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    Home > Coatings News > Coating Technologies > [Information of the Tu Society] How much do you know about the water separation of water-based coatings?

    [Information of the Tu Society] How much do you know about the water separation of water-based coatings?

    • Last Update: 2021-06-10
    • Source: Internet
    • Author: User
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    The coating industry refers to the separation of solid pigments and fillers in coatings from the dispersion system as "water separation", or sinking.

    It means that after the paint is made, in the storage process, due to the relatively high density of the pigments and fillers, they sink, and the dispersion carrier and water-soluble substances float up to cause paint delamination.

    The sinking of pigments and fillers will cause the components in the coating formulation to be uneven in the packaging, affect the construction performance of the coating, and even cause the coating film to bloom, orange peel, cracking, and blistering.

    Severe water separation causes the paint to sink to the bottom and it is difficult to stir evenly, resulting in the paint being scrapped.

    As people's environmental protection requirements are getting higher and higher, the country has imposed strict limits on the VOC emissions of paints, and it is very important to develop pollution-free green paints.

    Water-based coatings are becoming the mainstream products in the coating family.

    Water-based coatings are made by compatibility of water as a dispersion medium with film-forming materials, pigments, fillers, and additives.

    Such as water-based wood paint, water-based steel paint, water-based interior and exterior wall coatings, etc.
    have been greatly developed in recent decades.

    Since most of the pigments and fillers have a density of about 2, which is quite different from water, it is an inevitable trend for the pigments and fillers to sink due to the difference in density in the gravitational field.

    At the same time, the pigment and filler particles are wetted by water in the water, causing the particles to agglomerate, and the micro-agglomerations grow up and sink.

    How to reduce the sinking of pigments and fillers (ie water separation) through the formulation of the paint itself is a problem that the majority of paint workers have been working hard to solve.

    At present, most coatings on the market more or less have the problem of "water separation", which affects the storage period of the coating, and affects the workability and film performance of the coating.

    Research on the "water separation" of water-based coatings has not been reported yet.

    On the basis of many years of paint production and research, this article analyzes the causes of "water separation", starting from the dispersion system and thickening system, and carefully studied the type, quantity, and thickener types of dispersants that affect the "water separation".
    Influence, the experiment achieved satisfactory results.

    1.
    Experiment 1.
    1 "Water separation" characterization Take the interior wall latex paint formula as an example, store the prepared product in a test tube, and use 1 month, 3 months, 6 months, and 12 months as the time periods to investigate "Water divide" phenomenon.

    The height (mm) of the aqueous solution floating above is used as the judgment of the severity of the "water separation".

    1.
    2 The formulation design uses the interior wall latex paint as an example of the research problem, which has a certain representativeness.

    Because interior wall coatings are more cost-conscious, pigments and fillers account for about 50% of the weight of the coating, especially fillers that account for more than other water-based coatings.

    Such a large amount of powder material is more prone to "water separation" phenomenon.

    1.
    3 The preparation process of the interior wall latex paint is according to the formula in Table 1.
    First, weigh the water, dispersant, defoamer, film-forming aid, and glycol on the high-speed disperser and stir at a slow speed, and slowly sieve the cellulose under stirring.
    .

    Then add anatase titanium dioxide, heavy calcium, talc, and kaolin respectively, stir well and disperse at high speed for 30min (25000r/min), when the fineness is «45μm, slowly add styrene-acrylic emulsion, stir evenly, adjust pH= with ammonia 8.
    5 or so, finally adjust the viscosity to 8000mpa.
    S with a liquid thickener, filter and pack.

    2.
    Results and discussion 2.
    1 Research on the influence of dispersant types on "water separation": five types: anionic, cationic, non-ionic, polymer and polymer plus inorganic sodium hexametaphosphate (weight ratio 1:1) The effect of dispersant on "water separation".

    The dosage is 0.
    5% (weight percentage, the same below), and the thickening system is compatible with hydroxypropyl methylcellulose and polyacrylic liquid thickener.
    The other components and percentages in the formula in Table 1 remain unchanged.

    The results are as follows: It can be seen from the above that the five types of dispersants are preferably polymer dispersants, especially polymer polyhydroxy stearic acid polyester and inorganic sodium hexametaphosphate.

    This may be due to the fact that one end of the anchor group of the polymer dispersant is entangled and adsorbed with the film-forming material, and the other end is encapsulated with the pigment and filler particles, which separates the particle clusters from each other, which increases the space repulsion energy between particles, and the surface The formation of bimolecular structure is strong, the polar end of the outer layer has stronger affinity with water, which increases the degree of solid particles being wetted by water, and the repulsive force between particles is greater.

    The addition of sodium hexametaphosphate increases the number of charges, increases the force between the particles that form a steric hindrance, and further prevents the agglomeration of micelles.

    At the same time, its addition reduces the amount of organic dispersant, because the excessive amount of organic dispersant will bring more foam during high-speed dispersion.

    2.
    2 The influence of the amount of dispersant on the performance of "water separation".
    Dispersant is a surfactant with two opposite properties, hydrophilic and lipophilic in the molecule.
    It can uniformly disperse the solids of inorganic and organic fillers that are difficult to dissolve in liquids.
    , And can prevent particles from settling and agglomerating.

    Therefore, the dispersant plays a very critical role in the preparation of coatings.

    The dosage is generally 1-5% of the mass of the masterbatch.

    The experimental results are as follows: It can be seen from Table 3 that when the amount of dispersant is 0.
    5% of the mass of the masterbatch, the "water separation" is serious.

    When the amount of dispersion increased to 1%~2%, the "water separation" of various dispersants improved significantly, but when increased from 1% to 2%, various dispersants had little effect on the results of "water separation".

    It shows that 0.
    5% dispersant can not cover the pigment and filler particles well, the repelling energy produced is low, and the micro-agglomeration is easy to agglomerate.

    2.
    3 The influence of thickeners on the performance of "water separation" Cellulosic thickeners have high thickening efficiency for the water phase and are widely used in water-based coatings.

    The thickening mechanism is that the hydrophobic main chain and the surrounding water molecules are combined through hydrogen bonds, which increases the fluid volume of the polymer itself and reduces the free space for particles to achieve thickening.

    The use of cellulose thickeners has a certain effect on the construction performance of the coating, which is easy to cause splashing and poor leveling.

    The larger the molecular weight, the more serious the impact.

    Paint products must ensure a certain ex-factory viscosity, usually adjusted with liquid thickeners.

    The widely used liquid thickeners are acrylic thickeners and associative polyurethane thickeners.

    Acrylic thickener uses the electrostatic repulsive force of carboxylate ions to spirally stretch into a rod shape in the molecular chain.
    In addition, it also achieves thickening by forming a three-dimensional network structure between latex particles and pigments and fillers.

    Associative thickeners are the introduction of hydrophilic and hydrophobic groups into the molecule to form micelles in water.
    The micelles and polymer particles associate to form a network structure to thicken the liquid.

    Take the above-mentioned polymer polyhydroxy stearic acid polyester and inorganic sodium hexametaphosphate at a ratio of 1:1 as a dispersion system, prepare emulsion paint according to the formula in Table 1, and investigate the pairing of different cellulose thickeners and liquid thickeners.
    The impact of water.

    See Table 4 and Table 5 for details.
    In latex coatings, cellulose plays the main role of thickening, and the liquid thickener mainly plays the role of adjusting the viscosity.
    The amount is small, but the effect is great.

    It not only has an important influence on the performance of "water separation", but also has an important influence on coating construction and film performance.

    It can be seen from Table 4 that hydroxypropyl methylcellulose has the best effect on the preparation of "water separation".
    As the molecular weight of hydroxyethyl cellulose decreases, the "water separation" becomes more and more serious.

    This may be because the entangled network structure formed by hydroxypropyl cellulose, latex and pigments and fillers has stronger performance, and it is not easy to break the network structure and cause micro-agglomeration.

    With the increase of molecular weight, the hydrophobic performance of hydroxyethyl cellulose is better, and the entangled network structure gradually strengthens because of the decrease of "water separation".

    The carboxymethyl cellulose is more compatible with water, and the entangled network structure formed is weaker, so it is easier to "separate water".

    Table 5 specifically discusses the influence of two commonly used liquid thickeners on the performance of "water separation" under the determination of other ingredients and dosages in the formula.

    The results show that the use of polyacrylic thickeners is better.
    The reason is that the carboxylate ions of the polyacrylic thickeners bridge between the latex and the pigments to form a network structure, while the associative thickeners may be adjacent to the There is an interaction between the latex particles, causing the latex to stratify.

    3.
    Conclusion First, water-based coatings, especially latex coatings, using polymer polyhydroxy stearic acid polyester dispersant and inorganic sodium hexametaphosphate have excellent resistance to "water separation", and the amount is 1% of the masterbatch.
    %about.

    Second, the cellulose thickener should be hydroxypropyl methyl cellulose or hydroxyethyl cellulose with a larger molecular weight, with hydroxypropyl cellulose being the most preferred.

    Third, the liquid thickener is preferably polyacrylic acid.

    Not only can it resist "points.
    "

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