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First of all let's dispense with a myth. Mesh, today, is not actually made of silk, even though the term "silkscreen printing" is still around to confuse the issue. (Tell people you're a screenprinter, and they respond with a baffled expression; mention "silkscreen printing" and a look of comprehension dawns on their faces.) In the early days, silk was, in fact, used throughout the industry, but today most meshes are made of polyester, a few others of nylon or steel wire.

Polyester is a man-made material resistant to almost any kind of ink, solvent, and reclaiming chemical used in screenprinting. Incredibly rugged, it stands up to the abrading action of repeated squeegee strokes and the corrosive effects of the caustic chemicals used in the de-hazing process. Able to withstand tremendous tensions without tearing, it can maintain those tensions, with very little loss, through many print strokes and reclaiming operations.

Good mesh remains elastic. Push against it with your finger and you can cause it to distend. Release that pressure and it snaps back to its original shape. This characteristic lies at the very heart of the screenprinting process. The same push, release, and snap back will happen as you pull your squeegee across a screen in a printing stroke. The leading edge of the squeegee forces the mesh, and the stencil it carries, down onto the substrate. As the squeegee edge passes, the natural resiliency of the mesh causes it to lift up and away from the printed surface and return to its normal undistorted shape. With every printing stroke the screen is forced down and flexes back.

This is known as off-contact printing and, with few exceptions, it is the way most screenprinting jobs are printed. Off-contact simply means that mesh comes into contact with the substrate only when the squeegee forces it down onto the surface. For most jobs, an off-contact distance of a mere 1/16th to 1/8th of an inch is sufficient, the approximate distance properly tensioned mesh will flex without the printer expending unnecessary effort or causing excessive wear and tear on the screen. A very small distance to be sure, but an important one, because without it, the resulting print would be a smeared mess. Numerous printing problems can be traced back to failure to check this vital off-contact distance when setting up a print job.

PUTTING MESH UNDER THE MICROSCOPE: Monofilaments vs. Multifilament

Let's take a closer look at mesh and its marvelous flexing ability. In fact, let's take it right down to the level of a single thread. Under magnification, an individual thread appears as a single uniform strand, virtually identical in appearance to the fine monofilament line on your fishing reel. Monofilament simply means single strand and monofilament mesh happens to be the kind of mesh woven from such single uniform strands.

Monofilament mesh is, by far, the most common type of mesh used in screenprinting today. However, another type of mesh, called multifilament, is frequently available and it is important not to confuse the two. Multifilament meshes are woven from an entirely different type of thread and the results they produce are markedly different.

If you were to look at a thread from a multifilament mesh under magnification, it would appear to be formed by a number of smaller threads twisted together. It looks like the thread you use for sewing. Multifilament mesh became the first synthetic mesh introduced into screenprinting and strongly resembles the silk thread it was designed to replace.

Multifilament’s popularity has suffered in recent years because these tiny threads tend to obstruct part of the open areas of the mesh, especially as wear takes place. And it has a couple of other drawbacks: it doesn't hold tension as well as monofilament, and it tends to be difficult to reclaim.

The other alternative, stainless steel mesh, is commonly used in printing ceramics and printed circuit boards, but would have little application in sign printing. Surprisingly, steel meshes are easily damaged; the slightest kink puts them out of service and they wear rather quickly.

WEAVING FACTS

Mesh is made up of perpendicular threads. Threads that run longways are called the warp and the ones that run crossways, the weft or woof. These threads cross over one another creating a mesh approximately two thread-diameters thick. There are two basic ways to weave mesh: the common 1:1 over-and-under grid pattern called plain weave, and the more complicated patterns that create twill. In twills, some threads are doubled, or even tripled. The weaving pattern is described numerically, for example 2:1, 2:2.

The threads-per-inch and thread-diameter in a twill weave can be exactly the same as in a plain weave mesh, but the weaving pattern produces a thicker mesh with more open area. Typically you will find twills only in higher mesh counts. Few sign shops will ever have to use anything but a plain weave, but it's important, however, to know that twills exist should you ever encounter them.

MEASUREMENTS OF MESH

Most meshes are imported from highly specialized manufacturing facilities in Europe. So rigorous is the manufacturing process that you can handle literally thousands of yards of fabric and never find a single flaw; and meshes remain remarkably consistent from bolt to bolt and from year to year.

The care taken in manufacturing and measurement is aimed at creating meshes so uniform that we can accurately predict how much ink will pass through them and onto the surface of a substrate. This is referred to as ink deposit and some think that controlling it is the Holy Grail of screenprinting.

In North America, mesh count refers to the number of threads-per-inch. In Europe, the measurement is calculated in terms of centimeters-per-inch. In fact, almost every figure originating with a European manufacturer has to be converted into English measurements, producing oddball results that end up getting rounded off and subjected to a number of fudge factors, so that North American measurements rarely correspond exactly to their metric-system originals.

A 230 monofilament mesh will have 230 tiny threads in an inch-long piece of fabric. Fortunately for screen stretchers, manufacturers almost always print this figure repeatedly along the whole length of fabric, because it is almost impossible to tell mesh count with the naked eye. Even someone who handles mesh daily probably couldn't come up with a reliable guess within 50 threads per inch unless they had some sort of measuring device handy.

The number of threads per inch can tell us approximately how fine the detail that a mesh can reproduce and how much ink will be deposited on the substrate. But, it also helps if we know how thick those threads are. So, most meshes are identified with a second number giving us thread diameter. A typical mesh designation will be something like "230.34". The ".34" gives the thread diameter in microns. A micron is a thousandth of a millimeter and is pretty much the standard unit of measure in referring to thread diameter, mesh opening, and ink deposit.

The higher the number the thicker the thread. Two meshes can have the same mesh count, but different thread diameters. Of the two, the one with the greater thread diameter will be the stronger and probably a better choice for tight registration work. But because it will also have less open area, it may significantly reduce the amount of ink that gets passed through to the substrate. This can be the reason why two screens stretched with 305 mesh produce very different imprints, an important factor to keep in mind when ordering screens for jobs where consistent results are essential. Thread diameter becomes crucial in four-color work.

WHY SO MANY DIFFERENT MESHES?

A well-supplied screen stretching service may stock twenty or more different meshes with thread counts ranging from a low of 35 per inch to more than 400. They may stock a number of rolls with identical thread counts but each with a different thread diameter. The need for such variety is simply explained. Screenprinting has become such an adaptable printing method that the customers will be applying a wide range of inks to an almost endless variety of substrates. The solid components in those inks may vary in size from huge chunks of glitter in certain textile inks to the microscopic pigments used in UV printing. Materials as different from one another as plastic and T-shirts will absorb ink at different rates.

The common factor in all those different print jobs is that they all rely on mesh to control the ink deposit.

In Part II, our in-depth look at meshes continues with some thoughts on screen tension. Stay tuned for "Mesh Part II: The Tension Rises".