The role and dosage of fillers in rubber products

The rubber industry uses a large number of fillers as compounding agents, and its dosage is second only to rubber consumption. Reinforced filler used in rubber, not only can improve the strength of rubber products, but also can improve the processing performance of rubber, and give products good wear resistance, tear resistance, heat resistance, cold resistance, oil resistance and other properties, can extend the service life of products. Non-reinforcing filler for rubber, mainly from the role of filling capacity, some varieties also have the role of isolation, demoulding or coloring.

Rubber product requirements for fillers

1 General requirements

(1) The surface of the reinforcing filler particles must have strong chemical activity, which can produce a good combination with rubber, and can improve the mechanical properties, aging resistance and adhesion properties of vulcanized rubber. The surface of non-reinforcing filler particles is chemically inert, and does not produce chemical combination with rubber, and does not affect the mechanical properties and weather resistance, acid and alkali resistance and water resistance of vulcanized rubber.

(2) It has high chemical purity, uniform fineness, and good wettability and dispersibility to rubber.

(3) It is not volatile, odorless, tasteless, non-toxic, and has good storage stability.

(4) Fillers for white, light-colored and colored rubber products also require no pollution and no discoloration.

(5) cheap and easy to get.

2-PERFORMANCE REQUIREMENTS

(1) Fineness: Generally speaking, the finer the reinforcing filler particles, the larger the specific surface area, the larger the contact area with the rubber, and the better the reinforcing effect. The finer the non-reinforcing filler particles, the better the mixing effect after adding rubber. However, it must be evenly dispersed, such as uneven dispersion, even if the particles are very fine, the mixing effect is not good.

(2) particle shape and crystal form: the shape of the filler particles is better to be spherical, and the sheet-shaped or needle-shaped filler is easy to produce directional arrangement when the vulcanizate is stretched, resulting in an increase in permanent deformation and a decrease in tear resistance. Reinforced filler in carbon black and white carbon black is amorphous, other fillers also have crystalline. For example, although the chemical composition of silica powder and white carbon black is silica, the former is crystalline and the latter is amorphous. Crystalline packing is divided into two kinds of heteroaxial crystallization and equiaxial crystallization. Coaxial crystalline x, y, z triaxial similar, isotropic. Heteroaxial crystallization x, y, z triaxial has significant difference, anisotropy in the commonly used non-metallic mineral filler, clay, graphite, diatomite belong to heteroaxial crystallization system. Calcium carbonate is an equiaxed crystal system. Rubber products with good wear resistance and tear resistance are required, and it is not suitable to use non-axial crystalline materials as reinforcing fillers.

(3) Surface properties: The powder filler is mixed with rubber, and its particles are surrounded by rubber molecules. The degree of wetting of the particle surface by rubber has a great influence on the reinforcement performance. Not easy to wet particles, in the rubber is not easy to disperse, easy to agglomerate, reduce its reinforcement. This condition can be improved by adding certain substances that help to increase wetting. For example, the reinforcing effect of calcium carbonate is very small. After adding fatty acids, the surface tension is reduced, the wetting degree is increased, and the reinforcing effect is improved.

Carbon black is the main reinforcing filler of rubber, and its composition is 90% ~ 99% of elemental carbon, and the rest is a small amount of volatile matter and water. In the production process of carbon black, its surface adsorption or combination of a small amount of carboxyl, quinone, phenol, lactone and other chemical groups. In the past, it has been considered that the reinforcing efficiency of carbon black depends only on its particle size (specific surface area) and structure, and has nothing to do with the chemical nature of its surface. In recent years, a large number of research results show that the chemical groups on the surface of carbon black particles can chemically react with rubber in the mixing process, so that the binder increases, and then improves the mechanical properties and aging resistance of vulcanizates.

The surface chemical groups of silica particles are completely different from those of carbon black. The surface of fumed silica contains silanol-based Si-OH, and the surface of precipitated silica contains silanol-based Si-OH and Si<(OH):.

Fumed silica is acidic, precipitated silica surface is acidic or alkaline. Acidic will delay the curing rate, alkaline will accelerate the curing rate. Silica surface microporous, hygroscopicity is strong, bad for reinforcement. The surface modification with silane coupling agent can overcome its disadvantages and improve its reinforcement performance. The surface modification treatment of non-metallic mineral powder filler also has a good application effect.

3. The amount of filler in rubber products

In rubber products, filler is the second largest raw material after raw rubber (natural rubber and synthetic rubber). In the product formulation, if the amount of raw rubber is 100, the amount of reinforcing filler is about 50, and the amount of non-reinforcing filler is about 25, which is the sum of all kinds of rubber products. Specific to each product, some fillers even more than rubber, and some are lower than the total average amount. Take the main product formula as an example, the raw rubber is 100 parts.

Tire-tread carbon black dosage of 40~50 parts. Basically no non-reinforcing filler, or with a small amount of clay. About 20 parts of clay or calcium carbonate can be used in the inner tire rubber.

Adhesive tape-the amount of carbon black 25~45 parts. Calcium carbonate can be used for each part, the amount of 10 to 113 parts. Magnesium carbonate can be used for flat belt sealing glue and edge glue paste, the dosage is 40 parts, 50 parts respectively. Barium sulfate is used for flat belt rubbing glue, the amount is 25 parts.

Hose-the amount of carbon black 15~45 parts. The dosage of calcium carbonate is 33-128 parts, clay is 20-50 parts, magnesium carbonate is 25 parts, and barium sulfate is 30 parts in the acid and alkali hose.

Rubber shoes -50 parts of black sole carbon black, 50 parts of superfine active calcium carbonate (Bai Yanhua), 40 parts of clay, 55 parts of white sole white carbon black, 15 parts of superfine calcium carbonate and 2 parts of titanium dioxide.

Tape products-calcium carbonate and clay can be used for all kinds of tape products, the amount of 30~150 parts, barium sulfate for airtight tape, the amount of 11 parts.

Model products-the amount of carbon black 40~75 parts. White carbon black can be used in 30 parts, clay can be used in 35 parts. Calcium carbonate can be used in 20 parts.

Sealing products-oil seal available white carbon black 70 parts. 25 parts of carbon black for sealing strip, 10 parts of calcium carbonate, 30 parts of clay for oil-resistant vacuum sealing and 40 parts of carbon black. 15 parts of carbon black and 54 parts of calcium carbonate for separator.

Latex products-latex gloves can be used in 10-15 parts of barium sulfate or 5 parts of calcium carbonate, 20 parts of talc powder in sponge latex formula, 2-3 parts of clay in neoprene latex silk formula, 100 parts of clay or 100-300 parts of calcium carbonate in porous model latex formula.

From the above examples, it can be seen that a large number of reinforcing fillers and non-reinforcing fillers are used in various rubber products, and the types and varieties of fillers used in different products vary greatly. In actual use, the formula design should be carried out according to the performance requirements of rubber products, the selection of rubber species, the addition of reinforcing fillers to improve mechanical properties, and the addition of non-reinforcing fillers to improve processing performance and reduce production costs. The formulation is optimized by adjusting the vulcanization system and the protection system. This is the basis for the production of high-quality rubber products.

In addition to the above-mentioned calcium carbonate, clay, barium sulfate and talc, many natural inorganic mineral powder materials can also be used as rubber fillers, such as magnesium carbonate-containing dolomite, calcium silicate-containing wollastonite, sulfate-containing barite, gypsum, amorphous carbon-containing stone black, coal powder and other silicon-containing powder quartz (diatomite), asbestos, pyrophyllite, coal gangue, oil shale, fly ash, attapulgite, red clay, etc. Rubber products manufacturers can choose different fillers according to product performance requirements and prices, and determine the best dosage through formula tests.