Coatings Technology Handbook Episode 3 Part 8 doc

117 -2 Coatings Technology Handbook, Third Edition the paint that forms a film. A synonym for vehicle is binder. Vehicles come in many types. The types that will be discussed in this chapter include oil, tempera (based on egg yolks), watercolor (based on gums, sugar, and starch), alkyd (normally a polyester), and latex (plural is latices, chemically these are emulsions). Artist’s colors are generally sold in two grades: professional and student. The professional grade is generally used by those who make a living by producing and selling their artwork. The student grade is intended for use by students who aspire to a career in art. There are many differences between the two grades. The professional grade generally contains high percentages of pure color (pigment). Student grade is normally characterized by lower percentages of color. Very often, student grade does not contain the “pure color” that is listed on the label. In this case, the word “HUE” appears on the label. This means that a single pigment or combination of pigments is being employed to approximate the “pure color.” Very often, the “pure color” is very expensive, while the hue is cheaper. In addition, the hue rarely has the brilliance of the “pure color.” A further difference is that the student grade often contains extender pigments to help reduce cost while still maintaining the consistency (artist term for this is “feel”) of the professional grade. Artist’s colors are produced in a number of vehicle systems. As vehicle systems evolved, so did pigments. This chapter will outline historical development of vehicles and enumerate their compositions. Con- jointly, this time-line formulary will contain the pigments associated with the system at discovery time. It will also list those pigments in use today, as well as what they replaced. Discovery dates of pigments, as well as the approximate date of first usage in artist’s colors, will also be listed. The very first artist’s color created by prehistoric man was a black made from charcoal. This was used for drawing. There was no binder involved — just pure charcoal put onto surfaces such as rocks, cave walls, and hides. Soon after charcoal came into use, early man began using mud, which was available in various colors. These muds were various shades of natural iron oxide pigments (yellow, red, and brown) and were applied directly to cave walls. As was the case with charcoal, no binder was involved, just pure color. These muds were derived from riverbanks, lakefronts, and other similar places. They were used to create the now celebrated Cro-Magnon cave paintings. The paintings were of stick figures. They were thin lines of mud smeared across a cave wall in the form of a recognizable animal or human shape. Art stayed at this stage until the ancient Egyptians invented watercolor. Watercolor came into prominence around 4700 B.C. in ancient Egypt. For the most part, watercolor is based on a transparent pigment system. The background of a brilliant white comes from the paper, which is used as the substrate. It is utilized to make white and light tints. Pigmentation consists of both transparent and nontransparent colors. The nontransparent colors are applied in an extremely diluted state. These colors are diluted to the point where they are almost as brilliant as the transparent colors. There is an alternate pigment system that employs white pigment as an opacifier. The choice of pigment system, whether in ancient times or today, has always been left to the artist. Neither system is wrong nor better. The choice depends on the desired artistic effect. The palette (pigment choice) available in ancient Egypt for use in watercolor included a host of list is set up by color type. This is then broken down to individual colors designated by color title and composition. The composition of the vehicle used to make watercolor is basically unchanged from ancient times. The major ingredients used by the Egyptians were gum arabic (a product of Somalia), water, sugar syrup, glycerin, dried extract of ox bile, and dextrin, which is derived from white potatoes. Some more modern formulae replace the sugar syrup with pure glucose. The ox bile can be replaced with modern wetting agents of the type generally associated with latex house paint production. The ancient Egyptians had no need to use a preservative, because arid conditions in Egypt produced an atmosphere in which bacteria could not survive. There is a system of similar composition called Gouache (pronounced GWASH). This system uses the same vehicle but employs opaque colors, usually with extender pigment added to increase dry opacity. Both systems employ the same pigmentation types. DK4036_book.fm Page 2 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC pigments known from the dawn of recorded history. Table 117.1 lists colors used by the Egyptians. The 117 -4 Coatings Technology Handbook, Third Edition Now let us turn our attention to oil color. Oil color, which was invented in the year 1400 A.D., originally had a palette that was very similar to that of the ancient watercolor palette. The most noticeable exception is the addition of a white color called Flake White (basic lead carbonate). Technology to make basic lead carbonate dates back to the days of ancient Rome. Another color, which, if it did not exist in the year 1400, was available shortly thereafter, is Naples Yellow. In its original form, Naples Yellow was lead antimoniate. Today, it is made as a hue from a combination of Cadmium Yellow, zinc oxide and Ochre (Natural Yellow iron oxide). As time went on, the modern palette evolved to the point where it matched the modern watercolor palette with the exceptions noted above. The composition of oil color is fairly simple. Generally, only three items are used in an oil color formula. They are the colored pigment, the oil (usually alkali refined linseed oil) and a stabilizer (normally aluminum stearate). Over the years, different grades of oil have been used to make oil color. In the beginning of the 15th century, only raw linseed oil was available. Soon afterward, purification by heating was discovered. At the same time, people learned how to make “sun-bleached linseed oil.” This is made by mixing linseed oil with water and exposing the mix to sunlight. The water acts to remove impurities in the oil, while the sun bleaches and lightens the oil. After a few weeks or months of exposure, the oil is separated from the water and then used. In later years, oil made by this technique was called “superior linseed oil.” By the 17th century, both stand oil and refined linseed oil were in common use. Stand oil is partially polymerized linseed oil. The oil is polymerized by heating it to 550 ± 25˚F and maintaining that temperature for a few hours. This causes the viscosity to increase significantly. A number of other effects can also be seen. These include the excellent leveling and gloss. Upon aging in dry films, stand oil shows much less yellowing than regular linseed oil. Less polymerization occurs during drying, because it is partially polymerized during the heating process. This, in turn, leads to less yellowing. Originally, refined linseed oil was refined by an acid process. The mechanism called for acid (usually sulfuric acid) and water to be added to the oil. This removes impurities and lightens color. The best grades have all the water and acid removed before packaging. While acid refined linseed oil is still available, it has, for the most part, been replaced by alkali refined linseed oil. Here, a strong alkali replaces the acid. The use of alkali to refine linseed oil often removes more impurities and provides better color than would be seen with the use of acid as the refining agent. Occasionally, other types of oil are used in the formulation of artist’s colors. The most notable of these is poppyseed oil. It is used mainly in whites, because it is naturally colorless. This makes a white paint made from it appear “whiter” than paint made from amber-colored linseed oil. Less frequently, walnut oil is used as a linseed oil replacement. Walnut oil has the same clarity as poppyseed oil, but, upon aging, it can turn rancid and give off a strong odor. While the paint is perfectly useable, the perception of quality is totally ruined. Well-formulated oil-based paint dries to a glossy, durable finish. The pigment volume concentration (PVC) is low, especially when compared to other types of artist’s colors. A good example of this is tempera paints. Tempera and oil color were invented at the same time, but, due to tempera’s radically different composition, it dries to a flat finish. The finish is due to the high PVC of the paint. The high PVC is a result of the tempera vehicle. Tempera paint was the first emulsion paint ever created. This emulsion is a naturally occurring phenomenon. The basis of tempera is egg yolk. The yolk contains a water solution of albumin, a nondrying oil called egg oil, and lecithin. Each ingredient has its own function. The albumin is a binder. When heated, albumin will coagulate to form a tough, insoluble permanent film. A cooked egg is an example of this coagulation. Likewise, when albumin is diluted with water and spread out in a thin film to be dried by sunlight, it coagulates to form a film. The egg oil acts as a plasticizer, and the lecithin is an excellent emulsifier. All that is needed to create a tempera paint from the yolk is pigment and water. Over the years, egg yolks were replaced with other substances to form alternate tempera paints. These emulsions are based on any of the following: gum arabic, wax, casein, and oil. All have some degree of acceptance. After the acceptance of oil and tempera colors in the 15th century, creativity to develop new vehicles fell into a dark age. Yes, pigments did continue to develop. However, vehicles did not. The next few DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Artist’s Paints: Their Composition and History 117 -5 changes in vehicle technology came in the 1920s. Two developments occurred simultaneously. These were the invention of the alkyd resin and the development of latex emulsions. The original alkyds were made by the reaction of glycerol (a polyhydric alcohol) with phthalic anhydride (a polybasic acid) in an oil medium. In time, glycerol was replaced by pentaerythritol (penta imparts greater flexibility and color stability to the resin). Alkyds were originally used in industrial and house paint systems. However, around 1960, some manufacturers of artist’s paints began to partially replace linseed oil in selected colors. Full product lines based upon alkyd resin technology did not appear until the late 1970s/early 1980s. Today, almost every artist’s paint producer has a full line of alkyd colors. In the late 1920s, latex emulsion technology was also emerging. The original latices were made from styrene-butadiene. These were very poor in quality. Sometimes the emulsion would break. Sometimes reactions after processing occurred. These reactions included gelation and seeding of the emulsion. In the 1930s, resin producers began using methylmethacrylate as a basis for emulsions. By the end of World War II, latex emulsions were being used in house paint formulae. By 1952, boutique art shops began carrying a line of latex (now called acrylic) colors. The name change was the result of the switch from styrene-butadiene to methylmethacrylate. By 1960, all major manufacturers had complete lines of acrylic colors. The color palette for acrylic colors is the same as the palette for watercolor. There is no Flake White (basic lead carbonate) or zinc oxide due to the reactivity of these pigments with the latex. The last advance in artist’s paint technology came in 1993, with the advent of water-thinnable linseed oil paint. As stated earlier, water-thinnable linseed oil paint was created by dismissing the old myth that water and oil did not mix. Chemists were able to do this alteration of linseed oil. Linseed oil is a composite of between 17 to 21 different fatty acids. The number varies with the source of the oil, as is the case with most naturally occurring materials. All of these fatty acids are at varying percentage levels in the oil. Some of these acids are hydrophobic, while some are hydrophilic. By adding more of the hydrophilic acids, an oil that will accept water by forming a temporary emulsion is made. The beauty of water- thinnable oil colors is that they eliminate the need for solvents by serving as both thinner and cleanup agent. This greatly reduces studio toxicity. If, however, one wishes to use the solvents that have been used since the 15th century, the system will accept them. The palette that is in use for water-thinnable oil colors is the same as the palette for conventional oil color. composition of the pigment, the date of discovery, the date of first usage in artist’s colors, and the pigment replaced. This table refers only to pigment. Vehicle type has been deleted. All colors listed are available in all vehicle types described herein, with very few exceptions. In the discovery and first usage columns, the notation “Ant” means that the discovery or first usage goes back into antiquity. Hopefully, this gives the reader an overview of the history and composition of artist’s paints. DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Ta ble 117.2 summarizes the modern palette. Listed are the artist’s name for a color, the chemical Artist’s Paints: Their Composition and History 117 -7 Naples Yellow Hue Mixture of zinc oxide, Cadmium Yellow, and Ye l l o w Oxide Not Applic. 1920s Lead antimoniate (known since the 1500s) Phthalocyanine Blue A 16-member ring comprised of four isoindole groups connected by four nitrogen atoms; in the center of the ring is a copper atom 1935 1936 Prussian Blue (ferric- ferrocyanide) discovered in 1704 and introduced in 1724 Phthalocyanine Green Same as Phthalocyanine Blue but four chlorine atoms are added to each isoindole group 1938 1938 None Quinacridone Colors 1. Red (Yellow shade) Gamma trans-linear Quinacridone 1955 1962 None 2. Red (Blue shade) Gamma trans-linear Quinacridone 1955 1962 None 3. Violet Beta trans-linear quinacridone 1955 1962 None 4. Magenta Disulfonated trans-linear Quinacridone 1955 1962 None Raw Sienna A natural earth composed mainly of hydrous silicates and oxides of iron and aluminum Ant. Ant. None Raw Umber A natural earth composed mainly of hydrous silicates and oxides of iron and manganese Ant. Ant. None Strontium Yellow Strontium chromate 1836 1950 None Titanium White Mainly titanium dioxide ~60% with some zinc oxide and/or barium sulfate ~40% combined 1870 1920 Flake White (basic lead carbonate) known since antiquity Ultramarine Colors 1. Blue 2. Green 3. Red 4. Violet All are complex silicates of sodium and aluminum with sulfer. The degree of sulfonization determines the color 1828 1828 Ground gemstone Lapis lazuli Ve r million Mercuric sulfide Ant. 8th century Cinnibar, an ore with mercuric sulfide in it Viridian Hydrous chromic oxide 1838 1862 None Ye llow Ochre A mixture of synthetic hydrous iron oxide with alumina and silica 19th century 19th century Natural version of the same mixture. It dates into antiquity Zinc White Zinc oxide About 1820 1834 in watercolor; 1900 in oil color Chalk (calcium carbonate) Flake White (basic lead carbonate) Source: Lewis, Peter A., Federation Series on Coatings Technology-Organic Pigments, 3rd ed., revised September 2000. Mayer, Ralph, The Artist’s Handbook of Materials and Techniques, 3rd ed., revised 1970. TA BLE 117.2 The Modern Palette (Continued) Artist’s Name Chemical Composition Discovery Date First Used Date Pigment Replaced DK4036_book.fm Page 7 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 118 -1 118 Fade Resistance of Lithographic Inks — A New Path Forward: Real World Exposures in Florida and Arizona Compared to Accelerated Xenon Arc Exposures 118.1 Florida and Arizona Outdoor under Glass Exposures 118- 2 118.2 Accelerated Xenon Arc Exposures 118- 5 118.3 How long will an ink remain fade resistant under the variety of lighting conditions that it may encounter during its service life? What is the cost of product failure? What is the price/performance trade-off between affordability and performance? Is there a quick method to determine which ink is best for a specific application? This paper answers these questions and provides a useful roadmap for assessing ink durability. First, results are presented from real world sunlight through window glass exposures in Florida and Arizona. These internationally recognized test locations provide a “worst case” scenario by exposing inks to high ultraviolet (UV), high temperatures, and high relative humidity (RH). Second, test results are presented from laboratory xenon arc exposures performed on an identical set of lithographic ink specimens. The purpose was twofold: (1) How well do laboratory xenon exposures correlate with Florida and Arizona exposures in terms of actual degradation and relative rank order? (2) How much faster are the accelerated laboratory exposures compared to the natural exposures? This definitive study correlates real world and accelerated laboratory test results for lithographic inks. Eric T. Everett Q-Panel Lab Products John Lind Graphic Arts Technical Foundation (GATF) John Stack National Institute for Occupational Safety & Health/National Personal Protective Technology Laboratory DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Test Program • Effect of Seasonal Variation • Arizona Exposure Conclusions 118-9 Compared to Florida Outdoor under Glass Exposure Why Xenon Arc Testing? • The Test Program • Xenon Arc Further Reading 118-10 Test Results • Relative Humidity • Xenon Arc Exposure Fade Resistance of Lithographic Inks 118 -3 FIGURE 118.2 GATF technical staff selected eight representative lithographic ink colors printed on a standard substrate for fade resistance testing. FIGURE 118.3 Ink specimens were placed in ASTM G24 glass-covered exposure racks in Florida and Arizona benchmark locations. TA BLE 118.1 Total Sunlight Outdoor Exposure Summary MJ/m 2 at 300 to 3000 nm Exposure Days MJ/m 2 Florida fall 90 1926.17 Florida winter 90 1541.13 Florida spring 90 1252.54 Florida summer 90 1081.73 Arizona fall 90 1611.20 DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 118 -4 Coatings Technology Handbook, Third Edition However, by 35 d, the inks exhibited a wide range of fade resistance, from excellent to poor. Therefore, 35 d was chosen to evaluate the performance of the inks in the various outdoor exposures. Figure 118.5 shows the range of durability for the three Yellow ink test specimens in the Florida fall exposure. Despite being the same color, the three Yellow inks had significant differences in their fade resistance. Yellow A performed dramatically better than Yellow B or Yellow C. This is because Yellow A is fade resistant and suitable for fine art reproductions or outdoor applications, while Yellow B and C are intended for general commercial printing. FIGURE 118.4 Fade resistance range for eight colors. FIGURE 118.5 Fade resistance range for one color. DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 118 -6 Coatings Technology Handbook, Third Edition FIGURE 118.7 Fade resistance correlation for Florida: winter vs. summer. FIGURE 118.8 Fade resistance correlation: Florida: vs. Arizona. TA BLE 118.2 Rank Order Correlation Matrix Florida Summer Florida Fall Florida Winter Florida Spring Arizona Fall Florida Summer — 0.98 0.93 0.98 0.90 Florida Fall 0.98 — 1.0 0.95 0.98 Florida Winter 0.93 1.0 — 0.97 0.96 Florida Spring 0.98 0.95 0.97 — 0.93 Arizona Fall 0.90 0.98 0.96 0.93 — DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC FIGURE 118.10 GATF and Q-Lab tested inks in Q-Sun Xenon Test Chambers. TA BLE 118.3 Xenon Arc Exposure Test Conditions Q-Sun Xenon (Xe-1 and Xe-3H) ASTM D3424, Method 3 Window Glass Filter Irradiance Level: 0.55 W/m 2 /nm at 340 nm RH: Xe-1 Effective RH = 15% Xe-3 RH = 50% Exposure Cycle: Continuous Light at 63 ± 3 ° C (145 ± 5 ° F) Test Duration: 31 d Total Radiant Exposure = 1473 kJ/m 2 at 340 nm FIGURE 118.11 Q-Sun fade resistance range. DK4036_book.fm Page 8 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC [...]...DK4 036 _book.fm Page 11 Monday, April 25, 2005 12: 18 PM Fade Resistance of Lithographic Inks 1 18- 11 Bugner, Douglas, Joseph LaBarca et al, “Survey of Environmental Conditions Relative to Display of Photographs in Consumer Homes,” IS&T Publications, 20 03 Lucas, Julie, “Keep Your True Colors: Lightfastness and Weathering Testing,” . 1252.54 Florida summer 90 1 081 . 73 Arizona fall 90 1611.20 DK4 036 _book.fm Page 3 Monday, April 25, 2005 12: 18 PM © 2006 by Taylor & Francis Group, LLC 1 18 -4 Coatings Technology Handbook, Third. Francis Group, LLC 1 18 -6 Coatings Technology Handbook, Third Edition FIGURE 1 18. 7 Fade resistance correlation for Florida: winter vs. summer. FIGURE 1 18. 8 Fade resistance correlation:. 0.95 0. 98 Florida Winter 0. 93 1.0 — 0.97 0.96 Florida Spring 0. 98 0.95 0.97 — 0. 93 Arizona Fall 0.90 0. 98 0.96 0. 93 — DK4 036 _book.fm Page 6 Monday, April 25, 2005 12: 18 PM © 2006 by Taylor &