How to do the offset prepress design

How to do the offset prepress design

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“A good start is half the success”. Regardless of the type of printing method, the prepress design is closely related to the printing and finishing process, and directly affects the quality of the printing and the control of the process. There are many details and elements that need attention in the prepress design. The author now combines the characteristics of our existing printing equipment and offset printing to discuss the issues that need attention and consideration in the prepress design.

Printing color arrangement

Monochrome offset printing machine color arrangement

The monochrome offset printing machine is a wet-stack overprinting, and the printing color sequence is generally: cyan, magenta, yellow, black. In order to minimize the overprint chromatic aberration and better bring out the important colors of the graphic, a reasonable printing color sequence should be adopted. For example, the graphic with red as the main color should be printed in the order of magenta and yellow, so that the main color can be highlighted. In addition, in the printing process of the monochrome offset printing machine, it is possible to first print the yellow and black which are not particularly high in the accuracy of the overprinting, and the paper is gradually stabilized and then printed with the post-printing color which requires high precision of the overprinting, which can effectively avoid the cause. The post-printing color has high requirements on overprinting accuracy and causes inaccurate overprinting, thereby improving the quality of the printed product.

Two-color offset printing machine color arrangement

In the printing process of two-color offset printing machine, 1 color and 3 colors are wet overprinting, and printing of 1-2 color and 3-4 color is wet wet overprinting. Therefore, the following printing color sequence is generally adopted: 1-2 colors are magenta - Blue or Cyan - Magenta, 3-4 colors are black-yellow or yellow-black, but flexible adjustments are also required according to specific requirements. If you want to highlight an important color (such as green), you should print in the magenta-yellow, cyan-black overprint order to achieve better printing results.

Four-color offset printing machine color arrangement

The printing color sequence of the four-color offset printing machine is generally black, cyan, magenta, and yellow, and the order of cyan and magenta can be flexibly changed in the view. Multi-color printing (more than four colors) color sequence arrangement is more complicated, in general, large area spot colors should be arranged behind the color group, but need to be placed in front of the yellow. Gold and silver inks are generally placed in the later color group, and the overlays of the dots and the field must be placed in front and placed in the back.

The transparency of the color is also considered in the process of color sequence arrangement. For example, black ink and red ink are printed at the same time, because red is a transparent color, so no matter which ink is printed first, the red ink cannot completely cover the black ink. If the white ink and the black ink are printed at the same time, no matter which ink is printed first, the portion of the black ink and the white ink overprinting always has a fading effect. Therefore, when wet-wet printing, white ink, gold ink, and silver ink cannot be overprinted simultaneously with other color inks, and must be printed twice or hollowed out. However, when UV printing is used, overprinting of white ink and other color inks can be achieved. This is because a UV lamp is added between the color group and the color group to cure the first printed white ink, and then overprint other inks. At this time, the white ink is generally arranged in the first two color groups.

In addition, the color sequence arrangement also needs to consider the viscosity of the ink. If the viscosity of the post-printing ink is large, the ink anti-stick phenomenon will occur under the action of the viscoelastic force, thereby affecting the overprint quality. Therefore, in general, the printing color sequence of the ink viscosity should be used to ensure the quality of the printed product.

Hot stamping design elements

When designing the hot stamping parts of the printed products, it is necessary to pay attention to: when using the method of hot stamping and printing, it should try to avoid printing white ink on the anodized aluminum. This is because the printing products are prone to ink in the printing process. The visual effect will be very obvious, which is not conducive to the special effect of the first hot stamping; the large area is designed as much as possible, and the UV lamp is used for curing to prevent the ink from being reversed.

For packaging and printing enterprises that do not have a round stamping machine, it is also necessary to pay attention to the area of the hot stamping pattern of the hot stamping product, which is not too large, because large-area hot stamping is prone to quality problems such as white spots and bubbles. In addition, the first hot stamping is to make the ink layer not thick, the color depth transition is gentle; the hot stamping line can not be less than 0.12mm, and the embossed line can not be less than 0.09mm.

Spot color design elements

When designing the spot color, try to avoid printing two pieces of spot color after designing the white ink, and directly print the two spot colors, which can ensure the consistency of color in a large number of printing production, and it is not easy to have chromatic aberration.

In the prepress design, if there is an offset printing on the offset screen, the pearlescent ink should be selected, and the 500 mesh screen printing should be used for printing. If the larger pearlescent ink (300 mesh screen printing) is selected, The ink layer is thicker and has a strong hiding power, and almost 60% of the dots are covered, and the transition net cannot achieve the design effect.

Hollow overprint design elements

When the normal offset printing is overprinted, the whitening size is uniformly 0.05~0.08mm. For the printing with larger ink volume, the whitening size can be increased to 0.10~0.15mm. When the offset printing is followed by screen printing, the hollow overprint design will be carried out. The size of the white mark should be increased by 0.15~0.25mm. Because the screen printing ink layer is thicker, the ink curing method is light solid or dry. Therefore, when white cardboard or glass paper is used as the printing material, the number of screen printing is as small as possible. More than twice. If the customer has a need for secondary screen printing, the exact position of the second screen printing needs to be determined based on the deformation of the paper.

When the product has a need for embossing surface finishing, it is necessary to design the embossed version according to the customer's needs. When designing the embossed film, the pattern needs to be reduced by 0.1mm than the actual pattern. If a special bitmap is displayed, it cannot be retracted in the pre-press electronic file. The entire embossed film should be kept at the original size, and the plate making workshop is notified to make the whole at the time of plate making. Abbreviated.

Choice of dot angle

In the prepress design, the design of the dot angle is particularly important. If the design is not correct, the printed matter is prone to interference fringes during the printing process. Common dot angles are 15°, 45°, 75°, and 90°. Among them, the 45° screen angle has the best performance, stable and not dull; the 15° and 75° screen angles are relatively poor, but the visual effect is not dull; the 90° angle is the best. But the visual effect is the worst, it looks very dull. Under normal circumstances, the normal dot angle is cyan 15°, magenta 75°, yellow 90°, black 45°, and the main tone dot with a large amount of ink in the design before the cigarette package is printed with 45° mesh angle output to achieve the most Good printing results.

Precautions

When designing a large version, attention should be paid to designing auxiliary marks, such as pull gauge lines, cross lines, and color mark points, to facilitate inspection and proofreading during process realization, and is also an important identification indicator for print quality control. Under normal circumstances, the size of the bleeding should exceed 2~3mm of the finished product size to avoid problems such as misalignment and whitening during die cutting or cutting.