2017/09 | ARTICLE
Conti-TDS - A New Dispersion Technology in Lacquer and Paint Production
Dissolvers were invented in the middle of the last century and have survived in lacquer and paint production until today. They have too many disadvantages, limitations and negative effects on final products.
YSTRAL's Conti-TDS - a new and advanced dispersion technology - has started to displace traditional high-speed dissolvers in lacquer and paint production. This new technology enables enormous reductions in production costs and process times. Additional effects are a higher degree of dispersion, improved quality and raw material savings. The energy consumption is reduced to about 30% compared to the old dissolver technology.
Finally, this new technology is highly flexible and easy to expand if required. The investment costs are 40% lower than that of traditional high-speed dissolvers with the same production capacity.
Dispersion is the most important process in lacquer and paint production and has the highest influence on the quality of final products. The better the dispersion, the higher the efficiency of the dispersed pigments, extenders, rheology modifiers and all other functional additives in the final coating.
Traditional high-speed dissolvers are simple free rotating discs with up- and down-bent teeth at their circumference. Due to the wide distance between the rotating dissolver disc and the static wall of the vessel the shear gradient is very low: just about 50 reciprocal seconds. To create shear forces with such a low shear rate, a dissolver needs a very high viscous liquid or at least a shear thickening or dilatant rheology.
Lacquers and paints have exactly the opposite rheology: they are low viscous, shear thinning and thixotropic. A dissolver cannot create significant shear in a low viscous lacquer or paint. To shear with a dissolver, the viscosity has to be increased extremely. For that reason, the dissolver process starts with more thickeners than required and just a part of the liquids to get a higher viscosity.
This is completely paradox since the most ingredients which have to be dispersed are very fine powders (pigments, silica, fillers and extenders). Making a liquid extra high viscous before adding finest powders is absurd. The higher the viscosity, the worse the wetting and dispersion of fine powders. A high viscous liquid will not get into smallest capillaries and cannot wet fine particles as fast and complete as a low viscous liquid. The consequences are stable agglomerates, low qualities, extra-long dispersing and milling times, heat generation and a waste of energy.
Adding thickeners at the beginning of the process is negative for another reason: most thickeners are shear-sensitive polymers. During dispersion, the polymers get partially destroyed. The effect goes down in an uncontrolled manner. For that reason, you have to add more thickeners than required and you get uncontrolled and unpredictable viscosity levels at the end of the dissolver process. Finally, you have to adjust the viscosity again.
YSTRAL's Conti-TDS technology is based on an inline dispersing machine which is able to induct and disperse powders into liquids under high speed and vacuum. The machine is installed outside the process tank and recirculates the liquid with high speed. Additional pumps are not required.
The core of the machine is the dispersing chamber equipped with high shear tools. In the high shear dispersing zone, it creates a shear rate of 50,000 reciprocal seconds. The shear rate is 1,000 times higher than that of dissolvers. High liquid viscosities or additional thickeners are not required.
Exactly in this zone, the machine creates a very strong vacuum. With this vacuum, it inducts powder directly from bags, bag tipping stations, hoppers, drums, containers and big bags into the liquid. No vacuum tank and no vacuum pump is required which pulls uncontrolled amounts of powder or effluent vapor out of the liquid into filters or exhaust systems as it happens in vacuum dissolvers. The induction is dust-free because 100% of the powder goes into the liquid. Dust pollution of the working area is completely avoided.
The powder is inducted into the recirculating liquid loop and arrives in the vessel as a liquid dispersion. No dust appears above the liquid; no partially wetted agglomerates and crusts are built up above the liquid surface and then fall into the liquid and reduce product quality, that is a common problem with dissolvers.
The dispersion of the powder into the liquid is always done under equal, constant and controlled conditions, independent from the speed of the operator. The product quality is absolutely reproducible, even for different batch sizes.
Constant quality has been one of the biggest problems with dissolvers. Particle size, colour strength, viscosity, matting effect and film formation are influenced by the way how the operator adds the powder. The quality varies from batch to batch, and operator to operator. Slower powder addition caused longer process times, higher temperatures, and lower viscosities. Fast addition causes more agglomerates and further processing time, longer shear, higher temperatures and lower viscosity. Dissolver batches always need to be quality checked – adjusted – checked and adjusted again. These steps take time and block the process tanks during waiting for the QC results.
Some results with Conti-TDS
The Conti-TDS produces absolutely constant qualities. The viscosity is constant. And thickeners are not destroyed – which means that often up to 20% of the thickener can be taken out. This is the amount which is typically over dosed and destroyed by the long dissolver process.
Figure 3 shows a typical particle size distribution for the induction and dispersion of titanium dioxide.
Immediately after induction, the result is better than reference samples produced with dissolver and mill. The medium particle size is already at 0.46 µm. 99.9% of the particles are below 2µm. Not any oversized particle is visible. The distribution is very narrow. After 120 seconds of additional dispersion, the medium particle size reduces to 0.38 µm. 100% are below 2µm and 98% are below 1µm (Figure 3).
The colour strength of the titanium dioxide dispersions produced with Conti-TDS is always higher. For that reason, the amount of titanium dioxide may be reduced with even better performance than dissolver dispersions.
Titanium dioxide is the most important pigment in lacquer, paint and ink production. It covers more than 59% of the global pigment demand. The prices for titanium dioxide have been rising since 2009. Companies which use Conti-TDS for titanium dioxide have reported about enormous savings. They save time, energy and a significant amount of raw materials because of better dispersion.
But even all other pigments, matting agents, extenders and fillers are dispersed faster and with better results – it also apply to all water borne and solvent-borne lacquers, paints and printing inks.
Installation and operation
The machine is installed in recirculation with a process tank. This way it operates independently from vessel size and filling level. To double the capacity with minimum additional costs, one machine is often installed between two vessels (Figure 4). You need just one machine, one control system and one powder addition point to double the production output.
During production in one vessel, the other vessel is discharged from the last batch and filled with the liquid for the next batch already. In the average of 50 seconds after finishing the powder induction, the required particle size is reached and the product is ready to transfer. When the batch is ready to discharge, the machine automatically switches over to the second tank and starts the process there. In this way, it is possible to produce up to 20,000kg of finished paint per hour with just one machine, even in a continuous and uninterrupted production.
All Conti-TDS systems have an integrated and paint industry approved automatic cleaning unit. To keep the process system always clean, every single batch requires a cleaning step. A part of the process liquid is added through the cleaning heads and keeps the tank and all relevant parts clean. Even if the following batch is the same product, the vessel is cleaned automatically. Additional cleaning with extra liquid is possible if there is a product change between incompatible materials or different colours.
Inside the process tanks, there are high effective jet stream mixers installed which move and turn the liquid vertically. These mixers provide an instantaneous homogeneity. This is important because of the high speed powder addition. Simple agitators with mainly horizontal rotation are not able to mix the liquid homogenously and are not fast enough.
Economic advantages and flexibility
Additional to the technical advantages, there are obvious economic advantages with this new Conti-TDS-technology as well. The production costs of paint are typically reduced 10% compared to the dissolver process. Additionally, a significant reduction in raw materials is possible because of better dispersion, higher colour strength and less thickener demand. A reduction of the production times to below 20% is typical. Consequently, 35% energy savings are reported as well. Generally, the Conti-TDS guarantees higher product quality, higher flexibility in the production and higher level of safety.
The foot print of a Conti-TDS system is just some square meters. Because of the faster process, one Conti-TDS can always replace a number of dissolvers – on a very small space.
Investment costs are lower. For a new installation, the investment costs are about 60% lower compared to conventional dissolvers. The return of investment is often shorter than six months. Another advantage is the short realization time: normally, it takes just between half year and one year from the decision to the production.
Today, flexibility is getting more and more important. With such a system, it is possible to produce very effectively different formulations and variable batch sizes. Because of the compact design, it is easy to expand the capacity if required in future.
Since the machine works independently from the vessel size, it is possible to enlarge the process tanks in future if required. Therefore, just the process tanks and their mixers are exchanged – nothing else. The core of the system – the Conti-TDS and the automatic control - remains untouched.
The machines are already used in all fields of the industry in an extremely wide field of applications. All types of products, all viscosity ranges and all types of raw materials are processed. If there are completely new demands in future, it is easy to restructure the process. The final product quality of the produced lacquers and paints is at least equal, in most cases are better than those produced by traditional dissolvers.
With our vast knowledge and many years of experience in Process- and Application Engineering we offer targeted, customer-oriented solutions across industries - from lab equipment to production machines or plants.
Together with you, we develop concepts and implementations for your individual applications, which for you immediately realisable and quantifiable added value