How to Prepare & Bond Glass with Industrial Adhesive
Glass is a common material and found in various applications – from windows and doors to glass staircases, balconies and other architectural products. On a smaller scale, items such as kitchenware, artwork, jewellery and lenses also make use of this versatile, clear material.
There are many benefits of bonding glass with industrial adhesives:
- Many adhesives are clear and non-yellowing – offering an “invisible” bond that is more attractive than mechanical fixtures and fastenings
- Less machining required – no need to drill holes to accommodate mechanical fixings = less risk of breakage through extra handling. Drilling holes adds a weak area to the glass and often stress is concentrated into this weak area (think about the tiny hole where the arm is fixed on frameless spectacles – this often cracks around it).
- Faster joining process than drilling and using a mechanical fastener – glass can be joined in seconds. Less skill required than machining holes in glass.
- Joints are sealed as well as structurally bonded
Surface Preparation of Glass
Even though it may look clean, it is a good idea to give glass surfaces a solvent wipe. This will remove any greasy residues from handling or slip additives used during processing. Acetone or isopropanol are good choices. Products such as meths or white spirit may leave a residue so it is better not to use these materials. Allow the solvent to fully evaporate before bonding.
Permabond offers a surface pre-treatment “2K Primer”, this special product contains a silane-based adhesion promotor which helps improve adhesion to glass as well as improves long term durability. This is worth considering if bonded parts are going to be exposed to harsh conditions or if you are looking to improve bond strength (particularly useful if you are looking to use an epoxy adhesive).
Consider the “usual suspects” such as:
- Is colour important? Most likely a clear / colourless adhesive is preferred
- Gap fill or vertical application – do you need a high viscosity non-drip industrial adhesive?
- Do you need a low viscosity grade – if you are sandwiching glass together and trying to minimize air bubbles a low viscosity adhesive would be a sensible choice
- How quickly do you need the adhesive to cure – seconds, minutes, hours?
- What materials are you bonding? This is a really important consideration, if you are bonding glass to metal you need to expect differential thermal expansion and contraction – you don’t want the glass to crack when the temperature changes!
- What sized bond area / length / width? This is another important factor if bonding dissimilar materials as long sections will be even more affected by differential thermal expansion and contraction e.g. a glass solar panel into a metal frame will see big temperature fluctuations which will cause the frame to expand and contract.
- What conditions will the joint be exposed to?
- Do you require any special refractive index? (Particularly important for lens bonding)
Industrial Adhesive Recommendation for Glass Bonding
First choice: UV-Curable adhesives. These offer the best adhesion and optical clarity for bonding glass. Coupling that with the fact they are non-yellowing, do not require mixing and cure in seconds on demand (by exposing to UV light) they are a surefire winner!
Flexible sealant-type products such as MS-polymer and silicone adhesives are suitable for long joints where flexibility and water resistance is required. They are a good option for bonding long profiles or U channels made of metal where differential thermal expansion and contraction are an issue. The products are normally very slow curing and cure from the outside in (skinning over first).
Structural acrylic adhesives – some are better than others, some even have a built in silane adhesion promotor to improve adhesion and long term durability (make sure to put the resin with the silane in it on the glass and the initiator on the metal!). The products cure to a handling strength in minutes.
Epoxies – epoxies offer good environmental resistance and can bond strength can be maximized by using the silane-based primer. These products can occasionally be prone to yellowing, especially if laid in a thick layer it can become visible. Choosing a more flexible or toughened grade will be important if bonding dissimilar materials.
For further help, please contact Permabond.