Plastic bottles made of polypropylene material through injection molding process are basically outer packaging materials for light industrial products, such as cosmetic bottles, detergent bottles, drinking bottles, grease bottles and the like. These bottles are very good in weather resistance, chemical resistance and mechanical strength and are therefore commonly used in the packaging industry. The smaller bottles are made into a cylindrical shape, a conical shape, and an elliptical shape. These curved body bottles are generally printed using a domestic semi-automatic curved printing machine, and the overprinting color does not exceed 3 to 5 colors. Optical Lenses,High Precision Optical Lenses,Large Diameter Optical Lenses,Plano Convex Cylindrical Lenses Changchun Bena Optical Products Co., Ltd , https://www.benaoptic.com
The monochrome printing of the curved body supports the substrate by four rollers, and the movement of the screen drives the substrate to rotate to complete the printing, and the plastic bottle printing cannot use this method. It is to clamp the substrate by the moving and static clamps, and through the occlusion process of the rack and the gear, the movement of the screen and the rotation of the substrate are rotated to complete the printing. The following is a brief description of the process points in the overprinting process.
First, the various color screens need to be ruled and plated. The so-called rule plate has two aspects: the blank screens with the same number of meshes and the same tension are coincident with the same position on the printing table; the positioning cross lines on several overprint negatives overlap. On the same position on the printing table.
1. Positioning of the screen: The positioning of the screen is relatively simple, generally using a square or three-point positioning block positioning. The positioning block needs to have a certain thickness. It can be made of 3~5 mm plexiglass and fixed on the printing table with double-sided tape. If the frame is not at 90° angle, the longest side of the frame must be positioned with the positioning block or square. Rely on, to ensure the flatness of the 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 is finished, do not remove the film from the printing table, but place the second film on the top of the first film and make the positioning crosses overlap. Scotch tape is fixed on one side, and then the first film is removed from the plate. The replacement method is also called the left and right side shortage positioning method, that is, the same side of the upper and lower negative films, and the size should be changed. The size of the first negative film (A piece) shown in Figure 2 is slightly smaller than the size of the second negative film (B piece) (5~10 mm), so that when the second screen is made, the first A negative film can be successfully removed from the printing platform. The positioning of several negatives is similar. (2) Centerline extension method: When using a computer to separate the originals, each color separation film does not use the method of overlapping the crosshairs, and the centerline positioning method, that is, the center positions of several sets of color negative films are 4 positioning short lines, short line length 5~10 mm, width 0.3~0.4 mm. When making the plate, put the screen printing face up on the desktop, draw the center line on the frame, then place the film on the screen, and use the ruler to connect the four short lines in the vertical and horizontal directions together. There is a misalignment, after the correction is completed, the negative film is fastened to the screen with a transparent tape, and then the screen is turned over and pressed against the three-point positioning block or the positioning square of the printing table to inhale the printing plate.
Because the curved printer squeegee and ink repellent knives occupy a large area of ​​the screen (about 200 mm), the screens are generally rectangular, and in the process of printing, often only 4 points in the vertical direction are connected accurately. And 4 points in the horizontal direction, 3 points or 2 points can be connected together (the square squareness is biased). This will ensure that the printed graphics will not be tilted.
In addition, there are two factors that cannot be underestimated in the plate making, that is, the correct choice of mesh size and film thickness. The screen is generally made of a yellow polyester mesh of 300 to 350 mesh, the solvent type ink is a mesh of 300 mesh, and the photocurable ink is selected to be a mesh of 350 mesh. If there are longer lines and bar code lines in the printed graphic, it is necessary to use a 22.5~30° oblique stretch net. The smooth substrate photosensitive film can be thinner, and the matte and grain surface substrate photosensitive film should be slightly thicker to improve the ink hiding rate.
Second, the gear and the positioning pin sleeve of the reasonable preparation of the surface color printing is through the gear and the rack bite process, driving the substrate to rotate to complete the printing task. The rack is an inherent part of the press, and the gear is a component that changes over time depending on the size of the substrate. Optional gears should follow the following principles: substrate diameter = gear diameter, that is, the rotation circumference of the gear should be consistent with the rotation circumference of the substrate, and the tooth profile of the gear should also match the rack. Screen printing factories generally do not have the ability to make their own gears. The solution is to remove the rack and gear mounts from the press and send them to the mold factory or gear processing factory to process a gear of the right size. Since the ellipse is part of a perfect circle, when gears are equipped, it is necessary to find the center and radius of the object and then customize the gear. There are two points to note when making the positioning fixture: (1) The positioning pin position should match the plastic positioning groove; (2) The fixture is generally rounded. The center of the disc is provided with a sleeve, and the sleeve is screwed with the gear holder. The circumference of the disc is also welded with a stainless steel strip to prevent the plastic bottle from being pulled out of the chuck. The height of the retaining wall is 5~10 mm. The oval plastic bottle should also be welded with the inner retaining wall. The inner retaining wall has the same curvature as the plastic bottle.