In the meticulous art of signmaking, the choice of the right adhesive is as important as the design of the sign itself. The materials used, with their unique properties and reactions to environmental conditions, often dictate the choice of adhesive. Understanding how substrates interact with adhesives under various conditions is fundamental to achieving durable, visually appealing signs that stand the test of time. In this article, we look at the factors that influence adhesive selection for signmaking.
Substrate Influence on Signmaking Adhesive Selection
The choice of the right adhesive for signmaking is strongly influenced by the materials (substrates) used. Different materials expand or contract differently with temperature changes, which affects the choice of adhesive.
While metals need adhesives capable of withstanding considerable thermal movement, plastics require flexible bending-resistant options due to their sensitivity to temperature-induced deformation. Thin, lightweight substrates such as aluminum composites, for example, require adhesives with lower curing temperatures to avoid deformation. In addition, materials exposed to outdoor conditions require environmentally resistant adhesives, such as UV protection, to prevent premature degradation.
Knowing the individual material properties of your sign and the environmental stress factors to which it will be subjected helps you select the right structural adhesive for signage.
Understanding Adhesive Behaviour
The integrity of a sign’s bond lies in understanding the root causes of adhesive failure – read-through and cracking. But what sets these events into motion?
Some adhesives, or misuse of adhesives, are known to cause read-through, which in turn distorts or warps substrates. Here are some of the most common reasons adhesives can cause read-through:
- Shrinkage: Adhesives with high filler or solvent content may shrink upon curing, pulling on substrates and causing stress that leads to deformation and read-through.
- High curing temperatures: Overly high curing temperatures for certain adhesives can lead to substrate warping or deformation, especially in thinner, more temperature-sensitive materials.
- Inadequate flexibility: Adhesives with high modulus lack the necessary elasticity, preventing them from stretching with substrate thermal movement, causing stress and potential warping.
- Inadequate environmental resistance: Adhesives lacking resistance to UV or moisture can degrade over time, compromising bond strength and leading to substrate failure.
- Dissimilarity of coefficient of thermal expansion (CTE): Misalignment of the adhesive’s CTE value with that of the substrate increases bond line stress and the risk of distortion due to temperature fluctuations.
- Low modulus of elasticity and yield strength: An adhesive must balance flexibility and strength. If either the modulus of elasticity or the yield strength of the adhesive is too low, it may not be able to hold the substrate in place and prevent read-through.
- High glass transition temperature (Tg): Adhesives with too high a Tg may not adapt to thermal expansion of the substrate, causing stresses that compromise adhesion and lead to shrinkage.
- Incorrect application: Poor adhesive application, including non-uniform distribution and incorrect curing conditions, can lead to stress and substrate shrinkage.
- Poor fatigue resistance: Signs must withstand repeated stresses without failure. Fillers that may be added to ensure initial elasticity may degrade over time, leading to fatigue.
Cracking, on the other hand, is a common adhesive failure in sign manufacturing. The following conditions are known to lead to adhesive cracking:
- Excessive mechanical stresses: when a substrate bends or twists beyond the capacity of an adhesive, the bond can break.
- Temperature fluctuations: thermal variations can cause materials and their adhesives to expand and contract to different degrees, putting a strain on the adhesive’s bond.
- Adhesive/substrate incompatibility: when adhesives and substrates are incompatible, particularly in terms of their reaction to thermomechanical stresses, the likelihood of cracking increases.
- UV exposure: exposure to UV rays can lead to adhesive degradation and loss of bond strength, eventually resulting in cracking.
- Moisture: an adhesive can swell or soften under humid conditions, leading to stress cracking.
- Chemical exposure: cracks can also occur when an adhesive degrades or loses its bond strength after exposure to chemicals.
Careful selection that aligns adhesive properties with substrate behavior and environmental factors is essential to avoid bond failure and extend the life of the sign.
The Role of Flexibility and Modulus in Adhesives
Flexibility in adhesives doesn’t imply a lack of strength; rather, it denotes the adhesive’s ability to stretch and recover, accommodating movements of the bonded materials. A low modulus adhesive indicates a lower level of stiffness, which translates to more give under stress, allowing for movement without breaking. In contrast, a high-modulus adhesive is like an inflexible ruler – it resists bending and eventually yields under pressure. Modulus is a particularly important characteristic for thin and lightweight sign materials, which are increasingly prevalent due to their cost-effectiveness and ease of installation.
Adhesive flexibility is not only desirable; it’s vital to maintaining a bond that adapts to its environment without fracturing. A sign waving in a gust of wind or expanding under the midday sun must have an adhesive capable of such movements. The modulus of elasticity in structural adhesives for signage is, therefore, a key player in the longevity of signage. Matching the adhesive’s modulus with the substrate’s properties ensures a synergy that prevents failures, ensuring signs retain their intended appearance and structural integrity over time.
The Expertise Behind the Right Adhesive Selection
To ensure optimal selection and application of adhesives, signmakers must embrace the technical expertise of adhesive engineers like those at MPI Matco. These specialists understand the complex interplay of factors that affect adhesive performance, including chemical composition, curing processes, and environmental durability. Their insights can anticipate and circumvent potential issues, guiding signmakers through the maze of product specifications and industry jargon to find the ideal adhesive solution.
A partnership with industrial tapes and adhesive experts empowers signmakers to move beyond trial and error, saving time and resources by getting it right the first time. In this collaborative space, signmakers can share the specifics of their project—material choices, expected environmental conditions, and aesthetic requirements—to tailor an adhesive strategy that ensures lasting bonds.
Making a successful sign involves more than just aesthetics. It also involves the perfect match between materials and adhesives. From the adhesive’s modulus and curing temperature to environmental factors, the selection of adhesive for signmaking must take into account many factors to ensure a safe and durable design. Signmakers are encouraged to look beyond product labels and build relationships with adhesive specialists who bring a wealth of knowledge and a history of innovation.
MPI Matco is a specialist in industrial tapes and adhesives, renowned for meeting the most stringent bonding requirements. We offer high-performance structural adhesives and sealants for a variety of industries, including signmaking. In addition to our products, we help signmakers solve their unique adhesion problems and can develop custom solutions if required. Don’t hesitate to contact us, we’re here to help.