Plotting transparent solid hatches - 2011

Lately I've been trying to plot a drawing with solid hatches of varying transparencies to pdf in Autocad 2011. I have plotted drawings like this successfully before, but with this particular document, the hatches are being rendered with a strange texture of horizontal lines as if printed by an inkjet printer running low on ink. An example is attached - all hatches should be smooth.

zone sections.pdf

I have experimented with some variables and found that it only happens when the layers containing these hatches have any value for transparency other than 0, regardless of whether they overlap.

I've tried copying just the lines and hatches shown in the attachment to a separate dwg and the result is the same.

Any ideas what I might be doing wrong?

My problem looks like the same one posted previously here: http://www.cadtutor.net/forum/showthread.php?12884-Problem-plotting-solid-hatches-to-pdf

The solution suggested there involved rasterizing the pdf, which I would prefer not to have to do. Also, in my case the lines were still there.

this may be a problem in your plot settings, as it always seems to be the problem for many cad printing issues. go to plot options and maybe highring the image quality or even lineweight selection could help out. all i know is that this is an issue with your plot settings. good luck man.

Thanks for the reply WRADKE. I tried changing the plot quality and several other properties, but the problem remained.

The solution that worked for me was the one advised against by every guide I found out there: I plotted it with CutePDF rather than DWG to PDF.

For the benefit of anyone who stumbles on this post, here are some things I learned about the problem:

The problem was caused by the way DWG to PDF represents hatches with complex boundaries. The complex boundaries are broken down so they can be drawn with hundreds of straight-edged triangles; this can be demonstrated by opening this pdf in Illustrator.

The scratchy lines were the result of aliasing of the edges between these triangles, causing tiny gaps or overlaps. This is why zooming in on the pdf makes the scratches appear smaller and why increasing the drawing quality only makes the scratches finer (more triangles).

CutePDF makes files that can be clunky and time consuming to render, but at least the solidity of transparent hatches is shown correctly.