The surface view of the printing label of the ligh

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As a direct representation of goods, the label should bring consumers a strong visual impact. Flexographic printing has become the first choice for label printing because of its bright and bright colors. This paper will give a brief introduction to the label printing of the unit flexographic press

selection of color sequence

at present, the graphics and text of labels printed with flexo are mainly field, line, text, etc., and most of the printing materials are paper, aluminum foil, plastic film, self-adhesive, etc. When printing absorbent substrate materials with water-soluble or solvent-based inks, the materials will swell after drying with infrared hot air, which will affect the overprint accuracy. Therefore, it is necessary to be careful when considering the printing color sequence to avoid such problems. The color plate with large area of field should be printed in the back unit as far as possible, because the substrate absorbs a large amount of ink and then passes through infrared drying. The pumping change of the field unit is naturally larger than that of other units, which also has a great impact on the overprint process. If such units are printed behind words and lines, it will more or less have a positive impact on the overprint. If the field part must be printed in the front color deck, the compensation in the up and down direction can be consciously increased to make up for the loss caused by the pumping of printing materials and make the overprint more accurate

precautions for plate making

1. trapping

when making flexo, a certain amount of trapping is conducive to printing registration, provided that the trapping size is appropriate. Trapping is set too small or no trapping treatment will cause poor registration (white leakage) in printing; If the trapping is set too large, a large outline will appear at the edge of the printed product, which will also provide an inexhaustible driving force for the extruder industry to affect the visual effect, thus affecting the overall effect of the label

2. layout design

due to flexo printing basically uses web paper for printing, especially the application of seamless sleeve technology, which greatly saves paper. However, some flexo printing machines can not realize online die cutting, and they still need to go through subsequent processing (cutting, etc.) to produce finished products. Therefore, when designing the layout, we should fully consider leaving sufficient margin for subsequent processing, The paper saving rate should not be considered unilaterally and the qualification rate of subsequent processing should not be ignored

selection of raw and auxiliary materials

when printing labels with flexo, the selection of raw and auxiliary materials will directly affect the quality of printed products. Therefore, the selection of raw and auxiliary materials should not be limited to the unit price, but should take the quality of printed products as the first element, and summarize and analyze the comprehensive cost of products. The main raw and auxiliary materials to be considered are paper and ink

1. paper

generally speaking, the label pattern is mainly on the spot, which puts forward certain requirements for the smoothness, whiteness and gloss of the paper. If you want to obtain a satisfactory label field printing effect, the smoothness of the paper must be high to ensure that the printed matter has a uniform density value and that the printed matter surface will not be scratched. As the paper with high gloss and whiteness can enhance the contrast between ink and paper, make the picture and text more clear, and make the flexo printing ink show more bright effect, therefore, when the technology of selecting flexo label paper is expected to enter the market in 2015, gloss and whiteness are particularly important. Compared with the above two indicators, the opacity of paper has a greater impact on the quality of flexo labels. Therefore, the whiteness and gloss of paper should be selected under the condition that the opacity of paper is consistent. Generally, the whiteness should be higher than 85% and the gloss should be higher than 55%

in addition, since flexo printing is generally carried out on Web, the tensile strength of paper is an important selection index. Only when the tensile strength is good, can the paper be stable and continuous in the whole printing process, and make the label maintain good overprint accuracy. In addition, the surface strength of the paper is also an important selection index. Only when the paper has good surface strength can the field printing be full, and the printing surface will not be scratched and the color will not be uneven

2. ink

the proportion of pigments in the ink will be increased to a certain extent due to the bright colors to be given to the label, but this will have a certain impact on the printing. If the proportion of pigment is too high (higher than 35%), the viscosity of the ink will increase, and the thixotropy of the ink will increase, which will affect the transmission of the ink during the printing process. At this time, it is necessary to stir the ink and store the ink at a suitable temperature (20 ℃) as far as possible

when selecting the ink, the particle size of the ink and the drying performance of the ink should also be considered. Especially when there are not only large-area color blocks, but also words, lines or eye tone images on the label, it is more important to consider that different patterns have different requirements for the drying speed of the ink, so as to make the printed products clean and tidy (there is no paste and galling). In addition, too thick pigment will cause certain wear on the roller, and attention should also be paid to the selection of ink

in a word, we should strive to save raw and auxiliary materials, but we should not only consider the price factor. We should consider it from the perspective of comprehensive cost, and conduct comprehensive evaluation according to the product qualification rate and man hour consumption rate, so as to select appropriate printing materials

requirements for printing environment

when applying flexographic printing labels, environmental factors are very important. As we know, the graphic part of the label has both large-scale field and text, lines and eye tone images. Due to the limitations of these conditions, the drying of the ink will be affected to some extent. The drying speed of the ink in the printed text, lines and other parts will be accelerated due to the volatilization of ammonia and amines. At this time, it is necessary to improve the micro environment of the ink and install a humidifying device at the ink tank to inhibit the volatilization of such substances, So as to control the drying speed

in addition to controlling the micro ring, the control of the overall environment in the printing process is also very important. Flexo printing is highly sensitive to the environment. When printing labels with different types of paper and different patterns (mainly on the ground or lines), the selection of humidity is different. Generally, the humidity of waterproof paper printing needs to be higher. When printing a large area of the field, the humidity should be lower. Too high ambient temperature will affect the drying effect of inks (water-based inks, solvent based inks), resulting in printing paste and other phenomena; If the temperature is too low, the viscosity of almost all kinds of inks will increase, which will reduce the fluidity of inks and bring inconvenience to printing. Therefore, it is necessary to stabilize the temperature and humidity of the printing environment within a certain range

in China, the four seasons in northern China change obviously, the temperature and humidity vary greatly, and the climate is mainly dry. It is best to close the printing environment and install humidifiers, air conditioners and other equipment to create an environment suitable for flexo printing; The climate in the south is advantaged for flexo printing, but due to the plum rain weather in the south, workshop dehumidification should be a key to create a flexo printing environment. Suitable for flexo printing environment temperature and humidity range is generally 6 Select the appropriate force value and gear and clear it: the temperature is about 25 ℃ and the humidity is 50% ~ 60%

operator quality

in label flexo printing, the human factor is also crucial. Operators shall mainly have the following qualities

1. high heart. The heart comes first. It is useless to talk about anything without the heart

2. have a certain understanding of mechanical principle and electrical knowledge. When operating the flexographic press, the mechanical and electrical characteristics of the press can be fully considered to avoid unnecessary waste in printing, and some problems existing in the press can be eliminated

3, have certain chemical knowledge foundation. When adjusting the ink, it can be considered from the physical and chemical point of view to make the ink achieve the best use effect

4. master various printing processes. Only after mastering various printing processes can we timely feed back some problems in the design and make the label design suitable for flexographic printing as much as possible, so as to save raw and auxiliary materials and avoid waste.

5. be good at summarizing. Only by summarizing and refining the problems in printing in time can we continuously improve our ability

at present, flexographic printing is favored by packaging and printing manufacturers because of its environmental protection, bright colors and stability. It accounts for an increasing proportion in label printing. Therefore, how to give full play to its characteristics is becoming a subject for the majority of flexographic printing workers. It is believed that flexographic printing will play a more important role in label printing on the premise that the state vigorously advocates environmental protection

information source: Printing Technology

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