Learn How To Screen Print!   

This is a progressive list of the articles on this page. Scroll down the page to find articles further down the list. Scroll down to read articles!

Understanding Emulsion

Outputting Artwork To Film

Mesh Count And Thread Diameter Nomenclature

Squeegee Durometer And Print Results

Scorched Garments And Scorch Out

Check the Article Archive for the newest articles!

Understanding Emulsion

The first and foremost important thing to remember with emulsions is that they react to ultraviolet light. This reaction causes it to “cure” or become hard. Normal ambient white light has enough UV to expose emulsions over longer periods of time. This is why emulsions are worked with under yellow or red safelight conditions.

That means your exposure source has to output a good amount of UV in order to expose your screens within a reasonable time. The less UV your light source outputs, the longer your exposure times will be.

Because emulsions can also react to excessive heat, prolonged exposure times to high intensity light sources with low UV output can be problematic. An example of such a light source would be the sun. Light sources like the sun can literally cook the emulsion with heat alone causing it to solidify.

Different emulsions vary in their photo sensitivity. Some will expose faster than others depending on light sources. This is why it is necessary to consider your light source when choosing an emulsion.

Today’s emulsions use only two types of photo sensitizers. Diazo, which has been around for some time and Styryl Basolium Quaternary photopolymers called SBQ photopolymers which are relatively newer. The sensitizers are added to a resin base of polyvinyl alcohol or polyvinyl acetate to make the emulsion.

This means that emulsions can be categorized into three groups based on the two photo sensitizers; diazo, photopolymer, and dual cure emulsions. Dual cure emulsions combine the best features of the other two. At the same time they compensate for some of their individual flaws.

The basic three types of direct emulsions: Diazo, Photopolymer, and Dual Cure.

Diazo emulsions are the least expensive and have the lowest light sensitivity of the three. If your light source is weak, a diazo emulsion can cause you difficulty. However, they also have the widest exposure latitude and can be forgiving. Diazo emulsions are not well suited for fine detail because they tend to make a thicker stencil. You will want a thinner stencil for the reproduction of fine details and halftones.

Another thing to note about diazo emulsions is that they come in either solvent-resistant or water-resistant types. That means if you use both solvent and water based inks, you would need to stock two types of diazo emulsions. They also have to be mixed with the sensitizer correctly to achieve optimum results. Once mixed, they have a shelf life of about two to three months depending on conditions.

Photopolymers or SBQ photopolymers are also called one-pot emulsions. These are the most light sensitive and therefore fastest emulsions. They also have excellent shelf lives in excess of one year but they tend to cost a lot more too. Because the sensitizer is mixed with the polyvinyl base by the manufacturer, SBQ photopolymer emulsions are excellent at the reproduction of fine detail.

Although SBQ photopolymer emulsions are faster, they tend to perform best with good light sources because their exposure latitude is small. If you work with water based inks, you can find some SBQ emulsions formulated to be specifically water resistant. They are also less affected by ambient humidity most of the time.

Dual cure emulsions have a combination of the qualities of both diazo and SBQ emulsions. As a result their exposure times fall in the middle range of diazo and SBQ emulsions. The exposure latitude is wider than diazo and they can reproduce fine detail better as well. Dual cure emulsions are less expensive than SBQ photopolymers and work well in high humidity. The shelf life of a dual cure is less than that of a SBQ photopolymer emulsion.

The dual cure emulsions are also a two part mixture. They have to be mixed well to achieve their best performance much like the diazo emulsions. You can find many water resistant varieties of dual cure emulsions.

Viscosity and solids content of emulsions can also affect the performance in your application. The higher viscosity, the thicker the liquid is. Thicker emulsions do a better job of clinging to lower mesh counts. Thinner emulsions, on the other hand, easily penetrate higher mesh counts. Higher viscosity emulsions will have a higher percentage of solids. Emulsions with higher solids content will reproduce fine details and halftones better. Solids can also help fill gaps in course mesh.

Tips:

- Emulsions may be stored in a refrigerator to prolong shelf life. Make sure not to let the

  emulsion freeze.

- Do not expose your emulsion to excessive heat.

- Always work in darkroom conditions with your emulsion to avoid problems.

- Mix your emulsions well before each use.

- Make sure the emulsion container lid is secure and tight during storage.

Outputting Artwork To Film

Outputting your film properly is a key factor in being able to produce an excellent stencil easily. If your film is not opaque enough, you will have trouble making a good stencil. Films that lack the opacity to block the exposure source 100% will end up semi curing the areas that you will need to wash out. Trying to wash out semi-cured emulsion is problematic for many reasons.

It will take far longer in the washout booth to get the emulsion to completely wash out. This will cause the emulsion to become saturated with the water and possibly swell, wrinkle or details will wash out as well. If you try to underexpose your emulsion to compensate for inferior opacity in a film, saturation problems and loss of detail will become more apparent.

There are many output media available for printing your film from a computer. There are clear inkjet and laser films as well as laser vellum. Making an opaque piece of film at home with standard printers is a challenge. Most professional screen printers use Epson or Xanté printers with RIP software. RIP software is designed to make your computer and printer function ideally and output graphic art with 100% opacity. It controls the functions of the printer, in many cases, to output in only black. In some instances you are able to replace color ink cartridges with all black. In other situations the printer itself is designed to output film and only prints in black. You can create your artwork normally in any graphic design program and send the file to the RIP software via the print function. From the RIP software, you will print the opaque film. The bottom line is RIP software will make the printer lay down much more ink or toner than without it. RIP software is a must for any high volume, high quality commercial screen printer.

The biggest drawback with RIP software is the cost. The prices can range from $400 to well over $1000. There are many different RIP software packages which may or may not include printers. Manufacturers will often offer various solutions for RIP software purchases. You will have to do your research well in order to find the best RIP for your applications. The need for performance, ease of use and low cost are hard to balance.

There are many, many companies out there who make and sell RIP software. There are a couple of Shareware versions of RIP software that I understand work very well. The most popular is called Quad Tone Rip or QTR. This is RIP software that is configured for Epson printers. Quad Tone Rip is really designed for photographs and will do nothing more than control color and resolution. Therefore QTR is not well suited for making film for screen printing but it does clean the black up to a nice rich black and improves the image quality quite a bit.

Some people will say that the film opacity is not so important because it is more about curing the emulsion that gets exposed. To me it’s the same difference, just put a different way. The bottom line is opaque film makes making screens easy in any situation. Opaque film will make your life easier and allow you to teach anyone to make screens.

Here are the links:

Quad Tone RIP/QTR

Here are the links for Xante and Epson:

Xante

Epson

And finally, here are some additional links to premium RIP software:

MultiRIP

WASATCH SOFTRIP

AccuRIP

ULANO RIP

Mesh Count And Thread Diameter Nomenclature

You will often see specifications for screen printing mesh that looks like this,

355-34Y PW

The number 355 represents the mesh count of 355 threads per inch. The number after the dash, in this case 34, refers to the thread diameter. The thread diameter, mesh count, and solid content of the ink will determine the amount of ink that passes through the mesh.

The letter Y tells us if the mesh is yellow or W for white. Those are the two most common colors of mesh.

The letters PW refers to the weave type of the mesh. PW stands for plain weave and TW stands for twill weave.

To put it very simply, mesh opening is the spacing between adjacent threads. It is determined by the thread count and diameter. Mesh openings dictate the maximum particle size you can use in an ink and it affects the overall detail printed as well as the ink release characteristics. For best ink passage through any mesh count, the maximum particle size must be smaller than 1/3 of the mesh opening.

There are some other specifications that may be referenced in this same line but this is pretty common of what you will see for textile screen printing mesh. And probably the information you will be most concerned with.

Knowing certain technical aspects of screen printing will help you better understand the process and gain more control over it.

Squeegee Durometer And Print Results

This is one of those topics that veteran screen printers may be divided over. Some printers believe that squeegee durometer does not affect ink coverage or opacity.  It may not be as important as having the squeegee blade sharp but there are physical properties of squeegee durometers that can affect your print.

In general a softer squeegee will transfer less force and tend to leave the ink on top of the fabric rather than pushing it into the knit. Softer squeegees give more and as a result make the printer stroke accordingly. This is a softer stroke to avoid over bending the flexible squeegee. Even though the squeegee may be soft and flexible, you do not want to bend the squeegee blade at severe angles. It should remain almost straight with a slight curve as you stroke. All of this lends to a heavier ink layer being deposited onto the shirt fabric.

Harder squeegees will transfer more of your force to the ink pushing it into the knit much more than a very soft squeegee. Harder squeegees may be easier for beginners to learn with and it is possible to get the same results as with a softer one.

In manual screen printing there are many variables that can affect the print. One of those variables is the manual flooding and stroking of the ink. Whatever squeegee you end up using, it will be your skill in using it that will ultimately be the determining factor in your end results.

The one factor that is very important to the squeegee is the condition of the blade edge. It should be straight, clean, and sharp. There shouldn’t be any nicks, grooves, chips or marks at all. A sharp squeegee blade will “sheer” the ink off in the open mesh, with a better deposit, allowing it to pull nicely through the screen.

Squeegee durometer is based on a 2 digit number system. The lower the number is, the softer the squeegee will be. 65 durometer is very soft and 95 durometer is very hard. 75 durometer is a common textile squeegee for manual printing.

Squeegee comes in different shapes like ball nose, single bevel, and double bevel. The best style squeegee for textile would be rectangular in shape. Squeegee can also vary in the way it is made. Single durometer is the most common. It also comes in dual and triple durometer styles where 2 different durometer squeegees are combined. This gives the squeegee the benefit of having some of the characteristics of each different durometer. For instance, you could have a soft blade part with a firmer over all feel.

To conclude, I would say a sharp blade edge is most important in textile printing. But the very fact that squeegee does come in so many shapes, sizes, and durometers would lead me to believe that technically it does make a difference in what type of squeegee you choose. 

Here is a link to an article that supports this and goes into squeegees in much more detail. 

© 2009 ST Media Group International.

Better Garment Printing through Squeegee Consciousness

Scorched Garments And Scorch Out

Sometimes garments that get to much heat in the oven will become yellow, brown or “scorch”. This means that the fabric will turn yellow slightly. It is especially true of 100% cotton, white fabrics. There are a few properties of garments that can warn you for potential scorching.

First of all any 100% cotton garment that is very light in color or white will have a natural tendency to scorch under excessive heat. Whether you want to attribute scorching to the actual burning or scorching of the cotton fibers themselves or you believe it is a chemical reaction from left over bleaching chemicals, the result and solution is the same. The truth is it is probably a combination of these two factors. I know that sending already washed and worn shirts through a tee shirt oven can make all sorts of stains show up. Especially white shirts. But be aware it is very possible to burn the fabric slightly which can cause scorching and degrade the integrity of the shirt itself.

The weight of the garment will also be a predicting factor in the scorching of white shirts. Usually lighter weight garments are more likely to scorch. That is to say an 8-ounce shirt will not scorch as easily as a 4-ounce product.  Shirts that are sold in retail stores as undershirts are very light weight. This includes many “wife beaters” or A-shirts. Be careful when working with these types of garments.

The quality or brand of the garment is also very important. Off brand shirts can be unpredictable in their behavior under the same conditions you may print name brand garments. Name brand shirts are more stable in all respects to off brands. Even the lightest weight name brand shirt will outperform the heaviest weight off brand.

The easiest way to solve this problem is to avoid it all together. Be sure not to expose your white shirts to unnecessary, excessive heat.  Always keep checking your white shirts as they come out of the oven. Sometimes residual heat buildup can cause your oven to run hotter over extended print runs. It is always a good idea to monitor oven temperature during print runs.

The other way to deal with slight scorching is to use a product known as Scorch Out. This is a product designed to work as a weak bleach. It comes in a liquid and is often dispensed by spray bottle or mister. You can spray it evenly and lightly over the entire shirt where needed. This is done after the shirt is printed and run through the oven so it will not affect the ink and can even be used on colored shirts like light blue. It will bleach the slight yellowing out of the shirt without affecting much else.

Some points about Scorch Out to remember:

- Scorch out will not remove stains from pre washed and worn garments that are sent through the  oven. These types of stains are most likely permanent and will not wash out either. It is best not to print and send used garments through the tee shirt oven for reasons involving ink adhesion.

- Scorch out is most helpful with white or very light colored shirts only. Darker shirts don’t necessarily scorch, they burn.

- Scorch out will not work on severely scorched or browned shirts.

BACK TO TOP