JP3893130B2 - Rubber material stress measuring device - Google Patents

Description

  The present invention relates to an apparatus for measuring a stress of a rubber material, which can easily and quickly specify a blow point of a rubber material with a small sample volume without using a special dedicated device.

として表わされる反応状態を示す尺度であり、加硫温度(T) と加硫時間(t) との関数となる。 Here, the blow point means that when a rubber material is vulcanized under pressure, bubbles generated during the vulcanization process exist inside the rubber material when it is brought into a non-pressurized state to complete the vulcanization. This means the minimum degree of vulcanization necessary to prevent the failure, that is, the critical degree of vulcanization.
The degree of vulcanization is experimentally determined according to the Allenium equation.

As a function of vulcanization temperature (T) and vulcanization time (t).

When vulcanizing a rubber material under pressure, especially when the pressure vulcanization is completed without the central portion of the rubber material reaching a certain degree of vulcanization, the central portion of the rubber material after vulcanization is foamed. Usually, the degree of vulcanization is determined in order to completely prevent the presence of such bubbles in the rubber material.
Therefore, it is extremely important to specify the blow point of the rubber material in order to determine the appropriate degree of vulcanization for producing a product having a sufficiently short vulcanization time and no bubbles.

  By the way, this blow point differs greatly depending on the composition, kneading method, kneading conditions, etc. of the rubber compound. Therefore, when performing quality control of rubber materials, development of rubber composition, etc., the blow point identification work is very frequently performed. In addition, it is necessary to specify the blow point easily and quickly with high accuracy.

Therefore, the applicant previously proposed a blow point measuring device as Japanese Patent Application Laid-Open No. 62-11163 (Japanese Patent Publication No. 7-18870).
The depth varies from one end to the other, and a plurality of penetrating holes are located in the cavity in which the sample rubber is satisfactorily accommodated and spaced apart in the direction in which the depth of the cavity changes. A vulcanizing mold having holes, a heating source for heating the vulcanizing mold from the depth direction of the cavity, and a plurality of temperatures for measuring the temperature of each part of the sample rubber in and out of the through hole It is possible to calculate the vulcanization degree distribution inside the sample rubber in the direction in which the cavity depth changes in order to specify the blow point of the sample rubber.

The blow point using such a device is identified by vulcanizing the sample rubber in the cavity and measuring the internal temperature of the sample rubber during vulcanization over time at a plurality of locations. When the calculated degree of vulcanization reaches a predetermined state, the vulcanization is terminated and the sample rubber is taken out of the cavity. In addition to cutting in the direction in which the bubbles change, the presence of bubbles inside the sample is visually observed in the direction in which the thickness changes, and the portion where the vulcanization has progressed to the extent that no bubbles remain is added. This is done by determining the degree of sulfur.
JP-A-62-11163

  For this reason, in such a prior art, there is an equipment problem that a dedicated device only for obtaining the blow point is indispensable, and there is also the presence or absence of bubbles in the sample. Since the rubber is inspected by cutting and visual observation after taking out from the cavity, the time required to specify the blow point is lengthened, the accuracy of specifying the blow point is lowered, and the thickness of the sample rubber is Since the difference between the maximum thickness and the minimum thickness is changed within a predetermined range by changing gradually or stepwise from one end to the other end, the sample rubber needs to be set within the predetermined range. There was also the inconvenience that the volume of inevitably increased.

  The present invention has been made as a result of studying as a subject to solve such problems of the prior art, and the object of the present invention is to use existing materials such as a Mooney viscosity measuring device and a rheometer for rubber materials. The present invention provides a stress measuring device for a rubber material, which can be applied to various stress measuring devices to accurately specify a blow point in a short time, and which can sufficiently reduce the volume of a sample rubber. .

In the present invention, when a sample rubber sealed under pressure in a cavity having a constant volume is vulcanized, the compression stress of the sample rubber changes with time as the vulcanization of the sample rubber proceeds. When the stress curve reaches a specific state, the bubbles in the sample rubber have disappeared, etc., based on various new experiments,
A sample rubber sealed under pressure in a fixed volume cavity defined by a pair of dies is vulcanized, and the compression stress curve of the sample rubber during vulcanization is measured over time. It is used to specify the blow point by calculating the degree of vulcanization when it reaches the maximum value following the first minimum value based on the above-mentioned Arrhenius equation, measured vulcanization temperature and vulcanization time. An apparatus for measuring stress of a rubber material according to the present invention defines a cavity having a constant volume for enclosing sample rubber under pressure, and includes a pair of dies for heating the sample rubber in the cavity. , in relation to one of the die, it is provided with a respective compressive stress measuring means and sample rubber temperature measuring means of the sample rubber.
Here, preferably, the detection unit of the compressive stress measurement unit is configured by a pressure sensor that contributes to the cavity definition of one of the dies.

As apparent from the above description, according to the present invention, it is possible to specify a blow point using an existing stress measuring device without providing an independent blow point specifying device, and it is possible to specify a rubber material. The blow point can be accurately identified in a short time with a small sample amount.
Therefore, when a rheometer is used in the apparatus according to the present invention, it is possible to specify a blow point in combination with measurement of the degree of vulcanization, and it is possible to automate various tests. The accuracy can be improved to the same level as the measurement accuracy of the degree of vulcanization with a rheometer.

  When sample rubber sealed under pressure in a fixed volume cavity defined by a pair of dies is vulcanized by heating each die, compounding in the sample rubber is performed at the beginning of the vulcanization. Due to the gasification of the agent and moisture, and the gas pressure of the generated gas gradually increases with the temperature rise, a foaming phenomenon appears inside the sample rubber when the sample is brought into a non-pressurized state. . By the way, when the vulcanization further progresses and the crosslinking density increases, these bubbles are gradually suppressed by the crosslinking reaction, and finally shrink or disappear so that they cannot be visually detected.

  As described above, the generation, expansion, disappearance, etc. of gas in the sample rubber are closely related to the progress of the crosslinking reaction by vulcanization. If it can be detected quantitatively and accurately without direct modification to the rubber, the vulcanized sample rubber of each degree of vulcanization will be cut, and for each of them the internal foam The blow point can be quickly identified with high accuracy without visually observing the presence or absence.

  Therefore, the inventor must perform various experiments to measure the change in compressive stress of the sample rubber in a constant volume cavity for each of the conditions such as gas generation, expansion, and disappearance in the sample rubber. Quantitative detection is possible, and the relative relationship between the change in compression stress over time and the degree of vulcanization is determined, and the presence of bubbles in the vulcanized sample rubber as the compression stress changes In the compressive stress curve shown by curve A in FIG. 1, the foam in the vulcanized sample rubber has a maximum value that appears after the first minimum value after the first minimum value. It was confirmed that it disappeared substantially when it changed.

The fact that there is no phenomenological problem is that the presence of internal bubbles in each of the sample rubber vulcanized to just before the maximum value and the sample rubber vulcanized to just after the maximum value, and It was verified by careful observation.
In other words, in the sample rubber vulcanized until just before the maximum value, as a result of detailed observation, a small amount of foam was observed, whereas in the sample rubber vulcanized up to the maximum value and just after that, The presence of bubbles was not observed at all.
In FIG. 1, curve A shows the change in compression stress of the sample rubber in the cavity with respect to time, curve B shows the change in the degree of vulcanization of the sample rubber, and curve C shows the torsional vibration deformation of the sample rubber. The transmission torque with respect to is shown, respectively.

  Based on the above, here, for example, sample rubber is sealed under pressure in a fixed volume cavity defined by a pair of upper and lower dies, and the sample rubber is paired with each pair of dies. While the vulcanization is performed based on the heating, the compression stress of the sample rubber during vulcanization is measured over time.

  During this vulcanization, measurement of the vulcanization temperature (T) and vulcanization time (t) of the central part of the sample rubber is also performed so that the vulcanization degree based on the above [Equation 1] can also be calculated over time. Also do it.

  Here, the compressive stress tends to change as shown by curve A in FIG. 1, and the degree of vulcanization also tends to change as shown by curve B in FIG. According to the inventor's new knowledge described above, when the compressive stress curve reaches the point D in the figure, which is the maximum value that appears after the first minimum value, the degree of vulcanization is reduced. In this case, the foam in the sample rubber is substantially lost, so here, the degree of vulcanization when the compression stress is detected to reach the maximum value is calculated based on the above [Equation 1]. The degree of vulcanization is taken as the blow point.

  In this way, when specifying the blow point, by providing a sample rubber compressive stress measuring means in an existing stress measuring device having a die or other cavity partitioning means, for example, a Mooney viscosity measuring device, a rheometer, Without the need to install an independent blow point identification device, the blow point can be obtained, and the sample rubber after vulcanization is cut and the presence of bubbles in the sample rubber is visually observed. The blow point can be accurately identified in a short time as no need at all.

  Moreover, since the blow point can be specified by vulcanizing a small weight sample rubber of uniform thickness, from one end to change the vulcanization status gradually or stepwise in one sample rubber. Compared with the prior art that changes the thickness of the sample rubber toward the other end, the amount of rubber used can be greatly reduced.

FIG. 2 is a longitudinal sectional view of an essential part showing an embodiment of a stress measuring apparatus for a rubber material according to the present invention, which can be used for specifying a blow point as described above. Middle 1 indicates the upper die and 2 indicates the lower die.
Here, the upper die 1 includes a ring-shaped fixing member 4 attached to the die holder 3 and an upper die body 5 disposed at the center of the ring-shaped fixing member 4 via a sealant as main components. The die body 5 can be driven to rotate in one direction when the device is also used as a Mooney viscosity measuring device, and can be driven to rotate in a reciprocating direction when used as a rheometer.

  The lower die 2 includes a ring-shaped fixing member 7 attached to the die holder 6 and a lower die main body 8 disposed at the center of the ring-shaped fixing member 7 via a sealing material as main components. Here, the lower die body 8 also functions as a stress detector when the device is used as a Mooney viscosity measuring device or a rheometer.

  As shown in the figure, a shaft connected to the lower die body 8 via a heat insulating material 10 under a state in which the die holder 6 is firmly fixed to the rigid frame 9 in order to exert the function applied to the lower die body 8. One end portion of the torque arm 12 is fastened and fixed to the lower end portion of the member 11, and the other end portion of the torque arm 12 extending horizontally is connected to the die holder 6 by the bracket 13 and is positioned in the horizontal plane. A support plate 14 that is deformed but not deformed with respect to torsional torque is connected via another bracket 15, and a torque sensor 16 is disposed in the middle of the torque arm 12.

  According to this, for example, the heating state of the upper and lower dies 1 and 2 with respect to the sample rubber 18 enclosed under pressure in the cavity 17 having a constant volume defined between the upper and lower dies 1 and 2. Then, when rotation or reciprocating torque is applied by the upper die body 5, torque corresponding to the physical properties of the sample rubber 18 is transmitted to the torque arm 12 through the lower die body 8 and the shaft member 11, where This is detected by the torque sensor 16.

  In this case, even if the lower die body 8, and thus the shaft member 11, may be displaced in the vertical direction, the displacement is absorbed by the deformation of the support plate 14. Does not affect detection.

  Under such a configuration of the upper and lower dies 1 and 2, here, the sample rubber 18 sealed under pressure in the cavity 17 is heated by heaters 19 and 20 embedded in the upper and lower dies 1 and 2, respectively. In order to measure the change in compressive stress of the sample rubber 18 when vulcanized, the tip of one die body, in the figure, the lower die body 8 is placed in a flat surface that contributes to the definition of the cavity 17. A pressure sensor 21 having a surface is disposed in the lower die body 8, and this pressure sensor 21 is connected to the rigid frame 9 and is rigidly supported by a backup rod 22 penetrating the shaft member 11 and the heat insulating material 10. To do.

  The pressure sensor 21 here is, for example, a cylinder having an inner diameter of 3 to 6 mm and a depth of about 10 mm filled with mercury and the opening of the cylinder is sealed with a SUS material sheet having a thickness of about 0.1 mm. According to such a pressure sensor 21, the mercury pressure changes directly in response to the internal pressure of the sample rubber 18 in the cavity under the rigid support of the backup rod 22. Mercury pressure is converted to electrical pressure by acting on the load cell attached under the mercury reservoir and electrically converted, thereby obtaining the sample rubber internal pressure, and hence its compressive stress, with high accuracy. be able to.

  Therefore, by measuring the compressive stress of the sample rubber 18 during vulcanization with the pressure sensor 21, the compressive stress curve as shown by the curve A in FIG. 1 can be obtained sufficiently accurately. By calculating the degree of vulcanization when the stress curve reaches the maximum value D, the blow point can be specified easily and quickly with high accuracy.

  Although not clearly shown in the figure, either one of the upper and lower dies 1 and 2 is provided with a temperature sensor for detecting the vulcanization temperature (T), which is essential for calculating the vulcanization degree, preferably Of course, a temperature sensor for detecting the internal temperature of the sample rubber 18 is provided.

  By the way, a diaphragm can also be used as a pressure sensor here, and it is also possible to obtain | require the compressive stress of sample rubber by detecting the deformation force of the diaphragm with a load cell.

  FIG. 2 is a view showing another embodiment of the measuring apparatus, which supports the shaft member 11 by radial bearings 23 and 24 and has a load meter or a strain gauge at its lower end via a thrust bearing 25. The weight sensor 26 that can be used is disposed. Here, the lower end of the weight sensor 26 is rigidly supported by the rigid frame 9.

  According to such a configuration, the weight detected by the weight sensor 26 changes according to the internal pressure of the sample rubber in the cavity 17 and, consequently, the compressive stress of the sample rubber 18. Thus, in this case as well, by calculating the degree of vulcanization when the compressive stress curve reaches the maximum value D, the blow point can be determined quickly and sufficiently accurately. Can be identified.

It is a graph which shows the change with respect to time of a compressive stress, a vulcanization degree, and transmission torque. It is a principal part general line longitudinal cross-sectional view which shows one Embodiment of invention apparatus. It is the same longitudinal cross-sectional view as FIG. 2 which shows other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper die 2 Lower die 3,6 Die holder 4,7 Ring-shaped fixing member 5 Upper die main body 8 Lower die main body 9 Rigid frame
10 Insulation
11 Shaft member
12 Torque arm
16 Torque sensor
17 cavity
18 Sample rubber
19, 20 Heater
21 Pressure sensor
22 Backup rod
23, 24 Radial bearing
25 Thrust bearing
26 Weight sensor

Claims (2)

  A sample rubber compressing stress measurement means provided in association with one of a pair of dies that define a fixed volume cavity that encloses the sample rubber under pressure and heats the sample rubber in the cavity. And a rubber material stress measuring device comprising a sample rubber temperature measuring means. The rubber material stress measuring device according to claim 1, wherein the detecting portion of the compressive stress measuring means is constituted by a pressure sensor that contributes to defining a cavity of one of the dies.

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