Background Under normal conditions, bisphenol A-type liquid epoxy resins are colorless, transparent and flowable. When the external temperature is lowered, the molecular chain is less active and prone to crystal seeding. Liquid epoxy resin appears grey in color, free-floating crystals, crystal clusters, or hard lumps like curing, we call it the crystallization phenomenon.   Reasons for the crystallization of epoxy resin The reasons for the crystallization of epoxy resin are complex, we mainly summarize the following. High purity. We all know that crystals are highly pure substances, and so is epoxy resin, the higher the purity, the narrower the molecular distribution, the easier it is to crystallize. Low viscosity. The lower the viscosity, the faster the crystallization. Impurities. solid impurities are usually crystalline species for crystal growth, and the addition of certain precipitating pigment fillers can easily lead to crystallization. In contrast, larger particle sizes and higher additions are less likely to induce crystallization. Temperature. A narrow temperature cycle of 20-30°C is a common cause of crystallization, with diurnal temperature fluctuations initiating or accelerating the rate of crystallization. In addition, ultra-low temperatures (below 5°C) will accelerate crystallization. Moisture. The higher the moisture content, the more likely crystallization will occur.   Does crystallization affect the properties of epoxy resins? The crystallization phenomenon does not affect the performance of the epoxy resin, only the epoxy resin morphology has changed, not deterioration. However, it brings a lot of inconvenience to the operation. After practice, the crystalline epoxy resin is dissolved by heating and mixed with the corresponding proportion of curing agent, its tensile strength, flexural strength, compressive strength, and bonding strength have no change in comparison with epoxy resin without crystallization. It can be seen that the crystallization phenomenon does not affect the performance of the epoxy resin, only the epoxy resin morphology has changed, not a qualitative change. In general, the crystallization of epoxy resin adhesive is a reversible process that can be changed with the temperature and has no effect on the bonding performance and reinforcing effect of epoxy resin cured products. Even if the crystallization occurs, heating until it softens and disappears, it can be used normally.   Nanjing Yolatech provides all kinds of high purity and low chlorine epoxy resins, including Bisphenol A epoxy resin, Bisphenol F epoxy resin, Phenolic epoxy resin, Brominated epoxy resin, DOPO modified phenolic epoxy resin, MDI modified epoxy resin, DCPD epoxy resin, Multifunctional epoxy resin, Crystalline epoxy resin, HBPA epoxy resin and so on. If you are interested in them, pls kindly contact us. We will be at service for you any time, thank you.  

Description Epoxy diluents are mainly used to reduce the viscosity of the epoxy adhesive system, dissolve and disperse and dilute the adhesive, and improve the coating and fluidity of the adhesive. Epoxy diluents also play a role in extending the service life. There are many ways to classify the diluent, according to its use mechanism, it can be divided into two categories of inactive diluent and active diluent.   Inactive diluents Inactive diluents do not contain active groups in their molecules and are mostly inert solvents. They do not react with epoxy resins, hardeners, etc. Inactive diluents are purely physically mixed into the resin. In addition to playing a diluting role, it has an impact on mechanical properties, heat distortion temperature, media resistance and aging damage. In the choice of inactive diluent should consider the solvent evaporation rate, if the evaporation rate is too fast, the surface of the adhesive layer is easy to form a film, preventing the adhesive layer of solvent inside the escape, resulting in bubbles in the adhesive layer. If the evaporation rate is too slow, the solvent remains in the adhesive layer, which will affect the strength of the bond. Usually, several solvents with different boiling points are mixed to regulate the evaporation rate. It is mostly used in rubber adhesive, phenolic adhesive, polyester adhesive and epoxy adhesive.   Reactive diluents Reactive diluents are generally low molecular compounds with one or two or more epoxy groups. They can be directly involved in the epoxy resin curing reaction, become part of the epoxy resin curing material crosslinking network structure. Reactive diluents have almost no effect on the properties of the cured product and can sometimes increase the toughness of the curing system. Active diluent is divided into monofunctional active diluent and difunctional active diluent. Active diluents are generally toxic and must be used with safety in mind. Prolonged contact will often cause skin irritation and in severe cases, even ulcers. Monofunctional active diluent dilution effect is better, aliphatic type has better dilution effect than aromatic type. The acid and alkali resistance of the curing products using aromatic active diluents does not change much, but the solvent resistance is reduced. The use of monofunctional reactive diluents will reduce the heat distortion temperature, which is due to its use will make the cured product crosslinking density decreased. Flexural strength and impact toughness are improved with long carbon chain active diluents. When used in small quantities, it has no effect on the hardness of the cured product, while the coefficient of thermal expansion increases.   Diluent selection principle Try to use active diluents, to improve the processability and at the same time improve its adhesive and mechanical properties. Choose those diluents that are similar to the chemical structure of the main resin. They will participate in the reaction with the main resin in the presence of other additives, and greatly improve the performance of the adhesive layer. Select low volatility, small odor and as low as possible toxicity varieties, to reduce the harm of using active diluent on the human body. Because most of the active or inactive diluents have odor and low toxicity. Should choose the source of easy, non-flammable and non-explosive, low-priced active diluent. Should be through the theory and experiments to choose the most appropriate amount to add.   We Nanjing Yolatech can provide a variety of high purity low chlorine epoxy resin active diluents, widely used in insulation materials, electronic potting, electrical casting and other fields, including 1,4-Butanediol diglycidyl ether(YLD-6018),1,6-Hexanediol diglycidyl ether (YLD-6008), Neopentyl glycol diglycidyl ether(YLD-6009), Neodecanoic acid glycidyl ester(YLD-8001) and so on.   Welcome new and old customers to consult at any time!    

  Epoxy resins are commonly used as a matrix for materials such as adhesives, coatings and composites, and are widely used in construction, machinery, electrical and electronic, aerospace and other fields. A complete concept of epoxy resin constituents by four aspects of the composition. However, in practice, it is not necessary to have all four aspects of the components, but the resin composition must include the curing agent, which shows the importance of the curing agent. Epoxy resin components Epoxy resin Epoxy resin Main part，bisphenol A type and other types of epoxy resins Curing agent Reacts with epoxy resins to form three-dimensional network polymers Components for modification Plasticiser Gives epoxy components plasticity, but reduces its heat and chemical resistance Toughening agent Improved impact resistance without compromising other properties Filler Increase weight, improve curability, mechanical properties, such as calcium carbonate, mica, etc Flame retardant agent To make the epoxy Components with flame resistance, there are filler flame retardant and reactive flame retardant Components used to regulate fluidity Diluent Reduce components viscosity, including active and inactive diluents Thixotropic agent Imparts thixotropic properties to epoxy compositions, e.g. asbestos, silica micropowder Other components Pigments, solvents, defoamers, levelling agents, tackifiers, etc. The reason why epoxy resins are widely used is the result of the versatile co-ordination of these components. Especially the curing agent, once the epoxy resin is determined, the curing agent plays a decisive role in the processability of the epoxy resin composition and the final performance of the cured product. Classification of epoxy curing agents 1. Classification by acid-base properties Type Curing agent name acidity Organic anhydrides, boron trifluoride and its complexes alkali Aliphatic diamines, polyamines, aromatic polyamines, dicyanodiamines imidazoles, modified amines   2. Classification by reactivity and chemical structure Curing agent Apparent curing agent Addition reaction Polyamine Simple amine Straight chain fatty amine DETA，TETA，DEPA，TEPA Polyamides Polyamides with different amine values Aliphatic amine MDA，IPDA Aromatic amine m-XDA, DDM, m-PDA, DDA Modified amine Anhydride Monofunctional group PA, THPA, HHPA, MeTHPA, MeHHPA, MNA, DDSA, HET Bifunctional group PMDA, BTDA, TMEG, MCTC Carboxyl group TMA, PAPA Polyphenol PN Polythiol PM, PS Catalyst reaction Anionic polymers DMP-30, 2E4MZ Cationic Polymers BF3∙MEA Latent curing agent Dicyandiamide Organic acid hydrazide Ketimine microcapsules   3. Classification by curing temperature Curing Temp. Curing agent type Curing agent name 0-20°C Low temperature curing agent Polythiols, aliphatic polyamines or promoters, aromatic polyamines or promoters 20-40°C Normal temperature curing agent Polyamide, tertiary amine 60-100°C Medium temperature curing agent Dibasic aminopropylamine, imidazole, tertiary amine salts, aliphatic amines 100-150°C Medium and high temperature curing agent Anhydride or promoter, BF3-ammonium salt, dicyandiamide/promoter, imidazole derivatives, hydrazides 150°C+ High temperature curing agent Aromatic polyamines, polyphenols, acid anhydrides   4. Classification by different usage Curing agent Curing at room temperature Heavy Duty Anti-corrosion Coatings Adhesives for civil engineering and construction Civil Engineering Coatings FRP General Adhesives Alicyclic polyamines Denatured polyamines Straight chain aliphatic polyamines Polyamides, polythiols Heat curing Electrically insulating material Acid anhydride, imidazoles, BF3 complexes Laminated materials Dicyandiamide, aromatic polyamines, linear phenolic resins Coatings   Tank materials Amino resins, methyl phenolic resins Powder material Dicyandiamide, aromatic polyamines, acid anhydrides Moulded material Linear phenolic resins Adhesives Aromatic polyamines, anhydrides, imidazoles, BF3 amine complexes     Structure and properties of curing agents A comprehensive understanding of the properties and characteristics of polyamine curing agents with the same functional group but different chemical structures is very important for the selection of curing agents. The main characteristics (color, ripeness, duration of use, etc.) also show a certain regularity. Color: (good) alicyclic->aliphatic->amide->aromatic amine(bad) Maturity: (low) alicyclic->aliphatic->aromatic->amide(high) Application period: (Long) Aromatic->Amide->Alicyclic->Aliphatic (Short Curability: (Fast) Aliphatic->Alicyclic->Amide->Aromatic (Slow) Irritation: (Strong) Aliphatic->Aromatic->Alicyclic-Amide (Weak) Gloss: (Excellent) Aromatic->Alicyclic->Polyamide->Aliphatic amide (Poor) Flexibility: (Soft) Polyamide->Aliphatic->Alicyclic->Aromatic (Rigid) Adhesion: (Excellent) Polyamide->alicyclic->aliphatic->aromatic (Good) Acid resistance: (Excellent) Aromatic->Alicyclic->Aliphatic->Polyamide (Inferior) Water Resistance: (Excellent) Polyamide->Aliphatic Amine->Aliphatic Cyclic Amine->Aromatic Amine (Good)     Development trend of curing agent Curing agent as a core substance to play the value of epoxy resin, the nature of the cured product depends on the performance of the curing agent, so the road of research on the curing agent has far-reaching significance. From the research of curing agent to date, combined with the current situation at home and abroad, curing agent is currently facing some of the following challenges and changes. The development of high activity and excellent heat resistance curing agent. The use of modified polyether amine, aliphatic amine or mixed compound to prepare high activity and heat resistance curing system. Due to the traditional epoxy resin in the curing performance is poor, especially low toughness, brittle, greatly affecting its use, so improve the performance of epoxy resin needs to improve the toughness. Improve the curing environment, overcome the volatility and toxicity of amine curing agent, and promote the development of room temperature curing agent by modifying amine with physical or chemical method. Improve the adaptability and specialty of epoxy resin in special environments, to meet the special environments such as humid, underground low temperature environment or underwater of reservoir dam repair. Curing agent and curing technology matching, will be a variety of curing technology (heat curing, microwave curing, light curing) combined with the selection of the appropriate curing agent may be able to get a comprehensive performance of the curing product. Heating type latent curing agent has great potential, can continue to study the dicyandiamide and its modified products, organic acid hydrazide, boron - amine complex, imidazole, microcapsules and other latent curing agent.

1. Indicators of epoxy groups This is the most important characteristic index of epoxy resin, which is used to indicate the content of epoxy group in the resin molecule, and there are three main ways of expression, including  epoxy value, epoxy index and epoxy equivalent. Epoxy value is defined as the amount of epoxy groups(mol) per 100g of epoxy resin，unit is mol/100g. The definition of the epoxy value is mainly for the purpose of calculating the amount of curing agent to be added to the epoxy resin for curing. The amount of curing agent is the mass of curing agent to be added per 100g of epoxy resin cured. Epoxy index is the amount of epoxy groups(mol) per 1kg of epoxy resin, the unit is mol/kg. In terms of the International System of Measurement (SI units), the epoxy index is more appropriate than the epoxy value, which is 10 times larger than the epoxy value. Epoxy equivalent is the mass (g) of an epoxy resin containing 1 mol of epoxy groups ,the unit is g/mol. The chain segments between the epoxy groups become longer and longer as the molecular weight of the epoxy resin increases, so the epoxy equivalent of epoxy resins with a high relative molecular mass is also elevated. The physical quantity of epoxy equivalent is usually used to describe the epoxy group of epoxy resin in the United States, Japan and Europe.   2. Hydroxyl content Bisphenol A-type epoxy resin molecular chain contains a large number of secondary hydroxyl structure, the larger the polymerization degree n value, its molecular weight is also larger, the higher the hydroxyl content. It can cross-link with phenolic resins, amino resins or Poly isocyanates, and it can promote the curing reaction. Therefore, when controlling the curing process of epoxy resin paint, the hydroxyl content of epoxy resin must be determined. There are two most used methods to express the hydroxyl content. The hydroxyl value F is the amount of hydroxyl contained in 100g of epoxy resin, the unit is mol/100g. And the hydroxyl equivalent H is the mass(g)of epoxy resin containing 1mol of hydroxyl, the unit is g/mol.   3. Softening point Epoxy resin is a mixture of homologous prepolymers with different degrees of polymerization and has no fixed melting point or melting process. The softening point generally refers to the temperature at which the epoxy resin turns from hard to soft and shows a certain fluidity in the process of heating. The softening point of epoxy resin can characterize the average molecular weight size and distribution of the resin, the molecular weight of the high softening point is large, and the molecular weight of the low softening point is small. Epoxy resins can be broadly classified according to the softening point into three types. Type Softening point Degree of polymerisation Low molecular weight epoxy resin <50°C <2 Medium molecular weight epoxy resin 50~95°C 2~5 High molecular weight epoxy resin >100°C >5     4. Viscosity The viscosity of epoxy resins affects the fluidity and workability of resins and coatings. Viscosity increases as the average molecular weight of the epoxy resin increases and decreases as the molecular weight distribution decreases. The viscosity of epoxy resins is extremely sensitive to temperature and decreases rapidly with increasing temperature, so it is generally expressed as the viscosity at a specific temperature.   5. Chlorine value The amount of chlorine contained in an epoxy resin (including organic chlorine and inorganic chlorine) is called the chlorine value. The chlorine in the epoxy resin is divided into organic chlorine and inorganic chlorine by the form of its existence. Organic chlorine comes from the residue of insufficient ring closure in the manufacture of the epoxy resin, which is called easily hydrolysable chlorine. Inorganic chlorine comes from the residual sodium chloride that is not washed sufficiently when manufacturing epoxy resins. Organic chlorine measures the resin reaction, and inorganic chlorine measures the level of post-production treatment processes for epoxy resins. Both are detrimental to the electrical properties of the cured substance and to corrosion resistance.    

Definition of epoxy resin Epoxy resin refers to the molecular structure of the molecular structure contains two or more epoxy groups and in the appropriate chemical reagents under the action of the compound can form a three-dimensional mesh curing material. Epoxy resin is an important class of thermosetting resins. Epoxy resins include both epoxy oligomers and low molecular compounds containing epoxy groups. Epoxy resins are widely used in the fields of water conservancy, transport, machinery, electronics, home appliances, automotive and aerospace as the resin matrix for adhesives, coatings and composites.   Characteristics of epoxy resins and their curing compounds 1. High mechanical properties. Epoxy resin has strong cohesion, dense molecular structure, so its mechanical properties are higher than phenolic resin and unsaturated polyester and other general-purpose thermosetting resin. 2. Strong adhesion. Epoxy resin curing system contains very active epoxy group, hydroxyl group and ether bond, amine bond, ester bond and other polar groups. So epoxy cured products have excellent adhesion to polar substrates such as metal, ceramics, glass, concrete and wood. 3. Curing shrinkage is small. Generally its shrinkage is 1% to 2%. It is one of the smallest varieties of curing shrinkage in thermosetting resins (phenolic resins for 8% to 10%, unsaturated polycool resins for 4% to 6%, silicone resins for 4% to 8%.) The coefficient of linear expansion is also very small, generally 6*10-5/°C, so there is little change in volume after curing. 4. Good processability. Epoxy resin curing basically does not produce low molecular volatiles, so it can be low-pressure molding or contact pressure molding. It can cooperate with various curing agents to manufacture solvent-free, high solid, powder coatings and water-based coatings and other environmentally friendly coatings. 5. Excellent electrical insulation is excellent. Epoxy resin is one of the best varieties of thermosetting grease intermediary electrical properties.   6. Good stability and excellent resistance to chemicals. Epoxy resin without alkali, salt and other impurities is not easy to deteriorate. If it is stored properly (sealed, not moisture, not meet high temperature), its storage period can reach 1 year. If the test is qualified after the period, it can still be used. Epoxy curing material has excellent chemical stability. Its resistance to alkali acid, salt and other media corrosion performance is better than unsaturated polyester resins, phenolic resins and other thermosetting resins. Therefore, epoxy resin is used as anti-corrosion primer. Because the epoxy resin cured material is three-dimensional mesh structure, and it can resist the impregnation of oil and so on, so it is used in a large number of tanks, tankers, aircraft, the overall fuel tank lining and so on.   Disadvantages of epoxy resin Epoxy resin also has some disadvantages, such as poor weather resistance. Epoxy resin generally contains aromatic ether bond, its cured material is easy to be degraded after sunlight irradiation to break the chain, so the usual bisphenol A-type epoxy resin cured material is easy to lose luster in outdoor sunlight and gradually chalking, so it is not suitable to be used as outdoor topcoat. In addition, epoxy resin low temperature curing performance is poor, generally need to be cured at 10 ° C or more. Below 10°C, the curing is slow, which is very inconvenient for large objects such as ships, bridges, harbours, oil tanks and other cold season construction.   History of epoxy resin development Epoxy resin research began in the 1930s, in 1934 Germany I.G. Farben company's P. Schlack found that amines can react with epoxy groups to polymerise polymers to produce low shrinkage plastics, which was awarded a German patent. Later, Switzerland Gebr. de Trey Pierre Castan and the United States Devoe & Raynolds S.O. Greelee, they use bisphenol A and epichlorohydrin by polycondensation reaction to produce epoxy resin, with organic polyamines or phthalic anhydride can make the resin curing, the cured material has excellent adhesive properties. Soon, Switzerland's Ciba, the United States of Shell and Dow Chemical Company have begun the industrial production of epoxy resins and application development research. Into the 1950s, the production and application of ordinary bisphenol A epoxy resin at the same time, some new epoxy resins have come out. 1960 years ago, the emergence of thermoplastic phenolic epoxy resin, halogenated epoxy resin, polyolefin epoxy resins.  The development of epoxy resins in China started in 1956, and the first successes were obtained in Shenyang and Shanghai, and the industrial production started in 1958 in Shanghai and Wuxi. In the mid-1960s, some new alicyclic epoxy began to study, including phenolic epoxy resin, polybutadiene epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, etc. By the end of the 1970s, China has formed a complete industrial system from the monomer resins, auxiliary materials, from scientific research and production to application.