aqueous coating problem

[Arshad]

I am having sm74+L brand new machine on my floor , the trouble i am having is when i am running any thin stocks with aqueous gloss varnish running the ir on 50 and hotair on 60 which is maintaining 36 degree pile tempreture, which is auto in my machine, my printed sheet gets waivy on the second pass , when i run the job single side, it seems to be ok and when i work and turn the job the sheets gets waivy and give set off problems on certain waivy areas, we are having double roller coater unit not the anilox. please advice,

 

[richck]

Personally i would say 36c is too hot, we never run ours above 32c and never have any problems.
We always reduce the heat on the second pass as well.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

If you have a Drystar dryer and run on Automatic settings try and lower the IR output to 15% and set the hot air at 65-70%. If you run the first side at 36 degrees and the lower it on the second side by 4 degrees. Body temperature is 37 degrees Celcius . Refer to the Drystar manual to get recommended settings for heat output and printing speed. You also mentioned that you have a 2 roll system. The settings tend to default to 25% coating applicationon your ink seeting values. Try to start at 15% and get the minimum amount of coating to seal the printed work. I found that more AQ did not add more Gloss but could distort the paper. If you run too hot there is a chance of reactivating the printed side creating more problems and possible blocking. Is the preheating function turned on? In my previous experience I found a few presses with the pre-heat of,f and on a short run the Dryer would not reach optimum temp before the job was finished. If you need more help with the problem consult with Heidelberg service. You mentioned that the press was new.

 

[Arshad]

Thank you very much for the reply, well i tried today running at the suggestion you gave, pile tempreture was maintained at 34 on single pass and 30 on backside, but i have a question to ask whether i should maintain the pile temperature on auto or manually set the ir and hotair , if it is auto and ir and hotair are setted automatically ,
regards
arshad.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

The sensor in the delivery is measuring the temperature in the delivery and not what is in the pile. You might want to get a probe thermometer to measure the pile temperature. The hot air will promote the drying of the coating. Generally if you set the values of IR at 15% and hot air at 65 -70% you can run on automatic and change the temperature. Higher for the first si and lower for the second side. See what happens when you move the temp up by a few degrees running in automatic. It is also possible to run in manual mode and control the heat output via potentiometer on the delivery console. If you get good results running manually then input those numbers into automatic mode and compare the results. Press room temperature is also a factor, I recall a customer in a plant with no AC trying to try dry coating at 36 degrees Celcius on a summer day. The pressroom temperature was pushing 40 degrees Celcius with high humidity. Needless to say drying he sheets became a real problem.

 

[trever9]

Use fast dry coating

Use fast dry coating

I would try using a low curl fast dry coating. Prisco has a good one. Don't run a real glossy coating. The higher the gloss the wetter and wavier the stocks will be on lightweight paper.
Run pile temp around 85 degrees. Be sure your humidity isn't to high in pressroom.

 

[Arshad]

well, would definately try using prisco, but the problem is quite unusual according to me, because the first pass doesnt create any problem at all i am taking out the pile of 1000 sheets with 60% ink coverage on the whole sheet, but the problem is when i take the back side of that particular job for coating , set off comes especially where the paper is waivy and has lost its strength. within minits i can the pile has started getting waivy and i can see lot of set off in the bottom sheets. please advice, i am using 40 ir and 70 hot air ,

 

[Arshad]

problem is quite unusual according to me, because the first pass doesnt create any problem at all i am taking out the pile of 1000 sheets with 60% ink coverage on the whole sheet, but the problem is when i take the back side of that particular job for coating , set off comes especially where the paper is waivy and has lost its strength. within minits i can see the pile has started getting waivy and i can see lot of set off in the bottom sheets. please advice, i am using 40 ir and 70 hot air , or mainting the pile temp at 34 and back side on 32, i am tried various settings but all in vain, I even added I.P.A in the coating to get the drying faster , i had reduced the squeeze pressure on the back side , but no success, .

 

[turbotom1052]

sounds like your rewetting the coating on the first side. I would suggest getting pile tempetures adjusted to manually measure (in the printed load) no more than 98F. The best way to arrive at that is with more hot air knife and less infared heat. Its the hot air drying that helps to evacuate the moisture from the aqueos coating. Then when backing up the job id suggest no more than 90 to 92F. arrived at in the same manner. this 5 to 6 degree drop in temp on the backup combined with the evacuation of moisture via the hot air knives should reult in no rewetting of the coating on the 1st side. Of course the assumption here is that your using a good quality coating thats flowing correctly and that your delivering the sheet smoothly with not too much fan speed and minimal blower bar air pressure. I usually try to control my delivery with mostly my release cam and my slow down wheels as opposed to running a bunch of air!!! at times you must run the fans up a little higher to deliver but i try to keep them at lowest possible settings.

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

All responses to your problem so far have been well thought out by all the responding parties. Sounds like you have a real problem that is on going. You said that your machine is new so get a Heidelberg Instructor back in to see what is going on. I am going to offer one more suggestion but it is labor intensive and you may not like it. To eliminate the possiblility of poor quality paper and other elements and in order to save your printed jobs. Print the first side with ink on paper only and no coating and minimum heat. Print the second side with the coating unit on. Then send the 1st side back through and coat only. Monitor the results. I stress that this is a Bandaid solution but it is worth a try. I also stress again that you bring Heldelberg if possible (I do not know you are located) back and get their input on your problem. Sometimes another pair of eyes can identify the problem sooner than later.

 

[TheProcessIStheproduct]

cheap coating

cheap coating

I have had similar problem, all settings are the same as always everything seems to be operating properly, someone told me that to hold price some major manufactures are changing formula to cut down on raw materials, I tend to agree because I tried another brand and problem was fixed overnight...

 

[Arshad]

thanks let me try

 

[Arshad]

well well, finally i have started understanding the concept of coating though it took me a hell lot of time and money, due to waste of printed sheets set off problem, but cliche works on it , you have to pay to learn,. ... my standard delivery is a issue to me, as it takes a second or two less to dry the sheet from hotair, But i have succeeded a little by not running pile temp on auto, my ir runs on 15 and hot air on 40. it is acutally avoiding the rewetting of coating on the backside of the job when i do work and turn, but still have a little blocking, like i can say out of 14 different jobs i had a problem in 2 jobs. i think its absolutely HIT AND RUN case. pure trial and error, if you have any more suggestions , please do let me know.

 

[turbotom1052]

tell us a bit about your powdering? is it working up to snuff? If youve heard that no powder is required when aqueous coating, consider it a myth. A reduction of powder is ok but you will need some. Id suggest a minimum powder size of 25 microns for commercial work. When backing up a job are you showing an even dusting of powder on the first blanket? you should turn off any sheet cleaner you may have when backing up a few jobs and look to see if your showing a light dusting of powder on the first blanket after running about 2000 to 3000 sheets. If you see no powder after about 3000 sheets you may want to consider turning it up a bit. You may also want to check the pile temp. with a thermometer in the delivery load to verify the drystar settings!!! Also try and do your very best to avoid wedges in the load in the areas of heavy ink coverage. Try and deliver sheets smoothly, with minimal fans and air blowdown. Between your gripper release cam and sheet brake try and stretch the sheet out to drop the sheet in the pile with as little air, and as smoothly as possible. You mention having to "pay to learn". This can be done in one of 2 ways. You can pay the price of ruined jobs and lost good will with your customers, or you can pay the money up front by hiring and paying experienced help to run your multi million dollar investment. Dont believe the press manufacturers hype when they tell you that these new presses can run with crews lacking in experience!!!

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

Glad to see that you are making progress. Here are some other tips you can consider. They do manufacture Work and Turn type coatings designed for short run work. Also if if have the floor help or capabilities in your shop try this. Run the first side of a work and turn or a sheetwise form and about 10 minutes after the 2nd side is printed get someone to air up and repile the job. The introduction of more air while repiling the job will promote really good drying of the sheet and prevent blocking or making a brick. It was explained to me that coating will cure hard after 24hrs. It may seem alright and feel dry to the touch but when you re-activate it the blocking problem can occur when the 2 sides cure together. Do some tests to satisfy your self. Leave a pileuntouched that is completed after coating both sides and try one that was re-piled. Hope this helps, unfortunately sometimes there are no light -switch answers to a problem.

 

[Arshad]

will surely try it and give you a feedback..

 

[Arshad]

hay guys,, today i had a very nice day , thanks to you all, cuz there was no night mare called "set off " at my press, finally succeding on all the jobs with work and turn with courage, well the offset line is been said as off-set. first it gets off and then gets set . well one thing for sure its a very deep line and always comes with new ideas and thought and suggestions. I am now going to try to run PP sheets ie plastic sheets of 300 microns on the press, intially when i ran it , it was a fail effort, but now since i am all guns loaded with courage i will try again, since my fellow printer is printing on a ryobi 4 with coater, he is not finding any problem of sheets getting dried but as i m having standard delivery it will be a trojan war for me. will surely need some suggestion by you guys,

thanks again...

 

[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

Congratulations. Just curious as to what finally worked out the best for you in achieving good results. Perhaps you could share your findings with the forum so that other printers with similar problems can also find solutions. Knowledge is great but it should not be exclusive. Once again Congratulations.

 

[turbotom1052]

id strongly suggest using a special coating if your going to be printing on any synthetic non porous substrate like plastic. you want a coating for non porous surfaces. also it wouldnt hurt if you were to up the size of your powder to a 35 micron size. fully oxidizing inks are also in order. this issue has been adressed on this forum and there are tips available to do this safely!!!

 

[Arshad]

Congratulations. Just curious as to what finally worked out the best for you in achieving good results. Perhaps you could share your findings with the forum so that other printers with similar problems can also find solutions. Knowledge is great but it should not be exclusive. Once again Congratulations.

well surely would share the findings... it was very logical , too much heat is no good for coating, it just needs a midas touch of hot air to clear the trouble, i just maintained the pile temp of 32 degree on the first side and 29 degree on back side with with manual settings ie ir on 10 or 15 and 45 on hot air, I dint touch the pile for atleast 15 mins , i allowed it to settle for a while. it worked..

thanks all.