APPLICATIONS
Embossing
Embossing is the process of transferring the micro-structures from the nickel shim onto a polymer film substrate. This is the stage where the holographic pattern is replicated at production scale, creating the raw holographic film that will subsequently be metallized and laminated. ROEM employs two primary embossing technologies: thermal pressing and UV-cured microstructure transfer.
Thermal Pressing and UV-Cured Microstructure Transfer
In thermal embossing (also known as hot embossing or hard embossing), the nickel shim is mounted onto a heated embossing cylinder. A thermoplastic film substrate, typically PET, BOPP, or PVC in thicknesses ranging from 12 to 50 micrometers, is fed through the embossing station. As the film passes between the heated embossing cylinder and a pressure backup roller, the combination of heat (which softens the thermoplastic) and pressure causes the film surface to flow into the microscopic grooves of the nickel shim. When the film cools, it retains an exact positive impression of the shim's micro-structured surface.
The thermal embossing process requires careful optimization of three key parameters: temperature (which must be above the glass transition temperature of the polymer substrate but below its melting point), pressure (sufficient to force the polymer into the micro-grooves without causing deformation), and line speed (which determines dwell time and affects replication fidelity). Modern embossing machines can achieve production speeds exceeding 1,000 meters per hour with precise tension control and automatic edge guidance.
UV-cured microstructure transfer represents a more recent advancement in embossing technology. In this process, a UV-curable resin is first coated onto the substrate film. The nickel shim is then pressed against the uncured resin, imprinting the micro-structural pattern. While the shim is still in contact, ultraviolet light is applied to cure the resin, hardening it and locking in the micro-structures. The shim is then separated, leaving a precise replica on the cured resin surface. UV embossing offers several advantages: it operates at lower temperatures, produces sharper feature definition, and can be used on temperature-sensitive substrates.
After embossing, the film carries the complete micro-structured surface relief pattern but appears nearly transparent because the micro-grooves alone do not efficiently reflect light. The next stage, metallizing, will transform these invisible structures into brilliant optical effects.
