Cobalt salt adhesion enhancer
I. Overview
Cobalt salt adhesion enhancers (hereinafter referred to as cobalt salt adhesives) are direct additive adhesives for high-strength bonding between rubber and metal, mainly used in the rubber products industry such as steel wire radial tires, steel wire reinforced transportation belts, steel braided hoses and rubber rollers. Cobalt salt binders are used in small quantities in rubber products, but they are very important additives for rubber products with metal skeleton materials and are among the most expensive of all additives. Since cobalt salt binders do not participate in the chemical reaction of the bonding process, but only act as bonding enhancers, i.e. catalysts, the exact name should be cobalt salt bonding enhancers. Due to the importance of cobalt salt binders in rubber products, the formulation design, manufacturing process, quality control and inspection process of these products need to be especially fine to ensure the superior performance and stable quality of the products and to ensure the provision of high quality cobalt salt binder products to customers.
II. History and status of cobalt salt binder development
In the early 1940s, cobalt resin and cobalt stearate were already used in the production of radial tires of Dunlop and other companies, and later, liquid cobalt naphthenate, which was used as a paint drying agent, was also used as cobalt salt binder. In the mid-1960s, it was noticed that the liquid cobalt naphthenate was a natural naphthenic acid as one of its raw materials, and the components of natural naphthenic acid were particularly complex, with the naphthenic acid content generally ranging from 70% to 80%, and the refined naphthenic acid content only reaching about 90%, while the other components were neutral oil, butter, asphalt and a small amount of esters. The low boiling part contains neutral oil such as diesel oil, and the high boiling part (above 320℃) has asphalt impurities as high as 15%~30%, which will cause swelling and damage to the rubber and are unacceptable for rubber products, so the high purity solid cobalt naphthenate has gradually replaced the liquid cobalt naphthenate. In the 1980s, the British “Manchem” company launched a new series of cobalt salt type borylated cobalt adhesives named “Manobond”, because of its excellent adhesive properties, but also has a heat-resistant oxygen, humidity and heat, salt water resistance Because of its excellent bonding properties, it is also resistant to heat and oxygen, humidity and heat, salt water and metal corrosion, and is favored by the international rubber industry and has been recognized as a revolution in adhesive technology. In the early nineties, VAS-SET (France) and Manchem (UK) launched a new generation of solid cobalt naphthenate, Manobond 740C, which has improved and broken through in terms of adhesion performance and anti-aging property than solid cobalt naphthenate. The above-mentioned products constitute a large series of cobalt salt adhesives. The cobalt salt bonding system, the m-methyl-white bonding system and the m-methyl-white-cobalt bonding system constitute the three major bonding systems in the rubber industry.
They are widely used in the rubber products industry.
Until the late 80’s, our country could not produce these products and all of them were imported from abroad. The imported products were expensive, with Manobond 680C (cobalt boride 23) costing up to RMB 480,000 per ton and Manobond 740C (cobalt decanoate) costing up to RMB 420,000 per ton. In order to realize the localization of such raw materials, the former State Planning Commission and the Ministry of Chemical Industry organized the national “Seventh Five-Year Plan” and “Eighth Five-Year Plan” key scientific and technological research projects, and I had the honor to be the head of the public relations team, leading the team to successfully complete the public relations task, adopt foreign standards equivalently, and develop the Manobond series products. Successfully developed Manobond series of products and achieved the goal of localization. It forced the price of similar imported products from abroad to drop significantly. At present, the domestic production capacity of such adhesives can fully meet the needs of the domestic market, and it is imperative to realize the localization of raw materials for cobalt salt adhesives. However, although the domestic production of cobalt salt adhesive manufacturers as many as ten, except for a few manufacturers, most of the products are specious, from the formulation technology to the level of equipment are extremely low, it is impossible to ensure the quality and level of products, it is also impossible to compete with similar foreign products.
III. Manufacture of cobalt salt binder products
Cobalt salt binders include cobalt stearate, solid cobalt naphthenate, cobalt decanoate and cobalt borylate (23, 16), among which cobalt stearate, solid cobalt naphthenate and cobalt decanoate are cobalt diacid products, whose molecular structure is schematically as follows: R1-Co-R2
Where: R is the organic acid root, which can be a single organic acid root or a mixed organic acid root composed of several organic acids. Cobalt borylide has a spatial steric structure with B as the central atom, and its structure schematic formula is
At present, there are usually four methods for the manufacture of organocobalt salts as follows.
1. Metal substitution method
Direct replacement reaction between active metal powder and organic acid, the reaction schematic formula is
CO+2HR=COR2+H2↑
Where HR is a valent organic acid (the same below).
2. Metal oxide neutralization method
Direct neutralization reaction by metal oxide powder and organic acid, the reaction schematic formula is: COO + 2HR = COR2 + H2↑:
COO + 2HR = COR2 + H2O
3. metal hydroxide neutralization method
The metal is first made into hydroxide CO (OH)2, and then neutralized with organic acid, the reaction is shown as follows:
CO (OH)2 + 2HR = CO R2 + 2H2O
4. metal salt decomposition method
The organic acid is first made into sodium soap, and then the metal salt for the decomposition reaction, the reaction schematic formula is.
2NaR+Co2+=CoR2+2Na+
At present, the metal hydroxide neutralization method is mainly used in China to produce cobalt salt binder series.
In this process, the cobalt ions are first turned into cobalt hydroxide or alkaline cobalt carbonate precipitate, and then the excess alkali and the resulting sodium salt are rinsed and cleaned, dried and powdered for use. Since the divalent cobalt ion is stable under acidic conditions (ionic state) but quite unstable under alkaline conditions, it is easily oxidized by oxygen or oxidizer in the air to become trivalent, and trivalent cobalt cannot react with organic acid, it will become impurities (insoluble matter) into the product and affect the product quality, therefore, maintaining the valence stability of cobalt in the powder making process is one of the key technologies. The rotary flash system with DCS fully automatic control can make the cobalt hydroxide filter cake drop from 75% to less than 5% moisture in about 3 seconds and be collected in the state of cobalt powder with more than 200 mesh, which is used as the raw material for synthesizing cobalt salt binder, in which the trivalent cobalt is effectively controlled to less than one part per thousand to ensure the quality of the binder product.
The prepared cobalt powder and various organic acids and boronic ester intermediates given in the formula are synthesized in the reactor to obtain the required cobalt salt binder products. During the whole synthesis process, the main parameters such as the dosage of various liquid materials, the temperature, pressure and vacuum at each stage of the reaction, and the reaction time are automatically controlled and recorded by the DCS control system to ensure the controllable and stable quality of each kettle product.
VI. Product Quality Judgment Method
Due to the importance of cobalt salt binder in rubber products, it is very important to carry out meticulous quality inspection of the cobalt salt binder products used, only the cobalt salt products that fully meet the standard can guarantee the physical and chemical properties of the rubber. Although each company has similar corporate standards and industry standards for cobalt boride 23, products that meet the standard indexes are not necessarily good products. We suggest that, in addition to the conventional index inspection, some simple internal control methods can be added to discriminate:
①Discrimination from appearance
The degree of borylation reaction of cobalt borylide is the key index of product quality, whether the borylation reaction is complete can be reflected by the color, section condition and crispness of the product. The color of good cobalt borylation product is dark blue, if the color of the product is red in blue, it means that the product is not dehydrated completely and the borylation reaction is definitely bad. The product section should be bright and flat, like a mirror, if the section is hairy and dark, it indicates that the product borylation reaction is not complete. The product section appears more pores, it reflects the product desolvency is not exhausted; the section appears obvious small granular material, it reflects the product pre-reaction is not complete, the borylation reaction is certainly not good. The crispness of the product reflects the degree of complete reaction of the product and the dispersion of the product in the process of use. Good crispness of the product, gently crushed by hand into a beautiful blue powder, while the crispness of the product is not good, it is not easy to become powder when crushed by hand, it will be seriously crushed into small groups or strips, sticky hands, the color is also dark, so the product performance and dispersion performance is certainly not good, in the process of packaging and storage and transportation is also easy to caking.
② Judging from heptane solubility
The good cobalt boride products are very easy to dissolve in heptane, the solution is beautiful blue-purple, clear and transparent, and no butadar phenomenon occurs when irradiated by beam light. The product with heptane insoluble substance added should be like this after the insoluble substance is separated by centrifuge, and the separated insoluble substance should be gray-white powder after washing by heptane, insoluble in dilute sulfuric acid and hydrochloric acid. Bad cobalt borylation products dissolve very slowly in n-heptane, and the solution is cloudy and opaque; the insoluble matter is pink or black-red after centrifugal separation, and the quantity is high, and the solution is pink when it is dissolved by dilute sulfuric acid or hydrochloric acid in water bath with heat, and the precipitate is off-white or earthy yellow, which indicates that the product is not good in the manufacturing process due to the activity of cobalt powder or high trivalent cobalt, which makes the reaction between cobalt and organic acid not completed completely, and the boron The boron acylation reaction is not good, and the performance of the product can be imagined.
③ Judgment from melting point
Cobalt dibasic products are amorphous substances, and there is a softening point in their testing index. Cobalt borohydride is not an amorphous substance, and it has no softening point.
