JP2007136998A - Injection molding method of rubber molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method of a rubber molded body capable of suppressing the bonding of the rubber molded body to an upper mold at the time of mold opening in molding an unvulcanized rubber molded body by vertical injection molding. <P>SOLUTION: A mold 6, which is constituted so that an upper mold 8 is opened and closed in an up and down direction with respect to a lower mold 7 and the cavity surface 7a of the lower mold 7 is smaller in surface roughness than the cavity surface 8a of the upper mold 8, is used to inject an unvulcanized rubber composition in the cavity 11 of the mold 6 in a mold clamped state. Thereafter, the mold 6 is opened during a period when the rubber molded body molded in the cavity 11 is an unvulcanized state to leave the rubber molded body in the lower mold 7 before the rubber molded body is taken out of the lower mold 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 comprising 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. 5, 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. 6, the bead member 10 includes an annular bead filler 1b made of hard rubber having a substantially triangular cross section that is vertically long in the radial direction, and an annular bead core 1a disposed on the inner periphery of the bead filler 1b. Have. The bead core 1a is composed of, for example, a converged steel wire covered with rubber.

  Such bead filler is generally formed by extrusion. Specifically, an unvulcanized rubber composition is extruded by an extruder through a die having a predetermined cross-sectional shape, cut into a predetermined length, and then formed into an annular shape by joining ends of the extruded product. The However, extrusion molding requires a process such as cutting and joining, and there is a problem that man-hours increase. Moreover, the part which becomes thick locally was formed by press-contacting the edge parts to join, and there existed a tendency for uniformity to fall.

  On the other hand, as described in Patent Document 1 below, for example, it is conceivable to form a bead filler by injection molding. In such a case, a bead filler with good uniformity can be molded by injecting and injecting an unvulcanized rubber composition into the cavity of the mold using a mechanism similar to an extruder. However, in normal injection molding, heat and pressure are applied to the rubber molded body in the molding die for a certain period of time, and demolding is performed after the vulcanization step. Therefore, the resulting bead filler is vulcanized. . For this reason, when molding a tire, the adhesion with an unvulcanized carcass ply was not good.

  On the other hand, when molding an unvulcanized rubber molding by injection molding, there is a problem that the rubber molding tends to stick to the mold after opening due to its high adhesiveness. . In particular, in the vertical (vertical) injection molding in which the mold is opened and closed vertically, it is often attached to the upper mold provided with the gate, and the high temperature rubber molded product is peeled off from the upper mold each time. This is a complicated task. Furthermore, in order to automate the apparatus, it is useful to stably leave the rubber molded body in the lower mold when the mold is opened.

The following measures (a) to (d) can be considered for this problem.
Countermeasure (a): An eject pin that can be retracted toward the lower mold side is provided in the upper mold, and the rubber molded body is separated from the upper mold by projecting the eject pin when the mold is opened.
Countermeasure (b): An undercut portion capable of fixing the molded bead filler is formed in the lower mold, and the rubber molded body is fixed to the lower mold when the mold is opened.
Countermeasure (c): An air passage that opens at the cavity surface is provided in the upper die, and the rubber molded body is separated from the upper die by supplying air to the air passage when the die is opened (see Patent Document 2 below).
Countermeasure (d): The temperature is controlled so that the upper die is lower in temperature than the lower die, and a difference in the adhesiveness is provided so that the rubber molded body is left in the lower die when the die is opened.

However, since the rubber molded body is not vulcanized, the rigidity is low and the shape is likely to be lost. Therefore, the countermeasures (a) and (b) are both ineffective and not good. In the measure (c), the supplied air may be short-circuited from the opening of the cavity surface and may not spread over the entire cavity surface. In such a case, the rubber molded body does not separate properly from the upper mold. Not right. Further, it is difficult to provide a temperature difference between the lower mold and the upper mold as described above while ensuring the fluidity of the unvulcanized rubber composition injected into the cavity, and the measure (d) is not practical. .
JP-A-5-69500 Japanese Patent Laid-Open No. 11-58463

  The present invention has been made in view of the above circumstances, and its purpose is to suppress sticking of the rubber molded body to the upper mold when the mold is opened when molding an unvulcanized rubber molded body by vertical injection molding. Another object of the present invention is to provide a method for injection molding a rubber molded body.

  The above object can be achieved by the present invention as described below. That is, in the method for injection molding a rubber molded body according to the present invention, the upper mold opens and closes in the vertical direction with respect to the lower mold, and the cavity surface of the lower mold is smaller in surface roughness than the cavity surface of the upper mold. Using a molding die, an unvulcanized rubber composition is injected and injected into a cavity of the mold in a clamped state, and then the molding is performed while the rubber molded body molded in the cavity is in an unvulcanized state. After the mold is opened and the rubber molded body is left in the lower mold, the unvulcanized rubber molded body is taken out from the lower mold.

  The operation and effect of the rubber molding injection molding method according to the present invention will be described. First, in the present invention, a molding die in which an upper die is opened and closed with respect to a lower die is used, and an unvulcanized rubber composition is injected and injected into a cavity of the die that is clamped. 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 injected unvulcanized rubber composition is filled into a cavity and molded as a rubber molded body. In normal rubber injection molding, demolding is performed after vulcanization in a mold. In the present invention, the mold is opened while the rubber molded body is in an unvulcanized state. In addition, since the cavity surface of the lower mold is smaller in surface roughness than the cavity surface of the upper mold, the suction cup effect between the lower mold cavity surface and the unvulcanized soft rubber molded body is enhanced, The rubber molded body that is relatively firmly attached to the lower mold is left in the lower mold.

  This eliminates the troublesome work of peeling off the rubber molded body from the upper mold, and can stably leave the rubber molded body on the lower mold when the mold is opened, which is useful for automation of the apparatus. The molded rubber molded body is taken out from the lower mold after mold opening in an unvulcanized state. 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.

  In the above, the surface roughness Ra (L) of the cavity surface of the lower mold and the surface roughness Ra (U) of the cavity surface of the upper mold are 0.4 μm <Ra (U) −Ra (L) <6 μm. It is preferable to satisfy the above-mentioned conditions. This makes it possible to cause an appropriate difference in the adsorption action between the cavity surface of the lower mold and the cavity surface of the upper mold, and appropriately leave the rubber molded body in the lower mold when the mold is opened. it can. The “surface roughness Ra” is the arithmetic average roughness Ra defined in JIS B0601-1994.

  The present invention is particularly useful for molding an annular bead filler in which the rubber molded body is made of hard rubber. In such a case, an annular bead filler that is a tire constituent member can be molded with good uniformity and high accuracy, and adhesion to an unvulcanized carcass ply at the time of tire molding becomes good. In addition, in the bead filler made of hard rubber, it is important to secure the fluidity of the unvulcanized rubber composition injected into the cavity. In the present invention, the rubber molded body is left in the lower mold due to the above-described effects. Therefore, there is no need to provide a temperature difference between the lower mold and the upper mold, and the fluidity can be easily ensured. Here, the hard rubber refers to rubber having a hardness of 70 ° or more according to JIS K6253 durometer hardness test (A type). Furthermore, since the present invention is vertical injection molding, the bead core can be easily inserted into the mold and is useful when the bead filler is molded as a bead member formed integrally with the bead core.

  Embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a bead filler is taken 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 vertical cross-sectional view of a mold in a clamped state. 2A is a plan view of the lower mold, and FIG. 2B is a longitudinal sectional view thereof. The molding die 6 includes a lower die 7 and an upper die 8, and an annular cavity 11 having a cross-sectional shape corresponding to the bead member 10 is formed in a clamped state in which they are in close contact. The cavity 11 is formed between a concave cavity surface 7 a formed on the upper surface of the lower mold 7 and a cavity surface 8 a forming a part of the lower surface of the upper mold 8.

  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 extending from the end of the runner 13 with a relatively small cross section to the cavity 11. And a gate 14 communicating therewith. 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 via the runner 13 and the gate 14.

  In the present embodiment, an air passage 18 that opens at the cavity surface 8 a is provided in the upper mold 8. Air is supplied to the air passage 18 from an air supply mechanism 28 described later, and the supplied air is injected into the interface between the bead filler formed in the cavity 11 and the cavity surface 8a. Moreover, the warm water hole 15 is provided in the upper vicinity of the runner 13, and it is comprised so that warm water supplied from the warm water supply mechanism 30 mentioned later can be poured.

  The lower mold 7 is provided with a hot water hole 21 so that hot water supplied from a hot water supply mechanism 30 described later can flow. The peripheral portion of the cavity 11 is held within a predetermined temperature range by hot water. This temperature range is a temperature range in which the fluidity of the unvulcanized rubber composition injected into the cavity 11 is ensured, and the bead filler is not vulcanized between injection and demolding. In addition, you may embed a heater in the shaping | molding die 6 and control it so that it may become said temperature range.

  Each of the cavity surfaces 7a and 8a is preferably subjected to a coating process or a mirror finishing process for improving the releasability. Since the bead filler molded as a rubber molded body in this embodiment is bonded to another rubber member at the time of tire molding, it is not preferable to apply a release material to the cavity surface. Examples of the coating treatment include fluorine coating and silicon coating. In this embodiment, the cavity surface 7a and the cavity surface 8a are coated with fluorine, and the demoldability is improved by suppressing the adhesion of rubber.

  The cavity surface 7 a of the lower mold 7 is formed with a smaller surface roughness than the cavity surface 8 a of the upper mold 8. Specifically, in the blasting process, which is a pretreatment for fluorine coating, the surface roughness of the cavity surface 7a is adjusted to be smaller than that of the cavity surface 8a. The adjustment of the surface roughness is performed within a range that does not affect the fluorine coating (for example, the surface roughness Ra is 1.0 to 10 μm). Thereby, in the molding process of the bead filler described later, the sucker effect between the soft bead filler and the cavity surface 7a in the unvulcanized state is enhanced, and the adsorption action of the bead filler on the cavity surface 7a is greater than the cavity surface 8a. Will also be great. As a result, when the mold is opened, the bead filler is stuck to the lower mold 7 and remains.

  Here, it is preferable that the surface roughness Ra (L) of the cavity surface 7a and the surface roughness Ra (U) of the cavity surface 8a satisfy 0.4 μm <Ra (U) −Ra (L) <6 μm, More preferably, 1 μm <Ra (U) −Ra (L) <5 μm is satisfied. If this is 0.4 μm or less, the difference in adsorption action between the cavity surface 7a and the cavity surface 8a may not be sufficient, and the above-described effects tend to be small. On the other hand, when the thickness is 6 μm or more, the anchor effect on the cavity surface 8a is increased, and the above-described effects tend to be reduced. In addition, said surface roughness Ra (L) and Ra (U) are surface roughness measured after fluorine coating.

  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, aluminum alloy, and zinc alloy, can be appropriately used.

  FIG. 3 is a schematic configuration diagram schematically showing the configuration of the injection molding machine. This injection molding machine is a vertical injection molding machine in which the upper mold 8 opens and closes in the vertical direction with respect to the lower mold 7, and has a pair of plates including a fixed platen 24 and a movable platen 25. The lower die 7 is attached and the upper die 8 is attached to the movable platen 25. The stationary platen 24 is supported on the table 23 and can reciprocate between a front side position (left side in FIG. 3) and a back side position (right side in FIG. 3) as viewed from the operator by a transport mechanism (not shown). It is configured.

  In addition, the movable platen 25 is moved from the lower mold 7 to the upper mold 8 by a lifting mechanism 26 driven by a hydraulic cylinder, for example, in a lowered position where the upper mold 8 comes into contact with the lower mold 7 at the back side position and is in a mold clamping state. Is configured to be movable up and down with respect to an ascending position at which the mold opens. The operator inserts a bead core into the lower mold 7 or takes out the molded bead filler on the front side of the table 23 (left side in FIG. 3). Therefore, it is required that the molded bead filler is stably left in the lower mold 7 when the mold is opened.

  The injection mechanism 27 fixed above the movable platen 25 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 air supply mechanism 28 has a function of supplying air to the air passage 18. The hot water supply mechanism 30 has a function of supplying hot water to the hot water holes 15 and the hot water holes 21. The control device 29 has a function of controlling the operation of each mechanism.

  Next, a method for forming the bead member 10 will be described. FIG. 4 is a longitudinal sectional view of a forming die showing a forming procedure of the bead member. For convenience of illustration, the front side position and the back side position of the lower mold 7 are not distinguished. First, as shown in FIG. 4A, an annular bead core 1a is inserted into the inner peripheral side portion of the cavity surface 7a of the lower mold 7 at the front side position with respect to the mold 6 in the mold open state. . When the lower mold 7 moves to the back side position together with the fixed platen 24 and is disposed below the upper die 8, the movable platen 25 is lowered, the upper die 8 is brought into close contact with the lower die 7, and the mold clamping is performed. Is called.

  After the mold clamping, as shown in FIG. 4B, the unvulcanized rubber composition R is injected and injected into the cavity 11 by the injection mechanism 27. At this time, the mold 6 is heated and held at a temperature at which the fluidity of the unvulcanized rubber composition R is ensured. This temperature may be lower than the vulcanization temperature, or may be the vulcanization temperature as in conventional injection molding. The unvulcanized rubber composition R injected and injected is filled in the cavity 11, and an annular bead filler 1b in which the bead core 1a is integrated on the inner periphery, that is, the bead member 10 is formed.

  When heat and pressure are applied to the molded bead filler 1b for a certain period of time, vulcanization is performed. In this embodiment, the movable platen 25 is raised while the bead filler 1b is in an unvulcanized state, and FIG. The mold is opened as shown in c). In addition, cooling water holes are provided around the cavity 11, and cold water is supplied to the cooling water holes while the molded bead filler 1b is in an unvulcanized state so that the bead filler 1b is lower than the vulcanization temperature. By doing so, you may make it hold | maintain in an unvulcanized state.

  Further, the molded unvulcanized bead filler 1b is soft and the cavity surface 7a is formed with a surface roughness smaller than that of the cavity surface 8a, so that the bead filler 1b and the cavity surface 7a Since the suction effect of the bead filler 1b on the cavity surface 7a is larger than that on the cavity surface 8a, the bead filler 1b is placed on the lower mold as shown in FIG. 7 is left attached.

  In addition, although the suction cup effect is exhibited by both the cavity surface 7a and the cavity surface 8a, the adsorption action is larger in the cavity surface 7a, and in the cavity surface 8a having a relatively large surface roughness, When the mold is opened, the rubber is deformed to form a gap at the interface, and air enters the gap, so that the adsorption action is released and the bead filler 1b is easily separated. In the state before the mold opening, the bead filler 1b is connected to the rubber in the gate 14, but the rubber is cut at a relatively small cross section near the cavity surface 8a when the mold is opened.

  In this embodiment, when the mold is opened, air is supplied to the air passage 18 and air is injected into the interface between the bead filler 1b and the cavity surface 8a, so that the bead filler 1b can be separated from the upper mold 8 more reliably. it can. For example, gases other than air, such as nitrogen and argon, can be used as appropriate. Such air injection may not be effective by itself, but a great effect can be obtained by using it together with the setting of the surface roughness of the cavity surface.

  After the mold is opened, the lower mold 7 moves to the near side position together with the stationary platen 24, and the molded unvulcanized bead filler 1b (bead member 10) is taken out. As illustrated in FIG. 5, the bead member 10 is combined with another unvulcanized rubber molded body such as the carcass ply 4 to constitute a pneumatic tire. Since the bead filler 1b molded according to the present invention is in an unvulcanized state, the bead filler 1b is superior in adhesion to the carcass ply 4 as compared with the case of using the bead filler that has undergone the vulcanization process.

  Here, the bead filler 1b 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 4, it is preferable to start cooling immediately after injection injection of the unvulcanized rubber composition and to prevent the vulcanization from proceeding as much as possible.

  The rubber molded body molded by the present invention is not limited to the bead filler 1b. For example, a rubber molded body constituting a tire component such as the sidewall rubber 2 shown in FIG. 5 or a rubber composite other than a tire. It may be.

  The present invention is not limited to the embodiment described above, and various improvements and modifications can be made without departing from the spirit of the present invention. Therefore, for example, instead of the upper mold used in the above-described embodiment, an upper mold having a concave cavity surface formed on the lower surface may be adopted, and various shapes are molded according to the rubber molded body to be molded. A mold can be used.

  In order to specifically show the configuration and effects of the present invention, a bead filler is actually molded and the state of sticking to a mold is investigated, which will be described. The cavity surface of the lower mold and the cavity surface of the upper mold were each coated with fluorine after blasting. Table 1 shows the measurement results of the surface roughness Ra (L) of the cavity surface of the lower mold and the surface roughness Ra (U) of the cavity surface of the upper mold measured with a surface roughness meter after fluorine coating. That's right.

  Each of the bead fillers was molded three times, and the pasting state was evaluated in four stages of ◎, ○, Δ, and ×. When the mold was opened, the number of times that the bead filler was left in the lower mold was ◎: 3 times, ◯: 2 times, △: 0 times, and x: 0 times. That is, the number of times that the bead filler is attached to the upper die is 0, 1, 2, and 3 in the order of ◎, ○, Δ, and x.

  As shown in Table 1, in each example, the number of times the bead filler was left in the lower mold was higher than in Comparative Examples 1 to 4, and the surface roughness of the lower mold cavity surface was higher than the upper mold cavity surface. By making it small, it turns out that it can suppress that a bead filler sticks to an upper model at the time of mold opening. Among these, the rubber molded body can be appropriately left in the lower mold by satisfying 0.4 μm <Ra (U) −Ra (L) <6 μm.

Longitudinal sectional view of the mold in the clamped state Lower plan view and vertical section Schematic configuration diagram schematically showing the configuration of the injection molding machine Longitudinal section of the mold showing the procedure for forming the bead member Pneumatic tire meridian cross section Perspective view showing a partially broken bead member

Explanation of symbols

1 Bead part 1a Bead core 1b Bead filler 6 Mold 7 Lower mold 7a Cavity surface 8 Upper mold 8a Cavity surface 10 Bead member 11 Cavity 18 Air passage

Claims (3)

  The mold cavity is clamped by using a mold whose upper mold opens and closes vertically relative to the lower mold and whose cavity surface is lower in surface roughness than the cavity surface of the upper mold. The unvulcanized rubber composition is injected and injected into the cavity, and then the mold is opened while the rubber molded body molded in the cavity is in an unvulcanized state, and the rubber molded body is used as the lower mold. A rubber molded body injection molding method for removing the unvulcanized rubber molded body from the lower mold after being left behind.   The surface roughness Ra (L) of the cavity surface of the lower mold and the surface roughness Ra (U) of the cavity surface of the upper mold satisfy 0.4 μm <Ra (U) −Ra (L) <6 μm. Item 2. A method for injection molding a rubber molded article according to Item 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 hard rubber.

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