Printing Blanket Test

[Petronella]

Hi all, we are planning to run a test on blankets from different suppliers.

Question is:

1. What kind of test form do we use for a blanket test?

2. What should we be looking for in the test form?

3. Are the differences significant enough for us to tell which ones are good?

Thanks for helping.

 

[jlind]

I worked on a project like this once, and here is what I learned:
1. Test form should have ladder targets, since they are good for showing mechanical movement
2. Be careful about torquing the blankets to the recommended tension, and roll them in and check the tension again, but I bet you know this
3. Big variable is the "interference" to test at, since each manufacturer gives a range of "interference."
4. Get a high power scope to examine dots and solids, preferably a digital camera on a microscope, (think send sheets to RIT maybe.) Then you can lay pictures out side by side and compare
5. Some blankets print a better dot than a solid, look for slurred or doubled dots
6. Out of about 10 blanket suppliers, there was a range of TVI for the same ink level, paper, and plate of about 5%
7. Now you have fewer blankets to test. The list should include the following manufacturers and whatever OEM's:
Contitech, DYC Kinyo, Meiji, Reeves/Trelleborg, Day/Flint Group
8. If you are really organized and have some clout with the press manufacturers, you can get their digital register analysis targets on the test form and they can measure and show movement over 10 or 100 sheet intervals, really dial in to the dynamics of each blanket

Have fun,
John Lind
Cranberry Township, PA
724-776-4718

 

[Petronella]

Hi John, thanks for your message. Will discuss this with the printing manager.

 

[billy gold coast]

gday i would also try on a light solid perhaps green have experienced pressure marks(look like rollermarks) from some blankets

 

[Petronella]

Tks. Will try to gather more info before conducting the test. Will add in the light solid.

 

[gordo]

[SNIP]
3. Big variable is the "interference" to test at, since each manufacturer gives a range of "interference."

John, could you explain this statement in more detail.

thx, gordo

 

[jlind]

Gordo:
Interference is pressure between plate and blanket. If the blanket is packed 0.005 inches over the bearers and the plate is flush with the bearers, there is 0.005 inch "interference" between the the plate and the blanket. The blanket manufacturers list a range of "interference" for a blanket, typically between 0.002 and 0.006. Where in that range should you be? At the lowest pressure, the dots will look good and the solids will be weak. At the upper range, the solids will be better, but the dots might be slurring. A press operator will over-pack at installation, knowing from experience that the blanket will "drop" or lose a certain amount of interference. The operator can always measure where he is at with a packing gauge, but the moral here is that it is always changing. When comparing different blankets from various suppliers, should they all be tested at the same "interference" or will the face compound or fabric construction or compressible layer have optimum performance at some other "interference?" It is difficult to objectively measure this point.

Then again, the dots and solids could look fine, but the blanket could pick and pile after a few thousand sheets.

John Lind
Cranberry Township, PA
724-776-4718

 

[Petronella]

Hi John, we recently had a meeting to finalize on issues before we proceed with the test. Interestingly, the printing manager is not sure with your point 2. He is asking what you mean by "roll in the blanket"? Are you saying that after mounting the blankets to the recommended tension, we should then take it off, roll the blanket as if it were new and mount the blankets again? After that, to check the tension again? We use a blanket tightener set at a certain torque so that we can get a consistent pressure.

As you said, each manufacturer gives a range of interference. We set ours to 0.005 inches regardless of brand which got us thinking what the optimum would be. The manufacturers will definitely not commit to one.

The printing manager wants to put 4 solid single patches of C,M,Y,K to check on the solids. What about the trapping? Do we need to test that too?

 

[arfamoe]

I think what is meant is that after you tension a blanket on the press you run some sheets on impression and then re-torque the blanket. The blanket will stretch slighty during printing and this needs to be taken up. If yo udont you can have problems such as miss-register at the tail, scumming and on a web press you can crack the plates.

 

[jlind]

Arfamoe is correct on the roll up thing.
As for the trapping, I'm not sure what effect the blanket will have on that relative to the ink set and paper characteristics. Solids are good, bigger the better, and large screens, say 30%. I realize that real estate is limited on a test form.
Think about this for a minute. When a new press is commissioned, one of the tests that consultants perform is a break away solid and printing of a uniform 30% screen. Turn this around and use a constant press to compare variable blankets. I would think that the ability to print a uniform screen, or an equally non-uniform screen, would be a good test of a blanket. It would show differences in blanket warp and weave tension and construction, not to mention buffing and grinding of the surface and uniformity of the compressible layer.

Think of the blanket as a printing roller with 10 thousandths of an inch of rubber on the surface. Amazing that it works as good as it does.

John Lind
Cranberry Township, PA
724-776-4718

 

[arfamoe]

I think you also have to consider what type of work and stock you will be printing on to select a blanket. Is it carton work on really crappy recycled board where you need to print in the hills and valleys of the stock, will you have to run excessive 'squeezes'(Interference) to print good solids. If your running good quality coated paper the blanket choice will probably be different.
my 0.02c

 

[Alois Senefelder]

re Blanket Test

re Blanket Test

Hello, fellow Lithographers and Smudgers of Ink on Paper !

Blanket Mounting, adopt a standard mounting procedure :-
1 Only pull up slack initially 2- Run the blanket cyl. in pressure for approx. 3mins stop and take up the slack 3- again run Blkt. Cyl. in pressure for 2 mins. and take up the slack "Again"


Regards, Alois

PS some PDFs that may be of interest ????

 

[Robilious]

So, JLIND, I believe that your term "interferance" is a newish term that I certainly didn't hear of before?! I thought you meant that the Blanket Sales Rep was "Interfering" with your Test?

I am suspecting that Gordo's inquiry was Voiced because in Gordo's (and My World of terminology) this is called "Squeeze"? No? You require about 4 thou to print, and build in about 1 thou of "insurance" for normal "sinking", so 5 thou "Squeeze" is great!

 

[janezl]

Alois, which book are your scans coming from?

Janez

 

[Alois Senefelder]

re Blanket Quality

re Blanket Quality

Janzl, the Pdfs are from "Roland News " Spring 1970




Regards, Alois