Types of Edible Ink for Confectionery and Pharmaceutical Products

Selecting which edible printing ink to use for your product should involve careful consideration. A number of solvent and aqueous ink variations are available to print onto the surface of tablets, capsules, candies, gums, chocolates and more. Confectionery and pharmaceutical ink should be chosen to assure compatibility with the product surface that is being printed upon. With many types of coatings now available, each one has its own particular reaction to the ingredients contained in printing inks.

Types of Edible Printing Inks 

• Solvent base
• Water base
• Solvent/Water base

Solvents and Ingredients Used in Edible Printing Inks

• SDA-3A
• Ethyl Alcohol
• Isopropyl Alcohol
• Normal Butyl Alcohol
• Purified Water
• Propylene Glycol (Used Sparingly)
• Ammonium Hydroxide or Ethyl Acetate
• Shellac or Hydroxypropyl Methyl Cellulose (binder or “glue”)
• The color selected, usually composed of FD&C or D&C lakes or dyes or synthetic iron oxide pigments (Carbon black is allowable in some countries)
• Polysiloxane (Medicinal Anti foam)
• 2 – Ethoxyethanol (Cellosolve)
• The use, acceptance and regulations of the above ingredients vary per country

Solvents are used to dissolve some ingredients, such as shellac, to suspend color particulates and also to control drying rates. Always be sure to mix and prepare pharmaceutical ink as required to assure good suspension or solution of ingredients.

The addition of Ammonium Hydroxide to some ink formulations helps the ink to “bite” into waxed surfaces, literally penetrating the waxes and getting under and into the surface.

With the exception of the color medium and Shellac or Hydroxypropyl Methyl Cellulose, all other ingredients contained in the ink evaporate or “flash” away.

It will be necessary to compensate for solvent loss by adding a small amount of thinner from time to time, during operation, to keep ink viscosity optimum for use. The evaporative rate of the thinners used can have an effect on print quality and run ability.

The following list of solvents gives the relative rate, fastest to slowest:

• SDA-3A
• Ethyl Alcohol
• Isopropyl Alcohol
• Normal Butyl Alcohol
• Purified Water
• Propylene Glycol (Used Sparingly)

An equal mixture by volume of isopropyl and Butyl alcohol is a good average dry-time solvent. However, each ink and its use on various machines and types of products, can be different.

Propylene Glycol is used when an ink needs to dry slower, but not be made thinner.

A mixture of Propylene Glycol and Isopropyl Alcohol (10-20% Propylene Glycol, 90-80% Isopropyl Alcohol) can often be used as a substitute for Butyl Alcohol to slow down the drying time of the ink.

Common Printing Observations and Probable Causes

• Weak Printing or Thin Lines – Ink is probably too thick, or drying too quickly, add appropriate solvents, e.g. Isopropyl / Propylene Glycol mix.
• Broad, Fuzzy or Washed-Out Printing – Ink is probably too thin, replace ink.
• Missing or Incomplete Printing – Possibly debris on rubber roller, clogged etches, insufficient print impression, or damaged rubber roller or ink drying too quickly.
• Smudged or Spotted Printed Product – Rubber roller print impression too high, “squash effect” – loose print rollers or debris in roller gears, product hitting stripper plate. Spotting – ink has not dried sufficiently before discharge.
• Ink is Drying Too Quickly and is Too Thin to Add Solvents – Add Propylene Glycol. Be sure to add incrementally, in small amounts of 5 ml each as too much may cause the ink to become too wet and result in ink spotting.

Printing and Pharmaceutical Ink Maintenance

Thankfully, printing and pharmaceutical ink maintenance are skills that can easily be learned. Once the printing environment is established for a particular product and inks are adjusted to suit their proper purpose, maintaining the integrity of the printing inks is a seamless process. Of course, investing in high quality printing machinery and having the right tools, guidance and accessories available makes it even easier.

While we typically expect customers to assume the responsibility of ink and product coating compatibility, we urge you to take advantage of our decades worth of printing experience before submitting your ink formulation information to governing authorities.

We request that the ink manufacturer, formulation and solvent specifications be submitted to us no more than two weeks after the receipt of an order. It is advisable that inks contain quantities (even in small amounts) of all ingredients that will allow adjustments to be made (by the operator) as conditions dictate. If a necessary ingredient does not exist in the ink formulation when submitted for approval, it can be difficult, time consuming, and labor intensive to get approval afterwards.