JP5270419B2 - Extruder die and extruder for rubber member for pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extrusion nozzle for a pneumatic tire rubber member and an extruder equipped with the extrusion nozzle, wherein the nozzle is used for producing the pneumatic tire rubber member having an upper surface with a groove shape and a flat shaped lower surface. <P>SOLUTION: In an extrusion nozzle 1 for pneumatic tire rubber member, which has an opening formed by combining an upper mold 1A and a lower mold 1B; a plurality of protrusions 3 are arranged inside the upper mold 1A for forming the groove shape 4 and a plurality of recessions 5 are arranged in the countering positions to the protrusions 3 inside the lower mold 1B. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an extrusion die for extruding a pneumatic tire rubber member, and an extruder provided with the die, and more particularly to an extrusion die for forming a groove shape in advance in a pneumatic tire rubber member, and The present invention relates to an extruder including the die.

  In general, a pneumatic tire includes a pair of annular beads each having a bead core, a carcass layer wound at both ends by a pair of annular beads, and a belt layer that is disposed outside the carcass layer in the tire radial direction and reinforces the carcass layer. And a tread portion disposed on the outer side in the tire radial direction of the belt layer, and a sidewall portion extending outward in the tire radial direction from the pair of annular beads and continuously provided on the tread portion. On the tread surface, the circumferential direction and width direction are used to increase the coefficient of friction between the pneumatic tire and the road surface, to improve braking performance, drive performance, steering stability performance, and drainage performance. A tread pattern composed of various grooves, sipes, and the like extending in the direction is formed.

  A typical example of the groove is a circumferential groove that continuously extends in the circumferential direction and defines a rib pattern or a block pattern. This circumferential groove is used in many pneumatic tires because it has excellent performance of draining water particularly on wet road surfaces and can sufficiently secure the frictional force.

By the way, the pneumatic tire is generally manufactured by the following method.
(1) Each member constituting an annular bead, a carcass layer, a belt layer, a sidewall portion, a tread portion, and the like made of an unvulcanized rubber composition or a steel cord topped with rubber is produced.
(2) These members are bonded together in the order of the carcass layer, the belt layer and the tread portion from the inside in the tire radial direction on a forming drum that can rotate around the drum axis, thereby forming an unvulcanized green tire. Mold.
(3) The green tire is put into a vulcanizing mold (hereinafter referred to as “mold”) and vulcanized at a predetermined temperature and pressure for a predetermined time to be molded into a predetermined tire shape.

  Here, when forming a circumferential groove on the tread surface, a bone portion (protrusion portion) extending continuously in the circumferential direction is disposed on the inner peripheral surface of the mold in contact with the green tire. The corresponding circumferential groove is formed in the tread surface of the tread portion by this bone portion biting into a rubber member (hereinafter referred to as “tread rubber”) constituting the tread portion of the green tire at the time of sulfur molding. Conventionally, as the tread rubber, one having a flat surface shape without irregularities is often used, and therefore the outer peripheral surface of the green tire is also formed flat. Such a tread rubber is generally formed by using an extruder with an unvulcanized rubber composition containing a reinforcing agent such as unvulcanized rubber or carbon black, and further containing a compounding agent such as sulfur, with a predetermined opening. It was continuously extruded from the extrusion die and had a predetermined length to be molded.

  However, when forming a circumferential groove in a green tire having a tread rubber having such a flat surface shape on the outer peripheral surface, the bone portion of the mold described above needs to bite into the tread rubber while excluding a large amount of rubber. is there. Along with this, rubber is pressed in the protruding direction of the bone part of the mold (inner direction in the tire radial direction), and pressing force acts in that direction, and the back side of the groove part formed in the tread rubber (the tire of the tread rubber) There was a tendency for dents to occur in the belt layer that abuts on the radially inner side. When such a dent occurs in the belt layer, there is a problem in that a reinforcing cord such as a steel cord constituting the belt layer is distorted and the reinforcing performance is not exhibited, and the ground contact performance of the tire is lowered.

  In order to improve such a problem, in the following Patent Document 1, a tread rubber is manufactured by using an extruder provided with a die having a convex portion corresponding to a bone portion of a mold. Describes that a groove shape is formed in advance to prevent the belt layer from being deformed. FIG. 2 is a cross-sectional view of a conventional extrusion die in which a groove shape is previously formed in the tread rubber.

  As shown in FIG. 2, the conventional extrusion die 10 includes an upper die 10 </ b> A in which a plurality of convex portions 13 for forming a groove shape 12 is formed on the upper surface of the tread rubber 11, and a lower surface of the tread rubber 11. A lower die 10B for forming a flat shape, and an opening formed by combining the upper die 10A and the lower die 10B. The extrusion die 10 is provided at the tip of an extruder (not shown), and an unvulcanized rubber composition is extruded from an opening thereof to shape the tread rubber 11 into a cross-sectional shape substantially the same as the opening. Since the groove shape 12 corresponding to the mold bone portion is formed in advance in the tread rubber 11 extruded from the extrusion die 10, the amount of rubber that the mold bone portion bites into and eliminates during vulcanization molding is reduced. can do. As a result, the pressing force acting on the rubber in the protruding direction of the bone portion of the mold is reduced, so that it is possible to suppress the dents in the belt layer.

  However, as a result of the study by the present inventors, when the tread rubber is extruded using the extrusion die described in Patent Document 1, even if the inner surface of the lower mold is flat, the unvulcanized rubber composition It has been found that when the product passes through the opening of the extrusion die, the flow rate of the unvulcanized rubber composition becomes nonuniform at each site within the opening. Due to the non-uniform flow rate of such an unvulcanized rubber composition, the tread rubber molded using the extrusion die described in Patent Document 1 is formed on the lower surface near the top of the groove shape. There was a tendency for dents to occur. When such a dent is formed on the lower surface of the tread rubber, there is a problem in that air existing in the dent remains without being discharged when it is bonded to the belt layer, resulting in a product defect.

  Further, in Patent Document 2 below, a plurality of groove forming protrusions for forming grooves corresponding to the circumferential grooves of the product tire are provided on one opposing surface, and the other surface is opposed to the groove forming protrusion and the A base for extruding a tread rubber for a pneumatic tire is described, which has an opening provided with a plurality of correction groove forming protrusions having a protrusion length shorter than the groove forming protrusion. It is described that the use of this extrusion die solves the above-described problem in Patent Document 1 when a groove shape is formed in advance in a tread rubber.

  However, as a result of the study by the present inventors, in the tread rubber produced using the extrusion die described in Patent Document 2, the flow rate of the unvulcanized rubber composition found in Patent Document 1 is not uniform. However, the flow rate of the unvulcanized rubber composition becomes more uneven at each part in the opening of the extrusion die. As a result, the tread rubber molded using the extrusion die described in Patent Document 2 tended to have larger dents on the lower surface near the top of the groove shape. Thus, it has been found that it is very difficult to manufacture a rubber member for a pneumatic tire having a groove shape on the upper surface and a flat surface on the lower surface, and it has been found that further improvement is necessary regarding the shape of the extrusion die. .

JP 09-150465 A JP 2007-30310 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pneumatic tire rubber member for producing a pneumatic tire rubber member having a groove shape on the upper surface and a flat lower surface. An object of the present invention is to provide an extrusion die and an extruder provided with the extrusion die.

  In order to achieve the above object, the present inventors have provided an unvulcanized rubber composition in an uneven shape in an extrusion die for a rubber member for a pneumatic tire having an opening formed by combining an upper die and a lower die. The present invention has been intensively studied with respect to the flow rate when passing through an opening having an inner surface and the shape of a rubber member for a pneumatic tire after extrusion. As a result, when there is a flow rate difference in the unvulcanized rubber composition passing through the opening, a rubber member for a pneumatic tire having substantially the same cross-sectional shape as the opening cannot be manufactured. It has been found that the rubber member for a pneumatic tire swells and tends to dent on the part where the flow velocity is low. The present invention has been made as a result of the above-described studies, and achieves the above-described object with the following configuration.

  That is, the extrusion die for a pneumatic tire rubber member according to the present invention is an extrusion die for a pneumatic tire rubber member having an opening formed by combining an upper die and a lower die. A plurality of convex portions for forming a groove shape are disposed on the inner surface, and a plurality of concave portions are disposed on the inner surface of the lower mold at positions facing the convex portions. To do.

  A plurality of projections for forming a groove shape are provided on the inner surface of the upper die, which is one of the constituent members of the extrusion die for the pneumatic tire rubber member. In the rubber member for a pneumatic tire, a groove shape corresponding to the bone portion of the mold is formed in advance. This reduces the amount of rubber that the mold bone part bites and eliminates during vulcanization molding, reduces the pressing force acting in the protruding direction of the mold bone part, and deforms the rubber member for the pneumatic tire Can be prevented.

  Here, the inventors of the present invention have a pneumatic tire using an extrusion die in which a plurality of convex portions for forming a groove shape are provided on the inner surface of the upper die and the inner surface of the lower die is flat. When the rubber member for molding is molded (corresponding to the case where the extrusion die shown in FIG. 2 is used), the flow rate of the unvulcanized rubber composition passing through each part in the opening is measured, and the following phenomenon is found. It was. That is, in the opening portion of the extrusion die shown in FIG. 2, in the region S ′ between the top of the convex portion 13 and the inner surface of the lower mold 10B and having a small thickness (vertical direction in FIG. 2), It was found that the flow rate of the unvulcanized rubber composition was high in the region L ′ where the flow rate of the vulcanized rubber composition was slow and the region between the plurality of convex portions 13 was thick. Therefore, when the extrusion die 10 shown in FIG. 2 is used, the unvulcanized rubber composition passing through the opening has a large flow rate difference, and therefore a dent is generated in the region S ′ having a small thickness. As a result, the rubber member for a pneumatic tire having a flat bottom surface (in FIG. 2, the tread rubber 11) cannot be manufactured.

  However, in the extrusion die of the rubber member for a pneumatic tire according to the present invention, since the plurality of concave portions are disposed on the inner surface of the lower mold at positions facing the convex portions, The flow rate of the unvulcanized rubber composition passing through the region between the inner surface of the mold is increased. For this reason, in the area | region between the top part of a convex part and the inner surface of a lower mold | type, and another area | region, the flow rate difference at the time of an unvulcanized rubber composition passing can be reduced. As a result, in the rubber member for a pneumatic tire according to the present invention, the protruding portion formed by the concave portion is eliminated in the region where the flow velocity is relatively slow (the region between the top of the convex portion and the inner surface of the lower mold). The degree of dents can be reduced moderately. As a result, it is possible to manufacture a rubber member for a pneumatic tire having a desired cross-sectional shape, specifically, a groove shape on the upper surface and a flat lower surface.

  In the extrusion die of the rubber member for a pneumatic tire, the surface shape of the concave portion is preferably formed in a smooth concave curved surface shape. According to this configuration, it is possible to more reliably manufacture a pneumatic tire rubber member having a groove shape on the upper surface and a flat lower surface at each part of the pneumatic tire rubber member.

  The extruder which concerns on this invention is equipped with the nozzle | cap | die for extrusion of the rubber member for pneumatic tires described above. By using such an extruder, it is possible to produce a rubber member for a pneumatic tire having a desired cross-sectional shape, specifically a groove shape on the upper surface and a flat shape on the lower surface.

Sectional drawing which shows an example of the nozzle | cap | die for extrusion of the rubber member for pneumatic tires which concerns on this invention Sectional view of a conventional extrusion die in which a groove shape is previously formed in the tread rubber

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an extrusion die for a rubber member for a pneumatic tire according to the present invention. In FIG. 1, the extrusion die 1 is symmetric with respect to the center line CL (the two protrusions 3 are disposed on the right side and the two protrusions 3 are disposed on the left side of the center line CL). Only one side (right side in FIG. 1) of the center line CL is shown. However, in the present invention, the extrusion die 1 does not necessarily have left-right symmetry with respect to the center line CL. For example, two protrusions are provided on one side and three protrusions are provided on the other side. It may be.

  Although not shown in the drawings, a pneumatic tire according to the present invention is disposed on a pair of annular beads having a bead core, a carcass layer wound at both ends by a pair of annular beads, and on the outer side in the tire radial direction of the carcass layer. A belt layer that reinforces the carcass layer, a tread portion disposed on the outer side in the tire radial direction of the belt layer, a side wall portion that extends from the pair of annular beads to the outer side in the tire radial direction, and that is connected to the tread portion; Is provided. In such a pneumatic tire, each member composed of an unvulcanized rubber composition or a steel cord topped with rubber is sequentially bonded on a molding drum that can rotate around a drum shaft, and then unvulcanized. It can be manufactured by molding a sulfurized green tire, putting it in a mold, and performing vulcanization for a predetermined time at a predetermined temperature and pressure.

  The extrusion base of the rubber member for a pneumatic tire of the present invention can be used for manufacturing each member constituting the pneumatic tire. In this embodiment, the rubber constituting the tread portion is used as the rubber member for the pneumatic tire. An example of manufacturing a tread rubber as a member will be described. In the present embodiment, an unvulcanized rubber composition containing a reinforcing material such as unvulcanized rubber or carbon black, and a compounding agent such as sulfur is continuously used by an extruder equipped with an extrusion die 1 shown in FIG. The tread rubber is molded by extruding and cutting into a predetermined length.

  As shown in FIG. 1, the extrusion die 1 used in this embodiment has an opening formed by combining an upper mold 1A and a lower mold 1B. Since a plurality of convex portions 3 for forming the groove shape 4 are arranged on the inner surface of the upper mold 1A, the tread rubber 2 extruded from the extrusion die 1 corresponds to the bone portion of the mold. A groove shape 4 is formed in advance. As a result, the amount of rubber that the bone portion of the mold bites into and eliminates during vulcanization molding can be reduced, the pressing force acting in the protruding direction of the bone portion of the mold is reduced, and deformation of the tread rubber 2 is prevented. be able to. In the present embodiment, the number of the convex portions 3 disposed on the inner surface of the upper mold 1A is four, two on each of the left and right sides. The number of the convex portions 3 is the circumference disposed on the tread portion. It can be set as appropriate according to the number of directional grooves.

  The protrusion height H1 and the upper side width W1 of the convex portion 3 can be appropriately set according to the groove depth and groove width of the circumferential groove disposed in the tread portion. Specifically, the protrusion height H1 of the protrusion is 5 to 15 mm, and the upper side width W1 is 5 to 25 mm. The “projection height of the convex portion 3” means the height in the direction perpendicular to the extrusion direction of the unvulcanized rubber composition (the height in the vertical direction in FIG. 1). “Width” means the width in the direction orthogonal to the extrusion direction of the unvulcanized rubber composition (the width in the left-right direction in FIG. 1). Moreover, the lower side width | variety of the convex part 3 can be suitably set according to the shape of the circumferential groove | channel arrange | positioned in a tread part.

  On the other hand, the same number of concave portions 5 as the convex portions 3 are disposed on the inner surface of the lower mold 1B at positions facing the convex portions 3. Thereby, in this embodiment, in the area | region S between the top part of the convex part 3 and the inner surface of the lower mold | type 1B, the flow rate of an unvulcanized rubber composition can be accelerated, and the top part of the convex part 3 and the lower mold | type 1B can be increased. In the region S between the inner surface and the other region, the difference in flow rate when the unvulcanized rubber composition passes can be reduced. For this reason, in the tread rubber of the present embodiment, in the region S where the flow velocity is low, the degree of dent can be reduced to such an extent that the protruding portion 6 formed by the recess 5 is eliminated. As a result, it is possible to produce a tread rubber having a desired cross-sectional shape, specifically, a groove shape on the upper surface and a flat shape on the lower surface.

  In the present embodiment, the surface shape of the concave portion 5 is a smooth concave curved surface, and the surface facing the convex portion 3 is formed in a circular arc shape. As a result, a tread rubber having a groove shape on the upper surface and a flat shape on the lower surface can be more reliably manufactured. Furthermore, it is preferable that the corners of the recesses 5 are also formed in a cross-sectional arc shape.

Moreover, the recessed part 5 of this embodiment is arrange | positioned in the position which opposes the convex part 3, Comprising: The convex part 3 arrange | positioned by the inner surface of 1 A of upper mold | types, and a center line substantially correspond. The convex portion 3 and the concave portion 5 represent the difference in flow rate when the unvulcanized rubber composition passes through the region S between the top of the convex portion 3 and the inner surface of the lower mold 1B and other regions. Set to decrease. Specifically, it is preferable to set the shape of the convex part 3 and the concave part 5 in the following ranges.
(1) 0.4 ≦ H1 / T ≦ 0.8
(2) 1.2 ≦ W2 / W1 ≦ 3.0
(3) 0.15 ≦ H2 / H1 ≦ 0.35
(4) 1.5 ≦ R1 / W1 ≦ 3.0
(5) R2 / R1 ≦ 2.5
Here, W2 is the width of the upper side of the concave portion 5, and when the corner portion of the concave portion 5 is formed in a circular arc shape, it means the distance between the contact points on both sides of the corner portion of the concave portion 5 and the flat portion of the extrusion die 1. To do. T is the total thickness of the extrusion die 1, R 1 is the radius of curvature of the recess 5 formed in an arc shape in cross section, R 2 is the radius of curvature of the corner of the recess 5 formed in an arc shape in cross section, and H 2 is the depth of the recess 5. Means. When these ratios are out of the above range, the flow rate difference of the unvulcanized rubber composition becomes large at each part in the opening of the extrusion die 1, and accordingly, irregularities are generated on the lower surface of the tread rubber. There is a case.

  As described above, a tread rubber having a groove shape on the upper surface and a flat shape on the lower surface can be produced by using the extrusion die illustrated in the present embodiment and the extruder including the die. By using this tread rubber, it is possible to prevent the occurrence of air accumulation on the bonding surface with the belt layer. Furthermore, since unnecessary force does not act on the belt layer at the time of bonding, it is possible to prevent distortion from occurring in a reinforcing cord such as a steel cord constituting the belt layer.

  [Other Embodiments] Other embodiments of the present invention will be described below.

  (1) In the above-described embodiment, the convex part 3 has a trapezoidal cross section, but the convex part 3 has a triangular, rectangular, or arcuate cross section. Also good.

1: extrusion die 1A: upper die 1B: lower die 2: tread rubber 3: convex portion 5: concave portion

Claims (3)

In the extrusion die of the rubber member for a pneumatic tire having an opening formed by combining the upper die and the lower die,
A plurality of protrusions for forming a groove shape are disposed on the inner surface of the upper mold, and a plurality of recesses are disposed on the inner surface of the lower mold at positions facing the protrusions. A base for extruding a rubber member for a pneumatic tire.   The base for extrusion of a rubber member for a pneumatic tire according to claim 1, wherein the surface shape of the recess is formed into a smooth concave curved surface.   The extruder provided with the nozzle | cap | die for extrusion of the rubber member for pneumatic tires of Claim 1 or 2.

Images