JPS6330137B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for conductive crosslinking and bonding of vulcanized rubber and vulcanized rubber. Generally, the vulcanization bonding method involves interposing an intermediate layer of a thermally crosslinkable rubber composition between two vulcanized rubbers, heating the upper and lower vulcanized rubbers, and using the heat transmitted through the vulcanized rubber layers. This method crosslinks the intermediate layer and simultaneously bonds the intermediate layer and the vulcanized rubber layer, but this conventional method requires heating the vulcanized rubber layer, which does not need to be heated, for a long time. Therefore, a large amount of wasted thermal energy is required, and the vulcanized rubber itself cannot avoid thermal deterioration due to heating of the vulcanized rubber, which is disadvantageous in terms of economy and physical properties. Further, as a special vulcanization bonding method, there is a method in which an electric heating wire is embedded in the intermediate unvulcanized rubber layer and the wire is energized to perform vulcanization bonding. However, since the vulcanized adhesive rubber obtained by this method uses an electric wire as the heating element, it generates heat unevenly, resulting in uneven adhesion, and because the electric wire is inserted, stress concentration tends to occur between the rubber and the electric wire, resulting in poor durability and poor durability. It had drawbacks such as poor bending resistance and repeated fatigue resistance. As a result of intensive research to solve the above-mentioned drawbacks of conventional vulcanization bonding methods, the present inventors have discovered that by uniformly heating only the intermediate layer, the intermediate layer can be vulcanized, and the vulcanized rubber between the intermediate layer and the upper and lower layers can be cured. The present invention was achieved by finding a method for bonding the two. That is, in the present invention, an intermediate layer of a thermally crosslinkable rubber composition comprising conductive carbon black is interposed between vulcanized rubber, and a voltage is applied to the intermediate layer to generate self-heating of the intermediate layer. The present invention relates to a conductive crosslinking bonding method characterized in that vulcanized rubbers are bonded to each other simultaneously with crosslinking of an intermediate layer. The present invention will be explained in detail below. The conductive carbon blacks blended into the thermally crosslinkable rubber composition of the intermediate layer are Ketschen Black EC (manufactured by Akzo, Netherlands), Vulcan XC-72,
Vulcan SC, Vulcan C (both in the US,
Conductive furnace blacks such as CABOT Co., Ltd., product name) and Asahi HS-500 (Asahi Carbon Co., Ltd., product name), among which KETSUCHEN BLACK EC
is preferably used. Conductive carbon black has a thermally crosslinkable rubber composition with a specific volume resistivity of ¹⁰⁴ in the temperature range of 0 to 200°C.
The amount must be blended so that the resistance is Ω・cm or less. If the specific volume resistivity exceeds 10 ⁴ Ω·cm, it is unsuitable because it requires a high voltage or a long time to raise the temperature to the temperature required for crosslinking. Also, the specific volume resistivity is 10 ⁴ Ω・
cm or less, there are some changes depending on the type of conductive carbon black, but usually the rubber component is
It is sufficient to add 7 parts by weight or more to 100 parts by weight.
However, although the lower the specific volume resistivity is, the more advantageous it is for crosslinking, if the amount of conductive carbon black is too large, the physical properties will be significantly deteriorated, so the amount is limited to 80 parts by weight or less based on 100 parts by weight of the rubber component. Rubber components of the thermally crosslinkable rubber composition include natural rubber, diene rubbers such as butadiene rubber, isoprene rubber, and chloroprene rubber, diene copolymer rubbers such as styrene-butadiene rubber and acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. , olefin rubber such as ethylene-propylene rubber, etc. are preferably used;
Organosilicon rubbers that are siloxane condensates, fluorine rubbers such as vinylidene fluoride-propylene hexafluoride copolymers, polysulfide rubbers such as alkylene sulfide polymers, and vinyl rubbers such as acrylic ester polymers. , urethane rubber is used. These rubbers can be used alone or in combination of two or more. As for the rubber component of the vulcanized rubber to be bonded, those exemplified as the rubber component of the thermally crosslinkable rubber composition can be similarly used. The thermally crosslinkable rubber composition used for the intermediate layer is interposed between two vulcanized rubbers as an intermediate layer, and then a voltage is applied to crosslink and simultaneously bond the vulcanized rubbers together. Various methods can be employed as the crosslinking method at this time. Most preferably used is sulfur vulcanization (adding a vulcanization accelerator if necessary). Examples of crosslinking agents other than sulfur vulcanization include p-quinonedioxime, p,p'-dibenzoylquinonedioxime, 4,4'-dithiodimorpholine, poly-p-dinitrosobenzene, and ammonium benzoate. Organic vulcanizing agents used for vulcanization: dicumyl peroxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, α,α'-bis(t-butylperoxyisopropyl) Organic peroxides such as benzene, resin crosslinkers such as methylolated or brominated alkylphenol resins, organic polyvalent amines such as triethylenetetramine, hexamethylene diamine carbamate, and metals such as magnesium oxide, lead oxide, and zinc oxide. Oxides and the like are preferably used. Of course, it is also possible to use other known vulcanizing agents. Conventional rubber compounding agents such as vulcanization accelerators, anti-aging agents, reinforcing agents, softeners, and tackifiers can be optionally added to the thermally crosslinkable rubber composition of the intermediate layer depending on the purpose of use. Next, the procedure of conductive cross-linking adhesion of the present invention will be illustrated. As shown in Figure 1, an intermediate layer C made of a thermally crosslinkable rubber composition is interposed between vulcanized rubber A and vulcanized rubber B, and electrodes are attached to both ends of the intermediate layer while pressing the vulcanized rubbers together. A voltage is applied to D from an AC or DC power source P. The voltage applied during conductive crosslinking is determined by the specific volume resistivity of the intermediate layer, the cross-sectional area of the intermediate layer, the length between the electrodes, the temperature required for crosslinking, etc.
Practically speaking, a range of 1 to 400 volts is preferred. The temperature required for crosslinking is usually in the range of 80-200°C;
The desired temperature is reached in a short time after voltage application. In addition, by changing the applied voltage, it is possible to arbitrarily change the temperature during crosslinking, and the shape of the intermediate layer,
Various reactions can be easily controlled depending on the properties of the crosslinking agent. Although the mold surface of the vulcanized rubber may be used as the bonding surface as it is, it is preferable to apply cement after chemical treatment with acid or mechanical treatment such as buffing for the purpose of improving adhesive strength. As described above, according to the present invention, crosslinking and bonding can be achieved by self-heating of the intermediate layer, so there is no need to heat the vulcanized rubber of the upper and lower layers, and there is a large advantage in terms of energy costs. Furthermore, since the upper and lower vulcanized rubbers are not heated, thermal deterioration of the vulcanized rubbers in the upper and lower layers can be prevented. Furthermore, since this intermediate layer does not contain electric wires or non-reinforcing conductive fillers, it has excellent durability, bending resistance, repeated fatigue resistance, etc. Furthermore, the conductive crosslinking bonding method of the present invention has a great effect especially when the vulcanized rubber is thick. Furthermore, since thermal deterioration of the vulcanized rubber is kept to a minimum, it can be applied to tire retreading, endless belt adhesion, etc. The invention will be illustrated with reference to the following examples and comparative examples. Examples 1 to 5 As shown in Table 1, sulfur-containing intermediate layer rubber compositions containing different amounts of conductive carbon black (Ketsuchen Black EC) were used for unvulcanized intermediate layers with a thickness of 1 mm to 3 mm. Got a sheet. The vulcanized rubbers A and B to be bonded are sulfur vulcanizates containing 100 parts by weight of natural rubber (NR) and 60 parts by weight of carbon black (HAF), and the bonding surfaces were buffed and then washed with n-hexane. . Measurement of volume resistivity of intermediate layer is performed by ASTM
Followed D991-60. Evaluation of adhesive strength is JIS
T-shaped peel test in accordance with K6854, sample width 25mm,
Testing was carried out under the conditions of a vulcanized rubber thickness of 2 mm and a tensile speed of 200 mm/min. As shown in Figure 2, the peel test piece was prepared by interposing a conductive intermediate layer C between vulcanized rubber A and vulcanized rubber B, applying pressure to the extent that intermediate layer C does not flow, and increasing the temperature of the intermediate layer to 150°C. A voltage was applied to the electrodes D at both ends so that the voltage was applied for a predetermined period of time to perform cross-linking adhesion. The results are shown in Table 1.

【table】

[Table] As is clear from Table 1, vulcanized rubbers A and B were sufficiently crosslinked and bonded under these conditions. Comparative Example 1 Example 1 except that 35 parts by weight of HAF black and 5 parts by weight of conductive carbon black were blended.
An intermediate layer rubber composition with the same formulation was prepared. The volume resistivity of this intermediate layer rubber composition is 5×10 ⁴
It was Ω・cm. Follow the same procedure as in Example 1, except that the intermediate layer has a thickness of 3 mm, a width of 100 mm, and a distance between electrodes of 50 mm.
When electricity was applied for 30 minutes at an initial applied voltage of 400 V, the temperature was 55°C, and no vulcanization occurred.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the vulcanization adhesion method of the present invention, and FIG. 2 is a sketch showing the method for producing a T-shaped peel test piece. A, B... Vulcanized rubber, C... Intermediate layer, D... Electrode, P... Power source.

Claims (1)

[Claims] 1 A material with a volume specific resistivity of 0 to 200°C, which is made by blending 7 to 80 parts by weight of conductive furnace black as conductive carbon black between vulcanized rubber and vulcanized rubber, based on 100 parts by weight of the rubber component. Temperature range 10 ⁴
It is characterized by interposing an intermediate layer of a thermally crosslinkable rubber composition having a resistance of Ω・cm or less, applying a voltage to the intermediate layer, and simultaneously crosslinking the intermediate layer and adhering the vulcanized rubber to each other due to self-heating of the intermediate layer. A conductive cross-linking bonding method between vulcanized rubber and vulcanized rubber.