(a) The holographic logo stamping printing
Molding replication is the final process for forming an embossed hologram. Its process is: heating a holographic metal stencil to a certain temperature and embossing the thermoplastic material with a certain pressure, so that the fine embossed stripes on the holographic metal stencil are formed. Transfer to the thermoplastic surface, after cooling set and separation, the surface of the thermoplastic material is formed with the same energy as the holographic metal stencil can be under the same streak, which is copied out of the molded hologram.
The process flow for the production of the press hologram production print and postpress processing is as follows:
Below we introduce the process conditions of the raw materials and equipment used in each process.
1 thermoplastic material
Thermoplastic materials suitable for holographic compression replication are the following:
1 PVC film or sheet (transparent or aluminized);
2 polyester film or sheet (transparent or aluminized);
3 Suitable for hot stamping metal foils that are transferred to paper, fabric or plastic. When different types and thicknesses of materials are used, different equipment and process conditions need to be matched.
At present, the most used materials in the manufacture of molded holograms are polyvinyl chloride (PVC) and polyester (PET) materials, which can be selected according to the specific equipment and process conditions in the production process. In general, the following principles should be considered when selecting materials.
(1) Regardless of whether PVC or PET is used, the material is required to be transparent, flat, uniform in thickness, with an error of ≤±10%, no watermarks, stains, scratches, plasticizers containing as few impurities as possible, and good abrasion resistance. The transmittance of sexual and holographic layers exceeds 90%.
(2) The use of aluminum-plated PVC and PET can reduce the number of subsequent processing steps by using a corresponding transparent material. However, due to the simultaneous deformation of the thermoplastic material and the metal reflection layer during the press-molding, the processing temperature and pressure are higher. Requires that the aluminum-plated reflective layer is solid, dense, and free of blisters, and the thickness should be greater than 200Ω.
(3) The roll material is suitable for rolling processing methods. Generally, the film is required to be between 0.05 and 0.1 mm. The sheet is suitable for flat pressing. Flat pressing can only process thicker and harder sheets. When the thickness of the metal stencil is well uniform, the minimum thickness of the sheet can be 0.1 mm.
For the selected molding material, only the exact physical and chemical properties can be accurately determined. The following uses hard PVC film as an example to illustrate the physical and chemical properties that must be mastered.
1 PVC is a polymer of vinyl chloride, with an average relative molecular mass of 50,000 to 120,000, a relative density of 1.35 to 1.45, a Rockwell hardness of 110 to 120, and a coefficient of thermal expansion of (5 to 18.5) 10-5/oC. High strength, wear resistance, acid corrosion resistance, good chemical stability and shape stability. The heat distortion curve of a rigid PVC film is shown in Figure 10-61. Similar to common thermoplastics, PVC can be in three different states of glass, high elasticity and viscous flow depending on the difference in heating temperature under constant pressure. For rigid PVC film, the glass transition temperature Tg=-55 oC, and softening temperature Tm=70 oC, decomposition temperature Td=150 oC. The PVC film should be in a viscous flow state during the compression replication. The viscous flow state is also called plastic state. Plastic can be formed only when processed in this temperature range.
Under the long-term action of sunlight, ultraviolet rays and heat, PVC will undergo molecular structure changes and decompose HC1. In addition, long-term in a warm environment, it can also be eroded by bacteria.
2 Plexiglass polymethyl methacrylate is a kind of polyester material (PET), its transparency is high, light transmittance reaches 91% ~ 93%, chemical dielectric and optical stability, light weight, high strength, Strong adhesion to the product. Because of the high viscous flow temperature of this material, the temperature and pressure required for printing are higher. The disadvantage is poor heat resistance and wear resistance.
For a variety of thermoplastic materials, a large amount of static electricity is generated during processing, so cleaning and dust removal in the processing plant are very necessary.
(to be continued)
