Application of Aluminum Pigment Technology in Ink Coatings (1)

Aluminium flakes produce the following oxidation reactions in water, leading to gas evolution:

2Al+6H2O--→2Al(OH)3+3H2

There are two techniques based on different principles for overcoming the above problems. One of them is the additive technology, which involves physically mixing additives on the surface of aluminum pigment particles to form a protective layer on the outer layer of the aluminum sheet through a barrier mechanism. Prevent aluminum and water from reacting. The second technique is called cladding technology. The aluminum sheet is wrapped and the individual pigment particles are completely encapsulated.

1, additive technology

The most commonly used method to prevent aluminum flakes from generating gas is to use organophosphorus compounds for processing. This type of product has been in the market for many years and is already very mature. It usually appears as a 65% aluminum pigment slurry in various solvents. Different solvents are necessary because different resin systems and their compatibility with stabilizers must be combined.

One of the product series (STAPA Hydrolac Series) contains solvent gasoline and another solvent. The solvent can be water (STAPAHydrolacW-series), methoxypropanol (STAPAHydrolacPM-series), or butanediol (STAPAHydrolacBG-series) ). The next step is to develop a series of products that contain only one of the above solvents without solvent gasoline (STAPAHydroxal). This type of product can eliminate surface defects (such as fish eyes) caused by poor compatibility with solvent gasoline in coating systems. The hydrous STAPAHydroxalW series can be used to produce zero "VOC" coating products.

One of the side effects of stability is that some properties of the coating can be adversely affected (eg, drying time, adhesion between coatings, moisture resistance). To compensate for these adverse effects, the amount of stabilizer used can be minimized to protect the performance of the product from damage.

2, coating technology

The second technique for developing aqueous aluminum flakes is to completely coat the pigment particles to provide better protection.

The first generation of coating technology uses a layer of insoluble chromium (III) compound (STAPAHydrolux): These pigments contain no soluble chromium (VI) salts (<1ppm) and are therefore non-toxic. The second generation (newest product) is coated with silica and then further processed by organics (STAPAHydrolan). Because of its unique sandwich structure, this generation of products is more stable when used on the circulation line. .

The amount of gas generated in these same coating formulations can be determined for these aluminum pigments with different stabilization methods. A standard formulation of water-borne paint was prepared and stored in a special device to determine the amount of hydrogen produced at 40°C for a certain period of time. The advantage of this test is that the results are very close to the real situation, with the disadvantage that the final result is not available until after 10 or 30 days, depending on the resin system used. However, many years of experience show that after 3 days of testing, a good estimate of the final result can already be made. Experts pointed out that various types of stabilizer products should be tested in individual resin systems in order to seek the best overall stability.

3, formula design

To optimize the optical performance, technology, and gas performance of the product, all raw materials, resins, pigments, and additives, as well as production technologies, must be considered by the formulator.

Good mixing of the metal flake pigments with the resin: Improper mixing of the two - the shear force used is too high - can have a negative impact on the optical properties of the product. High shear forces can damage the flake pigment in two ways: first, it will bend the flake particles, thereby reducing their brightness; second, it will also peel the protective layer from its surface, resulting in the generation of gas.