Innovative paint and coating manufacturing: flexibility is crucial

Fig. 1: The filling level range within which a jetstream mixer (left) can be used at full power (see ranges marked in green) is significantly larger than for a conventional agitator or high speed dissolver.

Flexibility in production is not only required with regard to batch sizes and recipe versions, but also in relation to the processes themselves. It is often the case that the product range is expanded or new raw materials and additives are used which can no longer be processed with conventional technologies. The drive towards new raw materials often finds its origin in the purchase department as well, which is successful in procuring a more cost-effective raw material, however, this is more difficult to be processed, as it is available in agglomerated form for example, and must now be granulated much more extensively. In addition, new provisions and safety regulations are constantly being added – this powder must no longer be added openly, this additive has undesirable side effects, biocides must only be used from now in smallest quantities. Ultimately, customer requests change. Quality requirements are constantly increasing.

Conventional process engineering systems can often only be adapted to the changing requirements with great effort. This applies for example to the trend from solvent-based towards water-based products. Due to the high surface tension of the water, the induction of powders and polar liquids into water-based media is more difficult than induction into solvent-based products. This is why new processes are required.

With regard to the batch sizes that can be realised in one process vessel, traditional technologies such as agitators and high speed dissolvers only allow minimum flexibility. The significantly limited usability of a conventional agitator or high speed dissolver is shown in Fig. 1. The machines cannot be used in the filling level ranges shown in red, as the filling level is too low. It is as much as three ranges for the propeller mixer (middle). The two upper switch-off ranges result from the impermissible pass-through operation. If the agitator is running when the propeller passes through the liquid surface, the propellers splash, inject air, vibrate, and can destroy the bearing and seal. Thus, in case of a falling or rising fill level, as can always be found in processes, the agitator must be switched off early enough. The ranges marked in yellow only permit a reduced power input, as the fill level above the respective tool is too low. 

Whilst it may be possible to lift and lower dissolver discs within certain limits, the range of optimum power input is also compromised.

Traditional agitators and dissolvers can only be used to a limited extent for variable filling levels. Different system sizes are required for different batch sizes.

Fig. 3: System concept for the production of seed coatings with a jetstream mixer inside the vessel and a powder wetting and dispersing machine outside the vessel.

Example: Flexible production of seed and tablet coatings

The demand for variable batch sizes is higher in the production of seed coatings or tablet coatings than in many other areas of the coating and inks industry. These products are not optimised for storage. A high degree of flexibility is required for the production of these coatings, as they are directly processed and often very different seeds or tablets are coated. An extremely large range of batch sizes must be covered with just one system. 

The mixing and dispersing technology supplier ystral designed a process system for one producer of seed coatings with which any batch sizes between 30 and 900 litres can be produced in one process vessel – so at a ratio of 1:30 (s. Fig. 3).  

For this purpose, the powder wetting and dispersing machine Conti-TDS is positioned below the process vessel, which is connected to the vessel in a recirculation loop. For smallest batches between 30 and 90 litres, the circulation of the inline disperser is sufficient for homogeneous mixing of the vessel content. The jetstream mixer is used for homogeneous mixing of bigger batches. With the dust-free induction of the powders directly into the liquid, and processing in the closed system, risks of explosions and health hazards for the operator can be ruled out with such a circulation process.

Fig. 4: Process plant for tablet coating production.

Fig. 4 shows a process plant for tablet coating production using modern mixing and dispersing technology. Compared to conventional methods for producing tablet coatings, the system is much more flexible: All solvent-based and aqueous coating suspensions can be prepared. The powder can be inducted either via an induction lance or directly from the container. Colloidal wetting and dispersion are performed under vacuum and the raw materials are completely de-agglomerated. The process plant can also easily process challenging powders that, for example, are difficult to wet, swell spontaneously, foam heavily, or clump together. Storage stability has increased by up to 90 % which allows a hopper agitator to be omitted during the coating process. Moreover, the new process plant reduces production time by up to 80% and cuts energy consumption by about 60% compared to the previous process.

Flexibility through modularisation

If systems have a modular design from the start and are thus not redesigned from scratch, but composed of individual modules according to the modular principle, later process adjustment or capacity increase is easily possible at a later stage. Physical modules, such as Big Bag emptying stations, dosing units, but also control modules can thus be flexibly combined with each other and adapted to requirements or extended. If required, manufacturers can then expand their plant with a second module for example for Big Bag handling, or switch from powder handling with bags to powder silos.

In combination with innovative mixing and dispersion technology, this results in a wide range of process options: A powder wetting and dispersing machine operated outside the vessel can be operated on a process vessel inline or in the recirculation, and be connected via pipes to several process vessels or storage tanks. In case of low room heights, production processes with two powder vessels and one liquid vessel can be realised. In case of twin tank plants, an inline disperser is installed between two vessels, which can work with the vessel on the right as well as the left. Liquid dosing, powder infeed systems and control are only required once. Depending on the application, two jetstream mixers can also be installed in one vessel, for example in the production of highly concentrated dispersions for industrial coatings. 

Fig. 5: Flexible twin tank process system for batch sizes between 100 and 3,000 litres.

Example: Flexibility in the production of industrial coatings through modularisation

Up to now, in a factory for the production of wood coatings, 20 high speed dissolvers were in use to manufacture 400 different recipes in variable batch sizes. The entire production can be realised on two Conti-TDS twin tank plants from ystral. The process vessels of such a twin tank plant can be of very different sizes (s. Fig. 5) – as in this case. This way, a wide range of batch sizes is possible with only one inline disperser, while the time needed for cleaning is minimised simultaneously – because small vessels can be cleaned significantly quicker than large vessels. The manufacturer of wood coatings can produce batch sizes between 100 and 3,000 litres on one twin tank plant. Both plants cover the complete range of recipes and batch sizes, transparent and in colour. None of the 20 high speed dissolvers used so far are needed any longer. 

Fig. 6: Process system with inline disperser and three process vessels with jetstream mixers installed therein. Image: ystral

If the differences between the batch sizes are even larger, or processes with a very large growth in volume are realised, it might be advisable to use three instead of two process vessels of different sizes (s. Fig. 6). 

Adding another, very small process vessel to a production plant is often also done for another reason: for the manufacturing of small batches for product development, for testing new ingredients and recipes, for weathering or application tests or for sampling at the customer. Two crucial advantages are used for this: When using the Conti-TDS dispersion technology, the batch size is not relevant for the machine, the powder induction and dispersing machine is installed outside of the process vessel and produces smallest and largest batch sizes with precisely the same efficiency. Furthermore, all preconditions for a safe powder and liquid handling, control and process monitoring in the production plant have already been met. 

When such smallest batches are alternatively produced in a lab, this is only possible with compromises. Laboratory equipment often uses much smaller tools with different designs, it uses more power and energy in relation to the product volume and often even uses old and less efficient batch technology instead of the inline dispersion process. And of course the possibility to be able to use the existing process system for small trial quantities means crucial time and cost savings.

Fig. 7: Process times and output quantities of a twin tank plant based on the Conti-TDS in the production of wall paint with different batch sizes. Source: ystral

More flexibility through smaller batches 

In previous years, the unavoidable deviations in quality in a traditional dissolver process have led to a trend in the paint and coatings industry towards larger batch sizes. Every single dissolver batch had to be checked, corrected and rechecked before it could finally be released. All these checks were time-consuming and stopped the production process. This led to a tendency to produce larger and larger batches so that the time required for testing and correction in bigger batches was somewhat more affordable in relation to the quantity produced. However, this tendency towards ever larger batches in the dissolver process led to an enormous reduction in flexibility, because it is simply not possible to produce variable batch sizes in a large dissolver tank.

When using the Conti-TDS technology, there is no fluctuating dispersion quality any more. Readjusting of viscosity, colour strength or hiding power is not necessary. This enables a significantly faster, more effective and most of all flexible production in small batches. 

Fig. 7 shows a process time comparison of batches with 2, 6 and 20 m3 for the production of wall paints according to the twin tank concept. When using the Conti-TDS technology a small plant can yield exactly the same production quantities as a large plant. However, the small plant is associated with lower investment costs, enables even the smallest batches, and allows for quick product changes.

Fig. 8: Multipurpose systems with changeover shafts (left) and replaceable tool heads (right). Image: ystral

Multipurpose systems in the process vessel

Additional flexibility is enabled through modularisation of the process technology on machine level, for example in the form of multipurpose mixing tools in the process vessel (s. Fig 8). With multipurpose systems, the head of the machine can be replaced, which means different processes and product quantities can be realised with the tool best suited to the relevant purpose. Multipurpose systems from ystral are used for different tasks such as jetstream mixing, mixing and dispersing processes as well as inducting and wetting of powders. This is the best preparation for future changes of the process conditions. Such flexible units, which had so far only been known in the laboratory environment, can be used in process sizes between 5 and 50,000 litres. For smaller machines (up to a size of approx. 7.5kW), not only the mixing head, but the entire shaft can be replaced here by one employee using a quick coupling. 

Inline dispersing machines for flexible use

ystral uses easily replaceable conversion sets for inline machines to adapt a universal basic machine to changed requirements, different raw materials and variable tasks. These consist of few parts, can be easily replaced, and in addition to the dispersing tools with different geometries, they also include the powder and liquid connections, sensors and accessories tailored to the task. For instance, the Conti-TDS is not limited to a specific individual process for which the machine was originally procured, but can be easily adapted to new requirements by replacing the tool head – for example to the processing of extremely sticky or thickening powders, to the processing of media that are shear-sensitive and must therefore be mixed with great care and not dispersed at all, up to the processing of products that require particularly intensive dispersing. The machine can be converted from a powder induction machine to an inline dispersing machine with up to six different tool collars lying inside each other. For the user, such a modularisation of the process technology up to machine level means security of investment, as with a changed or completely new process, it is not the whole machine, but only individual tools that must be replaced.

For internationally operating companies, variability in precisely reverse direction is required. The same tools and processes are used everywhere to ensure the same product quality worldwide. However, there are different standards for the electrical equipment, particularly for motors and the non-uniform standards for explosion protection. Therefore, identical tools are combined with country-specific basic machines. This can also be realised for a modular, flexible machine design.

Flexibility is often essential for producers’ survival

There are applications where product changes almost never happen. This is the case for the manufacturing of mass products such as printing inks, corrosion protection primers or paper coatings. Due to the very low number of product versions, flexibility is not really relevant at all, however, the modular concept provides an advantage here also. Having said this, for most lacquers, paints and other coatings, a flexible, easily scalable production is vital for today’s manufacturers, particularly where new products are being developed or products are manufactured customised to order with a large range of recipes and batch sizes. The solution for this is a flexible modularised manufacturing technology, which is adaptable and safe – not only today, but also in future.

This article has been published in an edited version in the European Coatings Journal (issue 09/2024).

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