The choice of emulsion depends on several factors, including the planned print length, the desired ink film thickness, the fineness of the image detail, the ink system used and whether the screen is to be reused for future print runs.

Direct emulsion

Direct emulsion is a versatile stencil system in which a liquid emulsion is applied directly to the screen mesh. In my experience, direct emulsion offers several advantages:

• Durability: direct emulsion stencils are extremely robust and are suitable for a wide range of inks, including water-based inks.
• Detail: Because the emulsion is embedded into the mesh, direct emulsion excels at retaining fine detail, which is essential for halftones and intricate designs.
• Reusability: Direct emulsion screens can be cleaned and stored after printing so they can be reused for future projects.
• Easy reprocessing: In most cases, direct emulsion screens can be reprocessed with household bleach or a special reprocessing solution.

Dual-cure emulsions, also known as photopolymer or diazo-sensitised photopolymer emulsions, are a popular type of direct emulsion that offer several advantages over conventional diazo emulsions:

• Reduced shrinkage: dual-cure emulsions contain less water than older diazo emulsions, resulting in minimal shrinkage during drying and therefore sharper stencil edges.
• Faster screen production: The lower water content also contributes to faster drying times.
• Improved durability with water-based inks: Dual-cure emulsions are generally suitable for use with water-based ink systems.

For printers who require even greater durability and longevity, I recommend two other direct emulsion options:

• Water-resistant emulsion: when using water-based inks for runs of more than 500 prints, a special water-resistant emulsion is required to prevent stencil breakdown.
• Pure photopolymer emulsion: Pure photopolymer emulsions are favoured by some large printers. They are premixed, offer very short exposure times and have an almost unlimited shelf life. However, they are also more expensive than dual-cure emulsions.

Capillary film

Capillary film, also known as capillary direct film, is a practical alternative to direct emulsion. It consists of a clear acetate carrier film that is pre-coated with an emulsion. The film is adhered to the screen mesh with water, avoiding the mixing and potential mess associated with direct emulsion.

In my experience, capillary film is particularly well suited to applications that require exceptionally sharp edges, such as:

• decals
• bumper stickers
• posters

This is because capillary film does not shrink as it dries and the emulsion only adheres to the underside of the screen, resulting in a very precise stencil edge.

Whilst capillary film offers several advantages, there are also some potential disadvantages:

• Mesh count limitation: capillary films may not work as well with finer mesh counts, especially mesh counts above 200 (78 cm).
• Halftone reproduction: Direct emulsions may be a better choice for capturing fine halftone dots and may provide higher quality results.

General recommendations

Based on my many years of experience in screen printing, I would like to recommend the following guidelines that should be followed when working with direct emulsion and capillary film:

• Thorough degreasing: regardless of the stencil system chosen, it is important to thoroughly degrease the screen mesh before applying the emulsion or adhering the capillary film. Proper degreasing ensures optimum adhesion.
• Roughening the mesh: To improve the adhesion of the capillary film, especially with higher mesh counts, a light roughening of the mesh with an abrasive solution can be advantageous.
• Wetting agent: Applying a wetting agent to the mesh before applying the capillary film can also improve adhesion as it helps the mesh to retain moisture.
• Coating thickness: I recommend applying a thinner coating with direct emulsion or using a thinner capillary film if you are working with detailed designs that contain fine lines or halftone dots.
• Exposure time: Thicker stencils require a longer exposure time. A light source of at least 5 kilowatts is recommended to ensure adequate exposure.

Ultimately, the choice between direct emulsion and capillary film depends on the specific requirements of the print job and the printer’s preferences. From my experience, I can say that both methods can deliver high quality results when done properly.