First, the arrangement of printing colour sequence

   Gravure printing in flexible packaging, the arrangement of the printing colour sequence is very critical, generally follow the following rules.

(1) the printing ink printing colour sequence in accordance with the rules from deep to light to arrange, generally black, green, magenta, yellow, white.

(2) surface printing ink printing colour sequence in accordance with the rules from light to dark to arrange, generally white, yellow, magenta, green, black.

(3) Spot-colour inks are generally arranged before white ink and after yellow ink, and can also be arranged after black or tri-colour inks, but are generally not arranged between cyan, magenta and yellow inks. Usually, a printing job should not be more than three kinds of spot-colour ink.

　　It should be noted that, for the more stringent overprinting requirements of the pattern, cyan, magenta, yellow, three mesh toning colour should not be added between any spot colour, and for the series version, sometimes to ensure that the printing process does not replace the ink tank, the requirements of the printing colour sequence must be consistent. In addition, because the surface printing ink is more vivid than the colour of the printing ink, so it is customary to use the surface printing ink when sampling, but in some special cases, such as the customer provides a colour sample, the need to use the anti-counterfeiting version, the need to print gold ink or anti-counterfeiting ink and other special inks, but also pay attention to the surface printing ink printing colour sequence for reasonable arrangements and adjustments.

Expansion and contraction of adjacent colours

　　In the gravure production, in order to make up for the overprinting is not allowed and caused by the adjacent different colours between the resulting leakage of white, usually need to expand the printing part of the processing, also known as the trap or make up for the leakage of white.

　　When the two colours of the ink connected, stacked, cut, generally need to do the expansion processing, and sometimes also mutual expansion, in special circumstances, it is necessary to carry out the reverse expansion, and even in the adjacent two colours to make up for overprinting errors by increasing the gap between the two colours in order to make the printed matter more beautiful. Expansion and shrinkage treatment generally follow the principle of: expansion of the next not expansion, expansion of shallow not expansion of deep, expansion of flat network not expansion of the field.

　　The size of the expansion should be based on the characteristics of the substrate material, the overprint accuracy of the printing press and printing methods vary. In general, offset printing expansion and contraction to be smaller, gravure and flexo printing expansion and contraction to be larger, generally 0.2 ~ 0.3mm (according to the printing accuracy and other specific requirements), similar to the colour of the expansion and contraction is usually 0.3mm, the opposite of the colour of the expansion and contraction of the amount is usually 0.2mm, and also requires the expansion of the printed pattern is not deformed.

Third, the determination of surface tension

　　In actual production, the surface of the printed film should be corresponding corona treatment to ensure that it has a reasonable surface tension. Determination of surface tension of the printed film is generally: the use of cotton swabs dipped and the size of the measured film surface tension corresponding to the dyne liquid, coated on the surface of the film with a length of 10mm or so of the liquid film. If within 5 seconds, the liquid film film surface does not shrink or shrinkage is small, it can be considered that the film surface tension qualified; if the liquid film completely ruptured or contracted to a length of less than 8mm strip, it can be considered that the film surface tension is not qualified.

Fourth, the determination of the direction of the roll

　　Composite process should pay attention to check whether the composite material rolls used by the same designated manufacturers to provide special material composite material rolls have special requirements, but also to determine the direction of the special film (such as yin and yang film) out of the roll is correct.

　　Out of the roll to determine the direction of the principle of: the first stroke of the text or the first letter of the word first for the head out, to the end of the text or the last letter of the word first for the tail out; to the top of the pattern or the left side of the first out of the head out of the pattern underneath or the right side of the first out of the tail out of the first.

V. Determination of ink and adhesive viscosity

　　To get good printing results, the production process should also pay attention to the determination of ink and adhesive viscosity. Determination method: in the Charn cup filled with ink or adhesive to be measured, with a stopwatch to determine the ink or adhesive from the bottom of the cup small holes out of the time to determine the viscosity of the ink and adhesive.

　　In addition, it is necessary to understand and be familiar with the manufacturer of the selected ink, the scope of application and solvent ratios, in order to ensure the accuracy of the measurement data.

Sixth, control the production of signs

　　In order to ensure that the printed film overprint accuracy, as well as to facilitate the subsequent bag making, cutting work smoothly, usually need to make some of the printing plate for the location of the control and judgement of the logo. In the production process of the control mark should pay attention to the following issues.

(1) the production of cross register mark: cross register mark is generally used in conjunction with the bar mark, the number indicates the printing colour sequence, respectively, produced on each colour printing plate.

(2) Mark line (light point logo) production: Mark line in the slitting bag can play a role in tracking the role of slitting, generally use the darkest colour, the width is greater than 2mm, less than 10mm, the length is generally greater than 5mm.

(3) the production of detection line: detection line is mainly used to ensure that the film in the slitting, bag making horizontal not run, the colour is generally dark.

Seven, printing quality control points

　　The main points of printing quality control include colour difference, registration deviation, ink fastness, defect detection, etc. The basic requirements are as follows.

(1) Colour difference: ΔE≤5, ΔH≤1.5 for spot-colour part; ΔE≤5, ΔH≤2.5 for light-colour part.

(2) Overlay deviation: the main pattern overlay deviation of bi-directional stretch films is required to be ≤0.20mm, and the secondary pattern overlay deviation is ≤0.35mm; the main pattern overlay deviation of non-bi-directional stretch films is required to be ≤0.30mm, and the secondary pattern overlay deviation is required to be ≤0.60mm.

(3) Ink fastness: usually 24mm wide, 250px long transparent tape pasted on the printing surface, the tape will be torn open, and observe the ink left on the printing surface of the paste to judge.

　　In addition, in the printing production can also use the strobe light (synchronous light) to observe the knife line, stains, lost points, colour registration and other abnormalities occur.

　　Thousands of miles of dike, collapse in an ant hole, gravure printing process is often because of the neglect of these small details and caused by the larger quality problems, therefore, gravure production must pay special attention to these subtleties, in order to ensure high-quality printing results.

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