JP2019209629A - Kneading method of rubber material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the effect of suppressing the occurrence of bagging, and to uniformly heat. SOLUTION: An unvulcanized rubber material G is kneaded by using an open roll machine 1 having a first roll 2 and a second roll 3. With the difference between the surface temperature T1 of the first roll 2 and the surface temperature T2 of the second roll 3 being 20 ° C. or more, the rubber material G is allowed to be caught in the gap 6 between the first roll 2 and the second roll 3. Including the step of kneading. [Selection diagram] Figure 2

Description

  The present invention relates to a method for kneading a rubber material that can be suitably used particularly for the kneading work of a rubber material for a tire.

  For example, in the molding processing of rubber members for tires such as tread rubber, an open roll machine is used to knead and heat a rubber material of a predetermined composition and then put it into a rubber extruder. Yes.

  As shown in FIG. 7, the open roll machine has two rolls a <b> 1 and a <b> 2 that are parallel to each other, and a rubber material G is put between them. When the rolls a1 and a2 rotate, the rubber material G is caught between the rolls a1 and a2, and when passing through the gap, the rubber is heated and plasticization is promoted. Usually, the rotational speed of one roll a1 is set to be larger than the rotational speed of the other roll a2, and the plasticized rubber ga is wound around the one roll a1 to form the rubber gb in the bank portion b. Joining and kneading is repeated.

  At this time, the rubber ga wound around the roll a1 is peeled off from the roll surface, and so-called bagging J is generated in which the roll a1 is idle, and there is a problem in that the heating efficiency and the kneading efficiency are lowered.

  Conventionally, the occurrence of bagging is suppressed by adjusting the gap between the rolls a1 and a2, the rotation speed of the rolls a1 and a2, the rubber temperature, and the like.

  However, in recent years, in order to improve the fuel efficiency of tires, for example, there is a tendency to use low heat generation rubber for tread rubber or the like. This low heat generation rubber has characteristics that it is inferior in tackiness, has a relatively high peak torque and a low rate of torque relaxation for stress relaxation as compared with conventional tire materials.

  Therefore, with the conventional method, it is difficult to sufficiently suppress the occurrence of bagging for such a low heat generation rubber.

  The following Patent Document 1 proposes forming a film of a roll processing aid on the surface of one roll. This film improves adhesion to rubber and prevents the rubber from peeling off from the roll surface. However, in this proposal, it is necessary to form a film frequently, and the film may be peeled off and mixed into the rubber. Moreover, it is difficult to sufficiently suppress the occurrence of bagging for the above-mentioned rubber having a low heat generation specification.

JP 2003-89112 A

  An object of the present invention is to provide a method for kneading a rubber material that can enhance the effect of suppressing the occurrence of bagging.

The present invention is a method for kneading an unvulcanized rubber material using an open roll machine having a first roll and a second roll that are arranged in parallel to each other and rotate in opposite directions,
In a state where the difference between the surface temperature T1 of the first roll and the surface temperature T2 of the second roll is 20 ° C. or more, the rubber material is bitten into the gap between the first roll and the second roll and kneaded. Process.

  In the rubber material kneading method according to the present invention, in the kneading step, the surface temperature T1 of the first roll is set lower than the surface temperature T2 of the second roll, and the rotation speed N1 of the first roll is It is preferable that the rotation speed is set to be larger than the rotation speed N2 of the second roll.

  In the method for kneading a rubber material according to the present invention, it is preferable that a friction ratio N2 / N1, which is a ratio of the rotation speed N2 of the second roll to the rotation speed N1 of the first roll, is 70% or less.

  In the method for kneading a rubber material according to the present invention, it is preferable that a friction ratio N2 / N1, which is a ratio of the rotation speed N2 of the second roll to the rotation speed N1 of the first roll, is 30% or more.

  In the rubber material kneading method according to the present invention, the surface temperature T2 of the second roll is preferably 50 ° C. or higher.

  In the rubber material kneading method according to the present invention, the rubber material preferably has a peak torque (80 ° C.) of 30 (dN · m) or more.

  In the method for kneading a rubber material according to the present invention, the rubber material preferably has a torque reduction rate of stress relaxation of 85% (after 80 ° C./5 seconds) or less.

  As described above, according to the present invention, in the step of kneading the rubber material in the gap between the first roll and the second roll, the difference between the surface temperature T1 of the first roll and the surface temperature T2 of the second roll is 20%. It is set to over ℃.

  As a result, the peeling of the rubber from the low temperature side roll can be suppressed, and the effect of suppressing the occurrence of bagging can be enhanced. In particular, by combining with the friction ratio, for example, it is possible to suppress the occurrence of bagging to a low exothermic specification rubber, and it is possible to perform heating with an open roll machine.

It is a top view which shows notionally the open roll machine for enforcing the kneading | mixing method of the rubber material of this invention. It is AA sectional drawing of FIG. It is sectional drawing explaining the generation | occurrence | production mechanism of bagging. (A), (B) is the perspective view and graph explaining the measuring method of the peak torque of a rubber material, and a torque decreasing rate. (A), (B) is sectional drawing explaining the mechanism of the effect | action by a friction ratio. (A), (B) is a graph which shows the relationship between friction ratio, the thickness of rubber | gum, and the amount of shrinkage | contraction of rubber | gum. It is sectional drawing which shows generation | occurrence | production of bagging in an open roll machine.

Hereinafter, embodiments of the present invention will be described in detail.
In FIG. 1, the top view of the open roll machine 1 for implementing the kneading | mixing method of the rubber material G of this invention is shown, and the AA cross section is shown in FIG.

  As shown in FIGS. 1 and 2, the open roll machine 1 of the present embodiment includes a first roll 2 and a second roll 3 that are arranged in parallel to each other. The first roll 2 and the second roll 3 have a cylindrical body 4 having the same diameter, and are rotatably supported by the frame 8. A gap 6 is formed between the body 4 of the first roll 2 and the body 4 of the second roll 3 for biting the unvulcanized rubber material G charged into the bank 5.

  The open roll machine 1 includes a driving device (not shown) including a motor and the like. By this driving device, the first roll 2 and the second roll 3 are rotationally driven in directions opposite to each other. The driving device further includes a rotation speed adjusting means, and can adjust the rotation speed N1 of the first roll 2 and the rotation speed N2 of the second roll 3, respectively.

 Further, the open roll machine 1 includes temperature adjusting means (not shown). By this temperature adjusting means, the surface temperature T1 of the first roll 2 and the surface temperature T2 of the second roll can be adjusted respectively.

  Reference numeral 7 in the drawing denotes, for example, a guide plate, which can dam the inserted rubber material G between the guide plates 7 and 7 and prevent the rubber material G from flowing out of the bank portion 5 outward in the axial direction. .

Next, a method for kneading the rubber material G using the open roll machine 1 will be described.
In the kneading method of the present invention, the step of kneading the rubber material G into the gap 6 while the difference between the surface temperature T1 of the first roll 2 and the surface temperature T2 of the second roll 3 is 20 ° C. or more. S is included.

  In this example, the rotation speed N1 of the first roll 2 is set to be larger than the rotation speed N2 of the second roll 3. Here, when the first roll 2 and the second roll 3 rotate in opposite directions, the rubber material G in the bank portion 5 is caught in the gap 6 and the gap 6 is directed downward. pass. At this time, the rubber is heated and plasticized. At this time, since N1> N2, the rubber ga that has passed through the gap 6 is wound around the first roll 2 in a sheet shape and returned to the bank unit 5. Further, the rubber ga merges with the rubber gb in the bank portion 5 (sometimes referred to as bank rubber gb), and kneading is repeated.

  In this example, the surface temperature T1 of the first roll 2 is set lower than the surface temperature T2 of the second roll 3. And generation | occurrence | production of bagging in rubber | gum ga wound around the 1st roll 2 is suppressed low because a temperature difference (T2-T1) shall be 20 degreeC or more.

  FIG. 3 shows the generation mechanism of bagging. As shown in FIG. 3, a collision A occurs when the rubber ga wound around the first roll 2 joins the bank rubber gb. At this time, the rubber ga rebounds without being crushed. This is the starting point, and the rubber ga is peeled off from the first roll 2 and floated, and the lift B proceeds downward. Further, since the tightening force F on the first roll 2 due to the shrinkage of the rubber ga is weak, the rubber ga does not roll up following the first roll 2, and bagging occurs.

Therefore, bagging is
(A) The greater the rebound when the rubber ga collides with the bank rubber gb;
(A) The weaker the adhesive strength of the rubber ga with the first roll 2;
(C) The smaller the shrinkage and the smaller the fastening force F of the rubber ga to the first roll 2;

  Here, the low heat generation specification rubber is inferior in tackiness to the conventional tire material, has a relatively high peak torque Kmax, and a low stress relaxation torque reduction rate ΔK.

  Among these, when the peak torque Kmax of the rubber is high, the sheet-like rubber ga is hard and is not easily bent. Therefore, the rebound when colliding with the bank rubber gb is large, which is disadvantageous for the occurrence of bagging. Further, when the torque reduction rate ΔK is low, the internal stress of the rubber is difficult to decrease. That is, it is difficult to shrink, and the fastening force F of the rubber ga to the first roll 2 is small, which is disadvantageous for the occurrence of bagging. Thus, it can be said that the rubber with a low heat generation specification is a rubber that tends to generate bagging.

  The present invention is such a low heat generation rubber, particularly a rubber having a peak torque (80 ° C.) of 30 (dN · m) or more, and a torque reduction rate ΔK of 85% (after 80 ° C./5 seconds) or less. It is possible to suppress the occurrence of bagging to a small amount of rubber.

The peak torque Kmax and the torque reduction rate ΔK are measured by a stress relaxation test using a torsional shear type viscoelasticity tester conceptually shown in FIG. 4A (for example, trade name: RPA2000, manufactured by Alpha Technologies). Reference numeral 20 in the drawing is a disk-shaped sample rubber, and reference numerals 21U and 21L are disk-shaped support plates that hold the sample rubber 20 concentrically with the sample rubber 20 sandwiched between the upper and lower sides. One support plate 21U is rotated and twisted until the sample rubber 20 at a temperature of 80 ° C. receives a predetermined strain (shear strain) of 41%. The support plate 21U is fixed at the twist angle θ at that time. And the change (stress relaxation) of the torque K with respect to time when it is left to stand in this state where the twist angle is fixed is measured. FIG. 4B illustrates a “torque-time” curve, and the maximum value of the torque K in this curve is obtained as the peak torque Kmax. In the curve, the torque reduction rate ΔK (%) can be obtained from the torque K ₅ when 5 seconds have elapsed from the peak torque, by the following equation.
Torque reduction rate ΔK = {(Kmax−K ₅ ) / Kmax} × 100

  In the present invention, the temperature difference (T2−T1) is 20 ° C. or more, and thereby the occurrence of bagging of the rubber ga wound around the first roll 2 in a sheet shape is suppressed to a low level. The mechanism is not fully understood, but the following is presumed.

  Since the surface temperature T2 of the second roll 3 is relatively high, the amount of rubber pushed into the gap 6 by the second roll 3 is reduced as shown in FIG. Therefore, the thickness t of the rubber ga that passes through the gap 6 and winds around the first roll 2 is relatively thin. And, as the thickness t becomes thinner, the rebound when the rubber ga collides becomes smaller.

  Further, since the surface temperature T1 of the first roll 2 is relatively low, the contact surface of the rubber ga that contacts the first roll 2 is cooled by the first roll 2. Thereby, shrinkage is promoted on the contact surface, and the tightening force to the first roll 2 is increased. Since the main part other than the contact surface of the rubber ga is still sufficiently warm, an adverse effect on the rebound when colliding with the bank rubber gb is avoided. As described above, since the rebound is weakened by reducing the thickness t of the rubber ga and the tightening force to the first roll 2 is increased by promoting the shrinkage, the effect of suppressing the occurrence of bagging is exhibited. (For convenience, this effect may be referred to as a temperature difference effect).

  The effect due to this temperature difference can be exhibited highly when the temperature difference (T2-T1) is 20 ° C. or higher, and further 30 ° C. or higher. At this time, the surface temperature T1 is preferably in the range of 30 to 50 ° C. The surface temperature T2 is preferably 50 ° C. or higher, more preferably 60 ° C. or higher.

  In this example, as shown in FIG. 5 (A), the amount of rubber pushed into the gap 6 by the second roll 3 is reduced even when the rotational speed N2 of the second roll 3 is relatively low. Further, since the rotational speed N1 of the first roll 2 is larger than the rotational speed N2 of the second roll 3, as shown in FIG. 5 (B), the rubber ga passes through the gap 6 when passing through the gap 6. Is stretched on the contact surface side. However, after separating from the second roll 3, a force (shrink) for returning to the rubber ga acts, and the tightening force to the first roll 2 is increased. Thus, even when N1> N2, the effect of suppressing the occurrence of bagging is exhibited (for the sake of convenience, this effect may be referred to as an effect due to the rotational speed difference).

  The effect of this rotational speed difference can be exerted highly when the friction ratio N2 / N1, which is the ratio of the rotational speed N2 to the rotational speed N1, is 70% or less, and further 60% or less. FIG. 6A shows the relationship between the friction ratio N2 / N1 and the thickness t of the rubber ga. As the friction ratio N2 / N1 decreases, the thickness t of the rubber ga decreases and rebounds. It can be confirmed that it becomes weak. FIG. 6B shows the relationship between the friction ratio N2 / N1 and the shrinkage amount of the rubber ga. As the friction ratio N2 / N1 decreases, the shrinkage amount increases and the tightening to the first roll 2 is performed. It can be confirmed that the power increases.

  However, when the friction ratio N2 / N1 is too low, the thickness t of the rubber ga becomes too thin and the shrink amount becomes too large, so that the rubber ga is easily broken on the first roll 2 due to the shrink. Therefore, the lower limit of the friction ratio N2 / N1 is preferably 30% or more, more preferably 40% or more.

  By combining the temperature difference (T2-T1) and the friction ratio N2 / N1, the effect of suppressing the occurrence of bagging can be further enhanced by the synergistic effect of both.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  Using the kneading method according to the present invention, various rubber materials were kneaded (heated) based on the specifications in Table 1. Thereafter, the rubber was put into a rubber extruder, and a tread rubber for a tire was extruded as an extrudate. And the dimensional stability after extrusion of an extrudate was compared, and the suppression effect of bagging generation was evaluated.

  The peak torque Kmax and the torque reduction rate ΔK of the rubber material were measured based on the measurement method described in Paragraph No. 0034.

<Dimensional stability>
The extrudate is cut in the thickness direction, the cross-sectional area variation is calculated by a coefficient of variation (CV value), and Comparative Example 1 is indicated by an index of 100. The larger the numerical value, the higher the effect of suppressing the occurrence of bagging, and it can be determined that the dimensions are stable due to more uniform heating.

  As shown in the table, in the examples, the effect of suppressing the occurrence of bagging is high, and it can be confirmed that the dimensions are stabilized by uniformly heating.

1 Open Roll Machine 2 First Roll 3 Second Roll 6 Gap G Rubber Material

Claims (7)

A method for kneading an unvulcanized rubber material using an open roll machine having a first roll and a second roll that are arranged in parallel to each other and rotate in opposite directions,
In a state where the difference between the surface temperature T1 of the first roll and the surface temperature T2 of the second roll is 20 ° C. or more, the rubber material is bitten into the gap between the first roll and the second roll and kneaded. A method for kneading a rubber material including a process.   In the kneading step, the surface temperature T1 of the first roll is set lower than the surface temperature T2 of the second roll, and the rotation speed N1 of the first roll is higher than the rotation speed N2 of the second roll. The method for kneading a rubber material according to claim 1, which is set to be large.   The method for kneading a rubber material according to claim 2, wherein a friction ratio N2 / N1, which is a ratio of the rotation speed N2 of the second roll to the rotation speed N1 of the first roll, is 70% or less.   The method for kneading a rubber material according to claim 2 or 3, wherein a friction ratio N2 / N1, which is a ratio of the rotation speed N2 of the second roll to the rotation speed N1 of the first roll, is 30% or more.   The method for kneading a rubber material according to any one of claims 1 to 4, wherein a surface temperature T2 of the second roll is 50 ° C or higher.   The method for kneading a rubber material according to claim 1, wherein the rubber material has a peak torque (80 ° C.) of 30 (dN · m) or more.     The method for kneading a rubber material according to any one of claims 1 to 6, wherein the rubber material has a torque relaxation rate of stress relaxation of 85% (after 80 ° C / 5 seconds) or less.

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