Screen printing 1000 questions (142-147)

â–¼142. Screen printing type

Screen printing can be divided into many types according to its layout, type of printer, nature of ink and type of substrate. However, the printing methods can be divided into the following types:
1. Plane screen printing screen printing is a method of printing on flat substrates using a flat screen printing plate. During printing, the printing plate is fixed and the ink blade moves.
2.Surface Screen Printing Curved Surface Screen printing is a method of printing on surface printing objects (such as balls, cylinders, cones, etc.) with flat screen printing plates. In printing, the ink knife is fixed and the printing plate moves in the horizontal direction. The substrate moves with the printing plate.
3. Rotary screen printing Rotary screen printing is the use of cylindrical screen printing plate, the cylinder is equipped with a fixed squeegee, cylindrical printing plate and printing materials for simultaneous printing speed, such as printing method, also known as round Web printing.
4. Indirect Screen Printing The first three methods are directly printed by the printing plate, but they are limited to some regular geometric shapes. Such as flat, round, and conical, etc., are complex in shape, with ribbed solutions and concave surfaces. Other shaped objects, such as indirect silk screen printing method. The process is often composed of two parts; Indirect screen printing = plane screen printing + transfer printing that is not directly printed on the substrate printing materials, but first printed on the plane, and then Certain methods transfer to the substrate. Silk printing paper + thermal transfer printing paper + pressure sensitive silk transfer printing paper + solvent activated transfer indirect silk screen printing has become an important field of the silk screen industry.
5. Electrostatic screen printing Electrostatic screen printing is a method of transferring ink from a screen printing plate to a printing surface by means of electrostatic attraction. This is a non-contact printing method using a conductive wire mesh for printing plates, and high pressure The positive pole of the power supply is connected, and the negative pole is a metal plate parallel to the printing plate. The substrate is between the two poles. When printing, the toner on the printing plate passes through the mesh with a positive charge and is attracted by the negative electrode. Fall on the printing surface, and then fixed into a print by heating and other methods. This method is currently mainly used for high-temperature substrates, such as the printing of steel plate.

â–¼143. Problems with ink color matching

1. Carefully observe the color sample, pay special attention to the substrate to be printed, select the ink from the roughness and smoothness of the substrate, and the degree of reflection. For example, the ink is printed on a smooth, highly reflective aluminum plate or can, and the ink with high transparency is selected. Will help enhance the metallic luster of the ink.
2. When choosing the ink for color matching, try to avoid mixing too much ink as much as possible. Try to use inks that are close to the standard color and made of a single pigment. The more colors are used, the more color ink is used. The farther from the standard color, the worse the brightness is. , The higher the degree of matteness of the mixed colors, the impossible to use the color to modulate the primary colors.
3. Special attention should be paid to the coloring power of the ink. If the selected ink concentration is not high enough, no matter how it is blended, the standard color density cannot be achieved.
4. When it is necessary to add white and black ink, special attention should be paid to the accuracy of the added weight and weighing. Among all the inks, the black ink has a particularly strong hiding power, and adding too much will not only dilute the color but also stop it. The degree of reflection of the substrate. However, for the uneven printed substrate nylon cloth, cardboard, in order to ensure the appearance of printed products, it is best to print a layer of white as the background color. Due to the strong coloring power of black ink, accidentally added Too much, you need to add a lot of other color inks to adjust the color, causing waste. So pay special attention.
5. When producing pale inks, determine how much white ink or varnish (spraying agent) should be added to adjust the degree of transparency of the ink film. Absolutely not allowed to use solvents to dilute the color. Too much solvent will not only affect printing. Performance, and will destroy the ink structure, resulting in pigment and resin oil separation, often or greatly reduce the ink gloss.
6. Improve the printing ink film gloss method 1. Add appropriate amount of varnish within the allowable range of color density. 2. Apply a layer of varnish or varnish on the surface of the printing ink film. 3. Increase the ink transparency, such as the use of high transparency High gloss ink or adding appropriate amount of varnish, using smooth. Increase the reflection of strong reflective substrate. 4. Prevent the adsorption of the substrate surface, and reasonably improve the smoothness of the printed surface of the substrate. 5. Pay attention to the temperature of the printing environment. Humidity, high humidity and low temperature, when the plastic gravure printing is performed, because the solvent volatilizes quickly (usually the surface of the ink film is dry within 1 minute), the heat around the ink film is absorbed and the water vapor in the air is drastically generated. Condensation forms a fog on the surface of the printing ink film, which makes the ink layer dull. In the rainy season, special attention must be paid to controlling the temperature and humidity of the printing environment to ensure a good printing effect. 7. Fluorescent inks cannot be processed with a large amount of non-fluorescent inks. Mix color, otherwise it will lose the ink fluorescence effect.
When the tension is too high, when the screen is printed, it is more laborious to scrape the ink and it is easy to tear the screen printing film. If the tension is too small, the springback force during printing is too small to achieve the desired springback effect and easy to paste lines.

â–¼144. Best Screen Requirements

1 Keep the tool clean and ready for use. The plate making room should be free of dust.
2 Check the screen tension. All multicolor overprint screens need the same tension.
3 Fully degreasing: Clean with a soft brush and a water source with a certain pressure.
4 Dry at a temperature below 40°C.
5 According to the manufacturer's recommended method, sensitize the photoresist 2 hours in advance.
6 Use a clean, slightly rounded edge sizing device to apply the glue. The area of ​​the sizing should be at least 10% smaller than the inner diameter of the frame.
7 When gluing, start with the printing surface first. The number of gluing depends on the solid content of the sensitized adhesive, the viscosity, the number of screen meshes, and the desired screen thickness.
8 When drying the screen, place the printed side face down (avoiding the flow of photosensitive glue back to the ink side).
9 For fine line printing and halftone printing screens, apply one or more photoresists on the printed surface after each drying until the printing surface is smooth.
Keep the glass cleaner vacuum cleaner clean. Check the film is correct? Does the film surface fit on the screen? Does blackness meet the requirements and is it placed correctly? And make the exposure machine has enough time to reassure.
11 Set the correct exposure time and keep a record. Every three months or when the exposure decreases, the exposure time should be tested and adjusted to correct.
12 Keep the exposed screen away from the light source (daylight, incandescent light).
13 Use water with proper pressure for development during development. In particular, the ink surface should be thoroughly cleaned and cannot be flushed until the surface is not slippery. Insufficiently exposed photographic film will be stripped after cleaning.
14 Use a soft, clean paper, a clean cloth, or a vacuum cleaner to remove excess moisture.
15 Use a suitable patching material to repair the screen.
16 Write all parameters to the web: thickness, exposure time, date, name.

â–¼145. "The Cause of Printing Accuracy Deviation"

1 When making screens for multicolor overprinting (halftone printing), the screens are dried at different temperatures, thereby causing errors in the printing accuracy.
2 The screen has low tension or overprint (halftone) screen tension.
3 Use dry air to dry and screen dry unevenly.
4 The use of too old, unsturdy, and deformed grids to make plated webs results in deviations in the printed image due to poor web frame stability (these problems can be detected with negatives)
5 When using multi-color overlay, the net pitch used is inconsistent.
6 Squeegee deformation.
7 Changes in the size of the substrate due to certain factors

â–¼146. "The Cause of Moire"
1 The template is too thick or too thin.
2 Compared with the wire diameter, too small dots will be lost (the dot range should be 5-95%).
The reason for the color change:
1 The ink consistency changes (different viscosities) due to evaporation of the solvent.
2 Change the squeegee angle during printing.
3 Change the hardness of the squeegee during printing.
4 Change speed during printing.
5 The adhesive edge is damaged.

â–¼147. Causes of premature damage to the template
1 Insufficient rubber grease.
2 Insufficient drying before exposure.
3 Insufficient exposure time.
4 The net distance is too high.
5 The ink blade is too dry and the pressure is too great.
6 Use the wrong cleaning solvent for cleaning (including a small amount of water).

Source: Qilu Graphic Arts