JP4819557B2 - Manufacturing method of tire bladder - Google Patents

Description

  The present invention relates to a method for manufacturing a bladder used in a tire vulcanization process.

  A mold containing a bladder is used in a vulcanization process of a pneumatic tire. In the vulcanization process, first, a preformed green tire is put into an opened mold. When thrown, the bladder is contracted. When thrown, the bladder is positioned inside the green tire. The bladder expands by filling with gas. This expansion causes the green tire to deform. This deformation is called shaping. Next, the mold is tightened and the internal pressure of the bladder is increased. The green tire is pressed between the cavity surface of the mold and the outer surface of the bladder. The green tire is heated by heat conduction from the mold and the bladder. The rubber composition of the green tire flows by pressurization and heating. The rubber causes a crosslinking reaction by heating, and a tire is obtained.

  The bladder is used repeatedly. The bladder repeats expansion and contraction. The bladder is made of a material suitable for repeated deformation. Specifically, the bladder is obtained by crosslinking a rubber composition. A preferred base rubber of the rubber composition is butyl rubber. The rubber composition contains an oil such as a softener and a plasticizer.

  In making the bladder, the rubber composition is heated in a mold. The mold for the bladder includes an upper mold, a lower mold, and a core. The shape of this mold is complicated. In this mold, temperature distribution tends to occur on the cavity surface. Due to this temperature distribution, a distribution occurs in the crosslink density of the bladder. Even if the thickness of the bladder is not uniform, the crosslink density is distributed. The distribution of crosslink density hinders the durability of the bladder.

  JP-A-6-182775 discloses a method for manufacturing a bladder. In this manufacturing method, the rubber composition is first heated with a mold. This heating causes the rubber to undergo a crosslinking reaction. The rubber composition is further heated in an oven. The crosslinking reaction proceeds by heating in the oven. The distribution of the crosslinking density is suppressed by heating in the oven. In heating in the oven, a large amount of heat can be conducted to the rubber composition in a short time. In this manufacturing method, a bladder can be obtained in a short time.

JP-A-8-132441 discloses another method for manufacturing a bladder. In this manufacturing method, the rubber composition is first heated with a mold. A molded body is obtained by heating. This molded body is further heated in an oven. A release layer is formed on the surface of the molded body. In this manufacturing method, the oil content on the surface of the molded body evaporates by heating in the oven. Therefore, there is little oil contained between the molded body and the release layer. In this bladder, the release layer firmly adheres to the molded body.
JP-A-6-182775 JP-A-8-132441

  As described above, in heating in the oven, a large amount of heat can be conducted to the rubber composition in a short time. However, further improvements in bladder productivity are desired. The scorch time of the rubber composition using butyl rubber is long. In the bladder made of this rubber composition, improvement in productivity is particularly desired.

  In the oven, the rubber composition is exposed to oxygen. On the surface of the bladder obtained by heating in the oven, the rubber deteriorates. Degradation hinders the strength of the bladder.

  An object of the present invention is to provide a high-quality tire bladder.

The method for manufacturing a tire bladder according to the present invention is as follows.
When the rubber composition is pressurized and heated in the mold, the rubber undergoes a cross-linking reaction, and a primary cross-linking step in which a molded body is obtained, and the rubber is further cross-linked by being exposed to an atmosphere of superheated steam. Including a secondary crosslinking step.

  Preferably, the temperature of the superheated steam is 130 ° C. or higher and 200 ° C. or lower. As for the temperature of superheated steam, 170 degreeC or more and 200 degrees C or less are more preferable.

  Preferably, this manufacturing method further includes a release treatment step in which a release layer is formed on the surface of the molded body after the secondary crosslinking step.

  In the manufacturing method according to the present invention, superheated steam is used. This superheated steam is excellent in heat conduction ability. In this manufacturing method, the bladder can be manufactured in a short time. In this manufacturing method, since the molded body is exposed to an atmosphere of superheated steam, the rubber is hardly deteriorated by oxygen. Superheated steam also contributes to the removal of oil adhering to the surface of the molded body. By this manufacturing method, a bladder with excellent quality can be obtained.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view showing a mold 2 used in a manufacturing method according to an embodiment of the present invention. FIG. 1 shows a rubber composition 4 together with a mold 2. The mold 2 includes an upper mold 6, a lower mold 8 and a core 10. The upper mold 6 includes a main part 12 and a jacket 14. A space 16 is formed between the main portion 12 and the jacket 14. The lower mold 8 includes a main portion 18 and a jacket 20. A space 22 is formed between the main portion 18 and the jacket 20. The core 10 is hollow and has a space 24. In FIG. 1, the upper mold 6 is combined with the lower mold 8. In FIG. 1, a cavity 26 surrounded by the upper die 6, the lower die 8 and the core 10 is formed. The cavity 26 is filled with the rubber composition 4.

  FIG. 2 is a block diagram showing the secondary crosslinking apparatus 28 used in this manufacturing method. The apparatus 28 includes a water vapor generator 30, a heater 32, and an oven 34. The heater 32 is connected to the steam generator 30. The oven 34 is connected to the heater 32.

  3 is a cross-sectional view illustrating the oven 34 of the apparatus 28 of FIG. The oven 34 includes a main chamber 36, an intake port 38, an exhaust port 40, and a table 42. A molded body 44, which will be described in detail later, is placed on the table 42. The molded body 44 is accommodated in the main chamber 36.

  In this production method, the base rubber, sulfur, carbon black, softener, plasticizer and the like are first kneaded to obtain the rubber composition 4. This rubber composition 4 is preformed into a predetermined shape. This rubber composition 4 is put into the mold 2. The rubber composition 4 is pressurized by fastening the mold 2. The main portions 12 and 18 and the core 10 receive heat from the heat medium filled in the spaces 16, 22, and 24 and rise in temperature. The rubber composition 4 is heated by this temperature increase. The rubber composition 4 flows by pressurization and heating. The base rubber undergoes a crosslinking reaction by heating. This step is referred to as the primary crosslinking step. A shaped body 44 is obtained by crosslinking. The mold 2 is opened and the molded body 44 is taken out. In the primary crosslinking step, the crosslinking temperature is preferably from 160 ° C. to 200 ° C., and the crosslinking time is preferably from 10 minutes to 30 minutes.

  As shown in FIG. 3, the molded body 44 is placed on the table 42. On the other hand, in the water vapor generator 30 (see FIG. 2), water is heated to generate water vapor. The water vapor is guided to the heater 32 through a path not shown. In the heater 32, the water vapor is further heated by a means such as a burner or electric heating. The temperature of the steam after heating is higher than the saturation temperature. In other words, superheated steam is obtained by the heater 32.

  The superheated steam is guided to the oven 34 through a path not shown. The superheated steam flows into the main chamber 36 through the intake port 38. Superheated steam is continuously supplied to the main chamber 36 through the intake port 38. At the exhaust port 40, superheated steam continues to flow out. The interior of the main chamber 36 is controlled at a constant temperature. The molded body 44 is exposed to an atmosphere of superheated steam.

  The compact 44 is heated by the superheated steam. By this heating, the rubber crosslinking reaction proceeds. This process is referred to as a secondary crosslinking process. After heating for a predetermined time, the supply of superheated steam is stopped, and the molded body 44 is taken out from the oven 34. The extraction may be performed in a state where the main chamber 36 is at a high temperature, or may be performed after the temperature of the main chamber 36 is lowered.

  A release layer is formed on the surface of the molded body 44. This process is referred to as a mold release process. The bladder is completed by the mold release process. FIG. 4 shows the bladder 46. The bladder 46 includes a main body 48 and a release layer 50. A typical mold release treatment is application and baking of a mold release agent. A preferable mold release agent is based on silicon resin or fluororesin. The release layer 50 suppresses adhesion of the bladder 46 to the tire in the tire vulcanization process. The bladder 46 may not include the release layer 50.

  As described above, the molded body 44 is heated in an atmosphere of superheated steam. When heating, the oxygen concentration in the main chamber 36 is extremely small. In this production method, the rubber is hardly deteriorated by oxygen in the secondary crosslinking step. By this manufacturing method, the bladder 46 having excellent durability can be obtained.

  In the secondary cross-linking step, heat is uniformly conducted to the entire formed body 44. In this manufacturing method, the distribution of crosslink density is suppressed. By this manufacturing method, the bladder 46 having excellent durability can be obtained. From the viewpoint of uniform heat conduction, the table 42 is preferably rotated.

  In heating with water vapor, the speed of convective heat transfer is extremely high. The speed of convective heat transfer of water vapor is 10 times or more compared with that of dry air. By using water vapor, the secondary crosslinking step can be completed in a short time.

  When the surface of the compact 44 is touched, the superheated steam condenses. At this time, the molded body 44 receives heat. This phenomenon is called radiant heat transfer. Due to radiant heat transfer and convective heat transfer, the secondary crosslinking process can be completed in a very short time. From the viewpoint of heat transfer rate, the temperature of the superheated steam is preferably 130 ° C. or higher. From the viewpoint of preventing the deterioration of the rubber, the temperature of the superheated steam is preferably 200 ° C. or less.

  Oils such as softeners and plasticizers bleed out and adhere to the surface of the molded body 44. Water has a property of holding oil during evaporation. By being exposed to the atmosphere of superheated steam, the condensation and evaporation of water vapor are repeated on the surface of the molded body 44. The oil is removed from the surface of the molded body 44 by evaporation. In this bladder 46, the amount of oil interposed between the molded body 44 and the release layer 50 is small. In this bladder 46, the release layer 50 is firmly attached to the molded body 44. The life of the release layer 50 is long.

  As for the temperature of superheated steam, 170 degreeC or more is more preferable. The drying power drying inversion temperature of superheated steam is 170 ° C. Superheated steam at 170 ° C. or higher has better drying power than dry air. By using superheated steam at 170 ° C. or higher, the oil can be sufficiently removed from the surface of the molded body 44.

From the viewpoint that the crosslinking reaction proceeds sufficiently, the crosslinking time in the secondary crosslinking step is preferably 10 minutes or more, and more preferably 15 minutes or more. In light of suppression of rubber deterioration, the crosslinking time is preferably 30 minutes or less , and more preferably 20 minutes or less .

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
The rubber composition was heated with the mold shown in FIG. 1 to cause a primary crosslinking reaction in the rubber to obtain a molded body. The crosslinking temperature was 170 ° C. and the crosslinking time was 30 minutes. This compact was put into the oven shown in FIG. A superheated steam at 170 ° C. was allowed to flow into the main chamber to cause a secondary crosslinking reaction in the rubber. The crosslinking time was 20 minutes. A release layer was formed on the surface of the molded body, and the bladder of Example 1 was obtained.

[Examples 2 to 3 and 6]
The bladders of Examples 2 to 3 and 6 were obtained in the same manner as in Example 1 except that the temperature of the superheated steam was changed as shown in Table 1 below.

[Example 4]
A bladder of Example 4 was obtained in the same manner as Example 1 except that the time for primary crosslinking was as shown in Table 1 below.

[Example 5]
A bladder of Example 5 was obtained in the same manner as Example 1 except that the time for secondary crosslinking was as shown in Table 1 below.

[Comparative Example 1]
A bladder of Comparative Example 1 was obtained in the same manner as in Example 1 except that dry air was allowed to flow into the main chamber in the secondary crosslinking.

[Comparative Example 2]
A bladder of Comparative Example 2 was obtained in the same manner as in Example 1 except that the time for primary crosslinking was 45 minutes and no secondary crosslinking was performed.

[Evaluation of durability]
A bladder was incorporated into the mold and used in the tire vulcanization process. In the vulcanization process, the bladder was repeatedly expanded and contracted. The results of counting the number of times of use until breakage are shown in Table 1 below as an index when Comparative Example 1 is set to 100.

  As shown in Table 1, the tires of the examples are excellent in durability. From this evaluation result, the superiority of the present invention is clear.

  The bladder according to the present invention can be used for manufacturing various tires.

FIG. 1 is a cross-sectional view showing a mold used in a manufacturing method according to an embodiment of the present invention. FIG. 2 is a block diagram showing a secondary crosslinking apparatus used in this manufacturing method. FIG. 3 is a cross-sectional view illustrating the oven of the apparatus of FIG. FIG. 4 is a cross-sectional view showing a bladder obtained by this manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Mold 4 ... Rubber composition 6 ... Upper mold | type 8 ... Lower mold | type 10 ... Core 28 ... Secondary bridge | crosslinking apparatus 30 ... Water vapor generator 32 ... Heating Container 34 ... Oven 36 ... Main room 38 ... Intake port 40 ... Exhaust port 42 ... Table 44 ... Molded body 46 ... Bladder 48 ... Main body 50 ... Separated Mold layer

Claims (3)

A primary crosslinking step in which the rubber composition undergoes a crosslinking reaction by being pressurized and heated in the mold, and a molded body is obtained;
The molded body has Nde contains a secondary crosslinking process causing rubber further crosslinking reaction by exposure to an atmosphere of superheated steam,
The temperature of the superheated steam is 130 ° C. or higher and 200 ° C. or lower,
The manufacturing method of the bladder for tires whose crosslinking time in this secondary crosslinking process is 10 minutes or more and 20 minutes or less . The manufacturing method according to claim 1 , wherein the temperature of the superheated steam is 170 ° C or higher and 200 ° C or lower. The manufacturing method of Claim 1 or 2 which further includes the mold release process process in which a mold release layer is formed in the surface of a molded object after the said secondary bridge | crosslinking process.

Images