Sticking With It | Pressure-Sensitive Adhesives 101

Published: March 05, 2016, By Ingrid Brase

Adhesives expert Ingrid Brase provides a nuts and bolts overview of PSAs in her inaugural column, which will focus on making the right adhesive choices.

A key component of any self-adhesive product is the adhesive; it is what makes the whole product work, providing adhesion of label, graphic, or tape to a surface, i.e., it makes it stick! Gaining an understanding of how these adhesives work and key factors to keep in mind when selecting an adhesive will ensure successful product development.

I am Ingrid Brase, and I am pleased to contribute some insight into adhesives to the readers of PFFC. So a bit about my background: I have almost 20 years of experience in the pressure-sensitive adhesives business. Most recently I was the market segment director for Henkel Corp.’s North American pressure-sensitive adhesives business unit. Prior to that, I held various market and business management roles for the same unit. I began my career as a research scientist but soon realized working in the lab was not a long-term career interest; I was more interested in how to apply science than in creating it.

I was fortunate to learn the ropes of business by taking an assignment doing business development where I was part of a small team tasked with bringing a new technology to market. I pursued my MBA at night at the same time. Both helped me progress my career and identify my interest in market strategy and product applications. When I took my first assignment with the pressure-sensitives team as the marketing manager, I knew I had found a place where I could make a contribution, leveraging my technical background as well as love of working with people to help our customers grow.

My objective in future columns will be to share my insights into adhesives and how an understanding of where and how they will be used can assist in making the right adhesive choice. There will be a flavor of marketing strategy and tactics woven in; the best product in the world won’t sell without a solid plan to back its launch and promotion. Your feedback and questions are welcome, as they may spur future columns in which we can explore specific areas or properties of adhesives that are of interest to you. The focus will be on applications and practical nuts and bolts ideas on how they can be used; I will leave the fancy science to my more learned colleagues in R&D.

So where to start? Well, let’s plunge in and begin with a very broad pressure-sensitive adhesive overview, Pressure-Sensitives 101 if you will!

Adhesives come in many forms and types. Simplistically for the types of applications we will be discussing, adhesives are available in two main forms: pressure-sensitive and those applied at point of adhesion (glue-applied). Glue-applied adhesives were the original products used most broadly. However, over time pressure-sensitive adhesives have replaced them. For the end-user, pressure-sensitive adhesives have many advantages, key amongst them ease of use. Instead of dealing with messy glue pots and worrying about adhesive shelf life and application details, now the end-user can simply dispense a label from a pre-coated roll or pull off a liner to apply a sign to a surface.

Pressure-sensitive adhesive laminations comprise three main components: the facestock or carrier, liner, and adhesive. Facestocks or carriers, the ultimate material that will be adhered to a surface, vary by use and include paper and film materials. Liners protect the adhesive on the reverse side of the label and allow for easy dispensing. The final component, adhesive, must stick to the surfaces where the laminate needs to adhere.

Adhesive performance is described by three key characteristics:

• Adhesion
• Cohesion
• Tack

Adhesion is used to describe the bond strength between the adhesive and the substrate. Here the development of the bond does involve some pressure application leading to the adhesive “wetting out” on the surfaces, that is, forming a continuous film between the facestock and surface. Adhesion is measured by peel strength. Peel values are obtained by applying a force to remove the laminate from a surface at a 180- or 90-deg angle.

Cohesion is best described as the internal strength of the adhesive. This is reported as shear strength or the ability of the adhesive to hold in place when weight is applied. Shear is critical for prevention of edge lift, especially on very curved surfaces where the facestock wants to return to its flat rigid shape. All three properties are important; relative importance is very dependent on the type of laminate and where it will be used.

Tack is the initial grab or attraction of the adhesive to a surface with no external pressure applied. Other terms used to describe tack are “thumb appeal” or “quick stick.” This is a critical property in auto dispensing of labels where sometimes the only force is slight air pressure and immediate adhesion to the substrate is critical.

The three adhesive properties can be used to divide adhesives into three very broad categories:

• Permanent adhesives have higher adhesion and last for the life cycle of the substrate. They form a bond that removal from a surface very difficult.
• Removable adhesives will generally have lower adhesion to substrates and remove cleanly with the facestock remaining intact even after aging.
• Repositionable adhesives will build a stronger bond over time; they exhibit some “open time” where they remove cleanly allowing for the laminate to be adjusted.

Adhesives are specifically formulated to achieve the type of permanence, repositionability, or removability required in end use.

Pressure-sensitive adhesives come in a variety of forms. The three most common are hot melts, emulsion, and solvent-based. The selection of the correct adhesive chemistry to use is very dependent on available coating equipment as well as end-use performance targets. The table below summarizes the differences between the adhesive forms.

Adhesive manufacturers are constantly striving to improve shortcomings of the various adhesive types so these properties should be used as general guidelines. For instance, in recent years, clear UV-stable hot melts have been offered as well as acrylic emulsions that are more water resistant.

In my next column, we will explore the important factors to consider when selecting an adhesive. I will share a handy checklist on what information would be useful to gather before calling your adhesive supplier for a recommendation. Of course, before developing any new product it is always important to do the marketing/business research to be sure that there is a good business case in place for the new product. Developing the business case is just as critical as developing the product!

Until next time…

About the Author

Ingrid Brase is a technical market strategist recognized for her ability to translate technical needs into business solutions. Her understanding of pressure-sensitive adhesives and their use is complemented by her strengths in strategic marketing, project management, new product development, and key account management. She is available for consulting or contact assignments in these areas. Ingrid’s expertise is a result of more than 20 years of experience in the p-s adhesives business. She was most recently the market segment director for Henkel Corp., rising to that position after various assignments in the p-s business unit. She began her career as a research scientist then progressed to market-focused roles. Ingrid earned her MBA at Rider Univ. and holds a BS in chemistry from SUNY/Oneonta. She has served on the board of directors for TLMI and AIMCAL in addition to chairing technical teams for both trade associations. Ingrid is a well-known speaker and author on topics related to adhesive use. To learn more about Ingrid or contact her, visit www.ingridbrase.com or call her at 609-558-9760.