Circular screen printing mechanism
Round screen printing machine is usually composed of four parts: cloth feeding device, printing head, drying device and cloth dropping device. At present, the screen printing machine usually has eight colors, twelve colors, sixteen colors, twenty-four colors and other kinds of screen printing machine. There are mainly two kinds of printing machines, such as 640mm and 904mm. Among them, 640mm flower back screen printing machine is mostly. Round screen printing machine has easy operation, low labor intensity, high output, suitable for a variety of fabrics printing, while it is suitable for multi-variety small batch of fabric printing.
Feeding device
Round screen printing machine into the cloth device has cloth car into the cloth and cloth roll into the cloth two kinds. When the cloth roll into the cloth, can swing the fabric roller pressure on the cloth roll, relying on the fabric roller rotation into the printing device. When the fabric is fed into the fabric, the fabric moves forward with the rubber track that runs in a cycle and completes the printing. This track is first coated with a thin layer of thermoplastic resin on the surface by the rubber feed roller, which can adhere the fabric smoothly. Infrared radiation heater is installed next to the rubber feed roller to heat the resin on the track. The thermoplastic resin coating can process 200 to 1 million meters of fabric at a time. If it is found that the viscosity is not good, it can be recoated with a layer.
Printing device
Round screen printing device includes round screen, squeegee, pulp giving device, etc.
Round net
Round net is the flower plate of printing machine. Made of nickel metal, also known as nickel mesh, is hexagonal mesh. The two ends of the round net are fixed with bored head to prevent the net from deformation when printing, which affects the accuracy of the flowers, and can withstand the pressure of the color paste and squeegee when printing. In order to improve the elasticity of the round net and reduce the pressure, the net should be installed away from the center line of the support roller, generally about 16mm away. Each round screen machine seat has a display reading device, can show the pressure of the squeegee in each direction.
Scraper
Round screen printing machine squeegee installed in the center line of the round screen on the squeegee frame. Scraper frame is equipped with both scraper and slurry tube. Scraper system using chrome, molybdenum, vanadium, steel alloy manufacturing, with a small coefficient of friction and can be adjusted at any angle. When printing, the scraper’s knife mouth and the inner circle of the round net tangent, scraper to the color paste to apply pressure as the main, scraping as a complementary compound action.
Printing device
The circular screen printing machine is automatic sizing. Each round screen is equipped with a sizing system. When supplying color paste, one end of the plastic tube on the machine is put on the metal paste feeding tube, while the other end of the hose outside the machine is inserted into the color paste barrel and pumped into the round screen, and the height of the color paste liquid level is controlled automatically by the electrode.
Drying and cloth out device
Round screen printing machine adopts loose hot air drying. After printing, the outside is separated from the rubber track and imported into the drying part, which is placed loosely on the polyester net, and the cloth is dried by hot air. Out of the cloth by the electric swing shaft traction into the cloth car.
The advantages and disadvantages of circular screen printing machine
Round screen printing machine has the advantages of low labor intensity, high production efficiency and strong adaptability to fabrics. Suitable for chemical fiber fabrics, knitted fabrics, light fabrics printing. It can obtain the effect of lively pattern and bright color, and can avoid the defects of color transfer. But by the limitations of the circular network structure, the effect is not very satisfactory when printing fine lines.
The preparation of the round net
Network making process
Round tube core mold — copper plating — polishing —- rolling point — polishing —- chrome plating —- embedded insulator —- heating —- hardening —- polishing —- cleaning — demoulding — nickel mesh forming
The role of each main process
① Copper plating can make the core mold to meet the requirements of the circumference of the round mesh, and because of the soft texture of copper metal is easy to roll the point.
② Rolling point is to roll out the mesh specification on the core mold of copper plating.
③ Chromium plating Because the combination of chromium and nickel is poor, so that the nickel mesh can be easily removed from the mold after molding.
④ Embedded insulator is to insert insulator into the mesh part so that no current is passed during plating: the unembedded part is plated with nickel metal to form a nickel mesh with dot holes. Generally, epoxy resin 604 is mixed with epoxy resin catalyst 650 in equal amount. After coating, the insulator is baked at 175℃ for 7 minutes to cure.
⑤ Nickel plating is done in nickel sulfate and nickel oxide plating solution. Nickel mesh thickness:. After reaching the requirement, the nickel mesh is demoulded by mechanical extrusion method.
Circular mesh making
(1) The process of circular screen making
Checking and preparation of black and white draft — Round screen selection —- Round screen cleaning —- on photosensitive adhesive — Blinding — Development — Baking — Adhesive bogging — Checking for use
(2) Checking and preparation of black and white manuscript
The black-and-white draft of color separation and portrayal can be directly blurred. However, when the pattern is 1/2 and 1/3 joint, it is appropriate to use the full roll of the positive film exposure. The black-and-white draft should be checked thoroughly before exposure to prevent defects.
(3) Round net selection
According to the fabric width, flower type and other factors to choose different specifications of the round net for the net.
Round net specifications
The perimeter is 480, 640, 913, 1826mm, etc. The working width is 1280, 1620, 1850, 2400, 2800, 3200mm, etc. And the length of round wire mesh is calculated according to the following formula Length of circular mesh = working width + 2x59mm (59mm is the left edge). At present, the most commonly used circumference is 640mm, and the working width is 1620mm round mesh.
Round Mesh Mesh Specifications
| Common circular mesh specifications | |||||
| Number of items | Number of holes（cm2） | Mesh area（mm2） | Mesh diameter（mm） | Thickness（mm） | Open area/total area（%） |
| 25 | 120 | 0.2 | 0.48 | 0.2 | 24 |
| 40 | 290 | 0.07 | 0.285 | 0.11 | 20 |
| 60 | 670 | 0.05 | 0.152 | 0.1 | 18 |
| 80 | 1150 | 0.01 | 0.108 | 0.08 | 11 |
| 125 | 1630 | 0.006 | 0.083 | 0.08 | 9 |
Mesh selection basis
① Pattern structure Fine pattern and line choose the mesh number larger net.
② fabric nature thick fabric absorbing pulp, should choose the mesh number of small mesh. Cotton fabrics with a smaller mesh, chemical fiber and mixed fabrics with a larger mesh.
③ color paste nature color paste fluidity is good, can choose the mesh number of large network.
④Printing machine speed The speed is fast, the color paste through the net rate is low, choose the mesh number of small net. When printing large area pattern (with border line) choose 60 mesh: small area pattern (no border line) choose 80 mesh: electronic-based pattern choose 80 mesh mesh is better: line based pattern to 100 mesh is more common.
Determine the mesh mesh to integrate a variety of conditions, combined with the actual production situation to choose. Various mesh mesh can be printed on the finest line width as shown in the table.
| circular mesh quanity and line size | ||||
| circular mesh quanity | 100 | 80 | 60 | 40 |
| line size （mm） | 0.25 | 0.3 | 0.4 | 0.6 |
(4) The cleaning of the circular screen
Before the photopolymerization, the round net must be cleaned. Put the round net on the cleaning rack, first use 60% chromic acid reciprocal cleaning, rinse with water, then 10% soda ash rinse, and finally rinse with water. Because the flushing water is from inside to outside, the flushing water pressure should not be too large. To present a uniform water film on the surface of the round net, you can prevent into the low temperature oven drying.
(5) coating photopolymer
① Prescription Photographic solution is composed of photographic adhesive and photosensitizer. Prescriptions refer to the product description. The viscosity of the photosensitive liquid is to be dipped in a glass rod and can flow down in a straight line.
② method of applying liquid when the liquid will be clean and no water damage rubber scraping ring set in a clean under the iron ring outside, pour in 200 – 300g of photosensitive glue to take a clean round net will be under the iron ring set, and then into the iron ring, and adjust the upper rubber pressure plate pressed. Hold the inverted ring with both hands and move from bottom to top at equal speed (250mm/s), so that the photographic solution is evenly coated on the surface of the net. Bake for 20 – 25 minutes at 20 – 25℃.
The speed of coating liquid should be appropriate, too slow, too much glue, back into the mesh wall, washing out the difficulties; too fast, the film is not firm, easy to appear bubbles. Coating liquid is generally operated under the yellow light.
(6) Exposure
Exposure will be set in a round net outside the inflatable rubber cylinder, photographic positive film immediately attached to the round net for exposure. Exposure time depends on the nature of the film, the brightness of the light, the performance of the light-sensitive liquid, the thickness of the film layer and the mesh of the round net. Exposure conditions: room temperature of 25 ℃, relative humidity of 65%, exposure time is shown in the following table.
| Exposure schedule at 25°C and 65°C relative humidity | |||||
| circular mesh quanity | 100 | 80 | 60 | 40 | 25 |
| Exposure schedule （sec） | 5 | 6-7 | 10 | 15-20 | 25 |
The exposure time should be strictly controlled, otherwise the exposed part produces small holes, and even the coating comes off, affecting the quality of the round net.
(7) Development
After exposure round net in 18 – 28 ℃ water soaking 10 – 15 minutes to remove the unexposed part of the gel layer, and from the inside out with cold water or warm water rinse. Finally, use salt-based violet easy coloring, easy to check the defects.
(8) Inspection and baking
After careful inspection and repair by 50 ℃ hot air blowing dry, in 180 ℃ baking 2 – 2.5 hours.
(9) Gluing stifling
The round net is very thin and needs to be held up by the bore on both sides to keep the shape of the round net. The round net should be well marked with the bore, and epoxy resin should be used to fix the round net with the bore.
