Rubber Curing Systems
Rubber curing systems
Vulcanization of rubber through the Intermolecular Crosslinking of rubber-plastic rubber into the elastic and dimensionally stable products, physical stability of Vulcanized rubber, expanded temperature range. "Curing process (Curing)," a term commonly used in the rubber industry as a whole, plays an important role in rubber chemistry. Vulcanization of rubber molecules chains (cross-linking) response depends on its structure. Unsaturated diene rubber (such as natural rubber and styrene-butadiene rubber and nitrile rubber) molecular chain containing the unsaturated double bond with sulfur, phenolic resins, organic peroxides such as substitution or addition reaction to form Intermolecular cross-linking. Saturated rubbers in General with the energy of a certain free radicals (such as organic peroxides) and high-energy radiation cross-linked. Rubber with special functional group (chlorosulfonated polyethylene), formed by various functional groups with established material specific reactions, such as n-sulfonyl radicals in the rubber by reacting with oxides of metals, amines and cross-linking.
Different types of rubber and cross-linking agents react to form a crosslinked structure varies, and vulcanizate properties are also different.
① is to use sulfur or sulfur donor for the cross-linking agent, can be generated by a single disulfide bond (x=1), disulfide (x=2) and multiple disulfide (x=3~8);
II species is the use of resin and oxime;
Third is to use peroxide Crosslinking cured with peroxide and use of radiation vulcanization of radiation Crosslinking, generating carbon-carbon bond.
Most general purpose rubber using sulphur or sulfur vulcanization, rubber adding sulphur or sulfur to give body and shortening the time for promoters and ensure efficiency of sulfur crosslink zinc oxide and stearic acid composition of active agents. Usually in practice according to sulfur content and accelerator ratio of several types of curing system is divided into the following:
① ordinary sulfur curing system by common sulphur (> 1.5) and commonly used dose of make up. Using this system can form more sulfur Vulcanized rubber keys and a small amount of low-sulfur bonds (single sulfur bonds, and disulfide bonds). Vulcanized rubber of high tensile strength, good fatigue resistance. Disadvantages are poor heat and ageing resistance.
Second half effective curing system by sulphur 0.8~1.5 (or part of a sulfur donor) composed in conjunction with commonly used doses. Use this system to make Vulcanized rubber to form a proper proportion of low-sulfur bonds and disulfide, curing adhesive tensile strength and fatigue resistance of medium, heat-resistant, anti-aging properties.
③ efficient vulcanization system consists of low-sulphur (0.3~0.5) or part of a sulfur donor with high doses (typically 2~4) make up. Using this system to make Vulcanized rubber form the dominant low-sulfur bonds (single sulfur bonds, and disulfide bonds), the vulcanizate heat resistance, good resistance to aging, disadvantage is the low tensile strength and fatigue resistance.
④ sulfur curing system all without using a sulfur-sulfur and accelerator make up. The curing system similar to the effective curing system performance.
Second, the reinforcement of rubber and reinforcing fillers
Rubber reinforcement refers to the rubber the tensile strength, tear strength and abrasion resistance, substantially improve the role. For non-reinforced synthetic rubber, if there is no add reinforcing agents, will have no value. Add reinforcing agents such as carbon black, you can make these rubber strength several times to 10 times. Strength factor of carbon black on rubber, see table 8.4-5
Reinforcing agents also make changes of other properties of rubber, such as hardness increases, increased stress, stress relaxation performance variation, loss of elasticity, lagging behind larger, increasing the compression, and so on.
① reinforcement of rubber reinforcing filler is classified according to particle size and particle size effect of fillers on the properties of the main basis. Reinforcing filler particles is extremely small, can give useful to non-crystallization of rubber strength properties and crystallization of rubber strength has improved. Packing quality and particle size can be used to control the stretch properties of two kinds of rubber.
Carbon black is a good rubber reinforcing agent, usually used where reinforcement is required. White or light colored rubber reinforcement is used known as silica, silica (SiO2).
Table 1 coefficient of carbon black for rubber reinforcement
Reinforcement of adhesive tensile strength MPa coefficient is not reinforced Vulcanized rubber reinforced Vulcanized rubber
Styrene butadiene rubber (SBR) 2.5~3.5 20.0~26.0 5.7~10.4
Acrylonitrile-butadiene rubber (NBR) 2.0~3.0 20.0~27.0 0.6~13.5
Ethylene propylene rubber (EPDM) 3.0~6.0 15.0~25.0 2.5~8.3
Butadiene rubber (BR) 8.0~10.0 18.0~25.0 1.8~3.1
Natural rubber (NR) 16.0~24.0 24.0~35.0 1.0~2.2
Is based on the method of carbon black (furnace or hot cracking methods), particle sizes (20 nm to 50 microns) and "" (particles into short-chain or group) classification of by how much. Each parameter has a significant effect on properties of rubber. Its representation is 25~50phr, this is expressed as a number per cent of rubber parts. (phr)
With the increase of carbon black, carbon black rubber physical properties is not in a single dosage reaches its optimum value. Vulcanizates of elongation increasing with the decreasing carbon black, while its modulus or stiffness has been increased. As the modulus or stiffness increases, the deformation of the rubber (flexible) then weakened, and more like leather, leading to dynamic strain hysteresis and heat generation increase.
II increase particulate filler this is size much larger than the reinforcing filler material, grain size is usually 20 microns. Main function is to reduce the cost of packing and capacity expansion. As the dosage increases the compound, tensile strength and tear resistance is proportional to reduction. So the amount determined by the physical requirements. Typically in the same compound with reinforcing and capacity increase of filler in order to increase the content of cheaper non-rubber material, and not damage the properties of rubber. Representative capacity increase of fillers are calcium carbonate and clay.
③ plasticized (softened) oil type oil is used for increasing capacity and softening material, causing plastic increases to offset a lot of filler of rubber processing flow resistance caused by increased and increased rigidity of Vulcanized rubber. And will cause hysteresis loss increases and an increase in stress relaxation and creep speed. Figure 7 the properties of natural rubber and carbon black content
Third, the aging of rubber and antioxidant
As with many other organic materials, rubber strength, elongation properties and other useful mechanical properties will deteriorate gradually with the extension of the time, known as the ageing of the rubber. Its main cause is aging and ozone aging, it will light or heat or some trace elements (such as copper or manganese) and worse.
Thermal aging is a complex process, including many reactions. Effect of reaction conditions: conditions, metal catalyst, temperature and ingredients recipes. Hot-oxygen aging results in two ways:
① rubber soft sticky due to chain. The oxidation of natural rubber and butyl rubber is mainly this kind of reaction mechanisms.
Second, the hardened rubber brittle due to constantly. Styrene-butadiene rubber, neoprene, nitrile rubber and EPDM rubber oxide is mainly this kind of reaction mechanisms.
In most cases, this mechanism of two kinds of damage occurs, what mechanism is dominant mechanism which determines product trends. And no matter what kind of damage mechanism of rubber elongation of the loss are the most sensitive indicator test rubber.
Some metal (primarily copper, manganese, iron and cobalt) rubber catalyzed by ionic can affect the decomposition of peroxide oxidation, oxygen-accelerated erosion. This rubber Vulcanized rubber to rubber is more obvious. Sulfur vulcanization of rubber
Only natural rubber and other rubber containing unsaturated isoprene units will be affected to a significant degree. Method is for the Elimination of harmful sources of metals, and joined in a compound reacts with metal ions to form stable products metal stabilizers.
Erosion mechanism of ozone is usually attributed to ozone and unsaturated parts of rubber ("double") reaction of ozonolysis, ozonolysis break down easily, cause rubber surface cracking caused by the broken chain, cracking with mechanical breakdown and further growth. Cracking if products are in strain conditions. History repeated with ozone erosion, cracking grew larger. Stress-free rubber outer surface to form a layer called "cream" silver grey thin-layer, in hot and humid environment is prone to this phenomenon.
Rubber antiagers are able to prevent (strictly speaking is slow) rubber material. Rubber rubber is the essence of thermal aging and ozone aging of rubber, rubber antioxidant include rubber antioxidant and ozone resistance agents. Under normal circumstances, an efficient antiozonant is also an antioxidant, otherwise not. Antioxidant of choice is based on the minimum cost of satisfying old age effects, factors to consider include pollution of the antioxidant, color changing, volatile, solubility, stability, and physical condition.
Amine antioxidant--different types of amine and diamine are effective antioxidants, but will have a more severe discoloration and pollution in General. Typical of this antioxidant widely used types are:
① amino-phenyl class;
② two hydrogenated quinolines;
③ diphenylamine derivatives;
Black-substituted DIAMINES of benzene.
Effect of phenolic antioxidants are generally less amine antioxidant, but color is not a problem. Cannot use amine antioxidant light rubber, can be use phenolic antioxidant. Non-pollution does not change color additives are of the following 5 categories:
① hindered phenolic antioxidant;
② hindered Bisphenol type antioxidant;
③ Terephthalic phenolic antioxidants;
④ antioxidants such as phosphite esters;
⑤ organic sulfur compounds antioxidants.
Antiozonant choice according to the different application of rubber may be, still has many different ozone protection and dynamic ozone protection requirements. For different conditions and different ozone concentrations, there are four types of materials can be selected as an antiozonant, ozone resistance of some of these substances have certain limitations.
② dibutyl dithiocarbamate salts;
③ 6-Ethoxy- -2,2,4-3 methyl-dihydro-quinoline;
④ instead of hydroquinone.
In the antioxidant loss by volatilization, and antioxidant of molecular weight and molecular type. Typically, large molecular weight, less volatile. Molecular type than its bigger. For example, volatile than hindered phenol antioxidants have the same molecular weight amines high.
Antioxidant in rubber antioxidant solubility depends on the chemical structure of rubber type and temperature, and other factors. High solubility in rubber, low solubility in water and organic solvents are ideal. Low solubility in rubber, is prone to blooming. High solubility in water and organic solvents are used in the process of being lost through water or solvent extraction.
Physical state is also an important feature of antioxidant. Rubber polymers manufacturing sector need liquid and easier to emulsify material, while the rubber sector need to use solid, free flowing but no dust material.
Antioxidant is able to guarantee the principle of rubber products in the long run, you can't all be consumed. Must also take into account a number of factors, such as costs of materials, plastic, pollution requirements. Formula antioxidant consumption in General is about 3.
Two kinds of rubber or polymer can be important part of polymer blends theory first. Original concepts for process compatibility, when rubber-or plastic-added some ingredients within a certain time after blooming-free precipitation phenomenon, said two compatible instead were incompatible. Many blends of polymers, molecular compatibility, can also be a chain, but in most cases to segment the compatibility standards and basis. Are known, most of incompatible polymer blends are mechanics, simply because the viscosity may remain in a stable state, and two rubber compatibility can still be used, and good performance. In practice, as long as the distributed and dynamic stability is good, you can still get a good mixing effect. That is, disperse more easily blends, greater stability, better compatibility, while the worse.
From blending theory, full compatibility of blends is not the ideal system, made up of two immiscible polymers, but interface system that combines very well, is the most ideal system.
(1) the relationship between structure and properties of blends
A. microstructure of blends two kinds of rubber, or rubber and plastic blends, most do not have the thermodynamic compatibility, blending may occur when the micro-structure of the complex and diverse state, which has three. That is homogeneous. A dispersed two-phase continuous system and two are continuous two-phase system. General the basic structural unit of the mixture is divided into two kinds, the dispersed phase.
B. blend morphology and properties of blends, components for the successive phases, blending performance plays a decisive role. In General, the continuous phase reflects the community's basic properties, in particular mechanical and stress-strain properties, such as swelling and model of elasticity and strength properties of large, distributed with respect to the performance impact is extremely limited. Disperse the relative heat of friction, tensile, gas diffusion, heat, osmotic, adhesive bonding performance of optical properties of great impact.
C. factors influencing the phase morphology of blend ratio, viscosity, the cohesive energy density.
D. dispersion parameters of structure and properties of polymer blends. Tend to generate two kinds of systems, which dispersed structure parameters on the blend of performance impact. Distribution uniformity, the dispersed phase size and dispersed elastic modulus and hardness.
E. factors influencing the grain size of disperse phase: mixing content, viscosity and solubility of polymers and dispersed phase and structural similarities, the processing temperature, compatibilizer, blending process.
(2) the blend interface layer structure and its relationship to performance
A. interface layer structure and morphology of blends blends, there is always a transition layer between the two interface. Interface layer is most typical polymers dissolve, non-generated interface layer.
B. interface layer structure and its influence on properties of blends
(A) the boundary layer structure in which there is always a transition layer at the interface-interface. Interface layer structure is robust and weak-two-part phase structure.
(B) effect of interface Interface more complex, here try the rubber blend play an important and direct role in several aspects: coupling, passing, blocking and absorbing and scattering and induced.
(C) effect of interface layer to blend performance performance depends primarily on the composition of polymer blends, proportions and mixing State, while the effect of interface layer has special significance.
Interface layer is an important influence on vulcanizate blends features improved fatigue resistance and abrasion resistance. Interface layer structure on electrical properties of carbon black blend effect is more obvious. Under the same varieties and amount of carbon black, CR/NR blends of resistance value is lower than a single rubber, conductive and better performance.
C. interface layer structure influence factor
(A) the thermodynamic factors: surface tension, solubility parameter.
(B) kinetic factors: temperature, time, shear force, a total of sulfide.
Benzene rubber of mixed refining more used two paragraph mixed refining, because two paragraph Zhijian of cooling helps carbon black of dispersed, styrene-butadiene rubber mixed refining of key is makes carbon black good dispersed, for total of principles is softening agent should in carbon black input and has in rubber in the dispersed Hou after must time again joined, softening agent ahead of joined or in carbon black gel rubber formed zhiqian joined, easy makes carbon black-softening agent caking, rubber material physical performance declined (15~20%), but softening agent in carbon black completely dispersed Hou joined, also will makes rubber material broken, extended mixed refining time, Reduce the mixing efficiency, so there are 1/5 carbon black in the mixing chamber is not absorbed and dispersed into Bates, which easily mix or the rubber compound to slip and broken, adhesive curing adhesive tensile strength increases 2~2.5Mpa and wear resistance of 7%.
The mixer when mixing, eating powder should be folding back and thin through the narrow pitch 0.75 ± 0.1mm, Eli and carbon black filler dispersion, properties and dispersed temperature curing adhesive.
In the mixing process, styrene-butadiene rubber and carbon black or silica reinforcing agents containing rubber combined with gel, gel content changes with reinforcing agent types and mixing temperature. Gels can increase the material modulus and tensile strength, but too much can slow processing performance. Carbon black and silica in the water will reduce the SBR rubber scorch time and speed up the curing rate.
1. Open mill
Greater heat of styrene-butadiene rubber, adhesive mounted capacity shall be less than natural rubber, roller spacing should be smaller to facilitate heat dissipation, roller Wen Yi at 60 ± 5 ℃ of styrene-butadiene rubber roller and different natural rubber, wrap the roll at low temperature, so roll after roll before the temperature should be higher than 10℃.
When used on mill roll refining, roller spacing effect, tensile strength in styrene-butadiene rubber roller spacing is 2mm is the highest, 1mm, rubber molecule chain is serious, 3mm spread malnutrition.
General used two paragraph roll refining, which first paragraph of order is first with small roll from broken rubber, then zoom roll from to 1.4 ± 0.1mm, rubber material package roll, added stearic acid, zinc oxide, anti-old agent and 1/3 softening agent → 1/3 fill agent and 1/3 softening agent → 2/3 fill agent and 1/3 softening agent, added powder material finished relaxed roll from to 1.9mm pound rubber, in carbon black no all mix rubber zhiqian cannot pound rubber. then again adjustable small roll from to 0.75 ± 0.1mm, thin pass 5~6 times, to Lee dispersed, Glue cools, add sulfur breaks down again, using a mix, you can enlarge roll away from folding back to join the other ingredients such as sulfur, promoter sequence according to their stability, and more stable can be joined early in the period when mixing and stability may be joined in the two-stage mixing.
Styrene-butadiene rubber with high pressure, high speed mixer is appropriate, can invest in a Tablet press, softener should be added (that is, after she finished in carbon black pigmented). sulphur General dosing in the Tablet press, but uses a two-stage also in the second mixer when mixing dosing.