Hot Melt Adhesive - Open Vs Set Time I
Open time and set time are two key processing parameters for EVA-based Hot Melt Adhesive, which will significantly affect the extent of instantaneous bonding and eventual fracture energy. It is not necessary to offer long open time and fast set time for any application. As a rule, the optimum open time and set time are determined by the application system, actual bonding process, and bonded substrates.
Open time is the time after adhesive is applied during which a serviceable bond can be made. Many factors affect open time, including temperature, substrate, adhesive, and amount of adhesive applied.
Set time is the time it takes to form an acceptable bond when two or more substrates are combined with an adhesive.
It is easy to define open time and set time described above. In most hot melt adhesive labs, however, the open time and set time are often determined by touch, which is a very fast but subjective test. Test methods are described as follows.
1. Completely melt a hot melt adhesive in a beaker at 325F.
2. Dip a glass rod inside the molten adhesive until it reaches the equilibrium temperature.
3. Remove the glass rod from the beaker and immediately apply a thin layer of adhesive on a piece of paper.
4. Immediately press fingers on the adhesive film and count the time in seconds until finger print and separation force is diminished.
5. Those finger print numbers are recorded as open time.
1. Completely melt a hot melt adhesive in a beaker or a jar at 325F.
2. Tilt the beaker or jar and pour a long bead of hot melt adhesive on a piece of Kraft paper.
3. Laminate another piece of Kraft paper on the top of the coated one immediately.
4. Slowly separate the two pieces of paper and count the time when one of the Kraft paper is torn. Record the time required to tear paper as set time.
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