In-mold decoration (IMD) is popular in making mobile phones, electrical appliance panels, transparent lenses for display screens, dials of automotive instruments, washing machine panel, etc.. It has developed to decorate large casings, such as car shell.

IMD not only makes the decoration effect beautiful, but also has a long service life. It has better dust and moisture resistance compared with other manufacturing methods. Those are the reasons why it is popular. Let's talk about the application of water-based adhesives in IMD.

Water-based adhesive and IMD

Speaking of special light-curing ink for IMD, to enhance adhesion between ink and injection molding resin, a layer of water-based adhesive must be printed on the ink after it is cured. This is because the surface tension of the light-curing ink is small after it is completely cured, and it is closed. It is not easy to overprint the next color ink.

There are two ways to improve low adhesion of the light-curing ink layer. One is that the light curing of the previous color ink cannot reach 100%. The other one is to add interlayer curing agent to the light-curing ink to improve adhesion between the layers.

However, in IMD, these two methods are not feasible. So, after the UV light-curable ink is completely cured on the transparent sheet, a layer of water-based adhesive must be printed. It protects the ink layer from damage before the ink is formed, and to facilitate the compatibility of ink and injection molding resin, and enhance the adhesion between them.

The water-based adhesive used with IMD ink is AQUATEX SC adhesive. Its process requirements are as follows:

1. Before printing the adhesive, make sure the ink on the transparent substrate is completely dry.

2. Make sure the ink surface on the transparent substrate is clean and free of residue.

3. When the environment is humid (relative humidity is greater than 50%), the printing effect is better. When the environment is dry, the screen should be kept moist.

4. Use 77T/cm monofilament PET screen to make water-resistant screen. Use HS80 hardness squeegee for continuous printing. Otherwise, there will be problems such as screen blocking.

5. Dry in convection hot air at 80°C for about 2 minutes.

6. After using the screen, clean it immediately with warm water.

These are about the process of water-based adhesive on the surface of IMD special photocurable ink. But in fact, water-based adhesive is also needed in solvent ink.

Mirror ink is a solvent-based ink. It cannot be protected by solvent ink. Therefore, to prevent the IMD mirror ink from falling off, dissolving in layers, and oxidizing, the protective ink can only be selected with water-based adhesive. Because it has no effect on the mirror effect, and will not damage the coating.

There is more. If the injection molding material is ABS, ABS+PC or PS, since these materials have poor adhesion to HTR ink, water-based adhesives can improve the bonding strength between the ink layer and the substrate. There will have good softness and formability, reducing delamination and cracking.

After using water-based adhesive during silkscreen printing, if the injection molding is not done in time (2 days), or it is placed at a temperature above 60°C, the adhesion between the injection molding material and the PC sheet will be reduced.

IMD is complicated. The features of sheet, the ink performance, the quality of adhesive, the structural features of the mold, the injection molding material, and the temperature, pressure, and speed can all affect the yield rate and quality of the finished product.