without using the preserve pure black

when i take bw laser print from corel draw, the output is not pure black. As suggested in this forum, I tried using the the 'Preserve Pure Black' setting in corel draw. But it turns out to have some adverse effect while converting image from one format to the other (like rgb to cmyk) bitmaps, the black shade on the image looked washed out in multicolor offset print.

what should i do now to get pure black output from bw laser printer without using the preserve pure black setting.

printer : hp 1020

operating system : windows 7

corel draw version : x5