There are many types of adhesives.
There are many types of adhesives for different
purposes.
Various adhesives are used to meet customer’s production processes
or applications.
Adhesives are categorized in different ways as follows:
Categories by main components
Inorganic adhesives
In this category, there is cement and other materials that endure a high temperature of 1000℃ or higher, however this category is minor now.
· Silicone-based (water glass and
silicate)
· Calcium-based (cement and plaster)
Organic adhesives
Most adhesives are organic.
· Thermoplastic resins
· Heat-curing resins
· Rubber and elastomer
Categories by forms
Moisture Scattering type
They are water-based adhesives that are made by emulsifying the resin and dispersing it in water.
· Epoxy resin-based
· Polyvinyl acetate-based
· Nitrile rubber-based
Solvent type
They are adhesives that are made by dissolving a resin into a solvent, like volatile-solvent type adhesives.
· Phenol resin
· Polyvinyl acetate
· Chloroprene rubber-based
Nonsolvent type
They are adhesives that cure by the chemical reaction including the silicone-based and the epoxy-based.
· Epoxy resin-based
· Acrylic resin
· Silicone rubber-based
Solid type
They are solid type adhesives in the form of lumps, powders, and films.
· Epoxy resin-based
· Styrene-butadiene Rubber-based
Categories by curing methods
Volatile solvent type
They cure by vaporizing organic solvents.
ex.) Rubber pastes and adhesives for plastic models
· Polyvinyl acetate
· Nitrile rubber-based
Moisture curing type
It cures when reacting with moisture in the air.
ex.) Instant adhesives and silicone based liquid gaskets
· Cyanoacrylate-based
· Silicone rubber-based
Heat curing type
The hardener in the resin is activated and cured by heating
ex.) One-part epoxy resins
· Epoxy resin-based
· Acrylic resin
Curing-agent-mixed type
Curing occurs, when the base agent is mixed with a hardener.
ex.) Two-part epoxy resins
· Epoxy resin-based
· Silicone rubber-based
Anaerobic curing type
It cures when air is repelled at the metal part. It is used for screws, joints, and pipes.
· Acrylate based (acrylic resin)
UV-curing type
It cures in a short time by irradiating ultraviolet rays. It is used as a bonding sealant and adhesive for glass and transparent plastics.
· Acrylic resin
· Epoxy-based
Heat melting type
It is coated at a molten state and cures and bonds as it gets cold. It is used for wrapping and bookbinding.
· Styrene-butadiene rubber-based
Pressure-sensitive type
It bonds by applying pressure at room temperature. It is used for adhesive tapes and seals.
· Acrylic resin
Two-time humidifying type
This adhesive can glue stamps and other items after wetting the dry adhesive surface with water, to recover its adhesion.
· Chloroprene rubber-based
· Starch-based
To begin with, what is adhesion?
I will briefly explain the concept of adhesion. Let us think of factors that decide the strength of adhesion. Strength of adhesion will be one of the key points in your design requirements.
Factors to decide strength of adhesion
Soaking of adhesives
It is necessary that the adhesive soaks on the adherend. Adhesive strength differs depending on the soaking of the adhesive and the contact angle of two adherends.
Bonding mechanism in interface
There are various theories on bonding mechanisms. Adhesive strength differs depending on each bonding process.
Types and materials of adhesives
The adhesion strength varies depending on the type and material of each adhesive.
Bonding mechanism in interface
There are various theories about bonding mechanisms. Adhesive strength differs depending on each bonding process.
Soaking and contact angle
Ideally the adhesive completely soaks onto the adherend.
Mechanism of bonding
There are several theories on the mechanism that joins one substance to another, as shown below.
Chemical bonding theory
The adhesive causes a chemical reaction between the adhesive and the adherend. As this chemical reaction joins moleculars together, the adhesion becomes strong.
Absorption theory
The adhesive causes bonding of hydrogen atoms in the adhesive and the adherend. This produces the pulling force of atoms towards each other. This pulling force makes the adhesion, however the adhesive force is rather weak.
Anchoring effect theory
The adhesive penetrates into pits on the surface of the adherend and bonds to the adherend. The adhesive force depends on how strong the anchoring effect is.
Static electricity theory
The bonding force is generated by the effect of static electricity. The bonding force is rather weak.
Mutual diffusion theory
Bonding takes place between two adherends, the surfaces of which are dissolved by the adhesive.
Due to both adherends having dissolved surfaces, the bonding force is strong.
How the adherend receives peeling force
Several different peeling forces are applied on the adherend.
Select an adhesive or application method considering the following forces:
Force to pull up and down (pulling)
Force to shear (shearing)
Force to pull and tear off from the edge (cleavage)
Force to peel off (peeling)
When you select an adhesive, you need to consider the following.
The amount of force or load the bonded area receives
- Required adhesive strength
- Use or non use of chemicals
- Structural design of bonded area
- Use duration
- Temperature and humidity at production
The materials and surface condition of adherend
- Contamination from oil or other foreign matter
- Adhesion-retardant material or oxide film
- Roughness or smoothness of surfaces
Workability and automation
- Allowable curing time and ageing time
- Handleability ageing time
- Ease of storage
- Applicability
Health and safety
- Effects on external environment
- Legal regulations (Fire Service Law, Industrial Safety and Health Law, etc.)
- Safety and emergency measures for workers