The surface of molded pulp products is relatively rough, and its printability is obviously different from that of ordinary paper printing materials such as offset paper, art paper, and cardboard paper. Moreover, the general paper-molded packaging products have a geometric shape that matches the shape of the packaged object. Its structure is diverse, convex and concave changes are many, and the printing width is small, it is difficult to meet its requirements with traditional conventional printing technology, and more flexible printing methods should be considered, such as pad printing, inkjet printing, screen printing, letterpress offset printing. In this way, multi-color exquisite printing can be completed on the uneven surface of the paper mould packaging product.
Pad printing is an indirect printing method. It uses a hemispherical pad made of silicone rubber to press against a copper or steel intaglio plate, so that the graphic ink on the plate is stained, and then transferred to the substrate to complete the printing. It can achieve multi-color exquisite printing on irregular concave-convex surfaces.
Pad printing is ideal for small printing products such as paper mould packaging products with small print area and variable geometric shapes, considering the factors such as equipment investment, cost accounting, and convenient operation.
Paper-molded packaging products have many uneven changes in their structure, and inkjet printing can also be used to complete the decoration and printing of their surface. Inkjet printing is a non-contact plateless imaging printing method. It uses a counter to store information instead of storing graphics and text information on the printing plate. The print head does not touch any part of the substrate and can change in operating conditions. In the case of a wide range, clear characters and patterns can be reliably printed on the concave and convex surfaces of the paper mould packaging products.
The principle of inkjet printing is to eject tiny dots of ink from one or more print heads through the gaps onto the surface of each molded pulp product on the production line to form text and patterns composed of a dot matrix. The printing machine adopts a microprocessor to control the required text patterns, and keeps synchronization with the speed of the production line through the action of sensors to ensure that each pulp molded product can be printed with graphics and text data correctly. The ink jet is done by pressure or static electricity, and can be jetted from bottom to top, top to bottom, or from any angle in the horizontal direction. It is especially suitable for surface printing of paper mould packaging products with various structural shapes.
The screen printing method is to put the thick ink on the screen plate, and then use a scraper to contact the screen plate to form a certain angle, and move while applying pressure, so that the ink is printed through the screen plate on the objects.
The main characteristics of screen printing are simple plate making and printing methods, low equipment investment, low cost, suitable for small batch production; it is not restricted by the type, size, and shape of the substrate, and can be printed on curved surfaces, spherical surfaces, and fragile objects. It is also more suitable for surface printing of paper-molded packaging products with more changes in structure and shape, and its printed product has a thick ink layer, bright colors, three-dimensional effect and strong hiding power. Therefore, small screen printing equipment can be used to print on the surface of paper mould packaging products.