KR100433187B1 - Dielectic sensor and manufacture method for the cure monitoring of the high temperature composites - Google Patents

Abstract

The present invention relates to a high temperature dielectric sensor for measuring the degree of cure of the composite material and a method of manufacturing the same, wherein the curing process of the thermosetting resin composite material changes depending on the properties of the material and chemical reaction and heat, density, and momentum in the polyphase Because of the change, it is necessary to measure the degree of cure for quality control of thermosetting resin composites. Among the methods of measuring the degree of cure of such thermosetting resin composites, in particular, there are no high-temperature dielectric sensors for measuring at temperatures above 180 ° C. The present invention has a stable structure even at high temperature, by providing a high-temperature dielectric sensor using the electrical insulator as the base substrate material and a method of manufacturing the composite material that does not cause a change in the base even at high temperature, the electrical properties are good and is cured at high temperature To improve the product quality by measuring the degree of curing By a chrome plating on the surface by reducing the effect of improving the sensitivity by reducing the stability and the electrical resistance of the sensor surface, the measurement error below the maximum of 1% has an excellent effect capable of more accurate measurements.

Description

High-temperature dielectric sensor for measuring the degree of cure of a composite material and its manufacturing method {Dielectic sensor and manufacture method for the cure monitoring of the high temperature composites}

The present invention relates to a Wheatstone bridge dielectric circuit and a high temperature dielectric sensor for measuring the degree of cure of the composite material, and a method of manufacturing the same. More specifically, a thermosetting resin composite having good electrical characteristics without causing a change in base at high temperatures. The present invention relates to a high temperature dielectric sensor for measuring the degree of curing of a material and a method of manufacturing the same.

In recent years, thermosetting resin composites, which are rapidly increasing in use, have high specific strength and non-rigidity compared to conventional materials, and thus their use ranges from sports and leisure goods to aerospace and aerospace industries are very diverse. Curing process changes material properties with time and involves chemical reactions in the multiphase and changes in heat, density and momentum, so curing monitoring of the composite material plays a very important role in quality control and performance evaluation of products. Conventional dielectric sensors for performing such curing monitoring are based on epoxy or glass-epoxy series, and there is a low temperature dielectric sensor that can be used only at a low temperature of 150 ° C or lower. At the temperature, it causes its own electrical change, which leads to many errors in the measurement of the dissipation coefficient of the composite resin. As shown in FIG. 1, when the low-temperature dielectric sensor is left at 220 ° C. for a long time, the base carbonizes after about 25 minutes and exhibits very unstable characteristics. Also, as shown in FIG. When measuring the dissipation coefficient of BMI (Matrimid 5292) made by CIBA-GEIGY using a dielectric sensor, the dissipation coefficient of BMI resin is 3.6 or higher after about 3 minutes under the atmosphere of 220 ℃ and it is lowered after about 10 minutes. Afterwards, the dissipation factor value increases again, indicating unstable characteristics. Accordingly, there is a problem that the measurement of the degree of cure of the high temperature composite resin such as BMI resin involves a lot of errors.

It is an object of the present invention to provide a dielectric sensor having excellent electrical characteristics and a method of manufacturing the same without causing a change in base even at a temperature of 200 ° C. or more.

In order to achieve the above object, the present invention provides a base substrate manufacturing process (S1) for manufacturing a base substrate of a glass material; A metal mold fabrication process (S2) using a discharge wire cutting method for fabricating a sensor pattern; A sensor pattern manufacturing process (S3) of applying a copper paste to the metal mold and curing the metal mold to separate the metal mold; Polishing the sensor pattern separated from the metal mold (S4); The object of the present invention is to provide a method for manufacturing a high temperature dielectric sensor and a high temperature dielectric sensor comprising a chromium plating process (S5) in which a surface of the polished sensor pattern is chromium plated.

1 is a graph measuring the dissipation coefficient of a sensor by leaving the conventional low temperature dielectric sensor at 220 ° C. for a long time;

Figure 2 is a graph measuring the dissipation factor of the BMI (Matrimid 5292, CIBA-GEIGY Co.) resin using a conventional low temperature dielectric sensor,

3 is a process chart showing the manufacturing method of the high temperature dielectric sensor of the present invention;

Figure 4 is a photograph showing a metal mold manufactured to manufacture a pattern of the high temperature dielectric sensor of the present invention,

5 is a graph showing the maximum stress value acting on the base portion and the sensor pattern portion according to the height of the sensor pattern;

Figure 6 is a photograph showing a state in which the dielectric sensor is destroyed by the thermal residual stress after the curing test of the BMI resin,

7 is a simplified diagram showing an experimental apparatus for forming a chromium plating layer having excellent electrical properties on the sensor surface;

Figure 8 is a photograph showing a high temperature dielectric sensor of the present invention,

Figure 9 is a graph showing the result of leaving the high-temperature dielectric sensor of the present invention for a long time at 250 ℃ atmosphere,

10 is a graph showing the results of monitoring the curing of the BMI resin using the high-temperature dielectric sensor of the present invention,

11 is a Wheatstone bridge circuit diagram,

12 is a circuit diagram showing a Wheatstone bridge dielectric circuit of the present invention;

13 is a graph comparing the error of the resistance between the series circuit and the Wheatstone bridge circuit,

Fig. 14 is a graph comparing errors of a capacitor of a series power circuit and a Wheatstone bridge circuit.

Explanation of symbols on the main parts of the drawings

8: high temperature dielectric sensor 9, 10, 12, 14: buffer

11: differential amplifier circuit 13: voltage compensator

15: phase difference compensator 17, 18: comparator

16, 19, 21: converter 20: exclusive OR gate

Hereinafter, a configuration according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.

As shown in Figure 3, the manufacturing method of the high-temperature dielectric sensor for measuring the degree of cure of the composite material of the present invention includes a base substrate manufacturing process (S1) for manufacturing a glass base substrate; A metal mold fabrication process (S2) for fabricating the sensor pattern; A sensor pattern manufacturing process (S3) using the metal mold; Polishing process (S4) of the produced sensor pattern; It is composed of a chromium plating process (S5) of the polished sensor pattern surface.

Hereinafter, a method of manufacturing a high temperature dielectric sensor for measuring the degree of curing of the composite material of the present invention will be described in detail for each process.

First step: base substrate fabrication process (S1)

The dielectric sensor may be divided into a copper foil and a base substrate supporting the copper foil, which form the sensor pattern. To use the dielectric sensor at a high temperature, the material of the base substrate should be replaced for a high temperature.

The material of such a high temperature base substrate has a low coefficient of thermal expansion, has a stable structure at high temperatures, and can use high temperature thermosetting resins, glass and ceramics, which are electrical insulators. Ceramic-based products, such as glass, which are not easily produced and are easily obtained, are used as the base substrate material.

Second Process: Metal Mold Manufacturing Process (S2)

The present invention applies a method of applying a copper paste after manufacturing a metal mold to produce a sensor pattern.

In particular, the metal mold is manufactured as shown in Figure 4 using the discharge wire cutting method for the accuracy of the sensor pattern.

Third process: sensor pattern manufacturing process (S3)

Viscosity (ps at 25 ° C) 400-600 Specific gravity (g / cc at 25 ° C) 3.2 Curing condition 150 ℃ x 30min Hardness (H) 3 Humidity(%) ± 30 Coupling Resistance (%) ± 30 The processed metal mold is subjected to a release treatment, and then coated with copper paste to cure at 120 ° C. for about 2 hours.

Since the copper paste is completely cured at 150 ° C., the sensor pattern produced by the metal mold is not completely cured and then cured at 150 ° C. for about 30 minutes, and then the sensor pattern is separated from the metal mold.

Fourth Step: Polishing Sensor Pattern (S4)

The sensor pattern separated from the metal mold cannot be used as it has a non-uniform surface, and the non-uniform surface becomes a uniform surface and is ground to have a suitable height.

The release material on the glass base substrate has a bad effect on the sensor, so wipe it off with acetone.

On the other hand, the higher the height of the sensor pattern, the higher the sensitivity, but the excessive height of the sensor pattern is the most suitable sensor pattern because it cannot act as a sensor by destroying the glass base substrate in contact with the resin due to the thermal residual stress caused by curing of the resin. The height of the shall be determined.

The height of the sensor pattern was determined through the following examples.

Example

In the present invention, thermal stress analysis using an finite element program, Ansys, was performed to determine the optimal height of the sensor pattern.

The temperature difference before and after curing was assumed to be 180 ° C., and the thermal residual stress around the sensor was analyzed by changing the height of the sensor pattern to 35 μm, 100 μm, 150 μm, 200 μm, and 250 μm. 5 shows the maximum stress value applied to the base portion and the sensor pattern portion according to the height of the sensor pattern, the shear strength of the copper paste pattern used in the experiment is about 15MPa, below the fracture strength value as shown in FIG. However, the stress acting on the underlying glass becomes 35MPa, which is the breaking strength of the glass, when the height of the sensor pattern reaches 250 µm. In order to verify the results of the finite element analysis described above, the BMI resin was cured on the sensor pattern by changing the height of the sensor pattern. At this time, the curing temperature of the BMI resin was selected as 220 ℃. As a result of the experiment, when the height of the sensor pattern was more than 250㎛, it was observed that the sensor pattern was destroyed. FIG. 6 is a photograph showing a state in which a sensor is broken after a curing test of a BMI resin, and it can be seen that a base portion of glass is broken.

From the above results, it can be seen that the height of the sensor pattern is preferably about 200 μm or less in order to prevent destruction of the sensor due to thermal residual stress.

5th process: Chrome plating process of high temperature dielectric sensor (S5)

As described above, in the high temperature dielectric sensor manufactured by the metal mold, since the sensor pattern is formed of copper paste, the surface of the sensor may be electrically uneven.

In order to stabilize this electrically non-uniform sensor surface, the sensor surface was metal-coated using the electroplating method.

The experimental apparatus as shown in FIG. 7 was configured to obtain optimal conditions for forming a chromium plating layer having excellent electrical characteristics on the sensor surface. The plating solution used is a standard plating solution, consisting of 250 g of hexavalent chromium powder per liter of water and sulfuric acid with 1% of chromium mass. Since 1 g of sulfuric acid had a volume of 1.84 ml, sulfuric acid was added to the dropper by calculating the volume corresponding to the mass. The DC power supply used can be used from 0 to 100V and 0 to 20A. Insoluble lead was used for the positive electrode, copper was used for the high conductivity, and the negative electrode was not touched with the plating solution except for the plating part so that chromium did not precipitate on the electrode. The temperature of the plating liquid was room temperature (25 ° C.), and the experiment was performed while changing the operating current to 0.2, 0.4, 0.6, 0.8, 1.0 A. Table 2 is a table showing the results of experiments in the resistance change of the sensor pattern according to the current used.

Current (A) Resistance of the sensor Before plating After plating 0.2 34 0 0.4 34 20 × 10-6 0.6 34 42.75 0.8 34 - 1.0 34 -

As shown in Table 2, when the operating current is 0.2A, the electrical resistance is almost zero, and the electrical characteristics are excellent. In addition, when the use current is more than 0.8A, it could be observed that the plating layer was not formed due to cracking of the sensor pattern.

8 is a photograph showing the state of the high-temperature dielectric sensor manufactured by the above manufacturing process.

Hereinafter, in order to confirm the properties and effects of the high temperature dielectric sensor for measuring the degree of cure of the composite material of the present invention was evaluated through the following experimental example.

Experimental Example 1

In order to compare the performance of the existing low-temperature dielectric sensor with the high-temperature dielectric sensor of the present invention, the following conditions were used in each experiment.

Initial temperature: Room temperature (25 ℃)

Measuring circuit: Wheatstone bridge dielectric circuit

Dielectric Sensor: Low Temperature Sensor, High Temperature Sensor, High Temperature Sensor with Chrome Plating

Experimental resin: 0.08g of BMI resin (Matrimid 5292 of CIBA-GEIGY)

Experiment temperature: 200 ℃ at 10 ℃ / min

Experiment time: about 120 minutes

Figure 2 is a graph measuring the dissipation coefficient of BMI (Matrimid 5292, CIBA-GEIGY) using a low temperature dielectric sensor, the curing temperature of the BMI resin is 220 ℃. As can be seen from the measured results, the BMI resin has a dissipation factor of 3.6 or more after about 3 minutes in a 220 ° C atmosphere and drops after about 10 minutes. However, after about 10 minutes, the dissipation factor is increased again, indicating unstable characteristics.

In order to investigate the characteristics of the fabricated high temperature dielectric sensor, the characteristics of the sensor itself were investigated by leaving it in a high temperature atmosphere for a long time. 9 is a diagram showing the result of leaving the high temperature dielectric sensor in a 250 ° C. atmosphere for a long time, and it can be seen that the dissipation coefficient has a constant value of almost zero.

Curing monitoring of high temperature resin, BMI resin, was carried out to examine the applicability of high temperature dielectric sensor. Curing temperature was maintained for a long time at 200 ℃ same as the experiment of low temperature dielectric sensor. 10 is a diagram showing the results of curing monitoring of the BMI resin, it can be seen that the dissipation coefficient value reaches a maximum after about 3 minutes. Also, after about 10 minutes, the dissipation coefficient value has a constant value, so it can be seen that the curing is completed. From the above results, it was confirmed that the fabricated high temperature dielectric sensor can be applied to the curing monitoring of the high temperature composite material.

As a result of the above experiment, the high temperature dielectric sensor has no effect on the curing monitoring of the resin cured at high temperature, so it is useful to study the properties of other resins or to manufacture molded products of composite materials.

On the other hand, in order to measure the degree of cure of the composite material, a dielectric circuit for measuring the signal from the high-temperature dielectric sensor manufactured as described above is required, the dissipation coefficient of the resin to measure the curing process of the resin using such a dielectric circuit ( Disssipation factor) value was used. The dissipation factor D _f can be defined in terms of the equivalent resistance R _m of the resin and the equivalent capacitor C _m , where the following relationship holds (where ω: frequency) (One)

Next, there are various methods for measuring the equivalent resistance and the equivalent capacitor value of the composite resin, but conventionally a series circuit is generally applied, but in the present invention, the measurement range of the equivalent resistance R _m is reduced from infinity to MΩ. In order to improve the precision of the Wheatstone bridge circuit shown in FIG. The bridge circuit is largely divided into a balanced bridge method and an unbalanced bridge method, and the present invention uses an unbalanced bridge circuit because it is necessary to measure the resistance and capacitor values of the sensor portion that change over time.

Predetermined resistance R _2, R _3, R ₄ impedance Z _2, Z _3, Z ₄ ask the impedance Z _m of the resin and the composite of, (where, j: imaginary unit)

(2)

to be. The voltage applied to the resin is expressed as follows.

Where V _i : input voltage

(4)

This is the difference between the output voltage of the sensor part minus the output voltage on the opposite side. The above equation can be summarized as follows.

(5)

Voltage ratio between V _i and V _m in equation (5) And phase difference If you find

(6)

(7)

to be. At this time, if R = R ₂ = R ₄ , and substituted by the formula (6) and (7) in the formula (5) as follows.

(8)

A =

B =

C =

Therefore, solving equation (8) above, the equivalent resistance R _m and equivalent capacitor C _m of the resin are as follows.

(9)

10

The dissipation factor D _f of the resin is defined by

(11) where I _RM : current flowing through the equivalent resistance (R _M ), I _CM : current flowing through the equivalent capacitor (C _M ) Z _RM : equivalent resistance (R _M ) impedance, Z _CM : equivalent capacitor (C _M ) impedance

to be. Therefore, by substituting Equations (9) and (10) into Equation (11), the dissipation factor of the composite resin can be measured.

In the Wheatstone bridge circuit as described above, the resistors R and R ₃ should be selected properly to improve the accuracy of the measurement. In the present invention, a circuit was configured by selecting R = R ₂ = R ₄ = 10 ms and R ₃ = 1 ms.

Next, in order to measure the dissipation coefficient of the composite material, as shown in equations (10) and (11), the voltage ratio V _r and the phase difference Should be measured.

12 is a voltage difference V _r and a phase difference A circuit configuration diagram for measuring.

As shown in FIG. 12, a Wheatstone bridge circuit with a high-temperature dielectric sensor 8 of the present invention, a differential amplifier circuit 11, and a plurality of buffers for measuring the values of V _m and V _i 9, 10, 12, and 14, the phase difference compensator 15 and the voltage compensator 13 were installed, and the phase difference ( Two comparators 17 and 18, a transducer 16 and 19 connected in parallel to the two comparators 17 and 18, an exclusive OR gate 20 and the exclusive OR gate And a converter 21 connected in parallel with (20).

The comparators 17 and 18 output square signals by + 5V when the input AC signal is positive voltage and 0 V when the negative voltage is negative, and the two comparators 17 and 18 function. Square wave of V _i and V _m passes through the exclusive OR gate 20. If you convert this signal to an RMS value, the phase difference Can be obtained. The defining formula of RMS is as follows. Where V _{RMS is the} effective voltage and T is the period.

V _rms (12)

Equation (13) is converted to the following equation because of the characteristic of the square wave passing through the exclusive OR gate, that is, only the phase difference is detected as the square wave. Where V _{MAX is the} maximum voltage

V _rms (13) Phase difference in equation (14) If we derive the equation

(14)

Becomes

In order to confirm the characteristics and effects of the Wheatstone bridge dielectric circuit for measuring the degree of cure of the composite material of the present invention was evaluated through the following experimental example.

Experimental Example 2

The optimum input frequency and input voltage should be selected to improve the accuracy of the measurement in the dissipation factor measurement circuit.

A frequency of 1kHz and a voltage of 1V were used for the series circuit, and the Wheatstone bridge circuit selected the most suitable value through experiments.

In the present invention, an input frequency of 400 Hz and an input voltage of 3 V are selected. The performance of the series circuit and the Wheatstone bridge circuit was compared and evaluated using five previously measured resistors and capacitors. FIG. 13 is a graph comparing the resistance error. In contrast, the Wheatstone bridged circuit exhibited an error of ± 0.5%.

On the other hand, Figure 14 is a graph measuring the error of the capacitor, the error of the series circuit is ± 2%, the error of the Wheatstone bridge type circuit is ± 1%. Therefore, the Wheatstone bridge circuit has a maximum error of ± 1% or less, and thus has a higher precision than the conventional series circuit.

As confirmed through the above examples and experimental examples, the high-temperature dielectric sensor for measuring the degree of cure of the composite material of the present invention has a stable structure even at high temperature, and by using an electrical insulator as a base substrate material, Good electrical properties without causing any change to improve the quality of the product by measuring the degree of cure of the composite material cured at high temperature, and chromium plating on the surface of the sensor to improve the sensitivity by reducing the surface stability and electrical resistance In addition, when the high temperature dielectric sensor of the present invention is connected to a Wheatstone bridge type circuit and the degree of cure is measured, the measurement error can be reduced to a maximum of 1% or less, so that an accurate measurement can be made. It is an industrially useful invention.

Claims (5)

A base substrate fabrication process (S1) for fabricating a glass substrate base substrate; A metal mold fabrication process (S2) using a discharge wire cutting method for fabricating a sensor pattern; A sensor pattern manufacturing process (S3) of applying a copper paste to the metal mold and curing the metal mold to separate the metal mold; Polishing the sensor pattern separated from the metal mold (S4); Method for producing a high-temperature dielectric sensor for measuring the degree of cure of the composite material, characterized in that consisting of a chromium plating process (S5) to the surface of the polished sensor pattern. A high temperature dielectric sensor for measuring the degree of cure of a composite material comprising a base substrate made of glass and a sensor pattern formed of copper paste on the base substrate, and chromium plating the surface of the sensor pattern. delete delete delete