offset printing technique

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Rich Smylie, GMN
By Richard Smylie | Dec 18, 2018
Pad printing at GMN

Pad printing is an offset printing process where ink is transferred from a cliché to the required component via a pad. Bringing together a blend of consistency, repeatability, and durability, pad printing can help you achieve intricate patterns and designs. While most decorative techniques such as screen and lithographic printing require a flat surface, pad printing is one of the very few processes that is well suited for decorating gently curved, irregular, textured, and/or cylindrical surfaces. Predominantly seen in the automotive, electronics, appliance, personal care, and medical industries, pad printing is often chosen for applications that will endure significant handling and need to withstand the test of time.

Our latest video was created to not only equip you with the essentials of pad printing, but also to walk you through the step-by-step process. First, the artwork is etched onto the cliché (flat plate), and ink is deposited into the etched recess. Next, a silicone pad picks up the inked image and descends onto the part to transfer a clean, crisp, and lasting image. Then, the pad is pressed on a polyester film to remove any excess ink. Comprising of a low-tack pressure-sensitive adhesive, the polyester film removes any residual ink from the pad prior to the next printing cycle.

From standard to programmable multi-axis printers, this video offers a glimpse into the different pad printing presses utilized at GMN. Armed with a rotating fixture, the programmable multi-axis printer is capable of numerous hits in multiple color combinations on different axes, all in a single set-up. This capability eliminates the need to transfer the part manually from one station to the other, resulting in significant time and cost savings.

Pad printing is compatible with a broad range of substrates including stainless steel, polycarbonate, polyethylene terephthalate (PET), glass, polyvinyl chloride (PVC), acrylic, and acrylonitrile butadiene styrene (ABS). Very few plastic materials such as low (LDPE) and high-density polyethylene (HDPE), and polypropylene aren’t cohesive with pad printing inks and require a pre-treatment to ensure good adhesion.

For every project, custom fixtures are designed and built to register the component to the pad printing head. The alignment of the ink pad with respect to the size and geometry of the part is specifically engineered to ensure exact registration. As seen with the Nissan badge in the video, the pliability of the silicone pad allows for printing with extreme precision, preventing the ink from coming in contact on the inside walls of the recessed letters. Maintaining the viscosity of the ink is extremely crucial to ensure the ink deposition accuracy and consistency. While the ink needs to be fluid enough to deposit on the substrate, it should not bleed out of the impression area. Thinners and adhesion promoters can be added to inks to achieve the desired viscosity level. Most of the inks used for pad printing at GMN are air-dried and are usually cured in conveyor ovens. Several other factors including the shape, material and durometer of the pad, location and color of the etched artwork, and tilt of the ink pad, are critical to the success of any project.

To see the pad printing process in action, watch our video here.

Debbie-Anderson-GMN
By Debbie Anderson | Jul 27, 2018
Example of lithographic printing at GMN

Lithographic printing, an offset printing technique, is based on the basic principle that oil and water do not mix. It is a process in which ink is transferred from a photographic plate to a rubber blanket, which then presses the image onto the printing surface. Allowing for extremely tight tolerances and consistently high-quality images, GMN’s sheet-fed lithographic process is frequently utilized for printing graphic overlays and labels.

While lithographic printing is often performed on standard substrates such as paper and vinyl, GMN walks the unbeaten path by predominantly using materials including polycarbonate, polyester, and aluminum. Lithographic printing at GMN utilizes UV-cured inks. GMN also offers custom color matching services to help customers achieve their exact specifications and uphold brand consistency. To formulate a custom color, the different colored inks are meticulously weighed, poured over a flat glass surface in carefully measured proportions, and mixed together using a putty knife. With projects requiring custom color matches, a small sample sheet is first tested on a machine called the orange proofer. This counter-top machine is simply a condensed version of the actual printing press, that allows GMN to test the color and make necessary alterations before the final production run.

The first step in lithographic printing is creating the artwork on a photographic plate through a chemical process. Similar to the process of developing photographs, lithographic printing also requires the creation of a “negative” and a “positive” image. First, a thin aluminum plate is coated with a hydrophobic material so that it attracts oil (ink) and repels water. The plate is then selectively exposed to light, thereby curing the hydrophobic coating only in areas comprising the artwork. Finally, the coating from the remaining areas is chemically stripped off and the plate is ready for use.

The lithographic printing press consists of a series of rollers laid next to each other. The foremost roller transfers water, placed in a tray beneath it, to the photographic plate. The ink is manually applied to the second roller with a putty knife, which then wets out to the entire cylindrical surface as the roller spins and transfers the ink to the plate. The photographic plate, carrying the artwork, is wrapped around the next roller in the series. Given the immiscibility of ink and water, the ink adheres only to the artwork on the photographic plate, while the water adheres only to the remaining background.

On the other side of the photographic plate are two other rollers called the blanket roller and the impression roller respectively. The blanket roller simply acts as a medium to transfer the artwork from the plate to the substrate. When printing, a stack of printing sheets is placed on the top tray of the machine. A gripper grabs one sheet at a time and wraps it around the impression roller. The artwork on the photographic plate is imprinted on the rubber blanket roller, which in turn transfers it to the substrate on the impression roller. Then, the ink is cured by exposing the printed sheet to UV light. The process is repeated for every unique color in the image.

Ideal for high-volume manufacturing, a lithographic printer can run from 3,000 to 6,000 impressions per hour, with the largest sheet size being 18”x24”. It can produce detailed and intricate artworks with half-tones, gradients, or a four-color process (a four-color process uses a CMYK color module to create four separate dotted patterns, which when printed on top of each other, yield the required color). However, lithographic printing comes with its own limitations. It can only accommodate substrates with thickness ranging from 0.003” to 0.020”. The printing system is not compatible with metallic or conductive inks. Also, the ink used is very transparent, and typically requires extra layers of printing for opacity.

As multiple factors go into consideration before selecting a suitable printing technique, GMN works closely with each customer to understand the project needs and requirements to determine the best printing solution for every unique application. To learn more about our other printing technologies, visit our blog on GMN’s printing capabilities.