Applications of Pigments

Pigment is any substance used as a colouring matter and comprises particularly finely ground particles held in suspension within a binder medium. It is a substance that colours other materials. It has a very wide range of applications, from medicine to decoration. The main applications are as follows:

1. Colorants in the Packaging Sector

The packaging and cardboard box sector is an extremely specialized division within the paper industry. There is significant demand for colorants in this sector. This growing demand is supported by conventional basic colorants, as well as highly advanced and modified basic colorants and direct colorants. Conventional basic colorants have held an unrivalled position for many years due to numerous important factors such as high colour strength, acceptable properties, and relatively affordable prices. However, over time, other types of colorants, including direct colorants, have become an excellent choice in the packaging sector by shifting the economic indicator in their favour.

Criteria for Selecting Colorants

When it comes to packaging types, the selection of colorants is limited to three broad categories: basic colorants, modified basic colorants, and anionic direct colorants. However, an important point to be remembered here is that the selection of colorant type cannot be made independently of one another. If the end product will be added at the print size or wet end (stock addition), other factors must also be carefully considered. Below are a few of the criteria applied in turn, taking into account the type of colorant to be used here. • Shade and desired colour depth, • Required technical properties such as light fastness, • Primary colours and derivatives obtained from them, • Environmental regulations, • Cost factors.

Colorant Applications in Packaging

Colorants find application in the following popular packaging sectors. 1. Newspaper papers, 2. Bags, 3. Reels, 4. Cardboard boxes, 5. Fibre boards, 6. Kraft papers, 7. Cationic sized printing formulations, 8. Anionic sized printing formulations.

Comparison Between Colorant Types Used in the Packaging Sector

The table below provides a comparative overview of the advantages and disadvantages of the three types used in the packaging sector: basic colorants, modified basic colorants, and anionic direct colorants, respectively.

2. Colorants in the Glass Industry

Currently, various pigments are used to colour glass materials in the global glass market. Previously, the colours in eyeglass lenses could not be obtained from pigments. At that time, various types of foreign substances were considered responsible for colouring glass materials. For example, in the 17th century, due to iron impurities, the colour of 'black bomb eyeglasses' appeared as dark brown or green. These foreign substances reached eyeglass lenses from two sources. The first was that iron was used to make these lenses, and the second was sulphur from the smoke produced by coal used to melt these lenses. However, today glass is coloured using various pigments (pure metal salts). Some examples of ancient coloured glass are as follows: Ruby glass (gold chloride, discovered in 1679, was used as pigment), uranium glass (uranium oxide, discovered in 1830, was used as pigment). It cannot always be said that coloured glasses are useful. Sometimes, glass with no particular colour may be required. In that case, the unwanted colour must be removed from the glass. The colour removal process is called decolorizing. There are some commonly used decolorizing additives. These are: manganese dioxide and cerium oxide.

Special Effects in Eyeglasses Using Pigments

By using some pigments alone or in combination with other types of pigments, special colour effects can be created in eyeglasses. For example, iridescent glass (iris glass) has a special colouring effect. This colouring effect in iris glass can be created by adding certain metallic compounds (pigments). Sometimes, the colouring effect in iris glass can be created by spraying tin chloride or lead chloride on the glass surface and then heating in the presence of a reducing agent. Another coloured glass is dichroic glass. When viewed from different angles, the glass colour appears to change. This occurs because a very thin layer of colloidal metals (gold or silver) is applied to the glass surface.

Some Useful Pigments in the Glass Sector

Cobalt Inorganic Pigments: Cobalt inorganic pigments are used in various applications. These applications range from colouring to produce finished glass products to the desired colour intensity. Nickel Inorganic Pigments: Nickel inorganic pigments are used to add colour. They are used to increase the colour strength of final glass products and to develop other properties of glass products. Antimony Trioxide (Sb2O3): This pigment is also known as white pigment. These pigments are used as decolorizing agents in the glass industry. They can be used to remove unwanted colours from eyeglasses. These pigments have very high purification capacity and are free from all types of foreign substances. Sodium Antimonate: Sodium pigments are also used as decolorizing agents in the glass sector. This pigment is used as a purification additive.

3. Colorants in the Rubber Industry

In the rubber industry, different pigments are used to impart different properties such as durability, resistance to heat and light, reinforcement capacity, etc. Some of the pigments used/applied in the rubber sector are as follows: Carbon Black: Carbon black is a type of pigment obtained from petroleum refinery processes. In the production of automobile tyres, it is used to provide high durability, wear resistance, long life, and ground grip. These qualities apply to any successful tyre. Carbon black is used in various applications in different types of rubber products. This range of products in rubber extends from aerospace to ordinary household items. Powder Organic Pigments: Powder organic pigments are used in colouring processes and to develop other specific properties in rubber products. Titanium Dioxide: In rubber applications, titanium dioxide pigments are also used. These pigments are used in rubber applications because of some of their good qualities. These good qualities include high refractive index, density of particle size, dispersion, and high ultraviolet light resistance. Fluorescent Pigments: Fluorescent pigment, a type of bright pigment in powder form called powder colour, is used in the rubber industry. These types of pigments can be of organic or inorganic structure. Appropriate colour selection depends primarily on the requirements of certain manufacturers. These requirements can include light stability, heat resistance, bleeding resistance, migration resistance, and the required colour shade. Bifunctional Organic Silicon Compounds: Pigments used in the rubber sector are generally bifunctional organic silicon compounds. These compounds have two reactive groups. These pigments are used for high-quality rubber compounds. When these types of pigments are used in the rubber sector, they are combined with pigments carrying a silanol group. In this way, their effectiveness will be more effective. Molybdenum Pigments: Another pigment used in the rubber sector is molybdenum pigment. These pigments are light and heat resistant and are bright colours ranging from bright red-orange to red-yellow. Outside of rubber products, these pigments are also used in ceramics, plastics, paints, and inks. Another type of pigments known as ultramarine pigments are also used in rubber products. These pigments have high resistance to heat, light, and environmental exposure. Cadmium Pigments: Although cadmium pigments do not have a significant application area in the rubber sector, they are used in the rubber industry for some minor purposes. Zinc Oxide as Pigment (Zinc White): Since its establishment, the rubber industry has used zinc oxide. The great importance of zinc oxide in the rubber industry comes from its physical and chemical properties and many of its optical properties. Automobile tyres for heavy pneumatic loads and durability require high zinc oxide loading for high heat conductivity, in addition to support given the critical nature of the thermal structure at high operating speeds. In the vulcanization process, for many types of synthetic rubber sand and natural rubber, the chemical reactivity of zinc oxide is required to activate organic accelerators.

Some special properties that make zinc oxide popular in the rubber industry are as follows:

Heat Stability: Zinc oxide has very high heat stability (resistance). For this reason, when it is used in the production of automobile tyres, the tyres remain more solid and durable even at high temperatures. Latex Gelation: When latex foam rubber products are produced, it provides sufficient stability in foam gelation. Light Stability: Apart from all other white pigments, zinc oxide has the highest ability to absorb UV rays. For this reason, when used in rubber tyres, it provides additional resistance against destructive sunlight. Because these types of rubber require additional durability, zinc oxide is specially used in white and coloured tyres. Pigmentation: Due to zinc oxide's high brightness, high refractive index, and suitable particle size, when this pigment is mixed with rubber products, the products will become more whitish. This pigment is particularly used in medical surgical equipment made from rubber, rubber coatings, and in the sidewalls of automobile tyres. Reinforcement: Natural rubber derives its reinforcement strength from this pigment. Rubber-Metal Bonding: Zinc oxide reacts with copper oxide to bond rubber to brass.

4. Colorants in Cosmetics

Colorants have found wide application in the cosmetics sector. They have important uses in many places such as hair dyes, lipsticks, shampoos, or nail polishes. If we look at hair dyes, most commercial hair dye formulas found on the market now use complex materials and their formulas differ significantly between manufacturers. The subject that concerns us here is what types of colorants are used in hair dye manufacture. The commonly used colouring chemicals consist of amino compounds such as 4-amino-2-hydroxytoluene and m-aminophenol. Metal oxides such as titanium dioxide and iron oxide pigments are also used. Types of Raw Materials Used in Cosmetics: Pigments make up the majority of colours used in the decorative cosmetics category. These are inorganic pigments that are popular in cosmetics but do not require high levels of heavy metals. Inorganic pigments used in cosmetics generally consist of types composed of various chemicals. A few popular ones are given in the table. In addition to these types of organic pigments used in cosmetic applications, water-soluble and oil-soluble colorants can be counted as soluble pigments (dyestuff). Some examples of water-soluble colouring pigments (dyestuff) are given below.

5. Colorants for the Agricultural Sector

Basically, there are three main types of colorants used in the agricultural industry. 1. Crop protection industry, 2. Fertilizer industry, 3. Seed protection industry. The purpose of colorant use here is in the identification process of agricultural chemicals or in the colouring of agricultural chemicals. The basic selection criteria depend on the following properties: • The colouring strength of the colorant, • The colour of the colorant, • Colour stability, • Compatibility of the colorant with the additives used. The evaluation of details in applications can be performed as follows: Crop Protection Industry: In crop protection, colorants are used to clearly distinguish between processed and unprocessed insecticide and fungicide type additives. Additionally, the use of colouring dyes helps with safety in application processes. The colouring of pesticides or herbicides is usually done by mixing chromatic pigments with dry powder additives in the formulation. Here, milori blue pigment, which works well with viticultural fungicides, is the most popular pigment. Other pigments that can be used here are pigments such as lithol rubin red, phthalocyanine blue. Other colorants used in the crop protection industry, such as solvent colorants (solvent dyes), acid colorants (acid dyes), or basic colorants (basic dyes), can be considered good alternatives. Fertilizer Industry: Fertilizers are mostly coloured to distinguish their qualities and to prevent any errors in applications. In addition, fertilizers are also coloured entirely for marketing purposes. Generally, water-based pigment pastes, usually diluted, are used and sprayed onto the fertilizer or sometimes dissolved and mixed. Seed Coating Industry: The main purpose of colouring in seed coating is to use it for marking and warning information. It is used to prevent any type of confusion and to ensure that it has not been consumed as animal feed. The most important colorant used here is red, and the typical usage concentration is 600 ppm. Namık Kayaalp (Chemical Engineer / Ecelak Boya Kimya Ltd. Co.) References: 1. Organic Coating Technology, H.F.Payne, 2. PCI, 3. K. Hunger, Industrial Dyes, Chemistry, Properties, Applications 4. W. Herbst, K. Hunger, Industrial Organic Pigments 5. Industrial Inorganic Pigments, G. Buxbaum and G. Pfaff 6. Ullmann's Encyclopedia of Industrial Chemistry Vol.A-20 VCH Publishers,Inc.-1992