A holistic perspective of coatings technology.
Keywords: Gas chromatography, corrosion, corrosion protection, accelerated testing, service life prediction, surface chemistry, coating-substrate interface
In the broadest sense, nearly everything we see, touch, and use is coated in some fashion. Some of these applications have obvious major consequences on our lives, while others are nearly invisible yet still affect almost everything that we do. Consider that for most of our society, two of the largest investments we make are in our homes and automobiles. Coatings are a primary contributing factor to the attractiveness, protection, and longevity of these investments. The proper design, selection, and application of coatings for these applications are critical to their successful long-term attractiveness and performance. We experience many other uses of coatings on nearly a minute-to-minute basis, often without even noticing the benefit or importance. Would you enjoy playing cards without their durable coatings that have low coefficient of friction and abrasion resistance? Would your golf and tennis be as enjoyable without the bright and attractive coatings on balls, clubs, and racquets? Would you be safe driving without the reflective coatings on roadways and traffic signs? Would your electronic equipment work and have a long lifetime without protective coatings on the components? These examples illustrate the myriad of applications we demand of coatings. Other examples of the use of coatings may be even less obvious but can have even greater consequences.
In July 1967, the USS Forrestal, a U.S. Navy aircraft carrier, was sailing off the coast of Vietnam. She had just received a full load of missiles and bombs, and the crew was preparing for aircraft flight operations. Without notice, a missile accidentally launched from one of the aircraft parked on the carrier's deck, exploding into another aircraft. A tremendous fire ensued, with hundreds of active bombs and missiles, dozens of freshly fueled aircraft, and just below the flight deck, a liquid oxygen plant. Within 90 seconds the fire caused a bomb to explode. The ensuing explosions and fire raged for four and a half days, killing 134 men and wounding hundreds more. One suspected cause for the accidental firing of the missile was electromagnetic interference (EMI), which activated the firing mechanism. Coatings may have prevented this tragedy. Coatings that provide EMI shielding and current grounding are now used extensively on avionics equipment, such as housings and cable connectors to minimize these types of risks. The extremely short time between the release of the first missile and the first bomb explosion, about 90 seconds, was because the missiles and bombs had only an aesthetic coating on their exterior, which provided no thermal insulation from the fire. Coatings could have greatly minimized the explosions and the extent of the fire. Now intumescent coatings are applied which delay up to 10 minutes before a bomb or missile will reach its detonation "cook off" temperature during a fire, allowing more time to fight the fire and move the explosives. The USS Forrestal was severely damaged but was saved due to the heroic efforts of her crew. (1)
[FIGURE 1 OMITTED]
On September 11, 2001, the World Trade Center South Tower collapsed just 54 minutes after being struck by an aircraft; the North Tower fell one hour and 54 minutes after the aircraft impact. One major cause for the collapse was the fire that ensued, which weakened the load-bearing steel structure. Coatings designed to provide thermal insulation during a fire were applied to these structures; these coatings can be effective at temperatures well above 1500[degrees]F. However, the thermal insulating coatings used on the towers were not designed to withstand the mechanical forces resulting from the aircraft collision. Upon impact, the coatings flew off of the structures, leaving them unprotected from the fire, which further weakened the structure. If the coatings remained intact, the buildings may not have collapsed. (2)
What Are Paints and Coatings?
By the simplest definition, paints are "any pigmented liquid, liquifiable, or mastic composition designed for application to a substrate as a thin layer which is converted to an opaque solid film after application." (3) On a more detailed and fundamental level, coatings and paints are complex materials. Organic coatings usually consist of polymers, pigments, organic solvents and/or water, and numerous additives. A mature coating formulation may contain up to 20 different ingredients, all required to perform in the wet and dry state of a coating (and the transition from one state to the other--film formation). These ingredients do not exist or perform independently; they interact both physically and chemically. These interactions are complex and have been the subject of many studies. From another perspective, coatings are almost always applied in systems. Some coatings systems may consist of a primer and topcoat, while others have four to six coatings (e.g., automotive coating systems). Again, these coating layers do not perform independently. Coating systems are applied for a reason; each coating has functions to perform, and those functions are affected by the other coatings in the system. Interactions between coatings and coating system performance are complicated even further by the various interfaces, which include interfaces between coatings and at the substrate and surface. Finally, coatings are applied to products: cars, houses, cans, ships, airplanes, appliances, etc. The "appeal" and "performance" of these final products, which includes appearance, is very much dependent upon these coatings. So, coatings can and should be considered from a number of perspectives: as complex materials, in the coating systems they form, and for the role they play on the final end product. Of course this discussion has not begun to address other broader coating types, such as inorganic, metallic, and ceramic coatings. These also perform critical functions but will not be considered in this presentation due to the breadth of those technologies and the narrower scope of this paper.
Various Narrow Views of Coatings Technology
Coatings technology involves many disciplines, from the basics of chemistry and physics, to more advanced and specialized areas such as organic, polymer, and surface chemistry, to the applied fields of materials science and engineering, to real-world knowledge of how materials behave, how they work, and how they fail. With these disciplines as a basis, along with the demands of career positions, technologists within the coatings industry take many specialized forms, each of us having our own perspective of coatings. The chemist at a raw material supplier of resins or additives may have expertise in polymer, organic, or surface chemistry, but may not be familiar with how to most effectively combine these ingredients (i.e., formulate) to obtain desired properties and performance of the applied coating. The paint chemist for a coatings manufacturer has the goal of formulating ingredients to develop a coating for production and sale, but may not have in-depth knowledge about polymer chemistry, mechanical properties, or failure mechanisms. Engineers, designers, and specifiers have the responsibility of selecting coatings and coating systems for various end-use applications but may not be familiar with how coatings are developed, how they perform, and how they may or may not succeed in their end-use application. Similar statements may be made about coating applicators and end-users.
Considering the areas of concentration within the industry, it seems that very often we take a narrow, specialized view of coatings technology. For example, it is not unusual for a student studying the field of organic coatings to have a number of polymer courses, but no course on basic materials science. Such a course would provide at least a preliminary understanding of other materials, such as those that are common substrates for coatings. It also may provide a perspective of coatings composition, properties, and performance other than the traditional polymer perspective. Another frequent omission is knowledge of corrosion, which is a primary reason for many coating applications. The message is that all too often we take a narrow view of and approach to coatings technology, only the narrow view that seemingly is needed to complete the immediate task at hand.
[FIGURE 2 OMITTED]
A Holistic Perspective of Coatings Technology
Holism is the concept that whole entities have an existence other than the mere sum of their parts and that a broader perspective will yield better understanding and results. A coating is not just a polymer or pigments; a coating system is not just a primer and topcoat acting independently; an end product (i.e., the product to be coated) would not be as valuable without a properly functioning coating system. A coating is a complex material that is typically a component of a coating system, which provides added value (appearance, protection, etc.) to a final product. Coatings technology spans a wide spectrum, from the complex interactions and effects of individual paint ingredients, to the design of coating systems to perform specific functions, to the design and manufacture of end products. The focus of this paper is to suggest a holistic perspective of coatings technology, to illustrate that diversity of knowledge, thought, and approach in designing these coatings, coating systems, and final products will yield better science, better coatings, and better final products. This diversity can be obtained by individuals who have the ability, desire, and fortitude to learn and practice multiple disciplines. It also can be displayed by utilizing functional teams of people, with various skills and disciplines, each providing their own perspective and value.
COATINGS AS COMPLEX MATERIALS
One approach to study and understand materials is to view the cause-effect relationships between composition, structure, processing, properties, and performance. (4) In essence, a material's composition, structure, and processing determine its properties and performance. When viewing coatings as materials, this approach can be expanded as illustrated in Figure 1, and could be expanded even further with a greater focus on raw materials. To discuss and understand all of these relationships is well beyond the scope of this paper. In fact, this topic may be beyond the scope of several undergraduate and graduate level courses. These statements reflect one message of this section: coatings are complex materials and if they are to be thoroughly understood, advanced, and utilized, it is essential that we take the time and effort to understand these relationships with a much broader perspective and far beyond a basic level. The following is an introductory view of these contributing factors, followed by an illustration of their complexity and importance.
Composition and Structure
Many have expressed the complexity and uniqueness of coatings in both composition and function. Coating formulations contain many materials with an exceptionally wide variety of chemistries. It is generally agreed that formulations consist of four classes of materials: polymers, pigments, solvents, and additives, each having the potential to provide selective properties. Commercial paint formulations may contain several ingredients within each of these material classes, leading to recipes that can include 20 or more ingredients of different chemistries, each contributing certain facets to final properties and performance (see Table 1 for an example). From a thermodynamic perspective it is amazing that this variety of ingredients can be combined to form a stable product (paint) in both the wet and applied (dry) states. On the other hand, thermodynamic interactions between ingredients can have a tremendously positive impact on coating material properties. For the most part, compositional effects of established ingredients used in coatings are fairly well understood and have been well documented. From a practical standpoint of coating formulation development, we certainly have learned how to "put raw materials together" to obtain some desired properties. However, it is not clear that we have taken full advantage of more intricate ingredient interactions and effects to obtain the best performance.
What do we mean by "structure" in a coating? The structure of a material describes the arrangement of its internal components. The structure of coating ingredients and applied coatings is multi-faceted and spans orders of magnitude, much more than many other materials.
Some facets of material structure within coatings include:
* Subatomic structure; e.g., electrons within atoms interacting with nuclei ([10.sup.-11]-[10.sup.-10] meters)
* Atomic structure; e.g., organization of atoms relative to one another ([10.sup.-10]-[10.sup.-9] meters)
* Molecular structure of ingredients polymer, pigments, solvents, and additives ([10.sup.-9]-[10.sup.-7] meters)
* Larger scale polymer morphology ([10.sup.-7]-[10.sup.-4] meters)
* Pigment particle size, distribution, and packing ([10.sup.-8]-[10.sup.-4] meters)
* Latex particles and resulting cell structure from film formation ([10.sup.-8]-[10.sup.-6] meters)
* Macroscopic structure of coating thickness and form, defects, etc. ([10.sup.-6]-[10.sup.-4] meters)
These structural aspects are interesting in that some levels of structure create composition (i.e., sub-atomic, atomic, molecular) and some levels of structure are created by composition (i.e., polymer morphology, pigment packing, latex cell structure, macroscopic structure). Nonetheless, all of these "structural" components affect coating properties, but it is not clear that practical commercial formulations have benefited to the fullest extent from an understanding of these effects. To illustrate the magnitude and importance these ingredients and interactions can have, pigment-polymer interactions and the resulting effects will be discussed in greater detail below.
Processing (Paint Manufacture and Application)
Processing a material usually refers to making the material. In the case of coatings, two types of processes must be considered: paint manufacturing and application. In the former, the wet coating is being produced, while the latter is the first step in producing the applied, dry coating. In essence, application is a step in producing or refurbishing the final product (e.g., car, appliance, etc.). Most concerns with paint manufacturing deal with obtaining the proper dispersion (pigment size and stability), combining ingredients to get thorough and stable mixing, and completing this in an energy-and time-efficient manner. Of course improper processing certainly can produce bad paint. Some potential problems include instability, incompatibility, pigment settling and compaction, and short shelf life. Subsequently, these problems can then lead to another broad set of unattractive symptoms that can cause premature failure of an applied coating.
Application procedures certainly can have major effects on coating properties. Most savvy people in the industry know and have experienced that the applicator can "make or break" the coating. Experienced applicators have the knowledge and ability to do what needs to be done to make a coating work in an application. Some key factors are: surface preparation and paint preparation prior to application, application method and associated parameters, coating thickness, and environmental factors (e.g., temperature, humidity, air flow, sunlight). Fundamental research in this area is relatively thin. Most advances are made empirically at the manufacturing or application site. It is important to note that many application processes have been automated, for example OEM automotive, appliance, and can coating applications. These processes have improved efficiency, uniformity, and reliability--in general, overall performance. A broader knowledge of this area would assist in understanding paint properties and performance.
Properties and Performance
"Property" is a trait describing the kind and magnitude of response a material has to a specific imposed stimulus (e.g., the mechanical response a material has to a tensile force; chemical response to UV exposure; physical and thermal response to temperature changes). Typically, properties are defined solely by the composition, structure, and processing of a material, independent of the material's size and shape. However, with some types of materials, especially coatings, properties are affected dramatically by other imposed parameters. Coatings are specifically designed to be applied and dried under certain conditions (application method, substrate type, film thickness, temperature, humidity, etc.). It would be inappropriate and misleading to measure properties of coatings prepared outside the boundaries of these parameters; for example, measuring properties of a coating that is 10 mils thick while the coating was designed to be applied at 2 mils. Therefore, with coatings, it is important to understand all of the parameters associated with the intended application and service life to obtain an accurate assessment of properties and performance as measured within these parameters. It also is important to relate these properties to fundamental characteristics associated with composition, structure, and processing.
The "performance" of a material is its ability to provide its intended in-service function. For example, how long will the coating last; will it maintain appearance; will it prevent corrosion; will it perform the function(s) it was intended to provide? The relationship between properties and performance is interesting. Properties are normally evaluated in a laboratory or other controlled or documented environment and condition. Performance occurs in the "real world." While we can try to reproduce or simulate what happens in the real world over a coating's lifetime, it is extremely difficult to be exact or to provide a response that is always indicative. Nonetheless, extensive efforts to accomplish this are necessary and are being pursued. An excellent example is coating durability and weathering, which have been the focus of much intensive and fruitful research over recent years (for example, see references 5-8). Tremendous strides have been made at understanding natural weathering, mimicking and accelerating these conditions in a laboratory environment, and assessing their effects on coatings. Although advances have been made in this area, even leading experts profess that further improvements are necessary. This body of work is an excellent example of the importance and value of a holistic perspective of coatings technology, including fundamental understandings of composition and structure, coating system interaction and properties, real-world performance, and analytical methods to assess these effects. Considering the work that has been reported in this area, it becomes even more evident that a holistic perspective of coatings technology is essential to understand factors that contribute to a coating's level of success.
[FIGURE 3 OMITTED]
To conclude these thoughts on properties and performance, it is important to recognize that properties suggest how a material will perform in service; they are not a guarantee of in-service performance. It also must be recognized that during a coating's service life, it will be subjected to multiple stimuli and stresses, often at the same time. In many cases, failure is not due to one specific stress or weak property; it is due to the cumulative effects of multiple stresses over a period of time. This often is not observable or considered in the laboratory environment, sometimes this is not even considered when doing failure analysis.
Interactions Within Applied Coatings--An Example
As an applied solid film, coatings consist of dispersed pigment particles throughout a polymeric matrix. In this regard, paints are a subset of a more general material type, namely polymeric composites and, more specifically, particulate-filled composites. There have been many studies on the variety of aspects related to the effects of pigments and fillers in paints. The geometry, size, and concentration of filler particles affect nearly all properties of a coating. One aspect that has been studied, but to a lesser extent, is that of pigment (filler)-polymer interactions, which result in polymer adsorbed onto pigment particle surface and the formation of an adsorbed polymer layer (adlayer) around the particle. This polymer adlayer has distinct features (conformational, morphological, mechanical, etc.) that can be noticeably different from the bulk polymer. Although somewhat more obscure in their contributions than other factors, these interactions still play a major role in coating properties and performance. One vivid illustration of this is effects on mechanical properties. If there were no attractive interaction between a filler particle surface and the polymer matrix, the filler particle would be seen as a flaw within the polymer that would act as a stress concentrator and dramatically decrease mechanical properties of strength and modulus. In contrast, strength and modulus can increase with addition of filler particles with favorable filler-polymer interactions. Particles can disperse an applied load; they also can stop crack propagation. They can help restrict plastic deformation thereby improving yield and tensile strength, as well as hardness. Figure 2 illustrates an example of this effect. Other observable and important effects from pigment-polymer interactions include: rheology modification, prohibited pigment settling, (9,10) increased [T.sub.g] (11-16) decreased permeability, (17,18) and viscoelastic behavior. (19)
How and why do these effects occur? This question can be answered with an explanation of the thermodynamic and physical aspects of polymer adsorption onto filler particles and the subsequent effects on the properties of the composite. Before providing this explanation, or at least a summary of some salient issues, it should be noted that much of the research on this subject has been done for particulate-filled systems, but not necessarily coatings. Nonetheless, similar fillers and polymers have been used in these studies and the findings certainly can be and should be applied to coatings technology.
The interaction between filler particle surface and an adsorbing polymer species is caused most commonly by Van der Waal forces, the most notable of these being London (dispersion) and Keesom (polar) forces. It is informative to compare the potential energy-distance relationships for various types of bonds (Figure 3). At relatively close distances (1-3 [Angstrom]), primary bonds have a deep energy well, indicating strong but highly localized forces. In contrast, dispersion forces have lower potential energy but they are more significant at longer distances. The implications are that intermolecular forces, especially dispersion forces, not only cause polymer adsorption onto pigment, but they have effects well past the immediate adsorbed surface. In fact, Fowkes suggested that only dispersive forces transcend phase boundaries. (20) Both theory and empirical results indicate that polymers adsorbed onto filler particles can have noticeable effects tens, possibly hundreds, of nanometers into the polymer matrix of the material. The strength of these interactions can range up to 80 kJ/mole. Some evidence strongly suggests that an increased attraction (strength of interaction) between adsorbent and adsorbate produces a tighter and denser layer of polymer, with decreased overall mobility, and morphological and physical properties distinct from that of the bulk matrix polymer phase. (21,22)
One method of characterizing pigment surfaces and potential interactions with polymers is inverse gas chromatography (IGC). In this technique, a column is packed with solid particles of interest (e.g., pigment, polymer particles). Specific probes are introduced into the column to measure their distinct retention times through the packed column, which is affected by a number of factors including secondary bonding forces between the probe and particles. Retention times can then be used to calculate thermodynamic parameters of the system, such as surface tension of the particles, as well as the free energy, enthalpy, entropy, and work of adhesion. Although polymers and pigments must be analyzed separately, they are done so with common probes so that both qualitative and quantitative associations between pigments and polymers can be concluded from the analysis. Reference 23 provides a review of IGC technique and analysis.
IGC studies have illustrated the potential magnitude of these thermodynamic parameters of pigment surfaces and polymer-filler interactions. (24-26) For several grades of titanium dioxide with various surface treatments, the dispersive component of the solid surface tension, [[gamma].sup.D], ranged from 50 to 125 mJ/[m.sup.2], with higher surface tension for grades with greater surface treatments of alumina and silica--also commercially promoted as "high quality" grades. [[gamma].sup.D] for poly(methyl methacrylate) and poly(acrylic acid) was around 41 mJ/[m.sup.2], indicating that these polymers fulfill the thermodynamic requirement to wet all of the pigments evaluated. (27) This result would hold for most common pigment-polymer combinations but the specific magnitude of the interactions can vary dramatically. This is illustrated by comparing the dispersive work of adhesion, which ranged from 91 to 145 mJ/[m.sup.2] for the particular pigment-polymers assessed. The free energy, enthalpy, and entropy of adsorption also provide a quantitative means for assessing interactions. Free energy of adsorption ranged from -15 to -30 kJ/mole, indicating spontaneous and stable interactions. Enthalpies of adsorption up to -80 kJ/mole were measured, which is quite impressive. In comparison, the strength of hydrogen bonding can be up to 30 kJ/mole. Free energy and enthalpy of adsorption were more negative (indicating more favorable and stronger interactions) with probes that had greater polarity. However, in comparing the dispersive versus polar contributions, it is interesting that the dispersive component can contribute up to 90% of the adsorption enthalpy, even for highly polar probes. These parameters certainly help provide a quantitative understanding of the likelihood, strength, and stability of interactions that can occur between polymers and pigments in paints.
Another technique that has been used to study polymer adsorption onto filler particles is flow calorimetry, which entails percolating a polymer solution through a bed of pigment particles and measuring the heat produced. (28-30) By subsequently flowing just the solvent through the column and "rinsing" the pigment bed, a measure of reversibility of the polymer adsorption can be obtained. Several benefits of this technique are: (1) solutions of monomers and polymers can be used as opposed to model or probe compounds; (2) the measurement is a direct enthalpy of adsorption as opposed to a calculated value; (3) irreversible adsorptions can be studied and a measure of reversibility can be obtained; and (4) the amount of polymer adsorbed can be determined by using a detector (refractometer or UV spectrophotometer) on the effluent stream of the calorimetry column.
Using flow calorimetry, the same pigment-polymer interactions were studied as those discussed above with IGC. (31) Enthalpies of adsorption of methyl methacrylate onto various grades of Ti[O.sub.2] ranged from 0.04 to 0.99 J/gr of adsorbent and, normalizing per pigment surface area, 5 to 28 mJ/[m.sup.2]. As with the IGC analysis, pigments with greater surface treatments had higher adsorption enthalpy. Desorption endotherms, measured by "rinsing" with the carrier solvent, indicated most of these adsorptions were nearly 95% irreversible. In addition to the strength of the interaction, another contributing factor is the concentration of potential interaction sites on a filler. For example, some silica treatments can have about 2 SiOH sites/n[m.sup.2]. Consider a Ti[O.sub.2] grade that has a silica surface treatment, an average particle size of 0.3 nm, and a specific surface area of 15 [m.sup.2]/gr. This pigment can have up to [10.sup.7] SiOH groups/particle, resulting in about 3 X [10.sup.19] SiOH groups/gr pigment. A paint formulated at 20% pigment volume concentration with this Ti[O.sub.2] would contain about 2.5 X [10.sup.19] SiOH sites per milliliter of applied dry paint. Considering both the strength of adsorption and the number of available sites, this certainly allows for ample opportunity for extensive pigment-polymer interaction throughout the applied film.
What are the physical consequences of these interactions from an adsorbed layer perspective? As mentioned above, a number of researchers have proposed that stronger interactions result in thicker and more influential polymer adlayers on filler particle surface. There are a number of experimental approaches to measuring this adsorbed layer thickness. Table 2 summarizes various techniques and previous findings with various filler-polymer systems. One observation from these results is the wide range in the magnitude of the adlayer thickness, from several nanometers up to microns. This apparent discrepancy may be due to differences in size and concentration of filler particles, the chemical differences in the systems studies, the technique used to measure this thickness, and/or to the variation in interpretation of the adlayer (i.e., where it ends in relation to the bulk polymer phase). For the Ti[O.sub.2] systems discussed above, the adlayer of PMMA was measured using both centrifugation and rheological energy dissipation. (32) PMMA adlayers ranged from 10 to 100 nm depending upon the measurement technique, Ti[O.sub.2] grade, and PMMA molecular weight. Using these measurements, the effective filler volume concentration in an applied film (i.e., volume of pigment and adsorbed polymer) was calculated to be nearly double that of the pigment volume concentration alone. In addition, there was a definite trend that pigment-polymer systems having stronger adsorption had thicker adsorbed layer. This work led to a proposed scheme for the adlayer being tightly bound and very immobile near the pigment surface but farther from the surface polymer chains that are not directly anchored to the surface are more mobile than the tight adlayer but not as mobile as the bulk polymer. Figure 4 illustrates the concept in terms of rigidity of the adlayer as a function of distance from the filler particle surface.
With some understanding of the thermodynamic and physical extent of filler-polymer interactions, what practical implications do they have and how can we take advantage of these interactions in real world formulations? To answer this we can look at effects on coating properties. To extend the study of the above systems, a number of coatings were formulated and evaluated. (33) Some definitive trends in properties were observed. As filler-polymer interactions increased, pigment particles were less likely to settle. This is caused by the bonding between polymer and particles, which minimizes the potential for particle-particle interaction by providing steric stabilization. This allows the particles to remain suspended throughout both the wet and applied coating. As a result of this effect, contrast ratio also is improved. Improved pigment dispersion generally enhances coating opacity due to more efficient light scattering.
Flexibility tests indicated that coatings with stronger pigment-polymer interactions were less flexible. Scrape adhesion evaluations indicated the same trend because of brittle failure of the film. It has been reported that glassy type polymer coatings follow a general trend of poorer adhesion with decreasing flexibility. (34) In addition, other reports have indicated that coatings with higher internal stresses exhibit lower adhesion to their substrate. (35,36) These internal stresses cause the coating to be less flexible and to fail (adhesively and/or cohesively) when external forces are applied. For the systems evaluated, filler-polymer interactions may decrease adhesion because polymer chains that firmly attach to the filler surface decrease mobility and may increase the internal stress within the polymer matrix, resulting in reduced adhesion to the substrate.
Finally with regards to coating performance, there was a definite trend of improved coating performance during salt spray exposure (i.e., less blistering and uplifting) with improved pigment-polymer interactions. This is probably caused by decreased permeability due to increased immobilization of the polymer adlayer or, stated another way, increased effective filler volume concentration. These coating performance test results, when studied in light of the thermodynamic and adlayer thickness results, clearly indicate the potential effects of these interactions and the role they can play on properties and in-service performance.
The message of this section is that ultimately, the function of the "coatings technologist," whatever specific role they may play, is to provide coatings that perform as intended when applied to the real-world end product. One contributing factor to succeeding at this goal is to understand how coatings behave as materials, and to use that knowledge to develop better raw materials, to formulate better coatings, to manufacture and apply better coatings, to specify better coatings, and to understand how coatings perform when applied to their end product. We must create the composition and structure, and use processing techniques that will give coatings desirable properties to perform as desired--in paint systems and on final end products.
COATINGS AS PART OF A PAINT SYSTEM
Paints are almost always applied as a system of layered coatings. In some cases, these systems are comprised of three to four coatings plus a substrate and usually some form of substrate pretreatment(s). More demanding applications typically require multiple coatings to meet a multitude of stringent requirements. Vivid examples of demanding applications are automotive, aircraft, and structural steel, all of which have different requirements but typically contain multiple coatings in their finishing systems. To further illustrate, Figure 5 shows sample coating systems for metal and plastic automotive exterior substrates.
As exemplified by automotive paint systems, all of the individual coatings in multi-coat systems provide critical functions for the entire system to succeed. Each of the individual coatings has its own set of attributes, and they also have interfaces between them, at the substrate, and at the surface. Aside from properties of the individual coatings, the layers of coatings and their respective interfaces (including the top surface) have chemical and mechanical interactive effects, some of which may be quite substantial and possibly unexpected. These effects can be synergistic, and they can be beneficial or detrimental. It is essential to consider not only individual coatings, but also their interactions and performance in the coating system design and assessment. The following examples of substrate and coating layer interactions illustrate the potential magnitude of these effects and the importance of such a perspective--to view not only individual coatings, but also their properties, as a system of layered materials, from substrate to surface.
Chemical Interactions between Coatings and Metal Substrates
Along with a myriad of other functions, corrosion prevention is one of the main responsibilities of coating systems in high performance applications, such as automotive, aerospace, and structural steel. By definition, coatings are applied to a substrate. The origin of interactions between the layers within a coating system begins at the substrate-coating interface. The most obvious property affected is adhesion, but there are many others. One illustration of this is the work presented by Kumins. (37) From the previous discussion concerning polymer adsorption onto filler particles, one can deduce that similar adsorption processes can occur when a coating is applied to a substrate, especially a metal substrate; that is, the polymeric binder can adsorb onto the substrate in a similar fashion as adsorption onto pigment particles. This adsorption anchors polymer chains onto the substrate, thereby restricting segment mobility. Although there is an immediate and distinct adsorbed polymer layer, other polymer chains further from the substrate also are affected and this may extend well into the coating, up to 500 nm (yet another structural feature within the coating). This is consistent with the model proposed and described previously for adsorption of polymer onto pigment particles (Figure 4). This adsorption can cause properties of the polymer to be striated throughout the film. Restriction of the adsorbed polymer increases [T.sub.g], decreases diffusion of foreign species, decreases solvent solubility, and increases strength and stiffness. Kumins focused on adhesion and corrosion protection. Stronger adsorbed polymer yields stronger adhesion along with less diffusion of corrosive contaminants, and therefore, noticeable improvements in corrosion protection can be realized. However, in more general terms, Kumins' work illustrates that chemical interactions at interfaces can change a number of physical and mechanical properties of coatings and these changes can be observed throughout the coating system.
Interactions at coating-metal interfaces are complicated even further when contaminants (e.g., water, oxygen, ions) reach this interface with subsequent effects on adhesion and corrosion processes. Of these contaminants, water is generally the most insidious. The majority of coatings allow enough water diffusion to the coating-metal interface to allow corrosion. (38) However, it is generally considered that a prerequisite for corrosion processes to occur under paint films is the loss of adhesion or disbondment of the coating from the surface. A large body of research has illustrated the myriad of potential mechanisms for corrosion processes and coating failure in the presence of water, as well as corrosion inhibition mechanisms (see, for example, references 39-41). One common feature through this work is that good adhesion of coatings to metal substrates, especially with the presence of water, is a great contributing factor to corrosion prevention. Furthermore, yet another contributing factor is the resistance of the interface to attack. Both coating and metal substrate can be prone to chemical attack via a number of mechanisms during corrosion. (42) Degradation of either can lead to additional corrosion. But stability of the coating and the metal surface (including pretreatments) improves chances of preventing corrosion. Our understanding of how various adhesion phenomena and adhesion loss processes affect corrosion performance is a focused example of the need and benefits to take a broader view of coating performance-substrate material and preparation, pretreatment, coating types and systems, application processes, product design, test details, real world environment, and so on.
[FIGURE 4 OMITTED]
Interactions within Coating Systems on Plastic Substrates
Plastic materials provide numerous benefits, including cheaper and easier processing, lower weight, and inherent corrosion resistance. This is especially true in automotive applications. However, as with all materials, plastics have their own set of drawbacks and one drawback is generally poor adhesion of applied coatings. Thermoplastic polyolefin (TPO) is a particularly problematic substrate. Ryntz and co-workers have led the research of paint adhesion to and mechanical effects on plastic. (43-46)
Traditional explanations for the lack of coating adhesion to TPO are its low surface energy and "inertness," which prohibit favorable coating-substrate interactions. A number of pretreatments are used to promote adhesion to plastics, including flame and plasma treatments, as well as chlorinated polyolefin (CPO) primers. Focusing on CPO treatments, Ryntz, et al. have presented a mechanism for paint system adhesion and causes for failure. Upon application of the CPO coating, solvent and CPO polymer chains diffuse through the crystalline polypropylene at the TPO surface and into the underlying region containing rubber domains. Although the CPO primer thickness is only 10-15 microns, solvent may penetrate hundreds of microns into the TPO, and CPO chains may penetrate up to 14 microns. This diffusion causes solvent to swell rubbery domains within the TPO while CPO chains interact with the TPO by dispersion forces and molecular entanglements. This CPO-TPO interaction is responsible for increasing adhesion of the primer and subsequent coating system. An interesting anecdote is that often times apparent paint system damage is actually cohesive failure within the TPO. The cause for this can be solvent retention within the TPO, causing rubbery domains to remain swollen, thereby decreasing the mechanical integrity of the TPO. To maximize adhesion of the coating system, the CPO formulation requires a solvent system that will diffuse into the TPO; however, to minimize extended weakening of the TPO, the solvent system must diffuse out of the substrate and coating system during the coating cure (bake) process.
The contribution of the coating system on automotive plastics does not end there. These researchers also have shown that surface and mechanical properties of the topcoat (topcoat/clearcoat) assist the mechanical integrity of coated plastic components. Decreasing the topcoat's coefficient of friction improves the damage resistance of freshly painted plastic parts by causing the impacting object to be more prone to slide across the surface as opposed to gouging into it. However, this effect usually is temporary since coefficient of friction frequently increases through a coating's lifetime due to surface chemistry and topography changes from weathering and other exposures. Increasing topcoat toughness, hardness, and tensile strength improves performance of the painted plastic by absorbing and dissipating potentially damaging energy during impact events and this effect is more permanent throughout the coating system's lifetime if it can maintain mechanical properties. In addressing these performance issues, these researchers have noted: "It is not the CPO alone, the solvent blend alone, the substrate alone, or the topcoat alone that affects the adhesion/cohesion level in the painted plastic, but rather the system attributes that do."
Mechanical Interactions within Coating Systems
Stresses can form within applied coatings from a number of sources. One source is their application to and drying on a substrate. As they dry, coatings adhere to the surface but they typically also shrink because of solvent evaporation and/or polymer cure. These conflicting forces give rise to tensile stress within the coating. Another source of stress is that multi-coat systems are layers of different materials, each going through the phenomena of adhesion versus shrinkage during drying. In addition, there are differences in how these materials react to imposed stresses such as changes in temperature, humidity, and other environmental factors, as well as mechanical stresses such as flexing. A third source of stress may be chemical changes in the various coatings caused by aging and environmental exposure (e.g., chemical reactions causing increased crosslinking and/or chain scission, loss of plasticizer). A fourth source of internal stress may be irregularities of the substrate (e.g., porosity, corners, edges, or screws and fasteners) that demand conformation of the applied coating system.
Internal stress may lead to immediate failure, such as delamination or cracking, or it may lend a contributing factor when other stresses are applied. As stated previously in the discussion on properties and performance, coatings frequently fail from the cumulative effects of multiple stresses. For example, a coating may have adequate adhesive and cohesive strength to withstand an internal stress, but if the coating system experiences some other stress such as thermal shock or mechanical flexing, the infliction of multiple stresses along with the existing internal stress may lead to failure. On the other hand, development of internal stress can be used for benefit. For example, aircraft coating systems traditionally consist of epoxy primer and polyurethane topcoat. Periodically, usually every four to six years, aircraft are refurbished, which includes re-painting. The old paint must be removed and this was done almost exclusively with chemical paint strippers. The paint strippers contained methylene chloride, which diffuses through the polyurethane topcoat and dramatically swells the epoxy primer. The forces caused by swelling of the primer overcome the adhesive strength of the system, causing it to delaminate from the substrate, thereby stripping the paint. In short, the internal stress from the swelling of the paint would cause it to "pop off" the substrate.
Perera and co-workers have led the research in the area of internal stress of coatings. They have looked at crack formation and stress development, (47) environmental contributions, (48) coating compositional effects, and measurement in multi-coat systems. (49,50) When investigating a multi-coat system containing a primer, basecoat, and polyurethane clearcoat, these researchers found noticeable changes in coatings and the coating system during QUV accelerated weathering exposure (1000 hr), which led to paint system failure. Exposure to UV, water, and oxygen caused breaking of bonds in the polyurethane clearcoat and formation of new crosslinks and groups, including hydroxyls, hydroperoxides, and carbonyls. These new groups are more hydrophilic, causing the clearcoat to be more susceptible to water uptake as evidenced by water absorption of an unexposed coating versus one exposed for 725 hr being 2.2% vs 10.3%, respectively. This extent of water uptake leads to swelling, which causes compressive internal stresses. Chemical changes also caused an increase in the clearcoat [T.sub.g] from 70 to 106[degrees]C (over 30[degrees]C increase as measured by dynamic mechanical analysis) during the first 336 hr of exposure. This increasing [T.sub.g] suggests embrittlement of the coating and formation of internal tensile stresses. Stress development over the entire exposure period of 1000 hr can nearly double or triple. The QUV exposure was a repetitive eight-hour cycle composed of four hours UV exposure followed by four hours of condensation. In addition to the ongoing chemical changes, this cyclic exposure introduced repetitive physical changes (e.g., swelling and shrinkage) and the resulting mechanical stresses, which is a fatigue cycle. Materials generally will fail under fatigue at lower stress levels than a single stress event. The exposure causes chemical and mechanical property changes, as well as fatigue stresses, which cause the coating system to crack.
In a subsequent study, these researchers noted that most multi-coat systems have coatings with noticeably different chemistries, mechanical and physical properties. Each of these layers reacts differently to applied stresses. This difference is due in part to interlayer interactions which include adhesion, diffusion of species across interface boundaries, etc. The greater the difference in mechanical properties of the various coatings, the more susceptible the system is to development of more substantial internal stress. Of course, it is common in materials for stresses to be transmitted throughout the material and ultimately concentrate at the weakest areas such as flaws and defects. In the case of coatings, this can be an interface at the substrate or between coatings. When the adhesion between two films is less than cohesion of the coatings, adhesive failure (delamination) of coatings within the coating system can readily occur. Stress also will concentrate at surface defects and irregularities such as pinholes and irregular geometries, which can cause cracking and delamination failures.
The above discussions illustrate that coatings are not stand-alone entities when they are applied in a coating system. They chemically and mechanically interact with each other and their substrate; and they interact with their environment. These interactions can vary dramatically throughout the lifetime of the coating system, rendering substantial contributions to the coating system's success or failure. It is incumbent to understand not only the basic material aspects of coatings, but also their function and performance within the intended coating system.
COATINGS AS PART OF AN END PRODUCT
An important yet often unappreciated concept related to coatings is their value-to-performance ratio. This concept was emphasized by Wismer in his 1989 Mattiello Lecture. (51) This ratio is the cost of a coating system (and its application) relative to the cost of the end product on which it is applied. Table 3 lists Wismer's estimates for various applications, which generally hold true today. The cost of a coating is just a small fraction of the end product, often less than 1%, yet it provides a disproportionately high value to that product. For example, consider the appearance, corrosion prevention, chip resistance, etc. that a coating system provides to an automobile during the course of its lifetime. Picture what that automobile would look like without a coating, and what it would look like after several years of service. Relating this value-to-performance concept to earlier examples: What is the cost of an intumescent coating versus the loss of life and property experienced on the USS Forrestal? What is the cost of a thermal insulating coating versus the loss experienced from the 9/11 tragedy?
The initial and premier thought of all those working in the coatings industry, and especially coatings technologists (e.g., polymer chemist, applications chemist, formulator, applicator, design engineer, etc.) should be: The ultimate value of a coating is the value it provides during the application to and performance on the end product through its desired lifetime. Without an understanding and consideration of a coating's requirements and value, the success of that coating, or any technology associated with it (e.g., raw materials, equipment), is highly unlikely. Yet another example will illustrate the point further.
The U.S. Navy operates in a highly corrosive environment. These operations often involve the use of expensive and critical equipment, such as high performance aircraft. A constant, diligent effort is required to maintain this equipment for operational readiness and mission success and this includes corrosion prevention procedures. Because of these issues, the Navy and related organizations have performed much research and development related to corrosion prevention, including structural material development, coating pretreatments, organic coatings, cleaners, and corrosion preventive compounds. The constant close proximity to water, especially seawater, causes surfaces to be susceptible to water condensates and spray, which cause a corrosion problem. To address this problem, a type of corrosion preventive commonly used is water-displacing compound. These materials are designed to be applied to corrosion prone areas, displace water from the substrate upon application, and subsequently prevent corrosion of the underlying metal. A wide variety of corrosion preventive compounds exists for a number of end uses.
About 22 years ago, an effort was started to extend the menu of corrosion preventive compounds to include water-displacing paint. This paint was designed to be applied in the field for touch-up repair of damaged original paint. The principle investigator for the effort reviewed the considerable body of scientific literature on the subject and proceeded to develop the product. References 52-55 describe some of the associated technical findings, including the development of the coating. To summarize, the displacement of water from a metal surface by an applied coating is a complicated event that is dependent upon a number of contributing factors, most critically:
(1) Even and efficient flow and wetting of the coating when applied to the substrate. As with all coatings, this is necessary for thorough coverage. It is even more critical in this application since the coating must remove and isolate water away from the substrate. Typically, lower viscosity, better wetting coatings are more favorable.
(2) Preferential adsorption of the coating onto the substrate versus water. When the coating contacts the surface, at some point it will come into contact with water and the substrate. Water generally has a high affinity for metal substrates; however, the coating (actually components within the coating) can preferentially adsorb onto the metal substrate, diffuse under the water, and cause the water to flow or rise from the surface over top of the applied coating. This can be facilitated by additives that have a high affinity for metal such as petroleum sulfonate salts similar to those used in penetrating oils and lubricating fluids.
(3) A designed limit of water solubility. Limited solubility of water in the coating is required to ensure that no substantial amounts of water remain near the metal surface or within the coating. Again, this can be designed into the coating by selecting ingredients, especially solvents, that have low water solubility.
The performance of the coating is further complicated with the requirement of corrosion inhibition after application and cure. This is accomplished with the use of corrosion inhibiting pigments such as molybdates and phosphates. Of course, the ingredients within the coating formulation determine its performance and they were selected and formulated based on scientific principles and empirical results to yield the desired properties. Certainly, many of the concepts previously discussed in this paper were considered and utilized to develop a coating that would successfully fulfill its desired function.
The R & D efforts leading to this coating were followed by development of a product specification and introduction to the fleet. Several months later, a conference of Navy corrosion field engineers, who experience the day-to-day problems, was held. One of the topics discussed was the water displacing paint that was recently introduced. Following a presentation by the inventor, one of the engineers vehemently commented that his maintenance crews could not use this product because it would not dry on their equipment. In fact, there were times when the coating would not spray from its aerosol container. The scientist questioned how that could be possible when the coating clearly was applicable and dried in the laboratory and during other real-world scenarios. The field engineer sharply replied, "We are stationed in Alaska!" Upon hearing this, it struck me that in all of my research on the subject, I never talked with anyone in the field about their needs and perspectives of this application. I had formulated a coating that could be applied and cured in a laboratory setting, but not in a number of areas where the Navy is stationed, in this case at temperatures at or below 40[degrees]F. This coating did not add value to a notable number of end users because it could not be adequately applied and cured.
This example illustrates that, although successful application of scientific principles may be a requirement for a successful technological development, it is not the sole requirement. As stated above, without an understanding and consideration of a coating's requirements and value, the success of that coating is highly unlikely. In a broader sense, a fuller holistic approach to and understanding of the coating and its application requirements would have provided better chances for success.
The discussion throughout this paper, including the examples, was presented to illustrate a myriad of concepts from R & D through commercial use that are responsible for the success of a coating. It is not always important to understand the detailed chemistry of every ingredient within a formulation, or the fundamental materials science of ingredients and coatings, or the thermodynamics of all the interactions that may occur within a coating, or all of the chemical and mechanical effects within a coating system. However, it is important to understand that these effects exist and they in turn determine a coating's performance. The broader and deeper the understanding, the more potential for success.
The theme of this paper is to suggest a holistic perspective of coatings technology, to illustrate that diversity of knowledge, thought, and approach in designing raw materials, coatings, coating systems, and final products will yield better science, better coatings, and better final products. A holistic view of the various aspects of coatings technology can provide tangible benefits in R & D, application, and performance of coatings. Of course, it would be beneficial if we all expanded our horizons to have a broader knowledge and perspective of these issues. Many of the previous Mattiello Lecturers display(ed) great insight in a broad spectrum of coatings technology. This diversity can be obtained by individuals who have the ability, desire, and fortitude to learn and practice multiple disciplines. However, this holistic perspective does not have to be displayed or employed by individuals, it also can be displayed by teams of people with diverse abilities and disciplines, each providing their own knowledge, experience, and perspective.
In reading previous Mattiello Lectures, it is interesting and informative to note numerous discussions of "coatings engineer," "paint engineer," and "paint as an engineering material." (56-58) In fact, Joe Mattiello's Edgar Marburg Lecture at a national ASTM meeting in 1946 was entitled "Protective Organic Coatings as Engineering Materials." (59) This is interesting since for many years the coatings industry strived to transition from an "art" to a "science," and it has done so as exemplified by great scientific and performance advancements which extend far beyond the coatings industry. However, these authors were not debating coatings as a science versus an engineering discipline, nor were they commenting on the art form associated with coatings formulation and performance. They were discussing how coatings technologists were well rounded in knowledge and ability, and that coating materials function in the real world as engineering materials. There are those in the industry that display this quality, and there are groups that display this quality; however, the terms "coatings engineer" and "paint engineer" are rarely used these days, literally or figuratively. In some respects it appears that many working in the area of coatings technology have become extremely specialized, and knowledge within the industry has become overly focused and somewhat fragmented. Specialized knowledge in many cases is necessary for technological advancement; however, a broader knowledge of the entire coatings technology pipeline and industry also would greatly increase probability of successful development, application, and service life of coatings. These thoughts lead to a principle: The more you learn, the more you can do; the more you do, the more you learn. This applies to nearly every facet of life, but it certainly would be a benefit if applied within the coatings industry.
And now I thank those that have helped and continue to help me form my perspective and understanding of coatings technology ...
Table 1 -- A Sample Coating Formulation, Chemistry of Ingredients, and Properties Affected. Low Gloss Interior Wall Paint, Low VOC Material Chemistry Function GRIND Water Water Solids, viscosity Tamol 850 (Rohm & Haas) Polymethacrylic Dispersion acid stability KTPP (FMC) Potassium Dispersion tripolyphosphate stability AMP-95 (ANGUS) pH Amine neutralization Igepal CO-630 (Rhodia) Ethoxylated nonyl phenol Surfactant Drewplus L-475 (Ashland) Silica Foam control Nuosept 95 Hydroxymethyl Formaldehyde- dioxabicyclo releasing octane preservative Add the following under agitation: TiONA RCL-3 (Millennium) Titanium dioxide Color, hiding Mattex (Engelhard) Clay Extender filler No. 10 White (Imerys) Calcium carbonate Extender filler Celatom MW-27 (Eagle Picher) Diamatomaceous Extender filler Attagel 40 (Engelhard) Attapulgite clay Rheology modifier Sub-Total: Grind to 4+ H.S. LET-DOWN Airflex EF811 (Air Products) VAE emulsion Resin binder Drewplus L-475 Silica Foam control Bermocol CST-347, 2.5% Solon (Akzo) Cellulose Rheology modifier Water Water Solids, viscosity Add the following under agitation: Texanol (Eastman) Ester alcohol Coalescing solvent Yellow iron oxide "C" colorant Iron oxide Colorant Red iron oxide "F" colorant Iron oxide Colorant Lampblack "B" colorant Iron oxide Colorant Total PHYSICAL PROPERTIES Density (lb/gal) 11.4 % Solids, by weight 46.3 % Solids, by volume 27.2 % PVC 65.9 % C.S. on latex NVM 5.0 % Disp. solids on pigment 0.6 Lb/gal of water 582.2/69.9 VOC (g/L) 25.2 Material Pounds Gallons NVM-Lb NMVM-Gal GRIND Water 170.0 20.41 Tamol 850 (Rohm & Haas) 9.0 0.91 2.7 KTPP (FMC) 1.5 0.08 AMP-95 (ANGUS) 2.0 0.25 Igepal CO-630 (Rhodia) 3.5 0.45 Drewplus L-475 (Ashland) 2.0 0.27 Nuosept 95 1.5 0.18 Add the following under agitation: TiONA RCL-3 (Millennium) 140.0 4.46 140.0 4.46 Mattex (Engelhard) 100.0 4.57 100.0 4.57 No. 10 White (Imerys) 150.0 6.64 150.0 6.64 Celatom MW-27 (Eagle Picher) 45.0 2.34 45.0 2.34 Attagel 40 (Engelhard) 5.0 0.25 5.0 Sub-Total: 629.5 40.55 440.0 18.01 Grind to 4+ H.S. LET-DOWN Airflex EF811 (Air Products) 159.0 17.87 87.5 9.30 Drewplus L-475 1.0 0.14 Bermocol CST-347, 2.5% Solon (Akzo) 267.0 32.05 6.7 Water 74.0 8.88 Add the following under agitation: Texanol (Eastman) 4.4 0.56 Yellow iron oxide "C" colorant 2.2 0.12 Red iron oxide "F" colorant 0.2 0.01 Lampblack "B" colorant 0.7 0.06 Total 1138.0 100.24 527.5 27.31 PHYSICAL PROPERTIES Density (lb/gal) % Solids, by weight % Solids, by volume % PVC % C.S. on latex NVM % Disp. solids on pigment Lb/gal of water VOC (g/L) Table 2 -- Polymer Absorbed Layer Thickness on Filler Particles for Various Polymer-Filler Systems Measurement Thickness System Method (nanometers) Polyurethane/glass Energy dissipation-- viscosity 2500 PS & PMMA/glass & mica Energy dissipation-- dynamic mechanical analysis (DMA) 60-1400 CPE/Ti[O.sub.2] Energy dissipation-- DMA 1-20 PVC & PVAc/Fe203 & Ti[O.sub.2] Energy dissipation-- DMA 30-110 PVAc/PS particles Ultracentrifuge 3-25 PVAc/PS particles Ultracentrifuge Slow-speed centrifuge Intensity fluctuation Electrophoreses 3-40 SBR/carbon black Dilatometry Thermal expansion 3 Alkyd/Ti[O.sub.2] Viscosity 2-40 Linseed oil/carbon black Oil absorption 2.5 SBR/carbon black DMA 2 Sulphonic acid/calcium carbonate Neutron scattering 2 Elastomer/carbon black Bound (unextractable) rubber 2.2-5.5 Linoleic triglyceride/Ti[O.sub.2] Oil absorption/ theoretical model 12 Polymethacrylate/Ti[O.sub.2] Adsorption isotherm 1.8-9.6 Adlayer Thickness/ System Filler Radius References Polyurethane/glass 0.14 19 PS & PMMA/glass & mica 0.04 63 CPE/Ti[O.sub.2] 0.01-0.20 22 PVC & PVAc/Fe203 & Ti[O.sub.2] 0.20-0.35 64 PVAc/PS particles 0.08-0.70 65 PVAc/PS particles 0.08-1.1 66 SBR/carbon black Not reported 12 Alkyd/Ti[O.sub.2] 0.02-0.40 9 Linseed oil/carbon black 1.0 57 SBR/carbon black Not reported 67 Sulphonic acid/calcium carbonate 0.3-1.0 68 Elastomer/carbon black 0.06-1.14 69 Linoleic triglyceride/Ti[O.sub.2] 0.06 70 Polymethacrylate/Ti[O.sub.2] 0.01-0.05 71 Clearcoat 40-50 microns Basecoat ~20 microns Primer (~30 microns) Electrocoat (~0.25 microns) Zinc phosphate treatment Metal substrate Clearcoat 40-50 microns Basecoat ~20 microns Primer (~30 microns) Plastic substrate Figure 5 -- Schematic representation of automotive exterior coating systems for metal and plastic. (73) Table 3 -- Wismer's Estimates of the Percentage of the Cost of Coatings to the Total Cost of Various End Products (51) Automotive paint 0.9% Fire protective mastic on oil platform 1.0% Cable coating on ship 0.2% Ink on paper <6.0% Ink on packaging <0.5% Paint on whole house 0.5%
ACKNOWLEDGMENTS, THANKS, AND DEDICATION
I did not know Joseph Mattiello but I have read about him, mainly in previous Mattiello Lectures and especially from the brief biography written by Bob Brady. (60) Without exception, the words used to describe him are: creative, visionary, dedicated, inspirational, leader, and friend. One of the most touching testimonials was stated by Bill Greco: "Joe Mattiello, the charismatic individual, the man of human and humane qualities, the warm-hearted devoted human being, devoted to his family, his profession, his country, and to the coatings industry--he gave so much of his time and energy to transform the industry from an art to a science and to take its rightful place in the science of chemistry. If there is one outstanding quality of Joe Mattiello that should be stressed, it was the friendship he offered, sincere and heartfelt, which brought its just reward with the legion of friends he made not only in the U.S., but all over the world." (61) In short, Joseph Mattiello was a great scientist and a fabulous person. I urge all of you to read about this great man to appreciate his character and achievements and to be inspired by them.
I do know a number of recent Mattiello Lecturers. They are reflections of Joe Mattiello, providing great contributions to this industry and society. Many of their contributions have been captured within the JOURNAL OF COATINGS TECHNOLOGY, both in their Lectures and other published works. I urge you to read their writings to learn, to explore, and to help create your own holistic view of and approach to coatings technology. It is an overwhelming honor to be considered among these previous Lecturers and I thank the Mattiello Lecture Committee for this tribute. I would also like to extend my sincere and deep appreciation to all of the FSCT Staff, especially Pat Ziegler, Bob Ziegler, Rod Moon, Alicia Hoffmayer, and the always pleasant Dottie Kwiatkowski, for their support throughout my career.
Success can be defined and perceived in many ways, but regardless of the definition or perception, teamwork is an absolute requirement for successful achievements and a successful career. I have had the fantastic fortune of working with talented, dedicated, and selfless people throughout my entire professional life, and an even greater fortune to call these people friends--many of them "Best Friends." They have taught me things that could not be learned from books, provided creative and challenging ideas, performed meticulous lab work, kept me motivated, and most importantly increased the joy in my life. All of my professional successes are a direct result of and credited to these friends. Therefore, I thank them and accept this honor on behalf of all my former, current, and future teammates and colleagues, and most notably those listed below who have had an amazingly positive impact on my life.
From the Naval Air Development Center: Don Hirst, Gabe Pilla, Steve Spadafora, Tony Eng, John De Luccia, Irv Shaffer, Ken Clark, Paul G. Prale.
From Air Products and Chemicals: Frank Pepe, Jeanine Snyder, Denise Lindenmuth, Sherri Bassner, Fritz Walker, John Dickenson, Renee Keller, Tom Panunto.
From industry and academia: Bob Brady, Ray Dickie, Clive Hare, Cliff Schoff, Darlene Brezinski, Loren Hill, Kurt Best, Dave McClurg, Leon Boretsky, Ihab Kamel, Roger Corneliussen.
On a final, but most important note, my father worked hard his entire life to make my life better. I have tried to do the same for my son, Tony. I dedicate all that this award represents to him, the proudest part of my life.
(1) Situation Critical: USS Forestal (video), Henninger Media Development Publication, New York, 1997.
(2) Why the Towers Fell (video), BBC (New York)/WGBH (Boston) co-production, 2002.
(3) Coatings Encyclopedic Dictionary, LeSota, S. (Ed.), Federation of Societies for Coatings Technology, Blue Bell, PA, 1995.
(4) Callister, W.D., Jr., Materials Science and Engineering, J. Wiley and Sons, Inc., New York, p. 2-3, 2003.
(5) Service Life Prediction of Organic Coatings: A Systems Approach, Bauer, D.R. and Martin, J.W. (Ed.), ACS Symposium Series 722, Oxford University Press, 1999.
(6) Service Life Predictions: Methodology and Metrologies, Martin, J.W., and Bauer, D.R. (Ed.), ACS Symposium Series 805, Oxford University Press, 2001.
(7) Papers in JOURNAL OF COATINGS TECHNOLOGY, 74, No. 924 (2002).
(8) Gerlock, J.L, Peters, C.A., Kucherov, A.V., Misovski, T., Seubert, C.M., Carter, R.O. III, and Nichols, M.E., "Test Accelerated Weathering Tests for Appropriate Weathering Chemistry: Ozone Filtered Xenon," JOURNAL OF COATINGS TECHNOLOGY, 75, No. 963, 34 (2003).
(9) Rothstein, E.C., "Role of the Adsorbed Resin Layer in the Dispersion of Pigmented Alkyd Systems," Official DIGEST, 36, 1448 (1964).
(10) Buttignol, V. and Gerhart, H.L., Ind. Eng. Chem., 60, 8, 69 (1968).
(11) Kamel, I., "Thermal and Mechanical Stability of Submicron Fillers Reinforced Composites," North American Thermal Analysis Society Conference, Cincinnati, OH, Sept. 1986.
(12) Kraus, G. and Gruver, J.T., J. Poly. Sci, Polymer Physics Ed., 8, 571 (1970).
(13) Howard. G.J. and Shanks, R.A., J. Macromol. Sci.-Chem, A17, 2, 287 (1982).
(14) Greenberg, A. R., Messaros, M., and Kamel, I., Poly. Preprints, 6, 28 (1985).
(15) Greenburg, A.R., J. Mat. Sci. Let., 6, 78 (1987).
(16) Reid, C.G. and Greenbergy, A.R., J. Appl. Poly. Sci., 39, 995 (1990).
(17) Manson, J.A. and Sperling, L.H., Polymer Blends and Composites, Plenum Press, New York, 1976, p. 411.
(18) Kwei, T.K., J. Poly. Sci., A3, 3229 (1970).
(19) Ziegel, K.D., J. Coll. Inter. Sci., 29, 72 (1969).
(20) Fowkes, F.M., Ind. Eng. Chem., 56, 40 (1964).
(21) Schrieber, H.P., Org. Coat. App. Poly. Sci., 45, 22 (1982).
(22) Boluk, M.Y. and Schreiber, H.P., Poly. Comp., 7, 295 (1986).
(23) Hegedus, C.R. and Kamel, I.L., "A Review of Inverse Gas Chromatography Theory Used in the Thermodynamic Analysis of Pigment and Polymer Surfaces," JOURNAL OF COATINGS TECHNOLOGY, 65, No. 820, 23 (1993).
(24) Papirer, E., Vidal, A., and Balard, H., "Analysis of Solid Surface Modification," Inverse Gas Chromatography: Characterization of Polymers and Other Materials, Lloyd, D.E., Ward, T.C., and Schreiber, H.P. (Ed.), ACS Symposium Series 391, American Chemical Society, Washington, D.C., 1989.
(25) Ziani, A., Xu, R., Schreiber, H.P., and Kobayashi, T., "Inverse Gas Chromatography, Surface Properties, and Interactions Among Components of Paint Formulations," JOURNAL OF COATINGS TECHNOLOGY, 71, No. 893, 53 (1999).
(26) Burness, J.H. and Dillard, J.G., Langmuir, 7, 1713 (1991).
(27) Hegedus, C.R. and Kamel, I.L., "Thermodyamic Analysis of Pigment and Polymer Surfaces Using Inverse Gas Chromatography," JOURNAL OF COATINGS TECHNOLOGY, 65, No.820, 31 (1993).
(28) Lloyd, T.B., Li, J., Fowkes, F.M., Brand, J.R., and Dizikes, L.J., "Surface Studies of Hydrous Oxide Coated Rutile in Non-Aqueous Media," Presented at the Federation of Societies for Coatings Technology Annual Meeting, Washington, D.C., 1990.
(29) Fowkes, F.M., Dwight, D.W., and Cole, D.A., J. Non-Crystalline Solids, 120, 47 (1990).
(30) Joslin, S.T. and Fowkes, F.M., Ind. Eng. Chem. Prod. Res. Dev., 24, 369 (1985).
(31) Hegedus, C.R., "Pigment-Resin Interactions in Coating Systems," Ph.D. Thesis, Drexel University, Philadelphia, June 1991.
(32) Hegedus, C.R. and Kamel, I.L., "Adsorption Layer Thickness of Poly(methyl methacrylate) on Titanium Dioxide and Silica," JOURNAL OF COATINGS TECHNOLOGY, 65, No. 821, 49 (1993).
(33) Hegedus, C.R. and Kamel, I.L., "Polymer-Filler Interaction Effects on Coating Properties," JOURNAL OF COATINGS TECHNOLOGY, 65, No. 822, 37, 1993.
(34) Payne, H.F., Organic Coating Technology: Volume I, John Wiley and Sons, 1954, p. 17.
(35) Croll, S.G., "Adhesion Loss Due to Internal Strain," JOURNAL OF COATINGS TECHNOLOGY, 52, No. 665, 35 (1980).
(36) Nate, K. and Kobayashi, T., "Adhesive Characteristics of Ultraviolet Curable Resins," JOURNAL OF COATINGS TECHNOLOGY, 52, No 668, 57 (1980).
(37) Kumins, C.A., "Physical Models for Organic Protective Coatings," JOURNAL OF COATINGS TECHNOLOGY, 52, No. 664, 39 (1980).
(38) Haagen, H. and Funke, W., J. Oil & Color Chemists' Assoc., 58, 359 (1975).
(39) Funke, W., Ind. Eng. Chem. Prod. Res. Dev., 24, 343 (1985).
(40) Leidheiser, H., Wang, W., and Igetoft, C.L., Prog. Org. Coat., 11, 19 (1983).
(41) Nguyen, T., Bentz, D., and Byrd, E., "A Study of Water at the Organic Coating/Substrate Interface," JOURNAL OF COATINGS TECHNOLOGY, 66, No. 834, 39 (1994).
(42) Dickie, R.A., "Chemical Studies of the Organic Coating-Steel Interface After Exposure to Aggressive Environments," in Polymer Materials for Corrosion Control, Dickie, R.A. and Floyd, F.L. (Ed.) ACS Symposium Series 322, American Chemical Society, Washington, D.C., pp 136-154, 1986.
(43) Ryntz, R.A., Xie, Q., and Ramamurthy, A.C., "Effects of Coating Solvents on the Morphology of Thermoplastic Polyolefins (TPO)," JOURNAL OF COATINGS TECHNOLOGY, 67, No. 843, 45 (1995).
(44) Prater, T.J., Kaberline, S.L., Holubka, J.W., and Ryntz, R.A., "Examination of the Distribution of TPO Adhesion Promoter Material in a Painted TPO System," JOURNAL OF COATINGS TECHNOLOGY, 68, No. 857, 83 (1996).
(45) Ryntz, R.A. and Mihora, D.M., "SAE Technical Paper # 1999-01-1205," SAE International, Warrendale, PA, 1999.
(46) Ryntz, R.A., Britz, D., Mihora, D.M., and Pierce, R., "Measuring Adhesion of Poly(Olefins): The Role of Adhesion Promoter and Substrate," JOURNAL OF COATINGS TECHNOLOGY, 73, No. 921, 107 (2001).
(47) Oosterbroek, M., Lammers, R.J., Vander Ven, L.G.J., and Perera, D.Y., "Crack Formation and Stress Development in an Organic Coating," JOURNAL OF COATINGS TECHNOLOGY, 63, No. 797, 55 (1991).
(48) Perera, D.Y. and Oosterbroek, M., "Hygrothermal Stress Evolution During Weathering in Organic Coatings," JOURNAL OF COATINGS TECHNOLOGY, 66, No. 833, 83 (1994).
(49) Boerman, A.E. and Perera, D.Y., "Measurement of Stress in Multicoat Systems," JOURNAL OF COATINGS TECHNOLOGY, 70, No. 881, 69 (1998).
(50) Perera, D.Y., "Stress Phenomena in Organic Coatings," in Painting and Coatings Testing Manual, Koleske, J.V. (Ed.), 14th Edition of the Gardner-Sward Handbook (ASTM, MNI 17), 585 (1995).
(51) Wismer, M., "Learning to Leap: Rising to the Technical Challenge of Today's Coatings Industry," JOURNAL OF COATINGS TECHNOLOGY, 62, No. 780, 83 (1990).
(52) Hegedus, C.R., "Displacement of Water from a Steel Surface," JOURNAL OF COATINGS TECHNOLOGY, 56, No. 711, 51 (1984).
(53) Hegedus, C.R., Metal Finishing, 81, No. 6, 53 (1983).
(54) Hegedus, C.R., "Water Displacing Corrosion Preventive Compounds," in Corrosion Control by Coatings, Leidheiser, H. Jr. (Ed.), National Association of Corrosion Engineers, Houston, TX, 1981.
(55) Hegedus, C.R. and Clark, K.C., U.S. Patent 4,359,543, "Water Displacing Paint," Issued Nov. 16,1982.
(56) E.G. Bobalek, "Paint Among Engineering Materials," Official DIGEST, 34, No. 455, 1293 (1962).
(57) Patton, T.C., "Reflections of a Paint Engineer on Paint Flow, Interface Physics, and Pigment Dispersion," JOURNAL OF PAINT TECHNOLOGY, 42, No. 551, 665 (1970).
(58) Gerhart, H.L., "The Coatings Engineer, the Corporation and the University," JOURNAL OF COATINGS TECHNOLOGY, 49, No. 624, 37 (1977).
(59) Mattiello, J.J., Am. Soc. Testing Materials Proc., 46, 493 (1946).
(60) Brady Jr., R.F., "Clean Hulls Without Poisons: Devising and Testing Nontoxic Marine Coatings," JOURNAL OF COATINGS TECHNOLOGY, 72, No. 900, 44 (2000).
(61) Glaser, M.A., "Innovation in Organic Coatings," JOURNAL OF PAINT TECHNOLOGY, 46, No. 599, 39 (1974).
(62) Coating formulation supplied by Andy Defusco, Air Products and Chemicals, Inc., Allentown, PA.
(63) Iisaka, K. and Shibayama, K., J. Appl. Poly. Sci., 22, 3135 (1978).
(64) Isobe, Y., Okuyama, K., Hosaka, A., and Kubota, Y., "Effect of the Pigment Vehicle Interaction on the Properties of Magnetic Coatings," JOURNAL OF COATINGS TECHNOLOGY, 55, No. 698, 23 (1983).
(65) Garvey, M.J., Tadros, T.F., and Vincent, B., J. Coll. Inter. Sci., 49, 57 (1974).
(66) Garvey, M.J., Tadros, T.F., and Vincent, B., J. Coll. Inter. Sci., 55, 440 (1976).
(67) Smit, P.P.A., Rubber Chem. Tech., 41, 1194 (1968).
(68) Markovic, I., Ottewill, R.H., Cabula, D.J., Field, I., and Marsh, J.F., Coll. Poly. Sci., 262, 648 (1984).
(69) Pliskin, I., and Tokita, N., J. Appl. Poly. Sci., 16, 473 (1972).
(70) Long, J.S., "Creative Imagination as It Applies to the Decorative and Protective Coatings Industry," Official DIGEST, 26, No. 358, 989 (1954).
(71) Idogawa, H., Shimizu, O., and Esumi, K., "Adsorption Phenomena of Polymers Having Functional Groups on Ti[O.sub.2] Particles in Nonpolar Solvent," JOURNAL OF COATINGS TECHNOLOGY, 65, No. 823, 67 (1993).
(72) Sumita, M., Shizuma, T., Miyasaka, K., and Ishikawa, K., J. Macromol. Sci.--Phy., B22 (4), 601 (1983).
(73) Adamsons, K., "Chemical Depth Profiling of Automotive Coating Systems Using Slab Microtome Sectioning with IR/UV-VIS Spectroscopy and Optical Microscopy," JOURNAL OF COATINGS TECHNOLOGY, 74, No. 924, 47 (2002).
Charles R. Hegedus--Air Products and Chemicals, Inc.*
Presented at the 81 st Annual Meeting of the Federation of Societies for Coatings Technology, Philadelphia, PA, Nov. 12-14, 2003.
* 7201 Hamilton Blvd., Allentown, PA 18195-1501.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||2003 Mattiello Memorial Lecture|
|Author:||Hegedus, Charles R.|
|Date:||Jan 1, 2004|
|Previous Article:||2003 Joseph J. Mattiello Memorial Lecture.|
|Next Article:||2002 Roy W. Tess Award.|