Need help with printing issue

[Louiscamp]

I'm self taught on an AB Dick 9850. I have no one to mentor me and I've started having a problem I can't solve.

Trying to print large solid black letters, I'm getting a lot of white spots in the printing area, not a solid black color.

I've tried adjusting the pressure, adding more ink, broke down the whole machine and cleaned it. It may be solid for 10-150 pieces
then it starts the look again.

I'm using a new box of polyester plates (same type I've always used). Van son Rubber base black ink, Kompaq water.

I've attached a picture so you can see what I'm getting.

Any help?

Lou

 

[gordo]

It looks to me like over emulsification - the water proportion of the ink/water emulsion is too high and the emulsion is on the brink of reversal. There are many possible causes, too much water at start up, wrong or uncontrolled pH, dampening additives, etc.

 

[keith1]

Aside from what Gord has already suggested, and if you're certain all your pressures are good (rollers, cylinders), you should reduce the tack of the ink as much as possible. This will permit the ink to flow better. Small machines such as yours don't have enough rollers to carry enough ink to sustain an even solid over a large area. Reducing the tack will assist in carrying more ink smoothly through the roller train. Smoothly is the key word. This is why large presses have a lot of rollers – to better mill the ink before it hits the plate & paper. You'll know if you've thinned the ink too much because the plate will start toning in.
Depending on the length of your press run, you may also find it useful to manually skip feed the paper through the press. This gives the roller train an extra cycle to replenish enough ink between impressions. Obviously you wouldn't want to skip feed a 50,000 run. Hamada's (also small presses) came with a built in skip feed mechanism for this purpose.

 

[Louiscamp]

Thanks for your suggestions, will look into the water chemistry.

 

[Magnus59]

I agree it looks lik emulsification.
Running large solids on a small offset press using poly plates is something even a tradesman would find challenging
The ABdick has an integrated fountain, emulsification is a common issue with such presses
Rubber based inks don't perform well on large solid areas, they seem to be favoured by Itek & ABDick operators but I never liked using them.
I would suggest trying something like a Best One or Hartmans ink, make sure your fountain solution is the correct ratio, too much additive is as bad as too little, and a few drops of isopropanol in the fount may also help
Keep the water to a minimum and don't over-wet the plate before startup, the water or etch on the plate will travel straight into the ink train and start causing problems., you should have just enough water to avoid catch up, too much will emulsify your ink and once it's emulsified, there's no way to fix it apart from a full washup.

 

[gordo]

I agree it looks lik emulsification.
Running large solids on a small offset press using poly plates is something even a tradesman would find challenging
The ABdick has an integrated fountain, emulsification is a common issue with such presses
Rubber based inks don't perform well on large solid areas, they seem to be favoured by Itek & ABDick operators but I never liked using them.
I would suggest trying something like a Best One or Hartmans ink, make sure your fountain solution is the correct ratio, too much additive is as bad as too little, and a few drops of isopropanol in the fount may also help
Keep the water to a minimum and don't over-wet the plate before startup, the water or etch on the plate will travel straight into the ink train and start causing problems., you should have just enough water to avoid catch up, too much will emulsify your ink and once it's emulsified, there's no way to fix it apart from a full washup.

Just being picky about the terminology. Emulsification of ink and fountain solution is normal for the process. In fact it is a necessity for offset. The goal is to have a stable emulsion. Over emulsification, (proportionally too much fountain solution in the ink) on the other hand, creates an unstable emulsion. And that's a bad thing.

 

[turbotom1052]

the very fact that the image starts out good and then within 150 sheets goes bad most definitely point to an over emulsification problem. I would AVOID reducing the ink. Instead try to tighten up the nip on your water feed to reduce the amount of water entering the roller train. If tightening the nip does not help your problem then you need to think about a mechanical problem such as worn bearings, or bad rollers etc. Considering the level of experience you've mentioned Id say that if tightening the roller nip of water feed doesn't help you should probably call someone in. be sure to pick that persons brain about everything you have doubts about while they are there. Good luck.

 

[Louiscamp]

Well it turned out to be the rollers. Looks like the water was backing up somehow to the ink and causing it to break down. New rollers, now I'm good.

Thanks for all of the suggestions.

 

[Skyishere]

The rollers on them can be super finicky, absent if some of the precision adjustments on other machines. You may want to start over with the chemistry of the water system when you have down time anyway. We found using a different solution we got more control and less catastrophic issues.

We can run most things that can feed straight on our smaller ab dicks machines (similar to yours).

Feel free to message me to compare notes on chemistry.

We have run rubber base even on tyvek on the machine but prefer to use it for, small run letter stuff with pdi inks from Braden sutphin. And are running Millennium silver in our fountain.