The most important step in silicone screen printing is to prepare the surface properly for the silicone because of silicone’s low surface energy. Even the best silicone inks can bead and crack or peel off after only a few uses or washings if they are not properly cleaned, activated and primed. Production teams and OEM buyers can master these techniques to avoid rework expenses and create professional, long-lasting products each production.
We have been developing these processes at HT Silicone over many years supporting custom molded parts and professional silicone screen printing to brands all over the world. In this guide we will address the actual steps on the shop floor (cleaning, physical activation, primers and verification) and develop a repeatable process that will consistently produce strong bonds.
What Makes Silicone So Hard to Print On?
The silicone rubber is chemically inert and has an extremely low surface energy of about 20-24 dynes/cm. Most inks do not absorb into the surface, but instead lie on it. In addition, processing residues, dust, finger oils, or mold release agents are frequently present on the parts, which also contribute to a weak boundary layer.
The result? Prints which appear OK immediately after print, but are not acceptable in the field. The most common adhesion issues we encounter with our new clients are due to not doing surface prep properly or at a slow enough pace.
Why General Plastic Cleaning Rules Are Not Enough
Alcohol wipes that are effective on polycarbonate or PVC generally don’t work on silicone. Because of the material’s non-polar nature, its energy levels need to be raised and bonding sites need to be created for ink and primers in a more disciplined way of thorough cleaning and surface activation.
Cleaning Silicone Parts — Removing Oils, Dust and Mold Release
The base is always cleaning. Surface contamination will prevent proper contact of primers and inks.
Recommended Cleaning Methods and Solvents
Use a mild detergent and warm water for heavier deposits, and then rinse thoroughly. Isopropyl alcohol (IPA) at 90%+ concentration is effective when using a lint-free cloth, for most applications. To remove persistent mold release agents (MRAs), there are specialized silicone-based cleaners that are better suited to this application and will not swell the silicone.
Do not use aggressive solvents such as acetone or toluene as these solvents may cause issues with certain silicone formulations or may leave behind residues which can create further issues. When moving parts to activation, always let parts dry completely and in a clean environment.
Shop-Floor Best Practices for Consistent Cleaning
Wear clean nitrile gloves, and do not touch treated areas with bare skin. Have a regular routine (double wiping one way, double wiping another way, etc) and make a record of it. Using a controlled low dust area, assists with consistency throughout shifts. These small adjustments make a big difference in the end product!
Physical Surface Activation — Plasma, Flame and Corona Treatment
Physical activation increases surface energy and produces functional groups that are polar, which are needed for good anchorage of inks.
When to Use Plasma Treatment on Silicone Parts
Plasma treatment provides reliable, reproducible performance, suited to applications such as medical, food contact or high wear applications. It’s ideal for complex geometries or when parts are used for repeated flexing, stretching or washing. Important parameters: Treatment time, power setting and only the print area is switched on for efficiency.
Flame and Corona Treatment as Practical Alternatives
For many factories, flame and corona systems are more available and can greatly enhance the adhesion if properly controlled. The methods are labor intensive, and need the expertise of trained operators to avoid the problems of under-treatment or over-treatment which can affect the surface of the silicone. Simple Dyne Pen testing helps to confirm results before full production runs.
Using Primers and Adhesion Promoters for Silicone Screen Printing
Primers are a chemical link between the low energy silicone and the ink system, especially useful for challenging applications.
How to Select the Right Primer for Silicone
Select silicone compatible primers that are compatible with your ink system. If producing food grade or medical parts, ask for low-migration parts or parts certified for medical or food applications. Always use primers which are consistent with the manufacturer’s recommendations for compatibility and curing conditions.
Application Best Practices: Coating, Drying and Handling
Prime using wiping, spraying or dipping technique to form thin even layers. Do not pool or drips, as this can result in weak areas or noticeable imperfections. Give sufficient flash-off and drying time, maintain the primed surface clean and undisturbed until it is printed. Excessive application can cause brittle layers and lack of flexibility.
Combining Cleaning, Activation and Priming into a Stable Process
The general process is generally: clean, dry completely, activate (plasma / flame / corona), apply primer (if necessary), print, cure. Not all ink and silicone combinations work well with all three steps, but the benefit of using all of them gives you a degree of flexibility with various projects.
Common Surface Prep Mistakes and How to Avoid Them
- Cleaning is not performed when parts appear clean → Adhesion failure occurs at once
- Activating before proper cleaning → reducing the effectiveness of the treatment of the wastes.
- Not washing hands after activation or priming → Adds additional contaminants
- Inconsistent treatment parameters means that there is a batch-to-batch variation.
Documenting a clear SOP and training operators on these details prevents most issues.
Simple Tests to Verify Surface Preparation Quality
Do not assume that surface preparation is in effect; always perform quick and practical tests to confirm it before using the surface for full production.
Adhesion Tests on Sample Prints
After complete curing, conduct normal tape tests, cross hatch tests and flex/bend tests. If required for critical applications, add simulated washing or alcohol rub. Use these on first-article samples whenever cleaning agents, treatment settings and/or primer batches are changed.
Visual Indicators During Production
For the printing, look for the occurrence of ink beading, fish-eyed, retraction or uneven wetting. 99% of the time these visual issues are related to issues in the surface preparation, not the press settings.
When to Ask Your Supplier About Their Surface Preparation Process
When selecting manufacturing partners, consider asking the following questions:
- What do you do before printing to prepare the surface?
- Have documented SOPs for cleaning, plasma or corona processes?
- What is the way to ensure adhesion for each batch of production?
- What primers shall we use for our silicone formulation and ink system?
Suppliers will typically be able to give a confident answer to these questions and present supporting evidence if they have controlled repeatable processes.
Summary — Stable Adhesion Starts Long Before the Ink Hits the Screen
The most common issues in silicone screen printing that result in poor adhesion are not the adhesive properties of the screen printing ink, but rather surface preparation.Poor surface preparation for silicone screen printing is the most common problem and not the properties of the ink. When cleaning, activation and priming are done with intent and control and with verification, production teams can consistently and professionally deliver results that meet the most rigorous brand and regulatory standards.
These best practices are applied to our compression molding, LSR and finishing processes every day at Dongguan HT Silicone & Rubber Co., Ltd. Whether you’re having adhesion problems or creating new printed silicone product, our staff is available to help you optimize your process from material selection to final quality control!
