About basics of adhesion

1. Categories of adhesives

There are many types of adhesives.

There are many types of adhesives for different
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
· 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


2. Theory of adhesion

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

Bonding power between an adhesive’s molecules and adherends
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.


Cohesion force of adhesives
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)


3. How to select an adhesive

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

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