Bonding LSE Materials
Low Surface Energy Materials
The basic principle of adhesion is the molecular attraction between dissimilar materials. The strength of adhesion is determined by the surface energy of the material and for adhesive to form a strong bond with a substrate it must ‘wet out’, flowing across the surface of the substrate, increasing the adhesives surface area and allowing maximum bond strength. It's crucial that the correct selection is made when using adhesive tape for bonding low surface energy (LSE) plastics.
Fig.1 represents a High Surface Energy that supports adhesion and the droplet of liquid is wetting out to the surface.
Fig.2 is a Low Surface Energy and the droplet is clinging to itself rather than the solid surface.
Many material manufacturers will not publish the surface energy of a substrate and identifying this at an early stage is critical to providing a successful bonding solution. Surface energy is normally measured in energy units called dynes/cm. A dyne is the amount of force required to produce an acceleration of 1 cm/sec² on a mass of 1g. Traditionally the surface energy of a substrate is measured using a contact angle measuring device. This is often impractical in a normal manufacturing environment so a more common solution is to apply a dyne solution to the solid surface.
Typical Surface Energies (Dynes/CM)
|High Surface Energy||Medium Surface Energy||Low Surface Energy|
|Material||Surface Energy||Material||Surface Energy||Material||Surface Energy|
The dyne level of a substrate is one of the most significant factors in selecting the correct bonding solution. With the ever increasing use of LSE engineering plastics in many areas this element of bonding considerations is becoming more and more important. Many Pressure Sensitive Adhesive (PSA) manufacturers are directing a large percentage of R&D resource into developing PSA technologies that will provide superior adhesion to LSE substrates.
It is strongly recommended that an adhesive Application Engineer is consulted at the design stage of any project which requires adhesion. For one they will have an in depth knowledge of the polymer construction of materials and secondly they are in touch with the latest developments within PSA technology. Tecman Speciality Materials offer technical support to Design Engineers for selecting the most effective adhesive product.
There are two basic ways that adhesion can be formed to a LSE substrate:
Increase the surface energy of a substrate through use of a surface treatment process. This can be a mechanical treatment such an Inline Corona Treatment or plasma or a chemical treatment. There are many chemical treatments commercially available today which will promote superior adhesion. There are a number of benefits to selecting a surface treatment. Perhaps the most significant is that it opens up the range of PSA’s that can be used in an application. The Design Engineer has greater freedom of choice to meet all of the requirements of the project including adhesion performance and cost considerations.
It is often not possible or unviable to apply a surface treatment in a manufacturing environment. In these cases an LSE compatible adhesive needs to be selected to achieve the adhesion performance required. These PSA’s have additional polymers within their core construction which will increase adhesion to LSE substrates. These polymers are a mix of synthetic and natural resins. By their very nature rubber based adhesives, whether hot-melt rubber or a solvent rubber have superior bond strength to LSE substrates.However there are a number of limitations to a rubber adhesive which often excludethem from selection when choosing a bonding solution.
Benefits of Adhesive Tape for LSE Substrates
- No need for investment in machinery
- Eliminates structural weak points
- Spreads stress evenly
- Can withstand movement and vibration
Typical Rubber PSA Characteristics
|Very high initial bond with as much as 80% of total bond strength on contact|
|Good adhesion to LSE substrates|
|Soft adhyesive causes rapid 'wet out' for quick adhesion build up|
|Low temperature resistance|
|Little or no UV resistance making them unsuitable for external environments|
|Soft adhesive lacks cohesive strength giving low shear adhesion values|
|Low resistance to chemicals, alkalis and acids|
This leaves acrylic PSA technology to provide high performance bonding to LSE. However pure acrylic PSA in its natural state will not bond to LSE substrates without the aid of a surface treatment. To overcome this, special tackifier additives are blended with the pure acrylic PSA construction. There is always a compromise on the performance of pure acrylic as it will take on some of the characteristics of a rubber. However a modified acrylic PSA will still offer significantly higher levels of performance than a rubber based PSA. Some of the characteristics of a pure acrylic and modified acrylic are as follows;
Typical pure acrylic PSA characteristics
|Very high ultimate bond|
|Excellent resistance to high temperatures (up to 280℃ short term)|
|Hard adhesive gives good cohesive strength and excellent shear properties|
|Excellent resistance to chemicals and solvents|
|Excellent resistance to UV light|
|Low initial tackwith as little as 20% of bond strength on contact|
|Hard adhesive causes slow wet-out|
|Very low adhesion to LSE substrates|
|High cost base|
Modified acrylic adhesives with carefully selected additives give the best of both acrylic and rubber adhesives, however not all modified acrylics will give high adhesion to LSE substrates. It is important to consult an Application Engineer before making a selection.
Most common alternatives for bonding or fixing LSE substrates are mechanical fixings such as welds, rivets and screws or solvent welds. These traditional methods require investment in major equipment for labour intensive operations to be carried out, such as hole spotting, drilling, tapping welding and surface refinishing. These create structural weak points or areas were rust or corrosion can set in.
Solvent welds rely on hazardous solvents which require specialist equipment for dealing with fumes and health and safety requirements.
Tecman has a range of PSA tapes for bonding LSE substrates, including transfer adhesives, film tapes and Very High Performance Bond (Vhpb) tapes. Tecman’s Application Engineers regularly specify adhesive tape for bonding LSE substrates as they are fast becoming the preferred choice for design and engineering projects due to the demand for cleaner, quicker and more cost effective solutions.
Adhesive Tapes for Bonding LSE Substrates
||Product Type||Adhesive Type||Adhesion to LSE Substrates||Colour|
|11-TR10||Adhesive Transfer Tape||LSE Acrylic||Medium High||Hazy|
|12-TS02||Tissue Tape||Synthetic Rubber||Synthetic Rubber||Hazy|
||Film tape||Modified LSE Acrylic||Very High||Hazy|
||Film tape||Modified Acrylic||Very High||White|
|15-Vhpb06||Vhpb tape||Vhpb Acrylic||High||Grey|
|15-Vhpb07||Vhpb tape||Vhpb Acrylic||High||Grey|
|15-Vhpb AB064 LSE||Automotive Grade Vhpb Tape||Vhpb LSE Acrylic||Very High||Black|
|15-Vhpb AG080 LSE||Automotive Grade Vhpb Tape||Vhpb LSE Acrylic||Very High||Grey|
|15-Vhpb AG110 LSE||Automotive Grade Vhpb Tape||Vhpb LSE Acrylic||Very High
For more information about our range of adhesive tapes for bonding LSE substrates, please contact us on +44 (0) 1926 337466 or alternatively contact us