Rubber metal bonding-detailed explanation of cobalt salt

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 naphthenate. Cobalt acid acid (cobalt content: 10-11%), cobalt stearate (cobalt content: 9-10%), cobalt neodecanoate (cobalt content: 20-21%), boron modified cobalt neodecanoate (cobalt content :22-23%).

3 Cobalt salt dosage

Cobalt salts are used to enhance the adhesion between rubber and metal and have been widely recognized and widely 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 recipes can be calculated using the following formula:

Parts of formula = parts of metal cobalt/percentage of cobalt 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.

Formula portion=0.25/23%=1.08 portion

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． Inter, A, White adhesive 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. Coated type such as Kailok, Leka and SodiumIndustry standards, but products that meet standard indicators are not necessarily good products. We suggest that in addition to inspection according to conventional indicators, some simple internal control identification methods can be added:

①Judge from appearance

The degree of borylation reaction of cobalt borylate is a key indicator of product quality. Whether the borylation reaction can be fully reflected from the color, cross-section condition and crispness of the product. For a good cobalt borate product, the color of the product is dark blue. If the color of the product is blue with red, it means that the product is not fully dehydrated and the boric acid reaction is definitely not good. The cross section of the product should be bright and smooth, like a mirror. If the cross section is hairy or dark, it indicates that the borylation reaction of the product is incomplete. If there are many pores in the cross section of the product, it means that the product is not fully desolvated; if there are obvious small particles in the cross section, it means that the early reaction of the product is incomplete, and the borylation reaction is certainly not good. The crispiness of a product reflects the degree to which the product reacts completely and how well the product disperses during use. Products with good crispness can be easily crushed into beautiful blue powder by hand, while products with poor crispness cannot easily become powder when crushed by hand. In severe cases, they will be crushed into small balls or strips. If the product is sticky, dark in color, and has poor usability and dispersion properties, it will also easily agglomerate during packaging, storage and transportation.

②Discrimination based on heptane solubility

Good cobalt borate products are easily soluble in n-heptane. The solution is beautiful blue-purple, clear and transparent, and no Tyndall phenomenon occurs when irradiated with beam light. Products with added heptane insoluble matter should also be like this after the insoluble matter is separated by a centrifuge. At the same time, the separated insoluble matter should be an off-white powdery substance after being washed with heptane and insoluble in dilute sulfuric acid and hydrochloric acid. Bad cobalt borate products dissolve very slowly in n-heptane, and the solution is turbid and opaque; after centrifugation, the insoluble matter turns pink or black-red, and the amount is large. Use dilute sulfuric acid or hydrochloric acid water bath to heat and dissolve, and the solution turns pink. Color, the precipitate is off-white or earthy yellow, which indicates that during the manufacturing process of the product, due to poor activity of cobalt powder or high trivalent cobalt, the reaction between cobalt and organic acid was not fully completed, and of course the boric acylation reaction was not completed. Not good, the performance of the product can be imagined.

③Judge from the melting point

Cobalt diphosphate products are amorphous substances, and their test indicators have a softening point. Cobalt borate is not an amorphous substance. It does not have a softening point, but it does not have a constant melting point like typical crystalline substances such as metals. Cobalt borate is a crystalline substance with a relatively concentrated melting point area. The melting point areas of good cobalt borate 23 and 16 products measured by a microscopic melting point instrument are around 120°C and 110°C respectively. . A product with a melting point that is too high reflects the incomplete reaction of the product and poor dispersion during use; a product with a melting point that is too low may indicate that the product is a mixture of cobalt diphosphate and other organic and inorganic cobalt salts. Not a uniform cobalt boroacylate product.

For cobalt diphosphate products, in addition to melting point inspection, also refer to the above method for inspection and judgment