1, epoxy resin is a kind of polymer, the molecular formula is (C11H12O3)n, which refers to a class of polymers containing more than two epoxy groups in the molecule.
It is A condensation product of epichlorohydrin and bisphenol A or polyol. Due to the chemical activity of the epoxy group, it can be opened by a variety of compounds containing active hydrogen, curing crosslinking to form a network structure, so it is a thermosetting resin. Bisphenol A type epoxy resin not only has the largest yield and the most complete variety, but also the new modified varieties are still increasing, and the quality is constantly improving. Epoxy resin is A general term for polymer compounds containing two or more epoxy groups in the polymer chain structure, which is a thermosetting resin, and the representative resin is bisphenol A type epoxy resin.
2: Characteristics of epoxy resin (usually refers to bisphenol A type epoxy resin)
1. The application value of epoxy resin alone is very low, and it needs to be used with curing agent to have practical value.
2. High bonding strength: The bonding strength of epoxy resin adhesive is at the forefront of synthetic adhesives.
3. The curing shrinkage rate is small, and the shrinkage rate of epoxy resin adhesive is the smallest in the adhesive, which is also one of the reasons for the high curing bonding of epoxy resin adhesive. For example: phenolic resin glue: 8-10%; Silicone rubber: 6-8% polyester resin rubber: 4-8%; Epoxy resin glue: 1-3% If the shrinkage rate of epoxy resin glue after modification can be reduced to 0.1-0.3%, and the coefficient of thermal expansion is 6.0×10-5/℃
4. Good chemical resistance: the ether group, benzene ring and fatty hydroxyl group in the curing system are not easy to be eroded by acid and base. In seawater, petroleum, kerosene, 10%H2SO4, 10%HCl, 10%HAc, 10%NH3, 10%H3PO4 and 30%Na2CO3 for two years; Soak in 50%H2SO4 and 10%HNO3 at room temperature for half a year; Soaking in 10%NaOH (100℃) for one month, the performance remained unchanged.
5. Excellent electrical insulation: The breakdown voltage of epoxy resin can be greater than 35kv/mm
6. Good process performance, stable product size, good resistance and low water absorption.
The advantages of bisphenol A epoxies are good, but they also have disadvantages:
①. The operation viscosity is large, which is somewhat inconvenient in construction
②. The curing property is brittle and the elongation is small.
③. The peeling strength is low.
④. Resistance to mechanical shock and thermal shock.
3: the characteristics of epoxy resin
1, epoxy resin adhesive is reprocessed or modified on the basis of epoxy resin characteristics, so that its performance parameters meet specific requirements, usually epoxy resin adhesive also needs to be used with curing agent, and needs to be mixed evenly before it can be fully cured, generally epoxy resin adhesive is called A glue or main agent, curing agent is called B glue or curing agent (hardener).
2. The main characteristics of epoxy resin adhesive before curing are: color, viscosity, specific gravity, ratio, gel time, usable time, curing time, thixotropy (stop flow), hardness, surface tension, etc. Viscosity (Viscosity) : refers to the internal friction resistance generated by colloids in the flow, and its value is determined by the type of substance, temperature, concentration and other factors. Gel time: The curing of glue is the process of transformation from liquid to solidification, and the critical state time from the reaction of glue to the critical state when the gel tends to the solid is the gel time, which is determined by the mixing amount of epoxy resin glue, temperature and other factors. Thixotropy: This characteristic refers to the phenomenon that when the colloid is touched by external forces (shaking, stirring, vibration, ultrasonic, etc.), it becomes thinner with the action of external forces, and when the external factors stop acting, the colloid returns to the original consistency. Hardness: refers to the resistance of the material to external forces such as stamping and scratching. According to different test methods, Shore hardness, Brinell hardness, Rockwell hardness, Mohs hardness, Barcol hardness, Vichers hardness and so on. The value of hardness is related to the type of hardness tester, in the commonly used hardness tester, Shore hardness tester has A simple structure, suitable for production inspection, Shore hardness tester can be divided into A type, C type, D type, A type for measuring soft colloids, C and D type for measuring semi-hard and hard colloids. Surface tension: The attraction of the molecules inside the liquid causes the molecules on the surface to be subjected to an inward force, which causes the liquid to minimize its surface area and form a force parallel to the surface, called surface tension. Or the mutual pull between two adjacent parts of the liquid surface within a unit length, it is a manifestation of molecular forces. The unit of surface tension is N/m. The size of the surface tension is related to the nature, purity and temperature of the liquid.
3. The main characteristics of epoxy resin adhesive after curing are: resistance, voltage resistance, water absorption, compressive strength, tensile (tensile) strength, shear strength, peel strength, impact strength, thermal deformation temperature, glass transition temperature, internal stress, chemical resistance, elongation, shrinkage coefficient, thermal conductivity, induction rate, weather resistance, aging resistance, etc. Resistivity: The resistance characteristics of a material are usually described in terms of surface resistance or volume resistance. The surface resistance is simply the resistance measured between two electrodes on the same surface, in Ω. The surface resistivity per unit area can be obtained by calculating the electrode shape and resistance value together. Volume resistance, also known as volume resistivity and volume resistivity, refers to the resistance value through the thickness of the material, which is an important indicator of the electrical properties of dielectric or insulating materials. Indicates the resistance of a 1cm2 dielectric to the leakage current, expressed in Ω•m or Ω•cm. The greater the resistivity, the better the insulation performance. Proof voltage: also known as compressive strength (insulation strength), the higher the voltage added at both ends of the colloidal, the greater the electric field force the charge in the material is subjected to, the more prone to ionization collision, resulting in colloidal breakdown. The lowest voltage at which an insulator breaks down is called the breakdown voltage of the object. When the 1 mm thick insulation material is broken down, the voltage thousand volts that need to be added is called the insulation compressive strength of the insulation material, referred to as the voltage resistance, the unit is: Kv/mm. The insulating properties of insulating materials are closely related to temperature. The higher the temperature, the worse the insulation performance of the insulation material. In order to ensure the insulation strength, each insulation material has an appropriate maximum allowable operating temperature, below which it can be used safely for a long time, and beyond this temperature it will rapidly age. Water absorption: A measure of the extent to which substances absorb water. Refers to the percentage of mass increased by soaking a substance in water for a certain time at a certain temperature. Tensile strength: The tensile strength is the maximum tensile stress at which a colloid is stretched to break. Also known as tearing force, tearing strength, tensile strength, tensile strength. The unit is MPa. Shear strength: also known as shear strength, refers to the unit bonding area can withstand the maximum load parallel to the bonding area, the commonly used unit is MPa. Peel strength: also known as peel strength, refers to the maximum damage load that can be borne per unit width, which is a measure of the force capacity of the line, the unit is kN/m. Elongation: refers to the increase in length of the colloid under tensile force, expressed as a percentage of the original length. Heat deflection temperature under load: It is a measure of the heat resistance of the cured material, which is to soak the cured sample in a suitable heat transfer medium with constant temperature rise, and measure the temperature when the bending deformation of the sample reaches the specified value under the static bending load of the simple supported beam, which is the thermal deformation temperature, referred to as HDT. Glass transition temperature (Glass transition temperature) : refers to the approximate midpoint of the narrow temperature range of the solidification from the glass form to the amorphous or highly elastic or fluid state transition (or vice versa), called the glass transition temperature, usually expressed in Tg, is an indicator of heat resistance. Shrinkage: defined as the percentage of the shrinkage to the size before and after the shrinkage, and the shrinkage is the difference between the size before and after the shrinkage. Internal stress: In the absence of external forces, colloids (materials) due to defects, temperature changes, solvent action and other causes of stress. Chemical resistance: The ability to resist acids, alkalis, salts, solvents and other chemicals. Flame resistance: The ability of a material to resist burning when it comes into contact with a flame or to hinder continued burning when it leaves the flame. Weatherability: It refers to the resistance of the material to exposure to sunlight, hot and cold, wind and rain and other climatic conditions. Aging: In the process of processing, storage and use, due to external factors (heat, light, oxygen, water, rays, mechanical forces and chemical media, etc.), a series of physical or chemical changes occur, making the polymer material cross-linked brittle, cracking sticky, discoloration cracking, rough foaming, surface flour, delamination peeling, performance gradually deteriorated. Even the loss of mechanical properties can not be used, this change is called aging. Dielectric Constant: also known as Permittivity or permittivity. It refers to the amount of "Electrostatic Energy" stored per "unit volume" of an object under each unit of "potential gradient". When the "permeability" of the colloid is greater (indicating that the quality is worse), and there is current working in the two approaching wires, the more difficult it is to achieve the effect of complete insulation, in other words, the easier it is to produce a certain degree of leakage. Therefore, the dielectric constant of the insulation material should be as small as possible under normal circumstances. The permittivity of water is 70, and very little moisture can cause significant changes.
4, epoxy resin glue is mostly thermosetting glue, it has the following main characteristics: the higher the temperature curing faster; The more the amount of mixing at one time, the faster the curing; There are exothermic phenomena in the curing process.
4: the application and development of epoxy resin
The excellent physical mechanical and electrical insulation properties of epoxy resin, the bonding properties with various materials, and the flexibility of its use process are not available to other thermosetting plastics. Therefore, it can be made into coatings, composite materials, casting materials, adhesives, molding materials and injection molding materials, and has been widely used in various fields of the national economy.
1. History of the development of epoxy resin: Epoxy resin was applied for Swiss patent by P.Castam in 1938, the earliest epoxy adhesive was developed by Ciba company in 1946, and the epoxy coating was developed by S.O.Creentee in the United States in 1949. China began the industrial production of epoxy resin in 1958.
2. Application of epoxy resin:
① Coating industry: epoxy resin in the coating industry needs the largest amount, the current more widely used water-based coatings, powder coatings and high solid content coatings. It can be widely used in pipeline containers, automobiles, ships, aerospace, electronics, toys, crafts and other industries.
② Electronic and electrical industry: epoxy resin adhesive can be used for electrical insulation materials, such as rectifier, transformer seal perfusion; Sealing protection of electronic components; Insulation treatment and bonding of mechanical and electrical products; Sealing bonding of battery; Surface covering of capacitors, resistors and inductors.
③ Hardware jewelry, crafts, sporting goods industry: can be used for signs, jewelry, trademarks, hardware, rackets, fishing tackle, sporting goods, crafts and other products.
④ Photoelectric industry: can be used for light-emitting diode (LED), digital tube, pixel tube, electronic display, LED lighting and other products packaging, perfusion and bonding.
⑤ Construction industry: It will also be widely used in roads, Bridges, floors, steel structures, buildings, wall coatings, DAMS, engineering construction, cultural relics repair and other industries.
(6) Adhesives, sealants and composite materials: such as wind turbine blades, crafts, ceramics, glass and other substances between the bonding, carbon fiber sheet composite, microelectronics material sealing and so on.
