The first class of crosslinkers is typically a polar polyfunctional group of low relative molecular weight compounds that can be homopolymerized or grafted onto the polymer chain. Such as trimethylolpropane triacrylate (TMPA), trimethylolpropane trimethacrylate (TMPTA), ethylene glycol diacrylate (EGDA), ethylene glycol dimethacrylate (EGDMA), N, N'- p-phenylbismaleimide (PDM or HVA-2), zinc diacrylate (ZDA), zinc dimethacrylate (ZDMA) and so on. Among them, TMPTMA and TMPTA, also known as hardeners, can effectively increase the hardness of vulcanized adhesives when vulcanizing with peroxides, and the general dosage of 1 part can increase the hardness of 1 unit; PDM is a multifunctional vulcanization additive that can increase crosslinking efficiency and improve the constant elongation stress of vulcanizing adhesives in sulfur vulcanization, peroxide vulcanization or resin oxime vulcanization.

The second class of co-crosslinkers can form free radicals with weak reaction performance, and only for the degree of vulcanization

Works. They form free radicals mainly by grabbing hydrogen. Such as triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), 1, 2-polybutadiene (1, 2-PBR), sulfur and the like. Among them, the most commonly used are TAC and TAIC, and the commonly used amount is 50% to 100% of peroxide; Sulfur can often be used as an effective organic peroxide crosslinker for EPDM, which improves the tensile and tearing properties of vulcanized glue to a certain extent, but the addition of sulfur will increase the odor of vulcanized glue.

Crosslinkers refer to a class of additives that improve the efficiency of peroxide crosslinking, mostly compounds with polyunsaturated functional groups. The contribution of co-crosslinkers to crosslinking efficiency is generally understood as providing higher concentrations of reactive points, inhibiting side reactions such as polymer radical disproportionation or chain breaking, and contributing to the formation of more crosslinking bonds.

The specific use effect of the co-crosslinker is not only related to its chemical structure and the amount of additives, but also to the type of polymer and crosslinked peroxide and other conditions.

1. The effect of the co-crosslinker on physical properties

The use of crosslinking agents helps to increase crosslinking density. In terms of physical properties, it is characterized by the improvement of modulus, hardness, and the reduction of tearing elongation and compression set. In some cases, tensile strength, tear strength, heat resistance, abrasion resistance, or dynamic properties can also be improved.

The effect of the use of crosslinkers on physical properties is mainly manifested in the following aspects: (Not all properties can be obtained at the same time, and some of these properties can be achieved with specific additives)

Reduce the permanent compression set;

Improve elasticity;

Increase modulus;

Increase hardness;

Reduce the viscosity of the compound and improve the processability;

Improve oil resistance;

Improve heat aging resistance;

Improve the adhesion of rubber to metal products;

Increase the vulcanization rate;

Reduce the amount of peroxides;

Improved tensile strength;

Improve tear and thermal tear performance;

Improve dynamic flexural performance;

2. The influence of the structure of the co-crosslinker on the performance of the co-crosslinker

The structure of the crosslinker is closely related to the performance of the assistive crosslinker. The type of functional group of the co-crosslinker, the number of functional groups, the structure of the bridge bond, the polarity of the molecule, the size of the molecular weight, etc. will all affect the performance of the co-crosslinker.

The type and number of functional groups, which are the primary parameters affecting the vulcanization performance of the co-crosslinker, directly affect the activity of the co-crosslinker, the solubility in the polymer and the physical properties of the product. Common crosslinking agents, mostly auxiliary agents of bifunctional groups and tri-functional groups;

The structure of the bridge, which includes the polarity of the bond, the length of the bond and the molecular structure. Although the structure of the bridge bond usually has no direct effect on the activity of the co-crosslinker, it may affect the efficiency of the co-crosslinker, the solubility in the polymer and the strength of the crosslinking bond, which is also a very important parameter;

The size of the molecular weight can have an impact on the efficiency of the crosslinker, and can also be used as an important evaluation parameter for the volatility of the crosslinker. If the molecular weight is small, it may be volatile;

The polarity of the crosslinker can directly affect its solubility in the polymer and other factors, and then affect the vulcanization efficiency and performance;

3. Classification of co-crosslinking agents

According to their contribution to vulcanization, co-crosslinkers can be divided into two main categories. One is to improve the degree of vulcanization while also increasing the vulcanization rate, also known as the first type of crosslinkers; Another large category is only to increase the degree of vulcanization or crosslinking density, but not to increase the vulcanization rate, also known as the second type of crosslinking agent.

The following figure shows the vulcanization performance of the first type of crosslinker and the second type of crosslinker:

Image

Compared with the A curve without crosslinkers, the B vulcanization curve using the first type of crosslinker not only obtained higher torque, but also shortened the positive vulcanization time T90; In contrast, the C vulcanization curve using the second type of co-crosslinker only achieves a higher crosslinking density or torque without a significant change in the positive vulcanization time;

It should be noted that the first type of crosslinker usually shortens the scorch time of the rubber compound, while the second type of crosslinker usually has no significant effect on the scorch time;

The mechanism of action of co-crosslinkers is generally considered to be the following two kinds:

The molecule contains two or more unsaturated groups, which may polymerize in the presence of free radicals to form resin-like reinforcing substances. The modulus of elasticity of the compound increases to a greater extent than the peroxide used alone. The mechanism of this reaction is not very clear. One hypothesis is that, in the presence of free radicals, active additives polymerize into multi-stranded resin-reinforced fillers; Another hypothesis is that the active additive acts with free radicals on the polymer to become branched chains of the polymer. The actual mechanism may be a combination of two mechanisms

Common peroxide crosslinkers:

TAC crosslinkers

Chinese name: triallyl isocyanate

English name: Triallyl isocyanurate

Molecular formula: C12H15N3O3

MW: 249.2688

CAS number: 1025-15-6

Density Density: 1.11

Melting point Melting point 26-28°C

Boiling point boiling point 119-120 °C

Project metrics

Exterior

Micro yellow liquid or crystal Micro yellow liquid or crystal Colorless transparent liquid or crystal White powder

Content

Boutique ≥99%

Industrial Grade ≥70%

Acid value ≤ 1.0mgKOH/g

Physical

MW: 249.27

Shape: Colorless liquid or crystal traits at room temperature (25 ° C): Colorless or slightly yellow liquid or hexagonal flake crystals at room temperature. Specific gravity: 1.155 (30 °C) Specific heat: 0.6 (40 °C) melting point: 23 °C - 26 °C (pure) 17 °C - 21 °C (industrial grade) flash point: 355 °C viscosity: 86±3 centipe (30 °C) boiling point: 144 °C / 3mmHg; 297°C/N2, 760mmHg Uses:

1. Crosslinking and modification of a variety of thermoplastics (polyethylene, polyvinyl chloride, chlorinated polyethylene, EVA, polystyrene, etc.). The general addition amount of thermal cross-linking is 1-3%, and the addition of diisopropylbenzene peroxide (DCP) is 0.2-1%; The amount of irradiation crosslinking added is 0.5-2%, and DCP can no longer be added. After crosslinking, it can significantly improve the heat resistance, flame retardancy, solvent resistance, mechanical strength and electrical properties of the products. It significantly improves product quality and is odorless than crosslinking with a peroxide system alone. Typically used in polyethylene, polyethylene/chlorinated polyethylene, polyethylene/EVA cross-linked cables and polyethylene high and low foam products.

2, ethylene propylene rubber, a variety of fluoroelastomer, CPE and other special rubber vulcanization (used in conjunction with DCP, the general dosage of 0.5-4%), can significantly shorten the vulcanization time, improve strength, wear resistance, solvent resistance and corrosion resistance.

3. Crosslinking of acrylic acid and styrene ion exchange resin. It is less than divinylbenzene crosslinker, high quality, can prepare anti-stain, strong strength, large pore size, heat resistance, acid and alkali resistance, oxidation resistance and other excellent performance of ion exchange tree esters. This is a newly developed new type of ion exchange resin at home and abroad, with excellent prospects.

4. Modification of polyacrylate, polyalkyl acrylate, etc. It can significantly improve heat resistance, optical performance and process performance. Typically used for heat resistance modification of ordinary plexiglass.

5. Modification of epoxy resin and DAP (polyphthalate diallyl ester). Improves heat resistance, adhesion, mechanical strength and dimensional stability. Typically used for the modification of epoxy potting and encapsulating compounds.

6. Crosslinking and modification of unsaturated polyester and thermoplastic polyester. It can significantly improve heat resistance, chemical resistance, dimensional stability, weather resistance and mechanical properties. Typically used to improve the heat resistance of hot pressing unsaturated polyester FRP products, the modified product use temperature can reach more than 180 °C.

7, TAC itself homopolymer - polytriallyl isocyanate is a transparent, hard, heat-resistant, electrically insulated resin with excellent resin, can also be used to bond glass and ceramics. Typically used in the manufacture of multi-layer safety glass.

8, polystyrene internal plasticization, styrene and TAC and other copolymerization modification, can be made transparent, crumb-resistant products.

9, metal heat-resistant, radiation-resistant, weather-resistant protective agent, TAC prepolymer in the metal surface for baking plating, its baking coating has a very good heat, radiation, weathering resistance and electrical insulation. Insulation materials such as printed circuit boards that are typically used in the manufacture of microelectronic products.

10. Used as an intermediate for light-curing coatings, photo-corrosion resists, flame retardants and flame retardant crosslinkers. Typically used in the synthesis of high-efficiency flame retardant TBC and flame retardant crosslinker DABC.

Rubber multifunctional anti-reversion vulcanizing agent HVA-2

The main technical indicators

Chemical Name: N,N'-m-Benzene-bis-maleimide

English name: N,N '-m-Phenylene dimaleimide

Short-term: rubber vulcanizing agent HVA-2

Properties: This product is a yellow or brown powder, specific gravity 1.44, soluble in dichlorohexacyclic, tetrahydrofuran and hot acetone, insoluble in petroleum ether, chloroform, benzene and water, melting point greater than 198 °C.

■Quality standards

Name Unit Metric

Appearance Visual yellow or brown powder

Melting point °C ≥ 198

Ash % ≤ 0.5

Heating reduction % ≤ 0.5

Sieve residue (0.150 mm) % ≤ 0.1

■Uses

The vulcanizing agent N,N'--m-benzene-braced bismaleimide, known as HVA-2 by the American company, is a versatile rubber additive. In rubber processing, it can be used as a vulcanizing agent, can also be used as a peroxide system of vulcanizing agent, can also be used as an anti-focus agent and tackifier, both suitable for general rubber, but also suitable for plastics, but also suitable for rubber and rubber combined use system.

In natural rubber, it can be combined with sulfur, which can prevent vulcanization from returning to its origin, improve heat resistance, reduce heat generation, resist aging, improve the adhesion of rubber with cord and steel wire, and improve the modulus of vulcanized glue. Used in the shoulder rubber cushioning layer of load tires, it can solve the problem of diagonal load tire shoulder hollow, especially suitable for rubber large-scale thick products, special tires and various rubber magazines.

HVA-2 in neoprene glue, chlorosulfonated polyethylene glue, styrene-butadiene glue, nitrile glue, isoprene glue, styrene-butadiene glue brominated butyl glue, acrylate glue, silicone rubber and rubber and plastic and other special adhesives, can significantly improve crosslinking performance, improve heat resistance, suitable for high-temperature vulcanization system, reduce compression permanent deformation, but also reduce the amount of peroxide, prevent the scorch of the rubber in the processing process, improve the adhesive and cord and metal adhesion strength.

HVA-2 is a sulfur-free vulcanizing agent for cable rubber, which can replace the thialamue and thiazoles and other sulfur-containing vulcanizing agents to solve the problem of blackening copper wires and copper electrical appliances due to contact with sulfur-containing vulcanizing agents to generate copper sulfide pollution.

■Dosage

0.5-1.0 parts as a gum inhibitor, 2-3 parts as a vulcanizing agent, 1.5-2.0 parts for improved compression set, and 0.5-5.0 parts for improved adhesion strength.

Bridging Agent PL400 (TMPTA)

Application: 1, with peroxide vulcanization, as a bridging additive, can improve the density of the bridge, improve the tensile strength, reduce the compression permanent deformation, shorten the vulcanization time. 2, mixing has a plasticizing effect, after vulcanization there is a hardening effect, can be made of high hardness products hardener, about every increase of 1PHR PL400, can increase the hardness by one degree. 3. Improve the crosslinking efficiency and reduce the amount of peroxide used. 4. Because this product is a colorless transparent liquid, it can also be applied to the transparent products industry. Recommended dosage: 1, in the general rubber as a co-crosslinking agent (bridging additive), it is recommended to add 2-4PHR2, in EVA foam products, it is recommended to add 0.5-1.0PHR3, in high hardness products, it is recommended to add 10-30PHR