Direct-to-screen is one of the most exciting and greatest innovations in the screenprinting industry today. Many choices abound with several manufacturers using different types of technologies to put an image on the screen. Of the choices available, ink-jet and wax-jet use consumables – DLE (digital light engraver) uses light and no consumables. The purpose of this article is to help you make an informed decision so that you purchase what is right for your company.

 

Direct to screen (DTS) eliminates the use of film positives and the problems associated with films. Screens are prepared by applying emulsion to the mesh and letting it dry. But, rather than taping a piece of imaged film on the screen and vacuuming it to the glass, a screen is simply placed onto a DTS platform designed for the frame size and held into position. Then either an ink-jet print-head with a UV blocking fluid or an opaque wax is applied directly to the emulsion then sat in front of a light source and exposed without any vacuum. Rinse out is the same as with film process.

 

DTS SYSTEM ADVANTAGES

 

Printers who move to a DTS system notice advantages right away including reduced pinholes, faster exposures and greater detail with some units. Press set up time is cut about in half, exposure times are cut by about 40%, there is no more film handling or storage, and problems related to poor quality film positives are non-existent. Indeed, the move to DTS is one that can pay for itself quickly.

 

In deciding which of the DTS technologies to consider, I’d like to discuss specifically the importance of density. DTS can be so exciting that you may forget to ask the important questions that must be considered if you are to be happy with your purchase. One of the most overlooked questions is density. For printers using films, they understand the importance of a good film positive to produce a quality screen. Vellum film may work well for single colour or block art prints, but one would struggle with this type of positive if producing halftones or multi colour artwork with tight registration and fine detail. A high quality transparency would be required to produce such work with a quality result. So it is with Direct to screen.

 

I mentioned above three types of DTS. First, DLE (digital light engravers) which is a technology that uses a scrolling light to expose the image without using any consumables (still need to coat the screen). These units are very expensive and require very fast exposing emulsions. The detail they are capable of is second to none, but they are slower because they have to expose all of the emulsion across the screen. This is definitely an exciting technology, but cost and time usually eliminate it from serious consideration.

 

WHERE INK-JET CAN’T GO

 

Next, wax-jet is a highly opaque technology which requires a wax ink to be heated and then applied though a head with about 256 nozzles. It is fast, very opaque and capable of producing some of the most difficult details where ink-jet can’t go. Wax when applied to the screen returns to a solid state resulting in a precise dot and sharp edge. Detail is consistent and repeatable. Screens can be properly exposed because wax has the opacity to prevent UV light from getting through which allows the light source to fully expose the stencil making a durable, quality screen to go to press and last.

 

Thirdly, ink-jet is a technology quite common in the industry as it’s sufficient to meet the need, but underexposure is a common place issue when using this technology. Ink-jet uses a UV blocking fluid which inhibits the UV light from exposing the image; however, this UV blocking fluid is not as opaque as wax, so a proper exposure will penetrate the ink and start to expose the blocked emulsion which will cause loss of detail and quality. Under exposed screens create problems in other areas of production such as on-press durability is weakened, and reclaim is more difficult and time consuming because of the difficulties associated with underexposure. Ink is a liquid before and after it is applied and will splatter when applied, then wick (spread) into the emulsion creating unwanted dot gain as it does. This can be controlled by adjusting a tonal compression curve in the RIP software, but still will not match the quality of a wax-jet printer. Ink-jets can be really fast, but at a cost to quality somewhere down the line. Several printers with ink-jet machines are happy with the overall performance and benefits of their machine, but many of those same printers also revert back to high quality film positives for the top 20% of their work as they need better dots and details which the ink-jet can’t currently give them. I have yet to find a company with a wax-jet printer that needs to do this.

 

FOOTPRINT AND ENVIRONMENTAL CONDITIONS

 

How much room does a DTS require? Shops need to consider the footprint and environmental conditions when deciding on a DTS. Ink-jet machines all require a much larger foot print because of the ink – it has to be printed horizontally because of the printhead and this requires a much bigger footprint. Wax-jet uses electrical pulses to an industrial print-head to apply the wax ink through its print-head, so wax units print in the vertical position which requires significantly less room. Typically two wax-jet units can sit where one ink-jet unit would go giving businesses the option to have a backup unit if needed or increased production capabilities for future growth. Environmental room conditions are strongly encouraged and sometimes required for performance of inkjets so they don’t dry out or have static issues in the print. Wax-jet units can go just about anywhere in the screen room, but not where water can get on them.

 

Do I need to change emulsions? With DLE – yes; with wax-jet – no and, with ink-jet – possibly. If you’re happy with your current emulsion and don’t want to change, then wax is the way to go. If you want to go with ink-jet, then you need to consider if your emulsion is compatible with the ink from the ink-jet machine. Not all emulsions will work with inkjet. There is a compatibility issue to consider. It’s surface tension versus surface energy. To help understand what this is, think about waxing a car. Before waxing, rain would spread over the car; after waxing, rain will bead up and run off. Waxing lowers the surface energy of the car to make it lower than the surface tension of the rain. This same concept is necessary to understand with ink-jet. Most dual cures are capable of working with ink-jet, but printers wouldn’t have the advantage of the speed the DTS promotes, especially those inkjet machines with built in curing lights. Pure photopolymers are fast, but have different surface energies which may or may not be compatible with the surface tension of the ink used in the DTS. The wrong emulsion will cause the ink to repel and look distressed. There are a handful of photopolymer emulsions that are fast enough, but have the right surface energy for ink-jet. Then we deal again with density or opacity of the ink. A faster emulsion can be cured through the ink as it’s not dense enough to protect the image.

 

EXPOSURE CONSIDERATIONS

 

Exposure is also something that needs to be considered. Understanding lights can help with your decision. For years, metal halide lights have been the industry standard because they cover the wavelengths necessary for the different types of emulsions; typically a range of 360nm through 420nm would expose most emulsions. Today, LEDs are making a big presence in the industry. They are cheap to run and don’t generate much heat like metal halide. They are dialled into a specific wavelength rather than having the range metal halide offers. Wax again is opaque and not affected by these lights but ink-jet, being less opaque or dense, is affected. The wavelength gets shorter as the number goes down, and longer as the number goes up. A higher wavelength has better ability to penetrate deeper into the emulsion to assure a proper cure through the emulsion. A shorter wavelength may not be able to penetrate deep enough to cure the inside of the emulsion properly which can cause breakdown at the press due to poor exposure. Companies promoting ink-jet technology like to use a 385nm for exposure which is sufficient for exposure without much penetration through the ink. Post exposure in the sun or a higher wavelength would be recommended to get better durability after the screen is developed and dried. This 385nm is less likely to penetrate the ink and helps to produce better quality, but the stencil will be weaker.

 

What are replacement costs when a print-head goes bad? Typically a wax-jet head, if it needs replacement, will cost around $4,500.00. An ink-jet head will be around $1,500.00 to $2,000.00. Both print-heads are capable of producing screens for years. Some wax-jet machines have a tendency to use at least one print-head per year and other waxjet machines have been going for more than five years on the same print-head. It’s a matter of the manufacturer you choose for your wax unit. Some units have bells and whistles which require more power, which can short out some of those print-heads. Some wax jet units are simplified and meant to be a workhorse in the screen room with little issue to worry about. Ink-jets and wax-jets alike can last if those working with the units really care about the condition of the screens they put in them. Both print close to the emulsion and a screen with tape or tears in the fabric could brush the print-heads causing damage.

 

SPEED AND QUALITY

 

How fast is a DTS? Some ink-jet printers can print and expose in less than a minute, while others can print higher detail, but slow down to do so. This can be as long as five to eight minutes per screen to image it. Wax machines also have options as speed is something everyone appreciates and desires. Some waxjets tout bi-directional printing, which can increase speed, but quality will suffer. Density also suffers with wax in a bi-directional print as the print-heads can’t fill fast enough for each pass. Wax-jets pass over the same image six times to get proper opacity. If using a waxjet in a bi-directional mode, the head can’t refill with ink fast enough and, as a result, will only print where the head is filled, thus the top of the 256 jets will be less dense than the lower jets. Wax works best with uni-directional printing as well as producing the best quality. Ink-jets have both options available also. Typically bi-directional is meant for speed and general art, not detail. To produce detail, you should print in a uni-directional method. Most wax-jets will produce a screen in about one to one-and-a-half minutes which is plenty fast.

 

In summary, with wax-jet units, you get opacity, speed, consistency, and don’t have to change your emulsion. With ink-jet units being promoted so strongly, you really need to do your research and be willing to make the changes necessary to obtain the results you’d like. I come across many shops that have purchased ink-jet and really like it, but are frustrated with the struggles that go along with them. They will say: “For what we do, it works for us.” However, there is someone out there who has done their due diligence and won’t settle with “for what we do”.

 

I’ve been able to go into many shops that have both technologies side by side. We’ve produced the same image from both machines onto one screen. I’ve developed the wax and ink at the same time in one of the machines that prints and exposes, first by printing half on the wax machine, then the other half with the ink-jet, then allowing the ink-jet machine to expose the emulsion. After wash out, both images looked good but, at the press, the waxjet image was by far superior. It was because of the density as much more detail was held with the wax-jet. We had speed, quality and consistency with the wax-jet that the ink-jet just wasn’t delivering. I’ve also done the same test, but letting a metal halide expose the screen, and again the same conclusion, the metal halide improved both, with significant improvement on the ink-jet print.

 

There is a place in the industry for both types of DTS, but I encourage you to do your due diligence and test screens produced from both technologies. Some manufacturers will offer performance guarantees, or even print some test screens for you to run. I’d encourage you to try this before purchasing as I’m sure you’ll see, as I’ve found out, that density can’t be overlooked. The prints from an opaque stencil are visibly a better quality.

 

Once at an open house where direct to screen was the subject, ink-jet print machines and wax-jet print machines were present and producing screens. The owners from Integriteez of Tulsa were there to purchase a DTS unit and were able to compare side-by-side the screens of ink versus wax. Their conclusion was: “There’s no comparison.” They chose what gave them the best quality, speed and consistency – they chose the wax-jet unit.

 

David Makin works in Technical Sales at SAATI

 

 

 

One pass through Novac in the wall between the yellow room and wet room for developing saves a lot of steps – one Nova can easily do 500 screens per day and keeps the unit free to start the next image

 

Novac’s pass-through exposure unit means there is no double handling of screens

 

Douthitt’s CTS 30 wax-jet computer-to-screen imaging unit has the best track record and highest quality