Evolution can be described as a continuing process of change from one state or condition to another. A gradual change in characteristics developed over successive generations. I believe this describes the flexographic engraving process as well as changes in ink chemistry, plate technologies, substrates, graphic demands and machinery that have occurred over the past 100 years.
The metering of ink once employed two rubber rolls to transfer the fluid to a rubber print die. The only adjustment was in the pressure
of the rolls. It was not until 1939 when the first chemically etched roller was used to meter ink. From that time the anilox roll has experienced many changes in how the cell is formed. These changes were driven by the improvements in ink metering systems, plates, and substrates as they evolved to meet the ever changing requirement for better graphic quality.
Mechanically engraved rolls are still in use today but are mainly used for coating and very coarse rolls for glue and starch application. The process uses an engraving tool that is pressed at high pressure into the surface of a roll. This displacement method of engraving results in the slight growth of the roll diameter. Most of these engravings are at a 45 degree angle. One significant change in the cell of a mechanical engraving came with the introduction of the channeled cell. The QCH engraving is at 90 degrees and has a channel that connects all the cells around the roll allowing for a very smooth lay down of ink or coating. The next innovation was the Roto-Flo engraving. The cells form a “Z’ pattern and are engraved at 26 degrees. This engraving supported the doctor blade and virtually eliminated striations. Another advantage of this engraving was the elimination of potential moiré patterns coming from the plate line screen. Ink systems at this time were mostly solvent and the plates were rubber.
Further development came in the 1960’s and 70’s with the introduction of a random ceramic roll. This type of roll was produced by blending titanium dioxide and aluminum powders that we sprayed at high temperature onto a roll. These melted particles solidified on the roll in a random pattern of holes and an irregular surface of heights. While this was an improvement in durability it did not compare to the quality of the engraved chrome plated rolls.
Next in the evolution was the micro-ceramic roll engraved rolls. In 1973 Pamarco incorporated applied and was granted a Patent for and anilox roll that was engraved and spray coated with ceramic 0.0025-0 .003inches thick. The size of the ceramic particles had to be controlled or the engraved cells would fill and not transfer ink. The limitation was also in line screen that were only 220cells per inch.
Pamarco’s Europe division had been laser cutting continuous rubber rolls for the wall paper industry. An idea was brought forward to manufacture a more durable Anilox roll, and leveraging a relationship the Company had with Union Carbide (now Praxair) who specialized in coatings; they jointly worked towards laser engraving ceramic rolls. Union Carbide brought this technology to the United States and Pamarco became their sales agent for 2-3 years. The contract ended and Pamarco purchased its first laser and installed it in Roselle New Jersey in 1984.
The need for a controlled ink transfer became more important as the other parts of the flexographic printing system developed. Advances in ink chemistry and plates demanded an anilox roll with improved ink release and uniform transfer to the plate.
In the early 1980’s CO2 lasers had 400 to 800 watts of energy and produced cells with a single hit. Screens were limited to less than 500 lpi with limited volume capacity.
Later in the 1980’s CO2 lasers were developed with 1000 watts of power and a split beam technology that increased the volume range. The Ablative YAG Laser of the 1990’s had very little thermal energy but made well formed cells with little recast. Line screens of 900- 1000 were possible and were successful to attain high levels of graphics. The drawback of this type of laser was the lack of re-cast ceramic that made these engravings prone to wear and scoring, thus cutting the life span.
As the power of the lasers continued to climb, the ability to produce higher line screens followed. Through the 1990’s the Ablative Multi hit YAG and CO2 lasers continued to improve as new optical and electronics were developed. These allowed for improved cell structure and volume ranges. At this time the photopolymer plates were being introduced to the market with the ability to produce fine or higher line screen on the plates. The major advantage of these plates was the ability to hold register and not distort under pressure. This meant a need for the higher line screen and improved controlled volume on the anilox. Press manufacturers also changed the ink transfer from a two roll system to a bladed or chambered system All these meant better control of the ink film.
The drawback of the CO2 type lasers were the maintenance time and expense and the speed of engraving. A CO2 laser engraved at around 10,000-15,000 cells/second, which for very fine screens for Flexible Packaging and Label applications meant extremely long engraving times, the more modern Fiber Optic laser is upwards of 50,000-60,000 cells/second.
The development of the Thermal Fiber Optic YAG lasers in the early 2000’s opened the line screen options to higher than 1200lpi. These higher line screens on the anilox became more important as digital plate technology developed. Due to the optical path and the power of these lasers they were not capable of producing effective screen counts below 500.
Then next major leap in Thermal YAG lasers was increased power, new software and electronic capabilities that combined to allow for a full range of screen counts from 35 to 1800lpi. With the advanced software packages now available from the machinery manufacturers, hybrid screens such as the E Flo are now able to be engraved into ceramics in a very controlled and consistent manner.
E Flo cell offers a new tool for printers striving for greater graphic capability. The unique elongated shape of the cell and dual line screen allows for improved ink release resulting in improved solid coverage and the ability to print screens cleanly even where the image is on the same plate with a solid. This new innovation produces low dot gain, clean type while achieving high ink densities.