In our cold foil best practice blog series, we discuss best practice for successful wet lamination cold foil printing. Previously, we discussed proper press set up to ensure successful cold foil printing, from the start in our part 1 blog: Proper Press Set Up for Successful Cold Foil Printing.
Now that we’ve discussed how to set up the press properly, it’s time to prepare for the print job at hand. In part 2 of this series, we dive into considerations for choosing the right consumables, press cleaning, and other need-to-know for successful press preparation and print production. Here are some things to consider when preparing your press for successful cold foil printing.
Choosing the adhesive
In the wet lamination process, the adhesive must cure while it’s laminated to the foil. This requirement results in some limitations. Halftone and screenwork have a tendency to fill in during the wet lamination process. For absorbent substrates, more adhesive laydown is required to compensate for the soak in.
K Laser Cold Foil Business Unit currently has two UV Curable adhesives for wet lamination: foilKURE 5596 for use with conventional UV dryer and foilKURE 5600 for use with LED UV dryers. Each adhesive has been fully tested to work with KOLDfoil ONE products and has passed the industry-standard tape test; top coating or lamination is not required. Remember that adhesive formulations are different depending on the manufacturer you are purchasing from and may not be compatible with the foil that you are using. It is best practice to procure your cold foils and cold foil adhesives from the same supplier.
Choosing the foil
When choosing a cold foil, remember that although the basic construction of the different foils is the same, each foil manufacturer has their own proprietary manufacturing techniques and components. The K Laser Cold Foil Business Unit has tested samples from all major foil manufacturers and found that each behaved differently depending on the printing job. Each foil has its own properties regarding release, porosity, adhesion, and printability. You must take these factors into consideration when choosing the right foil for a specific job.
There is no single foil construction that can be used for all types of cold foil printing. We recommend requesting a free sample from your cold foil manufacturer to test within your print process. K Laser would be happy to send you a free cold foil product sample, along with a sample of our compatible foilKURE adhesive, to test on your applications before purchasing. (Click here to request a quote)
Choosing the anilox and plates
To choose the right anilox, start with 300 line, 5 bcm. The logic line count is the same as when printing UV inks. Fine detail requires a higher line count while large block areas need lower line counts. For uncoated paper stock, use a lower line count to compensate for absorption. We recommend the use of a doctor blade to maintain a consistent and even distribution of the adhesive.
In regard to photopolymer plates, cold foil printing does not require a special plate for cold foil - you may use a standard .067 or .045 plate. Standard sticky-back tapes and print cylinders are also required, although better results have been reported when using harder sticky backs.
Cleaning the print station
foilKURE is a free radical adhesive. Although this type of adhesive is compatible with water based and solvent based inks, the print station must be cleaned thoroughly to avoid adhesive contamination. If you used the print station with a water or solvent-based ink, wash the station with vinegar before starting cold foil printing. If dried ink is in the anilox cells, clean them with Xylene and then dry with acetone. Make sure that the solvents have sufficiently evaporated before you pour the adhesive.
Setting the foil unwind and rewind
Set the foil unwind tension to medium high, about 20 psi, and set the foil rewind tension to low, just enough to remove the slack. A higher rewind tension makes the foil transfer faster than the substrate and results in rough edges and a smeared foil image.
Keep in mind that each roll of KOLDfoil will have a different wind tension. You will need to reset the tension controls when changing from roll to roll.
Setting the UV dryer
The UV dryer should be inspected before you run a job. Remove the UV lamp housing and inspect the reflectors and UV curing lamps, looking for any marks or contamination. A contaminated reflector or UV curing lamp can easily reduce its curing power by 40 to 50 percent.
A printer’s maximum running speed is dependent on the UV dryer’s curing performance. When running a cold foil job, always set the UV dryer on high. If the UV dryer burns or melts the KOLDfoil at idle speed, move the setting to low but don’t forget to reset it to high when you switch over to standard running speed.
The K Laser foilKURE adhesives have been tested on 600-watt UV lamp in the 32nm range. However, these adhesives will easily cure on most UV dryers installed on flexographic presses (minimum of 400 watts/inch output). Keep in mind, the UV light that cures the foilKURE adhesive must not vary in energy output as the press changes speed. Variations will make it difficult for the UV dryer to cure the adhesive at low or idle speeds. If your UV dryer has an auto ramp, turn this option off.
Let’s do this!
You’ve set up the press for maximum efficiency and gathered your job materials wisely – now it’s time to run the job:
- Set the fountain roll and doctor blade and pour the adhesive into the ink tray. Make sure the adhesive is metered correctly.
- Mount the photopolymer plate onto the print cylinder and position the print cylinder inside the print station.
- Adjust the plate cylinder manually or with a check gauge.
- Load the foil onto the laminating arm and web the foil according to the press manufacturer guidelines.
- Apply a slight pressure to the nip roll.
- Make sure the UV dryer is on, the auto ramp option is off, and the heat setting is high.
- Run the press at approximately 50 fpm and activate the impression. Set the print cylinder’s fine adjustment using standard printing procedures.
- Increase the nip pressure until an image appears. The cold foil adhesive has been slighted tinted to enable the operator to see the image. Make sure that even pressure is applied to prevent the substrate from tracking.
- Adjust the tension on the laminating arm and the waste windup and make sure that the foil is traveling as the same speed as the substrate.
- Increase the speed until the image becomes clearer and full foil transfer is achieved. When increasing speed during a production run, perform a tape or scratch test to ensure that the adhesive has been fully cured.
Congratulations, if you’ve followed our flexo and cold foil knowledge so far, you should have successfully achieved a beautifully embellished print product using the cold foil printing process. The K Laser Cold Foil Business Unit (CFBU) is here to help you navigate the complexities of cold foil printing like a pro. With the largest variety of cold foil colors and holographic substrates, K Laser takes pride in delivering quality cold foil products, on time and on budget. Contact us today to learn more about our KOLDfoil ONE products, adhesives and print services and choose the CFBU to be your cold foil partner for the long run (and short runs too).
Seems like our job is done here, we’ll be going…. WHOA what is that? Did the foil not transfer correctly? Was the cold foil transfer not even across the web? Maybe there are lines showing across the print? As we all know, there are many variables at play here and we haven’t told you yet about troubleshooting for defects and efficiency issues in the cold foil printing process. No problem! We cover that in the third part of our cold foil best practice series, in our blog: “Cold Foil Troubleshooting for Flexo Printers”. READ HERE or contact our team to assist with any cold foil service and support needs HERE.