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    Home > Coatings News > Paints and Coatings Market > The viscosity of the coating and its determination method

    The viscosity of the coating and its determination method

    • Last Update: 2020-11-28
    • Source: Internet
    • Author: User
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    0 Foreword
    viscosity is an important index in coating performance, which has a great impact on coating storage stability, construction performance and film-forming performance. For example, for latex paint, the shear stress of the coating during storage τ0>10 dyn/cm2 is conducive to preventing subsidion, viscosity of 15 to 30 Pa.s can guarantee the appropriate amount of paint, viscosity in 2.5 to 5.0 Pa.s guarantees brush coating and optimal paint film performance. After brushing, if the viscosity can >250 Pa.s can be very good control of the flow hanging, so the determination of the viscosity of the coating has become a routine item in coating production and inspection
    China
    .
    1 viscosity
    the viscosity can be considered as the internal resistance of a liquid to flow. Power viscosity refers to the ratio of shear stress to velocity gradient applied to a liquid, and its international unit is Pascal P. Seconds (Pa.s), the habit unit is perimeter (cP), 1 cP , 1 mPa.s. By comparing the changes in viscosity at different shear rates, we can divide the fluid into Newtonian and non-Newtonian fluids. In the national standard GB/T 6753.4-1998, the flow type of fluid is divided into Newtonian flow and irregular flow. Newtonian flow, when the shear stress and velocity gradient ratio changes neither with time nor with the velocity gradient mode, the type of flow presented by this material is called Newtonian flow, when the ratio changes very little, mechanical disturbance (such as stirring) has a negligible effect on viscosity, this material is called a flow with an approximate Newtonian type. General varnish and low viscosity paint belong to this liquid. Irregular flow The type of flow presented by this material is called irregular flow when the ratio of shear stress to velocity gradient changes over time or with the shear rate.
    2 Coating viscosity measurement method
    coating viscosity measurement method is many, including outflow cup, Stommer viscosity meter, drop ball viscosity meter, rotating viscosity meter, capillary viscosity meter, taper viscosity meter and so on.
    2.1 National standard for coating viscosity determination
    2.1.1 outflow cup method
    outflow cup is the most easily available coating viscosity measurement instrument in laboratories, production workshops and construction sites. Because the flow cup volume is large and the outflow hole is short, it is convenient to operate and clean, and can be used for opaque paint. The viscosity measured by the flow cup viscosity meter is the motion viscosity, i.e. a certain amount of sample, at a certain temperature from the specified diameter of the hole flow time, expressed in seconds. This is the most commonly used method for determining the viscosity of coatings. Because it can be easily used in many occasions, it can be widely used all over the world.
    In the national standard, the method standard for measuring the viscosity of the outflow cup coating is GB/T 1723-1993 coating viscosity determination method and GB/T6753.4-1988 color paint and varnish with the outflow cup to determine the outflow time. In GB/T 1723-1993, apply-1 cup and coat-4 cup,
    -1 cup is used to determine the outflow time of no less than 20 s coating products, coating-4 cup is suitable for measuring outflow time of 150 s or less paint. Comparing the difference between the two measured values is not greater than 3% of the average, and taking the average of the two measured values as the result of the measurement. In GB/T 6753.4-1988, four outflow cups with similar sizes and outflow apertures of 3 mm, 4 mm, 5 mm and 6 mm are used to determine experimental materials that accurately determine the flow break point from the outflow of the cup out of the hole. For experimental materials with outflow time of more than 100 s, break points are difficult to determine and have poor repeatability due to the delay effect.
    2.1.2 Rotary viscosity meter method
    touch-variant coating with the outflow cup method measured by the large, need to use a rotating viscosity meter, there are rotary paddle viscosity meter, coaxial drum rotary viscosity meter, tapered flat viscosity meter and so on. In the national standard, the method standard of rotating viscosity meter to measure the viscosity of coatings is commonly used in GB/T 9269-1988 building paint viscosity determination Stommer viscosity meter and GB/T 9751-1988 paint in high shear rate viscosity determination. GB/T 9269-1988 is suitable for the determination of the viscosity of architectural coatings, as well as for the determination of the viscosity of suitable coatings. It is expressed in grams (g) of the load required to produce 200 r/min speeds. Conversion to the load and Krebs unit (KU) required to generate 200 r/min speeds can also be obtained by checking the tables in GB/T 9269-1988. The Krebs unit (KU) is a number function that produces the load required to produce 200 r/min speeds and is generally used to represent the viscosity used for brushing and roller coating. GB/T 9751-1988 in 5,000 to 20,000 s-1 shear rate, to determine the dynamic viscosity of the coating, in comparison with the viscosity of various coatings, shear rate should be about the same. This standard applies to all brush coatings, regardless of their Newtonian properties. Rotating viscosity meters and tapered viscosity meters can be used in this standard. The relative error between the two measurements achieved by the same tester using a device in the same laboratory should not be greater than 5%.Comparison of 14 coating viscosity measurement methods in Table 2.2 International standards for viscosity determination of coatings
    ISO 2431 in international standards solves the problem of the impact of individual differences in outflow cups in different national standards on the measurement results by introducing a series of international standard outflow cups. The flow cup viscosity meters used in various countries of the world have different names, china mainly has a cup viscosity meter, ISO cup viscosity meter, the United States has a Ford (FORD) cup viscosity meter, Germany's DIN cup viscosity meter. They are available in different models by aperture size, and each model has its best measuring range for viscosity cups. If below or above the outflow time range, the measured data is not accurate, so when using flow cups to determine viscosity, according to the sample viscosity to select the appropriate model of the viscosity meter, the measured outflow time is best in the middle of the specified range, and indicate which model of viscosity meter is used to measure. General coatings often choose to apply -4 cups, DIN-4 cups, ISO-4 cups and other viscosity meters to determine their viscosity. In the paint production workshop or coating construction site commonly used impregnated viscosity meters, domestic and foreign use of Ford Cup and Zahn Cup.
    2.2.1 International standard
    (1) ISO 2431-1993 color paint and varnish for the viscosity of the coating with an outflow cup.
    flow time (using ISO outflow cups) is used to test the outflow time of Newtonian or approximate Newtonian liquids, and the results are expressed as s.
    (2) ASTM D 5125-1997
    The standard test method for determining the viscosity of coatings and related materials (using ISO outflow cups) is used to test the outflow time of Newtonian or approximate Newtonian liquids, with results expressed in s.
    (3) ASTM D 4212-1999
    impregnated viscosity cup to determine viscosity test method, using impregnated viscosity cup to determine viscosity, the results are expressed as s.
    2.2.2 International standard for rotary viscosity meters to measure paint viscosity
    (1) ASTM D 562-2001
    standard test methods for measuring coating viscosity in Krebs units using Stormer-type viscosity meters. The standard specifies a method for determining the viscosity of the coating using a Stommer viscosity meter, and the results are expressed in grams and Krebs units (KU).
    (2) ASTM D 4287-2000
    standard test method for determining high-speed shear viscosity with a tapered viscosity meter. The standard specifies a method for determining the viscosity of the coating using a tapered viscosity meter under high-speed shear conditions (12,000 s-1), with the result expressed as mPa.s.
    (3) ISO 2884-1-1999
    paint and varnish, using a rotary viscosity meter to determine viscosity. Part 1: Tapered and plate viscosity meters used at high shear rates. The standard specifies a method for determining the viscosity of the coating using a tapered viscosity meter under high-speed shear conditions, with the result expressed as mPa.s.
    (4) ISO 2884-2-2003
    varnishes and varnishes, with a rotating viscosity meter to determine viscosity. Part 2: A disc or splattered viscosity meter that works at a specified rate. The standard specifies a method for determining the viscosity of the coating using a disc or spruct viscosity meter, with the result expressed as mPa.s.
    3 conclusion
    , the method of measuring the viscosity of the coating can be divided into two categories, namely, the outflow cup method and the rotational viscosity metering method. 4 methods in the national standard (GB/T 1723-1993 paint viscosity determination, GB/T6753.4-1988 color paint and varnish with outflow cup determination outflow time, GB/T 9269-1988 building paint viscosity determination Stommer viscosity The calculation method and GB/T 9751-1988 paint in the high shear rate of viscosity determination) each have its advantages and disadvantages, through these methods obtained viscosity values can be adjusted to each other by certain methods, but some conversion relationship is empirical formula, can not reflect the paint viscosity, so should be based on the actual situation to choose the appropriate method to determine the viscosity of the coating.
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