Sticking With It | Selecting the Right Adhesive for Your Self-Adhesive Graphic
- Published: July 12, 2016, By Ingrid Brase
Preparation of self-adhesive graphics is complex. If you are developing this type of product, here are some factors to consider.
Selection of the adhesive is one of the keys to a successful pressure-sensitive product as it provides the main functionality. In my previous column, we explored some of the factors that are important to consider when creating a label. So this time, we will explore the self-adhesive graphic, or as some may classify it, really, really big labels!
Because it’s defined differently by different people, let’s start by trying to define a scope for what I will be describing today. For me, self-adhesive graphics include film and vinyl-based pressure-sensitive labels and filmic materials, including durable labels, car wraps, container marking, and signage. My criteria are based on including constructions that must survive various environmental conditions for six months or more. It is still a broader category, but there are a number of common factors that must be taken into consideration to ensure the right adhesive is selected for the job.
As before, let’s use the checklist approach from one of my previous columns, namely:
- Materials: What facestocks (carriers) and liners will we use?
- Manufacturing: What equipment?
- End Use: What are the requirements?
- Cost: What can we sell the product for and what profit do we want to make?
Materials
This time we will start with materials. As stated in the definition, one of the key facestocks of choice in graphics applications is vinyl. As I learned very early in my adhesive career, all vinyls are not created equal. First, there are the two major categories of calendered and cast. These terms refer to the different ways the actual vinyl sheets are formed. Cast vinyl is created by “casting” the materials onto a sheet and slowly allowing them to dry whereas calendered vinyl is coated to a sheet and dried much more rapidly.
Cast vinyl generally is prepared in-house by the large format coating company that will make the final construction, whereas calendered vinyl is available commercially. As a general rule, due to its increased stability and longer shelf life, cast vinyls are used in longer-term applications and coated with solvent-based adhesives that are more stable to longer-term aging and environmental conditions.
Calendered vinyls come in two forms, polymeric and monomeric. Polymeric is a bit more stable than monomeric. Other filmic materials, such as polyethylenes and polyolefins, also are used to manufacture durable labels and signage, but vinyls still are the major facestock used. Vinyls present some true challenges to adhesives. First and most importantly is the fact that all of them will emit some of their components, namely plasticizer, as they age. These plasticizers have an adverse effect on adhesives. For rubber-based adhesives like hot melts, they “unzip” the polymers that provide the main adhesion characteristics, softening them to the point where they no longer perform. Water-based and solvent-based acrylics have been developed that are engineered to withstand degradation by these plasticizers.
Next is the fact that as vinyls age and the plasticizer leaches, they also shrink; again, a challenge for the adhesive to keep the construction in place as it ages, withstanding this shrinkage force. Adhesive manufacturers evaluate their products by aging on test vinyls to determine shrinkage and how their products maintain peel and shear over time.
It is vital to evaluate adhesive on the specific vinyl being considered for your construction so that good stability over the lifecycle of the product can be assured. Liner selection is always a factor as well. Testing and aging of coated rolls is highly recommended.
Manufacturing
Let’s next move to manufacture of the self-adhesive graphic. As we have just discussed, if we focus on vinyls, then our coating equipment must be suitable for a liquid coating, i.e., either a water-based or solvent-based acrylic. Understanding the coating capability of existing machinery—including operating speed capability, process requirements such as viscosity, and coating method (gravure, slot die, etc.)—is a key basic. Having a coatweight target based on end use and cost, as well as a desired line speed, helps narrow adhesive selection.
As indicated in previous articles, the manufacturing environment also must be considered. How will the adhesive be stored? What type of container is optimal for adhesive delivery—is there a bulk tank and does usage warrant bulk? Is the plant climate controlled, or will there be seasonal variations in temperature that need 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 is also a factor of consideration as this will impact how the vinyl ages. Accelerated aging tests can give indications of longer-term storage, but also running real life aging under plant conditions is suggested.
I recall one project where the customer was going to discontinue testing of an adhesive based on accelerated aging on vinyl. They remembered having an early test roll in the plant and found it in their scrap pile. Evaluation of the material that was over a year old showed that shrinkage and adhesive performance were well within specification, whereas the accelerated aging test gave out-of-spec results. They moved forward with the construction, met their target launch goal, and experienced no customer complaints related to adhesion or shrinkage.
End Use
As in the case of labels, selection of materials and adhesive are largely dictated by the end-use requirements for the graphics construction. Factors to consider include the following:
- How long will the product be used?
- Under what environmental conditions does it need to survive heat, humidity, cleaning agents?
- What type of bond strength is needed? Bond strength will be determined by both the facestock and the surface to which the product needs to adhere; this may also influence the target coatweight.
- Does the product have to stick immediately or will the end-user want some “open time” before a permanent bond develops?
As an example, in the car wrap application, the sheets of flat vinyl must be adhered to a three-dimensional surface requiring the installer to lift and smooth the vinyl during the process. Having the flexibility to manipulate the vinyl is a key factor. The ability for the wrap to remove as cleanly as possible at the end of its lifespan is also a desired property, reducing cleanup time.
For large format signage, this repositionability at installation is also required. For container marking, the challenge is immediate adhesion to a surface where the paints used may not be completely dry.
Regulatory requirements must, of course, also be taken into consideration. End use will determine what set of regulations, i.e., UL, AAMA, CONEG, REACH, etc., may be applicable. For many durable labels, there are specific UL standards that can impact design so they can be certified. Determining point of sale—domestic only or overseas sale to Europe—will indicate if REACH guidelines will need to be followed.
Cost
Finally, but probably most importantly, is considering a price point for the final product. At what price can we offer our new product and gain market interest? 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.
Preparation of self-adhesive graphics 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 of this or other applications you are working on where you have question, just ask!
Next time we will explore the world of 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.
