What Are “Good” Hot Melt Pressure Sensitive Adhesives?

Many HMPSA (Hot Melt Pressure Sensitive Adhesives) users frequently request good products at low prices without knowing or telling suppliers what they actually need. In reality, there is no ideal product for a variety of applications. Each application may need a specific performance of the HMPSA.

How does a manufacturer select an appropriate HMPSA for a specific use? Adhesive users should always consider the following subjects:

Price: Price is not always related to the raw material cost, processibility and adhesion performance. However, it is directly related to the volume purchased, color, and lot-to-lot consistency. Most water white HMPSAs contain hydrogenated hydrocarbon tackifying resins, which are generally more expensive than non-hydrogenated yellow tackifying resins. Quality raw materials normally offer narrower specifications and result in more consistent products. These quality materials are normally more expensive.

Quality: Quality is not equivalent to processibility and adhesion performance. Instead, quality is a reflection of aging stability and the consistency of color, clarity, and other physical and adhesion performances. Adhesives with the correct bonding and machining characteristics do no always have to be the most expensive product to be considered of high quality. It is worth emphasizing that to make a quality HMPSA requires both quality raw materials and a more sophisticated production system. Pulling vacuum during mixing at a temperature higher than 325F is crucial for obtaining consistent products. Without pulling vacuum, polymeric materials tend to oxidize at elevated temperatures, which will result in poor aging stability and lot-to-lot deviations.

Processibility: If a HMPSA offers high adhesion performance in the lab, but not in the real world application it was design for, it is not a good adhesive. Depending upon various application techniques, such as slot die, spraying, fiberization, beads, and etc., in addition to offering good adhesion performances, adhesive formulators should always include a good machining or processibility for end users. The processibility is normally related to the viscoelasticity of HMPSAs, which is not simply related to the melt viscosity and softening point. Ideally, an adhesive should be designed and applicable for any hot melt applicator. Unfortunately, very often, in order to offer certain specific adhesion performance, it is very difficult to obtain raw materials which can the bond characteristics to a wide range of substrates. For such formulation, an adjustment of process condition is needed.

Adhesion Performance: It is impossible to develop a HMPSA possessing excellent adhesion performance for all different applications. If a HMPSA meets certain a manufacturer’s performance needs, it is a good product for them. If a multi-purposed product is requested, end users must first clearly define performance targets and test to see if those desired performances are conflicting with each other. It is not possible to achieve any performance disobeying adhesion principles and science. Simply put, “good adhesion” does not help formulators in designing appropriate products. Detailed descriptions of backing materials, release liner, substrates, processing applicators, bonding methods, performance specifications, aging requirements, servicing conditions, etc. are all very important information for developing adequate product imparting optimum adhesion performances.

Most HMPSAs are market or customer orientated products. There is no ideal product for every market. In order to develop an appropriate product, a detailed description of actual needs is very helpful and critical.

For more information call or email Pierce Covert,
Glue Machinery Corporation


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