Rapid Prototyping Injection Molding Explained The rapid prototyping injection molding process…
From finishing touches and vibrant graphics to instructions and lettering, this printing process is vital.
Injection molding allows the ability to craft plastic components of every size, shape, and dimension imaginable. But by also incorporating pad printing on plastic, manufacturers can also add distinct, detailed graphics and information to those productions — no matter the complexity of the part or component shape.
Pad printing — also called tampography or tampo printing — is a process that transfers a two-dimensional image onto a three-dimensional object. This is accomplished using an indirect offset (gravure) printing process that involves the image being transferred from a laser engraved printing plate (also called the cliché) through the use of a silicone pad onto a substrate. The use of a pad allows printing on otherwise difficult-to-print shaped products, be they convex (curved), concave (hollow), cylindrical, spherical, or textured surfaces.
Pad printing comes with several advantages, beyond versatility and reliability, that has made it a popular and effective alternative to hot stamping and screen printing. It can be used on a variety of substrates and doesn’t require an even or flat surface to be effective, unlike stamping or screen printing. It can use single- or multi-color graphics and lettering from incredibly precise or complex designs. The process can also deposit functional materials like conductive inks, dyes, lubricants, adhesives, and more.
The versatility that comes from pad printing on plastic can be seen across many industries that make use of the substrate material and have a need for instructional graphics, lettering, eye-catching designs, and more.
- Medical — Printing on components of medical devices like syringes, inhalers, catheters, etc.
- Sporting Goods — Lettering and graphics on golf balls, footballs, tennis rackets, and more.
- Consumer Electronics — Keycap lettering for keyboards, cables, connectors, etc.
- Household Appliances — TV housings, coffee bots, cordless phones, and more.
- Children’s Products — Graphics and lettering for toys, pacifiers, baby bottles, etc.
With a firm grasp on what pad printing is and where it’s used, let’s look at each of the components involved in pad printing on plastic.
Step by Step: Pad Printing on Plastic
How does the pad printing play out? Let’s go through a brief walkthrough of the process before examining each of the components that make it possible.
- The ink cup — sealed in a closed system or an open inkwell in an open system — is positioned over the etched artwork area on the cliché. The etched image is filled with ink.
- The ink cup moves away, taking excess ink with it and exposing the ink-filled image. This exposure causes the top layer of the ink to become tacky, helping it adhere to the transfer pad and then the substrate.
- The transfer pad quickly presses down on the printing plate, pushing air outward. This causes the ink to lift (or transfer) out of the etched artwork area and onto the transfer pad.
- The transfer pad then shuttles to the waiting substrate and compresses down on its surface. This transfers the ink to the substrate’s surface.
This is a simplified version of the process but generally holds true for all versions of pad printing. Next, let’s delve into some of the individual components that execute the process.
Open Inkwell — This older method uses an ink trough for the ink supply. A flood bar pushes a pool of ink over the plate, and a doctor blade removes the ink from the plate surface. The result is exposed ink on the etched artwork area ready to be picked up.
Sealed Ink Cup — Here a sealed container acts as the ink supply, flood bar, and doctor blade all in one mechanism. A ceramic ring with a polished working edge provides the seal against the printing plate.
Pads are three-dimensional and typically molded of silicone rubber. They function as a transfer vehicle, picking up ink from the printing plate, and transferring it to the part (substrate). They vary in shape and diameter depending on the application. When choosing a silicone pad there may be several shaped pads and/or a variety of durometers that imprint your product in varying degrees of acceptable quality. Working with an experienced service provider will alleviate any confusion here.
Image plates (also called clichés or print plates) are used to contain the desired artwork “image” etched on its surface. Their function is to hold ink in this etched cavity, allowing the pad to pick up this ink as a film in the shape of the artwork, which is then transferred to the substrate.
Ink is used to mark or decorate parts. It comes in different chemical families to match the type of material to be printed and in many variable forms — such as more ecological variants or those FDA approved to be edible (for use on medical capsules, candy, etc.). In general, inks are separated into two broad types for pad printing on plastic.
One Component Inks — These inks are used to print on thermoplastic substrates, like polystyrene, polycarbonate, and soft and rigid PVC. With a long pot life, these kinds of inks can be used for a longer period of time.
Two Component Inks — If high mechanical or chemical resistance of the printed ink is needed, a two component ink (ink plus hardener) is recommended. These are suited to print thermoset plastics (melamine, polyester, etc.) as well as thermoplastics and various other substrates. According to ink and hardener type, the expected pot life lies between 6 and 12 hours. Since the pot life of the mixture is predictable, two component inks are widely used in industrial pad printing applications.
Mold Your Next Project: Deluxe Plastics has all the mold-related services you need, from mold-flow analysis to in-house making and repair capabilities. Learn more here.
Deluxe Plastics is the Full-Service Partner You Need
Since our inception in 1928, Deluxe Plastics has strived to deliver superior service and products to all of our customers. With a robust quality management system, ISO 9001:2015 certification, and more, we are the high-performance injection molding partner you need in a variety of industries, including the commercial, industrial, appliance, and hygiene markets.
We understand that molding your part isn’t the last step in the process. Therefore, we offer a wide array of secondary operations to better serve your company and help you get your product to market faster. From pad printing on plastic, hot stamping, in-mold decorating, manual and robotic assembly, inventory management systems, and more, we’re here to take your project from the initial design to a fully functional, molded part.