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    Home > Coatings News > Paints and Coatings Market > Three-point printability of flexo water-based inks: physical and chemical properties of the ink layer, compatibility with flexo plates, and spot color printability

    Three-point printability of flexo water-based inks: physical and chemical properties of the ink layer, compatibility with flexo plates, and spot color printability

    • Last Update: 2022-05-10
    • Source: Internet
    • Author: User
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    Although water-based ink has many intuitive advantages, there are still some printability problems in the practical application of flexo printing and gravure printing, which restricts the application of water-based ink and makes it unpopular
    .
    At present, flexo printing water-based inks are mainly used for the printing of simple packaging such as corrugated boxes and environmental protection bags

    .


    1.
    Physical and chemical properties of the ink layer


    (1) Physical properties


    Physical properties mainly refer to friction resistance, because the printed matter will inevitably wear during printing and post-press processing, so there are higher requirements for the friction resistance of flexo water-based inks
    .


    The rubbing experiment was carried out on the flexo printing water-based ink by a plane rubbing instrument, and the rubbing resistance of the water-based ink was evaluated by checking the change of the density of the ink layer of the printed matter
    .
    Through years of test data collection, we found that the main factors affecting the friction resistance of flexo water-based inks are the surface smoothness of the printing material, the thickness of the ink layer (color density), and whether the surface of the ink layer is varnished

    .


    In order to improve the rub resistance of flexo water-based inks, it is usually necessary to add a certain proportion of anti-friction additives to the ink and increase the proportion of film-forming resin emulsion in the ink formulation, so that the ink layer on the surface of the printed matter has good rub resistance
    .
    It is particularly important to note that the proportion of the film-forming resin emulsion in the ink formulation needs to do certain printing tests.
    If the proportion of the film-forming resin emulsion is increased blindly, there will be poor ink transfer during printing, resulting in printing color deviation, ink bars and other quality issues

    .


    (2) Chemical properties


    For the chemical properties of the ink layer of the flexo water-based ink, such as alcohol resistance, n-hexane resistance, light fastness, etc.
    , the ink company needs to choose the appropriate raw materials

    .
    Especially in terms of the chemical properties of pigments, corresponding physical and chemical tests should be carried out to select the corresponding raw materials to ensure that the output inks have good chemical properties

    .


    2.
    Compatibility with flexo plate


    Since the graphic carrier in the flexo printing process is a solid photosensitive resin plate, the matching between the water-based ink and the flexo plate largely determines the stability of the printing quality in the flexo printing process
    .
    The biggest problem of flexo water-based ink is that it is easy to cause blockage

    .


    The reason for the blockage


    For the printing of four-color halftone images in early flexo printing products, there is usually a blockage of dots
    .
    Front-line production workers often think that this is caused by factors such as too fast drying of ink, unreasonable selection of anilox rollers, and too thick printing ink layer, but rarely consider the matching relationship between printing plate and ink

    .
    Through multiple tests, we found that the surface tension of the graphic area (inking area) on the surface of the flexo plate is 37-39mN/m, while the surface tension of the non-graphic area is 39-41mN/m, which is higher than that of the graphic area.
    out of 2 ~ 3mN/m

    .
    A schematic diagram of the two regions is shown in Figure 2

    .
    Our analysis is that the washing brush affects the surface tension of the non-graphic area on the surface of the printing plate

    .
    It is precisely the difference of 2 to 3 mN/m that makes the non-text area easier to absorb ink than the graphic area during the printing process

    .


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