Handbook of Adhesion Promoters

George Wypych

• Publisher: ChemTec Publishing
• Year: 2018
• Topic: Technology & Engineering
• eBook ISBN:
  9781927885307
• Subtopic: Materials Science
• Index: Technology & Engineering

Handbook of Adhesion Promoters provides a comprehensive review of the current options and the latest knowledge on adhesion promoters. Essential aspects of adhesion promoters are discussed, including properties and potential applications of all adhesion promoters. The book outlines known mechanisms, principles of use and the application of different groups, and includes two chapters explaining requirements for preparing substrate surface. A full chapter is devoted to polymer modification, which can help improve adhesion. The last four chapters contain information on the evaluation and selection of adhesion promoters, which work with different polymers or products, improve filler-matrix performance or help prevent corrosion. This handbook is a useful source of information for engineers, technicians and researchers involved in development, manufacture, legislation or production of a variety of products. Adhesion promoters form a very important group of additives, without which many industrial products cannot perform according to requirements. Silanes originally formed the most widely used group of adhesion promoters, but increasing numbers of new additives have been entering the market, increasing options and possibilities. These additives are needed for a variety of products in which silanes do not function or are too expensive, or where better performance can be achieved with the new additive. - Presents detailed and current information on adhesion promoters, including additives that are both widely used and recently introduced - Covers the critical aspects involved in the application of adhesion promoters - Supports the reader in the selection of adhesion promoters, in terms of properties, application and potential

1

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 performance requirements needed for the end product such as a painted automotive plastic surface. 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 possible 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, especially 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 considered 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.

1.2 HISTORY

Various simple technological processes of binding were used as early as 10,000 years. In the Neolithic period, a resin from birch trees was used to attach the heads of spears and axes. Later, when Iceman was discovered on Hauslabjoch (lived around 3300 BC), tools and pieces of clothing were found, including an ax made from yew wood whose blade was attached with birch pitch (adhesive) and strips of leather.

Other examples of products used as adhesives include animal blood, protein, various plant resins and asphalt that were used as adhesives in Babylon to build houses and temples. Such applications were used all over the world, even recently (Asia, Africa). It is expected that this technology is known for at least 7,000 years.

Fish and animal glues were known to Egyptians 4,000 years ago. They were obtained by boiling of animal hides, hooves, and connective tissues and used for reinforcement of papyrus scrolls and production of furniture (Tutankhamun casket was glued using this technology). This was the first technology of adhesive production which involved professional people having knowledge of how to make a glue. Glue produced in this way was expensive and, therefore, used only for furniture for noble people. The technology was later transferred to the Greeks and Romans.

Greeks and Romans further developed the technology. The ancient Greeks used adhesives in carpentry. The glues were usually made out of egg whites, blood, bones, milk, cheese, vegetables and grains. Tar and beeswax were implemented later by the Romans. Also, Chinese used ox and stag horns for the production of adhesives at least 3,000 years ago.

In South America, the developments came in this area later or perhaps earlier developments are still unknown. In the mid 14^th century, the Aztecs used the adhesive properties of blood for construction work. The structures are still in an excellent condition.

The modern area of adhesives begins in the 19^th century with the use of natural rubber as adhesive in 1830. Eleven years later vulcanization of rubber was discovered by Goodyear and used for adhesive purposes, followed by celluloid (1864) and phenolic resin (Bakelite, 1905). The big developments came about during second world war including polybutadiene (1935 and later developments, Buna or earlier in Russia), epoxy resin (1938 and later), cyanoacrylate (1942-1951, Eastman, superglue), and thermoplastic glue (hot melt, Procter & Gamble, 1940).

Bookbinding illustrates how important was the development of adhesives to the book production. Books were produced in various forms (scrolls, tablets, parchment sheets, etc.) for millennia but “pages” could only be held together by threads, ropes, etc. because of lack of durable glue. In 1447, Gutenberg introduced printing press which automatized printing process, but bookbinding was still done by manual work because there was no glue available to match the developments in printing. So book production remained manual process until developments in the 20^th century. Perfect binding was invented in 1895 but it was first adapted for book production by Penguin Books (UK) in 1935 using cold glues which were quite rapidly becoming brittle with time. Hot-melt bookbinding¹ was developed by DuPont in 1940 which started the modern area of publishing and made books available to anyone who was interested in reading (because their price was not any longer an issue). Polyamide having softening temperature in the range of 45-155°C was the first polymer used for bookbinding by hot-melts.

Just before the second world war, polyurethanes were invented by Otto Bayer in 1930 which also opened the door to many applications depending on adhesion.

In the early days of production of adhesives in the 20^th century, little scientific studies were done regarding the reasons for adhesion or its lack but it became obvious in the 1940^th that the further development of composites containing glass fibers cannot proceed if problems of adhesion between glass fibers and polymer matrix would not be addressed.² Dow Corning, producer of glass fiber, had vital interest in this field. The first application of the low molecular compounds for enhancement of adhesion was patented for Dow Corning by Joseph Keil in November 1954 when Edwin Plueddemann was still working in Westvaco Chlorine Product Corporation. The proposed adhesion primer was based on titanate. In 1957, Plueddemann moved to Dow Corning and begun his work resulting with a large body of knowledge which we have today on synthesis, compounding, and application of silane products which are extensively used today. His work also resulted in over 100 patents for Dow Corning and fundamental monograph² which has been republished in extenso by Springer in a soft cover in 2013, suggesting that there is still interest in the book and that the findings are still relevant.

Silane-based adhesion promoters still dominate the field of adhesion promotion but as Chapter 7 will show materials which belong to more than 30 categories of chemical are now involved in the adhesion promotion of many manufactured goods and the field has grown to importance in polymer processing technology worthy of thorough review in the context of new developments and applications.

REFERENCES

1. Brown, R G, US2612463, DuPont, Sep. 30, 1952.

2. Plueddemann, E P. Silane Coupling Agents. New York: Springer; 1991.

2

MECHANISMS OF ADHESION

There many methods which help in adhesion improvement. Technical literature usually contains a discussion of roles of interlocking (mechanical adhesion), diffusion, adsorption, surface reaction (chemical bonding), wetting, and electrostatic forces in the fostering adhesion in various material pairs.¹

There are several other important mechanisms in play which are to be considered in order to form the full picture of combinations of principles for the overall adhesion in a given product. In the case of diffusion, the effect of chain entanglement has to be included which emphasized the mechanics of the chain effect on adhesion.

Hydrogen bonding is a mechanism by which adhesion properties can be reversed depending on the physical state of matter. This differs substantially from the surface reaction which is base...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1: INTRODUCTION
• Chapter 2: MECHANISMS OF ADHESION
• Chapter 3: MECHANISMS OF ADHESION LOSS
• Chapter 4: SUBSTRATES – SURFACE CONDITION AND TREATMENT
• Chapter 5: TYPICAL PRIMER FORMULATIONS AND APPLICATIONS TO DIFFERENT SUBSTRATES
• Chapter 6: POLYMER MODIFICATION TO IMPROVE ADHESION
• Chapter 7: PROPERTIES OF ADHESION PROMOTERS
• Chapter 8: SELECTION OF ADHESION PROMOTERS FOR DIFFERENT SUBSTRATES
• Chapter 9: SELECTION OF ADHESION PROMOTERS FOR DIFFERENT PRODUCTS
• Chapter 10: ADHESION AND CORROSION PROTECTION
• INDEX