JPH0929749A - Tire vulcanizing bladder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a vulcanizing molding time by increasing the thermal conductivity of a vulcanizing bladder used in the step of vulcanizing to mold a green tire to a tire, and accelerating the temperature rising of the green tire. SOLUTION: The tire vulcanizing bladder comprises rubber composition obtained by mixing at least phenol resin, halogen element-containing polymer and conductive carbon black with butyl rubber in such a manner that its electrical conductivity is 1.0×10<-6> Ω<-1> .cm<-1> or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bladder used for vulcanizing and molding a tire, and more specifically, it has a high thermal conductivity to accelerate temperature transfer to a green tire and to improve tire vulcanizing and molding time. The present invention relates to a vulcanization bladder capable of shortening the length.

[0002]

2. Description of the Related Art In a pneumatic tire manufacturing process, a green tire incorporating a tire constituent member is put into a mold, and a rubber having a cylindrical shape called a bladder or a horseshoe-shaped rotating body is further placed in the inner cavity of the green tire. A bag-shaped product is inserted, and then an internal pressure fluid such as steam or pressurized hot water is introduced into the inside of this bladder to press the green tire strongly against the mold and at the same time it is heated from the inside, while at the same time the steam is applied to the green tire. The tire is obtained by heating from the outside by vulcanization molding by heating the mold.

[0003] In the heating of the green tire in the vulcanization molding step, a rubber member made of a highly plastic unvulcanized rubber composition incorporated in the green tire is heated to a high temperature to cause a cross-linking reaction, which changes into an elastic rubber. Done until. Generally, the heating time is determined by the time until the portion where the temperature rises most at the central portion of the thickness of the portion where the green tire has the largest thickness becomes the elastic body. Since rubber has poor heat conduction, it takes time to raise the temperature of the part where the temperature rise is the slowest to the temperature at which the vulcanization reaction proceeds actively. For vulcanization molding, it takes 10 to 20 minutes for tires for passenger cars and for trucks and buses. It takes 40 to 100 minutes for tires and 10 hours for large tires for construction vehicles.

Since the bladder used in the above vulcanization molding process is repeatedly used at high temperature until it breaks, 100 parts by weight of butyl rubber (hereinafter, simply referred to as "part") is used as a crosslinking agent for phenol. 5 to 2 of resin
0 parts, 5 to 20 parts of a halogen element-containing polymer such as chlorinated butyl rubber, brominated butyl rubber, and chloroprene as a crosslinking accelerator, and HA that is a large reinforcing material and inexpensive as a reinforcing material.
It was formed of a rubber composition having excellent heat aging resistance, which was prepared by blending 40 to 60 parts of furnace carbon black such as F, ISAF and SAF.

[0005] In the vulcanization molding step, heating of the inner surface of the green tire with a high-temperature fluid is performed through a bladder having a thickness of 5 to 10 mm inserted into the green tire cavity.
The actual wall thickness to be heated is the wall thickness of the green tire plus the wall thickness of the bladder, and it takes time for the central portion of the thickness to rise to a temperature at which the vulcanization reaction is substantially carried out. Generally, when heating a thick rubber plate from both sides, if the thickness doubles, the time required for the central portion of the thickness to reach the same temperature as the outer surface is said to increase four times.
The temperature increase of the green tire is delayed only by adding the bladder, and the time required to vulcanize and mold one tire is longer than the time required to mold the green tire, and it is necessary to have many vulcanizers and molds of the same shape. As a result, capital investment increased, and energy costs increased, pushing up manufacturing costs. Therefore, in order to shorten the vulcanization time and reduce the manufacturing cost, the temperature of the mold and the internal pressure is increased, and the wall thickness of the bladder is reduced to set the center portion of the maximum thickness of the green tire to a predetermined temperature. Has been attempted, or a method of adjusting the vulcanization accelerator of the rubber composition of the tire constituent member to accelerate the vulcanization reaction and completing the crosslinking reaction in a short time.

[0006]

However, in the method of increasing the temperature of the mold and the internal pressure to shorten the vulcanization molding time, the surface portion of the tire is excessively heated and overvulcanized, resulting in deterioration of physical properties. Is caused and the quality of the tire is deteriorated, which is not preferable. With the method of reducing the thickness of the bladder, aging proceeds quickly,
It is not preferable because the number of tires that can be vulcanized before one bladder breaks, the so-called bladder life, becomes shorter and the manufacturing cost becomes higher. Further, in the method of adjusting the vulcanization accelerator to accelerate the vulcanization reaction of the rubber composition and change it into an elastic body in a short time, a phenomenon called scorch in which the vulcanization reaction starts in the processing step of the member easily occurs. Therefore, it is necessary to make the temperature control precision extremely strict, which is not preferable because the manufacturing cost becomes high.

It is an object of the present invention to provide a tire vulcanizing bladder capable of shortening the vulcanization molding time of a green tire without deteriorating the quality of the tire.

[0008]

SUMMARY OF THE INVENTION The present invention was made based on the finding that a rubber composition having electrically conductive carbon black blended therein to have high electrical conductivity also has high thermal conductivity.

That is, the present invention comprises a rubber composition in which butyl rubber is blended with at least a phenol resin as a crosslinking agent, a halogen element-containing polymer as a crosslinking accelerator, and conductive carbon black as a conductivity-imparting agent.
A bladder for tire vulcanization having an electric conductivity of 1.0 × 10 ^-6 Ω ^-1 cm ^-1 or more.

Chloroprene, chlorinated butyl rubber, brominated butyl rubber, brominated nitrile rubber, halogen-containing polymers such as hypalon and the like contained in the rubber composition of the present invention, and a large amount of methylol group prepared as a crosslinking agent for butyl rubber. The amount of the phenolic resin such as an alkylphenol formaldehyde resin or a halogenated product thereof is not particularly limited, but butyl rubber 85 to 9
A halogen element-containing polymer was blended at a ratio of 5 to 5% by weight (total 100% by weight), and 5 parts by weight of the phenolic resin was added to 100 parts of the blend.
A range of 15 parts is preferred. The amount of conductive carbon black such as acetylene black and conductive furnace black to be compounded is 40 to 60 parts by combining 50 parts or less of general-purpose carbon black such as HAF, ISAF and SAF with 10 parts or more of conductive carbon black. Alternatively, the range of 40 to 60 parts of conductive carbon black is preferable.

[0011]

[Function] Since the bladder is made of a rubber composition having a high electric conductivity, the thermal conductivity of the bladder is increased and the temperature of the high temperature internal pressure fluid introduced into the bladder is quickly transmitted to the green tire. The time required for vulcanization molding is shortened by rapidly raising the temperature to a temperature at which the vulcanization reaction substantially proceeds. When the electric conductivity is less than 1.0 × 10 ⁻⁶ Ω ⁻¹ · cm ⁻¹ , the thermal conductivity is the same as the conventional one, and the reduction of the vulcanization molding time cannot be achieved.

When the total amount of the conductive carbon black and the general-purpose carbon black is less than 40 parts with respect to 100 parts of the blend of the butyl rubber and the halogen-containing polymer, or when the total amount is 40 parts or more, the conductivity is increased. When the blending amount of carbon black is less than 10 parts, the electric conductivity becomes smaller than 1.0 × 10 ⁻⁶ Ω ⁻¹ · cm ⁻¹ , and the vulcanization molding time cannot be shortened. If the total amount of conductive carbon black or other carbon black is more than 60 parts, the processability will decrease. Therefore, it is necessary to increase the amount of softening agent to maintain processability. As a result, the resistance is increased, and as a result, the conductivity does not increase as much as the increased amount in spite of the increase in the conductive carbon black, and conversely, the physical properties are deteriorated and the bladder life is shortened, which is not preferable.

[0013]

[Example] Eight types of mixed rubbers were made in accordance with the formulations shown in the table, and the mixed rubbers were sampled and tested for thermal conductivity and temperature rising rate. The results are shown in the table.

Further, a bladder was prototyped with each of the remaining mixed rubbers, and the electric resistance and the temperature rise state of the green tire were tested as described below. That is, the temperature-sensitive part of the thermocouple is arranged in advance in the center of the thickness of the shoulder, and the green tire of size 10.00R20 is put into the mold as it is,
The bladder was inserted into the inner cavity, and vulcanization molding was performed while continuously measuring the temperature rise. The progress of the relative vulcanization reaction was determined from the above temperature measurement, and the progress was represented by blow points and the results are shown in the table. The blow point is the time until the next state is reached. That is, when vulcanization molding is being performed, oil, moisture, etc., contained as impurities in the rubber composition of the green tire are liquid because they are pressurized even when the temperature exceeds the boiling point, If the pressure is released to take it out of the mold, it is rapidly vaporized and foamed. However, if the vulcanization reaction proceeds sufficiently, the elastic modulus of the rubber becomes larger than the vapor pressure of the liquid, and the rubber does not foam. The blow point is the time required for the crosslinking reaction to proceed until foaming stops.

[0015]

[Table 1]

The above-mentioned tests of thermal conductivity, heating rate and electric conductivity were conducted as follows. Thermal conductivity: Thermal conductivity measuring machine model “Aut” manufactured by Eiko Seiki
Using oΔ, a test piece having a thickness of 5 mm was sandwiched between an upper heating plate having a temperature of 40 ° C. and a lower heating plate having a temperature of 10 ° C. at a pressure of 250 kgf / m ² and measured. Indicated in the table. The larger the value, the better. Temperature rising rate: 5 mm thick by vulcanization molding of the rubber composition to be tested,
Create a 100 mm x 100 mm size test piece with a thermocouple temperature sensing part placed in the center and a test piece with the same dimensions without a thermocouple. It was sandwiched between two hot plates kept at 200 ° C., and the time until the thermocouple showed 195 ° C. was measured.
Is set to 100 and is shown in the table in index form. The smaller the value, the faster the temperature rises, which is preferable. Electrical conductivity: 100 mm x 100 with the surface wet with saline
A copper electrode of mm is pressed against the portion of the outer surface of the fladder that has been cleaned with an organic solvent, and the corresponding inner surface that has been cleaned in the same manner is wetted with saline solution and pressed with a cylindrical electrode with a diameter of 50 mm. A voltage was applied to measure the resistance, then the thickness of that portion was measured to calculate the volume resistivity, and the reciprocal thereof was taken as the electrical conductivity.

Compared to Comparative Example 2 containing no conductive acetylene black, the example containing 10 parts or more of acetylene black had a large electric conductivity and thermal conductivity, and as a result, the temperature was raised quickly and the blow point time was increased. Is getting shorter.
Moreover, as the blending amount of acetylene black increases, the electrical conductivity increases and the blow point becomes faster even with the same amount of carbon black.

[0018]

EFFECT OF THE INVENTION Polymer 10 containing butyl rubber as a main component
To 0 parts, a total of 40 to 6 using 50 parts or less of general-purpose carbon black and 10 parts or more of conductive carbon black in combination.
A bladder formed from a rubber composition having 0 parts or 40 to 60 parts of conductive carbon black blended therein to increase electric conductivity has high thermal conductivity, and the temperature of the green tire increases rapidly during vulcanization molding. The time required for vulcanization molding is shortened.

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Claims (1)

[Claims] 1. A rubber composition comprising butyl rubber and at least a phenolic resin, a halogen element-containing polymer and conductive carbon black blended therein, and having an electric conductivity of 1.
A bladder for tire vulcanization characterized by having a ^{value of} 0 × 10 ^-6 Ω ^-1 cm ^-1 or more.