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Low Tension Could Be Causing More Problems Than You Think

If you are currently having problems with ink transfer, making multiple strokes, have rough ink finishes, uneven color consistency, poor registration, and slow setup times then the information in this article will provide data and information that once applied will provide knowledge and with a bit of proper experience, you will gain the wisdom necessary to make the needed improvements. If you are currently using a SAG (stretch-and-glue) frame system this article will help you better understand that many, if not most, of the problems you are incurring in your daily work life.


The screenprinting process is ripe with variables. There are certainly more than the 620 known main variables, as hidden within each of those 620 are hundreds of more sub-variables that can create problems in which the job might be rejected, either by the printer or the client. There is, however, a variable that has a massive effect on everything that follows it in the screenprinting process and especially in the ink transfer process — consistent and proper mesh tension.

One of the most common questions in the screenprinting process concerns the benefits of proper mesh tension. The question arises because most of the problems that screenprinters are experiencing are related to tension, and a majority of my advice to my clients is to start the problem solving by increasing the tension to, at least, the suggested level as stated by the mesh manufacturer for a particular mesh count and thread diameter and type of mesh. If you do not start with the correct tension level and maintain that level across all frames with a particular mesh, you are going to continue to experience a failure to be as successful as you might be otherwise.

As Don Newman, founder of Stretch Devices and the inventor of the Newman Roller Frame[1] is fond of saying…

Remember, new technology is rarely a quick fix. Improvements in print quality and speed usually come at the price of hard work, testing, and an open mind to new possibilities. The press-persons that get better and faster each year are constantly testing, working harder, applying constant creativity, and are more persistent than their peers might think.

SAG Frames

SAG frames exist for one reason only — the buy-in cost is inexpensive. However, the true cost of anything is the return on investment, not the buy-in cost. You can buy an inexpensive $25 pair of shoes that will last you a year, or you can buy a $75 pair that will last you for twenty years or more for three times the cost. The cost is divided by the lifetime of the shoes. The less expensive pair have a lifetime cost of $25 per year or less, where the $75 pair have a lifetime cost of $3.75 per year. In the course of twenty years, you will either pay $500 for the inexpensive buy-in shoes or $75 for the better shoes. Of course, this does not include the cost of going back to the shoe store an additional 19 times over the 20-year-period.

Tension Loss

SAG frames are much like buying that pair of shoes with the lesser buy-in. While SAG is the acronym for Stretch-And-Glue, it might as well stand for what will occur over time with the frames as the mesh begins to lose tension causing the mesh to “sag” loosely in the frame. All screenprinting mesh will lose tension with each print stroke as the mesh is pushed down to meet the substrate, resulting in costly problems;

  • The mesh openings become smaller, resulting in less ink being transferred, which will require additional print strokes to be made.
  • With a loss of 2N/cm2, there is a noticeable change in the hue of the printed ink, so color matching becomes problematic.
  • As the mesh relaxes, the off-contact distance must be increased, which causes faster tension loss.
  • When the off-contact distance is increased the image is stretched out of shape.

And, at some point, the SAG frames will need to have new mesh installed on them. The printer will absorb the cost of cleaning, packing, and shipping both ways to have the frames re-meshed. I recently had a client in Ohio tell me that their cost to re-mesh a 150-threads-per-inch at their distributor was $50 per frame, and they were sending between 25 and 50 frames a month for re-meshing. The $50 price point does not include the cleaning, packing, and shipping costs absorbed by the shop.

However, the real cost in using SAG frames is that when the mesh tension drops below a certain point the ink starvation is so severe that it will take more than a single stroke to transfer enough ink to produce opacity. As an example, Figure 1 shows the difference in ink transfer on a 150 thread per inch mesh with a 64-micron thread diameter. In our study at the Screen Print Technical Research Center, we begin with a mesh tension of 14N/cm2 and progressed upward until we found the tension level that would provide an opaque ink layer with a single print stroke. Using Wilflex Epic Max White, which is a commonly used maximum opacity ink that is stated to provide a full white finish on blended fabrics. The suggested tension levels for the Nittoku Smartmesh from Murakami used in our research are from 25N/cm2 to 39N/cm2. As you can see the information from Nittoku’s Mesh Specification Guide worked well for the Wilflex Epic Max White, however, the results would vary with a different ink or any changes in the viscosity of the ink.

Single Stroke at Different Tensions

Figure 1: As tension decreases on the mesh in a SAG frame so does the amount of ink transferred.

Maximum Mesh Tension of SAG Frames

In our testing, we used a Newman Roller Frame, which allowed us to alter the tension level and reach the correct tension level. The square or rectangular frame profile of SAG frames will not allow the needed tension level to produce a One Hit White™.  When the mesh on most aluminum SAG frames is stretched above 27N/cm2 the aluminum will flex inward. The flexing creates a pattern in the mesh that will produce moiré patterns on textile substrates. Thus, the mesh is normally stretched to a maximum of 27N/cm2. And, as mesh loses tension during shipping, storage, and over time, the mesh tension will usually be below 24N/cm2 upon arrival in the shop.

The Making of SAG Frames

The SAG frame has become a commodity with no regard for the brand. The price is typically determined as a function of the market and the wide availability has led to a diminishing of important factors such as quality of materials and construction. It should come as no surprise that to maintain this commodity pricing that little attention is given to the manufacturing process, other than to create screens at the lowest cost that will pass a quick visual inspection. In the video below you can see how the frames are made and how the mesh is tensioned onto the frames. Before you click the play button, note the shadow below the frame, which increases from the left to the right. This is a sure sign that the frame is not flat on the table, and it will not be flat on your substrate when installed on your press. As you watch the video, see if you can find the other problems that render these screens almost useless to anyone other than a hobbyist.

Hopefully, as you watched the video, you notice the problems created by the manufacturer of these SAG frames. The most noticeable errors are:

Figure 2: 90-degree Right Angle Welding Clamp

  1. Non-Flat Work Surface During Welding: The welding was done on a non-flat surface, which created a frame that is not flat and transfers an uneven amount of ink during printing. The uneven ink deposit is created by different amounts of off-contact.
  2. 90-degree Right Angle Corner Clamp: Ideally, the four frame members would be clamped with four right angle clamps (see Figure 2) that would properly align the frame members.
  3. Order of Welds: The order of the welds as they are heated and cooled must be maintained to produce a perfect joint and all welds should be made and allowed to cool without moving the frame out of the clamp.
  4. Tensioning Table: The tensioning table is actually several tables, each at a different plane and covered with adhesive residue that lifts the frames unevenly and prevents even tension on the frames.
  5. Weight Usage: The weights you see placed around the frame are necessary as the frame is not on the plane and are used to pull the mesh down to the low sides of the frame to assure contact. This would not be necessary if the frames were on a plane with the tabletop.
  6. Use of Tension Meter: A tension meter should be used to assure that tension is equal throughout the tensioning area.

Unfortunately, this SAG frame manufacturer is not using any standard welding or tension procedures to ensure the making of a quality screen and is apparently not concerned about the product. And, sadly, this is repeated the world over by other manufacturers of SAG frames. The odds of purchasing a SAG frame that is of high quality is low. And no SAG frame can be tensioned to the mesh manufacturer’s suggested tension levels, nor expected to produce an ink deposit that is opaque with one stroke.

Background

SAG frames were used in most screenprinting shops prior to 1981, but they quickly lost their edge on the market when a young man fresh out of the University of Pennsylvania brought a new product to the SGIA Screenprint 1981 in Dallas, Texas. The product was overwhelmingly applauded for its ability to solve an enormous number of problems that screenprinters worldwide had been suffering since the beginning of the screenprinting process 100 years earlier. That man was Don Newman and the product was the Newman Roller Frame.

Now, some 40 years later, the vast majority of highly successful shops use Newman Roller Frames and the SAG frames are relegated to schools, hobbyists, and novices just entering the screenprinting process. Many times, those just beginning in the screenprinting process will purchase their equipment from a distributor. Of course, there is always a budget to be considered by the printer.

You can easily resolve all of your frame problems by doing only one thing – taking the initiative to progress to a retensionable frame system. The purpose of Newman Roller Frames is to allow the mesh to be brought quickly and easily to proper tension levels, then occasionally retensioned to maintain a consistent level while the mesh becomes work-hardened which allows for a precision ink transfer, smoother finishes, even and consistent color, improved registration and faster setup times. All of these equate to an increase in margins due to more efficient and effective processes, to bring about consistent, predictable, and reliable standards.

Case In Point

Mike Knox of Stormforce Screenprinting in Cerritos California printed apparel for schools and unfortunately, school athletic apparel has large solid areas of white ink on a darker color substrate. Many of the prints would take three or four passes to achieve opacity. He had just invested in a new automatic press and was unable to achieve a One Hit White™[2]. He called us in to train him on printing these larger images with a single stroke.

 

References

  1. Newman Roller Frame, Stretch Devices, Inc. http://stretchdevices.com
  2. One Hit White™ was coined by the author Bill Hood in 1983. http://billhoodconsulting.com


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