Flexo printing ink transfer (2)

2. The material of the anilox roller and the shape of the ink hole. The anilox roller is a precision part of the flexographic printing press. Its role is to quantitatively and evenly transfer the required ink to the graphic part of the printing plate.

The anilox roller generally adopts seamless steel pipe as the base material, and a small concave hole with uniform shape and even distribution is carved on the surface of the anilox roller. These concave holes are called ink holes, and the number of ink holes per unit length direction is called the number of anilox roller lines. According to the material coated or sprayed on the surface of the anilox roller, there are two kinds of chrome-plated roller and ceramic roller.

The chrome-plated anilox roller is made by engraving an ink hole on the surface of a metal roller with an electronic engraving machine and then chrome plating. The thickness of the chromium layer is about 1.2 μm, and the hardness is Rockwell (HRC) 60° to 70°. The number of roller lines can reach 80 lines/cm (200 lines/inch) or more, the resistance force is about 1000 to 30 million times, the cost is relatively low, and it is widely used on general level flexographic printing machines.

The ceramic anilox roller is a plasma method that melts and sprays metal oxides (Al2O3 or Cr2O3) onto the surface of a metal roller to form a ceramic film with high hardness and a firm and dense bond with the metal roller, and then uses laser engraving. Made of.

Ceramic anilox roll, wear resistance 20 to 30 times higher than the chrome roll, up to 400 million impressions. Due to excellent abrasion resistance, it is advantageous to reduce the number of operations for changing the anilox roll and improve printing efficiency. The number of ceramic mesh lines can be up to 600 lines/inch and is suitable for printing fine color prints. It is a high-quality anilox roll used by an anilox roller squeegee ink inking system.

Anilox roller ink hole shape as shown in Figure 6-18.

The V-cone of the quadrangular pyramid ink-receiving hole can be calculated as follows (see Figure 6-19):

V cone = 1/3H3tg2α/2

V station = 4/3tg2 (3H2h-3Hh2+h3)

The above two formulas show that if there is a quadrangular pyramid ink-receiving hole and a quadrangular pyramid ink-inking hole, and the bottom area is equal and the height is equal, then V stage > V cone.

The hindering effect of the corner of the ink hole on the transmission of ink is called the "corner effect." The corner effect of the bottom of the quadrilateral pyramid ink-receiving hole is the most serious, and about 1/3 of the height of the ink-receiving hole cone can not release the ink. Therefore, the ink repellency of the quadrangular pyramid ink-type anilox roller is good. In addition, the side surfaces of the pyramidal ink-receiving holes are more vertical than the pyramid-shaped ones, and the partition walls between the ink-inking holes are wider on the surface of the anilox roller than the prism-shaped ink-receiving holes, and have high partition wall and wear resistance.

During long-term use, the anilox roller will be worn out due to the action of the squeegee, so that the opening of the ink hole will become smaller and the depth will become shallower, resulting in a decrease in the volume of the ink transfer unit (ink hole) of the anilox roller and the total amount of ink transferred. Also reduced accordingly. From the calculation formulae of the V-cone and the V-table, it can be seen that the decrease of the depth has a great influence on the ink hole volume. The curves in Figure 6-20 are plotted based on the calculations. The three curves of A, B, and C in the figure are quadrangular pyramid, quadrangular pyramid (cone angle α is 110°) and quadrangular pyramid (cone angle α is 90°). The three inking volume decreases with depth. Relationship lines. ΔH is the depth change, H is the original depth, ΔV is the volume change, and V is the original volume.

Comparing the curves A and B, it can be seen that the influence of the variation of the depth of the quadrangular ink receptive hole on the volume is smaller than that of the quadrilateral pyramidal ink receptive hole; as compared with the curves B and C, it can be seen that for the quadrangular reed shaped ink repelling hole, the taper angle α is large. The reduction in volume caused by the decrease in depth h is more pronounced. For example, when ΔV/V=20%, the taper angle α=110°C, ΔH/H=30.61%; taper angle α=90°

Time,

ΔH/H=24.55%, it can be seen that the stability of the quadrangular ink-receiving hole is superior to that of the four-angled ink-receiving hole.

The hexagonal table-shaped ink receptive hole shown in Fig. 6-18(c) is an improvement of the quadrangular pyramid-shaped ink receptive hole. The opening angle of the ink hole is large, and the partition wall between the ink holes has higher strength, and the performance of ink release and ink release are better than those of the first two shapes. It is the most commonly used flexographic printing anilox roller. Ink hole shape.

The normal cross-section of the slanted ink reticles shown in Figure 6-18(d) is an isosceles trapezoid. This ink hole can ensure the ink or (coating liquid) fluidity, with good ink transfer performance. Slanted ink-lined screen rollers are commonly used for coating, gluing, and special flexographic printing.

The additional channel inker shown in Fig. 6-18(e) is an improvement to the prismatic ink indentation. Along the axis of the vertical anilox roller, channels are carved between adjacent ink cells to increase the flow of ink in the ink cells. Sex. This ink-receiving hole has a good ink-transmitting property, and is particularly suitable for high-line anilox roller with mesh reconciliation and color printing.