Screen Printing on Painted and Powder Coated Metal

Screen printing (still called silk screening on a lot of drawings) is the workhorse process for legends, nomenclature, logos and part markings on production metal parts. Ink is pushed through an open stencil in a fine mesh onto the part, one color per screen. Once the screen and fixture exist, every part in the run gets the same print in the same place.

On painted and powder coated parts, though, the print is a coating on top of a coating. Most print problems are decided before the part ever reaches the press: by the powder or paint chosen, the ink called out, and how the artwork and print location are drawn. This guide walks through those decisions in order. If you just want to know how we run the job, see our screen printing service page.

The sequence: coat, cure, then print

The legend always goes on last. The standard sequence for a coated and printed part is:

1. Prep and coat. Clean, pretreat, mask and apply the powder or paint to the drawing callout.
2. Full cure. Powder is baked to its cure schedule. Liquid paint is cured or dried per its data sheet before anyone handles it for printing.
3. Cool and keep clean. Parts are cooled, inspected and packed so the print areas stay free of fingerprints, oils and silicone.
4. Print and cure the ink. The ink is mixed, printed and cured to the ink maker’s schedule.
5. Inspect against your criteria. Legibility, location and any adhesion check your procedure calls for.

Two practical points come out of that order.

Keep the print surface clean between coating and printing. Skin oils, silicone from sprays or gloves, and release agents are all classic causes of ink that looks fine on day one and lifts later. Handle coated parts with gloves and pack them so faces don’t rub.

Liquid paint needs its full dry time. A two-component paint can feel dry well before it is ready to take a solvent-bearing ink on top. The paint’s data sheet sets the time to handle and the time to overcoat. Build that into the schedule.

Products Finishing’s powder coating clinic also describes slightly under-curing a powder to help ink penetrate, then finishing the cure after printing. That changes the coating’s cure history, so it does not belong on spec work unless the spec and powder maker allow it.

Why ink sticks, or doesn’t, to powder coat

Powder coat is tough partly because it is slick and chemically resistant, which also makes it harder for ink to grab. Two issues come up most.

Additives in the powder

Powder makers add waxes and similar additives to control gloss, add slip and improve mar resistance. A Products Finishing powder coating Q&A names wax as the most common additive behind adhesion trouble with labels, clear coats and silk screens, and says the fix belongs at the formulation stage, not on the shop floor. Readers in a follow-up argued wax hurts labels more than screen ink. Either way, the takeaway is the same: if a part will be printed or labeled, say so before the powder is chosen. Some low-gloss and mar-resistant powders are formulated in ways that make printing harder.

Solvent resistance

The same clinic points out that some powders, epoxies in particular, have excellent solvent resistance. Solvent-based screen inks rely partly on biting into the surface, so a very solvent-resistant coating can be harder to print. The consultant’s advice is to tell the powder formulator what you plan to print, and to involve the ink supplier, who may have more aggressive inks for the job.

Texture

Screen ink is a thin film, and the LCSC guide puts the finest screen-printed lines at roughly 0.1 to 0.3 mm. Strokes that fine have the best chance on smooth and fine-texture finishes. Treat heavy wrinkle, hammer or coarse texture under small characters as a risk: if a textured finish and small text have to share a face, flag it at quote so the coating and the printer can agree on what will read. For more on choosing finishes and surfaces at the design stage, see designing parts for powder coating.

Choosing the ink

Industrial screen inks for metal fall into a few families. The right one depends on what the part has to survive and what the drawing calls out.

A front-panel printing guide from LCSC lists the same three (solvent, UV-cure and two-component epoxy) as the usual screen ink systems and describes two-part epoxy inks as having excellent resistance to fuels, oils and many solvents. Real performance comes from the ink’s data sheet, tested over the actual coating.

A-A-56032 epoxy marking ink

A lot of defense and aerospace drawings carry a note like “silk screen or stencil, black epoxy ink per A-A-56032.” A-A-56032 is a commercial item description for a catalyzed epoxy marking ink for metal and other non-porous surfaces. Revision D, dated 21 March 2003, is listed as active, with later notices (2009, 2014, 2019), and it superseded MIL-I-43553B and MIS-37271. MIL-STD-130 itself lists A-A-56032 among its referenced documents.

The ink comes as two parts, a base and a hardener mixed just before use, and it cures through a chemical reaction at room temperature or under other time and temperature combinations. The CID divides the ink into types, including general-use, nonconductive and outside-exposure types, and colors are ordered as specified. Commercial kits are sold by type and color number, for example a Type I black in color 37038.

What that means for your drawing:

• Call out the type and color, not just the spec number. “Epoxy ink per A-A-56032” leaves the printer guessing. “A-A-56032, Type I, black” does not.
• Cite the revision if your contract requires one. Primes often control revisions on flow-down.
• Don’t confuse ink color with coating color. Both may use AMS-STD-595 numbers. Put each on its own line of the callout. Our coating callout checklist shows how to lay that out.

Artwork that prints well

• Vector, full scale. PDF, AI, EPS or DXF at 1:1. Raster images of text print poorly.
• Fonts outlined or supplied with the file, so the characters come out exactly as drawn.
• One layer or file per color, since each color becomes its own screen.
• Stroke weights that hold up. The LCSC guide puts the minimum screen-printed line width at roughly 0.1 to 0.3 mm depending on mesh. Hairlines and tiny counters in small text are where prints fill in or break up, especially over texture.
• Clear location and orientation. Dimension the print from part datums, edges or holes, and show which way the text reads.
• A print location tolerance. If the drawing does not give one, the printer will apply their own. If the position matters to a mating panel or a bezel, give a number.

Registration and fixtures

Screen printing on loose parts depends on holding each part in exactly the same spot under the screen. That is the job of the fixture, often called a nest: a plate or jig that locates the part off its edges, holes or other features so the print lands in the same place every time.

A few things affect how well that works:

• Locating features. Parts with square edges or holes near the print area are easy to nest. Parts with loose edge tolerances move the print with them, so dimension the print from the feature that actually controls the assembly.
• Flat, open print faces. The screen has to lie close to the surface. Studs, PEM nuts, weld beads, bends and flanges near the print area get in the way. Leave clearance around legends.
• Masked areas. If part of the face is masked for grounding, a fit or a bare-metal callout, make sure the print location is on coated area. See powder coating masking for how masked areas are handled.
• Multi-color registration. Each color is a separate pass, so color-to-color alignment matters. Artwork that does not depend on tight overlap between colors runs more reliably.

Screens and fixtures are one-time setup work for a part number. That is why screen printing pays off on production runs: screens and the nest can usually be kept for the part number, so repeat orders avoid most of the setup.

MIL-STD-130 marking, in brief

MIL-STD-130 is the DoD standard for identification marking: what goes on an item, the format, the minimum text size, fonts and placement. EverySpec lists MIL-STD-130N with Change 1 (November 2012) as active, with a 2019 notice; confirm the revision your contract cites.

Points that touch screen printing:

• Human-readable text. The standard recommends a minimum character height of 0.08 in (0.2 cm, 6 pt) and calls for capital letters without serifs, such as Arial or Futura.
• Durability. Markings must be as permanent as the item’s normal life expectancy and withstand its environmental tests and cleaning procedures. The standard also says marking methods must account for the finished condition of the item, including paints and coatings. That is a strong argument for an epoxy ink over a printable coating.
• Machine-readable marks. The 2D Data Matrix used for Item Unique Identification is normally applied as a durable label or plate or by direct part marking (laser, dot peen, chemical etch, ink jet), and it must verify to the standard’s print-quality grade. Screen printing is not a common method for it, so plan for that mark separately.

Your part number, your CAGE code and other identification text come from your drawing. For how coating and marking requirements flow down on defense programs, see our page for defense and government subcontract finishing.

What to define for inspection

Agree on print acceptance up front. Tell us:

• Legibility and defects. Allowable voids, pinholes, smears and edge fuzz, and at what viewing distance.
• Location. The tolerance on print position and rotation.
• Adhesion. Whether your procedure calls for a tape adhesion check such as ASTM D3359, and on what sample.
• Resistance. Any solvent, fuel or cleaning-fluid exposure the marking has to survive.
• First article. Whether you want a first-article part approved before the run.

On programs with your own QC procedure, we follow it and flow the print requirements down to our screen-printing partner. Certificates of Conformance are available on request.

How we coordinate it

We do the coating in-house in Colorado Springs. Printing is done by our screen-printing partner. We prep and coat the parts to the specification on your drawing or PO, send them to the printer with your artwork, ink callout and print locations, then receive the printed parts and deliver them to you. You get one quote, one PO and one ship date. We are upfront that printing is done by a subcontract partner; ask if your program requires subtier disclosure.

Coating alone runs about a week for standard jobs; the print step adds to that, and we quote one combined date. When you are ready, upload the drawing and artwork on the request a quote form and note the ink callout exactly as it appears on the drawing.