Get out of the misunderstanding of corrugated box flexo printing
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One of the misunderstandings:
The selection of the plate is more blind
Many plate-making companies do not consider the actual situation of the printing plant, such as the type of printing machine, the thickness of the tape, the type of ink used, etc., blindly arrogant. For example, in the case of printing plates for corrugated boxes, many customers only know DuPont's well-known TDR plates. TDR is a widely used corrugated printing plate with excellent plate-making performance, but the resolution is not as high as a batch of thin plates such as EXL/UXL. When printing E-type corrugations and images up to 120 lines/inch, you should use a thin plate such as EXL/UXL and use a sponge pad to achieve high resolution. At the same time, as the hardness of the plate material is increased, the dot enlargement can be reduced, so that the printed product achieves an excellent effect.
Misunderstanding 2:
Pre-press system configuration is not reasonable
Because the special software for flexo printing is relatively expensive, it can be tolerated by small and medium-sized plate-making companies. Therefore, only a few overseas companies in China can afford it, and most of the plate-making manufacturers have localized according to local conditions. In general, small-scale plate-making factories mostly use platform scanners and digital cameras as input devices, and modify the PC or Apple G3 used in the computer, plus the imagesetter and punching machine as output devices. Due to the limitation of the scale of the plate, many domestic manufacturers copy the configuration of offset printing plates, and even adopt the hysteresis technology of print output and photography, which makes the domestic corrugated box flexo printing technology always in a low level, only as a hand-carved rubber version. The alternative has not yet entered the era of color corrugated box printing, compared with foreign counterparts, we are nearly 10-15 years behind.
Misunderstanding three:
Use offset film as the final output film
Admittedly, offset film has a series of advantages such as convenient procurement, economy, and timely delivery, and the process conditions are relatively mature. However, offset films have a fatal weakness: the surface is too smooth.
Photosensitive resin flexo will release a certain amount of oxygen during photopolymerization (physical and chemical mechanism is patented, not disclosed), only the matte film can smoothly guide the oxygen out, so that the film and the plate remain unchanged. Should be in contact with and accurately transfer images. On the contrary, the surface of the offset film is smooth, and the oxygen cannot be smoothly exported, resulting in a large gap between the film and the plate, causing image distortion, roughening of the image, blurring, and the like. Some plate-making operators use the method of squeezing the body powder to alleviate these problems to a certain extent, but at the same time, the light transmittance is reduced, and the cloudiness of the film is increased.
Misunderstanding 4:
Plate machine design is defective
Some domestic plate-making machine manufacturers, in order to compete for price, are shoddy at low prices. The typical practice is to copy the circuit design of fluorescent lamps and use low-cost domestic ordinary UV lamps. Since the circuit of the fluorescent lamp is directly activated by the starter, the flashing generated after the lamp is activated tends to cause uneven back exposure such as EXL/TDR and short back exposure time, resulting in a base material. Uneven sensitization, such a plate, after washing, will give a wavy substrate.
The correct way is to use high-quality UV light source. For example, PH ILIPS VA-R series lamps are equipped with high-quality ballasts and starters, and a filament voltage of about 5 volts is applied to both ends of the filament (important). In this way, the filament can be kept in a red hot state, and only the main loop power supply needs to be turned on during the exposure, and the lamp can be started in an instant and reach a uniform exposure state.
The PH ILIPS lamp with this connection can reach more than 160m w/cm 2 , while the ordinary lamp is only 40m w/cm 2 , and the radiant energy is 4 times different, which means that under the same exposure. The efficiency is 4 times different.
Misunderstanding 5:
Misunderstanding exposure latitude
According to the internationally recognized standards of FTA, the exposure latitude is as follows:
Tolerance = cut-off time - formation time
1. For the corrugated box printing plate (2.84mm or more), the exposure time from the 3% dot on the 34L/cm plate is reduced, and the depth to the 0.8mm wide pan is reduced to 0. Lmm time.
2 For the thin plate (below 2.84mm), it means that the exposure time from the 2% dot on the 48L/cm plate is reduced to 0. Lmm is deep.
The greater the tolerance, the less sensitive the exposure time changes in the media. Some inferior plates are filled before the dot is formed, and the exposure tolerance is negative, that is, the dot and the negative effect cannot be simultaneously exposed on the same plate.
Some plate makers excessively demanded the depth of the plate relief, making the base too thin, making the main exposure time too long and losing the depth of the negative line.
Misunderstanding six:
Do not pay attention to keep the fresh solvent in the plate
Each time you wash the plate, you should add a proper amount of fresh plate-washing solvent to keep the photosensitive resin component in the solvent too much.
Never use an old solvent that has not been distilled as a fresh solvent to the fresh solvent pipe. Otherwise, it seems to save costs, but considering the downtime and paper waste caused by the printing plate problem and the acceleration of the plate machine damage, it is not worth the candle. There used to be such an example. The plate-making machine worth more than 100,000 US dollars, due to the lack of long-term supply of fresh solvent, causing many problems such as agglomeration of the brush, clogging of the spray, poor circulation inside the machine, etc., almost caused the plate making machine to be scrapped. The French engineers from the original factory repaired them to avoid more losses.
Therefore, ensuring a certain amount of fresh solvent supply can not only reduce the stickiness and swelling of the plate material, but also improve the washing speed, and also prolong the life of the plate washer and improve the quality of the plate washing.