Additives are important raw materials for the rubber industry, although the amount is small, but the role is very large, polyurethane elastomers from synthesis to processing applications are inseparable from the additives, according to the role of different, can be divided into synthetic system, modification and operation system, vulcanization system and protection system four types of additives.
Synthetic additives
01 Catalyst and polymerization inhibitor
In the synthesis of polyurethane elastomers, in order to speed up the main reaction, often need to add catalysts, commonly used catalysts are tertiary amines and organic tin two types, tertiary amines are triethylenediamine, triethylamine, trimethylbenzylamine, dimethylethanolamine, morpholine, etc., of which triethylenediamine is the most important; organic tin class of stannous octanoate, dibutyltin laurate, etc.. In addition, there are organic mercury, copper, lead and iron, with organic lead and mercury being the most important, such as lead octanoate and phenylmercury acetate. Organic dibasic acids, such as adipic acid and azelaic acid, can be used as catalysts for polyether-type polyurethane casting rubber.
02 Chain extender and chain extender crosslinker
In the synthesis of polyurethane elastomers, chain extenders refer to diols and diamines that are essential for chain growth reaction, while chain extender crosslinkers refer to compounds that both participate in chain growth reaction and form crosslinking points between chain links, such as tertiary alcohols and quaternary alcohols, allyl ether diols, etc. Cast polyurethane elastomers can use all chain-expanding or chain-expanding cross-linking agents except allyl ether diols, and thermoplastic polyurethane elastomers use only diols; blended polyurethane elastomers can use both diols and allyl ether diols.
Modifier operating additives
Some of these additives can improve the performance and appearance of products, and some can improve the operation process, such as plasticizers, abrasion reducers, lubricants, fillers, colorants and release agents.
01 Plasticizers
Plasticizer is mainly used in polyurethane compounding rubber, the purpose is to increase the plasticity of the compounding rubber, improve the processing performance and low temperature performance of vulcanized rubber, reduce the hardness and tensile strength of vulcanized rubber. The amount of plasticizer should not be too large, otherwise it will reduce the wear resistance of vulcanized rubber.
Polyurethane rubber has strong polarity, so the general choice of polar plasticizers. Benzenedicarboxylic acid esters, phosphate esters, aliphatic alkyd and other resins, such as benzodicarboxylic acid dimethoxy glycol ester, trimethylene phosphate ester, benzodicarboxylic acid dipropylene glycol ester, triethylene glycol dinonanoate, gummaron-indene resin, etc.. The test results show that: when using dioctyl sebacate, there is the phenomenon of ejection after vulcanization; when using Gummaron resin, the tensile strength is higher and the permanent deformation is small, but the hardness is reduced obviously; when using tricresyl phosphite, the tensile strength is second to Gummaron resin, but the hardness is reduced more obviously.
02 Abrasion Reducer
In some special occasions, in order to reduce the friction coefficient of polyurethane elastomer and further improve wear resistance, it is necessary to add wear reducing agents in polyurethane elastomer, such as silicone oil, molybdenum disulfide, titanium disulfide, graphite and tetrafluoroethylene, etc. This modified material has self-lubricating properties and is used as bearings, bushings and other parts, which has great economic significance.
03 Lubricant
Lubricants used in polyurethane elastomers, mainly used in the processing of thermoplastic and blended elastomers, commonly used stearic acid and its salts, paraffin waxes, stearamide class.
04 Release agents
Mold release agents are indispensable operating aids for the production of all three types of polyurethane elastomer products. Polyurethane is a strong polar polymer material, which has a strong bond with metal and polar polymer materials, so it is difficult to release the products from the mold without the release agent.
Commonly used mold release agents are silicone rubber, silicone ester, silicone oil, soap and paraffin, etc. You can also choose non-polar polymer materials such as PTFE, silicone rubber, polystyrene, polyethylene and other materials to make molds to avoid rubbing or spraying release agent process.
05 Filler
Filler is added to reduce the cost of products and improve heat resistance, reduce shrinkage and thermal expansion coefficient and other certain properties. In the blended polyurethane rubber often add 20-30 parts of carbon black, the purpose is not to strengthen, but to reduce the cost of products while maintaining the basic physical and mechanical properties of rubber.
As the amount of carbon black added increases, the tensile strength and elongation of rubber gradually decreases, while the hardness rises linearly. Different specifications of carbon black have different effects on the strength and other properties, with easy to mix slot black as the best, followed by wear-resistant carbon black, semi-reinforced carbon black is poor. Other fillers such as clay, white carbon black, calcium carbonate, barium sulfate, etc. can also be used.
06 coloring agent
Polyurethane elastomer products colorful, beautiful and generous appearance relies on colorants. There are two kinds of coloring agents, organic dyes and inorganic pigments, organic dyes are mostly used in thermoplastic polyurethane products, decorative beautification of injected parts and extruded parts.
There are generally two ways to color elastomer products: one is to grind pigments and other additives and oligomeric polyol into a color paste master batch, then mix the appropriate amount of color paste master batch with oligomeric polyol by stirring and mixing well, and then react with isocyanate components after heating and vacuum dehydration to produce products, such as thermoplastic polyurethane color granules and color paving materials.
Another method is to grind pigments and other additives and oligomeric polyol or plasticizer into color paste or color paste, dehydrate it by heating vacuum, and seal it for use. When using, a small amount of color paste is added to the prepolymer, stirred well and then reacted with chain-expanding cross-linking agent to pour into products. This method is mainly used for MOCA vulcanization system, the pigment content in the color paste is about 10%-30%, and the amount of color paste added in the products is generally below 0.1%.
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Vulcanization auxiliaries
Vulcanization auxiliaries mainly refer to vulcanizing agent and accelerator, which are only applied in blended polyurethane elastomer. Vulcanizing agent includes isocyanate, peroxide and sulfur three types. Isocyanates are commonly used in TDI and its dimer, MDI dimer and PAPI, etc. The cross-linked bond generated is the urethane-formate bond, due to the volatility of diisocyanate, easy to react with water, and toxic, so pay attention to safety and prevent moisture from entering the compounding rubber.
The advantage of using isocyanate as vulcanizing agent is good wear resistance, high strength and hardness; peroxide vulcanizing agent with diisopropyl peroxide (DCP) with the most common, other varieties of tert-butyl peroxide isopropyl benzene, dibenzoyl peroxide and other dialkyl, alkyl, aryl alkyl and diaryl peroxide, vulcanization temperature of 140-150 ℃ is appropriate.
With peroxide vulcanizing agent with isocyanate as vulcanizing agent compared with the compounding rubber, the former can greatly reduce the early vulcanization, extend the storage time of the compounding rubber, the vulcanized rubber has good dynamic performance, compression permanent deformation is small, slightly lower hardness, moderate strength, elasticity and aging resistance are better, the disadvantage is that it can not be directly vulcanized with steam, tear strength and temperature resistance is poor, there is odor; when the polyurethane compounding rubber structure When the structure of polyurethane compound contains unsaturated chain segments, sulfur vulcanization can be used.
Stabilization system additives
In order to prevent the aging of polyurethane rubber and prolong the service life of the products, heat stabilizers, light stabilizers, hydrolysis stabilizers, anti-toxic agents and flame retardants can be added.
01 Heat stabilizer
3,5-di-tert-butyl-4-hydroxyphenylpropionic acid octadecyl ester (antioxidant-1076), triphenyl phosphite (TPP), tri-nonyl phenyl phosphite (TNP), etc.
02 Light stabilizer
Also known as ultraviolet absorbers, can significantly improve the light stability of aromatic isocyanate polyurethane, commonly used light stabilizers are benzophenones, benzotriazoles and piperidines, such as 2-hydroxy-4-methoxybenzophenone (UV-9), 2, 2′-dihydroxy-4-methoxybenzophenone (UV-24), 2 (2-hydroxy-3 ‘,5’-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-328), bis(2,2,6,6-tetramethylpiperidine) sebacate, etc.
03 Hydrolysis stabilizers
Polyester-type polyurethane rubber in a humid environment, especially when used in hot water, must be added hydrolysis stabilizer, the industry is widely used hydrolysis stabilizer is carbodiimide compounds. There are two grades of carbodiimide (PCD) produced by Germany Rhein Chemie: Stabaxol-1 (monocarbodiimide) and Stabaxol-P (polycarbodiimide), the former has low molecular mass, melting range 40-50℃, mainly used in molten state for polyester-type liquid polymers, such as cast polyurethane, polyurethane coatings; the latter has high molecular mass, used in thermoplastic and blending type polyurethane elastomer in.
04Anti-mold agent
Polyether polyurethane elastomer is very strong mold resistance, 0-1 level, basically not subject to microbial erosion, will not grow mold; and polyester and poly ε-caprolactone polyurethane rubber in the hot and humid environment is susceptible to microbial erosion and mold, especially poly ε-caprolactone polyurethane rubber mold is more serious, for this reason must add mold inhibitors.
Commonly used mold inhibitors are 8-hydroxyquinoline, 8-hydroxyquinolone, pentachlorophenol, sodium pentachlorophenolate, tetrachloro 4-(methylsulfonyl) pyridine, salicyl toluidine, double (tri-n-butyltin) oxide, benzene acetate
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