Ink Adhesion Part 3: Ink Mixing, Contamination, Blooming and Mold Release Agents

Before printing on any parts there are several factors which are of vital importance: ink mixing, product cleanliness and substrate additives. Regardless of proper ink preparation and chemistry, surface contamination, blooming and mold release agents may all interfere with your ability to achieve satisfactory adhesion.

The two most important factors that must be addressed when dealing with ink mixing are: How are you mixing the ink? What components are you using? Inks are formulated to be mixed at specific ratios, and any deviation may result in adhesion failure. You must choose the correct ink and mix it to the exact manufacturer specifications. It is a common misconception that adding hardener over manufacturing specifications will allow for better adhesion.

Surface contamination is a huge factor in whether or not the ink will adhere to any given object. The first reason contamination may occur is because people are not handling the object correctly. Oils on the handler’s hands can be transferred onto the objects. Contamination can also occur as a result of secondary processes being performed on the parts. For instance, if you choose to wash the objects with a detergent, this may leave a residue behind on the object and the ink may not adhere properly. Here at EPS we use alcohol. This is a standard solution which readily flashes off and is used to wipe the parts of any dust, oils or any contaminants before printing. With proper handling, cleaning the parts may be unnecessary, but wiping with alcohol does assure that there will be a clean surface to print on.

Blooming is a term used in the plastic industry and it denotes a plasticizer or other additive coming to the surface of a part over time. The difficulty with this contamination is that you can wipe the surface of the part free of contaminates but over time the part will re-bloom and the contaminants will interfere with the bond between the ink and the parts.

Mold release agents (also known as de-molding agent, form oil, parting agent or release) are substances used in molding and casting that aid in the separation of a mold from the material being molded and reduce imperfections in the surface. While these additives make the plastic manufacturing process simpler, they can wreak havoc on attempts to achieve adhesion.

In the end, experience is the best weapon in attaining adhesion. If you have any questions or concerns please contact Technical Service.  For more information about Engineered Printing Solutions’ custom solutions, standard pad printers, industrial digital ink jet, consumables and other auxiliary equipment, email sales@epsvt.com or call 1-800-272-7764.

Ink Adhesion Part 2: Bi Component, Pre-Treatment and Post Cure

Have you ever looked on the back of an object and seen the recycle symbol? It tells you what material the object is made of. When it comes to plastics, Polypropylene and Polyethylene are considered the two of the most difficult materials to get ink to adhere to due to their relatively low surface energy. Polypropylene is used to make a wide variety of items and low and high density Polyethylene is commonly used in food packaging. When it comes to these difficult substrates it becomes necessary to pre-treat to affect a change in surface energy to make the surface amenable to bonding with – or cross-linking – with the ink.  This causes the substrate surface to become more receptive.

The most commonly used methods of pre-treatment are:

  • Plasma and Corona: Electricity applied to the surface.
  • Flamer: Liquid propane (LP) or natural gas. With Flamer there may be variation due to cleanliness of the burn and how the flame will pre-treat any given substrate.
  • Chemical Pre-Treatment: Usually manually applied with a liquid soaked rag.

Unfortunately on any given substrate you cannot assume that you will affect an equivalent change in the surface energy from one pre-treatment to another. Finding the correct ink pre-treatment may consist of 3 different segments: cleaning, activation and surface bonding.

Plasma surface treatment is a process that raises the surface energy of various materials in order to improve the bonding characteristics when ink is applied. Plasma is used widely in the medical industry. This is because you don’t have the bi-product of the other 2 pre-treatments such as carbon from the flaming process or residual VOC’s left behind from the from the flashing process of a chemical pre-treatment. Corona treatment is commonly used on materials such as polymers, papers, films, glass and metals.

Plasma is a good option for components that require a longer treatment hold. Some of the key advantages include: surface chemistry and 3 dimensional treatments. Corona is another form of plasma that can be used with in-line processes. When working with corona the systems are easy to maintain and user friendly.

Flame pre-treatment can also be integrated into inline processes, and require careful and sometimes precise setup in order to be safe and effective. Proper air to gas ratios, flame intensity and dwell time all play into successful pre-treating. Flame plasma systems combine compressed air and a flammable gas which is combusted to create a flame. One advantage is that the material surface only has to be exposed to the flame for a brief period of time to become polarized through oxidation. One setback is the heat level required for this treatment may cause damage to the parts.

Chemical priming is yet another way to pre-treat difficult to adhere to substrates and is generally considered a last resort due to the generally manual nature of application. Essentially primers are used to chemically modify the surface by removing contaminants, adding reactive sites for bonding and increasing surface energy. One disadvantage is that these primers often contain chlorinated solvents that are considered volatile organic contents.

Many substrates will require pre-treatment to satisfy customer’s individual requirements for print longevity. But with the correct treatment and testing, our technical service technicians will test the inks and provide samples for the individual customer’s review.

For information about Engineered Printing Solutions’  custom solutions, standard pad printers, industrial digital ink jet, consumables and other auxiliary equipment, visit Ink Adhesion Part 3: Ink Mixing, Contamination, Blooming and Mold Release Agents, email sales@epsvt.com or call
1-800-272-7764.

Ink Adhesion Part 1: General Education

Have you ever looked down at a water bottle and wondered how the logo got there? Personally I know I have. Before the colors and image can get put together on the object the first question that needs to be answered is how to choose the right ink for the job. Simply put, ink adhesion is ink that sticks to any given product to a known specification. One of the most common tasks our Technical Service team are charged with is to “find me an ink that sticks to the surface of my product.” It wouldn’t be realistic if I told you that our Technical Service team has magic powers and can automatically determine the perfect ink for the material being printed on. Even though inks are produced to stick to a particular substrate; the question is which ink is best suited to adhere to your particular substrate based on your requirements?

There are many different substrates and even more sub-sets within each . Not all polypropylene’s (PP), for example, are created equal. An ink that may exhibit flawless adhesion to one PP product may not adhere at all to another. We therefore need to match the ink series with the particular substrate being presented. However if you supply our Technical Service team with the parts you wish to print on, they will be able to begin working their “magic”. They will be able to first make an educated guess as to which ink will meet the customers’ expectations based on experience, then begin testing the inks and provide samples for the individual customer’s review.

For information about Pad Print Machinery of Vermont’s custom solutions, standard pad printers, industrial digital ink jet, consumables and other auxiliary equipment, visit Engineered Printing Solutions, email sales@www.epsvt.com or call 1-800-272-7764.

Save on Pad Printing Ink!

Our customers have told us many times how frustrated they are with the amount of pad printing ink they have to throw out at the end of the day. Well we heard you and designed a handy little device to help utilize those small volumes of the ink mixed in the cups. Plus when the ink volume is less than 25 grams, the print quality can deteriorate – not with the new Ink Saver-Ring!

The Ink Saver-Ring fits into a sealed ink cup where it agitates the ink as the cup slides across the cliché. This is a great tool for pad printers who use bi-component inks that must be throw out at the end of the day. Plus this ring will also help prevent the ink pigments from settling in the cups. Over time, less ink waste will add up to a significant cost savings!

Available for all sealed ink cup sizes, call us for pricing and click Ceramic Ring Cups for details.

Pad Print Thinners and Hardeners

Pad printing’s smooth transfer of an image from the inked cliché to the subtrates is facilitated by additives used in the ink’s mix. Pad Print thinners and hardeners are additives critical in handling ink adjustments for better adhesion and extending image life.

Thinners

Transferring pad printing inks requires that a percentage of thinner be mixed into the ink. Thinners are volatiles; that is, they evaporate quickly (“flash off”) to dry out the ink mixture so it becomes “tacky.”

This “tackiness” is what enables the silicone pad to pick up an image/ink and transfer it to the part.

Ink manufacturers provide special, chemically-formulated thinners to work with their inks. They usually provide thinners in different.” The “speeds” refers to how fast the thinner evaporates. Typically, you’ll find fast, medium and slow (sometimes referred to as “retarder”) options.

As you may know, there are different ink “series” that adhere best to specific substrates. Manufacturers will provide charts that cross-reference different substrates and which inks work best with them. Each of these inks may utilize one (or many) different thinners, depending on the application. Here is a link to the Ink & Materials Table from the website.

Another important function of a pad printing thinner is it also cross-links the ink/pigment to the surface of the part while the thinner is evaporating, also aiding adhesion. Some substrates are more porous than others, which makes it easier for ink to bond, so the cross-linking happens quickly. Other substrates require more time, so you’ll use a “slower” thinner. In any case, once the ink transfer (print cycle) is complete, the thinner continues to evaporate and perform its cross-link duties simultaneously, eventually leading up to a “cured” image.

Images pad printed with solvent-based inks are usually “dry to the touch” in a matter of seconds, which means you can handle the parts relatively quickly. However, most pad print inks don’t achieve a full cure until at least 24 hours, sometimes longer.

Hardeners

Where do hardeners fit into this, you may ask? They have very little effect on ink adhesion, but have a huge influence on image durability.

Again, ink manufacturers provide hardeners that are formulated specifically to their inks. Some hardeners work with more than one ink series. This formulation also includes different ink-to-hardener ratios. Some are 4:1 (ink-to-hardener), some are 10:1 and others as much as 20:1. Technical data sheets on inks will detail all of that for you.

Hardeners are always added for inks used on metal, glass and ceramics, as well as parts (regardless of substrate) that may face exposure to abrasives, chemicals, sterilization procedures, etc.

The good thing about hardeners is they enhance image durability. The bad thing about hardeners is that they decrease the “pot life” in an ink cup (normally 8–10 hours max). The important thing is your customer gets a quality, long-lasting image.

Join the conversation! Our dedicated ink experts can get your ink problems solved and your printer up and running in no time!

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