SCREENS: The biggest issue in your shop – part two

In the concluding part of his two-part series, Marshall Atkinson explains exactly what you need to do in order to create perfect screens

In the last issue, I explained how shops can dramatically increase the number of impressions they print each day simply by creating perfect, production-ready screens each and every time. I laid out the importance of analysing what is going on in the screen room and the production area in order to understand how much downtime a shop has each day versus printing time, and how many impressions an hour each press is managing. Once this data is analysed, it is obvious that maximising the printing time on each press by minimising the downtime is hugely profitable – and a cheaper option than buying another carousel.

There are certain steps that need to be perfected in order to maximise the number of impressions from each press; I covered tension last issue, so this month I‘m looking at reclaiming and coating, imaging and exposing, and rinsing and washing out screens.

Reclaiming and coating

These steps go hand-in-hand with building a foundation for the image we use to print. These are also the two biggest pain-in-the-butt steps in your entire building.

Reclaiming is easily the worst job. It’s like doing dishes forever.

Coating screens with emulsion isn’t much fun either, as it is usually a lonely task, often in a dank room.

However, these are crucial steps in the process as we need the screens to be cleaned, degreased and coated with emulsion perfectly. This sets up the foundation for the image.

How dialled in is your process in your shop? Do you have someone that is detail-minded doing this work, or do you, like a lot of shops, stick your worst employee on this as a punishment? In essence, are you leaving the cleanliness and quality of your number one production tool in the hands of someone who doesn’t care and is the lowest paid employee you have? Yes? Uh-oh.

If you don’t think apathy in this area can backfire and hit you squarely in the face with a Murphy’s Law skillet, I don’t know what to tell you.

Here are some recommendations…

Don’t skimp on products Buy the best you can afford. Better products might cost more, but their performance will pay off later as they will be easier to clean, or expose, or produce a better stencil than cheaper varieties.

Humidity counts Get a hygrometer and use it to measure the relative humidity in your screen room. Ideally, the humidity should be less than 30%. Use a commercial grade dehumidifier to control this if it‘s a problem. Don’t forget a stack of wet screens will increase the humidity in the room, so expect to see a spike in humidity after a coating session.

Keep it clean This is a messy business and the screen room is one of the messiest. Keep it debris- and lint-free – lint floating in the air creates pinholes – especially on vacuum table glass. Be meticulous for better results. After being in countless shops, I can tell you that in the best ones the floors and walls sparkle.

Training Screen making is a craft and requires precision. Make sure your training and management of the process are up to scratch. Screens are the keystone of your entire operation. Do not let just anyone do it.

Understand EOM Make sure you have a firm grasp on the concept of ‘emulsion over mesh‘ or EOM. This is the thickness of the emulsion you are coating on the screen. Consistency counts. Want better quality screens? Upgrade from a manual scoop coater to an automatic coater. A machine will standardise this important step so that every screen will have the perfect coat of emulsion.

You can measure the EOM on your screens with a tool called an EOM meter. Your goal should be to get a 12-15% stencil thickness. An easy way to test this is to determine your EOM and set your coating process (1:2 or 2:2) and then see how many screens you get out of a set amount of the emulsion. Let’s say that you get 42 standard-sized screens on average for your target EOM. If you are tracking this with a log, and your screen room coater now shows over 50+ screens for the day, you know the EOM is less than it should be. Predictability and consistency matter. Create your standards.

I am far from being a screen-making expert. To really geek out on this stuff, read anything by Dave Dennings with KIWO, or listen to my The Big Idea podcast with Alan Howe with SAATI.

Imaging and exposing

So let’s assume that your screens are coated and ready to go. The next step in the process is to get the image for the art burned onto the screen. But before we handle that step, ask yourself one question: is my screen dry? Sure, it might be dry to the touch, but so is a tomato… until you slice it open. Your emulsion has to be 100% dry throughout.

I’ve been in shops that give little or no thought to the UV sneaking in and pre-exposing the emulsion on screens. “Why do we keep having screen image problems?” they ask. It’s not hard to work out.

For lighting, be sure to have the correct UV filter covers. These will cast a yellow glow in your screen room. A good practice also is to paint the screen room a different colour than white. I’ve seen shops use black or even yellow.

How you get the image to the screen has a direct impact on the quality of the image to be burned, and its placement on the screen. Currently, the absolute best practice is to use a computer-to-screen (CTS) unit. This piece of equipment is the number one tool to increase efficiency on the production floor.

Some CTS units use a water-soluble ink, others use a wax, and SAATI has a new unit that uses a laser to image the screens. These systems are superior because they place the image directly onto the screen.

Film or vellum is placed on top of the screen and taped down. During the exposure process light can seep in around the film (or vellum) and erode the quality of the exposure. This directly aff ects the edges of your image and halftones. With a CTS unit, this doesn’t happen so you create a better channel for your ink to pass through.

Also, because the CTS unit locks in each screen frame with three points of contact, the images for a print run are all exactly pre-registered to each other. Duplicating this pre-registration on press with a registration bracket allows your crew to quickly get your screens set up in less time than manually registering them.

Finally, CTS units completely eliminate the need for the vacuum table step for exposure and this saves time and rules out the aforementioned pinholes caused by lint on the glass.

Some CTS models have an LED exposure system built in, so as the screen frame comes out of the machine it is exposed. The SAATI laser unit exposes and images the screen in one step, without any consumables.

Of course, the use of film or vellum will work. Plenty of shops travel down this road every day. However, if you are creating over 40-50 screens a day you should be looking into getting a CTS unit.

Rinsing and washing out

Another key problem in the screen creation journey is the final step of rinsing and washing out screens.

If your screen printers have to keep a roll of masking tape, a needle and a Q-Tip handy to poke holes in the emulsion, and tape up and correct dodgy emulsion edges, you’ll already understand the importance of washing out your screens.

This drives home that there is a big problem in this industry: underexposed screens. Do you feel that your shop has a grasp on how to expose screens correctly and what’s involved in ensuring craftsmanship in this critical step? If your shop has your exposure dialled in properly you can use a commercial pressure washer to blow out the emulsion for the print areas without worry. A quick rinse with some water, a few moments to let it sit and then whoosh!

Under-exposed screens show up with premature emulsion breakdowns during a print run. You shouldn’t have to worry about this if you are confident in your process.

Here are some more recommendations…

Use an exposure calculator This will be provided by your emulsion manufacturer to dial in your exposure times for each screen. They will happily provide you with one and, if you are unsure how to use it, even train you to use it correctly.

Check your light source If you are having trouble with under-exposed screens look at your light source. When was the last time you changed the bulb? Commonly, the answer is: “We don’t know. We’ve never changed it.”

Check for under-exposure After you have exposed a screen, use a moistened white towel or T-shirt and wipe it around on the side of the screen not directly exposed; if any of the emulsion colours come off, you have an under-exposed screen. Time your washout How long does it take to wash out a screen in your shop? Properly imaged and exposed screens should take only a few minutes with a power washer. If you are in the 10-minute+ category, you have problems.

Use a production log Document the frequency with which your press crews are stopping to fix a screen problem. This is the number one tool to use to investigate these challenges because it will tell you when the challenges are showing up. You can then link this to a change in your process, the person who created the screens, when a different brand of the emulsion was used, or some other variable.

Wave goodbye to taping After washing out the screens, the next common step is to block out and tape. With a CTS unit, you rarely need to block out a screen for any problem pinholes or areas on the screen. If you are using aluminium static frames, you can also invest in screens that don’t have to be taped and avoid this step. Imagine the freedom of not having to add tape to screens or pull it off in reclaim!

A final word

I would highly encourage you to spend a good chunk of time examining the screen-making process in your shop. Take an honest assessment.

Who do you have in charge of this process, or doing the work? Hopefully, you can say they are one of your top employees.

Do you honestly feel you have the right tools and techniques to run a top notch screen department? If not, what are you going to do about it?