JPH0124253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a slit die rheometer for measuring the fluidity of fluid substances such as raw rubber, rubber compounds, polymer melts, and the like.

Knowing the flow properties of rubber resins, ie, elasticity, viscosity, extrudate shape stability, etc., is extremely important in knowing the processability of these materials.

b. Prior Art Conventionally, as a method of obtaining a measure of fluidity, a Mooney viscometer has been widely used for rubber, and a melt indexer has been widely used for resins. However, these only provide an indication of the material's ease of flow under a particular shear strain rate.

On the other hand, a capillary rheometer has been conventionally used as a method for determining viscosity and elasticity in a wide range of shear strain rates. Furthermore, Tokukai Akira
No. 51-2453 discloses, for example, a method for measuring the flow rate and viscosity properties of liquids consisting of gases, liquids, combinations of gas and liquid, gas and suspended solids, or combinations of gas, liquid and suspended solids. ing. In this case, viscosity is determined from the static pressure difference, with the pre-pressure fluid source adjusted to maintain a constant fluid density and constant mass through the fluid passageway.

Similar methods are also disclosed in the following documents.

CDHAN, et al Poly.Eng.Sci., 12 No.2 81
(1972) CDHAN, et al Trans.Soc.Rheo., 17 No.2
151 (1973) c Problems to be Solved by the Invention When such a method is applied to viscoelastic fluids such as rubber, complicated repetitive operations such as pipe length correction are required;
Furthermore, since it is not determined whether the system is in a steady state, it is practically impossible to perform measurements with reproducibility. The reason for this will be explained based on the principle of measuring the steady flow viscosity η in a capillary rheometer that has been commonly used in the past.

FIG. 1 is a conceptual diagram of a capillary rheometer, in which 1 is a plunger, 2 is a cylinder, 3 is an introduction part, 4 is a capillary die, and F is an external force that presses the plunger 1.

If the pressure loss of the fluid flowing through the capillary die 1 with length l and radius r at a flow rate Q per unit time is ΔP, then the shear stress τ〓 on the capillary tube wall and the apparent shear strain rate _γ〓 on the tube wall are as follows. It is given by the following formula.

τ = (ΔP/l) × (r/2) γ = _a = 4Q/πr ³ Then, if the correction of the shear strain rate when the fluid is a non-Newtonian fluid is omitted, the steady flow viscosity η is given by the following formula. Given.

η=τ〓/γ _a = (ΔP/l)×(r/2)/4Q/
πr ₃ Therefore, by determining the pressure gradient (ΔP/l) and the flow rate per unit time (Q), the steady flow viscosity η can be determined.

However, in such a conventional method, ΔP/l cannot be directly determined, so it is indirectly determined from the pressure P applied to the lower surface of the plunger 2 = external force F/πR ² . Moreover, this pressure P is caused by various complicated components such as pressure loss ΔP in the capillary die 1, pressure loss in the cylinder 3 and introduction part 4, and residual pressure at the outlet of the capillary die 1 (hereinafter referred to as "outlet pressure"). Therefore, several capillary dies with different lengths are prepared, and for one Q value (∝γ〓), (1) sample filling, (2)
Adopts a method (so-called pipe length correction) that calculates the pressure gradient (dP/dl) from several plots of (P, l) obtained by repeating sample temperature adjustment, (3) plunger lowering, and (4) die exchange several times. are doing. Therefore, it takes several hours to measure η at several different points of γ for one capillary die.

In addition, since the pressure P applied to the lower surface of the plunger 2 is composed of various components as described above, the pressure P applied to the lower surface of the plunger 2 is
It is possible to separate and take out the outlet pressure by correcting the pipe length, but it is also impossible to separate and take out the pressure loss in the introduction section 4, which is also important for determining elastic properties. Therefore, the elastic properties of the introduction section 4 cannot be determined.

In view of the above circumstances, it is an object of the present invention to be able to measure the flow characteristics of fluid materials such as rubber and resins over a wide range of shear strain rates in an extremely short time and with high precision, and to simultaneously measure elasticity and viscosity. An object of the present invention is to provide a slit die rheometer that can be used to differentiate and obtain information.

d Means for solving the problem The above problem is caused by a slit-die rheometer that measures the flow characteristics of a sample filled in a cylinder by pressing it with a plunger and pushing it out of the slit die. A pressure sensor installed in the slit die, one or more pressure sensors installed along the flow direction of the sample in the slit die, and pressure signals obtained from each of the above pressure sensors are used to determine the pressure time fluctuation rate and pressure inside the die. It is equipped with a means for determining the gradient, pressure loss at the die inlet, and die outlet pressure, and a shear strain rate control means for controlling the extrusion speed of the plunger based on the pressure signal, so that the time fluctuation of the pressure inside the die is less than a predetermined value. The problem was solved by a slit-die rheometer, which is characterized by measuring the flow characteristics of a sample when it reaches .

e Action Obtain a displacement signal of the plunger using a displacement gauge, detect the difference between the displacement signal and the sawtooth signal generated by the functional generator, and lower the plunger at a constant speed based on this difference signal. let

By lowering the plunger at a constant rate, the apparent shear strain rate γ〓 _a is precisely controlled.

The pressure of the sample at this γ〓 _a is detected by each pressure sensor, and the pressure signal is sent to a microcomputer to calculate the time variation rate of the pressure.

In a viscoelastic body such as rubber, the pressure detected by the pressure sensor may exhibit a high value when the plunger starts to descend, but generally converges to a constant value over time.

Pressure fluctuation range or relative fluctuation [(dP/dt/
When [P, t: time] becomes below a certain value, the pressure gradient inside the slit die, the outlet pressure of the slit die, and the pressure loss at the die inlet are calculated based on the above pressure signal, and the pressure gradient and the pressure loss per unit time flowing through the slit die are calculated. The steady flow viscosity η at a specific shear strain rate is calculated from the flow rate Q of .

f Embodiment FIG. 2 is a conceptual diagram showing an embodiment of the slit die rheometer according to the present invention, and as shown in the figure,
The slit die rheometer according to the present invention is a slit die rheometer that measures the flow characteristics of a sample filled in a cylinder 11 by pressing the sample with a plunger 12 and extruding the sample from a slit die 13. One pressure sensor 14 provided in the section 13a and one pressure sensor provided in the slit die 13 along the flow direction of the sample.
The pressure loss at the die inlet, the pressure gradient inside the die 13, and the pressure signal obtained by the pressure sensors 15 and each of the above-mentioned pressure sensors are used to determine the pressure loss at the die entrance, the pressure gradient inside the die 13,
3, and a shear strain rate control means 17 for controlling the extrusion rate of the plunger based on the pressure signal.

Both the cylinder 11 and the slit die 13 are surrounded by a constant temperature bath 18.

The pressure sensor 14 is provided so that its tip surface coincides with the inner circumferential surface of the cylinder bottom 11a. Note that the tip surface of the sensor 14 is located at the bottom of the cylinder 1.
It may be provided between 1a and the die 13, that is, so as to coincide with the inner circumferential surface of the die introduction part 13a.

As shown in FIGS. 2 and 3, two pressure sensors 15 are provided on the same straight line along the flow direction of the sample at the center of the wide wall surface of the die 13.
The tip surface of the die 13 is aligned with the inner wall surface of the die 13.
Note that arrow A in FIG. 3 indicates the flow direction of the sample.

The means 16 for determining the pressure loss at the die inlet, the pressure gradient within the die, and the die outlet pressure is comprised of a pressure amplifier 19 and a microcomputer 20, and the shear strain rate control means 17 is comprised of a pressure amplifier 19 and a microcomputer 20. It consists of a computer 20, a functional generator 22, a displacement gauge 23, a displacement gauge amplifier 24, a differential servo amplifier 25, a hydraulic servo pump 26, and a hydraulic cylinder 27. 21 is an input/output device.

Next, the effect will be explained. First, the displacement signal of the plunger 12 is obtained by the displacement gauge 23 and the displacement gauge amplifier 24, and the difference between the displacement signal and the sawtooth signal generated by the functional generator 22 is detected and amplified by the differential servo amplifier 25. Based on this difference signal, the hydraulic servo pump 26
is driven to lower the plunger 12 at a constant speed via the hydraulic cylinder 27.

By lowering the plunger 12 at a constant rate, the apparent shear strain rate γ〓 _a is precisely controlled.

The pressure of the sample at this γ〓 _a is the pressure of each pressure sensor 1
4 and 15, and the pressure signal is amplified by a pressure amplifier 19 and sent to a microcomputer 20. The pressures detected by the pressure sensors 14 and 15 may exhibit a high value when the plunger 12 begins to descend, but generally converge to a constant value over time. In the microcomputer 20 of this embodiment, each pressure sensor 1
When the pressure fluctuation width or relative fluctuation [(dP/dt)/P, t: time] detected by 4 and 15 becomes below a certain value, the pressure gradient in the slit die 13 is changed based on the pressure signal. At the same time, the outlet pressure of the slit die 13 and the pressure loss at the die inlet (between the cylinder bottom 11a provided with the pressure sensor 14 or the die introduction part 13a and the slit die 13) are calculated, and at the same time, the pressure gradient and the unit flowing through the slit die 13 are calculated. The steady flow viscosity η at a specific shear strain rate is calculated from the flow rate Q per hour (determined from the descending speed of the plunger 12), and these are printed by the input/output device 21.

In this way, when measurement at a specific shear strain rate is completed (each of the pressure sensors 14, 15
When the fluctuation ratio of the pressure signal becomes less than a certain value, it is determined that the measurement has ended. ), the microcomputer 20 instructs the functional generator 22 to issue a signal corresponding to the next shear strain rate.

By repeating the same measurement operation, the flow characteristics under different shear strain rates can be measured.

The pressure gradient is obtained from the pressure signals of two pressure sensors 15 provided in the slit die, the outlet pressure of the slit die is obtained by estimation calculation from the pressure gradient, and the pressure loss at the die inlet is calculated from the cylinder bottom 11a. Alternatively, it can be determined from the difference between the pressure measured by the pressure sensor 14 provided at the die introduction part 13a and the pressure at the upper end of the slit die calculated by estimation from the pressure gradient.

When the number of pressure sensors 15 provided in the slit die is one, the above pressure gradient is
It is determined from the pressure signal and the distance from the sensor to the slit die exit. This approximates the slit die outlet pressure to zero. In addition, in this case, the pressure loss at the die inlet is determined by the pressure caused by the pressure sensor 14 provided at the cylinder bottom 11a or the die introduction section 13a and the pressure gradient, as in the case where there are two pressure sensors provided on the slit die. It can be determined from the difference between the pressure at the upper end of the slit die and the pressure at the upper end of the slit die calculated by estimation. This is just a simple method.

The above-mentioned shear strain rate can be arbitrarily changed by changing the horsepower of the drive mechanisms 26 and 27 for lowering the plunger 12, the inner diameter of the cylinder 11, or the thickness of the slit. When placing importance on a region, a mechanical drive mechanism such as a worm gear is used to control the plunger's descending speed, and when a relatively high strain rate region is important, a high-speed fluid pressure drive mechanism such as a hydraulic pump is used to control the plunger's descending speed. Preferably controlled.

g Effect (1) Using a slit die 13, a plurality of pressure sensors 15 are installed along the flow direction on a wide wall surface of the die.
A pressure sensor 14 is also provided at the cylinder bottom 11a or the die introduction section 13a. Therefore, the pressure gradient in the flow direction can be directly detected without troublesome pipe length correction, and at the same time, the die outlet pressure and the pressure loss at the die inlet can also be determined. Therefore, measurements can be carried out quickly and accurately, and furthermore, elastic properties such as die outlet pressure and pressure loss at the die inlet can be measured separately as well as the pressure gradient that indicates viscosity (steady flow viscosity). .

(2) When there is only one pressure sensor 15, by approximating the slit die outlet pressure to 0, the pressure gradient in the flow direction can be directly detected without making troublesome pipe length corrections, and at the same time, the pressure gradient at the die inlet can be detected directly. Pressure loss can also be determined.

In addition, one pressure sensor is installed on the slit die.
By making it into a book, the manufacturing cost can be reduced and it can be used as a general-purpose machine.

(3) In conventional flow testers, there were strict restrictions on the ratio and shape of the plunger diameter and die diameter due to strict requirements for flow stability in the plunger and die parts. By adopting the method of directly determining the pressure, the only necessary condition is the stability of the flow in the slit die section, so the plunger diameter can be made significantly larger (larger cylinder capacity). Therefore, by filling the sample and adjusting the sample temperature once, it is possible to measure many quantities related to steady flow viscosity and elasticity at different shear strain rates, and from this point of view as well, the measurement time can be shortened.

(4) Equipped with a shear strain rate control mechanism that changes the plunger descending speed based on pressure signals from each pressure sensor, so it can cover a wide range of shear strain rates and change the speed quickly and accurately. can.

Figure 4 shows the pressure gradient of SBR1500 compound rubber measured by this slit die rheometer at 110℃ and γ = 10 sec ^-1 , the pressure P _S at the bottom of the cylinder, the pressure loss P L at the die inlet, and the pressure loss P _L at the top of the die. Figure 5 shows the extrapolated pressure P _I and die outlet pressure P _O.
FIG. 3 is a diagram showing a shear strain rate dependence curve of steady flow viscosity at 110° C. of SBR1500 compounded rubber. These figures show that the present slit die rheometer can accurately measure elasticity and viscosity in a wide range of shear strain rates (γ).
Furthermore, the measurement of η at the six points in FIG. 5 could be carried out in an extremely short time of 20 minutes in total (3 minutes for sample filling, 10 minutes for temperature adjustment, 5 minutes for lowering the plunger, and 2 minutes for cleaning).

As explained above, the slit die rheometer according to the present invention can be used in a wide range of shear strain rates (10 ⁰ to ^{10 5} sec ^-1 ) by one-time sample filling and sample temperature adjustment and without changing the die. Viscosity and elasticity can be separated and measured simultaneously in a short time and with high precision.

Moreover, according to the present slit die rheometer, it is possible to evaluate the shape and observe the surface texture of extrudates over a wide range of shear strain rates.

Note that the present invention can be modified in various ways without departing from the gist thereof, and is not limited to what is shown in the drawings.
In particular, the plunger lowering drive mechanism, pressure gradient, pressure loss, means for determining outlet pressure, shear strain rate control means, etc. can be modified in various ways according to known techniques as necessary.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing a conventional capillary rheometer, FIG. 2 is a conceptual diagram showing an embodiment of a slit die rheometer according to the present invention, and FIG. 3 is a perspective conceptual diagram of the slit die shown in FIG. FIG. 4 and FIG. 5 are diagrams showing measurement results using the present slit die rheometer. 11... Cylinder, 11a... Cylinder bottom,
12...Plunger, 13...Slit die, 1
3a... Slit die introduction section, 14, 15... Pressure sensor, 16... Means for determining the pressure gradient within the die, pressure loss at the die inlet and die exit pressure, 17... Shear strain rate control means.

Claims (1)

[Claims] 1. In a slit die rheometer that measures the flow characteristics of a sample filled in a cylinder by pressing the sample with a plunger and pushing it out of the slit die, a pressure sensor provided at the bottom of the cylinder or at the die introduction part; , one or more pressure sensors installed along the flow direction of the sample in the slit die, and pressure signals obtained from each of the above pressure sensors to determine the time fluctuation rate of the pressure inside the die, the pressure gradient, and the pressure gradient at the die inlet. means for determining the pressure loss and die exit pressure, and a shear strain rate control means for controlling the extrusion speed of the plunger based on the pressure signal, and when the time fluctuation rate of the pressure in the die becomes less than a predetermined value. A slit die rheometer that measures the flow characteristics of a sample. 2. The slit die rheometer according to claim 1, wherein the cylinder has a volume capable of being filled with a sample for multiple measurements. 3. A slit die rheometer according to claim 1, wherein said shear strain rate control means comprises a combination of a mechanical drive mechanism and/or a hydraulic drive mechanism.