I was recently asked what the current acceptable dry down time was for digital inkjet prints prior to mounting or framing, but that cannot be answered without delving deeper into what is meant by inkjet in 2020.
Inkjet began as aqueous dye ink designed to print on standard bond papers. Since then, many different types of inkjet printers, ink formulations, and materials have been developed and embraced from aqueous to solvent, eco-solvent, latex, UV-curable, and dye-sublimation, all considered inkjet. Wide format inkjet includes roll printers, 18"-100" wide having been developed for outdoor signs, billboards, packaging boxes, fabrics, wallcoverings, vehicle wraps, promotional products, fashion, and fine art.
Desktop inkjet printers tend to use aqueous inks based on a mixture of water, glycol and dyes or pigments and are used to print text, graphics, or line drawings on uncoated and coated bond papers, coated photo, fine art papers, canvases, vinyls, display films, window graphics, and backlit films. The coatings on these materials help control the performance of the ink droplets on the surface of the print, but neither dye nor pigment inks are considered waterproof.
Dye inks are more susceptible to fading and water damage, and lamination or clear coat is recommended to protect large format dye prints from water, humidity, and prolonged exposure to UV light. Pigment inks have a higher level of resistance to fading and water than dye inks and when printed on archival fine art and photo papers may last for generations.
Solvent and Eco-solvent Inkjet
Prints from solvent inks use volatile organic compounds (VOCs) known as solvents that are generally waterproof and ultraviolet-resistant without requiring coatings. Solvent inks provide exceptional durability without the need for lamination or protective clear coat and are lightfast, waterproof, and scratch-resistant, making them ideal for large, outdoor presentations. Eco-solvent inks use milder solvents that don’t require extra ventilation in enclosed spaces, and decorative art printed on coated canvas do not require any protective varnish or clear coat to remain resistant to fading or abrasion.
A water-based carrier mixes with pigment as latex or resin-based polymer dye that bond to a substrate after passing beneath radiant heaters. Unlike traditional solvent inks, latex ink is odorless, eliminating ventilation issues. Used for outdoor signs, wallcovering, durable fabrics, backlit signs, canvases, banners and signs, latex ink is being presented primarily as an alternative to solvent inks. They retain their appearance outdoors for three years without lamination, and the print is dry immediately upon extraction from the printer, removing the additional time required for other inks to dry down.
These inks have chemistries that cure to form a rigid film when exposed to controlled intensities of UV light, and once the ink has been cured, is completely dry. It is highly versatile, printing to a huge range of coated and uncoated materials, including wood, metals, plastics, ceramics, glass, acrylics, objects, fabrics, paper, and flexible materials in very bright, bold colors.
However, these inks are quite expensive, requiring not only the purchase of the ink itself, but also a printer with a built-in curing function. This type of ink is also rather heavy, which creates a raised surface on the substrate which may result in cracking on flexible materials.
Dye Sublimation Inkjet
Since the chemical process is very specific for dye sublimation, you’ll need to use a specific type of ink known as disperse dyes, referred to as dye-sub inks. These inks go from solid to gaseous under high temperatures and will easily bond to polyester fabrics resulting in vibrant colors. The images are initially printed on coated heat-resistant transfer paper as a reverse image of the final design, which is then transferred onto polyester fabric or other surface like aluminum panels using a heat press around 375°F. Textile inks are designed to print on the many different types of washable fabrics used to produce curtains, sheets, T-shirts, and fashion apparel.
Dry Down (Curing) Time
Back in 2013 I wrote that inkjet prints required two weeks of dry down time to fully cure prior to mounting or enclosing in a frame. There are two factors for consideration: first, is it dry enough to be handled, and second is dry enough to be framed, with the time being different for each. Most modern photo printers and photo printing inks can be handled the moment they are processed. However, they are only dry enough to be lifted gently and moved to another place. Even when the ink surface is dry to the touch the ink beneath the surface skin may still have moisture that has not yet fully evaporated and set. This is called curing, and full curing is what prevents outgassing of moisture within a sealed package.
Many manufacturers support the 24 hour standard of dry down, for aggressive handling and placement in photo albums. Framing before curing is ill-advised because of the outgassing of solvents during the curing process. If you frame photo printed inks before these solvents have had time to evaporate, the inside of the glazing may get cloudy.
While 24 hours may be acceptable, the actual time period will vary depending on type of inkjet ink, paper, printer, technology (aqueous, solvent...), room temperature, and humidity all impact drying. When normal printing ink is used to print on photo paper, it could take weeks to dry, and the problem is you may know all the variables to make an informed decision.
If you are printing the image for your client you will have control over assorted elements. If the amount of ink printed on photo paper is high, then it’s natural that it will take longer to dry. The only way for you to evaluate how much photo printing ink is on the photo paper is to find out the color density of the image. If it’s high, then you may need to wait longer, and the brand of the photo printing ink also factors in. Matte photo paper dries faster than glossy photo paper because matte papers have a top layer and photo printing ink goes under this top layer to create photo texture. Like in the case of photo printing ink, the brand of the photo paper also matters. So to expedite the drying of a printed photo, use the right amount of ink on glossy paper and place the print on a flat surface in a room with low humidity, high temperature and a fan.
Dried vs. Cured
Many people think that dried and cured mean the same thing, while others believe that the difference is based on ink chemistry, such as solvent or UV-curing. When an inkjet is printed the initial point where the ink becomes hard and does not smear when touched is when it is considered dried, and this is true of all inkjet.
Aqueous and Solvent Drying
Aqueous and solvent inks dry by evaporation resulting in a dried ink film. The dried ink is non-tacky and resists scratching. A common test for dryness is twisting a thumb on the ink and twisting with medium pressure. If ink does not smudge, it is an indication of dryness. And while a film may initially be dry to the touch, inks in which a chemical reaction takes place--known as reactive inks--take longer to dry. This longer hardening of the ink is sometimes referred to as the curing stage, not to be confused with curing of UV ink when exposed to ultraviolet light.
The high print speed of many solvent printers demands special drying equipment, usually a combination of heaters and blowers. The substrate is usually heated immediately before and after the print heads apply ink. Eco-solvent inks have rapidly gained popularity in recent years as their color quality and durability have increased while ink cost has dropped significantly.
Instead of evaporation, UV inks become dry due to a chemical reaction in the ink when the print is passed under ultraviolet light. Molecules in the ink start a reaction that causes other molecules to grab onto one another and produce a dry-to-the-touch ink film after the print exits the unit and cools down. This reaction happens very quickly, which leads to instant drying that result in a completely cured graphic in a matter of seconds. This also allows for a very fast print process. As a result of this instant chemical reaction no solvents penetrate the substrate once it comes off the printer, which also allows for high quality prints but they can be expensive and the surface has a bit of relief from cured ink volume, which can crack if printed to flexible substrates.
These inks contain sublimation dyes and are used to print directly or indirectly onto fabrics which consist of a high percentage of polyester fibers. After printing a heat drier causes the dyes to transfer and fuse from the a printed sheet into the fibers to create an image with strong color and good durability.
The ideal length of time to allow for aqueous inkjet curing is currently being agreed to as 7 days. Framing or mounting a print before it is dried or cured will be sealing it in an moist environment. This moisture can then cause effects such as color bleed and discoloration. Allow as long as possible for prints to cure before framing, I continue to push for two weeks.
In Asia a new ink painting cannot be traditionally scroll mounted until it ages (cures) for two years. So your scroll master will say thank you, I will do this for you...come back in two years. So waiting two weeks doesn't sound so bad now.
Copyright © 2020 Chris A Paschke
Digital Technology Processes 2020 chart.
https://blog.inkjetwholesale.com.au/printer-education/how-long-does-photo-printing-ink-take-to-dry/—Inkjet Wholesale, Australia
https://www.largeformatreview.com/blog/cured-ink-vs-dried-ink-what-s-the-difference—Large Format Review-LFR news
https://www.marrutt.com/support/inkjet-articles/print-storage—Marrutt Professional Photographic
For more articles on mounting basics look under the mounting section in Articles by Subject.
Additional information on all types of mounting is found in:
The Mounting and Laminating Handbook, Second Edition, 2002,
The Mounting And Laminating Handbook, Third Edition, 2008 and
Creative Mounting, Wrapping, And Laminating, 2000 will teach you everything you need to know about getting the most from your dry mount equipment and materials as an innovative frame designer.
All books are available from Designs Ink Publishing through this website.
Chris A Paschke, CPF GCF
Designs Ink Publishing
785 Tucker Road, Suite G-183
Tehachapi, CA 93561