annealing conditions and coating amount, the measured oxidation current (μA) may exceed 6.0 μA and may cause discoloration. Therefore, the final evaluation of discoloration resistance should be made by measuring the oxidation current.
Then, for each type of copper tube and release agent, bright annealing conditions and coating amount that do not cause discoloration should be selected based on the measurement value of the oxidation current.

(Method of Applying Release Agent) The method of applying the release agent is as follows.
In the current copper tube manufacturing process, an ordinary method of coating or coating a copper tube or a copper tube coil after plastic working such as drawing before bright annealing is appropriately selected. Since the amount of the release agent applied varies depending on the type of the release agent, the copper tube, the annealing conditions, and the like, it is generally difficult to specify the amount. The lower limit is determined from the required amount of the release agent for exhibiting its function. However, if the applied amount is too large, it adversely affects the process of processing the piping for refrigeration and air conditioning and the quality of the piping. Therefore, the upper limit is determined from this viewpoint. Further, the upper limit of the coating amount is, as described above, the measured value of the oxidation current.
(μA) and conditions that do not cause discoloration.

(Applicable Copper Tube) As described above, the copper tube according to the present invention is a phosphor-deoxidized copper tube or a copper tube having a crystal grain size of 0.030 mm or more after annealing, which is liable to undergo the discoloration targeted by the present invention. Use an oxygen copper tube. As the phosphorus deoxidized copper tube or the oxygen-free copper tube, a tube having a normal component composition is appropriately selected according to required characteristics and applications. In addition, the present invention is of course preferably applied to a straight tubular copper tube, but in particular, the discoloration easily occurs.
Most preferably applied to copper tube coils such as LWC
(Corresponding to claim 3).

(Manufacturing method of copper tube) The manufacturing method of the copper tube is the above-mentioned usual manufacturing method, that is, a copper and copper alloy ingot is formed into a raw tube by hot extrusion or the like, and the raw tube is drawn or drawn. After a copper tube or a copper tube coil is formed by cold working with a reducer or the like, a bright annealing process is performed to obtain a copper tube product. Among these, bright annealing treatment is performed by reducing DX gas containing a reducing substance such as CO, depending on the mechanical properties required for the copper tube.
For example, the heat treatment is performed at the above-mentioned temperature of 550 to 650 ° C. and an appropriate time. In addition, the shape of the copper tube is also commonly used, grooved tube on the inner and outer surfaces, inner fin tube, corrugated tube, double tube,
It can be used as appropriate for a low fin tube, an inner spiral tube, a fin tube, a fruited tube, a smooth tube, or the like.

(Adjustment of Copper Tube Outer Surface) The oxidation current measurement value (μA) of the copper tube outer surface when the mold release agent was not applied and on the copper tube outer surface even when the mold release agent was applied was 6.0 μA. The following method will be described. Since the copper itself does not change before and after bright annealing on the surface of the copper tube, the control of the oxide on the copper surface greatly contributes to the control of the oxidation current. In this regard,
Among the oxides on the copper surface, Cu ₂ O is more easily oxidized and has higher discoloration sensitivity than CuO. Therefore, oxides generated after drawing are once removed by etching or the like, and the oxide on the surface of the copper tube before bright annealing is made mainly of CuO, or the oxide on the surface of the copper tube after bright annealing is CuO. A method of adjusting the annealing conditions so as to be the main body is recommended.

However, as in the case of the mold release agent, depending on the type and shape of the copper tube, or the bright annealing conditions and the amount of coating, even if the oxide on the surface of the copper tube is mainly made of CuO, the measurement of the oxidation current is performed. The value (μA) may exceed 6.0 μA and discoloration may occur. Therefore, the final evaluation of discoloration resistance should be made by measuring the oxidation current. For each type of copper tube and release agent, the surface of the copper tube that does not cause discoloration, in other words, the measured oxidation current (μA) should be 6.0 μA or less, should be selected based on the measured oxidation current. is there.

[0049]

Next, examples of the molding method of the present invention will be described.
According to the above-mentioned conventional method, a deoxidized copper smooth tube drawn to a thickness of 0.8 mm and a diameter of 6.35 mm was washed with acetone and hexane to degrease the surface of the copper tube. The degreased copper tube was coated with an oil agent (release agent) under the conditions shown in Table 1 (including uncoated), and the coil (LWC)
(Coil single weight about 300kg). This copper tube coil is subjected to a reducing process to reach the actual temperature of the copper tube of 570 ° C in order to reach the actual temperature of the copper tube of 570 ° C in order to perform soft annealing with a crystal grain size of the copper tube after annealing of 0.04 mm or more.
In a DX gas (mixed gas composed of CO 2, H ₂ , N ₂ ) atmosphere, bright annealing was performed for 3 hours in a semi-continuous annealing furnace consisting of a heating zone, a soaking zone, and an outlet cooling zone. For comparison, the crystal grain size of the copper tube is less than 0.030 mm or 0.030 to 0.040 mm.
In the case of JIS O and OL materials, only the actual copper tube temperature is 500
Annealing was performed at a low temperature of ~ 550 ° C. Table 1 shows the crystal grain size of the copper tube.

Thereafter, five test pieces were sampled from each coil over the entire area in the longitudinal direction of the copper tube, and the oxidation current on the copper tube surface of each test piece was measured by the three-electrode method using the reference electrode. And the average value of the oxidation currents of the five test pieces was determined. Table 1 shows the results.
(Examples Nos. 1 to 10 and Comparative Examples Nos. 11 to 19).

In the case where the release agent is not applied, after the drawing, the generated oxide is once removed by etching, and the oxide on the surface of the copper tube before bright annealing is adjusted to be mainly composed of Cu ₂ O. Example in which bright annealing was further performed in an oxygen-free atmosphere
No.8 and 9 were prepared. After drawing, the generated oxides (mainly CuO) are brightly annealed as they are, and furthermore, in a bright annealing atmosphere, 100 ppm in the heating zone and 200 to 300 ppm in the outlet cooling zone.
Comparative Example No. 19 containing about oxygen was also prepared, and the average value of the oxidation current was determined in the same manner. Table 1 shows the results.

The discoloration resistance and releasability of these test pieces were evaluated in the following manner. The discoloration test conditions were as follows: the annealed copper tube coil was placed in a room at room temperature of 40 ° C and 70% RH in a packing state sandwiched between rust-proof cardboard and body-wrapped with rustproof cardboard. % Of each tube, the temperature was raised to room temperature and the temperature was lowered to room temperature in each room, and then evaluated by the degree of discoloration generated on the outer surface of the copper tube. And, while rewinding the copper tube coil with a payoff reel, including the oxidation current test piece sampling position,
The state of discoloration occurrence was confirmed over the entire area in the longitudinal direction of the copper tube. As a result, the case where no discoloration occurred on the outer surface of the copper tube in both coils was evaluated as ○, and the outer surface of the copper tube of either or both coils was longer than 100 mm in the longitudinal direction and 5 mm or more. When the band-shaped discoloration of the width occurred, the evaluation was evaluated as x, and when any of the coils had small (slight) discoloration less than the magnitude of the above-described discoloration on the outer surface of the copper tube, the evaluation was evaluated as Δ.

Further, at the time of rewinding the coil subjected to the discoloration test, the copper tubes are joined together over the entire area in the longitudinal direction of the copper tubes.
At the same time, it is visually determined whether or not there is
The release properties of the release agent and the copper tube were evaluated. As a result, the case where the bonding did not occur in the coil was evaluated as ○, the case where the bonding partially occurred only in several places of the coil was evaluated as Δ, and the case where the bonding occurred throughout the coil was evaluated as ×. The results are also shown in Table 1.

As can be seen from Table 1, naphthenic mineral oil
(Invention Example No. 1: viscosity 300 cst, at 40 ° C.) or a lubricating oil composed of a polyα-olefin synthetic hydrocarbon (Invention Examples No. 2 and 3
, 4: viscosity 155 cst, at 40 ° C), oleic acid (Invention Example No. 5)
, Methyl oleate (Invention Example No. 6), oleyl alcohol (Invention Example No. 7), etc., and a release agent having a measured oxidation current of 6.0 μA or less after bright annealing. Nos. 1 to 7 and Invention Examples Nos. 8 and 9, in which the surface of the copper tube was not coated without using a mold release agent, showed no discoloration, indicating that discoloration could be prevented.

Inventive Examples Nos. 1 to 7, 10 using a release agent
Has also suppressed the joining of the copper tubes during bright annealing, and also fulfills the original function as a release agent. Examples of the invention
Nos. 2 and 5 are other invention examples because the amount of release agent applied is small.
It is presumed that the suppression of joining of copper tubes during bright annealing was inferior to that of Nos. 1, 3, 4, 6, and 7. Furthermore, the inventive examples No. 8 and 9 in which the release agent was not used (uncoated) were also inferior to the invention examples using the release agent, but the joining of the copper tubes during bright annealing was also suppressed. .

On the other hand, Comparative Example No. 11 using a commercially available rust-preventive oil containing benzotriazole (BTA), Comparative Example No. 12 using a water-insoluble polyalkylene glycol, and are widely used as release agents. Comparative Examples Nos. 13, 14, and 15 using silicone oil (dimethyl silicone, viscosity 100 cst, at 40 ° C.), heat-resistant silicone oil (methylphenyl silicone, viscosity 13
0cst, at40 ° C), Comparative Example No.17 using octanol, Comparative Example No.18 using octanoic acid
In Comparative Example No. 19, in which no coating was applied, the bright annealing at a high temperature of 550 ° C. or higher resulted in a measured oxidation current (μA) of 0.030 mm or more, particularly 0.040 mm or more. 6.
Exceeds 0 μA. For this reason, although the joining of the copper tubes during bright annealing is suppressed, the copper tube (surface) has a coating layer that promotes oxidative discoloration. , Significantly inferior to the invention examples.

From these examples, it can be seen that, in particular, silicone oil which has been widely used as a mold release agent has a high bright annealing temperature and a grain size of 0.030 mm or more, especially 0.040 mm or more, which causes discoloration. In addition, if the BTA-based discoloration prevention coating agent has a high bright annealing temperature and a crystal grain size of 0.040 mm or more, it does not have the effect of preventing discoloration of the copper tube, but rather causes discoloration. You can see that.

In this embodiment, even when the same release agent is used, the measured value (μA) of the oxidation current is different even when the bright annealing is performed under the same conditions due to the difference in the conditions such as the coating amount.
It can be seen that the discoloration resistance is also significantly different. Therefore, even if the same release agent is used, the measurement value of the oxidation current greatly differs depending on the conditions such as the amount of application and the bright annealing conditions, and in order to guarantee the discoloration resistance, the measurement of the oxidation current according to the present invention is performed. Indicates that the value must be verified.

Further, Comparative Example No. 1 using the same silicone oil
In the comparison between No. 3 and Comparative Examples Nos. 14 and 15, in the case of Comparative Example No. 13 in which the crystal grain size of the copper tube was less than 0.030 mm (when the annealing temperature was relatively low), the same release agent and coating amount were used. However, no discoloration occurred in the copper tube coil. Therefore, as described above, the discoloration of the copper tube due to oxidation, which is a problem in the present invention,
It can be seen that this is a problem peculiar to high-temperature annealing in which the grain size is 0.030 mm or more, and particularly more than 0.040 mm.

Then, copper tubes not coated with the same release agent
Also in the comparison of (Invention Examples Nos. 8 and 9 and Comparative Example No. 19), the difference in the bright annealing atmosphere (Comparative Example No. 19, as described above, in the annealing atmosphere, 100 ppm in the heating zone, It can be seen that the measured value (μA) of the oxidation current varies depending on the amount of oxygen contained (about 200 to 300 ppm of oxygen), and the discoloration resistance also varies greatly.

Therefore, from these results, the measured value of the oxidation current varies greatly depending on the conditions such as the type of the copper tube and the release agent, the coating amount, and the bright annealing. It shows that it is necessary to verify with the measured value of the oxidation current of the invention. In addition, these facts support the significance of the evaluation of discoloration by the oxidation current of the present invention.
Further, the critical significance of the upper limit value of the oxidation current of the present invention is supported.

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[Table 1]

[0063]

According to the present invention, it is possible to provide a copper tube excellent in discoloration resistance, which can fundamentally suppress discoloration of a copper tube coil. Therefore, it has a great industrial value in that the use of the copper tube can be expanded.

Continuing from the front page (72) Inventor Takeki Otsuka 1-5-5 Takatsukadai, Nishi-ku, Kobe City Inside Kobe Steel Research Institute, Kobe Steel Ltd. (72) Inventor Akinori Tsuchiya 65-8 Hirasawa, Hadano-shi, Kanagawa, Inc. F term in Kobe Steel Hadano Works (reference) 4K062 AA01 AA05 AA10 BB06 BC07 CA10 EA02 FA04 FA05 FA16 GA10

Claims (3)

[Claims] 1. A phosphor deoxidized copper tube or an oxygen-free copper tube having a crystal grain size of 0.030 mm or more after annealing, wherein an oxidation current value of an outer surface of the copper tube after annealing is 6.0 μA or less. A copper tube with excellent discoloration resistance. 2. The copper tube having excellent discoloration resistance according to claim 1, wherein the copper tube is annealed after applying a release agent to the surface. 3. The copper tube according to claim 1, wherein the copper tube is wound in a coil shape.