JP2743532B2 - Defect inspection method for organic coating layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a coating metal plate having an organic coating layer such as a coating film or a plastic film layer on at least one side, such as a metal can lid, and the like. The present invention relates to a method for inspecting defects such as sticking.

(Prior Art) An organic coating layer such as a coating film or a plastic film layer is formed on the inner surface of cans such as food cans, beer cans and coffee beverage cans in order to prevent metal corrosion due to contents. The inner organic coating layer may have a reduced or lost anticorrosive action due to scratches or the like in the can making process.

As a method for evaluating defects such as scratching of the inner organic coating layer,
Conventionally, the enamel rater method has been mainly used (for example, "Handbook of Packaging Technology", p. 1845, July 20, 1983, published by Nikkan Kogyo Shimbun; JP-A-61-1354).
No. 86). This is performed by applying a constant voltage (usually 6 volts) between an electrode (negative electrode) immersed in an electrolytic solution (for example, a 1% Nacl aqueous solution) so that the metal plate side having the organic coating layer serves as a positive electrode, This is a method of measuring a flowing electrolytic current, and this electrolytic current is said to be substantially proportional to the exposed metal area.

In the enamelizer method, since the test object is contaminated with the electrolyte, it is difficult to flow the test value to a subsequent production process even if the test value is normal, and the test object is not easily transferred to a test device. Also, there is a problem that the installation requires time and effort for preventing leakage of the electrolytic solution and the like. For this reason, the enamellator method has heretofore been employed only for sampling inspection.

(Problems to be Solved by the Invention) The present invention provides a coated metal plate that can be inspected in the atmosphere, can be easily attached to an inspection device of an object to be inspected, and can be applied to 100% inspection. It is an object of the present invention to provide a method for inspecting a defect of an organic film layer.

(Means for Solving the Problems) The defect inspection method for an organic coating layer of a metal plate according to the present invention is a method for inspecting a defect of an organic coating layer of a coated metal plate having an organic coating layer on at least one side, and comprises the steps of: A high voltage is applied between the electrode and the metal plate in a state in which a conductive elastomer having an electrode surface capable of contacting the entirety of the electrode is pressed against a portion of the organic coating layer to be contacted with a predetermined force so as to be in close contact with the metal plate. Apply
When a current slightly higher than the peak value of the charging current flowing between the electrode and the metal plate having the defect-free organic coating layer is detected, it is determined that the organic coating layer is defective.

In the present specification, the term “covered metal plate” includes a molded product of the coated metal plate.

(Operation) The inspection is performed in a state where the conductive elastomer having an electrode surface capable of contacting the whole of the swelling of the electrode is pressed against the portion of the organic coating layer to be inspected and brought into close contact therewith. There is no need to stroke and move the electrodes along the entire surface of the portion of the organic coating layer to be formed. In addition, since a voltage is applied between the electrode and the metal plate and the inspection is performed based on the magnitude of the current flowing between the electrode and the metal plate, the inspection can be performed in the atmosphere, and the metal to be inspected is Attachment of the plate to the inspection apparatus is performed by, for example, clipping or pressing a roll electrode against an edge portion, which is extremely simple. Therefore, the labor and time required for the inspection are small.

In the case of a metal plate having no defect in the organic coating layer, no current flows except for the charging current when a direct current is applied, so that the metal plate and the organic coating layer are not damaged by the inspection. Therefore, 100% inspection is possible.

When a current slightly higher than the peak value of the charging current is detected, it is determined that there is a defect in the organic coating layer. The above-mentioned "when a slightly higher current is detected" is the same as the discharge start time ( 4 (b) and 4 (c)), even if the application of the high voltage is stopped immediately after the detection, that is, immediately after the start of the discharge, the inspection is not hindered. Therefore, the inspection can be performed such that the discharge time is extremely short. Therefore, there is almost no damage to the electrodes due to discharge at the time of inspection.

Since the elastic conductive elastomer body of the electrode is pressed against the part of the organic coating layer to be inspected, the electrode is in close contact with the whole part even if there is some unevenness over the whole part. Therefore, the inspection is reliably performed.

Since the conductive elastomer body of the electrode is pressed with a predetermined force, the amount of deformation of the conductive elastomer body at the time of inspection, that is, the degree of close contact between the conductive elastomer body and the organic coating layer, is determined between each coated metal plate. Becomes constant. Therefore, there is substantially no variation in the inspection between the coated metal plates as the inspection objects.

Since a high voltage is applied between the electrode and the metal plate and the current between the electrode and the metal plate is detected, void-like coating defects that do not penetrate the organic coating (that is, are not pinholes) can also be detected. (See FIG. 4 (c)).

(Embodiment) In FIG. 1, reference numeral 1 denotes a metal cover as an object to be inspected, and reference numeral 2 denotes an electrode. The metal cover 1 is formed by coating a coating 1b (for example, a baking coating of an epoxy-amino-based coating; A polyethylene terephthalate layer 1c (thickness: about 30 μm;
This is formed by a conventional method from a blank of an organic-coated steel sheet having an inner layer (see FIG. 3; hereinafter referred to as an inner layer) bonded through an adhesive layer (not shown). That is, in the metal lid 1 of FIG. 1, although not shown, a coating film 1b is formed on the lower surface side, and an inner surface layer 1c is formed on the upper surface side.

As shown in FIG. 2, on the outer surface side (the lower surface in FIG. 1) of the peripheral annular portion 3 between the outer peripheral reinforcing ring 3c and the inner peripheral reinforcing ring 3b of the metal lid 1, a V-shaped main score is provided. Department
4a and sub score section 4b (shallower than main score section 4a)
Are formed in a circumferential shape. The score portions 4a and 4b are formed by an anvil (not shown) with the metal lid 1 facing the inner layer 1c.
In the state of being placed on the top, it is formed at the same time by pressing the portion with a score blade type die (not shown). During the formation of the score portion, the metal near the main score portion 4a undergoes a large plastic flow.
1c 'becomes thin as shown in FIG.
Or, cracks occur, and the metal is exposed.

The lower end of the electrode 2 is made of a ring-shaped conductive elastomer body 5 fixed to a metal support 6, and its inner and outer diameters are set to be substantially equal to the width between the inner and outer reinforcing rings 3a and 3b. (See FIG. 2). As the conductive elastomer, conductive elastic rubber, conductive elastic plastic,
Alternatively, an elastic rubber or a plastic having an evaporated metal film or a metal foil adhered to the outer periphery, an elastic metal composite, or the like is exemplified.

The left part of FIG. 1 shows an example of an electric circuit for inspection, in which 7 is a DC high-voltage power supply, 8 is a resistor for overcurrent prevention connected to the negative electrode side of the DC power supply 7 (for example, 10 MΩ).
), 9 is an ON / OFF circuit of the power supply 7, and 10 is an ammeter. 11
Is the end face 1 of the peripheral curl portion 1x of the metal cover 1 where the metal is exposed.
It is a clip that comes in contact with x '. That is, the metal plate of the metal cover 1 (the tin-free steel 1
a), the DC power supply 7, the resistor 8, and the electrode 2 are connected in series. The resistor 8 suppresses discharge currents 17 and 18 to be described later, thereby preventing the conductive elastomer body 5 from being damaged.

Inspection of a defect which may occur in the inner surface layer 1c when the score portion of the metal cover 1 is formed by the above-described apparatus is performed as follows.

After placing the metal lid 1 on a mounting table (not shown) with its outer surface facing downward, the electrode 2 is lowered and the inner surface (upper surface) of the peripheral annular portion 3 is pressed with a predetermined force. At this time, the conductive elastomer body 5 is elastically deformed, and comes into close contact with the inner surface thereof along the entire periphery of the peripheral annular portion 3 including the portions facing the score portions 4a and 4b (FIG. 3). It is desirable that the hardness (Shore A) of the conductive elastomer body 5 be 40 to 80 in order to freely elastically deform as described above.

In this state, the DC power supply 7 is turned on, and a predetermined voltage (for example, 1 kV) predetermined by an experiment is applied between the electrode 2 and the metal lid 1.

A metal lid with no defects, for example, 100 enamellator removal tests were performed, but the enamellator value of all lids was 0 mA
In the case of the lid of the lot, as shown in FIG. 4 (a), the charging current 15 (on the order of several μA) flows for the first about 30 msec, but no current flows thereafter. 4 (a), 4 (b) and 4 (c), the horizontal axis represents time, and the vertical axis represents current.

When a metal lid with a defect, for example, 100 enamel rate extraction tests were performed, the enamellator value of all the pieces was 0.01 to 0.
In the case of a lid of a lot of 1 mA, as shown in FIG. 4 (b), the charging flow 16 flows for the first approximately 20 msec for all the lids (the conductive elastomer 5 and the tine-free steel 1a are in direct contact with each other). Thereafter, a discharge occurred through a defective portion of the metal lid (for example, the small hole 13 in FIG. 3), and a discharge current 17 flowed. In FIG. 4B, the difference between the charging current value 16 and the discharging current value 17 is relatively small for the sake of illustration, but the discharging current value 17 is actually much larger than the charging current value 16.

For comparison, the same inspection was performed on the lid of the defective lot using the same all-metal electrode except that the portion of the conductive elastomer body 5 was made of a rigid metal (copper). Discharge current 17 did not flow in 12 sheets out of 100 sheets. This is because even if the surface of the peripheral annular portion 3 to be inspected appears to be flat at first glance, there may actually be fine irregularities along the entire circumference. In this case (that is, 12 sheets), there is no elasticity. This is probably because the all-metal electrode did not completely contact the part to be inspected.

In the case of a metal cover in which the coating defect is void and does not penetrate the coating, as shown in FIG. 4 (c), the air in the void is broken down, and the coating is delayed by the impact (about 0.5 seconds in the figure). ), And subsequently a discharge through the destroyed portion occurred, causing a large discharge current 18 to flow.

Therefore, the presence or absence of a defect in the inner surface layer 1c can be detected based on the presence or absence of the discharge currents 17 and 18.

5 shows an example of an electric circuit of the inspection device for rejecting the metal cover 1 having the coating defect, and the same reference numerals as those in FIG. 1 indicate the same parts. In the figure, 20 is a resistor for preventing overcurrent and converting a current value to a voltage value, 21 is a discriminator, 22 is a synchronizing signal for notifying the presence or absence of a lid, and 23 is a normal metal lid 1. The detected current is slightly higher than the peak value 15a of the charging current 15 in FIG. 4 (for example, point 30 in FIG. 4B or point 31 in FIG. 4C).
Equal to the current in the current; discharge current 17 and 18 compare voltage upsilon ₁ of the input signal corresponding to the smaller current), 24 is a reject signal. Note that points 16a and 4b in FIG.
A point 29a in FIG. 9C indicates a peak of the charging current.

When the metal lid 1 enters the inspection station, a synchronization signal 22 is input to the discriminator 21, while the metal lid 1 is connected to the electric circuit 19, the switch 9 a operates and the DC power supply 7 is turned on, and the discriminator 21 is turned on. voltage upsilon ₂ corresponding to the current flowing between the electrodes 2 and the metal cover 1 is input. Discriminator 21 compares the voltage upsilon ₂ voltage upsilon
₁ compares, when the voltage upsilon ₂ higher than the voltage upsilon _1, and is configured such that a predetermined time delay to generate a reject signal 24 with a (metal lid 1 is a time delay from the inspection station to reach the reject station) .

The present invention is not limited by the above embodiments, and for example, the form of the coated metal plate or the organic coating layer may be any appropriate one. For example, the organic coating layer may be a coating film for repairing the inner surface of a welded portion of a welded metal can (see JP-A-61-135486). Alternatively, an AC power supply may be used as the inspection power supply. In this case, the inspection can be performed in a short time by increasing the frequency.

The organic coating layer may be formed only on one side of the metal plate.

(Effect of the Invention) The method for inspecting a defect of an organic coating layer of a coated metal plate of the present invention comprises:
It can be performed in the air, the metal plate of the object to be inspected can be easily attached to the inspection device, it can be applied to 100% inspection, and it detects void-like coating defects that do not penetrate the organic coating. It has the effect that it can be done.

Further, there is an effect that the time required for the inspection is short, there is almost no damage to the electrodes due to the discharge at the time of the inspection, and there is substantially no variation in the inspection between the coated metal plates to be inspected.

Also, since the conductive elastomer body of the electrode is pressed against the portion of the organic coating layer to be inspected, regardless of the form of the coated metal plate, the inspection is reliably performed without any leakage of the inspection. Has benefits.

[Brief description of the drawings]

FIG. 1 is a partially cut front view of a first example of an apparatus for carrying out the present invention, FIG. 2 is a bottom view of a metal cover of FIG. 1, and FIG. 3 is a line III-III of FIG. FIG. 4 is an enlarged view showing the vicinity of a score portion along the line A, and FIG. 4 is an example of a current-time diagram when an inspection is performed using the apparatus of FIG. FIG. 4A shows the case where there is no defect, and FIG.
(C) shows the case where there is a defect, and FIG. 5 is an electric circuit diagram of a second example of the device for carrying out the present invention. 1 ... metal lid (coated metal plate), 1a ... taine-free steel (metal plate), 1c ... polyethylene terephthalate layer, inner surface layer (organic coating layer), 3 ... peripheral annular part (part to be inspected), 5: conductive elastomer, 7: DC power supply, 10: ammeter, 15a: peak charging current.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-7489 (JP, A) JP-A-51-106486 (JP, A) JP-A-52-56987 (JP, A) JP-A 50-50 11286 (JP, A) JP-A 48-89279 (JP, U) JP-A 44-7702 (JP, Y1) JP-B 51-41074 (JP, B2) JP-B 52-4954 (JP, B2)

Claims (1)

(57) [Claims] 1. A method for inspecting a defect of an organic coating layer of a coated metal plate having an organic coating layer on at least one surface, wherein a portion of the organic coating layer to be inspected is provided with an electrode capable of contacting the entirety of the electrode. A high voltage is applied between the electrode and the metal plate in a state where the conductive elastomer body having the surface is pressed with a predetermined force and brought into close contact, and flows between the electrode and the metal plate having a defect-free organic coating layer. A defect inspection method for an organic coating layer of a coated metal plate, wherein when a current slightly higher than a peak value of a charging current is detected, it is determined that the organic coating layer is defective.