Metal coating board and box printing process and process

Abstract The printing process of the metal coating plate and the box is introduced. The screen printing, the design and output of the manuscript, and the selection of the printing ink are described in detail. According to the specific conditions of the surface of the coating plate, full-page printing or partial printing can be adopted.

Keywords metal plate; platemaking; ink

The metal coating plate and the box are the iron plates after the cutting, bending, welding, rust and other processing, coating a protective film on the surface, the protection of the film has both the role of anti-corrosion, beautification . There are two kinds of coating processes for the coating board and the box from the paint film: painting and spray. Spray painting refers to the spraying of a layer of metallic paint on the surface of a metal plate with a spray gun. The paint is bright, wear-resistant, chemical-resistant, and resistant to aging. It is often used for outdoor billboards and promotional vehicles. The commonly used types of resin paint are alkyd enamel, amino baking paint, acrylic paint, and lacquer. Spraying is also known as electrostatic powder spraying. It uses an electrostatic generator to charge the plastic powder and adsorb it on the surface of the iron plate. After baking at 180-220 °C, the powder melts and adheres to the metal surface. Mostly used for indoor use of the box, the film has a flat or matte effect. The powder types mainly include acrylic powder, polyester powder and the like.

There is also an art paint in the painting process, such as hammer paint, ice flower, wrinkle, etc. The paint is not suitable for screen printing because of uneven surface. In recent years, paint or ink manufacturers have introduced a suede paint for Local painting has a very good decorative effect and also has excellent printability and is worth promoting.

First, depending on the surface color of the coating plate making screen

Coating plate printing is mainly spot color printing. In addition to paying attention to the process of color fastness, overprint accuracy, and color correction, the printing plate work should also pay great attention to the problem of ink hiding power, especially for dark color coating plates. Take appropriate technical measures to make the solidified ink layer completely cover the background color of the coating plate, namely, "red and white impermeable powder, black and white Mo back to gray." There are four main methods for improving the hiding power of inks: (1) increasing the thickness of the photosensitive film; (2) using a wire with a larger wire diameter and a correspondingly lower mesh; (3) adding less diluent to ensure that the ink has a certain viscosity Degree; 4 individual colors scraped twice.

The application of photosensitive film should follow the principle of “less scraping of the bottom board and thick paint at the dark bottom”. Taking domestically produced two-component photosensitive adhesive as an example, the thin film printing method is “2+2+(1)”, that is, the photosensitive resin is scraped once on the screen printing surface and the printing surface, and then placed in a drying box at 40°C. Dry, wait 20 minutes to remove, and then scrape the rubber on both sides once again for the second drying, and finally make up a print surface to increase the thickness of the photosensitive film. In order to further increase the hiding power of the ink, the amount of over ink may be squeegee pattern of “2+2+ (2)” or “2+2+ (3)” (the numbers in parentheses indicate the number of times of single-wiping of the screen printing surface. ). For some of the imported high-sensitivity photoresist can reduce the number of squeegee, often using "1 + 1 + (2)" gluing method.

Printed metal coating board, suitable for 250 ~ 350 mesh screen, monochrome printing or large graphic printing available white nylon screen, color printing should use yellow polyester screen. If there is a back box or multiple sets of horizontal and vertical lines in the printed graphic, a 22.5° diagonal stretch net should be used. Otherwise, the edge of the line text is not neat and there is a sawtooth. The range of solvent-based ink screens is 250-300 meshes, and 350-mesh screens are suitable for photo-curable inks. The film version can be dried with UV lamps. The small, thin-line version must be plated with a high-powered iodine lamp and has a vacuum suction device. A large screen plate of 1 m or more can be placed outdoors for exposure.

Second, the design and output of the manuscript

There are many kinds of metal coating plates and their shapes are different. Screen printing companies often receive a number of advertising signboards, switchgear panels and cabinets for printing tasks, both monochrome, color, and also some local printing.

The color printing needs to perform color separation on color originals. In general, screen printing companies do not have professional color separation software, and artificial color separation is performed using A dobe I llustrator or CorelDRAW. The process of color separation is to cut a complete multi-color image to form a number of monochromatic patches. Attention should be paid to the following issues in the color separation work: 1) Dots can not be lost in each monochrome block, especially with CorelDRAW software. When separating colors, pay more attention to this issue. Because this principle of software separation is to retain one of the sections, and to manually delete other sections, when the operator's attention is not concentrated or the proofreader is not properly calibrated, the problem of oversizing or losing the point is often caused. 2 The main part of the graphic text should be kept as it is and cannot be scaled. Zooming will cause changes in the shape and thickness of the graphic and text, which will distort the graphic text. 3 The sub-panel outside the graphic can be properly scaled (commonly referred to as bleeding) because the screen itself is an elastomer, the elastomer material is stretchable, and the stretchability is directly affected by the screen tension and printing pressure. influences. The metal coating plate itself has a slight distortion of the material base, paint film sagging and so on, it is not suitable for printing with a screen printing press, and the use of manual scraping. Manual squeegee can not fully guarantee the consistency of the printing pressure. In order to ensure the accuracy of overprinting, it is necessary to properly scale the sub-panel graphic and edge contours. The degree of zooming depends on the screen size, low power, low light energy, long printing time, thick film version of the dried film residue, suitable film version power, penetrating ability, short print time , Suction evenly, no residue, fine lines and small words, clear light energy, four seasons are different, suitable for larger screens, need to be equipped with support frame, pressure plate, sun shield, more laborious large screen version can be scaled 0.2 ~ 0.4 mm, small screen version The size can be controlled from 0.1 to 0.2 mm. 4 Each monochrome plate should have a uniform positioning line and cutting line. The positioning line should have a directionality so that the plate-making workers will not reverse the direction of the negative plate. At the same time, the printed serial number and Pantone color number shall be marked in the lower right space. 5 Proofreading on the light table by professional proofreaders. The proofreading work should be based on a color manuscript, which can be divided into two steps: contrasting the color separation negatives with the color manuscripts to check whether there are any missing or redundant images; each color separation negatives is subjected to the overlap test according to the printed serial number. Check whether the positioning line and the edge rise line are reasonable and accurate. After the correctness is determined, it is submitted to the plate-making workers for screen printing.

Metal coating board printing belongs to borderless printing. Since the substrate has no margin, it is impossible to imprint the positioning points on the substrate. This brings certain difficulties to overprinting work. Some screen printing companies adopt the method of determining the position of the screen, that is, they do not register the positioning points on the single-color screens at all. They rely on the eyes of the printing workers to perform the overprint work. This method is suitable for overprinting large texts, but Should not be fine overprint. The design of metal coating plate overprint positioning points can adopt irregular triangle positioning method, that is, design three overprint positioning points in the blank space of the original graphic and text, and each of the monochrome versions has this positioning point. When the first color is printed, the graphic and text will be printed on the coating plate together with the color registration point, but only 2 or 3 pieces can be printed. The sample is used as a proof sheet, the ink on the screen plate is then cleared, and the overprint is sealed with a sealer. Positioning is used as a proof sheet, and then the ink on the screen is removed, and the overprinting positioning point is sealed and dried with a sealer, and the formal printing operation can be started. The overprint positioning points on other layouts are also sealed with glue (the sealant should have a certain degree of transparency) as a registration window for the next color printing. For monochromatic text printing, poly and distributed design methods can be used, such as graphic design of switchgear panels, especially those with larger dimensions. It is not necessary to design the manuscript with the same size as the panel, but to design each one. The text and font size of the printed part are densely arranged on a film. Before the printing, a piece of transparent polyester film is used to cover the panel. Then the text of each part is cut off and pasted on the switch and the instrument mounting hole respectively. Below, the text on the paste is used to measure the horizontal line with a 90-degree square. If there are individual texts that are not in good position, they should be re-stamped. Using this negative-plate making is economical and practical.

Third, the ink selection and squeegee method

The metal coating board has the points of spray painting. When selecting inks, they must be distinguished. This is because there is a difference between the ink used for the painting board and the sprayed board. In general, the lacquer board can use oxidative polymerization type, heat curing type, two-liquid reaction type, UV light curing type ink; sprayed board is often used for two-fluid reaction type, UV light solid type and plastic ink (PET, PEP).

The thermosetting metal ink is the preferred ink for the paint coating board. The ink resin has the same chemical composition as the paint film on the surface of the paint coating board, and the binding force between the ink and the paint film is good, and the wear resistance, the anti-sunshine, and the outdoor use are used outdoors. The paint plate must be printed with this ink. The thermosetting ink can be completely cured in an oven at 100-120°C for 1 hour. Therefore, a lot of ovens and drying racks are often provided in the screen printing factory to bake and cure the ink layer on the surface of the coating plate. When baking, special attention should be paid to the baking temperature and time of the white ink and the red ink. Do not make the color of the ink layer yellow or black. Such ink can be diluted with xylene.

Oxidation polymerization type inks (glass inks) can also be used to print metal coated panels. The disadvantages are long drying time (2 to 3 days), and the firmness is not as good as that of thermosetting metal inks. Adding manganese, cobalt, lead, etc. The agent can reduce the drying time while also improving the firmness. This ink is suitable for screen printing companies that do not have baking equipment, and is also more suitable for printing some large billboards and boxes. The ink can be diluted with solvent oil, or a small amount of 783 solvent can be added at the same time.

Two-fluid reactive epoxy ink is also commonly used by many screen printers. The ink layer is bright, strong, chemical-resistant, and has a quick drying time. It is very convenient for printing small batches and short-lived cards. The defect is the deployment. A good ink must be used up within the specified time (4 to 8 h), otherwise the ink itself cannot be used for cross-linking and curing. Therefore, the ink cannot be dispensed too much. Otherwise, the ink will be wasted, and the printing work must be done at one go. Intermittent, but also to control the change due to viscosity, ink thickening problem. UV metal ink is more suitable for printing small panel fine lines. Large panel printing can not be placed in the photo-curing zone for ink curing due to the influence of the width of the UV light curing machine itself. The advantage of UV metal inks is that the fine lines do not block the web, and the printer can easily operate. The power of the light and solid machine should be more than 3 kW. The low-power light curing machine must not allow the UV light to smoothly pass through the ink layer to the surface of the coating plate, causing the ink to adhere poorly. In addition, the text on the panel of the switchgear is basically a dark color, and thin-film printing should be adopted so that the ink passing through the screen can be kept as small as possible so that the ink can be cured well. The printing of large-volume, thin-line small panels, and relatively small factory area, using UV metal ink printing can be described as a superior strategy. In addition to the above-mentioned ink printing, the spray-coated board can also be printed with PET ink or PEP ink among plastic inks. Because the surface of the coating plate itself has a certain solvent resistance, the problem of poor adhesion between the ink and the coating plate can also occur. To improve the fastness, baking can be used, that is, the coating plate that has not yet dried is placed. In an oven at about 80 °C, bake for 15 to 20 minutes. Enterprises without ovens can use a temporary custom-made open oven. Place an iron grid on the oven and place the printed coating on the oven. It can also be used to increase the fastness when the surface of the coating plate is hot and the dryness is removed.

Metal coating plate deformation in the machining and spraying process, so that the printing surface is uneven, it must be depending on the surface of the coating board to adopt different methods of printing, the commonly used printing methods in two ways: 1 full-stencil printing; 2 partial squeegee. The former is suitable for smoothing the surface, the latter is suitable for uneven printing surface and there are many