Prepress production and selection of raw and auxil

Prepress production of commercial rotary printing and selection of raw and auxiliary materials

in modern China's printing industry, commercial rotary printing has sprung up. The launch of the commercial turning machine is actually to raise commercial printing to a higher level. It adapts to the requirements of modern printing market with the characteristics of shorter production cycle, large print batch, high quality, fast and efficient. With the standardization of working environment and machine operation, the quality of prepress production in rotary printing plays an important role in the volume control of the main venue of "macro policy trend" in 2016 IFAM. If the preliminary work is not in place and the prepress production is not suitable for commercial rotary printing, it will cause the delay of the genuine rate and a large amount of waste of paper, which will seriously affect the printing quality and timeliness of its products. To give full play to the advantages of commercial rotary printing, prepress production that meets the actual needs is indispensable

I. prepress production process

1 Design

high speed commercial rotary machines generally use web printing. The paper path is relatively long, and the physical and optical properties of the paper surface are not very uniform. They mainly rely on drying to accelerate ink drying, and have different requirements for prepress design from lithographic offset printing and paper offset printing

(1) application of grey component substitution: GCR (abbreviation of greyccom p o n e n t replacement) refers to that in color image reproduction, the achromatic value of the multicolor area overprinted or mixed with trichromatic ink can be replaced by ink ink equal to the weakest color in the trichromatic ink, and the same visual effect can be obtained

in the actual production process, the experimental speed is 200mm/min. Sometimes the ink color of the commodity Express (referred to as dmsingle) in some hypermarkets is difficult to adjust, especially the dark tone or field part in a large area. The reason is that the Y, m and C versions are too heavy to achieve neutral gray balance. After many times of practice, it is found that when the yellow, magenta and cyan versions are deep, the ink color is not only difficult to print evenly, easy to paste, but also not conducive to registration. In front-end production, GCR technology must be used to increase the depth of the black version, replace neutral gray with black, and reduce the ink consumption of other colors. In this way, as long as the black version is normal, the ink consumption of other color versions fluctuates slightly, and the color of the print is easy to maintain stability, which is mainly due to the skeleton function of the black version. By reducing the amount of color ink, it is not only easy to meet the requirements of the sample, but also reduces the production cost

(2) application of background color removal

under color removal (abbreviated as UCR) is different from the GCR mentioned above. GCR is a non color structure process, which is full-scale background color removal, while background color removal is partial removal, and its black version is a short version

in commercial rotary printing, there are often sticky dirt, ink piling, title or virtual on the ground. On the one hand, these phenomena cannot rule out the printing suitability and equipment factors of the paper and ink used, but part of the reason is that the prepress design fails to integrate the actual requirements of printing production well

the reason why the prepress design causes stickiness is the sum of the image gradation values, that is, the total amount of ink is set unrealistically. The sum of the gradation values of the cold set ink without drying is not more than 260% for single sheet paper, and not more than 300% for thermosetting web printing. Many people don't understand this. They only pursue full color, and the total number of tone values is set very high, resulting in ink accumulation and weakness in the title or large area of dark tone pressed out on the ground, and the thickening of the ink layer also requires the rise of drying temperature, resulting in the increase of wrinkles on the surface of the print. And when the total number of step values is high, phenomena such as poor overprint, back transparent printing and back rubbing caused by insufficient drying of the ink will occur.

in the continuous process of printing practice, an effective solution has been found:

1 Set the sum of the steel gradation values of the picture stack thickness or diameter greater than 60mm reasonably, and try to be lower than the national standard value as much as possible, so that the printed image can have both layers and clarity, and at the same time, it can reduce the ink drying time, so that the print is not easy to stick dirty

2. Reasonably use background color removal. Partially remove the background color, reasonably control the neutral gray balance, enlarge the image contrast and increase the saturation. This can effectively ensure that the picture is bright in color, and it is not easy to stack ink and dull. Considering the point expansion of commercial rotary printing, using about 90% of the depth to replace the field is very effective to solve the false and color deviation of the title or the field

2. Printing plate drying

the commercial rotary machine adopts the soft pressing design that the rubber drum is the embossing drum for each other. The paper completes the ink transfer under the rolling of the rubber drum, and the dot expansion (mainly the mechanical dot expansion) is much larger than the single sheet offset press. It is tested in the process of multiple printing, aiming at different papers, and considering the mechanical and optical dot expansion, X-rite528 spectrodensitometer is used to measure that when the Heidelberg M-600 starts printing normally, the print point expansion is generally 13% - 19%. When drying the printing plates used in commercial rotary machines, increase the exposure and expose the dots of 3% or less

the increase of mechanical point is affected by many factors, such as ink, fountain solution, blanket, blow molding industry dominated by plastic blow molding machine, which has a large proportion in the market, paper surface performance, etc. The main reason for the increase of optical point is that the refracted light increases the apparent area of the point. Because the expansion of the dot area will have a certain impact on the gray scale and the balance of various colors of the printed matter, the degree 13 ladder section will be exposed to the sun, the third level, and the yin-yang micron concentric circle coil section 8 μ M the Yin and Yang lines are aligned. If it is not 175 lines/inch, it should be adjusted reasonably according to the actual situation of each printing factory

3. Plate scanning:

commercial rotary printing machines have fast printing speed, and there will be a large number of waste products and defective products before reaching the normal ink color and registration. In order to improve work efficiency, produce qualified prints as soon as possible, and reduce unnecessary waste of ink, paper, etc., prepress production should adopt printing plate scanning. It can control the color difference between printed matter and design within a small range

generally, the printing plate scanning can reach about 80% of the normal amount of ink required for the actual printing, and then through the adjustment of the overall ink characteristic curve, the authentic products can be produced quickly, which can greatly improve the work efficiency. It is particularly important for those printing jobs without proofing, and the effect of printing plate scanning is more obvious for those short edition printing with proofing, It can greatly shorten the time for commercial rotary machines to produce normal ink, save a lot of raw and auxiliary materials such as paper and ink, and reduce costs and increase benefits for enterprises. If there is a great difference between the scanned curve and the normal ink curve of the printed matter at the time of actual printing, generally check the following aspects before printing:

first, check whether the width of the long red film on the edge of the film trailing tip is correct. The width of the red film of different models is different. For example, the Heidelberg M-600 drum with a perimeter of 598 mm requires a red film width of 23mm, while the M-600 drum with a perimeter of 578 mm requires a red film width of 23.1mm, The greater the difference between the width and the actual required width, the greater the scanning result will be affected. Therefore, in actual operation, it is necessary to combine with the model used to sun out a solid plot of suitable width through the red film

secondly, check whether the smoothness of the used plate is ideal. Sometimes the plate is sunken and the surface is uneven, and the scanning results will also be affected. Generally, the flatness of the domestic printing plate is slightly inferior to that of the original imported foreign version. Of course, you can reduce the impact of uneven printing plates by adjusting the suction volume of the printing plate scanner. Generally, when scanning imported plates, the suction level is selected as level 1, while when scanning domestic plates, the suction level of level 2 or level 3 can be selected, which can be used flexibly according to the flatness of the printing plate surface, because increasing the suction will make the printing plate more smoothly adsorbed on the scanning panel, which is conducive to correctly reflect the ink demand of the graphic part on the printing plate. However, blindly increasing the suction volume may suck in a large amount of dust, and the suction hole will be blocked over time, affecting the scanning quality

in a word, in prepress production, we should gradually realize that prepress production can only be used to adapt to commercial rotary printing, and commercial rotary printing cannot be used to adapt to prepress production. The prepress production of commercial rotary printing is complex and abstruse, which requires continuous exploration and summary in practical work in order to continuously improve the production level

II. Selection of raw and auxiliary materials

1 Paper

① there are tension rollers at the front and rear of the commercial rotary machine. The paper is transmitted between the printing units in a tight state, coupled with the viscous resistance of the ink, so there are high requirements for the mechanical properties of the paper, such as fracture length, folding resistance, tear strength, etc. The better the mechanical properties of the paper, the less likely it is to break, which can save a lot of unnecessary waste

② at present, some commodity newsletters in hypermarkets and real estate advertisements in advertising companies require printed products to be bright in color and high in saturation. Correspondingly, the paper should have excellent printability: water resistance, oil resistance, wear resistance, folding resistance, high surface strength, appropriate pH and water content

light coated paper, which is widely used now, has different product properties from different manufacturers: for example, UPM paper imported from Switzerland has serious surface wrinkles after printing and drying, but the surface does not lose much powder. However, some domestic papers have serious powder loss and some have low smoothness

2. Ink

commercial rotary printing machines are generally fast. For example, the speed of Heidelberg m - 600 is 44000 folio/h, which requires excellent ink performance. ① Wiredrawing: the characteristics of wiredrawing, fracture and rebound of the ink layer during the splitting process. In the process of high-speed printing, the wiredrawing is too long, which often forms the phenomenon of flying ink. At the same time, the rebound is weak, and the dot expansion is obvious; The drawing is too short, so the ink transfer is not solid, so the size of the ink used is required to be moderate. ② Heat resistance: that is, the ability of the ink on the surface of the print to resist discoloration under high temperature heating. If the ink layer changes color and the image and text are blurred after the print is dried in the oven, it indicates that the heat resistance of the ink is poor. It is found that the ink with deep hue has better heat resistance, because the ink with deep hue has uniform, fine pigment particles and high purity, and the heat resistance depends on the performance of the pigment

③ the ink fineness should be less than 15 μ m. Because the rough ink will accelerate the wear of the printing plate and reduce the gloss of the printing surface, the smaller the ink fineness is, of course, the better for the commercial rotation in pursuit of high quality

3. Fountain solution

the fountain solution of commercial rotary offset printing machine is different from newspaper rotary printing, and more different from offset lithography. It requires that the fountain solution should be conducive to a stable balance of water and ink, with less water on the ink, ensuring the concentration of the ink and reducing emulsification. Even if the machine runs for a long time, it can still ensure stable printing quality and rapid start-up of the machine. In the continuous water conveyance system, the dosage concentration ratio of the imported bucket liquid additive is 2% - 3%, and the ratio of IPA (isopropyl alcohol) is 6% - 8%. The hardness of the solvent water used is 4 ° ~ 25 ° DH, the pH value is controlled at 4.9 ~ 5.2 (slightly adjusted according to the hardness of the water), and the conductivity is 800 ~ 1200 μ s/cm； At the same time, the fountain solution used should make the ink roller free of calcium deposits and reduce the residual calcium on the blanket