Factors Influencing Hot Melt Adhesive Open Time and Curing Time




Hot melt adhesive is a kind of plastic adhesive. Its physical state changes with temperature within a certain temperature range, but its chemical properties remain unchanged. It is non-toxic and tasteless, and it is an environmentally friendly chemical product. Widely used in hygiene, food, home furnishing, automobile, packaging, electronics, shoemaking and other industries. During the application of hot melt adhesives, the hot melt adhesive machine has become one of the factors that affect the adhesion of hot melt adhesives. Another important factor is the opening time of hot melt adhesives. The opening time and curing time of hot melt adhesive are closely related to the speed of glue binding. Therefore, the following is a brief analysis of the factors affecting the opening time and curing time of hot melt adhesives:


Definition

Opening time: refers to the maximum time interval between the hot melt adhesive being applied and the surface still being able to bond to the substrate. The adhesive has a good bonding effect within the opening time. The opening time for the low-speed machine is 15-20 seconds, the medium-speed machine is 5-10 seconds, and the high-speed machine is 2-7 seconds.

Curing time: The shortest time for the hot melt adhesive to be pressed between two substrates to form a firm bond. The holding time should not be less than the curing time to bond well. When using, it should be selected reasonably according to the length of the conveyor belt, conveying speed, and seasonal changes. The curing time of the hot melt adhesive is generally 3 to 5 minutes.

Hot melt adhesive viscosity - temperature curve

Description of Figure 1

▲Must b<a, the exposure time is less than the opening time. The second substrate must be bonded at a sufficiently high hot melt temperature. Beyond point c, the open time is exceeded, and the glue is too cold to bond the substrate.

▲Must be d>c, the pressing time is longer than the curing time, and the hot melt adhesive must be cooled enough before the pressing force can be released. If the pressing force is released earlier than point d, the glue is not fully cured and the substrate will bounce off.


Hot melt adhesive viscosity - temperature curve




Description of Figure 2

▲The premise of hot melt adhesive bonding is the infiltration and penetration of the substrate, so the fluidity of hot melt adhesive is the key. Point c corresponds to the critical viscosity of the wettable substrate. If the viscosity is higher than this, the hot melt adhesive cannot fully infiltrate and penetrate the substrate, and thus cannot form an effective bond.

▲The cooling of hot melt adhesive is the process of rising cohesion. When the cohesive force of the hot melt adhesive is sufficient to overcome the rebound force of the substrate opening, the curing of the hot melt adhesive is initially completed. The cohesion of the melt is called melt strength and hot tack. Point d corresponds to the critical viscosity of the cohesion required for the initial curing of the hot melt adhesive.


The opening time of hot melt adhesive is very important to the influence of material adhesion. Understanding these factors can control the opening time of hot melt adhesive to a large extent, and choose the appropriate hot melt adhesive according to different needs.


Factors affecting the open time of hot melt adhesives:

*The performance of hot melt adhesive itself. The opening time can be designed, and a good recipe can have a longer opening time.

*Glue application temperature. Increasing the glue coating temperature can prolong the open time.

*Ambient temperature. If the ambient temperature is low, the hot melt adhesive will cool down faster and the open time will be shortened.

*Substrate temperature. The temperature of the substrate is low, the cooling of the hot melt adhesive is accelerated, and the open time is shortened.

*Amount of glue applied. As the amount of glue applied increases, the specific surface area of the hot melt adhesive decreases, the cooling becomes slower, and the opening time is prolonged.

*Glue mode. Glue application modes that reduce the specific surface area of the hot melt adhesive can slow down the cooling of the glue, thereby prolonging the open time.


Is the article on hot melt adhesive curing and hot melt adhesive sol time helpful to you or your company; at us Purking, our understanding of hot melt adhesives will help you choose and customize the right hot melt adhesive.