Chemical flame retardants in acrylic pressure sensitive adhesives

Chemical flame retardants refer to flame retardants with clear chemical composition and small dosages, and some can indeed have a chemical reaction with polymer. Although the dosage of this kind of flame retardant is small, their efficiency is generally high, and the number of varieties is large, which has the role of similar polymer chemical additives, and they are divided into halogenated flame retardants and halogen-free flame retardants.

(1) The halogen-containing pressure sensitive adhesive widely used at present has excellent flame retardancy.

Organic halide produces active halogen groups in the gas phase, which can effectively change the thermal oxidation process of polymers. The HX released by the decomposition of flame retardants interacts with the H and OH free radicals produced by polymer degradation so that the concentration of free radicals is reduced, thus delaying or terminating the combustion chain reaction.

(2) Chemical flame retardants——halogen-free flame retardants include phosphorous flame retardants, nitrogen flame retardants, antimony flame retardants, boron flame retardants, silicon flame retardants, and smoke suppressors.

1. Phosphorous flame retardant: phosphorous flame retardant is added to the polymer pressure sensitive adhesive when heated, it will decompose into polyphosphate, polyphosphate is a stable compound that is not volatile, forming an isolation layer on the surface of the combustion material. In addition, the dehydration of poly meta phosphate promotes carbonization, so that the surface of the carbonized film, so as plays a flame-retardant role. The main products of inorganic flame retardants containing phosphorus are red phosphorus flame retardant, microcapsule red phosphorus flame retardant, ammonium phosphate, ammonium polyphosphate, and so on. Organophosphorus flame retardants include phosphate ester, phosphonic acid and phosphonate ester, phosphonic oxygen compound, cyclic phosphate ester, phosphorus-containing diols, and polyols. Red phosphorus is easy to hygroscopic hydrolysis, releases toxic phosphine, and industrial products need to be stabilized and coated.
   With the increase in the amount of halogen-free flame retardant materials, the amount of red phosphorus flame retardant (microencapsulated red phosphorus flame retardant) is also increasing, and its flame retardant effect is better than that of phosphate esters. Phosphorous flame retardants also have some disadvantages, such as a large amount of smoke, high toxicity, easy hydrolysis, and poor thermal stability. Therefore, phosphorous flame retardants need to be further studied and improved.
2. Nitrogenous flame retardant: in the decomposition process to form ammonia and other non-combustible gas, dilution and dilution of flammable gas or covered in pressure sensitive adhesive surface and flame retardant. Mainly melamine and its salt, guanidine salt. It has no halogen and low smoke, which is conducive to environmental protection. However, the flame retardant efficiency is generally not high when used alone, and a large amount is required, which often leads to problems in the processing and mechanical properties of the polymer. It is often used in combination with other flame retardant systems (such as phosphorus or halogen).
3. Antimony-containing flame retardant: mainly antimony trioxide (SbO) and antimony pentoxide (Sbs), in the flame retardant application, is mainly used with halogen flame retardant, as a synergistic agent.
4. Boron containing flame retardant: mainly as a synergistic agent of the flame retardant system to use, through melting and then covering in the surface, so that oxygen can not contact with the combustion surface, the further oxidation of the carbon layer has a protective effect. Zinc borate is the most commonly used flame retardant containing boron, its cost is low, and has a synergistic effect with a variety of flame retardants.
5. Silicon-containing flame retardants: The addition of silicon-containing compounds can promote the combustion of carbon in the solid phase, and can capture active free radicals in the gas phase, which is generally considered to be environmentally friendly additives. It mainly includes silicate, polymer nano-layered silicate, and other inorganic silicon as well as linear silane, siloxane, and another organosilicon.
6. Smoke suppressant: the smoke and gas generated when the polymer combustion is the main culprit of death, adding a smoke suppressant can reduce the amount of smoke. The main smoke suppressants available now are zinc borate, alumina trihydrate, molybdenum compound (molybdenum dioxide, ammonium molybdate) and its complex, magnesium-zinc complex, ferrocene, ammonium polyphosphate, tin compounds, etc.