Updated: May 31, 2024
Jump To:
- Why Surface Preparation Is Important
- Pretreatment
- Using Primers and Accelerators
- Surface Preparation for Different Materials
- Determining the Best Surface Preparation
When bonding two substrates together, you want to make sure you get the best bond possible for lasting success. One important aspect of achieving an optimal bond is to perform the proper surface preparation.
Why Is Surface Preparation Important in Adhesive Bonding?
Preparing a surface for adhesive bonding is one of the most important things you can do to obtain a sturdy and lasting bond. No matter how strong your adhesive is or how well suited it is for the specific application, proper surface preparation is often still required to achieve the cleanest contact and ultimately, the strongest bond.
If you skip this step, the bond will not set the way it should. Eventually, outside stressors could lead to bond failure. In some applications, this could just mean a cheap end product that breaks easily, but in others, a bond failure could even be life-threatening.
Pretreatment Surface Preparation for Adhesive Bonding
Adhesive bonding surface preparation can refer to many things and will depend on the materials, specific adhesive, and the environment. There are three primary aspects of pretreatment surface preparation for adhesive bonding including removing contaminants, abrasion, and modifying the chemical composition.
1. Contaminant Removal
One of the goals of surface preparation for glue is to increase the surface energy of the materials being bonded. Substrates with higher surface energy are easier to bond with than those with lower surface energy. This difference is because of the wettability factor or how easy it is for the adhesive to make contact and spread over the substrate.
When contaminants are present on the substrates, it decreases the available surface energy and impairs the adhesive’s ability to reach its optimum bond. Contaminants can refer to dust, grease, oil, rust, and more.
To remove these contaminants, use a detergent or solvent. Certain solvents are better than others at removing specific classes of contaminants, and some may react with metals causing an unfavorable chemical reaction that can weaken the bond or the metal. If you use detergents, rinse the metal thoroughly and dry it well.
In many cases, removing the contaminants involves just a thorough cleaning with isopropyl alcohol and water. Once the surface is dry, the adhesive may be ready for bonding. In other cases, more preparation is needed. Contaminant removal may require techniques such as laser cleaning, abrasive blasting, or manual degreasing.
2. Abrasion
After the contaminants are removed, the next adhesive bonding surface preparation step may be abrasion or scraping the surfaces of the substrates to increase roughness. This process can be done through various techniques including sanding, scrubbing with steel wool, wire brushing, sandblasting, chemical etching, or laser texturing. Making an abrasion can help improve bond strength because it increases the contact area for the adhesive.
While not always necessary for every bond, some materials such as plastics or metals do benefit from some abrasion before bonding.
3. Chemical Modification
In some cases, surface preparation for adhesive bonding may also involve altering the chemical composition of the surface to achieve a stronger bond. This step could involve introducing or removing elements from the surface. It could also mean breaking down or rearranging the chemical bonds between atoms.
Acid etching, laser texturing, and plasma treatments are all techniques used to modify the chemical composition of the substrates.
Using Primers & Accelerators
Primers, also known as adhesion promoters, modify the surface energy to ensure a chemical reaction occurs between the adhesive and the substrate. They can also protect the surface from contamination after the pretreatment process. Primers come in many types and are designed for the type of adhesive they will come into contact with, so it is important that the primer you use matches the adhesive you want to use. MMA adhesives have the advantage of not usually needing primer.
In addition to primers, you can also use an adhesive accelerator to help promote adhesion. There are several types available. Some are specifically designed for certain types of surfaces or glues, and others are manufactured to work on various brands and types of glue.
Surface Preparation for Different Materials
Three of the most common substrates that are often bonded together using adhesives are metal, wood, and plastic. Each surface has its own properties and should be prepped differently before applying adhesives.
Metals
Metals are known for their strength and durability but are often tough to work with and difficult to mold into the desired shape. Along with choosing a glue for metal specifically, chemical cleaning and treatments are often recommended.
Wood
Wood surfaces are often contaminated with bits of resin and wax. Pretreatment is strongly recommended before applying an adhesive for wood. You also need to dry the wood first prior to pretreatment.
Plastic
Dust, dirt, oil, and grease can easily contaminate plastic. These contaminants can also migrate around the surface due to the nature of plastic material. Surface preparation for adhesive bonding with plastic means more than just using an adhesive for plastic specifically. Liquid solvents, abrasion, and chemical surface modification are usually recommended.
Determining the Best Surface Preparation
Preparing your surface for adhesive bonding is an important part of ensuring a secure and strong bond. These surface treatment processes should be tailored to the surface you are working with as well as the adhesive you are using and the environment you are in.
Although you may now have a better understanding of how to prepare a surface for adhesive bonding, execution can be more difficult. Fortunately, our team is available to offer guidance on techniques, products, and tips to make this process a bit easier. If you need help or advice, just contact us.
