I’ve written several articles over the years about screen printing, but in reality it has been a long time since I have done a lot of that work personally. Kelly Drennan was our screen printer for nearly 20 years, but a better job in the booming oil and gas business took her away this past spring.
We ran articles in two local classifieds trying to locate anyone with screen printing experience, but came up with no one who knew what a silk screen was, let alone how to print anything using one.
However, our clients still demanded that work, and the work kept piling up, so I took on yet another night job (or evenings, or Saturdays, etc.) and have become our temporary screen printer.

One change I made was to color code all our screens, since using the right mesh is important, especially when printing light ink on dark substrates or reproducing fine text, and now I can grab the right one every time.

I soon found out that even though I learned the principals and basic techniques of sign shop screen printing decades ago, I had become rusty on the actual hands-on application of those skills. There were some things that needed improving in our screen printing department, which we had just moved to a secondary location a few weeks before.
For this month’s article, let me share some of my recent experiences, and mistakes, as well as some of the changes that have been made to how we do screen printing in-house.

One thing I noticed after setting up a few printing jobs is that we really had too many screens of dubious value, and too many sizes of screens as well. Some of our old screens were wooden and some were made with metal frames we had fabricated ourselves, and there was no real consistency to our stock of screens.

Very soon I had our fab shop weld up six new screens, from 1.25" light wall steel tubing (yes, I know most metal screen frames are aluminum) and painted each one on three sides, leaving the side the fabric would glue to uncoated. The screens were color coated blue for fine mesh (195 threads per inch), red for medium mesh (156 tpi), and yellow for coarse mesh fabric (125 tpi). There were two each, which we had professionally stretched.

Now, at an instant, and without trying to read some ink-covered marking about which mesh is in which screen, I can tell which mesh is there. All the frames are the same size and can be used for large jobs, or for small-sized jobs. Most all the other screens hit the trash or scrap metal bin.

Keeping screens clean and in good shape is always a top priority.

As soon as one job is printed, the screen is washed out completely and a new stencil (most always capillary film) is put into the mesh and stored in an air conditioned mop sink closet, which is perfect as a dark room. These photo-stencil screens will keep a week to two weeks in good shape in this cool, dark room.

Let’s spend a few minutes on the subject of stencils. Our old light sensitive stencil of choice was direct emulsion (Ulano FX-88 SR), along with a few screens made from capillary film (Ulano CDF-4). I soon decided that capillary film stencils were superior in most ways, producing sharper prints and being more consistent in every way even if a bit more expensive.

Capillary film has become my favorite stencil, but I found that Ulano CDF-3 works just as well as the thicker and more expensive CDF-4, and this change will save hundreds of dollars in a year’s time.

I also learned, as I realized again how much a 300" roll of capillary film costs, that a film with a thinner coating of emulsion works just as well for us and costs more than 25% less. So, I shifted to buying rolls of Ulano CDF-3 (approximately 30 microns of emulsion on a clear carrier sheet). This will constitute a savings of several hundred dollars a year to the shop.

I recruit my daughter, Lacey, from time to time, and she has not trouble printing with our M&R Saturn semi-automatic press.

We use a Saturn semi-automatic press by M&R for most all our screen printing, and I also found that I am ahead to put the stencil, and then the image, into the screen a bit forward of the geographic center of the screen for most printing jobs. This makes it easier to handle the media in and out of the press for printing, and easier to register a screen, as well as giving the squeegee stroke a bit more room to clear the substrate before the press automatically lifts the screen and squeegee to the up position. If it lifts the screen too soon, and the snap-off behind the squeegee has not completed, the print will be ruined, of course. So, having the image a bit closer to the front with more “runway” to the back is a good idea, even though my ex-screen printer always seemed to put each image in the direct center, which is not the best idea.

We do not have a really good drying rack for screen printing, though at one time we had an old one that didn’t really hinge well, and took up too much floor space. My screen printer used a system of wire racks and strips of wood to build up a rack as she went. This worked fairly well, and she was a bit of a creature of habit and liked the collapsible and storable system she had.

After a few jobs, I could see that I did not agree and devised a simple system of drying racks that holds 105 shelves of corrugated plastic or 105 printed 18" x 24" sign blanks.

It is seldom that we print more than 100 at a time, and I actually sub out the larger orders to a company that has an automatic UV screen press setup. My system, using shelves of fluted plastic, will hold 400+ metal warning signs 9" x 12", or 300-plus printed signs 10" x 14", and many decals as well.

So, this system, as shown in the photos, has really worked great and was simple and inexpensive to build. It is made from ½" MDO and strips of corrugated plastic 1" wide put in place with a 1" space between each shelf. Each of three units, which sit side by side on the tops of our flat files just to the right of our screen press, holds 35 shelves, and so far this arrangement has worked great.

After a bit of practice, I became very proficient at printing corrugated plastic signs and also metal signs for our oilfield and industrial customers. But, I had problems printing on decal material, and I remembered so did my recently retired screen printer.

The key to solving our decal printing problems was two fold. First, we must not cut the decal blanks off a roll of decal stock (we use five- and six-year IP vinyls for decals), until just before we are to print them. Humidity and heat, which we have plenty of here in wet East Texas, will cause the decal blanks to distort or become wavy while waiting on us to print them. The sooner we print them, the flatter they will be, and the longer the delay, the more distorted the sheets become.

Printing on decal stock is easy, but high gloss decal material can stick to the capillary film on humid days. A satin or semi-gloss decal sheet is best, and the orientation of each sheet to the direction of the squeegee can be very important.

Also, very shiny or glossy decal stock is a pain to print on especially using capillary film or any type of film stencil. Film stencils, which are essentially water based, become tacky when the humidity is very high and tend to make an instant bond to a glossy plastic or vinyl surface. This attraction or tackiness keeps the less than flat decal blanks from being able to flex and flatten out perfectly when the squeegee presses down on them, and will produce blurred and messy prints, a disaster! You can actually hear the stencil grab and rip loose from a high gloss decal stock, and no amount of vacuum suction will solve this problem (ask me how I know!). So, from now on we use a decal stock with a satin finish (Avery A-6 is a good one), and have little problems even using capillary film for our stencil of choice.

Two other notes on decal printing are worth mentioning here. First, when printing decal blanks cut off a roll of vinyl material, I always have the factory-cut edge meet the leading edge of the squeegee as it makes its printing pass. The factory-cut edge will always lay flatter than the edge we cut with an X-acto or shear. The shop-cut edge will be more distorted and will lay flat only as the squeegee moves across it and should not be the edge the squeegee contacts first.

Also, after registering the screen image to the decal blank size, I mask off a ½" wide strip, which will be under the leading edge of the decal to be printed, and spray it with a light coat of mist-type spray adhesive. This will hold the edge of the decal blank perfectly flat (the factory-cut edge)\ but will allow the rest of the sheet to shift slightly as necessary when the squeegee passes over it, and the vacuum will keep it from snapping up with the screen.

These steps have made decal printing as non-problematic screen printed jobs on fluted plastic or metal. Of course, for every job we choose the correct mesh for the image and color of ink to be printed, and as mentioned, color coding our screens makes that step foolproof as well.

Before the year is over, we’ll take another look at sign shop screen printing. For now, I am back in the saddle again, and will gladly share any information or helpful tips I learn, or re-learn along the way.

Metal pipeline signs and warning signs are good jobs for us, and are one reason we need a screen printing department. I do all the stacking while nephew Jered prints two signs at a time.

The simple rack system we made from scrap MDO and strips of corrugated plastic holds 105 sheets, and can hold hundreds of smaller signs or decals when fluted plastic signs blanks are used as shelves.