Glass is the substrate that fails most quietly. A printed glass panel can look perfect at the end of the bed and develop a lifting edge three weeks later, once the panel has been handled, cleaned or exposed to temperature change. By then the cause — surface preparation, primer coverage or curing energy — is no longer visible in the workshop.

Adhesion on glass is a process question rather than a consumable question, and it is decided before the print head moves. This guide covers the production sequence for printing on glass, how the surface should be prepared, how the primer requirement works, how white ink behaves on clear and coloured glass, which settings protect the bond, and how to prove the result with a physical test rather than an impression.

Why does glass need a primer when other substrates do not?

Because the ink has nothing to key into.

Andresjet recommends a special primer for non-porous materials such as glass and metal, and supplies the correct primer with a demonstration of the application.

On wood, MDF or foam board, UV ink penetrates the surface and forms a mechanical bond as it cures. Glass offers no such structure: the surface is dense, chemically stable and smooth, so the bond depends entirely on what has been applied to it beforehand and on how completely the ink cures. The published substrate list for this range explicitly separates glass and ceramic tiles from the porous materials, and the primer recommendation applies to the non-porous group.

That has a commercial consequence for quoting. A glass job carries a preparation step that a PVC panel does not, and that step has to be costed, scheduled and staffed. Shops that price glass as though it were acrylic usually discover the omission in the first month of production rather than in the quotation.

What is the production sequence for printing on glass?

Clean, prime, print white, print colour, then inspect.

The order is fixed because each step protects the next: contamination defeats the primer, the primer carries the bond, and the white layer carries the colour on clear or dark glass.

In practice the sequence runs through five stages. First, confirm the glass specification, because float, tempered, laminated and coated glass are different surfaces. Second, clean and dry the surface, since dust, oil and fingerprints sit between the primer and the glass. Third, apply the primer as recommended and allow the stated interval before printing. Fourth, print the white underlay and then the colour layer, both in the mode you have qualified. Fifth, inspect for coverage and edge definition before the panel leaves the printer, because a defect visible now is a reprint rather than a customer complaint.

The panel itself has to be held flat throughout. The published platform across this range is hard-anodised aluminium with a four-zone vacuum system, and because glass does not conform to a bed, any warping or debris under the sheet shows through as a print defect. Cleaning the bed is part of every glass job, not a weekly task.

How should the glass be cleaned before printing?

Remove oil, dust and residue, then handle by the edges.

Cutting debris and handling oils are the two most common causes of a primer that appears to work and then releases at the edge of a panel.

Glass arrives with more contamination than it appears to have. Cutting and edging leave fine debris, packaging leaves residue, and gloves transfer oils. Whatever cleaning method is used, the test is whether the surface is uniformly water-break-free, and the discipline is procedural: clean in one direction, change wipes rather than reusing them, and handle the glass by the edges from that point onward.

The environment matters as well. Operating conditions for several models in this range are published as 20–30 °C at 40–60 percent relative humidity, with the AJ3220G/R specified from 40 to 80 percent non-condensing. High humidity combined with a cold glass panel promotes condensation on the surface, which is invisible on clear glass and defeats both primer and ink. Panels that have been stored cold should be allowed to reach room temperature before printing, especially where the primer requires a defined flash interval.

Which primer should be used?

The one supplied for your ink and glass, applied as shown.

Primer is not a generic product: it is matched to the ink chemistry and the substrate, so the published recommendation is to obtain it from the machine supplier.

Two application variables decide whether the primer does its job. Coverage is the first: an incomplete film leaves islands of untreated glass that become the first points of failure. The interval between primer and print is the second, because a primer that is still releasing solvent, or one that has fully dried beyond its open window, will not bond. Both are specified by the primer supplier and both should be written into the work instruction rather than judged by the operator.

Where the printed product is intended for a regulated market, the chemical composition of primers and inks brings its own obligations. In the European Union the registration, evaluation and authorisation framework for chemicals applies to substances placed on the market (European Commission, REACH), and the operator-level handling of waste primer and cleaning materials falls under national waste rules (US EPA). Confirm what the primer contains before it becomes part of a production process.

How does white ink behave on clear or coloured glass?

White is the image, not a background.

On clear glass the white layer is what makes the colour visible and what determines whether the panel is viewed from the front or the back, so its order in the print sequence is a design decision.

Three configurations are common in decorative and functional glass work. A front-viewed panel prints white first and colour on top, so the colour is seen through the glass. A back-viewed panel reverses the order, printing colour first and white behind it, which produces a mirrored image and a solid backing. A panel that must be opaque from both sides needs the white to be dense enough that no light passes through, which is a coverage question rather than a colour question.

Published ink configurations across this range vary in how much capacity is assigned to white. The AJ2130G/R is specified with CMYK plus light cyan, light magenta, white and varnish; the AJ3220EX with CMYK plus light cyan, light magenta, white and varnish in an extended seven-colour set; the AJ2513G/R with CMYK plus white and optional light cyan, light magenta and varnish; and the AJ3220G/R with CMYK plus white and varnish, expandable to eight colours. Where glass is a core product, the white channel allocation deserves as much attention as the head count.

What curing settings protect adhesion?

Enough energy at the surface, measured hot rather than cold.

UV LED output falls as the emitter warms, so a setting qualified on a cold machine can under-cure after several hours of production, which appears as poor adhesion rather than as a lamp fault.

Curing is where glass differs most from porous substrates. Because the ink cannot penetrate the surface, an under-cured layer has no mechanical anchor at all, and the failure appears at the edges of the image where coverage is thinnest. The practical discipline is to qualify the curing setting by measurement at the substrate plane, and to re-qualify it after any change to the module, the power supply or the production pattern.

The published curing system across the flatbed range is UV LED, and the same technology is published on the AJ360i cylinder printer, so the measurement principle applies across the range. Where a printed glass panel will be handled, stacked or cleaned frequently, the published guidance is to add a topcoat or lamination for maximum durability, which is a finishing step rather than a printer setting.

How is adhesion actually proven?

By a tape test on the real glass, not by opinion.

Adhesion is measurable: the ASTM D3359 tape test is the recognised method for assessing coating adhesion, and it should be run on your specific glass, primer and curing combination.

Running the test on a representative sample before quoting the job converts an argument into a measurement. It also produces the baseline that makes later diagnosis possible: if a panel releases in service, a stored test result from the same materials shows whether the process changed or the incoming glass did. Where the printed surface will be cleaned, stacked or abraded in handling, abrasion resistance is assessed separately under ASTM D4060 (ASTM D4060), with the adhesion method itself published by ASTM (ASTM D3359).

Andresjet publishes an outdoor lifespan of 3 to 5 years for its high-quality UV inks without significant fading, depending on sun exposure, and states that prints are waterproof and suitable for most indoor and outdoor applications with good resistance to general handling and scuffs. Those statements describe the ink system; the result on a specific glass panel still depends on the process used to apply it.

What changes with tempered, laminated or coated glass?

The surface changes, so the process may not transfer.

Tempered glass can carry coatings or markings, and low-emissivity coatings are not the same surface as bare float glass, so primers qualified on one may not hold.

The practical rule is to qualify per glass type rather than per project. If a shop runs float glass this month and a coated architectural panel next month, the primer and curing combination should be re-tested on the new specification rather than assumed. The same applies to laminated glass with an interlayer near the surface, and to glass that has been acid-etched or sandblasted, where the surface profile changes the way ink and primer behave.

Thickness and weight are usually well inside the published limits: this range accepts media from 1 to 100 mm thick at up to 50 kg/m² on the AJ2130 series, AJ2513G/R and AJ3220EX. The exception to watch is heavy laminated architectural glass, where both thickness and mass can approach the published boundary, and where the hold-down requirement differs from a standard decorative panel.

What finishing steps follow printing?

Edge work, optional topcoat, and careful storage.

Glass is usually cut and edged before printing, but where post-print processing is required it must not touch the printed area, because mechanical finishing on a cured ink layer will damage it.

Three finishing decisions belong in the quote rather than being left to the workshop. Whether the printed face receives a topcoat or a protective film, which the published guidance recommends for high-wear or extreme conditions. How panels will be stacked and transported, since glass stacked face to face with fresh prints and no interleaving will mark. And what happens to a panel that fails inspection, because reprinting glass requires removing the cured ink, which is a chemical process with its own waste obligations.

Handling also affects throughput planning. The published ink cost of approximately $0.80 to $1.20 per square metre for a full-colour print covers the printing element only, and it should be understood as one line in a costing that includes primer, preparation labour, inspection and waste. For glass, preparation time is frequently the largest of those lines, which is why it belongs in the quotation rather than in the overhead. Where the same panel is reordered months later, colour consistency depends on the profiles maintained for that glass rather than on the printer alone (International Color Consortium).

What the decision comes down to

Printing on glass is a surface-preparation process with a printer attached. If the panel is clean, the primer is correct and complete, the white layer is placed deliberately, and the curing energy is measured at the surface rather than assumed, the print survives handling and weathering. If any one of those steps is treated as routine, the failure appears weeks later where it cannot be diagnosed.

Qualify the process once on each glass type you sell, store the tape test result as a baseline, and put preparation time into the quotation. Configuration detail for the two formats used for glass work is published within the UV printers for glass panels collection and the wide format UV flatbed range.