Blanket is one of the important materials for offset printing. The correct choice and use of blanket CTP is extremely important for ensuring the quality of the product and improving the service life of the blanket. Here we will introduce to you the main characteristics of the blanket and the choice and use of the road.
1. The main characteristics and options of the blanket
(1) Elasticity. Refers to the ability of the blanket to restore its original shape immediately after removal of external forces. This is the most basic and most important technical requirement for the blanket. It determines whether the printing ink can be transferred normally. During the printing process, the blankets are subject to several thousand compressions per hour. Due to the compression fatigue, permanent deformation occurs, resulting in thinning of the blanket thickness and proofing. The elasticity is reduced, and the ink receiving and ink transfer properties are affected. Therefore, the elasticity of the blanket is required to be better, and the compressive deformation value should be smaller in order to prevent the shrinkage of the blanket and to ensure the transfer of the graphic and text and the quality of the printed matter. Plate making
(2) Hardness. Refers to the ability of the blanket to withstand the collapse of external forces. The hardness of the blanket is generally between 60 and 70 (HS). The high hardness of the blanket marks clear equipment maintenance and maintenance, and easy to get a uniform ink, but it is also easy to abrade the plate, the accuracy of the machine and the blanket itself is also higher; the hardness of the blanket can compress a large amount of The amount of ink received is relatively large, but the outlets tend to increase. Therefore, the hardness of the blanket should be suitable for EFI, and three factors should be considered: the quality of the printed matter, the life of the printing plate, and the accuracy of the printing press and the blanket itself.
(3) Smoothness. Refers to the smoothness of the surface of the blanket. The smoother the surface of the blanket is, the clearer the outline of the printing dots and the graphics, but the surface of the blanket with good smoothness is poor in ink absorption, which will affect the ink acceptance and transfer, and it is easy to absorb paper and other impurities. Therefore, printing materials, blankets must be surface treatment, so that the distribution of numerous small sand. When the blanket is smoothed over a long period of time, a cleaning agent can be used to destroy the smooth film layer and enhance the roughness of the surface.
(4) Elongation. Refers to the percentage of the original length of the blanket under a certain tension. The amount of elongation depends mainly on the number of layers, material properties, and strength of the base fabric. The fabric structure of the bottom fabric is dense and uniform, and the mechanical strength is high. Therefore, the elongation of the blanket is small and the deformation coefficient of the small dairy product is also small. Thus, it has the advantages of accurate overprinting, small transfer and deformation of the graphics and text, clear marking, and the like; on the other hand, the printing quality is poor. .
(5) Oil and solvent resistance. Refers to the ability of the surface of the blanket to resist the infiltration of oil or certain solvents. During the printing process, the surface of the blanket is constantly in contact with ink, solvents, cleaning agents, etc. If it lacks resistance, its contact portion will inflate the Beiren shares and affect the printing quality. Therefore, the blanket must have good oil and solvent resistance in order to ensure the stability of the printing quality. Print
(6) acid and alkali resistance. Refers to the ability of the surface of the blanket to resist the erosion of acids and bases. The offset fountain solution contains weak acids, while the PS plate revision paste contains alkaline substances. Therefore, the blanket is required to have acid and alkali resistance and corrosion resistance.
(7) Wear resistance, heat resistance and aging resistance. Refers to the ability of the blanket to withstand friction and heat. When the printing press runs at a high speed, the blanket will be heated and aged by friction. Therefore, it is required that the blanket has good physical and mechanical properties, and has various properties such as abrasion resistance, heat resistance, and aging resistance, so that it can prolong its service life.
At present, offset rubber blankets are mainly divided into ordinary blankets and air-cushion blankets, and there are also several points to be noted in terms of selection.
Air-cushion blankets are suitable for printing machines with hard-lining or neutral-overlining and high-speed printers to print color products with high-line screens. It has a micro-foam sponge layer, which effectively reduces the dot gain and loss of gradation, enhances the sharpness and gravure of printed graphic and text, and improves the accuracy of tone and color reproduction. At the same time, its sensitivity to elasticity and impact resistance is higher than that of conventional blankets. For high-speed printing, it can stabilize the printing pressure, reduce the internal wear and aging speed of the blanket, and prolong the service life. film
If soft liners are used to print common products, because of the large amount of compression of the soft liner and the wide embossing area, the spread of the dots will increase, offsetting the advantage of high accuracy of the graphic transfer of the air-cushion blanket, and it is not worth adopting the price. It is much higher than the air blanket blanket of ordinary blanket. If the accuracy of the print is not high, it would be more cost effective to use a plain blanket when using a soft lining.
In addition, the use of UV inks or UV varnish may result in swelling of the general ink roller, blanket, or resin plate, and may even cause ink layer peeling or surface chipping. Therefore, proper or UV-specific blankets and resin plates (such as EPDM-based blankets are particularly suitable for UV inks and UV varnish) should be selected.
2. The correct use of the blanket
(1) Blanket cutting
On the back of the blanket, there is a mark or color line indicating the latitude and longitude position of the blanket. When cutting, the required size is cut according to the specification data so that the direction of the warp is consistent with the direction of rotation of the drum, and the weft is parallel to the plate clamp. When cutting, it is necessary to ensure that the four corners are right-angled and cannot be skewed. Otherwise, the blanket will be subject to uneven force, which may cause peristalsis or distortion and cause dot distortion.
(2) Measurement of Blanket
Printing pressure is an important part of offset printing. Newspaper printing. The size of the printing pressure is usually expressed indirectly by the maximum amount of compression when the liner linings the cylinder. In order to ensure that the printing pressure is constant, when replacing the new blanket, the blanket and the liner should be measured, the total thickness of the liner should be calculated, and the thickness of the liner should be adjusted at any time according to the change in the thickness of the paper. The request. During the measurement, the cylinder pressure gauge was used to measure the tightness of the liner lining at different positions in the circumferential direction of the blanket cylinder to calculate the printing pressure. If measuring with a micrometer, it is better to measure the four sides of the blanket, and to correctly estimate the color management of the difference between the thickness of the blanket after tightening and the thickness in the free state to reduce the deviation. Digital Printing Machine
(3) Installation of Blanket
When installing the blanket, note that the depth of the blanket inserted into the plate should be the same. First tighten the screws on one plate and measure with a ruler whether the plates are parallel. Then tighten the screws of the second plate. After tightening all screws, check with a ruler to prevent the position of the blanket from changing during tightening. offset printing
Newly-changed blankets are prone to stress relaxation. Therefore, new blankets cannot be stretched too tightly for the first time. After being printed for a period of time, they are tense again. Repeating three or four times can weaken stress relaxation and make it stretched. The tightness remains stable for a longer period of time. After the blanket has been installed, it is required to evenly and tightly surround the outer surface of the liner. The tension in all places should be consistent. Too tight standards and certification will lead to thinning of the adhesive layer, reduced elasticity, uneven printing pressure, poor ink transfer, etc.; too loose, and the blanket will be displaced under the effect of the pressing force. Cannot reset in time, causing ghosting failure.
(4) Blanket cleaning
Should use strong solubility, volatile organic solvent as a blanket of detergent, such as special cleaning agent or gasoline manuscript, if you use slow evaporation of kerosene or other solvents to clean the blanket, easy to make the blanket swelling. Clean the blanket in a timely manner, and to wash and dry ink, do not allow the ink to remain in the microporous surface of the blanket, otherwise it will oxidize the conjunctival packaging container over time, resulting in a smooth and glossy film on the surface to reduce its ability to absorb ink, Affects product quality and accelerates aging. If the blanket has a slight embossing phenomenon, or the ink transfer performance is reduced, use a blanket recovery agent to wipe off the investment purchase, and then wipe with a clean water or a damp cloth. When cleaning, prevent the cleaning agent from penetrating into the bottom cloth of the blanket, so that the edge of the blanket expands. The blankets should be cleaned during long-term shutdowns and after work.
(5) Blanket Storage CTP
The rubber blanket should avoid colliding with oils, acids, alkalis, salts and other chemicals. At the same time, it must avoid glare, high heat and humidity. Otherwise, the surface is prone to swelling deformation, stickiness, crusting, dry cracking, hardening, and the phenomenon of bottom layer mold rotten. . The general storage blanket is wrapped in black paper, stored in a dry and ventilated place, and maintained at a relative humidity of 65% to 70% at a temperature of about 22°C. For those that are not used temporarily, they should be washed in time, put on talcum powder and then stored. When the blanket is stored, it is necessary to prevent heavy pressure and folding so that the elasticity and flatness are not affected by the pressure deformation. When storing multiple blankets, use a face-to-face or back-to-back stacked digital press to avoid affecting the flatness of the surface.
