JP2008213365A - Injection molding method of rubber molded article and injection molding mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method and an injection molding mold of a rubber molded article which can raise the uniformity of configuration of a rubber molded article without prolonging a cycle time in molding an unvulcanized rubber molded article by injection molding. <P>SOLUTION: The injection pour of an unvulcanized rubber composition is carried out in a cavity formed in the inside of a molding mold in a mold clamping state and a bead filler 1b is molded, thereafter the pressing of an opposite part 30 corresponding to a gate connection 20 is carried out while the bead filler 1b is in a unvulcanized condition, the symmetrical compressive stress to the stress generated by the injection pour of an unvulcanized rubber composition is made to interact on the bead filler 1b, and thereafter the bead filler 1b which is in an unvulcanized condition is taken out from a molding mold. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an injection molding method and an injection mold for molding a rubber molded body such as a bead filler.

  Various products are conventionally known as a product made of a rubber composite in which a plurality of rubber molded bodies are combined. A typical example is a pneumatic tire. For example, as shown in FIG. 7, the pneumatic tire is formed by bonding a plurality of rubber molded bodies such as a sidewall rubber 2, a tread rubber 3, an inner liner rubber 5, and a width between the pair of bead portions 1. A carcass ply 4 is disposed in which the end portion in the direction is rewound and the bead member 10 is sandwiched. The bead member 10 has an annular bead filler 1b made of hard rubber as shown in FIG. 8 and an annular bead core 1a integrated on the inner periphery of the bead filler 1b. The bead core 1a is a rubber-coated steel. Consists of lines convergent.

  By the way, when a rubber molded body such as a bead filler is formed by extrusion molding, there is a problem that the end portions of the extruded product are brought into close contact with each other to be locally thickened, resulting in deterioration of uniformity. Moreover, in the method of pressurizing the spirally laminated linear rubber as described in Patent Document 1 below, there is a problem that the number of steps increases and the molding time becomes longer than necessary. On the other hand, according to the injection molding, the uniformity of the rubber molded body can be ensured better than the extrusion molding, and the molding time does not become longer than necessary.

  However, in injection molding, when an unvulcanized rubber composition is filled in a cavity in a mold, a stress distribution state as shown in FIG. 9 is obtained, and a gate connection portion of a rubber molded body (bead filler 1b in the illustrated example). There is a problem that a large residual stress is generated in the vicinity of 35 to cause deformation accompanied by the formation of the raised portion 36 as shown in FIG. 10 after demolding (see Patent Documents 1 and 2 below). Such residual stress is alleviated by holding the clamped state for a predetermined time or more after molding the rubber molded body, but in this case, the molding time is prolonged.

On the other hand, as in the inventions described in Patent Documents 3 and 4 below, it has been proposed to demold a rubber molded body in an unvulcanized state without performing a vulcanization step in the mold. According to this method, the adhesiveness of the rubber molded body is improved. For example, if it is a bead filler, the adhesion with the carcass ply is improved and peeling can be effectively prevented. However, since such a rubber molded body is less rigid than the case where it has undergone a vulcanization process and is liable to be deformed, when the deformation due to the residual stress described above occurs, the shape as a whole is shown in FIG. It has been found that the film is tilted and deformed unevenly, which greatly deteriorates the uniformity.
JP 60-157840 A JP-A-3-166916 JP 2006-248036 A JP 2006-248037 A

  The present invention has been made in view of the above circumstances, and its purpose is to achieve uniformity in the shape of a rubber molded body without prolonging the molding time when molding an unvulcanized rubber molded body by injection molding. An object of the present invention is to provide an injection molding method and an injection mold for a rubber molded body that can be enhanced.

  The above object can be achieved by the present invention as described below. That is, the method for injection molding a rubber molded body according to the present invention includes an injection process for molding a rubber molded body by injecting and injecting an unvulcanized rubber composition into a cavity formed inside a mold in a mold-clamping state. And while the rubber molded body is in an unvulcanized state, a pressing step for pressing a facing portion opposite to the gate connecting portion of the rubber molded body, and the unvulcanized state after the pressing step And a demolding step of taking out the rubber molded body from the mold.

  According to the above method, it is generated by injection injection of an unvulcanized rubber composition by pressing a facing portion opposite to the gate connecting portion against a rubber molded body in an unvulcanized state after the injection step. Compressive stress symmetrical to the stress to be applied can be applied to the rubber molded body. As a result, it is possible to reduce the residual stress of the rubber molded body, to suppress a large uplift deformation in the vicinity of the gate connecting portion of the rubber molded body, and to prevent the shape of the rubber molded body from deforming unevenly. it can. After the pressing step, a rubber molded body excellent in adhesiveness can be obtained by taking out the rubber molded body in an unvulcanized state from the mold.

  As described above, in the present invention, the vulcanization step in the mold is omitted, and further, it is not necessary to secure a holding time for relaxing the residual stress, so that the molding time is not prolonged. Further, the uniformity of the shape of the rubber molded body can be improved and deterioration of uniformity can be suppressed. Here, the “unvulcanized state” refers to a state in which vulcanization is not performed, but is not limited to those in which the vulcanization reaction has not progressed at all, and vulcanization is insufficient (optimum vulcanization) as defined in JISK6200. The vulcanized state that has not yet reached) is also included.

  In the above, in the injecting step, the cavity surface portion forming the facing portion is recessed to form the facing portion, and in the pressing step, the cavity surface portion recess is eliminated and the facing portion of the facing portion is formed. It is preferable to eliminate the protrusion. According to this method, after forming the facing portion in the injecting step, the compressing stress generated by the pressing step can be efficiently increased by pressing the facing portion so that the protrusion disappears. It is possible to effectively reduce the residual stress of the molded body and to satisfactorily suppress deformation after demolding.

  The present invention is particularly useful when molding an annular bead filler made of hard rubber having a substantially triangular cross-section that is vertically long in the radial direction as a rubber molded body. That is, such a bead filler tends to cause non-uniform deformation as shown in FIG. 10, but according to the present invention, such non-uniform deformation can be suppressed as described above, and unvulcanized By obtaining the bead filler, the adhesion with the carcass ply becomes good at the time of tire molding. Furthermore, in the bead filler made of hard rubber, the viscosity of the unvulcanized rubber composition is high and the mold flow is poor, so that it tends to be injected and injected at a high pressure and overshot, and the occurrence of residual stress is remarkable. On the other hand, according to the present invention, the residual stress can be reduced as described above, and the shape deformation after demolding can be suppressed.

  Also, the rubber mold injection mold according to the present invention is configured such that a cavity is formed inside in a clamped state, and a rubber molded body can be molded by injection-injecting an unvulcanized rubber composition into the cavity. In the injection molding die for the rubber molded body, the gate connected to the cavity for injecting and injecting the unvulcanized rubber composition and the gate connecting portion of the rubber molded body formed in the cavity face each other. And a pressing device that presses the facing portion.

  According to the injection mold of the present invention, as described above, the unvulcanized rubber composition is provided with the pressing device that presses the facing portion opposite to the gate connecting portion of the rubber molded body formed in the cavity. A compressive stress symmetric to the stress generated by injection injection of can be applied to the rubber molded body in the cavity. As a result, it is possible to reduce the residual stress of the rubber molded body, to suppress a large uplift deformation in the vicinity of the gate connecting portion of the rubber molded body, and to prevent the shape of the rubber molded body from deforming unevenly. .

  In the above, a standby state in which the pressing device can dent the cavity surface portion that forms the facing portion, and can project and form the facing portion when the unvulcanized rubber composition is injected and injected into the cavity. It is preferable that a pressing state in which the depression of the cavity surface portion is eliminated and the protrusion of the facing portion is eliminated can be selectively taken.

  According to such a configuration, when injecting and injecting the unvulcanized rubber composition, the opposing portion can be formed to protrude by keeping the pressing device in a standby state, and then the opposing portion can be formed by shifting the pressing device to the pressing state. Can be pressed. At this time, by pressing so that the protrusion of the opposing portion disappears, the compressive stress generated by the pressing can be increased efficiently, and the residual stress of the rubber molded body is effectively reduced, and the deformation after demolding Can be suppressed satisfactorily.

  As a preferred embodiment of the present invention, there is one in which the pressing device has a piston member that can advance and retract with respect to the cavity. Thereby, a press apparatus can be comprised simply and the handling becomes easy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a mold clamping state (a) and a mold opening state (b) of a molding die according to the present invention. FIG. 2 is a longitudinal sectional view of the molding die in the clamped state, and corresponds to the AA section of FIG. FIG. 3 is an enlarged vertical sectional view showing the periphery of the cavity of the mold, and shows a state in which a bead core is provided.

  This injection mold 6 (hereinafter simply referred to as mold 6) has a bead filler 1b (an example of a rubber molded body) in which a bead core 1a as shown in FIG. Used for injection molding. As shown in FIGS. 1 and 2, the mold 6 includes a lower mold 7 having an annular groove 9 formed on the upper surface, and an upper mold 8 disposed above the lower mold 7. The upper mold 8 has a mold clamping position (see FIGS. 1A and 2) that closes the annular groove 9 to form an annular cavity 11, and a mold opening position that opens the annular groove 9 (FIG. 1B). Between the lower mold 7 and the lower mold 7.

  The upper die 8 includes a sprue 12 extending downward from the center of its upper surface, a runner 13 extending from the sprue 12 to both sides in the width direction, and a cavity extending from the end of the runner 13 with a reduced cross-sectional area. 11 is connected to the gate 14. The gate 14 is provided in a ring shape corresponding to the bead filler 1b. An unvulcanized rubber composition is supplied to the sprue 12 from an injection mechanism (not shown), and the supplied unvulcanized rubber composition is injected and injected into the cavity 11 through the runner 13 and the gate 14.

  Here, the unvulcanized rubber composition refers to a material prepared by blending a raw material rubber with a compounding material such as a vulcanizing agent by a conventional method and capable of heat crosslinking. The raw rubber is not particularly limited, and general-purpose rubbers such as natural rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR) can be used.

  The annular groove 9 has a cross-sectional shape corresponding to the bead member 10, and an annular bead core 1 a is disposed on the radially inner portion thereof as shown in FIG. 3. On the radially outer side of the bead core 1a, a cavity 11 is formed in a state where the annular concave groove 9 is closed by the upper die 8, and a gate 14 is connected to the vicinity of the bead core 1a on the cavity surface 11a on the upper die 8 side. Become.

  The lower die 7 is a combination of a main body die portion 15, a ring-like die portion 16 placed on the upper surface thereof, and a core die portion 17 that is inscribed in the ring-like die portion 16 and supports the bead core 1 a from below. It is configured. The boundary surface 18 between the ring-shaped mold part 16 and the core mold part 17 is formed in an upwardly tapered shape. If the mold is open, the core mold part 17 is separated from the main body mold part 15 and the ring-shaped mold part 16. It can be spaced upward.

  A pressing device 21 is provided in the vicinity of the bead core 1a on the cavity surface 11b on the lower mold 7 side so as to face the gate connecting portion 20. When the unvulcanized rubber composition is injected and injected into the cavity 11, a bead filler 1b as shown in FIG. 4 is formed. The pressing device 21 is opposed to the gate connecting portion 20 of the bead filler 1b. It has a function of pressing the portion 30. As will be described later, by pressing the facing portion 30, a compressive stress symmetrical to the stress generated by injection injection of the unvulcanized rubber composition can be applied to the bead filler 1 b.

  The pressing device 21 has a ring-shaped piston member 22 for pressing the facing portion 30 of the bead filler 1b. The lower mold 7 is provided with an accommodation hole 23 for accommodating the piston member 22 and an air supply hole 24 communicating with the accommodation hole 23, and compressed air is supplied to the air supply hole 24 from a compressor (not shown). As a result, the piston member 22 can be advanced and retracted relative to the cavity 11. Examples of the piston member 22 include those having a tip portion diameter of 2 to 5 mm and a lifting stroke of 1 to 10 mm.

  In the present embodiment, the cavity surface portion 11c that forms the facing portion 30 opposite to the gate connecting portion 20 is formed in a ring shape, and the tip of the lowered piston member 22 is positioned at the bottom of the cavity surface portion 11c. Is configured to do. As a result, when the unvulcanized rubber composition is injected and injected into the cavity 11, a facing portion 30 that protrudes downward from the cavity surface 11b is formed. Further, when the piston member 22 is raised, the facing portion 30 of the bead filler 1b is pressed, and the depression of the cavity surface portion 11c is eliminated as shown in FIG. 5 so that the protrusion of the facing portion 30 disappears. Yes.

  In short, the pressing device 21 is opposed to the cavity 11 when the unvulcanized rubber composition is injected and injected into the cavity 11 by recessing the cavity surface portion 11c forming the facing portion 30 in accordance with the elevation of the piston member 22. A standby state in which the portion 30 can be formed and a pressed state in which the depression of the cavity surface portion 11c can be eliminated and the protrusion of the facing portion 30 can be eliminated can be selectively adopted.

  Although not shown in the drawing, the mold 6 is provided with a temperature control mechanism. Such a temperature control mechanism has a function of supplying hot water or cold water to a flow path provided in the molding die 6, for example, and is configured to be able to control its temperature, flow rate, supply timing, and the like. Alternatively, a heater or a cooling element may be embedded in the mold 6 and temperature control thereof may be performed based on the detection result of the temperature sensor.

  Hereinafter, a method for injection molding the bead filler 1b using the above-described mold 6 will be described. First, the bead core 1a is disposed in the annular groove 9 of the lower mold 7 in the mold open state, and then the upper mold 8 is displaced to the mold clamping position and is crimped to the lower mold 7. As a result, the annular concave groove 9 is closed by the upper mold 8 to be in a mold clamping state, and a cavity 11 is formed inside the mold 6 as shown in FIG.

  Next, an unvulcanized rubber composition is injected and injected into the cavity 11 to form a bead filler 1b as shown in FIG. 4 (corresponding to the injection step). The bead filler 1b is molded as a bead member 10 in which a bead core 1a is integrated on the inner periphery. The mold 6 in such a process is heated and held at a temperature at which the fluidity of the unvulcanized rubber composition is ensured. This temperature may be lower than the vulcanization temperature, or may be the vulcanization temperature as in the case of conventional injection molding.

  In the present embodiment, the cavity surface portion 11c facing the gate connecting portion 20 and the bead filler 1b in the thickness direction is formed in a ring shape so that the facing portion 30 of the bead filler 1b is below the cavity surface 11b. And projecting in a ring shape. At this stage, the stress distribution state as shown in FIG. 9 is obtained by injection injection of the unvulcanized rubber composition, and stress is concentrated in the vicinity of the gate connecting portion 20 of the bead filler 1b. .

  And as shown in FIG. 5, compressed air is supplied to the air supply hole 24, and the piston member 22 of the press apparatus 21 is raised. Thereby, the pressing device 21 in the standby state shifts to the pressing state and can press the facing portion 30 of the bead filler 1b (corresponding to the pressing step). As a result, the residual stress remaining in the bead filler 1b can be reduced by applying a compressive stress symmetrical to the stress generated by injection injection of the unvulcanized rubber composition. The magnitude of this compressive stress is preferably at a level comparable to the residual stress remaining in the vicinity of the gate connecting portion 20, and the diameter of the piston member 22 and the lifting stroke are set so as to obtain such an appropriate magnitude. .

  In the present embodiment, the facing portion 30 of the bead filler 1b is formed so as to protrude, and the piston member 22 is raised so that the protrusion of the facing portion 30 is pressed to disappear. Therefore, the compressive stress generated by the pressing of the facing portion 30 can be efficiently increased, and the residual stress of the bead filler 1b can be effectively reduced. In addition, since the bead filler 1b is in an unvulcanized state and has low rigidity, the facing portion 30 is pushed relatively smoothly by the pressing of the piston member 22.

  The tip of the piston member 22 is preferably arranged on the same plane as the cavity surface 11b when the pressing device 21 is in the pressing state. Thereby, a dent mark is not formed in the opposing part 30 of the bead filler 1b, and the influence on an external appearance can be suppressed.

  Subsequently, while the molded bead filler 1b is in an unvulcanized state, the mold 6 is opened and the bead member 10 is removed (corresponding to the demolding step). In addition, after pressing the opposing part 30 of the bead filler 1b, it is preferable to remove the mold after passing through a process of cooling the bead filler 1b, and thereby the bead filler 1b is securely added while applying compressive stress due to the pressing. It can be held in a sulfur state. The bead filler 1b can be cooled by the temperature control mechanism described above.

  When the bead member 10 is removed from the mold, the core mold part 17 may be separated upward from the main body mold part 15 and the ring-shaped mold part 16. As a result, the bead core 1a having a high rigidity is demolded in a state where the bead core 1a is uniformly supported in the circumferential direction, and the unvulcanized and low-rigidity bead filler 1b is smoothly taken out without causing deformation. Although the unvulcanized bead filler 1b has high adhesiveness and tends to be difficult to separate from the mold 6, the bead filler 1b can be smoothly separated by lifting the bead core 1a evenly in the circumferential direction. .

  The residual stress in the bead filler 1b is reduced by the pressing of the facing portion 30 described above. For this reason, the removed bead filler 1b is not greatly raised and deformed in the vicinity of the gate connecting portion 20 as shown in FIG. 6, and can be prevented from being deformed unevenly. Particularly in the present embodiment, the unvulcanized rubber composition is injected and injected through the ring-shaped gate 14, and the opposed portion 30 formed in a state of protruding in the ring shape is pressed by the ring-shaped piston member 22, A cross-sectional shape as shown in FIG. 6 is obtained over the entire circumference of the bead filler 1b, and the uniformity of the shape can be ensured well in the circumferential direction.

  Further, the vulcanization step in the mold 6 is omitted, and further, it is not necessary to secure a holding time for relaxing the residual stress, so that the molding time is not prolonged. The molded bead member 10 is combined with other unvulcanized rubber molded bodies such as the carcass ply 4 to constitute a pneumatic tire, and has excellent adhesion as compared with the case where the vulcanization process is performed. The bead filler 1b is not limited to one in which vulcanization has not progressed at all, and may be in a state corresponding to insufficient vulcanization, but from the viewpoint of shortening the molding time and adhesion to the carcass ply 4 It is preferable to start cooling immediately after injecting and injecting the vulcanized rubber composition and pressing the facing portion 30 so that the vulcanization does not proceed as much as possible.

  The rubber molded body molded by the present invention is not limited to the bead filler 1b, but constitutes a rubber molded body constituting a tire such as the sidewall rubber 2 illustrated in FIG. 7 or a rubber composite other than the tire. It may be a rubber molded body. However, the present invention is useful for injection molding of bead fillers. The reason for this is that the bead filler made of hard rubber has a poor mold flow due to the high viscosity of the unvulcanized rubber composition, and tends to be injected and injected at high pressure and overshot, and the occurrence of residual stress is remarkable. However, according to the present invention, the residual stress can be reduced as described above. Here, the hard rubber refers to rubber having a hardness of 70 ° or more according to JIS K6253 durometer hardness test (A type).

  The present invention is not limited to the embodiments described above, and various improvements and modifications can be made without departing from the spirit of the present invention, and the structure of the mold can be changed as appropriate. For example, horizontal injection molding in which the opening / closing direction of the mold is horizontal may be adopted, or the rubber molded body may be removed using an ejector pin. The structure of the pressing device is not particularly limited to that shown in the above-described embodiment as long as the opposing portion of the rubber molded body can be pressed directly or indirectly. Therefore, for example, the cavity surface portion forming the facing portion may be divided and formed, and the facing portion may be pressed by advancing and retracting the cavity with a motor drive.

The perspective view which shows the (a) clamping state and (b) mold open state of the shaping | molding die which concern on this invention Longitudinal sectional view of the mold in the clamped state Longitudinal section showing the periphery of the mold cavity Longitudinal section showing the periphery of the mold cavity Longitudinal section showing the periphery of the mold cavity Sectional view of a bead member formed according to the present invention Sectional drawing which shows an example of a pneumatic tire Perspective view showing a partially broken bead member Sectional view conceptually showing stress distribution caused by injection injection of unvulcanized rubber composition Sectional view of a bead member formed by a conventional method

Explanation of symbols

1a Bead core 1b Bead filler (an example of a rubber molding)
4 Carcass ply 6 Mold 7 Lower mold 8 Upper mold 9 Annular groove 10 Bead member 11 Cavity 11c Cavity surface portion 14 Gate 20 Gate connecting portion 21 Pressing device 22 Piston member 23 Housing hole 24 Air supply hole 30 Opposite portion

Claims (6)

An injection step of injecting and injecting an unvulcanized rubber composition into a cavity formed inside the mold in a mold-clamping state, and molding a rubber molded body;
While the rubber molded body is in an unvulcanized state, a pressing step of pressing a facing portion opposite to the gate connecting portion of the rubber molded body,
And a demolding step of taking out the rubber molded body in an unvulcanized state from the mold after the pressing step.   In the injecting step, the cavity surface portion forming the facing portion is recessed to form the facing portion, and in the pressing step, the cavity surface portion is removed to eliminate the protrusion of the facing portion. The method for injection molding a rubber molded body according to claim 1.   The method for injection molding a rubber molded body according to claim 1 or 2, wherein the rubber molded body is an annular bead filler made of a hard rubber having a substantially triangular cross section which is vertically long in the radial direction. In a mold-clamped state, a cavity is formed inside, and an injection mold of a rubber molded body configured such that a rubber molded body can be molded by injection-injecting an unvulcanized rubber composition into the cavity,
A gate connected to the cavity for injecting and injecting the unvulcanized rubber composition, and a pressing device for pressing a facing portion opposite to a gate connecting portion of a rubber molded body formed in the cavity. An injection molding die for a rubber molded body, comprising:   A standby state in which the pressing device dents a cavity surface portion that forms the opposing portion, and the opposing portion protrudes when the unvulcanized rubber composition is injected and injected into the cavity; and the cavity surface The injection molding die for a rubber molded body according to claim 4, which can selectively take a pressed state in which the depression of the portion can be eliminated and the protrusion of the facing portion can be eliminated.   6. The injection molding die for a rubber molded body according to claim 4 or 5, wherein the pressing device has a piston member capable of moving back and forth with respect to the cavity.

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