Problem statement:

Customers usually describe the issue as “Ink marks on printouts” or “Ink smearing”.

These marks are not located everywhere, but at very distinct places on the printout. Depending on their location, we have identified two different problems that can create these marks.

As a summary:

It is very important to identify the problem very clear, because their work-arounds are different.

It is important that you thoroughly follow the qualification steps explained in this document in order to solve correctly the customer’s problem.

You will see that replacing any printer’s hardware part can not solve these problems. Let’s go problem by problem…

Problem description:

As we have already explained before, ink marks on printouts is caused by two different issues each with a different resolution:
Cause 1: Aerosol and Cause 2: Static. Let’s describe both problems:

Cause 1: Aerosol

Aerosol: Background

Through its normal operation the DesignJet 5000 printer fires drops of liquid ink from a printhead on to a media surface. As the ink is fired from the printhead, minute droplets of the ink often break away from the main drop. Because of their small size and weight, these droplets can form a fine mist inside the printer. The mist settles on the printer components and, after a while, visible ink deposits form inside the printer. The term we use to describe the mist is “aerosol”.

We have seen in the DesignJet 5X00 printers that the majority of the aerosol is attracted to where the airflow is strongest; this is at the lateral sides of the media at any given width and inside the linear blade. We have also seen aerosol build-up on the pinch-wheels and cutter.

Given that the DesignJet 5X00 series printer is a production speed printer and customer usage was expected to be at high volume; aerosol affects were an expected occurrence that customers would see. Because of this occurrence HP included cleaning and maintenance instructions with the printer. HP provided a clear message that the DesignJet 5X00 series printer is a production
printer that would have to be cleaned from time to time.

Aerosol ink accumulation will grow with time and usage. This accumulation is not a big problem if the usage of the customer allows the ink to dry. The issue is more severe under HEAVY USAGE (more than 30 high-density prints a day). This usage profile does not allow the ink on the platen (or other places) to dry and thus causes marks on the printouts.

Aerosol ink accumulation is a result of the printhead architecture and the way the printer manages it (the writing systems). DO NOT REPLACE any internal hardware component because of this issue.

Aerosol: What customers see.

1. Presence of marks on the backside of the media. This is the first manifestation of aerosol.

Remember that the media “drags” along the platen while printing. If there is aerosol ink accumulation on the platen, the backside of the media will collect some of that ink. The following figure shows the typical marks you can get:

2. Presence of marks on the front side of the media.

The following figure shows the typical marks on the front side of the printout due to aerosol:

So, as you have seen, we can have marks caused by the ink accumulation on:

   -The center platen (and overdrive).
   -The pinch-wheels.
   -The cutter wheel.

Our recommendation is to clean the printer once per roll.

Cause 2: Static

Static: Background

Over the past few years, HP has been improving image quality by using smaller and smaller drops of inks. Without this it would have been impossible to achieve a level of photo quality unmatched by any other printer in its class. For example, the DesignJet 5X00 fires 12 pl drops when using dye-based ink and 18 pl drops with the UV inks, compared to the 24 or 40 pl used in previous DesignJet printers.

However, reducing the size of the drops has made them more susceptible to:

   -Airflow and/or
   -Static charges.

Any of these two effects may force the ink drops to deviate from its trajectory causing them to position at the wrong place of the media.

The HP DesignJet 5X00 series is already optimized to minimize the static build up within the printer, i.e. the spindle is connected to ground, the print zone is made out of carbon filled plastic to make it conductive, there is an antistatic brush in front of the printer, etc.

Another of the measures we took to reduce the static charges was to place an anti-static back coating to the HP plastic media type. Without this backcoating, the media charges itself.

So, despite the printer antistatic features, we have discovered that the anti-static backcoating of the media is a MUST for the 5X00 Series in order to avoid the image quality and ink accumulation issues we will describe later on.

Which printers are affected by this?

-Customers who print on a 3rd party polyester-based film without anti-static back coating are more susceptible to static related issues. If they do not see any of the below mentioned symptoms, the media probably has an anti-static back coating, thus they are not affected.

-Printers are not affected if they print using:
   -HP media approved for HP DesignJet 5000 Series or
   -Any paper-based media.

-Customers use only photo-based media are probably not affected. Most photo-based media work fine. However, there are some photo-based media with a plastic back coating that is conducive to static-build up. These media could be affected too.

What can you see?

1. Presence of “shadows” on the printout.

See the following image to see an example. These “shadows” are particularly visible next to black areas or at the border of the print.

2. Presence of ink smears or even drops on the printout.

See the following image to see an example.

These marks are caused due by the fact that the static charge of the media forces the aerosol to accumulate at the edges of the printheads and at the bottom of the carriage.

When there is too much ink accumulated, it may:

   -Fall onto the media
   -Smear the media

Causing the problem.

See the following images:

3. Ink stains on the media after changing/reseating the printheads

See the following image to for an example.