The Search For Non-Staining, Bleachable Acid Dyes
Mike Pembery, Technical Manager, Sensient Colors UK Ltd, looks at the color challenges facing manufacturers of household cleaning and fabric care products.
Color is a key ingredient in many household cleaning and fabric care products. Marketers use it to create distinctive brands, to emphasize product qualities and to enhance the customer experience. But color has a secret: many standard acid dyes do not rinse away completely in water, leaving residue that can, with repeated exposure, slowly discolor the fabrics and hard surfaces the products are meant to clean.
A particular shade of blue might denote the hygienic properties of a household cleaner. Yellow fabric softener can stimulate consumers’ senses so they perceive the product’s floral perfume to be more intense and evocative, while some brands of detergent have colors as recognizable to the consumer as the red of a famous Italian sports car. These are all attributes that marketers value, but they come at a price.
Manufacturers tell us they face a trade-off between ‘rinsablity’ and cost when choosing dyes. Premium brands tend to use expensive polymer-based acid dyes because the molecular size makes the colors almost completely non-staining to skin; but if fabrics are discolored they can be difficult to bleach out. Mass-market products tend to use standard acid dyes because they are cheaper and any gradual discoloration of whites is seen as an unavoidable side-effect that bleaching can sometimes solve.
Skin and fabric rinsable acid dyes?
A highly concentrated alternative to standard acid dyes has to offer more than superior color consistency and non-hazardous ingredients. It has also to be both rinsable from skin and at 40°C from common fabrics and hard surfaces – and fully bleachable in domestic bleach solutions (should the need arise).
Meeting manufacturers’ needs
Although polymer-based dyes are virtually non-staining, many manufacturers tell us they won’t switch to them because they normally require complex product reformulation. So, aside from the end product benefits, any new acid dyes created to replace standard acid dyes would need to fit easily into current manufacturing processes. In other words, new dyes have to be as similar to existing standard dyes as possible, so as to be interchangeable without reformulating the product.
A new liquid dye needs low viscosity (less than 5 Ps) like standard dyes to facilitate ease of blending and dosing through standard pumps. To have minimal impact on the pH of a formulation. Liquid dyes need to have the same palette of fully intermixable liquid colors, enabling manufacturers to give marketers the choice of a wide range of bespoke colors, including black, with no gelling.
Keep whites white and colors bright
The challenge for chemists has been to create completely non-staining acid dyes for use on fabrics and hard surfaces that are both skin and fabric rinsable and (should the need arise) fabric bleachable. Such new dyes have to be cost effective to compete with standard dyes, while offering the superior color consistency and stability of polymer dyes. They must also use safe and readily available ingredients that meet all REACH* requirements.
Ideally, such new dyes should be water-based so as to reduce their environmental impact. They should be available in liquid form to make handling as easy as possible. And they should integrate easily into existing production processes, so as to avoid the need for formula recalibrations or new equipment.
Liquid Vs powdered dyes
Many large-volume producers we’ve spoken to tell us they prefer liquid dyes to powdered dyes because they are cleaner to handle, allow more accurate dosing and are easier to blend with other liquids. Powdered dyes are dusty and notoriously tricky to blend because they tend to form clumps when dissolving in liquid. Since most non-staining polymer dyes are only available as liquids, any cheaper alternatives would need to fit seamlessly into existing processes.
Going with liquidity
According to our research, an ideal new acid dye would be available in liquid form, and offer the dust-free cleanliness and blending ability of liquid with the color intensity of a powder. It would come in pre-measured and bespoke pack sizes for simple dosing and the ability to mix the right quantity of solution exactly when it’s needed.
Until now, the closest the colorants industry has come to this has been with granular acid dyes. Granular dyes rapidly disperse in liquid because the color is pre-dispersed with other soluble solids. Our customers tell us, however, that none of the standard granular dyes possess the non-staining properties of polymer dyes.
The need for bold, safe and stable colors
Marketers love bold colors to reinforce brand identities and perceived product functionalities. They would prefer those colors to be integral to the product, rather than simply part of the packaging. That means the dyes they choose must be stable both over time and across a range of storage temperatures, particularly under commercial lighting, so as not to cut short the product’s shelf-life.
Standard acid dyes are a popular choice with manufacturers of hard surface cleaners, fabric care products, household detergents, car washes, and children’s coloring pens.As such, any new dyes must be REACH compliant and as safe as standard dyes for users and the environment. That includes being free from heavy metals, solvents and preservatives, as well as being microbiologically stable to resist bacterial infection.
Other vital ingredients
Many leading manufacturers say they prefer liquid dyes that are water-based. This is partly for environmental considerations and partly because they don’t pose a risk to water-based emulsions. The lack of solvents also makes it easier to formulate products.
We believe the household cleaners and fabric care market is ready for a new generation of non-staining liquid acid dyes. With skin and fabric ‘rinsability’ and fabric ‘bleachability’ as standard, and a color range to impress the most discerning brand manager, these new dyes will fit seamlessly into existing acid dye processes, so giving users a real competitive advantage in terms of process costs and brand recognition.