1. Introduction
The main component of white carbon black is SiO2, which is named because it is white, and its main physical properties and uses are similar to carbon black.
Silica can be divided into precipitated silica (precipitated hydrated silica) and fumed silica (fumed silica) according to different production methods. The production methods of the two products are different, and their properties and uses are also very different. , The products introduced below are produced by sulfuric acid precipitation method, that is, precipitated silica, and the silica involved in the following are all precipitated silica.
2. Name definition and molecular formula
The scientific name of white carbon black is: precipitated hydrated silica.
Definition: Precipitated hydrated silica is a material composed of amorphous particles obtained by precipitation from a soluble silicate water precipitation solution.
Chemical formula: SiO2 nH2O
3. Main properties
1. Physical properties
Appearance: White powder or granular or irregular lumps.
True density: about 2.0g/ml False density: about 0.2g/ml (common product).
High temperature resistance, non-flammable; good electrical insulation.
2. Chemical properties:
Can react with caustic soda SiO2nH2O+2NaOH=Na2SiO3+(n+1)H2O
Can react with hydrofluoric acid SiO2nH2O+4HF=SiF4+(n+2)H2O
2. Main chemical indicators
SiO2 content (dry product) ≥ 90%
Sieve residue (4.5цm)≤0.5%
Heating loss: 4.0-8.0%
Loss on ignition: (dry product) ≤ 7.0%
PH value: 5.0-8.0
Total copper content: ≤30mg/kg
Total manganese content: ≤50mg/kg
Total iron content: ≤1000mg/kg
DBP absorption value: 2.00-3.50cm3/g
Specific surface area: different uses have different ranges, generally 145-165m2/g (HT2#) 165-185m2/g (HT1#)
200-300m2/g(HT3#)
3. Main physical properties (combined with rubber products)
Tensile strength ≥ 17.0Mpa 500% elongation strength ≥ 6.3Mpa
Elongation at break ≥ 675%
4. Production principle
Water glass reacts with sulfuric acid to produce hydrated silicic acid
Na2O·mSiO2+H2SO4+nH2o-→Na2SO4+mSiO2·(n+1)H2O↓
The reaction completed liquid is dehydrated by pressure filtration, washed and beaten to obtain a white carbon black slurry, and spray dried to obtain a white carbon black finished product.
5. Process diagram
6. Main purpose
Since its industrial production in the 1940s, silica products have been widely used in various industries after more than 60 years of continuous development and improvement. In addition to being widely used as a reinforcing agent in rubber products, it can also be used in the pharmaceutical industry , pesticides, inks, paints, coatings, toothpaste, paper, food, feed, cosmetics, batteries and other industries. Here is a brief introduction to the main application industries where white, gray and black are applicable:
1. Tire industry
Silica was initially only made into decorative strips for use in white sidewall car tires, and later its use gradually expanded, and it has been used in various parts of tires at present. In general, if the hysteresis loss of the tread rubber is reduced, the wet grip is also reduced. However, the use of silica in tire tread rubber, especially high-dispersion precipitated silica and coupling agent, can simultaneously improve tire life (improving wear resistance) and safety (improving wet skid resistance), Reduce fuel consumption (reduce rolling resistance). Therefore, at present, foreign tire manufacturers mostly use highly dispersible silica in the tread, which can effectively improve tire performance. In addition, precipitated silica is used in the tire carcass and belt layer to improve the adhesion between the rubber compound and the steel cord (such as m-methyl white system); the silica part is used in the tire sidewall rubber Replacing carbon black can greatly improve the durability of the rubber compound, improve the flex resistance and impact resistance, and can maintain the dimensional stability of the rubber compound and improve its ability to resist mechanical damage when used in tire wraps for cars and truck tires .
(1) Tread
The tread is the part of the tire in contact with the road surface. Therefore, three basic requirements are put forward for it: one is to have a higher grip on the wet road or better traction to ensure the safety of vehicles and personnel; the other is to roll Small resistance to save fuel. Generally speaking, the tire rolling resistance is reduced by 3-4%, and the fuel consumption can be reduced by 1%. The rolling resistance based on the tread is about 50% of that of the tire, and reducing rolling resistance is an important way to save fuel; the third is wear resistance and long service life.
a. Passenger tire tread
It has been found that the combined use of highly dispersible starch silica with special solution polymers and silane coupling agents, coupled with the optimal mixing process can overcome the defects of reduced hysteresis loss and reduced wet grip of tread rubber . A tread compound completely filled with silica can reduce the rolling resistance of the tire by 20%, which means that the hysteresis loss of the tread is reduced by about 50%, and the fuel consumption is reduced by at least 30%.
At present, the amount of precipitated silica used in passenger tire treads is generally 65 parts.
b. Heavy-duty tire tread
Silica is used in truck tires to improve the puncture resistance and tear resistance of the tread. Precipitated silica is especially suitable for its tread, because it not only reduces rolling resistance, but also has low running temperature. Low running temperatures or low heat generation are extremely important for truck tires.
c. Off-road tire tread
The purpose of using precipitated silica in the tread of off-road tires is to reduce its heat generation, improve heat resistance and resistance to chipping and chipping, and combine the off-road tire tread containing precipitated silica with the pure carbon black filled tire In comparison, the cut growth resistance and tear strength of the former are greatly improved compared with the latter, and the tread of natural rubber engineering machinery tires using high-dispersion precipitated silica can obtain low heat generation and better performance. The effect of tear resistance and block fatigue tear resistance.
(2) sidewall
The sidewall is a layer of outer rubber that can protect the carcass from weather erosion. It should have good toughness, anti-oxidative aging, wear resistance, tear resistance, circumferential and radial crack resistance, and long fatigue life. . For this reason, tire sidewalls generally use natural rubber/polybutadiene rubber compounds containing anti-aging agents, anti-ozonants and paraffins. But after the anti-aging agent is exhausted, the sidewall will harden and crack; resistance to anti-ozonant and paraffin will make it fade, and the anti-ozonant is polluting. At this time, if the precipitation method is used, the above phenomenon can be made obvious. weakened.
(3) Steel cord bonding
Precipitated silica is widely used in steel wire hanging glue. It can be used together with resorcinol formaldehyde resin to form RFS adhesive system to increase the adhesion between plated steel wire and rubber, and it can also be used together with organic cobalt to form silica/cobalt and silica/resin/cobalt adhesive system. Both bonding systems are hot. The adhesion before and after moisture and saline aging showed an alkaline increase with the increase of silica content.
To sum up, silica has been more and more widely used in tires, and various tires represented by "green tires" are increasingly favoring silica. Therefore, it is necessary to develop silica that improves tire performance will be an important part.
2. Rubber shoes and other rubber products
(1) White carbon has high blackness and fine particles, and the vulcanizate made of white carbon black has high transparency and can improve the comprehensive physical properties of the rubber. Therefore, silica, as the main reinforcing filler, is widely used in the production of rubber shoes, especially in transparent and translucent sole rubber. At present, most Korean-funded shoe-making enterprises in Qingdao are using highly transparent and transparent silica.
(2) In the production of adhesive tape, in order to improve its wear resistance, a large amount of white carbon black is added. At the same time, the silanol on the surface of white carbon black plays a role in improving the wetness of rubber and fabric, which is beneficial to the diffusion of rubber and penetration.
In addition to the above-mentioned products, white carbon black is also used in rubber rollers, rubber hoses, rubber plates, wires and cables, household appliances, rubber parts in stationery, etc.
3. Silicone rubber
Silicone rubber has high heat resistance and excellent cold resistance, ozone resistance, aging resistance and atmospheric aging resistance, as well as excellent electrical insulation. It can be used for a long time in the range of -60°C-250°C, and physical indicators such as strength change little with temperature changes. In addition, silicone rubber has low water absorption and can be stored in a humid place for a long time, with a moisture content of ≤0.015%. Due to the above-mentioned characteristics of silicone rubber, it is widely used in aerospace, electronics, and instrumentation industries, but silicone rubber The application of white carbon black began with the appearance of white carbon black, especially the price of fumed white carbon black was too high. Recently, precipitated white carbon black was used to replace fumed white carbon black, but now domestically produced precipitated white carbon black can only be used for low-end use of silicone rubber.
4. Pharmaceutical industry
Silica is physiologically inert, highly absorbable, dispersible and thickening, and is widely used in pharmaceutical preparations. For example, quasi-vitamin E powder now uses white carbon black as a carrier in large quantities.
5. Pesticide industry
The main role of white carbon black in the pesticide industry is as a carrier to improve fluidity and prevent caking. At present, white carbon black is mainly used in various wettable powders.
6. Application in ink
Silica mainly acts as a thickener in ink and is used to control the flow of printing ink. It is also used to control the flow of printer ink so that it cannot flow or sag randomly to obtain clear printing.
7. Matting agent for paints and coatings
Silica is widely used in water-based and solvent-based transparent wood coatings (wood varnishes), high-solid coatings, architectural coatings, wallpaper coatings, etc. For wood coatings, the coating film has excellent optical properties and only has soft precipitation in use.
Due to the many functions of silica products, it has become an indispensable additive in many industrial sectors, especially the production environment has little pollution, and has broad development prospects.
7. The role of each indicator in the application
1. Specific surface area
The reinforcing effect of white carbon black mainly depends on its specific surface. Generally, as the specific surface area increases, the strength indicators of rubber products increase, but the resilience decreases, the tear strength decreases, and it is not wear-resistant. Mixed Difficult to disperse during refining, high heat generation, high Mooney viscosity of the rubber material, and easy scorch. Therefore, different formulations and different uses require different specific surface areas, and the impact of specific surface areas on the physical and mechanical properties of vulcanized rubber is not consistent.
2. Oil absorption value
The oil absorption value reflects the level of structure, the oil absorption value is large, the structure degree is small, the elongation strength of vulcanized rubber is generally large, the tensile strength and hardness are large, especially the wear resistance is small, but the elongation is low .
3. Loss on ignition at 900°C
It shows that when there are too many hydroxyl groups on the surface, it is easy to cause the structure of the rubber composite material and make the material brittle. It affects the processing performance, and the vulcanized rubber is easy to fall off, and the surface hydroxyl group has a strong adsorption effect on the vulcanization accelerator, prolonging the vulcanization time.
4. Heating loss at 105°C
It reflects the amount of free water in the particle voids. If it is too small, it will be difficult to mix the rubber with a high degree of structure. If the heat loss is zero, the white carbon black is useless. Generally, it is more appropriate to control it at about 6%.
5. pH value
Generally around 7, the PH value increases (acidity decreases), and the vulcanization speed of the rubber is accelerated.
6. Soluble salt
The less the better, but the less, the more costly.