JP2003014679A - Method and apparatus for inspecting inner surface film of metal can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for inspecting an inner surface film of a metal can which accurately detects a defect of the film of the can and which prevents occurrence of a defective product due to an inspection. SOLUTION: The apparatus 2 for inspecting the non-conductive inner surface film 4 of the metal can 1 to inspect the film 4 of the can 1, in which the film 4 is executed, comprises a voltage applying unit for applying an arbitrary voltage in which a metal part of the can 1 is one polarity and a conductive member 9 disposed in the can 1 is a negative polarity, a regulator for setting a specific resistance of pure water to a value in response to the film, a filling unit for filling inspecting water 17 set in proportion to the voltage to be applied in the can 1, and a judging unit for detecting the defect of the film based on a detected current value at the time of applying the voltage. Further, the apparatus sets a criterion value in response to the specific resistance of the water 17, and compares the detected current value with the criterion value to judge the defect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting defects such as scratches and pinholes on an inner surface coating covering the inner surface of a metal can made of a surface-treated steel plate or an aluminum alloy plate. And the device.

[0002]

2. Description of the Related Art The inner surface of a metal can is coated with a synthetic resin insulator such as a thermosetting resin coating film or a thermoplastic resin film film so that the metal can is not corroded by the filling material. Has been widely practiced. The material and thickness of the coating applied to the inner surface of the metal can and the method of forming the inner coating are determined by the properties of the filling material of the metal can. The thickness of the inner coating is usually 4 μm to 13 μm in the case of a thermosetting resin coating and 10 μm to 30 μm in the case of a thermoplastic resin film.

However, defects such as scratches and pinholes may occur in the inner surface coating during the formation of the inner surface coating and the subsequent processing steps of the metal can. Then, if the filler is sealed inside the metal can while leaving the defects of the inner surface coating,
The filler may corrode the metal that composes the metal can and cause corrosion holes, or the metal used in the metal can may elute into the filler and impair the flavor of the filler. was there. Therefore, in the process before filling the metal can with the filling material, a defect of the inner coating is detected by a sampling inspection.

The enamellator method is generally known as a method for detecting defects on the inner coating (coating) of the metal can. The enamellator method will be described. First, the electrolytic solution is injected into a metal can whose one end is closed and the other end is opened, and the negative electrode of the detection device is immersed therein. Next, the positive electrode of the detection device is brought into contact with the exposed metal part of the metal can, and a voltage of about several V (for example, 6 V) is applied between these electrodes for a predetermined time (for example, 3 seconds). Then, the leakage current flowing by applying a voltage of about several V is measured to detect defects in the inner coating of the metal can.

However, in the enamellator method, since an aqueous solution of sodium chloride or an aqueous solution of sodium sulfate is used as an electrolytic solution, even a metal can obtained a test result that there is no defect in the inner coating, Since the inner surface of the metal can may be corroded or contaminated with the passage of time due to the electrolytic solution adhering to the inner surface, the metal can used for the inspection is not returned to a normal product but is discarded and presumed to be a sampling inspection. Has become. Therefore, if this method is adopted for 100% inspection of metal cans, a cleaning process is required to completely remove the highly corrosive electrolytic solution from the inside of the metal cans, which complicates the process and makes metal cans. There is a problem that the cost increases.

An example of a method and apparatus for detecting defects in the inner coating of a metal can which can cope with such a problem is described in Japanese Patent Laid-Open No. 2000-046776. In this publication, a conductive brush is inserted inside a metal can to bring it into contact with the inner coating, and a conductive liquid is supplied to the surface of the inner coating to rotate the brush and the metal can in relative rotation. It is described that the liquid is made into fine particles by the brush, a low voltage (for example, 5 V to 30 V) is applied between the brush and the metal can in that state, and the current flowing through the inner surface coating is measured. There is. According to the method and apparatus described in this publication, by using pure water as the liquid having conductivity, it is possible to naturally dry the metal can or blow air (air at room temperature or warm air). It is said that after drying, no trace of water is left on the inner surface coating of the metal can, the metal can can be returned to the state before the inspection, and it is not necessary to provide a cleaning step.

[0007]

However, in the method and apparatus described in the above publication, since the conductive liquid is made into fine particles by the brush, the inner surface of the metal can is complicated and the tip of the brush is hard to reach. In the case of a shape (for example, a shape with a small diameter in the middle or a shape with spiral irregularities formed near the opening on one end side), the conductive liquid is applied to the surface of the inner surface coating. It is difficult to spread evenly. As a result, there is a possibility that the defect detection accuracy of the inner coating and the reliability of the inspection may decrease. Even if the inner surface of the metal can has a shape in which the tip of the brush reaches, if the brush is relatively rotated while being in contact with the inner surface of the metal can, the inner surface of the brush may be damaged or repeatedly performed. Due to contact with the inner coating, the tip of the brush may be worn or broken, and the broken portion of the brush may remain attached to the inner coating. Therefore, after inspecting the inner coating, it is necessary to inspect whether the fragments of the brush are attached to the inner coating of the metal can. However, if the fragments are minute, it is difficult to detect the fragments. However, in order to remove such debris, a separate washing and removing process of washing the inner surface of the metal can to remove debris is required, which complicates the inspection process and may reduce the inspection efficiency.

The present invention has been made in view of the above circumstances, and is a metal can having an opening formed at least at one end, even if the inner surface has a complicated shape. An object of the present invention is to provide a method and an apparatus for inspecting an inner surface film which can detect defects in the film well and can be applied to 100% inspection.

[0009]

In order to achieve the above-mentioned object, the invention of claim 1 is such that the metal portion of a metal can having a non-conductive inner surface coating has one polarity. After the conductive member placed in the can has the opposite polarity and the gas is dissolved in deionized water to fill the metal can with the test water adjusted to the specified specific resistance value, an arbitrary voltage is applied between both electrodes. Then, the current generated at the time of application is detected, and the inner coating is inspected based on the detected current value.

According to the first aspect of the present invention, not only when the inner surface of the metal can has a simple cylindrical shape but also when the metal can has a complicated shape, for example, a metal can having one end opening. In the can, which has been subjected to a multi-stage neck molding in the opening, the opening end is reduced in diameter to form a small-diameter mouth-neck portion, and the opening tip portion of the small-diameter mouth-neck portion is curled, Even if it is a metal can with a complicated inner surface shape, such as a screw-shaped bottle type can with spiral irregularities formed in the middle of the small diameter mouth and neck, etc. Since the test water can be evenly contacted, a voltage is applied to the entire area of the inner surface coating, and the accuracy and reliability of detecting defects in the inner surface coating can be improved. That is, instead of directly contacting the conductive member, which is one of the electrodes, with the inner surface coating, it is contacted via inspection water, that is, the inspection water is in close contact with the inner surface coating, so that the quality inspection of the inner surface coating is performed. It can be done enough.

Further, the inspection water used for the inspection reduces the detection sensitivity of defects even in the case of the inner surface coating having a low withstand voltage by adjusting the specific resistance value thereof to a predetermined value by dissolving the gas. Since the inspection voltage for inspection can be set to a voltage according to the withstand voltage of the inner coating without causing it, it is possible to detect defects in the inner coating without causing dielectric breakdown of the inner coating due to the inspection voltage. A metal can having an inner coating having a low voltage can be an inspection target, and in this case as well, the accuracy and certainty of detecting defects in the inner coating can be improved.

Further, since pure water whose specific resistance value is adjusted to a predetermined value by dissolving gas is used as the test water,
After a defect inspection of the inner coating, it is not necessary to cause a residue such as a metal or a trace of adhesion on the inner coating, and it suffices to discharge the inspection water from the metal can and remove the water. Therefore, after performing a defect inspection of the inner surface coating, it is possible to eliminate the need for a dedicated step of cleaning the inner surface of the metal can to remove residues and traces of adhesion, and to remove the inspection water simply by drying the metal can, As a specification of the inspection, there will be no problem in food hygiene law, and it will be possible to support 100% inspection.

Further, since the conductive member, which is one of the electrodes, is brought into contact with the inner surface film through the inspection water without directly contacting it, spark contact at the time of applying the inspection voltage is avoided, and the inner surface is prevented. The dielectric breakdown of the coating film can be prevented, and the durability of the electrode can be improved without damaging the electrode. In particular, in the conventional inspection method, since the conductive brush, which is one of the electrodes, is brought into direct contact with the inner surface coating, the inner surface coating is damaged by the brush, the tip of the brush is broken, and the broken portion becomes the inner surface coating. There is a risk of adhesion, and a dedicated cleaning / removing process to deal with this is required, and the inspection process is complicated. However, according to the present embodiment, such a situation can be avoided in advance. .

A second aspect of the present invention is the method for inspecting the inner surface coating of a metal can according to the first aspect, wherein the inspection water is used for the inspection and recovered, and then the ionic component is removed.
This method is characterized in that the gas is dissolved, the specific resistance value is adjusted to a predetermined value, and the gas is reused for inspection.

According to the invention of claim 2, in addition to the same effect as that of the invention of claim 1, the test water used is circulated and used after being collected and adjusted to a predetermined value. By adopting the additional method, it is possible to prevent unnecessary waste of water resources that are the raw material of the test water, and even if the specific resistance of the test water changes due to changes in the test environment during its operation, The adjustment process can be rapidly performed to restore the specific resistance value of the test water to an appropriate value, and the reliability of the test can be improved.

Further, since the specific resistance value of the inspection water is adjusted by dissolving the gas in the inspection water, after the defect inspection of the inner surface coating, no residue such as harmful metal is generated in the inner surface coating. All you have to do is to drain the test water from the metal can and remove the water, eliminating the need for a dedicated cleaning process to remove harmful residues and traces of adhesion, and removing the test water by simply drying the metal can. As a result, the process time required for the inspection process can be shortened, and the inspection specifications do not cause any problems in the Food Sanitation Act, and it is possible to support 100% inspection.

The invention of claim 3 is the method for inspecting the inner surface coating of a metal can according to claim 1 or 2, wherein the specific resistance value of the test water is 0.05 MΩ · cm to 2.0 MΩ · c.
This is a method characterized by being set in the range of m.

According to the invention of claim 3, in addition to the same action as the invention of claim 1 or 2, the specific resistance value of the test water is adjusted to 2.0 MΩ · cm or less. Then, even in the case of an inner surface coating with a low withstand voltage that could be inspected only by the dielectric breakdown method, while maintaining sufficient defect detection sensitivity of the inner surface coating, it is possible to apply a low inspection voltage according to this. It is possible to avoid damage to the inner surface coating and make it a defective product by inspection.

The lower limit of the specific resistance value of the test water is 0.05.
By setting MΩ · cm, it is not necessary to use a large amount of gas for adjusting the specific resistance value, the operating cost for adjusting the specific resistance value of the test water can be reduced, and the economical efficiency can be improved.
Along with this, the setting of the specific resistance value of less than 0.05 MΩ · cm is substantially close to the dielectric breakdown method. Therefore, the inspection voltage must be lowered to prevent the dielectric breakdown of the inner surface coating. Since the detection sensitivity decreases with the above, such a situation can be avoided by setting the lower limit of the specific resistance value of the test water to 0.05 MΩ · cm.

According to a fourth aspect of the present invention, there is provided an inner surface coating inspection apparatus for inspecting a defect of an inner surface coating of a metal can having a non-conductive inner surface coating, wherein the metal portion of the metal can has one polarity and The conductive member placed in the can has the opposite polarity,
An application device that applies an arbitrary voltage, an adjustment device that sets the specific resistance value of pure water to a value according to the inner surface coating, and pure water adjusted to a predetermined specific resistance value is filled in a metal can as inspection water. And a filling device to be in the state, after the filling, an arbitrary voltage is applied between both electrodes by the applying device, a current value detected at the time of voltage application, and a judgment reference value according to the specific resistance value of the test water. Based on the above, a discriminating device for detecting defects in the inner surface coating film is provided.

According to the invention of claim 4, in addition to the same effect as that of the invention of claim 1, the test water is not complicated even if the inner surface shape of the metal can is simple. Since the inspection voltage can be applied to the entire area of the inner coating from the inside of the metal can in close contact with the entire area, the accuracy and certainty of detecting defects in the inner coating can be improved.

Further, the inspection water used for the inspection is filled in the metal can after adjusting the specific resistance value thereof to a predetermined value by the adjusting device in advance, so that the inspection film is an inner surface coating having a low withstand voltage. In addition, the voltage applied for inspection can be set to a voltage according to the withstand voltage of the inner surface coating without lowering the detection sensitivity of defects, and the metal can having an inner surface coating with a low withstand voltage can be used as an inspection target. The defect of the inner coating can be detected without causing the dielectric breakdown of the inner coating due to the inspection voltage, and the accuracy and reliability of detecting the defect according to the withstand voltage of the inner coating can be improved.

Further, even if the specific resistance of the test water fluctuates during the process of supplying the test water, the fluctuation is detected to set the judgment reference value, which is the judgment standard. The accuracy and certainty of detecting a defect can be further improved.

The invention of claim 5 is the inner surface coating film inspection device for a metal can according to claim 4, wherein the inspection water used for the inspection is recovered, and the ionic components of the recovered inspection water are removed. The apparatus is characterized by being provided with an inspection water circulating device that circulates and uses the inspection water after processing, dissolving the gas and adjusting the specific resistance value of the inspection water to a predetermined value.

According to the invention of claim 5, in addition to the same effect as that of the invention of claim 4, the used test water is recovered,
After removing the ionic components, the gas is melted to adjust the specific resistance value of the test water to a predetermined value, and it is circulated and used for the test. In addition to being able to prevent it, it is also effective in reducing the manufacturing cost of the metal can and downsizing the inspection device itself.

Further, since the test water constantly adjusted to a constant specific resistance value can be used for the test, the test reliability of the inner surface coating can be improved.

Further, even if it is necessary to reset the specific resistance value due to the change of the inspection object during the operation of the inspection device, the adjustment function of the inspection water circulation device can sufficiently cope with it, and a wide variety of metals can be used. It is also possible to easily deal with the inspection of the inner coating of the can.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the present invention will be described below with reference to the drawings. The method for inspecting the inner surface coating of a metal can according to the present invention comprises an inspection device schematically shown in FIG. 1 and an inspection water circulating device schematically shown in FIG. First, the configuration of the inspection device will be described with reference to FIG. 1 is a schematic diagram mainly showing a can body 1 to be inspected and an inspection device 2 for inspecting the can body 1, and FIG. 2 is a schematic diagram mainly showing an inspection water circulating device. Note that FIG. 3 is a correlation diagram of detection characteristics for explaining the inspection principle of the inspection device of the present invention. Can body 1
A metal can body part 3 formed in a tubular shape with one end opening and a bottom part and a body part integrally formed, and an inner surface coating 4 applied to the entire inner peripheral surface of the metal can body part 3, It is held by a support device (not shown) that is interlocked with the inspection device 2 with the opening facing upward.

The metal can body 3 is made of a conductive material, for example,
Using aluminum plate, aluminum alloy plate, surface-treated steel plate such as tin-free steel, tin plate, chrome-plated steel plate, aluminum-plated steel plate, nickel-plated steel plate, and other various alloy-plated steel plates to perform redrawing or drawing and ironing It is formed by. The metal can body 3 is formed on a cylindrical body 6 having an opening 5 on one end side, and is formed such that the bottom of the body 6 on the side opposite to the opening 5 is reduced in diameter. In addition, a recessed portion 7 is formed on the bottom surface of the bottom side so as to be recessed inward of the can. In addition, the metal can body portion 3 is screwed on the metal can body portion 3 which is finally neck-in processed and flanged on the peripheral end portion of the opening 5 and the neck-in processed mouth / neck portion. -A curled can body with a screw may be used.

As a method of manufacturing the can body 1 as described above, there are the following first method and second method. The first method is to apply a paint such as an epoxy-phenol-based paint, an acrylic-modified epoxy-phenol-based paint, or an epoxy-urea-based paint in a liquid state on the inner peripheral surface of the metal can body portion 3 processed into a cylindrical shape. A can body 1 having an inner surface coating 4 by spraying with a paint and drying and baking the paint.
Is a method of manufacturing. In the second method, a thermoplastic resin film is attached or extruded on the surface of a metal plate to produce a resin-coated metal plate. As the thermoplastic resin film, a polyester-based film, a polypropylene-based film, a nylon-based film or the like is used, and there are a resin film having an oriented crystal structure and an amorphous structure. Below, a can body 1 provided with an amorphous resin film having a relatively low withstand voltage.
The application example of the inner surface coating will be described.

The resin-coated metal plate is formed into a cylindrical can body with a bottom by redrawing or drawing and ironing, and then drawn several times on the bottom side of the bottom can body. And the smoothing process are performed to form the small-diameter mouth-neck and shoulder, and the tip of the small-diameter mouth-neck is cut to open, and the tip of the small-diameter mouth-neck is externally wound to curl. A bottle-shaped can body having an inner surface coating produced by forming an annular protrusion for fixing a breaking band of a cap with a tamper evidence mechanism, or a screw part formed below the molded part, or The present invention can also be applied to a welded can body or a three-piece can in which a can lid is wound around one open end of the welded can body.

On the other hand, the inspection device 2 has an inspection head 9 which is inserted into the can body 1 through the opening 5. The inspection head 9 is configured such that at least most of the portion located inside the can body 1 at the time of performing the inspection is formed by using stainless steel which is a conductive material, and ensures rust resistance and low cost. The conductive portion 9 is electrically connected to the positive electrode of a DC power supply (hereinafter, simply referred to as a power supply) 22. As the power source 22, a power source in which alternating current is placed on direct current may be used. Further, although stainless steel is used for the conductive portion of the inspection head 9, platinum or carbon electrodes may be used instead. The outer surface shape of the inspection head 9 is formed to be slightly smaller than the inner surface shape of the can body 1, and the gap distance between the outer surface of the inspection head 9 and the inner surface of the can body 1 is defined by The distance is appropriately set to a constant distance according to the amount of the inspection water 17 to be filled. A drive device (not shown) for moving the inspection head 9 to an inspection position inside the can body 1 and a storage position outside the can body 1 is provided.

When the inspection head 9 is set at the inspection position, the inspection water inlet 15 which is one end of the inspection water supply pipe 14 facing the upper opening of the can body 1 is provided in the inspection head 9 and the inspection head 9 is inspected. The other end of the water supply pipe 14 is connected to the pressure regulating tank 19 via a constant flow valve (not shown). The constant flow valve is for adjusting the flow rate of the test water passing through the test water supply pipe to a constant value when the constant flow valve is opened. The pressure regulating tank 19 is connected to the test water circulating device 30 via a pipe, and the test water circulating device 30 stably supplies the test water 17 whose specific resistance value is adjusted as described later. In addition,
The test water 17 used for the test is collected in a recovery tank 26 via a water receiving / recovering section 25 provided directly below the can body 1 of the test apparatus 2, and the recovery tank 26 circulates the test water. It is connected to the device 30 via a pipe. That is, the pressure regulating tank 19 of the inspection device 2 is the inspection water circulation device 3
0 is supplied to the adjustment tank 31 of the inspection water circulating apparatus 30, and the inspection water 17 adjusted for inspection is supplied from the inspection water circulating apparatus 30, while the recovery tank 26 of the inspection apparatus 2 is supplied to the supply tank 3 of the inspection water circulating apparatus 30.
2, the test water used for the test is adjusted by the test water circulating device 30 so that the test water can be used again for the test.

Further, an edge electrode 20 is provided at a predetermined position of the inspection head 9 so as to come into contact with the metal base material at the opening end of the can body 1 at the time of inspection. The edge electrode 20 is made of a conductive material. There is. The edge electrode 20 may be formed in a ring shape having a wide width in the inner and outer diameter directions. In this case, the outer diameter of the edge electrode 20 is set larger than the outer diameter of the can body 1. The inner diameter is set to be slightly smaller than the outer diameter of the can body 1. Further, the edge electrode 20 is electrically connected to the negative electrode of the power source 22.

The voltage of the power supply 22, that is, the voltage applied to the inspection head 9 is the withstand voltage of the inner coating 4 (this withstand voltage varies depending on the type of the inner coating 4, the thickness of the inner coating 4, the degree of orientation, etc.). (It changes depending on the conditions). An ammeter 23 is provided between the negative electrode of the power source 22 and the edge electrode 20. Further, the inspection water supply pipe 14 is provided with a highly sensitive resistivity meter (not shown) for detecting the specific resistance value of the inspection water 17. further,
The ammeter 23 and the highly sensitive resistivity meter are electrically connected to an electronic control unit (not shown). Then, this electronic control unit determines from the current value detected by the ammeter 23 whether or not the inner coating film 4 has a defect. It should be noted that the electronic control unit has a calibration curve (this is a threshold value for comparison judgment and a judgment reference value) according to the specific resistance value detected for the inspection water 17 filled in the can. A correction circuit for correcting the above is provided.

Further, the operation of loading the can body 1 from the pre-process to the inspection station, the operation of transferring the can body 1 from the inspection station to the drying station, and the operation of discharging the can body 1 from the drying station to the subsequent process. A carrying device (not shown) for carrying out is provided. This carrier is an electric motor,
A known actuator such as a cylinder (not shown),
It is provided with a known mechanism such as a turntable, a belt conveyor, a chuck, etc. which is operated by these actuators. Further, various sensors (not shown) for photoelectrically or mechanically detecting the position, movement, stop, etc. of the can body 1 in each station or between each station are provided. Furthermore, a discharging device (not shown) for discharging the can body 1 which is determined to have a defect in the inner surface coating 4 to the outside of the line is provided.

The above-mentioned electronic control device for controlling the operation of the defect detection device and the operation of the transfer device in a coordinated manner includes the arithmetic processing unit (CPU or MPU) and the storage device (RA).
M and ROM) and an input / output interface as a main component, and controls the operation of each device in accordance with a program stored in a storage device and determines the presence or absence of a defect in the inner coating of the metal can body 3. ing. That is, the detection value signal of the ammeter 23, the signals of various sensors, and the like are input to the electronic control device. On the other hand, from the electronic control device, a signal for driving and controlling the holding means of the inspection device 2, a signal for driving and controlling the flow rate control valve, a signal for controlling the operation of the transport device and the discharge device, and a specific resistance value of the inspection water 17 are adjusted. Outputs command signals to control.

Next, the inspection principle and the inspection method of this embodiment will be described. First, a conductive material is used for the metal can of the present embodiment, and the inner surface coating is formed of a material exhibiting non-conductive properties. Therefore, since this inner surface coating exhibits electrical insulation, if the inner surface coating has no defects at all, even if the metal part of the metal can is basically energized, the inspection voltage, the specific resistance, etc. Depending on various conditions, a conduction phenomenon, a discharge phenomenon, etc. are observed, but no electrical conduction occurs through the inner coating. That is, even if a conductive test water is filled in a metal can and a voltage of one polarity is applied to the test water and a voltage of the other polarity is applied to the metal can, it is blocked by the non-conductive inner surface coating and becomes conductive. The current will not flow. On the other hand, if even small defects such as pinholes and cracks are generated in the inner coating, the metal base of the metal can and the inspection water come into direct contact with each other, and the conductive member and the metal base are electrically connected via the inspection water. As a result, a conducting current flows when a voltage is applied, and this conducting current can be detected. However, depending on the setting of the applied voltage and the specific resistance of the test water, in the case of a normal inner surface film with no defects,
Even if the conduction phenomenon as described above is not observed, a discharge current flows when the amount of charge stored in the inner coating layer, which is an insulating material, exceeds the maximum capacity that can be stored in the inner coating layer.

Here, the same inspection object (a metal can having an inner surface coating of an amorphous structure having a relatively low withstand voltage) was inspected, and a detection result (Q
TV value) and the detection result (FDD value) by the inspection method of the present invention
The relationship diagram with The former (enamellator method)
Uses an aqueous solution of sodium chloride (1% saline solution) as an electrolytic solution and sets the applied voltage to 6V. On the other hand, in the present invention, carbon dioxide gas is dissolved in pure water as the inspection water, and the specific resistance value of the inspection water is adjusted to 2.0 MΩ · cm or less, 1.0 MΩ · cm. The inspection voltage is set to 1000 V, which is lower than the withstand voltage of the inner coating. Then, the relationship between the two is compared with that in which the flaw defect characteristics are gradually changed from a defect-free property to a gradually increasing defect grade. That is, the current value (FDD value) is obtained by inspecting with the inner surface coating inspection device of this example for each metal can with a different defect state, and then with the conventional enamellator method for each metal can with the same defect state. Then, we got the leakage current value (QTV value) and plotted what happened. Then, since the correlation can be confirmed between the two, instead of the conventional enamellator method,
It has been found that it is possible to reliably detect inner surface defects by using test water in which carbon dioxide gas is dissolved in pure water obtained by the ion exchange method to adjust the specific resistance value. Incidentally, in the case of a normal inner surface coating having no defect, in the inspection method of the present invention, a minute current of 30 μA or less may be detected, but this is not the one in which the conduction current due to the defect is detected, It shows that the discharge current is detected when the amount of charge accumulated in the inner coating layer which is an insulating material exceeds a predetermined amount.

In the inspection method of the present invention, even when a voltage of 500 V, which is lower than the inspection voltage of 1000 V, is applied,
The specific resistance value of the test water is 1.0 MΩ · cm to 0.18 MΩ
-If it is lowered to the cm range, the defect detection sensitivity can be maintained at the detection sensitivity equivalent to that of the conventional enamellator method, that is, the detection sensitivity at the inspection voltage of 1000 V can be maintained.
It was solved from various experimental results. That is, it was found that the detection sensitivity can be maintained by reducing the specific resistance value of the test water by dissolving the carbon dioxide gas in proportion to the lowered test voltage.

Therefore, when detecting a flaw defect in an inner surface coating having a large withstand voltage, for example, an inner surface coating having a large film thickness and a large oriented crystallinity, an inspection voltage depending on the withstand voltage of the inner surface coating is used. It suffices to use test water having a specific resistance value increased corresponding to the test voltage. The withstand voltage varies depending on the composition, orientation degree, thickness, etc. of the inner coating. That is, specifically showing an example of the withstand voltage of the organic coating, when the thermosetting water-based paint is spray-coated and baked, the thickness of the inner coating is 5
When μm to 6 μm, the inner coating is 300V to 400V
Having a withstand voltage of 10 μm to 13
When the thickness is μm, the inner coating has a withstand voltage of 800V to 900V. Further, in the case of a can body which is obtained by thinning and deep-drawing a plate material obtained by coating a surface-treated steel sheet with an oriented crystalline polyester resin film, the thickness of the inner coating is 10 μm.
~ 13μm, the inner coating is 1500V ~ 2000
It has a withstand voltage of V and the thickness of its inner surface coating is 17 μm to 2
At 0 μm, the inner coating has a withstand voltage of 2500V to 3000V. Furthermore, in the case of a can body formed by thinning, drawing, and ironing a sheet material of an amorphous-structured polyester resin film coated on an aluminum alloy plate, when the thickness of the film which is the inner surface coating is 23 μm to 26 μm, the inner surface coating is used. Some films have a withstand voltage of 600V to 1100V. Therefore, an inspection voltage lower than the withstand voltage of the inner surface coating to be inspected is used, and in the case of this inspection voltage, the specific resistance value of the inspection water is set to 2.0 MΩ in order to make the detection sensitivity of the scratch defect of the inner surface coating as good as possible. -By properly adjusting in the range of cm or less, it becomes possible to detect defects while preventing dielectric breakdown of the inner coating.

The specific resistance value of the test water is 0.05 MΩ.
A value smaller than cm approaches the current detection method based on the dielectric breakdown method. If the voltage applied in this case is high, the inner surface coating may be dielectrically broken even with a normal product, and the inner surface coating may be damaged. , It is inappropriate to apply it to 100% inspection. Moreover, in order to reduce and maintain the specific resistance value of the test water to such an extent, it is necessary to use and consume a large amount of carbon dioxide gas, resulting in high running cost and uneconomical. Therefore, from the viewpoint of preventing the dielectric breakdown of the inner surface coating film due to the inspection voltage and the economical aspect, the specific resistance value of the inspection water is set to 0.05 MΩ · cm or more.

As a result, in order to keep the inner coating film of the metal can at an inspection voltage that does not cause dielectric breakdown and to maintain good detection sensitivity at the inspection voltage, the specific resistance value is 0.05 MΩ · c.
Test water with a specific resistance of 2.0 MΩ · cm or less was used, and the specific resistance was adjusted to 0.35 MΩ · cm or less, especially when the inner coating had a low withstand voltage. It is preferable to use test water. In this example, the specific resistance of the test water is set to 0.18 MΩ · cm, and the output voltage of the power source 22, that is, the test voltage is set to 50.
It is set to 0V.

The inspection device 2 having the above-mentioned configuration and the inspection method for detecting the presence or absence of a defect in the inner coating 4 of the can body 1 will be described based on the principle described above. First, the can body 1 provided with the inner coating 4 is processed from the previous step, for example, on a conveyor,
It is carried into the inspection process by a metal can supply device (not shown) including a chuck mechanism and the like. Then, as shown by the solid line in FIG. 1, the support means moves to the inspection position K1 of the inspection device 2 so that the axis of the can body 1 is oriented vertically and the small-diameter mouth / neck portion 8 is oriented downward. Is set.

When the setting of the can body 1 is completed, the inspection head 9 starts descending. Then, the inspection head 9 passes through the opening 5 and enters the inside of the can body 1, and the edge electrode 20 provided on the inspection head 9 is attached to the opening end of the metal can body portion 6 facing the large diameter opening 5. At the time of contact, the inspection head 9 stops. In this way, a space is formed between the outer surface of the inspection head 9 and the inner coating 4 when the inspection head 9 is inserted inside the bottle-type can body 1.

The distance between the outer surface of the inspection head 9 and the inner coating 4 is not particularly limited, but by reducing the amount of inspection water 17 supplied to the inside of the can body 1,
In order to increase the time required for filling and discharging the canister 1 with the inspection water 17, that is, the inspection speed corresponding thereto, the distance between the outer surface of the inspection head 9 and the inner coating 4 is set to about 1 to 4 mm. Preferably. Further, considering the insertability when the inspection head 9 is inserted into the can body 1 and the radial and axial positioning properties of the inspection head 9 and the can body 1, the outer surface and the inner surface of the inspection head 9 are considered. It is more preferable to set the distance from the coating 4 to about 2 to 3 mm.
The inspection water inlet 15, the electrode portion of the inspection head 9 for detecting the current, and the inner coating 4 face the space.

Then, when the body part 3 of the metal can passes through the predetermined inspection water supply position, the inspection water 17 is transferred from the pressure regulating tank to the inspection water supply pipe 14 and the inspection water injection by the opening operation of the flow rate control valve 18. It is supplied to the space via the inlet 15. The specific resistance value of the test water 17 is set to 0.18 MΩ · cm. Here, the fact that the prescribed amount of the inspection water 17 has been injected into the space is determined by a known detection means, and the supply of the inspection water 17 is stopped by the closing operation of the flow rate control valve 18 based on this determination. .

Then, when the metal can body portion 3 reaches a predetermined inspection position, an inspection voltage is applied from the power source to the inspection head. This voltage is set to 500 V, which is lower than the withstand voltage of the inner coating 4, because the inner coating 4 made of a polyester resin film having an amorphous structure is used as an embodiment in the present invention. It should be noted that the defects that occur in the inner surface coating 4 include cracks, scratches, pinholes, mesh defects such as surface mesh-like cracks (macro cracks), and minute metal pieces generated when the can body 1 is molded.
There is a metal piece sticking defect etc. That is, when defects such as cracks, scratches, and pinholes occur, the inspection water 17 enters the cracks, scratches, and pinholes, and the can body 1
Directly contact with the metal base of, and current flows by energization. In addition, in the case of the network defect, when the crack does not reach the metal substrate, or in the case of the metal piece adhesion defect, the inner surface coating 4
In the case of a partial defect in which the inner surface coating 4 is damaged even if the metal base and the inspection water 17 are not electrically connected, as in the case where the metal piece stuck in the bottom does not reach the metal base, A current flows due to discharge. Even in the defect-free inner surface coating 4, a current due to the discharge may flow (although it does not normally flow), though it is smaller than the defect. Therefore, by applying the voltage, the inspection head 9,
An electric circuit closed by the inspection water 17 and the edge electrode 20 is formed, and an electric current passing through a defect in the electric circuit,
Discharge current through partial defects, defect-free inner surface coating 4
An overlapping current flows through the discharge current through. on the other hand,
The specific resistance value of the supplied test water 17 is detected by the highly sensitive resistivity meter, the measurement signal is output to the electronic control unit, and the detected current is measured by the ammeter 23. It is output to the electronic control unit. Then, in the electronic control unit, the noise component of the measurement signal is removed, and the determination reference value of the detection current determined by an experiment in advance is corrected according to the specific resistance value of the supplied test water,
Based on the corrected determination reference value, if the measured detected current value is less than this determination reference value, it is a non-defective product with no defects, and if it is greater than the determination reference value, it is a defective product with defects, and it occurs in the inner coating 4. The presence or absence of a defect is determined to determine whether the can body 1 is good or bad, and subsequent processing is determined. Therefore,
Even if the resistivity value of the test water fluctuates due to the test water supply process, the change in the resistivity value is detected and the judgment reference value is corrected, so defects in the inner coating of the metal can are detected. The accuracy and certainty of the inspection can be maintained, and the accuracy and certainty of the inspection can be improved.

When the determination of the presence or absence of a defect in the inner surface coating 4 is completed as described above, the inspection head 9 is retracted to the outside of the can body 1, and then the can body 1 is vertically reversed by the supporting means. The test water 17 is reversed and the test water 17 is discharged from the inside of the can body 1, and the test water 17 is sucked into the water receiving and collecting section 25 below and collected in the collecting tank 26 through the pipe. Then, the non-defective can body 1 which is judged to have no defect or is within the allowable range is delivered from the supporting means to the conveying device and transferred to the drying station K2 by the conveying device for drying treatment, while having a defect or exceeding the allowable range. The judged defective can body 1 is discharged out of the line from the supporting means.

The inspection water 17 used for the inspection and recovered from the inspection device 2 is unsuitable for reuse as it is as the inspection water 17. That is, the collected test water 17 has its water quality changed, and the specific resistance value of the test water itself becomes higher than the set value due to the release of carbon dioxide gas as described later, and the specific resistance value is 0.8. ~ 1.2 MΩ · cm
Grows to a degree.

Therefore, it is necessary to adjust the test water thus collected and used so as to have a predetermined specific resistance value. Below, such test water is supplied to the test device 2 again. The circulating device 30 incorporating the adjusting device for the test water for adjusting the specific resistance value will be described. That is,
The supply tank 32 of the inspection water circulation device 30 has a larger capacity than the recovery tank 26, and the supply tank 32 is stable even if the amount of the inspection water 17 to be recovered changes due to a change in the operating state of the inspection device 2. The water is received inside and stable water can be sent downstream. Also, the supply tank 3
2 is connected to a pure water supply tank (not shown) through a supply valve (not shown) by piping to supply an arbitrary amount of pure water or tap water into the supply tank 32 to supply the supply tank. The rise of the water temperature in 32 is prevented, and the water temperature of the inspection water 17 is maintained at an appropriate room temperature. A cooling mechanism may be additionally provided in the supply tank 32 to prevent the temperature of the water in the supply tank 32 from rising, and the test water 17 may be maintained at an appropriate room temperature. Therefore, it is possible to prevent the carbon dioxide gas from becoming difficult to dissolve due to the rise in the water temperature, and to appropriately adjust the specific resistance value of the test water 17 using the carbon dioxide gas described later. Further, the supply tank 32 is provided with a drain valve (not shown) so that an organic substance or an inorganic substance having a certain size or more is discharged to the outside of the supply tank 32. Furthermore, the supply tank 32 is provided with a pump 33 having a predetermined capacity, and the test water in the supply tank 32 is supplied to the activated carbon adsorption tower 35 through a filter 34 that removes dust and particulate solid impurities. It is pumped.

In the activated carbon adsorption tower 35, activated carbon is housed in a fixed layer, and the activated carbon adsorbs and removes organic components (color, odor, taste, etc.) and free chlorine (Cl ₂ ) in the test water 17. In addition, the activated carbon adsorption tower 35 is connected to the ion exchange section 37 through a safety filter 36 that removes fine particles of impurities, and is connected to the ion exchange section 37 by piping to remove impurities.
7 is being sent to the ion exchange section 37. A bypass line 50 is connected between the safety filter 36 and the ion exchange unit 37, and between the ion exchange unit 37 and the adjustment tank 31, and a flow rate control valve (Fig. Therefore, the ion exchange unit 37 is bypassed so that an arbitrary amount of the test water 17 can be supplied to the downstream side, and the amount of water passing through the ion exchange unit 37 is adjusted.

The ion exchange section 37 uses a cation exchange resin and an anion exchange resin in combination to remove a predetermined amount of ionic components in the test water. Further, the ion exchange unit 37 is composed of a plurality of ion exchange units (not shown) in which a predetermined ion exchange resin is housed and arranged. These ion exchange units are connected in series in multiple stages to connect the final stage of the ion exchange units. The unit is pipe-connected to the adjustment tank 31 via a sterilizer (not shown) and an ozone sterilizer (not shown) using ultraviolet rays, and water is supplied from the ion exchange section 37 to the adjustment tank 31. The treated test water 17 sent from the ion exchange unit 37 is referred to as pure water at this stage, and its specific resistance value is significantly different from that before the treatment because impurities are removed. Becomes higher, for example, 15 to 20 MΩ · c
It has become m.

A delivery pipe for carbonated water and a delivery pipe for carbon dioxide gas produced by the mixing and adjusting device 41 are connected in parallel to each other at a predetermined position on the way between the ion exchange section 37 and the adjusting tank 31. Then, the carbonated water or carbon dioxide gas is added to the test water 17 in an arbitrary amount to add the test water 1
By dissolving the test water 17 as described above, the specific resistance value of the test water 17 treated as described above is reduced to a predetermined value. That is, the mixing adjusting device 41 includes a carbon dioxide gas cylinder 42 filled with carbon dioxide gas, a mixing tank 43 pipe-connected to the carbon dioxide gas cylinder 42 via an output valve (not shown),
It is composed of an injection pump 44 which is connected to the mixing tank 43 and has a pumping ability for sending the mixed water in the mixing tank 43 to the middle of the piping path. The mixing tank 43 contains mixed water in which carbon dioxide gas is dissolved in a predetermined manner. It is housed. Therefore, in order to maintain the specific resistance value of the test water 17 at a predetermined value, it is possible to inject an arbitrary amount of mixed water of adjusted carbon dioxide gas solubility into the circulation path from the mixing adjusting device 41. Further, the carbon dioxide gas cylinder 42 is connected to a pipe path between the ion exchange section 37 and the adjusting tank 31 via a solenoid valve (not shown). Therefore, due to the gas pressure of the carbon dioxide gas cylinder 42, carbon dioxide gas is diffused and released into the piping path to cause bubbling, and the carbon dioxide gas is directly supplied from the mixing and adjusting device 41 to the inspection water 1
It can be dissolved in 7. The ion exchange unit 3
A water quality meter (not shown) for measuring the specific resistance value of the test water 17 at a position upstream of the ion exchange part 37 side from the connection position of the mixing and adjusting device 41 in the middle of the piping path between the 7 and the adjusting tank 31. Is installed and the water quality meter is electrically connected to the electronic control unit described above. A method of adjusting the test water executed based on the instruction of the electronic control unit will be described later.

On the other hand, the mixing tank 43 is composed of a carbon dioxide gas cylinder 42.
It is a closed container corresponding to the gas pressure of, and the mixed water is sent from the mixing tank 43 to the circulation path through the injection pump 44 in accordance with the circulation operation of the inspection water, and the mixed water in the mixing tank 43 has a predetermined amount. When the amount decreases below, the test water is replenished from the circulation path into the mixing tank 43 through a water collecting channel (not shown), and carbon dioxide gas is introduced from the cylinder 42 into the mixing tank 43 to mix them. Stirring is carried out by the stirrer in the tank 43 to promote the dissolution of carbon dioxide gas, and new mixed water adjusted to have a predetermined solubility of carbon dioxide gas is produced.

The adjusting tank 31 is connected to a pipe for supplying water from the ion exchange section 37, and a pipe for supplying water from the adjusting tank 31 is connected to the pressure adjusting tank 19 of the inspection device 2, and the adjusting tank 31 has a pressure adjusting device. A capacity larger than that of the tank 19 is secured. Therefore, the adjusting tank 31 is the mixing adjusting device 4
Even if the amount of the inspection water 17 in which the mixed water is injected by 1 and the mixture water and the inspection water 17 is increased, the adjustment tank 31 is stably provided.
Even if the amount of the test water 17 to be supplied fluctuates due to the fluctuation of the operating condition of the test device 2
The inspection water can be constantly and stably supplied to the inspection device. Further, the adjusting tank 31 and the supply tank 32 are connected by a pipe by a return path 51 whose path can be arbitrarily opened and closed. Therefore, when the amount of the inspection water 17 in the adjusting tank 31 exceeds a predetermined amount, the inspection water 17 is directly returned from the adjusting tank 31 to the supply tank 32 through the return path without passing through the inspection device 2. The inspection water 17 can be prevented from overflowing from 31.

As described above, a flow meter for the test water, a pressure gauge, and a resistivity meter (not shown) are appropriately provided at predetermined locations of the pipe which is the circulation path for the test water. The electronic control device is electrically connected to the control device,
Based on these detected values, the opening degree of the bypass path 50 is controlled, the operation of the mixing adjusting device 41 is controlled,
In order that the inspection device 2 can perform an appropriate inspection, the amount and quality of the inspection water 17 are adjusted and supplied while being stably maintained. That is, when the specific resistance value of the inspection water 17 detected by the resistivity meter of the inspection device 2 is out of the allowable range of the predetermined specific resistance value, carbon dioxide mixed water of a constant concentration is injected into the circulation path. , Bubbling carbon dioxide gas into the test water to adjust and maintain the specific resistance value of the test water 17 within a predetermined allowable range, and based on a signal from the test device 2, the test water 17
The water is controlled to be supplied to the pressure regulating tank of the inspection device 2 by 19 and the return circulation is performed.

In the test water circulating device 30, the returned test water is stored in the supply tank 32, the temperature of the water is maintained at room temperature, and then passes through the filter 34 to remove dust and particulate solid impurities. Meanwhile, water is sent to the activated carbon adsorption tower 35. In the test water stored in the activated carbon adsorption tower 35, mainly organic substances in the test water are removed, fine particles are removed by the next filter 36, and the test water is sent to the ion exchange section 37. The test water sent to the ion exchange unit 37 sequentially passes through a plurality of ion exchange units (not shown) to be subjected to ion exchange treatment, and the ion component of the test water returned or supplemented is removed. Along with that, the specific resistance value becomes higher,
For example, it becomes 15 to 20 MΩ · cm and is sent to the adjusting tank 31. The specific resistance value of the test water passing through this route is measured by a water quality meter (not shown) installed at a predetermined location on the way of this water supply route, and the electronic control unit determines the specific resistance value according to the measurement result. The operation of the mixing and adjusting device 41 is controlled so that the value becomes, for example, 0.18 MΩ · cm. That is, the injection operation of the injection pump of the mixing adjusting device 41, or
By the opening operation of the valve, an arbitrary amount of carbonated water or carbon dioxide gas is injected into the water supply path from the mixing and adjusting device 41. As a result of these, the adjusting tank 31 is optimal for inspection, for example, 2 MΩ
The test water adjusted to a specific resistance value of 0.18 Ω · cm, which is a value of cm or less, is stored, and the test device 2 is stored in the adjusting tank 31
Is supplied to the pressure adjusting tank 19. The collected inspection water 17 is also treated in the same manner.

As described above, according to the inner surface coating inspection method and the inspection apparatus of this embodiment, the presence or absence of defects in the inner surface coating 4 of the can body 1, that is, when inspecting the inner surface coating, carbon dioxide is added to pure water. Since only the inspection water 17 that has been mixed and dissolved contacts the inner surface coating 4, it is not necessary to provide a dedicated cleaning step after the inspection, and this man-hour is reduced, and the time required for all the steps is shortened. be able to. In other words, in the enamellator method that uses an electrolytic solution to inspect for defects in the inner coating of a metal can, the residue such as the electrolytic solution adhered to the body of the metal can. There was a possibility that traces of adhesion would remain on the surface and that the filling filled with the residue would be contaminated. But,
According to the inner surface coating inspection method and the inspection device of the embodiment of the present invention, by using the inspection water 17, there is no possibility that a residue is generated on the can body 1, and a sticking mark due to the residue may remain, and The possibility that the packing in 1 is contaminated with residue can be completely eliminated. This is effective in the case of 100% inspection, in the case where the filling of the can body 1 is food or medicine such as food and drink, and particularly in the case where the conditions of both of them overlap.

Further, the inspection water 17 is filled in the space formed between the inner surface coating 4 of the metal body 3 and the outer surface of the inspection head 9. Specifically, the inspection water 17 is filled in the entire area facing the inner coating 4 and the area facing the detection head 9. Therefore, not only when the inner surface shape of the metal can is simple, but when the inner surface shape is complicated, for example, when the neck portion is formed in a stepped shape, a narrow rib portion is formed in the bottom portion, or a spiral Even if there are irregularities in the shape,
The inspection water 1 is evenly distributed over the entire surface of the inner coating 4.
The inner surface coating 4 and the test water 17 can be brought into contact with each other by making them spread over 7. That is, instead of directly contacting the conductive member, which is one of the electrodes, with the inner surface coating, the contact is made via the inspection water 17, that is, the inner surface coating 4 is contacted with the inspection water 1
Since 7 is in intimate contact, the quality inspection of inner surface coating 4 can be performed satisfactorily and sufficiently. Therefore, not only the inner coating film 4 of a metal can having a simple inner surface shape but also the inner coating film 4 of a metal can having a complicated inner surface shape can be easily judged for defects and even minute defects can be judged. Can be improved.

Further, since the inspection head 9 which is one of the electrodes is contacted through the inspection water without directly contacting the inner surface film, the spark contact at the time of applying the inspection voltage is avoided and the inner surface is prevented. The dielectric breakdown of the coating film 4 can be prevented, and the durability of the electrode can be improved without damaging the electrode. In particular, in the conventional inspection method, since the conductive brush, which is one of the electrodes, is brought into direct contact with the inner surface coating, the inner surface coating is damaged by the brush, the tip of the brush is broken, and the broken portion becomes the inner surface coating. There is a risk of adhesion, and a dedicated cleaning / removing step to deal with this is required, and the inspection step is complicated. However, according to the present embodiment,
Such a situation can be avoided in advance.

Furthermore, it is possible to set the specific resistance value of the inspection water to a value substantially proportional to the inspection voltage according to the withstand voltage of the inner surface coating 4, and in the case of the inner surface coating 4 having a low withstand voltage. Even while maintaining the defect detection sensitivity of the inner coating 4 without causing dielectric breakdown of the inner coating due to the inspection voltage,
It is possible to detect defects in the inner coating 4 while preventing damage to the inner coating 4 due to the inspection voltage.

Particularly, the specific resistance value of the test water 17 is 2.0 MΩ.
-If it is adjusted to be not more than cm, it is possible to prevent dielectric breakdown due to discharge even if the inner surface coating of the metal can to be inspected has an amorphous structure and the withstand voltage is low.

In addition to this, by setting the lower limit of the specific resistance value of the test water 17 to 0.05 MΩ · cm,
In addition to preventing damage to the inner coating due to dielectric breakdown,
The large consumption of carbon dioxide gas is suppressed, the operating cost for adjusting the specific resistance value can be reduced, and the economical efficiency can be improved.

Further, the inspection water circulating device 30 for collecting and inspecting the inspection water 17 used in the inspection device 2 and adjusting the specific resistance of the inspection water 17 to a predetermined value and then circulating the inspection water supplied to the inspection device 2 is constructed. By adding, it is possible to prevent unnecessary waste of water resources that are raw materials for the inspection water. Furthermore, since the test water 17 that is constantly and stably adjusted to a constant specific resistance value can be used for the test, it is possible to improve the test reliability of the inner surface coating. Furthermore, even when the specific resistance value needs to be reset due to the change of the inspection target when the inspection device 2 is in operation, the adjustment function of the inspection water circulation device 30 can promptly respond.

Further, the inspection water circulating device 30 always removes impurities and supplies the inspection device 2 with clean inspection water 17 whose specific resistance value is adjusted to a predetermined range. Therefore, this inspection water 17 flows. The path and the contacting portion of the inspection device 2 are washed with the inspection water 17, and these paths and portions including the inspection head 9 can be kept in a clean state, and the inspection accuracy can be improved while preventing erroneous detection. It is possible to improve.

Here, the correspondence between the structure of the embodiment and the structure of the present invention will be described. The inspection device 2 corresponds to the inspection device of the present invention, and the can body 3 corresponds to the metal can of the present invention. The inner surface coating 4 corresponds to the inner surface coating of the present invention, the inspection head 9 corresponds to the conductive member of the present invention, the inspection water 17 corresponds to the inspection water of the present invention, and the carbon dioxide gas corresponds to the gas of the present invention. However, the flow rate control valve, the test water inlet 15, the test water supply pipe 14, and the pressure adjusting tank 19 correspond to the test water supply device of the present invention, and the test head 9, the power supply 22, and the edge electrode 20.
The electric circuit formed by the above, the ammeter 23, and the electronic control device correspond to the determination device of the present invention, and the inspection water circulation device 30
Corresponds to the inspection water circulating device of the present invention, and the ion exchange section 3
7 corresponds to the ion exchange device of the present invention, and the mixing adjustment device 41 corresponds to the adjustment device of the present invention.

The metal can which is the object of the present invention is not limited by the inner and outer shapes as long as it is a metal can having at least one end open. For example, it can be applied to a bottle type can body having both ends open. You can Further, in this embodiment,
As a method of adjusting the specific resistance value of the test water, a method of dissolving carbon dioxide gas in the test water is adopted, but the method is not limited to this. That is, the specific resistance value can be adjusted arbitrarily, only removing water does not impair the flavor of the filling material that is subsequently filled in the metal can, and there are no residual substances or traces of adhesion that may cause food hygiene problems. An adjusting substance that does not leave the substance may be used as the dissolving substance, and for example, alcohol may be used.

[0069]

As described above, according to the first aspect of the present invention, the metal member of the metal can having the non-conductive inner surface coating has one polarity, and the conductive member is disposed in the metal can. After filling the inside of the metal can with inspection water adjusted to the opposite polarity and dissolving the gas in pure water and adjusting the specific resistance value, an arbitrary voltage is applied between both electrodes and the current generated at the time of application is detected. However, since the inner surface coating is inspected based on the detected current value, it is possible to perform these tests not only when the inner surface of the metal can has a simple shape but also when the inner surface of the metal can has a complicated shape. Since the inspection water can be evenly contacted with the entire area of the inner coating along the inner surface shape of the, the voltage can be applied from the inside of the metal can to the entire inner coating, and the accuracy and reliability of detecting the inner coating defects can be improved. It is possible to improve the quality of internal coatings It can be carried out.

According to the invention of claim 2, in addition to the same effect as that of the invention of claim 1, after the test water is used for the test and collected, the ionic components are removed and the gas is dissolved. Since the specific resistance value is adjusted to a predetermined value and reused for inspection, it is possible to prevent unnecessary waste of water resources that are raw materials for inspection water, improve economic efficiency, and improve the inspection environment during operation. Even if the resistivity of the test water changes due to fluctuations,
The adjustment process can be performed quickly, and the reliability of the inspection can be improved.

According to the invention of claim 3, the same effect as that of the invention of claim 1 or 2 can be obtained, and the specific resistance value of the test water is in the range of 0.05 MΩ · cm to 2.0 MΩ · cm. Since it has been set, by adjusting the specific resistance value of the test water to 2.0 MΩ · cm or less, even in the case of the inner surface coating with a low withstand voltage that had to be inspected by the conventional dielectric breakdown method,
Since the inspection can be performed by applying a low inspection voltage corresponding to this while sufficiently maintaining the defect detection sensitivity of the inner surface coating, dielectric breakdown due to discharge of the inner surface coating is prevented, and the inner surface coating is damaged by the voltage application inspection. It is possible to prevent the metal can from becoming a defective product in advance, and the lower limit of the specific resistance value of the test water is set to 0.05 MΩ · cm, so that a large amount of gas for adjusting the specific resistance value is not used. The operating cost for adjusting the specific resistance value of the test water can be reduced, and the economical efficiency can be improved.

According to the invention of claim 4, the same effect as that of the invention of claim 1 can be obtained, and even if the specific resistance value of the test water changes due to the supply process of the test water, the changed specific resistance Since the judgment reference value is set according to the value, it is possible to determine the defects of the inner surface coating based on this judgment reference value and the detected current value, and maintain the accuracy and certainty of detecting the defects of the inner surface coating. Therefore, the accuracy and certainty of the inner surface coating inspection of the metal can can be improved.

According to the invention of claim 5, in addition to the same effect as that of the invention of claim 4, used test water is recovered and subjected to a predetermined treatment to bring the specific resistance value of the test water to a predetermined value. Since it is adjusted and recycled for inspection, it is possible to prevent unnecessary waste of water resources that are raw materials for inspection water.
Since it is possible to use the test water that is always stably adjusted to a constant specific resistance value for the test, it is possible to improve the test reliability of the inner surface coating. Even if it is necessary to reset the specific resistance value, the adjustment function of the inspection water circulation device enables quick response, and it is possible to easily inspect the inner coating of various metal cans. Become.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention, and is a schematic view showing an inspection device mainly used in an inspection station and a metal can body of a metal can to be inspected.

FIG. 2 is a block diagram showing an embodiment of the present invention and mainly showing an inspection water circulating device.

FIG. 3 shows a detection current value (F
DD value) and leakage current value (QTV value) by the enamellator method
It is a relationship diagram which shows mutual relevance with.

[Explanation of symbols]

2 ... Inspection device, 3 ... Metal can body, 5 ... Opening, 4
… Inner coating, 9… Inspection head, 14… Inspection water supply pipe, 15… Inspection water inlet, 19… Pressure control tank, 1
7 ... Inspection water, 20 ... Edge electrode, 22 ... Power supply, 2
3 ... Ammeter, 30 ... Examination water circulation device, 32 ... Supply tank, 37 ... Ion exchange part, 41 ... Mixing adjustment device.

Continued front page    F-term (reference) 2G060 AA06 AA10 AA20 AE03 AF02                       AG11 EA04 EA07 EB05 HC13                       KA12 KA14

Claims (5)

[Claims] 1. A metal can of a metal can coated with a non-conductive inner surface has one polarity, and a conductive member disposed in the metal can has the opposite polarity, and a gas is dissolved in pure water to obtain a predetermined polarity. After filling the metal can with the inspection water adjusted to the specific resistance value, apply an arbitrary voltage between both electrodes, detect the current generated at the time of application, and inspect the inner coating based on the detected current value. A method for inspecting an inner surface coating of a metal can. 2. The test water is used for the test and recovered, and thereafter, the ionic components are removed, the gas is dissolved, the specific resistance value is adjusted, and the test water is reused for the test. A method for inspecting the inner surface coating of a metal can. 3. The specific resistance value of the test water is 0.05 MΩ.
The method for inspecting the inner surface coating of a metal can according to claim 1 or 2, wherein the setting is in the range of cm to 2.0 MΩ · cm. 4. An inner surface coating inspection device for inspecting a defect of an inner surface coating of a metal can having a non-conductive inner surface coating, wherein the metal part of the metal can has one polarity and is arranged in the metal can. An application device for applying an arbitrary voltage with the conductive member having the opposite polarity, an adjusting device for setting the specific resistance value of pure water to a value according to the inner coating, and pure water adjusted to a predetermined specific resistance value. A filling device for filling the inside of the metal can as inspection water, and after filling, an arbitrary voltage is applied between both electrodes by the applying device, and the ratio of the current value detected when the voltage is applied to the inspection water. An inner surface coating inspection device for a metal can, comprising: a determination device that detects a defect in the inner surface coating based on a determination reference value according to a resistance value. 5. The test water used for the test is collected, the ion component of the collected test water is removed, the gas is dissolved to adjust the specific resistance value of the test water to a predetermined value, and the test is performed. An inner surface coating inspection device for a metal can, which is provided with an inspection water circulation device that circulates water.