Inquiries

Improving water-based ink performance Research Department of Company Y, an ink manufacturer

Oxazoline crosslinker reduces curing temp

Want to improve the water resistance and adhesion of water-based inks? You’ll need the power of our crosslinking agents, developed to meet your needs!

Inks & Coatings
Adhesion, Bonding, and Tack Dispersion / Aggregation

Recently, the packaging materials industry has been under increasing pressure to be more environmentally conscious, prompting efforts to develop easily recyclable products and reduce CO₂ emissions during manufacturing. A flexible packaging manufacturer consulted Ink Manufacturer Y about improving the performance of water-based inks. Y proceeded with development, but...

Challenges

We want to improve the water resistance and adhesion of water-based inks for olefin-based films, but...

The use of single-material packaging films (mono-materialization) to facilitate recycling has been increasing within the packaging materials industry. The use of olefin-based films such as PP and PE is also on the rise. One day, Interviewee Q from Ink Manufacturer Y was approached by a client—a flexible packaging manufacturer producing films for daily necessities and cosmetics—with a request to improve the performance of water-based inks.

Interviewee Q recalls that time:
"They asked us to improve the water resistance and adhesion of the printed coating of water-based inks after drying. In recent years, water-based inks have been gaining attention due to safety concerns and VOC regulations." (Interviewee Q)

Company Y decided that Interviewee Q’s development team would take charge of this project. After discussions among the team members, they decided to add a crosslinking agent to the current ink formulation and explore heat curing to improve water resistance and adhesion.

"Through discussions with our clients, we learned that the films they use are made of PP and PE, which have lower heat resistance than materials like PET. To minimize damage to the films, we needed to set the heat curing temperature as low as possible."

"We immediately began selecting a crosslinking agent. Since the binder resin of the current ink contains carboxyl groups, we decided to choose a crosslinking agent that reacts with them." (Interviewee Q)

We evaluated several crosslinking agents. However, we encountered issues such as insufficient adhesion and water resistance, a gradual increase in ink viscosity over time, and a short pot life after adding the agents.

"When I felt stuck in the development, I remembered having previously evaluated the oxazoline-based EPOCROS™ WS. At that time, EPOCROS WS had a good pot life after addition, and the cured coating film showed excellent water resistance, solvent resistance, and adhesion—achieving good performance, but..."

"For EPOCROS WS to achieve sufficient performance, it requires a curing temperature above 100°C. Therefore, I unfortunately thought it might not be suitable for the thermal curing process required this time." (Interviewee Q)

Although Interviewee Q and his team members felt that EPOCROS WS had potential, the issue of the curing temperature became a hurdle and they were forced to give up.

Key Challenges

  • A flexible packaging material manufacturer requested performance improvements to water-based inks in order to enhance environmental compliance.

  • We decided to try adding a cross-linking agent to water-based inks to improve their performance.

  • The target substrates are olefin-based films such as PP and PE, so the curing temperature required for the crosslinking agent to react must be kept as low as possible.

Solutions

Solution Summary

  • Nippon Shokubai has developed a technology to lower the curing temperature of oxazoline-based crosslinking agents, enabling crosslinking at around 80 °C instead of the previous 100 °C.

  • The oxazoline groups in EPOCROS™ WS react with the carboxyl groups in the binder resin, resulting in a coating film with improved adhesion, water resistance, and blocking resistance.

During this time, a researcher at Nippon Shokubai, with whom we had been exchanging information for some time, contacted us to share that they had developed a technology to lower the curing temperature of EPOCROS WS and wished to introduce it to us.

"I immediately spoke with the person in charge, who told me that due to many requests to lower the curing temperature of EPOCROS WS, they conducted technical investigations. They also explained that a relatively simple heat treatment greatly improves the reactivity between the carboxyl groups in the resin and the oxazoline groups in EPOCROS WS. This was exactly the information I had been looking for."

"Furthermore, we were informed that there were no issues with storage stability after the specified treatment and that the conventional pot life was maintained, so we immediately began reconsidering EPOCROS WS." (Interviewee Q)

Interviewee Q and his team added EPOCROS WS to the binder resin and used the heat treatment method recommended by Nippon Shokubai to create a prototype ink.

"I was concerned about the ink’s viscosity increasing after heat treatment, but there were no issues at all. We also succeeded in improving the performance of the ink film, which had been a challenge at a curing temperature of around 80°C. With EPOCROS WS as our primary crosslinking agent, we were well on track to complete the ink." (Interviewee Q)

Interviewee Q's team has asked a film manufacturer to evaluate the prototype ink. They are also discussing the possibility of applying this curing technology to add EPOCROS WS to primers, which require more stringent adhesion. It looks like there will be growing use of EPOCROS WS.

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