Self-adhesive label
Self-adhesive labels or adhesive labels were developed by Avery in the USA in the 1930s and were first used as sheet goods . This is a multi-layer material composite, which in its simplest form consists of the actual label , an adhesive layer , a silicone layer and the carrier paper.
History and description
For economical industrial use it was necessary to bring the labels into a machine-processable form. This goal was achieved with the development of self-adhesive labels on rolls. The industrial application of roll labels began in the early 1950s; but it was not until after 1960 that they were used on a broad scale.
A few years later, various devices were developed and offered for the non-industrial sector with which individual self-adhesive labels could be created in small numbers. With the first devices (embossing devices) - similar to the functionality of the type wheel on a typewriter - the letters of the word to be created were set one after the other and transferred by manual pressure to a stable plastic tape with an adhesive layer on the back. Here, the plastic tape, which had a backing film, was fed back after each letter was printed. The plastic straps always had their own dark color, and the printing made the raised letters appear white due to the stretching of the material. After removing the carrier film, the self-adhesive labels could be stuck to the desired location after completion.
Embossing devices of this type are only rarely used for special applications today and have largely been replaced by electronic devices that can also print on multiple lines and in different fonts. Thermal printing or similar processes are often used here. Some of these devices are specifically designed to be used as printers for the computer.
Simple, paper-based self-adhesive labels have also been offered for some time in many different forms as standard goods (e.g. DIN A4) with mostly associated programs for use on the home PC and can be printed with standard printers.
Manufacturing
Self-adhesive labels in roll form are produced on roll printing machines in specially equipped printing houses. In principle, the following work steps are carried out:
- In a coating company or a material manufacturer, the composite label material is produced in the form of large rolls (“ parent rolls”).
- These rolls, which are usually purchased by the printing works as raw material, are put on the printing machine and unwound.
- The composite material web is printed in one or more colors according to the printing templates.
- The label is then punched on the printing machine , ie the top layers of the composite material ("upper material") are cut according to the later label contour.
- In the following step, also on the printing machine, the so-called grid is pulled off and rolled up. This is the excess material around the labels.
- In the last step on the printing machine, the finished printed and punched labels are rewound into large rolls, often several webs next to each other.
The large rolls are cut into single-lane label rolls on converting machines and wound into individual label rolls with defined diameters or label quantities in accordance with the specifications of labeling machine manufacturers.
Label materials, printing processes and adhesives
Today's label market offers a wide variety of different label materials. Depending on the application and technical requirements, paper or plastic labels are offered in various qualities and with various surface finishes. The choice of adhesives is just as large, depending on whether normal or strong adhesiveness, removable or water solubility are required. Another factor in the choice of material is the environmental conditions in which the labels are to be processed. In particular, temperature, humidity and dust influence the decision as to which label material is to be used with which adhesive. Since labels are information carriers, the appropriate printing method must also be selected according to the requirements.
Adhesive labels are mainly printed using flexographic printing , letterpress printing or screen printing. As an additional technique for high-gloss gold, silver or metallic prints, the hot stamping printing process is often used , mostly in conjunction with another printing process. Alternatively, however, a metallic printing ink can also be used, which can be significantly cheaper than an embossing foil for certain surface coverages. Recently, roll labels have also been produced using web offset printing .
A few printers also use gravure printing . However, since this process is very complex and causes high initial printing costs, it is only used for very long print runs.
In terms of adhesives, water-based pressure-sensitive adhesives based on acrylate or pressure-sensitive hotmelt adhesives based on thermoplastic rubber ("hotmelt) or UV acrylate (UV hotmelt) are predominantly used today. Due to their higher price, UV hotmelts are mostly used today for special applications where, for example Resistance to sunlight, high temperatures or chemicals is required. For special applications such as the production of multi-layer labels or booklets, UV-polymerizable pressure-sensitive adhesives can also be used. The latter are liquid at room temperature and can be printed using a screen or flexographic printing unit instead of printing ink The adhesive (for example Novarad RCL 6011) is only partially applied to the desired areas. Directly after the adhesive is applied, UV crosslinking takes place, which polymerizes the adhesive, giving it internal strength and a sticky surface.
As in all branches of industry, specialization can also be observed in the printing industry. In practice, this means that printing companies often only use a few printing processes and often concentrate on specific industries. In the industrial application of self-adhesive labels, new requirements continue to arise, which the label industry is responding to with constant further and new developments.
Areas of application
Today, self-adhesive labels are mostly used in the packaging industry. Compared to the glue label, self-adhesive labels are produced in a variety of high-quality materials and with high print quality. They are therefore particularly suitable for decorating high-quality products in the food, cosmetics, pharmaceutical and chemical industries as well as in many other industries. Labels are often part of the product design, provide information about the product, contain production-specific data, can be information carriers in logistics or have a technical function within packaging. Labels are widely used to allow a high degree of flexibility in the packaging industry. In many cases, the storage of product-specific packaging or packaging materials can be reduced to a minimum, which leads to savings in packaging costs. As a rule, self-adhesive labels do not compete with glue labels, but there are overlaps in some industries, for example in the beverage industry. Further alternatives to the adhesive label are the in-mold process and "sleeving". In addition, labels are used for inventory marking, as safety instructions in danger areas or in transport and shipping. The label is also widely used in the healthcare sector, e.g. B. for sample identification or for recipes and files.
Label quality in terms of machine processability
During the automatic processing of the labels, the label material is pulled taut over a blade-shaped edge. Due to the greater rigidity and the silicone layer, the label with the adhesive detaches from the carrier material and remains stuck to a product that has passed by.
With regard to machine processability, there are some general requirements for self-adhesive labels:
- The labels must have a constant distance from one another on the backing paper. Usually the distance is 2 - 5 mm, but can be larger depending on the production process.
- When punching the labels, the silicone layer or even the carrier paper must not be damaged. “Die-cut carrier material” is a quality defect that is frequently observed, but which must be avoided at all costs in the print shop. If problems arise with the use of "punched" labels, this is often blamed on the labeling machine. The consequence is that the user must be informed that error-free labeling is only possible with label material of perfect quality.
- Adhesive must not come out of the label edges. Due to this lack of quality, the layers within the label roll can stick together. The result is that labels stick to the back of the carrier tape and cause malfunctions within the labeling machine.
- The backing paper must not be too thick. It must be easy to direct it around a sharp dispensing edge. The usual quality for the carrier material is paper with 65 g / m 2 .
- The label material must not be too flexible. During the dispensing process, it must continue to move in a straight line while the backing paper is deflected at the dispensing edge. Problems can arise here in some cases with very flexible plastic labels.
- The backing paper should have a minimum width of 15–20 mm, especially for very small labels. If this width is not reached, the labeling machine can quickly break the tape.
- The adhesion between the adhesive and silicone layer (release factor) must be selected so that the labels only peel off at the dispensing edge, but not elsewhere in the machine, for example on pulleys. The release factors must be different within a multi-layer label, with the least amount of adhesion between the lower backing paper and the rest of the composite.
- The roll core diameter should be selected as large as possible. Internationally (standard) a diameter of 76 mm or 3 inches is often used.