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In-Mold Painting: An Innovative Solution

Painting a molded product can be an expensive, time-consuming process. You have to set aside a special part of your workspace just for the painting. You have to apply several coats of primer or risk poor adhesion between the paint and the part. You have to employ skilled laborers who suffer health risks from being in the vicinity of potentially toxic substances and fumes. And, even after all of that time and effort, there’s the risk that your paint job will quickly begin to chip, flake, or crack.

But what if there was another way? What if there was a process that eliminated nearly all of those time and labor costs, while still producing a high-quality, aesthetically pleasing finish?

Luckily, there is – and it’s called in-mold painting.

In-mold painting (sometimes referred to as in-mold coating) is a process pioneered by Romeo RIM for commercial use with products created using our reaction injection molding (RIM) and long fiber injection (LFI) technologies. Since beginning work with IMP in the 1980s, we have used it to create high-quality parts for the automotive, heavy truck, agriculture, construction, and personal spa and watercraft industries.

In-mold painting provides innumerable aesthetic advantages over its more traditional counterpart, post-mold painting, while being a quicker, easier, and more efficient process overall.

The In-Mold Painting Process

As the name suggests, in-mold painting occurs when the cavity of the mold is painted prior to the injection of the polyurethane material. At Romeo RIM, we use both gel coats and two-component paints designed specifically for working with polyurethane.

Because of this, we are able to offer in-mold painting for our parts produced using either RIM or LFI processes. Both RIM products which contain reinforcing fibers (RRIM/SRIM) and those which do not can be painted in this manner. However, we are unable to offer in-mold painting for parts produced using dicyclopentadiene (DCPM) injection molding due to the nature of the materials used.

Painting happens right on the molding line – all of our manufacturing clamps are set up with the necessary equipment for in-mold painting. There’s no more need to set aside large areas of workspace just for painting!

During the molding process, the paint bonds chemically with the polyurethane material, creating a strong adhesion. For this reason, in-mold paint jobs are more resistant to flaking, chipping and cracking than those applied post-mold.

At Romeo RIM, we are careful to ensure that all of our in-mold paint jobs use just the right amount of paint, as too much or too little can damage a product’s surface. Most coatings applied in-mold have a thickness of 2.5 mils with a tolerance of 1 mil.

Advantages of In-Mold Painting

In-mold painting removes the need for the specialized workspace, skilled labor, and expensive equipment such as drying ovens used in the post-mold painting process. With in-mold painting, you can save time, money and manpower all at once!

In addition, the in-mold paints used at Romeo RIM are more environmentally friendly and pose less of a health risk than traditional paints applied post-mold. Our paints contain low to no amounts of VOC (volatile organic compounds).

Besides allowing customers to save on time and money, in-mold paintjobs are more aesthetically pleasing and damage-resistant than those created post-mold. Excellent adhesion prevents flaking, chipping and lowers the risk of blemishes and improper finishes. The paint moves and flexes along with the part without any cracking or crazing in the part surface.

In-mold paint jobs aren’t just hardy and long-lasting – they’re gorgeous to look at, too! IMP is capable of producing a UV-stable high- or low-gloss Class A finish directly out of the mold. It can accommodate absolutely any color, including two-tone designs. And that’s not all – IMP can easily mimic finely detailed textures such as wood grain or stone.

Paint applied directly to the mold will also follow the contours of the mold more closely than paint applied once the molding process is complete. This allows for the creation of paint jobs that mimic even the finest details of the mold perfectly clearly. IMP is also an excellent choice for customers who wish to add logos or branding to their part designs.

Disadvantages of In-Mold Painting

It is important to note that, despite its numerous advantages, in-mold painting does have a few small disadvantages which may mean that it is not the ideal solution for every product. As mentioned above, in-mold painting cannot be used alongside DCPD injection molding. It may also not be the best choice for extremely complex molds, as spraying the mold may take time to ensure complete accuracy.

Finally, there are a few instances in which in-mold painting may require a few touchups during the post-mold period. An example of this is in a situation where the mass color of the polyurethane system is not a particularly good match for the paint finish, such as a black substrate with a red topcoat. In this case, the flash or split line will stand out unless additional paint is applied post-mold.

However, in the majority of situations, IMP is a cost- and time-efficient solution to the problems caused by traditional post-mold painting. Contact Romeo RIM today to learn more about our IMP processes and how they can work for your next project!