Sticking With It | Selecting the Right Adhesive for Your Pressure-Sensitive Tape
- Published: February 14, 2017, By Ingrid Brase
Tape is a broad category, but there are common factors to consider in choosing the right adhesive for the job.
Selection of the adhesive is one of the keys to a successful pressure-sensitive product, as it provides the main functionality. In this column, we will explore one of the largest and most complex applications for pressure-sensitive adhesives: Tape.
Pressure-sensitive tape products span a broad range of applications from packaging tape to sealing cartons to tapes used in the construction of electronic equipment. Pressure-sensitive tapes are used as an alternative to other fasteners, such as screws or rivets. They provide a full contact bond between the two surfaces, are more aesthetically pleasing to the eye, and are also lighter in weight. Applications are unlimited, and the industry continues to view replacement of other fasteners as an opportunity for expanding and “growing the pie” of tape applications.
Tape is a very broad category but there are several common factors that must be taken into consideration to ensure the right adhesive is selected for the job. The adhesive is the most critical part of these products, as it provides the mounting or bonding performance of the tape; in some cases, it is only single component of the product in use.
As before, let’s use the checklist approach, namely:
- Materials: What facestocks (carriers) and liners will we select?
- Manufacturing: What equipment will we use?
- End Use: What are the requirements?
- Cost: What can we sell the product for and what profit do we want to make?
Before we begin to review the checklist, a good place to start is to think about the application where the tape will be used. This will enable us to determine how the product will be constructed and applied in use. For instance, if the tape is used as a protective mask, proper selection of both liner and facestock or carrier will come into play. If the application needs only adhesive to bond two surfaces and ensure a complete bond, then perhaps we will need to only focus on liners to protect the adhesive prior to application.
Many of the recommendations that follow are also applicable to medical tapes. However, since there is the added complexity of both regulatory and skin contact to consider, I will cover medical tapes in a future article.
MATERIALS
Let’s start with materials. To make my comments easier to follow, I will talk about materials by the type of tape.
First, let’s look at mounting applications. This is where we would use a transfer or unsupported film tape. In application, the adhesive film bonds to the two substrates. The adhesive is coated to a liner and then a second liner is laminated to the adhesive to create the tape product. The liner can be coated with release coating on both sides to create a self-wound tape. The liners must be carefully selected so there is a differential between their release, i.e., one requires a much lower force to remove than does the second. In the self-wound application, the same principal would apply, the coatings must have enough difference in their release properties. The liners must allow for easy removal of one side to expose the adhesive to the first surface (the “transfer”) then removal of the other side once the adhesive is in place, allowing it to bond to the second surface. The key to a transfer tape is to ensure the adhesive does not experience “confusion,” that is, it releases smoothly from the first then the second liner. Collaboration between the liner and adhesive supplier that you engage can sometimes be beneficial as they may have recommendations based on work they have done together.
But what if you are trying to bond two different types of surfaces? Then a tape type to consider is a double-sided tape. Here there is a carrier, usually a film like polyester, various foams, or a tissue layer, that separates the adhesives. The carrier will add some structural integrity to the tape as well. Films or foams will add more stiffness, whereas a tissue layer may be used to provide a coating surface for the two different adhesives. Liners will need to be selected that allow for easy removal from both sides of the tape.
If the tape will provide a protective function, then the constructions will be similar to the labels and graphics we have discussed in previous columns. Determining the carrier (or facestock) to be used will narrow adhesive selection. For instance, if a vinyl tape is being developed, then we should limit adhesive choice to those that are not sensitive to degradation by the plasticizers in the vinyl. If a metal foil tape is our desired product, we will need to choose an adhesive with excellent bonding to the metal surface. There are a variety of carriers that can be used in a single-faced tape construction including foam, foil, paper, and cloth. As in all pressure-sensitive applications, it is critical to know what the carrier will be so that it ensures the adhesive selected will have good adhesion to the carrier.
Liner selection for all the various types of adhesive is also very important. In many cases, the developer may have a liner in mind; if this is the case, then that should be shared with the adhesive supplier to narrow down adhesive recommendations. Adhesive suppliers also may be able to recommend liners that are compatible with their products.
manufacturing
Let’s next move to manufacture of the self-adhesive tape. Ultimately the adhesive selected will be primarily based on end-use requirements. Understanding the coating capability of existing machinery, including operating speed capability, process requirements such as viscosity, and coating method (gravure, slot die, etc.) are key basics. Having a coatweight target based on end use and cost, as well as a desired line speed, helps narrow adhesive selection.
The manufacturing environment also must be considered. How will the adhesive be stored? What type of container is optimal for adhesive delivery? If we select a liquid adhesive, is there a bulk tank and does usage warrant bulk? Is the plant climate controlled, or will there be seasonal variation in temperatures that needs to be taken into consideration? For some applications, this last point can be a serious factor in determining how an adhesive will dry and release from a liner. The storage of the coated rolls also must be considered as this will impact how the tape ages and impact release properties. Accelerated aging tests can give indications of longer-term storage but also running real life aging under plant conditions is suggested. If the liner-adhesive construction is sensitive to humidity, perhaps packaging the final tape construction in a sealed package is necessary.
End Use
Selection of materials and adhesive are largely dictated by the end-use requirements for the tape. Factors to consider include: How long will the product be used? Under what environmental conditions does it need to survive—heat/cold, humidity, cleaning agents? What type of bond strength is needed?
For single-faced tapes, the bond strength will be determined by both the carrier and the surface to which the product needs to adhere; this may also influence the target coatweight. For transfer tapes and double-faced tapes, knowing what two surfaces we want to bond together is critical.
As an example, if we are developing a double-faced tape for adhering a plastic nameplate to a metal door, we might select a rubber-based adhesive known for its strong affinity for plastics for the nameplate side and a solvent-borne acrylic with its strong affinity to metals for adhering to the metal door.
Shear performance is also critical criteria in many applications as the bond may be load bearing. Adhesive suppliers conduct both static and dynamic shear evaluations of their products to mimic the end-use conditions.
On the other extreme can be the wide range of temporary use tapes, such as masking tapes. Good adhesion to the carrier is vital and an understanding of the potential surfaces where the tape will be adhered allows for selecting an adhesive that removes without leaving residue. Some masking tapes are used in processing to protect surfaces during heat curing of components; knowing these exposure temperatures ensures the removability of the adhesive will not be compromised by the heat history.
Regulatory requirements must, of course, also be taken into consideration. End use will determine which set of regulations, i.e., UL, AAMA, CONEG, REACH, etc., may be applicable. Determining point of sale, domestic only or overseas sale to Europe, will indicate if REACH guidelines will need to be followed. In all cases, extensive testing of the final product may be required to meet specific requirements for certification of the final products.
Cost
Finally, I conclude by switching gears and putting on my marketing hat. One of the most important factors to consider is price point for the final product. At what price can we offer our new product and gain market interest? Is the opportunity large enough to consider the developmental costs associated with the new product? What profit do we want to make as a reward for our efforts?
If we subtract the profit from our selling price, we arrive at our target cost for the new product. There are various ways to account for manufacturing costs, whatever method is used by your company must be subtracted after target cost is determined. Now we can take a hard look at what adhesive and materials we can afford to consider.
Developing these targets up front saves development time and frustration. Development of a new pressure-sensitive tape is complex. This is but a brief insight to some of the factors to consider and hopefully helpful to anyone considering development of these types of products. If there are aspects of adhesive selection for this or other applications you are working on and you have a question, just ask!
Next time we will explore the world of medical tape manufacture. Until then, keep Sticking With It.
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.
