Chapter 2 Sheet-fed offset printing
Outline the history of printing:
Letterpress printing was the earliest printing technique ever invented by our ancestors and it has been more than 1300 years. Letterpress printing evolved from the seal stamp and the extension stone, and the earliest words carved stone and seal were before the Shang Dynasty. The real symbol of typography is the engraving, which originated in the Tang Dynasty and was hand-carved with anti-words and simple graphics on the wooden plate. At that time, the book was scroll-shaped. In the Song Dynasty, wax printing was used to wax the wood and then sculpt it. The engraving wax was much more efficient than the carved wood. The binding of the book became a butterfly in the form of a page book. In order to print new content, whether it is carved wood or engraved wax, it must be reprinted. All the same text and graphics must be re-engraved, which is very troublesome. In the Qing Dynasty of the Song Dynasty, Bi Yi invented movable type printing, which was a leap of Chinese printing. In the Yuan Dynasty, Wang Wei improved the technology of Bi Yi, and produced this type of movable type and rotary type dial. Later, this advanced technology was widely spread to the world. From 1440 to 1448, the German ancient lamp treasure improved the type of wooden movable type into a typeface and used the method of casting to create characters. In 1798, Austria's composer, Saier, managed to invent lithographs with Bavarian limestone. In 1905, Lubel invented the indirect lithography, which is now commonly used, based on the principle of Siegel's lithographic printing ink and water mutually exclusive.
Modern printing classification:
Letterpress printing: The history of letterpress printing is the oldest and most popular. The printed images and text projections receive ink. The recessed parts do not accept ink. When the printing paper is pressed tightly, the ink is printed on the paper. Printing plates are mainly available in movable type, lead plate, zinc plate, copper plate, photosensitive resin plate, etc. Some books, bills, envelopes, business cards, etc. are still using letterpress printing: special processing such as bronzing, silver, embossing, etc. is generally used for letterpress printing.
Lithography: Offset printing is the most common and widely used printing method. The image and the non-image are in the same plane, and the water and the ink are mutually exclusive. The graphic part accepts that the ink does not accept water, and the non-graphic part is the opposite. The indirect method is used in the printing process. The image is first printed on the blanket cylinder. The graphic is changed from positive to negative, and the graphic on the blanket is transferred to the paper. Pictures, periodicals, brochures, books, samples, calendars, etc. can be used for this printing method.
Intaglio printing: Intaglio printing is the opposite of letterpress printing. The text and image are underneath the concave and the layout, and the concave part carries the ink. The shade of printing is related to the depth of the recession. The depth is shallow and the light is light. Due to the different printing inks on the four plates, the printed lines have a protruding sensation. Coins, stamps, and securities are all intaglio. Intaglio printing is also suitable for the printing of plastic films and silks. Due to the long plate-making time of the intaglio printing and the complexity of the process, the cost is high.
The stencil printing: also known as screen printing, if you have seen the teacher engrave the wax paper in the elementary school, then a better understanding of this printing method. Using screens, metal and synthetic materials such as screens, wax paper, etc. as printing plates, the graphics and texts are made into fine holes.
The non-graphic area is protected with printing material. The printing plate is closely attached to the substrate. The ink is permeated to the substrate with a squeegee or ink roller. Screen printing can not only be printed on flat substrates but also printed on curved substrates, with bright colors and no change in durability. Applicable to the printing of labels, bags, T-shirts, plastic products, glass, metal objects and other objects.
The above is a brief introduction to the types of printing, while modern books and newspapers basically use offset printing. Therefore, professional printing houses are equipped with offset printing machines.
Sheet-fed printing presses are divided according to the number of printed colors, and can be divided into monochrome machines, two-color machines, four-color machines, five-color machines, etc.; printing methods can be divided into single-sided printing machines and double-sided printing machines; press printing paper Forms can be divided into sheetfed and rotary presses.
Flat sheet offset printing diagram:
The pros and cons of a book after it was printed, and the following factors:
The first is the printing press. It is easy for everyone to understand that “If a worker wants to do something good, he must first sharpen his tools.” If the accuracy of a printing press is not high and the stability is poor, it is difficult to expect it to print high-quality books and periodicals. ;
Followed by the ink, high-quality ink will make the graphic colorful, bright, accurate hue, give people visual enjoyment. Of course, this is not obvious for black and white books.
There are paper, the smoothness of the paper surface, and the uniformity of the coating layer will directly affect the effect of the graphic and text, of course, different types of prints should use different types of paper, we will introduce below.
In addition to the hardware conditions of the machine, ink, and paper, there will be factors such as printing accessories, which are not listed here. It is worth noting that there are software influences in addition to the hardware, and it is very important. For example, the person who presses the printer is turned by the person, the ink is adjusted by the person, and the color is chased by the person. Therefore, the operator's technique and operation specification are used. Responsibility is very important, and these are directly dependent on management.
Printing knowledge
*CTP advantages:
The CTP technology refers to the technology that the digital information of the graphic and text is output directly to the printing plate without outputting the film. It not only eliminates the process of film imaging, imposition, printing, and PS plate fixing of the traditional laser image processing but also Using digital technology instead of traditional analog technology or analog digital hybrid technology, CTP technology has been hailed as a technological revolution in the field of printing.
The technical superiority of CTP plate compared with the traditional PS plate lies in:
1. The speed of plate making has been improved, and the plate making time has been shortened from the traditional 50 minutes to only a few minutes, thereby shortening the production cycle of books;
2. Improve the printing quality, and can reproduce 1% to 99% of the outlets; and the traditional PS version is up to 5% to 95%;
3, Plate with high resolution (175 lines / inch or more), can meet the requirements of high-quality color printing.
* Plates and prints:
The picture and text dot on the original plate of the color separation plate is transferred to the printing plate by means of sensitization. For the lithography, the site of the printing plate has the ink affinity function, and the blank site has hydrophilic ink repellent performance. This image transfer program is for lithography printing. Only when the original picture is printed into a printed drawing board to form an ink graphic, and then transferred to the paper by printing, the reproduction of the graphic and text can be completed.
Shaiban is a bridge process between plate making and printing. On the color separation plate, it is required to transfer the graphic of the original picture without distortion. Under the printing, it is required that the hydrophilic property of the ink-repellent performance and the blank part of the graphic part be distinct, and at the same time, it must withstand tens of thousands of impressions and friction without changing its hydrophilic property.
However, it is an intermediate transfer process, and changes are bound to happen. In order to achieve stability and change, it is necessary to control plate sensitization performance, printing plate operation process, image transfer data, and adaptability to printing. The overall specification data of the process guarantees a smooth and good reproduction of the entire reproduction.
The printing plate goes through twice in the entire copying process, once in print and once in print. Therefore, printing is very important in the entire reproduction process. Its quality directly affects the quality of the printed product and the printing efficiency.
When printing colorful books (such as colored book covers, pictorial magazines, color magazines), we only need four basic colors. C, M, Y, and K are commonly used four primary colors. In the printing of the primary colors, the four colors have their own color version, and the dots of this color are recorded on the color plate. These dots are generated by the halftone screen. Combining the four color plates together is like The defined color. In fact, the four printing colors on the paper are separated, but the distance is very close. Because the human eyes have limited resolution, they cannot be distinguished. The visual impression obtained is the mixing effect of various colors. A variety of different colors.
Reprinted from: Hualian Printing "China Printing Light" Open Monthly Brochure
