Many of us have noticed various types of printed products – from notebooks and labels to consumer goods to a wide range of advertising products. They feature images and texts in both large and small formats, black and white, or colour. The application process involves various methods. Today, let’s talk about screen printing.
Simple silk screening has been known since the ancient times when mesh screens made of silk were available to reproduce artistic images on clothes, and later on, to decorate furniture, walls, and steel things. Today, images can be applied through a stencil onto leather, cardboard, glass, and synthetic materials with flat, uneven or cylindrical surfaces. The technique has expanded far beyond the decorative arts and is now here to create control panels, apply protective masks to circuit boards, manufacture flexible film keyboards, and print conductive composites.
The Application Technology
The silkscreen printing process involves three main steps.
- First, we need to prepare the image. The simplest single-coloured pattern made by hand on thick paper will contain no halftones. For more complex works, a computer is used, and the image is printed in black on transparent paper or film, with each colour layer printed on a separate sheet.
- Next, a stencil, or “silkscreen”, is created to form a frame covered with a mesh made of steel or synthetic threads. Initially, they were silk, through which the images were applied manually or photographically. That’s what “silk screen” is associated with. For multicoloured copies, there must be an individual screen per shade since each colour and tone is reproduced separately and layered during application.
- At the printing stage, the ink is forced through the mesh screen by a squeegee onto fabric or paper fixed horizontally in a reliable way along with the stencil form. The process may involve one of the two main options: direct printing or with an intermediate carrier, where the image is first transferred to paper and then to the article, which is then dried using a special fan or other drying equipment.
To ensure perfect quality, several important factors must be considered:
- The blade used to transfer ink must be adjusted so that the pressure and the printing angle ensure even distribution. Otherwise, there will be too much dye on the surface, or the layer will be loose.
- The squeegee must go one way first and then in the opposite direction.
- The viscosity of the ink must be constantly monitored. If the ink is too liquid, the contours will smear and spread. The higher viscosity, the greater effort is required for the rubber blade to press onto the mesh.
- The parameters of the mesh are to be selected from case to case, including the number of threads per cubic centimetre is considered, ranging from 10 to 200. The thickness of, and the distance between the threads are also important as they affect the dye layer density.
Machines and Materials
Each business uses a different set of tools based on their financial capabilities. For small-scale production, there is manual equipment to allow the printing of small, usually single-coloured. The simplest machine for making stencil imprints consists of a meshed frame and an elastic rubber or polymer blade. The squeegee serves to distribute the printing ink over the stencil and force it through the holes. More advanced print shops have semi-automatic and automatic carousels to reduce human assistance.
In addition, there should be frames, exposing devices, stencil meshes, drying cabinets, squeegees, emulsion application machines, intermediate drying racks, and special inks available on the stock.
The consumables required include printing inks and the materials the stencil and the mesh are made of.
The inks are composed of
- rosin-based binders;
- pigments;
- solvents;
- humectants;
- catalysts.
Mechanisation and modern automation enable superb printing on any substrates, a feature no other type of printing can offer.
Advantages & Disadvantages
Screen printing offers lots of benefits other methods cannot beat, e.g.:
- Application of various colours and shades, including metallised inks to imitate gold and silver. An image can be applied to surfaces with unusual textures to create embossed, glossy or metal effects that will add character and appeal to the printed article.
- The sufficient thickness of the layer ensures a decorative effect guaranteeing durability of the image. Although the dye does not penetrate deeply, we can enjoy superior quality prints. With proper care, it does not fade in the sun. Nor does it wear off with numerous washes, or during intensive operation.
- Possibility to use non-absorbents, e.g. rubberized or metallised materials.
- Compatibility with embossing, varnishing and other post-printing processes.
The following should be highlighted as the weak points:
- High price. There are no ready-made schemes or templates; each time a unique pattern must be created for which you have to pay. Special inks are also required, and their consumption is high. Custom printing involves different parameters, formats, and design solutions. They cannot be arranged automatically.
- Labour intensity. It takes much preparation, and if you want to change the drawing, the printing form needs to be remade.
Thus, being not intended for mass production, screen printing is an ideal printing option for the exclusive sphere where image products define the brand emphasising its high status.
