The requirements of offset printing on blankets and their loading techniques
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First, the three characteristics of offset printing
1. Offset printing utilizes the intermediate roller of the elastomer blanket to form a unique rolling method for indirect printing.
2. The solid surface selective adsorption rule of different properties is utilized, and the solid surface conforms to the needs of planar printing through technical treatment.
3. Utilizing the natural law that oil and water are not miscible, both the ink and the water are transported in the offset printing process.
One of the characteristics of offset printing is the use of an elastomeric roller for indirect printing. As an elastomer, the offset blanket and the airbag blanket play a decisive role in the transfer of printed graphics. First of all, we have to figure out the transfer process of offset printing: the original image - the text before the printing, the lines, the image of sulfuric acid paper or the output of the film is reversed - the PS version of the sun is positive. - Offset printing is reversed from the plate cylinder to the blanket cylinder - the blanket is transferred to the paper as a positive image.
The blanket plays the role of transferring the printed graphic in the printing. The quality of the blanket has a direct relationship with the quality of the transferred graphic.
Second, what are the requirements for offset quality for blankets?
In the offset printing process, the function of the blanket is to transfer the graphic on the printing plate completely and clearly to the substrate paper. In order to strive for the perfect transfer of graphics and texts, it is necessary to require the blanket to have the following characteristics:
1. The blanket should be even and thick. Even thickness and thinness will make the printing pressure evenly distributed. The color of the printed ink is also relatively uniform, and the graphic size is not easy to change during the transfer of graphics and text.
2. Has good elasticity. Ordinary solid blankets have good elasticity. The effect of image transfer and ink absorbing performance may be good. In the process of embossing of ordinary solid blanket, the surface rubber layer will often produce convex hull at the leading edge of embossing line. According to the imprinting principle, hard rubber The cloth does not shrink in volume under pressure, so it can only be squeezed to both sides of the nip. However, the choice of using an air-cushion blanket does not create a convex hull problem at the leading edge of the nip.
3. The blanket has a small elongation. The blanket structure is dense and has high mechanical strength, which is beneficial to the increase of the tensile strength and thereby reducing the deformation amount of the graphic transfer.
4. Good ink absorption performance and transfer performance. It ensures that the ink is well-proportioned and clear in writing.
5. The blanket is resistant to oil, abrasion, heat and aging, and has the above various properties, which can prolong the service life.
6. Has acid resistance, alkali resistance and corrosion resistance. The quality of the blanket is directly related to the quality of the graphic transfer. Although there are many factors involved in the quality of the graphic, such as mechanics, plate making, materials, and mastery of the craft, the quality of the blanket is one of the important factors. Because the blanket is infiltrated by gasoline, kerosene, and oil during the printing process, Under the pressure and the relative friction between the drum and the drum, periodically stretching, squeezing deformation, the blanket will become sticky due to sulfur loss, deformation and lack of good elasticity, thus affecting the transfer quality, in this case I have to replace the old blanket.
Third, the problem should be paid attention to when installing the blanket
1. When installing the blanket, pay special attention to the gasket should not have any wrinkles. In general, blanket + felt + paper; or blanket + worsted wool + paper. Felt, worsted wool, paper, these lining materials, a little careless, easy to wrinkle when the paving is not flat.
2. When tightening the blanket, both the tip and the bite should be carried out at the same time. Do not tighten on one side. Pay attention to safety during operation, avoid tools and screws from being inserted into the roller and crush the blanket.
3. The new blanket has good elasticity and good stretchability. The stretched blanket should be gradually carried out and tightened once. After the adhesive press is pressed for 3~5 minutes, it will be tightened again. This can be tightened 2~3 times. .
4. If the blanket and its pad are flat, if there is ink or paper debris in the blanket, the convex and concave phenomenon will occur, and the blanket should be reinstalled.
5. Before installing the blanket, the thickness of the blanket + felt or worsted wool + paper should be accurately measured with a micrometer to hear the four sounds of 千, 嗒, 嗒, 嗒. Soft lining: blanket + felt + paper, the thickness of the lining: 3.35 ~ 3.45mm. Neutral lining: blanket + worsted wool + paper or blanket + paper, the thickness of the lining: 3.20~3.25mm. Hard lining: blanket + insulating paper or photographic paper, the thickness of the lining: 3.18-3.20mm.
6. The cutting of the blanket requires the rectangular end to be correct. Only the direction of the selection of the blanket as the direction of cutting, tightening and tensile force can achieve the desired effect. The latitude and longitude of the natural roll can be known by observing the cylindrical shape of the natural roll, and the direction of the wire parallel to the core of the natural reel should be the weft direction, and the direction perpendicular to the weft direction is the warp direction. It is mainly determined according to the silk thread of the back (back) surface of the blanket.
7. The lining paper in the blanket lining should be shorter than the blanket to prevent the water from infiltrating into the paper fiber and deformed by water, reducing the rust erosion of the drum.
8. The blanket is an elastic object that must be stretched under stress during the entire assembly, transmission and embossing process. In order to accurately transfer the graphic size on the printing plate to the paper, the blanket is required to have a small elongation during the entire imprinting process and must be uniform. The above elongation is related to the quality of the blanket itself, and depends on the degree of tension of the blanket on the drum. The tighter the blanket is, the better it is? Of course, this is not the case in actual work, and the blanket should be stretched tightly. 1 The tighter the blanket is stretched, the less the elongation during the printing process, and the smaller the size of the graphic. However, if the cloth is stretched too tightly, it will lead to an increase in the amount of friction on the plate and a decrease in the life of the plate. 2 If the blanket is too loose, the stretch rate of the blanket will increase, and the amount of friction on the layout will decrease, which may cause double-printing (ghosting).