In 2016, there were a total of 5 quality plastic film products in the quality evaluation of Huaguang Cup national flexo print. The first and second ranked grades were two baby diapers sent by Jiasheng Plate (Shanghai) Co., Ltd. Bags. One is Unija baby diapers diapers XL44 bags, the background is a blue gradient mesh, with a large area of ​​pink behind the baby; the other is Mommy baby female treasure diaper XL32 film packaging bag, the background is large Pink area. The reviewer did not publicly print the products of the printing companies, but the technical parameters for the evaluation (W & H Satellite Flexo Press, Sakata Solvent Ink, Murata Anilox Rolls, Loman Medium Density Double Sided Tape, DuPont Plate) The two bags were printed by the same printing company, and they showed great skill in the development of printing quality control and printing processes.
The two award-winning products reflect the inherent characteristics of satellite-based flexo presses in the printing film printing accuracy and dot printing reduction of PE film. These characteristics are not only possessed by imported satellite flexographic presses, but also most of domestic satellite flexographic presses. The easily stretchable PE film is printed tightly on the surface of the central embossing roll, and the wrap angle reaches 80% to 85% . Under the action of the rubber pressure roll placed on the top of the center embossing roll, the film is almost synchronized with the center embossing roll. Operation, adjacent printing color group is registered under the condition of zero tension, so the ordinary register accuracy index is not difficult for this printing machine type. This type of model has some skill in controlling the inking pressure (the pressure between the anilox roller and the plate roller) and the printing pressure (the pressure between the plate roller and the platen roller) of flexo printing. From the two award-winning samples, the captain who operated the machine had a higher level of flexo and pressure control, and the integrity and expansion rate of the printing dots were within the controllable range.
Two award-winning products are printed on 120 lpi plates with a minimum of 1% . According to the plate-making company, the minimum network point can reach 0.4% . Theoretically, it may be. However, the author did not see such a small network point on the actual printed samples submitted. From 120 lpi plate, 1% dot, theoretically can be calculated bm  The dot diameter is approximately 24 μm . The 800 lpi Murata anilox roll can also be calculated to have a cell opening diameter of approximately 29 μm . On the printed sample, it was not seen that the minimum dot diameter was less than the diameter of the opening of the anilox roller hole, which caused the excess ink around the dot, resulting in a flexo-stamping failure. It is not easy to achieve this standard in printing, which is related to the control of actual dot diameter in the platemaking process, and is also related to the solvent type flexo ink used in the process. According to the author's previous calculations, the ink is about 1 dyn/cm higher than the surface of the same type of flexographic ink . It is this higher 1 dyn/cm that makes the ink less likely to adhere in the depressions of the printing plate, ie it is not easy to block the plate.
The level reached by the printed sample at the outlet control is directly related to the color of the child's image on the baby diaper bag. The color of the baby's skin is very tender. Therefore, red and yellow are the main colors, and blue is the fine dot and the black dot is smaller. Therefore, the difficulty in printing children's skin color lies in the control of the blue net and the black net. If the blue net and the black net are out of control, the baby image will lose the maternity characteristics of the Asian baby, and it is likely to become African-American, and the original intention of the designer will be lost. Far away. Judging from these two printed matters, the printing company's control over the expansion of outlets in the printing process was effective. Although the evaluation was not directly sent by the printing company, the awards were the same as the production site management and actual operation of the company. The level is inseparable. In fairness, half of the prize should be attributed to the printing company.
Both products are very skillful in prepress design and plate making, avoiding the two major printing quality issues that may arise in printing. One is the midtone tune of a circular dot network, or a jump-step. The printing performance is that the dots at 40% to 50% are abnormally connected with the neighboring dots due to the expansion during printing, which is called block-blocking. Foreign counterparts Called bridging . The other is a ghost, because of the typesetting reason, there is a regular unevenness of the same color density in the printing perimeter direction. This uses solvent-based inks on satellite-based wide-format flexographic printers, which is a difficult problem to solve when the perimeter of the plate roller is less than the circumference of the anilox roller. However, in these two products, this problem has not been found, that is, it has been solved in advance when the design draft or prepress adjustment.
The designs of the two products are mainly composed of Asian infants. The pink skin is mainly composed of red and yellow, and the dots are mainly midtones. If there is a jump in the middle yellow tone, due to the high brightness of yellow, the faults of the laps are not easy to detect. But the red color is different. If the red tone is in the middle tone, the red blocking version caused by the overlapping of adjacent dots will be very obvious. There is no room for disguise. Therefore, the use of chain-shaped dots instead of circular dots before printing is an excellent design. From the standpoint of the nature of outlets, the expansion of circular outlets is the smallest, because the definition of outlet expansion is the increase rate of the perimeter after the outlet deformation, and the increase rate of the perimeter is the smallest in the commonly used geometry. It is hard to see with the naked eye. However, the chain outlets are different, and the chain outlets are elliptical. There are two overlaps between more than 30% and 70% of the neighboring outlets. The increase rate of the perimeter is obviously higher than that of the circle, that is, the outlet expansion is larger than the circle. However, with the use of chain-shaped dots, even if the dots are spliced, the skin color is regular. This avoids the unexpected feeling of the circular dots when they overlap. At a glance, they know that the printing has failed. As for the expansion of chain outlets, it is not difficult for prepress, and the pre-adjustment of the restoration curve will not only solve the problems of skipping and overlapping, but also easily achieve the purpose of printing and restoration.
Another feature of prepress is to avoid ghosting. The so-called ghosting of flexo printing is characterized by the regularity of the density of colors on a single color. There are also colleagues in the industry who use multi-colored sets of punctuality and two-tone overlaps. The pollution-induced ink-printing caused by black ink is called ghosting, but this is not rigorous and the definition is wrong. When the circumference of the anilox roller is greater than the circumference of the plate roller, the difference between the two is the position where the ghost appears. Therefore, detecting whether there is a ghost image can be judged by a single color test, and generally it will not be misjudged.
The difference between the circumference of the anilox roller and the plate roller is actually the difference between the rotation speed of the anilox roller and the line speed of the plate roller. Because the two rollers are intermeshing, if the line speed is equal, the ink on the anilox roller is completely transferred by the printing plate, and there is no residue on the anilox roller. However, in actual printing, there are not many cases in which the peripheral length of the printing plate roller is equal to the circumference of the anilox roller, and the circumferential length of many product plate rollers is larger than the circumference of the anilox roller or smaller than the circumference of the anilox roller, which is difficult to be consistent. However, there is a rule to follow that the satellite-type flexo printing machine has a wide film width. In order to prevent the anilox roller from being deformed, the diameter of the anilox roller is generally set larger, and the circumference of the anilox roller is often 510 mm and 560 mm. And so on, choose 480 mm less, less than 480 mm . In order to save manufacturing costs, the narrow-width unit type flexographic printing machine with printed labels has a lot of anilox rollers, and does not have to worry about rigid deformation. The circumference is generally around 300 mm or even less.
The circumference of the anilox roller is greater than the circumference of the plate roller, which means that the amount of ink carried by the anilox roller can not be transferred by one revolution of the plate. It is not transferred due to the dry nature of the ink itself. When the ink is transferred to the next printing plate, there is a difference in the density compared to the new ink obtained on the anilox roller, and ghosts are easily generated. When the circumference of the anilox roller is smaller than the circumference of the plate roller, since new ink is continuously transferred to the plate, such traces are few or even absent. The ghosting of flexo can be observed on a rotating anilox roller, which is often encountered when using solvent-based inks. Therefore, the narrow-width unit type flexo presses rarely exhibit ghosting. If UV inks are used , it is not possible. The satellite type flexo presses are prone to ghosting, especially when solvent-based flexo inks are used. Solved problems.
The printing perimeter of the two award-winning products is not long. Since the W & H wide-format satellite flexographic printers are used to print the two products, it is inferred that the anilox roll circumference is about 510 mm or 560 mm , and the printed samples are not so long, so the circumference of the anilox roll is greater than that of the platen roll. Long, this can be basically determined. In other words, there is a possibility of ghosting. In particular, Mommy Baby Girl Po diapers XL32 film bags, shorter length, even if the vertical double fight, there may be ghosting. However, no ghosts were found in the samples. How is this done?
Take Unija baby diaper-type diaper XL44 bag as an example, here are two measures taken. One is the blue background is not covered, only half of the length of the full width, so the difference between the anilox roller and the perimeter of the plate roller is transferred to the place where the baby's red background appears, so the blue version may appear. The ghost loses the necessary conditions for existence. The other is the use of dark tone screens instead of the usual field printing, darker inks are much less than the actual field, and the difference in density is not easy to see. These two design features avoid ghosting that is likely to occur in printing. As for the Mommy Baby Girl Po diaper XL32 film packaging bag, a warm-colored magenta is used as the background color, and it is also replaced with a cloth net to replace the very sensitive blue with a slightly poorer hue, and the hue is used effectively. For cover, it is inevitable that no ghosts will appear.
It is necessary to talk about a failed case in the design of baby diaper bags. A unit that also received a quality award in the quality evaluation of the Huaguang Cup national flexo printing press once displayed a proof of a baby product bag on a technical forum. The background is a very dark blue with a very high texture. Strong. However, the author still saw a more obvious ghost on the packaging bag, and its position appeared to be the difference between the circumference of the anilox roller and the perimeter of the plate roller. Of course, the defect appears in the middle of the folded bag. Non-professionals will not go to this place. This design emphasizes the texture, with a large field to do the background, with the dark blue with a purple-based color, it is good, but did not count the location of the ghost appears, can be described as a small failure.
The two award-winning products also have the same flaw, that is, the number of printing plate lines is only 120 lpi . Compared with the 133 lpi and 2% outlets of the same type of products printed by the author that year , they have not progressed and have slightly declined. The color density is also low. Take blue as an example. The visual measurement is about 1.4 to 1.6 , which can meet industry standards. However, compared with gravure products, the gap is very obvious.
Flexographic products use high-line printing plates, which have two requirements. One is that high-gloss outlets should be small, gradients to zero, and the naked eye can't seem to have obvious hard ports. In the product design, it is necessary to directly see the true nature of the printing materials at the highest light, and the highlights reach the brightest, instead of replacing the white with a light gray ash in the C , M , and Y colors. The other is that the moiré fringe interference fringes produced when multicolors are stacked are as small as possible, highlighting the fine features, rather than showing a distinctly overlapping mottled spot. Observing whether the printed image is delicate or not, the size of the interference spot when three colors overlap is actually an important indicator. The same film flexographic printing , 100 lpi and 175 lpi , the mottled fringe interference color spot size of each color dot has great influence on the print quality.
The two award-winning products have a low plate number and a 120 lpi plate. When the color overlaps, Mole interferes with the larger spot size. Fortunately, the baby diaper bag is relatively large, and the large interference freckles are not very noticeable in the pattern of a large area, and end consumers can accept it. If the baby's pattern is reduced by a factor of two, there will still be such a large interference in the pattern that it will be very harsh, directly affecting the fineness of the print. The minimum network at the high-light spot is also the same, even if the plate-making unit has introduced 120 lpi , 0.4% of the outlets, if you do not use the FM-amplitude-mixed outlets, there is no way to expose the film at the highest light. Hybrid networks have now been used, but they are still lacking, and the dividing line is clearly visible to the naked eye. In addition, because of the fineness of the small dot printing, the amount of ink cannot be large, so the number of anilox roller lines must be selected to be high. The two award-winning products were selected by Murata's 800 lpi anilox roller. The author estimates that the ink storage volume is generally between BCM3.0 and 3.2 , which is unlikely to exceed 3.5 . Even if a Sakata solvent-based flexo ink with a pigment proportion of about 20% is used, and gravure ink with a proportion of only 10% of the pigment is used , the difference of 1.8 to 2.0 when the color density is blue is taken as an example , the difference is still very obvious.
The high gloss of the film flexo does not come out, and the dark tone represented by the density on the ground can not go deep. This has become the bottleneck of the current quality of domestic flexo printing. The image contrast is not enough, the tone is too flat, the level is concentrated in the middle tone, the three-dimensional sense is not strong, and the level cannot be pulled open. To increase the color density, the author's practice was to separate the field from the site, using high-line anilox rolls, small ink volumes, low-line anilox rolls in the field, and large ink volumes; or where high density is required. Two inks are processed to make the dark ink come out. It is a pity that the result of such a move must be to increase the cost. There is still reason for this to exist more than 10 years ago. However, in the highly competitive situation of the past few years, it is necessary to discuss whether this method is reasonable or not.
Is there a solution? there must be. The above problems have existed for more than 10 years but have never been overcome. Thin-film flexo printing, which uses hygienic packaging materials as its main market, frankly, these years have seen little progress. It is said that some technical leaders of printing companies in flexo printing and sanitary packaging also reveal ideas that they have not learned anything in the industry, indicating that the subjective lag has affected the enterprising spirit of technological development. It is very regrettable.
One of the key issues that cannot be achieved when the film flexo layer is stretched is to print small dots, such as 175 lpi or 150 lpi 1% dots, but also get a high color density on the same plate, close to gravure The color density on the film. This must impinge on an iron rule selected by the anilox roller, that is, using a high number of lines requires the use of a correspondingly high number of lined anilox rollers. Because the amount of ink stored by the anilox roller is limited by the number of anilox roller lines, the amount of ink of the high line number of the anilox roller must not be too large, and the color density must not go up. The usual thinking is that the amount of ink can neither be too large nor dark, and can only hope to increase the proportion of ink pigments. However, the proportion of pigments in flexographic inks cannot be increased without limit. The cost of inks is secondarily, and the printing suitability of inks after the increase of the proportion of pigments will be greatly reduced.
At the 2016 flexo annual meeting held in Dongguan, Guangdong , there have been related technologies. One is to analyze the surface tension of the printing plate from the interface, and the other is to specifically address the smooth and flatness of the depressions in the printing plate. It is very regrettable that it may have been imported from a foreign headquarters. The introduction at the meeting countered the problem and the explanation on the technical information was wrong. One had avoided the technical secret and provided no written technical information. With the combination and depth of these two technologies, it is possible to reach the self-cleaning theoretical experiment of the plate completed by the author two years ago on an industrial scale, that is, even if the small dots are inserted into the anilox roll under the action of a large amount of ink anilox roller. The cell site, but after the outlets are pulled out, the outlets are not covered with ink, and the ink only adheres to the top of the printing plate that needs to be inked. The experimental results at that time were that for the 500 lpi anilox roll of BCM 4.5 , the smallest dot of printing was 1% of 175 lpi , and the density of blue solid on the same plate was 1.8 .
As the representative of the first national unit for the quality evaluation of flexographic prints in China, the author obtained a PE heat-shrinkable film 6 cans in 1998 and a Pepsi-Cola World Cup promotional packaging to obtain a film product quality award. The award's acquisit 12Pcs Shoe Wet Wipe,Shoe Wipes Wet,Alcohol Wet Wipes,Wet Ones Individual Wipes DONGYANG COMEXA SANITARY PRODUCTDS LTD.,CO , https://www.comexawetwipes.com