q: Are all pigments the same?
a: No. Pigments vary obviously by their shade, hue, saturation, opacity and/or transparency. Among these visible differences, all pigments will react differently to the environment they are placed in. Consideration must be given to product resistance, exposure to direct sunlight and so forth. Please check with our technical reps to ensure your pigment selection is the best for the end use application you desire.

q: Occasionally we will come across an ink that fails a tape test; is there anything we can do press-side to remedy this occurrence?
a: Yes, there are several things you can do that will help. Let’s begin with the obvious and work our way up.

First, test the dyne level of the substrate itself. Most stocks for printing are treated to a dyne level of around 38-40. Subsequent corona treating on press will take that dyne level up to around 42-45. What most folks fail to look into is that the dyne of the stock must be compatible with the dyne level of the ink. The substrate should have a dyne level of at least 10 points higher than that of the ink. The dyne level of the ink is a component of surface tension.

Surface tension is described as phenomenon that results directly from intermolecular forces between molecules of liquids. In other words, molecules at the surface of a drop of liquid experience a net force drawing them to the interior, which creates a tension in liquid surface; almost as if the liquid was covered with a tight skin. The surface tension of a liquid is measured in dynes/cm.

The second force that affects the ability of the ink to wet out properly is the surface energy of the film or substrate. Surface energy is a term used to describe the reactivity of the surface of a solid substance. For practical purposes, the surface energy of a substrate is expressed in relation to dynes/cm as well.

If the ink has too high a dyne level, it will reticulate, or “bead up”, on the surface of the substrate. If this is the case, additives must be added to the ink that lower viscosity and still retain proper pH.

Remember, the corona treatment unit itself will degrade over time, regularly check the performance of your unit. Checking the performance can easily be done using simple, hand held dyne markers. If you read the stock before the corona unit and then after it, you will see how much of a charge your unit is giving.

Some printers will “cheat” a tape test by adding a slip agent to the ink. The slip agent generally consists of waxes and/or silicones that migrate to the surface of the ink film and provide a slick surface. This slick surface will provide an inferior surface for the tape to bond to. This may be OK for getting the job off, but remember, the underlying ink film still has poor adhesion. This poor adhesion may show up as “cracking” or “peeling” if the printed product will be exposed to large amounts of friction and/or rub.

The best way of passing a tape test is by improving the surface tension of the ink and/or the substrate.

q: What makes an ink fade?
a: Exposure to direct sunlight will bombard the pigment molecules and, over time, will cause them to “bleach out”. This phenomenon is actually a chemical reaction catalyzed by the UV wavelengths in light. Certain pigments fade more than others. Yellows and reds predominately will be the first shades to fade, but all pigments will fade over time.

Pigment fading is held to the “Blue Wool Scale” standard. This is a standard system devised by textile manufactures over 100 years ago and is based on a scale from 1 to 8. The higher in the scale you go, the better fade resistance you will see. Each incremental division in the scale is exponentially higher than the last, analogous to the Richter scale in measuring earthquake magnitude.

An ink is considered “lightfast” if it has a Blue Wool Scale rating above 6.

q: How do we control an inks’ scuff resistance?
a: Like mentioned above in the discussion on “tape tests”, scuff resistance is a factor of the inks’ surface dynamics. This attribute is moderated by the condition of the substrate, the viscosity of the ink, the pH of the ink and the rate of drying the ink has. Most inks can improve their resistance to scuff by the addition of waxes and/or silicones. Care must be given in this regard as excessive amounts of waxes/silicones can prevent subsequent after printing (foil stamping, ink jet printing and the application of a clear overprint varnish/coating). A large addition of surfactant will also affect adhesion.

q: How can we improve the adhesion of our inks on “difficult” substrates?
a: Usually the addition of an inks systems vehicle will drop viscosity and allow the ink to adhere better to the substrate. At times the body of the ink must be built up. Also, keep an eye on the pH of the ink as this will greatly affect how that ink transfers out of the anilox cells and wets out on the substrate.

q: What is the vehicle in an ink system?
a: The vehicle in an ink system is the “carrier” for the pigment portion of the ink. An inks strength and appearance is a product not just of the amount of pigment in the formula but an attribute of how the vehicle system transfers.

q: What is the resin in an ink systems?
a: The resin portion of the ink is the medium in which the pigment is dispersed or wet out in. The resin system must be homogenous with the vehicle system used. Different resins will affect the hardness, glossiness and other physical characteristics of the ink.