JP2006248036A - Injection molding method of rubber molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method of a rubber molded product capable of smoothly injection-molding an unvulcanized rubber molded product by ensuring the flowability of the unvulcanized rubber composition injected in a mold and the demolding properties of the molded rubber molded product. <P>SOLUTION: The mold 6 is heated to a temperature capable of ensuring the flowability of the unvulcanized rubber composition and, after the unvulcanized rubber composition is injected in the cavity 11 of the mold 6, the rubber molded product is cooled during a state that the rubber molded product molded in the cavity 11 is unvulcanized to eject the rubber molded product from the mold 6 in an unvulcanized state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an injection molding method 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. 8, the pneumatic tire is configured by bonding a plurality of members made of a rubber molded body such as a sidewall rubber 2, a tread rubber 3, and an inner liner rubber 5.

  The carcass ply 4 is a rubber molded body in which a plurality of carcass cords arranged in parallel are covered with rubber. The carcass ply 4 is arranged so as to be bridged between a pair of bead portions 1, and the end portion in the width direction has a bead member 10. It is rolled back so as to be pinched. As shown in FIG. 9, the bead member 10 includes an annular bead filler 1b made of hard rubber having a substantially triangular cross section, and an annular bead core 1a disposed on the inner periphery of the bead filler 1b. The bead core 1a is composed of, for example, a converged steel wire covered with rubber.

  The bead filler is generally formed by extrusion molding or injection molding. In the former, an unvulcanized rubber composition is extruded from a die having a predetermined cross-sectional shape using an extruder, cut by a predetermined length, and then molded by joining ends. The latter is molded by injection-injecting an unvulcanized rubber composition into a mold cavity using a mechanism similar to an extruder.

  By the way, in extrusion molding, since processes, such as a cutting | disconnection and joining, are needed, there existed a problem that a man-hour increased. Moreover, the part which becomes thick locally was formed by sticking the edge parts to join, and there existed a tendency for uniformity to fall. Patent Document 1 below discloses a method of forming a bead filler by laminating linear rubber in a spiral shape. In such a method, the tip of the bead filler is rounded depending on the thickness of the linear rubber. Therefore, when the tire is molded, the adhesion with the carcass ply is deteriorated, and it is easy to cause separation between members.

On the other hand, according to injection molding, for example, as described in Patent Document 2 below, uniformity can be ensured and the bead filler can be accurately molded. However, in normal injection molding, heat and pressure are applied to the rubber molded body in the mold for a certain period of time, and demolding is performed after the vulcanization process. Therefore, the resulting bead filler is vulcanized. It was. Therefore, the adhesion with the unvulcanized carcass ply was not good when the tire was molded. On the other hand, when an unvulcanized bead filler is molded by injection molding, there is a problem that in an unvulcanized state with low rigidity, it tends to stick to the mold, and the shape cannot be maintained and the shape tends to collapse. Further, the bead filler made of hard rubber has a problem that the viscosity of the unvulcanized rubber composition is high, and if the fluidity in the mold is impaired, molding failure may be caused.
JP-A-11-105155 JP-A-5-69500

  The present invention has been made in view of the above circumstances, and its purpose is to ensure the fluidity of the unvulcanized rubber composition injected and injected into the mold and the mold release of the molded rubber molded body. An object of the present invention is to provide an injection molding method for a rubber molded body, which can smoothly injection-mold an unvulcanized rubber molded body.

  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 a heating step of heating a molding die to a temperature at which fluidity of the unvulcanized rubber composition is ensured, and an unvulcanized rubber in the cavity of the molding die. An injection injection step of injecting the composition; a cooling step of cooling the rubber molded body after the injection injection process while the rubber molded body molded in the cavity is in an unvulcanized state; And a demolding step of taking out the vulcanized rubber molded body from the mold.

  According to the above configuration, when the rubber molded body is molded in the cavity, the mold is heated to a temperature at which the fluidity of the unvulcanized rubber composition is ensured, so that the mold is injected and injected into the mold. The fluidity of the unvulcanized rubber composition is ensured. Here, the temperature of the mold may be lower than the vulcanization temperature as long as the fluidity of the unvulcanized rubber composition is ensured, or the vulcanization temperature as in conventional injection molding. It doesn't matter.

  Then, after the injection molding process, the rubber molded body is cooled while the rubber molded body is in an unvulcanized state, whereby the rubber molded body is held in an unvulcanized state without being vulcanized. Such an unvulcanized rubber molded body is taken out from the mold in the demolding step. 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. It is also assumed that those corresponding to the vulcanized state that does not reach the above are included.

  The rubber molded body is improved in rigidity by being cooled in the cooling step, the adhesion with the mold is suppressed, and the rubber molded body is smoothly demolded without causing deformation. The unvulcanized rubber molded body obtained in this way is excellent in adhesiveness with other unvulcanized rubber molded bodies when constituting a rubber composite such as a pneumatic tire. Become. In addition, according to the present invention, since the vulcanization process in the mold is omitted, the cycle time can be greatly shortened as compared with the conventional injection molding in which the mold is removed through the vulcanization process. it can.

  In the above, it is preferable that the cavity wall surface constituting the cavity of the mold is subjected to a coating process or a mirror finishing process.

  The cavity wall that forms the cavity of the mold is coated or mirror-finished to reduce the anchor effect and improve the releasability, thereby effectively adhering the rubber molded body to the mold. It is suppressed. Examples of the coating treatment include fluorine coating and silicon coating, both of which can improve the release property of the rubber molded body.

  In the above, the heating step is performed by flowing a liquid heating medium through a first flow path provided in the vicinity of the runner of the mold, and the cooling step is provided in the vicinity of the cavity of the mold. It is preferable to carry out by flowing a liquid cooling medium through the second flow path.

  According to the said structure, temperature control can be efficiently performed instantaneously with respect to the part which needs heating or cooling of a shaping | molding die, and there can exist the above-mentioned effect effectively. That is, by flowing a heating medium through the first flow path, the vicinity of the runner is accurately heated, and the fluidity of the unvulcanized rubber composition injected and injected is effectively ensured. In addition, by flowing a cooling medium through the second flow path, the vicinity of the cavity is accurately cooled, the rubber molded body is not vulcanized and held in an unvulcanized state, and the rigidity of the rubber molded body is improved. This is useful for demolding. In addition, the time required for the heating process and the cooling process is shortened, and the cycle time of injection molding can be shortened.

  In the above, it is preferable that the rubber molded body is an annular bead filler made of hard rubber having a substantially triangular cross section that is vertically long in the radial direction.

  The present invention is particularly useful when a bead filler is molded as a rubber molded body, and can effectively eliminate the problems associated with conventional bead filler molding. That is, in the present invention, by adopting injection molding, an annular bead filler having a substantially triangular cross section that is vertically long in the radial direction can be molded with high accuracy while ensuring uniformity. In addition, in the bead filler made of hard rubber, the viscosity of the unvulcanized rubber composition is relatively high, and the problem of fluidity is remarkable, whereas according to the present invention, the unvulcanized rubber composition is as described above. The fluidity of the product is ensured. Further, since the unvulcanized bead filler is taken out from the mold, there is a problem of demolding property such as adhesion to the mold and shape loss. According to the present invention, the rubber molded body is improved by the above-described effects. Demoldability can be ensured. In particular, a bead filler made of hard rubber is useful for demolding because an appropriate rigidity can be obtained if it is cooled to around room temperature. In addition, since the unvulcanized bead filler is obtained, the adhesiveness with the uncured carcass ply is improved during the molding of the tire, so that the present invention is particularly useful.

  In the above, before injecting and injecting the unvulcanized rubber composition, a bead core disposing step of disposing an annular bead core in the cavity is provided, and the bead core is integrated on the inner periphery by the injecting and injecting step. Preferably, the bead filler is molded, and in the demolding step, the bead core is pressed in the demolding direction using a pressing member provided in the mold and the bead filler is taken out from the mold.

  By pressing the bead core integrated with the bead filler in the demolding direction, the bead filler can be easily separated from the mold, and the demoldability is improved. In addition, no depression or the like is formed in the bead filler, and the quality and appearance are not affected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a bead filler is taken up as an example of a rubber molded body, and specifically, molding of a bead filler 1b in which a bead core 1a as shown in FIG.

  First, a molding die used for molding the bead member 10 will be described. FIG. 1 is a perspective view illustrating a mold clamping state (a) and a mold opening state (b). FIG. 2 is a longitudinal sectional view of the molding die in the clamped state, and corresponds to the AA section of FIG. The molding die 6 includes a lower die 7 and an upper die 8, and a concave cavity wall surface 9 is formed in an annular shape on the upper surface of the lower die 7. The cavity wall surface 9 forms an annular cavity 11 in the clamped state. The cavity 11 has a cross-sectional shape corresponding to the bead member 10 as shown in FIG.

  The upper die 8 has a sprue 12 extending from the center of the upper surface toward the lower surface, a runner 13 extending from the sprue 12 to both sides in the width direction, and a cavity 11 extending from the end of the runner 13 with a reduced cross-sectional area. And a gate 14 communicating with. An unvulcanized rubber composition is supplied to the sprue 12 from an injection mechanism 27 described later, and the supplied unvulcanized rubber composition is 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.

  FIG. 3 is a cross-sectional view of the upper mold 8 and corresponds to the BB cross section of FIG. 1B and FIG. The flow path 15 (corresponding to the first flow path) is formed in a substantially annular shape, and has a supply port 17 and a discharge port 18 on the side surface of the upper mold 8. Hot water (corresponding to the heating medium) is supplied to the supply port 17 from a hot water supply mechanism 30 described later. The supplied hot water flows through the upper mold 8 along the flow path 15 and is discharged from the discharge port 18. The flow path 15 passes through the vicinity of the upper side of the runner 13 while avoiding the area above the cavity 11, and is formed in substantially the entire area of the upper mold 8.

  4 is a cross-sectional view of the upper die 8 and corresponds to the CC cross section of FIG. 1B and FIG. The flow path 16 (corresponding to the second flow path) is formed in a substantially annular shape like the flow path 15 and has a supply port 19 and a discharge port 20. The supply port 19 has a cold water supply mechanism to be described later. It differs from the flow path 15 in that it is formed so as to pass cold water (corresponding to the cooling medium) from 31 and to pass near the upper part of the cavity 11.

  Similar to the flow paths 15 and 16 formed in the upper mold 8, the lower mold 7 has a flow path 21 (corresponding to the first flow path) to which hot water is supplied and a flow to which cold water is supplied. A path 22 (corresponding to the second flow path) is formed. The flow paths 21 and 22 are provided substantially vertically symmetrical with the flow paths 15 and 16 in the mold clamping state shown in FIG. That is, the flow path 21 is formed so as to avoid the area below the cavity 11, and the flow path 22 is formed so as to pass near the lower part of the cavity 11. Further, the flow path 22 is formed so as to pass through the vicinity of the inner periphery of the cavity 11.

  An ejector pin 23 (corresponding to the pressing member) is provided below the cavity 11 of the lower mold 7. The ejector pin 23 is moved up and down by a pressing mechanism 28 to be described later, and is configured to be displaceable between a position where the tip end is aligned with the cavity wall surface 9 and a position where it enters the cavity 11. In the present embodiment, the tip of the ejector pin 23 is designed to enter the inner peripheral side portion of the cavity 11.

  The material of the mold 6 is not particularly limited, but a mold made of iron or a steel material mainly composed of iron is preferably used. Moreover, the material generally used for injection molding, such as aluminum, an aluminum alloy, and a zinc alloy, may be used. In the mold 6 of this embodiment, the cavity wall surface 9 is coated with fluorine.

  FIG. 5 is a block diagram schematically showing the configuration of the injection molding machine. The injection molding machine shown in FIG. 5 has a pair of plates including a fixed platen 24 and a movable platen 25, and the lower die 7 is attached to the fixed platen 24 and the upper die 8 is attached to the movable platen 25. The elevating mechanism 26 is driven by, for example, a hydraulic cylinder and has a function of elevating the movable platen 25. Thereby, the mold clamping and mold opening of the mold 6 are performed. The injection mechanism 27 includes a cylinder and a material supply device, and has a function of injecting and injecting an unvulcanized rubber composition into the cavity 11 of the mold 6. The pressing mechanism 28 is provided on the fixed platen 24 and has a function of pushing the ejector pin 23 upward from the lower surface of the lower mold 7. The control device 29 has a function of controlling the operation of each mechanism.

  The hot water supply mechanism 30 has a function of supplying hot water to the flow path 15 of the upper mold 8 and the flow path 21 of the lower mold 7. Similarly, the cold water supply mechanism 31 has a function of supplying cold water to the flow path 16 of the upper mold 8 and the flow path 22 of the lower mold 7. The hot water supply mechanism 30 and the cold water supply mechanism 31 are configured to be circulated so as to supply hot water or cold water discharged from the upper mold 8 or the lower mold 7 after temperature adjustment. The temperature and flow rate of hot water and cold water, supply timing, and the like are controlled by the control device 29.

  Next, a method for forming the bead member 10 will be described. FIG. 6 is a flowchart showing a procedure for forming the bead member. First, in the mold open state, the bead core 1a is disposed on the cavity wall surface 9 of the lower mold 7 (# 1). The bead core 1 a is disposed on the inner peripheral side portion of the cavity wall surface 9. Next, the movable platen 25 is lowered, the upper die 8 is brought into close contact with the lower die 7, and the die clamping is performed (# 2). Thus, the cavity 11 is formed, and the bead core 1a is disposed in the cavity 11 (corresponding to the bead core disposing step).

  After the mold clamping, warm water is supplied from the warm water supply mechanism 30 to the mold 6 (# 3, corresponding to the heating step). Thereby, the mold 6 is heated and maintained at a temperature at which the fluidity of the unvulcanized rubber composition is ensured. In addition, you may heat the shaping | molding die 6 before arrangement | positioning of the bead core 1a. Then, the unvulcanized rubber composition is injected and injected into the cavity 11 of the mold 6 by the injection mechanism 27 (# 4, corresponding to the injection injection step). Thereby, the unvulcanized rubber composition is filled in the cavity 11, and the annular bead filler 1b in which the bead core 1a is integrated on the inner periphery, that is, the bead member 10 is formed.

  In the bead filler 1b made of hard rubber, the unvulcanized rubber composition has a relatively high viscosity, but the flowability of the unvulcanized rubber composition is effectively ensured by the warm water flowing in the vicinity of the runner 13. . Here, the hard rubber refers to rubber having a hardness of 70 ° or more according to JIS K6253 durometer hardness test (A type).

  Subsequently, while the bead filler 1b molded in the cavity 11 is in an unvulcanized state, cold water is supplied from the cold water supply mechanism 31 to cool the bead filler 1b (# 5, corresponding to the cooling step). .) When it is maintained at the vulcanization temperature, it is cooled to a temperature at least deviating from the vulcanization temperature. Thereby, the molded bead filler 1b is not vulcanized but held in an unvulcanized state. In addition, by such cooling, particularly when cold water flows in the vicinity of the cavity 11, the rigidity of the bead filler 1b in the cavity 11 is improved, which is useful for demolding described later. In the bead filler 1b made of hard rubber, moderate rigidity useful for demolding can be obtained by cooling to 70 ° C. or lower.

  After a predetermined time has passed since the cold water was supplied, the movable platen 25 is raised and the mold 6 is opened (# 6). After the mold opening, the ejector pin 23 is pushed upward by the pressing mechanism 28, and the bead core 1a is pressed in the mold release direction (upward in this embodiment) (# 7). Thereby, the bead member 10 is partly separated from the cavity wall surface 9 and can be easily removed from the mold. When the unvulcanized bead filler 1b (bead member 10) is taken out from the mold 6 (# 8, corresponding to the demolding step), the next bead filler 1b is continuously molded. The above procedure is repeated. Therefore, in the present invention, heating and cooling are repeated for each molding, whereby the fluidity of the unvulcanized rubber composition injected and injected into the mold 6 and the demoldability of the molded bead filler 1b are effective. Secured.

  In the present embodiment, when the unvulcanized bead filler 1b is demolded, the cavity wall surface 9 is coated with fluorine so that the adhesion between the lower mold 7 and the bead filler 1b is suppressed, and the demolding property is reduced. Will improve. Further, the cooling of the mold improves the rigidity of the bead filler 1b, so that the mold can be removed smoothly without causing deformation. Furthermore, in this embodiment, since the flow path 22 formed in the lower mold 7 passes near the inner periphery of the cavity 11, the rigidity of the rubber portion of the bead core 1 a is effectively improved and is pressed by the ejector pin 23. Is pushed up properly.

  FIG. 7 is a diagram showing an example of a time chart for injection molding according to the prior art and the present invention, in which the horizontal axis represents molding time and the vertical axis represents rubber temperature. Of the broken lines in the figure, the dotted line is a conventional example showing injection molding of a vulcanized bead filler, and the solid line is an embodiment of the present invention showing injection molding of an unvulcanized bead filler. In addition, after molding the bead filler at least once, the bead core is subsequently disposed in the mold, the mold is clamped, and the state where the unvulcanized rubber composition is supplied to the injection mechanism is the initial state of the horizontal axis ( 0 min).

  The conventional example is not particularly provided with a cooling step, and in the initial state, the mold is heated and held around 160 ° C., which is the vulcanization temperature. The unvulcanized rubber composition is supplied to an injection mechanism and injected into a mold while being heated to about 100 ° C. Then, after reaching the vulcanization temperature and being held for 20 minutes, it is demolded. Thereby, the bead filler which passed through the vulcanization process is obtained.

  In the embodiment of the present invention, since the cooling step is provided before demolding, the temperature of the mold is low in the initial state, and it is necessary to heat the mold first. Such heating may be a temperature lower than the vulcanization temperature. For example, the fluidity of the unvulcanized rubber composition is ensured by heating to about 100 ° C. The unvulcanized rubber composition is supplied to an injection mechanism and injected into a mold while being heated to about 100 ° C. After injection injection, cooling is started after being held for ten seconds or more, and demolding at 40 to 70 ° C., for example. Thereby, the unvulcanized bead filler is obtained.

  From FIG. 7, it can be seen that the vulcanization step is omitted in the present invention, and the cycle time of the injection molding is greatly shortened as compared with the conventional case. In the time chart of the present invention shown in FIG. 7, the mold is heated by flowing 90 ° C. hot water at a flow rate of 50 l / min for 60 seconds or more, and the mold is cooled at 15 ° C. It is performed by flowing cold water at a flow rate of 50 l / min for 30 seconds.

  The unvulcanized bead filler 1b obtained according to the present invention is not limited to those in which vulcanization has not progressed at all, and may be in a state corresponding to insufficient vulcanization. However, from the viewpoint of shortening the cycle time and adhesion to the carcass ply, it is preferable to start cooling immediately after injection injection of the unvulcanized rubber composition and not to proceed with vulcanization as much as possible.

  For example, as shown in FIG. 8, the molded bead filler 1 b is combined with another unvulcanized rubber molded body such as the carcass ply 4 to constitute a pneumatic tire. The bead filler 1b molded according to the present invention is in an unvulcanized state, and has superior adhesion to the carcass ply 4 as compared with the case where a bead filler that has undergone a vulcanization process is used.

  The rubber molded body molded by the present invention is not limited to the bead filler 1b. For example, the rubber molded body constituting the side wall rubber 2 as shown in FIG. 8 or a rubber composite other than a tire may be used. Good.

<Another embodiment>
(1) The configuration of the mold and the injection molding machine is not limited to that shown in the above-described embodiment. For example, in the above-described embodiment, an example of a vertical injection molding machine in which the opening and closing direction of the molding die is vertical has been described, but a horizontal type or a horizontal horizontal folding type may be used instead. In the above-described embodiment, an example in which a single ejector pin is provided has been described. However, a plurality of ejector pins may be provided along the circumferential direction of the cavity.

  (2) In the above-mentioned embodiment, although the example which performs temperature control of a shaping | molding die using warm water and cold water was shown, this invention is not restricted to this, For example, various temperature control means, such as oil and a heater, can be used. it can. In such a case, a temperature sensor may be provided at an appropriate location of the mold, and temperature control may be performed based on the detected temperature.

  (3) In the above-described embodiment, an example in which the cavity wall surface is coated with fluorine has been shown. However, instead of this, for example, another coating treatment that can improve mold release properties such as silicon coating may be performed. . Alternatively, a mold made of a metal having excellent corrosion resistance may be used, and a cavity wall having a mirror finish may be used. Such coating treatment or mirror finishing treatment is preferably performed not only on the cavity wall surface of the lower mold but also on the lower surface of the upper mold constituting the cavity.

Perspective view of mold Longitudinal sectional view of the mold in the clamped state Cross section of upper mold Cross section of upper mold Block diagram simply showing the configuration of an injection molding machine Flow chart showing bead member forming procedure Injection molding time chart Pneumatic tire meridian cross section The perspective view which fractured | ruptured and showed the bead member which is an example of a rubber molded object partially

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 1a Bead core 1b Bead filler 4 Carcass ply 6 Mold 7 Lower mold 8 Upper mold 9 Cavity wall surface 10 Bead member 11 Cavity 13 Runner 15 Flow path through which hot water flows 16 Flow path through which cold water flows 21 Flow path through which hot water flows 22 Cold water Ejector pin 24 Fixed platen 25 Movable platen 27 Injection mechanism 30 Hot water supply mechanism 31 Cold water supply mechanism

Claims (5)

A heating step of heating the mold to a temperature at which the fluidity of the unvulcanized rubber composition is secured;
An injection injection step of injecting and injecting an unvulcanized rubber composition into the mold cavity;
After the injection injection step, a cooling step for cooling the rubber molded body while the rubber molded body molded in the cavity is in an unvulcanized state,
A demolding step of taking out the unvulcanized rubber molded body from the mold, and an injection molding method for the rubber molded body.   The rubber molding injection molding method according to claim 1, wherein the cavity wall surface constituting the cavity of the molding die is subjected to a coating process or a mirror finishing process. The heating step is performed by flowing a liquid heating medium through a first flow path provided near the runner of the mold,
The rubber molding injection molding method according to claim 1 or 2, wherein the cooling step is performed by flowing a liquid cooling medium through a second flow path provided in the vicinity of the cavity of the mold.   The method for injection molding a rubber molded body according to any one of claims 1 to 3, wherein the rubber molded body is an annular bead filler made of a hard rubber having a substantially triangular cross section that is vertically long in the radial direction. Before injection injection of the unvulcanized rubber composition, comprising a bead core disposing step of disposing an annular bead core in the cavity,
By the injection injection step, the bead core is molded with the bead core integrated into the inner periphery,
The rubber molding injection molding method according to claim 4, wherein, in the demolding step, the bead core is pressed in a demolding direction using a pressing member provided in the mold, and the bead filler is taken out from the mold. .

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