Denim fabric with fire-retardant properties and process of dyeing the warp with indigo blue dye

A process of dyeing the warp yarns of a denim fabric with indigo blue dyes, the warp yarns having a mixture of permanently fire-retardant fibres that contain natural, cellulosic and synthetic fibres, wherein the dyeing is performed continuously in a dyeing indigo machine and the fire-retardant fibres have intrinsic fire-retardant properties, comprising the following steps in order:

• in a preparation phase:
• preparing the warp yarns by applying a first dye in the form of reduced indigo blue dye to the warp yarns to obtain pigmentation of the synthetic fibres;
• oxidizing the warp yarns by subjecting them to air to oxidize the dye on the cellulosic fibres and to convert the reduced dye deposited on the synthetic fibres into a pigmented form,
• fixing the first dye on the synthetic fibres by cationization with quaternary amines, and
• washing the warp yarns to remove dye that is not fixed on the synthetic fibres;
• in a dyeing phase:
• applying reduced indigo dye to the warp yarns to obtain pigmentation of the synthetic fibres;
• and
• oxidizing the warp yarns by subjecting them to air to oxidize the dye on the cellulosic fibres and to convert the reduced dye deposited on the synthetic fibres into a pigmented form, wherein the dyeing phase is repeated in consecutive cycles;
• in a finishing phase:
• binding the dye on the synthetic fibres via application of a cationic polymer;
• drying the warp yarns,
• polymerizing the cationic polymer with the indigo dye on the synthetic fibres to achieve an integration of the indigo dye on the structure of the synthetic fibres;
• and
• in a gluing phase:
• applying vinyl copolymers to the warp yarns, and
• drying the warp yarns to fix the vinyl copolymers on the warp threads.