Developing a high-performing coating is not just selecting the right ingredients or having the best formulations. Understanding the dispersion equipment is a must to achieve a smooth and uniform coating.
The right equipment provides you with a homogenous mix of solid and liquid phases in your end coatings. It also ensures the safety, cost-effectiveness, and smooth operation of your manufacturing unit.
A clear understanding of whether you need a piece of more customized equipment, or a common setup would be good for you, can only come once you understand what to choose. Wrong or outdated machinery can do more harm than good for your manufacturing. Therefore, it is crucial for you to understand the issues behind bad mixing and when to choose what, as per your needs.
Need custom advice for your dispersion setup? Get in touch with our experts.
Problems One Can Face Because of Incorrect Mixing or Wrong Equipment
There could be numerous issues in the final coatings if the chosen equipment is incorrect or the technique used for production is not apt for your product.
Listed here are some of the common issues one can face due to improper mixing:
- Excessive Dispersion Time: This could be attributed to the use of outdated or redundant technology for mixing. The right equipment can save you time, money, and labor while maintaining the quality of your product.
- Inconsistencies between batches: One batch comes out fine, but the others have low finishing.
- Unable to Achieve Targeted Fineness of Grind: Wrongly chosen equipment, incorrect paddle size, or improper mixing speed could cause reduced fineness in your coatings. Watch in practice how to efficiently adjust the fineness of grind
- Color Tone Change After Storage: The wrongly chosen equipment can lead to your product having sedimentation issues in your coatings in the later stages.
- Pinholes: This could be a result of improper mixing blade size which may be whipping your coating and causing entrapped air.
- Underactivated material: This may happen because of the wrong equipment used or the time of mixing being insufficient.
- Bubble Formation: Air or solvent entrainment during mixing could be the cause of bubble formation.
Basic Principles Behind Agglomerate Separation
All mixing equipment from around the world are meant to act
on the principles of efficiently separating the agglomerates with high intensity. The better you understand the phases in your coatings and how your equipment complements them the better your final product will be.
Two main principles used to split agglomerates are:
Shear
The grinding equipment, disk disperser, often called dissolver, works using shear forces. The disk disperser utilizes the principles of point shear and pumping to mix higher-viscosity products.
A disk, with teeth on the edge, rotates with high speed in a liquid mill base of high viscosity. The dissolver introduces mechanical energy into the system. This shear forces energy breaks and separates the pigment agglomerates into smaller particles. This newly created surface is wetted by the grinding medium liquid.
In such cases where
shear forces are utilized to deagglomerate, it becomes crucial
to stabilize the temperature such that it helps in maintaining the viscosities as well as splitting the pigment particles into smaller sizes efficiently.
High shear dissolvers come in handy where the systems have dense fillers and pigments with various viscosities.
Impact
In a bead mill, often called a pearl mill, the impact principle (combined with crunching) is used to split agglomerates. Beads (pearls) collide with each other at high speed and agglomerates, finding themselves between two beads, are separated into smaller pieces. A moderate to low viscosity is needed to make high-velocity collisions possible.
(Source: ScienceDirect)
In the center of the mill, an axis with rotor blades rotates at high speed in the mill chamber. The input of a bead mill is a predispersion that is made by using, for example, a disk disperser. The output of a bead mill is a dispersion of solid particles like pigments or fillers in a liquid, containing particles that have the required particle size.
Types of Dispersion Equipment and When to Choose What
It is of utmost importance that different phases of your coatings are uniformly wetted and to achieve that we need to understand which type of equipment is the best fit for your final coating.
Selecting the right dispersion equipment calls for various attributes to be taken into consideration such as:
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The ingredients going in the coatings.
- The order of adding the ingredients.
- Viscosity and phase differences.
- The temperature at which the process is taking place.
Different types of coatings meant for specific applications are developed using a specific type of equipment and, hence, understanding which one you should choose is important.
Using different mixing equipment and the degree of mixing can easily impact the color, gloss, or even
stability of your product. Hence, selecting the right equipment is not that simple.
Most architectural, automotive, or industrial coatings use the following process equipment to achieve the right consistency:
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High-speed dispersers: This simple piece of equipment is a standard tool for various coating manufacturers. This mixing equipment can easily incorporate the powders into liquid and breaks down agglomerates to produce very fine dispersion.
Although fine dispersion can be achieved with the right dispersant, maintaining it over time is the real challenge.
Know more about the dispersion process
To achieve this, your formulation must have the right dispersant loading without which even the right equipment would not be able to save your product from failing.
Check if your dispersant loading is right as per your formulation or not!
The high speed of this tool helps to create turbulent flow in a low-viscosity batch. The said turbulence also causes the formation of a vortex which helps in the quick wetting of powdered ingredients when added directly into the mix.
The speed is adjustable and helps in maintaining the vortex when the viscosity of the mixture changes during the process. This equipment comes with setups to lift the vessels in which the coatings are made for easy transfer.
Depending upon the size of your batches, you can choose from a lab-scale model or a full-blown industrial setup (5 HP motor or above). Some of the models are even available with interchangeable disperser blades, propeller blades, and rotor/shaft assembly and heads to help manufacturers test various types of coatings in a single setup without occupying much space.
As there are multiple models and designs available of these dispersers, choosing the right one would depend on your batch sizes, manual labor to dispense, viscosity range of your batch, volumes associated, and more.
- Rotor-stator mixers (RSMs): These are the standard tools used for mixing and emulsification of dispersions. These are more commonly used for mixtures with higher viscosities in either batch or continuous modes. Batch mixing is the simplest form of equipment which can then be scaled up for more rigorous volumes.
These are single-shaft mixers with an impeller that rotates in proximity to a stationary housing with high-shear forces. They are usually used to deagglomerate pigments or emulsify liquids into liquids. They are very effective when it comes to chopping coarse particles such as rubber or flake resins.
RSMs are available for both continuous and batch models and it is important to understand what makes them different from each other. Things to pay attention to include the mixer location, mix rate, and the speed of the motor.
(Source: Research Gate)
Based on mixer location there are four types of RSMs available in the market:
✓ In-line: These are mounted on the process line.
✓ Top-entry: These are mounted through an entry port at the top of the tank.
✓ Side-entry: These are mounted through a nozzle from the side of the tank.
✓ Bottom-entry: These are mounted through an opening at the bottom of the process material tank.
Before selecting the right RSMs, you need to understand the media viscosity of your batches. The three choices available for media type when it comes to RSMs are:
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liquid,
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liquid with suspended solids,
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and powder form.
The thicker the material the more time and energy will be needed to mix it properly. Keep in mind also the operating capacity, feed rate, and volume capacity as they too play an important role.
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Media mills: When the high-speed dispensers and the rotor-stator mixers are not able to provide the desired particle size, then the preferred equipment is media mills. These are available in horizontal and vertical forms. For choosing the right type of media mill, it is important to understand what type of performance is expected. This helps achieve fine grinds of hard pigments or fillers. The machine combines the shear force and attrition as secondary forces for powerful impact. Media mills operate by generating impact from the collision of media and the vessel walls.
Sometimes the setup is so defined that a premixer is required and that adds to the cost and time for clean-up of the equipment. The experience with different types of machines in coating production becomes an added advantage in such cases.
These were the few of the popular equipments that are today available in the industry. Of course, as the needs of the manufacturers change the industry adapts by bringing newer and improved models along with innovative and effective raw materials.
Proper selection and thorough understanding of the above-mentioned mixers can help you develop finer and high-quality products with minimum wastage.
Facing other issues like loss of gloss or just need an alternative dispersant? Get in touch with our material specialists.