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Understand the metal packaging wire printing from the aspects of design and quality (III)

III. The quality characteristics and requirements of metal packaging wire printing. In terms of its process, the printed patterns and lines must be clear and the ink layer must be full, which is related to a series of printing data such as the number of wire mesh, tension, printing pressure, printing speed, ink viscosity, etc

1. Carefully select the silk

determine the silk according to the printed characters and lines, and generally use 300~350 mesh silk. Although better printing effect can be obtained by using more than 350 meshes of silk, due to the thin ink layer, the anti-corrosion ability of the drilling plate will be weak in the subsequent process. The selected silk shall be tightened under 8 tensions, and the glued frame and glue surface shall be placed upside down on the tightened silk surface for reverse tension, so as to tighten several small pieces at the same time and save silk. The frame can also be arranged at any angle to avoid right angle tension and reduce the chance of sawtooth when printing

2. Stretching

when printing general graphics, manual stretching can be used, which saves both money and labor. When printing complex or detailed graphics, the tension first affects the printing accuracy. If the tension is too small, almost all the consequences are unclear printing. Therefore, mechanical or pneumatic tensioning must be adopted. When stretching, the tension should be gradually increased. Do not pull to the required tension at one time. The wire shall be leveled evenly. When the tension reaches, it is necessary to use testing equipment to test whether the external wall insulation material is qualified. It shall be left for a few minutes before bonding. It is best to let the stretched one stand for 3~4 days, place it flat on the desktop or other places that are not easy to touch, and use it after the tension is uniform

3. Silk degreasing treatment

wet the silk with running water, apply washing powder or detergent on both sides of the silk, and scrub with a brush, which can not only remove the fingers, but also coarsen the silk. The alkaline detergent must be washed under running water, otherwise it will affect the quality of plate making

4. Drying

dry the washed silk in a ventilated and dust-free place or in an oven. The drying factor should not be too high to avoid affecting the deformation of the silk

5. Plate making

as silk printing requires clear patterns and characters. The ink layer is full, which requires a high-quality version. First of all, two situations should be excluded: the first is that the photosensitive film is too thin, and the printed patterns and lines are not only unclear, but also jagged, scattered lines, and blunt edges and corners; The second is that the photosensitive film is too thick. Although a large amount of pressure is added to the printing process, which can not bear the hypothetical consequences of electric leakage, the ink layer is still very thin, and the lines are seriously broken, which can not withstand the corrosion of liquid medicine. Therefore, the thickness of photosensitive film on 350 mesh silk is better than that of 242 scraping method. Among them, the scraping speed and the inclination of the scraper are also the main factors affecting the film thickness. The glue scraping speed should not be fast. Moving the scraper slowly can not only eliminate the bubbles in the glue solution, but also obtain a uniform photosensitive layer. The included angle between the back of the scraper and the wire is 25 °. The force of both hands should be uniform when scraping

it is worth mentioning that the printing accuracy of plate making with photosensitive adhesive is not as high as that of capillary film, but the printing resistance of film is not as good as that of photosensitive adhesive. So immediately after the coating of photosensitive adhesive, stick a piece of polyester film on the non printing surface, and use the scraper to press and scrape twice to drive away bubbles and prevent pinholes; Then it is put into the oven for low-temperature drying, and the temperature is controlled at 40 ℃ within a short time of 1 year; After drying, take out the silk, remove the polyester film, and then dry it for 1~2 minutes to expose. This method of "changing" the film film with photosensitive adhesive can improve the printing accuracy of silk

6. Exposure

most of them adopt solar exposure. Exposure shall be conducted for 30~45 seconds according to the content of photosensitizer. Before exposure, the negative film shall be inspected and cleaned to remove dust and stains. If the wire is facing up and the frame is facing down, a piece of black paper or blue carbon paper shall be clamped between the liner and the wire to prevent light refraction, resulting in unclear patterns or difficult development

7. Development

after the exposure, the development shall be put into operation immediately, and the plate shall be soaked in 30 ℃ warm water for 1~2 minutes, and the unexposed film shall be sprayed with tap water until the pattern is clear

8. Drying

absorb excess water with a sponge and dry it naturally under the ventilated sun or in a 40 ℃ oven

9. Revision and sealing

proofreading and revision with negatives, closing the holes outside the pattern and drying, which can be delivered to the printing process

10. The printing

adopts self drying corrosion-resistant printing ink to keep the distance between the plate and the metal packaging surface 3~4 mm; The scraper is required to be sharp, straight and without notch, and scrape from front to back. The scraper is inclined at an angle of 45 ° and parallel. It is not suitable to scrape ink too fast. Try printing for about 10 times. If the ink leakage is normal and the pattern is clear, batch printing can be carried out. In order to reduce the workload of the patched version, it is better to check the printing quality every 10 times so as to correct it in time. Often due to the dry environment and serious dust, white spots and hazy lines appear on the printing plate, which is mainly caused by the particles in the dust and ink. Wipe the dirt with cotton wool dipped in an appropriate amount of diluent. After printing, the edition shall be cleaned in time. Generally, propionic acid cleaning solution is better. When it is irritating to the skin, the ink stuck on the surface is easy to wash away. The cleaned version shall be wrapped in time and properly placed for reuse

11. Maintenance of printed parts

the printed parts shall not be directly corroded. After the printing ink is completely dry, carefully inspect and repair the deficiencies in the printing plate by plate; The places to be filled shall be repaired with plate making glue, and the unclear characters shall be modified with iron pen; Self inspection, mutual inspection and special inspection shall be carried out to control the deficiency of printing quality at a minimum, and then the next process can be carried out

12. Reasonably select ink

for multi-color overprint in layers, the next color shall be printed only when the previous color is dry enough to resist sticking. Once the latter color is damaged, do not rub the background color when erasing it. In order to ensure the yield and reduce the repair difficulties, the ink types and diluents are screened

when the background color on the surface of metal packaging is light, UV white ink can be added to resin ink for color matching to ensure uniform color matching. After printing, the color ink particles will be firmly embedded due to the curing of UV ink. The surface will not become sticky, and the next color can be printed immediately. The next color ink can be thermosetting metal ink, which is heated and cured after printing. It can not only obtain ideal adhesion and hardness, but also obtain a pearl like shiny background that is not expected at present. The general solvent will not be wiped off, so it is convenient to repair

13. Prepare the printing scheme and chromatic sequence before printing

use a non sticky coated paper for trial printing, check whether the picture and text are lacking, whether the blade is straight, whether the distance is appropriate, and whether the ink color is uniform. Try printing for 2~3 times, and formally print after the ink is uniform. During printing, continuous pictures and texts can be scraped by a large scraper at one time. For separated pictures and texts, small scraper of various specifications can be used for local printing. Lift it after all printing. A small area is easy to obtain a flat surface. After printing, the handwriting is full, and there will be no difference in depth

14. Silk cleaning is very important.

a little ink remains in the picture and text, especially in the recycled frame, which will cause masking holes, and the reproduction degree of the picture and text will be affected, that is, the printing defect. The silk can be wiped clean with the following methods

⑴ wipe with ink cleaner to remove the ink, but the smell is strong

⑵ wipe it with banana water, which has a small taste and a large amount of cotton yarn

⑶ wipe with cotton yarn dipped in alcohol, the ink leaves the surface in the state of film removal, and then wipe it with ink cleaner. This method is convenient and efficient

in a word, the best process conditions should be selected for every link from design to substrate production, from silk preparation to silk plate production, and from ink selection to printing

source: China steel drum packaging

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