# BS ISO 12644-1996 (2000)

BRITISH STANDARD BS ISO 12644:1996 Graphic technology — Determination of rheological properties of paste inks and vehicles by the falling rod viscometer ICS 87.080BSISO12644:1996 This British Standard, having been prepared under the directionof the Sector Board forMaterials and Chemicals, waspublished under the authorityofthe Standards Boardand comes intoeffecton 15March1997 © BSI 02-2000 ISBN 0 580 27209 5 National foreword This British Standard reproduces verbatim ISO12644:1996and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee PAI/36, Printing Inks, which has the responsibility to: — aid enquirers to understand the text; — present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; — monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theISO title page, pages ii to iv, pages 1 to 8 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd.No. Date CommentsBSISO12644:1996 © BSI 02-2000 i Contents Page National foreword Inside front cover Foreword iii Text of ISO 12644 1ii blankBSISO12644:1996 ii © BSI 02-2000 Contents Page Foreword iii 1 Scope 1 2 Definitions 1 3 Text method 2 4 Calibration 4 5 Calculation 5 6 Corrections 6 7 Report 6 Annex A (normative) Flow models 7 Figure 1 — Falling rod viscometer 3 Figure 2 — Aperture ring 4 Figure A.1 — Casson model 7 Figure A.2 — Bingham model 8 Figure A.3 — Power Law Model 8 Descriptors: Graphic technology, printing, printing inks, tests, determination, rheological properties, viscosity, viscosity measurement.BSISO12644:1996 © BSI 02-2000 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies).The work of preparing International Standards is normally carried out through ISO technical committees.Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee.International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO12644was prepared by Technical Committee ISO/TC 130, Graphic technology. Annex A forms an integral part of this International Standard.iv blankBSISO12644:1996 © BSI 02-2000 1 1 Scope This International Standard specifies the procedure for determining the viscosity and yield value of paste inks and vehicles which are unreactive under normal room conditions. It is applicable to inks in the apparent viscosity range of2Pa · s to200Pa · s. 2 Definitions For the purposes of this International Standard, the following definitions apply. 2.1 viscosity measure of the internal friction of a liquid in motion.The viscosity is generally defined as the ratio of the shear stress (2.2) to the shear rate (2.3): 2.2 shear stress, force per area in a direction parallel to the applied force.Unit: Pa NOTE 1For the falling rod viscometer, the shear stress is proportional to the total weight of the rod and the weight loads in accordance with the equation where (see Figure 1 and Figure 2) NOTE 2The shearing length of the aperture of a falling rod viscometer usually contains both a tapered and a parallel section; therefore, it is understood that A is not the true shearing area but an apparent shearing area. 2.3 shear rate, velocity gradient through a stressed liquid in a direction perpendicular to the shearing area.Unit:s –1 NOTEFor the falling rod viscometer, is inversely proportional to all fall time according to the equation where If the ratio of the radii of the rod and aperture is close to unity, the term may be simplified to where s is the thickness of the ink in the nip determined by the difference between radii of the aperture and of the rod. 2.4 apparent viscosity, ‰ a ratio of the shear stress to the shear rate for a given shear stress or shear rate.Unit: Pa · s 2.5 newtonian liquid liquid whose shear stress is proportional to shear rate 2.6 non-Newtonian liquid liquid whose shear stress is not proportional to shear rate NOTE 1There are two types of non-Newtonian liquids: With shear thickening liquids, the viscosity increases with shear rate;with shear thinning liquids, the viscosity decreases with shear rate. NOTE 2If the viscosity of a liquid decreases with application of steady mechanical stress from a value at the state of rest to a final value and increases again if the stress ceases, the liquid is called thixotropic. 2.7 flow curve graph of the shear stress as a function of the shear rate or vice versa 2.8 casson model (see A.1) flow model which assumes a non-linear increase of shear stress with increasing shear rate .A minimum stress 0is required to initiate flow 2.9 bingham model (see A.2) flow model which assumes a linear increase of the shear stress with increasing shear rate .A minimum stress 0is required to initiate flow 2.10 power law model (see A.3) flow model which assumes an increase of the shear stress of a liquid proportional to the Nth power of the shear rate .(1) .(2) is the shear stress; W is the total weight of the rod and the weight loads; A is the apparent shearing area; g is the gravitational acceleration; m is the total mass; r is the radius of the rod; l is the length of the aperture. .(3) ‰ --- = W A ----- mg 2;rl ------------ = = is the shear rate; L is the falling distance of the rod; r is the radius of the rod; R is the radius of the aperture; t is the fall time. .(4) L st ----- =BSISO12644:1996 2 © BSI 02-2000 2.11 yield stress, 0 minimum stress required to initiate flow of a liquid.Unit: 1 Pa 2.12 pseudo yield stress, y shear stress at a defined low shear rate when applying the Power Law model, typically to2,5s –1 2.13 reference temperature temperature (25 C) for which all results are reported.Unit: C NOTEMeasurements made at temperatures different from this temperature are corrected (see 6.2.2). 2.14 test temperature actual temperature of the aperture ring during measurements.Unit: C 2.15 shortness ratio ratio of yield stress or pseudo yield stress to the apparent viscosity.Unit:1s –1 3 Test method 3.1 Principle The principle of this test is the measurement of the relative velocity between a vertical rod and an aperture ring.The bottom of the rod is inserted into the aperture.The gap is filled with the test fluid, which is sheared when the rod falls. By loading the rod with different load weights, different shear rates are obtained.By applying linear regression methods to the measured fall times as a function of load weight, the viscosity and the yield stress can be calculated. 3.2 Apparatus 3.2.1 Falling rod viscometer The viscometer consists of — a cylindrical rod (Figure 1) madefrom metal or any other hard material.In order to obtain comparable values for shear stress and resulting shear rate the mass of the steel rod should be(132 – 1) g. — a metal ring (Figure 2) with a defined cylindrical or conical aperture.The ring is fixed on a support and should be temperature controlled.Since the diameter of rod and aperture are critical they are manufactured within low tolerances.These dimensions shall be supplied by the manufacturer.To minimize possible gap differences, only matching sets of rod and aperture ring shall be used. — load weights to be loaded on top of the rod.Series of load weights are combined to sets.Sets of load weights with the following masses should be used: The tolerance for the masses of load weights shall be – 0,2g; — a designated measuring distance marked on the strut.The tolerance shall be – 0,2mm. Sensors may be placed at the marks. — a levelling device. — a timing device.The tolerance shall be – 0,1s (should be – 0,01s). 3.2.2 Temperature control Means shall be provided for measurement and control of the test temperature. 3.2.3 Others Non-scratching spatulas. Standard viscosity oils (at least 2) for calibration. NOTEThe viscosity of the standard viscosity oils shall be in the same range as that of the test samples.The viscosity of these oils shall be traceable to a standards institution.An internal standard may be used for comparative studies only. 3.3 Ambient temperature control The test shall be carried out under controlled ambient temperature.This can be achieved either by placing the viscometer in a thermostatically controlled cabinet or by working under constant room temperature. If working in a cabinet, the inner temperature should not vary from the test temperature by more than – 0,5 C.For room conditioning, a difference of– 2 C to the test temperature is allowed.The standard reference temperature shall be (25 – 0,2) C. 3.4 Preparation for testing Prior to use, the test sample (about5g) shall be kneaded by a spatula and equilibrated to test temperature.The sample shall be homogeneous and not contain any coarse particles. The proper set of load weights is selected according to the expected results. NOTEThe fall time with the highest load weight should normally be in the range4s to10s.For heat-set printing inks it may be desirable to use a shorter fall time for the highest weight. A: 5 000, 4 000, 3 000, 2 000, 1 000 B: 3 000, 2 000, 1 500, 500 C: 1 500, 1 000, 800, 500 D: 800, 600, 400, 200 E: 400, 300, 200, 100 F: 200, 100, 50, 0BSISO12644:1996 © BSI 02-2000 3 Figure 1 — Falling rod viscometerBSISO12644:1996 4 © BSI 02-2000 An amount of the test sample sufficient to coat the rod and aperture is applied to the lower part of the rod.By turning the rod, the sample is distributed uniformly.Running a single pass with the highest weight load, the rod and the aperture ring are wetted by the liquid.The rod is inserted into the aperture and rests on the support before the test run is started. 3.5 Test procedure The sample is tested with the selected series of load weights in descending order.The fall time shall not exceed60s.After each run, the rod is scraped with the spatula and the liquid which was scraped off is reapplied on the lower part of the rod.During the test, additional liquid shall not be added. At the beginning and at the end of the test, the temperature of the sample is checked. For highly thixotropic samples, it may be necessary to make a dummy run first. 3.6 Cleaning After the test, the instrument shall be cleaned immediately with a lint-free wiper and a suitable solvent. 4 Calibration When installing the viscometer, locate the instrument on a sturdy bench in a draught-free environment.Use the levelling device to obtain proper vertical alignment.The timing device and the distance between the two sensors are calibrated during initial installation.The timing device should be recalibrated regularly. The calibration shall be performed by testing the standard viscosity oils according to the procedure described in 3.5. 4.1 Calibration for the Casson and Bingham models (see A.1 and A.2) Assuming that the standard viscosity oils are strictly Newtonian, the calculation is as follows: From (1), (2) and (4) follows: where Figure 2 — Aperture ring .(5) ‰ is the viscosity; is the shear stress; is the shear rate; m is the mass; g is the gravitational acceleration; r is the radius of the rod; l is the length of the aperture; s is the thickness of the ink in the nip; t is the fall time; L is the measuring distance.BSISO12644:1996 © BSI 02-2000 5 Fixed parameters and constants are combined as device factors and ¶ and The unit of is1and the unit of ¶ is Pa/kg. Since the shear rate and shear stress the viscosity of a Newtonian fluid can be calculated from the slope of a plot of versus for different masses.The measured viscosity is the reciprocal slope of the linear regression line. If a certain set of rod and aperture ring shows viscosity variations of 20% from the specifications of the standard viscosity oil it shall be discarded.Smaller differences are compensated by using a correction factor ˝: The correction factor ˝ is specific for a single set of rod and aperture.It is recommended that a calibrated set of aperture and rod be kept as an internal standard. 4.2 Calibration for the Power Law model For determination of the device factor ¶ (stress constant) defined in equation (7) it is necessary to measure the radius r of the rod and the length l of the aperture.Both dimensions shall be measured to0,01mm.Given these data the device factor ¶ is calculated according to equation (7). The value of the device factor defined in equation(6) shall be computed from fall time runs of the standard viscosity oils.For that purpose, measurements shall be taken with at least two such oils, covering the viscosity range of interest, and at least four fall times.The known viscosity of the oils is divided by the fall time t for each weight load with the mass m and this quotient is plotted versus the mass for each standard viscosity oil.According to equation (11), the slope of the regression line is the quotient ¶/ of the two device factors. where Having calculated ¶ from the geometric dimensions of rod and aperture according to the above method, can easily be calculated.With the device factors and ¶ determined, values for the shear rate and shear stress can be calculated from the fall time t and the mass m used as shown in equations (8) and (9). 5 Calculation 5.1 Calculation for Casson and Bingham models (see A.1 and A.2) Calculation for Casson and Bingham models requires: — at least 4 fall times as a function of different mass of the weight loads; — the device factors , ¶; — the correction factor ˝; — the test temperature at the beginning and the end of the test. 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