1. Determination of the number of screen lines for color separation:

When people observe at the same distance from the printed matter, they will not be distorted, but they can also reproduce at a fine level, and the hue and saturation are in the normal range, which should fully consider the relationship between the screen and the observation distance.

2. Selection of screening angle:

Choosing a good screening angle is an important link to reduce the turtle grain phenomenon. In color reproduction, different screening angles must be adopted for color separation of different colors, so as to suppress moire as much as possible. Therefore, for eye-catching color (cyan, magenta, black) version, the difference between screening angles is 31. The yellow version is an inconspicuous color. You can write the difference of other colors by 15, such as the specific screening angle of four-tone screening.

3. Application of color ink-jet printing technology in making outdoor advertising light boxes:

Ink-jet printing is a pressureless printing method that uses computer control to obtain characters and images by fine ink flow from nozzles onto the substrate. It integrates the technology of electronics, machinery, fluid, ultrasound, microcomputer and other disciplines, and has become one of the high and new technologies in the field of color printing. In recent years, large-scale outdoor advertisements have adopted ink-jet printing technology, which makes the tone level, clarity and color saturation of outdoor advertising light box patterns almost perfect.

(1) Composition system of ink-jet printing:

The ink-jet printing system consists of system controller, ink-jet controller, nozzle, substrate driving mechanism, substrate, etc.

the output dot of inkjet printing system is the key factor to determine the printing quality. The size of ink dots is expressed in dots per inch. Color picture printing generally has 311dpi, 611dpi, 721dpi, 1124dpi and so on. Some large-format advertising posters can meet the requirements by printing with 9 ~ 72 dpi.

(2) types of inkjet printers:

inkjet printers can be divided into continuous inkjet printers and intermittent inkjet printers.

(3) color ink-jet printing:

The host computer of color ink-jet printing system receives color information through a variety of different information sources, such as color graphic terminals, color scanners, digital cameras, color word processors and other analog or digital manuscript acquisition systems. The information source sends the information of three primary colors of spring light, namely red, green and blue, to the printer interface, and stores the information to be copied in the main memory. Then, the color converter converts the information of red, green and blue into the color separation and screening signals of cyan, magenta, yellow and black ink, and then the gray controller controls neutral gray, and sends the ink signals of the above four colors to the electrodes of the corresponding color nozzles to control the nozzles to spray ink.

(4) Ink-jet printing materials:

A. Color-developing materials:

Advanced special inks for yellow (y), magenta (m), cyan (c) and black (k) suitable for color ink jet. Their printing performance must be stable, non-toxic, not blocking the nozzle, and have good ejection performance, such as the performance index of a liquid ink.

At present, a wax-based solid ink is widely used, and its coloring material is pigment, which has excellent light resistance and is not easy to fade. The printing process is fixed on the surface of the substrate and does not penetrate into it, so the imprint has good clarity.

B. Printing materials:

The types of printing materials that can be used are mostly special paper, inkjet film and outdoor advertising light box cloth. As far as paper is concerned, in order to prevent the spread of ink spots on the paper, the surface of the paper is required to be smooth, and high-gloss photographic paper is generally used, and its surface is coated with an extremely thin transparent coating.

4. Application of color screen printing technology in making outdoor advertising light boxes:

Screen printing is an ancient and unique printing technology, which has advantages that other printing methods do not have. It has a considerable proportion of applications in various types of outdoor advertisements, and has the advantages of mass reproduction and low cost.

(1) The key of color screen printing lies in the plate-making of color continuous tone images, and there are several key issues to be considered in the plate-making process:

A. The proportion of screen plates must be considered in the enlargement of images.

B. normally, the original is a positive image, but if it is printed on a transparent material, the original should be a positive image.

C. The screen angles of yellow, magenta, cyan and black films should not only avoid mutual interference and turtle lines, but also consider the influence of warp and weft square doors of the screen on color reproduction.

(2) Matters needing attention in material selection and technological process:

A. All four mesh frames should be made of metal frames, and the specifications should be exactly the same.

B. The screen should be dyed with high precision and anti-halo, and its mesh number is determined according to the magnification of the printed pattern.

C. when stretching the net, the four plates shall be carried out on the same equipment or under the same conditions. It is appropriate to adopt the method of "one net stretching four" to ensure that the tension and accuracy of the four net frames are consistent. The stretched net should be left for 1 ~ 2 days before use to ensure that it is fully "slack".

D. the template is made by direct method, and the coating thickness of photosensitive adhesive should be uniform. When printing, keep the air extraction, light source, exposure time and development on the same step (with the plate ladder). Templates should be stored and used under specified conditions.

e. use a large or precision screen printer for printing, and control the temperature in the operation room at 18℃ ~ 25℃ and the humidity at 51% ~ 71%.

F. The screen spacing of printing should be as small as possible, so as to improve the overprinter accuracy and reduce the moire phenomenon.

g. the length of the scraper should be consistent and the pressure should be small. The angle of the doctor blade is about 75 ~ 81, and the hardness is slightly higher, that is, the Shore hardness is about 71, and the blade should be sharp.

H. uniform ink should be thin (about 21μm) and uniform to prevent ink from filling the mesh.

i. The choice of ink must be matched with the undertaking materials, and the spectral characteristics of tricolor ink should be better, the transparency should be higher, and the viscosity can be slightly higher, so as to make the dot stand up and avoid expansion. It is advisable to use ink that dries slowly on the printing plate and prints quickly.

J. Before printing, all kinds of printing materials must be treated with material suitability.

K. Generally, the printing color sequence is printed with darker non-dominant color first, and then with dominant color, so as to facilitate overprinting. If the printing color sequence is printed on transparent plastic materials, it should be reversed, and the background color should be printed first, and then overprinted according to the color sequence.

The pattern making of outdoor advertising light box seems simple, but in fact, it is very particular. A good design style and pattern configuration can determine the quality of outdoor advertising light boxes.