Direct to the Point: Shopping for Direct-to-Screen Equipment

Philip Wanzong is the product manager for EXILE Technologies, a manufacturer of pre-press equipment, including thermal imagesetters and direct-to-screen devices. He has worked in the graphic arts industry for more than 25 years, beginning as a typesetter and film stripper in the offset printing industry, and continuing on to be in involved in flexography, newspaper, and screen print. 
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Most textile screen printers today are well aware of the advantages of adding a direct-to-screen (DTS) system into their pre-press workflow. While they can be an expensive addition to a screen shop, in most cases they pay for themselves rather quickly by eliminating film, and reducing labor and overhead costs. A DTS can also provide an immediate quality improvement if it replaces an inkjet or toner-based film workflow.

So what’s important to look for when shopping for a DTS system? In today’s market there are several options, which is good for the buyer, but can make it more difficult to be sure you are purchasing the right product for your shop. To help decide what system is your best match, let’s start by defining the types of DTS equipment available today.

Direct exposure systems

These devices use a digital micro-mirror device (DMD) paired with a UV light source to directly expose coated screens without the need for a mask. They have excellent quality and the highest resolutions available. In some cases, they offer resolutions as high as 2,500 dpi. These systems work best with fast-curing emulsions for fairly obvious reasons. They tend to be expensive, so they are difficult to justify for smaller or even mid-size shops.

Liquid-based inkjet

These units use a high-density liquid ink as the image mask. The ink is formulated to be light blocking and unlike direct exposure systems, a secondary exposure is required. Due to the lack of film, a traditional vacuum exposure unit is no longer necessary. There are systems available with integrated UV exposure options, which allow the DTS machine to also expose the screen. This is a nice feature, but in some cases the online exposure can slow down production on the DTS machine itself. Many choose to continue to use offline exposure for better throughput and more compatibility with longer curing emulsions. Also, liquid ink can react differently on different types of emulsion. If your shop uses a variety of emulsions, it’s important to check compatibility with the DTS inks. Liquid ink systems benefit from a controlled environment with humidity and temperature controls to ensure consistency of image quality. Most of these systems have a range of resolutions from 600 dpi to 1,440 dpi, which is adequate for textile applications. The pricing on these printers vary significantly based on the type of print head technology used, the number of print heads installed, and any added accessories.

Wax-based inkjet

These systems use heated wax ink that is also formulated to be high density and UV light blocking. Ink is delivered to the machine in the form of a solid puck or brick. The DTS then melts the ink and jets it to the screen while in a liquid state. The ink re-solidifies as soon as it touches the emulsion, leaving a very dense ink deposit that blocks UV light exceptionally well, which helps hold fine details on the exposure. The instant hardening of the ink allows these machines to print vertically, so they tend to have a smaller footprint in the screen room. Although wax ink can be more expensive than its liquid counterpart, it does provide consistent results with any emulsion and in widely varying environments. It is also highly water soluble so it washes out easily after exposure. These DTS units are priced similarly to the more industrial of the liquid ink systems and have similar resolutions of a maximum 1,200 dpi.

Laminated thermal mesh

This option is a unique DTS product that uses a specially laminated screen mesh. The thin lamination layer replaces standard emulsion. Once stretched onto a frame, the printer uses a thermal head to melt the laminate wherever there is image area. These newly opened areas allow ink to pass through just like a traditionally coated and washed out screen. This cuts out many steps and hassles in screen preparation, but has its drawbacks as well.

The laminate on the mesh is very thin in order to properly melt, so the run length on press tends to be very short. The mesh is also disposable, so a new screen must be stretched for every print job. The mesh can also be fairly expensive. If just starting into screen printing, this could be a good choice, as it can minimize investments in exposure frames, washout and reclaim areas, as well as cut down on chemical usage.

What do you need?

So now that you know what’s out there, how do you choose the system that’s right for your shop? First, if you can justify the cost of a direct imaging DTS, fantastic. In reality, however, these systems are often overkill for the textile market. The resolution they are capable of just isn’t required for textile printing. Although it is nice that no consumable is required, it is possible to buy an alternative system, a backup alternative system, and many years worth of consumables for the difference in price.

The thermal mesh product is great for a screen printer that only focuses on very short print runs and perhaps hasn’t already invested in traditional screen prep equipment. The limited run length and other limitations of the mesh don’t always provide a complete solution for the typical textile screen shop.

Due to the price point and the ability to use standard emulsions and frames, most textile printers today choose between the liquid ink and wax-based printers. Here are things to consider when evaluating these systems.

Does it support your press registration system? Most DTS units are pre-configured to support the common three-point corner system, however, there are several other registration systems in the market. You will want to be sure there is a clamping system available for the DTS that supports your press. After all, the real advantage of a DTS is labor savings on press setup. The less time spent registering a job, the more time that press is running and making money.

Is the quality good enough? Quality is a very general term, and ultimately has little to do with the resolution of the device. With DTS, ink density can be a big contributor. If the ink is not dense enough, you will lose fine detail and small halftone dots on exposure. Ask the supplier what the D-Max measurement is for the ink. Although it will vary based on the amount of ink deposit set down, it should provide 3.5 UV D-Max or better for proper exposure. Another quality factor can come from emulsion compatibility. Some types of ink will soak and spread into certain emulsions and pool up on others, creating varying dot sizes and detail. Humidity and temperature, or using a screen that hasn’t dried completely, can also cause unpredictable prints with certain ink types.

Often overlooked is the software that drives the system. Most DTS equipment requires RIP (Raster Image Processor) software to operate. Be sure to evaluate this piece carefully. It can be frustrating to find out after an installation that a RIP requires a special file format, or is extremely slow to load jobs. The software should have all the features required without being overly confusing or complex. Also, it shouldn’t have to be tethered to the DTS equipment. Ideally, the RIP will be installed in the art room and not the screen room. Some do this by ripping the job and sending one-bit tiff files that are already templated and halftoned to a queue at the printer. The screen room operator then only has to select the correct job and color to begin printing. The software on the printer itself is also important. Does it allow the job to be repositioned if needed? Can the job be previewed before printing? Can templates be easily created for different screen sizes? Will it automatically add jobs from a server or hot folder?

The last bit of shopping advice can also be easily overlooked in the excitement of a new purchase, but is critical to consider: support. Make sure the company you purchase equipment from has a technical support staff that is available to you. DTS systems are not always in the most pleasant environments and they can take a beating. There’s a good chance something will go wrong at some point. You want to be sure you can count on a manufacturer or reseller to provide you with prompt and competent support. You will come to rely on this machine and can’t afford to have it down for a lengthy period of time. A support group should be knowledgeable on printing equipment, RIP software, and graphic arts applications.

Purchasing a DTS system is a big decision, but a very smart one for the busy screen shop. The payback will be seen in labor reduction, material costs, quality improvements and a simplified workflow. You may know you need a DTS, but have delayed a purchase for fear of making the wrong choice. Hopefully the tips in this article will make the shopping part a little easier.