What Is a Curing Agent?

Curing agents, also known as hardeners, curing agents or modifiers, are a class of substances or mixtures that enhance or control the curing reaction. Resin curing is through the chemical reaction of condensation, ring closure, addition or catalysis to make the thermosetting resin irreversible change process. The curing is completed by adding a curing (crosslinking) agent. The curing agent is an indispensable additive. Whether it is used as an adhesive, coating or castable, a curing agent must be added, otherwise the epoxy resin cannot be cured. The type of curing agent greatly affects the mechanical properties, heat resistance, water resistance, and corrosion resistance of the cured product.

Chinese name: Hardener

Definition of curing agent

Curing agents, also known as hardeners, curing agents or modifiers, are a class of substances or mixtures that enhance or control the curing reaction. The resin is cured by condensation,

Chemical reactions, such as ring closure, addition, or catalysis, cause the thermosetting resin to undergo an irreversible change. The curing is accomplished by adding a curing (crosslinking) agent.

Hardeners are classified by chemical composition 1. Aliphatic amines such as vinyl triamine DETA aminoethylpiperazine AE 2. Aromatic amines such as m-PDA diamine m-PDA MPD diaminodiphenylmethane DDM HT-972 DEH -50 3. Amidoamines 4. Latent curing amines 5. Urea substitutes.

Temperature characteristics of curing agent

Curing temperature and heat resistance of the curing agent

The curing temperature of each curing agent is different, and the heat resistance of the cured product is also greatly different. In general, a cured product having excellent heat resistance can be obtained by using a curing agent having a high curing temperature. For addition polymerization type curing agents, the curing temperature and heat resistance are increased in the following order:

Aliphatic polyamines <alicyclic polyamines <aromatic polyamines <phenol aldehydes <anhydrides

The heat resistance of the catalytic addition polymerization type curing agent is generally at the level of aromatic polyamines. The heat resistance of the anionic polymerization type (tertiary amine and imidazolation antiquities) and cation polymerization type (BF3 complex) is basically the same. This is mainly because although the initial reaction mechanism is different, they all form a network of ether bonds. structure.

The curing reaction is a chemical reaction, which is greatly affected by the curing temperature. As the temperature increases, the reaction speed increases, and the gel time becomes shorter. The log value of the gel time generally decreases linearly with the increase of the curing temperature. However, if the curing temperature is too high, the performance of the cured product often decreases, so there is an upper limit of the curing temperature; a temperature that compromises the curing speed and the performance of the cured product must be selected as the appropriate curing temperature. According to the curing temperature, the curing agent can be divided into four categories: the curing temperature of the low-temperature curing agent is below room temperature; the curing temperature of the room-temperature curing agent is from room temperature to 50 ° C; the curing temperature of the intermediate-temperature curing agent is 50-100 ° C; . There are few types of low-temperature curing type curing agents, such as polyisocyanate and polyisocyanate. T-31 modified amines and YH-82 modified amines developed and produced in China can be cured below 0 ° C. There are many types of room temperature curing types: aliphatic polyamines, alicyclic polyamines; low molecular polyamides and modified aromatic amines. Part of the medium-temperature curing type is alicyclic polyamines, tertiary amines, oxazoles, and boron trifluoride complexes. Among the high-temperature curing agents are aromatic polyamines, acid anhydrides, resole resins, amino resins, dicyandiamide, and hydrazides.

For high-temperature curing systems, the curing temperature is generally divided into two stages. Low-temperature curing is used before gelation. After reaching the gel state or a slightly higher state than the gel state, post-cure after high-temperature heating. The previous stage is cured into a pre-cure.

Structural characteristics of curing agent

The curing temperature of the curing agent is strongly related to the heat resistance of the cured product. Similarly, in the same type of curing agent, although they have the same functional group, due to different chemical structures, their properties and cured product characteristics are also different. Therefore, it is important to comprehensively understand the properties and characteristics of polyamine curing agents with the same functional groups but different chemical structures.

In terms of hue, alicyclics are the lightest and basically transparent, while aliphatics and aromatics have a considerable degree of coloration. In terms of viscosity, they are also very different. The cycloaliphatic is only a few tenths Pa · s, while the polyamide is very viscous, up to several Pa · s, and the aromatic amine is mostly solid. The length of the pot life is exactly the opposite of curing. The aliphatic reactivity is the highest, and the cycloaliphatic, amide, and aromatic are decreased in order.

Hue: (excellent) alicyclic aliphatic amide aromatic amine (inferior)

Maturity: (low) alicyclic aliphatic aromatic amide (high)

Application period: (long) aromatic amide alicyclic aliphatic (short)

Curability: (fast) aliphatic cycloaliphatic amide aromatic (slow)

Irritant: (strong) aliphatic aromatic alicyclic amide (weak)

Chemical structure and properties of polyamine curing agents

In addition, it also has certain regularity in terms of gloss, softness, adhesion, acid resistance, and water resistance.

Gloss: (excellent) aromatic alicyclic polyamide-fatty amine (inferior)

Softness: (soft) polyamide aliphatic alicyclic aromatic (rigid)

Adhesiveness: (excellent) polyamide alicyclic aliphatic aromatic (good)

Acid resistance: (excellent) aromatic alicyclic aliphatic polyamide (inferior)

Water resistance: (excellent) polyamide aliphatic amine alicyclic amine aromatic amine (good)

Chemical structure of polyamine curing agent and properties of cured product with bisphenol A resin

For gloss, aromatics are the best and aliphatics are the worst. This property is affected by the curing temperature. As the temperature increases, the gloss becomes better. As for flexibility, polyamides with longer distances between functional groups are better, while aromatic amines with higher crosslink density are worse. Heat resistance is exactly the opposite of softness, while adhesion is consistent with softness. Chemical resistance (acid resistance) is affected by the chemical structure, and its aromatics are better. Fatty amines and polyamides are susceptible to chemical corrosion. Water resistance is governed by the mass concentration of functional groups. Polyamides with a low mass concentration of functional groups and high hydrophobicity are more resistant to water, while aromatics with a higher mass concentration of functional groups are worse.

Classification of curing agent

Classification of curing agents

The curing agent can be divided into normal temperature curing agent and heating curing agent according to the application. Epoxy resins generally have excellent properties when cured at high temperatures, but coatings and adhesives used in civil construction need to be cured at room temperature due to difficult heating; therefore, fatty amines, cycloaliphatics, and polyamides are mostly used, especially those used in winter. Coatings and adhesives have to be used in combination with polyisocyanates, or using polyalcohols with a foul odor.

As for the medium-temperature curing agent and the high-temperature curing agent, the heat resistance of the adherend and the heat resistance, adhesiveness, and chemical resistance of the cured product are selected as standards. Selection focuses on polyamines and anhydrides. Because the cured anhydride has excellent electrical properties, it is widely used in electronics and electrical appliances.

The aliphatic polyamine cured product is excellent in adhesiveness, alkali resistance, and water resistance. Aromatic polyamines are also excellent in chemical resistance. Since the nitrogen element of the amino group forms a hydrogen bond with the metal, it has an excellent anti-rust effect. The higher the amine mass concentration, the better the antirust effect. The acid anhydride curing agent and epoxy resin form an ester bond, which shows high resistance to organic and inorganic acids, and generally has electrical properties that exceed polyamines.

Classification of curing agents by chemical composition

Aliphatic amines

Products in different ranges have different properties; high reactivity, fast curing at room temperature or low temperature; relatively insensitive to humidity. It has certain color stability; good chemical resistance, especially solvent resistance; good thermal performance when used for thermal curing; good chemical resistance and good electrical and mechanical properties.

Vinyl triamine DETA

Aminoethylpiperazine AE

Cured at low temperature under wet conditions; good film properties (such as excellent surface gloss); can prevent amine frost and water spots; good color stability; has good adhesion and chemical resistance; curing The time and storage time can be selected from a wide range; when used for thermal curing, it has good high temperature performance; it has good chemical resistance and has good electrical and mechanical properties.

Diaminocyclohexane DACH

Isophorone diamine IPDA

Methylene bicyclohexaneamine 4,4'-PACM

Ethylenediamine EDA

H2NCH2CH2NH2 molecular weight 60, active hydrogen equivalent 15, colorless liquid, 6-8 parts per 100 parts standard resin. Performance: Toxic, irritating odor, high volatility, low viscosity, fast curing at room temperature. For bonding, pouring, coating. With the increase of molecular weight, the amines have increased viscosity, reduced volatility, reduced toxicity, and improved performance. But they have a large amount of heat and a short pot life. Generally speaking, the larger their molecular weight, the less affected by the blending amount. Long-term exposure to fatty polyamines can cause dermatitis. Their steam toxicity is very strong, so you must pay attention to it during operation.

Diethylenetriamine DETA

H2NC2H4NHC2H4NH2, molecular weight 103, active hydrogen equivalent 20.6, colorless liquid, 8-11 parts per 100 parts standard resin. Curing: 2 hours at 20 ° C + 30 minutes at 100 ° C or 4 days at 20 ° C. Performance: 50 g at 25 for 45 minutes, heat distortion temperature of 95-124 , flexural strength of 1000-1160kg / cm2, compressive strength of 1120kg / cm2, tensile strength of 780kg / cm2, elongation of 5.5%, impact strength

0.4 foot-pounds per inch Rockwell hardness 99-108. Dielectric constant (50 Hz, 23 ° C) 4.1 Power factor (50 Hz, 23 ° C) 0.009 Volume resistance 2x1016 -cm Cured at room temperature, highly toxic, large heat generation, and short pot life.

Triethylenetetramine

TETA H2NC2H4NHC2H4NHC2H4NH2, molecular weight 146, active hydrogen equivalent 24.3, colorless viscous liquid, 10-13 parts per 100 parts standard resin. Curing: 2 hours at 20 ° C + 30 minutes at 100 ° C or 7 days at 20 ° C. Performance: 50 g at 25 ° C for 45 minutes, heat deformation temperature of 98-124 ° C, flexural strength of 950-1200kg / cm2, compressive strength of 1100kg / cm2, tensile strength of 780kg / cm2, elongation of 4.4%, impact strength

0.4 feet-pounds per inch, Rockwell hardness 99-106. Cured at room temperature, slightly less toxic than diethylenetriamine, exothermic, and short pot life.

Tetraethylenepentamine

H2NC2H4 (NHC2H4) 3NH2, molecular weight 189, active hydrogen equivalent 27, brown liquid, 11-15 parts per 100 parts standard resin. Same performance as above.

Polyethylene Polyamine PEPA

H2NC2H4 (NHC2H4) nNH2, light yellow liquid, 14-15 parts per 100 parts of standard resin. Performance: Low toxicity, low volatility, long pot life, and low price.

Dipropylene triamine DPTA

H2N (CH2) 3 NH (CH2) 3NH2, molecular weight 131, active hydrogen equivalent 26, light yellow liquid, 12-15 parts per 100 parts standard resin. Performance is the same as TETA.

Dimethylaminopropylamine DMAPA

(CH3) 2N (CH2) 3NH2, low viscosity transparent liquid, 4-7 parts per 100 parts of standard resin.

It is more toxic, has two reactions of curing and catalysis, has good adhesion performance, good flexibility, and long service life.

Diethylaminopropylamine DEAPA

(C2H5) 2N (CH2) 3NH2 Molecular weight 130 Active hydrogen equivalent 65 Low viscosity transparent liquid Use 4-8 parts per 100 parts of standard resin. Curing: 60-70 ° C for 4 hours. Performance: 50 g at 25 ° C for 4 hours, heat distortion temperature of 78-94 ° C, compressive strength of 920-1050kg / cm2, tensile strength of 480-640kg / cm2, impact strength of 0.2 ft-lb / inch, Rockwell hardness of 90 -98. The dielectric constant (50 Hz, 23 ° C) is 3.75, and the power factor (50 Hz, 23 ° C) is 0.007.

Medium temperature curing and low temperature performance.

Trimethylhexamethylenediamine TMD

(H2N) 2 (C6H9) (CH3) 3 is a colorless liquid, cold curing, long pot life and low toxicity. 21 parts per 100 parts of standard resin. Curing: 1 hour at 80 ° C + 2 hours at 150 ° C. Performance: 400 g at 25 ° C for 50 minutes or 50 ° C for 10 minutes, Martin heat-resistant 92 ° C, flexural strength 1150kg / cm2, impact strength 20Kg-cm / cm2 tg 0.0009 (23 ° C, 100C / S).

Surface resistance is 5.4x1011 (300V), volume resistance is 9x1015.cm (300V), medium temperature curing, and good low temperature performance.

Dihexyltriamine

H2N (CH2) 6 NH (CH2) 6NH2

Hexaamine modified AMINE248

Unknown molecular formula, transparent liquid, viscosity 1000-3000cps at 25 , 4-8 parts per 100 parts standard resin. Cured at room temperature -100 . Less toxic and flexible.

Hexamethylene diamine adduct

CH-2, L2505, unknown molecular formula, amine value 160-210, low viscosity transparent liquid, 65 parts per 100 parts standard resin.

CH3 amine value 400-500, low viscosity transparent liquid, 60 parts per 100 parts standard resin.

Hexamethylene diamine HDA

H2N (CH2) 6NH2, molecular weight 116, active hydrogen equivalent 29, colorless flake crystal, melting point 42 ° C, 12-15 parts per 100 parts standard resin. Very toxic, can cure at room temperature but not good. Shorter life.

Trimethylhexadiamine

Molecular weight 158, 20-25 parts per 100 parts of standard resin. Curing: 2 hours at 20 ° C + 30 minutes at 100 ° C or 7 days at 20 ° C. Performance: 50 g at 25 ° C for 45 minutes, heat distortion temperature of 105 ° C, flexural strength of 1150kg / cm2, tensile strength of 650kg / cm2, elongation of 4.4%, and impact strength of 0.4 feet-pounds per inch. Dielectric constant (50 Hz, 23 ° C) 4.0 Power factor (50 Hz, 23 ° C) 0.001 Volume resistance 9x1015 -cm.

Diethylamine DEA

HN (C2H5) 2, molecular weight 73, active hydrogen equivalent 73, colorless liquid, 12 parts per 100 parts standard resin. With curing and catalysis two reactions.

Polyether diamine H2N (CH2) nO (CH2CH2O) mNH2

2. Aromatic amines

M- Phenylenediamine m-PDA MPD

(NH2) 2C6H4, molecular weight 107, active hydrogen equivalent 26.7, white crystal (black solid?), Melting point 62 ° C, 14-16 parts per 100 parts standard resin. Cured at 60 ° C for 2 hours + 150 ° C for 2 hours. 500 g 2.5 hours at 50 ° C, heat distortion temperature 150 ° C, flexural strength 1050kg / cm2, compressive strength 710kg / cm2, tensile strength 540kg / cm2, elongation 3.0%, impact strength 0.2-0.3ft-lb / Inch, Rockwell hardness of 108. Dielectric constant (50 Hz 23 ° C) 3.3, power factor (50 Hz 23 ° C) 0.007, excellent heat resistance, corrosion resistance, good electrical properties, low toxicity. Because it is solid, it is not convenient to use. When heating and mixing with the resin, care must be taken to prevent gelation.

M-xylylenediamine MXDA

(NH2CH2) C6H4, molecular weight 135, active hydrogen equivalent 33.2, colorless liquid, 16-18 parts per 100 parts standard resin. Cure at room temperature for 24 hours + 70 ° C for 1 hour or at room temperature for 4 days. 100 g 25 for 50 minutes, heat distortion temperature 130-150 , flexural strength 1200 kg / cm2, compressive strength 1030 kg / cm2, tensile strength 720 kg / cm2, elongation 6.7%, dielectric constant (50 Hz 23 ) 4.0, power factor (50 Hz 23 ) 0.005, volume resistance is greater than 2x1016.cm, can be cured at room temperature, heat resistance, corrosion resistance is good, good electrical properties, low toxicity. Low curing temperature, low viscosity, low toxicity, long pot life and good solvent resistance. Its easy absorption of carbon dioxide in the air is the cause of product bubbles.

Diaminodiphenylmethane DDM HT-972 DEH-50

[(NH2) (CH3) C6H4] 2CH2, molecular weight 196, active hydrogen equivalent 49, white crystal, brown after long-term exposure to sunlight, melting point 89 ° C, 25-30 parts per 100 parts standard resin. Cured at 60 ° C for 2 hours + 150 ° C for 2 hours. Applicable period: 500g at 50 for 3 hours, heat distortion temperature 145-150 , flexural strength 1190kg / cm2, compressive strength 710kg / cm2, tensile strength 550kg / cm2, elongation rate 4.4%, impact strength 0.3-0.5 feet -Pounds / inch Rockwell hardness 106. Dielectric constant (50 Hz 23 ° C) 4.4, power factor (50 Hz 23 ° C) 0.004, volume resistance is greater than 1015.cm, excellent heat resistance, corrosion resistance, good electrical properties, and low toxicity. Heat resistance and high mechanical strength. Because it is solid, it is not convenient to use. When heating and mixing with the resin, care must be taken to prevent gelation.

Diaminodiphenylsulfone DDS HT-976

[(NH2) C6H4] 2SO2, molecular weight 248, active hydrogen equivalent 62, melting point 175 ° C, 35-40 parts per 100 parts standard resin. Cure at 130-150 ° C for 3 days-2 hours. 500 g at 130 for 1.5 hours, usually using BF3-amine complex as the accelerator (0.5-2%), heat distortion temperature 175-190 , flexural strength 1220kg / cm2, compressive strength 710kg / cm2 , Tensile strength of 580kg / cm2, elongation of 3.3%, impact strength of 0.3-0.5 feet-pounds / inch, Rockwell hardness of 110. Excellent heat and corrosion resistance, good electrical properties and low toxicity. slow response. Heat resistant to 175 ° C.

M-carbamoylamine MAMA (NH2)

(CH2NH2) C6H4, molecular weight 123, active hydrogen equivalent 30.7, melting point 38 ° C, 14-18 parts per 100 parts standard resin, curing 130-150 ° C for 3 days to 2 hours. Elongation at break is high.

Benzidine

(NH2) C6H4 C6H4 (NH2)

Chloro-o-phenylenediamine CPDA

(NH2) 2C6H3 CL

Xylylenediamine trimer GY-51 CH-2

Viscosity of 60 2000-6000cps, 30-60 parts per 100 parts of standard resin, curing at room temperature -60 for 7 days-1 hour. Low toxicity.

WA-060 CH-3 viscosity 60 6000-10000cps, 30-60 parts per 100 parts of standard resin, curing at room temperature -60 for 7 days-1 hour.

Xylylenediamine trimer derivatives

The viscosity is 25 cps, 5 cps, 40 cps, and 100 cps at 25 ° C, 25-30 parts per 100 parts of standard resin, and curing at room temperature of -60 ° C for 7 days to 1 hour. Low viscosity. Low toxicity.

Dibenzylamino ether

(H2NCH2C6H4) 2O, 30-60 parts per 100 parts of standard resin, can be cured at room temperature, long pot life, low exotherm, and heat distortion temperature 68 ° C.

Mixture of m-phenylenediamine and diaminodiphenylmethane

60-75% MPDA and 40-25% DDM are mixed and melted, and they are liquid at normal temperature. The 40:60 mixture of diaminodiphenylmethane and m-phenylenediamine has a melting point of 25 ° C, 20 parts per 100 parts of standard resin, and the epoxy resin is cured at 40 ° C for 5 hours. For example, the mixture of triphenyl phosphate and phenol is cured at 20 ° C for 9 hours. Thermal deformation temperature 150 , flexural strength 1150kg / cm2, impact strength 17Kg-cm / cm2, tensile strength 560 kg / cm2, elongation at break 4.8, Rockwell hardness 105-110, dielectric constant (50Hz 23 ) 4.5, Power factor (50 Hz, 23 ° C) 0.006, Mixture of m-phenylenediamine and diaminodiphenylmethane and toluenediamine, m-phenylenediamine: diaminodiphenylmethane: toluenediamine = 30-70: 10 -50: The mixture of 5-35 is a stable liquid. Example 50 is a liquid obtained by mixing 50 parts of m-phenylenediamine, 30 parts of diaminodiphenylmethane, and 20 parts of toluenediamine (meta: para-position = 80: 20) at 100 ° C, and the stability period is 9 months. For every 100 parts of standard resin, cure 18.5 parts at 80 ° C for 2 hours + 140 ° C for 2 hours. Impact strength is 115Kg-cm / cm2, Rockwell hardness is 105. The mixture of o-toluenediamine, m-toluenediamine and diaminodiphenylmethane, when their ratio is 26:14:60, does not precipitate at 23 ° C for 48 hours, and gels with epoxy resin at 23 ° C for 45 minutes. The mixture of diaminodiphenylmethane and isophorone diamine is 40-30% DDM mixed with 60-70% IPDA and melts. It is liquid at normal temperature. When 40% DDM is mixed with 60% IPDA, 25 parts of the mixture is used per 100 parts of the standard resin. The heat distortion temperature is 130-155 ° C. The physical flexural strength is 1160kg / cm2, the dielectric constant (50 Hz and 23 ° C) is 3.4 and the power factor is Her 23 ° C) 0.012.

Polyphenylenediamine (MPDA)

Methylene bisphenylenediamine (MDA)

3. Amidoamines

Different amides have different reactivity according to Europe. Low viscosity; good adhesion performance; good curability under humid conditions; faster curing speed and chemical stability after amide modification.

4. Latent curing amines

Dicyandiamide (DICY) is a potential curing agent with a stability of more than six months; the product has a variety of shapes and particle sizes. Imidazole is a latent catalyst for epoxy systems, and the storage time can be from several hours to 6 months. They can be used as good accelerators for other curing agents, such as dicyandiamide and anhydrides.

5. Urea substitute

Among dicyandiamide accelerators, it can be used as a low toxicity alternative to Monuron and Diuron.

Selection of curing agent

Consider the variety and performance of curing agent

The type of curing agent has a great impact on the mechanical properties, heat resistance, water resistance, and corrosion resistance of the cured product. For example, curing agents such as aromatic polyamines, imidazoles, and anhydrides have higher heat resistance than epoxy resins. Group polyamine, low molecular weight polyamide curing agent; aromatic acid anhydride cured epoxy resin has better water resistance than aromatic diamine and aliphatic polyamine curing agent; triethylenetetramine curing agent has good alkali resistance, but acid and Poor resistance to formaldehyde solutions. Alicyclic polyamines (such as isophorone diamine) cure epoxy resins with excellent chemical resistance. The acid resistance of acid anhydride curing agent curing epoxy resin is better than acid resistance. Appropriate curing agents should be selected according to different applications and performance requirements.

Combined use of several curing agents

Several kinds of curing agents can be used in combination to obtain mutually beneficial effects. For example, a low-molecular polyamide curing agent combined with a small amount of m-phenylenediamine curing agent can not only cure at room temperature, but also increase the toughness of the cured product while appropriately improving heat resistance. Sex. Trimellitic anhydride (TMA) is used in combination with methyltetrahydrophthalic anhydride. The eutectic mixture has a low viscosity (25 ° C, 200-250mPa · s), and is easily mixed with epoxy resin to improve processability.

Pay attention to the environmental protection of curing agents

The selected curing agent should be harmless to the human body and no pollution to the environment. Ethylenediamine must not be used alone as a curing agent. Modified amine curing agents should be used as much as possible.

Development of curing agent

Curing agent epoxy resin

Epoxy resin curing agents have developed rapidly, and many new high-performance curing agents have appeared. Epon HPT curing agents 1061 and 1062 developed by Shell Company, because they do not contain ether bonds in the molecular structure, and contain more hydrocarbon groups, which can improve water resistance and heat resistance. It can reach 207 ° C and absorb water from 1.4% to 1.6%. Ajicure PN-31 and PN-40 are latent curing agents. They are stable below 90 ° C and can be cured at 90 ° C. The one-component epoxy adhesive formulated with them has a storage period of more than 9 months. Dainippon Ink Chemicals Co., Ltd. uses nitrogen-containing phenolic resin (ATN) synthesized from phenol, formaldehyde and melamine as a curing agent for epoxy resins. It has good flame retardancy and can reach UL94 VO grade. ATU) reacts with various epoxides and acrylonitrile. The resulting adduct is liquid at room temperature. It is used as an epoxy resin curing agent with a long service life, strict measurement requirements, convenient use, and almost no toxicity. The cured product is tough, with small shrinkage, high bonding strength, tensile strength of 65 80MPa, and impact strength of 14 16kJ / . An aryl ether ester diarylamine prepared by the reaction of tetrabromobisphenol A bis (2-hydroxyethyl) ether with p-nitrobenzoyl chloride. It is used as an epoxy resin curing agent. The cured product has high strength, high toughness, High heat resistance, low water absorption, tensile strength of 95MPa, elongation at break> 12%, water absorption <1.3%. Japan has developed hydrogenated methyl nadic acid anhydride (H-MNA) in recent years. The curing temperature of bisphenol A epoxy resin is 162 ° C, and the heat-resistant aging time is 1.5 times that of MNA and MeTHPA. The flexural strength after 200 days at 200 ° C Almost unchanged. In order to meet the requirements of moisture resistance of electronic packaging materials, a variety of moisture and heat resistance curing agents have been developed, mainly containing phenolic resin structures. HardeneHY940 developed by Cibaeigy is a modified low-molecular polyamide latent curing agent. When mixed with liquid epoxy resin, it has a shelf life of 6 months at room temperature, exhibits high reactivity at 100 ° C, has excellent adhesion and Mechanical properties. Shenyang Southeast Chemical Industry Research Institute has recently developed and produced T-99 super flexible multifunctional epoxy curing agent, which is colorless, transparent, non-toxic and environmentally friendly. It can be cured at room temperature or under heating. For the first time, it has solved the brittleness problem of epoxidizing amine curing agent curing epoxy resin for the first time, which greatly expanded the application field of epoxy resin adhesive. Southeastern Chemical Research Institute successfully developed HTAC series modified acid anhydride curing agent, which is prepared by modifying methyltetrahydrophthalic anhydride. The cured product has excellent toughness and heat resistance (impact strength 24kJ / , glass transition temperature Tg is 120 ) . It has also successfully developed a weathering toughening anhydride curing agent, which is obtained by toughening and modifying methylhexahydrophthalic anhydride. There is no double bond in the molecular structure and it has good weather resistance. Humtsman Company has developed a new type of fast polyetheramine curing agent JeffamineXTJ-590, which is about 4 times faster than ordinary polyetheramine D-230. It can be used alone or mixed with ordinary polyetheramine to cure epoxy resin. The cured product is light in color and has high impact strength and thermal shock resistance. Air Products recently introduced water-based epoxy resin curing agents Anquanmine 721 and 731, which have excellent performance and environmental friendliness, and are cost-effective for concrete protection. Gabril Perfrmailce Prducts launched to the market in 2008 GPM-830CB and GPM-890CB thiolamine epoxy curing agent, which can improve the adhesion between glass and metal, especially bronze and brass. GPM-830CB is a yellow-brown liquid, medium Viscosity, gel time after mixing with liquid bisphenol A epoxy resin is 30min.

Three stages of curing agent epoxy resin curing

1.Liquid-operation time

Operating time (also working time or pot life) is part of the curing time. After mixing, the resin / curing agent mixture is still liquid and workable and suitable for the application. In order to ensure reliable bonding, all construction and positioning work should be done within the curing operation time. ^[1]

2.Gel-into solidification

The mixture begins to enter the solidification phase (also known as the maturation phase), at which point it begins to gel or "mutate". At this time, the epoxy does not work for a long time, and it will lose its viscosity. Do not interfere with it at this stage. It will turn into a soft gel like hard rubber, you can press it with your thumb.

Because the mixture is only partially cured at this time, the newly used epoxy resin can still be chemically linked to it, so the untreated surface can still be bonded or reacted. Regardless, these capabilities are diminishing for near-cured mixtures.

3.Solid-final curing

The epoxy mixture reaches the stage of solidification and solidification, at which time it can be sanded and shaped. At this point you can't press it with your thumb. At this time, the epoxy resin has about 90% of the final reaction strength, so you can remove the fixing clips and leave it at room temperature to maintain a number of angels to continue curing.

At this time, the newly used epoxy resin cannot be chemically linked to it, because the epoxy surface must be properly pretreated, such as sanded, to obtain good bonding mechanical strength.

Polyisocyanate

Hybrid polyisocyanate curing agents and other related curing agents are mainly used in paints, foams, coatings, etc. Among them, the closed water-dispersible polyisocyanate curing agent can also be used in combination with melamine assimilating agents. The melamine curing agent is used to reduce costs, and the closed water-dispersible polyisocyanate curing agent is used to improve performance. Substituted polyisocyanates are used in two-component polyurethane coatings. Two-component polyurethane coatings have become mainstream technologies in many application areas, such as automotive refinish paints, large vehicle paints, industrial paints, wood paints, plastic paints, etc. As the society pays attention to environmental protection, high-performance curing agents that can reduce the emission of organic volatiles, such as water-dispersible curing agents and low-viscosity curing agents, will be the focus of future development. Hybrid polyisocyanate curing agent is optimistic for its future development based on its wide range of uses.

The development direction of curing agents is multi-functional, high-performance, flame-retardant, toughened, latent, energy-saving, and environmentally-friendly. In particular, more attention should be paid to energy saving and environmental protection.