Manufacturing Larger Batches
Most ink manufacturers make large batches of common ink formulas, in order to maximize efficiency and manage costs. Most colorants must be “ground” to wet out their surface area in order to be effectively “carried” by the resin vehicle system through the printing process. Some sort of manufacturing method/device must be used that imparts physical energy to the colorant mixture, in order to break it up into smaller particles. Ink companies use machines like bead mills, shot mills, three roll mills and the like for this purpose.
The inks are then typically strained or filtered afterward to capture any large particles. The formula is often completed by the addition of other ingredients needed to make a “finished” ink that is ready for press.
For smaller batch sizes or for mixtures of different colored inks, blending is typically used at an ink company branch facility or a customer inkroom. Blending takes much less physical energy, and can be accomplished by using small mixers, stirrers or through hand mixing with a drill/blade combination, or even a stir stick.
Most ink manufacturers use stringent quality control methods and equipment to make sure their inks are on spec for their various attributes—such as measuring viscosity, seen here—as part of the internal manufacturing process.
Quality Control at the Manufacturer & Print Facility
Most ink manufacturers use stringent quality control methods and equipment to make sure their inks are on spec for their various attributes—color, strength, viscosity, adhesion, gloss—as part of the internal manufacturing process. Tools like a viscometer, grind gauge, proofer, spectrophotometer, gloss meter, pH meter, rub tester and COF tester are used during the development process, as well as during manufacture. Other tools are available for the ink manufacturer as needed, depending on the properties desired in the finished product.
Some of these same QC tools can often be used at the print facility, but some favored by ink manufacturers are cost prohibitive for a printer’s pressroom or inkroom. Typically, the printer can effectively monitor ink condition and suitability for use with tools like a Zahn cup for viscosity measurement for water-based and solvent-based inks (but not for energy-curable inks—these inks are too viscous for using a cup method), a pH meter for water-based inks, a hand proofer, a spectrodensitometer, and possibly a gloss meter, rub tester and COF tester for QC of the finished printed material.
On-Press Variables Affecting Ink Performance
It would take a completely separate webinar and accompanying article to adequately cover the on-press variables that can affect ink performance. Here are a few of the things a printer should be aware of that can affect how an ink performs on press and as a printed product:
- Anilox roll condition, cleanliness and volume
- Doctor blade type and condition
- A substrate’s absorbency, surface energy and cleanliness
- The type, condition and capacity/power of a drying or curing system
- The choice of plates and mounting tape, their compatibility with the ink, and condition for the graphic requirements of the job
- Press gears, bearings, age and maintenance
- Overall pressroom conditions
Basic Ink Troubleshooting
A few basic tips: In general, when you are troubleshooting, make one change at a time. Always follow your ink supplier’s recommendations. For specific problems, contact your supplier! And always check the basics first—don’t make major changes without confirming you have the right ink for the right job, using the right conditions.
Specific to ink adjustments—in general terms:
- Water-based: Check pH first! Always get pH right before adjusting viscosity or drying speed
- Solvent-based: Check viscosity; reduce viscosity with solvent, but reduce strength with extender
- UV/LED/EB: Mix well to break down thickened ink (energy-curable inks can be thixotropic, meaning they are thick until acted upon by a physical force; think of ketchup in a bottle), ensure proper film thickness (anilox volume) before adjusting color or cure
For color adjustments:
- For any color made from a combination of pigments, you should use pigments that are already in the color when making adjustments. Be very careful of adding additional colorants to the formula
- The colorant that is in your mix at the lowest percentage will generally be the dominating color when making adjustments. For example: if your mix is 75 percent warm red, 24 percent rubine, and 1 percent black, an addition of black will change the color very quickly, while it will take a larger amount of warm red to significantly change the color
- Think in terms of percentages for any additions, and be sure to record the changes you make on the container for any unused ink
No matter which type of ink chemistry you use, the bottom line is this: Take care of your ink, and it will take care of you. Treat the ink as a fundamental part of your printing process. Control its condition as you would any other aspect of the pressrun—equipment and materials.
About the Author: Ed Dedman is the North American flexo technical support manager for Zeller+Gmelin Printing Inks.