JPH0481646A - Method for measuring water content in film of coated metal member - Google Patents

Abstract

PURPOSE:To easily and rapidly measure water content by bringing the surface of a conductive elastic member and that of a coated metal member to a close contact state and applying AC across both electrodes to measure the frequency response of electric impedance. CONSTITUTION:A conductive elastic member 2 is used as an opposed electrode 3 and a coated metal member 1 is used as an acting electrode and the surface of the member 1 and that of the member 2 are brought to a close contact state to apply AC across both electrodes and, when the frequency response of electric impedance is measured by a CPU 6, the water content in a film is measured as a change of a dielectric constant. By this constitution using no solution or agar, the water content of the film is easily and rapidly measured without receiving the effect of moisture.

Description

[Detailed description of the invention] [Purpose of the invention]

(Field of Industrial Application) This invention relates to a method for measuring the water content in a coating film of a painted metal member, which is used to measure the water content in the coating film of the coated metal member as a change in the dielectric constant of the coating film. It is something. (Prior Art) Conventionally, the main methods for measuring the water content in a coating film of a painted metal member include (1) gravimetric method and (2) impedance method. Among these methods, ■The gravimetric method measures the weight change of a painted metal member such as a painted steel plate by immersing it in water for a predetermined time using an electronic balance, and determines the water content in the coating film. This is a method to find. ■The impedance method uses 0', 1 as shown in Figure 5.
There is a method of using an aqueous solution of MOC KC as an electrolyte. This is achieved by using a glass cell 51 and using 0.1 mofLK (
, Q aqueous solution 52 is filled in the glass cell 51, the painted metal member 53 is used as a working electrode, and a platinum electrode 54 is used as a counter electrode.
, a constant voltage power source 55 is connected between the painted metal member 53 and the platinum mold AI 54, an oscillator 56 is connected, an arithmetic unit (CPU) 57 is further connected, and a display device 58 is connected. In this case, a holding plate 61 is used to bring the coated metal member 53, which is the steel plate to be measured, into close contact with the cell 51 and the electrolyte 52.
It is fixed using a set screw 62. In such a measuring device, an alternating current of IHz-LX104Hz is applied from a constant voltage power source 55 between the platinum electrode 54 as a counter electrode and the painted metal member 53 as a working electrode, and the electrical impedance at this time is This method measures the water content in a coating film as a change in dielectric constant by measuring frequency response. In addition, as another impedance method, the above 0.1 mo
As an alternative to Bun KC Bun aqueous solution, 0.1 m o l K
There is a method of performing similar measurements by filling a glass cell with agar containing Cl and using a platinum electrode embedded therein as a counter electrode. (Problem to be solved by the invention) However, with the gravimetric method (2), it is difficult to measure continuous changes in water content in the same sample, and the sample to be measured can be measured using an electronic balance, etc. There was a problem in that it was difficult to directly measure the coating film on the surface of a large structure such as an automobile body. In addition, with the impedance method (■), it is possible to measure changes in water content over time, which was impossible with the weight method, but with the method using an aqueous solution, it is possible to measure Water enters the membrane and changes the impedance during measurement, making it difficult to make accurate measurements.The retaining plate and set screw also reduce the adhesion of the painted metal part to be measured. This poses a problem in that it takes time and effort to measure. Furthermore, although the method using agar shortens the time required for measurement compared to the method using an aqueous solution, the agar is severely damaged, making it impossible to measure the same area and under the same conditions, and it is difficult to use as an electrode. There is a problem that the service life of the sample is short, and because it takes time to fix the sample with the holding plate and set screw, there is a problem that the state of the sample may change due to evaporation of water in the sample, etc. The challenge was to solve the problems of the gravimetric method and impedance method (aqueous solution method, agar method). (Purpose of the Invention) This invention was made by focusing on such conventional problems, and it is possible to perform measurements without being affected by water from other sources, as seen in aqueous solution methods and agar methods. In addition, compared to the agar method, it can withstand repeated use, has good adhesion to painted metal parts, and has a structure that prevents it from shifting against painted metal parts. Easy and quick measurement that does not take time to fix is possible, and since the size of the object to be measured is not limited, it is possible to directly measure the coating film on the car body, and furthermore, it is possible to continuously track changes over time. It is an object of the present invention to provide a method for measuring the amount of water in a coating film of a painted metal member.

[Structure of the invention]

(Means for Solving the Problems) The method for measuring the amount of water in the coating film of a painted metal member according to the present invention is based on the electrical impedance of the coating film when measuring the water content in the coating film of the painted metal member as a change in dielectric constant. To measure the electrical impedance, a conductive elastic member is used as a counter electrode and a painted metal member is used as a working electrode.The surface of the conductive elastic member is brought into close contact with the surface of the painted metal member, and an alternating current is applied between the two electrodes to generate an electrical impedance. The water content in the coating film is measured by measuring the frequency response of the drawer, and the embodiment is characterized in that the conduction resistance of the conductive elastic member is 1Ω or less. The structure of the method for measuring the amount of water in a coating film of a metal member is a means for solving the above-mentioned conventional problems. (Operation of the invention) The method for measuring the amount of water in a coating film of a painted metal member according to the present invention has the above-mentioned configuration, and uses a conductive elastic member such as conductive rubber as an electrode (counter electrode) for use in oil mud. As a result, measurements can be performed without being affected by water from other sources, as was the case with the aqueous solution method and the agar method.Also, since the conductive elastic member is solid, it is easier to measure than the agar method. It has enough strength to withstand repeated use, and the viscoelastic properties of the elastic member make it an electrode (counter electrode) with good adhesion to painted metal parts such as painted steel plates to be measured, and the conductive elastic By providing a structure in which the component itself adheres closely to the painted metal component and does not shift, it becomes possible to perform easy and quick measurements that do not require time to fix the painted metal component. Since the coating film on the car body can be directly measured, it is also possible to continuously track changes over time. (Example) Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a diagram showing an embodiment of the method for measuring the amount of water in a coating film of a painted metal member according to the present invention. In FIG. 1, 1 is a painted metal member (in this example, a painted steel plate) which is the object to be measured, and conductive rubber (manufactured by Nippon Synthetic Rubber: PCR) is applied to the surface of the coating film of this painted metal member 1.
305-05, continuity resistance = 0.3Ω2 dimensions 40X40X
A metal plate (aluminum plate in this example) 3 to which a conductive elastic member 2 made of (0.45 mm) is bonded is closely attached, and the painted metal member 1 serves as the working electrode, and the conductive elastic member 2 serves as its counter electrode. . The conductive elastic member 2 used here is a silicone rubber sheet, and is made of an anisotropically conductive connector in which gold-plated metal particles are arranged in the thickness direction of the sheet. Furthermore, 4 is an oscillator that can generate any frequency, and inputs a signal to a constant voltage power source 5, which can output alternating current to the working electrode and its counter electrode. There is. Furthermore, 6 is a calculation unit (CPU) which has a function of storing frequency dependence of impedance in a memory, and 7 is a display device for measurement results. FIG. 2 shows an equivalent circuit for measurement of the embodiment shown in FIG. To explain the elements of the equivalent circuit shown in Fig. 2,
Rf and Red are the electrical resistance of the coating film, the electrode resistance of the conductive elastic member 2, Cd is the capacitance changed due to water intrusion into the coating film, and C(f-d) is the resistance due to water infiltration. There is no coating capacitance. FIG. 3 shows an example of the change in water content in a coating film over time, and (A) shows the water content in an immersion experiment assuming that measurement is performed in an aqueous solution system, which is a comparative example of the present invention. (B) shows the change in water content of the coated steel plate when it is assumed that a conductive rubber counter electrode is used as the conductive elastic member according to the present invention. (A) and (B) After immersing the sample in distilled water at room temperature for about 5 minutes, (A) is 0.1 mol K
A gravimetric method is used in which the coating film is immersed in a CfL aqueous solution, and (B) is left in the air, and the amount of water contained in the coating film is measured using a balance. As shown in Figure 3, in (B) the water content did not change at all for about 15 minutes, whereas in (A) the water content increased by about 4 times due to water penetrating into the coating film. Indicates the amount of water. FIG. 4 shows the impedance measurement results (port diagram )showed that. Here, regarding the equivalent circuit of (A), Cdl and Rc are the electric double capacitance and reaction resistance that occur at the metal/solution interface when water penetrates below the coating film. Further, Cf corresponds to the capacitance of the coating film, Rf corresponds to the resistance of the coating film, and Rso or the solution resistance of the external liquid. In Figure 4, the impedance of (A) is 100H
On the high frequency side from z, the impedance of the capacitance of the coating film is shown. Also, from the low frequency side to 100Hz, Rc+
An Rf+Rso statement is shown. Here, when water enters, the resistance Rf of the coating film decreases. Follow, 102Hz-
The capacitance Cf of the coating film shown between 104 Hz will decrease, and the impedance value will shift downward by that amount. As described above, in the measurement method using an aqueous solution, water enters the coating film and directly affects the measured value, making accurate measurement difficult. On the other hand, method (B) according to the present invention does not use an aqueous solution, so there is no effect like that seen in (A), and 10
It is possible to measure the impedance of capacitance from 0 to 104 Hz, and it can be said that this is a very effective measurement method. Also, since each impedance is displayed as the sum of Rel and other resistance values, it is desirable that the resistance value of the conductive rubber electrode is 103 or less, and it can be used if the resistance value is less than that. Yes, but there is no specific scope. Hereinafter, a specific example of the method for measuring the amount of water in a coating film of a painted metal member according to the present invention will be further explained together with a conventional example. A coated steel plate coated with a clear coating having a thickness of 0.3 gm was used as the coated metal member, and the coated steel plate was immersed in distilled water for about 10 minutes and used as a sample. Here, when the distance between the electrodes is taken, the area of the electrode plate is taken as A, and the dielectric constant of the coating film is taken as ε, the capacitance C is expressed by the following formula. In this case, when the dielectric constant changes, the capacitance changes. Brasher is also used to convert capacitance to moisture absorption.
The following equation, which is called the equation, can be used. Here, Xv is the water content (%) in the coating film, Cd is the capacitance of the coating film after moisture absorption, Co is the capacitance of the coating film before moisture absorption,
εH1 is the dielectric constant of water at each temperature. Further, in order to convert the content to water content (IXIO-3g/cm-3), the water content was calculated by multiplying the content by the coating film weight (IXIO-3g/cm-3). Therefore, water content measurement tests were conducted using the conventional gravimetric method, the same conventional method using an aqueous solution, and the present invention example using a conductive rubber electrode as a conductive elastic member. The results are shown in Table 1. As is clear from the results shown in Table 1, it was found that the gravimetric method and the method using conductive rubber electrodes are consistent, and in the method of the present invention, unlike the gravimetric method, the sample to be measured is placed on an electronic balance, etc. Since there is no restriction on what can be measured, it is possible to directly measure coatings on the surface of large structures such as automobile bodies.

【Effect of the invention】

This invention uses a conductive elastic member as a counter electrode and a painted metal member as a working electrode when measuring the electrical impedance of the paint film when measuring the water content in the paint film of a painted metal member as a change in dielectric constant. The water content in the coating film is measured by bringing the surface of the conductive elastic member into close contact with the surface of the painted metal member, applying an alternating current between the two poles, and measuring the frequency response of the electrical impedance. It is possible to accurately measure the water content in the coating film without being affected by water from other parts, and it must be durable enough to withstand repeated use. Not only is it possible to do this, but it also allows for easy and quick measurements that do not require time to fix the painted metal parts, and it is possible to directly measure the coating film on the car body regardless of the size of the object to be measured. It brings about remarkable effects such as being able to continuously track changes over time.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the main parts showing an embodiment of the method for measuring the amount of water in a coating film of a painted metal member according to the present invention, Fig. 2 is an explanatory diagram showing an equivalent circuit that can be considered in the measurement of Fig. 1, and Fig. 3 is an explanatory diagram showing an equivalent circuit that can be considered in the measurement of Fig. The figure is a graph illustrating the results of investigating the relationship between the elapsed time and the amount of water in the coating film when it is assumed that measurement is performed in an aqueous solution system and when it is assumed that a conductive rubber counter electrode is used. Figure 5 is a graph illustrating the results of examining the impedance measured in an aqueous solution and the frequency change of the impedance measured using a conductive rubber as a counter electrode. FIG. 2 is an explanatory diagram of main parts showing a method for measuring water content. DESCRIPTION OF SYMBOLS 1... Painted metal member (working electrode), 2... Conductive elastic member (counter electrode), 4... Oscillator, 5... Constant voltage power supply. Figure 1

Claims (1)

[Claims] (1) When measuring the electrical impedance of the coating film when measuring the water content in the coating film of the painted metal member as a change in dielectric constant, the electrically conductive elastic member is used as the counter electrode and the painted metal member is used as the working electrode. A method for measuring water content in a paint film of a painted metal member, which comprises: bringing the surface of a conductive elastic member into close contact with the surface of a painted metal member, applying an alternating current between the two poles, and measuring the frequency response of electrical impedance.