Advantages of Adhesive Technology

Types of adhesive

Adhesive, in India, is primarily  classified based on their curing mechanisms and chemistry.

Adhesives classification based on curing mechanism

Water based adhesives– cure ( dry ) when water evaporates  from the adhesive. Eg: Fevicol white glue used  for plywood bonding in interior furnitures

Solvent based adhesives – cure ( dry ) when solvent evaporates  from the adhesive. Eg-rubber adhesive used for type puncture  repair, shoe repair.

Non curing adhesives : Eg: butyl sealant for bonding car door fabric to metal body.

Reactive adhesives– cures when it reacts due to some external factor( eg- UV curing glue) and chnages phase from liquid to solid. Eg: 2 part araldite cures after expocy and hardener are mixed together.

Based  on chemistry

Acrylic adhesives – Generally 2 part adhesive system for structural bonding.

Anaerobic adhesives – one part adhesive used for threadlocking, threadsealing, flange sealing, bonding cylindrical assemblies. Used extensively in manufacturing and maintenance work. It is also called Engineering adhesive.

Cyanoacrylates – popularly called instant adhesive or super glue. It bonds instantly. It can bond alomost all material except telfon. It is not flexible after curing and  generally used for bonding small parts.

Epoxy adhesive – Araldite is a popular household name in India. It is used for bonding any material together. Generally 2 part system which either is mixed manually or used with a special 2 part dispenser.

Methyl methacrylate adhesive – 2 part system used for structural bonding.

Silicones– Silicone adhesive and sealant is popularly used for glazing applications. Some viscous silicone sealants are used for other bonding purpose also.

Polyurethane adhesive – It is a single component adhesive used for wood working applications, honeycomb bonding and other furniture manufacturing applications.

PVA ( Poly vinyl acetate) – Typical white glue used by students for project work like paper pasting, carboard pasting and sundry home use.

Synthetic rubber glue – Dendrite is a popular SR adhesive used in India. It can bond most substrates. It is also used for bonding solid gasket on the flange.

Hot melt glue – There are various types of hot melt adhesives used for book binding, wood working, packaging, automotive interior assembly, diaper and sanitary pad production etc.

MS polymer adhesive

MS polymers is the latest generation adhesive and sealant which combines advantages of silicones and polyurethanes. It can be used for bonding almost all materials except pp,teflon,hdpe, ldpe.

Advantages of MS Polymer adhesive

• High initial tack properties reduce the need for initial support.
• Fast curing, a quick build-up of end strength alongwith high sheer strength after full cure (no primer).
• Easy to apply and easy to tool and finish
• Remains elastic after curing.
• No odor.
• Does not contain neither isocyanates, silicones nor solvents.
• Paintable with all water-based paints.
• Excellent color stability. Likewise, weather and UV resistance.
• Good adhesion on wet substrates, bonds underwater.

Advantages of adhesive bonding technology

• Joining of different materials possible
• Planar load transfer and uniform stress distribution without stress peaks
• Preservation of material properties due to low thermal loads and no damage to the materials
• High freedom of design
• Integration of other functions (e. g. noise insulation, vibration damping, sealing)
• Thermal and electrical insulation
• Tolerance compensation
• In some cases increased productivity
• Prevention of contact corrosion’

Limitations of adhesives bonding technology

• Limited thermal loads
• For many materials and processes complex surface treatment necessary
• Specific processing and curing conditions must be observed
• In some cases long curing times
• Ageing due to weathering and/or other influencess

Adhesive selection parameters

MSECP 

1. M- Machine – How are you applying the adhesive? How Fast? What type of equipment are you using? 
2. S- Substrates – What are you adhering together?           
3. E – Environment– What will the bond / finished product be subjected to? (Hot Fill, Cold, Wet, Freezer, Blast Freezer)    
4. C- Cost and volume – Ballpark of where you would like this product to fall in your cost. How much & how often do you order?          
5. P- Plant conditions– What are the conditions in your plant? (Temp Controlled, Dusty, Wet, ETC.)

Summary  of questions to be  answered for adhesive selection.

• Details of the substrates to be bonded- low energy substrates like telfon, HDPE, LDPE, PP is diffcult to bond and requires special surface prepration before bonding.
• Gap between the surfaces- for higher gaps than 0.5 mm we need higher viscosity adhesive, else regular CA( cyanoacrylate, instant glue) will work.
• Max Temperature to be sustained by the assembly – If more than 100 Celsius:  silicone adhesives are the  best else you have to select special high temperature grade from other chemistries.
• Type of loading, stresses on the adhesive joint – instant glue is not good in cleavage, peel or shear strength.
• Production speed: How many assemblies per hour to determine how to dispense the glue.
• Environment: Will the adheive bondline come into contact with water, fuel, gas, harsh chemicals etc. knowing this we need to choose adhesive chemistry that can sustain that environment. 

Surface preparation for effective adhesives bonding:

• The surface must be firmly attached to the base material
• Effective wetting
• Good bonding properties
• The surface must not change in an uncontrolled way after the adhesive bond has been formed

→ In order to meet these requirements, surface treatment of the substrates is necessary!

Objectives of surface treatment:

• Improved wetting
• Improved adhesion
• Improved reproducibility of the surface
• Improved long-term stability of the bonded joints

The objective is hence to produce a defined surface that is suitable for the relevant bonding task.

The surface treatment of substrates is a key step in adhesive bonding processes.
In the simplest case, cleaning of the substrates suffices. More complex scenarios may involve several complicatedsurface treatmentsteps.

Besides improving the wetting properties, adhesion, reproducibility and long-term stability, time and costs aspects must always be considered. The following maxim applies for surface treatment: As much as necessary, but as little as possible