The technical parameters of tension network mainly refer to the size of tension network and the determination of tension network Angle.
(1) Tension network tension
Screen printing accuracy is related to screen plate accuracy, and screen tension is one of the important factors affecting screen quality.The tension of the screen and the frame of the material and strength of the screen material, temperature, humidity, tension network methods have a great relationship.Screen screen general requirements to not only do not lose elasticity, but also have good elongation, in order to ensure small screen distance, high precision printing requirements.The fine mesh tension that satisfies this condition is called the rated tension and is sometimes called the optimal tension.
Usually in the case of manual tension network and no tension meter, the tension is determined mainly by experience.Stretch the screen while the network, the side with the finger pressure screen, generally with the finger pressure screen feel screen has a certain elasticity.The mastery of elasticity depends on experience.
In the use of the network machine and the network frame stretch net, generally use tension meter test to determine the tension of the screen.The tension of the screen to be controlled within the elastic limits of the screen, and not the greater the better.Tension is too large, beyond the elastic limit of the material, the screen will lose elasticity, become brittle, and even tear, especially in the process of tension and tension network after the completion of the network, tension is too large if not careful use of sharp objects against the network, will make the screen tear.Lack of tension, soft screen, lack of resilience, in the process of printing, easy to stretch deformation, and even the phenomenon of rolling mesh.
Of course, the screen tension is not fixed, according to the different operating environment and print to determine the different tension.The operating environment includes the size of humidity, washing impulse, mesh size, scraping drawing, ink shear force.The surface of the substrate undulation and printing accuracy will affect the size of the tension.
The net surface tension should not only reach a certain size, but also make the entire net surface force uniform, the size of the net surface tension uniformity depends on the tension network used by the device and the way of the network, that is, the tension network device quality level and the uniformity of the silk line performance.The tension network requires each silk wire of the wire mesh theory must be the same tension, and the screen under the action of the tension of the deformation of the tension are in the elastic limit.The ultimate purpose of the uniformity of screen tension is to ensure the uniformity of screen tension, to ensure the relative stability of the plate image, prevent the plate image deformation in printing.The screen of each wire mesh only in uniform consistent case, in order to ensure that the screen under the uniform tension to produce uniform deformation.In actual production, no matter what form of stretch network machine, its four corners of the tension will be greater than the central area.In order to make the graphic tension uniform, it is necessary to make the stretch network clip shorter than the length of the screen, so that the four corners will form a weak force zone.In production, several frames can be stretched and glued at the same time to make the tension of the stretched network roughly uniform and consistent.
Screen appearance to be good, warp and weft threads to keep vertical.The appearance of the Internet version to clean without damage, no deformation of the screen frame.The warp and weft of the stretched screen should be as vertical as possible with the edge of the screen frame, of course, there are also diagonal tension network.When stretching the network to pay attention to the direction of the force and the screen to keep the same, the cable will make the direction of different, printing affects the quality of printing.In addition, pay attention to the direction of the force should be uniform, preferably at the same time, the size of the force should be as consistent as possible.When a force is applied in one direction, the silk perpendicular to the direction of the force will move in the middle.
Stretch the screen in place or use to prevent relaxation.The ideal screen, the tension should be the same or less.In the actual production process, we often find that over a long time, the screen will become loose or more loose, there is a tension drop phenomenon.There are many reasons for this phenomenon, such as mesh frame deformation and mesh tension relaxation, in order to reduce this situation, should take the “continuous network” and “repeated tension” tension network method, that is, make a part of the tension relaxation in the fixed network before the completion.Of course, the mesh frame will also produce deformation, even aluminum or alloy mesh frame in the stretch network tension will also produce deformation, you can use two ways to avoid the loss of tension caused by mesh frame bending.That is, at the same time, the network frame in advance stress or tension network in advance stress.
(2) Determination of tension
Figure 2-22 Screen tension
Because tension network tension directly affects the durability of the screen and printing quality.Now every silk screen printing factory must have tension tester to carry out fine product printing.In the process of stretching the network, in order to make the screen to get uniform and consistent tension, it is necessary to measure the tension of the screen with instruments at any time. When the standard tension value is reached, it should stop feeding, let the screen stand for 10-15 minutes, aging treatment, in order to make the tension further uniform conduction and stability.
There are two kinds of tension tester, mechanical and electronic: Newtonian tension tester and electronic tension tester.The mechanical tensiometer is inexpensive and the accuracy of the test can meet the special requirements of the printing.The difference between the two types of tension testers is that mechanical tension testers tend to suffer from mechanical fatigue after a period of use, so they often need to be re-calibrated.Electronic tension testers work with pressure sensors that transmit information to the display via electrical wiring.Electronic testers work with a range of 1/10n but are necessary for accuracy of screen tension.Mechanical testers test the flexibility of the screen under pressure, either from a specified weight or from a spring.Through a simulated measuring scale can not only show the screen flexibility, but also can show the stretched screen on the weight of the counteracting force.
When measuring tension with instruments, the five-point test method is generally adopted, that is, five test points are uniformly selected in the center and four corners of the screen frame. Each point is measured once in both meridional and zonal directions. The tension value should be within the standard range, but the smaller the difference between each point, the better.Large screen frame can be used to add test points, such as six or nine point test method.The tension of tension network after 48h has a significant downward trend, 3~5d after the decline is not obvious, more than 6d is basically stable, so the tension network should be reserved, it is best to stretch well in advance, to avoid tension.It is also important that the technician calibrate the tension meter to zero before each screen measurement.
(3) Tension net Angle
Silk screen
The tension network Angle refers to the Angle between the warp and weft of the screen and the edge of the screen frame.There are two types of tension net: one is straight tension net, the other is diagonal tension net.Is the wire mesh warp, weft respectively parallel and perpendicular to the four sides of the screen frame, using the wire mesh stretch to reduce screen waste, can also ensure uniform tension.However, in color printing using this form of stretch network plate prone to moire, so the color printing should be used diagonal stretch network.
It is beneficial to improve the printing quality and increase the ink penetration.Its shortage is a large screen waste.Although the color printing should take the diagonal stretch network, but in the actual stretch network, in order to reduce waste, the general majority of factories in the reproduction of printed matter still use the stretch network.In the color printing with high requirement of printing accuracy, sometimes the method of diagonal tension net is used.The choice of fine mesh Angle has a direct impact on the quality of printing, stretch network Angle choice is not suitable, there will be moire.Therefore, in general reproduction printing, the tensile network Angle is usually 20°~35°. When printing high resolution circuit board, due to the high number of mesh used.Only stretch network Angle match, to effectively prevent moire.
When the use of pneumatic stretch mesh machine like the active mesh clip, can not be made directly inclined screen, that is, the screen wire and frame edge into a certain Angle of the screen, also known as the small network frame stretch net method.This can be solved by the method of control frame or control panel.That is, when pulling the net, another use a larger screen frame or board as the layout and support of the control frame of the net clip, the screen is still maintained, is pulling, and in the control frame, according to the required Angle put a screen frame, and the net fixed in the frame above the oblique screen.