In screen printing, the appropriate and uniform printing pressure is the important guarantee of high quality silk screen printing.Printing pressure is too small, printing plate can't contact with the substrates and cannot be applied, cause the printing graphic is incomplete, the phenomenon such as uneven thickness of ink;Printing pressure is too big, can lead to mesh deformation is too large, printing graphic fuzzy, screen and scraping blade wear serious printing failures, etc.If uneven printing pressure, there will be additional printing failures, as a result, the control factors affecting the printing pressure, improve the printing pressure uneven phenomenon, become a silk screen printing process to solve the first problem.There are many influence factors in screen printing pressure uniformity, this paper mainly from the screen back stretch, net, net frame deformation and silk screen printing machine, etc, to analyze the effect of printing pressure uniformity, explore the technical measures to improve the uniformity of the printing pressure.
1. The screen back stretch affect printing pressure uniformity
Silkscreen printing pressure is by the pressure of scraping scraping blade, wire mesh deformation of resilience and ink viscous force the result of joint action.In screen printing, as a result of the existence of network distance, under the action of scraping blade pressure, screen will produce deformation of elongation, as scraping blade position, silk screen have different deformation, caused by deformation of wire mesh screen resilience is different also, in the same scraping pressure, printing pressure will appear uneven phenomenon.For flat screen printing, silk screen of the deformation can be divided into the scraping blade travel direction of deformation and deformation of the scraper length direction.
Suppose screen elastic obey hooke's law, for silk screen tension coefficient, the scraping blade travel direction screen tension formula can be expressed as network from stationary and network from the variable type.
Screen resilience is scraping blade left and right sides of the screen tension force component in the vertical direction, from the above expression shows: when the scraper movement on the screen, wire mesh deformation will varies with the scraping blade position, the resulting screen resilience is constantly changing, when scraping knife scraping the printing process, the constant scrapping printing pressure screen, screen printing pressure will change with the different of scraper location, which is the printing pressure uneven phenomenon.
In the deflection of the scraping blade length direction, either stationary or net margins variable type, mesh deformation is always the same, silk screen tension formula can be represented as:
Conclusion from the above expression: when scraping blade along the length direction towards net frame side, the screen left and right sides of the deformation, the back is different, resulting in uneven along the scraper printing pressure on the length direction.
Based on analysis of the scraper travel direction and the length direction of the printing pressure phenomenon is different, if for both uneven pressure compensation work, then along the scraping board length direction can make a plate in the middle of the plate position, guarantee the scraper with equal distance on either side of the screen on both sides, you can keep the direction along the length of the scraper printing pressure evenly;In scraper movement direction, it is necessary to calculate the printing pressure and scraping blade position, and then take corresponding measures to compensate.
2. Net is apart from the effect on the printing pressure uniformity
Network distance is determined by the characteristics of silk screen printing itself, as a result of the network from different, the influence on the uniformity of silk screen printing pressure are also different.From the section on screen tension formula, the network distance, the greater the deformation, the screen mesh of the range, the greater the scraper trip direction that would make a screen printing pressure range increased, thus increase the nonuniformity of printing pressure.Network from starts to cause network version, however, and the separation of substrates is not ideal, make the screen don't rebound immediately, affect the image resolution.Therefore, in order to improve the uniformity of silk screen printing pressure, should be in guarantee screen immediately under the condition of the springback, try choosing a smaller network distance.
3. The influence of ink viscosity on the printing pressure
When printing a batch of screen printing products, part of the ink solvent will evaporate with the extension of time, make the same batch of prints color inconsistencies, affect the uniformity of printing products.In general, with a number of printing products need ink need one-time with foot, and in the process of printing should timely adjust the ink viscosity, guarantee the uniformity of printing products.
4. Net frame's influence on the printing pressure uniformity
Net frame on the screen so tight, due to the effect of screen tension and screen for net framework asymmetric connection, make the screen frame deformation, which leads to the uneven tension generated on the screen, harmful to printing pressure uniformity.
In the printing process, in order to minimize net frame deformation after tension net, can make predeformation on net frame processing.Pretreatment method has two kinds: one is according to the principle of the strength of the arch structure, net frame made into convex,
5. The influence of the silk screen printing machine for printing pressure uniformity
Factors influencing the silk screen printing pressure uniformity machines are various, mainly have a guide rail parallelism and scraping blade component force application uniformity, etc.
(1) guide rail parallelism.In silk screen printing machine, guide for printing pressure uniformity play a key role.General screen printing press type has two columns or oblong shape guide rail, scraping blade components through the slider sliding back and forth on the guide rail, scraping movement, guide rail and the printing platen parallelism, is the guarantee of scraping pressure uniformity, if the rail tilt leads to scraping scraping pressure imposed by the component changes, causing the printing pressure is uneven.Can improve the guide rail parallelism in the installation guide, the guide rail is measured by parallel instrument, and the debugging unceasingly, in order to make the parallel guide rail to minimize the impact on printing uniformity.
(2) applying pressure scraping blade component uniformity.Scraping knife is scrapping printing pressure applying organization, ensure the uniformity of scraping knife work during working and the straightness of scraping blade surface is the key to ensure uniform printing pressure.If scraping cutter wear, will affect the uniformity of printing pressure, so you need to check scraping blade surface wear, grinding scraping in a timely manner.The uniformity of silk screen printing machine of printing pressure power works can be guaranteed by scraping blade component structure, the current commonly used by screen printing press is the use of two specifications of the same cylinder scraping blade control.
The uniformity of silk screen printing pressure is a comprehensive problem, its influence factors in addition to printing materials, printing machinery, and human factors and environmental factors, such as operating personnel's technical level, operation method, work attitude, etc., it's need to constantly improve the technical level of operators and operating experience, to reduce human factors, the influence of uneven printing pressure;In addition, keep the environment clean, temperature and humidity, air pressure, voltage stability, also is the key to ensure uniform printing pressure.Needs in according to the actual process of printing, printing products, control harmful to printing pressure uniformity, the main factors in order to effectively improve the quality of silk screen printing.
The uniformity of silk screen printing pressure is a comprehensive problem, its influence factors in addition to printing materials, printing machinery, and human factors and environmental factors, such as operating personnel's technical level, operation method, work attitude, etc., it's need to constantly improve the technical level of operators and operating experience, to reduce human factors, the influence of uneven printing pressure;In addition, keep the environment clean, temperature and humidity, air pressure, voltage stability, also is the key to ensure uniform printing pressure.Needs in according to the actual process of printing, printing products, control harmful to printing pressure uniformity, the main factors in order to effectively improve the quality of silk screen printing.