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NEWS FROM THE STAFF
PROPER SCREEN COATING: MAKE WHITES WHITER AND PRINTS CLEARER

Once your dark room is set up with essentials and you’ve chosen an emulsion, we come to the art of screen coating.  Yes, we describe it as an art because it takes an experienced touch gained through lots of practice to achieve a consistent coating every time.  Properly coated screens provide an even depth ink channel across the entire print surface.  An even ink channel results in a superior final print, meaning whiter whites and clearer prints.  Read on to learn more about proper coating techniques and how to troubleshoot issues you may be experiencing.

Things to Consider: Mesh Count and Substrate

            When coating a screen, you should always begin with the end in mind.  What artwork are you printing, and what will you be printing it on?  Emulsion creates a stencil “well” or “channel” that gets loaded with ink before the ink passes to the substrate itself.   Your coating decisions will depend on the stencil thickness required by the level of design in the artwork and the printing surface at hand. 

Your first important consideration will be mesh count.  Higher mesh counts (200 and above) will allow less ink to pass through the screen and can hold highly detailed designs.  You’ll generally need high mesh counts for printing hard and smooth surfaces like posters, stickers, and signs, or textiles printed with CMYK process or high detail designs.  Mid-range mesh counts (155 to 180) will allow a moderate amount of ink to pass through, and are primarily used for textiles.  Lower mesh counts (140 and below) will allow more ink to pass through with limited detail.  Low mesh counts are mainly used for printing textiles with block or athletic style designs.

When we talk about coating screens we use a coating ratio defined by “substrate side to squeegee side” of the screen (eg – 1:1 refers to one coat on the substrate side of the screen, and one coat on the squeegee side of the screen).  If you’re printing on a hard and smooth surface like a poster or sign and using a higher mesh screen, you will likely need less ink deposited and will probably only need a shallow ink channel achieved with a 1:1 coating ratio.  If you’re printing on textiles, the mesh count and ink well depth needed for any particular job can vary.  For example, a CMYK print on a t-shirt will probably need a higher mesh count with a shallow channel achieved with a 1:1 or 1:2 coating.  An athletic block print will probably need a lower mesh count and deeper channel achieved with a 2:2 coating. 

 

Substrate

Substrate Side Coats

Squeegee Side Coats

Hard & Smooth (Posters, Signs, etc.)

1

1

Textiles (CMYK or Highly Detailed)

1

1 or 2

Textiles (Block or Athletic Design)

2

2

 

The solids content of your emulsion will also need to be taken into account (read “Choosing the Right Emulsion” here).  These suggestions are not set-in-stone, but use them as a starting point until you gain experience that will allow you to make informed choices based on the job at hand. 

 

Preparing to Coat: Getting Set Up

The Screen - Your screen needs to be fully reclaimed.  Don’t skip the degreasing step!  Also make sure your screen is fully dried with no wet spots.  Be careful to not touch the mesh with your fingers, as this transfers oils to the mesh that can result in emulsion irregularities.

The Scoop Coater – Scoop coaters come in two different styles.  Single edged scoop coaters (like our Pro Angle scoop coater) have a handle on one side and a moderately sharp edge on the other. The handle is a nice feature to make coating a little easier, but it’s not necessary. 

Dual edged scoop coaters (like this basic Scoop Coater with removable end caps, the Pro Angle 2, or the Monster Max) feature one sharp edge for a thinner channel and one round edge for a thicker channel.  Make sure you understand the scoop coater you’re working with to achieve the coating you desire.

Your scoop coater should also start out clean, with no dried chunks of emulsion inside.  Check the coater’s edge to make sure there are no burrs or nicks that might damage your screen mesh.  Fill the scoop coater generously with emulsion – don’t skimp!  The weight of the emulsion pressing against the screen will aid in pushing the emulsion fully into the openings of the mesh.

 

Coating Location – The main factor in achieving a good coating is that you are comfortable and able to smoothly coat from the bottom to the top of your screen without having to raise your hands or arms above shoulder height.  The specifics of your set up will depend on your height, the size of the screen being coated, and the equipment you have available to you. 

Screen stands (like the Vastex C-100 Screen Coater Rack) will hold the screen in a stable 90º vertical position so you can hold the scoop coater with both hands, and are adjustable in height to give you the best position no matter what size screen you are coating. 

If additional equipment isn’t in the budget, you can set up to coat screens on the floor or a bucket up to about 18” off the floor.  This lower position will help when it comes time to press/angle the screen towards your coater as you move from the bottom of the screen towards the top.  Coating on a standard tabletop will likely be too awkward to achieve a smooth coat.

Screen Coating Table

 

Properly Coating a Screen: The Technique

  1. Start coating on the substrate side of your screen.
  2. Stabilize the bottom of the frame on the floor or raised surface, and grab the top of your screen on the frame.
  3. Place the coater’s edge at the bottom of the screen about 1” up the mesh from the frame.
  4. Pressing the edge FIRMLY against the mesh, tilt the coater towards the screen until the end caps are flush against the screen.

  1. Tilt the screen down to about a 45º angle from the floor.
  2. KEEP FIRM PRESSURE AGAINST THE SCREEN. Start drawing the coater up the mesh.
    1. Speed – maintain a slow, consistent pace from beginning to end in order to eliminate pinholes. 20x24” screens should take approximately 8 seconds per pass.  23x31” screens should take approximately 12 seconds per pass.
  3. Once coater is within a few inches of the top of the frame, return screen to the 90º vertical position.
  4. While maintaining firm pressure of the coater’s edge against the mesh, tilt the coater down to allow the excess emulsion to refill the trough.
  5. Once emulsion is away from the screen, gently “shimmy” the coater side to side while pulling away from the mesh.

  1. Repeat the process on the squeegee side of the mesh while emulsion is still wet. ALWAYS FINISH ON THE SQUEEGEE SIDE OF THE SCREEN.
  2. Once all coats are complete, the screen should be dried as it will be on the press – squeegee side up, substrate side down – to allow the emulsion to work with gravity and form the channel on the substrate/bottom side of the screen.
Screen Drying Rack

 

Troubleshooting Coating Issues

 

Heavy Deposits of Emulsion – A “tiger striping” effect or large areas of obviously heavy emulsion are caused by inconsistent pressure and speed “shaky”.  Pressing too hard will create thin spots, while not pressing hard enough will result in too much emulsion remaining on the mesh. 

Pinholes – Pinholes can be caused by coating too fast. A slower stroke will allow the emulsion to really get into all the nooks and crannies in the mesh.

Fish Eyes – Look like white dots in your emulsion.  Typically from backsplash of reclaiming chemicals left in the screen.  A flood rinse after degreasing should leave you with a clean screen to resolve this issue.

Specialty Screen Coating Options

            Face Coating is a technique that adds layers of emulsion to an already coated and dried screen on the substrate side of the mesh.  Face coating is effective in creating very deep channels appropriate for specialty inks like glitter flakes.

 Practice Makes Perfect!

            Proficiency in coating screens takes practice!  Don’t give up on yourself if you’re having trouble.  Be patient, take your time, follow the tips above and in due time you’ll find yourself producing consistent coatings that result in less issues further in the screen printing production process!

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

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). 

 

Pros

Cons

  • Easy application with water and squeegee (no scoop coaters or high level of technique required)
  • Easy to reclaim
  • Can be applied immediately after reclaim process with no dry time in between
  • Excellent for stencil thickness consistency, especially for high tolerance applications
  • Sheets can be stacked in application to create thicker microns (extends cure time)
  • Can be shipped during winter months (freezing temperatures)
  • Very light sensitive, need to be used in a UV protected dark room
  • Limited durability (stencil may break down after a few thousand prints)
  • Stacking for thicker micron can be difficult, and is still somewhat limited in tailoring to your specific needs

 

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.

 Dual Cure Emulsion

 

 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.

 

Pros

Cons

 

  • Holds good high detail due to the finely ground particles in its make up
  • Durability over long print runs (10,000+ pieces)
  • Forgiving exposure latitude over or under exposing your image
  • Can be exposed to UV light while wet without curing so you can coat screens in normal lighting (though not recommended)

 

  • Short shelf life once sensitized (6-8 weeks, up to 3 months if refrigerated)
  • Long exposure time
  • Not freeze/thaw stable (cannot be shipped in freezing temperatures over winter)

 

 

 Photopolymer Emulsion

 

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.

 

Pros

Cons

 

  • No mixing of diazo needed – ready to use straight out of the container
  • Longer shelf life
  • Faster exposing
  • Work well with weak light sources (homemade exposure units)

 

  • Must be applied in a proper UV-protected dark room
  • Short exposure range (easier to under or over expose)

 

 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.

 

TECH SUPPORT'S TOP 5 SCREEN ROOM ESSENTIALS
The screen room…where every great imprint begins and ends.  When our customers come to us with a production issue, we usually begin by back-tracking their process all the way to the screen room. Without a proper screen room set up, even the most experienced printer is doomed to suffer a variety of print issues further down the production line.  By investing in what we consider to be five essential screen room tools, your screen development and reclaiming processes will improve in consistency and speed to save your business time and money.

 

1. Dehumidifier

    #1 on the list for good reason!  If you don’t have one, chances are you have had issues like unpredictable under or over exposed screens, films sticking to your emulsion, inconsistent exposure times, and/or difficulty reclaiming.  Emulsion must be properly dried, meaning the moisture has evaporated from the interior of the emulsion coating.  Many printers struggle with what we call “the jelly doughnut” effect, meaning the emulsion appears dry on the surface but has a gel-like interior lurking beneath.  This very thin interior layer of moisture will wreak havoc on your exposure and development of quality stencils.  When properly dried, emulsion “cross-links” or sticks to the mesh resulting in easy exposure and reclaiming.

    Adding a dehumidifier to your screen room allows you to control the amount of moisture in the air which increases the speed and consistency of your emulsion properly drying once applied.  Ideal screen room humidity should be around 30%, never above 40%.  Your dehumidifier doesn’t need to be fancy, but ideally it should have a feature to set your preferred humidity level.  Once that level is reached, it will stop running until the air becomes too humid again.  Many models require you to empty the water tank once it is full to keep operating, while others offer continuous operation thanks to a hose bib attachment for constant draining (ideal if you have a floor drain).   They can be purchased at any general retailer starting at around $35.00 for a super basic, smaller model.  This screen room superstar won’t set you back much, and will pay for itself in time saved long term.

    Small Spaces / Budget Friendly  ||  Larger Spaces / Continuous Draining

     

    2. Space Heater

      Combined with a dehumidifier, a space heater will pack the one-two punch needed to achieve perfectly dry screens every time you’re ready to hit the exposure unit.  Colder temperatures (below 70ºF) make it difficult for moisture to evaporate properly from emulsion, while overly hot temperatures (above 105ºF) will cure the emulsion entirely and your screens won’t expose.  Ideally, your screen room temperature should hover around a toasty 90º F for optimal drying conditions.

      Basic space heaters can be purchased at any general retailer starting at around $25.00.  Make sure to choose a model that allows you to set a max temperature to kick off the heater once it senses the room is warm enough.  Similar to dehumidifiers, the size you should buy will largely depend on the size of your screen room and general climate based on your region.  Other safety features to consider are protected heating elements and tip-sensing auto-shutoff.

      Small Spaces / Budget Friendly  ||  High Efficiency / Premium Features

       

      3. Digital Thermometer/Hygrometer

        Just because you’ve set your dehumidifier and heater to the desired levels doesn’t mean your space will maintain that 100% of the time.  This little multi-purpose gauge will give you excellent monitoring capability to be sure your dehumidifier and space heater are getting your screen room to the 30% / 90ºF combo we’ve mentioned, or how to adjust accordingly.  The thermometer will read the temperature while the hygrometer will read humidity.  If your screen room is above or below the ideals, adjust your settings and wait a few hours before attempting to coat screens.  These are widely available at general retailers, and well worth a $10-$20 investment.

        All-In-One Option

         

        4. UV Resistant Lighting

        If your screen room is at the appropriate humidity and temperature levels and you’re still having issues with exposure, development, or reclaiming, the culprit may be your screen room lighting.  Screen emulsion is UV-sensitive, meaning it hardens when exposed to any UV light waves.  This includes overhead tube lighting, LED lights, and yellow bug-detracting lights.  WE REPEAT… DO NOT USE YELLOW BUG-LIGHTS IN YOUR SCREEN ROOM.  These lights simply eliminate the long-wave light spectrum humans see best and emit the short-wave spectrum of light closest to UV light waves (which bugs cannot see).  Therefore, when you use a bug-light in your dark room, you are essentially blasting your screens with the very UV light you want to avoid until your screen is dry and ready for the exposure unit.

        The best option is to cover your bulbs in UV filtering safety sleeves.  These are thin yellow sleeves that cover your bulbs to block the UV light they emit, while giving you optimal visibility in the dark room.  Tech Support offers top-quality safety sleeves of varying sizes starting at $12.00 each.  If you do not have tube lights and need a screw in bulb, look for red-bulb lighting similar to what you’ve likely seen in photography dark rooms.  They won’t provide the same visibility as a yellow safety-sleeve cover will, but it will avoid the issue of blasting your screen with UV light.  You can snag a two-pack for around $15.00 from general retailers or hardware stores.

        Safety Sleeve Tube Covers  ||  Safelight Screw-In Bulbs

         

        5. Power Washer / Garden Hose Nozzle / Two-Way Hose Splitter

         

            

        Last but certainly not least, every efficient screen room should have both a power washer and a standard garden hose nozzle connected by a two-way hose splitter leading to the wash out booth.  Why all three?  The intensity of a power washer is essential to a few steps of reclaiming, specifically in removing emulsion and ghost/haze images remaining in the screen.  If you try to do these with a basic garden hose nozzle, your screens will never get fully clean enough to recoat without issues.  The only power washer specification we’d recommend looking for is a model that is at least 1500 PSI. A basic power washer will get the job done, but is essentially disposable in nature and will need replaced relatively frequently.  We went through four or five before settling on the reliable Rhinotech 1500CP for our in-house screen room.

        Rhinotech Power Washers

        All other aspects of the development and reclaim processes benefit from a less-intense basic garden hose nozzle.  For example, you don’t need a power washer to rinse stencils out after exposing, or for removing ink or cleaning squeegees.  The consistent and even pressure supplied by a garden hose nozzle will provide an easily controlled and less messy option for most wash out booth activities. 

        Nothing fancy is necessary.  For about $4.00 you can get a classic nozzle with a single adjustment point that provides a range from jet-spray to gentle cone.  For just a few dollars more, there are nozzles that provide multiple spray patterns.  Our favorite settings include the shower spray, horizontal and vertical fan, or the cone.

        Basic / Budget Friendly  ||  Multi-Spray Pattern

        You’ll also benefit by adding two-way hose splitter to your wash out booth set up.  This will allow you to keep both your power washer and garden hose nozzle ready for use at a moment’s notice instead of swapping what is connected to your water source every time you get to work.  Prices for hose splitters average around $10.00 each.

        Two-Way Hose Splitter

        No matter your level of experience as a printer, setting up your screen room with these five essential items will dramatically improve the speed and consistency of your development and reclaim processes.  We’d love to see pictures of your screen room set up, or please comment below with screen room tools you couldn’t live without!

        *ALL PRODUCTS ARE LISTED ALPHABETICALLY