1. Introduction
The workshop Coatings on Glass grew out of a collaboration between the glass industry and the US Department of Energy's Office of Industrial Technologies (OIT). The 2-day workshop was held on 18–19 January 2000 in Livermore, CA, USA and brought 42 experts from the glass and coatings industries, universities, and the national laboratories together to identify key targets for improvement, technology barriers, and research needs relevant to the manufacturing of coated glass products. It was sponsored by the DOE/OIT Glass Industry of the Future program and PPG Industries, and was conducted in collaboration with the Glass Manufacturing Industry Council (GMIC).
The workshop began with overviews of coating manufacturing by representatives of each of the primary segments of the glass industry: flat (R. McCurdy, Pilkington-LOF), container (C. McKown, Atofina Chemicals), fiber (L. Campbell, Owens Corning), and specialty (C. Lampert, Star Science). In addition, four plenary speakers from academia reviewed important scientific and engineering concepts relevant to glass coatings: chemistry of on-line coating deposition (R. Gordon, Harvard Univ.); surface interactions (C. Pantano, Pennsylvania State Univ.); characterization techniques (S. Misture, Alfred Univ.); and theoretical approaches to modeling coatings (M. Teter, Cornell Univ.). The heart of the workshop consisted of two breakout sessions in which the participants divided into groups representing each of the four industry segments. In the first session, performance targets and technological barriers to achieving them were identified, while in the second session, a list of research needs required to meet these goals was compiled. The breakout sessions were linked by plenary gatherings at which summaries of the work of each group were presented. During each breakout session, members of the groups also compiled a list of individuals who were not able to attend the workshop, but who would be interested in reading the report.
In spite of the great diversity of products and functions involving coatings, a substantial number of common threads were revealed during the discussions of the breakout groups, pointing to the possibility for collaborative work within the industry. Examples of key needs that span the industry include:
• databases of information concerning film properties (optical, mechanical, electrical, etc.) and deposition chemistries;
• a pilot-scale facility for developing new coating processes;
• computational methods for rapid screening of potential coating materials;
• rapid prototyping methods for evaluating coating processes;
• fundamental data concerning deposition processes;
• improved understanding of surfaces and interfaces;
• low-cost deposition methods; and
• sophisticated sensors and process control.
In addition to these needs, participants identified 135 specific research needs in the four focus areas, of which approximately half were considered priority items. These research needs were analyzed to determine the time frame in which each research activity is expected to have an impact on the industry, either on a commercial product or on a manufacturing process. Research time frames correspond (roughly) to 0–5 years for near-term; 5–10 years for mid-term; and >10 years for long-term. In addition, some research is expected to be ongoing during all time periods and be able to produce useful results at all stages.
In the closing remarks at the end of the 2-day session, many participants expressed satisfaction with the openness of the discussions that occurred among members of a normally secretive industry. However, there was also concern that the momentum not be lost, but be used to pursue mutually beneficial collaborative research opportunities. It was also suggested that the group consider meeting again, possibly at a technical meeting (there are several devoted to coatings research) to review progress toward the goals identified during the workshop.
This paper provides a brief summary of the results of the workshop. Because of space limitations, however, it is impossible to discuss many of the research needs that were identified. An extensive report summarizing the results of the workshop is available for those wishing to have more details.
1 In addition to presenting a detailed summary of the discussions in the four breakout groups, the report gives condensed versions of the eight plenary lectures.
2. Background
Coatings applied to glass surfaces are an essential part of manufacturing in all segments of the glass industry. Without coatings, not only would many glass products not have the properties that make them so widely used, they would be impossible to make. Examples can be found throughout the industry:
• Because of its abrasive nature, glass fiber cannot be formed into products such as fiberglass insulation and composites for automobiles without protective and lubricating coatings.
• The dramatic increases in energy efficiency achieved by low-E and solar-control glass (a factor of nearly 2 increase in the R value of a dual-pane window over uncoated glass) are due entirely to sophisticated application of multiple coatings.
• The high throughputs of today's container lines (up to 700 bottles/min) would not be possible without lubricious coatings; coatings also increase the burst strength of glass containers by a factor of 3.
• New products on the forefront of the industry, such as ‘smart windows’ and flat-panel displays, rely on coatings to achieve their functionality.
The glass industry vision document, Glass: A Clear Vision for a Bright Future (Jan. 1996),
2 recognizes that the ‘development of innovative uses of glass is a linchpin of the industry's future’. Examples of some of the many glass products that use coatings are given in
Table 1. A partial list of industry-wide product categories essential to broadening the market for glass products, found in the Glass Technology Roadmap
3 (Sept. 1997), lists 10 products, at least seven of which will be likely to require coatings (
Table 2). This report is also a pointer to the importance of coatings in the glass industry, listing several key coating-related barriers that inhibit the greater utilization of glass:
• lack of basic understanding of the properties of glass at the molecular level (and) its interactions with other materials;
• sub-optimal measurement and control of processes; and
• limited processes for economical and effective on-line coating.
Table 1. Current products that use coatings and their functions
Table 2. Industry-wide product categories essential to broaden the market for glass products: categories involving coatings
Coatings are an integral part of glass manufacturing, not simply an ‘off-line’ process applied by end users. Consequently, they place demands on the entire manufacturing process. Glass temperature and speed are closely linked to the deposition efficiency achieved by on-line coating methods in the float glass industry. Off-line deposition methods, such as sputtering, rely on a high degree of cleanliness and reproducibility in the glass surface, which is tightly linked to initial manufacturing conditions. Similarly, line speeds used in the container industry must be compatible with the speed of the deposition chemistry and container temperatures must be carefully controlled to achieve the appropriate coating properties. In the glass-fiber industry, water-based coating solutions also serve to cool the fiber to a temperature at which it can be wound.
Coating processes can involve very large energy expenditures and have significant associated waste and environmental issues. The need for substantial improvements in coating manufacturing technologies is dramatically illustrated by the following examples:
• In the deposition of coatings on float glass, a best-case yield of approximately 70% is achieved using on-line methods (which are the most economical) such as chemical vapor deposition. In the absence of coatings, the yield is typically 75–80% (i.e. 25–30% of the glass is rejected, ground and remelted). In some cases, however, application of coatings can reduce the total yield to less than 50%. Such high rejection rates represent an enormous cost in energy. On average, roughly 4.0×1010 kJ/year must be expended to remelt this glass.
• The efficiency of reactant utilization in on-line float-glass coating techniques can be as low as 10%, necessitating the installation of multi-million dollar chemical scrubbing units or incinerators and requiring a landfill of more than 2 million pounds/year of waste.
• In the fiberglass insulation industry, which produces 1.9 million tons of material annually (1995), an average of 870 kJ/kg of insulation is expended in drying and curing coatings applied to the fibers using aqueous processing methods. Thus, approximately 1.5×1012 kJ/year could be saved if non-aqueous coating technologies could be developed.
• In the textile fiberglass industry, where almost none of the material is recycled, between 5 and 20% of the glass that is melted becomes ‘basement’ scrap (coated fibers resulting from quality-control rejection or trimming), amounting to almost 100 000 tons of material annually that must be landfilled due in part to non-recyclable organic coatings.
• In the container industry, hourly replacement of mold-release coatings used to ensure defect-free release of the newly formed container from the mold, causes 1.5% of all glass containers to be recycled and remelted (54 million containers in the US alone).
Clearly, there is considerable room for improvement with regard to energy utilization, process efficiency, and waste reduction in these manufacturing processes, and a great deal of research is required to surmount the many technical barriers that exist. In the following sections, we summarize the research needs that were identified in the breakout sessions, as well as the performance targets and technology barriers for each industry segment.
3. Coatings on flat glass
3.1. Performance targets
The flat glass breakout group organized its performance targets into four general categories: economics/market share; material performance; new products; and customer needs. Many targets are viewed as ongoing activities because of their technical complexity and the lack of understanding of the underlying problems. A major goal in this sector is to increase the market share of coated glass by over 50% within 10 years. A second goal, one that was also identified by the Specialty Coatings group, is to greatly reduce the manufacturing cost of electrochromic glass. In the material performance area, it is necessary to achieve product quality and consistency by reducing variations in the optical properties of low-E and solar-control glass that can occur over time on a given coating production line, thus achieving consistency in product quality. In addition, storage time and durability must be increased to allow facile storage for 3 months for both coated glass and assembled dual-pane windows. New coatings and materials with unique features are needed as well, such as coatings with the durability of CVD (pyrolytic) coatings but with the energy efficiency of sputtered silver, bendable coatings that can be used as automotive windscreens, and self-cleaning glass. Finally, the industry must increase its understanding of end-user needs and simplify coated-glass performance information for consumers so they can more easily make educated choices among available products.
3.2. Technology targets
The flat glass breakout group identified many technical barriers inhibiting the industry from reaching the performance targets just described. These range from very fundamental issues concerning the science of coating glass to institutional and educational issues involving companies and their customers. The large number identified may seem surprising given the relatively mature products produced. However, the number of barriers also indicates that the industry is facing major challenges in developing the next generation of coatings, which must perform better in all respects than existing ones while also being considerably cheaper in many instances. The diversity of barriers also reflects the diversity of the industry, which serves customers including window manufacturers, automobile companies, and the computer industry. In all respects, however, the breakout discussions reflected the increasing sophistication of the flat-glass industry as well as its direct customers and end users. Key barriers include:
• Lack of durability in active and passive coatings.
• Lack of precursor material (in particular, CVD precursors) with appropriate properties.
• Lack of computational tools (and understanding) needed to predict film properties.
• Lack of reliable, user-friendly predictive models for use in process control.
• Lack of diverse material knowledge (i.e. more information concerning properties of materials (optical, electronic, mechanical and magnetic) is needed to design new coatings).
• Lack of online process control.
• Low yields for coatings processes (i.e. poor conversion of reactants to deposited materials).
• Poor end-user education, which inhibits intelligent choices.
3.3. Research needs
Research needs in the flat-glass segment of the industry are numerous and diverse. Topics requiring work range from fundamental issues to institutional problems. The needs identified were divided into seven separate areas, with the ‘Fundamental Understanding’ area subdivided into experimental and theoretical needs. Most of the highest-priority needs fell into the area of Fundamental Understanding, which includes seven of the highest priority needs. Coating materials, process control, and process development each include one high-priority research need.
The primary concern in the fundamental area is the lack of understanding of the properties of very thin layers (<10-nm name="sec7">4. Coatings on container glass
4.1. Performance targets
Containers include bottles, jars, vases, envelopes, gas tanks, perfume bottles, etc. The glass-container industry is mature and highly competitive. Companies compete not only among themselves, but against other materials, such as plastics and cans made from steel and aluminum. As such, cost is a key, perhaps overriding, factor and in the evaluation of any new technology. The consumer is probably unwilling to pay more for an improved container; if anything, they want more performance at lower cost.
The performance targets identified for this segment probably cannot be fully achieved through the development of coatings alone. For example, it may be necessary to increase the strength of uncoated glass to permit the desired reduction in weight and increase in break resistance. Nevertheless, coatings can play a significant role in improving the properties of container glass. Unfortunately, most of these technologies are not currently cost effective.
Performance targets were divided into near-term (0–5 years) and long-term (5–10 years) time ranges. These ranges represent the time required to reach the goal, given adequate resources. Many of the near-term targets can be achieved with existing technologies. Examples of these targets include:
• Reduce container weight by 25% over average current weight (glass weight/volume). Technology and theory exist to do this today.
• Increase container resistance to breakage by using new self-healing coatings that are cost effective and maintain their attributes, coatings that apply a compressive strength to the bottle, and energy-absorbing coatings that increase resistance to mechanical impact. It is difficult to make this target quantitative due to the lack of a quantitative measure of container strength/resistance to breakage.
• Develop coatings that retain fragments in the event of breakage.
• Monitor the coating process on line to obtain information concerning deposition rate and coverage.
• Eliminate/reduce UV transmission to minimize light damage to product. This is especially important for flint glass and glass used for beer containers. Such coatings must be transparent.
• Manipulate color using coatings.
Long-term performance targets include: (1) use one coating to achieve all desired properties; (2) use permanent mold-release coatings; and (3) develop and market a break-resistant container.
4.2. Technology barriers
There appear to be no technical barriers to achieving some of these goals (e.g. improved break resistance, fragment retention, higher strength, energy absorption), even within 5 years. Much of the technology already exists. However, its cost is prohibitive. Cost and market size are the major barriers to improving container performance (and hence, utilization of advanced coatings). Overcoming these ‘market-pull’ issues as well as the problem of imparting new attributes to a container without increasing its cost were given the highest priorities.
The fact that this breakout group did not identify any kind of intermediate goal for strength, for example, is an indication of a mature industry. Materials available today appear to be sufficient, unless a major breakthrough can be achieved, such as an unbreakable container. Achieving a breakthrough of this magnitude will require out-of-the-box thinking; it cannot be done with existing technology.
Technology barriers to progress in the container-glass industry are divided into three categories: knowledge base (concerned with fundamental science/engineering problems), technical issues (concerned with specific coatings and manufacturing technologies), and market issues (related to institutional characteristics and limitations imposed by the market). As in all other segments of the industry, the lack of basic knowledge concerning coating processes and the materials themselves is a key barrier. Twenty-six barriers were identified; of these, the top priority items are:
• Container firms lack the facilities to develop new coating ideas/concepts (Knowledge Base).
• No single coating exists that has all of the desired attributes (currently, two coatings are typically used) (Technical Issues).
• It is difficult to add new properties to a container or improve the existing ones without increasing its cost (Market Issues).
4.3. Research needs
Research needs for coatings in the container sector are divided into five areas: market; expanding the knowledge base; benchmarking existing technologies; requirements for new technology; and technology development. Within these, several needs stand out in terms of the high priority assigned to them. Like other segments examined in the workshop, obtaining more and better data to expand the knowledge base received great emphasis; four of the nine top-rated needs fall into this category. All four are viewed as being capable of having an impact on the industry in the near-term (0–5 years). Three of the four deal with surface processes (topographical effects, real-time surface monitoring, and research to understand the molding process). The remaining item, development of an interactive database for coatings information, could impact the industry within significantly less than 5 years.
Two of the top priorities fall into the Technology Development category: (1) the need for a pilot-scale facility for testing coating technologies; and (2) the need to explore non-traditional coatings and/or processes that can place the container surface under compression. Ultimately, development of an unbreakable bottle would be a revolutionary advance for the industry, so an assessment of the theoretical requirements to achieve this was also given very high priority. In the short-term, however, evaluation of existing and potentially inexpensive coatings (such as hybrid coatings) could provide some intermediate improvements in container properties without increasing costs.
Clearly, market drivers have a strong impact on the manufacturing direction in the container industry. Thus, emphasis was placed on conducting a marketing study to understand the needs of both consumers and producers before attempting to design next-generation containers (in which coatings will likely be an important part).
5. Coatings on glass fiber
Since the manufacturing of glass fibers and their applications are unfamiliar to many readers, we provide some background on this subject. Glass fibers are used to make a wide range of products, including composites, shingles, automotive parts (fiberglass), fiberglass insulation, and optical fiber.
The glass used to make textile fibers and insulation is typically E glass, which is a borosilicate glass containing high concentrations of alumina and calcium oxide. Coatings are an essential part of the manufacturing of these products; without them, it would be impossible to manufacture products such as fiberglass insulation. Coatings used today are multifunctional, but their primary purpose is to protect the fiber surface and provide lubrication. They are also used to impart strength and to tailor the mechanical properties of composite materials.
Coatings for textile and insulation fiber are deposited by aqueous solution chemistry. Precursors consist of highly dilute organic compounds in water, which limits the kinds of coatings that can be applied to the glass. Fiber-coating technology has not progressed significantly over the last several decades with respect to solving problems related to fiber wetting, adhesion, and aging. It is largely a mature technology in terms of performance and need. New manufacturing methods and materials are required before improvements in product performance can be significantly improved.
One of the major problems with glass fibers is that they do not maintain their theoretical strength (approx. 7×106 kPa) after manufacturing. Typically, fiber strengths are a factor of 10 or more weaker than the theoretical value, even with strength-enhancing coatings. Coatings are designed to maintain fiber strength as much as possible; in fact, without coatings, cracking is instantaneous. This is evidently due to preexisting surface flaws, which lead to stress–corrosion cracking. Solving this problem is becoming increasingly important, since many fiberglass composites, particularly those used in the automotive industry, are now being put under continuous loads, which adversely affects their tensile fatigue and creep.
The glass fiber industry faces many technical challenges. There is a strong desire to increase the performance of standard resins (e.g. polyimides). However, the complexity of the problem and lack of underlying knowledge, particularly with regard to the fiber surface and how it interacts with the coating, make it difficult to know where to begin. In fact, the answer to a very basic question — what percentage of the fiber is coated? — is not known with certainty. Although techniques such X-ray photoelectron spectroscopy can be used to determine this, they are time-consuming and cannot be implemented on line where they are needed. Research is needed to explore the latest in analytical technologies, such as field-emission Auger, atomic force microscopy and X-ray scattering, to characterize the fiber surface more accurately. Knowledge of surface coverage is particularly important, since it affects fiber properties and aging behavior. In addition, increasing production rates (i.e. higher fiber draw rates) affect coating coverage and fiber surface properties.
Many environmental issues are associated with the manufacturing of fiber coatings and the resulting products. Because of recent regulations, it is no longer possible to use many of the raw materials (typically solvents) that were formerly commonly used. Pressure to reduce the use of hazardous materials goes beyond organic compounds and now extends to usage of compounds such as ammonium hydroxide. This makes it very difficult for coating designers to develop new technologies that can improve the performance of fiber-based products. Unfortunately, the least expensive resins, formaldehyde and pheno-formaldehyde resins, are also the least environment-friendly. Regulation of these resins is becoming increasingly stringent.
In addition to these manufacturing issues, there is a disposal problem with respect to glass-fiber waste. This material, which includes defective scrapped material, insulation trim, and edge cuts, is usually coated with organic materials that must be removed before disposal. Currently, incineration is the only viable technology. As a result, more material than is desirable is going to landfills. There is reluctance on the part of industry to build market for scrap, since this could compete with newly manufactured products. However, the industry does want to minimize waste and convert these materials to useful products.
Finally, the high concentrations of binder (i.e. organic coatings) on some products have implications for air quality inside the home. Low-density products such as fiberglass insulation contain only approximately 3% binder, but some products contain as much as 20% binder. It is known that binder aging leads to undesirable outgasing of formaldehyde; long-term exposure to this compound may have health implications.
5.1. Performance targets
Technology targets for coatings on glass fibers include several objectives common with other segments of the glass industry, including the need for a database containing information on interactions between coatings and the fiber substrate, the desire to have greater coordination among companies to develop important fundamental science, and the need to employ rapid screening techniques to improve the economics of developing new coatings. Environmental issues are more of a concern in this industry than in other segments. Consequently, several targets deal with recycling and recovery of waste products associated with fiber coatings. Near-term (0–5 years) targets include: (1) improved coating coverage, i.e. wetting behavior of fiber; (2) incorporation of state-of-the-art modeling capabilities to design fiber coatings; (3) and improved understanding of surface-coating interface. A single mid-term goal (5–10 years) was identified: to develop rapid screening techniques to evaluate new coating formulations. Long-term goals (>10 years) include: (1) use process control to measure and control coverage; (2) develop alternative coating systems (perhaps based on non-aqueous chemistries) while maintaining low cost; and (3) produce fiber coatings that do not lose their strength over time.
5.2. Technical barriers
Technical barriers in the glass-fiber industry were subdivided into four categories: institutional issues; process technology; fundamental knowledge; and analytical tools. In common with the other segments, the need to know more about the underlying physical and chemical processes that control coating formation and performance is a high priority. It is clear that the industry suffers from a major lack of fundamental knowledge about its coating processes.
Of the eight highest priority barriers, six of them occur in the Fundamental Knowledge category. In particular, lack of understanding of the glass/coating interface and how surface properties of the glass affect coating properties, such as adhesion, are major deficiencies. Fiber coating processes are very complex, usually involving multiple components to achieve a multifunctional coating. Interactions between these components lead to variable properties and great difficulty in process optimization. The barriers rated as having the highest need for attention are listed below:
• Lack of understanding of the glass/coating interface and how it affects coating and fiber properties as well as the functionality of the fiber.
• Little or no understanding of coating/fiber interactions at the molecular level.
• Not clear what properties a glass surface should have for optimal coating.
• Poor understanding of the origin of defects. Fibers clearly lack the theoretical strength they should have, but how defects occur and lead to strength reduction, as well as the effect of coatings on them, are unclear.
• Lack of enabling technologies for coatings. The glass-fiber industry has been using basically the same technology for decades. ‘Use what you know’ is the underlying tendency. Limitations due to reluctance to invest in capital equipment further limit the use of new and potentially superior (more efficient, higher-quality coatings, etc.) technologies.
• No technique is available that can provide quantitative spatially resolved information concerning coating coverage.
5.3. Research needs
Research needs in the glass fiber segment are divided into five categories: tool development; process technology; tools application; environment; and new markets. The overriding concern is to obtain a better understanding of the fiber surface and how it interacts with the various coatings applied to it. To this end, the highest priority needs are found in the tools development and tools application categories. In particular, there is a strong need to both develop new technologies that can be used to characterize fiber surfaces and interfaces as well as to apply existing analytical methods to this task. Closely related to this need is the requirement for online sensors capable of determining coating thickness, coverage, and properties such as fiber strength at the high drawing speeds used today. There is also a recognition that theory can make a significant contribution to this effort, but that new tools may need to be developed to address the issues unique to glass fibers.
The complexity of existing coating processes and the consequent difficulty in optimizing their performance points to the high-priority need for new high-speed coating technologies. Such methods may involve technologies that are well developed in other areas, such as CVD. In fact, there is also the recognition that fiber-coating technology might benefit from knowledge gained in the development of non-fiber-based coating technologies, in particular those used to coat particles.
Other high-priority research needs include: the need to develop rapid screening and prototyping methods; the need to obtain a better understanding of wetting phenomena; and the desire for a pilot-scale facility for testing new coating concepts and processing technologies.
6. Specialty coatings on glass
The Specialty Coatings working group agreed early in its discussions that, although this was the ‘none-of-the-above group’, i.e. it covered coatings applications outside of flat, container, and fiber glass, that the correct topic for the group is specialty coatings on glass, not coatings on specialty glass. The former includes coatings on large-area substrates, such as those produced by a float line, while the latter generally represents niche markets, such as optical components (by one person's definition, however, ‘specialty glass’ means everything except soda-lime and float glass, which would include some rather large markets, such as television tubes and optical fiber). It was also agreed that low-E coatings would not be an area of discussion, since the group expected that this would be covered by the flat-glass working group.
Specialty coatings include many value-added products that are essential for the survival of the glass industry; however, this is clearly a broad and diffuse area. As a result, the group chose to focus its discussions by defining specific functionalities for coatings. These are:
• electrochromics (glass that can be darkened or lightened electronically);
• conductive coatings (transparent materials such as doped tin oxide that can be used for touch screens, display panels (LCD), windshield defrosters, and highly reflective low-E architectural materials);
• optical applications (includes reflective and antireflective materials, coatings that provide selective transmission (i.e. filters) and non-linear optical applications);
• semiconducting coatings (primarily for display applications);
• catalytic coatings (such as TiO2 coatings used to make self-cleaning glass for the food and health industries);
• coatings to modify surface energies (typically organic films that can change the hydrophobicity, lubricity, etc., of glass); and
• nanodevices (nanoscale features with potential applications such as microscopic power sources, keyless entry, and on-window electronic devices).
The last three were included for purposes of long-term, ‘out-of-the-box’ thinking that goes beyond the more traditional optical applications.
A general conclusion reached is that for any of these materials to become widely used, their cost needs to come down substantially. This probably means some form of online processing, e.g. CVD on a float line. In fact, lack of economical manufacturing methods limits the markets for virtually all specialty coatings.
A second important point evident throughout the discussions is that, although many of the materials discussed are exotic and have only niche markets (if any) today, the challenges faced in making/manufacturing them now will also be faced in the near future by the flat glass (and possibly other segments) of the industry as they try to mass-produce these materials. As US industry moves from low-value commodities to high-value-added, high-tech materials, the future of the glass industry may be linked to successful development of these materials.
Near-term technical goals (0–5 years) outlined by the Specialty Coatings working group include reducing the loss of electrochromics to $100/m2 and achievement of measurement and control of film properties to within 0.1%. In the mid-term (5–10 years), an ability to deposit electrochromics using on-line chemical vapor deposition seems realistic, as well as development of economical 1-Ω/square transparent conductive coatings. In the long-term (>10 years), reduction in the cost of electrochromics to $20/m2 is desirable along with expanded materials sets for optical coatings that can provide a greater spread of refraction index.
6.1. Technology barriers
Barriers in the specialty coatings area were broken down into three broad categories: process; measurement and control; and materials. The six barriers with the highest priority are evenly distributed across these three categories. Process barriers include a range of problems common to the manufacturing of almost all specialty coatings. However, it also includes barriers specific to certain types of materials, such as electrochromics. The top priorities here are to develop the ability to consistently manufacture coatings on large pieces of glass and control the crystalline phase of the materials that are deposited. Measurement and control issues include feedback control, which is of high importance because of the need for very tight control over process conditions, and to remain within the narrow tolerances specified by coating design models. The two highest priority barriers in this area are: (1) the lack of high-precision intelligent process control, and closely related to this; (2) the inability to measure coating properties reliably and accurately across large substrates. Materials questions generally fall into the field of materials science and concern the difficulty of achieving films with specific properties. Many issues here are related to film defects. The highest priority barriers are the short lifetimes for electrochromic materials and the poor durability and adhesion of coatings.
6.2. Research needs
Research needs in the specialty coatings segment of the industry are divided into five areas, three of which are strongly process related: information; manufacturing processes; and measurement and control standards. Research in the information section addresses the need for more and better data concerning the properties of materials that either are now or may become of interest for possible coatings. The top research priority here is the need for a computational tool to rapidly screen possible new coating materials, a need shared by other industries. Research described in the manufacturing process section deals with problems associated with specific manufacturing processes. Two high-priorities for research are found here: the need to improve understanding of the titanium dioxide deposition process; and the desire for a flexible, atmospheric-pressure deposition process. Measurement and control standards concern not only the development of new methods for measuring film properties, but also the definition of standards for both coatings and virgin glass that can be used to evaluate materials.
In addition to these areas, research needs specific to certain material types were also identified. The electrochromics area includes three of the highest priority research needs: development of improved kinetic and thermodynamic models for simulating the formation and operation of these materials; the need for an online (probably CVD) method for manufacturing these materials; and the need for studies of the interface between ion conductors and the electrochromic layer. Under conducting materials, the need for improved solar-control films that can be bent and tempered (for automotive windshields primarily) and lower cost conducting transparent films was highlighted.
7. Conclusions
The Coatings on Glass workshop was an unprecedented gathering of glass and coating manufacturers, equipment suppliers, end users, and researchers in both academia and government, in which key issues affecting the entire industry were discussed. In the open and frank discussions that occurred, an extensive set of key research areas was identified. Targeted efforts in these areas should eliminate many of the key technology barriers to achieving long-term performance goals. The report summarizing the workshop thus provides guidance to potential government and industry sponsors of research. It is hoped that its publication will assist the many stakeholders in this complex industry to engage in joint research projects addressing the needs highlighted by the workshop.
