Panduan Penggunaan Bahan Tambahan Kimia: Bagaimana Cara Mengatasi Lima Masalah Umum?

Engineers working with paints and inks often encounter frustrating problems, such as uneven paint application, bubbling, and incorrect color. These problems are often not due to the main raw materials, but rather to the wrong selection of small amounts of “additives.” Below, I have compiled five of the most common problems and their solutions, based on practical experience in production. I hope this will be helpful to everyone.

Problem 1: What to do if the ink dries too slowly when UV printing on plastic film?

Specific situation:

Printing patterns on very thin plastic films (such as PE and PP films) used for packaging bags, using LED UV printing. The production line speed is required to be very fast (over 150 meters per minute), but the ink doesn’t dry completely, or dries too slowly, affecting efficiency.

Why this happens:

Traditional UV ink “inisiator foto” (which can be understood as “drying catalysts”) are designed for old-style mercury lamps and are not very “sensitive” to the specific ultraviolet light (mainly 395 nanometers) emitted by modern energy-saving LED lights, so the reaction is slow.

Solutions:

• Change the “catalyst”:

Replace the main ingredient with a inisiator foto of the “TPO” type, which is particularly good at absorbing 395-nanometer light, so it dries faster.

• Add a “helper”:

Using only TPO may still leave the surface slightly sticky (due to air inhibition). A small amount of an “amine” type co-initiator (such as EDB) can be added to eliminate air interference and ensure thorough drying of the surface.

• Note the side effects:

Avoid using the old-fashioned “benzophenone” (BP). Although it is effective, it tends to yellow the film and has a strong odor.

• How to determine if it’s working:

Use professional instruments to measure whether the conversion rate of the reactive components in the ink exceeds 95%; or use tape to test if the printed pattern is removed by the tape.

Question 2: When producing water-based coatings, stirring and filling generate a lot of foam that is difficult to eliminate. What can be done?

Specific situation:

When making latex paint, high-speed machine stirring, pump transportation, and final filling into buckets all introduce a lot of air, creating stable foam. This results in incomplete filling of the buckets and an unsightly appearance.

Why this happens:

Inexpensive mineral oil defoamers initially break down the foam, but their effect diminishes over time, and the foam reappears.  Adding too much can also cause “cratering” in the paint film (small pinhole-like pits).

What to do:

• Choose the right type:

Use a composite defoamer, ideally one containing both “polyether-modified silicone” and “hydrophobic silica particles.” The former acts like a “spear,” quickly puncturing large bubbles, while the latter acts like “sand,” continuously adsorbing and eliminating small bubbles, resulting in a more lasting effect.

• Check key data:

Ask the supplier for a “long-term foam suppression” test report to see if the foam remains at a very low level for half an hour.

• Pay attention to addition:

Do not add it all at once. Add it in two stages: add half during pigment grinding (to eliminate production foam), and add the other half before the paint is finished (to prevent foaming during filling). After adding, stir gently for a while to ensure thorough mixing.

• How to determine if it’s effective:

Place the finished paint in a 50°C oven for two weeks (to simulate long-term storage), then take it out and shake it to see how much foam is present; examine the surface of the sprayed paint film under a magnifying glass to check for smoothness.

Question 3: When applying a thick layer of paint to construction machinery, the paint tends to sag on vertical surfaces, but a smooth finish is desired. How can this be balanced?

Specific situation:

When painting large equipment like excavators and agricultural machinery, the paint has a high solid content (it’s quite viscous). When sprayed onto large vertical metal plates, it tends to sag before drying. However, for aesthetic reasons, a very smooth finish is desired after drying.

Why this happens:

To prevent sagging, the paint needs to be “thicker” (thixotropic), but this hinders its ability to flow and level. Conversely, to achieve a smooth finish, the paint is more prone to sagging. This is a contradiction.

What to do:

• Use two different components for different functions:

Anti-sagging: Add a small amount of fumed silica (e.g., R972). It acts like a network, making the paint “thicker” when stationary, preventing it from flowing easily, without significantly affecting the gloss.

• Promoting leveling:

Add a small amount of a high-molecular-weight acrylic leveling agent (e.g., BYK-361N). This primarily evens out the surface tension of the paint, helping it flow and level.

• Adjusting the “evaporation rate”:

Add a slow-drying solvent (e.g., S-150) to keep the paint surface “wet” for a longer time, allowing more time for leveling without causing severe sagging.

• How to determine if it’s right:

Use a specialized “sagging meter” to test whether a wet paint film of a specific thickness sags; after drying, measure whether the gloss is high enough and the surface is smooth enough.

Question 4:  We produce universal color pastes, but they cause problems (color separation, mottling) when used in different paint systems. What can we do?

Specific situation:

The color paste manufacturer sells its color pastes to different paint manufacturers. Some manufacturers use alkyd resins, while others use acrylic or polyurethane resins. The color paste works well in one system, but when switched to another system, the pigments aggregate (flocculate) or the color becomes uneven.

Why this happens:

The “dispersant” in the color paste acts like a hand, holding the pigment particles and keeping them stably dispersed. The resins in different paints are like different “environments,” and some “environments” can pull the “hand” of the dispersant away, leaving the pigments uncontrolled and causing them to clump together.

What to do:

• Choose a “hand” that holds tightly:

Use block copolymer dispersants. They have multiple “hands” that firmly grasp the pigments and are less likely to be pulled apart by different resin “environments.”

• Choose a “hand” with strong adaptability:

The chain extending from this “hand” (solvation chain) should be of medium polarity (e.g., a polyester chain), so that it can remain stable in both polar and non-polar resins, ensuring broad compatibility.

• Conduct mixing tests:

Mix the color paste with all the resins that the customer might use and perform a “finger rub test”: Scrape the mixture onto a black and white test card, rub a portion with your finger, and compare the color of the rubbed and unrubbed areas. If the colors are consistent, then there is no problem.

• How to determine if it’s good:

After mixing the color paste with at least 5 common resins, the fineness should not change, and there should be no sedimentation or clumping after one week.

Question 5: UV white ink easily turns yellow. How can we keep it white for a long time?

Specific situation:

UV white ink used for high-end labels and packaging looks very white when freshly printed, but after a while, or after being exposed to light for a long time, it turns noticeably yellow, which significantly affects its appearance.

Why does this happen?

Firstly, some photoinitiators in the ink (such as ITX and BP) are prone to yellowing themselves or after reaction; secondly, white is the most sensitive to yellowing, and light exposure triggers a continuous oxidation reaction, leading to increasing yellowing.

What to do:

• Avoid the source:

resolutely avoid using photoinitiators that are prone to yellowing, such as ITX and benzophenone (BP), and also avoid systems that require “amines” as co-initiators.

• Use a good combination:

We recommend the combination of Irgacure 184 and TPO. 184 is responsible for drying the surface, and TPO is responsible for drying the deeper layers.  These two work together effectively, and both are low-yellowing varieties.

• Add a “protective umbrella”:

Add a small amount of a composite light stabilizer, which contains “hindered amine light stabilizers (HALS)” and “ultraviolet absorbers (UVA)”. The former acts like a “bodyguard” to capture free radicals that cause yellowing, and the latter acts like “sunscreen” to absorb ultraviolet light, preventing yellowing from two aspects.

• How to determine if it’s good:

Use a colorimeter to measure. The whiteness L value should be high (>92) and the yellowness b value should be low (<1.0) immediately after curing; after a period of accelerated aging under ultraviolet light.

In summary

Solving the problems related to these chemical additives is actually quite simple: first, understand the specific circumstances under which the problems occur; then, identify exactly which step in the process is causing the problem; next, select an additive specifically designed to address that particular issue; and finally, set clear standards to verify whether the problem has truly been solved.

By following this approach, and through repeated trials and data collection, you can gradually move away from relying solely on experience and trial-and-error, and your work will become much more efficient and effective.