Dye innovations from Clariant16 November 2004
Derma Soft Historically, there have been two ways of producing pastel shades in a tannery. The first is by using very small amounts of normal dyes in recipes with a high amount of dispersing agents. The main drawbacks of this approach are that it is very sensitive to mistakes during the weighing of the dye and also that the dye is not dispersed by itself. Secondly, commercially-available pastel dyes can be obtained by physically mixing normal dyes and dispersing agents (Figure 1). In this case, the dye and the dispersant are mixed on a macroscopic level, but not on a microscopic one. Production of Derma Soft pastel shades Our approach, in this case, has been to improve the dispersion of the dye by working on a microscopic level. This is achieved by a chemical pre-dispersion of the dye before it is finished (Figure 2). The difference between the macroscopic and microscopic levels can easily be understood in Figure 2. For example, the tanner has two pastel dyes (in Figure 3 they appear as pale red), one obtained by physically mixing a red dye and a dispersing agent and the other by a pre-dispersion of a red dye. While both products have the same physical appearance at first glance (macroscopic level), when we go down to the microscopic level, we can see in the physical mixture that the molecules of the red dye are different from the molecules of the dispersant. On the other side, the pre-dispersed dye shows only pale red particles. Range definition and dye selection Once we have determined how to obtain the commercial form, it is very important to choose the coloured components, as they will determine the fastness properties and the shade of the new products. As we wanted to develop this range for the top-quality market where high fastness properties are required, we selected the main coloured components from our normal active range of products that already have such properties. Furthermore, the selected components are from our normal production palette, so we could control all aspects of quality, particularly ensuring the absence of impurities that could influence the fastness and migration properties. Another important aspect for the selection of the components is their compatibility. In order to reduce the number of products in the range, and to give flexibility to the tanners so that they can produce a full range of pastel shades with the fewest number of components, the selected dyes had to be compatible. Six different dyes were prepared, with the aim of covering the whole pastel colour spectrum: Derma Soft Brown Y: yellowish pastel brown Derma Soft Brown G: greyish pastel brown Derma Soft Brown R: reddish pastel brown Derma Soft Orange Derma Soft Red Derma Soft Grey Figure 4 contains the colour co-ordinates of the six new products. Advantages The excellent dispersability of these new dyes, as well as the selection of active substances, gives the following advantages to this new range: Levelness The range offers excellent levelness as the dyes are pre-dispersed. This also avoids agglomeration of dye particles. Fastness The table below summarises the average fastness properties of the new dyes. Lightfastness 3 Migration to pvc 5 Perspiration (WO) 5 Perspiration (CO) 4 Dry cleaning (WO) 5 Dry cleaning (CO) 4 Solubility >100g/l Flexibility All the dyes are compatible with each other and combining them will create almost all normal pastel shades. The basic components brown G, Y, R and orange are easily shaded by the grey and red dyes. Derma Flor dyes Objectives Cost reduction is increasingly becoming a key parameter for the success of a business. Costs can be reduced in a tannery in many different ways: process simplification, automatisation, waste reduction, stock reduction and, of course, cheaper raw material and chemicals. The objective of this new range was to provide our customers, from our existing range of dyes, a group of products that are more cost-effective. The range includes a smaller number of dyes but, by themselves or combined, they produce almost all possible shades of brown. Fastness levels are acceptable for most normal applications. Furthermore, the dyes are based on raw materials available from our normal sources and, therefore, do not require any special complexities or adjustments during the manufacturing process. Advantages Besides the economic benefits of their low cost, this range also has the advantage of comprising a selection of products that are less complex and covers all important brown shades. Fastness levels are also acceptable for all normal applications. Figure 5 contains the colour co-ordinates of the six new products developed. Especially remarkable is the new Derma Flor Cognac Brown, a medium-brown dye with a high fastness profile (see table below). Lightfastness 4 Migration to pvc 5 Perspiration (WO) 4 Perspiration (CO) 4 Dry cleaning (WO) 5 Dry cleaning (CO) 5 Solubility >100g/l Conclusion With the objective of improving the quality of leather, we have based our work on the idea that aggregation of dyes can cause unevenness during dyeing and have developed two new ranges.Derma Supra is a range of highly-concentrated dyestuffs without the presence of high amounts of salt that could aggregate the dye. For more information, see Leather International August/September 2004, pp40-41. As we have seen here, Derma Soft is a range of pre-dispersed dyes, where the dye is micro-scopically dispersed so that no aggregation can take place. Furthermore, the Derma Flor range has been developed with a selection of our dyes offering the most cost-effective profile.