aqueous coating problem

[Arshad]

well i will surely make a special coating for running non absorbent , which i already made once but failed, but will powdering it will solve my drying issue? and 35 mic will be too thick size? will I not get roughness on the printing after coating? pls advice,

 

[turbotom1052]

this is one of the many reasons why printing on these synthetic substrates is better suited for UV. Although 35 micron is pretty large and will make for a little roughness on the surface it will allow you to run a bit less powder, so its a kinda tradeoff. Be carefull untill you find the right combination of inks, coating, and powder. Run small lifts and air them out as soon as its safe to handle them. Gradually come down with your powder untill you notice slight offset and then turn it up a notch. Take notes of your settings and products as your working. Be sure to stick with the stock manufacturers recomendations for total ink density and know that your stock supplier is giving you something that dyne tests correctly with a recent corona treatment.

 

[3rd shift Bill]

Please talk to your coating supplier and find out what viscosity your coating should be kept at to run properly. This is measured with a Zahn cup and there are different sizes so your coating supplier will have to tell you what size to use. If your coating is to thick it will not dry properly and it will cause offsetting and it will cause your stock to drawup. We have 3- 40 inch Heidelbergs with coaters and we coat 80 percent of everything we run. We have been running coating for over 20 years and if we have a problem most of the time it has been the coating viscosity has been to thick. To measure the viscosity of the coating we use a Zahn cup [size 3] , you dip it into the coating barrel to fill it with coating and using a stopwatch you lift the cup up out of the coating and see how many seconds it take for the coating to drain out of the cup through the hole in the bottom. [ We use coating from INX and they recommend 18 seconds with a number 3 Zahn cup.] We check this at least once every shift on each press and everytime we open a new barrel of coating. As you circulate the coating through your system moisture [ water ] will evaporate from your coating and it will thicken up. When the coating is to thick we add small amounts of water to reduce the viscosity to what we want. Hope this helps.....

 

[Arshad]

i agree to what you said, viscosity is the killer, but i am confused regarding the layer of the coat, is it a "myth" , the more you release the coating the more shine you get or its the coating itself having the function of giving gloss or matte, suppose i use gloss varnish, if i release a minimum will it give the same amount of gloss compared to i use high gloss varnish? want to know whether the functionality changes by using specially high gloss .

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

More coating does not add more gloss. You need to use specific coatings for different applications. Think of the coating as a sealer that you apply. They manufacture and sell different types of coating. There are work and turn coatings designed to seal the sheet and provide quick turn around. There are high gloss coatings that will outshine work and turn. There are also matte or satin coatings that are used for different applications. They also have drip off coatings. See you coating reps and work with to arrive at a product that will work for you. You can try a test by sending coated printed sheets for a 2nd pass and recoating them to see if there is any difference. I always found that coating offset stocks was a waste of time unless it helped in the bindery operation.

 

[turbotom1052]

if its high gloss your after i think the best results will come from a high gloss sheet of paper. In my opinion its much easier to dull down a really glossy sheet of paper than it is to build gloss on a not so glossy sheet.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

I agree with the last post. Good quaility paper will produce the best results. I do recall a few years ago that there was a coating available that had what they described as optical brighteners. It could take a #3 low quality grade of white paper and enhance the paper and printed product after the coating was applied to make the job look better.

 

[Arshad]

i had tried high gloss with minimum coating layer, and it came out good. I think i am gaining confidence for coating the job and thanks to all of you guys...