Aim of this work is a broad-band study with INTEGRAL , Swift and XMM-Newton satellites of a sample of 9 blazars ( 7 FSRQ and 2 BL Lac ) with redshift up to about 4 .

The spectral analysis has shown clear evidence of a flattening of the continuum towards the low energies ( E < 3 keV observer frame ) .
This behaviour is well reproduced both with an absorbed power-law model ( N _ { H } \sim 10 ^ { 20 } - 10 ^ { 23 } cm ^ { -2 } in the rest-frame of the sources ) or a broken power-law continuum model ( with an energy break below 3 keV in the observer-frame ) .
No Compton reflection features , Fe K \alpha line and hump at high energies , have been detected , with the exception of the source IGR J22517+2218 that shows the presence of a weak iron line .

In this work we also investigate a possible correlation between the absorption column density N _ { H } and the red-shift .

We confirm the existence of a N _ { H } -z trend , with the higher absorption at z > 2 for a larger sample compared to previous results .
The distribution of the N _ { H } and the photon index \Gamma is also presented .
The hard X-ray data allow us to detect highly absorbed sources ( with N _ { H } \geq 10 ^ { 23 } cm ^ { -2 } in rest-frame of the source ) characterized by photon index distribution peaked at harder values ( \Gamma \sim 1.4 ) with respect to that obtained with XMM data only ( \Gamma \sim 2 ) .