Use of Colorants in the Plastic Industry

Pigment orange, pigment blue, pigment green; you name it and you have an attractive piece of plastic ware with that colour tint in some store or the other. However, in today’s times the scope of pigments and dyes in plastics are not limited merely to lending hues and shades. They also make an impact on sustainability, processability and compliance.

The question often arises as to which among the two; dyes or pigments are best suited for use in the plastics industry. Dyes are used to shade or tint a resin and as such they have to be transparent, strong and exhibit good heat stability. However, dyes are compatible with only a few resins and therefore their use in quite limited in this industry. Pigments on the other hand provide more options to the manufacturer due to their wider chrome range, pacifying ability and better heat stability for a large number of resins.

The base polymer actually decides the kind of colorant that will be most suitable for the application. Pigments work best with polyolefins while dyes give good results with polystyrene, poly carbonate and acrylic. All said and done, the basic determining factor for choice of colorant is its compatibility with the base resin. There are a few other factors that have to be kept in mind as well such as the method of dispersion, processing temperature, heat stability, gloss, weather fastness, application etc. A slight error in making the choice can drastically change the features of the plastic and therefore, a good selection of the colorant assumes great importance.

Today, there is more emphasis placed on using pigments that are less toxic and cause minimum harm to the environment. Millions of dollars are spent on research by several organisations in developing such pigments. Their efforts have not gone in vain and one of them has been successful in replacing lead based materials in pigments. Lead chromate pigments were banned from use in consumer plastics and in its place, organic yellow pigments have been developed which have better tint strengths in PVC and polyethylene. Another new development is with respect to pigment blue. The name of the new pigment is YInMn blue which stands for its chemical content namely yttrium, manganese, indium and oxygen. This pigment is also superior to the traditional cobalt blue pigments and has high reflectivity and high ultraviolet absorbance in the near-infrared area.

Colorants contribute to a number of performance aspects in plastics; however, lending colour will always remain their major contribution. When one sees the attractive world of colourful plastic ware one realises the important contribution made by colorants to this industry. At the same time, every individual connected with using and developing colorants for this industry has to try and make a difference to the colouring technology whereby Mother Earth is not harmed in any way whatsoever!

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Dyeing of Wool

Wool in its natural form has a neutral shade and has to be dye to obtain varied hues. In most cases, wool can be bleached or dye at any of the processing stages though it is commonly done after washing or when it is spun into yarn. Wool which is dyed at the yarn stage is referred to as yarn dye while stock dye wool is the name given to wool which is dye right after washing. Plant colours can be used for a natural dyeing process though chemical are the ones preferred for commercial applications. The dyes used for wool are chemically anionic in nature. Two factors that determine the rate of dyeing are the pH and the rate of increase in temperature of the dye bath liquor. Wool is said to be dye or bleached successfully if one achieves the uniformity, correct shade, requirements of colour fastness at minimum cost and least environmental damage on a consistent basis.

There are several which go down well with wool fabric to develop colourfast finish in varied hues ranging from soft pastels to intense brights. Wool is normally dye using acid dye. These require extremely hot waters for consistent results. Acid are cheaper and wash fast and give best results as far as wool is concerned. The resulting colour depends on the quantity of dye used, temperature, time for which the fabric is immersed in the dye and the length of the fabric. Wool can be dyed using direct too. However, these do not have the vivid brightness and are not so wash fast. Cellulose fibres are dyed with these directly without using mordants. Reactive on the other hand were initially used for cellulose fibres alone. However, today, varied types of this dye are used to dye wool, nylon, silk, acrylics along with their blends.

Yarn of wool is done either at hank form or at-package form; however, the hank form is more popular. Yarns of wool are immersed in a large container containing the dye bath from a rung over which they are hung. Wool yarns are dye in bulk by this method as this helps to achieve maximum colour penetration.

Wool can be dye in the loose-fibre stage too. Bales of scoured wool are first weighed before being brought to the house. They are then opened near the machine after which they are manually immersed into the vessel. For achieving even loading into the machine the fibre may be made wet before being packed.

Woolen garments in beautiful patterns are flaunted on fashion ramps with leather boots in various shades to match. All thanks to the acid direct dyes and leather dyes!

The continued growth and expansion led to formation of several subsidiary plants. However, one thing remains common across the plants is strict adherence to quality norms, compliance of statutory formalities and industry best practices.

The Magic of ‘Glow in the Dark’ Pigments

Certain specialty colorants stand apart from the regular organic pigments due to certain attributes possessed by them. One of the attribute is the ‘glow in the dark’ effect. The special substances are referred to as phosphors and glowing is sometimes called phosphorescence. Visible light is radiated by these Phosphors after they are energized. This implies that the phosphors have to be exposed to light for the required time for them to be energized and glow in the dark.

This stored energy is then released by the phosphors at a slow rate for a certain period of time. While this energy is being released small quantities of light is emitted and that is the reason for the object to glow in the dark. Many chemical compounds act as phosphors; however, strontium illuminate based after-glow pigments are being used to the maximum extent.

There are endless possibilities for use of these pigments and listing all of them will be truly difficult. But if a few areas where these ‘glow in the dark’ pigments are used were to be listed then they would include canvas paintings, epoxy and resin projects, costumes and props, hats, shoes and other clothing, wall murals and ceiling and in many other commercial items such as sporting goods, exit signs, toys, stickers, fluorescent textiles etc.

One of the major applications is the ‘glow in the dark’ fabric or textiles. Textile dyes, reactive dyes and others are used to lend colour to the four main naturally sourced fabrics like cotton, wool, linen, and silk. The glowing effect is due to the inclusion of certain other additives. ‘Glow in the dark’ fabrics are made from yarn or thread of the similar type. The yarn is skin friendly and besides being woven into the fabric it can be used to sew or embroider designs which glow in the dark. The chemical processes undergone by the fabric ensures that their special attribute remains untouched even after washing and ironing though direct ironing has to be avoided. Clothes made from this fabric are used by early morning or late night joggers, campers for their tents, as party costumes, t-shirts and jump suits of kids, bed sheets and blankets and other home furnishing material.

‘Glow in the dark’ paints are another popular area where these fluorescent pigments find a wide use. Different combinations of the basic ingredients give different resultant colour combinations ranging from green to blue to red to yellow green. The ‘glow in the dark’ paints are used in a number of items such as glow cars, fishing lures, police flashlight, vehicle painting, silhouette walls, children’s rooms and lots more.

Man has created these ‘glow in the dark’ objects but nature has given us bio-luminescent creatures in the form of jelly fish and fire flies that glow. Have you ever wondered why do they glow?

The company currently serves clients across broad spectrum of industries ranging from Textile, Paint, Printing Ink, Cosmetics & Food Industry, Plastic and several other industries and has presence in both local and international market. In fact, if you need colors of any type, for any industry, Vipul Organics Ltd. will serve the par excellent quality, guaranteed!