Custom Screen Printing: A Good Choice for Coating Offset Sheets

16 December, 2021 10:22 AM

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Description

A friend and colleague of mine is a sales rep for two different book printers. (This is a little like what I do, although I’m completely independent, working with multiple printers as a representative for my clients. In contrast, as a sales rep my colleague has the firm backing of two specific book printers. One printer focuses on color work. The other focuses on black-ink-only print books.)

Recently, my colleague sent me information on a custom screen printing press one of these two printers had bought and put into service to apply special coatings to print book covers.

I found this interesting, primarily because it is a hybrid process involving both offset printing and serigraphy (custom screen printing). So I did some research online in order to share this process with you.

The Equipment

My colleague’s book printer has a Sakurai Maestro MS-102AII screen press, a cylinder press which accepts a 29.5” x 41” press sheet and cures the screen printing inks and coatings using UV drying technology.

According to its online specification sheet, this screen printing press can print up to 4,000 images an hour on substrates ranging from .003 inches to .032 inches in thickness.

When you watch this press operate online in one of a number of YouTube videos, it’s a rather interesting machine. The overall build of the machine resembles a small offset press, with its automated feeder at one end of the press and its bin for completed press sheets at the other end. But in the middle, it has a stationary squeegie with a movable serigraphy screen underneath. When the screen moves, the squeegie forces ink (or cover coating) though the mesh screen and onto the cut sheets traveling through the press along the internal conveyor.

The Sakurai does not look like the multi-unit carousel screen printing presses used to print textiles. These have more of a wheel-like operation, with multiple screens accessible to the printing platform, all of them in a circle that can be rotated as needed to reposition new screens to print additional colors.

Rather the Sakurai looks and sounds more like an offset press.

If you continue to watch the videos, you will see the press sheets leaving the screen printing section of the press and traveling through the UV dryer. This drying process is based on the ability of UV inks to cure instantly when exposed to UV light. That the equipment specifications also reference LED ink-curing suggests that low-power, but equally effective, LED lights are used to cure the ink. This reduces the heat of the press and dryer (and also the resulting cost to cool everything).

How Would You Use Such a Press?

If this press lays down only one ink at a time, how would you use it?

According to its promotional material, the particular book printer my colleague represents uses this press for “specialty finishing applications over offset printed material, including: spot raised UV clear/high gloss, spot glow in the dark, and spot soft touch [coatings].”

What this means is that this book printer does not need to dedicate one unit of an offset press to a special coating process. Rather he can focus on printing the maximum number of inks in one pass on the offset press, and then after the press sheet has dried, he can send it through the Sakurai screen press to lay down a thick coating on the book cover (a coating that might not be appropriate for use on an offset press). Moreover, the printer’s promotional literature notes that the application can be either a “spot” application or a “flood” application. (It can cover the entire press sheet or only a portion of the sheet, allowing for a subtle, or not so subtle, contrast between one coating and another on the same book cover.)

The printer’s promotional information on the Sakurai Maestro MS-102AII screen press goes on to describe the substrates on which the equipment can print: “The Maestro is capable of printing on a wide range of substrates such as plastic film for electronic applications, membrane switches, display panels, touch screens, etc., as well as paper, board, and foil….”

This makes the Maestro useful not just for book printing and promotional printing but also for industrial or functional printing (printing on objects like computer screens or printing circuit boards for electronic devices).

But for a book printer it also opens up avenues for more dramatic cover coatings, such as the thick, almost rubbery soft-touch product, a tactile coating that will set a print book apart from any screen-based ebook.

The specification above also includes foils as substrates, allowing a printer to create metallic book covers. And with the UV formulations used in the process, the inks can easily cure and adhere to the non-porous surface of foil.

Now let’s revisit the size and speed of the press. When you consider the fact that a lot of specialty presses are rather small in format (closer to 13” x 19”), the 29.5” x 41” maximum sheet size accepted by the Sakurai Maestro MS-102AII is more than ample. So a book printer can impose multiple copies of the book cover onto a press form, which will allow more copies to be printed (or coated, as in the case of this book printer) more quickly. This is a real press that accepts standard press sheets.

Moreover, the 4,000-images-per-hour press speed noted in the printer’s promotional sheet is a respectable speed. (To put this in perspective, a Komori Lithrone offset press, which I just found at random on the Web, prints at a maximum speed of 13,000 sheets per hour, and this is a high-speed offset press, not a screen printing coating unit.)

Finally, it is useful to remember that not all coatings will adhere to all printed products. For instance, some digital presses using toner and fusing oil will have serious problems with various kinds of coatings not adhering to printed products. In the case of my colleague’s printer’s Sakurai Maestro MS-102AII, the coatings have been formulated to work well with offset printed book covers, providing both durability and visual enhancement to the printed product.

One Final Suggestion

My colleague’s promotional literature from the printers he represents doesn’t tell you this, but not every book press has this kind of coating equipment on the pressroom floor. If you are producing this kind of job, you will get better pricing and faster turn-around if your printer does not need to subcontract the cover coating work (which many printers need to do for certain coating processes). In this light, it will serve you well to request samples of the coating options your printer can provide with in-house equipment.

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