What Affects The Effectiveness of Hot Melt Adhesive Bonding?

Hot melt adhesives are widely used as adhesives in the disposable hygiene products industry. This article briefly introduces several process parameters that affect the bonding effect of hot melt pressure sensitive adhesives.

Hot melt adhesives and machine opening times

The machine's open time is the time it takes for the hot melt to travel from the tip to the laminating area, usually counted in seconds. It affects its temperature, as well as the wetting of the second substrate. In theory, it should be as short as possible. In practice, however, the limitations of the gluing head's placement or production speed also need to be taken into account. Its open time is the time for which it retains its initial viscosity after coating. The machine opening time must be much lower than its opening time, otherwise its already cooling and curing without laminating will make the bonding effect worse.

Hot melt adhesive and gluing temperature

The gluing temperature is the temperature of the hot melt in the tip, which affects the wetting of the substrate. Theoretically, the higher the temperature, the better, but taking into account its thermal stability, the heat resistance of the substrate and other factors, such as "bleeding". In some applications, temperatures higher than 180°C can affect the performance of the adhesive and the gluing process. In general, higher temperatures are required due to partial heat loss prior to lamination, longer open times and spray-type gluing processes. When adding glue, it should be done in small quantities, otherwise the temperature of the glue box will fluctuate greatly.

Hot melt adhesive and gluing volume

The amount of glue applied affects the cooling rate of the hot melt adhesive and therefore the wetting of the second substrate. Theoretically, the smaller the amount of glue applied, the better, but the final adhesion requirements as well as the open time must be taken into account. Usually, if the machine has a long open time, the amount of glue applied has to be larger. Generally speaking, the amount of adhesive applied to the backing of sanitary napkin or diaper is 25~35g/sqm, the amount of adhesive applied to the sanitary napkin wing adhesive is 30~40g/sqm, the amount of adhesive applied to the structural adhesive is about 3~4g/sqm, the amount of structural adhesive used for the base film lamination is 1~2g/sqm, and the amount of rubber band adhesive is 15~25g/sqm.

Hot melt adhesive and laminating pressure

Lamination is the bonding of two substrates under pressure. The laminating pressure is the pressure given by the machine during the laminating and bonding process of the two substrates. The laminating pressure affects the ability of the hot melt adhesive to wet the substrate, allowing it to penetrate into each of the two substrates, determining the surface form of the bonded area, which should be allowed to enter the laminating roller as soon as possible. Theoretically, the higher the laminating pressure, the better, but you need to take into account the ability of the substrate's mechanical properties to withstand, roller wear rollers, and glue penetration.

Hot melt adhesives are widely used in the disposable hygiene industry because they contain no organic solvents, are fast to apply and are safe and hygienic. Understanding the process parameters that affect the bonding effect of hot-melt pressure sensitive adhesives helps one to further understand this material.