How to make screen and dry screen in screen printing?

Detailed step analysis of screen printing—

The quality of screen printing is directly related to the quality of printed products. Therefore, the screen printing process is worthy of in-depth study and discussion by the industry.

A detailed description of the screen printing process

Generally speaking, the production process of screen printing is different because of the different photosensitive materials used, but no matter which process is adopted, the following steps are indispensable in the process of screen printing: screen plate and frame selection, screen pulling, screen washing, photosensitive material coating, exposure, development and drying.

Let's take a closer look at the operation methods and precautions of each process.

1, screen selection

At present, there are many kinds of screens on the market, such as silk screen, nylon screen, polyester screen and metal screen. Generally speaking, nylon screen is the most widely used screen in the market at present in terms of cost and applicability.

Introduction of nylon net characteristics

Nylon screen has the characteristics of smooth surface, good ink permeability, softness, high elasticity, strong adaptability, good tensile strength, elasticity and friction resistance, high fastness, long service life, excellent acid resistance, chemical resistance and organic solvent resistance, so it is favored by fine printing and widely used in fine line drawing patterns and dot printing.

Precautions for use:

In addition to the above advantages, nylon mesh has some disadvantages, such as high elongation and low heat resistance, so we should pay attention to the following points when making nylon mesh:

Due to the high elongation of nylon mesh, it is required to use solid mesh frame and mesh tension when printing;

In view of the low heat resistance of nylon screen, don't fix the screen by hot melting when printing;

Ultraviolet rays will also have some influence on nylon net, so pay attention to avoid light when storing nylon net or its corresponding screen.

2, the choice of network framework

According to the material, there are six kinds of mesh frames: wooden frame, aluminum frame, iron frame, plastic frame, stainless steel frame and copper frame. The commonly used ones are wooden frame, aluminum frame and iron frame.

Wooden frame: cheap and easy to make. It can be stretched manually or mechanically, but it has the disadvantage of low strength and easy deformation. Only suitable for printing low-precision products, not suitable for fast and high-precision screen printing. In addition, the Netease of wooden frame painting is slack and poor in recyclability.

Iron frame: Compared with wooden frame, it has the characteristics of stable size, firmness and durability, but it is easy to rust due to its heavy weight and inconvenient use, so it can only be stretched mechanically.

Aluminum frame: Although it is only suitable for mechanical screen stretching, it has the characteristics of small deformation, light volume, rust prevention and convenient movement, so aluminum frame is the most widely used screen frame in printing and plate making.

Second, pull the net.

In general plate-making, there are three methods to draw the screen: manual, mechanical and pneumatic. For example, the first two methods can be generally used if the silk screen processing factory does not require high accuracy; If the requirements are higher, the last stage pneumatic screen puller can be used, which is suitable for high-precision screen pulling. It has the characteristics of uniform tension and convenient use, can meet different screen tension requirements, and is especially suitable for drawing high-precision printing screens.

Third, wash the net.

When printing plate making, special chemicals are generally used to wash the screen (such as stripping water, thinner, detergent, etc.). ), but this method is time-consuming, so it is a bit troublesome for those factories that talk about timeliness. Here is an effective way to share with you: choose washing powder with strong detergency, such as tide, wet the screen and polish it with cotton cloth. This method is not only quick in decontamination, but also beneficial to the adhesion of photosensitive adhesive. (Note: In the above method, holes need to be punched on both sides when polishing, and the force should be light when polishing the front side to avoid the mesh falling off. ) Wash the net, cover it and put it in the dryer to dry.

Fourth, coating

1, selection of photosensitive materials

There are two kinds of photosensitive materials used in the market at present. One is photosensitive adhesive, which is simple in process, economical and practical, fast in exposure speed, durable in screen printing, easy to release film and excellent in solubility. The other is photosensitive film, which is a kind of photosensitive material that anticipates light. Stick it on the screen before screen exposure, it has hydrophilicity, strong resolution, good line sharpness, firmness and durability, and its performance is better than that of photosensitive adhesive. Because of its hydrophilicity, it is commonly known as "water film".

Generally speaking, the requirements of printing on photosensitive materials are: the plate film formed by photosensitive materials should meet the performance requirements of different kinds of inks, and have considerable printing resistance, can withstand considerable scraping pressure of the ink scraper, has good bonding force with the screen, will not cause stripping failure during printing, and is easy to peel off, which is beneficial to the recycling of screen plates.

2. Coating

Necessary items: photosensitive adhesive, sizing device (scraper), grid.

All the photosensitive pastes on the market need to be called by themselves. You can wet the photosensitive powder with hot water first, then pour it into the photosensitive paste and mix well. It will be available in a few hours. Small factories can be sized by plate-making workers, while large factories have automatic sizing machines with uniform thickness. The operation steps are as follows:

Put the dried screen on the gluing table, place the screen board stably, and pour the photosensitive glue into the scraper. (Note: Appropriate amount)

Use a scraper to evenly coat the photosensitive adhesive on the screen, first coating the printing surface (the convex surface of the screen) and then coating the ink surface (the concave surface of the screen), generally three times per surface.

Then hang the net, this is the first time. (Note: Screen printed lines and characters need secondary coating)

If thick screen printing is needed, it can be painted several times, that is, after the first painting, it is immediately put into an oven at 30-40℃ for drying, and then the screen is taken out and painted again. According to the required thickness, determine the coating times. Note that the general printing surface (convex surface) is coated 2-3 times more than the ink surface (concave surface), and this operation is secondary coating. (Note: This coating is only carried out on the contact surface of the screen)

Blow-dry with a hair dryer or oven, and don't let it dry or not, so as not to affect the quality of plate making. (Note: insensitive adhesive)

Note: The gluing process is very important. The quality of screen printing depends on gluing, which requires uniform and three-dimensional layout thickness.

dry

After the screen printing photosensitive adhesive is coated, let it stand for 1-2 minutes, then put the screen into an oven at about 40℃ to dry, and then take it out and put it in a dark frame for later use.

Note: the screen must be dry, otherwise it will affect the firmness of the screen.

Verb (short for verb) exposure

Stick the film surface of the negative on the printing surface (convex surface) of the screen, and then expose it in a vacuum exposure machine. The exposure time depends on the thickness of the photosensitive adhesive, the energy of the exposure lamp and the requirements of the screen (the exposure time required by general lines, solder masks, characters and screens is different). Generally, the exposure time should be determined by the exposure slide rule before use, and then the exposure time of the screen should be fixed.

Steps:

First of all, use a magnifying glass to aim at the latitude and longitude lines of the screen printing, and the lines should be parallel and perpendicular to the screen printing. (Note: especially lines and characters)

Put the calibrated screen into the exposure machine, adjust the time, and turn on the switch of the exposure machine after vacuuming.

Note: If the exposure time is too short, it will cause problems such as the sensitive adhesive falling off easily, the lines becoming thicker, the solder bumps being weak, and the characters and symbols being weak. However, long-term exposure will cause quality accidents such as incomplete development or thinning lines. Therefore, it is especially suggested that the accurate exposure time comes from scientific practice. Before production exposure, the exposure time must be measured with an exposure slide rule, and then the exposure time must be determined. Don't do things by experience and don't work blindly.

Development of intransitive verbs

Take the screen out of the exposure machine, remove the negative film, first wet both sides of the screen with mild non-pressure cold water (warm cold water at 20-30℃) for about 30-60 seconds, then rinse it thoroughly with a high-pressure water gun until an image appears, then use absorbent cloth to absorb the excess water around it, and then put the screen into an oven at 30-40℃ for drying.

Steps:

Wet both sides of the exposed screen with water for about 1 min, and rinse the screen with high-pressure water until it is completely clear;

Contrast under the lamp to see if it is completely clear, if the plate making is successful, if it is not good, redo it;

After the wet net is dried, put it under the light box, and repair the defects such as trachoma and burr with the net sealing paste.

Seven, check the use

After the screen is dried, carefully check whether the screen meets the production and processing requirements. If it meets the requirements, immediately seal the screen for production personnel to use for later use. If it does not meet the requirements, immediately repair or remake it. Principle:

Screen printing consists of five elements, namely screen printing plate, scraper, ink, printing table and substrate. The basic principle of screen printing is to use the basic principle that the mesh of graphic part of screen printing plate is permeable to ink and the mesh of non-graphic part is not permeable to ink. When printing, the ink is poured into one end of the screen printing plate, and the ink part of the screen printing plate is pressed with a scraper, while moving to the other end of the screen printing plate. During the movement, the scraper squeezes the ink from the grid of the graphic part onto the substrate. Because of the viscosity of ink, the imprint is fixed in a certain range. In the printing process, the scraper always contacts the screen printing plate and the substrate line, and the contact line moves with the movement of the scraper. Because there is a certain gap between the screen printing plate and the substrate, the screen printing plate generates a reaction force on the scraper through its own tension, which is called resilience. Due to the resilience, the screen printing plate is only in movable line contact with the substrate, while other parts of the screen printing plate are not in contact with the substrate. Make the ink and screen break, ensure the printing size accuracy and avoid rubbing the substrate. When the scraper is lifted after scraping the whole page, the screen printing plate is also lifted, and the ink is gently scraped back to the original position. This is a printed stroke.

Characteristics and process arrangement of screen printing

1. screen printing process arrangement

Screen printing is a direct printing method, which has three technological arrangements: ① cardboard → screen printing → post-press processing, that is, screen printing is first carried out on corrugated cardboard or other cardboard, and then cartons and carton products are made according to needs; (2) Carton → screen printing, that is, screen printing is directly carried out on the finished corrugated box or other cartons and cartons; (3) Secondary processing, that is, screen printing is carried out on tissue paper first, then corrugated board is made as required, and then cartons and carton products are made. 2. Screen printing features ① Wide adaptability: the screen printing format can be large or small; ② Thick ink color: Among all printing processes, screen printing has the thickest ink layer, high saturation and better spot color printing effect; (3) low cost: easy screen printing and simple printing process; ④ The quality of printed matter is stable; ⑤ Low production efficiency: the screen printing speed is slow, which is not suitable for online production; ⑥ Low image accuracy: the resolution of screen printing is not high, and the number of conventional screening lines is 24-32 lines /cm.

3. Application scope of screen printing

Screen printing is suitable for small batch production, which requires high printing appearance, unlimited paperboard thickness and does not damage the strength of packaging products.

Screen printing process

1. Screen printing (1) Selection ① Nylon screen printing: Nylon screen printing has high strength, high wear resistance, high alkali resistance, slightly poor acid resistance, good ink permeability, small line diameter, good elasticity and bright imprint; ② Polyester mesh: Polyester mesh has good stability, high strength, corrosion resistance, better performance than nylon mesh and high tension, and is suitable for high-precision printing; ③ Stainless steel wire mesh: Stainless steel wire mesh has high strength, good stability, small wire diameter, high mesh number, good resistance, long service life, poor elasticity, and is easily broken by impact, which is suitable for precision printing but not for curved surface printing; ④ Nickel-plated polyester screen: Nickel-plated polyester screen combines the advantages of polyester screen and stainless steel screen, with wide applicability, moderate price and poor corrosion resistance.

Screen has plain weave, twill weave, half twist weave and full twist weave. White silk screen exposure is easy to cause diffuse reflection, while gold, red and amber absorb ultraviolet rays to prevent halo. There are 30 meshes/cm, 40 meshes/cm, 60 meshes/cm, 80 meshes/cm, 120 meshes/cm, 140 meshes/cm and 160 meshes/cm, etc. Generally speaking, the mesh number is large and the wire warping is small. Fine lines and dense eyes, high resolution; Coarse silk and coarse mesh have low resolution. When printing curved surfaces, use elastic screen, such as nylon screen; When printing high absorption substrate, use a screen with large mesh area; When printing smooth surface, use high elasticity and high tension screen; When printing rough surfaces, use a low mesh screen; When printing high-precision printed matter, use a screen with low elongation and high tension; When printing signboards, textiles and knitwear, use 28 mesh/cm ~ 78 mesh/cm screen; When printing paper, metal, glass, leather and plastic, use a 40 mesh/cm ~ 140 mesh/cm screen.

(2) Pull the net

Screen frames include wooden frames, metal frames, plastic frames and composite frames. When stretching the net, the net frame should be cleaned first. The net can be stretched manually, mechanically or pneumatically, and then bonded and trimmed. It is required that the tension of the screen should be appropriate, uniform and stable, and the thread direction should be consistent, avoiding diagonal pulling, and the latitude and longitude lines should be parallel.

(3) plate making

① Direct method: screen cleaning → coating photosensitive adhesive → printing → development → revision. This method takes a long time, the film thickness is adjustable, the combination is firm, it is resistant to printing, and the pictures and texts are easy to sawtooth. ② Indirect method: photosensitive film → printing → development → sticking film → uncovering film base → modification. This method has complicated operation, smooth lines, weak film, low printing resistance and constant film thickness. ③ Mixing method: screen brushing → film pasting → printing → development → modification. This method is simple to operate, with fixed thickness and smooth and firm lines.

(4) screen direct plate making

Screen direct plate making is referred to as CTS (computer to screen). ① Direct plate making by laser ablation: firstly, screen photosensitive glue is coated on the metal screen, and the photosensitive layer is burned through by laser to make the grid of the graphic part transparent, and the computer of the prepress system controls the ablation position. This method can only be used for metal mesh. (2) Direct plate-making by laser exposure: firstly, photosensitive glue is coated on the screen, and the computer of prepress system controls the laser to image on the screen to make the screen. This plate-making method uses special photosensitive adhesive, which has narrow ultraviolet band and high price of laser exposure system. (3) Ink-jet imaging system: firstly, photosensitive glue is coated on the screen printing, and the computer of prepress system controls the ink-jet system to spray Guangmo on the photosensitive layer of the graphic part, and then ultraviolet light is fully exposed. The graphic part is not photosensitive, and the photosensitive glue is washed off; The blank part is photosensitive hardened. This method can use ordinary photosensitive glue without losing the details of the image.

2. Screen printing machine

Screen printers include manual screen printers, semi-automatic screen printers and full-automatic screen printers. There are also screen printing machines, such as open-book type, lifting type, sliding table type, roller table type, arc table type, curved surface type, roller screen layout, double drum type and so on. , you can choose according to your needs.

3. Special screen printing method

(1) UV imitation metal etching printing UV (ultraviolet) imitation metal etching printing is to print a layer of uneven translucent ink on a substrate with metallic mirror luster, and then cure it with ultraviolet rays, resulting in an effect similar to etching or polishing a bright metal surface. Printed products are elegant and luxurious, and are used for high-grade and exquisite packaging. This printing method uses metal-like etching ink cured by ultraviolet light, and the substrate is the gold card paper, silver cardboard or composite material, and a screen with 70 mesh /cm ~ 100 mesh /cm is used. 2 UV wrinkle pattern ink printing UV wrinkle pattern ink printing is printed on the surface of the substrate with UV wrinkle ink, and then cured with ultraviolet rays to form a special wrinkle pattern decorative effect. This printing method uses a screen of 40 mesh/cm ~ 60 mesh/cm, and the thickness of the ink film is 20 μ ~ 30 μ. The greater the thickness, the better the effect. 3 Ice flower effect printing Ice flower effect printing is to print ice flower ink on the surface of a substrate with metallic luster by screen printing, and after ultraviolet curing, it appears ice flower-like. The substrate of this printing method is gold and silver cardboard, and a screen of 60 mesh/cm ~ 100 mesh/cm is used. (4) Foam printing Foam printing is screen printing with microsphere foaming ink on paper or other substrates, with raised graphics and text, which is widely used for printing book binding, Braille, maps, packaging and decoration. This prin method uses a screen of 30 mesh/cm to 50 mesh/cm. The screen can also be used for screen printing of aromatic ink, pearlescent ink, liquid crystal ink, phosphorescent ink, fluorescent ink and crystal luster.

High speed rotary screen printing production line

Flat screen printing method can not meet the needs of large-scale and batch production of cigarette cartons because of its low printing speed, slow ink curing speed, difficult control of printing quality and high consumption of printing materials. The adoption of high-speed rotary screen printing production line has the advantages of high printing speed, high output, stable quality of printed products and low consumption, which changes the traditional flat screen printing, manual paper supply and ink supply methods and is suitable for high-speed automation and mass production of exquisite folding cartons.

Web rotary screen printing uses nickel metal rotary screen printing plate, built-in scraper and automatic ink supply system. The doctor blade transfers printing oil and ink from the rotary screen printing plate to the surface of the substrate supported by the impression cylinder. The whole printing process, including paper feeding, ink supply, color matching and UV drying, is all controlled by computer.

Rotary screen printing plate is suitable for large format rotary printing, the highest speed can reach 125m/min, and the screen plate can be reused. Therefore, web rotary screen printing can not only meet the requirements of special effects such as frosting and ice shaving, but also hot stamp holographic anti-counterfeiting marks, concave-convex tooth marks and die-cutting indentations online, and easily realize high-speed automatic printing of cartons: 1.