Application of rubber carbon black

People who have a little knowledge of carbon black know that carbon black can be divided into "reinforced carbon black", "conductive carbon black", "wear-resistant carbon black" and so on according to its performance. Carbon black can be used as a black dye to make Chinese ink, ink, paint, etc., and can also be used in chemical fibers and plastics... In fact, the industry with the largest amount of carbon black is still the rubber industry. What is the knowledge of the application of carbon black in rubber?

1、 What is rubber carbon black

We should first understand what rubber carbon black is. Rubber carbon black is actually rubber carbon black. This is not a strict concept, but a kind of carbon black products mainly used in rubber products, which have some statistical and standardized characteristics. It is a concept relative to special carbon black (used for inks, coatings, etc.). However, it is not that rubber carbon black can only be used in rubber products. In fact, many plastic products and other products also use the coloring property of rubber carbon black for product processing.

2、 What are the applications of carbon black in rubber industry

According to the comprehensive information of carbon black industry network, the carbon black used in the rubber industry accounts for about 90% of the total carbon black output. It is mainly used for automobile tires, tractor tires, aircraft tires, power tires, bicycle tires and other types of tires. Every ordinary car tire needs about 10 kilograms of carbon black. About three quarters of rubber carbon black is used in tire manufacturing, and the rest is used in other rubber products, such as tape, rubber hose, rubber shoes, etc. In the rubber products industry, the consumption of carbon black accounts for about 40-50% of the rubber consumption.

The reason why carbon black is used so much in rubber is that it has excellent so-called "reinforcing" ability. This "reinforcing" ability of carbon black was first found in natural rubber as early as 1914. It has been proved that the reinforcing ability of carbon black plays a more important role in synthetic rubber. The most important sign of carbon black reinforcement is to improve the wear performance of tire tread. Tires with 30% carbon black reinforcement can travel 48000 ~ 64000 kilometers; The mileage of filling the same amount of inert or non reinforcing filler instead of carbon black is only 4800 km. In addition, the reinforced carbon black can also improve the tensile strength, tear strength and other physical and mechanical properties of rubber products. For example, the tensile strength of vulcanizates with reinforcing carbon black added to crystalline rubbers such as natural rubber or neoprene can be increased by about 1 ~ 1.7 times than that of vulcanizates without carbon black; In non crystalline rubber such as styrene butadiene rubber or nitrile rubber, it can be increased to about 4 ~ 12 times.

In the rubber industry, the variety of carbon black and its mixing amount should be determined according to the different uses and use conditions of products. For example, for tire tread, wear resistance should be considered first, so high reinforcement carbon black is required, such as super wear-resistant furnace black, medium super wear-resistant furnace black or high wear-resistant furnace black; The tread and carcass compounds require carbon black with minimum hysteresis loss and low heat generation.

3、 Classification of different types of carbon black for rubber

Carbon black for rubber - carbon black for rubber was originally classified by particle size, but later classified by nitrogen surface area. In addition, factors such as the vulcanization rate and structure of carbon black pigments are also taken into account in the naming, which is composed of four systems. The first English letter represents the vulcanization speed of the compound, n represents the normal vulcanization speed, and s represents the slow vulcanization speed. The last three are Arabic numerals. The first number represents the range of carbon black nitrogen surface area, which is listed in 0~9 grades. The second and third figures are designated by the d24.41 Committee of the American Society for testing and materials in charge of carbon black and terminology, reflecting different structural degrees, that is, the approximate high and low structure of carbon black is determined, which is arbitrary. Relatively speaking, the larger the number, the higher the structure.

The naming system is composed of four systems, taking into account the vulcanization speed and structure of carbon black compounds. The first letter represents the curing speed of the compound. N stands for normal vulcanization rate, and s stands for slow vulcanization rate. The first letter of the last three letters represents the range of carbon black nitrogen table. The second and third numbers reflect different structural degrees. (these are all national standards)

N330 is the most widely used high wear-resistant furnace black. The wear resistance of this product is slightly worse than that of CSL wear-resistant series carbon black, but better than that of grooved carbon black. This product is used for tire tread, cord rubber, sidewall and various rubber industrial products. This product is a kind of carbon black with good reinforcing property, which can give the rubber better tensile property, tear resistance, wear resistance and elasticity. The rolling loss of the passenger tire using this product is only greater than N351 in N300 series, which is smaller than that of other varieties. It has good dispersion and extrusion performance in rubber, and is suitable for all kinds of synthetic rubber and natural rubber.

N220 is suitable for all kinds of rubbers, and its wear resistance is 10%-20% higher than N330. It can give rubber particles high tensile strength and tear strength, and has certain conductivity. It is mainly used for tread rubber of truck tires and passenger tires, and rubber products that need high strength and high wear resistance.

N550 is suitable for natural rubber and all kinds of synthetic rubber. It is easy to disperse and can give rubber a higher stiffness. It has the advantages of fast extrusion speed, small mouth expansion and smooth extrusion surface. Vulcanizates have good high-temperature performance and thermal conductivity, as well as good reinforcement, elasticity and recoverability. They are mainly used in tire cord compound, sidewall, inner tube and rubber compounds for extrusion and calendering products.

N660 this product is suitable for all kinds of rubber. Compared with semi reinforced carbon black, it has a higher structure, finer particles, and is easy to disperse in the rubber. The tensile strength, tear strength and secondary stress of the vulcanizate are higher, while the deformation is small, the heat generation is low, and the elasticity and yield resistance are good. It is mainly used for tire cord tape, inner tube, bicycle, hose, tape, cable, footwear, calendered products, model products, etc.

The wear resistance of n234 is about 10% higher than that of N220. It can show good wear resistance when used under high severity scale. It is mainly used for high-speed tires and high-quality rubber products.

N326 has high tensile strength, tear strength, wear resistance and spallation resistance in natural rubber. It is mainly used for tread rubber of tires (including off-road tires) that require high strength and low heat generation. It is also suitable for conveyor belts, sealing products and other high-quality rubber industrial products.

The reinforcement, wear resistance and crack growth resistance of N339 in tread compound are close to those of N220 carbon black, which is especially suitable for the system of styrene butadiene rubber and CIS butadiene. It is mainly used for tread rubber of passenger tires, truck tires, conveyor belts, rubber hoses and various rubber industrial products requiring high wear resistance.

The performance of N375 is basically the same as that of N339, and the heat generation is slightly lower than that of N339. It is mainly used for tread rubber of car tyres, truck tyres and off-road tyres.

N550 is suitable for natural rubber and all kinds of synthetic rubber. It is easy to disperse and can give rubber a higher stiffness. It has the advantages of fast extrusion speed, small mouth expansion and smooth extrusion surface. Vulcanizates have good high temperature properties and thermal conductivity, as well as good reinforcement, elasticity and recoverability. It is mainly used in tire cord rubber, sidewall, inner tube and rubber compound of extruded and calendered products.

N539 rubber used in this product has smooth extrusion surface, small mouth expansion, high tensile strength and elongation of vulcanizate, lower constant elongation stress than N550, and good elasticity and fatigue resistance. It is mainly used for tire carcass rubber, especially for buffer layer rubber based on natural rubber. It can also be used for tire base rubber, tape covering and other rubber products, wire and cable sheath materials.

N660 this product is suitable for all kinds of rubber. Compared with semi reinforced carbon black, it has a higher structure, finer particles, and is easy to disperse in the rubber. The tensile strength, tear strength, and tensile stress of the vulcanizate are higher, while the deformation is small, the heat generation is low, and the elasticity and yield resistance are good. It is mainly used for tire cord tape, inner tube, bicycle, hose, tape, cable, footwear, calendered products, model products, etc.

N990 the physicochemical properties of this product are similar to, but the specific surface area of nitrogen adsorption is slightly lower. The absorption value is slightly higher, which is a granulated product, and its toluene extract is less than. This product also has ultra pure products. This product is mainly used as a filler for rubber and plastic, and can also be used in metallurgy industry as a raw material for tungsten carbide products or high-temperature insulation materials, reductants, etc. Mixing a large amount of wood products in the rubber does not affect the adhesion of the rubber. When the mixing amount reaches parts, leather like rubber products can be obtained. The rubber used in this product is easy to process and does not affect vulcanization. Vulcanizate has small hardness, low heat generation, small deformation, good bending resistance and aging resistance.

4、 Selection of rubber carbon black dosage

Rubber carbon black has a strong reinforcing effect, so it can enhance the wear resistance and skid resistance of rubber when used in rubber products. Therefore, rubber carbon black has been widely used in rubber products, especially in automobile tires. Of course, there will be quantitative restrictions in everything. Rubber and carbon black should have a good proportion in order to give full play to the maximum effect. It is not that the more rubber carbon black is added in the process of making rubber, the better, If the amount of rubber carbon black is added too much, it will have a reaction and reduce its strength, so the problem comes. How much rubber carbon black should be added to the rubber to achieve our most satisfactory and perfect effect?

The amount of rubber carbon black in the compound will directly affect the properties of the vulcanizate, such as strength, wear resistance, hardness, elongation, yield flexibility, etc., and there is an optimal amount of carbon black. Therefore, in the formulation design, the reasonable selection of carbon black dosage is very important. For example, the hardness, constant elongation stress, heat generation, etc. all increase with the increase of the amount of rubber carbon black, while the resilience, expansion rate, elongation, resistivity, yield flexibility, etc. all decrease with the increase of the amount of carbon black. However, the tensile strength, tear strength and wear resistance have a high value with the increase of the amount of rubber carbon black. Therefore, the amount of carbon black should be reasonably selected according to the required performance, grasping the main contradiction, taking into account other factors. For example, in order to improve the wear resistance of the rubber compound, the amount of fine particle rubber carbon black is less, while the amount of fine particle rubber carbon black with high structure can be reduced, so that the elasticity will not be reduced due to the excessive amount, which is conducive to maintaining high flex cracking resistance, drinking elasticity, reducing heat generation, and ensuring better wear resistance in actual use.

Generally speaking, when the interaction between rubber carbon black aggregates in the rubber compound begins to increase sharply, the mixing amount of rubber carbon black is the best. The smaller the particle size of rubber carbon black, the greater the surface activity and the higher the structure, the amount of carbon black when reaching the maximum tensile strength tends to decrease. Generally, when the amount of carbon black is 40-60 phr, it can give rubber products better performance indicators. The best mixing amount is about 20% - 23% for hard carbon black and 23% - 26% for soft carbon black.

The optimal blending amount of rubber carbon black is different for different rubbers and different temperatures. For crystalline natural rubber, the optimal blending amount is to make the rubber molecular chain easy to be oriented and crystallized during large deformation, so the amount of rubber carbon black is less; For non crystalline styrene butadiene rubber, it is to increase the attraction between molecular chains, so as to increase the strength of elastomer and obtain reinforcement effect, so the amount of carbon black is more. In addition, the optimal filling amount of the same elastomer and the same filler at the mixing temperature of 100 ℃ is greater than that at 20 ℃.

The price of rubber carbon black is lower than that of rubber, so the general formula tends to use more rubber carbon black. However, if the amount of rubber carbon black is too much, the physical properties of the vulcanizate will decline and the due reinforcement effect will not be achieved. Firstly, the amount of rubber is relatively reduced; secondly, the interaction between rubber and carbon black is weakened due to poor dispersion, so the strength decreases. Therefore, the processability, hysteresis and damage characteristics of the compound should be comprehensively considered, and the appropriate mixing amount should be selected.

The maximum filling amount of rubber carbon black can be determined in advance by the DBP absorption value of carbon black. For example, if the DBP adsorption value of ISAF is 1.25cm3/g and the relative density of rubber is 0.95, 100g carbon black can be matched with at least 118g rubber (1.25 × 0.95=1.18), or 100g rubber can hold 85g carbon black (ISAF) at most. Similarly, the capacity of low structure carbon black can be more. If the carbon black is filled too much, it is easy to agglomerate and cannot be further dispersed. In fact, only the carbon black master batch can reach such a high carbon black concentration.

When determining the filling amount of rubber carbon black, we should also consider the temperature in the mixing process to determine the best proportion. Remember not to add too much rubber carbon black, which will affect the physical properties of vulcanizate, reduce the interaction between rubber carbon black and rubber, and reduce the tensile strength of rubber products, Because excessive use of rubber carbon black will make the dispersion of carbon black not uniform enough and cause condensation.

5、 What are the effects of the properties of carbon black on the properties of rubber

1. The chemical activity of carbon black is related to the performance of rubber. The chemical activity of carbon black plays an important role in enhancing performance. Experiments show that carbon black with high chemical activity has a greater enhancement effect; Carbon black with low chemical activity (such as graphitized carbon black) has little enhancement effect. This is because carbon black with high chemical activity has many surface active points, and there are many network structures (bonded rubber) formed by reacting with rubber molecules during rubber mixing and vulcanization. The network structure formed by carbon black and rubber gives the vulcanizate strength. Therefore, the chemical activity of carbon black is the most basic factor to enhance the performance, which is called the first factor (or strength factor) affecting the reinforcement performance of carbon black.

The greater the chemical activity of carbon black, the more bonded rubber is produced in the mixing process, which improves the Mooney viscosity of rubber materials, increases the oral expansion rate and the shrinkage rate of semi-finished products, and slows down the compression speed. Tensile strength of vulcanizates Tear strength The higher the wear resistance.

It is found that the oxygen-containing functional groups have little effect on the enhancement of unsaturated rubber in the active points on the surface of carbon black, which is one of the reasons why the development of modern furnace carbon black uses less tank carbon black. However, oxygen-containing functional groups have a greater strengthening effect on high saturation rubber (such as butyl rubber).

2. Because the active points of carbon black exist on the surface of carbon black, the smaller the carbon black particles, the larger the specific surface area, and the more active points of carbon black with the same quality, which can better play the chemical binding and physical adsorption of carbon black on rubber and improve the enhancement effect. Therefore, the particle size of carbon black is the second factor that affects the reinforcement performance of carbon black, that is, the breadth factor.

The smaller the particle size of carbon black, the smaller the tensile strength of vulcanizate Tear strength Constant extension stress Wear resistance The higher the hardness is, the better the bending crack resistance is, and the resilience and elongation at break are reduced. However, if the particle size is too small, due to the large cohesion between particles, it is easy to agglomerate, which makes it difficult to disperse when mixing, and reduces the plasticity and compression performance.

3. The relationship between the structural properties of carbon black and the properties of rubber. The structural properties of carbon black are the third factor that affects the reinforcing properties of carbon black, that is, the shape factor. This is because high structure carbon black has complex polymer melt shape, many branches and large internal gap. When mixed with rubber, it forms more absorbing rubber (or inclusive rubber). Because the carbon black polymer melt hinders the deformation of the molecular chain of the absorbed rubber, the fixed elongation stress of the vulcanizate The improvement of hardness and other properties plays an important role, which reflects the enhanced function. At the same time, the formation of retention rubber also plays an important role in improving the dispersion and extrusion performance of carbon black in the mixing process. Even if the expansion rate of extrusion port and the shrinkage rate of semi-finished products are reduced, semi-finished products also have great straightness and smooth surface.

The structure of carbon black has different effects on the reinforcement properties of crystalline and amorphous rubber. It is mainly reflected in the influence on tensile strength and tear strength. The general rule is: when the particle size is the same, the high structure carbon black has a greater strengthening effect on the amorphous rubber, and generally has higher tensile strength and tear strength, because the carbon black structure improves the crystallization tendency of the amorphous rubber. Carbon black with low structure is more conducive to improve the tensile strength and tear strength of crystalline rubber, mainly because less rubber is absorbed when the structure is low, which is conducive to the extended crystallization of rubber.

In addition, the structural properties of carbon black are also the most important factors affecting the conductivity of rubber. The higher the structure, the better the conductivity. This can be simply explained as the chain branch structure of carbon black polymer melt is easy to form interleaved conductive paths in rubber, thus improving the conductivity.

4. The surface roughness of carbon black is related to rubber properties. The surface roughness of carbon black will adversely affect the reinforcement performance of carbon black and reduce the process performance of rubber materials. When the particle size of carbon black is the same, increasing the surface roughness will reduce the reinforcement performance, because the rubber molecular chain cannot only enter the zero nm. In the surface pores of carbon black, the effective surface area of the interaction between carbon black and rubber is reduced, and the reinforcement effect is reduced. The result is the tensile strength of vulcanizates Constant extension stress Wear resistance The flexural cracking resistance decreases, but the resilience decreases The tensile elongation and tear resistance are improved.