16.Dandy Roll: A dandy roll is a light roller made of a fine metal mesh fixed on the paper making machines that can affix a watermark onto the sheet besides smoothing the surface. The dandy roll carry a design, which will create the watermark that identifies the sheet. The dandy roll situated near the end of the wire section is covered with a woven wire and is in contact with the upper surface of the forming web.
As the semi wet pulp passes under dandy roll, the design is impressed into the paper by the dandy roll which creates the watermark on to the sheet. A watermark is a recognizable image or pattern in embedded in the sheet. The three dimensional watermark , caused by thickness or density variations in the paper is also made possible . There are two main ways of producing watermarks in paper one by dandy roll and the other by cylinder mould process.
Watermarks are used as one of the tight security features on the currencies , passports, stamps and document paper to deter counterfeiting and dandy rolls play a vital part in this direction. The dandy roller was invented in the year 1826 by John Marshall.
17. Dampening system : The dampening system is a vital unit in the wet offset machine. The wet offset process works on the principle that ink and water does not mix, and the images on the printing plates are in the same level of the plate surface, the dampening of the non image areas becomes vital to resist ink which should adhere only to the image areas. Every wet offset machine will have a dampening unit fitted on them along with the inking unit. Without dampening unit the wet offset can not function.
18. Double Bump : Some times in order to increase the density of printed image this process is adapted. By this technique the same plate is used to double print the image – mostly solids- thus the image to get two layers of ink . This process is also called print on print process. This is done mostly on coated stocks and high value printing.
19. Dual Bond Paper : Strong inline coated bond paper suitable for printing by either offset or used on photo copier machines. This paper is mostly used for taking blue prints for architectural drawings, maps, and sketches.
20. Duplex Paper : Thick paper made by pasting together two thinner sheets, or a thin sheet and HDPE film, or two thick boards. Each side of the paper will be different such as different color on each side, different finish on each side, or different textures. This variety of paper is used for producing retail Store printed bags, travel bags , paper plates, paper cups, gift wrappers, carry bags, gift bags etc. They come in various colors and textures.
............Additions to alphabet D to be continued under D/4