Key Criteria for Successful Applications in the Adhesive and Tape Industry

Adhesive and tape technology today has become a far more extensive and detailed field than one might expect. Tapes and adhesives are now used not only to support traditional methods (screws, nails, rivets, etc.) but are increasingly being chosen as replacements for these methods. In this capacity, they have become cost-effective solutions that help manufacturers across many sectors save time, create flexible designs, and improve the quality and physical appearance of finished products. Of course, at this point, just as with any product, using tapes and adhesives in the proper manner will increase the efficiency gained from the adhesive and support the performance obtained from these products, thereby strengthening confidence among users. As Bestek Endüstri & Kimya, over 18 years we have supplied and sold industrial adhesive and tapes from both 3M and Lohmann brands to industrial manufacturers. With the goal of ensuring that the right product is used in the right application in the right way, we share all our knowledge and experience with our business partners. Today, we wish to convey some of this information to you, our valued readers. The existence of thousands of different types of adhesives should not be perceived as a marketing technique. In fact, inventing a single tape or adhesive and then using it in hundreds of different applications would contradict the natural flow of life and the laws of physics and chemistry. Different parameters affect the performance of an adhesive. Some of these parameters are shown in the table below. Through this table, it can be understood that even with just a few simple different parameters, it is possible to create dozens of different need combinations. Given this situation, it is clear that each adhesive meets a different application and expectation, and therefore hundreds and even thousands of types of adhesives and tapes exist for hundreds of different applications and user expectations. We can start with a couple of simple examples. For instance, on a smooth surface like glass, thin film or tissue tapes (100-200 microns), such as 3M 9088 or 3M 9448, may be preferred. However, on rough or uneven surfaces with waves or indentations, tapes of this thickness would not make full contact with the surface. In such cases, PE-PU foam tapes with greater thickness (800-3000 microns), such as 3M 4492 or 3M 4008, may be preferred. Similarly, if transparency is a criterion on glass, transparent carrier tapes may be preferred, while on metals, grey colored tapes more suited to metal colors may be chosen. Similar considerations apply to the liquid adhesive group. For instance, on a rough surface, a PU adhesive capable of serving as a filler up to 3.0 mm (3M PU 540) may be preferred. However, when a thinner bond line thickness is required, an epoxy or acrylic-based material from the structural adhesive group may be preferred (3M DP810 or 3M DP100). To make the subject more specific, in today's article we will focus on the polarity of surfaces. Surfaces, which can generally be grouped into three different main categories, are actually one of the first steps from which we need to request information from the user in proper product selection. It is essential to know on which surface or surfaces the adhesive or tape will be used. Based on this determination, it becomes possible to narrow down thousands of product options to hundreds or even dozens of varieties and select the right product. After a rainy day, pay attention to your vehicle's carport. Are the raindrops on your vehicle in small round shapes or ball-shaped, or have they run off in long lines? The conclusion you reach will provide you with information about surface energy and polarity. Specifically, if raindrops (water) remain on the vehicle in ball shapes, we can say that the surface tension of the water is greater than the surface tension of the paint on the carport. Conversely, if the water droplets cannot hold and flow off, remaining in ball shapes on the vehicle, then the surface tension of the vehicle's carport or paint is greater than the tension of the raindrops. But what effect could this have on adhesives and bonding performance? Let us see together.

1. Polar Surfaces:

We can classify material groups such as metals (copper, steel, aluminum, zinc, lead, etc.), porcelain, and glass as polar surfaces. Adhesives applied to these materials can spread and flow more easily on the surface (high wetting) and in this way affect the surface more extensively, increasing the adhesive's retention rate on the surface and providing strong bonding. Thus, when you want to bond two different polar materials together, you have taken the first step toward establishing a strong bond. Ignoring all other parameters, criteria, and expectations, acrylic-based adhesives can be said to be more preferred adhesive types for polar surfaces. Of course, since we can also classify acrylic-based adhesives within their own categories as reinforced acrylic, pure acrylic, water-based acrylic, etc., it becomes possible to change the acrylic adhesive type according to the type of polar surface. We do not wish you to conclude from this that "only acrylic adhesives should be used on polar materials." Because depending on other expectations and criteria, synthetic or natural rubber adhesives in the tape world and epoxies or urethanes in the liquid adhesive world can also be used. However, to make a general comment and explain the concept of polarity, it is possible to proceed with such an example. The adhesive type that has a longer lifespan, resists external conditions, and is less sensitive to conditions such as heat and humidity is acrylic in the tape world, and with these properties, it promises strong, long-lasting bonding solutions. (As a general comment, we can say that in structural adhesives, epoxies have a longer lifespan and higher aging resistance.) Many of 3M's liquid adhesives and tapes perform quite successfully on polar surfaces. 3M's 9088 polyester carrier film tape, the 4950 coded tape from the VHB group, and products such as DP8405 or DP8407 from the liquid group can be cited as examples.

2. Semi-Polar Surfaces:

The variety of materials in this group is greater. However, you will notice that most of them are plastic-derived materials. For instance, polyamide, PVC, epoxy paint, acrylic (PMMA), polycarbonate, and ABS are materials that we can say have medium surface tension. For adhesives applied to such surfaces, it can be observed that they spread less easily on the surface compared to polar surfaces (med. wetting), and an adhesive that performs very well on polar surfaces shows lower performance in final bonding for this reason. To overcome this and achieve high bonding performance, the other four parameters mentioned in the table can be examined, and surface preparation work can be performed on the surface (for example, by applying a thin layer of 3M Primer 94 to the surface) to increase the surface tension of the material to be bonded. As a second method, a different type of adhesive can be preferred instead of acrylic-based adhesives suitable for polar surfaces (for example, tape with synthetic or natural rubber adhesive).

3. Non-Polar Surfaces:

Materials in this group are perhaps what many adhesive and tape users find most challenging. Applications involving non-polar materials with low surface energy (LSE) are those where expectations for adhesives are highest and risks are greater. Materials such as polyethylene, polypropylene, PVA, PTFE (Teflon), powder coating, and silicone have LSE characteristics, and it is very difficult for a standard adhesive applied to them to spread on the surface. This is because the surface tension of the material is so low that the surface tension of the adhesive often exceeds it, causing the adhesive to remain in ball form and unable to flow across the surface. To overcome such situations, manufacturers have different solutions. For instance, 3M has specially formulated tapes and adhesives developed for LSE surfaces. From the liquid adhesive group, specially formulated two-component acrylics for plastics (3M DP8005, DP8010), and from the tape group, tapes with LSE characteristics (3M 93020, 93010, LSE VHB 110, and especially the combination of Primer 94 and 5952 VHB on powder-coated surfaces, etc.) can be preferred to achieve the desired spread and flow performance on surfaces such as PP, PE, or Teflon. In this way, it becomes possible to bond materials with low surface tension in a strong and permanent manner. Additionally, as a note, it is known that silicone adhesives perform better on surfaces containing silicone. If you have the opportunity to modify the structure of your surfaces, besides the adhesive you would choose, you can also bring your non-polar materials closer to semi-polar or polar characteristics through certain physical methods. For instance, by sending sufficient voltage to the surface through corona or plasma treatment, you can change the properties of an inert material through electric current and increase its tension. Additionally, in some applications, before applying liquid adhesives, you can perform light sanding or roughening on the surface. Since roughening is a physical intervention, it will increase the bonding area and contribute to obtaining more adhesion and better bonding performance for the adhesive. Independent of all these surface and material types, an important rule is that before the bonding process, surfaces must be cleaned of all foreign substances such as grease, dust, dirt, and liquids. It is recommended that you clean your surfaces with a liquid that does not leave a grease layer behind. For this purpose, you can use isopropyl alcohol, MEK for more difficult cleaning tasks, or if no cleaner is available, simply clean the surfaces with a clean cloth and water. Perhaps the most difficult and misunderstood topic in the world of tapes and adhesives is that there is no single right answer and each demand or customer need is unique. Although all the information we have provided are classification and explanation methods to better describe the adhesive and tape world, the most correct method will be to select an adhesive based on results obtained by first evaluating each request separately according to the specified different parameters and then evaluating them as a whole. In this first article, we have touched on the importance of material and surface structure in adhesive and tape selection. In our next article, we will continue with other criteria that lead to correct and successful application.  

Çağrı Bülbül Sales and Operations Manager Bestek