Handbook of Waterborne Coatings

Peter Zarras, Mark D. Soucek, Atul Tiwari

• Publisher: Elsevier
• Year: 2020
• Print ISBN:
  9780128142011
• eBook ISBN:
  9780128142028
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Handbook of Waterborne Coatings comprehensively reviews recent developments in the field of waterborne coatings. Crucial aspects associated with coating research are presented, with close attention paid to the essential aspects that are necessary to understand the properties of novel materials and their use in coating materials. The work introduces the reader to progress in the field, also outlining applications, methods and techniques of synthesis and characterization that are demonstrated throughout. In addition, insights into ongoing research, current trends and challenges are previewed. Topics chosen ensure that new scholars or advanced learners will find the book an essential resource. - Serves as a reference guide to recent developments in waterborne coatings for industrialists, scientists and engineers involved in the field of coatings - Presents coverage of the unique application methods for waterborne coatings and when those methods should be used - Provides foundational information on waterborne coatings and discusses current market trends that impact the field

Chapter 1: Water-based sol–gel coatings for military coating applications

Danqing Zhu ¹ , Naiping Hu ² , and Dale W. Schaefer ^{2 1} Ecosil Technologies LLC, Fairfield, OH, United States ² Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH, United States

Abstract

This review covers the basics of sol–gel technology and the chemistry of alkoxysilanes, which are the most valuable sol–gel precursors in preparation of sol–gel materials and coatings. Results from early and recent studies are presented showing that sol–gel coatings provide strong corrosion protection for metals. Protection is mainly attributed to the formation of highly cross-linked siloxane structure on a metal surface for improved water resistance and the formation of a high density of metallosiloxane bonds at the interface for strong coating/metal adhesion. The evolution of water-based sol–gel coatings is presented with a focus on their use in military coating applications: (1) water-based sol–gel pretreatment coatings as a replacement for chromate and phosphate pretreatments and (2) waterborne coatings enhanced by organofunctional trialkoxysilanes (“super primer”) as a replacement for military chromated epoxy primers.

Keywords

Corrosion protection; Pretreatments; Silane coatings; Sol–gel coatings; X-ray reflectivity (XRR); Zirconium oxide coatings

1. 1. Introduction
2. 2. Background of sol–gel technology
   1. 2.1 What is a sol–gel process?
   2. 2.2 Chemistry of alkoxysilanes
      1. 2.2.1 Silane coupling agents
      2. 2.2.2 Key reactions of silane coupling agents
      3. 2.2.3 Other organofunctional trialkoxysilanes used in the corrosion control of metals
3. 3. Water-based sol–gel coatings in military applications
   1. 3.1 Early research for sol–gel coatings on metals for corrosion protection in military applications
   2. 3.2 Water-based sol–gel pretreatment coatings
      1. 3.2.1 Water-based organofunctional silane–based pretreatment coatings
      2. 3.2.2 Water-based zirconium oxide pretreatment coatings
      3. 3.2.3 Water-based hybrid pretreatment coatings
   3. 3.3 Waterborne coatings enhanced by organofunctional trialkoxysilanes
4. 4. Conclusions
5. References

1. Introduction

A typical military coating system, such as the Chemical Agent Resistant Coating (CARC) system, consists of a metal pretreatment coating, an epoxy primer, and a polyurethane topcoat. These coatings impart excellent corrosion protection to a broad range of metal substrates. However, they also pose health/safety and environmental concerns due to (1) the use of carcinogenic hexavalent chromium compounds as a major pretreatment coating ingredient and as anticorrosion pigments in the epoxy primers and (2) the high content of organic solvents, often classified as volatile organic compounds (VOCs) and hazardous air pollutants (HAPs), in the epoxy primers. Examples of problematic military coatings are (i) MIL-PRF-23377 (solvent-borne, chromated epoxy primer), (ii) MIL-PRF-85582 (water-reducible, chromated epoxy primer), (iii) DOD-P-15328 (solvent-borne, chromated acid-etching wash primer), and (iv) MIL-DTL-5541 (chromate conversion coating—metal pretreatment).

Driven by strict chromate/VOC/HAP regulations and by demand for improved lifetime of coated military assets exposed in harsh environments, coating formulators have been seeking high-performance coatings that comply with current health and environmental regulations. With its unique merits, sol–gel technology has become especially attractive to the formulators in recent years. The major merits of sol–gel coatings include (1) process flexibility (e.g., ambient spraying or immersion application), (2) highly cross-linked coating structure as an excellent physical barrier to retard the ingress of water/corrosive species, (3) covalent bonding to metals substrates to provide strong adhesion at metal/coating interface, and (4) the use of environmentally friendly sol–gel precursors.

Solvent-based sol–gel coatings have demonstrated excellent corrosion protection performance on metals [1–31]. But the large volume of organic solvents required in the sol–gel process hinders the widespread use of these coatings. Water-based sol–gel coatings have been developed and commercialized. Typical applications of these water-based sol–gel coatings include (1) passivation coatings based on organofunctional silanes (1–2 μm) for bare corrosion protection to replace chromate passivation treatment on continuously produced galvanized steel sheets [32,33] and (2) metal pretreatment coatings based on zirconium/titanium oxide and/or organofunctional silanes for paint adhesion (20 nm–1 μm) to replace chromate/phosphate-based pretreatments in commercial and military applications [34–38]. In addition, researchers have also demonstrated that anticorrosion performance of waterborne coatings can be enhanced by adding hydrophobic organofunctional silanes [39–43].

This ch...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Chapter 1. Water-based sol–gel coatings for military coating applications
• Chapter 2. Photocatalytic waterborne sol–gel coatings
• Chapter 3. Waterborne anticorrosion coatings based on polyaniline
• Chapter 4. Nanostructured waterborne acrylic coatings: thermomechanical properties enhancement by molecular jamming and confinement
• Chapter 5. Dispersion and dispersion stability of graphene in aqueous media for waterborne coating application
• Chapter 6. Open time developments
• Chapter 7. Waterborne functional paints to control biodeterioration
• Chapter 8. Electrophoretic deposition of waterborne colloidal dispersions
• Chapter 9. Waterborne coatings from casein and carbohydrate biobased raw materials
• Chapter 10. Waterborne superhydrophobic coatings for the conservation of the cultural heritage: a case study for the protection of mortar, ceramic, and wood
• Chapter 11. Recent advances in waterborne polyurethanes and their nanoparticle-containing dispersions
• Chapter 12. Commercial waterborne coatings
• Index