JP2000283964A - Conductivity inspection method, and molding method using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique useful for an in-process inspection method for the conductivity of a conductive plastic molding or the like, saying in concretes, to provide a method of inspecting easily and highly precisely the conductivity without providing an elaborate electric terminal or the like onto an inspecting object. SOLUTION: A high frequency magnetic field is generated by making a high frequency current flow in a coil inside a sensor, a conductivity measuring object is laid within the magnetic field to make an eddy current flow in the object by electromagnetic induction, and conductivity of the measuring object is inspected, without providing directly an electric terminal or the like onto the object, based on the change of an impedance of the coil inside the sensor therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique useful for an in-process inspection method for a conductive plastics molded article or the like. More specifically, the present invention relates to a technique for simply and accurately providing a conductivity inspection method without providing a troublesome electric terminal or the like on an inspection object.

[0002]

2. Description of the Related Art Plastics such as thermoplastic resins and thermosetting resins, conductive fillers such as carbon fiber, carbon black and carbon-coated whiskers, and conductive polymers.
So-called conductive plastics in which conductive components are mixed have been put to practical use. It can be molded in a relatively short cycle using conventional plastics molding methods such as compression molding, injection molding, blow molding, and vacuum molding, and has a certain level of conductivity as a molded product. Used for required applications.

[0003] The problem with these conductive plastics is that even if the conductive component is accurately contained in a certain amount, the dispersibility of the conductive component, the dispersibility of the conductive component, and the like depend on the conditions such as the melting and kneading process of the material. Further, when the conductive component is a fibrous filler, the conductivity of the conductive plastics molded article may be changed by, for example, changing the aspect ratio by kneading the material. Also, even if the molding conditions are set to be constant, there is a possibility that the delicate disturbance such as the temperature around the molding machine changes the viscosity of the plastics and the aspect ratio and dispersibility of the filler change, It is industrially extremely difficult to simultaneously control many parameters that affect such conductivity and are difficult to predict.

[0004] The conductivity of a molded article is basically determined by providing a terminal for measuring electrical resistance on the molded article by a complicated operation such as applying a conductive paint to the surface of the molded article or press-fitting a metal terminal. Is usually measured by After molding a certain number of molded products, electrical terminals are provided by such complicated work, after measuring the conductivity, the molding conditions are not changed based on this, or in the worst case, the formulation of the material is not changed And there were many cases where the product according to the specifications could not be obtained. In addition, a method of providing a terminal for measuring electric resistance on a molded product as described above has a relatively short molding cycle. It has been extremely difficult to apply it to such a technique as to measure gender.

The sensor itself using the induced eddy current is a known technique. However, this is a displacement sensor that uses the fact that the oscillation amplitude, the phase shift with respect to the reference waveform, and the eddy current change when the distance between the sensor and a magnetic substance such as metal changes, It has been used as a non-destructive diagnostic method for scanning for internal damages of the device.
However, for example, with respect to conductive plastics using a substantially non-magnetic carbon material as a conductive filler, the conductivity can be accurately and very simply inspected without directly providing an electric terminal on such a material. There is no precedent for applying induced eddy current as a method.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique useful for an in-process inspection method of a conductive plastic molded article or the like. More specifically, the present invention relates to a technique for simply providing a highly accurate conductivity inspection method without providing a troublesome electric terminal or the like on an inspection object.

[0007]

In order to achieve the above object, an inspection method according to the present invention basically has the following configuration.

That is, a method of placing a conductive measurement object in a high-frequency magnetic field and inspecting the conductivity of the measurement object based on a change in impedance of a coil in the sensor at that time.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

In the basic configuration of the present invention, a high-frequency current is applied to a coil inside a sensor to generate a high-frequency magnetic field, an object to be measured is placed in the magnetic field, and an eddy current is caused to flow through the object by electromagnetic induction. In this method, the conductivity of the measurement target is inspected based on a change in the impedance of the coil in the sensor without providing an electric terminal or the like directly on the target.
When there is an object to be measured in the magnetic field,
The passage of magnetic flux and the eddy current in the vertical direction flow on the object surface,
It utilizes the fact that the impedance of the sensor coil changes, which affects the high-frequency oscillation state. More specifically, to obtain the conductivity of the object to be measured by changing the phase of the oscillation with respect to the reference waveform due to the change in the impedance of the coil, or by rectifying the oscillation amplitude and treating it as a change in the DC voltage. Can be. There is no particular restriction on the oscillation frequency at this time, but in order to secure the response characteristics,
It is desirable to set it to z or more. Hereinafter, the above-mentioned sensor in the present invention is simply referred to as an eddy current sensor in this specification.

Although there is a one-to-one relationship between the change in oscillation phase and amplitude and the conductivity of the test object when there is no disturbance, the relationship is not necessarily linear. You may give a device to do it. In addition, the phase and amplitude of oscillation also vary depending on the distance between the object and the sensor, so it is necessary to consider that the distance between the object to be measured and the eddy current sensor is always the same depending on the operation of the jig or robot. . Also, if metal is present near the eddy current sensor, it will disturb the measurement, so it may be necessary to take measures such as keeping away from metals and making jigs and robot parts with nonmetallic or insulating materials. . Also, the flow of the induced eddy current may change depending on the shape of the measurement object, such as the thickness, and the measured value may vary. Is provided to measure conductivity (for example, volume resistivity), and the correspondence between the measured value and the value measured by the eddy current sensor can be confirmed. It is particularly preferable to calibrate by an electric method or a computer operation so that parameters relating to conductivity to be obtained (volume specific resistance, surface resistance, etc.) can be obtained directly from the measured value by the eddy current sensor. .

The greatest advantage of the present invention is that the conductivity of an object to be measured can be inspected without providing an electric terminal or the like directly on the object. This is suitable for application to the inspection of plastics moldings which can be obtained in a relatively short molding cycle. That is, even if the molding cycle is short, the conductivity level is determined in a short time without contact, for example, by bringing the eddy current sensor close to a fixed distance to the molded article in accordance with the cycle. This is because it is possible.

Measurement object particularly useful by using the present invention
Materials include so-called conductive plastics.
You. Conductive plastics is a common name,
Does not necessarily indicate the electrical resistance of the conductive region,
10 in specific resistance¹³Excluding insulating plastics of Ωcm or more
10^-3-10¹²Any of the large conductive area of about Ωcm
In this specification, conductive plastics
Name. More desirable to be able to measure accurately with the present invention
The range of the volume resistivity of the measurement object is 10^-3-10 ⁶Ωc
m. Making plastics, which are essentially insulators, conductive
Carbon fiber, carbon black, carbon coated
Conductive fillers such as ska and conductive polymers
It is common practice to mix sexual components. Use
As plastics, thermosetting resin, thermoplastic resin
All things apply and there are no restrictions. Also conductive
For molding methods to obtain plastics molded products, for example,
Compression molding, injection molding, blow molding, vacuum molding, etc.
It is not specified, but the molding cycle such as injection molding is particularly short.
It is particularly preferred to combine the method with the present invention.

For example, after such a conductive plastic molded article is obtained in a molding step, a high-frequency current is passed through a coil inside the sensor to automatically generate a high-frequency magnetic field, and the conductive magnetic field is generated in the magnetic field. An object to be measured is placed, an eddy current is caused to flow through the object by electromagnetic induction, and the impedance of the coil in the sensor changes at that time, and the conductivity of the plastics molded article as the object to be measured is directly connected to the object by an electric terminal. It is possible to perform inspection without providing the above. INDUSTRIAL APPLICABILITY According to the present invention, in-process inspection related to conductivity can be performed at a high speed without providing a troublesome electric terminal or the like on an inspection object, which is extremely industrially useful.

When a conductive plastics molded product is obtained in the molding step, automatically taking out the molded product from the molding machine by a take-out robot is a technique often used industrially. By incorporating a sequence that brings the eddy current sensor closer to the object to be measured in the series of operations of the take-out robot, it is possible to perform an in-process inspection of the conductivity without largely changing the molding process. This is an example of use. Alternatively, the conductivity of the plastics molded article as the measurement target can be inspected in the process using a robot different from the molded article taking-out robot that moves the eddy current sensor near the molded article. It is preferable to generate an alarm when the conductivity is out of spec by the in-process inspection, and it is also preferable to sort out the molded products taken out according to the conductivity level.

Further, after the conductive plastics molded article is obtained in the molding step, the conductivity of the molded article is automatically and continuously measured by the eddy current sensor, and the result is fed back to the molding step, and the next molding is performed. A conductive plastics molding method that adjusts the molding conditions for shots can also be used. For example, in the case of conductive plastics in which fibrous conductive fillers are mixed with plastics, the length (aspect ratio) of the conductive fibers in the plastics may change depending on the molding conditions, which affects the conductivity. May be. Also, the dispersibility of the mixed conductive component may affect the conductivity of the conductive plastic molded article. Even if the molding conditions that affect such conductivity are set to be constant, slight disturbances such as the temperature around the molding machine change the viscosity of the plastics, so that the aspect ratio of the conductive fibers is still high. It is usually very difficult to control such a large number of parameters and predict the results, as the ratio and dispersibility may change. On the other hand, according to the conductivity level obtained in the process by the method of the present invention, molding conditions (for example, in the case of injection molding, cylinder temperature, screw rotation speed, back pressure during material measurement, etc.) are automatically adjusted to appropriate conditions. Feeding back to change to the above is excellent in that the molded article can be easily controlled to a desired conductive range with the parameter of the most essential conductivity itself.

As a measurement object to which the present invention is applied, a substantially non-magnetic object is more suitable than a magnetic substance containing a metal or the like. This is because the impedance change of the coil in the eddy current sensor is affected not only by the conductivity of the object to be measured but also by the magnetic permeability. According to the present invention, the conductivity can be measured accurately if the material is substantially non-magnetic such that the degree of disturbance can be ignored.

However, even when the object to be measured is a magnetic material, if the characteristic to be measured is not only the conductivity but also the impedance to an electromagnetic field such as electromagnetic shielding, the measured value including the influence of the magnetic permeability is rather changed. This may be useful, and the invention is not limited to measuring non-magnetic objects.

Since the carbon material has conductivity and is substantially non-magnetic, it is preferable to use an object containing the carbon material as the object to be measured in that the conductivity can be obtained with high accuracy according to the present invention. Specific examples of the object containing a carbon material include carbon fiber, carbon black, and carbon-coated whiskers. As the carbon fiber, any material having conductivity such as PAN-based, pitch-based, and vapor-grown carbon fibers is suitable. The production method and type of carbon black, such as furnace black, acetylene black, and thermal black, are not limited. However, so-called conductive grade carbon black is often used. In addition to the case where the main component of the material is carbon such as carbon fiber or carbon black, a material obtained by coating another material with carbon is also suitable for applying the present invention. For example, an object including a material such as a whisker having a composition of potassium titanate, aluminum borate, magnesium sulfate, or the like on which a carbon film is formed by a chemical vapor deposition method may be used as the measurement target.

Although the actual form of the object to be measured is not limited, it is a main application of conductive plastics, which is obtained by high cycle molding such as injection molding and has stable conductivity. Examples of those that need to be maintained within the specified range include electronic and electrical equipment housings or semiconductor auxiliary materials, and it is advantageous to use them as the measurement object of the present invention. Electronic and electrical equipment housings that handle high frequencies with wireless devices such as mobile phones, CDs,
Molded articles used in the field where conductive plastics are effective, such as housings of products handling digital signals such as DVD players and digital cameras, and other housings such as personal computers, which are required to have an electromagnetic wave shielding property, can be particularly exemplified. Items requiring antistatic properties and ESD dissipating properties can also be exemplified. These are, for example, generally referred to as semiconductor auxiliary materials, such as IC trays, wafer carriers, and wafer baskets, which are used in semiconductor manufacturing processes and are required to maintain a certain level of conductivity. is there.

If the conductivity of these molded products can be easily controlled by the present invention, industrially significant effects such as improvement in product yield can be produced.

[0022]

(Example 1) Carbon fiber (T70 manufactured by Toray Industries, Inc.)
0SC) and nylon 6 (CM1001 manufactured by Toray Industries, Inc.).
A 2 mm flat plate was obtained. At this time, various levels were prepared for the contents of carbon fibers and the like. These are the six levels shown in Table 1.
The conductivity of this molded product cannot be easily predicted because it changes due to slight variations in molding conditions and various external disturbances in addition to the type of material.

Keyence eddy current displacement sensor EX-2
Diversion 05, a high-frequency current is passed through the coil inside the sensor to generate a high-frequency magnetic field, and the injection molded product obtained earlier is separated by 0.5 mm in this magnetic field, and an eddy current is passed through the object by electromagnetic induction. The change in the impedance of the coil in the sensor at that time was extracted as a change in the DC voltage by rectifying the change in the oscillation amplitude of the high frequency, and was displayed as the following parameters (display values of the sensor).
In other words, this parameter is set by calibrating the electric circuit in advance so that the value when the sensor is brought close to a sufficiently large steel plate is 0.0, and the value in the air that is almost infinity from the conductor is 8.0. Was.

By bringing the sensor close to the center of the injection-molded article using the carbon fiber to be measured, different measurement parameters were obtained for each level of the molded article in a non-contact manner. The measurement was completed almost instantaneously because the sensor was only brought close to the injection molded product.

The molded article for which the measurement by the eddy current has been completed is
Cut out a strip of 2.7 × 70 × 2 mm, apply conductive paint to both ends in the longitudinal direction, measure the electric resistance between both ends with a digital tester, divide it by the dimensions of the strip test piece, and calculate the volume resistivity Was. FIG. 1 and Table 1 show the relationship between the cut-out volume resistivity obtained from the actual resistance and the parameters obtained by the eddy current measurement, and the one-to-one relationship was clearly shown.

By using this relationship, an accurate volume resistivity can be instantaneously obtained for various injection molded products only by bringing the eddy current sensor closer. It has become possible to determine the conductivity level without the need for laborious work such as providing electric terminals.

(Comparative Example 1) Injection molding pellets made of carbon fiber and nylon 6 were injection-molded in the same manner as in the example to obtain a 70 mm square, 2 mm thick flat plate. At this time, the carbon fiber content and the fiber length of the carbon fiber molded article were prepared at various levels (the same six levels as in the examples).

This molded product was cut into a strip of 12.7 × 70 × 2 mm using a diamond cutter while being sprinkled with water, a conductive paint was applied to both ends in the longitudinal direction, and then dried in an oven. After measuring the electric resistance between both ends to which the conductive paint was applied with a digital tester, the electric resistance was divided by the size of the strip test piece to obtain the volume specific resistance. From injection molding to obtaining the volume resistivity, one worker did complicated work and it took about one day.

[0029]

[Table 1]

Wf: Weight content of carbon fiber (%) CB: Weight content of carbon powder (%)

[0031]

According to the present invention, it is possible to provide a technique useful for an in-process inspection method of a conductive plastics molded article or the like. More specifically, it is possible to provide a simple and accurate method for inspecting conductivity without providing a troublesome electric terminal or the like on the inspection object.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a volume specific resistance obtained by providing an electric terminal on a measurement target and a parameter obtained by an eddy current sensor.

Claims (10)

[Claims] 1. A method of placing a conductive measurement object in a high-frequency magnetic field, and inspecting the conductivity of the measurement object based on a change in impedance of a coil in the sensor at that time. 2. The inspection method according to claim 1, wherein the object to be measured is a molded article of conductive plastics. 3. The inspection method according to claim 1, wherein the object to be measured is a substantially non-magnetic object. 4. The inspection method according to claim 1, wherein the object to be measured is an object containing a carbon material. 5. The inspection method according to claim 4, wherein the object to be measured is an object including at least one of carbon fiber, carbon black, and carbon-coated whiskers. 6. The inspection method according to claim 4, wherein the object to be measured is a conductive plastic. 7. The inspection method according to claim 1, wherein the object to be measured is an electronic / electric equipment housing or a semiconductor auxiliary material. 8. A molding method characterized by using the inspection method according to claim 1 automatically and continuously after a molded article is obtained in a molding step. 9. After the molded article is obtained in the molding step, the molded article is automatically taken out of the molding machine by a take-out robot, and the inspection method according to claim 1 is used for the molded article. A molding method characterized by the above-mentioned. 10. After the molded article is obtained in the molding step, the conductivity of the molded article is automatically and continuously measured by the method according to claim 1, and the result is fed back to the molding step. And adjusting the molding conditions for the next molding shot.