A prepared surface, free from contamination, is essential to securing the strongest possible bond. This is because surfaces are often covered in dirt, grease, oil, dirt, oxide films, rust inhibitors, and where plastics are concerned – mould release agents. Any contaminant, even at a microscopic level, can interfere with an adhesive when trying to bond components.
Generally, the more preparation you do on a surface, the stronger and more durable a bond will be. For simple bonds, minimal preparation such as simply wiping the area clean, may be effective, whereas structural bonds would require more treatment.
When it comes to preparation, there isn’t a ‘one size fits all’ approach to help you achieve the best bond. However, there are multiple options for surface preparation products and techniques, which this guide aims to help explain and find you the correct one for your application.
Below are the types of surface preparation that can be adopted, to help you achieve better bonds.
Standard Surface Cleaning
The surface(s) on which you wish to apply your adhesives, should at a minimum, be clean and dry. The bond area should be removed of as many surface contaminants as possible, including dust, dirt and grease. With delicate surfaces, as much as is practical should be cleaned off, especially any loose particles or surface films.
When using detergents or liquids to clean a surface, ensuring that the surface is dry and void of trace cleaners before applying an adhesive is key.
Chemical Cleaners & Degreasers
Chemical cleaners and degreasers have been designed to remove soiling such as oils, greases, lubrication fluids, metal cuttings and fines from surfaces which are due to be bonded. Due to their design, they are highly effective in preparing surfaces for adhesive application.
Common cleaners and degreasers include solvents such as methyl ethyl ketone (MEK), acetone, or isopropyl alcohol (IPA).
- Eurobond IPA, also available in a spray bottle, is a highly effective agent for preparing surfaces ahead of bonding. Containing a 70% IPA solution, this cleaner is also effective at protecting against viruses and bacteria, breaching cell walls and killing organisms
- A more user friendly and safer option are the Eurobond Heavy Duty IPA Surface Wipes. Available in handy plastic pots with a ‘flip-top’ lid containing 100 wipes, this product can help to maintain quality control, reducing the potential for the wrong liquid cleaner being used, whilst also helping to reduce costs incurred on waste or spilt liquid cleaners
When choosing a cleaner or degreaser, factors to consider include;
- Does the drying time required, fit within your timescales
- Ensure that the substrate is compatible – concerns can arise when dealing with plastics and solvent-based cleaners
- Will the cleaner or degreaser leave any residue? If secondary procedures, such as bonding or painting, are planned, then any residue could interfere with these processes
- Ensure that you always try a test area before full use
Abrasion
One of the most commonly used methods of surface preparation methods is mechanical abrasion. This method can be applied to most materials and it aims to remove weak boundary layers of a substrate.
Abrasion roughens the surface of substrates, getting rid of any surface films, paint and oxides. This results in an increased surface area for bonding, whilst also enhancing the adhesives ability to fully wet the substrate surface when applied.
There are various methods that are popular abrasion methods, including:
Manual Applicators
- Fine grain sand paper, emery cloth or steel wool are abrasion methods that can be applied manually
- Eurobond Abrasive Pads help to remove any difficult residues and contaminants that may be found on substrates prior to bonding
Sandblasting
- Sandblasting, with fine sand, can be used on substrates which are sufficiently thick enough that they will not then be distorted
Vapour Honing
- When a minimum reduction is desired/required in metal thickness, vapour honing is the ideal method to us
Following any abrasion treatment, all loose particles remaining must be removed before applying adhesive. The abrased surface can be brushed or blown with compressed air, followed by degreasing to clear away any remaining loose particles and residual oils. Other than the most demanding of industrial applications, abrading and degreasing is typically enough surface preparation.
Surface Alteration
There are some materials that are simply difficult to bond. Included in this group are materials such as EPDM rubber and “polyolefin” plastics, e.g. polyethylene, polypropylene, acetal and hard nylon. Additionally, some metals including copper, stainless steel and aluminium are slightly more challenging to bond compared to other metals.
When bonding these materials, the surface properties may need to be changed to enable better adhesion. Considered ‘low surface energy surfaces’, these materials require the surface to be altered to increase the surface energy. To do this, the use of chemical primers, scorching of the surface, grit blasting or acid etching of the surface is required.
As all materials are invariably different, it is always advised to consult your material supplier for the most effective method for treating the material to allow for the best adhesion.
Primers
Changing the base of a surface to enable more effective adhesion, primers have been designed to enhance the bonding quality of adhesives. Whilst not always a necessity, the requirement of a primer is generally based on both the material and substrate involved.
If using plastics, these will generally require the use of a primer. In some instances the type of primer required can be very specific to that material.
Accelerators and Activators
Acting as catalysts, both accelerators and activators are applied before an adhesive, designed to reduce both the cure time and improve the quality of the adhesion. Where possible, activators are recommended over accelerators; when accelerators are used to speed up the cure time, there can be a trade off with bond strength.
Cleaning & Preparation Solutions from Eurobond
As detailed above, Eurobond have both Abrasive Pads and Surface Cleaning Wipes, which are available both online or by contacting our sales team. You can find these products, along with Eurobond’s range of adhesives, online at www.eurobond-adhesives.co.uk.
Our experienced technical advisors are happy to discuss our range of cleaning and preparation products, or to advise on any project specific questions you may have. So get in touch on 01789 773232 or email sales@eurobond-adhesives.co.uk.