There are many things that happen during the sleeking process that can change the size of the paper. In some cases, the sheet grows as it runs between the heated rollers of the digital press or laminator, or the heat and pressure rolls it out like calendared plastic. At times, the sheet shrinks as the fibers are being dried out, and heat and pressure wring the moisture out of them. Multiple factors can affect this, including the environment you print in. Is it wet or dry? What is the moisture content of the paper? What is the force of the pressure?
What we know for sure is that these forces do change the size of the sheet. On a 4-process sleeking job there are two trips through the digital press and two trips through the laminator. This in turns plays with registration. If it is a 2-sided piece, there are more trips through the presses.
So, what are the steps to minimize the registration issues?
- The registration is usually good on the first crop mark and gradually gets off as you travel down the sheet.
- The more printed up on a sheet the worse the issue becomes.
- Use smaller sheets, like 8 ½” x 11”, so there is less sheet to change.
- Start working with only one side of the sheet at a time, front then back.
- Only print in simplex for the best registration.
- When laminating or sleeking, run the sheet landscape. This will have the least amount of time when the sheet is under heat and pressure.
- It may be the direction that is most critical.
- You may be able to creep the second printing to make up for the change of the sheet.
- You can also trap some of the areas as well.
This is when corners of letters or shapes are missing. These are usually small edges or fine points. Ink on the sheet is the only thing that is carrying the sheet through the laminator during the sleeking process. If there is not enough ink on the sheet to carry the weight of the sheet, separation happens while the ink is still hot. This is what causes the corners to pick.
- Printing a 3/8” box around the edge of the sheet, outside the crop marks will solve this problem. This extra ink will carry the sheet through the laminator. Not depending on these little points or small edges to carry the weight of the sheet yields much better results.
- Time is another factor that plays heavily on picking. The standard ink cure time is 24 hours. Sometimes during demanding projects with tight deadlines, we do not always have this luxury. If you are short on time, two hours may be enough.
- To ensure that picking does not happen it is imperative that the ink and the foil do not separate horizontally. The ink and foil need to stay together until the foil is pulled vertically away from the ink. This means that the pull rollers need to be turned off.
- The tension of the take-up roller is what should pull the film from the hot roller to the take-up angle or 90-degree roller.
- If the film is separating before this point, then you need to loosen the tension of the take-up roller. Some machines do not have a flatbed through the laminator. The film will separate on the de-curl bar. There may not be anything you can do to prevent it but try to loosen the tension as much as you can.
These are lines that run across the large sleeked areas. This happens when the sleeking foil is wrinkled under the hot roller. This is a tension issue. As a general rule, less tension is usually better than more. If you loosen the foil until you see a diamond pattern in the foil as it crosses the hot roller these wrinkles will usually disappear. If there are deep wrinkles in the foil before the hot roller then the issue is in the foil, change the roll. If your machine is equipped with a wrapless roller kit, the spread roller will eliminate wrinkles.
Dots on sheets
If the sheets are printed on a color printer there could be an anti-counterfeit dot pattern printed on the sheets. These dots can pick up the sleeking foil. Some printers will not print this pattern if black only is used or if yellow is turned off. Some sheets have a coating that is incompatible with the sleeking process and the whole sheet will be covered with dots. Sometimes sleeking film will not show the dots and stamping foil will. These sheets can be used if you laminate them with a printable laminate first.
Not all paper will sleek
It is best to qualify the paper before you sell the job. We recommend that you find 4-8 sheets that you know work well with your equipment and offer these. You need a 3 star or greater HP qualified paper. Others may work also. Felt paper with many hits of ink also works very nicely. Some paper may not work at all. It is best to test your paper before you print.
Ink build is not as big of a problem as we once thought it was. It is most important to have enough ink to do the job. If the sheet is a smoothly coated sheet, then 4 hits are good. If it is an uncoated sheet, 8 hits of ink may be needed. The rougher the sheet, the more ink you need to fill the valleys. It is best to start with these hits and test. If you are satisfied with less, that is fine, if not, use more. Remember, you are producing a piece that should demand enough margin to pay for the extra hits.
The recommended temperature of the stamping foil is 105°C or 221°F. It may work at 100°C to 110°C. Some machines are calibrated differently so you may have to run hotter or cooler.
Stamping or Sleeking
Stamping foil is the recommended foil for overprinting. You will still need to run a cleaner sheet every 15 to 25 sheets. Sleeking foil is not printable. Stamping foil is the best all-around foil. In most situations, it works better than sleeking foil. There may still be some situations where sleeking foil is better. It was once thought sleeking foil over lamination and stamping foil over paper. In our experience, stamping foil works better most of the time. It is very easy to tell what kind of film it is. Sleeking foil has a dull backing, a shiny foil is stamping foil. Rose gold sleeking foil works great everywhere.