Sheets sticking together when using coating

Hi
I run an xl-75 and I'm using the coating unit for a job and the sheets are sticking together because of the coating buildup at edge of shape. It is not a dryer issue, our dryer is cranked up. For more info on where the buildup happens I've done a small illustration to show you what I mean. [link to image]


Would the solution I have in mind as outlined in the illustration work out to prevent sheets sticking together?


thanks for any insights!

 

Move the coating blanket packing in the opposite direction a small amount.

 

I suggest the following:
- Check the thickness of your blanket underlays according to the manual.
- Reduce the pressure between the anilox roller and the blanket as much as you can.
- Try not to increase the pressure between the blanket and the sheet more than the desired default.
Please send us your feed back.
Good luck.

 

thats interesting, why would moving the packing make a difference?

the stripes are all set at what we want at 4mm.

 

First off I would suggest that you not "crank" the dryer unit. Temperature control is critical, especially when coating!!! When coating on the first side of a sheet, you should be looking at pile tempetures between 100f and 105f as measured with an infrared thermometer on the top of the pile. When backing up you should lower your temps to around 95f, so as not to re wet the coating on the first side. My preference is to arrive at these pile tempetures with most of the heat coming from your hot air knives, as opposed to your infrared bulbs. I like 75% of the heat coming from the hot air knives and 25% of the heat coming from infrared bulbs. As far as a hard coating line buildup... If you know that all your pressures are set correctly, I would suggest you try staggering your packing under the coating blanket if doing an overall coating. if your spot coating then it would be about pressures. If its a roller coater, you may want to check your clutches on the coater rollers. If clutches are slipping it can cause the problem you describe.

 

Check the quality of the blancket; it must be soft, otherwise change the blanket
- check the dressing of the blanket, it must be within the standards according to the depth of the cylinder hollow
- tighten the blanket with a dynamometric wrench so that it is well clamped and within the standards
- check the jaws of the blanket cylinder and check if the blanket slips at the time of production
Please note: it is better to work with blankets with bars to avoid the problem of the blanket slipping in case the jaws are worn
Good luck and let me know

 

Just took a look at the image you posted and I would ask if the buildup is at the lead or the tail of the blanket??? If I were to assume its the lead edge, and also assume that its a anilox coating unit, I would double down on it being pressure between anilox roller and blanket. It could be pressure between the roller and blanket because of the blanket being overpacked, or because of the roller setting being too tight. this of course assumes that your anilox roller is of the right cell count, and that your blade is metering correctly.

 

Check the viscosity of the coating
Zahn # 3 cup 18 to 20 seconds or # 4 cup 25 seconds

 

Please if you have not solved the problem yet, send another image to know is the overflow is at the end of printing or in the lateral sides.

 

May I add also something: check if maybe the wrench in the metering roller is worn out. To do so turn the roller by hand in the direction that it moves and than push it back fast- the roller should not move more than ca. 10mm backwords in best case it should stop immediatly. Try to check this at leats some 10 times...