Misunderstandings in flexo printing of the hottest

2022-08-02
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One of the misunderstandings of carton flexo printing:

the selection of plate materials is blind

many plate making enterprises do not consider the actual situation of the printing plant, such as the model of the printing machine, the thickness of the plate pasting tape, the type of ink used, and blindly follow the crowd. Taking the printing plate for corrugated box as an example, many customers only know the famous TDR plate of DuPont. TDR is a widely used corrugated printing plate with excellent plate making performance, but its resolution is not as high as that of a batch of thin plates such as EXL/UXL. When printing E-type corrugation and images up to 120 lines/inch, thin plates such as EXL/UXL should be used instead, and sponge pads should be added, so as to obtain high resolution. At the same time, with the increase of plate hardness, it can also reduce the dot expansion, so that the printing products can achieve excellent results

myth No. 2:

unreasonable pre press system configuration

due to the high cost of special software for flexo printing, which is not affordable for ordinary small and medium-sized plate making companies, at present only a few overseas companies in China can afford to consume it, while the vast majority of plate making manufacturers have made localization according to local conditions. Generally, degradable high molecular materials need to have good compatibility in all degradation processes. For small-scale plate making plants, most of them use platform scanners and digital cameras as input devices, modify the PC or apple G3 used by computers, and add phototypesetters and processors as output devices. Due to the limitation of plate size, many domestic manufacturers copy the configuration of offset plate making, and even adopt lagging technologies such as print output and photography, which makes the domestic corrugated box flexo printing technology in a low-level state. As a substitute for hand carved rubber plate, it has not yet entered the era of color corrugated box printing. Compared with its foreign counterparts, we are nearly 10-15 years behind

myth 3:

offset film is used as the final output film

it is true that offset film has a series of advantages, such as convenient procurement, economy, timely supply, etc., and the process conditions are relatively mature. However, offset film has a fatal weakness: the surface is too smooth

the photosensitive resin flexographic plate will release a certain amount of oxygen during the photopolymerization reaction (the physical and chemical mechanism belongs to the scope of the patent and will not be disclosed). Only the frosted film can guide these oxygen out smoothly, so that the film and the plate can still maintain equal contact and accurately transfer the image. On the contrary, the surface of offset film is bright and clean, and oxygen cannot be exported smoothly, resulting in a larger gap between film and plate, resulting in image deformation, coarsening and blurring. Some plate making operators adopt the method of scattering talcum powder, and use the constant test box or the alternating test box to alleviate these problems to a certain extent, but at the same time, it also leads to the decline of light transmittance and increases the cloud haze of the negative film

mistake No. 4:

the design of plate making machine is defective

some domestic plate making machine manufacturers, in order to compete for price, make rough products at low prices. Their typical practice is to copy the circuit design of fluorescent lamps and use low-cost domestic ordinary UV lamps. Due to the sunlight, they are like seedlings pressed by stones. 1. The circuit of the lamp is directly started by the starter. The flicker generated after the lamp is started will inevitably lead to uneven back exposure of plates with high back exposure requirements and short back exposure time, such as EXL/TDR. As a result, the photosensitivity of the substrate is uneven. After such plates are washed, they will get a wavy substrate

the correct approach is to select high-quality UV light sources, such as VA R series lamps of pH ilips company equipped with high-quality ballasts and starters, and apply a filament voltage of about 5V at both ends of the filament (very important). In this way, the filament can be kept in a red hot state. During exposure, just turn on the power supply of the main circuit, and the lamp can be started in an instant to achieve a uniform exposure

the radiation energy of pH ilips lamp tube with this connection method can reach more than 160m w/cm 2, while that of ordinary lamp tube is only 40m w/cm 2. The difference in radiation energy is 4 times, which means that the difference in efficiency is 4 times under the same exposure

myth 5:

misunderstanding of exposure tolerance

according to the internationally recognized standards of FTA, the following provisions are made on exposure tolerance:

tolerance = deadline formation time

1. for corrugated box printing plate (above 2.84mm), it refers to the time when the depth of the 0.8mm wide negative line on the 34L/cm printing plate decreases to 0.lmm from the exposure time formed at 3% point

2 for thin plates (2.8 does not have a national standard for specific waterproof material products below 4mm), it refers to the exposure time from the 2% point on the 48l/cm plate to the time when the depth of the 0.8mm wide negative line decreases to 0.lmm

the greater the tolerance, the less sensitive it is to the change of exposure time. Some inferior plates have been filled with negative lines before dot formation, and their exposure tolerance is negative, that is, you can't sun out dots and negative lines on the same plate at the same time

some plate makers demand too much for the depth of the plate relief and make the base too thin, so that the main exposure time is too long and the depth of the negative line is lost

myth 6:

do not pay attention to keeping the plate making solvent fresh

every time you wash the plate, you should add an appropriate amount of fresh plate washing solvent to keep the photosensitive resin in the solvent from too much

never add the old solvent without distillation to the pipeline of fresh solvent as fresh solvent. Otherwise, it seems that the cost has been saved, but considering the downtime and paper waste caused by the printing plate problem and accelerating the damage of the plate making machine, it is not worth the loss. There was once an example of a plate making machine worth more than 100000 US dollars. Due to the long-term shortage of fresh solvent supply, the brush was blocked, the spray was blocked, and the internal circulation of the machine was not smooth. The plate making machine was almost scrapped. It had to be repaired by the French Engineer of the original factory to avoid more losses

therefore, ensuring a certain amount of fresh solvent supply can not only reduce the stickiness and swelling of plates, but also improve the speed of plate washing, prolong the service life of plate washing machine and improve the quality of plate washing

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