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Label production stages

The production of self-adhesive labels is a series of stages, which take place sequentially and which are related to each other.

It is possible to distinguish such stages, which are directly related to the production of the finished label:

  • creation of the design
  • prepress
  • tooling production
  • material preparation
  • printing vadditional finishing
  • cutting and/or winding of finished labels

Label design

Creating a design on the one hand is not a technological process, but on the other hand it is important to know the technological features of flexoprinting when creating a design. Because of exactly the technological peculiarities, some design elements may not turn out when printed. In particular:

Small print and thin lines made up of 2 or more colors. If the design will be present in such an element, its edges may be blurry, indistinct.

fine print and thin lines, made up of 2 or more colors. The edges of the elements may be blurred.
Some types of gradient fills. The change in color in the fill may look uneven, unsteady. Gradient “to zero” is technologically very difficult to make on flexo printing and for such an effect it is necessary to carry out additional work, which still might not give the desired result.
Therefore, it is no coincidence that there are always certain design requirements for flexo printing.

Printing

Pre-printing preparation of a layout developed by designer and laid out by him consists of layout preparation in accordance with technical requirements of the printing house, peculiarities of equipment and technological processes used. Checking of formats, technological sizes and protrusions, determination of an order of imposition of paints in printing, correction of total amount of ink, color correction of images, reproducibility and readability of small elements of layout – these and many other things can be included in prepress.

Tooling fabrication

The main feature of flexoprinting is the principle of transferring the image to the material to be printed. This is done with the help of flexible forms that are glued to the printing rollers. For each color used in the label layout, one flexible form (flexoform, printing plate) must be made. This form is then glued to the plate cylinder using double-sided adhesive tape.

In addition to the forms it is necessary to make and label cutter according to its shape and size. The knife is made taking into account the desired location of the finished label in the roller, the label material and other parameters.

Each printing house has a set of ready-made knives, which can be used for different labels, including for different customers, if the geometric dimensions of the labels and their location in the rollers are the same.

Label material preparation

First of all we are talking about paints if you want to use colors from the Pantone palette. In this case Pantone colors are mixed from base colors.
As for the labelstock for printing, its preparation may consist first of all in cutting the roll to the right width. The width depends on the geometric dimensions of the label and its position on the ribbon.

The flexo printing process

One color at a time is applied to a strip of material in succession, running through the sections. The number of sections involved in the process depends on the number of colors and additional finishes – for example, a separate section is used for varnish coating – each printing section has a container of ink, which is transferred to the convex parts of the flexo plate by the ink transfer roller, which in turn leaves an imprint on the material passing through the section. Underneath the flexo plate is the material, and underneath the material is the back pressure roller, which ensures that the plate is pressed against the material.

The roller needs to have a fairly wide selection, as it adjusts the amount of ink transferred to the plate and to the material. A wide selection affects the ability of the print shop to adjust the desired image saturation during the run without altering the flexible plates.

We use UV inks which require drying. Therefore after inks are applied the material passes through the drying zone after each section – after the last printing section we have the punching section which cuts the label to the necessary shape. The main element of the punching section is a magnetic cylinder and knife, which is a flexible metal plate with a relief repeating the contours of the labels. This plate (knife or punching die) is magnetized to the cylinder and rotates with the cylinder to cut the labels. The height of the relief is such that only the top layer of material is cut through, while the backing remains intact.

The machine in our configuration is equipped with an additional device that allows you to adjust the pressure of the knife to the material. This makes it possible to compensate for all knife manufacturing inaccuracies, material thickness inaccuracies, etc., resulting in a guaranteed quality.

After applying ink the material after each section in the label printer passes through the drying area – after the last printing section there is a punching section, which performs cutting of the label to the desired shape. The main element of the punching section is a magnetic cylinder and knife, which is a flexible metal plate with a relief repeating the contours of the labels. This plate (knife or punching die) is magnetized on the cylinder and rotates with the cylinder to cut the labels. The height of the relief is such that only the top layer of material is cut through, while the backing remains intact.

The machine is equipped with an additional device which allows you to adjust the pressure of the knife to the material. This makes it possible to compensate for all the manufacturing errors of the knife, material thickness, etc., resulting in a guaranteed quality chip removal at the end.

Above the punching section is the tear winding section (residual material on the outside of the label). In the picture on the left you can see how the peel is removed from the label strip and wrapped around the roll, which is located on top.

After the punching section, the output is a ribbon with finished labels which is reeled off.
Depending on the equipment, the printing process may also include other steps such as web cleaning, etc.

Part of the printing process is the makeready of the print run and its further control in the printing process. In the process of makeready the printer achieves a perfect match of colors, the required color saturation, desired shades. Hue and saturation are usually regulated by selection of anilox rollers; color matching is regulated by adjusting each printing section lengthwise and crosswise to the web.
The process itself depends on the printing press used.

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