The "Oil Repellent Guardian" in Packaging: Unveiling the Application of Water-Based Ink Repellents
When you tear open a bag of instant noodles, pick up the lid of a milk tea cup, or fill a takeout container with fried chicken,
you might never have noticed the printed designs on these packaging—not only must they be vibrantly colored, but they
must also quietly "resist" grease penetration. A closer look reveals that the ink patterns on high-quality packaging remain
intact, even when exposed to hot oil, and the grease doesn't penetrate through the ink and contaminate the contents.
Behind this lies a silent "oil repellent guard"—the water-based ink repellent.
To understand its role, we must first examine the inherent shortcomings of water-based ink. Water-based ink uses water
as its solvent and is inherently hydrophilic. However, the molecular structure of oils (such as cooking oil and industrial
lubricants) is significantly different from that of water, making them susceptible to penetrating the ink coating like a
"small drill bit." Without the protection of grease repellents, two major problems arise: First, the ink pattern fades and
smears after being soaked in grease, affecting the packaging's aesthetics; second, grease can penetrate the ink layer
and penetrate the packaging, contaminating the food or corroding the contents, even weakening the packaging and
making it susceptible to damage. Grease repellents were developed precisely to address this "grease-resistance loophole"
in water-based inks.
I. The "Main Field" of Grease Repellents: Four Core Application Scenarios
Grease repellents for water-based inks have long permeated numerous areas of our lives and industrial production,
playing an indispensable role in packaging applications that come into contact with grease.
1. Food Packaging: Protecting "Food Safety"
Food packaging is the most common application for grease repellents and also the area with the highest safety
requirements. Whether it's the plastic composite bags for instant noodles and potato chips or the paper lunch boxes
for hamburgers and fried chicken, the water-based ink on the surface must be treated with grease repellent. Take
instant noodle bags as an example. The noodles themselves contain oil and come into contact with hot water during
brewing. Without oil-repellent ink, the oil will gradually penetrate the ink layer, blurring the bag's design and potentially
causing slight migration of ink components. Oil-repellent agents create an invisible protective film on the surface of the
ink coating, preventing oil molecules from penetrating. Furthermore, they must comply with food contact material safety
standards to ensure they release no harmful substances, thus preserving both the packaging's aesthetic appeal and food
safety.
Similarly, bakery packaging (such as cake boxes and bread bags) often comes into contact with oils like butter and cream.
Oil-repellent agents prevent the ink from being stained by these oils, keeping the packaging clean and tidy.
2. Takeout and Catering Packaging: Coping with the "High-Temperature Oil Challenge"
Takeout packaging faces even greater challenges—it not only comes into contact with room-temperature oils, but also with
hot oil straight from the wok (for example, fried chicken and stir-fried noodles often reach temperatures of 80-100°C). High
temperatures intensify the activity of oil molecules, increasing their ability to penetrate. Without an oil-repellent ink,
"oil haloing" can occur within minutes. For example, if the outer printing of paper takeout boxes isn't treated with an oil
repellent, noticeable oil stains will appear on the outside of the box after hot food is placed in it. This not only affects the
appearance but may also mislead consumers into thinking the packaging isn't waterproof or oil-resistant. However, adding
an oil repellent ensures that the ink coating remains resilient to high-temperature oils and fats. Even after prolonged exposure
to hot oil, the design won't deform, and the packaging surface remains dry.
Furthermore, oil repellent is also used on the outer printing of disposable paper cups to prevent trace amounts of residual oil
(such as in the sealant on the cup rim) from seeping through the ink when hot drinks are poured in, causing the design to fall
off.
3. Industrial and Specialty Packaging: Protecting Against "Strong Oils and Fat"
Beyond the food industry, industrial packaging also relies on oil repellents for protection. For example, the water-based ink on
plastic barrels containing mechanical lubricants and gear oils comes into contact with industrial-grade oils—greases with
higher viscosity and stronger penetration. Without an oil repellent, the ink is easily dissolved by the oil, blurring the barrel
markings and hindering identification during storage and transportation. There's also cosmetic packaging (such as makeup
remover and skincare essential oil bottles). These products contain high levels of oils and fats. If the ink on the bottle isn't
protected against oil, the oil can leak from the bottle opening during storage or use and soak into the ink, making the
bottle appear "dirty." Oil repellents stabilize the ink coating, preventing it from fading or dissolving even when exposed to
high concentrations of oil.
4. Printed Paper: Maintaining "Long-Term Oil-Repellency Stability"
Some printed paper products that require long-term storage and may come into contact with oils and fats also rely on oil
repellents. For example, product instructions for oil-based products (such as cooking oil and olive oil) are often placed inside
the packaging along with the product. If the water-based ink on the instructions doesn't have an oil repellent, even a small
amount of oil seeping into the packaging can cause the instructions to become blurred and the paper to become oily.
Oil repellents create a durable, oil-repellent layer on the paper surface, ensuring legibility and dryness even when the
instructions are exposed to oily products, ensuring accurate information transmission.
II. The "Secret of Oil-Repellent Agents": Two Core Working Principles
The key to their ability to repel grease lies in their ability to alter the surface properties of water-based ink coatings,
transforming them from being easily permeable to grease to being grease-repellent. There are two common working
principles:
1. Surface Modification: Making the Coating Hydrophobic and Oleophobic
Most oil-repellent agents belong to the class of surfactants. As the water-based ink dries into a film, they automatically
migrate to the coating's surface, acting like a "small shield" around the ink particles. One end of these molecules binds to the
ink coating, while the other end carries a hydrophobic/oleophobic group—a group that dislikes both water and grease.
When grease contacts the coating, the oleophobic group forms a repellent barrier, preventing it from adhering to the surface
and penetrating deeper. Much like the waxy coating on a lotus leaf that allows water droplets to roll off, an ink coating treated
with an oil-repellent agent allows grease to "slide" off, preventing it from penetrating and staining.
2. "Structural Filling": Blocking "Microscopic Gaps" in the Coating
During the drying process, water-based ink coatings may form tiny gaps (invisible to the naked eye) due to evaporation. These
gaps can become "channels" for oil to penetrate. Some oil-repellent agents have "film-forming" properties, filling these tiny gaps
during drying, making the ink coating denser and non-porous.
Without these penetration channels, even if oil contacts the coating, it remains on the surface and cannot penetrate deeper. This
principle is particularly suitable for paper packaging—paper itself has gaps between its fibers. Oil-repellent agents not only
protect the ink but also help fill the gaps between the paper fibers, further enhancing the overall oil-repellent effect of the
packaging.
III. Key Points to Note When Using Oil-Repellent Agent: Practical Tips to Avoid Pitfalls
To maximize the effectiveness of oil-repellent, it's not a matter of "adding more, the better." Instead, three key points must be
considered:
1. Controlling the Addition Amount: Finding the "Golden Ratio"
The amount of oil-repellent added must match the water-based ink formulation. Too little will result in insufficient oil-repellency,
while too much may affect other ink properties (such as adhesion and drying speed). Typically, the amount of oil-repellent
added is 0.5%-3% of the total ink volume (depending on the ink type and application).
For example, in food packaging inks, excessive addition of oil-repellent can weaken the ink's adhesion to the packaging
substrate (such as plastic film or paper), making the design susceptible to detachment. Excessive addition can render the
ink ineffective against high-temperature grease and oil, leading to oil bleeding.
2. Pay attention to compatibility with other additives.
In addition to oil repellents, water-based inks often contain additives such as defoamers and leveling agents. If the oil
repellent is incompatible with these other additives, adverse reactions (such as flocculent buildup and wrinkling) may occur.
For example, some defoamers contain hydrophilic groups. When mixed with highly oleophobic oil repellents, they may
interfere with each other, resulting in reduced defoaming effectiveness and the appearance of bubbles in the ink.
Therefore, before adding an oil repellent, conduct a small test—mix a small amount of ink with the oil repellent and other
additives to observe for any abnormalities and ensure proper compatibility.
3. Use the appropriate drying process.
To be effective, the oil repellent must migrate to the surface during the ink's drying process. Therefore, drying temperature
and time are crucial. If the drying temperature is too low or the drying time is too short, the oil repellent may not migrate
sufficiently, resulting in insufficient surface concentration and reduced oil repellency. If the temperature is too high, the
oil repellent may evaporate prematurely, rendering it ineffective. For example, ink drying on paper packaging typically
requires a controlled temperature of 60-80°C for 3-5 minutes to allow the oil repellent to migrate and form a stable
protective layer. Plastic packaging, on the other hand, may require a slightly higher drying temperature (80-100°C),
but excessive temperatures should be avoided to prevent deformation of the plastic substrate.
IV. Future Trends: More Environmentally Friendly and Efficient Oil Repellents
With increasing environmental protection requirements and advancements in packaging technology, water-based ink
repellents are developing in two directions:
First, "non-fluorine-based" oil repellents are becoming mainstream. Some traditional oil repellents contain fluorine,
which, while effective, may pose environmental risks. New non-fluorine-based oil repellents, made from natural plant
extracts or modified polymers, are not only environmentally friendly but also meet food contact safety standards, making
them suitable for applications with stringent environmental requirements (such as infant food packaging).
Second, "multifunctional" oil repellents are emerging. In addition to being oil-resistant, these oil-repellent agents also offer
water, stain, and abrasion resistance. For example, their addition prevents grease penetration while making the packaging
surface waterproof and dust-resistant. This reduces the number of additives required in inks and simplifies formulations.
From food packaging to industrial applications, water-based ink oil-repellent agents, though hidden deep within the coating,
silently safeguard the packaging's aesthetics and safety. The next time you use a takeout container for hot, greasy food or
tear open a clean bag of instant noodles, perhaps remember this "invisible oil-repellent"—it's its presence that makes our
everyday products both beautiful and safe.
