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 chemical bonding makes the colors almost completely non-staining; but if something does go wrong 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.
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 rinsable and (should the need arise) 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.
Our customers tell us that, ideally, such new dyes should be water-based and solvent-free so as to reduce their environmental impact. They should be available in both liquid and solid 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.
Solid grounds for an alternative to liquid 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 alternative would need to fit seamlessly into existing processes.
However, other manufacturers tell us they value powdered dyes because their concentrated colors are easier and cheaper to handle than bulk liquids. Powders are also valued by companies with production plants in countries that suffer freezing temperatures for prolonged periods. Since powdered dyes don’t freeze they can be stored in cold warehouses, saving money on heating and avoiding the color separation that can occur when liquids freeze and thaw.
Going with the grain
According to our research, an ideal new acid dye would be available in both liquid and solid forms, and offer the dust-free cleanliness and blending ability of liquid with the color intensity of a powder. At the same time, the solid dye would need to dissolve easily and quickly in liquids with no risk of clumping. And 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 you need it.
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 our clients for 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.
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 at 40°C from common fabrics and hard surfaces – and fully bleachable in domestic bleach solutions should the need arise. Our research suggests that, until now, customers have had to choose either/or – but have been unable to choose both.
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 the same low viscosity (less than 10 cPs) as standard dyes to facilitate ease of blending and dosing through standard pumps. To have minimal impact on the pH of a formulation, it would also need to be near neutral pH. Both granule and liquid dyes need to have the same palette of fully intermixable basic colors, so as to give marketers the choice of a wide range of bespoke colors, including black, with no gelling.
Other vital ingredients
Another important consideration for manufacturers we’ve spoken to is the ability to switch between liquid and granules without the need for reformulation. This is particularly important when the process parameters vary between different production centers. Essentially, they tell us there should be no difference in color outcomes if they switch from liquid to granules or back again – and all colors would be available in pre-calibrated strengths.
In addition, 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.
In summary, we think the household cleaners and fabric care market is ready for a new generation of non-staining liquid and granular acid dyes. With ‘rinsability’ and ‘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.