Application of Silica in Rubber Production
Silica is a general term for white powdery X-ray amorphous silicic acid and silicate products, mainly referring to precipitated silica, fumed silica and ultrafine silica gel, also including powdered synthetic silicic acid Aluminum and calcium silicate, etc. Silica is a porous material whose composition can be represented by SiO2·nH2O, where nH2O exists in the form of surface hydroxyl groups. . High temperature resistance, non-flammable, tasteless, odorless, and has good electrical insulation. There are many kinds of carbon black, such as pigment carbon black, special carbon black, white carbon black, etc. Among them, white carbon black is a kind of special carbon black, which is white in color and soft in texture, and is widely used in many fields.

Silica can be used as a reinforcing agent for rubber, and its reinforcing performance is even better than that of pigment carbon black after ultra-fine processing. It is more suitable for making light-colored rubber.

Silica can also be used as a thickener, which plays an important role in the blending of oils and paints. At the same time, it can also be used as a fading agent for paint, a thixotropic agent for packaging materials of electronic components, a precipitation agent for phosphor powder when coating a fluorescent screen, a filler for color printing rubber sheets, and a mold release agent for casting.

After adding silica into the resin, it can improve the moisture-proof and insulating properties of the resin. Filled in plastic products to increase slip resistance and oil resistance. Filled in silicone resin, it can be made into plastic resistant to above 200℃.

Silica is used in the paper industry as a filler and as a surface furnish for paper. It is also used as a carrier or dispersant for insecticides and pesticides, an anti-caking agent, and a liquid adsorbent and lubricant.

In general, white carbon black is a multi-functional carbon black type, which can emit light and heat in different fields.

Influence of Silica on Process Properties of Compounds

(1) Mixing and dispersion of rubber compound

Due to its large specific surface area, silica tends to aggregate twice, and it is easy to absorb moisture in the air, resulting in a strong hydrogen bond association between hydroxyl groups, which further improves the cohesion between particles. It is much more difficult to mix and disperse than carbon black, and when a large amount is mixed, it is easy to generate gel, which hardens the rubber compound and generates heat during mixing. In order to obtain good dispersion, it is required to maintain the shear force as high as possible during initial mixing, so that these aggregate particles of silica can be destroyed as much as possible without causing excessive mechanical degradation of the rubber molecular chain. . For this reason, silica should be added in small amounts in batches to reduce heat generation. Appropriately increasing the mixing temperature will help to remove part of the adsorbed moisture on the surface of silica, reduce the cohesion between particles, and help the dispersion of silica in the rubber compound.

(2) Structural control in silica reinforced silicone rubber compound

Silica, especially fumed silica, is the best reinforcing agent for silicone rubber, but has a problem of hardening the compound, commonly referred to as the "structuring effect". Its structure increases with the extension of the storage time of the rubber compound, and it is even serious to the extent that it cannot be reworked or scrapped. There are two explanations for this. One is that the end groups of silicone rubber are condensed with hydroxyl groups on the surface of silica; There are two ways to prevent structuring. One is to add some substances that can react with the hydroxyl groups on the surface of silica, such as hydroxy silicone oil, diphenylsilicon diol, silazane, etc. during mixing. When using diphenylsilyl diol, it should be treated at 160~200℃ for 0.5~1h after mixing. This prevents the structuring of the silica-filled silicone rubber. Another way is to modify the surface of silica in advance, first remove part of the surface hydroxyl groups, and fundamentally eliminate the structure.

(3) Mooney viscosity of rubber compound

The ability of silica to generate gel is comparable to that of carbon black. Therefore, when mixing silica, the Mooney viscosity of the compound increases, which deteriorates the processing performance. Therefore, in the compound formulation containing silica The choice and amount of softener is important. Paraffin hydrocarbons, naphthenic hydrocarbons and aromatic hydrocarbons are often added to IIR, and the amount varies depending on the amount of silica and the Mooney viscosity, generally up to 15-30%. In NR, vegetable softeners such as rosin oil and tall oil have the best softening effect, synthetic softeners have little effect, and mineral oil has the lowest softening effect.

(4) The vulcanization speed of the rubber compound

There are a large number of micropores on the surface of silica particles, which have a strong adsorption effect on the vulcanization accelerator, so the vulcanization is obviously delayed. In order to avoid this phenomenon, on the one hand, the amount of the accelerator can be appropriately increased; on the other hand, the active agent can be used, so that the active agent is preferentially adsorbed on the surface of silica, thus reducing its adsorption to the accelerator.

The active agents are generally nitrogen- or oxygen-containing amines, alcohols, and alcoholamines low-molecular-weight compounds. For NR, amines are more suitable, such as diethanolamine, triethanolamine, butanediamine, hexamethylenetetramine and the like. For SBR, alcohols are more suitable, such as hexanetriol, diethylene glycol, glycerol, polyethylene glycol, etc. The dosage of the active agent depends on the amount of silica, PH value and rubber type, and the general dosage is 1~3% of the silica.

Influence of silica on the properties of vulcanizate

Silica has a very significant reinforcing effect on various rubbers, and the reinforcing effect on silicone rubber is particularly prominent. Silica is a white reinforcing agent whose reinforcing effect is second only to the corresponding furnace carbon black. Compared with the vulcanizate reinforced with corresponding furnace carbon black (such as HAF), the vulcanizate containing a certain amount of silica has the advantages of high strength, high elongation, high tear strength, high hardness and good insulation. Usually, carbon black and white carbon black are used in combination to obtain better comprehensive performance.

1. The role of silica in tires. At first, white carbon black was only used as a decorative strip for white sidewall car tires. Later, its use was gradually expanded, and it has now been used in various parts of the tire. In general, if the hysteresis loss of the tread compound is reduced, the wet grip is also reduced. However, the use of silica, especially high-dispersity precipitated silica in combination with a coupling agent, in tire tread compounds can simultaneously improve tire life (improve wear resistance) and safety (improve wet skid resistance), Reduce fuel consumption (reduce rolling resistance), therefore, at present, most foreign tire manufacturers use high-dispersion silica in the tread, which can effectively improve tire performance. In addition, precipitated silica is used in tire carcasses and belt layers to improve the adhesion of rubber compounds to steel cords (such as m-A white system); in tire sidewall rubber, silica is used in part Replacing carbon black can greatly improve the durability of the compound, improve flex resistance and impact resistance, and can maintain the dimensional stability of the compound and improve its resistance to mechanical damage when used in tire wraps for passenger cars and truck tires. .

(1) Tread

The tread is the part where the tire is in contact with the road surface. Therefore, three basic requirements are put forward: one is to have a higher grip on the wet road or better traction to ensure the safety of the vehicle and personnel; the second is to roll Low resistance to save fuel. Generally speaking, the rolling resistance of tires 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 the tire, and reducing the rolling resistance during the period is an important way to save fuel; the third is wear resistance and long service life.

It has been found that the combination of high dispersibility of lake silica with special solution polymer and silane coupling agent, coupled with the best mixing process, can overcome the defects of reduced hysteresis loss and reduced wet grip of tread rubber. . A tread compound filled entirely with silica can reduce the rolling resistance of the tire by 20%, which means that the tread hysteresis loss 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.
Silica is used in truck tires to improve the puncture and tear resistance of the tread. Precipitated silica is particularly suitable for its treads because it not only reduces rolling resistance, but also has low running temperatures. It is extremely important for truck tires to have low running temperatures or low heat generation.

The purpose of using precipitated white carbon black in off-road tire treads is to reduce its heat generation, improve heat resistance and the ability to resist chipping. Compared with the surface of the former, the cutting resistance and tearing strength of the former are greatly improved. The effect of tear resistance and fatigue tear resistance of the blocks.

(2) Sidewall
The sidewall is a layer of outer rubber that can protect the carcass from weather erosion. It should have good resistance, anti-oxidative aging, wear resistance, tear resistance, circumferential and radial crack resistance, and long fatigue life. . For this reason, tire sidewalls generally use a combination of natural rubber/polybutadiene rubber containing antioxidants, antiozonants and paraffins. However, after the anti-aging agent is used up, the sidewall will become hard and cracked; the anti-ozonant and paraffin will make it fade, and the anti-ozonant is polluting. weaken.

(3) Steel cord bonding

Precipitated white carbon black is widely used in the hanging glue of steel wire. It can be used together with resorcinol formaldehyde tree tire to form RFS bonding system to increase the bonding between plated steel wire and rubber, or it can be used with organic diamond salt to form silica/cobalt and silica/resin/cobalt bonding system. The two bonding systems are hot. The adhesion force before and after moisture and salt water aging showed an alkaline increase with the increase of the amount of silica.
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, the development of silica with improved tire performance will be an important part.

2. Rubber shoes and other rubber products

(1) The white carbon has high black and white degree and fine particles. The vulcanized rubber prepared by using white carbon black has high transparency and can improve the comprehensive physical properties of the rubber. Therefore, as the main reinforcing filler, silica is widely used in the production of rubber shoes, especially in transparent and translucent sole compounds. At present, most of the Korean-funded shoe-making enterprises in Qingdao are using highly transparent and transparent silica.

(2) In the production of the tape, in order to improve its wear resistance, a large amount of silica is added. At the same time, the silanol on the surface of the silica plays a role in improving the wettability of the rubber compound and the fabric, which is beneficial to the dispersion of the rubber compound and the fabric. penetration.

In addition to the above products, white carbon black is also used in rubber rollers, rubber hoses, rubber sheets, wires and cables, household appliances, and stationery.

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℃-250℃, and the physical indicators such as strength change little with the change of temperature. In addition, silicone rubber has low water absorption and can be stored in humid places for a long time, with a moisture content of ≤0.015%. Because of the above characteristics of silicone rubber, it is widely used in aerospace, electronic industry, instrumentation and other industries, but silicone rubber is widely used. The application of silica started with the appearance of silica, especially the price of fumed silica is too high. Recently, precipitated silica has been used to replace fumed silica, but the domestic precipitated silica can only be used for low-grade silica. The use of silicone rubber.