1. Additives for rubber vulcanization system
In the rubber industry, it is customary to collectively refer to the same or related additives as the system. For example, vulcanizing agents, vulcanization accelerators, active agents and scorch inhibitors are collectively referred to as vulcanization systems because they are all related to vulcanization.
Vulcanizing agents include sulfur, selenium, tellurium, sulfur-containing compounds, organic peroxides, quinone compounds, amine compounds, resins, metal oxides and other vulcanizing agents;
Vulcanization accelerators include dithiocarbamates, xanthates, thiurams, thiazoles, sulfenamides, amines and aldehyde amine condensates, guanidines, and thioureas;
Activators include zinc oxide, magnesium oxide, stearic acid and the like.
The so-called rubber vulcanization is the process of transforming a plastic rubber into an elastic vulcanizate, that is, the rubber molecular chain undergoes chemical cross-linking under the action of chemical or physical factors, and becomes a spatial network structure. All chemicals that can cause cross-linking of rubber can be called vulcanizing agents.
Sulfur is one of the most commonly used. The vulcanizates vulcanized with pure sulfur not only have low crosslinking efficiency and crosslink density, but also have poor physical and mechanical properties, so pure sulfur systems are generally rarely used in rubber formulations.
Some organic polysulfides (the main varieties are TMTD, TMTT, DTDM, etc.) and organic peroxides (the commonly used varieties are DCP, DTBP, etc.). The use of these vulcanizing agents can make the rubber compound have some excellent special properties, such as heat resistance, aging resistance and so on.
In addition, some synthetic resin materials are also used. The vulcanizing agent can cross-link the linear rubber molecules into a network structure.
When sulfur is used as a vulcanizing agent, some chemicals are usually used to promote the vulcanization reaction, thereby improving production efficiency and rubber performance. Chemicals that can promote vulcanization are called vulcanization accelerators.
The commonly used varieties of vulcanization accelerators are: vulcanization accelerators M, DM, MZ, OZ, NOBS, DZ, TT, TMTT, etc. At present, the better vulcanization accelerators are quaternary phosphorus salts, such as 1-phthalimido acid 4-butyl triphenyl phosphonium bromide, bis (benzyl triphenyl phosphine) imine chloride The dosage is generally 0.4-0.7 parts. Of course, composite vulcanization accelerators can also be used. In addition to quaternary phosphate salts, quaternary ammonium salts can also be added, such as tetrabutyl benzothiazolyl ammonium sulfide, bis-cinnamon propylene diamine and the like. The vulcanization accelerator can shorten the vulcanization time, lower the vulcanization temperature, and reduce the amount of sulfur. Thiazoles and sulfenamides are the main body of vulcanization accelerators, accounting for about 70% to 75% of the total.
Chemicals that can increase the activity of vulcanization accelerators, improve vulcanization efficiency, and improve the performance of vulcanizates are called active agents. Commonly used are zinc oxide, magnesium oxide, calcium oxide, and stearic acid.
In order to prevent early vulcanization (scorch) during processing, it is often necessary to add some chemicals that can inhibit early vulcanization, that is, anti-scorching agent, but the addition of anti-scorching agent will slow down the vulcanization speed and cause vulcanization. Adhesive performance deteriorates, coupled with the high price, so it is rarely used under normal circumstances.
Anti-reversion agent is the latest class of additives at home and abroad, specially used to improve the anti-reversion property of vulcanized rubber. The anti-reversion agent can be regarded as a new auxiliary agent of the vulcanization system, and can also be regarded as a new auxiliary agent of the anti-aging system. It can protect the stability of the vulcanization network, improve the stability of the product against heat and oxygen, and maintain the general Semi-effective curing system has the advantages of good dynamic performance.
2. Additives for rubber protection system
Rubber or rubber products are affected by various external factors in the process of processing, storage and use, and will gradually lose their original excellent performance, and eventually lose their use value. This phenomenon is called rubber aging.
The characteristics of rubber aging: First, the appearance of the material changes, such as: the material becomes sticky, soft, hard, brittle, cracked, deformed, stains, mildew, spots, cracks, frosting, and chalking , Whitening, etc.; the second is changes in physical properties, such as changes in heat resistance, cold resistance, air permeability, and light transmission; third, changes in physical and mechanical properties, such as tear strength, elongation, and resistance Abrasion, fatigue resistance, etc.; fourth, changes in electrical properties. In order to prevent the aging and deterioration of rubber, an appropriate amount of anti-aging agent is usually added to the rubber compound. Therefore, all chemicals that can inhibit rubber aging are called anti-aging agents.
Generally, the main factors that cause rubber aging are: the role of hot oxygen, the role of ozone, the role of metal ions, the role of light, the role of mechanical force and so on. In terms of tire aging, due to tires under relatively harsh operating conditions, especially in the presence of mechanical force, heat, light, and ozone, aging cracks and fatigue aging will soon occur.
The additives of the rubber protection system include antioxidants, antiozonants, anti-flex cracking agents, light stabilizers, ultraviolet light absorbers, harmful metal inhibitors, physical antioxidants, anti-termite agents, and anti-fungal agents.
Anti-aging agents mainly include amines, phenols, heterocyclics, phosphites, protective waxes and flame retardants. Amine antioxidants include naphthylamine series, quinoline series, diphenylamine series, and p-phenylenediamine series; phenols include alkylated mononuclear phenols, alkylated binuclear phenols, and alkylated polynuclear phenols;
Other antioxidants include heterocyclics and phosphites; protective waxes include microcrystalline wax and ozokerite; flame retardants include bromine, chlorine, phosphorus and inorganic substances. Phenylnaphthylamine antioxidants, such as N-phenyl-1-naphthylamine (antioxidant A) and N-phenyl-2-naphthylamine (antioxidant D) have comprehensive performance and large dosage; p-phenylenediamine Class is the most important antioxidant with excellent performance. Its representative varieties include N-phenyl-N'-isopropyl-p-phenylenediamine (antioxidant 4010NA), ketone amine condensate, such as antioxidants BLE, RD, and its The anti-thermal oxidative aging effect is good, but the anti-flexural aging effect is poor.
The commonly used antioxidants mainly include RD, 4010, 4010NA, antioxidants A, D, H, antioxidant MB, antioxidant DFC-34 and physical antioxidant protective wax. There are different types of antioxidants and different protection mechanisms, but in general, chemical antioxidants are the antioxidants themselves that participate in the reaction of rubber molecules to generate some relatively stable chemical structures, thereby inhibiting or destroying the oxidative cracking reaction of rubber when it acts on the outside. Or weaken the reaction degree of the oxidation process to prevent aging. The addition of physical antioxidants will form a protective film on the rubber surface, thereby avoiding the contact of the rubber with oxygen and ozone, and it does not participate in the chemical reaction itself. In recent years, various countries have attached great importance to the research and development of reactive antioxidants, because the vulcanizates using reactive antioxidants have outstanding durability.
3. Additives for rubber process operation system
Rubber processing aids are mainly used to solve the basic process problems of molding or molding of high-viscosity rubber materials, and meet the process requirements of low energy consumption and high output in a short time. Rubber processing technology additives can increase economic benefits. After applying rubber processing technology additives, the same amount of work can reduce the operation time of mixing and extrusion processes; increase the output per unit time; stabilize the processing technology and increase the product qualification rate; improve the appearance and internal quality of the product , Improve the grade of the product. In recent years, with the continuous increase in the amount of rubber processing technology additives, the technology additives industry has made great progress. As a result of economies of scale and market competition, the price of process aids has been drastically reduced. From the other side, the application of process aids for rubber processing is possible. Rubber processing technology additives can improve rubber processing technology and product quality, making it possible for the rubber processing goal of "high quality, low cost, and high output"; it will greatly improve the economic benefits of the enterprise.
Rubber process control system additives include peptizers, solubilizers, plasticizers, softeners, homogenizers, lubricants, dispersants, tackifiers, lubricating additives, release agents, mold release agents, etc. The important ones are plasticizers, dispersants, homogenizers, tackifiers, mold release agents and anti-scorching agents.
The peptizer is actually a catalyst for the oxidative degradation of the rubber polymer chain, so it can also promote the chain scission of the vulcanizate, so it is used as a regeneration activator in the production of reclaimed rubber. Aromatic mercaptan derivatives and aromatic disulfides are the main categories of peptizers and regeneration activators.
The activator is required not only to promote the vulcanization reaction, but also to absorb acid. Commonly used activators are magnesium oxide, lead oxide, calcium hydroxide, and zinc oxide. Generally, highly active magnesium oxide can improve heat resistance; calcium hydroxide can improve compression set resistance; zinc oxide can improve water resistance; lead oxide can improve acid resistance. The amount of calcium hydroxide is generally 3-6 parts, and 6 parts are used in the polyol vulcanization system; the amount of high-active magnesium oxide is 3 parts; the maximum amount of low-active magnesium oxide is 15 parts. When the amount of activator is too high, the rubber compound will easily foam.
The function of the softener is to improve the plasticity of the rubber compound, reduce the viscosity of the rubber compound, and improve the dispersibility of other compounding agents. In the rubber industry, softeners also include a wider range of non-solvent softeners, such as petroleum-based softeners, petroleum resins, coumarone resins, pine tar, and natural oil vulcanized ointments. The composition of petroleum softener varies with the nature of crude oil, and the classification method is also very complicated. According to its molecular structure, it can be roughly divided into three categories: paraffin oil, naphthenic oil and aromatic oil. Petroleum-based softeners are mainly used to produce oil-extended styrene-butadiene rubber, which accounts for about three-quarters of petroleum softeners.
Dispersants mainly improve the dispersibility of carbon black and other powders in rubber. It can shorten the mixing time of the rubber compound, and the role of the dispersant: 1. Improve the dispersion of the powder in the rubber, increase the extrusion speed, stabilize the extrusion size, and reduce the extrusion temperature. 2. Promote the dispersion of powder in rubber to prevent early scorching and blooming of rubber.
Plasticizers can impart flexibility and good processing properties to the rubber compound. Low volatility liquids or low melting point solids with good compatibility with rubber are often used, such as phthalate esters and aliphatic dibasic acid esters. And low molecular weight liquid polymers.
4. Additives for rubber reinforcement and filling system
Reinforcing agents and fillers form a system in rubber processing, collectively referred to as fillers, which means materials that fill the gaps between rubber molecules. After adding a substance to the rubber, the abrasion resistance, tear resistance, tensile strength, modulus, swelling resistance and other properties of the vulcanized rubber can be greatly improved. Any substance with this effect is called a reinforcing agent. Filler is one of the main raw materials in the rubber industry and is a powder material. The amount of filler is quite large, almost equivalent to the amount of rubber itself, which can give rubber many valuable properties. For example, the mechanical properties of rubber are greatly improved, so that the rubber has special properties such as magnetism, conductivity, flame retardancy, and color; the rubber has good processing properties and reduces costs. Adding fillers to the rubber can increase the volume of the rubber, reduce the cost of rubber products, improve the performance of rubber processing technology, and have almost no effect on the performance of rubber products.
According to the role of filler in rubber, it can be divided into reinforcing and compatibilizing fillers. The main function of the former is to improve the physical and mechanical properties of rubber products, called reinforcing agents, such as carbon black. The main function of the latter is to increase rubber. Volume, reduce the gum content, reduce costs, called fillers or compatibilizers, such as calcium carbonate CaCO3, clay and so on. There are five types of carbon black, more than 40 kinds of varieties. Commonly used varieties are: super abrasion-resistant furnace black (SAF), medium and super abrasion-resistant furnace black (ISAF), high abrasion-resistant furnace black (HAF), and general-purpose furnace black (GPF). There are some very active sites on the surface of carbon black particles, which can chemically interact with rubber molecules to form strong chemical bonds. This chemical bond can slide along the surface of carbon black particles and finally produce two reinforcing effects: one is when The rubber deforms when subjected to a force, and the sliding of the molecular chain can absorb the impact of external force and act as a buffer; the second is to make the stress distribution uniform. The result of these two effects can increase the strength of the rubber, resist cracking, and play a reinforcing role. In addition, there is a kind of white carbon black, the chemical composition is mainly hydrous silicic acid and silicate substances, which is often used to make light-colored rubber products.
Additives for rubber reinforcement and filling systems include carbon black, silica, metal oxides, inorganic salts, and resins. There are mainly carbon black, white carbon black, inorganic reinforcing agents and fillers, and organic reinforcing agents and fillers. In typical rubber formulations, since fillers are cheap and easy to obtain, they are usually added to the main material rubber in large doses to increase the volume and weight of the rubber with its huge volume and dosage, thereby reducing the unit cost of the rubber. For this reason, natural mineral materials are generally considered when selecting materials, which are processed, crushed, and ground to a certain degree of fineness before being put into use.
Reinforcing resin, also known as reinforcing and hardening resin, is used in rubber compounds that require high hardness, high constant elongation, and are difficult to produce due to excessive increase of carbon black.
5. Additives for rubber bonding system
In the rubber industry, adhesion refers to the combination of the physical action of van der Waals force or the chemical action of bonding force when the rubber is in contact with the surface of the same or heterogeneous material. Generally, a substance that can bond adjacent surfaces of materials into a whole is called an adhesive. In fact, bonding and adhesives are broad concepts, and there are adhesives and bonding agents in the name.
Rubber adhesion system additives include meta-methyl-white system and cobalt salt system adhesives and adhesives, mainly meta-methyl-white system, cobalt salt adhesion promoter, triazine type adhesive, impregnating adhesive And adhesive.
The production practice of radial tires shows that there is good initial adhesion between steel cord and rubber, but the service performance and service life of the tire cannot be guaranteed. It is also required that the rubber and steel wire still have high adhesion after aging and corrosion.合holding rate. Adding rubber adhesion vulcanization accelerators to rubber can improve the adhesion between rubber and steel cord to varying degrees. Therefore, rubber adhesion vulcanization accelerators have become an indispensable component in the production of radial tires.
Rubber and metal vulcanization bonding problem
There are many parts that need attention in the bonding process. If there is a problem, you need to check
1. Has the metal substrate changed?
2. Are there any problems with the metal surface treatment, such as dust and oil?
3.Is the adhesive expired?
4. Has the adhesive applied to the metal surface dried out?
5. Is the curing temperature reasonable?
6. Has the rubber changed?
After vulcanization, the bonding is not good. You have to see whether the glue you apply follows the rubber or the skeleton! The glue follows the rubber, which proves that there is a problem with the handling of your metal parts. If the glue follows the skeleton, it proves that there is a problem with your vulcanization process. There are still some problems that need to be checked one by one, whether the glue is invalid, whether there is a problem with the rubber, and so on. When some problems cannot be found, you need to investigate them one by one patiently. Until the answer is found.
6. Other special additives for rubber
In order to increase rubber strength, hardness, reduce elongation, and improve wear resistance, heat resistance, and tear resistance, MT carbon black (medium particle thermal black) is often used as a reinforcing agent. The general amount is 20 parts. Of course Calcium fluoride, calcium carbonate, highly dispersible barium sulfate, etc. can also be added. Other special rubber additives include colorants, foaming agents, defoamers, thickeners, creaming agents, wetting agents, emulsifiers, stabilizers, coagulants, heat sensitive agents, anti-webbing agents, preservatives, preservation Agents, flame retardants, antistatic agents and fragrances, etc. Any substance added with rubber compound for the purpose of changing the color of the product is generally called a colorant. Most rubber products are colored in black, gray, or white, which are achromatic colors.
In addition, there are colored colors, including colors such as red, blue, yellow, green, brown, and pink. Rubber products can not only be colored by a mixture of pigments of various colors, but also specific pigments of non-mainstream colors, such as orange, green, and pink, for coloring. Mixing coloring is the main coloring method of colored rubber products at present, which can be divided into mixing method and solution method. The mixing method has several methods such as dry powder coloring, color paste coloring, pellet coloring and masterbatch coloring. Rubber coloring not only gives the product a beautiful appearance, but also protects the rubber product. If the coloring is appropriate, it can also absorb some light to improve the aging resistance of the product. In addition, the coloring of some rubber products has special meaning: for example, the coloring of rescue rubber products can make the target more obvious; the coloring of military rubber products can make the target more concealed.
In addition to considering the bright color, light fastness, durability, and transparency, the selection of rubber colorants should also pay attention to the following points:
(1) Must have a certain degree of heat resistance. Except for a small amount of low-temperature vulcanized rubber products, most of the products need to be heated and vulcanized at 110～170℃ for a certain period of time, at this time the colorant should not change color;
(2) Good stability to sulfur and other compounding agents (such as vulcanization accelerators, antioxidants, softeners, etc.). The coloring agent should not react with these compounding agents to cause the product to change color, and the coloring power and hiding power are strong, so as to reduce the amount of coloring agent;
(3) There should be no adverse effects on the properties of rubber products (such as physical and mechanical properties and aging properties);
(4) Attention must be paid to the content of harmful metals;
(5) Good migration performance in rubber, color bleeding performance in water and solvents, and pollution performance to fabrics or neighboring substances;
(6) Easy to disperse evenly to improve work efficiency and make the color of the rubber uniform;
(7) The fineness generally requires 100 meshes to be screened;
(8) The colorant used in rubber products in contact with food and human body must be non-toxic. In addition, the colorant requirements of the compound itself must also be considered. For example, the colorant used in neoprene must have a certain degree of acid resistance. The above-mentioned properties of general colorants are not all ideal, and not all rubber products have the same stringent requirements for various properties of colorants. In specific use, they should be appropriately selected according to the actual conditions of the product.
In addition to the use of vulcanizing agents, vulcanization accelerators, vulcanization activators and antioxidants similar to dry rubber processing, latex production also needs some additives for improving the processing performance of latex, called special latex additives, such as dispersants and emulsifiers , Wetting agent, thickening agent, coagulant, anti-foaming agent and heat sensitizer, etc. Tackifying resin is mainly used to improve the self-adhesiveness of rubber, especially synthetic rubber.
Detailed explanation of common latex additives:
1. Coagulant
It refers to any substance that can quickly solidify and agglomerate high polymer from latex; gelling agent refers to any substance that can gradually transform latex from a liquid state to a uniform semi-rigid solid gel; and a heat-sensitive agent refers to the addition of After being in the latex, after heating, the substance that can make the latex gel.
The coagulant is divided into internal coagulant and external coagulant. The internal coagulant is involved inside the clot. If it is produced with latex yarn, acetic acid or hydrochloric acid with a concentration of 25% to 30% is commonly used as a coagulant [acetic acid residue is small, but volatile odor is large, hydrochloric acid has small volatile odor but large residue], in addition, formic acid and Lactic acid can also be used as an internal coagulant. External coagulant is mainly used in ion deposition method, commonly used are divalent or trivalent metal salts and organic amine salts, such as anhydrous calcium chloride, calcium nitrate, barium chloride [Note: this substance is toxic, the only advantage It has good adhesion, and the semi-finished gel is not easy to slip.], cyclohexyl amine acetate, etc. It is used to produce various latex gloves, various weather balloons, festival balloons, hoses, finger cots, medical and sanitary products and rubber rings. In particular, cyclohexylamine acetate is an organic coagulant. This product is white crystals with an acetic acid taste and is soluble in water and alcohol. Used for impregnated products, it can be washed without water without affecting its physical and mechanical properties and aging resistance. Generally use 10% methanol and ethanol as a mixed solution. If you want to improve the gelling effect, you can add a small amount of glacial acetic acid.
2. Gelling agent
Gelling agents are mostly used as sponge products. The latex industry is most commonly used in styrofoam latex using the Dunlop method. Such as potassium silicon fluoride, sodium silicon fluoride, ammonium sulfate, ammonium chloride, zinc oxide, zinc chloride and so on.
Three, heat-sensitive agent
1. Zinc amine complex. A heat-sensitive agent commonly used in the latex industry. Generally, it is formed by complexing zinc chloride with ammonia water. When the temperature rises above 50 degrees Celsius, zinc ammonium complex ions will decompose ammonia, so that zinc ions are finally generated, and form insoluble soaps with carboxylic acid anions in the latex, which makes the latex lose its stability and gelatinize.
2. Polyvinyl methyl ether. This product is a non-ionic polymer, soluble in cold water, and precipitates out at 34 to 35 degrees Celsius. It has a stabilizing effect on latex at room temperature, and can gel latex at high temperature. When using, the latex must be de-ammoniac, the PH value is controlled at 9 to 9.6, and some "O" should be added to the glue. In the presence of zinc oxide, its heat-sensitive effect is significant.
3. Polyether polyoxymethylene dimethyl acetal. Brown viscous liquid. It is soluble in cold water and does not dissolve if the water temperature is higher than 50 degrees Celsius. The cloud point of 5% aqueous solution is 50 degrees Celsius, and the pH value of 15% aqueous solution is 2, which is a heat-sensitive agent for natural rubber latex. The heat sensitization temperature is relatively high, and the storage is stable at 35 degrees Celsius. It is generally used as a 15% aqueous solution and is suitable for impregnated products.
4. Polypropylene glycol. Colorless and low viscosity liquid. Easily soluble in water, but insoluble in hot water. Used as 25% to 50% aqueous solution. The ammonia content in the latex affects its element. When the latex's PH value is greater than 8.5, a certain amount of zinc oxide should be added. In addition, there are polyethylene glycol and trypsin, which can also be used as latex heat sensitizers. It can be selected according to actual needs. The above three types of chemical substances can all destabilize the latex, and rubber friends should treat them separately when using them.