Rubber metal bonding-Detailed explanation of cobalt salt
Cobalt salt refers to a substance composed of cobalt ions and acid radicals, which may also contain a certain proportion of other ions. There are many types of cobalt salts, and there are many different types. Cobalt salts include CoX2, CoF2, CoCl2, CoBr2, CoI2, CoOCo(OH)2, CoCO3, Co(NO3)2, CoSO4 and many other types.
1 Introduction
Cobalt salt refers to a substance composed of cobalt ions and acid radicals, which may also contain a certain proportion of other ions. There are many types of cobalt salts, and there are many different types. Cobalt salts include CoX2, CoF2, CoCl2, CoBr2, CoI2, CoOCo(OH)2, CoCO3, Co(NO3)2, CoSO4 and many other types.
English name: cobaltsalt
Appearance and properties: Rose red monoclinic crystal.
Melting point (℃): 96～98
Relative density (water=1): 1.948(25℃)
Boiling point (℃): 420(-7H2O)
Molecular formula: CoSO4·7H2O
Molecular weight: 281.15
Solubility: soluble in water, methanol, slightly soluble in ethanol. Cobalt salt
2 Types of cobalt salts
Organic acid cobalt salt is a special adhesive for rubber and brass-plated or galvanized steel cords. It can be used alone in the manufacture of high-performance steel wire radial tires and high-load steel wire hoses.
According to Huacheng Metal Network, the types of cobalt salts currently widely used at home and abroad include cobalt naphthenate, cobalt stearate, cobalt neodecanoate and cobalt borate: the commonly used ones are cobalt naphthenate ( Cobalt content: 10-11%), cobalt stearate (cobalt content: 9-10%), cobalt neodecanoate (cobalt content: 20-21%), boron modified cobalt neodecanoate (cobalt content: 22- twenty three%).
3 Cobalt salt dosage
Cobalt salts are used to enhance the adhesion of rubber to metal and are widely recognized and used in products such as radial tires and steel wire hoses. Cobalt salts can be added directly to rubber alone as a promoter for the adhesion between rubber and metal. Due to the differences in bonding technology between products and companies, in addition to cobalt salts directly used as adhesion promoters, many companies also use cobalt salts and metamethyl (white) resin bonding systems. However, whether used alone or in combination, and no matter which cobalt salt is used, the metallic cobalt content in the rubber compound must be controlled. This is because from the perspective of the bonding mechanism, if the content of cobalt ions in the rubber material is too high, it will not only promote the generation of a large amount of inactive copper sulfide, but also catalyze the accelerated aging of rubber hydrocarbons; while the content of cobalt ions is too low, it is difficult for brass to react with sulfur. Reactive cuprous sulfide so that good adhesion cannot be obtained. Considering the performance of the rubber formula itself, adding a small amount (appropriate amount) of cobalt salt is beneficial to adhesion. However, a high ratio of cobalt salt is not only harmful to the adhesion after steam aging, but also to the strength of the rubber after heat aging. Elongation properties are also adversely affected.
It is generally recommended that the amount of cobalt salt should not exceed 0.3% of the mass of the rubber hydrocarbon in the formula, that is, the content of metallic cobalt in 100 parts of rubber hydrocarbon should not exceed 0.3 parts. Due to differences in each company’s technology, this amount is only a reference.
Since the average molecular weight of various cobalt salt adhesives is different, it is necessary to convert the actual required amount of metallic cobalt into the proportion of cobalt salt adhesive in the formula. For this purpose, the actual number of portions of the recipe can be calculated using the following formula:
Formula parts = Metal cobalt parts/Cobalt percentage in the product (the amount of metal cobalt in the formula should be between 0.15-0.35 points)
Example: Calculate the formula parts of RC-B23 (cobalt content: 23%) adhesive with 0.25 parts of metallic cobalt added to the formula.
Number of formula parts=0.25/23%=1.08 parts
2. Several common adhesion promoter systems and characteristics ( y2 p N4 e. ?3 ]’ t7 {. B5 S2 u7 o( f, }
1. Cobalt binding system 7 Q) B% i( V3 y- r
That is, organic cobalt salts: cobalt stearate, cobalt decanoate, cobalt naphthenate, cobalt borate, etc. + B7 m, _, `( ?. ?” ?
2． Intermediate, nail and white bonding system; k) ]9 l0 T) L+ i1 G
A common adhesive added to rubber, consisting of resorcinol donor, methylene donor and white carbon black. Can bond rubber with fibers, metals, etc.
3. Coating adhesives such as Chemlock and Leka sodium) S7 [9 t; c5 O6 v& j. t$ I2 Y5 o
This bonding system has an ideal bonding effect between bare steel and rubber, but its heat resistance is poor. The product loses its due effect due to long-term exposure to the thermal environment and the heat generated within the product itself. : i, |” O( z- UFor new radial tires, depending on the degree of damage, a large part of the carcass has exposed metal cords. During the retreading process, the adhesion between the metal cords and the middle rubber must be involved, which requires the addition of cobalt salts. Adhesion promoter. Otherwise, after the tire is vulcanized, only the bonding between rubber is completed, and the bonding strength between rubber and metal cord is far from enough. Among rubber products with skeleton materials, the bonding between the skeleton material and the rubber is particularly important, especially radial tires, which require good dynamic effects. The adhesion between rubber and metal cords is not ideal, which not only affects the retreaded tires The service life of the tire may be extended, and in severe cases, it may cause serious consequences such as tire failure.
3. To choose a high-quality cobalt salt type adhesion promoter:
Although there are many manufacturers in China, the production scale and technical level are uneven. Due to many factors such as the grade of raw materials, production process control methods, technical testing and treatment methods, the zinc, iron, copper, manganese in the products have been reduced. and trivalent cobalt ions exceeding the standard, which will have a great negative impact on product adhesion.
7. How to use 7 b0 a” k* m0 p# f/ G! g4 e9 Z, M) y8 Y4 C
1. Prepare glue: i:
C. Add the middle pad film of the glue to be made into a certain proportion of 120# solvent oil. At the same time, add the cobalt salt adhesion promoter at a rate of 3 to 5% of the mass of the film, and then immerse and swell together in a mixer for about 24 to 48 hours, then stir thoroughly to ensure that the adhesion promoter is fully dispersed into the glue. In order to improve the beating efficiency and reduce solvent loss, 50 to 70% of the solvent can be added first. After the film is evenly swollen, the remaining solvent can be added and stirred quickly. Preparation of glue concentration: spraying can be adjusted to 10-15%, brushing can be adjusted to 25-30%. & ^7 ^/ y8 Y/ \ L( d! V+ k
2． Apply glue. c
Spray or brush the homogenized glue on the exposed metal wire parts of the carcass (try to ensure that the metal cord coating is not damaged during polishing and decontamination). In order to facilitate the control of the amount of glue attached, it is generally necessary to apply 2 to 3 times to ensure the glue is evenly applied. The remaining glue after use should be sealed and stored at room temperature, away from fire sources, and should be stirred evenly the next time it is used. 2 b’ r2 q r$ G3
3. Dry naturally at room temperature for 30 to 45 minutes to completely evaporate the solvent. Residual solvent will cause pores in the bonding area, thus affecting the bonding effect. After the glue application and drying are completed, vulcanization and bonding should be carried out as soon as possible, generally no more than 2 hours. , y7 c# 7 h４. Adhesive vulcanization + k
This product undergoes high-strength chemical bonding during the vulcanization stage. After the carcass coated with glue is attached with the mid-cushion rubber and tread rubber, it is vulcanized. If the traditional hot vulcanization retreading method is used, the vulcanization temperature is 145~150°C and the vulcanization time is 45~60 minutes; if pre-vulcanization is used In the refurbishment process, the vulcanization temperature is 100~115℃, the vulcanization time is 150~180 minutes, and the vulcanization tank pressure is 0.8Mpa, that is, the refurbishment process is completed. X) S% V [5 h7 I! V. \ W9 s+ r- x% @9 d7 g; H1 |8 H2 @. s! It has been accumulated in the past that there are many factors that affect the adhesion between metal and rubber, which are all related to the rubber formula system and operating technology. In addition, my country’s tire retreading industry started late, and we have insufficient experience in this area. How the production process, operating conditions and equipment conditions can achieve the best bonding effect are yet to be discussed and studied by our colleagues in the rubber industry.
