Refrigerator magnets are typically flexible, flat magnets used for attaching notes or decoration on metal surfaces. This common variety is a composite material engineered for easy handling and cutting. Understanding their composition involves examining the magnetic material, the binder that holds it together, the manufacturing process, and the layers that provide the finished appearance.
The Core Magnetic Compound
The magnetic force comes primarily from ferrite powder, a ceramic compound containing iron oxide. Strontium Ferrite or Barium Ferrite are often used due to their cost-effectiveness and good magnetic properties at room temperature. This powdered material is dispersed within a non-magnetic matrix.
The second component, which provides flexibility, is a thermoplastic polymer binder, such as polyvinyl chloride (PVC) or chlorinated polyethylene (CPE). This plastic material holds the ferrite particles in place. The magnetic strength of the final sheet relates directly to the density and proportion of the ferrite powder mixed into the polymer binder. The resulting composite material is pliable, allowing it to be bent and rolled without losing its magnetic characteristics.
Manufacturing the Flexible Magnet Sheet
The creation of the flexible magnetic sheet begins by thoroughly mixing the fine ferrite powder with the polymer binder. This blending ensures the magnetic particles are uniformly distributed. The mixture is then heated until it reaches a molten or highly pliable state, ready for shaping.
The shaping process involves either extrusion or calendering, depending on the desired size. Wide, flat sheets, common for refrigerator magnets, are usually formed by calendering. This process passes the mixture through a series of rollers that squeeze and flatten the material into a continuous sheet of precise thickness, often around 0.76 millimeters. Thinner strips or profiles are created using extrusion, which forces the material through a shaped die.
The final step is magnetization, which occurs after the sheet is formed and cooled. The material is exposed to a strong magnetic field, often generated by an electromagnet, which permanently aligns the ferrite particles. This is done in a multi-pole pattern, creating fine, alternating stripes of North and South polarity across the surface. This multi-pole arrangement provides the strong holding power on a flat metal surface.
The Decorative Layers and Adhesives
Once the magnetic sheet is complete, it is laminated with non-magnetic layers to create the finished product. The most common feature is a decorative face, usually a printable material like paper, vinyl, or plastic film. This layer receives the images, logos, or text.
An adhesive layer is applied between the decorative surface and the magnetic core to ensure they stay firmly attached. This is often a peel-and-stick backing, using acrylic or rubber-based adhesives, designed to withstand temperature fluctuations and handling.
A final clear coating, such as a thin laminate or a UV coating, is frequently applied over the printed surface. This protective layer shields the graphics from moisture, fading, and abrasion. The complete assembly is then die-cut into the custom shapes familiar on refrigerator doors.