Continuous and / or semicontinuous grindometer and method for fineness of grind measurement

Abstract

The present disclosure relates to continuously or semi-continuously measurement of the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, in particular in formulated liquid product, such as a paint. One embodiment relates to an apparatus for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a paint, which apparatus comprises a substrate and an applicator, wherein the substrate is arranged so that liquid can be applied onto a first surface of the substrate, for instance by immersing a part of the substrate in the liquid or by dousing the substrate with the liquid, wherein the substrate and the applicator are configured to continuously or semi-continuously move relative to each other, wherein the applicator is arranged so that, liquid, which has been applied onto the first surface, can pass through a gap defined between the applicator and the first surface, the gap and the relative movement of the substrate and the applicator thereby forming a liquid film on the first surface, wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby continuously or semi-continuously forming a scratch pattern in the liquid film.

Description

[0001] CONTINUOUS AND / OR SEMICONTINUOUS GRINDOMETER AND METHOD FOR

[0002] FINENESS OF GRIND MEASUREMENT

[0003] The present disclosure relates to continuous or semi-continuous measurement of the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, in particular in formulated liquid product, such as a coating, e.g. paint.

[0004] Background of the disclosure

[0005] One of the most common quality control methods for pigment dispersion in paint is the assessment of fineness of grind, typically executed using a Hegman gauge. The details of this method are described in the DS / ISO 1524:2020 standard and one example of a prior art Hegman gauge is shown in figs. 1A-C.

[0006] The method is based on the visual evaluation of the particle or scratch pattern that is left on a grindometer groove after manual scraping of the sample. The method provides a direct, quick, and semi-quantitative assessment of the size of the largest particles in the particulate system, fineness of grind, which is a key parameter to conclude on the dispersion or wet grinding time in various processes and industries, such as coating, ink, food, cosmetics, etc.

[0007] Despite its simplicity and cost-effectiveness, the Hegman gauge method is plagued by certain drawbacks such as being a discontinuous method that involves taking discrete offline measurements at different times, thereby extending the production time, and evaluating the observations subjectively by means of the naked eye. Furthermore, it is a time-consuming method involving a substantial amount of manual work, such as preparing a sample for the measurement, i.e. an offline technique, lacking the capability of automatic in-process determination of the fineness of grind and other relevant characteristics relating to particle sizes.

[0008] Automatic application of the sample and computer-aided evaluation of the particle / scratch pattern have been attempted to address the shortcomings of the technique. For example DE 2049463 from 1972 discloses a grindometer wherein a liquid suspension is continuously applied to the surface of a rotating disc shaped substrate having a scraper arranged perpendicular to the rotation axis of the disc such that the liquid film is formed with a increasing relative application speed toward the periphery of the disc. Summary

[0009] It is a purpose of the present disclosure to provide an apparatus and a method, which overcome the above-mentioned disadvantages of the prior art.

[0010] Thus, in a first aspect of the disclosure, it relates to an apparatus for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a coating, for example paint. The apparatus comprises a substrate and an applicator. The substrate is preferably arranged so that liquid can be applied onto a first surface of the substrate, for instance by immersing a part of the substrate in the liquid or by dousing the substrate with the liquid. The substrate and the applicator are preferably configured to move relative to each other, preferably continuously or semi continuously.

[0011] Advantageously the substrate can be configured for rotation around a rotation axis, and wherein the applicator preferably can be arranged to extend along with said rotation axis such that the substrate and the applicator move relative to each other during rotation of the substrate, the relative movement of the substrate and the applicator forming a liquid film on the first surface of the substrate,

[0012] The applicator is preferably arranged so that, liquid, which has been applied onto the first surface, can pass through a gap defined between the applicator and the first surface. The gap and the relative movement of the substrate and the applicator thereby preferably forming a liquid film on the first surface.

[0013] In the preferred embodiment the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby continuously or semi-continuously forming a scratch pattern in the liquid film. Hence, the applicator and the first surface may be mutually arranged so that particles suspended or dispersed in the liquid, which are larger than the gap size at the position, at which the particles attempt to pass the applicator, are held back by the applicator, thereby forming a scratch pattern in the liquid film.

[0014] The size of the gap may vary, for example gradually varying, along the applicator in such a way that the liquid film formed by the applicator has a larger film thickness at one end of the gap than at the other end. Typically, the relative movement between the substrate and the applicator defines an application direction of the liquid film. In a preferred embodiment the variation in the gap size extends transverse to the application direction of the liquid film.

[0015] Using an apparatus with such a configuration allows for measuring the fineness of grind and / or the maximum size of particles in a continuously or semi-continuously way with a minimum, if any, involvement of manual work and human assessments of the findings, whereby more objective results are obtained than by the standardised method known in the art. The apparatus according to the present disclosure allows for measuring fineness of grind and maximum particle size dynamically and a real-time in a production line. Thus, the apparatus can meet the increasing demands of digitalisation, continuous operations, and process intensification in alignment with the direction, in which the industry is moving these years. The continuous measurements resolve a problem, which is known from the traditional technique using a Hegman gauge or the like, namely that a given sample may not be representative of the entire batch.

[0016] In an embodiment of the disclosure, the apparatus further comprises an automated device, such as a motor, configured for providing a relative motion between the substrate and the applicator.

[0017] The use of an automated device for providing the motion ensures that an optimal and stable velocity of the motion can be obtained.

[0018] In an embodiment of the disclosure, the relative velocity between the substrate and the applicator is between 0.001 metres per second and 1 metres per second, preferably between 0.01 metres per second and 0.3 metres per second.

[0019] Correct, accurate, and repeatable results of the measurements have been obtained using velocities within these ranges.

[0020] In one embodiment of the disclosure the gap extends along the longitudinal direction of the substrate. The size of the gap can be defined as a width, a length, a cross-sectional area, or any combination thereof. Typically, the gap is defined as the distance between the applicator and the first surface of the substrate, and hence the size of the gap can be defined as the height (or distance) between a scraping surface (or edge) of the applicator and an outer surface of the substrate. In that regard it is noted that the concept of a “gap” in the field of grindometers is not a novel concept, cf. the Hegman gauge, where a “gap” of varying size is provided between the scraper and the applicator surface. However, as also explained herein, the size of the gap in the Hegman gauge varies along the application direction, such that the scratch pattern does not provide a direct correlation between gap size and particle size.

[0021] In one embodiment of the disclosure the size of the gap varies from one position of the gap to another position of the gap, such as from one end of the gap to another opposite end of the gap, such as from one end of the applicator to another opposite end of the applicator.

[0022] In one embodiment of the disclosure the variation of the gap is gradually uniform, e.g. a uniform variation along a predefined angle, e.g. the gap defines a predefined opening angle, linear, exponential, saw-tooth, stepwise, sinusoidal, or any combination thereof, however preferably linear.

[0023] In an embodiment of the disclosure, the varying gap sizes are within the range from 0.5 micrometres to 5000 micrometres, preferably within the range from 1 micrometre to 500 micrometres. Possibly gap size varies from 0 or about 1-10 micrometre and up to 100 micrometres, preferably 200 micrometres, more preferably 500 micrometres, even more preferably 1000 micrometres, most preferably 2000 micrometres, or even preferably 5000 or 10000 micrometres. Gap sizes within these ranges cover the different particle sizes, for which measurements using the apparatus are relevant.

[0024] In an embodiment of the disclosure, the applicator is arranged so that the gap size can be adjusted at one or more locations along the gap.

[0025] Making the gap size adjustable means that the same applicator can be used for different ranges of particle sizes, and that the operation of the apparatus can be optimised for different directions and positions of the substrate and for different drying rates of the sample liquid.

[0026] In an embodiment of the disclosure, the applicator is releasably attached to other parts of the apparatus.

[0027] The use of a releasably attached applicator allows for using different applicators configured for different ranges of particle sizes. Also, other parts of the apparatus may be releasably attached to each other, so that the apparatus may be configured in different ways, and so that cleaning of the apparatus may be facilitated by dismantling one or more parts thereof temporarily. In general, the cleaning of the apparatus may be done in the same way as the cleaning of circulation pipes, dispersion machines and other similar instruments is done, i.e. by circulating an appropriate solvent in the system while the apparatus is in operation.

[0028] In an embodiment of the disclosure, the apparatus further comprises an image capturing device arranged to capture images of the scratch patterns formed in the liquid film.

[0029] Using an image capturing device allows for automation of the analysis and evaluation of the scratch pattern, and it makes it possible to perform this analysis and evaluation later and / or at another place than when and where the physical scratch pattern is created.

[0030] In an embodiment of the disclosure, the apparatus further comprises an automated equipment, such as a computer, configured to analyse the captured images and calculate, based on the contents of the captured images, a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid based and, potentially, other statistical information, which statistical information may include, for instance, the size of the largest particle registered, the frequency of scratch appearances at different sizes, and / or the span of the data.

[0031] Using an automated equipment for analysing the captured images and calculate the fineness of grind and / or the maximum size of particles from the contents thereof, increases the objectiveness and, thereby, the accuracy and repeatability of the obtained results.

[0032] In one embodiment the substrate is configured for rotation, preferably continuous rotation, around a rotation axis, for example a horizontal rotation axis. In that regard the applicator and / or the gap may extend along with the rotation axis of the substrate.

[0033] In one embodiment the applicator and / or the gap is arranged at least primarily along a longitudinal direction of the substrate.

[0034] In an embodiment of the disclosure, the substrate is shaped as a cylinder or a truncated cone, which preferably is configured to be rotated around a longitudinal, rotationally symmetric axis thereof. The applicator may be elongated, preferably linearly, and arranged at least primarily along a longitudinal direction of the substrate. This configuration results in a relatively simple, stable and reliable apparatus.

[0035] Preferably the grindometer is configured such that the scratch pattern is formed perpendicular to a longitudinal direction of the substrate.

[0036] With the presently disclosed grindometer the scratch pattern is typically formed due to a relative movement between the substrate and the applicator. In some embodiments this relative movement is constant along the substrate and the applicator, e.g. along the extension of the gap. This has the result that the scratch pattern is formed with a constant relative application speed at all gap sizes.

[0037] A scratch pattern formed with a constant relative application speed at all gap sizes will for example be the case if the substrate is cylindrical and configured for rotating around the longitudinal axis of the cylinder and the applicator (and the gap) is arranged parallel to the rotation axis.

[0038] Another advantage of having cylindrical substrate is that viscosity measurements of the liquid can be integrated in the grindometer. The substrate can for example also be shaped as a truncated cone, however a cylindrical substrate is preferred for viscosity measurements. The presently disclosed grindometer may hence be configured for determining the viscosity of the liquid. Supplementary and / or alternatively the grindometer may be configured for monitoring a change in viscosity of the liquid, for example simply by monitoring a change in the torque exerted on a rotating substrate.

[0039] A Couette viscometer based on an inner cylinder and an outer cylinder, where one is fixed and the other is rotating, with the liquid filling the annular gap between the cylinders, provides the most accurate viscosity measurements, but such a solution is not readily integrated with the presently disclosed grindometer. A single vertical rotating cylinder is another option, but also not readily integrated with the presently disclosed grindometer. The option that best can be integrated with the presently disclosed grindometer is a horizontal rotating cylinder which is at least partly immersed in the liquid.

[0040] Viscosity measurements can for example be provided as follows: The substrate is partially or fully immersed in the liquid and rotated at a constant angular velocity co (rad / s). Due to the liquid’s internal friction (viscosity), it resists the motion of the substrate. This resistance manifests as a torque T on the substrate. The viscosity p can then be determined from the torque, geometry of the setup, and rotational speed. Hence, a torque sensor can advantageously be provided, for example attached to the substrate (and / or the motor) to measure how much force is required to maintain its rotation. Control, data acquisition and / or data analysis of the viscosity measurement can be provided by the automated equipment, such as a computer, mentioned herein. During viscosity measurement it is preferred that that the distance between the substrate and the applicator is increased, because a small gap therebetween might influence the torque measurement of the substrate.

[0041] The fluid flow around a horizontal cylinder is a circular shear field around the cylinder surface, but the upper part of the cylinder is more likely to be influenced by free surface effects (if partially submerged) and the lower part by sedimentation or stratified layers if the fluid isn’t uniform. For a fully immersed horizontal cylinder, the wetted surface area is: A =2nRh / where h is the length of the cylinder, i.e. the length of the substrate. If the cylinder is only partially immersed only the wetted perimeter of the cylinder contributes to viscous drag, but the reduced contact area can be accounted for when calculating torque and shear - and thereby viscosity. This is known in the art. For a fully immersed, long, horizontal cylinder of radius R and length h, in an infinite fluid domain the viscosity can be calculated as p=T 14TThwR2where:

[0042] • T = measured torque

[0043] • co = angular velocity

[0044] • h = length of cylinder

[0045] • R = radius of cylinder

[0046] In an embodiment of the disclosure, the length of the substrate is between 0.5 centimetres and 500 centimetres, preferably between 3 centimetres and 50 centimetres, most preferred between 5 centimetres and 25 centimetres. Substrate lengths within these ranges cover the different applications, for which measurements using the apparatus are relevant.

[0047] In an embodiment of the disclosure, the diameter(s) of the substrate are between 0.5 centimetres and 50 centimetres, preferably between 1 centimetre and 25 centimetres. Substrate diameters within these ranges have proven to be optimal for obtaining correct, accurate and repeatable results of the measurements.

[0048] A second aspect of the disclosure relates to a method for continuously or semi- continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a coating such as a paint. The method comprises:

[0049] - continuously or semi-continuously applying liquid onto a first surface of a substrate, for instance by leading the liquid, or at least a sample thereof, through a vessel, in which the substrate is partly immersed, or by dousing the first surface with the liquid,

[0050] - providing a relative motion between the first surface and an applicator, which is spaced apart from the first surface by a gap, so that liquid, which has been applied onto the first surface passes through the gap, whereby a liquid film is created on the first surface,

[0051] - wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby continuously or semi-continuously forming a scratch pattern in the liquid film, and

[0052] - determining the fineness of grind or maximum size of the particles suspended or dispersed in the liquid by analysing the scratch pattern in the liquid film on the first surface.

[0053] This method allows for measuring the fineness of grind and / or the maximum size of particles in a continuously or semi-continuously way with a minimum, if any, involvement of manual work and human assessments of the findings, whereby more objective results are obtained than by the standardised method known in the art.

[0054] In an embodiment of the disclosure, the substrate is partly immersed in a main flow of the liquid, such as in the circulation pipe in a paint production, or in a dedicated test flow of the liquid, such as in a parallel pipe to the circulation pipe in a paint production.

[0055] In an embodiment of the disclosure, the fineness of grind or the maximum size of particles suspended or dispersed in the liquid is measured continuously, such as in a flow of liquid during production of paint, or semi-continuously, such as for an offline test of liquid not being part of a flow of liquid.

[0056] This means that the method can be used, for instance, for inline, continuous or semi- continuous quality tests in a production line.

[0057] In an embodiment of the disclosure, the step of determining the fineness of grind or the maximum size of the particles comprises the step of continuously or semi-continuously capturing images of the scratch pattern using an image capturing device.

[0058] Using an image capturing device allows for automation of the analysis and evaluation of the scratch pattern, and it makes it possible to perform this analysis and evaluation at a later time and / or at another place than when and where the physical scratch pattern is created.

[0059] In an embodiment of the disclosure, the step of determining the fineness of grind or the maximum size of the particles further comprises the step of analysing the captured images by means of a computerised equipment using image processing tools, which computerised equipment is configured to calculate a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid based on the contents of the captured images. The presently disclosed grindometer may comprise a control unit for controlling the various elements of the grindometer, for example position and rotation of the substrate (on, off, speed, etc.), position of the applicator and thereby size and size variation of the gap, the motor for rotating the substrate, the image capturing device, and the like.

[0060] Using an automated equipment for analysing the captured images and calculate the fineness of grind and / or the maximum size of particles from the contents thereof, optionally also viscosity, increases the objectiveness and, thereby, the accuracy and repeatability of the obtained results.

[0061] In an embodiment of the disclosure, the image processing tools are configured to perform one or more of the following steps: receiving the image from the image capturing device, cropping the image to contain only the relevant section of the recorded image, processing the image by digital filters (for instance for reducing noise and for enhancing brightness, sharpness, contrast, and / or vertical lines in the image), converting the image to a binary image (for instance so that pixels within the scratches are given the value 1 , whereas pixels within the background are given the value 0), splitting the image length into sections (for instance corresponding to 1 pm in the physical world), and counting the number of pixels in each section.

[0062] Using combinations of these steps in the image processing has proven to enhance the precision and quality of the calculated values significantly. In some preferred embodiments, the image processing tools may be configured to count scratches rather than pixels.

[0063] In an embodiment of the disclosure, the calculation of a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid comprises one or more of the following steps: determining the average count of pixels within a given section of the (processed) image during a predefined period of time (in case of video recordings there will be numerous images), determining the fineness of grind using a predefined algorithm, such as determining the point, at which the occurrence probability exceeds a certain predefined value, calculating and / or showing other results, such as instantaneous fineness of grind, largest particle, overall largest particles, or average fineness of grind for a certain period of time, demonstrating graphs to show how fineness of grind or other values are changing calculating and / or showing secondary meaningful data, such as scratch occurrence probabilities of each image section, standard deviations, or span of the count distribution, and taking an appropriate action, such as sounding or showing an alarm or automatically stopping the process, when a certain predefined limit has been reached.

[0064] The above-mentioned steps of data processing are only to be seen as examples, and many other and different steps and features may be included in different embodiments of the disclosure.

[0065] In an embodiment of the disclosure, the method is performed using an apparatus as described above.

[0066] In a third aspect of the disclosure it relates to the use of an apparatus as described above and / or a method as described above in a batch production or a continuous production of a formulated liquid product, e.g. a paint, wherein the determined fineness of grind or maximum size or the particles is used as a deciding parameter for continuing or stopping the production process and / or as a continuously or semi- continuously recorded quality parameter of the production process.

[0067] Drawings In the following, a few embodiments of the disclosure are described in more detail with reference to the drawings, of which

[0068] Figs. 1A-C are schematic illustrations of a prior art Hegman gauge,

[0069] Fig. 2A is a schematic cross-sectional drawing of a grindometer according to a first embodiment of the disclosure as seen from above,

[0070] Fig. 2B is a schematic cross-sectional drawing of the same apparatus as shown in Fig. 2a as seen from one side,

[0071] Fig. 3A is a schematic cross-sectional drawing of a grindometer according to a first embodiment of the disclosure as seen from one end,

[0072] Fig. 3B is a schematic cross-sectional drawing of the same apparatus as shown in Fig. 3a as seen from one side,

[0073] Fig. 3C is a schematic cross-sectional drawing of the same apparatus as shown in Figs. 3a-b as seen from above,

[0074] Fig. 3D is a schematic cross-sectional drawing of the same apparatus as shown in Figs. 3a-c, as seen from above, but mor clearly illustrating the scratch forming mechanism,

[0075] Fig. 4 is a schematic cross-sectional drawing of the same apparatus as shown in Figs. 2a-b as seen from one end,

[0076] Fig. 5 is a schematic view of a grindometer according to a second embodiment of the disclosure,

[0077] Fig. 6 is a schematic view of a grindometer according to a third embodiment of the disclosure,

[0078] Fig. 7 is a schematic view of a grindometer according to a fourth embodiment of the disclosure,

[0079] Fig. 8 is a schematic view of a grindometer according to a fifth embodiment of the disclosure,

[0080] Fig. 9 is a schematic view of a system comprising a grindometer according to the disclosure,

[0081] Figs. 10-12 are pictures of the surface of a cylindrical substrate from a grindometer according to the present disclosure, wherein

[0082] Figs. 10A-D show examples where a scratch pattern with discrete scratches has been formed helping the determination of fineness of grind, Figs. 11 A-B show examples of scratch patterns without clear discrete scratches, but where a difference in shading across the substrate surface helps determination of fineness of grind, and

[0083] Fig. 12 shows an example of a scratch pattern where determination of fineness of grind is more challenging.

[0084] Fig. 13 is a histogram showing a normalised count distribution used in the disclosure for calculating the fineness of grind or the maximum size of particles suspended or dispersed in a liquid,

[0085] Fig. 14 shows a comparison of results obtained by using a grindometer according to the disclosure with results obtained by using a standardised method known within the art, for seven different types of commercially available paint

[0086] Detailed description

[0087] Figs. 1a-c are schematic illustrations of a prior art Hegman gauge functioning in accordance with hitherto known principles. In fig. 1a the Hegman gauge is seen from above, fig. 1b shows the Hegman seen from one end and fig. 1c shows the Hegman gauge seen from one side. A scraper 25 is provided above an application surface 26 a liquid film 28 of particulate liquid 27 has been placed. When manually scraping off the particulate liquid along the application direction 29, particles in the particulate liquid will leave a scratch pattern 16. As seen in fig. 1c, application surface 26 slopes along the application direction 29 such that the distance between the lowermost edge of the scraper 25 and the application surface decreases gradually when the scraper 25 moves relative to the application surface 26 along the application direction 25. The scratch pattern 16 formed in the liquid film provides direct, quick, and semi-quantitative assessment of the size of the largest particles in the particulate liquid 27. The maximum height between the scraper 25 and the application surface is marked as 30.

[0088] Figs. 2-4 are schematic cross-sectional drawings of a grindometer 1 according to a first embodiment of the disclosure as seen from the top, from one side and from one end, respectively. In this embodiment, the grindometer comprises a cylindrical substrate 2, which is mounted on a rotationally symmetrical rotational shaft 5, and a spring-loaded applicator 3 in the form of an elongated bar extends along the surface of the cylindrical substrate 2 in a longitudinal direction thereof. The cylindrical substrate 2 is arranged within a cylindrical housing 4 resting on four supports 8. This housing 4 is provided with an inlet 6 at its one end and an outlet 7 at its opposite end, so that a liquid flow enter into the housing 4 from the inlet 6, continue through the housing 4, and leave the housing 4 again through the outlet 7. The inlet 6 and / or the outlet 8 may be provided with a valve (not shown), which can be closed for stopping the flow of liquid through the housing 4. The inlet 6 and the outlet 8 are both arranged below the rotational shaft 5 at the two ends of the housing 4, respectively, and near the bottom of the housing 4 so that, when the grindometer 1 is in use, the surface level of liquid flowing through the housing 4 can be kept below the horizontal plane, through which the rotational shaft 5 extends.

[0089] A motor 9 is arranged outside the housing 4 near the inlet end thereof for rotating the rotational shaft 5 and thereby the cylindrical substrate 2 during operation of the grindometer 1. The function of the grindometer 1 does not depend on the type or the size of the motor 9 as long as the motor 9 is capable of delivering the necessary actuating force to accelerate the cylindrical substrate 2 to the desired rotational velocity and keep it rotating at that velocity. If no motor is present or if manual rotation is preferred, for instance in the case of semi-continuous operation of the grindometer 1, this does not affect the function of the grindometer 1 or the quality and characteristics of the scratch patterns formed.

[0090] One or more springs 10 are arranged in a spring housing 11, which extends adjacent to the housing 4 in the longitudinal direction thereof on the side, at which the surface of the cylindrical substrate 2 moves upwards, when the cylindrical substrate 2 is rotated. These springs 10 are configured to apply a pressure onto the applicator 3 so that it is kept in the correct position relative to the cylindrical substrate 2. In this position, a narrow gap is formed between the applicator 3 and the surface of the cylindrical substrate 2, the size of which gap varies gradually along the length of the applicator 3, so that the gap is larger at one end of the applicator 3 than at the other end thereof.

[0091] In a similar but slightly different embodiment, the applicator 3 may be parallel to the rotational shaft 5, and the surface of the substrate may form a very small angle with the same shaft 5. This means that the substrate is not strictly shaped as a cylinder, but rather as a truncated cone, which is so close to being a cylinder that it is impossible or at least very difficult to see the difference with the naked eye. The same effect with a gap, the size of which varies linearly as in the embodiment shown in Fig. 2-4, will be obtained by such an embodiment.

[0092] During operation of the grindometer 1, the rotating cylindrical substrate 2 is partly immersed into a liquid (not shown in Figs. 2-4), such as a paint, flowing through the lowermost part of the housing 4. When liquid sticking to the surface of the cylindrical substrate 2 moves upward with the surface due to the rotation and reaches the applicator 3, the gap between the applicator 3 and the surface of the cylindrical substrate 2 ensures that a liquid film 28 of varying thickness is formed on the surface of the cylindrical substrate 2 after, i.e. above, the applicator 3. Particles within the liquid, which are too large to pass between the applicator 3 and the surface of the cylindrical substrate 2, are held back by the applicator 3 and form scratches 16 in this liquid film 28.

[0093] If the particles of varying sizes are evenly distributed within the liquid, the scratch pattern 16 formed in the liquid film will be representative of the distribution of differentsized particles within the liquid. This is due to the fact that particles of a given size will pass through the gap where the size of the gap is larger than the particle diameter, while particles of the same size are held back where the size of the gap is smaller than the particle diameter. This is most clearly seen in fig. 3c, where the gap size, seen here as the distance between the applicator 3 and the substrate 2, decreases linearly from left to right, with the maximum gap size marked as 31. The particulate liquid 27 is seen inside the gap. As seen in figs. 3b-c the scratch pattern 16 formed in the liquid film 28 shows nicely distributed scratches lined up next to each other from particles blocked by the gap at each respective position, the particle size closely correlated to the corresponding size of the gap at that position. The gap size in fig. 3c is exaggerated to visualize the change in gap size across the substrate. In reality the size of the gap will typically be at a micrometre scale and thereby unable to be seen by the naked eye.

[0094] Fig. 3d corresponds to fig. 3c seen from the other side, more clearly illustrating the scratch forming mechanism. As seen in fig. 3d “small” particles 32 in the particulate 27 escape the gap if they are smaller than the gap size at corresponding positions, whereas “large” particles 33 are held back by the gap and leave a scratch pattern 16 in the liquid film 28, if they are larger than the gap size at corresponding positions of the gap along the applicator 3. Compared to the prior art principle used in the Hegman gauge shown in fig. 1 , the particulate liquid is applied at all gap sizes at the same time in the presently disclosed approach. One advantage of the presently disclosed approach is that scratches from particles with different sizes do not overlap because the variation in the gap size is typically distributed across, such as transverse, the application direction as illustrated in fig. 3b, whereas the variation in the gap size in the prior art Hegman gauge is distributed along the application direction 29, as illustrated in fig. 1c.

[0095] Fig. 3d more clearly illustrates formation of the scratch pattern. Particles that are larger than the gap size and the particular position are held back by the applicator and forms a scratch in the liquid film. Particles that are smaller than the size of the gap passes through the gap and are embedded in the applied liquid film.

[0096] An image capturing device 12 (seen in fig. 4), such as a camera or a video camera, potentially in combination with one or more light sources (not shown), is arranged to register and save images of the formed scratch pattern through an opening (not shown) in the housing 4. These images are processed and analysed for calculating a measure of the fineness of grind or maximum diameter (or other size-related characteristics) of the particles within the liquid. If no image capturing device 12 is part of the grindometer 1 or if the operator prefers to do so, the fineness of grind may be determined by interpreting the scratch pattern visually using only the naked eye.

[0097] For practical reasons, the cylindrical substrate 2 of the grindometer 1 is typically positioned with its longitudinal axis parallel to or at least substantially parallel to the flow direction of the liquid. However, as long as the contact between the liquid and the surface of the cylindrical substrate 2 is maintained, the housing 4 can be shaped differently and the cylindrical substrate 2 can be arranged in any direction relative to the flow direction.

[0098] Likewise, the cylindrical substrate 2 may be arranged in other directions than horizontal as long as the contact between the liquid and the surface of the cylindrical substrate 2 is maintained and as long as leakages are prevented. The substrate 2 may be configured for (continuous) rotation around a rotation axis. The applicator 3 and / or the gap may extend(s) parallel to the rotation axis of the substrate 2. This is illustrated in Fig. 2, where the substrate 2 is rotating around rotational shaft 5.

[0099] The applicator 3 may be arranged at least primarily along a longitudinal direction of the substrate 2, which in Fig. 2, and Figs. 3b-d correspond to the horizontal direction. The gap may extend along the longitudinal direction of the substrate.

[0100] The substrate 2 may be shaped as a cylinder, shown in Figs. 2-4, or a truncated cone. In such embodiments the relative movement between the substrate 2 and the applicator 3 is constant along the substrate 2 and the applicator 3, e.g. along the extension of the gap. And then the scratch pattern 16 will be formed with a constant relative application speed at all gap sizes.

[0101] Fig. 5 is a schematic view of a grindometer 1 according to a second embodiment of the disclosure. In this embodiment, the substrate is a vertically-oriented plate 13, which is configured to move up and down. When the plate-shaped substrate 13 is in its lowermost position, it is dipped into a liquid 15, such as a paint, which is contained within or flowing through a vessel 14. A fixed horizontally-oriented applicator 3 is arranged close to one of the surfaces of the moving plate-shaped substrate 13, so that a gap similar to the one described above in relation to the first embodiment is formed between the applicator 3 and the surface of the plate-shaped substrate 13. When the plate-shaped substrate 13 moves upwards, a liquid film with a scratch pattern 16 is formed above the applicator 3 similar to the one described above for the first embodiment.

[0102] Fig. 6 is a schematic view of a grindometer 1 according to a third embodiment of the disclosure, in which the substrate is a disc 17 partly immersed in a liquid 15, such as a paint, which is contained within or flowing through a vessel 14. A fixed applicator 3 is arranged to form a gap, so that a liquid film with a scratch pattern 16 similar to the ones described above is formed on the side of the disc-shaped substrate 17 when it rotates. A disadvantage of this embodiment is that the relative movement between the surface of the disc and the applicator is varying across the disc 17 due to the increasing circumference of the disc towards the periphery. Hence, the scratch pattern is formed under varying circumstances towards the periphery of the disc. Fig. 7 is a schematic view of a grindometer 1 according to a fourth embodiment of the disclosure. In this embodiment, a plate-shaped substrate 13 is fixed in an inclined position, while the applicator 3, which is mounted onto an applicator arm 18 together with a substrate cleaner 19, moves forth and back. The applicator 3 collects liquid 15 from a vessel 14 at its lowermost position and forms a liquid film with a scratch pattern (not shown) when moving upwards along the upper surface of the plate-shaped substrate 13. The substrate cleaner 19 and, potentially, another cleaning apparatus (not shown) cleans the paint and the scratch pattern of the surface of the plate-shaped substrate 13 so that it is ready for the next upward stroke of the applicator arm 18 and the next scratch pattern.

[0103] Fig. 8 is a schematic view of an apparatus according to a fifth embodiment of the disclosure, in which the substrate is formed as a belt 20 arranged on two or more belt wheels 21 to be partly immersed in a liquid 15 contained in or flowing through a vessel 14. A fixed applicator 3 is arranged above a horizontal surface of the belt, which is not immersed in the liquid 15, to form a liquid film with a scratch pattern (not shown) as described above.

[0104] Fig. 9 is a schematic view of a system comprising a grindometer 1 according to an embodiment of the disclosure. A liquid 15, such as a paint, is contained in or flows through a vessel 14, which may, for instance, be a circulation pipe in a paint production. Continuously, a small fraction of the liquid is led to a grindometer 1 according to the disclosure for measuring the fineness of grind, maximum diameter or other size-related characteristics of particles suspended or dispersed in the liquid. From the grindometer 1, the liquid is led back to the vessel 14. A pump 22 and one or more valves 23 are used for controlling the amount of liquid being led to and from the grindometer 1 for being tested. In systems, in which the grindometer 1 is arranged directly in a circulation pipe of a paint production or in another vessel 14, in which the liquid 15 is already flowing, the pump may be omitted.

[0105] Thus, in the embodiment shown in Fig. 9, wherein the grindometer 1 is arranged within a dedicated test flow of the liquid in the form of a parallel pipe to a main flow of the liquid. In other embodiments, the grindometer 1 may be arranged directly within the main flow. Whether the grindometer 1 is arranged in a dedicated test flow or directly within the main flow, it may be operated in a continuous mode. The same grindometer 1 may be operated in a semi-continuous mode if the liquid being 15 tested is not moving but simply contained in a vessel 14, in which the substrate 2, 13, 17 is partly immersed.

[0106] The material of the substrate and / or applicator is preferably a mechanically rigid and / or hard material, preferably chemically resistant to the liquid, and should be compatible with the liquid, i.e. it should be possible to form a substantially uniform liquid film on it. The material can for example at least partly be high grade stainless steel, in particular the first surface of the substrate and / or the scraping part of the applicator.

[0107] Examples of inline measurements using one embodiment (with a cylindrical substrate) of the presently disclosed grindometer 1 for determining the fineness of grind 24 of different coatings are shown in Figs. 10-12. These examples illustrate how the grindometer 1 can be used instead of a Hegman gauge.

[0108] The use of the grindometer 1 does not require manual placement of a sample on a gauge. Fineness of grind can be determined by manual visual inspection, for example by having a visual scale of the gap size associated with the scratch pattern, for example close to and extending along the substrate and / or the applicator. However, by integrating image processing technology the determination of fineness of grind can be automated. The basic principle is that when a coating I liquid is applied to the substrate surface, i.e. the surface of the rotating cylindrical substrate, particles in the coating I liquid cause scratches if they are larger than the gap size. At larger gap sizes, no scratches appear. As the gap narrows and scratches begin to occur consecutively, that point is identified as the fineness of grind.

[0109] Moreover, the grindometer 1 can be used for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles of a formulated liquid product. This can simplify the use of the grindometer during the manufacturing process of a formulated liquid product and can automate the analysis process.

[0110] To determine the fineness of grind value the following process can for example be followed: Starting from the thicker part of the liquid film formed on the substrate surface, scratches are scanned and noted. Individual scratches that are separate from the scratch group are not considered fineness of grind (FoG) values. To define the FoG, the applicator length can for example be divided into a number of equal segments for example 50 equal segments, for example each segment corresponding to a difference in gap size of 1 pm. Starting from the thicker end of the liquid film, the first occurrence of scratches in three consecutive equal segments marks the FoG value.

[0111] This is illustrated in Fig. 10A, where the first individual scratch appears at around 23 pm. No scratch is present at 22 pm and 21 pm. The next scratch appears at 20 pm, and consecutive 1-pm ranges (19 pm and 18 pm) have scratches as well. Therefore, the fineness of grind 24 in this example is noted to be 20 pm. Similar examples are illustrated in fig. 10B-D.

[0112] Scratch formation can be affected by parameters such as powder type, rotation speed, and coating viscosity. Sometimes, instead of scratches, a noticeable shade change can appear and can be used to determine the FoG value. This is illustrated in Fig. 11A, where scratches appear at 21, and 14 pm. In this case, no other distinctive scratches appear, but there is a clear shade shift starting at 14 pm. Therefore, the fineness of grind 24 is 14 pm. However, sometimes there are no scratches at the fineness of grind value. In Fig. 11b, the shade difference starts around 26 pm. Even though there is no distinctive scratch, 26 pm can be registered as the fineness of grind 24 due to clear shade shift.

[0113] In a continuous measurement, the scratch pattern is dynamic and multiple images are assessed together to determine the fineness of grind value. As an example, an average scratch pattern can be created by acquiring a number of images at discrete time intervals. For example ten images can be taken every 5 seconds. To determine the average pattern, each image is assessed individually as described above. If there is a scratch at a specific gap size in more than a predefined ratio (e.g. 10-50%, for example 40%) of the images, then in the average pattern, it is considered that a scratch exists at that gap size. If scratches appears in less than this predefined ratio of the images, then there will not be a scratch in the average pattern.

[0114] The distribution of scratches can help determine if the applicator size is appropriate; if scratches appear at the end with the large gap sizes, a larger maximum gap size may be needed, whereas more concentrated scratches at smaller gap size may indicate the need for a smaller maximum gap size. Hence, in some case it can be helpful to provide for a scratch-free section at the large gap end of the cylinder. In Fig. 12, three scratches can be seen above 40 pm. This indicates that a maximum gap size 31 of 50 pm is too small for this sample, and a maximum gap size 31 of up to 100 pm could be used instead.

[0115] Fig. 13 is a histogram showing a normalised count distribution used for calculating the fineness of grind or the maximum size of particles suspended or dispersed in a liquid. The horizontal axis of the histogram shows the particle diameter measures in microns (pm) in steps of 1 pm, whereas the vertical axis shows the normalised count distribution, in which the highest count number is normalised to 1.

[0116] In the standardised method, the value of fineness of grind is defined as the section, in which the particle count is at least 10 in a 3 mm band. For the sake of comparison, the corresponding value was found in the normalised 0-1 scale and applied to patterns obtained by the standardised Hegman gauge and to patterns obtained by a prototype grindometer 1 according to the present disclosure. In the count distribution shown in Fig. 13, the fineness of grind 24 is determined to be 18 pm.

[0117] Fig. 14 shows a comparisons of the fineness of grind 24 obtained by using a grindometer 1 according to the present disclosure and by using a standardised method known within the art, respectively, for seven different types of commercially available paint. The hatched bars relate to the results obtained using a continuous grindometer 1 according to the disclosure, whereas the non-hatched bars relate to the results obtained using the standard Hegman gauge.

[0118] It is clear from the graph that there is a very fine conformity between the results obtained by the two different methods, and it must be concluded that the presently disclosed grindometer can replace the Hegman gauge, however with the advantages of performing the fineness of grind measurements inline, e.g. integrated in a coating manufacturing process, and furthermore with the option of being fully automatic via vision technology for analysing images of the scratch patterns, as described herein.

[0119] List of reference numbers

[0120] 1. Grindometer 2. Cylindrical substrate

[0121] 3. Applicator

[0122] 4. Housing

[0123] 5. Rotational shaft

[0124] 6. Inlet

[0125] 7. Outlet

[0126] 8. Support for housing

[0127] 9. Motor

[0128] 10. Spring

[0129] 11. Spring housing

[0130] 12. Image capturing device

[0131] 13. Plate-shaped substrate

[0132] 14. Vessel

[0133] 15. Liquid

[0134] 16. Scratch pattern

[0135] 17. Disc-shaped substrate

[0136] 18. Applicator arm

[0137] 19. Substrate cleaner

[0138] 20. Belt-shaped substrate

[0139] 21. Belt wheel

[0140] 22. Pump

[0141] 23. Valve

[0142] 24. Fineness of grind

[0143] 25. Scraper

[0144] 26. Application surface

[0145] 27. Particulate liquid

[0146] 28. Liquid film

[0147] 29. Application direction

[0148] 30. Maximum depth

[0149] 31. Maximum gap size

[0150] 32. “Small” particles

[0151] 33. “Large” particles Items

[0152] 1. An apparatus for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a paint, which apparatus comprises a substrate and an applicator,

[0153] - wherein the substrate is arranged so that liquid can be applied onto a first surface of the substrate, for instance by immersing a part of the substrate in the liquid or by dousing the substrate with the liquid,

[0154] - wherein the substrate and the applicator are configured to move relative to each other, preferably continuously or at least semi-continuously, the relative movement of the substrate and the applicator thereby forming a liquid film on the first surface,

[0155] - wherein the applicator is arranged so that, liquid, which has been applied onto the first surface, can pass through a gap defined between the applicator and the first surface.

[0156] 2. The apparatus according to item 1 , wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby continuously or semi- continuously forming a scratch pattern in the liquid film.

[0157] 3. The apparatus according to any of the preceding items, wherein the applicator is spaced apart from a first surface of the substrate, such as slightly spaced apart from the first surface, the spacing preferably at least partly defined by the gap

[0158] 4. The apparatus according to any of the preceding items, wherein the applicator is arranged so that the size of the gap varies, such as varying gradually, along the applicator in such a way that the liquid film formed by the applicator has a larger film thickness at one end of the gap than at the other end

[0159] 5. The apparatus according to any of the preceding items, wherein the applicator and the first surface are mutually arranged so that particles suspended or dispersed in the liquid, which are larger than the gap size at the position, at which the particles attempt to pass the applicator, are held back by the applicator, thereby forming a scratch pattern in the liquid film.

[0160] 6. The apparatus according to any of the preceding items, wherein the relative movement between the substrate and the applicator defines an application direction of the liquid film, and where the variation in the gap size extends transverse to the application direction.

[0161] 7. The apparatus according to any of the preceding items, wherein the apparatus further comprises an automated device, such as a motor, configured for providing a relative motion between the substrate and the applicator.

[0162] 8. The apparatus according to any of the preceding items, wherein the relative velocity between the substrate and the applicator is between 0.001 metres per second and 1 metres per second, preferably between 0.01 metres per second and 0.3 metres per second.

[0163] 9. The apparatus according to any of the preceding items, wherein the varying gap sizes are within the range from 0.5 micrometres to 5000 micrometres, preferably within the range from 1 micrometre to 500 micrometres.

[0164] 10. The apparatus according to any of the preceding items, wherein the applicator is arranged so that the gap size can be adjusted at one or more locations along the gap.

[0165] 11. The apparatus according to any of the preceding items, wherein the applicator is releasably attached to other parts of the apparatus.

[0166] 12. The apparatus according to any of the preceding items, further comprising an image capturing device arranged to capture images of the scratch patterns formed in the liquid film.

[0167] 13. The apparatus according to item 12, further comprising an automated equipment, such as a computer, configured to analyse the captured images and calculate, based on the contents of the captured images, a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid based and, potentially, other statistical information, which statistical information may include, for instance, the size of the largest particle registered, the frequency of scratch appearances at different sizes, and / or the span of the data. The apparatus according to any of the preceding items, wherein the substrate is shaped as a cylinder or a truncated cone, which is configured to be rotated around a longitudinal, rotationally symmetric axis thereof, The apparatus according to any of the preceding items, wherein the applicator is elongated, preferably linear, and arranged at least primarily along a longitudinal direction of the substrate. The apparatus according to any of the preceding items, wherein the gap extends along the longitudinal direction of the substrate. The apparatus according to any of the preceding items, wherein the size of the gap varies from one position of the gap to another position of the gap, such as from one end of the gap to another opposite end of the gap, such as from one end of the applicator to another opposite end of the applicator. The apparatus according to any of the preceding items, wherein the variation of the gap size is linear, exponential, saw-tooth, stepwise, sinusoidal, or any combination thereof. The apparatus according to any of the preceding items, wherein the gap size varies from 1 micrometre to 500 micrometres. The apparatus according to any of the preceding items, wherein the length of the substrate is between 0.5 centimetres and 500 centimetres, preferably between 3 centimetres and 50 centimetres, most preferred between 5 centimetres and 25 centimetres. The apparatus according to any of the preceding items, wherein the diameter(s) of the substrate are between 0.5 centimetres and 50 centimetres, preferably between 1 centimetre and 25 centimetres. A method for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a paint, which method comprises the steps of

[0168] - continuously or semi-continuously applying liquid onto a first surface of a substrate, for instance by leading the liquid, or at least a sample thereof, through a vessel, in which the substrate is partly immersed, or by dousing the first surface with the liquid,

[0169] - providing a relative motion between the first surface and an applicator, which is spaced apart from the first surface by a gap, so that liquid, which has been applied onto the first surface passes through the gap, whereby a liquid film is created on the first surface,

[0170] - wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby forming a scratch pattern in the liquid film, preferably continuously or semi-continuously, and

[0171] - determining the fineness of grind or maximum size of the particles suspended or dispersed in the liquid by analysing the scratch pattern in the liquid film on the first surface.. The method according to item 22, wherein the substrate is partly immersed in a main flow of the liquid, such as in the circulation pipe in a paint production, or in a dedicated test flow of the liquid, such as in a parallel pipe to the circulation pipe in a paint production The method according to any of items 22 to 23, wherein the fineness of grind or the maximum size of particles suspended or dispersed in the liquid is measured continuously, such as in a flow of liquid during production of paint, or semi- continuously, such as for an offline test of liquid not being part of a flow of liquid. The method according to any of items 22-24, wherein the step of determining the fineness of grind or the maximum size of the particles comprises the step of continuously or semi-continuously capturing images of the scratch pattern using an image capturing device. The method according to item 25, wherein the step of determining the fineness of grind or the maximum size of the particles further comprises the step of analysing the captured images by means of a computerised equipment using image processing tools, which computerised equipment is configured to calculate a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid based on the contents of the captured images. The method according to item 26, wherein the image processing tools are configured to perform one or more of the following steps:

[0172] - receiving the image from the image capturing device,

[0173] - cropping the image to contain only the relevant section of the recorded image,

[0174] - processing the image by digital filters (for instance for reducing noise and for enhancing the brightness, sharpness, contrast, and / or vertical lines in the image),

[0175] - converting the image to a binary image (for instance so that pixels within the scratches are given the value 1 , whereas pixels within the background are given the value 0),

[0176] - splitting the image length into sections (for instance corresponding to 1 pm in the physical world), and

[0177] - counting the number of pixels in each section. The method according to any of items 26 or 27, wherein the calculation of a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid comprises one or more of the following steps:

[0178] - determining the average count of pixels within a given section of the

[0179] (processed) image during a predefined period of time (in case of video recordings there will be numerous images),

[0180] - determining the fineness of grind using a predefined algorithm, such as determining the point, at which the occurrence probability exceeds a certain predefined value, - calculating and / or showing other results, such as instantaneous fineness of grind, largest particle, overall largest particles, or average fineness of grind for a certain period of time,

[0181] - demonstrating graphs to show how fineness of grind or other values are changing

[0182] - calculating and / or showing secondary meaningful data, such as scratch occurrence probabilities of each image section, standard deviations, or span of the count distribution, and

[0183] - taking an appropriate action, such as sounding or showing an alarm or automatically stopping the process, when a certain predefined limit has been reached. The method according to any of items 22-29, wherein the method is performed using an apparatus according to any of items 1-21. The use of an apparatus according to any of the items 1-21 and / or a method according to any of the items 22-29 in a batch production or a continuous production of a formulated liquid product, e.g. a paint, wherein the determined fineness of grind or maximum size or the particles is used as a deciding parameter for continuing or stopping the production process and / or as a continuously or semi-continuously recorded quality parameter of the production process.

Claims

Claims1. An apparatus for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a paint, which apparatus comprises a substrate and an applicator,- wherein the substrate is arranged so that liquid can be applied onto a first surface of the substrate, for instance by immersing a part of the substrate in the liquid or by dousing the substrate with the liquid,- wherein the substrate is configured for rotation around a rotation axis, and wherein the applicator extends along with said rotation axis such that the substrate and the applicator are configured to move relative to each other during rotation of the substrate, the relative movement of the substrate and the applicator forming a liquid film on the first surface of the substrate,- wherein the applicator is arranged so that, liquid, which has been applied onto the first surface of the substrate, can pass through a gap defined between the applicator and the first surface,- wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby forming a scratch pattern in the liquid film.

2. The apparatus according to claim 1 , wherein the apparatus further comprises an automated device, such as a motor, configured for providing the relative motion between the substrate and the applicator.

3. The apparatus according to claim 1 or 2, wherein the applicator is arranged so that the gap size can be adjusted at one or more positions along the gap.

4. The apparatus according to any of the preceding claims, wherein the substrate is arranged so that liquid can be applied onto a first surface of the substrate by immersing a part of the substrate in the liquid.

5. The apparatus according to any of the preceding claims, wherein the applicator is releasably attached to other parts of the apparatus.

6. The apparatus according to any of the preceding claims, wherein the applicator is elongated and arranged at least primarily along a longitudinal direction of the substrate.

7. The apparatus according to any of the preceding claims, wherein the gap extends along the longitudinal direction of the substrate.

8. The apparatus according to any of the preceding claims, further comprising an image capturing device arranged to capture images of the scratch patterns formed in the liquid film.

9. The apparatus according to claim 8, further comprising automated equipment, such as a computer, configured to analyse the captured images and calculate, based on the contents of the captured images, a measure for the fineness of grind and / or the maximum size of the particles suspended or dispersed in the liquid, and, potentially, other statistical information, which statistical information may include, for instance, the size of the largest particle registered, the frequency of scratch appearances at different sizes, and / or the span of the data.

10. The apparatus according to any of the preceding claims, wherein the relative movement between the substrate and the applicator defines an application direction of the liquid film, and where the variation in the gap size extends transverse to the application direction.

11. The apparatus according to any of the preceding claims, wherein the rotation axis is horizontal.

12. The apparatus according to any of the preceding claims, wherein the substrate is shaped as a cylinder or a truncated cone.

13. The apparatus according to any of the preceding claims, configured such that the relative movement between the substrate and the applicator is constant along the substrate and the applicator.

14. The apparatus according to any of the preceding claims, configured such that the scratch pattern is formed with a constant relative application speed at all gap sizes.

15. The apparatus according to any of the preceding claims, configured such that the scratch pattern is formed perpendicular to a longitudinal direction of the substrate.

16. The apparatus according to any of the preceding claims, configured for determining viscosity of the liquid.

17. The apparatus according to any of the preceding claims, configured for monitoring a change in viscosity of the liquid.

18. The apparatus according to any of the preceding claims, wherein the size of the gap varies from one from one end of the applicator to another opposite end of the applicator, and wherein the variation of the gap size is gradually uniformly.

19. The apparatus according to any of the preceding claims, wherein the gap size varies from 0 or about 1-10 micrometre and up to 500 micrometres.

20. A method for continuously or semi-continuously measuring the fineness of grind or the maximum size of particles suspended or dispersed in a liquid, such as a formulated liquid product, e.g. a paint, which method comprises the steps of continuously or semi-continuously applying liquid onto a first surface of a substrate, for instance by leading the liquid, or at least a sample thereof, through a vessel, in which the substrate is partly immersed, or by dousing the first surface with the liquid, providing a relative motion between the first surface and an applicator, which is spaced apart from the first surface by a gap, so that liquid, which has been applied onto the first surface passes through the gap, whereby a liquid film is created on the first surface,- wherein the size of the gap varies along the applicator, such that particles suspended or dispersed in the liquid are held back by the applicator depending on their size, thereby continuously or semi-continuously forming a scratch pattern in the liquid film with a constant relative application speed at all gap sizes, anddetermining the fineness of grind or maximum size of the particles suspended or dispersed in the liquid by analysing the scratch pattern in the liquid film on the first surface.

21. The method according to claim 20, wherein the substrate is partly immersed in a main flow of the liquid, such as in the circulation pipe in a paint production, or in a dedicated test flow of the liquid, such as in a parallel pipe to the circulation pipe in a paint production.

22. The method according to claim 20 or 21 , wherein the fineness of grind or the maximum size of particles suspended or dispersed in the liquid is measured continuously, such as in a flow of liquid during production of paint.

23. The method according to claim 20 or 21 , wherein the fineness of grind or the maximum size of particles suspended or dispersed in the liquid is measured semi- continuously or discrete, such as for an offline test of liquid not being part of a flow of liquid.

24. The method according to any of claims 20-23, wherein the step of determining the fineness of grind or the maximum size of the particles comprises the step of continuously or semi-continuously capturing images of the scratch pattern using an image capturing device.

25. The method according to claim 24, wherein the step of determining the fineness of grind or the maximum size of the particles further comprises the step of analysing the captured images by means of a computerised equipment using image processing tools, which computerised equipment is configured to calculate a measure for the fineness of grind or the maximum size of the particles suspended or dispersed in the liquid based on the contents of the captured images.

26. The method according to any of claims 20-25, wherein the method is performed using an apparatus according to any of claims 1-19.

27. The use of an apparatus according to any of the claims 1-19 and / or a method according to any of the claims 20-25 in a batch production or a continuousproduction of a formulated liquid product, e.g. a paint, wherein the determined fineness of grind or maximum size or the particles is used as a deciding parameter for continuing or stopping the production process and / or as a continuously or semi- continuously recorded quality parameter of the production process.

Images