How flexo print works
It will be useful for entrepreneurs and sourcing managers who are first faced with the need to create and order labels for products. For connoisseurs of printing, the article will seem too simplistic.
Eight-color printing complex GiDue MX-370 in our workshop
The label is the face of the product for the buyer, and the process of its creation is an endless field for the imagination of the marketing specialist and the designer. This colorful information "marker" determines the attractiveness of the product on the shelves, emphasizes its uniqueness or membership in a particular group, and protects against counterfeiting. An original and well-crafted label attracts new customers. A bad label cheapens the product's appearance and reduces its value to the customer.
The most practical and economical type of label product is a self-adhesive label. This is a paper or polymer label with adhesive on the back. To protect the adhesive layer, the label is attached to a liner - a paper or film that is coated with silicone. The label can be easily peeled off from the base and glued to various surfaces: car windshield, cardboard packaging, rail tank car, glass and plastic bottles, bags, plastic and tin lids.
Self-adhesive label printing is relatively economical. The label can be made in a round, square or complex geometric shape, printed in one or two colors, or made in full color, photographic quality or multicolor.
Stamps use a mold of flexible material, and ink and print are done by hand or using tooling
Printing press device
Images on self-adhesive are printed using flexographic method. In this printing method, an elastic printing plate is used to apply ink. A simplified example of such a printing method is the postmark with which you certify documents.
Printing of labels is based on a similar principle. A flexo form made of flexible material is glued onto a cylindrical shaft - a printing cylinder. The shaft rotates, a sheet of paper or plastic film passes under it. The canvas goes around the support shaft - the impression cylinder.
Like a stamp pad, from which ink is transferred to the form of a round seal, the ink is transferred to the flexo form by a dispensing roller - anilox.
Flexo printing is a type of letterpress printing. This is when the printing elements are located above the blanks, that is, when printing, blanks do not touch the paper. There are also flat and gravure printing, when the elements are located on the same plane or print below the blank, respectively.
If the label is multi-color, several printing units with separate printing plates are used. Each plate transfers a drawing of its own color and contributes to the final image. Not every color on a label is necessarily a new plate. Different colors can also be obtained as a result of superimposing the basic process colors - yellow, cyan, magenta and black.
Schematic diagram of the flexo printing section
The image uses only black, but the different density of the dots gives the impression of a transition of shades from gray to black
But what if the image is complex and contains hundreds or thousands of different shades? For example, we want to print a photo. It is expensive and impractical to make a flexo plate for every color shade. The resolution of our vision solves the problem. Dot groups from afar merge into a solid color. The higher the density of the dots, the more densely they are located, the darker we perceive the shade. That is, to make the color darker or lighter, you can simply change the number or size of dots in the desired element of the image.
By using dots of different colors and sizes, you can get different shades. When dots are printed on paper using a printing plate, at a distance the human eye perceives them as a solid object. The method of converting a color image into a set of dots on printing plates is called rasterization, and the dots themselves are called a raster.
To obtain full-color images in the printing industry, four main colors are mixed: cyan, magenta, yellow and black. The English names for these colors - Cyan, Magenta, Yellow and Key color - form the abbreviation CMYK. You often see this acronym in the settings of the graphics editor.
This is a photo prepared for flexo printing
Preparing an image for printing
To do this, it divides the graphic image into four main color channels and converts them into raster format. There can be more than four flexo forms, if the image, in addition to the primary colors, uses corporate “brand” colors.
The file with the prepared image is transferred to the repro center - an organization that makes flexographic forms. We make our own molds using BASF and Esko equipment.
The image is divided into layers according to the primary colors
The image is loaded into the program of a laser engraver, which reproduces the points of the same sizes and frequency of location, which were specified by the designer at the stage of prepress.
To give the label the desired shape, it is cut with a special knife. A die cutter is a thin metal plate with a cutting edge along the contour of the future label. The knife is attached to a magnetic shaft. The printed paper or film passes under this roller, the label remains on the liner, and the excess material is wound onto a core and discarded. Special knives are made for labels of complex and original shapes. Flexo forms and knives are handed over to the printer for makeready and order printing.
If a “corporate” color or a color according to a sample is needed for printing a label, the technologist prepares the ink according to the recipe, by mixing various base paints in special proportions.
We print with fast drying UV inks. The ink dries in a fraction of a second after exposure to ultraviolet radiation, which the UV lamp emits after each printing unit. UV inks are environmentally friendly and do not contain solvents.
Flexo forms and a knife are attached to the rollers, ink is poured into printing units, colors are mixed, the order is approved and the print run is launched.
The printing process is automated as much as possible. For printing, we use printing complexes BOBST and GiDue of Italian manufacturers of narrow web printing equipment, with the ability to print up to 10 colors.
The unique ink section design allows for reduced dot gain. This means that we can better reproduce the transitions from light to dark areas, professionals say "stretches are smoother."
Short web paths in the printing area of the printing systems used, reduces makeready costs and ensures maximum productivity on short runs. The printer quickly converts the ink and comes out to the required color of the label.
DK-450 rewinding machine is used to cut the printed product into rolls
On small print runs, the makeready time can be several times longer than the print itself. By reducing preparatory work time, we free up time for printing. This way we print more in less time, reduce costs and offer a better price. Automatic web tension control ensures consistent color register. Register stability is the quality of the mixing of colors throughout the entire run. Mixing quality is a label that pleases the eye.
The web can be much wider than the label, then, to save material, the labels are printed in several rows (strands). After printing, the roller is cut on a slitter rewinder and rewound into separate rolls. When trimming and rewinding, the label is inspected by an operator who removes any defective areas.
The label is ready!
Rolls with labels are packed in boxes and sent to the client's production facility. At our partners, the label is glued manually or using a special machine - a labeler.
Ways to prevent defects
There is a technological defect in printing and defects in the material entered. Rejection during printing is caused by ink displacement (non-mixing), technological imperfections when stopping and starting the machine, wear of a doctor blade, which removes excess ink from anilox, film materials surface that is insufficiently prepared for printing, dust.
An example of a defect where yellow has shifted
There are many reasons, but an experienced printer and a modern printing press make it possible to track printing defects in time and mark them with bookmarks. In order for the printing to be perfect, it is important to glue the flexo plates evenly, to precisely align them along the register crosses and to maintain the accuracy of color alignment throughout the entire run.
Color deviations are possible if the technologist made a mistake while preparing the mixed paint. To eliminate such risks, the technologist compares the resulting print with the reference label, keeps a recipe log and records all technological parameters in the Order Process Sheet. A defect is possible when the label does not adhere well.
It is not at all good if the label peels off from the product after a while. Such a defect can lead to serious losses. Situations are known and are caused, as a rule, by the use of low-quality materials, as well as by the wrong choice of material in terms of its adhesive properties. We use strictly certified materials from world leaders - Fasson (USA), Raflatak (Poland), Ritrama (Italy).
These are the main manufacturers of self-adhesive materials, the aggregate share of which in the sector-specific market is about 85%.
Our designers carefully study the layouts and professionally carry out prepress preparation of layouts. The list of actions is wide: they check the dimensions, enter correction factors, do color correction of images from under the profile of the printing machine, evaluate and give recommendations on how to make a picture not only beautiful, but also technological. The latter is extremely important for the implementation of every idea, every detail, which are conceived by our partners.
Flexo printing is based on a simple principle. You can imagine that a flexo press is a large automated stamp. The difficulties are in the details. To produce a quality label, you need to know the features of the equipment and the properties of the materials. The technologist knows the specifics of the glue behavior, knows how storage conditions affect the quality of label fixing.
We advise clients on label design and production.
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