JP2879244B2 - Dynamic viscoelasticity measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring dynamic viscoelastic properties of a viscoelastic body such as rubber.

[Conventional technology]

Rubber is not a completely elastic body such as a spring, but exhibits viscoelastic properties. The characteristics of such a viscoelastic body include dynamic elastic modulus, dynamic viscosity coefficient, loss tangent, etc. These dynamic viscoelastic properties are measured under the condition where a certain initial strain is applied to the test piece. This is performed by applying vibration distortion of a predetermined frequency.

Conventionally, there are the following two methods for measuring the dynamic viscoelasticity of this viscoelastic body.

One is a measurement method in which a torsional vibration is applied to a ribbon-shaped or cylindrical test specimen to deform it (for example, RDS7700, manufactured by Rheometrics Co., Ltd.). A measuring method of giving and deforming (for example, Vibron DDV II manufactured by Toyo Baldwin Co., Ltd.).

Among them, the former method has a drawback that the strain rate is not uniform between the center part and the outer peripheral part of the test piece, and data of only a desired strain rate cannot be obtained. Are better. The Lupke resilience coefficient R (%) has the following relationship with the tan δ of the sample.

l _n (R / 100) = − π · tan δ FIG. 6 and FIG. 7 show a comparison between tan δ obtained from this Lupke resilience and tan δ obtained by viscoelasticity measurement using two deformation methods. FIG. Clearly, the elongation deformation shows a better correlation.

However, in the case of extensional deformation and the latter method, when a large vibration strain exceeding a certain level is given, there is a problem that a test piece generates partial heat and abnormal data is output, so that the measurement range is restricted. . That is, since rubber is a viscoelastic body, it generates heat due to vibration in measurement. The calorific value per one cycle of the vibration follows the following equation.

QE "× γ ² where, Q is heat value, E" dynamic loss factor, gamma is the amplitude.

This indicates that the greater the dynamic strain and the greater the dynamic loss rate, the greater the heat generation. Therefore, when a rubber having a large dynamic loss rate before and after the glass transition point is measured with a large deformation, heat generation during the measurement becomes remarkable. However, when a portion of the test piece having a slightly higher temperature is locally generated due to the heat generation, the portion is slightly softer than the surroundings and the dynamic strain is increased. Therefore, the portion generates more heat than the surroundings, and the local temperature is further increased. Such partial heat generation causes an abnormality in the measurement data. This problem does not occur if the amplitude is reduced to avoid fever, but J.App
As reported by ARPayne in l.Polym.Sci., 7, p873 (1963), the dynamic viscoelasticity of rubber varies greatly with amplitude, so measurements should be taken at the amplitude that the product actually experiences. Also, for reference, the shape of the test piece is 5 mm wide,
An example of an experiment performed on a rubber material (NR) having a length of 20 mm and a thickness of 2 mm is described below. FIG. 8 shows the results of measuring the dynamic viscoelasticity temperature spectrum from -100 ° C. to + 80 ° C. by giving 0.1% (20 μm) elongational vibration strain to a test piece length of 20 mm.

Next, elongational vibration strain 0.4% (80μ
FIG. 9 shows the result of measuring the temperature spectrum by giving m). Normal data was obtained in the measurement with a dynamic strain of 0.1%, but when a dynamic strain of 0.4% was given, E ′ dropped sharply near the glass transition temperature, and abnormal data was generated. . This is due to a sharp decrease in the elastic modulus caused by the local temperature rise of the test piece.

In addition, when measuring a high hardness test piece in a molecular frozen state below the glass transition point under conditions of a large strain rate,
Applying a mechanically set deformation at the start of measurement may generate a larger stress than expected, and a large power is required for an amplitude control circuit for constantly controlling the amplitude of dynamic strain. Control is disturbed. For this reason, a test piece in a molecular frozen state at a low temperature is subjected to excessive amplitude, which may cause fatigue or crackling. FIG. 10 shows the progress from the start of measurement until the amplitude is controlled to be constant. For this reason, it is necessary to strengthen the structure of the device and increase the capacity of the drive unit.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spectrometer-type measurement that provides elongational vibration strain without generating abnormal data even when performing measurement under a condition of a large strain rate, and furthermore, unnecessarily strengthening the structure and the driving unit. An object of the present invention is to provide a dynamic viscoelasticity measurement method capable of measuring dynamic viscoelasticity characteristics without increasing the capacity.

[Means for solving the problem]

That is, the dynamic viscoelasticity measuring method of the present invention is a method for measuring the dynamic viscoelasticity characteristics of the viscoelastic body by applying a predetermined frequency of elongational vibration strain to a test piece made of a viscoelastic body,
Before performing the main measurement of the dynamic viscoelastic property of the test piece, an elongational vibration strain having an amplitude smaller than the amplitude of the elongational vibration given in the main measurement is applied to the sample to be measured in advance, and then the main measurement is performed. Is characterized by

In this way, by applying a small vibration in advance to the test piece that is smaller than the elongational vibration strain condition given in this measurement, heat can be uniformly dispersed throughout the test piece,
It is possible to easily predict an output giving a predetermined distortion without locally generating a large amount of heat, and by immediately completing the main measurement, abnormal data due to the local heat generation does not occur. In addition, by obtaining stress and strain data during micro vibration, the stress and strain in this measurement can be predicted in advance, so that unnecessary stress is not generated. Here, the micro vibration strain to be preliminarily applied to the test piece is
The distortion rate of the elongational vibration measured in this measurement is preferably about 0.01 to 0.3 part, more preferably about 5 to 15%. That is,
The amplitude of the micro-vibration is preferably set to 1 to 30%, more preferably 5 to 15% of those measured. FIG. 5 shows a measurement program. A very small amplitude is added to the test piece as at the start of the measurement, and the amplitude is 10% of the amplitude given at the time of the main measurement. When the temperature reaches the specified temperature, the main measurement is performed by adding the amplitude of the main measurement. After the end of this measurement, apply micro vibration and wait until the next specified temperature is reached. When the next specified temperature is reached, the amplitude of this measurement is added again and measurement is performed. Repeat this program until the final specified temperature is reached.

Hereinafter, the method of the present invention will be described with reference to a dynamic viscoelasticity measuring apparatus for performing the method.

As shown in FIG. 1, the dynamic viscoelasticity measuring device includes a viscoelasticity measuring unit 1 serving as a measuring body of a test piece TP made of a viscoelastic body such as rubber, a thermocontrol unit 2 attached thereto, and an analog device. It comprises a unit 3, an interface unit 4, an amplitude control circuit 5, a CRT display 6, a computer 7, a printer 8, a mixed gas temperature control device 9, and the like.

The viscoelasticity measuring section 1 has an electric vibrator 11 installed at one end on a gantry 10 and a force detector 19 arranged at the other end. The shaft 13 and the force detector 19 attached to the electric shaker 11
Clamps 13a, 14a between shaft 14 attached to
, Both ends of the test piece TP are gripped. The screw shaft 20 attached to the force detector 19 has a test piece TP
Is extended to the right side of the figure to impart an initial distortion, and by rotating forward and backward, it moves rightward or leftward in the figure. The rotation of the screw shaft 20 is gear 2
This is performed by a servo motor 23 via the first and second motors 22. A compressed air disk brake 25 is attached to fix the vibration of the initial strain applying device including the force detector and the screw portion. The force detector side must be fixed end in principle of measurement. However, since a high-precision ball screw is used for the initial strain applying device, when the stress of the test piece increases,
Screw vibrates. Therefore, it is desirable to fix the initial strain applying device including the screw portion with the disc brake.

On the other hand, the electric vibration exciter 11 vibrates the shaft 13 at a predetermined frequency and amplitude as shown by the arrow in the figure, and applies elongational vibration distortion to the test piece TP to which the initial distortion has been given as described above. The extension vibration strain is read by the optical strain detector 12 facing the light emitting element 12a fixed to the end of the shaft 13.

As described above, the set test piece TP is
And is measured under a constant temperature condition. A gas mixture of air and nitrogen whose temperature has been controlled by the gas mixture temperature control device 9 blows out of the pipe 17 from the thermostatic bath 15 to apply a temperature to the test piece TP. The temperature of the thermostat 15 is detected by a temperature sensor 18 and used for temperature control.

As shown in FIG. 6, a curved dispersion plate 16 having three rows of small holes 27 is provided directly above the mixed gas jet pipe 17 so as to uniformly cool the test piece TP.

In the method of the present invention, the viscoelasticity measuring unit 1 described above includes:
A predetermined initial strain (for example, 10%) is given to the test piece TP, and while giving the elongational vibration strain of a predetermined frequency and amplitude,
The main measurement is performed by detecting the stress by the force detector 19, and the electric vibrator 11 is caused to minutely vibrate before the main measurement.

The viscoelasticity measurement method described above is automatically performed via an attached device.

The analog unit 3, the amplitude control circuit 5, the thermo control unit 2 and the like are connected to the computer 7 for automatic control via the interface unit 4. Therefore, a preliminary minute vibration is set via the amplitude control circuit 5 according to the measurement conditions input to the computer 7, and furthermore, the electric vibration exciter is controlled by the thermocontrol unit 2 or the vibration control circuit 5 via the interface unit 4. 11 is driven to perform the measurement. Also,
A predetermined measured temperature is maintained by the mixed gas ejected from the mixed gas temperature control device via the thermocontrol unit 2.

The data detected by the force detector 19 is transmitted to the computer 7 via the analog unit 3 and the interface unit 4.
Where the dynamic viscoelastic modulus E 'and the loss tangent tan
After being calculated into dynamic viscoelastic properties such as δ, it is output to the CRT display 6 and the printer 8.

Example Using the dynamic viscoelasticity measuring device shown in FIG.
This test was performed at a frequency of 20 Hz and an amplitude of 0.5% for the rubber test piece, and the rate of temperature rise from -80 ° C to + 10 ° C was 2
The dynamic viscoelastic modulus E ', the dynamic viscoelastic coefficient E ", and the loss tangent tan δ were measured at intervals of 2 ° C at a rate of ° C / minute. Further, as shown in FIG. In order to verify the cooling effect, the rate of temperature rise was 5 ° C / min under the same test conditions.
The temperature range from 150 ° C to + 100 ° C was measured. In this measurement, the frequency of the elongational vibration was the same for each measurement, and a microvibration with an amplitude of 10% of that in the main measurement was given in advance and measured. As a result, as shown in FIGS. 3 and 4, each of the dynamic viscoelastic characteristics was data having smooth continuity, and no abnormal data was recognized.

For comparison, when the measurement was performed directly under the conditions of the main measurement without applying the above-mentioned preliminary minute vibration, the measured value of the dynamic viscoelastic property appeared discontinuously and abnormal data was generated.

〔The invention's effect〕

As described above, the present invention preliminarily imparts a small vibration having an amplitude smaller than the amplitude of the elongational vibration strain given in the present measurement to the test piece, and then applies a predetermined elongational vibration strain to the test piece. Since the main measurement was performed in this way, even when measuring at a large strain rate, the heat generated in the test specimen due to the micro vibration given to the preliminary becomes uniformly dispersed throughout, causing abnormalities in the main measurement. No more data. In addition, the dynamic viscoelasticity can be measured without the need for further strengthening the structure of the apparatus or increasing the capacity of the drive unit by the uniform preliminary heat generation.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a dynamic viscoelasticity measuring device embodying the present invention, FIG. 2 is a perspective view of a baffle plate, FIGS. 3 and 4 are diagrams showing dynamic viscoelasticity temperature spectra, FIG. Is an explanatory diagram of a measurement program, FIG. 6 is a diagram showing torsion deformation characteristics, and FIG.
FIGS. 8A, 8B, 9A, and 9B are diagrams showing a dynamic viscoelastic temperature spectrum of the NR, and FIGS. 10A and 10B are explanatory diagrams showing a process of controlling to a constant amplitude from the start of measurement. 1. Viscoelasticity measurement unit 2, Thermo control unit 3, Analog unit 4, Interface unit 5, Amplitude control circuit 6, CRT display 7, Computer 8, Printer TR …… Test piece.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsumi Ishida 5-15-4 Takinogawa, Kita-ku, Tokyo Inside Toyo Seiki Seisakusho Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 19/00 G01N 3/00-3/62

Claims (1)

(57) [Claims] 1. A method for measuring a dynamic viscoelastic property of a viscoelastic body by applying an elongational vibration strain of a predetermined frequency to a test piece made of a viscoelastic body, wherein the dynamic viscoelastic property of the test piece is measured. A dynamic viscoelasticity measurement method in which, before performing the measurement, an elongational vibration strain having an amplitude smaller than the amplitude of the elongational vibration given in the main measurement is applied to the sample to be measured in advance, and then the main measurement is performed.