Film positioning
No matter how the positive film is made, the positioning of the film is very important. It is necessary to ensure the orientation of the emulsion surface of the film during pad printing so that the emulsion surface is in close contact with the pad plate during exposure printing.
Because different printing processes have different film orientations, people often confuse the orientation of the film. The orientation diagram of the film describes how the image should be oriented during exposure exposure.
The orientation of the film is usually referred to as "emulsion facing down", which means that when we look at the film, the above is the image we need to print, and the emulsion should be on the back of the film.
When printing a positive image on a special paper with a laser printer, the printed image should be reversed because when the image of the printed paper is brought face down on the pad, the ink transfer agent will directly contact the surface of the plate.
When using a dry film imaging system, the image and the film are integrated, not attached to the surface, so there is no problem with the orientation of the film. This type of imaging sometimes causes “halo†phenomena in the image, and the sharpness of the edges is not good, especially when printing small-sized symbols or fine lines.
Be sure to ensure the cleanliness of the film as much as possible, especially when printing plastic plates. Be sure to remove all stains, ink, residual emulsions, etc. before printing. Pay particular attention to the area of ​​the image to be imprinted by the transfer head.
Image distortion
There are some distortions when the printing head prints on the surface of the printing material, but sometimes the original needs to be deformed, such as printing on the combined triangular surface, printing on the convex surface or printing at the edge, all require the original to be deformed. .
There are some tricks about manuscript deformation that can help the printer decide how to make the deformation and where to make the deformation, thus saving time.
1. Make some small grids on the printing plate. The size of the small grid depends on the size of the printed image. Squares with a side length of 5mm are commonly used. With multiple types of printing heads of different shapes and multiple printing, the print head with the smallest deformation will be found. As a reference standard, the original will be deformed as necessary, and a small square can be used as a deformation unit at a time. . When performing experiments on each type of print head, it is important to make a record of which kind of print head, where it is printed, and how large it is to compress. The procedure for making a deformed manuscript using the small grid method is as follows:
Printing small grid;
· Measure the size of each small square deformation on the printed object;
· Use the measured value of the small squares to recreate a deformed grid pattern in the computer;
Use a variable table grid to make a deformed image for printing;
• Use an image with a deformed original to print on the object.
2. Use the "upside-down printing" method to print a single letter. The letters to be printed are circled and the print head is printed at a high speed so that it can completely cover the printing area. The ink is gently coated on the raised letters, then the print head is pressed against the ink-coated letters to pick up the ink, and finally printed on the white paper. Such a distorted letter is printed on the paper, the letter is entered into the computer using a scanner, and a deformed manuscript is relieved by the computer. The specific steps are as follows:
· Lightly spray on the letters with a small amount of ink or other transferable paint;
· Use the print head to bring up the ink on the letters;
The letter pattern on the print head is printed on the paper, the printed deformed pattern is input into a computer by a scanner, an image-deformed original is created on the computer, and the printing plate is used for printing. The raised letters are printed using the image-distorted original.
Original image size
When exposure printing is performed, the original is rotated on a steel plate (plastic plate), and its size should not exceed the area of ​​the steel plate (plastic plate) or the maximum area printed by the printer. The length and width of the original image in the open printing system should be controlled within 80% of the maximum length and width of the machine printable. If it exceeds this value, it will cause uneven ink coating, or the image is too close to the steel plate (plastic plate ) Edges, which cause the print heads to carry a lot of ink that should not be picked up. In a closed printing system, the image size should not exceed 90% of the ink tank diameter.
Also consider the working direction of the machine's ink plate when setting the original. If there is a straight line in the original, when the original is rotated, these straight lines should be perpendicular to the working direction of the ink pan, or have a small angle with the vertical direction. Correspondence between the eroded image in the printing plate and the way the inked plate works.
The best way is to check the positioning of the original image twice before you print the plate. Place laser prints or manuscripts together on a table to form a whole view, in accordance with the length of the working of the inked plate (in the multicolor printing press aligns the center axis of each plate), to see if all images are in one Straight line.