L25500 print quality issues

[TVsigns]

Hi everyone.
Hoping you can help. We have an HP L25500 using SAI Production Manager 10.5.1 as the RIP. When printing large blocks of dark colour, black dark blue especially, we get horizontal banding the print. WE have changed the print heads and run print head alignment. What's likely to be causing the banding and how do we prevent it?

I have attached a couple of photos

Thanks in advance

 

[tollerdad]

Did you do alignment on that specific material? Also check for fuzz on carriage. Run test plots too. We had a new black/yellow head that was bad out of the box.

 

[P Wagner]

Unfortunately, the images that you attached are not very helpful in helping diagnose the issue.

The place to start (always) with horizontal banding (in the carriage scan direction) is with the Test Print. This is accessed from the front panel, Ink Menu > Image Quality Maintenance > Clean Printheads > Test Print.

This test print will show the nozzle performance for each of the 12,672 nozzles in the printer, across all six printheads. While it is normal for there to be a fairly small number of nozzles that are not firing in this test print, if there are large blank areas in the pattern, that would be indicative that the head will need remedial measures (cleaning) to get regain it's functionality. The HP Latex machines include 'reserve nozzles' to replace primary nozzles to preserve print quality, and the printer will automatically asses nozzle performance at the start of each print job and map nozzles for that job. Because of these intelligent systems that are built into the printer (including the OMAS system), banding is typically seen only when large numbers of nozzles are non functional.

In cases where large numbers of nozzles are out, cleanings should then be performed (from the same menu), but only for the affected heads and colors. After the cleaning, run the Test Print again to determine the effectiveness of the cleaning procedure. Cleanings take about 1-2 minutes to complete.

If nozzles are dropping out midway through a job, there are additional settings that can be invoked from the Image Quality Maintenance Menu, including instituting an Inter-Pass Delay of a fraction of a second. This function has proven to be very effective in many cases.

 

[TVsigns]

more information

Thanks for your replies; it is much appreciated

A little more information - we do run test prints at the end/beginning of the job, at which point we change the printhead for a new HP one, and/or do a print alignment. The issue only seems to occur when printing almost solid blocks of dark colours, never on lighter colours. It will start at some point during the print and often correct itself before the print is finished. However, a 2 metre long print with a band of striping in the middle is useless as a wall graphic, so we have to print it again. Once we carry out the test prints and head clean we print the same file again and sometimes it print perfectly, sometimes it doesn't. Frustratingly this means we use approx 3 times more vinyl than we should have just to get a complete, quality job.

Could you explain a little more about the inter pass delay - we haven't tried that

Many, many thanks

 

[eahicks]

You didn't mention what Pass you print these on. Lower pass (like under 8) will always create banding I have found. When I need solid-solid, I use 10 pass. With a correct profile I have seen no evidence of banding, in solid blues, blacks, reds, etc...

 

[P Wagner]

Thanks for your replies; it is much appreciated

A little more information - we do run test prints at the end/beginning of the job, at which point we change the printhead for a new HP one, and/or do a print alignment. The issue only seems to occur when printing almost solid blocks of dark colours, never on lighter colours. It will start at some point during the print and often correct itself before the print is finished. However, a 2 metre long print with a band of striping in the middle is useless as a wall graphic, so we have to print it again. Once we carry out the test prints and head clean we print the same file again and sometimes it print perfectly, sometimes it doesn't. Frustratingly this means we use approx 3 times more vinyl than we should have just to get a complete, quality job.

Could you explain a little more about the inter pass delay - we haven't tried that

Many, many thanks

First, make sure that you are up-to-date on your machine's firmware. As of today, that is fw 7.0.0.4 which was released in May 2014. This firmware includes a function called an Inter-Pass Delay Offset which will cause a slight pause in between each print pass. This can be beneficial for several reasons, including helping to regulate the temperature of the printhead, which is good for nozzle performance.

You access this through the machine's Control Panel > Ink Menu > Image Quality Maintenance > Inter-Pass Delay Offset > [enter a value]. I would suggest around 0.3 second to start.

Another thing that I would suggest for this issue, is to enable 'print gutters' in your RIP. (This is sometimes called Color Bars). It ensures that you are exercising each printhead on each pass, and can result in more stable printhead nozzle performance on long print runs.

Finally, I would recommend printing SAV using a 10-pass or higher print mode on the L25. Pass counts below this are not recommended for SAV media on that model.

 

[TVsigns]

That seems to have solved it

Thanks for all the replies and suggestions. We are using 12 passes Uni directional which we have used on all SAV.

Changing the inter pass delay as suggested to 0.3 seems to have made a difference. We are also going to get the colour bars to print at the side of the print - currently the RIP only seems to be put them at the top of bottom of the print which doesn't help much. I'm sure it's just a case of figuring it out in the RIP software.

Have great day!

 

[Bly]

Another thing to check if you've tried everything else, and it sounds like you have.
Turn the printer off when the carriage is off the dock.
Take out the PH cleaning kit and drag the carriage over so you can check under the heads.
We once had a similar issue and found a strip of backing paper caught under there was hanging down enough to cause banding like yours.
You should be easily able to print 10 pass bidirectional with no banding all day with one of those printers.

 

[P Wagner]

Thanks for all the replies and suggestions. We are using 12 passes Uni directional which we have used on all SAV.

Changing the inter pass delay as suggested to 0.3 seems to have made a difference. We are also going to get the colour bars to print at the side of the print - currently the RIP only seems to be put them at the top of bottom of the print which doesn't help much. I'm sure it's just a case of figuring it out in the RIP software.

Have great day!

I am pleased to be able to help. By the way, printing in uni-directional (as opposed to bi-directional) will reduce throughput significantly. The HP Latex printers do not tend to exhibit any noticeable chromatic banding artifacts when printing bi-directionally on most common medias, so you might give that a shot after figuring out where to enable color bands/ gutters in the SAi RIP. You should be able to run at 10-pass or higher bi-directional on SAV without issues.