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The application of organic pigments in the coating industry: At present, China’s organic pigment industry is still in a transitional phase toward larger-scale development, and with the rapid growth of the Chinese economy, its development momentum is further improving. This is also thanks to the basic scaling up of intermediate production, the continuous improvement in quality, a wide range of options available, and the gradual introduction of intermediates for high-performance organic pigments into industrial production. In 2006, the production, operation, import, and export of organic pigments in China were in good condition; the annual output of organic pigments was 182,600 tons, representing a 16.6% increase compared to the previous year. Organic pigments, as a subset of dyes, come in a wide variety. They are classified based on the presence of specific chromophoric groups or functional groups in their molecular structure, and are typically divided into azo pigments, phthalocyanine pigments, high-performance organic pigments, and other types of organic pigments. Among them, azo pigments have the highest production volume, accounting for about 50%; phthalocyanine pigments account for about 40%, while other types of organic pigments account for about 10%. The proportion of organic pigments used in the coating industry is on the rise; currently, they account for about 26% of the pigments used for coloring coatings. In recent years, with the rapid development of China’s coating industry and the continuous creation of new types of coatings, the share of high-quality coatings has increased significantly. As a result, there is a growing demand for organic pigments, and higher demands are being placed on their varieties and properties. This presents excellent opportunities for the development of the organic pigment industry. 1 The influence of organic pigments on coating properties 1.1 The influence of the physical properties of organic pigments on coating properties The physical properties of organic pigments include density, specific surface area, particle size, crystal form, dispersibility, and stability. The density of organic pigments ranges from 1.0 to 2.0 g/cm3, while their specific surface area is between 10 and 100 m2/g ； The ideal state of organic pigment particles is primary particles with a particle size of 0.01–0.05 μm. However, due to the extremely high surface energy of such fine particles, strong agglomeration occurs to form aggregates (with sizes of 0.05–0.4 μm), and these aggregates further aggregate to form agglomerates (with sizes of 0.1–20 μm); therefore, ordinary organic pigment particles are a mixture of aggregates and agglomerates. The size of organic pigment particles has a significant impact on the color properties of coatings. On the one hand, it affects the covering power and coloring ability of the paint; within a certain range, an increase in pigment particle size leads to an increase in the paint’s covering power ； As the pigment particles become smaller, their specific surface area increases, thereby enhancing the coloring power of the coating. The particle size of pigments also affects the color of coatings; generally, larger particle sizes and a wider particle size distribution result in a darker color ； Conversely, the colored light is bright. On the other hand, pigment particle size also affects the UV resistance of coatings. As the particles become smaller, the specific surface area increases, leading to an increase in the amount of light energy absorbed. This in turn increases the degree of damage, causing the coating to fade more rapidly. With small pigment particle sizes, the gravitational force acting on them is low, so the coating does not tend to separate and settle ； However, pigments with a smaller particle size have a larger specific surface area; the increased surface energy raises the likelihood of flocculation and roughness in the coating, which is not conducive to grinding and dispersion. Most organic pigments exist in a crystalline state, and the phenomenon of \"isomorphism\" is quite common. The crystal forms of copper phthalocyanines include the Q-type red-blue variant (such as Pigment Blue 15), which has poor stability; it transforms into the stable P-type green-blue variant (such as 15:3) after treatment with certain solvents ； Pigment Violet 19 (quinacridone structure) has three crystal forms: α, β, and γ. The α form has no practical use; the β form is purplish-red, while the γ form is blueish-red. When designing paint formulations, it is important to use additives and solvents appropriately in order to prevent different crystal forms from transforming under certain conditions, which could lead to color shifts in the paint and make it difficult to match the color using standard samples. 2. Applications of organic pigments in the coating industry: To meet the requirements regarding application and functional performance, high-performance coatings must have good dispersibility and storage stability. Their coatings should also exhibit excellent UV resistance, weather resistance, solvent resistance, stain resistance, and scratch resistance, as well as good water resistance, acid resistance, and alkali resistance. If it is a baked-on coating, it must also have excellent heat resistance ； Especially for automotive topcoats, in addition to the aforementioned properties, they must also have vivid colors, high brightness, a good texture, and a full appearance. While general inorganic pigments have excellent durability and coverage, their colors are not as vivid as those of organic pigments, and they lack the texture that organic pigments offer. Therefore, many organic pigments with excellent properties are being increasingly used in the high-performance coatings industry. However, since different coating systems use different film-forming substances, when formulating a recipe, appropriate organic pigments should be selected based on the properties of the resin, the additives, and the solvent system. The following focuses on the applications of organic pigments in architectural coatings, automotive coatings, and coil coatings. 2.1 Application of organic pigments in architectural coatings: Due to the wide range of colors available in latex paints, with shades that can be chosen freely to achieve attractive decorative effects and a long service life, architectural coatings based on acrylic emulsions as film-forming agents are playing an increasingly important role in the decoration of cities. As an important component in latex paint, the selection and use of organic pigments have a direct impact on the color retention of the paint. An understanding of the properties and applications of these pigments can help in producing high-quality latex paint. Organic pigments are not affected by physical and chemical factors during use; they generally do not dissolve in the medium in which they are used and remain in their original crystalline state. The coloring of organic pigments is achieved through selective absorption and scattering of light. 2.1.1 Pigment pastes: The use of organic pigments in architectural coatings is primarily achieved through pigment pastes. Color paste is a highly dispersed pigment preparation. The organic pigment content in the color paste is 30%–50%, while the inorganic pigment content is 60%–75% ； The higher the pigment content, the lesser the adverse effect on the pigment paste system. It is required to have good dispersion of the pigment paste, good compatibility with water-based polymer emulsions, and to be free from binders, ethylene glycol, and heavy metal ions that are harmful to humans ； It is required that color paste batches have good uniformity, with the coloring strength error controlled within ±5% (with a stricter requirement of ±3%) ； The color paste is required to have good stability, with a storage life of at least 2 years. The color pastes are required to be mixable with latex paint in any proportion; the composition and production conditions of various color pastes vary depending on the properties of the pigments they contain. 2.1.2 Applications of pigment pastes Pigment pastes are widely used in various interior and exterior building coatings (latex paints), water-based industrial coatings, water-based wood coatings, etc. The use of color paste in latex paint involves the mixing of two dispersion systems. The pigments in the pigment paste are dispersed in water under the action of surfactant A; the properties and quantity of the surfactant determine the content of the pigments, the degree of dispersion, and their stability ； The film-forming substance (resin) in latex paint is dispersed in water under the action of surfactant B; the properties and quantity of this surfactant determine the average particle size, gloss, and stability of the latex paint. When the compatibility between two dispersion systems is poor, the following problems occur: ① If the types of dispersants used in the color paste are not compatible with each other, the dispersants will react with one another, leading to emulsion breakdown ； ②If insufficient amount of dispersant is used in the pigment paste, it will result in poor stability of the architectural coating ； ③If too much dispersant is used in the pigment paste, it will result in poor water resistance and drying properties of the coating film ； ④If the pigments agglomerate, it will result in a decrease in the coloring power of the coating, changes in hue, reduced coverage, lower gloss, poor flowability, and poor leveling properties. 2.1.3 Precautions for using pigment pastes: Choose high-quality pigment pastes. The color paste should have a stable hue and coloring power, as well as good light resistance, weather resistance, and acid-alkali resistance ； It must be compatible with the coating system and able to be mixed together with it ； Stable storage; no precipitation, no flocculation, neither dries out nor freezes ； Reasonable price-performance ratio. Before use, a compatibility test between the color paste and the coating should be conducted, and thorough mixing is necessary to prevent uneven conditions of the color paste due to temperature changes during transportation or prolonged storage (layering, differences in density between the upper and lower layers), which could affect the accuracy of the amount to be added ； It is best to add the color paste while stirring the paint, and ensure that the paint is well mixed as well. The color paste should be added directly; it cannot be diluted with water before use. If an incomplete bucket of color paste is used, the lid must be closed immediately after use to prevent contamination of the surface of the color paste or drying and crumbling of its surface due to water evaporation, which could affect its use in future. The maximum amount of pigment paste that can be added to latex paint must be kept within a reasonable range; exceeding this range will disrupt the balance of the latex paint system, and in severe cases it will affect the durability of the coating film, especially its water resistance. The maximum addition level for organic pigment pastes should not exceed 8%, while that for inorganic pigment pastes should be within 15%. When producing exterior wall coatings, it is advisable to choose color pastes with good sun resistance, weather resistance, and alkali resistance. Generally speaking, pigment color pastes based on iron oxides have better alkali resistance than those based on organic pigments. 2.2 Application of organic pigments in automotive coatings In 2007, China’s automobile production was expected to exceed 8 million units. From 2007 to 2010, the Chinese automobile industry was projected to maintain a double-digit growth rate each year, with annual production reaching 10 million units by 2010. Based on an estimate of 20 kg of original paint per vehicle, 10 million vehicles would require 200,000 tons of original paint to be purchased directly from manufacturers for use in the painting process. This creates significant opportunities for development in the automotive paint industry, especially regarding high-quality paints for luxury cars. Automotive coatings are mainly divided into three components: primer, intermediate coat, and topcoat. The topcoat, which contains pigments, accounts for about 1/3 of the total amount of coating used. Organic pigments make up 2% to 4% of the ingredients in topcoats. Based on the 300,000 tons of automotive coatings produced in 2006, the amount of organic pigments used in those coatings was between 2,000 and 4,000 tons. In the coating industry, automotive coatings require a high level of technical expertise and present significant challenges in terms of application. It can be said that the quality of automotive coatings in a particular region essentially reflects the overall level of that region’s coating industry, which in turn imposes high quality requirements on the resins and pigments used in these coatings. Automotive coatings must meet requirements such as the weather resistance, heat resistance, acid rain resistance, UV resistance of the coating film on metal surfaces, as well as the resistance to color shift. Pigments used in automotive coatings are high-quality colorants; changes in the color of vehicles are achieved by adjusting the organic pigments in these coatings. Therefore, organic pigments used in automotive coatings must possess light stability, chemical resistance, resistance to migration, and thermal stability ； For automotive topcoats, such as metallic finishes, organic pigments are required to have high transparency, so as to complement the covering power of inorganic pigments. This article explains the application of organic pigments in automotive coatings by categorizing several common colors of automotive coatings. 2.2.1 Red: Formulating red automotive paint is a complex task. The tendency of red organic pigments to fade when wiped is a significant problem; for example, automotive topcoats are prone to fading when baked at low temperatures, while excessive baking temperatures can cause the red organic pigments to yellow. For red, single-tone paints are the main choice, as multi-tone paints tend to result in batch-to-batch color variations. Some of the more important organic pigments used in red car paints are polycyclic pigments, including quinacridones, reds, and reduced pigments derived from anthraquinones and thioindigos ； There are also other pigments such as heterocyclic azo and condensed azo pigments, as well as metal-complexed pigments. Chromium scarlet is the only pigment that can provide a bright red color with sufficient covering power; it is also used in the production of medium red and blue-red coatings. To create chrome scarlet, a purple pigment is used to produce an organic red pigment with blue undertones; quinacridone and C.I. Pigment Violet 19 are purple pigments that are widely used for this purpose, as they possess the desired coloring power and durability. A wide range of colors, from medium red to blue-red, can be obtained by mixing quinacridone purplens and chrome alizarin; all of these compounds possess excellent covering power and good durability. To produce blue-red, bright red, and purple-brown colors, the use of single organic pigments is very important. C.I. Pigments Red 178, 179, 224, and 228 are commonly used for red and purple-brown colors, while anthraquinone red C.I. Pigment Red 177 is also frequently utilized ； Tetrachlorothionine C.I. Pigment Red 88 is another pigment used to create blue-red and purple-brown colors. 2.2.2 Yellow and Orange: In yellow and orange automotive paints, the formulation of various solid colors and metallic shades is quite complex; a wide range of inorganic and organic pigments can be used. The most important inorganic pigments are lead-chromium pigments and iron oxide yellows of the general and transparent types. Among organic pigments, there are heterocyclic azo pigments, such as C.I. Pigment Yellow 151 and 154, and C.I. Pigment Orange 60 ； There are isoindolinoline series yellows, such as C.I. Pigment Yellow 109, 110, and 173 ； As well as reduced pigments, such as yellow anthracene and C.I. Pigment Yellow 24, anthracene and pyrimidine C.I. Pigment Yellow 108, reduced orange (GR) C.I. Pigment Orange 43, pyranthrene and orange C.I. Pigment Orange 51. Some varieties of other structures can also be used, such as azomethine complexes C.I. Pigment Yellow 117 and 129, nickel dioxime complexes C.I. Pigment Yellow 153, and copper phthalocyanine C.I. Pigment Green 36. By using these varieties for coloring, it is possible to extend the color spectrum toward the green-yellow side. All chromium-based pigments used in automotive coatings can improve the acid and alkali resistance of the car surface. When lead-free and chromium-free coatings with dark yellow and dark orange tones are required, organic pigments in these colors are usually used. Adding a certain proportion of titanium dioxide and iron oxide yellow can improve the coverage and flowability of this coating. If good durability is required for this coating, heterocyclic azo pigments such as C.I. Pigment Yellow 151 and 154, as well as C.I. Pigment Orange 3, should be used ； It involves using green-yellow isoindolinones along with pigments such as C.I. Pigment Yellow 173; these can be used to create dark yellow colors that do not lose their brightness or change color upon exposure to sunlight. For monochromatic and metallic medium-yellow, light-yellow, and orange automotive coatings, polycyclic pigments are the most important type of pigments used, with the most significant varieties being reduced organic pigments and isoindolinone pigments. Reduced pigments include red-yellow pigments with high coloring power such as anthraquinone yellow and C.I. Pigment Yellow 24, as well as green-yellow pigments such as anthracene and pyrimidine C.I. Pigment Yellow 108. When formulating single-color and metallic paints in light orange, medium orange, and orange, Reduced Orange (GR) C.I. Pigment Orange 43 and Pyranthrene Orange C.I. Pigment Orange 51 can be used. Among light and medium yellows, it is more appropriate to use metal-complexed pigments, such as C.I. Pigment Yellow 129, 17, and 153. Among all shade intensities, the universal and transparent iron oxide yellows are used as matting agents; these iron oxide-based pigments are cost-effective to use and possess excellent durability. 2.2.3 Green: Most greens in automotive coatings are produced from phthalocyanine green pigments, and the color of each type of phthalocyanine green depends on the degree of halogenation and the type of halogenation. Phthalocyanine green pigments have a bright color; they possess the coloring power and durability required for automotive coatings, making them highly functional transparent pigments. Phthalocyanine green pigment is suitable for monochromatic coatings of various concentrations, but it should not be used in high amounts, as it can cause a \"coppery tint\" when exposed to sunlight. To create a bright dark green shade, phthalo blue and surface-treated lead chromate yellow pigments can be used for color mixing; this shade is slightly more intense than phthalo green, it shows little tendency to develop a coppery hue when exposed to sunlight, and they are also relatively inexpensive. To create a dull green shade, iron oxide yellow can be mixed with phthalocyanine green or phthalocyanine blue. 2.2.4 Blue and Purple: Most blue shades are produced by phthalocyanine blue, which is the cheapest among the colors used in automotive coatings. It is easy to manufacture, and its raw materials are readily available. In fact, phthalocyanine blue pigments can be regarded as organic pigments that have reached an almost ideal state; these pigments possess bright colors and high coloring power, making them highly functional transparent pigments. Phthalocyanine blue pigments used in automotive coatings are the solvent-stable α-type phthalocyanine blue with red light and the β-type phthalocyanine blue with green light; the phthalocyanine blue with red light is commonly used in automotive coatings. When phthalocyanine blue pigments are used in automotive coatings, flocculation is a common problem; typically, a phthalocyanine blue variant with good anti-flocculation properties is used in the surface coatings. After surface treatment, phthalocyanine blue exhibits good dispersibility, flowability, and antiflocculation properties, making it suitable for various shade concentrations in both metallic and single-color shades. Another blue pigment of interest for automotive coatings is phthalo blue, such as C.I. Pigment Blue 60. Thionine blue is a high-performance transparent red-blue pigment with excellent durability, and it can be used to create both very light and very dark shades. Vinylthionine blue shows a lesser tendency to develop a coppery tint under sunlight compared to phthalocyanine blue; it is thus most suitable for darker blue shades. However, it cannot be used to create topcoats or metallic finish paints with a single color tone, as it is mainly used in combination with phthalocyanine blue to produce blue shades with a red tint. Purple is not very popular in the automotive industry, but it can be seen occasionally. A purple shade can be achieved using carbazole diazine purple C.I. Pigment Purple 23, or it can be prepared with linear beta-quinacridone and C.I. Pigment Purple 19. The existing types of pigments cannot fully meet the actual color requirements of automotive coatings; it is still necessary to continue developing new types of pigments. The use of organic pigments in automotive coatings is achieved through original paint and repair paints; the color matching for the original paint is carried out by manufacturers of automotive coatings ； To prepare repair paint, it is first necessary to create a color paste by mixing aldehyde resins, tert-carbostearate resins and other common pigment resins with pigments and additives; thereafter, the repair paint is formulated by combining this color paste with paint, depending on the desired color ； The color matching for repair paint is done at repair shops; nowadays, color matching for repair paint is mostly carried out using a combination of manual methods and computers. 2.3 Application of organic pigments in coil coatings Coil coatings are classified by function into topcoats, primers, and backcoats; the main types of primers include epoxy, polyester, and polyurethane types ； The main types of topcoats and backcoats include PVC plastisol types, polyester types, polyurethane types, acrylic types, fluorocarbon types, and silicon-modified polyester types, among others. In the production process of color-coated sheets, 20–25 kg of coating material is required per ton of galvanized sheet, with the topcoat containing pigments accounting for about 70% of the total coating used. The common colors include off-white, sea blue, and crimson, among which off-white accounts for about 50%, sea blue about 30%, crimson about 10%, and other colors make up around 10%. Organic pigments in ocean blue and crimson account for about 3% to 5% of the amount used in coil coatings. In 2006, based on the production of 5 million tons of colored steel sheets, the demand for coil coatings was approximately 100,000 tons (with film thickness not meeting the standards); the demand for topcoats was around 70,000 tons. Coil coatings using organic pigments in shades such as ocean blue, crimson, and other colors accounted for about 35,000 tons, while the amount of organic pigments used in coil coatings was roughly 1,000–2,000 tons. Generally, coil-coated paints require pigments with high heat resistance and weather resistance. Therefore, when selecting organic pigments, it is necessary to choose those with a symmetrical structure, such as heterocyclic pigments, in order to meet these requirements. Similar to automotive coatings, this includes pigments like quinacridones, phthalocyanines, and DPP pigments. The requirements for pigments in coil coatings are generally as follows: ① Heat resistance, requiring the ability to withstand baking at temperatures above 250°C without any change in color ； ②Weather resistance, with particular attention to the weather resistance of light-colored shades ； ③Flocculation resistance: generally, a color difference ΔE of ≤0.5 is required ； ④Solvent resistance: Coating films require highly polar solvents such as ethylene glycol butyl ether and methylethyl ketone ； ⑤Migration resistance: Pigments exhibit partial slight solubility in solvents with high solvency. Due to the use of different pigments in coating systems, and particularly the difference in solubility between organic and inorganic pigments, color migration and discoloration can occur. Polyester and polyurethane coatings contain aromatic solvents, and some organic pigments crystallize in these aromatic solvents, which leads to a change in crystal form and thus alters the color tone as well as reducing the coloring strength. 3 Requirements for organic pigments in the development of high-performance coatings. Organic pigments have evolved alongside advancements in organic dye technology, forming a distinct class of organic coloring agents with specific properties; they are widely used in fields such as inks, coatings, and plastics. In recent years, the total output of the global organic pigment industry has not seen much growth, but the production volume, variety, and specifications of high-performance organic pigments have increased significantly. Although the output of high-performance organic pigments accounts for a small proportion of the total output, the high technology involved in their production confers high performance and high added value; as a result, their economic value exceeds that of mid-range organic pigments, and is comparable to that of low-range organic pigments, which make up half of the total output. The research, development, and production of organic pigments, especially high-performance ones, are still in the developmental stage in China. Compared with developed countries, there is still a significant gap in terms of technical level, variety of products, and quality. Our country is a major producer of organic pigments, but not a leading one. The synthesis technology for crude organic pigments in our country is generally on par with international standards. The products available are mainly those with lower performance and lower relative molecular weights; whereas, colorants suitable for use in high-quality automotive topcoats, advanced engineering plastics and resins, fiber products, and high-grade printing inks must be provided by high-performance organic pigments with large molecular weights. High-performance organic pigments are characterized by their macromolecular structure and complex chemical composition ； The intermediate used has a long preparation process, a complex synthesis route, and high technical requirements ； A large amount of money is also required to manage these three types of waste; as a result, the research and development and production of high-performance organic pigments have remained in the hands of a few large multinational companies in Europe and the United States that possess strong technical capabilities, such as BASF, Clariant, Covestro, and Solvay, and these products have become part of their company’s brand offerings. While developing new structural variants, these internationally renowned manufacturers of organic pigments are also committed to studying the surface properties of these pigments, thereby endowing traditional pigment types with superior performance, improving product quality, and expanding their areas of application. An increasing variety of high-performance organic pigments, to meet the high-performance requirements of various application areas, will be the trend in the future development of organic pigments. With technological progress, the demand for high-performance organic pigments and organic pigments with special functions will continue to increase ； At the same time, the concept of environmental protection will be fully integrated into every aspect of the production, trade, and consumption of organic pigments. Innovation in organic pigments should be market-oriented; efforts must be made to accelerate the development of an innovation system, place great emphasis on original innovation, and rely on independent innovation to strengthen the industry’s core competitiveness. In the future, research and development of organic pigments in our country should focus on new products in industries such as coatings, inks, and plastics, aiming to improve the performance of existing products and develop new types of organic pigments that are suitable for use with them. The manufacturing processes must also meet the increasingly strict environmental regulations. The requirements for the product can be summarized as follows: the product should be of high quality, that is, it must meet the requirements regarding the durability of the metal surface coating, its resistance to weathering, heat, solvents, and migration ； Developing special functional organic pigments with high purity and specific crystal forms, etc ； Two intermediates of organic pigments deserve attention, namely barbituric acid and phenylcyanide along with their para-substituted derivatives. It is expected that within the next 5 to 10 years, the former may replace 3,3’-dichlorobenzidine, while the latter serves as a key intermediate for DPP-type organic pigments. These two intermediates are currently primarily used in the production of pharmaceuticals. In terms of China’s coating industry, with technological advancements in areas such as architectural coatings, automotive coatings, coil coatings, and other types of coatings, the need for the specific functions that coatings provide has led to the exposure of the shortcomings of certain organic pigments used in coatings. This poses new challenges for the development of the organic pigment sector within China’s coating industry. Organic pigment manufacturers have a responsibility to work in conjunction with the development of this industry by creating organic pigments that meet the requirements of coatings, thereby helping to develop China’s own brands of organic pigments. This post was last edited by zxh6267 on 2009-4-6 17:59.]