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Screen printing can be divided into many types according to its layout, type of printing machine, nature of ink and type of substrate, but its printing methods can be divided into the following several。
1. Flat screen printing: flat screen printing machine is a method of printing on flat substrate with flat screen plate. When printing, the plate is fixed and the scraping plate moves.
2. Flat screen and curved surface screen printing: flat screen and curved surface screen printing is a method for flat screen printing plate to print on curved substrate (such as ball, cylinder, cylinder, etc.). During printing, the scraper plate is fixed, the plate moves along the horizontal direction, and the substrate follows
3. Circular screen printing: circular screen printing is a cylinder screen plate, which is equipped with a fixed ink scraper, and the cylinder plate and substrate move at the same speed.
4. Indirect screen printing: in the first three methods, the substrate is directly printed by the printing plate, but only some regular geometric forms, such as plane, cylindrical surface and conical surface, can be printed. For the complex shape
For special-shaped objects with edges, corners and concave surfaces, indirect screen printing must be used. The process is usually composed of two parts: plane screen printing and transfer printing, that is, screen printing images are not directly printed on the substrate, but first printed on the plane material, and then transferred to the substrate by a certain method. One of the indirect printing methods is to print the image on the flat glass with the flat screen printing method, and then use the elastic silica gel head to absorb the ink image from the glass plate as if it is sealed, and then transfer it to the irregular surface. The other method of indirect screen printing is to transfer the paper, such as: screen printing paper + heat transfer, screen printing paper + pressure-sensitive transfer, silk Screen printing paper + solvent activation transfer. Indirect screen printing has become the main field of printing industry.
① Flat screen printing machine。 Use the flat screen plate to print on the flat substrate。 Generally, the scraper plate presses the plate to move horizontally, and changes the substrate through the plate rise and fall。
② Curved screen printing machine. Use the flat screen plate to print on the circular substrate. Generally, the scraper plate is fixed, the plate moves horizontally, and the substrate rotates with the linear speed of the plate.
③ Rotary screen printing machine. Use cylinder screen.
④ Electrostatic screen printing machine. Using the stainless steel screen plate with good conductivity, the static electricity between the positive and negative electrode plates drives the powder ink to pass through the through-hole part of the plate and attach to the surface of the substrate, which is a non-pressure printing. The shape of the machine varies according to the substrate, but generally includes the substrate input part, the printing part, the ink fixation and drying part and the substrate collection part. The printing part is composed of screen printing plate, electrode plate and high voltage generating device.
3、 How it works
① The working cycle program of flat screen printing machine takes flat screen flat flat screen flat screen flat screen flat screen flat screen semi-automatic hand screen printing machine as an example. One of its working cycle is: feeding → positioning → plate dropping → falling to the ink plate, rising back to the ink plate → scraping stroke → rising to the ink plate → falling back to the ink plate → plate lifting → ink returning stroke → releasing positioning → receiving.
In the continuous cycle action, as long as the function can be realized, the time occupied by each action should be as short as possible to shorten the same period of each working cycle and improve the working efficiency.
③ Imprint line. In the printing process, the ink and screen plate are extruded on the ink plate to form a contact line between the screen plate and the substrate, which is called the embossing line. This line is at the edge of the scraping board, and numerous imprinting lines form the printing surface. It is very difficult to achieve the ideal imprinting line, because the printing process is a dynamic process.
③ Screen printing machine working principle. Taking the commonly used hand screen plane screen printing machine as an example, the working principle of the screen printing machine can be described as follows: the power is transmitted through the transmission mechanism, so that the scraper plate compresses the ink and the screen printing plate in the movement, so that the screen printing plate and the substrate form an imprinting line. Because the screen has tension N1 and N2, the force F2 is generated on the scraper plate, and the resilience makes the screen printing plate not bear the imprinting line except for the imprinting line The printing materials are in contact with each other. Under the extrusion pressure F1 of the scraper, the ink is leaked from the moving imprinting line to the substrate through the mesh.
In the printing process, the screen printing plate and the scraper plate move relative to each other, and the extrusion pressure F1 and the rebound force F2 also move synchronously。 Under the rebound force, the screen returns to contact with the substrate in time, so as not to rub the imprint dirty。 That is, the screen in the printing process, constantly in the deformation and rebound。
After one-way printing, the scraping board is separated from the substrate together with the screen printing plate, and at the same time, the return ink is returned, that is, a printing cycle is completed。 The distance between the upper part of the back ink substrate and the reverse side of the screen printing plate is called the same plate distance or screen distance, generally 2-5mm。 In manual printing, the skill and proficiency of the operator directly affect the formation of the embossing line。 In practice, the silk screen printing workers have accumulated a lot of valuable experience, which can be summed up as six points, namely, to ensure the straightness, uniform speed, equal angle, pressure equalizing piece, centricity and verticality of the scraping plate movement。 That is to say, during printing, the ink scraper should move in a straight line without shaking left and right; it should not be slow in front and fast in back, fast in front and slow in back, or slow and fast in back; the inclination angle to the ink scraper should be kept unchanged, especially to overcome the common problem of gradual increase of inclination angle; the printing pressure should be kept uniform; the distance between the ink scraper and the inner sides of the screen frame should be kept equal; the distance between the ink scraper and the frame should be kept vertical。
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