Among the products used in wet-end of leathers for acidification in stages of initial washing, dyeing and retannage and grease fastening, formic acid is the most widely used.
This happens because such acid has a constant ionization appropriate to this steps providing important characteristics to the leather, as good exhaustion of dyes and good fastening.
However, these positive characteristics oppose themselves in some negative aspects such as high volatility, which causes loses and complicates the handling, its unpleasant smell and incompatibility with nickel metallic components of high gloss used in various artifacts processes.
Seeking alternatives to remedy these problems, Brazil based leather chemical makers, MK started to study a number of acids that could fully replace formic acid in the wet finishing steps, seeking to keep the positive aspects and eliminate the negative ones.
Thus, a family of compounds derived from synthesis of inorganic and organic acids may be used in all processes of wet finishing of leather in place of formic acid. This new generation of fasteners currently has the following products:
Fixacid FN: A product very versatile, odorless, with easy handling and application, designed for the production of all types of leathers.
Fixacid NS: Free of sulphates and sulphur compounds, indicated to meet environmental restriction aspects to the presence of sulphates in industrial effluents.
Fixacid FK: May be used with little dilution of 1:3 to 1:5 for easy handling, and is suitable for processes with short baths.
Maxifix FC: Product with greater concentration than others, ideal for processes where neutralisation reaches a higher pH, requiring higher acidity for fastening and exhaustion.
All fasteners of this new generation share the following properties:
- Do not cause matting in metallic components: The formic acid used in the preparation of leather is a product with higher degree of aggressiveness to metal components, causing matting into pieces with bright nickel finishing. Due to absence of volatile acids, MK fasteners do not act on the surface of metal components eliminating completely the matting issue.
- Behavior similar to formic acid: Thus, the full use amount of MK fasteners is equal to the amount of formic acid typically used.
- Do not cause loss by volatility: The use of formic acid causes losses, especially when it is placed in open containers, since it has a high steam pressure. This problem is eliminated with the use of MK fasteners since they are non volatile.
- Easy to handle: Since it is non-volatile and no unpleasant smell product, the handling of MK fasteners within the tannery is tremendously easy. Formic acid has a high toxicity and is a product considered hazardous as it is corrosive and flammable.
- Give a high exhaustion of dye and dyeing fastening: With the use of MK fasteners you have the same level of dye exhaustion and degree of fastening equal to or greater than those obtained with formic acid.
- Do not interfere in the intensity and shade of dyes: It is also not observed significant differences in the intensity and shade of dyed and fastened leathers with the new generation of products compared with processes using formic acid.
- May be used in white leathers: It is not observed any change in the characteristics of white leathers as bleaching, shade and light fastness when the MK fasteners are compared with formic acid.
