Page 8 - Handbook of Adhesion Promoters

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Introduction

1.1 DEFINITIONS

Here are some of the most common definitions used in the field:
An adhesion promoter is used as an additive or as a primer to promote adhesion of
coatings, inks, or adhesives to the substrate of interest. An adhesion promoter usually has
an affinity for the substrate and the applied coating, ink, or adhesive. Without the adhesion
promoter, the properties of the applied coating may not be sufficient to meet the perfor-
mance requirements needed for the end product such as a painted automotive plastic sur-
face. In automotive coatings, the term adhesion promoter refers to the primer, which
achieves adhesion of the subsequent paint layer to TPO substrate. This adhesion promoter
is usually comprised of chlorinated polyolefin (CPO) as the active adhesion-promoting
component, other resins, and pigment(s). [Eastman Chemical]
The objective of adhesion promoters and coupling agents is to create as many stable
additional bonds on these phases (presumably substrate and coating). It is not always pos-
sible to differentiate the additives from one another. Other terms include also couplers and
modifiers. [BYK]
A coupling is defined as the act of bringing or coming together (pairing) or a device
that serves to connect the ends of adjacent parts or objects. [Merriam-Webster]
Primer is a substance used as a preparatory coat on wood, metal, or canvas, espe-
cially to prevent the absorption of subsequent layers of paint or the development of rust. In
cosmetics, a primer is a cosmetic applied to the face before another product, intended to
improve the coverage and lasting effect of the second product. [Oxford Dictionary]
With Latin prefix sub-, “below”, the substrate (substratum) refers to a layer under
something else. [Merriam-Webster]
With many other definitions adjusted to the needs of particular applications, we may
find even more confusing explanations of the meaning of these words because they are
used in many technical and non-technical disciplines.
For the purpose of this book, we will use adhesion promoter as a primary single
compound which is able to interact (either based on chemical or physical principles) with
two layers of materials for which adhesion needs to be improved. The primer will be con-
sidered rather as a formulated product (containing usually more than one component) to
perform according to a specific process of promoting adhesion (surface immersion, brush
coating, spraying, etc.). Under this definition primer should not only have the ability to
increase adhesion but also form a uniform sub-layer on the surface of the substrate due to
adjustment of its viscosity, wetting properties, drying rate, etc.