CHOOSING THE RIGHT EMULSION

In the screen printing industry, choosing the right emulsion is as important as proper knife selection is for a chef.  Imagine carving a roast with a butter knife.  Sure it can be done, but a more effective tool exists and the best chefs know how and when to choose based on their needs.  Similarly, different types of screen printing jobs benefit from different screen emulsions in order to increase print quality and save time on press.  We’ve broken down the different types of emulsions available, their general qualities, and the pros and cons of each for different types of print shop needs.  We’ve also provided some questions you should ask yourself before choosing an emulsion for your particular situation. 

Types of Emulsion

Capillary Film

Capillary film is a photo-sensitive emulsion that is manufactured and sold in sheets or rolls of a predetermined thickness (measured in “microns”).  It is applied directly to the screen using water and a squeegee.  The micron you select will basically depend on the substrate you will print on.  T-shirts require a thicker micron (eg. photopolymer EZ Film 50) that is usually used on screens with a mesh count of 200 or lower.  Four color process or simulated process require a thinner micron (eg. photopolymer EZ Film 30) to reduce the amount of ink deposited per print.  Capillary film is also used in industrial applications like circuit board printing with high levels of detail (eg. dual cure CDF Vision which is solvent resistant). 

Direct Emulsion 

Direct emulsion refers to liquid emulsions that are applied directly to a screen using a scoop coater.  It can be applied to both the ink and substrate sides of the mesh in multiple layers to achieve a stencil micron specific to the substrate the screen will be used to print.  There are two basic categories of direct emulsion; dual cure and photopolymers.  The third category is a diazo emulsion.  We won’t get into diazo emulsion here as manufacturers are phasing out this type of product.

 1. Dual Cure

Dual Cure emulsion is a (diazo) direct emulsion that is not pre-sensitized.  This means a photo-sensitive additive must be mixed into the emulsion before it can be applied to screens for exposure.  Dual cures utilize some of the straight diazo and some of the photopolymer properties.  Dual cure emulsions have a medium solids content that results in a thinner product that will require more coats be applied to achieve a thicker micron.  They generally require a longer exposure time.  Out of the bucket, Dual Cure emulsions are also generally appropriate for plastisol or solvent inks.  If you’re not using a water resistant formulated dual cure emulsuion and plan to print water base ink you may need to apply a hardener after rinsing out your stencil to avoid breaking the emulsion down on press when ink is applied.

2. Photopolymer

Pure photopolymers are a category of emulsions that are pre-sensitized and photo-sensitive directly out of the container.  Photopolymers typically have a high solids content that results in a thicker product that requires less coats being applied to achieve a thicker micron.   They are very sensitive to UV light.  As a result, they expose much quicker than Dual Cure emulsions.  This faster exposure capacity also makes for a less forgiving exposure range, meaning you will go from under-exposed to over-exposed in a much shorter time frame than with Dual Cure emulsions.  Traditionally, standard photopolymers will stand up to use with plastisol inks only.  If you intend to use solvent or water based inks, you’ll need to choose a photopolymer specifically formulated for that type of ink.

 How to Choose

We are often approached by customers asking what kind of emulsion they should choose, which leads to a series of questions about your shop’s set up and production capacity.  The answer to each question will inevitably spin off more questions because screen printing success relies on many factors interacting together to result in a final imprint.  This is by no means a comprehensive list of factors that will affect your final output, but should be a good place to start your thinking.

Do you have a dark room?

If you are just starting out and do not have a UV-safe darkroom set up, dual cure emulsions would be a good place to start since they are not sensitive to UV light while wet.  You could coat your screens in normal lighting, put them in a UV-safe place to dry and then get them right on the exposure unit with minimal interference in your final stencil quality.  A photopolymer would not be a good option due to their high sensitivity to UV-light and potential for pre-exposure issues.

If you do have a UV-safe dark room, you have the option to use either dual cure or photopolymer emulsion.  If you don’t already have them, our fluorescent tube UV Safety Sleeves will provide the best visibility and 100% blocking capacity for your dark room set up.

What kind of exposure unit do you have, and what is your output need for screens on a daily basis?

Take your model of exposure unit into consideration when choosing emulsion.  The key here is considering where your production process is reaching a bottleneck.  The intensity of your light source will have a dramatic impact on your exposure times and overall productivity of your screen room.  If you have a low intensity light source, your exposure time with a dual cure emulsion is going to be potentially very long, but could be cut in half if using a photopolymer emulsion.  This could potentially double the number of screens you prep in a day, turning into increased output from the production floor.

Quartz Halogen

Standard Flourescent Tube / Blacklight

LED

Metal Halide

Another benefit of photopolymers for low-output shops is their longer shelf life.  Once sensitized, a dual cure emulsion will only last about 2-3 months under average storage conditions.  If you’re only shooting a few screens a month, you could be wasting valuable product once it’s expired.  A photopolymer generally has a shelf life of up to one year and could save you from pitching what you paid for over time.

What kind of inks are you using?

Every emulsion is formulated to withstand certain types of ink bases.  There is NO emulsion that can be used with solvent, plastisol, and water base inks. If your shop prints with various inks on a wide range of substrates you will need more than one emulsion in your repertoire.  If you are a more specific niche printer that only uses one type of ink on a limited range of substrates, you may be able to coat all of your screens with the same emulsion. 

If your shop is printing exclusively with plastisol inks you can print with nearly any emulsion straight out of the container without experiencing stencil breakdown when properly dried and exposed. 

If you ever print with water base or discharge inks in addition to plastisol you’ll have a smaller selection of emulsions that can be used with both ink types.  Some straight-outta-the-bucket options for water base and discharge are Kiwo Multi-Tex or Ulano QT-Discharge.  There are even a few photopolymer emulsions that can be mixed with an extra diazo to make them water resistant. 

If you ever use solvent based inks for printing stickers or signs, you’ll need an emulsion that is solvent-resistant like Tech Support Dual Tech or a few options from Ulano or Kiwo. 

What kind of resolution do you need to achieve?

Do you primarily print lower-resolution graphics like spot color designs?  Do you also offer simulated process or four color process printing?  Or are you printing for industrial purposes like circuit boards?  Generally speaking, dual cure emulsions will hold a much higher resolution than photopolymer emulsions, but there are high resolution photopolymers on the market.  Each of these types of graphics have a typical ink type required as well, so make sure to ensure the emulsion you choose is ink-base friendly while meeting the resolution requirements for the job at hand.