Knowledge points for the most complete viscosity determination of water-based paints and oil-based paints!

What is viscosity
viscosity is an important index in coating performance, which has a great impact on coating storage stability, construction performance and film-forming performance.
for latex paint, for example, the shear stress of the coating during storage ъ>lO dyn/cm2 is conducive to preventing subsidion, the viscosity of 15-30 Pa.s can guarantee the appropriate amount of paint; 5 to 5. 0 Pa.s guarantees brush coating and optimum paint film performance. After brushing, if the viscosity can be >250 Pa.s can be well controlled flow hanging, so the determination of the viscosity of the coating has become a routine item in the production and inspection of

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the viscosity of
the viscosity can be considered as the internal resistance of the liquid to the flow.
dynamic viscosity refers to the ratio of shear stress to velocity gradient applied to a liquid in international units of Pascal seconds (Pa.s) and in the unit of habit (cP). l cP s 1 mPa.s. By comparing changes in viscosity at different shear rates. We can divide the fluid into Newtonian fluids and non-Newtonian fluids. In the national standard GB/T 6753. 4. _l998 fluid flow type is divided into Newtonian flow and irregular flow. When the shear stress-speed gradient ratio changes over time or with the shear rate. The type of flow presented by this material is called irregular flow.
coating viscosity measurement method
coating viscosity measurement methods are many, including outflow cup, Stommer viscosity meter, drop ball viscosity meter, rotary viscosity meter, capillary viscosity meter, taper viscosity meter and so on.
(the more commonly used 4 viscosity detection methods)
. 1. Coating-4 viscosity metering
-4 viscosity metering method is suitable for coating products with outflow time of less than 150s. Coating-4 viscosity meter capacity of 100mL, when the coating fills the container, the time from the bottom standard hole to determine the viscosity of the coating, in s, the measured value multiplied by the correction factor K, that is, the condition viscosity of the coating. In two parallel tests, the error should not exceed 0.5s. After the test, the residual liquid should be cleaned, especially the outflow hole, to ensure the finish of the inner wall of the cup. The application-4 viscosity meter is commonly used to measure low viscosity coating products such as floor varnishes and wood coatings. The advantages of applying-4 viscosity meters are simple structure and simple operation. The experimental data obtained by applying-4 viscosity meter can be adjusted with the results of Enciscome. However, if the cleaning is not thorough, the outflow hole is easily blocked, resulting in inaccurate measurement results.
2. Stomer viscosity meter
Stomer viscosity meter is a laboratory to determine the viscosity of coatings widely used instruments, can measure acrylic paint, epoxy primer, chlorinated rubber paint, epoxy zinc-rich primer, polyurethane paint and other different system coatings. The measurement principle is that when the torque produced by balancing the weight mass is equal to the viscosity resistance of the coating, the KU value of the coating is obtained by checking the table, and the measurement range is 40 to 140 KU. Dip the rotor blades into the sample under test until the hinge mark, select the appropriate weight from 5 to 500g weights to place on the weight rack, release the locking knob, start the timing, when the speed is stable at 200r/min, stop the determination. Due to hardware and software upgrades, the degree of instrument automation is constantly improving, STM-KU2 viscosity meter (Figure 2) can directly display the viscosity KU value, CP value, facilitate the work, improve efficiency, and the instrument to collect data for calculation and related processing, automatically delete data off the center area, improve the accuracy of instrument measurement. The test results of the measured fluid viscosity resistance to the Stommer viscosity blades were more repetitive than the viscosity moment that the rotary rotor was subjected to when the rotary viscosity meter was measured. The advantage of the Stommer viscosity meter is that it is easy to operate, the measurement is complete, just remove the blades for cleaning, it is convenient to carry out the viscosity determination of high-volume products at the same time. However, The Stommer viscosity meter has a precise structure and high environmental requirements, and the vibration and humidity of the environment have a direct impact on the accuracy of the instrument measurement, and will shorten the life of the instrument.
3.En viscosity method
en viscosity method is applicable to GB/T266, ASTMD1665, IP212 standards. The principle is that at a temperature of 20 degrees C, 200mL is the ratio of the time (s) required for the liquid to flow out of enciscosity meter (Figure 3) and the time (s) for distilled water to flow out under the same conditions, in Englada. En's viscosity is a relative conditional viscosity. In accordance with the test requirements, set up a good test instrument, adjust the viscosity meter level, to the viscosity meter in the pot 3 horizontal nails and liquid surface cut, poured into the liquid under test, the constant temperature to 20 degrees C. At the beginning of the test, the temperature of the digital thermostat can be set slightly higher, while turning the stirring in the outer pot to speed up the thermostat process. Unplug the plug bar at the same time, press the stopwatch to time and stop when the acceptance bottle 200mL scale is reached. At 20 degrees C, the standard water value is (51±1)s and the temperature score is 0.5 degrees C. The temperature control system of En's viscosity meter can set different temperatures according to the test needs, measure the viscosity of the coating, but its deficiency is that the test device is more complex, cleaning relatively troublesome, especially the products with greater viscosity are not suitable for using Enshi viscosity method.
4. Rotating viscosity meter
Rotary viscosity meter can measure the absolute viscosity of 10 to 100000mPa.s by combining different rotons and speeds. Range reference, rotary viscosity meter can be used to measure the resin viscosity and zinc epoxy zinc-rich primer TI value, but also for intermediate products organic bentoft pre-glue viscosity control. When measuring the unknown viscosity of the liquid, in accordance with the principle of the roulette from small to large, speed from slow to fast operation, to prevent the synchronous motor from burning, when the reading pointer is stable in the 30 to 90 minutes range, press the pointer locking rod and motor switch, directly read out the values on the dial, and then multiply the coefficients on the coefficient table, the result is the absolute viscosity of the sample under test (mPa.s). If the measurement range is exceeded, the measurement can be done by changing the rot and speed, which is 6r/min, 12r/min, 30r/min, 60r/min4. During the measurement process, the lifting screws should be fixed to prevent the motor from falling loose. When loading and unloading the roil, be careful, measure it, clean it, store it in a special box, and install the yellow collar at the shaft connection at the lower part of the motor to protect the sensitivity of the spring wire. Rotating viscosity measurement range is large, so it is widely used in coatings, oils, food, drugs, dyes, inks, adhesives, cosmetics and many other fields. Rotating viscosity meters require a high finish of the roiters of working parts, so corrosive liquids can not be measured.
5. Drop ball viscosity method
The principle is that the free falling speed of the steel ball is inversely inversely related to the viscosity of the liquid, the greater the viscosity, the longer the steel ball falls. Because bubbles are easy to produce in high viscosity fluids, the measurement results will be biased and parallel tests should be done to reduce errors. The drop ball viscosity meter is used in the laboratory to determine the viscosity of the resin used in the coating material. The disadvantages of the drop ball viscosity meter are also obvious, because the state of the steel ball needs to be observed, usually only transparent Newtonian liquid can be measured, and the determination of opaque liquid viscosity is not applicable.
6. Iwata viscosity cup method
because of its easy to carry, simple operation, is widely used in on-site measurement. When measuring, the Iwata Cup (Figure 7) is immersed in the fluid, and the fluid does not pass the upper end of the Iwata Cup, the cup is raised, and the stop time is pressed as the stopwatch occurs, when the fluid breaks for the first time, stop the timing, while doing 3 measurements, the average is the fluid outflow time. Iwata method is suitable for 20 to 105s outflow time fluid, and the result data should indicate the ambient temperature. Iwata viscosity cup measurement principle and structure is exactly the same as Tu-4 cup, but the size is smaller, is one of the necessary tools for field technical services. However, its deficiency is that it is not enough to measure the high viscosity value of thick primer paint.
the conversion of the viscosity unit
absolute viscosity, unit Pa.s, 1.0Pa.s, 10P, 1000cP;
motion viscosity, unit m2/s, s/, for the density of the fluid at the same temperature
(kg/m3); K20 is the water value of the viscosity meter at 20 degrees C;
coat-4 cup viscosity, unit m2/s, (T4-6.0)/0.223, T4 measured fluid outflow time s for 4 cups, test data obtained by different viscosity measurement methods can also be calculated by table. (Figure below) the effect of the various parts of the
coating on viscosity
the contents that have a greater impact on the coating are:
1 solvent, the change of solvent directly affects the solubility of the solution to the coating, and the effect of the strong and weak solubility on the viscosity is very obvious, such as the same coating when the solvent changes greatly, the final viscosity of the paint production will be more obvious deviation;
2 coating cellulose and thickener changes greatly, the viscosity of the coating will also have a more obvious deviation, (e.g. nitrate cellulose in nitro coatings when using 1/2" NC and 15" NC formulation of the same formula of the paint when its viscosity is very different, in water-based coatings thickeners are also very different from its viscosity is also a great influence.)
3 Pigments in color paint, because of the different oil absorption, density, PH value of pigments, so when the pigment changes on the viscosity of the paint is also obvious; )
effects of 4 additives. In color paint additives on the viscosity of the effect is also greater, such as black paint in the color paste preparation dispersion aids of the difference not only affect the grinding effect also affect the viscosity of the coating. Some additives also have a significant effect on the viscosity of the coatings in storage.
the relationship between viscosity and temperature and the measurement of coating temperature
We all know that viscosity changes with temperature, but how does it change, and is there any relevant law of change? After experiments can know the following laws: 1, when the higher the viscosity of the lacquer liquid, after the temperature change, the greater the change of its viscosity, when the viscosity of the lacquer liquid is lower, the temperature change, the smaller the change of its viscosity; When measuring the temperature of the coating, it should be observed while stirring, because the temperature of the coating is not consistent with the temperature of the environment when the coating is produced and stored, there will be a process of temperature data rise and fall when measuring. So when reading the temperature data, it must be the stable data when measuring.
the viscosity adjustment control method. The adjustment of viscosity in the control of paint viscosity is very important and common problem, because the change law of viscosity of each variety of products is different from its viscosity adjustment method will of course be different, and the same product due to the formulation of different viscosity adjustment ratio will also be inconsistent, so I think the adjustment of paint viscosity needs quality testing personnel and related technical personnel from practice to find the relevant viscosity change rate of each variety, after accumulation analysis, will get a relatively reasonable viscosity adjustment ratio data.
Viscosity stability in coating storage
Coatings may have more or less changes in viscosity during storage, such as increased viscosity of paint during storage and reduced viscosity during water-based coating storage are more obvious examples. Of course, some will be more change, some will change less, mainly because of different varieties of film-forming substances, additives, solvents, pigments and mutual coordination and other factors.
viscosity stability is difficult to achieve data accuracy of 100%, testing conditions, testing methods, viscosity adjustment, paint storage, will be biased on the final data, the need for paint quality testing personnel and coating-related technical and technical personnel unremitting efforts, through continuous practice, continuous improvement of the coating system, continuous improvement of testing methods to better ensure that the paint viscosity detection data deviation.
measurements vary depending on the measurement method, it is necessary to agree with the supplier and the customer on the test method. Temperature is an important factor affecting viscosity, and the test temperature is usually agreed to be 25 degrees C. In addition to the viscosity meter sent to the local metrology bureau every year, but also can use a stable viscosity standard silicone oil for correction, so that the viscosity meter in a good working condition.
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