JP2008044204A - Vulcanization process of pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vulcanization process of pneumatic tires which does not require the need for a nitrogen gas supply unit and warm water supply unit and reduces the running cost of a vulcanization apparatus in vulcanizing pneumatic tires with a silica-compounded rubber compound for cap treads. <P>SOLUTION: In vulcanizing pneumatic tires using a silica-compounded rubber compound for cap treads, unvulcanized tires are placed in the mold, pressurized and heated from inside with a high pressure steam at a pressure of 1.4 MPa-1.8 MPa. The pressurizing process with the high pressure steam lasts for 2-8 minutes. Then, the tires are pressurized and heated from inside with a low pressure steam which has a lower pressure than the higher one and satisfies the formula: Pi>Pt+0.2. Pi is the pressure of the low pressure steam (as expressed by MPa in unit) and Pt is the saturated steam pressure (as expressed by MPa in unit) at the same temperature of the inside of the treads. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for vulcanizing a pneumatic tire using steam as a heating and pressurizing medium, and more specifically, for vulcanizing a pneumatic tire using a silica compound rubber compound as a cap tread. The present invention relates to a method for vulcanizing a pneumatic tire that eliminates the need for a nitrogen gas supply device and a hot water supply device, and enables reduction in running cost of the vulcanizer.

  Normally, when vulcanizing a pneumatic tire, an unvulcanized tire is put into the mold, the mold is heated from the outside, and the inside of the tire is directly heated or pressurized directly through a bladder. By filling the medium, the tire is heated simultaneously from inside and outside. Steam (saturated steam) is mainly used as the heating and pressurizing medium, but when only steam is used, the temperature changes in proportion to the pressure, so only the temperature is maintained while maintaining the necessary internal pressure. Can not be lowered. Thus, nitrogen gas or hot water is used in combination with steam as a heating and pressurizing medium. For example, high-pressure steam is used to set high-temperature and high-pressure vulcanization conditions in the early stages of vulcanization, while low-pressure and high-pressure vulcanization conditions are set in an appropriate temperature range by mixing low-pressure steam and nitrogen gas in the late vulcanization stage. Is set. By performing such an operation, a decrease in durability due to overvulcanization of the carcass layer is avoided while applying sufficient pressure to the tire.

  However, when nitrogen gas and hot water are combined with steam as described above, a nitrogen gas supply device and a hot water supply device are required separately, which increases the equipment cost of the vulcanizer, and further reduces the nitrogen gas and hot water. There is a problem that the running cost of the vulcanizer increases because a large amount of energy is required to obtain it.

  In contrast, it has been proposed to vulcanize a pneumatic tire using only steam without using nitrogen gas or hot water (see, for example, Patent Document 1). In this proposal, high temperature and high pressure vulcanization conditions are set by high pressure steam in the initial stage of vulcanization, while low temperature and low pressure vulcanization conditions are set by low pressure steam in the late vulcanization stage. Is set based on the number of carcass layers. In particular, in order to overcome the heat shrinkage force generated by the carcass layer, the lower limit value of the pressure applied in the latter vulcanization period is set based on the number of carcass layers.

As described above, the method of vulcanizing a pneumatic tire using only steam as a heating and pressurizing medium is effective for a pneumatic tire using a rubber compound containing a general carbon black as a cap tread. However, when such a vulcanization method is applied to a pneumatic tire using a silica compound rubber compound which has been popular in recent years for a cap tread, the water inside the tread is foamed, and a good tire cannot be obtained. Currently.
JP 62-297115 A

  An object of the present invention is to eliminate the need for a nitrogen gas supply device and a hot water supply device for pressurization when vulcanizing a pneumatic tire using a silica compound rubber compound as a cap tread, and reduce the running cost of the vulcanizer. It is an object of the present invention to provide a method for vulcanizing a pneumatic tire that can be reduced.

In order to achieve the above object, the method for vulcanizing a pneumatic tire according to the present invention is a method of vulcanizing a pneumatic tire using a silica compound rubber compound in a cap tread. The tire is heated while being pressurized from the inside with high-pressure steam having a pressure of 1.4 MPa to 1.8 MPa, and after maintaining the pressurizing step with the high-pressure steam for 2 to 8 minutes, the tire is more than the high-pressure steam. Heating is performed while pressurizing from the inside with low-pressure steam satisfying the following formula at a low pressure.
Pi> Pt + 0.2
Pi: Pressure of low-pressure steam (MPa)
Pt: saturated vapor pressure (MPa) at a temperature equal to the internal temperature of the tread

  As a result of diligent research on the cause of foaming of water inside the tread when vulcanizing a pneumatic tire using a silica compound rubber compound as a cap tread using only steam as a heating and pressurizing medium. The silica compounded rubber compound absorbs moisture more easily than the carbon black compounded rubber compound. To prevent foaming of moisture contained in the silica compounded rubber compound, which is highly hygroscopic, the inner side of the tire is also in the late vulcanization stage. As a result, the present inventors have found that it is necessary to maintain the pressure applied from above at a predetermined value or more that is related to the internal temperature of the tread.

  That is, in the present invention, after maintaining the pressurizing step with high-pressure steam for a predetermined time, the tire is pressed from the inside with low-pressure steam set to a pressure sufficiently higher than the saturated vapor pressure at a temperature equal to the internal temperature of the tread. By heating, even when a pneumatic tire using a rubber compound containing silica as a cap tread is vulcanized, foaming of moisture contained in the tread can be prevented. Since only steam is used as the heating and pressurizing medium, a nitrogen gas supply device and a hot water supply device for pressurization are unnecessary, and the running cost of the vulcanizing device can be reduced.

  In the present invention, the pressure of the low-pressure steam is preferably 1.0 MPa to 1.2 MPa. Thereby, the fall of durability resulting from the overvulcanization of the carcass layer can be avoided while more reliably preventing the volatilization of moisture inside the tread. This low pressure steam pressure condition is suitable when the external temperature of the mold is 160 ° C to 185 ° C. In addition, when pressurizing a tire from the inside, steam may be directly filled inside the tire without a bladder, or may be indirectly filled via a bladder.

  The pneumatic tire that is the subject of the present invention uses a silica compounded rubber compound for the cap tread. The silica compounded rubber compound is 5 to 100 parts by weight of silica with respect to 100 parts by weight of rubber. It is blended in the ratio. Such rubber compounds tend to be highly hygroscopic. Additives such as vulcanizing agents, vulcanization accelerators, anti-aging agents, softeners, silane coupling agents, etc. can be added to the rubber compound as appropriate. Of course, carbon black can be used in combination with silica. It is.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the relationship between the internal pressure of a tire and the vulcanization time in the method for vulcanizing a pneumatic tire of the present invention.

In the case of vulcanizing a pneumatic tire using a silica compounded rubber compound for a cap tread, as shown in FIG. It heats, pressurizing from the inside with a high-pressure steam of 1.8 MPa (197 ° C. to 209 ° C. in terms of temperature). If the pressure of the high-pressure steam is less than 1.4 MPa, the tire cannot be sufficiently molded, and if high-pressure steam having a pressure exceeding 1.8 MPa is used, the cost of the steam production facility becomes excessive. In FIG. 1, the range from time t ₁ to time t ₂ is the pressurizing step with high-pressure steam. The pressurizing step using high-pressure steam is maintained for 2 to 8 minutes until the vulcanization reaction proceeds and the rubber flow in the mold stops. If the pressurizing process using high-pressure steam is too short, the tire cannot be sufficiently molded, and if too long, the tire component such as the carcass layer is excessively vulcanized. In the case of a pneumatic radial tire for a passenger car, the pressurizing process using high-pressure steam may be 2.5 to 3.5 minutes.

After pressurization with high-pressure steam, the tire is heated while being pressurized from the inside with low-pressure steam having a lower pressure than the high-pressure steam and satisfying the following formula. In FIG. 1, the range from time t ₃ to time t ₄ is the pressurizing process using low-pressure steam.
Pi> Pt + 0.2
Pi: Pressure of low-pressure steam (MPa)
Pt: saturated vapor pressure (MPa) at a temperature equal to the internal temperature of the tread

  By setting the pressure Pi of the low-pressure steam sufficiently higher than the saturated vapor pressure Pt at a temperature equal to the internal temperature of the tread, it is possible to suppress foaming of moisture and volatile components inside the tread. Here, the difference between the pressure Pi of the low pressure steam and the saturated vapor pressure Pt at a temperature equal to the internal temperature of the tread is set to be larger than 0.2 MPa. That is, the present inventor obtained the thermal contraction force (shrink back pressure) of each member based on the contraction of the cord during vulcanization for the carcass layer, belt layer, and belt cover layer of various tires. It was found that the pressure was less than 2 MPa. Therefore, if the pressure Pi of the low pressure steam is set as described above, the pressurization process by the high pressure steam can be shortened without overcoming the shrinkback pressure and causing a manufacturing failure such as residual air in the tire. As a result, the conventional nitrogen gas supply device and hot water supply device for pressurization are not required, and the running cost of the vulcanizing device can be reduced.

  The pressure Pi of the low-pressure steam is preferably 1.0 MPa to 1.2 MPa (184 ° C. to 191 ° C. in terms of temperature). When the pressure Pi of the low pressure steam is less than 1.0 MPa, it becomes difficult to suppress the foaming of moisture and volatile components contained in the tread. Will be invited. The difference between the pressure of the high pressure steam and the pressure of the low pressure steam is preferably 0.2 MPa to 0.8 MPa. If this difference is less than 0.2 MPa, the effect of suppressing overvulcanization is reduced. Conversely, if it exceeds 0.8 MPa, it is difficult to set the high-pressure steam and the low-pressure steam to appropriate pressures. On the other hand, the saturated vapor pressure Pt is a saturated vapor pressure at a temperature equal to the highest temperature measured inside the tread. The relationship between vapor pressure (gauge pressure) and temperature is shown in FIG.

  Although the vulcanization schedule described above relates to steam filling the inside of the tire, the mold is also heated from the outside simultaneously with the heating from the inside of the tire. At that time, the external temperature of the mold is preferably 160 to 185 ° C. In vulcanization premised on such an external temperature, by applying the pressurizing process with high pressure steam and low pressure steam described above, a pneumatic tire using a silica compound rubber compound for a cap tread is vulcanized. Even if it exists, the foaming of the water | moisture content contained in the tread and a volatile component can be prevented effectively.

  A rubber compound containing silica is used as a cap tread, and tires of tire sizes 195 / 65R15 having two carcass layers are respectively vulcanized by the vulcanization methods of Conventional Examples 1-3 and Examples 1-3. It manufactured and confirmed the presence or absence of the bubble in a cap tread. In Conventional Examples 1 to 3 and Examples 1 to 3, high pressure steam was used in the initial stage of vulcanization, low pressure steam was used in the late stage of vulcanization, and the pressure and pressurization time were set as shown in Table 1. The internal temperature of the tread during vulcanization is about 180 ° C., and the saturated vapor pressure at a temperature equal to the internal temperature of the tread is about 0.9 MPa. As the rubber compound containing silica, a rubber compound having the composition shown in Table 2 was used.

In Table 2,
SBR-1: "Nipol 9520" (37.5phr oil exhibition) manufactured by Nippon Zeon Co., Ltd.
SBR-2: "Nipol NS116R" manufactured by Nippon Zeon Co., Ltd.
Carbon Black-1: “Dia Black A” manufactured by Mitsubishi Chemical Corporation
Carbon Black-2: “Seast KH” manufactured by Tokai Carbon Co., Ltd.
Silica: “Nip seal AQ” manufactured by Nippon Silica Co., Ltd.
Silane coupling agent: “Si69” manufactured by Degussa
Activator: “Diethylene glycol” manufactured by Maruzen Chemical Co., Ltd.
Aromatic oil: “Process Oil X-140” manufactured by Japan Energy Co., Ltd.
Zinc flower: "Zinc oxide 3 types" manufactured by Shodo Chemical Industry Co., Ltd.
Stearic acid: “Lunac YA” manufactured by Kao Corporation
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
Wax: “Sunnock” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Tsurumi Chemical Co., Ltd. “Jinhua Indian Oil Fine Sulfur”
Vulcanization accelerator: “Noxeller NS-F” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As shown in Table 1, in the vulcanization methods of Examples 1 to 3, the pressure Pi of the low-pressure steam and the saturated vapor pressure Pt at a temperature equal to the internal temperature of the tread satisfy the condition of Pi> Pt + 0.2 MPa. There were no bubbles. On the other hand, bubbles were present in the cap tread in the vulcanization methods of Conventional Examples 1 to 3 that did not satisfy the above conditions.

FIG. 1 is a graph showing the relationship between tire internal pressure and vulcanization time in the method for vulcanizing pneumatic tires of the present invention. It is a graph which shows the relationship between vapor pressure and temperature.

Claims (3)

In a method of vulcanizing a pneumatic tire using a silica compounded rubber compound as a cap tread, an unvulcanized tire is introduced into a mold, and the tire is placed inside by high-pressure steam at a pressure of 1.4 MPa to 1.8 MPa. The tire is heated while being pressurized, and the pressurizing step with the high-pressure steam is maintained for 2 to 8 minutes, and then the tire is heated while being pressurized from the inside with low-pressure steam satisfying the following formula at a lower pressure than the high-pressure steam. A method for vulcanizing a pneumatic tire.
Pi> Pt + 0.2
Pi: Pressure of low-pressure steam (MPa)
Pt: saturated vapor pressure (MPa) at a temperature equal to the internal temperature of the tread   The method for vulcanizing a pneumatic tire according to claim 1, wherein the pressure of the low-pressure steam is 1.0 MPa to 1.2 MPa.   The method for vulcanizing a pneumatic tire according to claim 1 or 2, wherein an external temperature of the mold is 160 ° C to 185 ° C.

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