What are the printing substrates and printing inks?

Due to the flexibility and versatility offered by the flexo printing process, there is hardly any material without flexographic printing, regardless of material thickness, elasticity or stiffness, surface properties, intended application, or many other material-related properties. In addition, flexo permits the printing of metal strips or rolls of just a few centimeters wide as well as paper and film webs up to 3 meters wide. In addition, today's newspapers are printed flexographically at production speeds of around 700 m/min.

Obviously, suitable printing inks are therefore required, bearing in mind that very varied requirements are placed on the inks used according to the specific material being printed, their suggested application and printing speed. It is also important in this respect that very strict legal regulations exist in the field of food packaging.

printing substrate

Materials that can be flexographically printed include paper, carton, cellophane, plastic film (single-sided and multilayer), aluminum foil and a variety of specialty materials. The packaging industry, now as it was before, is packaging paper, which mainly consists of a mixture of different pulps.

Kraft kraft paper is a one-sided glossy pulp paper, mainly used in the production of bags and various sacks. Sulphite and kraft papers used for similar applications can also be flexographically printed . Recently, the field of preprints on kraft or test liners has experienced dramatic growth. Corrugated cardboard industry. Another area of flexo printing applications includes tissue tissue for packaging , toilet tissue for handkerchiefs and towels, and many other specialty papers. Also worth mentioning in this context is the direct printing of corrugated board for outer packaging and carton printing (for example, liquid packaging).

The first flexo-printed film posed major problems for all involved, the cellulose film. Depending on its surface treatment, cellulose films are mainly used in food packaging and textiles. Cellophane has lost much of its former importance since the advent of plastic films.

Polyethylene and polypropylene films have many good properties and are currently used in the field of flexible packaging. They are printed and processed in many different thicknesses (~10 to 250 μm), as either sheets or tubes. Their main applications include tote bags, all kinds of food bags, hygiene and hygiene products and many other products, fertilizer and peat bags, garbage bags, mulch films, shrink bandanas and the like. This wide selection of films consists of polyvinyl chloride and polyethylene dichloride films and other specialty films used as a single film or in combination with other materials for packaging or to give the container the characteristics required for the specific product to be packaged. This is achieved by laminating different materials, coatings and coextrusion.

All these materials and material combinations are printed by flexo printing process. This also applies to aluminum foil, which may be plain, laminated, painted or coated, from a thickness of 7 mm and upwards. It is mainly used in the confectionery and confectionary industry, as a lid foil, and for packaging butter, soup, coffee and bread, among many other packaging applications.

Printing ink

Substrates require a variety of different flexo ink properties. The composition of flexo inks is similar to that used in gravure packaging printing; they always consist of a colorant (dyes or pigments), a binder (natural resin, artificial resin or plastic) and a solvent or solvent mixture . Flexographic inks used to be based on basic (soluble) dyes, while pigmented inks are mainly used today because of stricter requirements on ink fastness. Achieving the desired properties such as gloss, adhesion and lamination quality, the correct adhesive and additive selection is required.

In addition to the aforementioned properties, flexo inks need to produce a high-quality end product. Fast and complete drying of the ink on the substrate during printing is another extremely important aspect, in which the solvent of the solvent mixture used is a decisive factor. Drying systems involve evaporating the solvent after the ink is applied to the web. This drying process is significantly accelerated within the press using hot air that is blown onto the web and appropriate exhaust.

Important solvents are hydrocarbons, alcohols, glycols, esters and ketones. Recently, water-soluble pigment inks have been specially used for the printing of multi-layer paper bags, gift packaging, and corrugated paper. Board and wallpaper have played an increasingly important role and have been adopted in the fields of newspapers and plastic films. An obvious reason for the growing trend to use water-soluble pharmaceuticals as inks in packaging, printing and plastic films is a new set of laws requiring the reduction of solvent emissions into the environment.