Gapless vs. conventional advantages?

[gufs_place]

Hi,

im trying to get a better understanding of offset printing technology but currently struggle to find a "nice" explanation of gapless vs. conventional printing ( a topic I heard in an interview that unfortunately didnt go into detail - the Goss Sunday was mentioned as an example) and hope you can let me know if my current understanding is correct or point me to useful resources:

So far I have gathered that usually blankets are put around the cylinders - the fact that they have to be attached in a cylinder gap means there are vibrations as the cylinder weight is not perfectly distributed. gapless doesnt have this problem as a kind of rubber sleeve is put over the cylinder. is this correct so far? also is this essentially the same as what is meant by "seamless" on some sites?

The issue I don't understand is that apparently the gap using the conventional way is only 0.2 inches or so. as the paper needs to be cut anyway between the different printed pages, are those gaps made by the conventional system really that much of an issue? or is the problem that its not possible to create "endless" images such as christmas wrapping paper?


many thanks in advance
Clemens
I have another questions about how paper type affects machine built but i guess that should go in a different post

 

[Deleted member 16349]

Hi,
the Goss Sunday was mentioned as an example)
So far I have gathered that usually blankets are put around the cylinders - the fact that they have to be attached in a cylinder gap means there are vibrations as the cylinder weight is not perfectly distributed. gapless doesnt have this problem as a kind of rubber sleeve is put over the cylinder.

The issue I don't understand is that apparently the gap using the conventional way is only 0.2 inches or so. as the paper needs to be cut anyway between the different printed pages, are those gaps made by the conventional system really that much of an issue? or is the problem that its not possible to create "endless" images such as christmas wrapping paper?

The vibration is not caused by an out of balance cylinder but the pounding of the gap at high speed. Almost like a speed bump but not quite. Maybe a pothole.

I believe that on the Goss Sunday press, the blanket is bonded to a steel tube which goes on the blanket cylinder by having air applied to the blanket cylinder shaft and this air then expands the tube as it is pushed onto the shaft. Shut the air off and the tube shrinks and fixes itself to the shaft. This type of technology has been used on gravure presses for over twenty five years.

The print can not be continuous like wall paper because there is the gap in the plate cylinder. Although I know of a company that developed a method, on an offset press, to print in the gap area of the print on the web of the paper to make it look continuous.

Having a small gap is not such a problem especially for commercial printers but for applications such as wallpaper or labels or other packaging, being able to print continuously has an advantage. There is a paper saving advantage by printing something like round labels in a staggered arrangement. This can not be done if there is a gap in the print as there is with offset. It can be done with flexo and gravure presses and that is one reason they are used for packaging printing.

 

[rich apollo]

We have webs here with 42" cylinders. At the lead and tail there is .375" of non-printing area. So, every impression loses .75". If I run 1 million impressions, I end up with 750,000 inches of unprintable area. That's 62,500 feet of paper or the equivalent of 17,857 impressions that I cannot print on. Narrow down that gap and I can print more image per linear measure of paper.

Secondly, the gapless presses are rated at unbelievable speeds. The Goss Sunday 3000 is rated up to 100,000 impressions per hour!

Take a look at the patent information here: Offset lithographic printing press including a gapless tubular printing blanket - Patent 5440981. Go just over halfway down to the Description.

 

[gufs_place]

Thank you Rich and Erik,

makes a lot more sense now!

 

[dancingfox]

Good point rich, the paper savings alone is why we purchase gapless technology.
Now were to the point where we can put Flint / Day Interantional Sleeves on Man Roland presses and Reeves / Trelleborg technology on Goss Presses.

 

[gufs_place]

just one follow-up question on the paper-savings -
i see how a gapless blanket would reduce waste but wont there always be a gap on the plate cylinder? (hence still waste?)
or are there gapless plates too?

 

[rich apollo]

The plates are essentially gapless on our presses.

 

[dancingfox]

Clemens: I think you may be referring to two different styles. I'd refer to them as blankets and sleeves.
Sleeves are steel, nickel, or fiberglass based tube that enters the manufacturing process to be converted with rubber. As rich said, the sleeve goes over the cylindar with compressed air that expandes the tube, then secures the sleeve onto the cylindar.

Their are many more sources for blankets than their is for sleeves.

 

[Internal_R&D_Analyst]

Goss had a patent on blanket sleeve technology. They settled a lawsuit against man roland in August of this year.

BOLINGBROOK, IL–Goss International and manroland resolved their U.S. patent infringement litigation Tuesday involving web offset press sleeve blanket technology. The terms of the agreement are confidential. Both parties acknowledged that the resolution was in the best interest of their companies and customers, allowing them to offer their full press portfolios to the worldwide marketplace.

The patent litigation was initiated in 2003 and alleged that the manroland Rotoman S press infringed three U.S. patents held by Goss International for sleeve blanket technology used in its Sunday web offset gapless press models.