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Epoxy resin adhesives are formulated with epoxy resin as the main body
.
The resin macromolecules have epoxy groups at the end, hydroxyl and ether bonds between the chains, and will continue to produce hydroxyl and ether bonds during the curing process.
The structure contains benzene rings and heterocyclic rings.
These structures determine the excellent performance of epoxy resin adhesives.
Performance
.
Epoxy resin adhesive is an adhesive that has a long history of use and is extremely versatile
.
Due to its strength, diversity and excellent adhesion to a variety of bonded surfaces, epoxy resin adhesives have been widely recognized by users
.
They have participated in and accelerated the technological revolution in certain industrial sectors
.
Epoxy resin can be used to bond metals, glass, ceramics, many plastics, wood, concrete and other surfaces
.
In the epoxy resin produced in the United States, more than 10% is used as an adhesive
.
In the past, people's modification of epoxy resin has been limited to rubber, such as carboxyl-terminated nitrile rubber, hydroxy-terminated nitrile rubber, polysulfide rubber and so on
.
In recent years, the modification of epoxy resins has continued to deepen, and the modification methods are changing with each passing day, such as interpenetrating network method, chemical copolymerization method, etc.
, especially liquid crystal toughening method and nanoparticle toughening method are the hotspots of research in recent years
.
With the establishment of the development model of "large scale, high purification, refinement, specialization, serialization, and functionalization", the research on the modification of epoxy resins is changing rapidly.
At present, it has become the focus of attention in the industry.
It will promote the development of epoxy resins in It has been applied more and more widely in economic construction and people's lives
.
1.
Extensive application of epoxy adhesives with excellent performance.
Gluing (adhesive, bonding, gluing, gluing) refers to the technology in which the surfaces of homogeneous or heterogeneous objects are connected together with adhesives, with continuous stress distribution adhesive cloth, Light weight, or airtight, low temperature in most processes
.
Gluing is particularly suitable for the connection of different materials, different thicknesses, ultra-thin specifications and complex components
.
Adhesive has the fastest development in the recent generations, has a wide range of applications, and has a significant impact on the progress of high-tech science and technology and the improvement of people's daily life
.
Therefore, research, development and production of various adhesives are very important
.
Epoxy resin adhesive (epoxy adhesive or epoxy adhesive for short) refers to a molecular structure that contains two or more epoxy groups and can form three-dimensional crosslinks under appropriate chemical reagents and appropriate conditions.
The general term for shaped curing compounds
.
Epoxy resin adhesive of epoxy resin, curing agents, plasticizers, accelerators, diluents, fillers, coupling agents, flame retardants, stabilizers consisting of liquid or solid adhesive
.
Among them, epoxy resin, curing agent, and toughening agent are indispensable components, and others are added or not according to needs
.
The bonding process of epoxy adhesives is a complex physical and chemical process, including steps such as infiltration, adhesion, and curing, and finally generates a cured product with a three-dimensional cross-linked structure, which combines the adherend into a whole
.
There are many types of epoxy adhesives.
Among all types of epoxy resins, bisphenol A epoxy resin is the one with the largest output and the most versatile
.
According to its molecular weight, it can be divided into low, medium, high, and ultra-high molecular weight epoxy resins (polyphenol oxygen resins)
.
Low-molecular-weight resins can be cured at room temperature or high temperature, but high-molecular-weight epoxy resins must be cured at high temperatures, while ultra-high molecular weight polyphenolic resins do not require curing agents and can form tough films at high temperatures.
.
With the successive advances of various adhesive theories, as well as the in-depth development of basic research work such as adhesive chemistry, adhesive rheology and adhesive failure mechanism, the properties, varieties and applications of adhesives have developed by leaps and bounds
.
Epoxy resins and their curing systems have also become an important class of adhesives with excellent performance, wide variety and wide adaptability due to their unique and excellent performance and the continuous emergence of new epoxy resins, new curing agents and additives
.
In recent years, high-strength lightweight fiber-reinforced composite materials have gradually been used in ultra-low temperature environments, and research on the ultra-low temperature properties of epoxy resins has also been strengthened
.
As the matrix material of composite liquid hydrogen storage tanks, and in the field of superconductivity as adhesives, impregnants and matrix materials of fiber-reinforced composite materials, China's research has made some progress
.
Pure epoxy resin has a high crosslinking density, even at room temperature, it also has shortcomings such as brittleness, low toughness, and poor impact resistance
.
As a composite material, the resin matrix generally needs to be cured at a very high temperature
.
During the cooling process after curing, thermal stress will be generated inside the heat shrinkable resin matrix.
When the temperature drops from room temperature to ultra-low temperature (below -150℃), the internal stress generated by heat shrinkage in the matrix will be more significant.
Stress exceeding the strength of the resin itself will cause the destruction of the resin matrix
.
Therefore, improving the toughness is very important for the use of epoxy resin at ultra-low temperature
.
At present, the method to improve the ultra-low temperature toughness of epoxy resin is mainly to use flexible aliphatic resin, liquid rubber and flexible curing agent to toughen epoxy resin
.
Because this kind of material has a low glass transition temperature and a large free volume at room temperature, when the temperature drops to an ultra-low temperature, the resin system will produce a large thermal shrinkage, resulting in greater thermal stress, which limits its use at ultra-low temperature.
Under the application
.
The blending modification of high-performance thermoplastics and epoxy resins at room temperature can make the blending system have the superior properties of both at the same time, that is, while maintaining the high modulus of thermosetting resins, it also has the high toughness of thermoplastics.
.
The bonding performance of the adhesive (strength, heat resistance, corrosion resistance, impermeability, etc.
) not only depends on its structure and performance, as well as the structure and adhesive properties of the surface of the adherend, but also on the joint design, the preparation of the adhesive and the adhesive The connection process is closely related and is also restricted by the surrounding environment
.
Therefore, the application of epoxy adhesive is a systematic project
.
The performance of the epoxy adhesive must be compatible with the above-mentioned factors that affect the bonding performance in order to obtain the best results
.
Using epoxy adhesives of the same formula to bond objects of different properties, or using different bonding conditions, or in different use environments, their performance will be greatly different, and full attention should be paid to them during application
.
Epoxy adhesives are mainly composed of epoxy resin and curing agent
.
In order to improve certain properties and meet different purposes, auxiliary materials such as toughening agents, diluents, accelerators, coupling agents and so on can also be added
.
Due to the high bonding strength and versatility of epoxy adhesives, it was once called "universal glue" and "strong glue".
It is used in aviation, aerospace, automobile, machinery, construction, chemical industry, light industry, electronics, electrical appliances and daily life.
It has been widely used in other fields
.
With the improvement of China's environmental protection regulations and the improvement of people's own health awareness, environmentally friendly epoxy adhesives with good quality, pollution-free and in line with international standards are gradually becoming the mainstream products of synthetic adhesives
.
2.
The molecular structure and category classification of epoxy adhesives Epoxy resin is a polymer compound with two or more epoxy groups in the molecule and a relatively low molecular weight.
1.
Classification of epoxy resins There are many brands, but bisphenol A glycidyl ether epoxy resin is usually called bisphenol A epoxy resin and is the most important category
.
It accounts for 90% of the total output of epoxy resin
.
Bisphenol A type epoxy resin Bisphenol A type epoxy resin is also called general type epoxy resin and standard type epoxy resin.
It is designated as type E epoxy resin in China.
It is composed of bisphenol (BPA or DPP) and epichlorohydrin.
(ECH) is obtained by polycondensation under sodium hydroxide: according to the ratio of raw materials, reaction conditions and methods used, viscous liquids with low molecular weight and high molecular weight and high softening point solids with different polymerization degrees can be prepared
.
The average relative molecular mass is 300～7000
.
Appearance is almost colorless or light yellow transparent viscous liquid or flake brittle solid
.
The epoxy resin itself is a thermoplastic linear polymer.
When heated, the viscosity of the liquid resin becomes low, and the solid resin softens or melts
.
It was dissolved in acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, benzene, toluene, xylene, ethanol, ethylene glycol and other organic solvents
.
Hydrogenated bisphenol A epoxy resin The chemical name of hydrogenated bisphenol A epoxy resin is hydrogenated bisphenol A diglycidyl ether, which is obtained by hydrogenating bisphenol A with hexahydrobisphenol A and epichlorohydrin.
It is obtained by polycondensation under sodium catalysis
.
It is an epoxy resin with very low viscosity, long gel time and good weather resistance
.
The chemical name of bisphenol F epoxy resin is bisphenol F diglycidyl ether, or DGEBF or BPF for short.
It is produced by the reaction of phenol and formaldehyde under an acidic catalyst to produce bisphenol F, which is then catalyzed by sodium hydroxide with epichlorohydrin.
Colorless or light yellow transparent viscous liquid prepared by polycondensation reaction; the chemical name of bisphenol S epoxy resin is bisphenol S dicondensed glycyrrhizin, abbreviated as BPS or KGEBS, which is composed of bisphenol S and epoxy Propane is prepared under the catalysis of sodium hydroxide.
Bisphenol S type epoxy resin has high heat resistance, heat distortion temperature is 60～700C higher than bisphenol A epoxy resin.
The cured product is stable and has good solvent resistance
.
Bisphenol P epoxy resin is prepared by synthesizing bisphenol P with 3-chloropropene and phenol as the main raw materials, and then polycondensing with epichlorohydrin under the catalysis of sodium hydroxide
.
Bisphenol P type epoxy resin has large molecular chain flexibility, good fluidity at low temperature, lower viscosity than bisphenol A epoxy resin, and higher compressive strength and impact strength than bisphenol A epoxy resin
.
Novolac epoxy resins mainly include phenol novolac epoxy resin and o-cresol novolac epoxy resin, as well as resorcinol novolac epoxy resin
.
In addition, tetraphenol ethane epoxy resin is also a novolac epoxy resin; phenol novolac epoxy resin (EPN) is a novolac resin obtained by polycondensation of phenol and formaldehyde in an acid medium, and then with excess A brownish-yellow viscous liquid or semi-solid prepared by polycondensation of epichlorohydrin in the presence of sodium hydroxide; ortho-cresol novolac epoxy resin is a linear ortho-cresol resin obtained by condensation of ortho-cresol and formaldehyde , And then react with epichlorohydrin in the presence of sodium hydroxide to obtain a yellow to amber solid after multi-step treatment; the chemical name of epoxy resorcinol formaldehyde resin is resorcinol formaldehyde tetraglycidyl ether , Is a tetrafunctional phenolic resin prepared by the reaction of resorcinol and formaldehyde with oxalic acid as a catalyst
.
It is an orange-yellow viscous liquid obtained by polycondensation with epichlorohydrin in the presence of sodium hydroxide; the chemical name of tetraphenol ethane epoxy resin is tetraphenol ethane glycidyl ether (PGEE), which is composed of phenol and ethyl The dialdehyde reacts in the presence of an acid catalyst to prepare tetraphenol ethane, and then reacts with epichlorohydrin under the catalysis of sodium hydroxide to prepare; naphthol novolac epoxy resin (EEPN) is a solution of a-naphthol and formaldehyde Polycondensation, synthesizing linear Cai phenolic resin, and then reacting with epichlorohydrin under the catalysis of sodium hydroxide to prepare; fluorinated epoxy resin has a dense molecular structure due to the introduction of fluorine atoms, and carbon and fluorine atoms are closely arranged in the main resin.
Around the chain
.
Therefore, the central tension, friction coefficient, and refractive index are very low, and it has excellent corrosion resistance, abrasion resistance, heat resistance, pollution resistance, and durability
.
But the high price cannot be used for general purposes
.
Polyurethane epoxy resin, also known as epoxy urethane resin, is made from polyester (or ether) polyol and epichlorohydrin under the action of BF3 and NaOH to generate polyol glycidyl ether and then to diisocyanate by polycondensation.
; Silicone epoxy resin is an epoxide containing silicon in its molecular structure, which is formed by the co-condensation of polymethylphenylsiloxane and epoxy resin
.
Toluene is a solution, light yellow uniform liquid; organic titanium epoxy resin is obtained by reacting the hydroxyl group in bisphenol A epoxy resin with n-butyl titanate
.
Because the metal element titanium is introduced into the resin, it not only solves the problems of increased water absorption, moisture resistance and reduced electrical properties caused by the presence of hydroxyl groups, but also because of the oxygen atoms with P electrons and the titanium atoms with D electron vacancies in the resin.
The direct connection leads to the PD conjugation effect in the macromolecular chain, which significantly improves the heat aging performance and better dielectric properties
.
The appearance is yellow to amber high viscosity transparent liquid
.
With the continuous development of high technology and technology
.
In recent years, the modification of epoxy resins has continued to deepen, and methods such as interpenetrating networks, chemical copolymerization and nanoparticle toughening have been widely used, and various high-performance adhesives prepared from epoxy resins have also been increasing
.
There are many types of epoxy resin adhesives, and their classification methods and classification indicators have not yet been unified
.
Usually classified according to the following methods
.
Classified according to the form of adhesives: such as solvent-free adhesives, (organic) solvent-based adhesives, water-based adhesives (which can be divided into water-emulsion type and water-soluble type), paste-like adhesives, film-like adhesives (epoxy adhesive film), etc.
.
Classified according to curing conditions: cold curing adhesive (non-heat curing adhesive)
.
It can be divided into low-temperature curing adhesives, curing temperature <15℃; room-temperature curing adhesives, curing temperature 15-40℃; heat curing adhesives can be divided into: medium-temperature curing adhesives, curing temperature about 80-120℃; high-temperature curing adhesives, curing temperature > 150 ℃; otherwise curable adhesive, such as a light-curing adhesive, moisture curable adhesive and the water surface, the latent curing adhesive and the like
.
Classified by bonding strength: The structural adhesive has high shear and tensile strength, and should also have a higher uneven pull-off strength, so that the bonded joint can withstand vibration, fatigue and impact for a long time
.
At the same time, it should also have high heat resistance and weather resistance; secondary stress structural adhesives can withstand medium loads, usually with a shear strength of 17-25Mpa, and uneven pull-off strength of 20-50kN/m; non-structural adhesives, that is, general-purpose Adhesive
.
The room temperature strength is still relatively high, but as the temperature increases, the bonding strength decreases faster
.
It can only be used on parts with little force
.
Classified by purpose: general-purpose adhesives, special adhesives, such as high temperature resistant adhesives (use temperature ≥150°C), low temperature resistant adhesives (resistant to temperatures of -50°C or lower), strain adhesives (for attaching strain gauges), conductive adhesives , sealant (vacuum sealing, mechanical seals), optical adhesive (colorless and transparent, light aging, refractive index and optical component matches), corrosion-resistant plastic, such as plastic structures
.
It can also be classified according to the type of curing agent, such as amine curing epoxy adhesive, acid anhydride curing adhesive and so on
.
It can also be divided into two-component glue and one-component glue, pure epoxy glue and modified epoxy glue
.
3.
The performance characteristics of epoxy adhesives.
Generally, the epoxy resin structure contains hydroxyl and ether bonds to make it have high adhesion.
Because of these polar groups, it can generate electromagnetic force at the adjacent interface, and there is less curing process.
, Accompanied by the chemical action of the curing agent, it can further generate the meridian and ether bond, which not only has higher cohesion, but also produces strong adhesion.
Therefore, epoxy adhesives are suitable for many kinds of materials such as metal, plastic, glass, Wood, fiber, etc.
have strong bonding strength, commonly known as "universal glue"
.
The molecules of epoxy resin are tightly arranged, and low-molecular substances are not precipitated during the curing process, and it can be formulated into a solvent-free adhesive, so its shrinkage rate is generally relatively low
.
If proper fillers are selected, the shrinkage rate can be reduced to 0.
1-0.
2%
.
Epoxy resin refers to the existence of stable benzene ring, ether chain and compact structure after curing, which determines that the epoxy adhesive has strong resistance to the effects of the atmosphere, humidity, chemical media, bacteria, etc.
, so it can be used in many In a more demanding environment
.
Epoxy adhesives have high bonding strength and high bonding strength; small shrinkage and stable dimensions.
The epoxy resin hardly emits low-molecular products during curing.
The coefficient of linear expansion is less affected by temperature, so the dimensional stability of the adhesive is good; the cured product of epoxy resin has excellent electrical insulation properties, with a volume resistivity of 1013～1016Ω.
cm and a dielectric strength of 30～50KV .
Mm-1 epoxy resin contains ether bonds in the molecule, and the molecular chains are closely arranged, and the cross-linking density is high, so it has good solvent resistance, oil resistance, acid resistance, alkali resistance, water resistance, etc.
, especially strong alkali resistance ;Epoxy resin has good compatibility with many rubbers (elastomers) and thermoplastic resins, and even chemical reactions; good dispersibility with fillers, can change the properties of epoxy resin in a wide range; good manufacturability, easy to use , Low toxicity, low hazard; resin contains many benzene rings and heterocycles, the molecular chain is less flexible, and the cross-linked structure after curing is not suitable for deformation.
Untoughened epoxy resin has poor toughness and greater brittleness , The peel strength is very low, and it is not resistant to shock and vibration
.
Epoxy resin contains a variety of polar groups and highly active epoxy groups, so it has a strong bond with a variety of polar materials such as metal, glass, cement, wood, plastics, etc.
, especially materials with high surface activity.
At the same time, the cohesive strength of the epoxy cured product is also very high, so its bonding strength is very high
.
Basically no low molecular volatiles are produced when the epoxy resin is cured
.
The volume shrinkage rate of the adhesive layer is small, about 1% to 2%, which is one of the varieties with the smallest curing shrinkage rate among thermosetting resins
.
After adding filler, it can be reduced to less than 0.
2%
.
The coefficient of linear expansion of the cured epoxy is also very small
.
Therefore, the internal stress is small, and the impact on the bonding strength is small
.
In addition, the creep of the epoxy cured product is small, so the dimensional stability of the adhesive layer is good
.
There are many varieties of epoxy resins, curing agents and modifiers, and reasonable and ingenious formulations can be used to make the adhesive have the required manufacturability (such as fast curing, room temperature curing, low temperature curing, water curing, low viscosity, high viscosity Etc.
), and have the required performance (such as high temperature resistance, low temperature resistance, high strength, high flexibility, aging resistance, electrical conductivity, magnetic conductivity, heat conduction, etc.
)
.
It has good compatibility and reactivity with a variety of organic substances (monomers, resins, rubber) and inorganic substances (such as fillers, etc.
), and is easy to be modified by copolymerization, crosslinking, blending, filling, etc.
to improve the adhesive layer Performance
.
It can withstand the corrosion of acid, alkali, salt, solvent and other media
.
Depending on the type of curing agent used, epoxy adhesives can be cured at room temperature, medium temperature or high temperature
.
Generally, only 0.
1-0.
5MPa contact pressure is required during curing.
Most epoxy resin screed agents do not contain solvents and are easy to operate
.
The construction viscosity of general epoxy glue
.
The application period and curing speed can be adjusted by formula to meet various requirements
.
This not only makes it easy to ensure the bonding quality, but also simplifies the curing process and equipment
.
After the epoxy resin is cured, good electrical insulation properties can be obtained; breakdown voltage>35kV/mm volume resistance>1015Ω·cm, dielectric constant 3～4 (50Hz), arc resistance 100～140s
.
Epoxy resin adhesive changes its composition (curing agent, toughening agent, filler, etc.
), and a series of adhesive formulations with different properties can be obtained to meet various needs, and it can be mixed with many modifiers to produce various properties.
Variety
.
Generally, the use temperature of bisphenol A epoxy resin ranges from -60 to 175°C and sometimes reaches 200°C in a short time.
If a new type of epoxy resin resistant to high and low temperatures is used, the use temperature can be higher or lower, and the epoxy resin The water absorption is small
.
General-purpose epoxy resins, curing agents and additives are produced in many places, large in output, easy to prepare, can be contacted and molded, and can be applied on a large scale
.
The main disadvantages of epoxy adhesives: when it is not toughened, the cured product is generally brittle, has poor peel resistance, crack resistance, and impact resistance; it has low adhesion to materials with low polarity (such as polyethylene, polypropylene, etc.
)
.
Surface activation treatment must be carried out first; some raw materials such as reactive diluents and curing agents have varying degrees of toxicity and irritation
.
When designing the formula, it should be avoided as much as possible, and ventilation protection should be strengthened during construction
.
It can be seen from the above that epoxy resin has good comprehensive mechanical properties, especially high adhesion, small shrinkage, good stability, and excellent electrical insulation properties.
It is used as an adhesive, composite material matrix, and powder coating.
And other products provide the material basis
.
4.
Progress in epoxy adhesive application technology.
Heat-resistant epoxy resin adhesive is an adhesive prepared from modified epoxy resin.
It can be used intermittently at 250°C, or even long-term use at 400°C, and short-term use at 460°C.
Use
.
The matrix resin of this adhesive generally introduces more rigid groups or increases the crosslinking density of the cured product
.
For example, epoxy resin with fluorene group, naphthalene ring and multifunctional epoxy resin, or epoxy resin adhesive modified by maleimide and silicone can reach the requirements of short-term high temperature resistance and high strength at 460℃.
.
In recent years, with the development of electronic appliances and aerospace industries, the requirements for high temperature resistance and ablation resistance have become higher and higher
.
When the aircraft is flying at high speed in the atmosphere, sometimes the temperature can reach thousands of degrees due to aerodynamic heating, and even the most heat-resistant metal materials have to be melted
.
Therefore, in order to reduce weight, high temperature resistant composite materials are generally used to replace metal materials
.
Even in the electronics and electrical industries, sealants that can withstand high temperatures of 350°C have been proposed, and even flame-resistant insulating adhesives that can withstand 500-1000°C have been proposed
.
The F series epoxy curing agent developed by China National Aviation Corporation and the newly developed B, H, HE series epoxy curing agent can make the epoxy resin resistant to high temperature of 500 ℃, and have excellent flame retardant performance and burning resistance.
Corrosion performance and good process performance
.
Modified epoxy resin adhesive and its preparation method overcome the shortcomings of general epoxy adhesives' brittleness and poor temperature resistance.
Its main technical feature is polyurethane prepolymer modified epoxy resin (component A) and homemade curing agent (Component B) According to the ratio of 10:1 to 1:1 (weight ratio), it is formulated into a curing system with high temperature resistance, good toughness and high reactivity
.
Among them, the polyurethane prepolymer is a hydroxy-terminated polysiloxane and a diisocyanate reacted in a certain proportion under certain conditions to form an isocyanate group-terminated polysiloxane polyurethane prepolymer, and then this polyurethane prepolymer is used for epoxy resin Carry out modification treatment
.
The self-made curing agent is composed of diamine, imidazole compound, silane coupling agent, inorganic filler and catalyst
.
This modified epoxy resin adhesive can be cured at room temperature, can be used for a long time at 200 ℃, or cured at -5 ℃ and can be cured at 150 ℃; the bonding strength can reach 15-30Mpa; the T-type peeling strength can reach 35-65N/cm, which is excellent of oil, water, acid, alkali, organic solvent resistance performance, wet surface adhesion, oil and metal, plastic, ceramic, hard rubber, wood and the like
.
To increase the strength of the epoxy resin, the resin is generally toughened by adding a second component to improve the toughness of the epoxy resin
.
According to reports, the main liquid toughening, toughening, toughening elastic microspheres, thermotropic liquid crystal (of TLCP) toughened and polymer blends, and the like copolymerization
.
The toughening modification of liquid rubber generally refers to liquid nitrile rubber, poly, etc.
containing terminal carboxyl groups, amine groups, hydroxyl groups, thiol groups, and epoxy groups, which are miscible with epoxy resin and precipitate during the curing process to form " The two-phase structure of the "sea-island model" has a toughening effect by forming chemical bonds on the two-phase interface through the interaction of active groups
.
In recent years, in addition to the use of purely active liquid rubber pre-reaction adducts, it has been developed to the second generation using high-functionality epoxy resin and the third generation using metallocene catalysts to prepare block copolymer modified epoxy prepolymers.
After this modification, not only the peel strength is improved, but the overall mechanical and thermal properties are not significantly reduced
.
Polyurethane toughened epoxy adhesive is formed by polyurethane and epoxy resin to form semi-vertical penetrating network polymer (SIPN) and interpenetrating network polymer (IPN), which play a forced mutual solubility and synergistic effect, so that high elastic polyurethane and good adhesion The epoxy resins are organically combined together to achieve a good toughening effect through complementation and reinforcement
.
One-component room temperature moisture curing epoxy adhesive is an epoxy adhesive cured with modified ketimine as a curing agent.
Its characteristics are that it can be cured under humid and low temperature conditions and can improve the resistance of the cured epoxy resin.
Temperature and corrosion resistance
.
Phenolic modified ketimine curing agent, which firstly reacts with formaldehyde, m-phenylenediamine to produce phenalkamine, and then reacts with methyl isobutyl ketone to produce phenolic modified ketimine
.
At present, domestic efforts are being made to study the fast curing technology of fast curing epoxy adhesive under low temperature and low humidity
.
At present, the two-component room temperature curing epoxy adhesive developed in China can withstand 200-260 ℃ temperature, up to 275 ℃, and it can be gelled in 2-6 minutes at 25 ℃.
It can be completely cured for 3-8 hours.
Polyether diamine is cured.
The peel strength can reach 4～5kN/m
.
Low-temperature fast-curing epoxy adhesive is made of bisphenol F epoxy resin.
It is combined with diphenyl decyl phosphite, DMP-30, etc.
, and can be cured quickly at -5°C.
It has been developed and applied Civil engineering field
.
Mainly used for concrete "overall project" bonding, building up, repair and supplies products such as adhesive
.
In construction projects, it can replace rivets, welding and other structural connection techniques, and is used to bond various, marble and artificial boards
.
The high-strength composite repair technology is the development trend of the future oil and gas pipeline external anti-corrosion coating repair technology.
It is a technology that forms a protective structure with high-performance resin matrix bonding and reinforcing materials, so it has high compressive and tensile strength And cohesion
.
During the repair construction, there is no need for pipeline shutdown or decompression operation.
At the same time, it has the advantages of simple and convenient operation, easy training of construction personnel, good reinforcement effect and significant economic benefits
.
Composite material repair technology can carry out on-site winding construction and on-site curing, and the construction process is open flame, safe and convenient
.
Thirdly, the strength of composite materials reinforced by glass fiber, carbon fiber or fabric far exceeds that of ordinary steel, making composite materials more efficient in repair and reinforcement; composite materials are designable, and thickness and layer can be adjusted according to the degree of defect damage and stress.
Targeted design in terms of number, fiber distribution, etc.
, and its repair reliability is high; the interlayer adhesive of glass fiber or carbon fiber reinforced resin-based composite material has good interfacial adhesion, airtightness and excellent corrosion resistance.
, Which can greatly reduce the secondary corrosion damage during the pipeline operation period
.
In composite repair technology, the choice of adhesive has a crucial impact on its protective performance
.
When the epoxy resin adhesive is toughened and modified by polyurethane, the polyurethane segment penetrates into the epoxy resin segment to form an interpenetrating polymer network structure (IPN) or a semi-interpenetrating polymer network structure (SIPN)
.
Because of the different solubility of polyurethane and epoxy resin, IPN materials show different degrees of phase separation, but due to the entanglement of the networks, "forced mutual dissolution" occurs, which increases compatibility; and once the polymers are crosslinked, they become entangled with each other.
The network fixes the phase zone.
Because the polyurethane particles are dispersed in the continuous epoxy resin phase, the toughness of the system is increased, the stress concentration of the cured product is dispersed, and the shear strength is increased
.
With the increase of polyurethane addition, the shear strength gradually increases, but when the polyurethane content exceeds 13.
04%, the degree of interpenetration of the interpenetrating polymer network structure formed by polyurethane/epoxy resin has reached saturation
.
If the amount of polyurethane is further increased, the interpenetrating polymer network will have a degree of interpenetration, the polyurethane and the epoxy resin will be separated to form cracks, and the compatibility of the polyurethane and the epoxy resin will drop sharply
.
Therefore, in terms of shear strength, the optimal amount of polyurethane is 13.
04%
.
The peel strength is mainly related to the bonding performance and flexibility of the epoxy resin adhesive.
The change law of the interpenetrating polymer network structure formed by polyurethane and epoxy resin shows that with the increase of the amount of polyurethane added, the flexibility of the cured product The properties of epoxy resin adhesives increase first and then decrease, so the peel strength of epoxy resin adhesives will increase first and then decrease with the increase of the amount of polyurethane added
.
When the polyurethane reaches 20%, the peel strength begins to decrease as the amount of polyurethane added increases
.
Therefore, for peel strength, the optimal amount of polyurethane is 20%
.
Among many epoxy resin toughening technologies, the toughening effect of elastomers represented by polyurethane is the most significant
.
However, epoxy resin is a linear thermoplastic resin and will not harden itself.
Only by adding a curing agent to make it cross-linked from a linear structure into a network or body structure can it be cured
.
Therefore, while using polyurethane to toughen the epoxy resin, it is necessary to add a curing agent to meet the requirements for curing performance during construction
.
The epoxy resin contains multiple benzene rings or heterocyclic rings, and the molecular chain is less flexible.
The cured epoxy resin has a high cross-linked structure, and the cross-linked structure is not easy to deform, resulting in insufficient toughness and brittle cracks in epoxy resin adhesives.
, Low peel strength and poor impact resistance, so its application is greatly restricted.
Therefore, the toughening modification of epoxy resin has important practical significance and application prospects for its application in pipeline repair
.
In practice, an adhesive that can be cured at room temperature and used in a high temperature environment is often needed
.
For example, structural adhesives used in construction are not only required to be able to withstand high temperatures to prevent the building from collapsing in a fire, but also cannot be cured by heating because of the large bonding area
.
However, room temperature curing EP adhesives generally cannot be used at high temperatures, and heat-resistant EP adhesives often require heating to be fully cured
.
The so-called room temperature curing usually refers to a curing method that can gel within a few minutes or a few hours at room temperature (20-30°C), and fully cure within 7 days, and achieve usable strength
.
Although room temperature curing and high temperature adhesives have made some progress, there is still a long way to go.
In the future, research on the curing mechanism of EP adhesives should be strengthened, and multifunctional active curing agents should be developed; new multifunctional EPs should be synthesized.
Base resin, explore new modification methods and new fillers of EP resin; on the basis of improving performance, make the research and development of adhesives develop in a resource-saving and environment-friendly direction
.
5.
Concluding remarks Epoxy resin adhesives have excellent bonding properties and chemical stability, so they are widely used.
The development of modern industry requires EP adhesives to have the ability to cure at room temperature and withstand high temperatures.
.
Epoxy resin adhesive has a wide range of base materials and is suitable for bonding a variety of substrates.
It has the characteristics of high strength, low curing shrinkage, corrosion resistance, thermal stability and good electrical insulation performance.
It also has simple construction techniques, high work efficiency, and energy The advantages of low consumption and low cost can greatly reduce labor intensity, save labor costs, and have huge market potential and broad application prospects
.
.
The resin macromolecules have epoxy groups at the end, hydroxyl and ether bonds between the chains, and will continue to produce hydroxyl and ether bonds during the curing process.
The structure contains benzene rings and heterocyclic rings.
These structures determine the excellent performance of epoxy resin adhesives.
Performance
.
Epoxy resin adhesive is an adhesive that has a long history of use and is extremely versatile
.
Due to its strength, diversity and excellent adhesion to a variety of bonded surfaces, epoxy resin adhesives have been widely recognized by users
.
They have participated in and accelerated the technological revolution in certain industrial sectors
.
Epoxy resin can be used to bond metals, glass, ceramics, many plastics, wood, concrete and other surfaces
.
In the epoxy resin produced in the United States, more than 10% is used as an adhesive
.
In the past, people's modification of epoxy resin has been limited to rubber, such as carboxyl-terminated nitrile rubber, hydroxy-terminated nitrile rubber, polysulfide rubber and so on
.
In recent years, the modification of epoxy resins has continued to deepen, and the modification methods are changing with each passing day, such as interpenetrating network method, chemical copolymerization method, etc.
, especially liquid crystal toughening method and nanoparticle toughening method are the hotspots of research in recent years
.
With the establishment of the development model of "large scale, high purification, refinement, specialization, serialization, and functionalization", the research on the modification of epoxy resins is changing rapidly.
At present, it has become the focus of attention in the industry.
It will promote the development of epoxy resins in It has been applied more and more widely in economic construction and people's lives
.
1.
Extensive application of epoxy adhesives with excellent performance.
Gluing (adhesive, bonding, gluing, gluing) refers to the technology in which the surfaces of homogeneous or heterogeneous objects are connected together with adhesives, with continuous stress distribution adhesive cloth, Light weight, or airtight, low temperature in most processes
.
Gluing is particularly suitable for the connection of different materials, different thicknesses, ultra-thin specifications and complex components
.
Adhesive has the fastest development in the recent generations, has a wide range of applications, and has a significant impact on the progress of high-tech science and technology and the improvement of people's daily life
.
Therefore, research, development and production of various adhesives are very important
.
Epoxy resin adhesive (epoxy adhesive or epoxy adhesive for short) refers to a molecular structure that contains two or more epoxy groups and can form three-dimensional crosslinks under appropriate chemical reagents and appropriate conditions.
The general term for shaped curing compounds
.
Epoxy resin adhesive of epoxy resin, curing agents, plasticizers, accelerators, diluents, fillers, coupling agents, flame retardants, stabilizers consisting of liquid or solid adhesive
.
Among them, epoxy resin, curing agent, and toughening agent are indispensable components, and others are added or not according to needs
.
The bonding process of epoxy adhesives is a complex physical and chemical process, including steps such as infiltration, adhesion, and curing, and finally generates a cured product with a three-dimensional cross-linked structure, which combines the adherend into a whole
.
There are many types of epoxy adhesives.
Among all types of epoxy resins, bisphenol A epoxy resin is the one with the largest output and the most versatile
.
According to its molecular weight, it can be divided into low, medium, high, and ultra-high molecular weight epoxy resins (polyphenol oxygen resins)
.
Low-molecular-weight resins can be cured at room temperature or high temperature, but high-molecular-weight epoxy resins must be cured at high temperatures, while ultra-high molecular weight polyphenolic resins do not require curing agents and can form tough films at high temperatures.
.
With the successive advances of various adhesive theories, as well as the in-depth development of basic research work such as adhesive chemistry, adhesive rheology and adhesive failure mechanism, the properties, varieties and applications of adhesives have developed by leaps and bounds
.
Epoxy resins and their curing systems have also become an important class of adhesives with excellent performance, wide variety and wide adaptability due to their unique and excellent performance and the continuous emergence of new epoxy resins, new curing agents and additives
.
In recent years, high-strength lightweight fiber-reinforced composite materials have gradually been used in ultra-low temperature environments, and research on the ultra-low temperature properties of epoxy resins has also been strengthened
.
As the matrix material of composite liquid hydrogen storage tanks, and in the field of superconductivity as adhesives, impregnants and matrix materials of fiber-reinforced composite materials, China's research has made some progress
.
Pure epoxy resin has a high crosslinking density, even at room temperature, it also has shortcomings such as brittleness, low toughness, and poor impact resistance
.
As a composite material, the resin matrix generally needs to be cured at a very high temperature
.
During the cooling process after curing, thermal stress will be generated inside the heat shrinkable resin matrix.
When the temperature drops from room temperature to ultra-low temperature (below -150℃), the internal stress generated by heat shrinkage in the matrix will be more significant.
Stress exceeding the strength of the resin itself will cause the destruction of the resin matrix
.
Therefore, improving the toughness is very important for the use of epoxy resin at ultra-low temperature
.
At present, the method to improve the ultra-low temperature toughness of epoxy resin is mainly to use flexible aliphatic resin, liquid rubber and flexible curing agent to toughen epoxy resin
.
Because this kind of material has a low glass transition temperature and a large free volume at room temperature, when the temperature drops to an ultra-low temperature, the resin system will produce a large thermal shrinkage, resulting in greater thermal stress, which limits its use at ultra-low temperature.
Under the application
.
The blending modification of high-performance thermoplastics and epoxy resins at room temperature can make the blending system have the superior properties of both at the same time, that is, while maintaining the high modulus of thermosetting resins, it also has the high toughness of thermoplastics.
.
The bonding performance of the adhesive (strength, heat resistance, corrosion resistance, impermeability, etc.
) not only depends on its structure and performance, as well as the structure and adhesive properties of the surface of the adherend, but also on the joint design, the preparation of the adhesive and the adhesive The connection process is closely related and is also restricted by the surrounding environment
.
Therefore, the application of epoxy adhesive is a systematic project
.
The performance of the epoxy adhesive must be compatible with the above-mentioned factors that affect the bonding performance in order to obtain the best results
.
Using epoxy adhesives of the same formula to bond objects of different properties, or using different bonding conditions, or in different use environments, their performance will be greatly different, and full attention should be paid to them during application
.
Epoxy adhesives are mainly composed of epoxy resin and curing agent
.
In order to improve certain properties and meet different purposes, auxiliary materials such as toughening agents, diluents, accelerators, coupling agents and so on can also be added
.
Due to the high bonding strength and versatility of epoxy adhesives, it was once called "universal glue" and "strong glue".
It is used in aviation, aerospace, automobile, machinery, construction, chemical industry, light industry, electronics, electrical appliances and daily life.
It has been widely used in other fields
.
With the improvement of China's environmental protection regulations and the improvement of people's own health awareness, environmentally friendly epoxy adhesives with good quality, pollution-free and in line with international standards are gradually becoming the mainstream products of synthetic adhesives
.
2.
The molecular structure and category classification of epoxy adhesives Epoxy resin is a polymer compound with two or more epoxy groups in the molecule and a relatively low molecular weight.
1.
Classification of epoxy resins There are many brands, but bisphenol A glycidyl ether epoxy resin is usually called bisphenol A epoxy resin and is the most important category
.
It accounts for 90% of the total output of epoxy resin
.
Bisphenol A type epoxy resin Bisphenol A type epoxy resin is also called general type epoxy resin and standard type epoxy resin.
It is designated as type E epoxy resin in China.
It is composed of bisphenol (BPA or DPP) and epichlorohydrin.
(ECH) is obtained by polycondensation under sodium hydroxide: according to the ratio of raw materials, reaction conditions and methods used, viscous liquids with low molecular weight and high molecular weight and high softening point solids with different polymerization degrees can be prepared
.
The average relative molecular mass is 300～7000
.
Appearance is almost colorless or light yellow transparent viscous liquid or flake brittle solid
.
The epoxy resin itself is a thermoplastic linear polymer.
When heated, the viscosity of the liquid resin becomes low, and the solid resin softens or melts
.
It was dissolved in acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, benzene, toluene, xylene, ethanol, ethylene glycol and other organic solvents
.
Hydrogenated bisphenol A epoxy resin The chemical name of hydrogenated bisphenol A epoxy resin is hydrogenated bisphenol A diglycidyl ether, which is obtained by hydrogenating bisphenol A with hexahydrobisphenol A and epichlorohydrin.
It is obtained by polycondensation under sodium catalysis
.
It is an epoxy resin with very low viscosity, long gel time and good weather resistance
.
The chemical name of bisphenol F epoxy resin is bisphenol F diglycidyl ether, or DGEBF or BPF for short.
It is produced by the reaction of phenol and formaldehyde under an acidic catalyst to produce bisphenol F, which is then catalyzed by sodium hydroxide with epichlorohydrin.
Colorless or light yellow transparent viscous liquid prepared by polycondensation reaction; the chemical name of bisphenol S epoxy resin is bisphenol S dicondensed glycyrrhizin, abbreviated as BPS or KGEBS, which is composed of bisphenol S and epoxy Propane is prepared under the catalysis of sodium hydroxide.
Bisphenol S type epoxy resin has high heat resistance, heat distortion temperature is 60～700C higher than bisphenol A epoxy resin.
The cured product is stable and has good solvent resistance
.
Bisphenol P epoxy resin is prepared by synthesizing bisphenol P with 3-chloropropene and phenol as the main raw materials, and then polycondensing with epichlorohydrin under the catalysis of sodium hydroxide
.
Bisphenol P type epoxy resin has large molecular chain flexibility, good fluidity at low temperature, lower viscosity than bisphenol A epoxy resin, and higher compressive strength and impact strength than bisphenol A epoxy resin
.
Novolac epoxy resins mainly include phenol novolac epoxy resin and o-cresol novolac epoxy resin, as well as resorcinol novolac epoxy resin
.
In addition, tetraphenol ethane epoxy resin is also a novolac epoxy resin; phenol novolac epoxy resin (EPN) is a novolac resin obtained by polycondensation of phenol and formaldehyde in an acid medium, and then with excess A brownish-yellow viscous liquid or semi-solid prepared by polycondensation of epichlorohydrin in the presence of sodium hydroxide; ortho-cresol novolac epoxy resin is a linear ortho-cresol resin obtained by condensation of ortho-cresol and formaldehyde , And then react with epichlorohydrin in the presence of sodium hydroxide to obtain a yellow to amber solid after multi-step treatment; the chemical name of epoxy resorcinol formaldehyde resin is resorcinol formaldehyde tetraglycidyl ether , Is a tetrafunctional phenolic resin prepared by the reaction of resorcinol and formaldehyde with oxalic acid as a catalyst
.
It is an orange-yellow viscous liquid obtained by polycondensation with epichlorohydrin in the presence of sodium hydroxide; the chemical name of tetraphenol ethane epoxy resin is tetraphenol ethane glycidyl ether (PGEE), which is composed of phenol and ethyl The dialdehyde reacts in the presence of an acid catalyst to prepare tetraphenol ethane, and then reacts with epichlorohydrin under the catalysis of sodium hydroxide to prepare; naphthol novolac epoxy resin (EEPN) is a solution of a-naphthol and formaldehyde Polycondensation, synthesizing linear Cai phenolic resin, and then reacting with epichlorohydrin under the catalysis of sodium hydroxide to prepare; fluorinated epoxy resin has a dense molecular structure due to the introduction of fluorine atoms, and carbon and fluorine atoms are closely arranged in the main resin.
Around the chain
.
Therefore, the central tension, friction coefficient, and refractive index are very low, and it has excellent corrosion resistance, abrasion resistance, heat resistance, pollution resistance, and durability
.
But the high price cannot be used for general purposes
.
Polyurethane epoxy resin, also known as epoxy urethane resin, is made from polyester (or ether) polyol and epichlorohydrin under the action of BF3 and NaOH to generate polyol glycidyl ether and then to diisocyanate by polycondensation.
; Silicone epoxy resin is an epoxide containing silicon in its molecular structure, which is formed by the co-condensation of polymethylphenylsiloxane and epoxy resin
.
Toluene is a solution, light yellow uniform liquid; organic titanium epoxy resin is obtained by reacting the hydroxyl group in bisphenol A epoxy resin with n-butyl titanate
.
Because the metal element titanium is introduced into the resin, it not only solves the problems of increased water absorption, moisture resistance and reduced electrical properties caused by the presence of hydroxyl groups, but also because of the oxygen atoms with P electrons and the titanium atoms with D electron vacancies in the resin.
The direct connection leads to the PD conjugation effect in the macromolecular chain, which significantly improves the heat aging performance and better dielectric properties
.
The appearance is yellow to amber high viscosity transparent liquid
.
With the continuous development of high technology and technology
.
In recent years, the modification of epoxy resins has continued to deepen, and methods such as interpenetrating networks, chemical copolymerization and nanoparticle toughening have been widely used, and various high-performance adhesives prepared from epoxy resins have also been increasing
.
There are many types of epoxy resin adhesives, and their classification methods and classification indicators have not yet been unified
.
Usually classified according to the following methods
.
Classified according to the form of adhesives: such as solvent-free adhesives, (organic) solvent-based adhesives, water-based adhesives (which can be divided into water-emulsion type and water-soluble type), paste-like adhesives, film-like adhesives (epoxy adhesive film), etc.
.
Classified according to curing conditions: cold curing adhesive (non-heat curing adhesive)
.
It can be divided into low-temperature curing adhesives, curing temperature <15℃; room-temperature curing adhesives, curing temperature 15-40℃; heat curing adhesives can be divided into: medium-temperature curing adhesives, curing temperature about 80-120℃; high-temperature curing adhesives, curing temperature > 150 ℃; otherwise curable adhesive, such as a light-curing adhesive, moisture curable adhesive and the water surface, the latent curing adhesive and the like
.
Classified by bonding strength: The structural adhesive has high shear and tensile strength, and should also have a higher uneven pull-off strength, so that the bonded joint can withstand vibration, fatigue and impact for a long time
.
At the same time, it should also have high heat resistance and weather resistance; secondary stress structural adhesives can withstand medium loads, usually with a shear strength of 17-25Mpa, and uneven pull-off strength of 20-50kN/m; non-structural adhesives, that is, general-purpose Adhesive
.
The room temperature strength is still relatively high, but as the temperature increases, the bonding strength decreases faster
.
It can only be used on parts with little force
.
Classified by purpose: general-purpose adhesives, special adhesives, such as high temperature resistant adhesives (use temperature ≥150°C), low temperature resistant adhesives (resistant to temperatures of -50°C or lower), strain adhesives (for attaching strain gauges), conductive adhesives , sealant (vacuum sealing, mechanical seals), optical adhesive (colorless and transparent, light aging, refractive index and optical component matches), corrosion-resistant plastic, such as plastic structures
.
It can also be classified according to the type of curing agent, such as amine curing epoxy adhesive, acid anhydride curing adhesive and so on
.
It can also be divided into two-component glue and one-component glue, pure epoxy glue and modified epoxy glue
.
3.
The performance characteristics of epoxy adhesives.
Generally, the epoxy resin structure contains hydroxyl and ether bonds to make it have high adhesion.
Because of these polar groups, it can generate electromagnetic force at the adjacent interface, and there is less curing process.
, Accompanied by the chemical action of the curing agent, it can further generate the meridian and ether bond, which not only has higher cohesion, but also produces strong adhesion.
Therefore, epoxy adhesives are suitable for many kinds of materials such as metal, plastic, glass, Wood, fiber, etc.
have strong bonding strength, commonly known as "universal glue"
.
The molecules of epoxy resin are tightly arranged, and low-molecular substances are not precipitated during the curing process, and it can be formulated into a solvent-free adhesive, so its shrinkage rate is generally relatively low
.
If proper fillers are selected, the shrinkage rate can be reduced to 0.
1-0.
2%
.
Epoxy resin refers to the existence of stable benzene ring, ether chain and compact structure after curing, which determines that the epoxy adhesive has strong resistance to the effects of the atmosphere, humidity, chemical media, bacteria, etc.
, so it can be used in many In a more demanding environment
.
Epoxy adhesives have high bonding strength and high bonding strength; small shrinkage and stable dimensions.
The epoxy resin hardly emits low-molecular products during curing.
The coefficient of linear expansion is less affected by temperature, so the dimensional stability of the adhesive is good; the cured product of epoxy resin has excellent electrical insulation properties, with a volume resistivity of 1013～1016Ω.
cm and a dielectric strength of 30～50KV .
Mm-1 epoxy resin contains ether bonds in the molecule, and the molecular chains are closely arranged, and the cross-linking density is high, so it has good solvent resistance, oil resistance, acid resistance, alkali resistance, water resistance, etc.
, especially strong alkali resistance ;Epoxy resin has good compatibility with many rubbers (elastomers) and thermoplastic resins, and even chemical reactions; good dispersibility with fillers, can change the properties of epoxy resin in a wide range; good manufacturability, easy to use , Low toxicity, low hazard; resin contains many benzene rings and heterocycles, the molecular chain is less flexible, and the cross-linked structure after curing is not suitable for deformation.
Untoughened epoxy resin has poor toughness and greater brittleness , The peel strength is very low, and it is not resistant to shock and vibration
.
Epoxy resin contains a variety of polar groups and highly active epoxy groups, so it has a strong bond with a variety of polar materials such as metal, glass, cement, wood, plastics, etc.
, especially materials with high surface activity.
At the same time, the cohesive strength of the epoxy cured product is also very high, so its bonding strength is very high
.
Basically no low molecular volatiles are produced when the epoxy resin is cured
.
The volume shrinkage rate of the adhesive layer is small, about 1% to 2%, which is one of the varieties with the smallest curing shrinkage rate among thermosetting resins
.
After adding filler, it can be reduced to less than 0.
2%
.
The coefficient of linear expansion of the cured epoxy is also very small
.
Therefore, the internal stress is small, and the impact on the bonding strength is small
.
In addition, the creep of the epoxy cured product is small, so the dimensional stability of the adhesive layer is good
.
There are many varieties of epoxy resins, curing agents and modifiers, and reasonable and ingenious formulations can be used to make the adhesive have the required manufacturability (such as fast curing, room temperature curing, low temperature curing, water curing, low viscosity, high viscosity Etc.
), and have the required performance (such as high temperature resistance, low temperature resistance, high strength, high flexibility, aging resistance, electrical conductivity, magnetic conductivity, heat conduction, etc.
)
.
It has good compatibility and reactivity with a variety of organic substances (monomers, resins, rubber) and inorganic substances (such as fillers, etc.
), and is easy to be modified by copolymerization, crosslinking, blending, filling, etc.
to improve the adhesive layer Performance
.
It can withstand the corrosion of acid, alkali, salt, solvent and other media
.
Depending on the type of curing agent used, epoxy adhesives can be cured at room temperature, medium temperature or high temperature
.
Generally, only 0.
1-0.
5MPa contact pressure is required during curing.
Most epoxy resin screed agents do not contain solvents and are easy to operate
.
The construction viscosity of general epoxy glue
.
The application period and curing speed can be adjusted by formula to meet various requirements
.
This not only makes it easy to ensure the bonding quality, but also simplifies the curing process and equipment
.
After the epoxy resin is cured, good electrical insulation properties can be obtained; breakdown voltage>35kV/mm volume resistance>1015Ω·cm, dielectric constant 3～4 (50Hz), arc resistance 100～140s
.
Epoxy resin adhesive changes its composition (curing agent, toughening agent, filler, etc.
), and a series of adhesive formulations with different properties can be obtained to meet various needs, and it can be mixed with many modifiers to produce various properties.
Variety
.
Generally, the use temperature of bisphenol A epoxy resin ranges from -60 to 175°C and sometimes reaches 200°C in a short time.
If a new type of epoxy resin resistant to high and low temperatures is used, the use temperature can be higher or lower, and the epoxy resin The water absorption is small
.
General-purpose epoxy resins, curing agents and additives are produced in many places, large in output, easy to prepare, can be contacted and molded, and can be applied on a large scale
.
The main disadvantages of epoxy adhesives: when it is not toughened, the cured product is generally brittle, has poor peel resistance, crack resistance, and impact resistance; it has low adhesion to materials with low polarity (such as polyethylene, polypropylene, etc.
)
.
Surface activation treatment must be carried out first; some raw materials such as reactive diluents and curing agents have varying degrees of toxicity and irritation
.
When designing the formula, it should be avoided as much as possible, and ventilation protection should be strengthened during construction
.
It can be seen from the above that epoxy resin has good comprehensive mechanical properties, especially high adhesion, small shrinkage, good stability, and excellent electrical insulation properties.
It is used as an adhesive, composite material matrix, and powder coating.
And other products provide the material basis
.
4.
Progress in epoxy adhesive application technology.
Heat-resistant epoxy resin adhesive is an adhesive prepared from modified epoxy resin.
It can be used intermittently at 250°C, or even long-term use at 400°C, and short-term use at 460°C.
Use
.
The matrix resin of this adhesive generally introduces more rigid groups or increases the crosslinking density of the cured product
.
For example, epoxy resin with fluorene group, naphthalene ring and multifunctional epoxy resin, or epoxy resin adhesive modified by maleimide and silicone can reach the requirements of short-term high temperature resistance and high strength at 460℃.
.
In recent years, with the development of electronic appliances and aerospace industries, the requirements for high temperature resistance and ablation resistance have become higher and higher
.
When the aircraft is flying at high speed in the atmosphere, sometimes the temperature can reach thousands of degrees due to aerodynamic heating, and even the most heat-resistant metal materials have to be melted
.
Therefore, in order to reduce weight, high temperature resistant composite materials are generally used to replace metal materials
.
Even in the electronics and electrical industries, sealants that can withstand high temperatures of 350°C have been proposed, and even flame-resistant insulating adhesives that can withstand 500-1000°C have been proposed
.
The F series epoxy curing agent developed by China National Aviation Corporation and the newly developed B, H, HE series epoxy curing agent can make the epoxy resin resistant to high temperature of 500 ℃, and have excellent flame retardant performance and burning resistance.
Corrosion performance and good process performance
.
Modified epoxy resin adhesive and its preparation method overcome the shortcomings of general epoxy adhesives' brittleness and poor temperature resistance.
Its main technical feature is polyurethane prepolymer modified epoxy resin (component A) and homemade curing agent (Component B) According to the ratio of 10:1 to 1:1 (weight ratio), it is formulated into a curing system with high temperature resistance, good toughness and high reactivity
.
Among them, the polyurethane prepolymer is a hydroxy-terminated polysiloxane and a diisocyanate reacted in a certain proportion under certain conditions to form an isocyanate group-terminated polysiloxane polyurethane prepolymer, and then this polyurethane prepolymer is used for epoxy resin Carry out modification treatment
.
The self-made curing agent is composed of diamine, imidazole compound, silane coupling agent, inorganic filler and catalyst
.
This modified epoxy resin adhesive can be cured at room temperature, can be used for a long time at 200 ℃, or cured at -5 ℃ and can be cured at 150 ℃; the bonding strength can reach 15-30Mpa; the T-type peeling strength can reach 35-65N/cm, which is excellent of oil, water, acid, alkali, organic solvent resistance performance, wet surface adhesion, oil and metal, plastic, ceramic, hard rubber, wood and the like
.
To increase the strength of the epoxy resin, the resin is generally toughened by adding a second component to improve the toughness of the epoxy resin
.
According to reports, the main liquid toughening, toughening, toughening elastic microspheres, thermotropic liquid crystal (of TLCP) toughened and polymer blends, and the like copolymerization
.
The toughening modification of liquid rubber generally refers to liquid nitrile rubber, poly, etc.
containing terminal carboxyl groups, amine groups, hydroxyl groups, thiol groups, and epoxy groups, which are miscible with epoxy resin and precipitate during the curing process to form " The two-phase structure of the "sea-island model" has a toughening effect by forming chemical bonds on the two-phase interface through the interaction of active groups
.
In recent years, in addition to the use of purely active liquid rubber pre-reaction adducts, it has been developed to the second generation using high-functionality epoxy resin and the third generation using metallocene catalysts to prepare block copolymer modified epoxy prepolymers.
After this modification, not only the peel strength is improved, but the overall mechanical and thermal properties are not significantly reduced
.
Polyurethane toughened epoxy adhesive is formed by polyurethane and epoxy resin to form semi-vertical penetrating network polymer (SIPN) and interpenetrating network polymer (IPN), which play a forced mutual solubility and synergistic effect, so that high elastic polyurethane and good adhesion The epoxy resins are organically combined together to achieve a good toughening effect through complementation and reinforcement
.
One-component room temperature moisture curing epoxy adhesive is an epoxy adhesive cured with modified ketimine as a curing agent.
Its characteristics are that it can be cured under humid and low temperature conditions and can improve the resistance of the cured epoxy resin.
Temperature and corrosion resistance
.
Phenolic modified ketimine curing agent, which firstly reacts with formaldehyde, m-phenylenediamine to produce phenalkamine, and then reacts with methyl isobutyl ketone to produce phenolic modified ketimine
.
At present, domestic efforts are being made to study the fast curing technology of fast curing epoxy adhesive under low temperature and low humidity
.
At present, the two-component room temperature curing epoxy adhesive developed in China can withstand 200-260 ℃ temperature, up to 275 ℃, and it can be gelled in 2-6 minutes at 25 ℃.
It can be completely cured for 3-8 hours.
Polyether diamine is cured.
The peel strength can reach 4～5kN/m
.
Low-temperature fast-curing epoxy adhesive is made of bisphenol F epoxy resin.
It is combined with diphenyl decyl phosphite, DMP-30, etc.
, and can be cured quickly at -5°C.
It has been developed and applied Civil engineering field
.
Mainly used for concrete "overall project" bonding, building up, repair and supplies products such as adhesive
.
In construction projects, it can replace rivets, welding and other structural connection techniques, and is used to bond various, marble and artificial boards
.
The high-strength composite repair technology is the development trend of the future oil and gas pipeline external anti-corrosion coating repair technology.
It is a technology that forms a protective structure with high-performance resin matrix bonding and reinforcing materials, so it has high compressive and tensile strength And cohesion
.
During the repair construction, there is no need for pipeline shutdown or decompression operation.
At the same time, it has the advantages of simple and convenient operation, easy training of construction personnel, good reinforcement effect and significant economic benefits
.
Composite material repair technology can carry out on-site winding construction and on-site curing, and the construction process is open flame, safe and convenient
.
Thirdly, the strength of composite materials reinforced by glass fiber, carbon fiber or fabric far exceeds that of ordinary steel, making composite materials more efficient in repair and reinforcement; composite materials are designable, and thickness and layer can be adjusted according to the degree of defect damage and stress.
Targeted design in terms of number, fiber distribution, etc.
, and its repair reliability is high; the interlayer adhesive of glass fiber or carbon fiber reinforced resin-based composite material has good interfacial adhesion, airtightness and excellent corrosion resistance.
, Which can greatly reduce the secondary corrosion damage during the pipeline operation period
.
In composite repair technology, the choice of adhesive has a crucial impact on its protective performance
.
When the epoxy resin adhesive is toughened and modified by polyurethane, the polyurethane segment penetrates into the epoxy resin segment to form an interpenetrating polymer network structure (IPN) or a semi-interpenetrating polymer network structure (SIPN)
.
Because of the different solubility of polyurethane and epoxy resin, IPN materials show different degrees of phase separation, but due to the entanglement of the networks, "forced mutual dissolution" occurs, which increases compatibility; and once the polymers are crosslinked, they become entangled with each other.
The network fixes the phase zone.
Because the polyurethane particles are dispersed in the continuous epoxy resin phase, the toughness of the system is increased, the stress concentration of the cured product is dispersed, and the shear strength is increased
.
With the increase of polyurethane addition, the shear strength gradually increases, but when the polyurethane content exceeds 13.
04%, the degree of interpenetration of the interpenetrating polymer network structure formed by polyurethane/epoxy resin has reached saturation
.
If the amount of polyurethane is further increased, the interpenetrating polymer network will have a degree of interpenetration, the polyurethane and the epoxy resin will be separated to form cracks, and the compatibility of the polyurethane and the epoxy resin will drop sharply
.
Therefore, in terms of shear strength, the optimal amount of polyurethane is 13.
04%
.
The peel strength is mainly related to the bonding performance and flexibility of the epoxy resin adhesive.
The change law of the interpenetrating polymer network structure formed by polyurethane and epoxy resin shows that with the increase of the amount of polyurethane added, the flexibility of the cured product The properties of epoxy resin adhesives increase first and then decrease, so the peel strength of epoxy resin adhesives will increase first and then decrease with the increase of the amount of polyurethane added
.
When the polyurethane reaches 20%, the peel strength begins to decrease as the amount of polyurethane added increases
.
Therefore, for peel strength, the optimal amount of polyurethane is 20%
.
Among many epoxy resin toughening technologies, the toughening effect of elastomers represented by polyurethane is the most significant
.
However, epoxy resin is a linear thermoplastic resin and will not harden itself.
Only by adding a curing agent to make it cross-linked from a linear structure into a network or body structure can it be cured
.
Therefore, while using polyurethane to toughen the epoxy resin, it is necessary to add a curing agent to meet the requirements for curing performance during construction
.
The epoxy resin contains multiple benzene rings or heterocyclic rings, and the molecular chain is less flexible.
The cured epoxy resin has a high cross-linked structure, and the cross-linked structure is not easy to deform, resulting in insufficient toughness and brittle cracks in epoxy resin adhesives.
, Low peel strength and poor impact resistance, so its application is greatly restricted.
Therefore, the toughening modification of epoxy resin has important practical significance and application prospects for its application in pipeline repair
.
In practice, an adhesive that can be cured at room temperature and used in a high temperature environment is often needed
.
For example, structural adhesives used in construction are not only required to be able to withstand high temperatures to prevent the building from collapsing in a fire, but also cannot be cured by heating because of the large bonding area
.
However, room temperature curing EP adhesives generally cannot be used at high temperatures, and heat-resistant EP adhesives often require heating to be fully cured
.
The so-called room temperature curing usually refers to a curing method that can gel within a few minutes or a few hours at room temperature (20-30°C), and fully cure within 7 days, and achieve usable strength
.
Although room temperature curing and high temperature adhesives have made some progress, there is still a long way to go.
In the future, research on the curing mechanism of EP adhesives should be strengthened, and multifunctional active curing agents should be developed; new multifunctional EPs should be synthesized.
Base resin, explore new modification methods and new fillers of EP resin; on the basis of improving performance, make the research and development of adhesives develop in a resource-saving and environment-friendly direction
.
5.
Concluding remarks Epoxy resin adhesives have excellent bonding properties and chemical stability, so they are widely used.
The development of modern industry requires EP adhesives to have the ability to cure at room temperature and withstand high temperatures.
.
Epoxy resin adhesive has a wide range of base materials and is suitable for bonding a variety of substrates.
It has the characteristics of high strength, low curing shrinkage, corrosion resistance, thermal stability and good electrical insulation performance.
It also has simple construction techniques, high work efficiency, and energy The advantages of low consumption and low cost can greatly reduce labor intensity, save labor costs, and have huge market potential and broad application prospects
.
