Uses of white carbon black (characteristics of white carbon black in rubber)

Silica has a wide range of uses, and different products have different uses. Used as a good reinforcing agent for synthetic rubber, its reinforcing performance is second only to carbon black, and even better than carbon black after ultra-fine and proper surface treatment. Especially when manufacturing white, colored and light-colored rubber products, it is more suitable. Used as a thickening agent or thickener, blending agent for synthetic oils and insulating varnishes, delustering agent for paints, thixotropic agent for encapsulating materials of electronic components, precipitating agent for phosphors when coating fluorescent screens, filling of color printing rubber sheets Agent, mold release agent for casting. Adding to the resin can improve the moisture-proof and insulating properties of the resin. Filling in plastic products can increase slip resistance and oil resistance. Filled with silicone resin, it can be made into plastic with resistance above 200℃. It is used as a filler and paper surface ingredient in the paper industry.


Precipitated silica is a widely used material for rubber reinforcement. Generally speaking, because the reinforce effect of precipitated silica (except for ultra-fine, surface treatment) is not as good as carbon black, it is a semi-reinforcing filler material. Therefore, the percentage to replace carbon black should be determined according to the use occasion. Precipitated white carbon black is used in rubber products such as inner and outer tires of automobiles, dump trucks, trucks, tractors, forklifts, bicycles, industrial belts, hoses, gaskets, rubber sheets, threshing rubber rollers for grain processing, rubber shoes, etc. Silica is used more or less in various rubber industrial products. Adding a certain amount of white carbon black to ordinary tires can increase the service life of tires. According to the results of the tire formula research test of a former West German company, if 10-20 parts of white carbon black can be added, the adhesion and tear resistance can be improved, the mileage of the tire can be increased, and the tire's resistance to the road can be enhanced. Holding power to facilitate safe driving. The mileage of tires in my country is lower than the international level, and the non-use of white carbon black is one of the reasons. In addition, due to the high heat of carbon black, white carbon black is also tended to be added to automobile tires used on highways abroad. At present, domestic and foreign markets have increasingly diversified requirements for bicycle tires. For example, new fancy varieties such as tire bead colorization and flashing rings are produced with white carbon black instead of carbon black. In the production of rubber shoes, people not only require fastness to rubber shoes, rain boots, sports shoes, travel shoes, fitness shoes, ballet shoes, etc., but also require beautiful colors, comfort and lightness. White carbon black not only has good reinforcement, abrasion resistance, slip resistance and upper adhesion, but also a good light-colored reinforcement material, so it plays an important role in providing quality and style of shoes in the development of rubber shoes. Important role.


White carbon black can be used as a filler in polyethylene, polypropylene, polybutene, epoxy resin and other plastics, which can improve the elastic strength and wear resistance of plastics, as well as the thermal stability of hardness. Used in cables can also improve the electrical insulation of cables. For example, methyl vinyl silicone rubber high-voltage wires should use fumed white carbon black or high-quality precipitated white carbon black. It is often difficult to separate between the two layers of plastic film, and the bag opening is difficult to open when bagging, so white carbon black is a very popular opening agent. When polyvinyl chloride is used as a household floor material, if a certain amount of white carbon black is added, the hardness, elasticity, and thermal denaturation properties of the product can be improved.


White carbon black is used as a sizing agent for paper, which can increase the whiteness and opacity of paper, and improve printability, oil resistance, abrasion resistance, feel and gloss. Used for printing drawings, the paper can have good surface quality, stable ink, and no cracks on the back; used in azide paper, can produce high-quality blue drawings; used in copper paper to replace titanium dioxide; especially used in newsprint, add 1 to 2% white carbon black can reduce the weight of paper by 10%, not only the paper is thin, but also can increase the strength, in addition to preventing ink penetration, making the printed text clear, it can also increase opacity. White carbon black has thixotropic properties. Adding a small amount of white carbon black to the coating can eliminate the phenomenon of droplet sedimentation in the coating. In the unsaturated polyester coating, as long as the 0.5-2% concentration of white carbon black is added, the coating can be applied on the vertical surface with 500g/m2 each time without droplets and wrinkles.


Adding white carbon black to the pigment can not only prevent the precipitation of the pigment, but also improve the absorption of the pigment and dye and improve the dispersibility. When used as a filler in emulsified coatings, it can improve thermal stability. In order to meet the requirements of white carbon black for paint and ink matting agents, special matting agents have been developed and produced abroad. When nitro varnish and similar coatings contain precipitated silica matting agent, it can improve the non-precipitating properties of the paint and make the coating easy to disperse, with only a small amount of thickening effect, good suspension, excellent matting characteristics, and high transparency And good wear resistance. Adding 0.5% white carbon black to the printing ink has a good printing effect, can eliminate the influence of undispersed ink penetration, improve the washing resistance of printed materials, and increase the gloss of colors.


In addition, white carbon black is also used in various degrees in pesticides, medicines, adhesives, toothpastes and daily cosmetics and exerts various beneficial functions.   


  


Where is carbon black used in the rubber industry, and where is white carbon black used?





As a rubber reinforcing agent, carbon black has a wide range of applications. All black rubber products use carbon black. 


In 1912, it was discovered that carbon black had a reinforcing effect on rubber. Since then, carbon black has gradually become an indispensable raw material for the rubber industry. At present, the raw material consumption of the rubber industry in the world ranks first in raw rubber, and the second is carbon black; in other words, carbon black has become the most consumed rubber compounding agent. The consumption of carbon black generally accounts for 40% to 50% of the consumption of rubber. That is to say, in rubber formulations, 1  part of carbon black is usually used in combination with every 2  part of rubber. 


 


White carbon black is divided into precipitation method white carbon black and gas phase method white carbon black. It is widely used in rubber products such as tires, tapes, hoses, rubber shoes, wires and cables. Silica and silane coupling agents are used in tire tread rubber. , It can improve the wear resistance and wet skid resistance of the tire while reducing the rolling resistance of the tire. The tensile strength, tear strength, abrasion resistance, etc. of the rubber compound using white carbon black are improved, and it is used in transparent and colored rubber products. China has its advantages. With the enhancement of people's environmental awareness, the development of the tire industry and the continuous improvement of the quality of silica, its application range will be further expanded.   


Silica began to be produced in 1948 and used as a filler in the rubber industry. By the 1980s, about 67% of the world’s precipitation method silica was used in the rubber industry, of which 45% were used in shoes and 16% were used in tires. , 6% is used for other rubber products. Since the French company Michelin announced in 1991 to vigorously carry out research on "green tires", major tire companies in Europe, the United States, and Japan have accelerated the pace of development. "Green tires" have become the mainstream of the tire industry in the 21st century. White carbon black can be used in a high proportion or replace carbon black as a reinforcing agent to produce "green tires." In 1999, it was standard practice in Europe to use white carbon in the original tires of cars. The amount of white carbon in the original tires of cars has reached 100,000 tons. Affected by the pressure of fuel tax, in order to reduce fuel consumption, automakers are actively developing "green tires" with low rolling resistance and low fuel consumption.  


There are too many non-black rubber products such as rubber shoes, balls, toys, etc.


one. Manufacturing of white carbon black


The preparation of white carbon black mostly adopts two methods, namely the calcination method and the precipitation method.


Silica prepared by calcination method is also called vapor-phase white carbon black or dry-process white carbon black. It is made by thermal decomposition of silicon polyhalide (SiClx) at high temperature and gas phase reaction.


Dry-process white carbon black has a very small particle size, about 15~25nm, and it has great flying properties. The vapor-phase white carbon black has less impurities and good reinforcement, but it is complex and costly. It is mainly used in silicone rubber. The resulting product is transparent and translucent. The product has good physical and mechanical properties and dielectric properties, and has excellent water resistance. .


Precipitation white carbon black generally uses silicate (usually sodium silicate) and inorganic acid (usually sulfuric acid) to neutralize the precipitation reaction to prepare hydrated silica.


Na2O nSiO2 + HCl SiO2 nH2O + NaCl


The precipitation method has a large particle size of about 20~40nm, with lower purity, and poorer reinforcement than the calcination method. The dielectric properties of the rubber compound, especially the dielectric properties after being damp, are poor, but the price is cheap. Good performance. It can be used alone in NR, SBR and other general-purpose rubbers, and can also be used in combination with carbon black to improve the flexural cracking resistance of the rubber compound and slow down the growth of cracks.


two. Structure of white carbon black


1. The chemical structure of silica


95~99% of silica is SiO2. X-ray diffraction has confirmed that the structure of silica is different due to the different preparation methods of silica. The internal structure of fumed silica is almost entirely a three-dimensional network structure of closely arranged silicic acid. This structure makes the particles have low moisture absorption, strong surface adsorption and strong reinforcement. In addition to the three-dimensional structure of silicic acid, more two-dimensional structure silicic acid remains in the structure of precipitation silica, which makes the structure loose, has many capillary structures, and is easy to absorb moisture, which reduces its reinforcement. active.


2. Structure of white carbon black


The structure of white carbon black is like carbon black, and its basic particles are spherical. During the production process, these elementary particles collide with each other at a high temperature to form a chain-branched structure linked by chemical bonds. This structure is called a basic aggregate. The chain-branched structures are adsorbed by hydrogen bonds to form a secondary aggregate structure, which is easily destroyed during processing and mixing.


three. The surface chemistry of silica


1. Surface group



The adjacent hydroxyl group (on the adjacent silicon atom) is very important for the adsorption of polar substances; the isolated hydroxyl group is mainly present on the surface of the white carbon black from which moisture is removed. The content of this hydroxyl group is higher than that of the precipitation method, and it is not easy to remove when the temperature is raised; the dihydroxy group has two hydroxyl groups connected to a silicon atom.


The groups on the surface of silica have a certain degree of reactivity. Surface reactions include: dehydration and hydrolysis, reaction with acid chloride, reaction with active hydrogen, and formation of hydrogen bonds.


2. Adsorption on the surface of white carbon black


The surface of white carbon black has strong chemical adsorption activity, which is related to the surface hydroxyl group. It can combine with water in the form of hydrogen bonds to form a multi-molecule adsorption layer. In addition, it can also adsorb many small organic molecules.


·The adsorptivity of polyfunctional amines or alcohols is higher than that of monofunctional ones, so polyfunctional compounds such as ethanolamine, ethylene glycol, and triethanolamine are commonly used as active agents in SiO2 rubber compounds.


3. Thermal behavior


When white carbon black is heated, water is released, and as the temperature rises, the amount of water released increases. Before 150~200℃, the most released water, after 200℃, it tends to be flat, with a clear turning point. Before the breaking point, it is mainly the desorption of adsorbed water, and after the breaking point is the surface hydroxyl shrinkage reaction.


Four. The influence of white carbon black on the performance of rubber compound and vulcanizate


(1) The influence of white carbon black on the performance of rubber compound


1. Mixing and dispersion of rubber


Due to its large specific surface area, white carbon black tends to re-aggregate. In addition, it is easy to absorb moisture in the air, which makes it easy to produce strong hydrogen bond associations between hydroxyl groups, which further improves the cohesion between particles, so white carbon black The mixing and dispersion of carbon black is much more difficult than that of carbon black, and when a large amount is mixed, it is easy to form a gel, hardening the rubber, and generating heat during mixing. In order to obtain a good dispersion, it is required to maintain as high a shear force as possible during the 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, white carbon black should be added in small quantities in batches to reduce heat generation. Properly increasing the mixing temperature will help remove part of the white carbon black surface adsorbed water, reduce the cohesion between particles, and help the dispersion of the white carbon black in the rubber compound.


2. Structure control in silica reinforced silicone rubber compound


White carbon black, especially fumed white carbon black, is the best reinforcing agent for silicone rubber, but there is a problem of hardening the rubber compound, which is generally called the "structural effect". Its structuring increases with the prolongation of the parking time of the rubber, and it is even so serious that it cannot be refined or scrapped. There are two explanations for this. One is that the end groups of the silicone rubber are condensed with the surface hydroxyl groups of the white carbon black; the other is that the silicon-oxygen chain links of the silicone rubber form a hydrogen bond with the surface hydroxyl groups of the white carbon black.


There are two ways to prevent structuring. One is to add certain substances that can react with the hydroxyl groups on the surface of the white carbon black during mixing, such as hydroxy silicone oil, diphenyl silicon diol, silazane and so on. When diphenyl silicon glycol is used, it should be treated at 160~200℃ for 0.5~1h after mixing. This prevents the silica-filled silicone rubber from structuring. Another way is to modify the white carbon black surface in advance, first remove part of the surface hydroxyl groups, and eliminate structuring fundamentally.


3. Mooney viscosity of rubber


The ability of white carbon black to form gel is comparable to that of carbon black. Therefore, when mixing white carbon black, the Mooney viscosity of the compound increases, which deteriorates the processing performance. Therefore, it is used in the compound formula containing white carbon black. The choice and amount of softener are very important. Paraffin hydrocarbons, naphthenic hydrocarbons and aromatic hydrocarbons are often added to IIR. The amount depends on the amount of white carbon black and the Mooney viscosity, generally up to 15-30%. Among 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. Vulcanization speed of rubber


There are a large number of micropores on the surface of the white carbon black 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 accelerator can be appropriately increased; on the other hand, an active agent can be used to make the active agent preferentially adsorb on the surface of the white carbon black, thus reducing its adsorption of the accelerator.


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


(2) The influence of white carbon black on the properties of vulcanizates


Silica has a very significant reinforcing effect on various rubbers, among which the reinforcing effect on silicone rubber is particularly prominent.


White carbon black is a white reinforcing agent whose reinforcing effect is second only to that of the corresponding furnace carbon black. Compared with the vulcanized rubber reinforced by the corresponding furnace carbon black (such as HAF), the vulcanizate containing a certain amount of white carbon black has the advantages of high strength, high elongation, high tear strength, high hardness, and good insulation. Generally, carbon black and white carbon black are used together to obtain better overall performance.


five. The development and application direction of white carbon black


1. The problem


(1) Processing performance;


(2) Static electricity problem;


(3) Price issues


2. The development and application direction of white carbon black


At present, the development of white carbon black is developing towards high dispersibility, refinement, granulation and surface modification.