Five steps to teach you how to properly use and maintain the blanket
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The blanket is one of the main consumables of the offset printing process, and it is also the medium for offset printing transfer. Its performance has a great influence on the printing quality of the product. Therefore, correctly understanding and mastering the structure and performance of the blanket, scientifically and rationally using and maintaining the blanket can not only improve the performance and life of the blanket, but also effectively improve the printing efficiency and product quality.
First, the difference between ordinary blanket and air cushion blanket structure
The blanket is made of 3 to 4 layers of plain cloth bonded with a rubber adhesive. Its surface is coated with a thick rubber layer. This rubber layer is further vulcanized to meet the printing requirements. The elasticity and hardness are then calendered to obtain a uniform and accurate thickness. Since the elongation and strength of the blanket mainly depend on the nature of the base fabric, the fibers of the cloth are pre-stretched, and the thick line is removed to make it uniform in texture, and then the synthetic rubber roller is used on the coater. The surface of the cloth is coated with a thin layer of viscous rubber solution - a layer of glue. It has good elasticity and small compression deformation. Therefore, natural rubber is generally used, and it contains a vulcanizing agent and an antioxidant. The excess solvent is scraped off with a rubber knife. The coated fabric is then fed into a steam heated roll such that a layer of dried vulcanized rubber adheres to the surface of the cloth. Thereafter, a layer of the bonding compound was uniformly applied over the entire surface, and a three- or four-layered blanket substrate with an additional back side of the linen was laminated. Since the rubber layer on the surface of the blanket is constantly in contact with the printing plate, the ink, the fountain solution, the gasoline, etc., and is continuously compressed, the surface rubber layer has good ink transfer and acid resistance. In addition to solvent resistance and other properties, it should also have certain mechanical properties. The surface rubber layer is generally made of a rubber having good oil resistance, such as nitrile rubber or neoprene.
Offset printing also has a blanket called air cushion blanket, which is mainly different from the above-mentioned ordinary blankets in that in addition to various fabric layers and rubber layers, there is a gas-filled or micro-bubble-like aeration layer in between. Between the aeration layer and the surface layer is a strong carrier layer to strengthen the bonding of the upper and lower layers. In the process of embossing, the air cushion blanket is reduced in volume due to the pressure of the air cushion layer, and the volume reduction is achieved by compression of the air groove or microbubbles. However, when the ordinary blanket is squeezed, the volume cannot be reduced. Therefore, a convex hull is formed before and after the embossing line, and the convex hull cannot be quickly taken down in an instant, so that the deformation of the embossing, the increase of the dot, and the graphic are easily caused. Blurring, ghosting, high-profile partial reproducibility and increased wear and tear on the surface of the printing plate. The air cushion blanket does not form a convex hull, and thus does not cause this series of ills. Therefore, it is best to use air-cushion blankets to print the fine products to improve the printing quality of the products.
Second, the technical requirements and characteristics of the blanket
1. Thickness. The thickness of the three-layer blanket is 1.6 to 1.7 cm; the thickness of the four-layer blanket is 1.8 to 1.9 cm. The thickness of the blanket should be uniform and the thickness difference should be less than 0.04cm. The thickness of the blanket should be reasonably selected based on the characteristics of the equipment or printing. When the blanket is used, it can be properly padded on the back side according to the pressure condition to meet the printing quality requirements.
2. Hardness. Hardness refers to the ability of a blanket to resist external force. Generally, the hardness of the blanket is between 60 and 70 (Shore). The high-hardness blanket is clear and easy to obtain a uniform ink color, but it is easy to wear the plate. The rubber with low hardness can compress a large amount, the receiving amount of the ink is correspondingly large, and the printing is easy to expand and deform, so it is suitable for printing materials with poor gloss and general products.
3. Elongation. The smaller the elongation of the blanket, the smaller the coefficient of deformation (such as elongation and thinning), and the elongation depends mainly on the number of layers of the base fabric, material properties and strength. A blanket with a small elongation has the advantages of accurate overprinting and clear graphic imprint. Conversely, the print quality effect is poor.
4. Elastic and compressive deformation values. When the blanket is pressed, it will sink down. Under the action of elasticity after pressing, its sinking surface should be quickly restored and restored. This requires the elasticity of the blanket to be good and the compression deformation value to be small to prevent the blanket. The shrinkage is thinned to ensure the stable printing quality of the product.
5. Smoothness and flatness. The smoothness of a blanket refers to the smoothness of its surface, while the flatness refers to the uniformity of its thickness. The surface of the blanket is smooth, and the dot and graphic contours are printed clearly. However, if the smoothness of the blanket is too good, the surface absorbency is poor, which will not only affect the smooth and uniform acceptance and transfer of the ink, but also easily adsorb. Impurities such as paper dust. Generally, there are numerous fine sands on the surface of the blanket. When the blanket is used for a long time, the surface is smoother. The cleaning agent can be used to destroy the shiny layer to enhance the ink absorption of the surface. The better the flatness of the blanket, the more uniform the printing pressure, ink absorption and ink transfer performance.
6. Oil and solvent resistance. During the use of the blanket, its surface needs to be constantly in contact with the ink and the cleaning agent, and the oil or solvent easily causes the rubber to swell, thereby affecting the printing quality of the product. Therefore, the blanket must have good oil and solvent resistance to ensure stable printing quality.
7. Transmissibility and hydrophobicity. The blanket is the medium for the transfer of the printed ink layer. Therefore, the blanket must have good ink adsorption and strong hydrophobicity to ensure the printing quality of the product.
Third, the surface of the blanket must be kept clean to achieve good imprinting transfer.
The principle of offset printing clearly shows whether the blanket can completely transfer the graphic ink layer on the printing plate to the paper surface or other substrates. In addition to its flatness and elasticity, it is very clean to keep the surface of the blanket clean. important. We know that in the high-speed printing process, due to the adhesiveness of the blanket and the "separation work" when the ink layer breaks, the surface of the blanket will inevitably gradually gather impurities such as paper dust, fillers and pigments. When the printing surface is inferior in strength, the filler is combined with the paper or paperboard which is not strong enough, or when the ink with coarse particles, large pigment ratio and uncomfortable viscosity is used for printing, impurities will be accumulated on the surface of the blanket, which affects normal lubrication. Conditions, which affect the normal transfer of the ink layer, can easily lead to the occurrence of plague quality defects. Based on this situation, the blanket must be washed frequently during printing, and the accumulated layer on the surface is often removed to achieve uniform ink absorption and ink transfer. Under normal circumstances, generally every 3,000 prints, it is necessary to scrub a blanket, but in the actual operation process, the printing effect should be controlled as appropriate to ensure the stability of printing quality.
Fourth, master the correct cleaning method of the blanket to achieve good imprinting transfer
In production, for safe operation and easy cleaning, the machine can be operated at low speed or jog, while wiping the water on the surface of the blanket with a clean wiper and then stopping the operation. At this time, the right hand can take a piece of rubbing cloth with a small amount of gasoline, first scrub the blanket, let the ink dirt and impurities melt, open the dry wipe with your left hand to wipe the dirt and wipe dry. If the accumulation layer on the blanket is thick, it will not be cleaned once. It can be wiped repeatedly with a petrol cloth until the dirt is completely removed, and then wiped clean with a petrol cloth. The gasoline on the wipes can't be rubbed too much at one time, so as not to drip onto the machine when the blanket is squeezed to cause dirt. If the oil is too small, it will not dissolve the dirt and it will be difficult to clean. Therefore, when the dirty stain on the blanket is cleaned with gasoline, the dry stain is used to wipe the stain, and the cleaning effect is better. To ensure that the printed image is just complete and clear, it is best to apply a layer of talcum powder after the blanket is washed so that the solvent remaining on the surface is blotted and then wiped clean with a cloth. In fact, cleaning the blanket is a patience and meticulous work, which must be done neatly and carefully, in order to improve the quality of the cleaning.
Five, the use and maintenance of blankets essentials
1. Use a blanket according to the characteristics of the product. Printing fine products and printing general products; printing paper good coated paper, glass cardboard and printing offset paper, white paper, etc., it is best to use two blankets separately, such as printing high-grade fine products, can be used new The blanket is used, but the old blanket can be used for printing products, which can better guarantee the printing quality and improve the economic benefits.
2. If the downtime is slightly longer or before each shift, the blanket must be carefully cleaned. In normal times, the surface of the blanket is also thoroughly scrubbed with pumice powder according to the degree of surface area of the blanket.
3. For the blanket that is not used temporarily, after washing and cleaning, apply a layer of talcum powder, then wrap it in black paper and place it in a cool place to prevent thermal aging, photoaging and deformation of the blanket.
4. In order to avoid rolling the blanket into dents, the length of the liner paper should be cut into 2 to 4 mm one by one, so that the trailing edge of the liner is stepped, which is also beneficial for wrapping the inner liner. .
5. In order to avoid accidental crushing of the blanket, it is necessary to concentrate on the paper feeder and the console during printing to prevent paper balls, angled paper and other foreign matter from being damaged by the impression cylinder.
6. When using the blanket, it must be tight and tight, and the force should be even, so as to avoid the printing ghosting failure due to the empty drum.
7. To master and adjust the dryness of the ink, prevent the ink from drying the conjunctiva on the surface of the blanket, affecting the ink absorption and ink transfer performance of the surface.
8. To master the printing pressure, so as to avoid the elasticity and flatness of the blanket due to excessive or uneven pressure, which affects the printing quality of the product.
9. Keep the blanket away from moisture and heat, and avoid the sunlight to prevent the moisture and high temperature from swelling and deforming the blanket, reducing the flatness and affecting the printing quality.
10. Avoid mixing xylene, toluene, volatile oil and turpentine to prevent oxidation and swelling on the surface of the blanket.
11. The blanket should be stored in a ventilated, dry place. The indoor temperature is generally required to be between 18 and 25 ° C, and the relative humidity is between 60% and 75%.
12. The blanket should not be in contact with harmful substances such as electromagnetic, chemical, oil, acid, alkali, salt, etc., to prevent the surface rubber layer from sticking, crust, hardening or cracking.
13. The blanket should be placed on the surface and the surface or the back and back should be placed in contact with each other. Do not allow the back layer to directly contact the front rubber layer, and prevent folding or heavy pressure from damaging its elasticity and flatness. .
14. The direction of the arrow on the back of the blanket must be consistent with the direction of rotation of the drum so that it has a low elongation and can withstand large tensile forces.
15. A remedy for the problem of depression of the surface portion under pressure. When the surface of the blanket is deformed by the foreign matter rolling, the softness can be restored by using a soft cotton gauze or a felt rubbing agent to wipe the depression a few times.