Overprinting instructions for polypropylene plastic bottles
The monochromatic printing of the curved surface is supported by four rollers to support the printing material, and the screen plate moves to rotate the printing plate to complete the printing. However, the plastic bottle trapping printing cannot use this method. It is based on moving and static fixtures to clamp the substrate. Through the process of meshing the rack and gear, it drives the screen to move and the substrate rotates to complete the printing. The following outlines the process points in the overprint process.
First, all kinds of screen version need rules plate
The so-called rules plate contains two aspects: the same number of blank mesh screens with uniform tension are all coincident with the same position of the printing table; the positioning cross lines on several negatives are overlapped on the same position on the printing table. on.
1. Positioning of the screen: The positioning of the screen is relatively simple, and the positioning is generally performed using a square ruler or a three-point positioning block. The positioning block needs to have a certain thickness, can be made of 3~5 mm plexiglass, and is fixed on the printing platen with double-sided adhesive tape. If the frame does not have a 90° angle, the longest side of the frame must be placed with the positioning block or square Cushioning to ensure the flatness of printed graphics.
2. Positioning of the film: There are many methods for overlapping the film and the following two methods can be used. (1) Replacement method: When the first screen printing is finished, do not remove the negative film from the printing platen, place the second negative film on the first negative film, and make the positioning crosshairs overlap. One side of the transparent tape is fixed, and then the first negative is peeled off from the printing table. The replacement method is also called the left and right side shortage positioning method, that is, the same side of the bottom two negatives, the size should be changed. As shown in Figure 2, the size of the first film (A film) is slightly smaller (5~10 mm) than the size of the second film (B film), so that the second screen plate can be cured when the second plate is printed. A negative film can be smoothly removed from the platen. A number of negatives are positioned in the same way. (2) Center line extension method: When using the computer to separate the originals, each color separation sheet does not use the cross-line overlapping positioning method, but adopts the center line positioning method, that is, the center position of several sheets of the color registration film 4 positioning short lines, short length 5~10 mm, width 0.3~0.4 mm. When making a plate, lay the screen with the printing surface facing up and place it on the desktop. Draw the center line on the frame. Then place the film on the screen and use a ruler to connect the four short lines in the vertical and horizontal directions. Dislocation, correction is completed, with a transparent tape to fix the film on the screen, and then turn over the screen and the printing plate three-positioning block or positioning angle bracket can be aspiration of the print version.
Since the squeegee blade and ink-recovering blade of the curved surface printer occupy a large area of ​​the screen (about 200 mm), the screen is generally rectangular. In the printing process, only four points in the longitudinal direction are often connected accurately. , and the four points in the horizontal direction, there are 3 points or 2 points can be connected together (the frame squareness deviation). In this way, it can be ensured that the printed picture will not be tilted.
In addition, the rules and regulations also include two factors that cannot be taken lightly, that is, the correct choice of the number of screen meshes and the thickness of the photosensitive film. Mesh screens generally use 300-500 mesh yellow polyester mesh, solvent-based inks use 300 mesh screens, and light-cured inks should select 355 mesh screens. If there are long lines and bar code lines in the printed graphics, 22.5~30° diagonal stretch nets are also required. The smooth substrate film can be thinner, and the matte and grain-surface substrate film should be slightly thicker to increase the ink coverage.
Second, the gear and positioning pin sets of reasonable preparation
The surface color printing is a process in which the gear and the rack are engaged and the substrate rotates to complete the printing task. The rack is an inherent part of the press, and the gear is a component that changes at any time depending on the size of the substrate. The following principles should be followed in the selection of gears: The diameter of the substrate = the diameter of the gear, that is, the rotation perimeter of the gear should be consistent with the rotation perimeter of the substrate, and the tooth profile of the gear should also be perfectly matched with the rack. Screen printing plants generally do not have the ability to make gears themselves. The solution is to remove the rack and pinion holder from the press and send it to the mold factory or gear factory to ask them to process a gear of the right size. Because the ellipse is a part of a perfect circle, when equipped with a gear, be sure to find out the center and radius according to the actual object and then customize the gear. There are two points to note when making positioning fixtures: (1) The position of the positioning pin must match with the plastic positioning groove; (2) The fixture is generally made into a round shape. There is a bushing at the center of the disc. The bushing is tightened with the screw and the gear seat. The stainless steel band around the disc must also be welded into a retaining wall to prevent the plastic bottle from being pulled out of the chuck. Retaining wall height of 5 ~ 10 mm, oval plastic bottles should also be welded inside the retaining wall, the inner wall of the arc and the plastic bottle consistent.
For large-cone-shaped bottles (small taper), the conical jet head cannot directly hold it, and the substrate cannot be rotated. At this time, a T-shaped cover can be made of metal or nylon material. The diameter of the circle in the cover is equal to the diameter of the circle in the bottle. At the same time, an air inlet opening of about 20 mm is required on the cover to enable the conical air-jet head to hold the bottle. And inject air into the bottle.
There are two printing methods for conical plastic bottles: (1) The screen is parallel, the worktable is inclined, the rotation tangent of the bottle is always parallel to the plane of the screen; (2) The screen is inclined, and the squeegee and the ink-returning knife also follow. Tilt, adjust the method is to attach the bottom of the screen clamp with a wooden tape consistent with the taper of the bottle, so that the screen can be tilted to the angle we need, while loosening the blade clamp, using the horizontal screws on both sides to adjust the squeegee With the ink blade angle, make them parallel to the screen.
In addition, the profile of the conical plastic bottle on the screen is a flat shape, so the multicolor screen should have a starting point mark to facilitate the smooth progress of the color sequence overprinting work.
The rack is in parallel with the ground during the squeegee process. When the table is in a stationary state, the rack and the floor should be at a certain angle. The formation of the angle is caused by the rise or fall of the table, regardless of the rack In what condition, the nylon pressure roller on the rack should always maintain a good contact state, otherwise overprinting may occur.
Plastic bottle printing is divided into full-week printing and half-week printing. Cylindrical plastic bottles can be printed for the entire week, while oval plastic bottles can only be printed for half a week.
The color printing of plastic bottles can be carried out as follows: (1) Loosening the screen positioning stopper fastening screws on the optical axis, tightening the screen into the net clamp, and moving the screen slide holder left and right to make the ink scrape The cutters are beyond the 15~30 mm of the printed graphic. The distance to be exceeded depends on the specific size of the printed seams in the middle of the bottle body. Finally, the left and right positioning stoppers are tightened; (2) The bottom groove of the plastic bottle is aligned and positioned The positioning bumps in the fixture make the contact tight, and the bottle mouth is erected with a support frame so that the bottle body is parallel to the working platform. Rotate the bottle body so that the seam of the bottle body faces upwards to become the rotary center line of the substrate. Put the rack down and make contact with the gear. At the same time, place the rack roller on top of the rack and loosen the fastening screw. When the pressure roller and the rack are in good contact, the screws can be tightened to print the ink.
Third, the flame processor and color fastness
Plastic bottles made of polypropylene materials, because of their low surface energy and poor affinity with inks, can be used for printing only after being surface treated with a flame processor. The flame processor is composed of conveyor belts, tapered inserts, flame nozzles and gas tanks. When used, the plastic bottle is placed on the tapered insert and the conveyor belt moves forward uniformly. Before reaching the flame nozzle, the conical insert starts to rotate, and at the same time, the bottle is rotated, and the blue flame ablates the surface of the plastic bottle. Improve the surface energy of plastic bottles and increase the binding force with ink. The strength of the flame, the running speed of the conveyor belt, and the smoothness of the rotation of the bottle all directly affect the treatment effect, among which the smoothness of the rotation of the bottle is the most critical. The degree of smoothness is proportional to the size of the bottle. The shorter the bottle, the smaller the radius and the better the effect after treatment.
For larger bottles, we must take measures to increase its smoothness. The common method is to add a nylon sleeve to the tapered insert, the inner diameter of the sleeve is also tapered, and the outer diameter is the same as the size of the bottle mouth. The jacketed bottle cannot drop on its own and must be removed manually.
Flame-treated plastic bottles should be printed immediately. Multi-color overprinting should be selected light-curing ink, monochrome printing can use ordinary ink. With ordinary ink printing, color separation interval should not exceed 6 h, otherwise the plastic bottle surface energy is reduced, easy to secondary dust, affecting the ink adhesion. Smaller production units, the second or third color printing, can use high-quality two-component ink, the effect is also very good.
Fourth, the plastic bottle overprint work procedures
â— Place the printing plate in the folder, calibrate the position, and pour the ink into the blank starting point of the screen.
â— Turn on the circuit, start the air compressor and turn on the press air pressure valve.
â— Place the plastic bottle on the work platform support frame. The positioning groove at the bottom of the bottle is aligned with the positioning bumps in the positioning jig.
◠Press the “ICYCLE†and “STOP/START†keys on the operation panel, the work platform is raised, the substrate clamps the Cylinder, the plastic bottle is clamped, and the conical jet head injects air into the plastic bottle.
â— The ink-return knife rises, the squeegee falls into the screen, and it is in linear contact with the plastic bottle.
â— The rack and rack gears on the screen slide frame fully mesh with each other, causing the screen plate to move to the left and driving the plastic bottle to rotate. The ink is transferred to the plastic bottle under the effect of the squeegee squeezing force.
â— The squeegee ascends and the ink-jet knife falls. The screen plate moves to the right and stops at the starting point. The table falls, the clamping cylinder releases, and the plastic bottle is removed.
In short, with the development of society and people's increasing awareness of packaging, the market potential of surface printing is large; at the same time, it is increasingly developing in the direction of refinement. This requires screen printing companies to continuously accumulate experience in the production process and increase The level of technology can keep pace with the development of the times.
BNF HARDWARE CO., LTD , https://www.bnfhandles.com