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Printer's Guidebook, Part X

Garment Characteristics

38. Substrate-surface texture
Those characteristics of a garment's surface that affect print quality.
Notice that every ink company's instruction sheet reminds us to always test before production. This is partly because-aside from differences from one ink to the next-each fabric has its own unique surface texture that must be conquered by the ink. A smooth surface is much easier to print on than a course fabric because-like a road crew filling potholes-the ink has to penetrate into the "valleys" of the fabric.

On the surface

The print surface is a function of the knitting or weaving method used to make the fabric in the first place. Weaving tends to be smoother, flatter, more tightly packed, with little compressibility. Knitting, because loops of yarn are drawn around each other (interlocking), is more flexible, looser, with more holes.

The texture of a knit is created by what are called wales and courses, similar to the warp and weft of screen mesh. Finished goods can be measured for fiber mass, which is a combination of the texture of the yarn, how thick it is and how tightly it was pulled during the knitting process. The greater the fiber mass, the fewer holes in the fabric-which makes it a better printing surface.

Knit fabric has a definite face (outside which is smoother) and back (inside). The face has distinct vertical lines which are different for all shirts and can-if not taken into account-cause moiré patterns with halftone or process prints. (Note: For the sake of experimentation, once you have a process job printing well, print as many different shirt brands as you can, and note the print differences that occur when this variable is changed.)

Jersey or "plain-knit" is the simplest knit found in most T-shirt fabrics. After jersey, rib-knit, Tompkins knit, interlock, piqué and thermal are other popular knitting methods found in garments. They all describe distinct shapes of the wales and courses in a knit (and they all make printing more difficult, because the surface has more texture).

Fleece (or pile knitting) and terry cloth (or toweling) is even more complicated, because an extra set of yarns is drawn out in long loops and then cut (sheared) or not, depending on the desired effect.

Fabric specifications

Thread count and thread thickness will affect the feel and bulk of the material. Just like screen mesh, more threads per inch and thicker fibers will produce thicker material.

A knit fabric will usually be specified according to the yarn number, the stitch count, the word "single" and, finally, the type of knit-something like this:

18/40 single jersey (which means number-18 yarn, 40 stitches per inch, single-ply cotton, plain knit).

It will take some effort with your suppliers, but ask them to provide you with such data on each shirt you buy. You want them, in particular, to tell you yarn number and the type of yarn; you can count the stitches per inch yourself.

The word single is used to describe the ply of the yarn. A single is the most popular and means single-ply, raw cotton twisted into a single thread.

Stitch count is measured in stitches per inch, much like mesh, and is the reason knitters and weavers-just like printers-carry "linen loupes." Put the loupe on the fabric and use a pointed object (such as a pin) to keep track of your place as you count stitches per inch. While you're at it, look at the detail of the fabric surface. Again, as with screen mesh, the spacing between the threads will determine how well the fabric breathes and how many holes it offers for ink to fall through.

Cotton yarn used for T-shirts is measured by an obscure method called "yarn number," based on how many hanks (840 yards) there are in a pound of yarn. Since this is always based on a pound of yarn, a higher yarn number means a thinner yarn. (Incidentally, there are about 7,500 yards of yarn in the average T-shirt.)

Man-made polyester yarn (which, spider-like, is squirted out of spinneret) is measured by denier. The denier system is based on the weight, in grams, of a 9,000-meter length of yarn. Notice that this is the opposite of the cotton-yarn measurement system, so lower numbers mean finer yarns. If this seems a little confusing, that's because it is. Don't worry, though: it's rare to see a shirt, even a poly/cotton blend, described using denier.


Your design and image details must bridge fabric gaps as the substrate gets coarse-unlike those flat-stock graphic printers with their smooth white paper. The composition of the yarn itself also influences this coverage aspect.

Our yarns for shirts are spun. The old, established method is "conventional ring-spun" which is 300 years old and requires more processing steps than "open-end spinning" which was invented in Czechoslovakia in 1967.

Spinners love open-end because it eliminates three steps and needs almost no knots in the long thread to repair breaks. This means higher production speeds at the mill, less power and space.

Both types of spun yarn have protruding fibers because of the way they were roughly spun together. This can actually be desirable for absorption of ink and perspiration, but it can also result in shedding of lint, fibrillation and pilling during handling and laundry. The ideal printing surface is one of high-mass fabric made of combed cotton. The combing aligns and smooths the cotton fibers so they behave.

39. Substrate porosity
The extent to which individual textile fibers offer ink the opportunity to penetrate.
Porosity refers to actual spaces in the substrate fibers which are minute channels in an apparently solid mass. Knowing the type of fiber on which you are printing is important, because a given fiber's chemical nature determines the kind of ink to be used. In apparel printing, mistaking one fabric for another isn't too likely, as the types of fabrics commonly decorated are so obviously different from one another.

Man-made, synthetic fibers such as nylon and polyester have fewer pores than natural fibers such as cotton, so ink and moisture are attracted to and retained in and around the fibers differently. Unlike synthetics, the pores in cotton allow ink to be absorbed into the fiber rather than just attached to it.

Knit fabrics tend to absorb more than wovens, because there is more fiber exposed (see Variable 38: SURFACE TEXTURE). The loose structure and stretchability of jersey-compared, for example, to tight, inflexible cotton sheeting-creates more surface area for ink to penetrate and wrap around the fibers.


The porosity of nylon jackets, caps, tent, banner and other materials is often affected by protective coatings that must be defeated prior to printing (if not, your ink will be just another stain to be repelled). This also defeats some of the performance benefits of a jacket or umbrella, if you must attack the coating with a harsh solvent such as acetone in order to print it. Some jacket and banner-material suppliers continue to produce products with impervious protective coatings, forcing us to use strong, catalyzed adhesive additives which insure permanence, but also lend a harsh, thick feel to the ink, so consider this aspect before placing a large order.

Finishes are also added during garment manufacture to help the dyestuffs bond with the fibers. We never know what might have been done to a fabric during processing, even if we have a long-standing relationship with a manufacturer. Finish coatings such as latex starches that make the fabric stiffer, easier to cut and push through sewing machines are meant to wash off the first time you launder them. If garments are printed prior to laundering (as they almost always are) such coatings act like removable barriers that prevent the ink from bonding well-some ink washes down the drain with the finish.

Some finishes can actually improve ink absorption. Towels and beachwear sometimes have absorbent finishes added to help the material absorb more pool or bath water than normal. This, of course, increases ink absorption (and will also increase your ink consumption).

Press loaders and packing workers will be the first to sense the difference between finishes, because shirts' feel and behavior is influenced by finish. This practical experience will give you feed-back on which shirts load, print and feel better than others-a very good thing to understand and exploit as a selling tool. The feel and look of a finished garment is something most consumers don't know they have a choice about. Thus, when they come to you, you can offer them a choice beyond price.

Relative Fiber Characteristics





 penetration of water-borne stains (including ink!)



 more difficult for the dyer to color



 absorption of resin finishes



static charges build up 



 quick drying



 less comfortable (clammy)



 easy evaporation of perspiration



 dimensionally stable to water



 good wrinkle recovery when washed


40. Garment color
The background color of the substrate can affect those colors that are printed on top of it.
Unless you're using totally opaque inks, garment color, like any colored background, will affect the imprinted colors. You can use this to your advantage if you incorporate the shirt color into the design, but many customers want the same imprint on six different shirt colors and are not pleased at the prospect of paying for separate designs for different garment colors.


The most common method to overcome a garment color's influence on the ink is to seal it with a light- or neutral-colored ink, gelling the ink with a flash-cure unit, then printing on top of the sealer. A sealer is also referred to as an underbase, an underprinter or a flash plate. White, gray, orange or blue-gray are common sealer colors, but these are certainly not the only ones you can use.

Depending on the finished look desired, you could seal with a plastisol ink, but then you're printing on a sheet of vinyl and it's more difficult to print wet-on-wet without smearing. Many printers design without the use of a flashed sealer, but they may also sacrifice crisp sharp prints because the ink blends together as they push down on it with successive blade strokes. This method is also difficult because you have to design with limited colors and design shapes in order to take advantage of considerable negative area.

There have been innovations in water-based printing that allow you to use discharge ink on certain shirts, without a traditional sealer. These are very interesting because water-based inks don't allow dye migration as plastisols do. As with flashed sealers, such inks are printed first, in order to be under the other colors.

Transparent inks on a sealer or colored shirt will also create new colors by overlapping transparent or semi-opaque inks. Designs on dark garments can exploit the fact that transparent inks lose their color when the shirt color shows through. This is also why you can't print process on dark garments without some form of light-color sealer behind it to reflect light.

Some dark colors such as maroon, deep red and blue create problems because the dye used is unstable and reacts with curing temperature, flashing or ink chemicals. Always test first.

Curing time

Shirt color can also affect the temperature in the dryer (see Variable 49: PANEL INTENSITY). If you're using an electric dryer, its infra-red energy is light energy. Light-colored shirts reflect the light energy, so it is "recycled" and helps to cure other shirts. Dark-colored shirts, though, absorb light energy. Thicker shirts, as well, will absorb more energy because there's more of them to absorb energy. These factors will change dryer temperature. All this puts a load on your system that it must recover from, as you send shirts through the cabinet. Accordingly, methodical cure testing is recommended.

41. Garment moisture content
Must be evaporated out of garment before ink will cure.
Unless your shop is in the desert where the relative humidity is low, your shirts have moisture in them which will retard the ability of the shirt to heat up for curing, because the water acts like a coolant.

Prints of both water-based and plastisol ink suffer from this problem when it comes to moisture in the garment, but in different ways. Neither type of ink will stick unless its resins are completely fused to the shirt. Thus, your oven must supply enough heat to remove all the water from a shirt and then the additional heat needed to raise the temperature of both shirt and ink to over 300°F. (Check with your supplier for the exact curing temperature required for a given ink.)

Plastisol ink must reach at least 300°F in order to fuse to the shirt. Water-based ink needs all the water evaporated out of the ink film first, then its resins can heat up and fuse to the shirt. Problems occur if the heat energy in the oven or flash cure is spent evaporating the moisture before it is able to heat up the shirt and ink. Because the time it takes to heat up shirts can change with moisture content, you must check shirts during the production run.

Try this moisture experiment in your shop. Take a misting spray bottle, or hand-pumped spray gun and lightly spray half of a T-shirt with water. (Don't get it soaking wet-that wouldn't be fair.) Run it through your dryer. You'll find that when you touch the shirt as soon as it comes out of the dryer, the dry side of the shirt is hot and the sprayed side of the shirt is cool. This is because just spending 90 seconds in the dryer won't remove the water from the shirt (much less bring it up to curing temperature). The water is absorbing the heat and keeping the shirt from heating up. Thus, more moisture in the garment means longer to heat up your shirts. The only way to check this is through regular monitoring with a thermometer.

Garments in the oven

Venting and convection is very important for curing shirts. Where will the moisture go? As you raise the temperature of a shirt to fuse the ink, moisture contained in the shirt before it was printed will evaporate, or vaporize. The water has turned into a gas, but has no place to go in a closed oven cabinet. When the air in a closed oven cabinet becomes saturated with as much moisture as it can hold, there is no more reason for moisture in the shirt to leave it and go into the air. Granted, air can hold more moisture as it heats up, but eventually all the air in an oven will become saturated.

"Dryer" means just what it says-to remove moisture or water-but an oven is simply a chamber in which to heat things. Thus, ideally, you need a dryer system in your shop which will not only heat, but will remove the moisture from the heating cabinet. This is much like Mom's clothes dryer which removes wash water from clean clothes. That moisture has to be vented out of the system for the clothes to dry. Just a vent on the top may help to remove some of this air from the cabinet, but you really need to send it outside where it can't interfere with intake air. The best dryers, therefore, use high air-pressure vacuum to pull hot air through the garment and back into the heating cycle again.

As a way of keeping an eye on the conditions of the shop, make sure there is a thermometer/hygrometer present. This helps you predict when a shirt might need extra time in the cabinet of the dryer, by assessing the shops ambient humidity. (Radio Shack has an inexpensive digital model.)

On Press

42. Off-contact distance
The gap between the bottom of the screen and the top of the substrate (or top of the ink deposit).
The affect high-tension (greater than 20 Newtons per centimeter) has on both the finished print and on press set-up is, in fact, a function of off-contact. Because screen printing is, by definition, an off-contact method of printing-wherein the force of the mesh (rather than the platen or substrate) must resist the blade-these opposing forces combine to make the ink transfer through the mesh, like toothpaste from a tube. This cannot occur without off-contact.

With older presses that lacked off-contact adjustment, we didn't care much about it because we couldn't change it. Now, though, off-contact adjustment is a standard feature, and a new plateau has been reached via computer-driven off-contact systems on some of the latest generation of automatics.

Manual presses

Beware, manual printers, if you don't adjust off-contact on your manual press, you'll be frustrated when you get an automatic press. With a manual press, the feedback you get from your arms and hands tells you to slow down and pull the mesh out of the ink film. The insensitive motors and gears that lift the heads on an automatic can't tell whether the mesh is out of the ink film or not. Thus the importance of getting used to adjusting off-contact (even if your press doesn't accommodate such adjustment).

Train your operators to raise the screen with solid (that can't compress) strips of plastic or wood under the frame, in the holders. Such shimming is necessary because most manual presses don't have the ability to change the entire head assembly to raise the rear pivot and the support that stops the head from coming down past a pre-set point. (If your press only has an adjustment under the print arm, you're likely to change the parallelism of the press by raising the screen like a cannon; this will frustrate your printers.)

It is also a good idea to put a shim under the screen away from the holders at the point where it hits the peninsula on the platen that sticks out from the garment's neck. This will support the screen as you push down with the blade, holding the frame like a bridge across the shirt and helping the mesh to pull itself out of the ink film.

Distorting the print

Tighter screens print better, and increasing off-contact is a common way printers simulate higher tension, especially when they use low-tension (below 20N/cm) screens. The price they pay for this is that they also stretch the image so that it won't fit together with the other colors in the design. Remember, if we stretch the stencil, it no longer matches the positive.

Beware, if every screen is a different tension, and every screen has a different off-contact distance, you will distort each screen differently which will make registration very time consuming if not impossible. It is fundamental that differences in off-contact and screen tension will cause set-up problems, because every screen will be unique and different. An ideal printing set-up specifies an off-contact distance that is the thickness of the ink deposit, plus a minute space between the stencil and ink film. This is very hard to achieve with textiles because of multiple-platen machines and shirt variances, but we must still strive for it. We also print with different types of ink and many different ink deposits within a single design. Naturally, the off-contact must be greater if there is more ink to be deposited.

(Demonstrate the extent to which tension is dynamic by putting a screen on blocks of wood with a tension meter in the middle. Push down with a blade and watch the tension shoot up. Could this be why you've been ripping screens during press runs?)

Measuring off-contact

The best shops create standard operating practices of screen tension and off-contact distance and try to return their presses to a "neutral" position before setting up a new job. (Imagine the standardization of audio cassette players and their tapes. Each and every one can play each other's tapes because the tape speed, pressure, head location, case size and so forth are always the same. You can do this in your shop.)

Measure off-contact with a dial indicator and straight-edge system. The level shown (at right) is the straight edge, and the dial is mounted on it. First, zero the dial indicator with the center shaft gently resting on the mesh. When you press down on the shaft, you can measure the off-contact distance. You can also use automotive feeler gauges or index cards to measure the gap, as long as whatever method you use is the same every time.

A change in off-contact distance will affect blade pressure and screen tension in an equalizing fashion. Increasing off-contact increases tension in the screen as the blade overcomes the off-contact distance, and the blade bends as it brings the stencil in contact with the substrate. Higher screen tensions have caused the use of stiffer blades so they don't bend against the increased resistance. More screen tension helps pull the mesh out of the ink film. Reducing off-contact has the opposite effect.

The correct setting of off-contact solves this problem by making sure the mesh is out of the ink film before the head picks up, but not so much as to over-stretch the stencil. You can snap up the head (which is what an automatic press does) as fast as you want to, because the mesh is already clear.

The ideal set-up has the mesh pulling out of the ink immediately after the blade passes, so the blade speed controls the stroke and peel. You need mesh that's tight enough to pull itself out of the ink film, or you'll be raising the off-contact and using the blade as a mesh-tensioning device. It's the job of the screen to pull itself out of the ink film. Manual printers suffer from low-tension screens because they have to do all the work, rather than sharing the work with a high-tension screen.

You must have at least the ink thickness as off-contact distance, but don't forget the thickness of the shirt. If you change from T-shirts to fleece, the thicker shirt will reduce the off-contact if you don't raise the screen. Newer presses have off-contact adjustments which, combined with an off-contact gauge, can accurately change off-contact in minutes.

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