Offset basics Q & A

1. What is offset printing?

A: Offset printing is a kind of lithographic printing. Simply speaking, offset printing is the printing method that transfers the image on the printing plate to the printing material by means of rubber (blanket). It is also the existence of the blanket. Named after the way. Blanket plays an irreplaceable role in printing, such as: it can well make up for the uneven surface of the substrate, make the ink fully transfer, it can reduce the water on the plate (the role of water in the printing see later ) Transfer to the substrate and so on. The above is only a general concept. The offset printing that we usually say may be more narrow, that is, there are three lithographic printing methods for printing plates, blankets, and imprints. We call this type of printing in the south of our country. Offset printing.

2. What is the role of water in offset printing?

A: We have this common sense in life: on the surface that is soaked in water, it is not easily contaminated by oil. Water and oil are always mutually exclusive. Since offset printing plates are almost on the same plane, it is necessary to find a method that can effectively distinguish the blank part from the graphic part. The role of water in offset printing is what we call the principle of “water and oil incompatibility”. In the printing process, a thin layer of water is uniformly applied on the surface of the printing plate (actually, due to the selective adsorption on the surface of the printing plate, the graphic part is not wetted), and then coated on the printing plate. When ink is used, it effectively protects the blank area.

3. Is offset printing the most widely used printing method?

A: In China, offset printing is an absolutely dominant printing method. Because of its fast printing speed, relatively stable printing quality, and short printing cycle, it has many advantages. Books, newspapers, and a considerable portion of commercial printing are all using offset printing. When one mentions printing, people immediately think of offset printing. Foreign brands such as Heidelberg, Roland, Mitsubishi and Komori are also familiar to ordinary people.

4. What are the three major processes in offset printing?

A: The three major principles of offset printing are: First, the principle of water and oil incompatibility, the chemical principle of the so-called similar compatibility is determined, there is a slight polarity of the molecular structure of water and non-polar molecular polarity between the oil molecules, As a result, water and oil cannot be attracted and dissolved. The existence of this rule makes it possible to use water for flat printing plates to distinguish between graphic and blank parts. Second, the surface of the adsorption principle, according to the different surface tension, it can adsorb different substances, which also provides the possibility of lithographic offset printing and graphic separation. Third, the dot structure principle, because the offset printing plate is flat, then you can not rely on the thickness of the ink to express the level of graphic arts on the print, but by dividing the different levels into tiny tiny unobtrusive dots Units can effectively represent a rich image hierarchy.

5. Is lithography and offset printing the same thing?

A: Now it seems that there is nothing wrong with this, but it is not entirely accurate, because in offset printing, in addition to offset printing and lithography, they are printing methods that do not require the use of blankets. However, since other types of offset printing methods except offset printing are rarely seen, we now refer to offset printing as offset printing.

Who was the first to invent lithographic printing?

A: From the birth of the first lithographic prints to today, more than 200 spring and autumn days have passed. Since the lithography was first developed by the Czechs, countless ancestors have been trying hard to explore in order to try more perfect printing methods. When it comes to the invention of the plain printing, then we may wish to take a look below.

In 1798, the Austrian (now Prague, Czech Republic) composer Alois Senefelder (7711- 1834) invented lithography (Lithography), which uses the principle of water and fat counterclockwise and prints on the plane, for lithography. (Planography) 嚆矢. And make a wooden lithograph. Sennerfeld's first law, followed by his father's song and dance, failed. He is engaged in composing for a living and is very popular among the people of the world because he thinks he will print and sell the music. The vast Indiana fee, with a meagre profit, was an apprenticeship in the printing house, but it was limited to capital and was unable to create itself. He is based in Solenhofen, near Munich, and has a large number of stone stones. He grinds copper plates on weekdays or sculpts on stone plates. When Sri Lankan family was poor, his mother was doing laundry, and on the 1st of the day his family remembered his laundry account. He inadvertently wrote the fat ink stick on the stone tablet. After a few days, he found that the handwriting could not be washed away. In the experiment, he wrote the letters on the lithograph by using fat ink, and after printing with nitric acid and a gum solution, he inked it and succeeded. He called himself Chemical Printing. The word Lithography, which was originally a combination of the Greek word "stone" Litho and "write" "Graphein", has now become a name for lithography.

In 1834, Seishi served as the supervisory officer of the Pakistani Kingdom of the Kingdom of India, and died in February of the same year.

In 1810, F. Weishaept assisted Sennafield in the completion of iron hand-held lithographs.

In 1817, Sennerfeld tried to replace the stone plate with a zinc plate for the flat plate.

In 1826, legal person Niepce invented the earthen asphaltic optical plate. In 1832 (Eleventh year of Qing Daoguang), British missionary WH Medhur established a lithograph printed Chinese document in Macau.

In 1837, the legal entity G. Engel Mann invented the color lithography and named it Chromography.

In 1840, the Englishman M. Ponton invented the AlbuMin process.

In 1868, the German J. Albert invented the Collotype.

In 1869, the British D. Hauron invented the subtractive color method as the trichromatic color lithography.

In 1876 (the second year of Qing Emperor Guangxu), the legal person Weng Xianggong (Catholic priest) and Chinese Qiu Ziang set up the "Tushan Bay lithographic institute" in Shanghai and used a lithographic printing church to pictorial. The "Spot Baizhai Shi Yin Bureau" was established.

In 1881, in the 7th year of the Qing Emperor Guangxu, Xu Yuzi of Guangzhou set up the “Issues for the Same Document”, purchased 12 lithographic machines, employed 500 people, and reprinted rare books.
In 1886, Englishman L. Johnston invented the offset rotary press.

In 1900, the British man F. Vandyke invented the positive image and made a printing plate with a metal plate coated with a chromate film called the Vandyke Process or Reverse Process. The Chinese called it the "original plate making method."

7. How is offset printing used?

A: The original lithographic printing directly printed the graphic on the printing plate onto the substrate. Until 1904, a beautiful person named IW Rubel made new improvements. In one printing, he accidentally The image on the plate was first printed on a blanket, and when the pattern on the blanket was transferred to the paper, he was surprised to find that the printed image was of higher quality than the normal print. This happened by chance. The discovery prompted him to work hard to invent an indirect-print offset press. From the 34th year of Guangxu (1908), China began to introduce the first offset rotary offset press. Today, offset printing has been widely used in China.

8. What kinds of plates are used for lithographic printing?

A: From the history of the development of lithography, there are some of the following media that have been widely used:

Lithography, until today, lithography has also been widely used in ancient painting reproduction, New Year printing, etc., in order to achieve special effects;

The Milo version is a transliteration of the English collotype. The printing of the Feilu version is a category of lithography. Is one of the earliest photolithography, because more use of thick glass as the base, it is also called "glass printing." On the thick frosted glass plate material, the Milon version is coated with a chrome glue photosensitive liquid. After the negative film and the photosensitive film layer are intimately exposed and exposed, a photochemical reaction takes place and the glue layer hardens to form an image. The depth of the image density is not composed of dots of different sizes, but the degree of hardening of the film varies depending on the amount of light received by the film. The degree of hardening determines the difference in the expansion of the film, and the different degree of expansion results in the formation of fine wrinkles with different densities. The greater the amount of light received, the greater the degree of hardening, the smaller the expansion, the more wrinkles, the less water absorbed, the more ink adhered, and the darker the tone after printing, and conversely, the brighter the tone, thereby reproducing various levels of the original surface, due to The Roland printing is direct printing, so the graphic on the printing plate should be reversed. The Milo Edition is a kind of direct printing and is best suited to reflect traditional Chinese ancient calligraphy and painting works.
Photosensitive protein plate, also known as the negative plate version or flat plate version, the base plate is aluminum or zinc plate. The lipophilic hydrophobic film in the graphic part is a sclerostin film with a high publication plane of about 3-5 [mu]m, and the blank part of the hydrophilic oleophobic film layer is an inorganic salt layer. Protein plate making process is simple, the cost of raw materials used is low, but the printing rate is low, generally 5000 to 10000 India. Because the photosensitive resin base is not strong, the quality of the plate is not stable, and the defects such as low printing rate have caused almost no use.

Flat intaglio plate, flat intaglio plate is also called positive plate plate, plate base is zinc plate. The plain intaglio plate is printed on the positive plate of the positive image, and the photo-hardened film is dissolved and removed by the developing solution, exposing the metal of the graphic part, and the metal is slightly corroded by the etching solution so that the metal of the graphic part is lower than the plate surface by 5 to 8 μm. Then it was painted with a oleophilic base paint, and the hydrophobic and hydrophobic graphic part was formed. Although the printing capacity and print quality have improved compared to the albumin, the intaglio plate is now hard to see.

Multi-layered metal plates, multi-layer metal plates use two kinds of metals with opposite hydrophilicity and oleophilicity as the printing plate, there are two kinds of metal plates and three metal plates. According to the shape of the concave and convex figures, it is divided into a flat gravure version and a peaceful type. The most commonly used are two-layer gravure and three-layer gravure. Copper chrome plated to make a two-layer gravure; metal plated copper and then chrome or nickel will be made of three-layer gravure. Multi-layered metal plate printing process. The oleophilic part of the multi-layered metal plate is the copper metal with the best lipophilicity and is treated with potassium ethylxanthogenate to directly adsorb the ink. At this time, the printing capacity has reached a very high level, but the ability of the multi-layer metal plate to restore the dots is not good. In addition, the plate-making cycle is too long and the process is complicated. Now it is no longer visible.

The pre-coated photographic plate (PS plate), PS plate is the abbreviation of the pre-coated plate. Because of its stable quality, printing capacity, and simple process, it is suitable for large-scale printing. Now, the PS plate has become the only version of the lithographic plate.

9. What is the PS version?

A: "PS version" is an abbreviation for "Presensitized Plate" in English.