β modified monoazo dye resistant to dyeing, its preparation and use

β modification of the dye of the formula I

• having an X-ray diffraction pattern (Cu Kα radiation) containing lines at the following diffraction angles 2θ (°):
• high intensity lines:
• 7.15, 10.25, 25.9,
• medium-intensity lines:
• 16.9, 19.5, 20.1 21.85, 22.65, 23.4, 25.2, 28.5, 32.45.