A dielectric is any insulating medium between two conductors. Simply put, it is non-conductive material. Dielectric materials are used to make capacitors, to provide an insulating barrier between two conductors (e.g., in crossover and multilayer circuits), and to encapsulate circuits.   Dielectric Properties Epoxy resin usually has the following four dielectric properties:VR, Dk, Df and dielectric strength. Volume resistivity (VR): It is defined as the resistance measured through the material when a voltage is applied for a specific period of time. According to ASTM D257, for insulation products, it is usually greater than or equal to 0.1 tera ohm-meter at 25°C and greater than or equal to 1.0 mega ohm-meter at 125°C. Dielectric constant (Dk): it is defined as the ability of the material to store charge when used as a capacitor dielectric. According to ASTM D150, it is usually less than or equal to 6.0 at 1KHz and 1MHz, and is a dimensionless value because it is measured as a ratio. The dissipation factor (Df) (also known as the loss factor or dielectric loss): defined as the power dissipated by the medium, usually less than or equal to 0.03 at 1KHz, less than or equal to 0.05 at 1MHz. Dielectric strength (sometimes called breakdown voltage): is the maximum electric field that the material can withstand before breakdown. This is an important characteristic for many applications that require running high currents or amperages. As a general rule of thumb, the dielectric strength of epoxy resins is about 500 volts per mil at 23°C for insulating products. As a practical example, if an electronic circuit needs to resist 1000 volts, a minimum of 2 mils of dielectric epoxy is required. Volume resistivity, dielectric constant, and dissipation factor can be determined experimentally by the adhesive manufacturer; however, dielectric strength depends on the application. Users of epoxy resins should always verify the dielectric strength of the adhesive for their particular application.   Variability of dielectric properties Many dielectric properties will vary with factors unrelated to the properties of the host material, such as: temperature, frequency, sample size, sample thickness and time. Some external factors and how they affect the final results. VR and Temperature As the temperature of the material increases, the VR decreases. In other words, it is no longer an insulator. The main reason for this is that the material is above its glass transition temperature (Tg) and the molecular motion of the monomers entangled in the polymer network is at its highest level. This not only means lower insulation compared to room temperature, but also leads to lower strength and sealing.  Dk and temperature The dielectric constant of room temperature cured epoxy resins increases with temperature. For example, the value is 3.49 at 25°C, becomes 4.55 at 100°C, and 5.8 at 150°C. In general, the higher the value of Dk, the less electrically insulating the material is. Dk and frequency (Rf)  In general, Dk decreases with increasing frequency. As described in the effect of temperature on Dk, room temperature cured epoxy resin has a Dk value of 3.49 at 60Hz, a Dk value of 3.25 at 1KHz and a Dk value of 3.33 at 1MHz. In other words, as Rf increases, the insulating properties of the adhesive increase. Therefore, the lower the Dk value, the more the material acts like an insulator.    Common Applications Dielectric adhesives are used in most semiconductor and electronic packaging applications. Some examples include: semiconductor flip chip underfill, SMD placement on PCBs and substrates, wafer passivation, spherical tops for ICs, copper ring dipping and general PCB potting and encapsulation. All of these areas require maximum insulation to eliminate and prevent any electrical shorts.    Insulation Products Epoxy Technologies offers a wide range of products for dielectric applications that have structural, optical and thermal properties as well as good dielectric properties. All dielectric products are electrical insulators, but many are also heat conductors.

Benzoxazine compounds can be synthesized from phenols, formaldehydes and amines with oxygen nitrogen heterocyclic structure with halogen free, which can be homopolymerized to form a polybenzoxazine thermoset networks by heating, also can be co-cured with traditional thermosetting resins like epoxy resin, phenolic resin.   Benzoxazine resins, when heated without curing agent, homopolymerize to form a rigid, nitrogen contained and strong cross-linking network structure that can be used for manufacturing products with excellent mechanical property, high temperature resistance and flame retardancy(UL94-V0). Furthermore, benzoxazine, as a curing agent, can be used in conjunction with all the epoxy resins, phenolic resins etc. to achieve high thermal resistance, strong, low CTE, flame retardancy with halogen free. With these qualities, benzoxazines offer many advantages for formulating halogen-free systems to be used in stringent requirement of CCLs, high speed PCBs, flame retardancy electrical materials and others.   Benzoxazine Key Properties The flame retardancy of benzoxazine series can reach UL-94 V0 level with halogen free, which can be used to improve flammability resistance of products. No byproduct releasing during the curing process, and the dimensional shrinkage rate almost 0. The whole series of products have low water absorption, which can greatly improve the rate of good products. The excellent dielectric property of low dielectric series products shows less effect in frequency fluctuation, witch is intended for use in M2/M4 class PCBs. Benzoxazine products with a wide coverage of Tg and selectivity(150~450℃), and with char yield 78% at 800℃. Benzoxazine resins can be toughened by using unique patented technology, which can significantly improve the machinability of plate products.

  n-Heptanol (1-Heptanol) and n-Hexanol (1-Hexanol) are both primary alcohols, which means they each have a hydroxyl group (-OH) attached to a primary carbon atom. These alcohols are important in various industrial applications due to their unique properties.   n-Heptanol (1-Heptanol) Chemical Structure and Properties Chemical Formula: C7H16O Molecular Weight: 116.2 g/mol Boiling Point: 175.8 °C (348.4 °F) Density: 0.818 g/cm³ 1-Heptanol, also known as heptan-1-ol or heptyl alcohol, is a clear, colorless liquid with a mild, characteristic odor. It is slightly soluble in water but more soluble in organic solvents such as ethanol and ether.   Uses and Applications Flavoring Agent: Due to its pleasant odor, 1-Heptanol is used in the flavor and fragrance industry to impart fruity and floral notes. Chemical Intermediate: It serves as a precursor in the synthesis of various esters, which are used in perfumes and flavorings. Solvent: 1-Heptanol can be used as a solvent in the formulation of resins, coatings, and pharmaceuticals. Lubricant Additive: It is sometimes used as an additive in lubricants to enhance performance and stability.   Production 1-Heptanol is produced through the catalytic hydrogenation of heptanal or by the hydroformylation of hexene followed by hydrogenation.   n-Hexanol (1-Hexanol) Chemical Structure and Properties Chemical Formula: C6H14O Molecular Weight: 102.2 g/mol Boiling Point: 157 °C (315 °F) Density: 0.814 g/cm³ 1-Hexanol, also known as hexan-1-ol or hexyl alcohol, is a colorless liquid with a slightly floral odor. It is moderately soluble in water and highly soluble in most organic solvents.   Uses and Applications Fragrance and Flavor: Similar to 1-Heptanol, 1-Hexanol is used in the fragrance industry to produce floral and green odors. Solvent: It acts as a solvent for lacquers, resins, and oils. Plasticizer: 1-Hexanol is used in the production of plasticizers, which are added to plastics to increase their flexibility. Intermediate in Chemical Synthesis: It is a building block in the synthesis of various chemicals, including plasticizers, pharmaceuticals, and surfactants.   Production 1-Hexanol is typically produced by the hydroformylation of pentene, followed by hydrogenation of the resulting aldehyde. Alternatively, it can be obtained from the reduction of hexanoic acid.   Conclusion n-Heptanol and n-Hexanol are versatile chemicals with a wide range of applications in various industries. Their roles as solvents, intermediates in chemical synthesis, and components in fragrances and flavors highlight their importance. Understanding their properties and production methods can help optimize their use in industrial processes and product formulations.  

Some reasons for epoxy resin yellowing Photo-oxidation reaction Epoxy resin is susceptible to ultraviolet rays and oxygen in the sunlight caused by the oxidation of the aniline group in the epoxy resin, which in turn leads to the phenomenon of yellowing of epoxy resin glue; Thermal degradation Long-term high temperature conditions, epoxy resin will find thermal degradation, which will lead to molecular chain breakage, yellowing phenomenon; Some chemical reactions Epoxy resin adhesive and some substances in contact with chemical reactions, yellowing; for example, substances containing sulfide and epoxy resin contact; Curing agent and accelerator reasons The free amine component in the amine curing agent directly polymerises with the epoxy resin, resulting in local heating of the glue and accelerated yellowing; In the heat aging process, the amine curing epoxy resin material surface has a large number of imine presence, thus easier degradation and yellowing. Tertiary amine accelerators, nonylphenol accelerators in the thermal oxygen, UV irradiation is also easy to yellowing;   How to avoid epoxy resin yellowing Reduce the irradiation of ultraviolet rays In the production and application process of epoxy resin, must avoid the influence of high temperature and ultraviolet rays, prevent epoxy resin oxidation reaction. Add yellowing-resistant additives Adding antioxidant and UV absorber can greatly delay the aging and oxidation of epoxy resin, thus prolonging its service life and preventing yellowing. Curing agent selection Amine curing agent, try to choose the amine curing agent with less free amine content; Anhydride curing agent, epoxy system in the anhydride curing agent is heat aging and light aging type of excellent.   The conclusion The yellowing of epoxy resin is caused by a variety of factors. The most important is ultraviolet radiation, if it is an outdoor product, it is recommended to add a certain amount of ultraviolet absorber to delay the yellowing, and it is best to add some antioxidants together as well, to play a concordant effect. Adding UV diluents and antioxidants can not fundamentally solve the epoxy resin yellowing, but only delay yellowing, so that the product transparency lasts for a period of time.  

We all know that a separate epoxy resin is not conductive, how to make it with conductive properties, we all know that to conduct electricity, then you need a conductive medium, that epoxy conductive adhesive is the same reason, in the glue filled with randomly distributed metal or conductive carbon particles and other conductive media, so that epoxy resin with conductive properties.   Types of conductive adhesive Generally speaking, conductive adhesive is composed of two parts: the matrix and conductive filler: 1. commonly used matrix including epoxy resin, silicone resin, polyimide resin, phenolic resin, polyurethane, acrylic resin and so on. Compared with other resins, epoxy resin has the advantages of good stability, corrosion resistance, low shrinkage, high bonding strength, bonding surface and good processability, therefore, epoxy resin is currently the most researched and widely used matrix materials. 2. conductive filler usually carbon, metal, metal oxide three categories. Conductive adhesive requires conductive particles itself to have good conductive properties, particle size should be in the appropriate range, can be added to the conductive adhesive matrix to form a conductive pathway. Conductive filler can be gold, silver, copper, aluminium, zinc, iron, nickel powder and graphite and some conductive compounds. Currently in actual production, the most widely used is silver powder.   The role of conductive adhesive Epoxy resin conductive adhesive belongs to is non-polluting welding materials. Under normal circumstances epoxy resin is not conductive, but if the conductive silver paste and epoxy resin combination, their mixture can conduct electricity. Generally silver paste is the most common conductive filler, but materials such as gold, nickel, copper and carbon can also be used. Another advantage of epoxy resins is that they are thermally conductive, which means they can cool electronic components. At present, many electronic components tend to be miniaturised, lightweight, highly integrated development, it is difficult to use a large number of welded materials to be made, if the use of conductive adhesive can be avoided the adverse effects of welding.   Epoxy resin conductive adhesive features Has excellent adhesive strength. With all types of substrates can achieve good adhesion; Formulation design is rich. With different curing agents, can prepare single-component adhesive or multi-component adhesive. Room temperature curing, medium temperature curing and high temperature curing. Good heat resistance; Low curing shrinkage and stable properties; Good chemical resistance.   The main application of epoxy resin conductive adhesive Instead of solder for electronic components and printed circuit boards, glass, ceramic bonding, such as a variety of consumer electronics, communications equipment, automotive parts, industrial equipment, medical equipment, to solve the electromagnetic compatibility (EMC) and so on. Electronic packaging: such as LCD, LED, integrated chips, printed circuit board components, ceramic capacitors and other electronic components and components of the package. Photovoltaic panel bonding: to improve the defective rate of the cell due to solder, reduce costs and increase the photoelectric conversion rate. Used as structural adhesive for bonding: metal-to-metal bonding, component lead bonding, battery terminal bonding.   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. And we also could provide all kinds of curing agents or hardeners and diluents.           We will be at your service 24 hours a day. Pls contact us freely.

  Reactive Diluent (Reactive Diluent) Definition Reactive diluents mainly refer to low molecular epoxy compounds containing epoxy groups. Reactive diluents can participate in the epoxy resin curing reaction, become part of the epoxy resin curing material crosslinking network structure.   Classification of reactive diluents Reactive diluents are divided into single epoxy-based reactive diluents and multi-epoxy-based reactive diluents.   Characteristics of reactive diluents Epoxy resin reactive diluent to participate in the curing reaction, do not have to worry about volatile emissions in the reaction. And the molecular structure of the active diluent contains epoxy group, in the case of the appropriate amount of use, the performance of the curing material does not have a great impact on the different molecular structure of the active diluent will also provide a certain function for the curing material, such as toughening, low-halogen, to improve the mechanical properties, to increase the temperature resistance and so on.   Active diluent product categories   Commonly used monofunctional active diluent Features: low viscosity, low colour, good dilution effect, widely used. C12-14 alkyl glycidyl ether: dilution effect is good, ordinary common type active diluent, widely used Butyl glycidyl ether: good dilution effect, high reactivity to amine curing agent, but heavy odour Phenyl glycidyl ether: benzene ring, high reactivity to amine curing agents, good temperature resistance   Commonly used bifunctional group active diluent Characteristics: contains double epoxy groups, lower viscosity at the same time, more prominent reactivity, good flexibility. Commonly used products include: 1,4 butanediol diglycidyl ether Polypropylene glycol diglycidyl ether Ethylene glycol diglycidyl ether   Trifunctional group active diluent characteristics: participate in the epoxy resin curing reaction, can form a three-dimensional network structure, because of the presence of special functional groups, help to improve the performance of some of the cured material.   The use of active diluents Monofunctional active diluent viscosity is low, the dilution effect is good, the dosage is 10-15%; the use of multifunctional active diluent viscosity reduction effect to achieve the standard of monofunctional active diluent, the dosage will be increased, generally in 20-25%.   Selection of active diluents   Active diluent can be widely used in coatings, adhesives, electronic and electrical and composite materials and other fields. When we choose the active diluent, we should not only consider the viscosity reduction effect, but also consider the performance needs of the epoxy curing material. On the basis of not affecting the original performance of the cured material, while meeting the toughness and strength requirements, low toxicity and safety, etc., are the conditions we need to consider when choosing.   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. And we also could provide all kinds of curing agents or hardeners and diluents.         We will be at your service 24 hours a day. Pls contact us freely.  

  Hello everyone, today we are going to talk about a very practical topic - how to repair the floor with resin, and how to choose the most suitable resin material. As an integral part of the home and office environment, the floor will inevitably wear and tear, scratches, dents and other problems will occur after a long time of use. Traditional repair methods are not only limited in effectiveness, but also costly to maintain. Resin repair materials for its high strength, wear resistance, easy to construct and other characteristics, and gradually become the first choice for ground renovation. So, in the face of a wide range of resin products on the market, how do we choose? Here, let's explore together. 　　 Understanding the type of resin Resin is mainly divided into epoxy resin, polyester resin, polyurethane resin and so on. Epoxy resin is widely used in the field of ground repair due to its excellent physical properties and chemical stability. Polyester resins and polyurethane resins, on the other hand, are also well used in certain specific applications due to their good elasticity and abrasion resistance.   Consider the floor material Different floor materials have different requirements for resins. For example, concrete floors are more suited to epoxy resins, whereas wooden floors may require the selection of a gentler resin material. Therefore, it is important to understand the material and characteristics of your own floor before choosing a resin.   Focus on environmental performance As people become more aware of environmental protection, choosing environmentally friendly resins has become a trend. When buying, you can pay attention to the product's environmental certification and VOC content, try to choose low-pollution, odourless products.   Consider the convenience of construction The ease of construction of the resin is also one of the factors to consider when choosing. Some products may require complicated construction process and long curing time, which undoubtedly increases the construction difficulty and cost. Therefore, choosing products with simple construction and short curing time can greatly improve the repair efficiency.   In conclusion, choosing the right resin material is crucial for floor repair. Only after comprehensive consideration of the type of resin, ground material, environmental performance, ease of construction and many other factors, we can select the most suitable product for you, so that the ground is new!   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. And we also could provide all kinds of curing agents or hardeners and diluents.       We will be at your service 24 hours a day. Pls contact us freely.  

1,3-cyclohexanedimethylamine CAS No.579-20-6,short for 1,3-BAC,is used as a raw material for epoxy resin curing agents in a wide range of applications around the world. 1,3-BAC, as an alicyclic amine, has excellent hardness, weathering, and chemical resistance, a refined appearance, and a faster cure rate.   Typical Physical and Chemical Data Appearance: Colourless transparent liquid Colour (G):1.0 Max Viscosity (mPa.s/20℃): 9.1 Active hydrogen equivalent(g/eq): 35.6   Advantages of 1,3-BAC as an epoxy resin curing agent Excellent UV resistance and transparency Fast curing speed Excellent curing at high temperatures & high humidity Low active hydrogen equivalents, low additions Low solidification point Good curing even at low temperatures.   Application of 1,3-BAC      In jewellery adhesive 1,3-BAC's excellent resistance to yellowing provides a long-lasting guarantee for the glossy appearance of the jewellery adhesive. 1,3-BAC provides hardness guarantee for jewellery. 1,3-BAC lower addition faster curing speed to improve the overall cost-effective advantage.      In seam sealer Improve the curing speed, 1,3-BAC can fully guarantee the curing time. 1,3-BAC low colour, high transparency to fully guarantee the appearance of the product colour. 1,3-BAC provides the required hardness and strength to the product.     In composite materials 1,3-BAC low active hydrogen equivalent, low additive quantity can bring higher cost-effective advantage for products. 1,3-BAC high hardness, to provide assurance for the strength of the product. 1,3-BAC good chemical resistance, to ensure that the product's lasting use.     In laminating adhesive 1,3-BAC's excellent resistance to yellowing provides assurance of long-lasting colour stability of the cured product. 1,3-BAC's excellent colour transparency ensures the transparent and clear quality of the product. The low viscosity of 1,3-BAC ensures good workability.   1,3-BAC (1,3-cyclohexanedimethylamine) is now widely used as epoxy resin curing agent in coatings, adhesives, composites, etc. 1,3-BAC is one of the amines with less additive quantity at present, and its excellent product appearance and performance make it have an outstanding cost-effective advantage.   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. And we also could provide all kinds of epoxy resin curing agents or hardeners and diluents.   We will be at your service 24 hours a day. Pls contact us freely.  

  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.