Quality Checking Process for 5 Colour Offset Printing

Hi all,
Can anyone please guide me on what standard procedure to follow during offset printing process to ensure that printing quality is always maintained at its best possible by reducing dependency on the Machine Operator's personal visual judgement.
We are planning to invest on a 5 Colour Sheet Fed Offset - 28" x 40" and our major jobs are 300 GSM Board for Carton Boxes.

Regards,
Aditya Jain,
Matrix Prints

 

closed loop inking!!!!

 

Hi. Thanks for responding.

Can I please know in detail as to what do you mean by closed loop inking ?

 

a real must in the modern printing proccess:
you get a file that is generated by the plate making system , feed it to the press , and the press will start printing with the right aount of ink on the rollers - that amount is the one that if maintained over the job will give you the nominal density for the jon on your sheets , all the same , and as close as possible - again , printing is never ablsolute.

Then , an online scanner to scan the sheet , and software to correct the press ink keys on line and on the fly , so no need to stop the press as long as you scan and correct , scan and correct all kthe time - Automatically.

Not very easy to find on a 1990-95 press but you may get a working system on a 1998 & up Komori 40@ for a reasonable price.
Do considder that you must keep your press , rollers . water system and so on in good known condition and consistant at all times for the system to give you a good result.

Good luck

 

Thanks Meny.
But what system can I keep in place other than this Closed Loop Inking as it goes way out of my budget.
Is there any other way like a software which determines the ink levels from my artwork and then I copy the same ink levels to feed it in my offset through my CPC Unit ?

 

Well , you can start with a software package that will give you the right blade opening for the press as a printed chart / file and you feed it in.
then all you need to do is go up/down in total , but keep the rate between the keys at no change.

A hand held densitometer will be helpfull to get to nominal density.

With the 2 above you can start way better then without them , but still a long way to go for perfection.
This solution should cost you about 3000-4000 Euro Max , but you wil need to train your operator as wel as get the press in good shape and when i say good - it is relative....
In most cases what is called good in India is called low quality in the western world. i mean good in western world eyes , or the 3-4000 Euro you spend will be a waste.

If you need help you can call me or email any time

 

Besides what mentioned by Meny and Turbotom, your press should be in optimum condition. Good rollers, Blankets, plates and chemistry. A skilled pressman. Otherwise this closed loop color control would be a waste of money.

 

on te other hand , if you do keep your press in top condition and do use quality controll , you will KNOW what you get out of the press on each job , you jet the right result on the paper and all sheets the same , and you do much more good work in less time , so it is worth yhe money...
I can help you with the setup , and you can buy the densitometer on line to save

 

Thanks Meny.
Can I get a few names of the softwares which can be reliable to help in setting ink levels in my CPC Unit. I can take note down the levels and enter it into my CPC Unit manually.

And yes, I ll also be interested in buying a densitometer which I believe is placed on different random positions of the printed sheet to check the consistency. I shall learn more about usage of densitometer before buying it.

 

Software - depending on the press you buy , but available for 95% of models and file formats - first tell me what press you buy and then i can recomend the SW
Densitometer - yes you can try on the sheet , but it is not the right way - you should have a color bar suitable for your jobs & proccess , and that is where you check ,
If you buy a good one , you can check many parameters
if you buy a basic one , then it is only density.

 

We will mostly go for Mitsubishi or Komori - 1990-1995 Model.
Here in India we use Corel Draw software to get the design and set the no. of ups before it is transferred to the plate exposing software.

Densitometer - I had a belief that the colour strip would stay the same for each and every job. Once the printing is OK, the density of the colour bar is noted and then frequently matched during the printing run with the Density noted down. Is that so ? Please correct me if I am wrong that the colour strip stays the same for all the jobs.

 

sorry , wrong again.
if you print a 4 color job you use one bar , if you print 5 color job you use another , and if you print duatones or solids....
the color bar as a tool that if & when used smartlly , can be very good. it is much more then some extra ink on paper...

 

I am mostly looking for Mitsubishi or Komori depending on the machine condition.
We use Corel Draw software to set the ups of the carton boxes.
I believe that there is nothing in corel draw or Adobe designing softwares that let you find out the ink levels which can be copied and manually feeded in the CPC unit. If there is any such thing then it would be of a great help if you can let me know.
Thanks.

 

I am mostly looking for Mitsubishi or Komori depending on the machine condition.
We use Corel Draw software to set the ups of the carton boxes.
I believe that there is nothing in corel draw or Adobe designing softwares that let you find out the ink levels which can be copied and manually feeded in the CPC unit. If there is any such thing then it would be of a great help if you can let me know.
Thanks.

 

I am mostly looking for Mitsubishi or Komori depending on the machine condition.
We use Corel Draw software to set the ups of the carton boxes.
I believe that there is nothing in corel draw or Adobe designing softwares that let you find out the ink levels which can be copied and manually feeded in the CPC unit. If there is any such thing then it would be of a great help if you can let me know.
Thanks.

 

Mitsu & Komori

Both presses deliver good quality and both are on the cheap side of the market.
But while you can get any part for a komori , when ever needed , it is becomming hard to get some parts for Mitsubishi presses , and the older they are the bigger the problem.
So cheap can become expensive at times....

 

Start with a good 'Color Bar' that has solids, 50% - 75% patches and a Grey patch of 50C-40M-40Y - next to a 50% Black (for visual reference).
Now you can measure Solid Ink Density - Midtown dot gain - Print Contrast - Grey Balance! Color comes from 2 places - Density - Dot again.
A great trick is to measure the grey patch with the densitometer set for ALL filters. When the SID is correct the Grey patch should measure the C-M-Y filters the same (within .03 of each other) - THUS Grey Balance! The "V" number is near .60 Density when printed correctly. If your at correct Density and the Grey Patch is off - Pre-press needs to make a new curve for press.

 

What you are looking for is referred to as CIP data. CIP data is an algorithm generated in pre press. The thing about CIP data is that is not based on an individual piece, or page of artwork. The algorithm needs to be generated from the entire form, as it layed out to print on press. The most accurate of this CIP data is usually refined through a trial process, that makes small improvements over numerous press runs. This fine tuning requires commitment to getting it just right, and some up front cost in the form of labor and materials. It would also be advisable to do this while pre press and the press are being brought into sync. It should be noted that even the most accurate CIP data will not get you all the way to perfect color. At best it will offer you a starting point. To consider this technology a replacement for a fully competent press operator would be foolish!!!
I would also add that the process of fingerprinting and getting accurate data is beyond the scope of many pressroom employees. You would serve yourself well to turn to your pre press suppliers for technical expertise, where they would send in a tech rep to spend a couple of days. This is not a process that your prepress guy can be walked through over the telephone, unless he is well versed in the process along with ALL the equipment.

 

Perhaps your RIP software has a way of calculating ink zones/feed. Else you might try Excourse presspercent combined with a mac.
Steps i would do in my humble opinion:

1. Buy a decent densitometer -unless you want to spend a few more money and get a spectrodensitometer-. By decent i mean at least to measure densities,dot gain/dot area, trap

2. Put on every job -as long as there is room in the sheet- color bars. I think this is a MUST to check up your densities and print as correctly as you can. Even if you dont buy densitometer/spectro you can compare with the proccess colors of your Pantone book. Also your color bars should include patches of each process color CMYK, one tint of CMYK 75% 50% 25% along with grey balance patch -as Dan mentioned-.
So if you put a 50% patch of K next to a grey balance 50% consisting of 50-40-40 CMY tints -same for 75%/25% with their respective tints- you have a quick way to inspect your sheet that you print neutral or biased towards a certain color.

3. Check your press thoroughly and constantly! Mechanical components -grippers, rollers, bearers, cams- as well as electronic to ensure you have a stable machine. I mean all of this talk is meaningless if your registration is slipping or your rollers are worn that far off when you do the makeready of a job and start production your ink feed goes haywire and pressman must chase the devil away.

4. Fingerprint press -this requires densitometer- and measure how press reacts towards 3 kinds of paper -though you will use it mainly for cardboard- gloss-satin-uncoated.

 

Here is a way to develop plate curves for the press. The pre-press rip must have 4 channels Y-M-C-K. Email me for more information.
danremaley@comcast.net 412.889.7643 Cell