Plastic screen printing process

First, the scope of application of plastic screen printing Plastic screen printing is not only simple, fast, wide application, and can be applied to other printing can not be applied to the production sector, such as the electronics industry, circuit board printing, glassware printing. Not only can be printed on the film, plane, three-dimensional, curved surface and can be printed on wood, plastic, glass, fabric. For example, clothing on the printing and design; boxes, bags, bags, folders, clothing, hats, shoes, printing and patterns; plastic folders, book covers, textile bags and other trademarks.

Second, the type and structure of plastic screen printing machine 1. Manual plane screen printing machine This is the most simple screen printing machine, flat screen platform, hinged connection. When printing, taking and placing printing materials, plate landing, ink scraping, ink return are all manual operations, the biggest advantage is simple, economical, regardless of the type of material, as long as the plane shape can be printed.
2. Plane platform lifting screen printing machine printing machine flat screen printing plate immovable, the plane table can be used for up and down movement, scraper for the horizontal direction to automatically scrape ink movement. The work balance and overprinting accuracy during printing can be used for multi-color overprinting.
3. Flat screen drum type automatic screen printing machine The machine consists of automatic paper feeding, printing mechanism, paper delivery mechanism and drying device. The screen printing plate used for printing is horizontally mounted on the frame. The squeegee printing platform is a roller type, and the blade can be moved up and down. Once printed, the screen moves left and right, and the blade moves up and down. The machine can be continuously automatic from paper feeding to printing, and it can also provide jog and semi-automatic devices according to different printing materials. This screen printing machine has high overlay accuracy and high production efficiency.
4. Circular screen platform Screen printing machine The screen printing plate is in the form of a roller. The squeegee is installed in a rotary screen plate. The printing worktable is a platform. Roll materials for printing materials. During printing, the flat table does not move, and the rotary screen plate rotates. The upright downward squeegee presses the ink. Through the overprinted part of the rotary screen, the horizontally moved printing material is exposed to ink and forms a print image. Text, this screen printing machine can be arranged in units, multi-color overprint, suitable for plastic film, textiles and other color printing.
5. Rotary cylinder type screen printing machine The screen printing plate and the embossing worktable of the machine are cylindrical. When the two rollers rotate during printing, the squeegee in the rotary screen plate presses the ink to hear the ink, and the printing material receives the ink through the over-ink portion of the rotary screen plate to form the printing. This screen printer is fast and suitable for high-volume prints.
6. Surface screen printing machine Surface screen printing machine can be divided into manual, semi-automatic and automatic curved screen printing machine. The screen plate is flat and can move horizontally around the sector axis. The printing material (cylindrical or conical) is supported by a rotating circular roller for synchronous rotation. Under the pressure of the vertical squeegee, the surface of the printing is in line contact with the screen plate, and the printing ink is squeezed on the squeegee. Depressed, printed on the surface of the substrate, forming a graphic. After each color is overprinted at the same location, it is rotated a certain angle (printed part), and then the printing plate is rotated and printed.
7. Conical side printing machine It is the same as cylindrical printing machine, mainly used for printing plastic containers, glasses and so on. Figure 34-1 shows the principle of various screen printers. The plastic cup (A) and the PE bottle (B) in the figure are both cones whose developments are a, b, c, d, and on the printing plate corresponding to e, f, g, h. The manual surface printer is shown in Figure 34-2.
The worktable can be lifted up and down, and the workbench is lowered when the substrate enters or exits. When printing, lift the table. Frames e, f, g, h are horizontally rotated with O as the axis, and the squeegee is fixed on Of, and can be swung up and down. When operating, first adjust the height of the four rollers on the worktable so that the substrate can contact the printer. Plate surface, and then install the frame, so that it is fixed on the fixing rod. The position of the table should be carefully adjusted and the position of the squeegee should be adjusted so that the printing plate is in close contact with the position of the substrate. Pour the ink into the plate frame, lower the table, place the conical printing member, raise the worktable, lower the squeegee, pressurize the plate, make the plate frame horizontally and the squeegee is in the screen printing. The pressure tool that presses the ink onto the substrate. The scraper is composed of two parts: an elastic rubber strip and a clamp that clamps the rubber strip. Rubber strips are available in natural rubber and urethane rubber. When printing, the front end of the squeegee is pressed against the inside of the printing plate to form an angle of 45°-70° with the platen, and the ink is pressurized and scraped so that the ink in the stencil frame passes through the opening and is printed on the printing member. The hardness of the squeegee rubber is based on The JIS K6301 is measured between 60 and 80 degrees. The rubber should have good abrasion resistance, and expensive fluoroelastomers can also be used. The eraser also needs good solvent resistance. The width of the scraper should be 2-10 cm larger than the edges of the image. Scraper can be ground with a fine grinding plate and talcum powder can be sprinkled during grinding.

Third, the screen printing operation procedures 1. Preparation before printing (1) Clean the surrounding environment, adjust the temperature and humidity of the workshop, rub the printer to prevent excessive dust.
(2) Prepare substrates and inks to understand their characteristics, and use suitable scrapers accordingly.
(3) ink mix, hue mix, viscosity adjustment, drying speed adjustment.
(4) Prepare and inspect the drying device.
2. Install the silk screen plate (1) to establish the position of the plate. According to the specific structure of the screen printing machine to determine the correct position of the printing plate, should be in the appropriate position of the bearing. Especially when the screen is overprinted, the vertical and horizontal position of each color should be carefully adjusted to make the overlay accurate.
(2) High speed and control of the gap between the plate and the substrate. Layout size is large, clearance should be larger; tension of the stretching net is large, sag of the screen is small, and the gap can be smaller; the metal wire mesh is more rigid than other materials, so it is not easy to droop, the gap can also be smaller; the ink is thin, The gap should be larger.
3. Test printing, observe the hue of the ink, the thickness of the printed coating, and the overprinting accuracy. Then adjust and then officially print. During the printing process, attention should be paid to the printing quality to prevent jamming and other accidents.
4. After the printing is finished, excess ink should be collected together and the printing plate should be washed with solvent to avoid agglomeration. After cleaning, remove the plate and stand upright in a clean place.

Fourth, screen printing common faults and troubleshooting

Table 34-1 Screen Printing Common Faults and Troubleshooting Methods
1. The ink is drying too fast
2. High viscosity
3. Poor ink quality 1. Use slow-drying solvent
2. Dilution with solvent
3. Change ink 1. The ink viscosity is too low
2 ink drying too fast
3. Printing speed is too slow
4. Ink quality problems 1. Increase the viscosity, less diluent
2. Use slow-drying solvent
3 speed up the printing speed
4. Replace ink 1. Less driers in ink
2. Use too much slow-drying solvent
3. Drying time and temperature are insufficient
4. Ink quality problems 1. Increase driers
2. Reduce the amount of slow-drying solvent
3. Increase drying time and temperature
4. Replace ink 1. The ink dries too slowly
2. Insufficient drying temperature and time
3. The printed material is not properly stored; the temperature is too high or it is under pressure 1. The quick-drying ink is used
2. Increase drying temperature and increase drying time
3. Improve storage, prevent pressure and reduce room temperature Bad ink itself
2. Use wrong solvent
3. Bad prints 1. Ink replacement
2. Use the specified solvent
3. Replace the substrate Insufficient drying
2. The solvent has a bad smell
3. The ink itself has an odor 1. Thoroughly dry
2. Use odorless solvents
3. Replace ink


Questions and Answers from Students in Previous National Soft Plastic Packaging Seminars

(a) The factory has several twin-screw extruders to produce low-foaming PVC foam boards. Currently, the market is small. We want to develop some new products. What new products are better developed?
The following products can be developed using twin-screw extruders: (1) Silane cross-linked PE cable material or silane-crosslinked PE hot water pipe granulation; (2) Thermoplastic polyurethane and PVC blend alloy material, can be used for pressure oil pipe (3) Production of various color masterbatch and functional masterbatch, such as double-degradable masterbatch, flame retardant masterbatch, antistatic masterbatch, conductive masterbatch, anti-fog drop masterbatch and so on.
(b) OPP / anti-printing / two-component PU glue / VMAlPET dry compound produced after the chicken skin, dry complex drying Road 3m long, 60 °C temperature, why?
The possible causes are: (1) VMAlPET shrinkage at drying temperature; (2) Ethyl acetate in dry reusable adhesive causes shrinkage of PET film. It is possible to pay attention to the low drying temperature - high-low arrangement, and to reduce the amount of vinyl acetate in the adhesive. The amount of ester used to increase the solids content. Spread the coating on the reverse printing ink and dry it thoroughly.
(3) When printing is reversed, it is printed in the order of black, blue, red, yellow, and white. Sometimes it cannot be printed in one color. Why?
The reverse printing must use the same ink factory production ink, can not be mixed with different ink factory production, but can not be mixed with offset printing ink, otherwise it will produce two kinds of ink is incompatible, can not be colored. Mixing two types of incompatible inks will result in the phenomenon that the latter color cannot be inked. On the other hand, the ink contains many brighteners and is not easily colored. Pay attention to using the same type of ink from the same manufacturer.
(d) Two-component high-temperature cooking ink (produced by Shenzhen Shenri Ink Factory) Because black, blue, and red inks are used in small quantities and light in color, in order to prevent blocking, no curing agent is added to the first few color inks. Just add curing agent in white ink, but the fine lines are still not printed. What is the reason?
Be careful not to print in humid climates, as water vapour in the air will also cure the two-component polyurethane ink. In particular, it is easier to absorb moist air on the plate roller and gather moisture on the plate roller, so pay attention to the relative humidity in the air.