Analysis of Reverse and Straight Fur Phenomenon in Offset Printing

Posted on 04-14-2024 by

I. Definition of Reverse and Straight Fur

When printing solid areas, lines, or text, there may be fuzziness at the edges of the graphics. This is commonly referred to as reverse or straight fur. Fuzz pointing towards the bite edge is called reverse fur, while fuzz pointing towards the tail edge is called straight fur. It exhibits consistency in direction on the plate, rubber blanket, and printed matter. Otherwise, it may be due to squeezing or ghosting phenomena.

II. Factors Influencing the Phenomenon

The reverse and straight fur phenomena occur only when the following three factors are present simultaneously:

1.Incorrect wrapping of the plate cylinder and rubber blanket, causing a significant difference in radii between them.

2.Presence of paper fibers, powder, or sand on the rubber blanket surface.

3.Insufficient hardness of the metal substrate of the plate. None of these factors are related to the impression cylinder.

III. Fault Analysis and Solutions

1.Straight Fur:

When R print > R rubber, reduce the padding inside the rubber blanket. If the plate padding is below standard, increase it, and reduce the center distance between the impression cylinder and rubber blanket. If the plate padding meets the standard, reduce the center distance between all three cylinders simultaneously.

2.Reverse Fur:

When the above three factors are present and R print > R rubber, the plate's surface speed exceeds that of the rubber blanket's surface. This results in sliding friction during contact, causing ink on the plate and rubber blanket to spread in opposite directions. Ink elongates towards the tail edge on the plate due to its higher surface speed, while it elongates towards the bite edge on the rubber blanket due to its slower surface speed.

Although ink elongation on the plate is temporary and continuously removed, ink elongation on the rubber blanket cannot be entirely transferred to the paper. Due to the adhesive properties of ink, more paper debris accumulates at the ink marks, forming oily deposits. When sliding friction occurs between the plate and rubber blanket during printing, these oily deposits accumulate in the direction of ink elongation on the rubber blanket. This results in abrasion and damage to the plate's grain surface and eventually leads to the development of fur. The shiny appearance of the fur on the plate during reverse fur occurrence is due to this reason.

Solution: Reduce plate padding, increase the number of padding layers inside the rubber blanket, and appropriately increase the center distance between the rubber blanket and impression cylinder. If the rubber blanket's padding meets the standard, reduce the center distance between the plate cylinder and rubber blanket after removing plate padding.