Painting plastics on an automated line

Modern industry and customer approach are changing every industry, including product decoration, which includes liquid varnishing of plastics. Questions arise more and more often about the greatest possible share of automated processes and limiting human intervention. But can every project be implemented this way?

Automation of the painting process

Liquid painting of plastics consists of a series of technological processes, which include:

    – preparation of parts, including blowing and removing electrostatic charge,

    – obtaining appropriate surface tension to ensure adhesion of the coating to the substrate,

    – preparation of the paint mixture and its dosing,

    – varnishing,

    – evaporation, initial and main drying, including product transport to drying zones,

    – seasoning,

    – quality control and packaging.

Sometimes the project requires additional processes, e.g. masking surfaces that are not to be covered with a layer of varnish or paint dust. Painting plastics in professional paint shops is usually at least partially automated. Painting robots or manipulators, as well as systems for automatic paint dispensing and parts transport in individual zones are usually used.

Sometimes automation is necessary – for example, when applying light-cured (UV) varnishes, which are harmful to employees when sprayed in liquid form. After hardening, they create an extremely resistant coating that no longer poses a threat, while the painting process itself must involve as little human intervention as possible.

The automatic painting process also often requires narrowing down the dimensions and types of coatings that can be implemented on a given line. The universal rule – “If something is good for everything, it is good for nothing” – is true in this case as well.

If we want to maximize the effects of automation in terms of efficiency and quality, it is necessary to determine from the beginning of the line design what type of products, what size and with what coatings we intend to cover. An example is our automatic line dedicated to cosmetics packaging – we paint caps, jars and other small shapes that can be rotated around their axis during individual processes. Not only the painting zone was designed to meet these requirements, but also the required line capacity (over 40,000 caps per production shift), coating hardening (IR and UV lamp zone), the type and size of the conveyor and the type of fastening.

Common knowledge says that an automated system can significantly reduce or eliminate human involvement in production. This is partially true, but it should be noted that the employee is extremely important here – the correct programming of the process and its maintenance depend on his competences. Therefore, there is a need to employ workers with other qualifications – operators and technologists instead of standard manual painters. It should also be kept in mind that an automatic system in this industry will not check the correctness of the processes in the same way as a qualified quality controller – here we will not limit the number of employees either.

When is an automated process not advisable?

A professional industrial painting shop should have both types of processes – manual and automatic painting of plastics. The main reasons why the manual painting process is necessary include:

    – problems with plastic – a very common situation in which the injection process is not fully repeatable, which results in the visibility of plastic defects in the painting process. This mainly includes the discontinuity of the material at the injection point, noticeable weld lines, strong flow lines, the heterogeneous structure of the material affecting the formation of flames, and the reaction of the material to thinners contained in varnishes. If the process is performed manually by an experienced painter, these defects are most often noticed during painting and it is possible to correct the method of applying the varnish to hide them. In an automated process, this is possible as long as the defect is repeatable, but random parts often have the indicated defects and an individual approach to each painted product is required.

    – non-standard shapes or customer requirements regarding the surface to be covered or the number of layers – in the case of automatic painting, such requirements overly complicate the process, prolong it and make it unprofitable.

    – lower volumes – automatic painting of plastics is often unprofitable if the order is for too few pieces to involve a team of people to program the process or start the automated painting only for part of the production shift. Such processes provide high efficiency, but their start-up is often longer, so it is profitable to implement them on large and regular orders.

Please contact us – we have automatic and manual lines, and we will be happy to discuss your needs to select the optimal painting process to meet your requirements.

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