There are three types of screen printing: manual screen printing, semi-automatic screen printing and automatic screen printing. Although the output of flat screen printing is low, it is convenient to make plate, with long recycle length and many colors. Fine patterns can be printed without color change, with a large amount of paste and a three-dimensional effect. It is suitable for printing woven fabrics and knitted fabrics such as silk, cotton and chemical fiber, and is more suitable for printing high-grade fabrics with small batch and small variety.
First, manual flat screen printing.
(1) Equipment structure Manual lithographic screen printing machine is installed on a wooden or iron frame. The length and width of the pressure plate depend on the fabric type. The silk printing table is rectangular, and the length is calculated by the length of the horse. The usual specifications are 32m, 48m and 64m. The width is generally 1.3- 1.5m, and the height is generally 0.6-0.7m The printed sheets are rectangular and square, and handkerchiefs and knitwear are mainly small tablecloths. The surface of the table top is covered with a layer of artificial leather with appropriate elasticity, and a blanket or double-sided thick cotton wool blanket is placed under it. There is a heating device under the platen to prevent the color paste from overlapping when printing the front and rear color frames. The surface temperature of the pressure plate is kept at about 45℃, which is called hot pressing plate. There are positioning holes on both sides of the pressure plate to fix the position of the frame to prevent cross stitch. It is also equipped with a drain tank for the sewage flowing out of the table after printing. The heat source of hot platen is usually steam pipe heating or electric heating, but it consumes a lot of electricity and is prone to accidents.
(II) Advantages and Disadvantages of Manual Flat Screen Printing Machine The manual flat screen printing machine not only has the advantages of the above flat screen printing machine, but also has no limit on the number of printing sets due to manual scraping of the platen. Because the printing interval of each color frame is long, it is not easy to produce color matching. However, due to manual pasting and manual scraping, the labor intensity is high, and uneven scraping is prone to occur.
Second, semi-automatic lithographic screen printing machine
(1) When printing equipment and mechanism, the semi-automatic screen printing machine sticks cloth manually, and the automatic control mechanism moves the screen frame and scraper. The pulp feeding equipment is mostly automatic pulp feeding, but there are also manual pulp feeding. The printing platen is a hot pressing plate. Due to the use of semi-automatic machinery, both ends of the printing platen need to be equipped with automatic printing steering devices. If there is no steering table, it can also be solved by reversing.
The screen frame of semi-automatic screen printing machine is generally made of aluminum alloy. The screen frame is called color frame or flower frame after stretching and plate making. The color frame is installed on the automatic printing device, and the automatic printing device controls its movement, lifting and scraping of the scraper.
Scraper is a scraping tool for flat screen printing. It is made of synthetic rubber, and its hardness is generally 48+-2 Shore. The selection of scraper should be based on fabric thickness, printing process and color paste performance.
See the following table for the specifications and usage of common scrapers:
Specification and use of ordinary scraper
Name: Blade shape, scraping effect, application situation.
The sharp mouth has a large inclination, so it is best to use less thin stems.
Small round mouth and semicircle are good. Generally, thin stems and small patterns are not commonly used.
The two sides of the bend are inclined in a meniscus shape. Generally, thin stems and small patterns are most commonly used.
The big round mouth is the same as the small round mouth, but thick thin stems are often used.
The inclination of hard inclined plane is smaller than that of fast inclined plane, so hard rubber can scrape the deep version, which is not commonly used.
The shape of soft inclined plane is different from that of hard inclined plane, and it can be scraped without exposing the bottom. It is most commonly used for large templates.
The hardness of the scraper, the shape of the blade and the scraping pressure are important factors affecting the screen permeability of the color paste. Screen permeability directly reflects the color yield of screen printing. If the transparency is good, the color yield is high and the color is rich, but the definition of the pattern outline is poor. Therefore, the use of scraper should be selected in combination with various factors and production conditions.
(II) Advantages and disadvantages of semi-automatic screen printing machine Semi-automatic screen printing machine can print wide fabrics, but it is easy to produce edge bubble defects, which can be solved by properly adjusting the scraper pressure.
See the following table for the specifications and usage of common scrapers:
Specification and use of ordinary scraper
Name: Blade shape, scraping effect, application situation.
The sharp mouth has a large inclination, so it is best to use less thin stems.
Small round mouth and semicircle are good. Generally, thin stems and small patterns are not commonly used.
The two sides of the bend are inclined in a meniscus shape. Generally, thin stems and small patterns are most commonly used.
The big round mouth is the same as the small round mouth, but thick thin stems are often used.
The inclination of hard inclined plane is smaller than that of fast inclined plane, so hard rubber can scrape the deep version, which is not commonly used.
The shape of soft inclined plane is different from that of hard inclined plane, and it can be scraped without exposing the bottom. It is most commonly used for large templates.
The hardness of the scraper, the shape of the blade and the scraping pressure are important factors affecting the screen permeability of the color paste. Screen permeability directly reflects the color yield of screen printing. If the transparency is good, the color yield is high and the color is rich, but the definition of the pattern outline is poor. Therefore, the use of scraper should be selected in combination with various factors and production conditions.
(II) Advantages and disadvantages of semi-automatic screen printing machine Semi-automatic screen printing machine can print wide fabrics, but it is easy to produce edge bubble defects, which can be solved by properly adjusting the scraper pressure.
See the following table for the specifications and usage of common scrapers:
Specification and use of ordinary scraper
Name: Blade shape, scraping effect, application situation.
The sharp mouth has a large inclination, so it is best to use less thin stems.
Small round mouth and semicircle are good. Generally, thin stems and small patterns are not commonly used.
The two sides of the bend are inclined in a meniscus shape. Generally, thin stems and small patterns are most commonly used.
The big round mouth is the same as the small round mouth, but thick thin stems are often used.
The inclination of hard inclined plane is smaller than that of fast inclined plane, so hard rubber can scrape the deep version, which is not commonly used.
The shape of soft inclined plane is different from that of hard inclined plane, and it can be scraped without exposing the bottom. It is most commonly used for large templates.
The hardness of the scraper, the shape of the blade and the scraping pressure are important factors affecting the screen permeability of the color paste. Screen permeability directly reflects the color yield of screen printing. If the transparency is good, the color yield is high and the color is rich, but the definition of the pattern outline is poor. Therefore, the use of scraper should be selected in combination with various factors and production conditions.
(II) Advantages and disadvantages of semi-automatic screen printing machine Semi-automatic screen printing machine can print wide fabrics, but it is easy to produce edge bubble defects, which can be solved by properly adjusting the scraper pressure.
1. Manufacture of screen frame for lithographic screen printing
The production of screen frame for lithographic screen printing includes the selection of screen frame and the stretching of screen.
(1) Selection of screen frame Making screen frame is an important process of screen printing. The screen frame used to be hardwood, but now it is mostly aluminum alloy. The size of the screen frame is determined by the width of printed fabric, unit pattern area, scraper coefficient and equipment conditions. In machine printing, the size of screen frame is very strict. Hand printing is made according to the size of printed fabric or pattern, mostly made of wood. For example, paper printing is based on the size of the pattern, not the size of the paper. Machine printing is made of aluminum alloy. If extra-large frames are needed, special-shaped steel pipes should be used. See the following table for common screen frame specifications and selected materials:
Specification and material selection of commonly used screen frames
Mesh frame material: mesh frame size: printable width in scraping direction (mm)
Outer diameter (mm) Inner diameter (mm)
Pine extra-large frame 2890x1330 2670x1kloc-0/00 times 1040.
Pine frame 2480x1750 2280x1370x 1220.
Pine frame 2344x16002140x1260x 1 160.
Pine box1440x14401260x1260x160.
Pine ultra-small box 580x1380 460x1260x 1 160.
Aluminum alloy frame1520x11501465x1150 weft 1200.
Aluminum alloy middle frame 1520x905 1465x850 latitude 1200
Small aluminum frame 1520x755 1465x700 latitude 1200
Extra-large special-shaped steel tube frame 2600 x1340 2600 x1240 latitude 2 170
Irregular steel pipe frame 2200x13402100x1240Weft 1200.
2) The choice of screen lithography screen printing requires that the screen is durable, easy to wash and dry, and resistant to chemicals. Square holes should be regular, wires should be even in warp and weft, deformation should be small, and heat resistance should be high. See the following table for specifications of ordinary polyester (nylon) mesh:
Specification for polyester (nylon) mesh
Model width cm Breaking strength is not less than (KG) Elongation at break (%) Density (root /cm)
Aperture (mm) (approximate value) Effective sieving area (%) (approximate value)
warp and weft
SP38 126 2 44 44 25 ~ 40 22 ~ 40 40 16 0 133 28.5
SP40 126 2 46 46 25 ~ 40 25 ~ 40 42. 12 0. 13 1 26. 1
SP42 126 2 32 32 25 ~ 40 25 ~ 40 44. 1 0. 12 1 33.3
SP45 126 2 35 35 25 ~ 40 25 ~ 40 47.64 0. 1 14 29.5
SP50 126 2 38 38 25 ~ 40 25 ~ 40 52.76 0.094 24.5
SP56 126 2 32 32 25 ~ 40 25 ~ 40 59.05 0.085 25.3
SP58 126 2 34 34 25 ~ 40 25 ~ 40 6 1.8 1 0.078 23.2
NX73 100 2 40 40 25 ~ 40 25 ~ 40 73 0.079 38.2
NX79 100 2 29 29 25 ~ 40 25 ~ 40 79 0.079 38.7
NX90 100 2 26 26 25 ~ 40 25 ~ 40 95 0.063 36
NX 103 100 2 28 28 25 ~ 40 25 ~ 40 103 0.055 32.2
Printing screen specifications are usually expressed in roots/cm. For convenience, it is usually explained by "number". The more marks there are, the more holes there are per centimeter. For example, the number 9 or 10 screen is commonly used on the hot platen, which is 40.8 /cm and 43.6 /cm respectively. Sp38 and Sp40 are equivalent to the sp number of chemical fiber screen. Generally, 15 and 16 screens are selected for cold plates, namely sp56 and sp57. The screen selection of automatic screen printing machine should consider the characteristics of mechanical scraping. According to the size of the pattern area, the thickness of the fabric and the hygroscopicity of the fabric. When printing large-area patterns, the screen with small size and large aperture should be selected because of the large demand for color paste. On the other hand, a small area pattern or a fine pattern requires a large screen with a small aperture. For thick fabrics, due to the large amount of color paste, the screen with small size and large aperture should be selected. For chemical fiber fabrics, due to poor hygroscopicity and small pulp absorption, large-size and small-aperture screens should be selected. Screen selection should be based on various factors and actual production conditions.
(3) performing screen stretching of lithographic screen printing on a compressed air screen stretching machine and a manual spiral screen stretching machine. Apply tension to the screen and lay it flat on the screen frame. Metal mesh frames are generally glued, and wooden frames can be glued or nailed.
1. Sticking method First, coat a layer of stretched mesh glue on the flat mesh frame and let it dry for 24 hours. Clip the cut screen into the holder of the screen stretcher, raise the pressure to 392.266kpa, send air to make it tight, and spray it evenly with direct steam for about 10 second, so that the screen can be further tightened by heating, which is convenient for the screen to contact with the rubber surface on the frame. Then use a paint brush to coat the screen frame with anhydrous alcohol or acetone, wipe it with a dry cloth to dissolve the solvent and glue it, and then glue the screen frame. Blow with a fan 15-25 minutes. When the organic solvent volatilizes, the mesh frame is successfully stretched. (Note: At present, it is generally recommended to use the fast-drawing adhesive produced by Zhejiang Zhong Da University. The specific method is shown in the manual, which may be slightly different from the actual operation. )
2. The net frame made by nailing method has simple equipment. The fillet can be made of plywood, rattan or elastic hard aluminum. Elastic duralumin is durable, with a width of 1.5-25mm and a thickness of 1.5-2mm. Nail holes are opened every 20-30mm. First, the aluminum strip is coated with foreign dry paint or polyvinyl aldehyde glue, and naturally dried for 24 hours. When the net is stretched, the net is matched with the aluminum strip along the length direction, so that the aluminum strip is embedded in the net and fastened on the frame. Stretching the net in the width direction is the same as the previous method. (Note: The actual operation can also be done directly by hand with large staples, and then coated with net-stretching glue to dry naturally. )
Second, lithographic screen printing plate making
Plate making is to accurately color the pattern to be printed and find out the cycle unit. Make the same color on each pattern on the screen according to the integer multiple of the cycle unit. Make the pattern part hollow, and block the grid of the non-pattern part to prevent the color paste from transferring to the fabric during printing. The commonly used plate-making methods are reverse painting method, photosensitive method and wax method. At present, various dyeing plants mainly use photosensitive plate making, and only the photosensitive method is introduced here.
Lithography is based on the principle of photography. The light shines on the screen surface of the rabbit photosensitive adhesive, so that the light in the pattern part is blocked, while the photosensitive adhesive in the non-pattern part is exposed to the light and photochemical action occurs. The photosensitive glue becomes a water-insoluble film to block the mesh, and the plate making is completed through reinforcement.
Photosensitive plate making process:
1. Pattern finishing-computer color separation-hair release
2. Photosensitive glue on screen-low temperature drying or air drying
3. Sensitizing-developing-(drying)-baking and strengthening-repairing-proofreading.
1.
(1) coating photosensitive adhesive: photosensitive is the key to photosensitive plate making. The quality of scraping photosensitive glue on the screen frame directly affects the photosensitive effect. Scraping photosensitive glue is to first coat the prepared screen frame with photosensitive glue in a dark room. Glue should be thin and even, without bubbles and trachoma. When applying glue, tilt the screen 60 degrees, and brush the photosensitive glue on the screen with a combination brush, first horizontally and then vertically, from left to right and from top to bottom, evenly once or twice. When gluing, the speed should be uniform to prevent bubbles and trachoma. Then scrape the floating liquid from top to bottom with a metal scraper. The dosage of glue is generally 140- 150ml/m2. After coating, put it flat on a drying rack in a black box, and dry it at 30℃ under hot air 1.5-2 hours, with a maximum of 4 hours. The relative humidity in the box should be controlled below 70%.
(2) exposure: put the computer color separation film flat on the exposure table, then stick the mesh surface of the mesh frame on the front of the film, and make it cling to it under the action of heavy objects such as sponge. Finally, turn on the light and expose it. See the instructions for purchasing photosensitive adhesive for details. Pay attention to the positive and negative films.