JP7807632B2 - Rubber Mixing Method - Google Patents

Description

The present invention relates to a rubber mixing method using a roll mixer and a circulating conveyor, and more specifically, to a rubber mixing method that makes it possible to reliably determine the mixing state of unvulcanized rubber and additives.

When manufacturing rubber products such as tires and rubber hoses, unvulcanized rubber, which is made by kneading raw rubber with non-vulcanization compounding agents such as carbon black and oil, is then further kneaded with vulcanization compounding agents such as sulfur.

In this type of kneading process, a rubber mixing device is used that includes a roll kneader with a pair of rolls that kneads unvulcanized rubber together with additives, and a conveyor that transports the rubber sheet that passes through the gap between the pair of rolls and circulates it over the pair of rolls (see, for example, Patent Document 1).

Using a rubber mixing device that uses an open-type roll mixer and a circulating conveyor, unvulcanized rubber can be mixed with vulcanization-related compounding ingredients while preventing excessive temperature rise. Furthermore, unvulcanized rubber scraps (returned materials) can also be added to the roll mixer and kneaded into the mix during mixing.

However, when unvulcanized rubber is mixed with additives using a rubber mixing device such as the one described above, it is necessary to evenly distribute additives such as vulcanization compounding agents and unvulcanized rubber scraps throughout the rubber sheet, but the mixing process may end with these additives unevenly distributed throughout the rubber sheet. Furthermore, if additives such as vulcanization compounding agents and unvulcanized rubber scraps are unevenly distributed throughout the rubber sheet, this could reduce the quality of rubber products made from it.

Japanese Patent Application Laid-Open No. 2009-35007

The object of the present invention is to provide a rubber mixing method that makes it possible to reliably determine the mixing state of unvulcanized rubber and additives.

In order to achieve the above object, the rubber mixing method of the present invention comprises kneading unvulcanized rubber together with additives using a roll kneader equipped with a pair of rolls, transporting a rubber sheet that has passed through a gap between the pair of rolls by a conveyor and circulating it over the pair of rolls, measuring the temperature of the rubber sheet transported by the conveyor along the width direction of the rubber sheet, and determining whether the additives have been added to the unvulcanized rubber and the mixed state of the unvulcanized rubber and the additives based on the temperature distribution in the width direction of the rubber sheet,
The temperature distribution in the width direction of the rubber sheet is used as reference information, and when a part in the width direction of the rubber sheet has a temperature lower than a predetermined threshold, it is determined that the additive has been added to the unvulcanized rubber, and if there is then a part in the width direction of the rubber sheet where the temperature is lower than the threshold, it is determined that the unvulcanized rubber and the additive are not sufficiently mixed .

In this invention, unvulcanized rubber and additives are mixed in a roll mixer equipped with a pair of rolls, and the rubber sheet that passes through the gap between the pair of rolls is transported by a conveyor and circulated over the pair of rolls. In this rubber mixing method, the temperature of the rubber sheet being transported by the conveyor is measured across the width of the rubber sheet. Additives such as vulcanization-related compounding agents and unvulcanized rubber scraps (returned materials) are added at a relatively low temperature compared to the unvulcanized rubber that serves as the matrix, and this influence is reflected in the temperature distribution across the width of the rubber sheet. Therefore, it is possible to determine whether the additives have been added to the unvulcanized rubber and the mixing state of the unvulcanized rubber and additives based on the temperature distribution across the width of the rubber sheet. In particular, because the temperature distribution across the width of the rubber sheet is used as reference information, the mixing state of the unvulcanized rubber and additives can be reliably determined even in cases where it is difficult to determine visually.

In the present invention, when at least a portion in the width direction of the rubber sheet has a temperature lower than a preset threshold, it is determined that an additive has been added to the unvulcanized rubber. If thereafter, at least a portion in the width direction of the rubber sheet has a temperature lower than the threshold, it is determined that the unvulcanized rubber and the additive are not sufficiently mixed. By comparing with such a threshold, the mixing state can be determined more accurately.

In addition to determining the mixing state of the unvulcanized rubber and additives, it is preferable to adjust the mixing conditions of the unvulcanized rubber and additives based on the results of the mixing state determination. This improves the mixing state of the unvulcanized rubber and additives, and ultimately improves the quality of the rubber product.

Furthermore, when determining the mixed state of unvulcanized rubber and additives, it is preferable to take into account the timing of adding the unvulcanized rubber and additives and the operating conditions of the roll mixer and conveyor. The timing of adding the unvulcanized rubber and additives and the operating conditions of the roll mixer and conveyor have a significant impact on the mixed state, so by reflecting these factors in determining the mixed state, the mixed state can be determined more accurately.

FIG. 1 is a side view showing an example of a rubber mixing device used in the present invention. FIG. 2 is a plan view showing a rubber sheet being transported by a conveyor in the rubber mixing device of FIG. 1 . 1 is a graph showing a temperature distribution in the width direction of a rubber sheet.

The configuration of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1 shows an example of a rubber mixing device used in the present invention, and Figure 2 shows a rubber sheet being transported by a conveyor in the rubber mixing device of Figure 1.

As shown in FIG. 1, this rubber mixing device includes a roll mixer 1 equipped with a pair of rolls 2, 2 for mixing unvulcanized rubber R with additives X, and conveyors 3, 4 for transporting a rubber sheet S that has passed through the gap between the pair of rolls 2, 2 and circulating it over the pair of rolls 2, 2. The pair of rolls 2, 2 are arranged with their rotation axes parallel to each other along the horizontal direction, and are driven to rotate in opposite directions under the control of a control unit 5. An actuator 6 that displaces the position of the rotation axis is connected to one of the pair of rolls 2, 2, and the gap dimension between the pair of rolls 2, 2 is adjusted by driving this actuator 6. The drive of the actuator 6 is controlled by the control unit 5. The unvulcanized rubber R fed onto the pair of rolls 2, 2 passes through the gap between the rolls 2, 2 and is discharged downward as a rubber sheet S.

Conveyor 3 is configured to transport the rubber sheet S horizontally after it has passed through the gap between rolls 2, 2, and then guide the rubber sheet S upward. On the other hand, conveyor 4 is configured to transport the rubber sheet S handed over from conveyor 3 upward, and then transport the rubber sheet S horizontally to the area directly above the pair of rolls 2, 2. Therefore, the rubber sheet S that has passed through the gap between the pair of rolls 2, 2 is returned to the bank above the pair of rolls 2, 2 via conveyors 3, 4 and is repeatedly kneaded. The driving of conveyors 3, 4 is controlled by control unit 5.

A non-contact temperature measuring device 11 is disposed along the transport path of the rubber sheet S. The temperature measuring device 11 measures the temperature of the rubber sheet S transported by the conveyor 4 along the width direction of the rubber sheet S. That is, as shown in FIG. 2, the temperature of the rubber sheet S is continuously sampled along a measurement line L spanning at least the entire width of the rubber sheet S. Such a temperature measuring device 11 can be, for example, an infrared thermograph. The infrared thermograph continuously captures temperature information in the width direction of the rubber sheet R3 as an image or video as the rubber sheet S is transported. Reference information is extracted from the temperature information thus captured. Of course, other devices can also be used as the temperature measuring device 11. The measurement results of the temperature measuring device 11 are input to the determination unit 12. The determination unit 12 determines the mixing state of the unvulcanized rubber R and the additive X based on the temperature distribution in the width direction of the rubber sheet S. The determination result of the determination unit 12 is input to the control unit 5.

Next, we will explain the rubber mixing method using the above-mentioned device. First, as shown in Figure 1, unvulcanized rubber R is placed on a pair of rolls 2, 2 of a roll mixer 1. A rubber sheet S passes through the gap between the pair of rolls 2, 2 and is transported by conveyors 3, 4 to circulate around the pair of rolls 2, 2. The unvulcanized rubber R is unvulcanized rubber obtained by kneading raw rubber with non-vulcanizing compounding agents such as carbon black and oil. Next, additive X is placed on the pair of rolls 2, 2 of the roll mixer 1 and kneaded into the unvulcanized rubber R. Examples of additive X include vulcanization compounding agents such as sulfur, as well as unvulcanized rubber scraps (returned materials). Such additive X circulates with the rubber sheet S and is dispersed throughout the rubber sheet S by being repeatedly kneaded by the roll mixer 1. It is also possible to simultaneously place unvulcanized rubber R and additive X on the pair of rolls 2, 2.

In the rubber mixing process described above, the temperature of the rubber sheet S transported by the conveyors 3 and 4 is measured along the width of the rubber sheet S by the temperature measuring device 11. The determination unit 12 determines whether additive X has been added to the unvulcanized rubber R and the mixing state of the unvulcanized rubber R and additive X based on the temperature distribution across the width of the rubber sheet S. Because additives X, such as vulcanization compounding agents and unvulcanized rubber scraps (returned materials), are added at a relatively low temperature compared to the matrix unvulcanized rubber R, the effect of the addition of additive X is apparent in the temperature distribution. Therefore, the addition of additive X can be determined based on the temperature distribution across the width of the rubber sheet S, and if there is no temperature drop, it can be determined that additive X has not been added. As mixing progresses and additive X is mixed with the unvulcanized rubber R, the temperature distribution across the width of the rubber sheet S becomes uniform. However, if the mixing state is insufficient, this will be apparent in the temperature distribution across the width of the rubber sheet S. Therefore, the mixing state of the unvulcanized rubber R and additive X can be determined based on the temperature distribution across the width of the rubber sheet S. In particular, by using the temperature distribution across the width of the rubber sheet S as reference information, the mixing state of the unvulcanized rubber R and the additive X can be reliably determined even in cases where it is difficult to determine visually.

During the rubber mixing process, if at least a portion of the rubber sheet S in the width direction has a temperature lower than a preset threshold, it is determined that additive X has been added to the unvulcanized rubber R. If thereafter, at least a portion of the rubber sheet S in the width direction has a temperature lower than the threshold, it is determined that the unvulcanized rubber R and additive X are insufficiently mixed. More specifically, the temperature distribution across the width of the rubber sheet S may be as shown in Figure 3. In Figure 3, the vertical axis represents temperature (°C) and the horizontal axis represents the widthwise position (mm) of the conveyor 4. Because the width of the rubber sheet S is narrower than the width of the conveyor 4, for example, the central side of the widthwise direction of the conveyor 4 is designated as the judgment region M, and the temperature distribution in this judgment region M is used as an index. The judgment region M can be determined based on mixing specifications such as the amount of rubber in the unvulcanized rubber R, the guide width and roll gap of the roll mixer 1, and conveyor settings. The width of the judgment region M can be set arbitrarily, for example, within a range of 30% to 90% of the total width of the conveyor 4. If the judgment area M is too wide, noise will increase during judgment, and conversely, if it is too narrow, judgment accuracy will decrease.

As shown in FIG. 2, when additive X is unevenly distributed in at least a portion of the rubber sheet S, causing a temperature lower than a preset threshold T in at least a portion of the width direction of the rubber sheet S in the judgment area M, it is determined that additive X has been added to the unvulcanized rubber R. If a portion with a temperature lower than the threshold T remains even after mixing has progressed, it is determined that the mixing state is insufficient. The threshold T can be arbitrarily selected using the local temperature of the rubber sheet S when clumps of additive X are formed due to insufficient mixing as an indicator. By comparing the temperature distribution in the width direction of the rubber sheet S with the threshold T in this way, the mixing state of the unvulcanized rubber R and additive X can be more accurately determined. The threshold T is not particularly limited, but can be set, for example, to 80% or less of the average temperature of the rubber sheet S in the judgment area M.

In the rubber mixing process described above, in addition to determining the mixing state of the unvulcanized rubber R and additive X, it is also advisable to adjust the mixing conditions for the unvulcanized rubber R and additive X based on the results of the mixed state determination. For example, based on the determination result of the determination unit 12, the control unit 5 controls the driving conditions of the roll mixer 1 and the conveyors 3 and 4. More specifically, if the mixed state is determined to be insufficient, it is possible to extend the driving time of the roll mixer 1 and conveyors 3 and 4, narrow the gap between the rolls 2 and 2 to increase shear force, increase the driving speed of the roll mixer 1 and conveyors 3 and 4, or apply a combination of these controls. This improves the mixed state of the unvulcanized rubber R and additive X, ultimately improving the quality of the rubber product.

In addition, when determining the mixed state of unvulcanized rubber R and additive X, it is advisable to take into account the timing of adding unvulcanized rubber R and additive X and the operating conditions of roll mixer 1 and conveyors 3 and 4. For example, it is clear that the mixing of unvulcanized rubber R and additive X is insufficient immediately after adding unvulcanized rubber R and additive X, or immediately after starting operation of roll mixer 1 and conveyors 3 and 4, and therefore such periods can be excluded from the determination process.

REFERENCE SIGNS LIST 1 Roll kneader 2 Roll 3, 4 Conveyor 5 Control unit 6 Actuator 11 Temperature measuring device 12 Determination unit R Unvulcanized rubber S Rubber sheet X Additive

Claims (3)

A rubber mixing method comprising kneading unvulcanized rubber together with additives using a roll kneader equipped with a pair of rolls, conveying a rubber sheet that has passed through a gap between the pair of rolls by a conveyor and circulating it over the pair of rolls, measuring the temperature of the rubber sheet being conveyed by the conveyor along the width direction of the rubber sheet, and determining whether the additives have been added to the unvulcanized rubber and the mixed state of the unvulcanized rubber and the additives based on the temperature distribution in the width direction of the rubber sheet,
A rubber mixing method characterized by using the temperature distribution in the width direction of the rubber sheet as reference information, and when a part in the width direction of the rubber sheet has a temperature lower than a predetermined threshold, determining that the additive has been added to the unvulcanized rubber, and if there is then a part in the width direction of the rubber sheet where the temperature is lower than the threshold, determining that the unvulcanized rubber and the additive are not sufficiently mixed . 2. The rubber mixing method according to claim 1 , wherein mixing conditions for the unvulcanized rubber and the additives are adjusted based on the result of the determination of the mixed state. The rubber mixing method according to any one of claims 1 to 2, characterized in that when determining the mixed state of the unvulcanized rubber and the additives, the timing of adding the unvulcanized rubber and the additives and the driving conditions of the roll kneader and the conveyor are taken into consideration.