Key Performance Indicators for Hot Melt Adhesives

Overview

Hot melt adhesive is an important category of the adhesive industry, with 100% solid content, no solvent, environmental protection, non-toxic, fast curing characteristics, widely used in automated packaging, sanitary products, labels and tapes, medical, automotive, construction, furniture, printing and binding, shoe, clothing, and other industries, usually refers to the room temperature presents a solid, when heated to a certain temperature will be fused into a thick liquid, coating, wetting the object to be adhered, after pressing and cooling to room temperature, the bond will be completed within a few seconds. It is usually solid at room temperature, when heated to a certain temperature, it melts into a viscous liquid, after coating and wetting the adhesive, after pressing and cooling to room temperature, the adhesive will be finished within a few seconds. The determination of the components of the hot melt adhesive and their dosage depends mainly on the ability to obtain the properties required for the application. At the same time, when using hot melt adhesives, it is also necessary to fully understand the properties of the adhesive used in order to determine the appropriate conditions of use.

Melt viscosity

This is a performance indicator that reflects the size of the hot melt adhesive flowability. It directly affects the adhesive on the adhesive coating, wettability and permeability, the phenomenon of pulling the glue also has an impact. Therefore, the melt viscosity is to determine the melt and coating process is an important basis. Melt viscosity and temperature has a close correlation, it is with the lowering of the temperature and growth, so it must be measured at a certain temperature.

Measurement is generally carried out at the average temperature of the hot melt adhesive at the time of use (190±2°C). Low melt viscosity hot melt adhesive can be measured directly with a rotational viscometer. Determination method is: the pre-melted hot melt adhesive sample 500ml into the viscometer drum, before the determination of the temperature (190 ± 2 ℃) under the maintenance of 5min, so that the rotor rotates 30-60s, readings. For high melt viscosity of hot melt adhesive, usually the determination of the hot melt index, is to use a special melt index tester to determine. Determination method is: 190 ± 0.4 ℃ molten glue poured into the measuring instrument in the drum, and then to the weight of 2160 ± 10g of the punch press down, measured in 10min within the glue was extruded out of the bottom of the drum hole in the number of grams, that is, the melt index. In order to obtain a good bonding effect, should be more the type of material to be glued, the shape of the adhesive surface and so on to select the appropriate melt viscosity of the hot melt adhesive.

Softening Point

It is the temperature at which a hot melt adhesive starts to flow and can be used as a rough indicator of the heat resistance, melting ease and drying time of the hot melt adhesive. It depends on the structure and molecular weight of the basic polymer. The softening point temperature is higher than the glass transition temperature, but there is no certain proportionality between them. Generally high softening point of the glue, heat resistance is good, but the drying time is short. However, the different composition of the glue may not always comply with this law. The softening point is usually determined by the globe method.

Thermal Stability

It is the performance of hot melt adhesive to resist oxidation and thermal decomposition under prolonged heating, which is an important index to measure the heat resistance of the adhesive. Although the hot melt adhesive are added to the antioxidant, there is a certain role, but if a long time in the use of high temperatures, even with the addition of antioxidants can not prevent oxidation and thermal decomposition. Therefore, it must be based on the thermal stability of the adhesive to determine the amount of each melt and the melt time of the adhesive heating, and in this way to design the capacity of the melt tank. The stability of hot melt adhesive mainly depends on the heat resistance of its main components. Generally because of its components in the viscosity enhancers and caused by the poor thermal stability of more cases.

Thermal stability is generally measured by the longest period of time that the glue can be experienced without oxidation and within 10% change in viscosity at the use temperature. If it can experience 50-70h, then the thermal stability is good.

Drying Time

The drying time refers to the time from the application of adhesive, after a period of effective exposure to the adhesive bonded to the time of compression, and after curing has a better adhesive bonding properties, more than this period of time, the adhesive bonding performance is greatly reduced, and even can not be adhesive bonding, which is an important process performance of the hot melt adhesive. The main factors affecting the drying time are the specific heat of the hot melt adhesive, coating temperature, the amount of adhesive coating, gluing method, ambient temperature, the type of material to be glued, the preheating temperature of the glued object and thermal conductivity. In practice, the adhesive should be quickly pressed together after application, i.e. to shorten the drying time as much as possible in order to ensure the quality of the adhesive bonding.

About Us

LONSUN is a supplier of raw materials for disposable hygiene products. If you need hot melt adhesives for the production of nappies, sanitary napkins, nursing pads, etc., please contact us.