Printing decoration

On the other hand, the resistance of laminates with printed decor papers depends very much on the substance weight of the overlay paper used to protect the ink layers. There is a tendency, unfortunately, for an overlay to impair the definition of print and brightness of colour—which can be undesirable, or, particularly with more exotic designs such as metallized and pearlescent effects, even unacceptable. 

In an extension of moulding-in printed decorations, using polyester resins and lay-up by hand, designs can be transferred from the printed substrate and sealed into the surfaces of articles—the feedstock originally carrying the effect being removed afterwards. 

Make ready time (printing machine). The make ready time is the time and labour required to set up a process ready for a print/decoration run. Since make ready times must be costed as part of a printing run, those costing the most to set up are usually associated with long runs and large quantities (e.g. gravure). 

Although decoration of paper and board is well covered by the literature, general understanding of the wider issues involved with other materials has frequently been poor. This particularly applies when artwork is produced which although reproducible on paper or board, is unsatisfactory in terms of the printing/decoration processes available for another material. 

The mold is then closed again, and the curing cycle is completed. The overlay consists of a cellulose sheet having printed decoration and covered with a thin layer of partially cured clear melamine resin. During the molding cycle the overlay is fused to the product and becomes a part of the molding. The process is relatively inexpensive, especially when a multicolor decoration is required. 

If a silicone release agent is used, be aware of certain situations. If the fabricated product is to be printed, decorated, bonded, etc. the bond or proper bond probably will not occur. It probably will interfere if electrical connections are to be made on its surface. 

Injection-molded articles can be decorated by in-mold labeling or by post-mold decoration. In the former method, printed film is inserted into the mold cavity before injection. The plastic forms an intimate contact with the graphic material. Post-mold decoration includes hot stamping, dry offset printing, and decal printing. 

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

A melamine laminating resin used to saturate the print and overlay papers of a typical decorative laminate might contain two moles of formaldehyde for each mole of melamine. In order to inhibit crystallization of methylo1 melamines, the reaction is continued until about one-fourth of the reaction product has been converted to low molecular weight polymer. A simple deterrnination of free formaldehyde may be used to foUow the first stage of the reaction, and the build-up of polymer in the reaction mixture may be followed by cloud-point dilution or viscosity tests. 

The decorative plastic laminates widely used for countertops and cabinets are based on melamine—formaldehyde resin (see Laminates). Several layers of phenohc-saturated kraft paper are placed in a press and a sheet of a-ceUulose paper printed with the desired design and impregnated with melamine—formaldehyde resin is placed over them. Then a clear a-ceUulose sheet, similarly impregnated with the resin, is placed on top to form a clear, protective surface over the decorative sheet. The assembly is cured under heat and pressure up to 138°C and 10 MPa (1450 psi). A similar process is used to make wall paneling, but because the surfaces need not be as resistant to abrasion and wear, laminates for wall panels are cured under lower pressure, about 2 MPa (290 psi). 

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