Tuesday, November 20, 2012
Overview of Adhesive Systems
By definition an adhesive is a substance, typically liquid or semi-liquid, which is capable of holding materials together by means of surface attraction. Surface attraction results from placing a thin layer of adhesive between 2 objects.
There are number of different types of adhesive available. The following list consists of the main types including some of their strengths and weaknesses.
Hot Melts
Advantages:
Good gap fill, versatile formulations, fast setting
Limitations:
Typically low strength, poor wetting, poor creep resistance, usually low solvent & heat resistance, special dispensing equipment required.
Silicones
Advantages:
Good gap fill, good for bonding glass, excellent sealant for low stress applications, excellent temperature resistance, flexible.
Limitations:
Low strength, limited solvent resistance, too flexible for structural loads, odour when curing, most require moisture to cure, slow curing.
Urethanes
Advantages:
Excellent toughness & flexibility, varying cure times, good flexibility at low temperatures.
Limitations:
Poor temperature resistance, sensitive to moisture (cured & uncured states), toxicity, short pot life, require special equipment to mix & dispense
Epoxies
Advantages:
High strength, can be filled with metals, versatile, wide range of formulations, good temperature & solvent resistance.
Limitations:
2 Component varieties require exact mixing ratios for optimal strength, one component products usually require refrigeration & heat cure, short pot life, slower fixturing, special equipment needed to weigh, mix & dispense.
Anaerobics
Advantages:
High strength (on some substrates), rapid cure at room temperature, good solvent & temperature resistance, versatile, non-toxic, easily automated.
Limitations:
Limited gap cure, won’t cure where air contact adhesive (wet fillets), primers required for many materials, 150-200C temperature limitations, generally brittle.
Cyanoacrylates
Advantages:
Rapid cure at room temperature, single component, excellent adhesion to rubber, high tensile strength, no mixing required, indefinite pot life.
Limitations:
Limited gap cure, low solvent & temperature resistance, poor impact & peel resistance, no water, chemical or environmental resistance.
Methacrylates
Advantage:
Good gap fill, excellent impact resistance, excellent peel & shear strengths, substrate versatility, medium / fast cure, tolerant to dirty surfaces, can be dispensed from most packages.
Limitations:
Some odour problems, flammable.
Please note that this is a generic list and the points listed are typical for the types but will vary between brands.