How accurate is the flexo ink consumption?

The industry regards the anilox roller as the "heart" of the flexo press, and its management will directly affect the flexo quality and ink consumption.

For label printing companies, the dull ink left after the flexographic short-run work is a big waste. These inks not only include 1 to 2 kg of ink that must be prepared in the ink tray, but also inks that are adjusted because of inaccurate predictions.

If label printing companies can accurately predict ink consumption, they can dispense ink as needed, reduce inventory and waste, and provide a more accurate basis for upfront costing and business quoting. To accurately predict the ink consumption, the anilox roller must be carefully managed. Of course, the fine management of the anilox roller is difficult. This article is not involved at this time. Let's take a look at the specific ink consumption. How to estimate.

Prerequisite for accurate estimation

Based on the fine management of the anilox roller, it is possible to accurately predict the ink consumption and further refine the production cost control.

The conditions for accurately predicting ink consumption are: ink consumption per unit area = print ink area ratio × total volume x specific gravity. The necessary conditions are: 1 printing ink area ratio. This can be either an absolute area or an area percentage. 2 Understand the printing method and the type of substrate, the ink wet ink thickness is different, the substrate type is different, the ink transfer rate is different; 3 the ink specific gravity, the specific gravity of different inks is also different.

Printing ink area ratio

First, the two commonly used methods for testing the area ratio of printing inks are introduced. 1 Take a printed sample or a 1:1 ratio of a monochrome print, and measure the area with a meter that measures the area. This method has a small error in the field, but the mesh portion of the text cannot be measured. 2 Using a 1mm2 square grid to measure how many squares the object is occupied to determine the area, this method is relatively large.

There is now a method for accurately measuring the percentage of printing ink. The specific process is to display each color of the graphic original separately on the computer of the plate making company, and the computer will automatically display the proportion of the total area of ​​the repeated circumference of the graphic ( That is, ink coverage), thereby calculating the graphic area of ​​a single label.

Factors that determine ink transfer rate

The printing method is inconsistent and the ink consumption is different. The thickness of the ink layer of the screen printing is generally greater than 8 μm; the thickness of the ink layer of the flexo and offset printing is generally 1 to 2 μm, rarely exceeding 2.5 μm; the thickness of the dry ink film of the electrogloss intaglio is generally 0.5 to 1 μm, and the wet ink is estimated according to the solid content. The thickness of the dry ink layer of the laser engraved gravure is generally 1 to 2 μm, and the thickness of the wet ink layer is estimated to be about 6 to 12 μm according to the solid content. The above data are the measured thickness of the ink layer on the film material. In contrast, only flexo printing can accurately predict the amount of ink used in proofing. Therefore, not only the dry ink layer thickness of flexo printing should be regarded as 1~2μm, but also to the number of digits after the decimal point. .

An anilox roll having a line number of 300 lines/inch and a BCM value of 5 will now be described as an example. Conversion of metric units: 1BCM=1.55cm3/m2

Ink layer thickness = BCM × 1.55 × ink transfer rate (this article is for short-run jobs, so UV ink as an example, the ink solid content is 100%).

Although the anilox roller manufacturer's ink transfer rate from the anilox roller to the printing plate is greater than 50% or even 55%, the label printing company cannot retest this data, and usually cannot measure the ink transfer rate of the printing plate to the substrate. . However, the specific transfer rate from the anilox roller to the substrate, the author has done many experiments, the following data: PE, PP and other film materials are 26% to 27%, mirror coated paper is about 28% to 30%, Ordinary coated paper is 31% to 32%, and the surface of the paper with very rough surface is more than 35%. The ink transfer rate of the substrates provided by each substrate supplier is mostly in this range.

Here, we must pay special attention to the fact that the printing speed will have a certain impact on the ink transfer rate. Generally, the printing speed is slow and the ink transfer rate is large. In contrast, paper-based substrates are much more affected than film-based substrates. Therefore, label printing companies should define the range of printing speeds suitable for the job of the company when testing the ink transfer rate of different substrates.

Based on the above values, you can get:

Ink layer thickness = 5 × 1.55 × (26% ~ 35%) = 2.015 ~ 2.7125μm

The influence of the type of substrate on the ink transfer rate is much greater than the effect of the anilox roller and printing plate on the ink transfer rate.

Ink specific gravity

Although it is possible to consult the ink supplier about the specific gravity of the ink, it is best to make actual measurements, which is more accurate. The weighing of the measuring cup (usually 100 ml) can be obtained by weighing the ink. Generally, the specific gravity of the flexo UV ink is 1.1 to 1.2 g/m3; the specific gravity of the flexo UV white ink is about 1.7 g/m3. In short, the ink suppliers are different, the solid content of the same ink will be different, and the specific gravity will be slightly different.

Assuming that the printing ink area ratio is 20% (provided by the plate making company), the anilox roll BCM value is 5, the number of lines is 300 lines/inch, the substrate is made of PP film, the ink is white ink, and the specific gravity is 1.7 g/m3. Calculated according to the formula of “ink consumption per unit area=printing ink area ratio×total volume×specific gravity”:

Ink consumption per unit area = 20% × (5 × 1.55 × 26%) × 1.7 = 20% × 2.015 × 1.7 = 0.6851g / m2

With the ink consumption of each print or reprinted print on the perimeter, it is a breeze to accurately estimate the ink consumption of the entire order. Finally, the minimum ink consumption of the ink tray is sufficient.

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