Open time and set time of hot melt adhesive

Open time and Set time are the important specifications in choosing the suitable hot melt adhesive for specific applications. Choosing a glue to agree with the specifications will be one of the factors in achieving the desired adhesion.

Open time: is defined as the period when the adhesive is applied to the surface of the material until it creates an adhesion with the other surface materials.

Set time: is defined as the time it takes for two surfaces to form to adhere together and create a satisfactory adhesion.

Set time & Open time depends on four main factors:

• Type of substrate
• Type of adhesive
• Amount of adhesive used
• Temperature

The current hot melt glue types include EVA-based adhesives, polyolefin-based, polyurethane-based, polyamide-based. Each type of glue will have its characteristics of open time and set time. Most EVA adhesive has a relatively long Open time and set time than other glues. Whereas polyolefin-modified types such as APAO or mPO will have a longer Open time but have a short Set time.

There are many ways to determine the Open time and Set time of the glue. The Open time and Set time of thermoplastics are determined based on the energy transition of energy under the influence of temperature. At room temperature, the adhesive exists in an elastic state (hard zone). It becomes softer at softening point and flows into a stream when it reaches the melting point. The cycle then moves from the molten back to the elastic as it cools. 

The way below is a fairly common method used in the lab.

Determine the Open time:

• Put the glue in the REKA gun and heat it to the desired temperature.
• Spray the adhesive onto the surface of the material (consisting of many samples).
• Apply the other surface to the other surface after different times (after 2 seconds, 4 seconds, 6 seconds,...) since the adhesive applied.
• Then allow the sample to dry completely after 5 minutes.
• Check by separating two layers of material. The last complete tear-off paper sample (with the longest time) is the open-time.

Determine the Set time:

• Put the glue in the REKA gun and heat it to the right temperature.
• Spray the adhesive onto the surface of the material (consisting of many samples).
• Put another surface onto the glued surface at the same time. 
• After pressing time (2 seconds, 4 seconds, 6 seconds,...) we tear two surfaces of the material.
• The sample that dries and completely tears off the paper (with the shortest time), that sample is selected to determine the set time for adhesive.

Test-recorded parameters may differ from each test, but that is the basic information for selecting a suitable adhesive. Therefore, it is necessary to apply reality to the production system to have a more accurate assessment.