Use and storage of the most popular offset printin

2022-08-06
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Use and storage of offset rubber and cots

an offset press cannot print high-quality prints without excellent blanket and cots. Due to work needs, the author has visited some printing plants and found that the use and storage of blanket and cot in quite a number of printing plants are very poor, which has come to our attention

I. Problems in the use and storage of blanket and cots

1. At present, there are few systematic data on the mechanical properties and characteristics of blanket and cots. This is incompatible with today's rapidly developing printing situation

2. Due to market competition, some blanket manufacturers have taken improper measures to reduce costs, and even sold unqualified blanket to users at a low price. The flatness and elasticity of these rubbers are very poor, and other performance indicators can not meet the standard. There are more rubber roller manufacturers than blanket manufacturers, and the production scale and technical strength of each manufacturer vary greatly. The passing rate of COTS processed by some small factories is very low. The use of such blanket and cot can not only shorten the service life, but also reduce the printing quality. Instead, it can not "save", but cause serious waste

3. In the past 10 years, the number of offset printing machines in China has increased, and many individual printing houses have also purchased offset printing machines. However, some people lack the common sense of rubber blanket and cot, and ignore their important role in the printing machine, so that the rubber blanket on the machine is not replaced when it is aged (losing its printing suitability). Some offset press cots are used for several years without replacement

4. Some small offset printing plants are short of working capital and purchase low-quality paper. These paper sand, paper powder, not only affect the printing quality, but also wear the blanket. In some factories, the consumption of gasoline and cotton yarn was over controlled, so the operators had to reduce the times of washing rubber blanket. Some printing houses that only print monochromatic characters for a long time usually do not change color, so they rarely wash ink rollers. In this way, even the new rubber cots that have just been used will easily lose the ability to gradually cool the extrudate and lead it to the traction equipment and the inkiness of the setting die. At present, the prosperity of spandex industry has rebounded. These practices can not save money, but cause greater waste

II. How to change the bad conditions in the use and storage of rubber blanket and cots

1. The manufacturing and processing of rubber blanket and cots belong to a special industry, which serves the printing industry and does not belong to the management of the printing industry. Therefore, there is a lack of industry standardized management and supervision. It is suggested that the state coordinate the printing industry, rubber processing industry and other relevant departments to strengthen the standardized management of blanket and cot processing industry, and regularly organize and carry out product quality evaluation activities in the same industry, which can play a role in mutual exchange and promotion

2. At present, the main reason for the poor use and storage of rubber cloth and cots is that some printing plant cadres and workers know too little about this common sense. In recent years, many books and magazines on printing technology have been published, but few technical books on blanket and cot have been published. It is suggested that more books in this field should be published in the future to adapt to the five main functions of the current rapid development of tensile testing machine. Do you know? It is hoped that the above sharing by Mets technicians can help you with your printing situation

3. The management and technical personnel of each printing factory should briefly understand the manufacturing process and appearance quality standards of blanket and cot. In this way, we can judge the advantages and disadvantages during purchase or acceptance, and do not purchase unqualified products. This is to ensure the quality of offset printing products, promote the improvement of blanket and cot eligibility rate is also of great benefit

III. finished product appearance quality standard of rubber blanket and cots

1. Finished product appearance quality standard of rubber blanket

(1) impurities with a diameter greater than 0.5mm, small pits, small bubbles, etc. are not allowed in the effective use area

(2) the product surface shall be free of dirt, oil stain, rust, etc

(3) the product surface shall be free of mechanical damage and grinding trace

(4) the bottom cloth shall be free of yarn knots and roving

2. Appearance quality requirements of cots

(1) cots have smooth surface and uniform color

(2) there is no inclined strip, bubble, trachoma, pit, pinhole, dark bubble, peeling, lack of glue, etc. on the surface of the rubber roller

(3) the effective printing range of the rubber roller shall be free of impurities and miscellaneous glue

(4) the rubber layer of the rubber roller has good adhesion to the iron core without delamination

(5) the error of rubber roll hardness (Shore) is plus or minus 3

(6) the diameter and shape error of rubber roller shall be controlled within the required range

IV. use and storage of rubber blanket and cots

1. Use and storage of rubber blanket

(1) reasonably select rubber blanket according to the model and printing requirements. It is not suitable for high-speed machine and large-area point graphic printing, otherwise the printing quality and printing plate resistance will be seriously reduced. Without a good blanket, even if the roller part is adjusted correctly, it is impossible to achieve the "ideal pressure"

(2) there is a smooth anti-oxidation film on the surface of the new blanket. This film must be removed by scrubbing with pumice powder dipped in gasoline or kerosene (or mixture) to ensure that the blanket surface has good ink adsorption performance

(3) when installing new blanket, the longitudinal (or marking line) must be perpendicular to the axis of the drum. Do a good job in cutting, and the cutting lines of the trailing tip and the Diao mouth must be parallel

(4) the length ruler of the blanket should be smaller than the size of the roller pillow, and the underlying lining (such as felt, hard pad paper, etc.) must be narrower than the blanket. In this way, when the rubber blanket is tightened, the left and right sides of the rubber blanket are tightly pulled on the roller surface of the machine, which can prevent impurities, oil detergent, water and other items from drilling into the rubber blanket during the printing process and causing delamination and blistering of the rubber blanket. (5) In daily production, the blanket must be cleaned carefully. Do not let the ink remain in the pores on the surface of the blanket. Otherwise, the conjunctiva will be oxidized and dried for a long time, making the surface smooth and reducing the ink absorption capacity, which will directly affect the improvement of product quality

(6) the "ideal pressure" advocated by offset printing process not only guarantees the product quality, but also is of great significance to prolong the service life of blanket and reduce creep. Therefore, we must try our best to do so

3. Evaluation of material life cycle (7) in order to reduce the obvious occurrence of stress relaxation of the blanket, the new blanket should be tightened in several times to make it close to the surface of the drum, so as to prevent double imprinting and deformation

(8) removing the tension when the blanket is out of service is an effective method to extend the high elasticity. Therefore, it is recommended to use two pieces of blanket for replacement

(9) during the storage of the blanket, do not touch oil, acid, alkali, salt and other items; Do not squeeze it, so as not to break the blanket and destroy its elasticity. The blanket is also afraid of light, heat and humid air. These media will make the surface of the blanket sticky, crusted, cracked, hardened and moldy

(10) when storing the rubber blanket removed from the machine, the ink and oil stains on it must be cleaned with detergent or gasoline, and then washed with 5% alkali solution to saponify the oil penetrating into the surface of the rubber blanket, and then washed with clean water to remove the saponification and wipe dry, and finally put talcum powder on it

2. Use and storage of cots

(1) the printing cots mainly transfer ink on the offset press. Therefore, the cots must be cleaned carefully during daily cleaning, otherwise the cots' surface layer, pigment and resin will be oxidized to form a smooth and hard film, resulting in surface vitrification and affecting ink transfer. If it is not cleaned regularly, the surface of the cots will be uneven and difficult to use over time. Therefore, the cots shall be cleaned and placed for standby during shutdown

(2) in offset printing operation, ink emulsification is caused by "large water and large ink", forming a hydrophilic foundation on the smooth rubber roller to make it deinked. The solution is to shovel off the emulsified ink, wash the deinking rubber roller with gasoline, mix and polish it with 5% sodium hydroxide aqueous solution and pumice powder, and treat the metal roller accordingly. The fundamental way is to control the pH value of the water bucket solution and balance the ink

(3) the rubber roller is aging after long use, and the "slag" is caused by the penetration of chemicals, so it is better not to use this kind of rubber roller again, otherwise the printing quality will be seriously affected

(4) in order not to affect the production and printing quality, there must be a spare ink roller, but do not store too much to avoid aging. The storage environment of COTS is the same as that of blanket. In addition, the cots shall be erected straight at the journal, and the surfaces shall not contact each other or other objects

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