 | Quote: |  | | |  |
Originally Posted by kineticesp |  | | | | | | | | | regarding to weight, how important is this parameter in screen printing?
I´ll appreciate some feedback here about other parameters/characteristics that one my find important. | |  | |  | |
Read about knitting standards at the ASTM
ASTM International
-Standards are in the store area
D 3887 Standard Specification for Tolerances for Knitted Fabrics
D 3776 Standard Method for Mass Per Unit Area (Weight) of Fabric
Control Without Confusion - Chapter 1 by Joe Clarke
How to Print T-shirts for Fun And Profit - Chapter 9 All About Garments by Fresener
Weight is important because it is a way to measure and compare.
Notice that every ink company's instruction sheet reminds us to always test before production. This is partly because 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 the ink has to penetrate into the "valleys" of the fabric, yet not fill in the holes like a road crew filling potholes.
On the surface
The print surface is a function of the weaving or knitting method used to make the fabric in the first place. Weaving tends to be smoother, flatter, tighter-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), and the face has distinct vertical lines. These vertical lines are different for all shirts and can cause moire patterns with halftone or process prints. Once you have a process job printing well, print as many different shirt brands as you can and notice the difference the shirt makes.
Jersey or plain knit is the simplest knit found in most t-shirt fabrics. After jersey, rib knit, fleece, Tompkins knit, interlock, pique 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 harder 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 diameter 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 data on each shirt you buy. You want them 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 all knitters and weavers carry linen loupes (just like printers). Put the loupe on the fabric and use a pointy object (such as a pin) to keep track of your place as you count stitches per inch. Take time to look at the detail of the fabric surface, while you're at it. 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.
Weight
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, 7,500 yards of yarn in the average T-shirt.)
Man-made polyester yarn (which, spider-like, is squirted out of spinnerets) is measured by denier. The denier system is based on the weight, in grams, of a 9000-meter length of yarn. Notice that this is the opposite of the cotton-yarn measurement system, naturally, so lower numbers mean finer yarn.
Confused, irritated? We're only just getting started. Don't worry though, it's rare to see a shirt, even a poly/cotton blend, described using denier.
Yarn
Your design and image details must bridge the 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 (think spinning wheel). The old, established method is "conventional ring-spun" which is 300 years old and takes many more processing steps compared to "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.
The yarn is made in a centrifuge so it has a very even diameter. Knitters love it because it runs through their machines like a dream, but the hand is very rough. They add LOTS of softners to make it feel better. Softners are chemical coatings that fill the irrularities of in the yarn to make it smoother like body putty on a car. Softeners are like sizing, they wash out during the first laundering. When you print on the softeners the print looks great, but after the first wash the softners carry away some of the ink.
Quality of the shirt effects the loading speed. Lint, fabric weight and hand. texture.
You may be better off suppling a higher grade of shirt when there might be a handling advantage. You might not be able to produce as many inferior shirts per day. You could pass this advantage to the customer.
Profits come from units per day. Don't be fooled by the illusion of
economy with a cheap shirt.
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 you also get shedding of lint, fibrillation and pilling during handling and laundry.
The best printing surface is a high-mass fabric made of combed cotton. The combing aligns and smooths the cotton fibers so they behave.
At the opposite end of the agony spectrum are more novel fabrics such as nylon or spandex and Swiss-cheese-like athletic mesh for football uniforms.
Elastic stretch and recovery from elongation (from 500 to 700 percent) are the most important properties of spandex. It is very smooth and takes ink well but it is very difficult to formulate and print with an ink that has those same stretching properties.
Athletic mesh offers more open area than fiber and you waste tremendous amounts of ink as you print; it passes through the holes and prints the platen
Tshirt weight and other parameters 
had a good laugh on that ! Nice one!
