Medical Device Pad Printing 101: An Engineer’s Guide

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Originally Posted On: https://libertyclarkinc.com/medical-device-pad-printing-engineers-guide/

Medical devices will no doubt present unexpected design challenges.  Decorating considerations should be planned early in the medical device pad printing design stage.  Oftentimes the decorating decision comes at the end of the design and after the substrate has been chosen.  Beware, there are many substrates that have poor adhesion qualities for decorating!  Adhesion is key.

Pad printing is a very common solution for decorating medical devices since the process allows artwork to be applied accurately and repetitively on curved surfaces.  And, most major ink manufacturers offer Class VI medical grade pad printing ink systems suitable for biocompatibility testing.

Learn more about this technology below and why it may be the right solution for your decorating needs.

Pad printing offers many advantages for decorating manufactured components.

First, pad printing provides precise and repeatable artwork registration on curved surfaces.  Syringe Barrels, Strain Reliefs, Handles, and Housings are just a few examples of medical devices well suited for pad printing.

Second, pad print ink systems provide proven durable adhesion on many types of substrates.  Plastics, Metals, and wood can all be decorated with pad printing ink.  However, there are many ink systems available for each substrate.  So, consult with an expert to help you choose the ink system for your project.

Third, pad printing inks may be mixed to match any color (PMS reference numbers are most commonly used).

Fourth, pad printing is often the most economical option to decorate manufactured components.  Depending on the project, thousands of components can be decorated daily.

The process of pad printing involves multiple steps to arrive at a finished product.

• An .eps artwork file is required.
• A cliche (printing plate) is etched with a laser or photosensitive process.
• The finished, etched, plate is attached to a pad printing machine.
• An ink cup slides over the plate adding ink to the etching while removing excess ink after sliding back to ready position.
• A silicone transfer pad picks up tacky ink from the plate.
• The ink from the pad is applied and transferred to the substrate surface.
• The process repeats.

It’s important the viscosity of the ink is initially calibrated, and maintained throughout production, to successfully transfer a precise image to the substrate.  Otherwise, voids, webbing, rough images, etc., will occur.  Multiple layers of ink may be applied to achieve a desired opacity.

There are two methods for creating printing plates.  Photosensitive and laser etching.

The Photosensitive method involved a metal plate coated with a thin photopolymer material when exposed to UV light is burned away leaving the artwork impression.  Photosensitive may offer more precise resolution for fine detail artwork, but is more time consuming and requires more skill to manage the process variables.

The other method is laser etching.  This method is fast, and repeatable.  However, fine detail may be lost due to digital technology limitations.

Plate depth may be controlled with either method.  Plate depth is very important to successfully transfer the artwork to the product.

Transfer pads are made of silicone and come in various sizes, colors, shapes, and hardness.  The hardness (durometer) and shape of the pad are very important considerations for proper image transfer.

After successful plate creation and pad selection, the choice of ink system is often the most crucial decision for successful decorating.  If you’re designing a medical device, will it require biocompatibility testing?  If so, you most likely will require Class VI medical grade ink for starters.

Unfortunately, a one-size-fits-all ink system for medical device pad printing does not exist.  Should you use a one or two component ink system?  Should I add other auxiliaries to my ink system?  Which ink manufacturer should I select?  Before selecting the ink system you should consult with an independent source with proven experience decorating various substrates.  Adhesion is key here.  And, not all manufacturer ink systems offer similar adhesion results for a given substrate.

The expected adhesion for any ink system is dependent on the surface tension of the material to be decorated.  Surface tension is measured in Dyne.  A Dyne level of 42 is usually required for durable adhesion when using pad print ink systems.  Some materials, such as Polypropylene, have a surface tension well below 42 Dyne.  Fortunately, there are pretreatment processes which raise the Dyne level to appropriate levels to achieve required adhesion.

The two most common pretreatment processes to raise Dyne level are corona discharge and flame.  Corona is a controlled low frequency plasma discharge, which when applied to the substrate raises the surface tension.  Corona is very effective for improving adhesion to Polypropylene, Polyethylene, Acetal, and other substrates.  Flame treatment also increases surface tension for Polypropylene, but is hazardous and not as easily controlled as Corona.

Post treatment processes most often involve heat curing.  Many ink systems strongly recommend the use of heat baking to fully cure the ink.

Medical device decorating may require a cleanroom production environment to avoid foreign material contamination.

Will the pad printing occur at a station adjacent to the production of the component?  If so, expect a lot of foreign materials to be present when decorating.

The design and production of medical devices offers an impressive set of challenges.

Substrates may need to be bio-inert.  If decorated, the ink applied may also require biocompatibility.  Together, the substrate and ink system must be compatible for durable adhesion.

Contamination from the decorating process must be controlled.

For decorated devices designed to be reused, the ink needs to withstand the heat and harsh chemicals of the sterilization processes without the loss of adhesion qualities.

Standards continue to evolve for the production of medical equipment.  If the medical device requires decorating, it’s important to understand the biocompatibility requirements.  Strong consideration should be given to major manufacturer ink systems to reduce the risk of obsolescence and need for recertification of alternatives.

Pad printing has been proven to be a compliant, efficient, and economical approach to decorating medical devices and industrial components.

Would you like a decorating estimate or further discuss your needs?   Contact the decorating experts at Liberty Clark, Inc. today.