Testing Paints Before Application

Combustibility Determination: BS 3900-A11

Scope and Field of Application

BS 3900-A11 is a go/no go procedure for use in the paint and allied industries to determine whether a product is combustible within the meaning of the UK Highly Flammable Liquids and Liquified Petroleum Gases Regulations 1972.

Combustibility is one of the properties which can be used to assess any potential fire hazard associated with manufacture, transport, storage and use. Another important and related property is flash point.

Summary of Method

The standard includes a detailed description of the equipment used to carry out the test. Essentially it consists of a small temperature-controlled dish which is heated to 50 °C

A barometric pressure reading is taken and used to correct the dish temperature to standard atmospheric pressure. A specified quantity of the test sample is placed in the dish and a test flame applied.

For the purposes of the Regulations, a product is judged to support combustion if it can be ignited and then continues to burn for 15 seconds after the flame is removed.

The equipment is available commercially and the image above shows a Series 3 instrument made by Stanhope-Seta

Sample Requirements

We require at least 200 ml of sample.

Density: BS EN ISO 2811-1, BS 3900-A19

Scope and Field of Application

BS EN ISO 2811-1 and BS 3900-A19 are alternative names for the same method which is intended for the determination of the density of paint, varnishes and related products using a pyknometer (otherwise known as a density bottle). This method can be used for most samples provided they do not contain entrapped air.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

Summary of Methods

BS EN ISO 2811-1: BS 3900-A19

The sample and the pyknometer are allowed to equilibrate in a constant temperature room then weighed before and after filling with the sample. Since the volume of the pyknometer is known, the density of the sample can be calculated.

Sample Requirements

We require no more than 500 ml of sample.

Density: BS EN ISO 2811-4, BS 3900-A22

Scope and Field of Application

BS EN ISO 2811-4 and BS 3900-A22 are alternative names for the same method which is intended for the determination of the density of paint, varnishes and related products using a pressure cup. The method is intended for use with products, like emulsion paints, which may contain small bubbles of entrapped air.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

Summary of Methods

BS EN ISO 2811-4: BS 3900-A22

The sample under test is compressed in a pre-weighed cylindrical pressure cup in order to reduce any error due to air bubbles which may be present. The cylinder is then re-weighed and the density is calculated from the mass of the sample and the known volume of the cylinder.

One limitation of this method is that the equipment can be too heavy to weigh on a standard four-place balance. This means the results are not as precise as those obtained using the BS EN ISO 2811-1: BS 3900-A19 method.

Sample Requirements

We require no more than 500 ml of sample.

Fineness of Grind Determination: BS 3900-C6, ISO 1524, EN 21524

Scope and Field of Application

BS 3900-C6, ISO 1524 and EN 21524 are alternative names for the same method which is intended for the determination of the fineness of grind of pigments in liquid paints, inks and related products using a suitable gauge. It is a simple and convenient method of monitoring the progress of the dispersion stage of manufacture and for a QC check on the finished product.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

We use a Hegman gauge which consists of a steel block into which is machined a groove which is uniformly tapered along its length from 100 microns at one end to zero at the other (25 and 50 micron gauges are also available). A scale denotes the depth of the groove at any point along its length. A portion of the sample is placed in the groove at the deep end and a blade used to draw the liquid down the length of the groove.

When the gauge is viewed at an angle, it is possible to note the point along the length of the groove where it becomes shallow enough for the pigment particles to protrude above the level of the liquid. The pigment particle size at this point can be read from the scale.

Sample Requirements

We require no more than 100 g of sample.

Flash Point Determination: BS EN 456, ISO 3679

Scope and Field of Application

BS EN 456 is a method which is used to determine the flash point of a paint, varnish, paint binder, solvent or related product when the flash point is below 110 °C.

ISO 3679 is technically identical to BS EN 456. The only difference is that the scope of ISO 3679 is extended to include flash point determinations of petroleum products.

The flash point of a material is defined as the lowest temperature that vapour from the material can be ignited by a flame or spark. It is one of the properties which can be used to assess any potential fire hazard associated with manufacture, transport, storage and use. Another important and related property is combustibility.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

Summary of Method

The standards include a detailed description of the equipment used to carry out the test. Essentially it consists of a small temperature-controlled chamber fitted with a lid. A specified quantity of the test sample is placed in the chamber and the temperature increased progressively. The chamber is opened at intervals and a small flame applied to the opening. The temperature at which the vapour above the sample first ignites is noted. A barometric pressure reading is taken and used to correct the flash point to standard atmospheric pressure.

Sample Requirements

We require at least 200 ml of sample. The standards stipulate that samples should be supplied in glass or metal containers which are at least 90% full.

Freeze-thaw Resistance Determination: ASTM D 2243

Scope and Field of Application

When water-borne coatings are shipped during cold weather, they may experience cycles of freezing and thawing. Freezing and thawing cycles cause more damage than when coatings are subjected to steady freezing.

This method is intended to evaluate the effect of freeze-thaw cycling on the viscosity and visual film properties of water-borne coatings. If you are only interested in the effect of freeze-thaw cycling on dry coatings then you may wish refer to the "Resistance to Temperature Change" test method in our Durability Testing section.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

Two identical portions of each coating are prepared. One, identified as the control, is stored at room temperature while the other, identified as the test specimen, is subjected to a cycle consisting of 17 hours at minus 18° Centigrade followed by 7 hours at room temperature. The number of repeat cycles is a matter of agreement between the parties concerned but up to 5 cycles is usual.

The test specimen and the control are then examined for any evidence of settlement, gelation or coagulation. The viscosity of each is then measured using ASTM D 562 and this is followed by the application of both to test panels. The dry films are examined visually in order to rate hiding, gloss, agglomeration, coagulation, particle formation and colour.

Sample Requirements

We require no more than 2.5 litres of sample.

In Can Properties Determination: BS 3900-A2, ISO 1513

Scope and Field of Application

BS 3900-A2 and ISO 1513 are alternative names for the same method which defines a procedure for the preliminary examination of paints, varnishes and related products.

Used primarily when comparing decorative coatings which are sold to the general public since it deals with those properties that become apparent when the user removes the lid from the container and carries out any mixing required prior to use.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

The container is opened and the contents are examined for ullage (how full the container is), surface skin, consistency, separation, settlement, extraneous matter, ease of mixing and, where appropriate, clarity and colour.

Sample Requirements

The method involves examination of a packed product and therefore a representative container (no larger than 5 litres) is required for each sample.

Non-volatile Determination: BS EN ISO 3251, BS 3900-B18, IS0 3251

Scope and Field of Application

BS EN ISO 3251, BS 3900-B18 and ISO 3251 are alternative names for the same method which is used to determine the mass of dry coating obtained from a given mass of liquid coating. It is used as a QC check and as a way of establishing if a coating has been excessively thinned prior to use.

The non-volatile content of a sample is not an absolute quantity but depends on the temperature and period of heating used for the test as well as the surface area to volume ratio of that portion of the sample under test.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

A specified amount of the liquid sample is weighed into a pre-weighed flat bottomed pan of defined dimensions. After about 15 minutes, the pan is transferred to an oven. The standard defines different temperatures and heating periods for different classes of sample. The parties concerned can also agree on a heating schedule.

When the heating period is completed, the pan is transferred to a desiccator, allowed to cool then re-weighed. The mass of non-volatile residue can then be expressed as a percentage of the mass of the original sample.

Sample Requirements

We require no more than 100 g of sample.

Oil Absorption Determination: BS EN ISO 787-5, BS 3483-B7

Scope and Field of Application

BS EN ISO 787-5 and BS 3483: B7 are alternative names for the same method which is intended for the determination of the oil absorption values of pigments and extenders.

Oil absorption is defined as the amount of oil required by a given weight of pigment to form a paste of specified consistency. It is affected by the particle size and surface chemistry of the pigment and consequently provides a convenient QC check for batch to batch variation in pigment properties. It is also an important value for those formulating coatings since it gives an indication of the amount of resin that will be absorbed by the pigment rather than be available for film formation.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

A defined weight of pigment or extender is placed on a glass plate above which is mounted a burette containing a specified grade of linseed oil. Oil is slowly added to the sample and mixed in using a palette knife. The volume of oil required to form smooth paste is noted and the oil absorption value expressed as the number of millilitres or grams of oil required per 100 g of sample.

Sample Requirements

We require 100 g of sample.

Particle Size Distribution

Scope and Field of Application

We can determine the size of particles in the 5 to 1000 nanometre range (0.005 to 1 micron) using photon correlation spectroscopy (PCS). This technique is also known as quasi-electric light scattering (QELS) and dynamic light scattering (DLS).

One characteristic of particles in this size range is that they are in constant random thermal or Brownian motion. This motion causes the intensity of light scattered by the particles to vary with time. Large particles move more slowly than small particles and consequently the rate of fluctuation of light scattered by the large particles is also slower. Photon correlation spectroscopy measures the rate of change of the light fluctuations and uses this information to calculate the size distribution of the particles.

This work is not carried out to any international standard, we use our own in-house method.

Summary of Method

We carry out the determination using a Malvern AutoSizer Model Hi-C fitted with a 64 channel 7032 correlator. The sample is diluted, if necessary, to give between 2 and 10% solids. In principle the method requires no calibration since the performance depends on fixed physical quantities such as temperature and the wavelength of the incident light. In practice however we check that the system is operating correctly using standard latex samples with a narrow size distribution.

Sample Requirements

Currently our experience is limited to measuring the size distribution of water borne latices of the type used to make emulsion paints. In fact the method is applicable to a stable dispersion of any homogenous material in water or organic solvents provided the particles are within the 5 to 1,000 nanometre size range.

The method is not suitable for samples that contain material outside this size range even if no information is required about the out-of-range particles. It is also unsuitable for dispersions within the size range if the particles are a mixture of different materials.

We require no more than 100 g of sample.

pH Determination

Scope and Field of Application

We can determine the pH of water borne coatings and their components. In many cases the stability of paints is pH dependent and measurement of this parameter is an important quality control check.

This work is not carried out to any international standard, we use our own in-house method.

Summary of Method

Although indicator papers are widely used for determining the pH of aqueous solutions, we find they are less than ideal when measuring coloured paint samples. We use a pH meter fitted with a flat tip electrode. This type of electrode has the advantages that it is easy to clean and can be used with highly structured paints. Calibration is carried out using commercially available buffer solutions in a temperature controlled environment.

Sample Requirements

We require no more than 100g of sample.

Determination of Spreading Rate: BS 3900-A16, ISO 7254

Scope and Field of Application

BS 3900-A16 and ISO 7254 are alternative names for the same method which is designed to measure the natural spreading rate of application of a liquid paint or coating when applied to a surface using a brush.

The standard defines "natural spreading rate" as the area covered by a given weight (or volume) of coating when applied uniformly by a skilled operator to give a film free of runs, sags and tears. The value (which is expressed as square metres per kilo or square metres per litre) is often quoted on the product label since it is a useful indication of how much coating needs to be purchased for a given project.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

BS 3900-A17 / ISO 7877 is a related standard. It does not involve the measurement of any coating properties but describes how to coat test panels at a specified spreading rate.

Summary of Method

A quantity of the coating is transferred to a suitable container and then weighed, together with a brush, to the nearest 10 mg. An experienced painter then applies the coating to a 300 x 600 mm test panel. The brush plus the container are then re-weighed. Since the weight of the coating used and the area covered are both known, the spreading rate can be expressed in square metres per kilo. A density determination on the paint will enable the spreading rate to be calculated in square metres per litre.

There are a number of factors that can affect the spreading rate including temperature, relative humidity, the nature of the test panel, its porosity, whether or not it has been primed and whether it is vertical or horizontal when coated. All of these are subject to agreement between interested parties and should be recorded.

Any solvent that evaporates from the coating in the container during the test will result in an erroneously low value for the spreading rate. Consequently the method is not suitable for coatings which contain highly volatile solvents.

Sample Requirements

We require 1 litre of coating.

Surface Tension and Contact Angle Measurements on Liquids

Scope and Field of Application

The techniques described on this page are the ones that are used to measure the properties of liquids (e.g. liquid coatings or raw materials). If you are more interested in the properties of solids, then please see "Surface Energy and Contact Angle Measurements on Solids" on the Mechanical properties page.

The end product of any successful painting or printing process is normally a dry film of the coating on a substrate. In cases where liquid paints or inks are applied, an essential intermediate stage in the process is the formation of a satisfactory wet film of the coating.

The success or otherwise of producing a satisfactory wet film depends on both the properties of the liquid coating and the properties of the substrate.

We use a Camtel CDCA-100 instrument which is a versatile computer controlled tensiometer capable of measuring surface tensions and contact angles and calculating surface energies. We can use this instrument to measure the surface tension of liquid samples using either the Du Nouy ring or the Wilhelmy plate method.

Measurement of Surface Tension: Du Nouy Ring Method

In this method, a platinum-iridium ring is lowered by the tensiometer onto the surface of the test liquid and then driven under the surface so that it is completely wetted. The ring is then progressively raised until contact with the liquid is broken. The maximum force exerted on the ring is measured and this value is used to calculate the surface tension.

Sample Requirements

We need no more than 250 ml of liquid.

Measurement of Surface Tension: Wilhelmy Plate Method

This method involves the use of a pre-weighed rectangular roughened platinum plate which is lowered by the tensiometer until it is totally immersed in and thoroughly wetted by the test liquid whose density has been determined. The plate is then raised until it is only partly immersed and allowed to equilibrate. The density of the liquid and the volume of the submerged portion of the plate are both know hence the upthrust can be determined.

It is assumed that all liquids totally wet roughened platinum and that the contact angle is zero. Consequently the surface tension force acts directly downwards on the plate.

Since the weight of the plate and the upthrust are known, the surface tension force can be calculated by dividing the surface tension force by the wetted length of the plate.

Unlike the De Nouy ring technique, this is a static method of determination. Since the liquid does not move during the measurement stage of the experiment, it is an ideal way of measuring variation of surface tension with time. Another advantage of the plate method is that it can be used to measure the surface tension of viscous liquids.

Sample Requirements

We need no more than 250 ml of liquid.

Measurement of Contact Angle: Plate Method

We use the Camtel CDCA-100 instrument and a variant of the Wilhelmy Plate Method. The platinum plate is replaced by a uniform non-porous solid. The calculations are similar to those described above and provided the surface tension of the liquid is known the contact angle can be determined.

This method can only be used to measure homogeneous samples i.e. those where all the surfaces of the solid are the same. You can, for example, use a piece of polyethylene as the test solid but you cannot use a piece of polyethylene which has one face coated with paint.

If you wish to measure the contact angle using a coated substrate then this can be done using a Contact Angle Meter. This is described in under "Surface Energy and Contact Angle Measurements on Solids" on the Mechanical Properties page.

Sample Requirements

This method can only be carried out on non-porous homogeneous solids. This rules out wood and also coatings applied to any substrate. It is the technique to use if you need to measure accurately (for example) the surface energy of a sample of polymer.

We need to be able to cut a test piece 20 x 30 x not more than 5 mm.

Viscosity Determination

Scope and Field of Application

The viscosity of paints, inks and allied materials is an important property. It affects how easy it is to mix the components of the product during manufacture, how stable it is in storage, how easy it is to apply to a substrate and the manner in which it flows out to form a smooth layer free of defects like runs and brush marks.

Many coatings exhibit non-Newtonian behaviour i.e. the viscosity changes with the shear rate. Thixotropic paints are a common example of non-Newtonian products with the paint having a high viscosity in the can but becoming much more fluid when sheared during application by brush or roller.

Using different viscometers, we can measure the viscosity of samples at low, intermediate and high shear rates. There are no pass/fail criteria defined in the Standards that cover the use of these instruments. This is a matter of agreement between the parties concerned.

Where appropriate the equipment is calibrated using our viscosity oils.

Viscosity Determination: ASTM D562

Summary of Method

This method uses a Stormer viscometer which consist of a paddle-type rotor which is driven (via a cord and pulley arrangement) by a falling weight. The Standard defines the consistency of a paint as the weight required to produce a rotation of 200 revolutions per minute. The standard also includes charts which enables the instrument weight and rotational speed data to be converted to Krebs units (a unit of viscosity measure unique to this instrument).

The range of viscosities that can be measured using this equipment is limited to between about 2 to 50 poise and the method is intended for measurements on DIY and trade paints applied by brush or roller. It is also a convenient method for measuring the viscosity of a sample under low shear conditions.

Sample Requirements

We require no more than 1 litre

Viscosity Determination: ASTM D2196

Summary of Method

This method uses a Brookfield type rotational viscometer which consists of a variable speed electrically driven shaft on to which can be fitted a number of different spindles. The choice of spindle and rotation speed enables measurements to be carried out in the low to medium shear rate range i.e. 0.1 to 50 sec-1.

The standard is intended for use with non-Newtonian samples and is particularly applicable to thixotropic paints. Methods are described for measuring the viscosity under constant and variable shear conditions.

Sample Requirements

We require no more than 1 litre

Viscosity Determination: BS 3900:A7-1, ISO 2884-1

Summary of Method

BS 3900: A7-1 and ISO 2884-1 are alternative names for the same method. The method uses a cone-and plate viscometer which, as the name implies, consists of an electrically driven shallow cone the vertex of which touches a rigid temperature-controlled plate. The test liquid fills the narrow gap between the cone and the plate and the torque is measured either electronically or mechanically. The choice of cone geometry and speed or rotation enables a shear rate of between 9,000 and 12,000 sec-1 to be attained and this high shear rate corresponds to that produced during brushing, roller coating and spraying operations.

Sample Requirements

We require no more than 100 ml

Viscosity Determination: BS 3900:A7-2, BS EN ISO 2884-2, ISO 2884-2

Summary of Method

BS 3900: A7-2, BS EN ISO 2884-2 and ISO 2884-2 are alternative names for the same method. The method uses a Rotothinner viscometer of the type produced by Sheen Instruments (A Division of Hartest Precision Instruments Ltd). A rotating disc is immersed in the sample in a 250 ml container. The container sits on a platform which can rotate but the rotation of which is counteracted by a spring. The greater the viscosity of the sample, the greater the torque acting on the container and the greater the angular rotation of the platform before it is counteracted by the spring. The angular rotation of the platform is read off from a scale which is calibrated in poise. The standard specifies the dimensions of the container and the dimensions and speed of rotation of the disc.

We can use this method to measure viscosities below 15 poise. One advantage of the method is that you can add solvent to a sample under test and measure any change in viscosity. This means it is a good way of determining the amount of solvent needed to thin a paint to a given viscosity. This is exactly the sort of information you need when making paint in a factory.

Sample Requirements

We require no more than 1 litre

Viscosity Determination: BS EN ISO 2431, BS 3900:A6

Summary of Method

BS EN ISO: 2431 and BS 3900: A6 are alternative names for the same method. It involves the use of flow cups to measure viscosity and the standard includes specifications of four flow cups together with calibration data relating the flow time through each cup to kinematic viscosity. Flow times measured in this way are only reproducible for liquids that are approximately Newtonian but with this limitation in mind, the method is useful for checking that a coating has the correct viscosity prior to spray application.

Sample Requirements

We require no more than 250 ml

Viscosity Determination: DIN 53211, ASTM D1200, ASTM D4241

Summary of Method

In a similar fashion to BS EN ISO 2431 and BS 3900:A6 we can also carry out viscosity determinations using other flow cup standards including DIN 53211, ASTM D1200 and ASTM D4212.

Sample Requirements

We require no more than 250 ml

Controlled Stress Rheometry

Using our TA Instruments AR2000 Rheometer and in-house methods, we can provide the following sample characteristics:-

• Flow including:
• viscosity vs shear rate
• viscosity vs shear stress
• shear stress vs shear rate
• temperature vs viscosity
• Creep
• Viscoelastic behaviour and time dependant effects

The maximum torque of the rheometer is 200 mN.m with a maximum resolution of 1 nN.m , the resultant measured shear rate is dependant on the geometry selected and the sample viscosity.

The AR2000 rheometer is also capable of acting as a pseudo controlled shear rate instrument, via an internal electronic feed back loop.

Sample Requirements

Controlled Stress Rheometry: No more than 100 ml

Volume Solids Determination: ISO 3233, BS 3900-A10

Scope and Field of Application

ISO 3233 and BS 3900-A10 are alternative names for the same method which is used to determine the volume of dry coating obtained from a given volume of liquid coating. This is considered to be the most meaningful measure of coverage (the area of surface covered at a specified dry film thickness by unit volume of coating).

Although it might appear possible for a paint manufacturer to calculate volume solids using the masses and densities of the raw materials in a formulation, in practice this may be unreliable. As there can be a loss (or gain) in volume when components are mixed. Also the volume of the dry coating depends on the relative amount of air and binder that fills the voids between the pigment particles. The more air in the voids, the greater the volume of the coating.

There are no pass/fail criteria defined in the Standard. This is a matter of agreement between the parties concerned.

Summary of Method

A metal disc is weighed in air and then re-weighed in water. The disc is then coated with the sample and the coating allowed to dry. The coated disc is weighed in air and then re-weighed in water. It is then possible to calculate the mass and volume of the dry coating

The density and the non-volatile content of the liquid coating are then determined. This enables the volume of the liquid coating that was deposited on the disc to be calculated.

Since the volume of both the liquid and the dry coating on the disc are known, the volume solids of the coating can be calculated.

Sample Requirements

We require a 1 litre sample.

Determination of Wet Edge Time: BS 3900-C1

Scope and Field of Application

A correctly formulated air-drying paint begins to dry as soon as it is applied to a surface. It is possible to formulate paints with a wide range of drying times but the actual choice is always a matter of compromise.

If the paint dries too slowly then this delays the application of any subsequent coats and also prolongs the time that the coating can be marred or can accumulate dust particles.

A short drying period also has disadvantages. If paint is applied to large areas then it is important to be able to blend in freshly applied paint with areas where the paint was applied several minutes earlier. If the paint applied earlier has already dried, the edge between it and the freshly applied paint will remain visible and the overall appearance of the surface will be patchy.

BS 3900-C1 is a method of measuring how long a paint remains workable after it has been applied.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Summary of Method

The method involves applying the test paint to a 600 x 300 mm burnished steel test panel. The panel can be primed or undercoated as required. Half the panel is coated and then left for an agreed time. The remaining half of the panel is then coated, starting at the edge of the surface already painted.

Once the paint has dried, the surface is examined to see if the join between the two paint applications is visible and if there is any evidence of lack of levelling or variation in colour.

Sample Requirements

We require 1 litre of coating.

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