On "Two Smalls" and Its Adjustment Techniques in Offset Printing

1, small amount of water

The role of the PS version of the wetting fluid is to achieve dampening, cleaning, and cleanup of the layout. The small amount of water means that the amount of water supply is controlled to be as small as possible without affecting the stability of the blank portion of the printing plate (ie, the blank portion is not sticky), and the amount of water supply and the amount of ink are in a relatively stable state.

The amount of water (ie wetting fluid) directly affects the ink, plate, and paper, while the ink, plate, and paper directly affect print quality. The small amount of water ensures consistency of darkness before and after ink and stable printing operations, and can print more ideal products.

The amount of wetting fluid is too large, the most influential is the ink and paper, followed by the printing plate. If the amount of wetting fluid is too large, the balance of ink and ink will be destroyed, the ink emulsification will be accelerated, the ink will not be transmitted normally, and even the layout will be “patterned”, and the blotting ink will become lighter. Too much water in the printing plate layout will cause the ink and ink performance of the graphic and text parts to be abnormal. The printed image will lose its luster, the color will not be bright, and the tone levels will be poor. The product will be dull. Too much wetting fluid will affect the printing performance of the paper and make the paper appear lint-free and powder-removing. Excessive water content of the paper will cause the paper to stretch and affect the quality of overprinting. In addition, if the water content of the paper is too high, the paper will change. Soft, resulting in uneven delivery, slow drying of the ink layer, and smearing of the back of the paper.

Pre-estimation of water consumption for layout is more important than adjustment afterwards. It is an important prerequisite for adjusting the ink-and-wash balance in the layout. Therefore, for the main factors affecting the amount of wetting fluid, there should be a more important understanding before determining the amount of water in the layout. In actual production, the amount of wetting fluid depends on: layout area distribution; paper properties; ink properties; machine speed; ambient temperature and humidity and air circulation.

2, low pressure

Printing pressure is the primary condition for the completion of lithographic offset printing. The ideal pressure between the rollers is the key to guarantee the printing quality. Pressure refers to the pressure in the ink to ensure good transfer (that is, to ensure that the printed material in the imprinted, full dot but not paved, clear and rich tone level), based on the best possible to reduce the printing pressure between the rollers. Whether or not the pressure can be achieved (ie the use of ideal pressure) is one of the important indicators for measuring the level of technology and is also an important condition for ensuring high quality and high output.

Excessive printing pressure has a great influence on product quality. Excessive pressure can easily cause dot distortion, stencil, product ink color, or even image distortion; excessive pressure can also accelerate plate wear and roller wear.

The optimal printing pressure adjustment method is: to make the gear in the standard mesh state, by changing the thickness of the liner to achieve the best printability.

When printing thick paper, the best printing pressure adjustment method is: reduce the blanket lining thickness accordingly, increase the lining thickness of the plate cylinder, the slight difference can be adjusted by changing the center distance between the rollers, and re-adjust the ink roller pressure.

The most commonly used and most intuitive and simple method for the inspection of printing pressure is the pressure bar method. The specific operation is as follows: lift the water roller, drop the ink roller, run the machine at a low speed and pressurize, wait until the surface of the three rollers is evenly inked, and then stop. Each cylinder has an ink stick at the parking place. For example, the width of the ink bar is within the value range given by the machine and uniform, and the width of the ink bar between the impression cylinder and the blanket cylinder is greater than the width of the ink bars of the plate cylinder and the blanket cylinder. , it shows that the pressure adjustment is even and suitable. If the width of the press bar is wide and narrow, the maximum distance between the two sides of the roller may be inconsistent.