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    Home > Coatings News > Paints and Coatings Market > Fine blend, faster processing

    Fine blend, faster processing

    • Last Update: 2020-12-30
    • Source: Internet
    • Author: User
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    Optimised pigment processing by selecting an effective premixer and tracking particle sizes prior to the grinding phase
    In order to keep pace with the mass production of modern consumer goods and luxury goods, the coatings industry has accelerated technology updates and delivered different types of coatings for a variety of applications that support anti-corrosion, weathering and fastening environmental regulations. One way to get a better product is to tightly control particle size and particle size distribution, as these two parameters affect many important coating properties.
    , pigments, fillers, etc. use "average particle size" to describe powders. In fact, powders are often supplied as aggregates, so when the average particle size of the initial particle is
    8-10
    microns, the average aggregate particle size can be
    200-600
    microns. Further aggregation may occur when the powder is added to the fluid. As a result, the mixing and grinding operation reduces the size of the aggregate rather than the initial particles. In this article,
    term
    "
    particle size
    is used in the language above.
    the particle size of solid paint directly affects the optical effect by affecting parameters such as opacity, gloss, phase and coloring force. Usually smaller particles produce more satisfactory products and combine with narrow particle size distributions to give the coating a smooth, highlight coating. Particle size also affects stacking properties including tentacles and stability. For example, in the case of constant solid content, reducing particle size not only improves color spread, but also increases viscosity and improves the stability of the final product. This can lead to a decrease in pigment usage.
    in terms of coating and operation, customer demand is driving manufacturers towards finer particle sizes and narrower distributions, increasing the need for tight control and efficient processing. This article discusses how researchers at Charles Ross' parent company optimized the production of commercial ink suspensions with laser diffraction granularity analyzers (model
    Mastersizer,
    Marvin Instruments
    ). The results show that the company's new mixer significantly improves the premixing
    /
    wetting efficiency, resulting in a finer premix that can be ground more quickly to the final product.
    pigment dispersion
    despite significant advances in the chemistry and formulation of pigment-based inks and coatings, industry production has always maintained a two-step process. First, the pigment is moistened to create a dispersion within the appropriate flow phase. The premixed sample is then ground to reduce the particle size through the rupture and friction of the aggregate.
    formation of premixed pigment dispersions is generally done using propellers and turbine mixers installed in open containers. The ability of these mixers is limited to simply wetting the powder before grinding. The introduction of high-speed dispersors is a welcome improvement. Blade end speed
    5,000
    ft
    /
    min (
    25
    m
    /
    s) or higher, and the high-speed dispersor causes more powerful flow in the container and gives (material) greater shearing force than propellers and turbines. This results in a significant reduction in wetting time. However, since grinding is considered to be the most important step in the abrasive process, the importance of particle size control during wetting was not recognized at first. The wetting phase is therefore controlled to ensure that pigment suspensions are converted into forms suitable for grinding in the next process, without considering the need for the final application.
    those who now realize that wetting steps play a key role in grinding, take steps to replace their propellers, turbo mixers or high-speed dispersors with more efficient equipment. In this case, efficiency is the measure of the extent to which the mixer can disperse the pigment aggregates as close as possible to the required specifications. This principle seeks to reduce the number of passes through the grinder and, in some cases, completely omits the grinding process. Particle size measurements before grinding have thus become a necessary means of ensuring premixed efficiency.
    laser diffraction particle size analysis
    laser diffraction is an accepted particle analysis technology, widely used across the manufacturing industry. Particle samples, between wet and dry, are scattered through their lasers, producing diffraction maps related to their size. Smaller particles scatter light faintly at wide angles, while larger particles produce stronger signals at narrower angles. The diffraction map generated by laser diffraction system detection, by virtue of the detailed mathematical description of electromagnetic wave behavior, is usually converted into particle size distribution according to Theory of Michele light scattering.
    laser diffraction systems are highly automated, eliminating the changes in operators associated with traditional particle size analysis techniques such as Hagmann fine meters.
    is widely used in the industry, but it only provides a measure of the largest particle in the model. Instead, laser diffraction analyzers measure all particle size distributions over a wide dynamic range (from
    0.02
    to
    2,000
    microns) to make them suitable for every stage of the process, from wetting to the final grinding of the product. Measurements take less than a minute, making it easy to detect dispersion quickly or track particle size reduction as it continues to work. These capabilities make laser diffraction an outstanding tool for product development, amplification, process optimization and quality control.
    to maximize process efficiency during premixing
    looking for more efficient mixing equipment during pigment wetting has led many users to consider using roors
    /
    serum high shear mixing devices. These mixers include a high-speed roors installed in a near-stop net space (blade end speeds between
    3,000
    and
    4,000
    feet
    /
    minutes or
    15
    to
    20
    m
    /
    seconds). This structure creates extremely strong mechanical and hydraulic shears by constantly pulling the product components up to the open ends of the roors and expelling them quickly through the openings of the seths.
    the main reason these devices cross the stage and prevent many people from relying on them for premixing is insufficient flow. Traditional roors
    /
    putts (groups) produce the strong shear necessary to disperse pigments, but cause poor product flow in the container, resulting in local heat concentration in the high shear area, and containers that require coats. Vortex usually occurs under the mixing head and, due to increased viscosity, is usually not strong enough to pull a solid down from the liquid surface to a high shear area.
    Charles Ross Parent Subsidiary, a special hybrid equipment manufacturer, recognized this limitation of roors
    /
    station mixers and developed
    PreMax
    (U.S. Patent No.
    6,000,840
    ) using "triangular" rotone
    /
    station technology. The flow plate, which is generally close to one end of the rotor
    /
    stortor, is made removable and adjustable, so the rate at which solids are pulled from the surface to the mix is now controllable. The roors are also rated at higher blade end speeds (
    5,000
    ft
    /
    minutes or
    25
    m
    /
    seconds) than normal high shear mixing devices, resulting in higher levels of mechanical, fluid and air-cut. The "triangular" shape creates a double vortex and much larger flow than conventional roor designs, pulling powder from the flow phase surface into a high shear area. This design enhances mixing performance by eliminating the possibility of raw material flowing to the top of the mixer and providing powder suction methods that minimize dust.
    the value
    preMax
    /
    -rated notation concept has been quantified in the laboratory and, importantly, is shown on the actual production line. With
    PreMax
    premixes often produce effects comparable to media grinding one or two times. Reduces the number of grinders required to reach the final product particle size, reducing processing time and production costs.
    laser diffraction test is
    The benefits
    preMax

    using the
    PreMax
    system to increase the shear force generated during wetting can be seen in figure
    1
    1. An independent consultant evaluated three premixed devices: a high-speed dispersor, a traditional rother
    /
    prosthion mixer, and
    PreMax
    to determine how the particle size of the ink product changes during processing and whether optimization of the wetting phase can lead to process improvements.
    laser diffraction particle size analysis shows that the average particle size (17
    ). D
    (
    4, 3
    ) is
    2
    microns. Premixed with a high-speed dispersor, the average particle size of the pigment dispersion in the flow phase is only
    14.2
    microns. This premix contains a large amount of aggregated material, so the number of times the final product needs to be generated through the grinder is high. The use of standard roors
    /
    high shear mixing devices during wetting does improve dispersion in premixes, resulting in an average particle size of
    8.2
    microns. In this contrast,
    PreMax
    produces
    average particle size of
    .3 microns and a particle size distribution within the acceptable range of commercial dispersion. This suggests that, using
    PreMax
    , manufacturers of these ink products have an option to remove grinding only once through a media grinder or completely, increasing the total processing volume of the product and reducing processing costs.
    experiments in other applications give the use of
    PreMax
    the value of the improvement in speed and dispersion. Particle size detection during wetting indicates dispersions of colored materials such as turquoise or zircon brown, using
    PreMax
    systems.
    Dv90 (90%
    particle size
    )
    can be reduced to
    40
    microns, compared to
    Dv90
    when using traditional high-speed dispersors, but greater than
    200-300
    microns.
    conclusion
    the manufacture of fine-grained solid-color coatings gives the product superior performance, including better masking and gloss, but requires processing. The particle size reduction that occurs during the initial wetting phase minimizes or eliminates the subsequent grinding process and is therefore beneficial for the optimization of the entire process. Laser diffraction is valuable analytical technique for studying pigment dispersion processes because it has the dynamic range and detection speed required to characterize the particle size at all stages of the manufacturing process and tracks the particle size reduction process as it continues to work. The results presented here illustrate its application in evaluating newly developed hybrid devices. The new mixing device increases productivity by improving the wetting process, resulting in faster grinding to finer premixes of the final product.
    This article is an English version of an article which is originally in the Chinese language on echemi.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to service@echemi.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

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