In-Mold Laminate – Combining Multi-Step Processes into One
In-mold laminate typically utilizes low-pressure plastic injection molding. This is often the case, for instance, when laminating fabrics or carpets onto a plastic substrate inside a mold.
In fact, several different in-mold laminating techniques use molding pressures no higher than 1000 psi, making them gentle to the laminate cover stock. These technologies can use a diverse range of equipment, such as horizontal and vertical injection machines, and vertical compression presses.
In-mold laminating applications are often used in the production of automotive interiors. Such as door panels, consoles, instrument panels, glove boxes, seat backs and trunk liners. Actually, just about any part of a car’s interior can be enhanced in appearance and quality by adding a laminate to a hard plastic.
Why In-Mold Laminate?
With conventional post-mold lamination, multiple process steps are required, using messy adhesives. This increases the costs of labor and parts handling. In-mold laminating is not only more cost-effective, but it provides a stronger melt bond than adhesives can provide.
Also, while standard injection molding requires high clamp tonnage, in-mold laminating allows the use of smaller presses. The lower pressure virtually eliminates the need for thick platens.
And in-mold laminating usually does not require preforming prior to bonding with the rigid substrate (although preforming may still be done with deep draws).
Closed and Open Plastic Injection Molds
There are basically two types of in-mold laminate techniques: closed-mold or open-mold. Both types can use either standard injection molds, standard compression molds, or a combination injection-compression. The type of mold used depends on the geometry of the part, the thickness of the cover stock and substrate, and several other factors.
For instance, high injection temperatures and pressures can sometimes create a “sunshine spot” on the cover stock opposite the gate area, or injection site. As a result, the cover stock may require some type of barrier behind it. (Generally, using a foam-backed cover stock without a barrier requires an injection/compression or open-mold process.)
If a tri-laminate construction (cover stock with foam and protective polypropylene backing) is used, then any of the open or closed in-mold laminating approaches can be used.
Open molding involves the use of a single-sided mold that acts as the form and cosmetic surface of the part. A gel-based resin is applied to the prepared mold surface, and reinforcements are then applied. Additional layers of laminate are added to build thickness and strength, as needed. Air is then rolled out of the laminate and the part is left to cure.
One benefit of open molding is the absence of molded-in stresses and weld lines.
In closed molding, dry reinforcements are laid into the base mold, the mold is closed, and resin is introduced into the closed cavity with a pressure pump or vacuum. Once the laminate is cured, the mold is opened and the part removed.
An advantage to closed molding is fewer emissions, which helps manufacturers meet federal and state emissions standards, while reducing the need for protective clothing and other personal protective equipment.
Both techniques (both closed molding and open molding) often integrate robot technology in the lamination process.
CS Tool Engineering is proud to participate in the development of these new technologies that continue to enhance the manufacturing environment.