Water-based Paint Systems

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-11-26 11:39

There is no way around water-borne paints today. However, many are reluctant to use these products.

The paints are now much better than their reputation - provided the coating material, tools and application process are optimally coordinated. If you ask painters and varnishers where they see the main disadvantage of water-borne paint in terms of processing properties, the answer is usually: the open time is too short - with a solvent-based alkyd resin paint it is much longer.

It may be surprising, but in fact the open time, i.e. the time until skin formation, is no longer longer with most solvent-based alkyd resin varnishes than with a water-dilutable acrylic dispersion varnish. However, the solvent-based alkyd resin paint has the invaluable advantage of reversibility due to the still considerable amount of solvent. When processing with a brush or roller, the already drying paint is loosened without being consciously noticed. The permanent dissolving of the already dried paint by the freshly applied enables a batch-free processing without too much time pressure. This inconspicuous processing property still makes the solvent-based alkyd resin varnish the preferred "painter varnish",because the optical surface quality is still the most important quality feature.

Due to its very limited amount of solvent, an acrylic dispersion varnish or an alkyd emulsion varnish cannot have a reversible effect. If the skin is already forming, it will no longer be removed from the wet paint. If you tried it, brush streaking and roots would result. Processing must therefore be completed within the wet phase, i.e. before the onset of skin formation. This period, known as the open time, is also noticeably shortened at higher temperatures and low air humidity, so that the painter has little time to evenly rework the applied paint. That is why every paint developer tries to extend the open time. This can be supported by special additives, but so far has mainly been done using solvents or alcohols. Since there are narrow limits here, attempts are currently being made to polymerize additives that extend open time directly into the binder. The results are still pending. But even with the paints currently on the market, a result that is acceptable and salable can be achieved at any time, provided that you change something during processing. This is not difficult, since all well-known manufacturers now provide very detailed information on the material-related processing technology and the right tool. One should not ignore this change, because the fact is: water-borne paints are becoming increasingly important. One reason is the greater sensitivity of customers who see any kind of chemical smell as a potential health hazard, but also the steadily increasing number of construction objects,to the certification systems for sustainable construction.

The right tool

As early as the 1970s, when the first acrylic dispersion paints came onto the market, it was recognized that special bristles were required for this type of paint. The brushes made of pig bristles that are used for solvent-based paints were not suitable. However, the first brushes made of polyester weren't quite so. After a short period of use, they often looked like the end of a cow's tail. Only the combination of natural bristles with suitable polyester bristles brought about a noticeable improvement. For about ten years now, the tool manufacturers, in cooperation with the paint manufacturers, have been able to achieve further leaps in quality. This applies not only to the type and quality of the bristles, but also to the construction of the brush.

Today there is a larger selection of brushes available that are basically suitable for water-based paints. From this offer, the manufacturer can now choose the brush that gives the optimal surface finish for his paint and then make a recommendation. Which brush is the right one can vary from paint to paint. This essentially depends on the rheology of the paint. To put it simply, that is what the painter feels under the brush as fluid behavior (tough, less tough or smooth). A bristle mixture that is too soft with a more compact varnish can result in the bristles not properly penetrating the wet paint film and “fluttering” when brushed over the surface. It is not possible to evenly distribute the paint. With a different rheological setting, however, this soft bristle or bristle mixture can be the right one. Finding that out is also part of paint development today. The top result can only be extracted from the paint with a precisely fitting brush or a suitable roller.

This seems to solve the problem. Nearly. Because you can find out in the application technology of the paint manufacturer that you can achieve the top result with this or that type of brush, but then you have to find that there is a problem with the area-wide availability of the product in specialist shops. A paint manufacturer must also think about this today and, if necessary, ensure availability.

Modern, water-borne varnishes of the new generation are not only mechanically highly resilient, but also particularly stable in color.

Sprayable water-based paints

Renovating large lacquered areas in the contract area - today you need rational working processes and the appropriate coating materials. Modern airless fillers and the matching airless paints offer new possibilities.

The ever increasing cost pressure makes complex spatula work increasingly impossible. Whether old doors, plinths or wooden ceilings, the flat filling with a lacquer filler can often be replaced in the contract area by using a spray filler. This possibility has existed for a long time, but for a long time only with fillers containing solvents. This makes the use of the usually large areas and order quantities not only very uncomfortable for the processor. Use in odor-sensitive objects is also problematic.

Fortunately, the accelerated development of VOC-compliant paints has helped here too. With airless fillers and the matching airless paints, dispersion paints with a sensational durability are now also available. In this way, modern airless fillers can be applied in wet layer thicknesses of up to 1,000 µm without running out. However, this layer thickness is to be seen more as a theoretical value. Application quantities of 200 to 500 µm are sensible in one spray application. This achieves an excellent filling power that can be measured against the solvent-containing qualities.

Very good sandability and quick drying result in an ideal substrate for all dispersion paints, but especially for the new airless paints. The special airless paint is also a new development with unprecedented painting safety. Even for an inexperienced spray painter, it is almost impossible to get this paint or filler to run off, even if the spray gun is guided somewhat awkwardly or the sprayer is not optimally adjusted. This high application tolerance is very important for the success of these products. It has been recognized that when developing contemporary spray paints it must be taken into account that many skilled workers only occasionally use the spray gun and have so little routine. The resulting uncertainty in spray painting also leads tothat orders are often processed in the conventional way, although the object environment would certainly allow spraying. This is understandable on the one hand, but on the other hand it is anything but contemporary entrepreneurial activity.

It is now up to the paint manufacturers to convince the skilled tradesman that the new airless products enable safe and efficient painting. Opportunities for this are seminars and training courses, which are also carried out by skilled trades on site. The participants on vertical surfaces are always surprised by the enormous wet stability of the filler of up to 1 mm, that is 1,000 µm or 1 liter / m², and with the coating of up to 0.5 mm, that is 500 µm or 0.5 liter / m². In practice, one spray job usually requires a maximum of half. Order quantities of one liter per m² (1.3 kg per m² for the filler) are generally no longer economically viable. But these theoretically possible order quantities make it clear what is currentlyFilling power and painting safety is possible thanks to modern additive technology.

Of course, wet film thickness and dry film thickness are not the same. The decisive factor is what remains after the water has evaporated, i.e. after drying. The dry layer thickness for dispersions reaches approx. 60 percent of the wet layer thickness. In the case of the airless filler and paint, this is completely sufficient in practice for most applications. With dry layer thicknesses of the airless varnish of 100 to 150 µm on average, excellent coverage is achieved with only one spray application, even with critical colors in the yellow-orange-red spectrum, apart from the excellent filling capacity. It is therefore not necessary to adapt the color of the filler to the subsequent airless paint.

As the name suggests, airless fillers and airless paints are rheologically geared towards processing with airless sprayers. Processing with a brush or roller is not possible. Diaphragm and piston pump devices with or without compressed air support (e.g. Aircoat or Airmix) from Wagner or Graco are suitable. Airless spraying with material heating has proven to be particularly advantageous. When the filler or paint is heated to 40 degrees Celsius, the spray pressure can be reduced by approx. 40 bar. This noticeably minimizes the spray mist. Retrofit kits for continuous material heating are available from well-known spray gun manufacturers (Wagner TempSpray or Graco ° C-MAX).

But the reduced spray mist is also perceived as significantly less annoying with the new airless products. The spray mist lies on the floor as dry dust and not as an annoyingly sticky film as is known from solvent-based paints. The new generation of airless fillers and paints enables pleasant, safe, quick and therefore inexpensive painting on medium and large areas.

With the right work technique, particularly difficult tasks can be accomplished, such as painting panel doors.

Bernhard Linck, Caparol Photos: Caparol colors, paints, building protection Source: Malerblatt 02/2013