The flame retardancy of pressure-sensitive flame retardant adhesives often conflicts with its three physical properties (peel force, retention force and initial tack force). In order to obtain a certain flame retardant performance, adding more flame retardant fillers will inevitably reduce the initial tack and peeling force of the adhesive; it is difficult to achieve satisfactory flame retardant properties with a small amount of flame retardant fillers. At the same time, the addition of flame retardant fillers will cause the adhesive to settle during storage and use, seriously affecting the normal use of the adhesive.
Pyrogenic silica is mainly composed of silicon halide that is hydrolyzed at high temperature in a hydrogen-oxygen flame and then condensed into amorphous nano-sized particles. It has the characteristics of high purity, no pollution, high porosity and high temperature resistance. Its particle size is small, its specific surface area is large, and it can be well dispersed in the matrix resin. It can improve the heat resistance of many polymer materials, so it has good comprehensive performance in terms of processing performance and flame retardant performance.
Oxygen index (OI index) refers to the oxygen concentration required for a material to reach the ignition point. Generally speaking, the higher the oxygen index of a material, the higher the concentration of oxygen required to catch fire and the less likely it is to ignite, and vice versa. It is generally believed that materials with an OI index less than 21 are flammable materials, 21 to 27 are slow-burning materials, and materials with an OI index greater than 28 are flame-retardant materials.
Take solvent-based acrylic glue as an example: adding an appropriate amount of fumed silica to acrylic glue has little effect on the three physical properties of the glue. At the same time, it has thickening, thixotropic and anti-sedimentation effects, and also has the flame retardant effect of adhesives. Sex has a certain promoting effect. In the acrylic system without flame retardant fillers and fumed silica, its OI index is 18; after adding flame retardant fillers, the OI index reaches 28; while the amount of flame retardant fillers remains unchanged, add 1% fumed silica. Silicon oxide Silicon oxide, OI index can reach 30. As the fumed silica content increases, the OI index increases. When the added amount of fumed silica reaches 5%, the OI index can reach 40. This shows that the application prospects of fumed silica in the field of flame retardant adhesives are very optimistic.
