Comparison of 300 network cable and 150 network cable print
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
1 Introduction
The quality of print reproduction is mainly evaluated from two aspects: image color reproduction and tone level reproduction. The tone level replication mainly depends on the number of dots in the unit area and the number of dots whose dots change continuously from small to large. The more the number of dots in the unit area, the more the number of dots in the copy area, and the clear copying of the printed matter. The higher the degree, the richer the level, the more realistic the color; the more the level of change in the dot, the stronger the performance of the print level and the more delicate it looks. In the printing production process, people control the number of dots in a unit area by changing the number of screen lines. The higher the number of screen lines, the more the number of dots in a unit area, and the smaller the size of the dots reproduced. At present, the number of commonly used coated paper lines is between 150 and 175 lpi. However, with the continuous improvement of people's appreciation level, this precision printed matter can no longer meet people's visual needs. Therefore, more and more printing companies use high-speed cable technology to obtain prints with more layers, higher definition, richer colors, and copying effect close to the original, to meet the needs of high-end albums and famous packaging.
As one of the important contents of the Hefei Sino-German Printing Training Center and the German Gaobao Company's printing seminar and Gaobao equipment exhibition held in Hefei, it is the printing test of 300 network printing products. We completed the printing comparison test of 300lpi prints and 150lpi prints with the help of KBA technicians.
2 test analysis
It is well known that dot enlargement in the printing process (including mechanical dot enlargement and optical dot enlargement) is an inevitable phenomenon in which printing by image transfer is realized by pressure. The size of the dot gain value is usually proportional to the sum of the perimeters of the dots in the unit area. For the same dot value, the total circumference of the 300 lpi dot is larger than the sum of the perimeter of the 150 lpi dot. That is to say, the dot enlargement rate of 300 lpi is larger than the dot enlargement rate of 150 lpi. In view of this, we will test and produce a suitable output characteristic curve for output when the output is printed.
The 300 lpi 2% dot diameter is about 11.6 μm, which is almost the same as the diameter of the dust particles. Therefore, the dust falling on the glass of the printing frame or the film is easy to be exposed, forming a so-called "pseudo-mesh", which interferes with printing. The normal operation, so we should strictly ensure the dust-free process in the PS version of the drying process. In addition, the PS plate should be developed with a PS plate developing machine and the development process must be stable.
The selection of test materials is also strict. We should fully consider the characteristics of 300lpi print dots and select suitable printing materials.
In the printing process, the printing workers are required to have a good professional level and a good professionalism, to do "three diligence", and to maintain a good ink and wash balance in the printing process.
3 Test equipment and test materials
1 Printing equipment: The KBA Rapida 74 four-color five-color plus light sheetfed offset press has just been introduced by the Sino-German Printing Training Center.
2Paper: Korea Hansen 157g/m2 coated paper with high smoothness and good energy absorption.
3 Printing ink: CMYK ink provided by German Hostmann Steinberg (part of Amber Group) free of coloring strength, low strength and good rheological properties.
4 dampening solution: Ace DINDH2010 dampening solution (pH control between 4.8 and 5.2) provided by Vega, Germany.
5PS version: The locally produced Jin Dongyang pic PS version.
6 blanket: Use a special blanket provided by KBA.
7 lining: special polyester base with smooth, flat and uniform thickness provided by Gao Company.
4 test process
(1) Original production
We used digital manuscripts provided by KBA in Germany. These digital manuscripts were stored on CD in eps format, for a total of eight images, each with an image volume of 83MB. We selected three representative images as test originals, which are skin color images, wine images, and furniture images. We did not do anything with the originals, imported them directly into the Pagemaker group, then called the specific output characteristic curve in the Delta workstation, and finally output the film on the Hercules. Since the imagesetter cannot achieve simultaneous output of 300lpi and 150lpi on the same page, we may output 300lpi and 150lpi films separately, and then combine the page information of 300lpi and 150lpi on the same layout by manual imposition.
(2) Printing version of the sun
We did a series of tests before printing 300lpi dots, including the PS version resolution and the search for the right exposure time. If the parsing power of the PS version cannot reproduce the minimum dot, it is obviously not satisfactory. We use the UGRA1982 print proofing control strip and apply the graded exposure method to test the Jindongyang pictogram PS version. After developing the PS plate under normal development conditions, observe the reproduction of the yin and yang circle on the UGRA1982 print proof control strip for testing the PS version of the angular resolution (according to at least 505, the clear reproduction is subject to), and the PS version is judged accordingly. The resolution is 6 μm. According to calculations, 100% of the dots on the 300 lpi print have a diameter of 83 μm, and 2% of the dots have a diameter of 11.6 μm. It can be said that the PS plate completely satisfies the test requirements.
Let's look for the right exposure time. Here we mainly consider the drying conditions of the 300lpi cable. If the 2% dot and 98% dot of the 300 lpi cable are clearly reproduced, the 2% dot and 98% dot of the 150 lpi cable must be clearly reproduced. We also use the UGRA1982 print proofing control strip to find the appropriate exposure time by means of grading exposure. In this process we walked a detour. We first clean the glass on the plate with glass, rub the 300lpi signal strip with alcohol (we measured the maximum solid density of the signal strip with a transmission density meter to 5.6) and clean the PS plate with clean gauze, then expose it with 450 Beat, 380 exposure beat, 315 exposure beat normal exposure of the plate (without the use of supplemental exposure process), after normal development found: more than 90% of the dot on the positive version exposed with 450 exposure beats, less than 10% The dot has been lost; more than 80% of the dots on the positive plate with 365 exposure beat and 315 exposure beat exposure are lost, and the dot below 5% is lost. Obviously, such a printing plate can not meet the printing requirements, mainly in the following: the brightness of the layer is lost, and the dark tone will appear unacceptable dot enlargement under the pressure of printing pressure. Therefore, we must shorten the exposure time of the plate and reduce the maximum solid density of the film.
According to a German colleague, as long as the maximum field density of the original film is above 2.4, the original Internet site can be completely transferred to the PS version. Therefore, we changed the output characteristic curve, set the maximum solid density to 3.4, and again output the 300lpi signal strip film for testing, and then normalize the printing plate with 250 exposure beat, 300 exposure beat, and 380 exposure beat respectively (the same No re-exposure process was used. After normal development, it was found that 90% of the dots on the positive plate with 300 exposure beat, 380 exposure beat, and 250 exposure beat are clearly visible, and only the positive version exposed at 250 exposure beats. The top 5% of the outlets are still retained. Therefore, we set the printing time to 240 exposure beats.
(3) Printing process
In order to achieve the desired print reproduction, we replaced the new air cushion blanket with special transfer performance and special pad before printing. The specific printing work was completed by Mr. Hasse, a experienced printing technician from KBA in Germany, and the young backbone of the Sino-German Printing Training Center. During the printing process, Mr. Hasse impressed the Chinese counterparts with the unique dedication of the Germans. He carefully sampled and compared with the reference samples to get the best possible prints. At the highest printing speed, it reached 10,000 sheets/hour.
5 Results analysis
By observing the contrasted images after printing, we found that the difference between 300lpi prints and 150lpi prints is still obvious, mainly in the following aspects.
(1) The presence or absence of rose spots
When we watched the prints at close range, we found that the bright and midtone areas of the 150-pi screen image showed a rose spot that was easily recognizable by the human eye, making the print look rough and the color lacking luster, while the print at 300 lpi I can't see the rose spots on it. This rose spot is produced by overprinting of multiple dot inks, and the diameter is usually 2 to 4 times the length of the dot. The 150 lpi dot length is 167 μm (1×2.54×10000/150), that is, the diameter of the rose spot is between 334 μm and 668 μm. When the distance between the bright spots is small, the rose spot will be clearly visible when the distance is very bright. When large, the rose spots will be clearly visible. When the distance between the bright spots is large, the size of the rose spots is within the limits of the visual resolution of the human eye, and people cannot see the phenomenon of rose spots. The side length of the 300 lpi dot is 83 μm, and the diameter of the rose spot is also reduced to 167 μm to 334 μm. Due to its small diameter, even at a small distance, we cannot see the phenomenon of rose plaque.
(2) The clarity of the printed matter
The image clarity of 300lpi prints is significantly better than that of 150lpi prints, because the dot size of 300lpi prints is only a quarter of the size of 150lpi print dots, that is, the content originally reproduced by a dot is now composed of four Small dots are reproduced to cause sharpness enhancement of the image layer boundaries, which in turn improves the sharpness of the image.
(3) Color softness
The amplitude modulation screening process reproduces the gradation change of the original and the change of the color depth through the change of the dot size. In the current color printing field, we often scan the original at a scanning resolution of 300 lpi, and then output it on the imagesetter with a 150 lpi number of hanging lines. That is to say, the first dot replicates the color information of the four ingested pixels. In most cases, the grayscale values of the four pixels are different, but the computer ignores four pixels when the dot is generated. The difference between the gray levels is taken as the gray value of the half point of the four pixels. This is the main reason why we think that low-line prints are not as soft as the original. If we use the 300lpi hanging line number output, that is to say, each dot replicates the color information of one pixel, the original gray scale can be copied one by one, and the resulting color is softer and harder.
(4) Level of expressiveness of printed matter
The hierarchical expression of the printed picture is the degree of reproduction of the subtle level, that is, the so-called texture is based on the subtle resolution of the original image, but is affected by other factors such as the number of screen lines. Because when the imagesetter is output with 150lpi of hanging nets, its laser precision is 2400dpi (150×16, of which the medicine 50 represents the number of screen lines, 16 represents the arithmetic square root of the gray scale 256), and the phototype machine has a hanging line of 300lpi. When the number is output, its laser precision is 4800 dpi (300 × 16). Obviously, the number of 300 lpi dots in the same area is 4 times the number of 150 lpi dots, and the size of a single 300 lpi dot is one quarter of the corresponding 150 lpi dot size, so that the hierarchical expression of the 300 lpi print is significantly improved.