Drum screen printing is a new process developed in recent years. It not only has good printing quality, but also is beautiful, generous and efficient. It is an ideal process for printing on the outer surface of steel drums. At present, most of the texts and patterns printed on the surface of steel drums are printed. The original stencil printing process has gradually been eliminated due to its small text and pattern capacity, poor quality, low efficiency, and large pollution.
The basic principle of the drum screen printing is: part of the mesh of the screen printing plate can penetrate the ink and leak to the surface of the steel drum; the mesh of the rest of the printing plate is blocked and cannot pass through the ink in the steel drum. Blanks form on the surface.
The plate-making method that is now more commonly used is the photochemical platemaking method. The plate making method uses a wire mesh as a support body to tightly stretch the wire mesh on the frame, and then coats the photo resist on the web to form a photosensitive plate. The positive plate is then tightly sealed on the plate and exposed. Developing, the part of the plate that does not need to be over ink receives light, forms a cured film, seals the mesh, and does not penetrate the ink during printing; the part of the mesh that needs to pass over the ink on the plate is not sealed, and the ink passes through during printing. Ink is formed on the surface of the drum.
When printing, ink is poured into one end of the screen plate, and the ink does not leak through the mesh hole on the surface of the steel drum without external force. When the ink is scraped with a squeegee blade at a certain inclination angle and pressure, the ink is transferred through the screen plate to the steel drum under the screen plate so as to realize the reproduction of the pattern.
The initial process for the drum screen printing is the full manuscript. At this point, the size, shape, position, number of prints, etc. of the steel drum to be printed are to be clearly defined. According to these requirements, the accuracy of the printed pattern and the quality of the image are determined. For steel drums, due to the fact that they are used outdoors, special attention should be paid to their weather resistance when choosing inks.
Screen printing is based on manuscripts. Then choose the plate making method. Printing process and determine what printing materials should be used. In the case of silk screens, its materials are now mostly made of nylon nets with ideal elasticity and recovery, and its concave and convex surfaces can be printed. The methods of plate making can be roughly divided into two methods: manual excavation and platemaking and photolithography. The former is suitable for patterns with less precision and capable of depicting; for patterns requiring higher precision and with emphasis on tone levels, photolithography must be used. In the photolithography method, a direct method can be used when manufacturing a printing plate with strong print resistance. This method results in poor image quality because the positive master plate clings to the photosensitive film of the screen during printing. When high quality images are required, indirect platemaking is preferred.
For steel drums with few prints and low print quality, manual printing is the most convenient. If you need a large quantity and require a certain quality, you need to use a printer. Due to the vast differences in screen printing materials, quality, and shapes, there are many types of presses. Due to the difference in texture of the printed materials (some are printed on the film and some on the galvanized sheet, etc.), the adhesion properties of the inks are different, and care should be taken when selecting the appropriate drying method.
Screen printing plate making is the basis of screen printing. If the plate making quality is not good, it is difficult to print a good quality product. The failures in printing are often related to the improper selection of materials in plate making process technology and plate making. Therefore, if we want to make a good screen board, we must correctly master the platemaking technology according to the requirements of the platemaking process, and strictly select plate-making materials for plate making. The main issues involved in the platemaking work are: how to properly use the material of Chuanchuan in the process of making plates, such as screens, net frames, and photosensitive materials, and how to master the bottom plate making, stretching, coating, printing, developing, light source, etc. .
First, the screen
The screen is the skeleton of the screen, and it is the substrate that supports the photosensitive film. The common screens for steel drum screen printing are monofilament nylon screens and thin nylon screens.
1. Nylon screen
It is a nylon monofilament woven, heat-treated and dimensionally stable after weaving. Plain weave can reach 380 mesh and twill weave is larger than 330 mesh. Nylon mesh has the following characteristics:
(1) The nylon mesh has a smooth surface and good ink permeability, and can use inks with large viscosity and large particles, so that a fine print pattern can be obtained;
(2) Use fine mesh woven mesh nets, suitable for very fine line drawing patterns and dot printing;
(3) Large elasticity, appropriate flexibility, good adaptability to the surface of steel drum, suitable for printing curved surface of steel drum;
(4) The tensile strength, nodule fastness, elasticity and friction resistance are good, and the service life is long;
(5) Good resistance to acids, chemicals, and organic solvents. Recycling is easy, especially for alkalis.
Use nylon mesh should pay attention to the following points:
(1) Compared with polyester silk and silkworm silk screens, nylon silk screens have high elongation. In order not to cause a printing failure, it is necessary to increase the tension of the stretching net, and at this time, the contraction force also becomes large. Therefore, it is required to use a strong frame and a stretching machine.
(2) Because of its low heat, if the net is fixed to the frame by the hot melt method, the operation is difficult;
(3) It is not resistant to erosion by strong acids, phenols, cresols, formic acid, etc.;
(4) Poor light fastness, easy to degrade under ultraviolet light, avoid light when storing.
2. Polyester mesh
Polyester mesh has the following features:
(1) It has small elongation and strong elasticity when it is under tension, and single-line screen is suitable for high-precision printing;
(2) The tensile strength, structural strength, resilience, and print resistance are all good;
(3) It has sufficient chemical resistance, especially acid resistance and organic solvent resistance, and can be recycled and utilized like nylon.
(4) Low hygroscopicity, hardly affected by humidity;
(5) Heat resistance is higher than that of nylon and is less affected by ultraviolet light than nylon.
Polyester mesh should pay attention to the following points:
(1) It needs more stretch tension than nylon mesh, and needs stronger frame, stretcher and firmer bonding method;
(2) Due to the hydrophobicity of polyester, it is difficult to adhere to the plate, and care must be taken to wash and degrease the plate before plate making.
(3) Poor ink resistance is worse than nylon, not resistant to alkali corrosion.
Nylon mesh and polyester mesh are two commonly used screen printing materials. Nylon mesh has good resilience, good ink resistance, less static electricity than polyester mesh, good wear resistance, moderate cost, and is generally printed on steel drums. The preferred screen. However, due to the high elongation of nylon mesh, it is not suitable for printing high-precision patterns. For screen printing, such as multi-color overprinting, polyester webs are preferred.
Second, the frame and the stretch net
1. Frame
The frame used to support the wire mesh is made of metal, wood or other materials and is divided into two types: fixed and adjustable. The most commonly used is a frame made of aluminum material. The materials used to make the frame can meet the requirements of stretch tension and are strong, durable, light and inexpensive.
Square and rectangular frames are generally used for printing on the top surface of a drum. However, when printing on the circular surface of the barrel body, a frame adapted to its shape is generally used.
The cross-sectional thickness and shape of the frame material are also different due to the different methods of fixing the screen, its use, and strength. For example, when fixing a screen with an adhesive, angles and corners are generally used; in the case of physical fixation, a slotted frame is generally used. In the case of higher strength requirements, strengthen the ribs on the inside of the tube and use a certain thickness of the tube. In addition, some special frames themselves are equipped with stretching nets, which can be stretched without stretching the net.
In order to ensure plate making, printing quality and other requirements, the frame can be selected based on the following conditions.
(1) Strong resistance to strain. The material of the frame should have sufficient strength capable of resisting the tension of the mesh, because when the mesh is stretched, the mesh creates a certain pulling force on the frame, and if the strength is not enough, the frame is deformed so that no good print can be printed.
(2) It should be prestressed. After the netting, the bending deformation of the frame will affect the tension stability of the screen. To reduce this effect, the network box can be pre-processed. There are two methods for handling: First, according to the strength principle of the arch structure, the net frame is made into a convex shape, its deflection is about 4mm/m, each internal angle is slightly larger than 90°, or the finished metal frame is used. The special tool is stretched into this shape. This kind of pre-distortion treatment can resist the influence of the screen tension. Another method is to do a pre-stress treatment while doing pneumatic pulling, that is, the front end of the drawer is tight against the outside of the frame, the net frame is bent by the top force, and when the net is fixed, the frame is subjected to force. Although the surface is moved from the outside to the top, the force direction and size are basically the same, so no more bending is added. Due to these features, the pneumatic stretching machine has become the most popular one at home and abroad.
(3) Suitable size. The production of different specifications of the network box configuration, use the size of the printing according to the size of the appropriate frame to determine, you can reduce waste, but also easy to operate.
The size of the frame should be larger than that of the printing plate. If the plate pattern is a × b, the inside size of the frame is 2a × 2b, which can be fully printed. The selection of the frame size is based not only on the printing area, but also on the needs of the squeegee and the start and end positions of the squeegee and the ink return plate at the time of printing; the need for printing ink on the plate; and the uniform screen tension at the plate of the plate is guaranteed. The need for silk screen printing in the squeegee printing stroke.
2. Stretch net
The stretch net stretches the wire mesh to the frame, which is manually operated and mechanically operated. Manual stretch nets are simple and easy to use and are commonly used methods, while mechanical stretch nets are of good quality. Whether it is hand-stretched or mechanical stretched nets have to pay attention to the tension of the screen. It is not easy to stretch the tension of the screen too much. If it is too small, the screen tends to be loose (the stainless steel screen will also appear premature relaxation); if it is too large, the screen will break easily. In the actual stretching operation, the tension of the stretching net can be determined empirically, and while the screen is stretched, the screen is pressed with a finger until the screen feels like an elastic member. Commonly used stretching methods are:
(1) Manual Stretching Nets Manually stretching nets is performed as follows: 1 Cut out a screen with a larger size than the outer net. Generally, the length and width of the screen are 40-60 mm larger than the dimensions of the outer net frame.
2 soak the screen in water.
3 The screen is placed on the frame. The latitude line of the screen is parallel to the frame (vertical). However, when used for high-precision printing or level printing, the latitude line is at an angle to the frame. It is 20°-45°.
4 Place one side of the molding, nail the frame, and then pull the screen towards the side of the frame. Then all the bars are nailed and the side is fixed.
5 Tighten the screen toward the opposite side of the frame, place the opposite molding, and then nail the end. Then, while pulling the screen toward the corner, tighten the molding so that the opposite side is fixed.
6 In the same way, nail the other two strips and fix the other two.
(2) Stretching of the device The device is also called self-expanding net. This kind of stretch net method uses more simple devices to assist manual stretch nets. Its frame is called self-tensioning frame. This kind of frame is mostly made of metal. Its outstanding feature is that it can be pulled at any time. After the stencil is loose, it does not have to be replaced and it can be used again. In recent years, roll-type self-expanding nets have been successfully used for precision printing, and the market has expanded rapidly. Among them, the rolling frame has the best performance. It is composed of four aluminum tubes. The tube has a simple fastening device that clamps the screen. The two ends of each frame tube can be twisted with a wrench to complete the stretching.
(3) Motorized stretch net The motorized stretch net uses a mechanical stretcher. The mechanical stretcher has a buckle type, a screw type and a gear type. Large-scale stretch nets are generally motorized, while medium- and small-size stretch nets are mainly manual.
The biggest feature of the manual mechanical stretching machine is that it does not require electricity and gas. The quality of the stretching net is significantly higher than that of manual stretching, and it is close to the quality of the pneumatic stretching net.
(4) Pneumatic Stretch Net Pneumatic stretching machine uses compressed air as the air source to drive multiple cylinder pistons to synchronously push the net clamps to perform relative contraction movements in both vertical and horizontal directions, resulting in uniform and consistent tension on the screen. Generally, the net pressure of the nylon mesh can be controlled at 0.8-1.0MPa; the stretch net pressure of the polyester mesh can be controlled at 0.8-1.0MPa; the stretch net of the stainless steel mesh
The basic principle of the drum screen printing is: part of the mesh of the screen printing plate can penetrate the ink and leak to the surface of the steel drum; the mesh of the rest of the printing plate is blocked and cannot pass through the ink in the steel drum. Blanks form on the surface.
The plate-making method that is now more commonly used is the photochemical platemaking method. The plate making method uses a wire mesh as a support body to tightly stretch the wire mesh on the frame, and then coats the photo resist on the web to form a photosensitive plate. The positive plate is then tightly sealed on the plate and exposed. Developing, the part of the plate that does not need to be over ink receives light, forms a cured film, seals the mesh, and does not penetrate the ink during printing; the part of the mesh that needs to pass over the ink on the plate is not sealed, and the ink passes through during printing. Ink is formed on the surface of the drum.
When printing, ink is poured into one end of the screen plate, and the ink does not leak through the mesh hole on the surface of the steel drum without external force. When the ink is scraped with a squeegee blade at a certain inclination angle and pressure, the ink is transferred through the screen plate to the steel drum under the screen plate so as to realize the reproduction of the pattern.
The initial process for the drum screen printing is the full manuscript. At this point, the size, shape, position, number of prints, etc. of the steel drum to be printed are to be clearly defined. According to these requirements, the accuracy of the printed pattern and the quality of the image are determined. For steel drums, due to the fact that they are used outdoors, special attention should be paid to their weather resistance when choosing inks.
Screen printing is based on manuscripts. Then choose the plate making method. Printing process and determine what printing materials should be used. In the case of silk screens, its materials are now mostly made of nylon nets with ideal elasticity and recovery, and its concave and convex surfaces can be printed. The methods of plate making can be roughly divided into two methods: manual excavation and platemaking and photolithography. The former is suitable for patterns with less precision and capable of depicting; for patterns requiring higher precision and with emphasis on tone levels, photolithography must be used. In the photolithography method, a direct method can be used when manufacturing a printing plate with strong print resistance. This method results in poor image quality because the positive master plate clings to the photosensitive film of the screen during printing. When high quality images are required, indirect platemaking is preferred.
For steel drums with few prints and low print quality, manual printing is the most convenient. If you need a large quantity and require a certain quality, you need to use a printer. Due to the vast differences in screen printing materials, quality, and shapes, there are many types of presses. Due to the difference in texture of the printed materials (some are printed on the film and some on the galvanized sheet, etc.), the adhesion properties of the inks are different, and care should be taken when selecting the appropriate drying method.
Screen printing plate making is the basis of screen printing. If the plate making quality is not good, it is difficult to print a good quality product. The failures in printing are often related to the improper selection of materials in plate making process technology and plate making. Therefore, if we want to make a good screen board, we must correctly master the platemaking technology according to the requirements of the platemaking process, and strictly select plate-making materials for plate making. The main issues involved in the platemaking work are: how to properly use the material of Chuanchuan in the process of making plates, such as screens, net frames, and photosensitive materials, and how to master the bottom plate making, stretching, coating, printing, developing, light source, etc. .
First, the screen
The screen is the skeleton of the screen, and it is the substrate that supports the photosensitive film. The common screens for steel drum screen printing are monofilament nylon screens and thin nylon screens.
1. Nylon screen
It is a nylon monofilament woven, heat-treated and dimensionally stable after weaving. Plain weave can reach 380 mesh and twill weave is larger than 330 mesh. Nylon mesh has the following characteristics:
(1) The nylon mesh has a smooth surface and good ink permeability, and can use inks with large viscosity and large particles, so that a fine print pattern can be obtained;
(2) Use fine mesh woven mesh nets, suitable for very fine line drawing patterns and dot printing;
(3) Large elasticity, appropriate flexibility, good adaptability to the surface of steel drum, suitable for printing curved surface of steel drum;
(4) The tensile strength, nodule fastness, elasticity and friction resistance are good, and the service life is long;
(5) Good resistance to acids, chemicals, and organic solvents. Recycling is easy, especially for alkalis.
Use nylon mesh should pay attention to the following points:
(1) Compared with polyester silk and silkworm silk screens, nylon silk screens have high elongation. In order not to cause a printing failure, it is necessary to increase the tension of the stretching net, and at this time, the contraction force also becomes large. Therefore, it is required to use a strong frame and a stretching machine.
(2) Because of its low heat, if the net is fixed to the frame by the hot melt method, the operation is difficult;
(3) It is not resistant to erosion by strong acids, phenols, cresols, formic acid, etc.;
(4) Poor light fastness, easy to degrade under ultraviolet light, avoid light when storing.
2. Polyester mesh
Polyester mesh has the following features:
(1) It has small elongation and strong elasticity when it is under tension, and single-line screen is suitable for high-precision printing;
(2) The tensile strength, structural strength, resilience, and print resistance are all good;
(3) It has sufficient chemical resistance, especially acid resistance and organic solvent resistance, and can be recycled and utilized like nylon.
(4) Low hygroscopicity, hardly affected by humidity;
(5) Heat resistance is higher than that of nylon and is less affected by ultraviolet light than nylon.
Polyester mesh should pay attention to the following points:
(1) It needs more stretch tension than nylon mesh, and needs stronger frame, stretcher and firmer bonding method;
(2) Due to the hydrophobicity of polyester, it is difficult to adhere to the plate, and care must be taken to wash and degrease the plate before plate making.
(3) Poor ink resistance is worse than nylon, not resistant to alkali corrosion.
Nylon mesh and polyester mesh are two commonly used screen printing materials. Nylon mesh has good resilience, good ink resistance, less static electricity than polyester mesh, good wear resistance, moderate cost, and is generally printed on steel drums. The preferred screen. However, due to the high elongation of nylon mesh, it is not suitable for printing high-precision patterns. For screen printing, such as multi-color overprinting, polyester webs are preferred.
Second, the frame and the stretch net
1. Frame
The frame used to support the wire mesh is made of metal, wood or other materials and is divided into two types: fixed and adjustable. The most commonly used is a frame made of aluminum material. The materials used to make the frame can meet the requirements of stretch tension and are strong, durable, light and inexpensive.
Square and rectangular frames are generally used for printing on the top surface of a drum. However, when printing on the circular surface of the barrel body, a frame adapted to its shape is generally used.
The cross-sectional thickness and shape of the frame material are also different due to the different methods of fixing the screen, its use, and strength. For example, when fixing a screen with an adhesive, angles and corners are generally used; in the case of physical fixation, a slotted frame is generally used. In the case of higher strength requirements, strengthen the ribs on the inside of the tube and use a certain thickness of the tube. In addition, some special frames themselves are equipped with stretching nets, which can be stretched without stretching the net.
In order to ensure plate making, printing quality and other requirements, the frame can be selected based on the following conditions.
(1) Strong resistance to strain. The material of the frame should have sufficient strength capable of resisting the tension of the mesh, because when the mesh is stretched, the mesh creates a certain pulling force on the frame, and if the strength is not enough, the frame is deformed so that no good print can be printed.
(2) It should be prestressed. After the netting, the bending deformation of the frame will affect the tension stability of the screen. To reduce this effect, the network box can be pre-processed. There are two methods for handling: First, according to the strength principle of the arch structure, the net frame is made into a convex shape, its deflection is about 4mm/m, each internal angle is slightly larger than 90°, or the finished metal frame is used. The special tool is stretched into this shape. This kind of pre-distortion treatment can resist the influence of the screen tension. Another method is to do a pre-stress treatment while doing pneumatic pulling, that is, the front end of the drawer is tight against the outside of the frame, the net frame is bent by the top force, and when the net is fixed, the frame is subjected to force. Although the surface is moved from the outside to the top, the force direction and size are basically the same, so no more bending is added. Due to these features, the pneumatic stretching machine has become the most popular one at home and abroad.
(3) Suitable size. The production of different specifications of the network box configuration, use the size of the printing according to the size of the appropriate frame to determine, you can reduce waste, but also easy to operate.
The size of the frame should be larger than that of the printing plate. If the plate pattern is a × b, the inside size of the frame is 2a × 2b, which can be fully printed. The selection of the frame size is based not only on the printing area, but also on the needs of the squeegee and the start and end positions of the squeegee and the ink return plate at the time of printing; the need for printing ink on the plate; and the uniform screen tension at the plate of the plate is guaranteed. The need for silk screen printing in the squeegee printing stroke.
2. Stretch net
The stretch net stretches the wire mesh to the frame, which is manually operated and mechanically operated. Manual stretch nets are simple and easy to use and are commonly used methods, while mechanical stretch nets are of good quality. Whether it is hand-stretched or mechanical stretched nets have to pay attention to the tension of the screen. It is not easy to stretch the tension of the screen too much. If it is too small, the screen tends to be loose (the stainless steel screen will also appear premature relaxation); if it is too large, the screen will break easily. In the actual stretching operation, the tension of the stretching net can be determined empirically, and while the screen is stretched, the screen is pressed with a finger until the screen feels like an elastic member. Commonly used stretching methods are:
(1) Manual Stretching Nets Manually stretching nets is performed as follows: 1 Cut out a screen with a larger size than the outer net. Generally, the length and width of the screen are 40-60 mm larger than the dimensions of the outer net frame.
2 soak the screen in water.
3 The screen is placed on the frame. The latitude line of the screen is parallel to the frame (vertical). However, when used for high-precision printing or level printing, the latitude line is at an angle to the frame. It is 20°-45°.
4 Place one side of the molding, nail the frame, and then pull the screen towards the side of the frame. Then all the bars are nailed and the side is fixed.
5 Tighten the screen toward the opposite side of the frame, place the opposite molding, and then nail the end. Then, while pulling the screen toward the corner, tighten the molding so that the opposite side is fixed.
6 In the same way, nail the other two strips and fix the other two.
(2) Stretching of the device The device is also called self-expanding net. This kind of stretch net method uses more simple devices to assist manual stretch nets. Its frame is called self-tensioning frame. This kind of frame is mostly made of metal. Its outstanding feature is that it can be pulled at any time. After the stencil is loose, it does not have to be replaced and it can be used again. In recent years, roll-type self-expanding nets have been successfully used for precision printing, and the market has expanded rapidly. Among them, the rolling frame has the best performance. It is composed of four aluminum tubes. The tube has a simple fastening device that clamps the screen. The two ends of each frame tube can be twisted with a wrench to complete the stretching.
(3) Motorized stretch net The motorized stretch net uses a mechanical stretcher. The mechanical stretcher has a buckle type, a screw type and a gear type. Large-scale stretch nets are generally motorized, while medium- and small-size stretch nets are mainly manual.
The biggest feature of the manual mechanical stretching machine is that it does not require electricity and gas. The quality of the stretching net is significantly higher than that of manual stretching, and it is close to the quality of the pneumatic stretching net.
(4) Pneumatic Stretch Net Pneumatic stretching machine uses compressed air as the air source to drive multiple cylinder pistons to synchronously push the net clamps to perform relative contraction movements in both vertical and horizontal directions, resulting in uniform and consistent tension on the screen. Generally, the net pressure of the nylon mesh can be controlled at 0.8-1.0MPa; the stretch net pressure of the polyester mesh can be controlled at 0.8-1.0MPa; the stretch net of the stainless steel mesh
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