How To Coat A Screen With Emulsion


How To Coat A Screen With Screen Printing Emulsion or Capillary Film



by Douglas Grigar


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Printwear's annual how-to issue is a great resource to keep on hand year-round to refer to as you enhance your garment printing business. It can also be a good tool to help you get back to the basics, such as applying a photo stencil.


This guide will present one method for each top methods that are widely applicable to the available products. One disclaimer is that specialty products, such as thick, heavy-coating liquid emulsions and special-purpose capillary films may require alternate methods. Be sure and ask your manufacturer, or check their website for technical specifications.


Coating a Screen With Screen Printing Emulsion




Step one: Get ready
The most widely-implemented tool for coating a screen with liquid emulsion is the an aluminum coating trough. Clean the coater with your mesh degreaser such as Lawson's MD-100, and check for flaws or damage to the coater's surface edges.


Next, fill the coater with emulsion until the level is about 1/2- to 3/4-full (choose a comfortable level of fill) and position your screen into a rack for two-handed coating. Building or buying a screen holding rack allows a two handed coating that is often far more comfortable and consistent. No time or resources? You can make do. Grasp the screen firmly and hold in position with your free hand to coat single-handedly.


help with consistency. Holding the screen vertical will allow tilting of the screen into the coater at the beginning and end of the stroke, preventing spills.

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Watch a video on coating a screen frame with an emulsion coater


Coating the screen in an upright/vertical, or almost vertical, position without changing the angle of the frame will

Tips: Always make sure the emulsion is level in the coater. Get into the habit of setting the coater down on a level surface when not in use; it is very easy to forget about the emulsion inside the coater and tip the unit, spilling the emulsion.


Always choose a coating position that is comfortable and an area that allows unobstructed movement of your hands and arms.


Step two: Positioning
Starting at the bottom of your coating stroke, place your coater against the mesh, press into the mesh and rotate the coater into the mesh. Tipping the coater into the mesh is almost like a fixed-point rotation: Slowly rotate the coater until you reach the desired position or until the coating guides touch the mesh.


The emulsion will start to flow onto the mesh. Once the emulsion has reached the mesh across the full length of the blade of the coater, you can start the coating stroke.


I suggest starting the coating stroke just a tad above the edge of the mesh and the frame. You can fill that empty open mesh with a block-out product if needed.


Tip: Make sure to place the guides against the mesh but do not push the guides into the mesh, this creates a second lever point and can cause the blade of the coater to lift from the mesh and spill.


Step three: Coating travel
Make sure you apply a considerable force to the coater to keep the blade in intimate contact with the mesh all across the coater. You must keep the pressure on the blade pressed against the mesh at all times.


Start your coating stroke, keeping the pressure on the blade against the mesh, and move the coater up the mesh to apply the liquid screen printing emulsion.


Tips: Timing or consistent speed in moving the coater along the mesh is everything! Any change in speed or pressure will change the thickness of the coating.


Move the coater more slowly than you want to. Coating should take about two-to-three seconds for each 24 inches of mesh. Count out until you know the speed by feel or ear. (Coating with pressure applied to the mesh has a zipper like sound.)


You can also use that sound to help with the coating procedure. Any changes in the coating pressure or speed will be evident in the sound the blade makes while against the mesh.


Step four: Ending the stroke
Once the stroke nears the end of your intended travel, stop the movement of the coater and rotate the coater back, away from the mesh, allowing the silk screen emulsion to flow back into the coater.


Tips: When rotating the coater away from the mesh, make sure to keep the same pressure on the coater blade against the mesh. Releasing any pressure at this point would cause the emulsion to spill.


When the emulsion has flowed back into the coater, continue the stroke for the last short distance of and inch or so for a dry scrape all with the continuous pressure against the mesh. You should now be able to pull the coater away from the mesh without spilling any emulsion.


You can use this same procedure on both sides of the mesh while coating, coating the squeegee side requires tilting the screen to the coater or a quick movement or jump into the frame before the emulsion starts to flow.


Step five: Dry the screen


The hard work is done! Place the emulsion-coated screen squeegee-side up and face-side down into your drying cabinet, for example the Lawson Pro-Cure screen drying machine. Find other screen drying units for your shop.




Capillary films: Behind the Mystique




Capillary films have a strange mystique attached to them for many in our industry. I have always found this odd for a product that is so basic and useful. Part of the problem is simply that the name capillary film is so misunderstood. Hence, I find myself calling them emulsion films in classes and conversations because so many screen printers think that they are something hugely different and foreign when the fact is, they are simply sheets of film backing with an emulsion layer on one side.


Capillary film simplifies the drying cycle as well. Utilizing the wet roll-on method of applying capillary films, as I explain here, can eliminate one wet and one drying cycle from the typical procedure of stencil application.


Step one: Cleaning the mesh
Capillary film uses the travel or flow of water to complete the adhesion to the mesh (the reason for the name). As such, it is sensitive to contamination on the mesh. Because screen mesh should be thoroughly clean, take care to remove as many contaminates as possible from the mesh with degraders, stain/ghost removers and degreasers. Often capillary film makers will suggest a particular regimen of cleaning chemicals and procedures.




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Watch Capillary Film Demonstration




Step two: Chemical preparation with a wetting agent
I discourage my students from abrading screens because it damages the threads of the mesh. As an alternative, I encourage the wet roll-on method on clean mesh using one of the capillary film preparation chemicals, often referred to as a wetting agent. These are chemicals that improve the flow of water around the mesh threads, helping the emulsion from the film flow with the water into the mesh openings and aid in adhesion.


Most of the wetting agents will also include a degreaser to combine the two steps. Once applied to the mesh, a slight agitation with a brush and a thorough rinse with water will show that the water will sheet over the mesh, creating a smooth layer for the film application.


Step three: Ready the film
Prepare the capillary film by rolling it onto a tube of plastic pipe (I prefer 1.5 to 2 pipe) with the emulsion side out to roll onto the mesh. If you are not sure which is the emulsion side, moisten a finger and touch a corner: The emulsion side will stick! Be sure to touch the film as little as possible, as every area touched to skin is likely to be contaminated and will not adhere correctly. I often prepare several sheets of film in advance by carefully clipping the edges to the pipe with clothespins and placing them into a clean, light-safe box.


Step four: Flood the screen
Just before rolling the film onto the mesh, flood the screen with copious amounts of water to gain a good sheeting layer of water on the mesh.


Step five: Apply the film
Position the roll so that the film will unroll down the screen, pressing the starting edge to the mesh. While rolling, press your fingers into the pipe and press the film to the mesh while unrolling down. This movement acts as a squeegee as well as ensures intimate contact between the mesh and the film product.


Step six: Dry the screen
Drying capillary emulsion film is similar to drying liquid emulsions, except the frame's position in the dryer is unimportant with film, as the film backing holds the emulsion to the mesh. Make sure you peel the film backing off the emulsion before you expose for you final stencil!


Note: A demonstration of this application is viewable on www.YouTube.com by searching for Douglas Grigar and capillary film.


Every great print needs a great stencil. For beginners, applying emulsion may seem difficult. But with practice the procedures are simple and quick.




Reprinted from Printwear Magazine September 2008


 

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