The Screen Print Column
What is off-contact and how to get it right?
In this article, industry veteran, Jason Chapman of BezierOne, looks at the concept of off-contact, what it means and how you can get it right.
O
ff-contact in screen printing refers to the gap or distance between the screen and the substrate (such as a T shirt, paper, or any other material being printed on) when the screen is in the resting position.
This distance is crucial for several reasons: 1) Ink transfer: Proper off-contact ensures that the ink is transferred evenly from the screen to the substrate. When the squeegee passes over the screen, it pushes the screen down onto the substrate, allowing the ink to pass through the open areas of the stencil. Once the squeegee moves past, the screen snaps back up due to the off-contact distance, leaving a clean print behind. 2) Avoiding smudging: If there is no off-contact, the screen would be in constant contact with the substrate, leading to potential smudging and blurry prints as the screen is lifted after each pass of the squeegee.
3) Durability and precision: Off-contact helps in reducing wear and tear on both the screen and the substrate, leading to more precise and durable prints. It minimises the friction and pressure on the screen mesh, extending its lifespan. 4) Accommodating different substrates: Different materials and thicknesses require different off-contact distances. For example, printing on a thick sweatshirt might need a larger off-contact distance compared to printing on a thin sheet of paper.
Types of off-contact • Direct off-contact: A small gap, typically used for very fine and detailed prints where minimal movement of the screen is needed.
• Indirect off-contact: A larger gap, used for substrates that are uneven or have a texture that requires the screen to clear the surface cleanly.
Adjusting off-contact
Adjusting off-contact involves setting the screen at a slight angle or using shims/ spacers under the screen frame to create the desired gap. The exact distance can vary based on the type of ink, screen mesh, squeegee, and substrate being used, but it typically ranges from 1/16in to 1/8in (1.5mm to 3mm).
In summary, off-contact is a critical aspect of the screen printing process that influences print quality, accuracy, and the longevity of the equipment. Properly setting the off-contact distance ensures clean, crisp, and consistent prints.
Here’s a diagram illustrating the concept of off-contact in screen printing:
• Substrate: The material being printed on, shown in light grey. • Screen: The screen used for printing, shown in blue, positioned above the substrate.
• Squeegee: The tool used to push the ink through the screen onto the substrate, shown in green.
The off-contact distance is
indicated by the double-headed arrow between the substrate and the screen. This distance is crucial for ensuring clean and precise prints.
There are only four printing parameters.
Other things to consider • Screen tension
To ensure you build your knowledge about off-contact and standardise for each ink type, mesh and substrate, screen tension is an area often misunderstood, but is an essential part of standardising printing parameters.
Measuring screen tension in screen printing is a vital step that requires precision and meticulous attention. By investing in a reliable tension meter, understanding the specific needs of each print job, and adhering to best practices, screen printers can ensure their screens are consistently tensioned for optimal print results. The skill of measuring tension plays a crucial role in achieving the overall quality and success of each print project. • Frame balance
A well-balanced frame ensures that the screen maintains a uniform distance from the substrate across the entire print area. This is vital for achieving even ink distribution and high-quality prints. • Frame strength
A strong frame can hold the screen mesh at the required tension without warping or bending. Consistent screen tension ensures that the off-contact distance remains stable, leading to consistent prints. • Practical implications
When setting up the screen for printing, a balanced and strong frame allows for more accurate and straightforward adjustment of the off-contact distance.
Uneven or weak frames can lead to variable off-contact distances, resulting in uneven ink deposits, distorted images, and inconsistent print quality.
Using a balanced and strong frame reduces the need for constant adjustments and maintenance, increasing overall printing efficiency and reducing downtime.
| 74 | September 2024
www.printwearandpromotion.co.uk
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