Hot Melt Adhesives (HMA) are types of adhesives applied when hot, in a liquid form and once cooled down to become solid. HMA has no carrier, whether water or solvent, for the adhesive; in effect, heat is the carrier that allows for the adhesive to be applied.
In most cases, HMA does not undergo any chemical reaction like cross-linking, carrier removal, or solvent evaporation. This states that there is a 100 % formulation of the adhesive, and there is no need for a correct ratio of components to be obtained. No other processes like mixing are required either before or at the time of the application.
All hot melts work by “wetting out” the surface of the substrates that are being adhered together, and this can be achieved when the hot melt is being applied in the form of the liquid. The hot melt may quickly cool, which can sometimes make adhesion to the second substrate complex. This, however, is dependent upon the substrate temperature.
There are two subcategories of hot melt adhesive tape :
Pressure Sensitive Adhesives (PSA)
Non-Pressure Sensitive Adhesives (non-PSA)
The difference between the both is that PSA hot melts remain tacky once cooled to room temperature and when bonding non-PSA hot melts; the joining of substrates must be done whilst the HMA is desirable to allow for the wetting of adhesive onto both substances to ensure a good bond is achieved.
Therefore, the HMA must be hot for as long as thus. To achieve this, specialist equipment depends on the adhesive and application requirements.
While using PSA, substrates can be joined when hot, depending on the adhesive and substrates being used. This may occur at room temperature, as the glue will still be tacky. If the substrates are bonded together at room temperature, then the tack level of the PSA must be such that it can wet out the second substrate that has been applied to the HMA. Bagla Group is a top tape manufacturers.
After cooling, regardless of the type of HMA used, it must have enough cohesive internal strength and maintain its adhesive properties to keep the two substrates bonded.
Properties of Hot Melt Adhesives
If one is making usage of the HMA, several properties need to be considered:
Pot life stability
Pot life stability is when the adhesive is stable at elevated temperatures. At the moment you are applying the hot melt, it becomes essential to make sure that the thing that bonds doesn’t break down or decompose too quickly when at an elevated temperature.
Open time is the time after the adhesive is applied to make a suitable bond. The higher the application temperature, the longer the available time will be.
Tack is the term used for knowing how sticky the surface is and can be referred to as hot tack or for PSA hot melts – room temperature tack. Room temperature tack can be measured by using the rolling ball test. Apart from this, there are also several other tests, including a loop tack test.