WO2009136851A1

WO2009136851A1 - Procedure and coating colour analyzer for on-line analysis of coating colour

Info

Publication number: WO2009136851A1
Application number: PCT/SE2009/050483
Authority: WO
Inventors: Håkan KARLSSON
Original assignee: Mattssonföretagen I Uddevalla Aktiebolag
Priority date: 2008-05-06
Filing date: 2009-05-05
Publication date: 2009-11-12
Also published as: SE532408C2; SE0801004L

Abstract

A coating colour analyzer (20) is used for on-line analysis of coating colour with regard to air content, etc. that comprises a. a measurement vessel (21), b. means to remove a sample of coating colour from a flow of deaerated coating colour for a coater (I)5 which means comprises an inlet conduit (22) to the measurement vessel and an outlet conduit (23) from the measurement vessel (21), b. means for sealing the measurement vessel (21), which sealing means comprises a first valve (Vl) in the inlet conduit (22) and a second valve (V2) in the outlet conduit (23), c. means (24, V3) for exposing the sample of coating colour in the measurement vessel (21) to a predetermined increase of pressure that, when the sample of coating colour still contains captured air, decreases the volume of the sample of coating colour and increases its density, and d. means (28, 31) for determining the decrease of volume / increase of density at the predetermined increase of pressure. In order to avoid the need to decrease the volume of the measurement vessel (21) by use of moveable components in the measurement vessel (21), the increase of pressure is by means (24, V3) which apply compressed air in direct contact with the sample of coating colour.

Description

PROCEDURE AND COATING COLOUR ANALYZER FOR ON-LINE ANALYSIS OF COATING COLOUR TECHNICAL AREA

The present invention concerns a procedure for on-line analysis of coating colour, whereby a sample of coating colour is taken out on-line from a flow of deaerated coating colour to a coater and put into a measurement vessel, the measurement vessel is sealed, and the sample of coating colour in the measurement vessel is exposed to a predetermined increase of pressure that, when the sample of coating colour still contains captured air, decreases the volume of the sample of coating colour and increases its density and the decrease of volume / increase of density are determined at the predetermined pressure increase.

The invention also concerns a coating colour analyzer for on-line analysis of coating colour that comprises a measurement vessel, means for removing a sample of coating colour from a flow of deaerated coating colour for a coater, which means comprises an inlet conduit to the measurement vessel and an outlet conduit from the measurement vessel, means to seal the measurement vessel, which sealing means comprises a first valve in the inlet conduit and a second valve in the outlet conduit, means for exposing the the sample of coating colour in the measurement vessel to a predetermined increase of pressure that when the sample of coating colour still includes captured air decreases the volume of the sample of coating colour and increases its density, and means for determining the decrease in volume / increase in density at the predetermined pressure increase.

STATE OF THE ART

A number of measurement techniques are used for measuring concentration of various fluid suspensions such as density and microwave methods or optical methods in order to measure the content of dry substance. Common to all of these methods is that they are sensitive to mixed-in air. The effect of air on measurement precision varies for different methods. The density of air is approx. 1000 times lower than for water. Nuclear density meters are especially sensitive to air, which makes them especially suitable for measuring amounts of air in all fluid suspensions containing air.

A procedure and coating colour analyzer of the type indicated above is previously known from, for example, US 6 138 498 (Hofer et al.). It is proposed there that the sample of coating colour in the measurement vessel may be exposed to a predetermined increase of pressure that diminishes the volume of the sample in that the volume of the measurement vessel is decreased by use of a piston that is pressed into the measurement vessel. The piston is sealed against the wall of the measurement vessel with a membrane and maneuvered by a motor via a piston rod. Such a design may gradually cause problems based on, for example, wear of the moveable components needed to decrease the volume of the measurement vessel.

BRIEF ACCOUNT OF THE INVENTION

The object of the present invention is to achieve a procedure and a coating colour analyzer for on-line analysis of coating colour, where no moving parts are needed, and to decrease the volume of the measurement vessel in order to analyze a coating colour with respect to air content.

This object is achieved by the procedure indicated above in that the predetermined increase of pressure is achieved in accordance with the invention by bringing compressed air into direct contact with the sample of the coating colour.

In a corresponding way this object is achieved by the coating colour analyzer indicated above by means according to the invention for exposing the sample of the coating colour to the predetermined increase of pressure by bringing compressed air into direct contact with the sample of the coating colour.

In that the coating colour sample is compressed with direct action of compressed air no moveable components are required that decrease the volume of the measurement vessel and in this way improves operational safety.

It is suitable that the coating colour is caused to flow through the measurement vessel for a predetermined time and that the dynamic viscosity of the coating colour is measured during this predetermined time and the measurement value stored

The flow introduced to the measurement vessel is then stopped and the coating colour in the measurement vessel is allowed to stabilize during a first predetermined amount of time before certain parameters of the coating colour sample are determined, for example, its static viscosity, temperature, and density at atmospheric pressure and the measured values are stored.

The measurement vessel is then sealed and said application of pressurized gas, for example compressed air, is brought into direct contact with the sample of coating colour, whereby the sample of coating colour in the measurement vessel is first allowed to stabilize during a second predetermined amount of time, after which certain desired parameters are again determined, for example static viscosity, density, pressure, and temperature.

The coating colour is preferably pressurized in the measurement vessel by means of the compressed air to a predetermined beginning pressure and measurement values from a density sensor are sampled until a first constant density signal is reached, after which the pressure from the compressed air is increased to a second predetermined value and a new reading of density values is carried out until a second constant density signal is reached. In that the sample is enclosed in a measurement vessel it is isolated from such process variations as temperature, density and pressure. By varying the pressure in the measurement vessel and measuring the density at different pressures, the volume of air in the sample can be calculated with the help of the variation in the measured value for density at the two measured different pressures. Since the volume of air varies with the temperature, the temperature must also be considered and possible recalculation of the density values to a single temperature.

If the two constant density signals are not the same, the pressure from the compressed air increases to a third predetermined value and a new reading of density values is carried out until a third constant density signal is achieved that is compared with the second constant density signal.

Density is suitably measured with a nuclear density meter. This kind of meter is especially sensitive to air, which makes it especially suitable for measuring the amount of air in fluid suspensions that contain air. A suitable source of radioactivity is the isotope Cs-137 with a typical level of activity of 1.85 GBq (50 mCi).

After any possible necessary processing the read-out measured values like dry matter content, air content, temperature, and viscosity are presented. The means by which compressed air is introduced into the coating colour analyzer preferably comprises a conduit provided with a third valve from a compressed air source, which compressed air conduit is connected to the outlet conduit from the measurement vessel at a point upstream of the second valve.

The coaing colour analyzer further suitably comprises a pressure release conduit provided with a fourth valve, which conduit is connected to the compressed air conduit at a point downstream from the third valve.

It is also suitable that the coating colour analyzer further comprises a conduit from a source of water provided with a fifth valve, which water conduit is connected to the supply conduit for coating colour to the measurement vessel at a point downstream the first valve and a conduit with a sixth valve for outlet of used water.

Preferably, the means for determining the decrease in volume / increase in density comprises a PLC and sensors mounted in the measurement vessel for detection of temperature, pressure, and density, which sensors are connected to the PLC.

As mentioned above, the density sensor is suitably a nuclear density meter. This kind of meter is sensitive to air, which makes it suitable for measuring the amount of air in fluid suspensions that contain air.

It is also suitable that a sensor for detection of viscosity is mounted in the measurement vessel and connected to the PLC.

All valves are preferably arranged to be opened and closed by the PLC, through which the coating colour analyzer can easily be designed to operate automatically and cyclically.

The first and fourth valves are suitably regulation valves and the remaining are shut- off valves. In this way pressure changes in the measurement vessel can be carried out in accordance with predetermined ramping.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will be described in more detail in the following with reference to preferred embodiments and the accompanying drawings. Figure 1 is a principle diagram for a coating kitchen provided with a coating colour analyzer according to a preferred embodiment of the invention and positioned at a coating station for coating of a running web. Figure 2 is an enlargement of the coating colour analyzer shown in Figure 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In Figure 1 a coater 1 is shown in which the coating colour is applied with a fountain applicator 2 or a rotatable coating roller 3 on a running web 4 of paper or cardboard that is supported by a rotatable carrying roller 5. Coating roller 3 is located in a coating colour trough 6 and the coating layer on web 4 is evened out and excess coating colour is wiped away by a scraping blade 7 mounted on a scraper beam 8. The coating colour comes from a coating kitchen 9 that comprises a tank 10, to which water is conducted through a conduit 11 and other ingredients that are to be included in the coating colour through a conduit 12. A feed conduit 13 extends from the bottom of tank 10 in which coating colour is pumped by a pump 14 with a motor 15 to fountain applicator 2 and coating colour trough 6. From trough 6 a return conduit 16 goes back to tank 10. In a dashed frame a coating colour analyzer 20 is shown connected to coating kitchen 9.

Coating colour analyzer 20, which is shown in enlargement in Figure 2, comprises a measurement vessel 21, means for removing a coating colour sample from a flow of deaerated coating colour for coating 1, which means comprises an inlet conduit 22 to the measurement vessel 21 and an outlet conduit 23 from the measurement vessel 21 and means for sealing the measurement vessel 21, which means for sealing comprises a first valve Vl in the inlet conduit 22 and a second valve V2 in the outlet conduit 23. Coating colour analyzer 1 further comprises means for exposing the coating colour sample in measurement sample 21 to a predetermined pressure increase that, when the coating colour sample still contains captured air, decreases the volume of the coating colour sample and increases its density along with means for determining the decrease of volume / increase of density with the predetermined increase in pressure.

According to the invention the means for exposing the coating colour sample to the predetermined increase of pressure comprises means for application of compressed gas, preferably compressed gas in direct contact with the coating colour sample. With the preferred embodiment shown in the drawings the means for applying compressed gas in the coating colour analyzer comprises a conduit 24 provided with a third valve V3 from a source of compressed air (not shown), which compressed air conduit 24 is connected to the outlet conduit 23 from the measurement vessel 21 at a point upstream the second valve V2.

The coating colour analyzer further suitably comprises a pressure release conduit 25 provided with a fourth valve V4, which conduit 25 is connected to the compressed air conduit 24 at a point downstream third valve V3. The pressure release conduit 25 is preferably used before the supply of compressed air to the measurement vessel 21 to ensure that the measurements that will be carried out at atmospheric pressure are not carried out at a different pressure. The pressure release conduit 25 is further used when the last measurement at increased pressure has been carried out to lower the pressure in the measurement vessel 21 to atmospheric pressure.

It is also suitable that the coating colour analyzer also comprises a conduit 26 from a water source (not shown) provided with a fifth valve V5, which water conduit 26 is connected to the supply conduit 22 for coating colour to the measurement vessel 21 at a point downstream the first valve Vl, and a conduit 27 provided with a sixth valve V6 for outlet of used water. In the shown embodiment the outlet conduit 27 for used water is connected to the coating colour supply conduit 22 downstream the connection of water conduit 26. Valves V5 and V6 are mainly used only with manually controlled water calibration.

In the shown preferred embodiment the measurement vessel 21 has the form of an elongated (approx. 3 - 7 times the diameter) vertical pipe with a conically narrowing bottom 21' that transforms into the coating colour inlet conduit 22 and a conically narrowing top 21" that transforms into the coating colour outlet conduit 23. The measurement vessel 21 has a diameter in the order of magnitude of 0.05 - 0.3 m, preferably approx. 0.1 m. Bottom 21' and top 21" taper off to a pipe dimension that is generally called one-inchers. Both the measurement vessel and the connecting conduits and valves are made of non-corroding, durable material, preferably stainless steel.

The means for determining the decrease of volume / increase of density preferably comprises a PLC 28 and sensors 29, 30, and 31 mounted in the measurement vessel, which are connected to PLC 28 for detection of temperature along with pressure and density. The temperature sensor 29 is suitably of conventional design and has a metering range of 0-100 ⁰C with a permitted inaccuracy of ± 0.5 %. The pressure sensor 30 is also suitably of conventional design and has a metering range of up to 10 bar (1 MPa). The PLCis understood in the present context as a programmable conventional control system, i.e. electronic equipment with a programmable memory for storage of instructions for control and regulation of industrial processes. The equipment is further accommodated to the industrial environment so that it survives disturbance from electrical and magnetic fields as well as from vibration and moisture.

The density sensor is suitably constituted of a nuclear density meter 31. Meters of this kind are especially sensitive to air, which makes them especially suitable for measuring the amount of air in fluid suspensions that contain air. A suitable radioactive source is isotope Cs-137 that emits gamma radiation with a typical level of activity of 1.85 GBq (50 mCi). Radiation sources of this kind are marketed by well-known manufacturers and produced according to applicable requirements from ISO class C66445 and corresponding "IAEA special form requirements GB/23/S". A suitable density meter is DT-9300 from Sensor Technology AS (S-Tec AS) in Gralum, Norway, which has been developed for exact, continuous, and contact- free density measuring of fluids and suspensions in pipes. When the density meter is mounted externally on tubular measurement vessel 21 by means of a simple clamp, the density meter's radiation source 32 sends a collimated gamma ray toward its detector 33, which registers the amount of gamma radiation that is not absorbed by the sample of coating colour inside measurement vessel 21. Other nuclear density meters and other radioactive isotopes may, of course, also be used. It is also suitable that a sensor 34 for detection of viscosity is mounted in the measurement vessel 21 and connected with the PLC 28. AU valves are preferably provided to be opened and closed by the PLC 28, whereby the coating colour analyzer 20 may easily be designed to work automatically and cyclically.

The valves V1,V2, V4, and V6, are suitably regulation valves, for example program- controlled ball valves, and V3 and V5 are shut-off valves, for example program- controlled magnet valves. In this way the desired pressure changes in measurement vessel 21 are carried out in accordance with predetermined ramping up and predetermined ramping down. In order to avoid with certainty that the coating applicator 2 in the coater 1 may be exposed to a pressure shock during the course of analysis, a bypass valve (not shown) can be arranged in a conduit (not shown) outside of the coating colour analyzer.

A measurement cycle carried out on the PLC 28 runs preferably through the following procedural steps in the order given below. The regulation valve V4 first opens in the pressure release conduit 25 so that any required pressure release in the system occurs. The pressure is then preferably controlled in the measurement vessel 21 with the pressure sensor 30. If the pressure is then different from atmospheric pressure, the PLC 28 emits an alarm signal. When the pressure in the measurement vessel 21 is estimated to be equal with the atmospheric pressure, the regulation valve V4 closes and the PLC 28 checks that all valves are closed. The valve V2 then opens in the coating color outlet conduit 23 from the measurement vessel 21 after which the regulation valve Vl in the coating color inlet conduit 22 opens in accordance with predetermined up-ramping. The coating colour will now flow through the measurement vessel 21 for a first predetermined time, which mainly is less than ten minutes and normally approx. 40 seconds are sufficient. During this time, or at least in its final phase, it is suitable that the viscosity sensor 34 samples the viscosity values (for example every fifth second), i.e. measures the dynamic viscosity of the coating colour and the measured value is stored. The first regulation valve Vl in the coating colour supply line then closes in accordance with the predetermined ramping and the valve V2 in the coating colour outlet conduit 23 also closes. In certain cases regulation the valve V4 in the pressure release conduit 25 may also open. After a stabilization period, mainly about one half to one minute, temperature, pressure, density, and static viscosity are measured at atmospheric pressure by respective sensor 29, 30, 31, and 34 and the values are stored. This is suitably done by collecting the average pressures or density values for a given time interval (for example 60 sec.) while the viscosity values are sampled.

The valve V3 in the compressed air conduit 24 is then opened (with the regulation valve V4 in the pressure release conduit 25 closed) for pressurizing the coating colour sample in the measurement vessel 21. With valve V3 open, the coating colour analyzer is now inactive for a predetermined time while the coating colour sample is being compressed by compressed air. Measured values are then sampled for a suitable period of time, for example approx. one half minute, for desired parameters, suitably temperature, pressure, density, and pressurized static viscosity.

Alternatively, the valve V3 is opened in the compressed air conduit 24 for pressurization of the coating colour sample in the measurement vessel 21 to a predetermined initial pressure, mainly in the order of magnitude of 2.5-3 bar. The pressure rises towards this constant value within a few seconds. Measured values from the density sensor 31 will, however, follow a curve that shows compression of air bubbles in the coating colour. Instead of setting pressure and time as hi the case above, values are now sampled from the density sensor until a constant density signal is obtained, after which the meter reads in the density value. In the next step the pressure is increased to a predetermined value, for example 0.3 bar, a new reading of the density signal is made, and the density value is stored. If both density values are not equal, the pressure is again raised and the two latest density values are compared. This procedure is repeated until the density values are equal or a predetermined maximum pressure is reached. In the latter case the density signal at maximum pressure is chosen as final value and the density value and the pressure are stored.

According to a further alternative pressure is added via V3 to a higher level directly, for example 4 bar, and then monitored for a longer period, approx. 2 - 3 min, whereby average values of density, pressure, and temperature are sampled during a final phase (for example 20 sec).

The stored measured values are processed in the PLC 28 and the result is given as, for example, dry matter content expressed in %, air content expressed in %, and viscosity expressed in cP.

With a preferred control that there is no leakage in coating colour analyzer 21 the PLC 28 then closes compressed air valve V3. After a short while, for example 5 seconds, the pressure is read a first time and after approx. one half minute a second time. If the pressure has decreased, the coating colour analyzer 21 is leaking and a leakage alarm is activated. Finally, the regulation valve V4 opens in the pressure release conduit in accordance with the predetermined ramping and the measuring cycle can start again.

Before restarting the measuring cycle it may, however, be suitable to clean the coating colour analyzer 1. For this purpose it may include a conduit 26 provided with a fifth valve V5 from a water source (not shown), which water conduit 26 is connected to supply conduit 22 for coating colour to the measurement vessel 21 at a point downstream from first valve Vl, and conduit 27 provided with a sixth valve V6 connected downstream the water conduit 26 for outlet of used water.

The PLC 28 may of course also be used for other purposes than to carry out coating colour analysis according to the invention and present the result. It may, for example, be suitable that it also controls mixing of the coating colour.

Claims

PATENT CLAIMS

1. A procedure for on-line analysis of coating colour, whereby a. a sample of coating colour is taken out from an on-line flow of deaerated coating colour to a coater (1) and put in a measurement vessel (21), b. the measurement vessel (21) is sealed, c. the sample of coating colour in the measurement vessel (21) is exposed to a predetermined increase of pressure that, when the sample of coating colour still contains captured air, decreases the volume of the sample of coating colour and increases its density, and d. the decrease of volume/increase of density at the predetermined increase of pressure is determined , characterized in that e. the predetermined increase of pressure is attained by application of compressed gas, preferably compressed air, (from V3) in direct contact with the sample of coating colour.

2. A procedure according to claim 1, characterized in that the coating colour is made to flow through said measurement vessel (21) for a predetermined time, and that the dynamic viscosity of the coating colour is measured during at least part of this predetermined time and the measured value is stored.

3. A procedure according to claim 2, characterized in that flow of coating colour to the measurement vessel (21) is then stopped and the coating colour in the measurement vessel (21) is allowed to stabilize for a first predetermined amount of time.

4. A procedure according to claim 3, characterized in that the static viscosity, temperature, and density of the coating colour is determined at atmospheric pressure and the measured values are stored.

5. A procedure according to claim 4, characterized in that the measurement vessel (21) is sealed and said application of compressed air (21) is made in direct contact with the sample of coating colour.

6. A procedure according to claim 5, characterized in that the coating colour in the measurement vessel (21) is allowed to stabilize during a second predetermined amount of time, after which static viscosity, density, pressure, and temperature are determined.

7. A procedure according to claim 5, characterized in that the coating colour in the measurement vessel (21) is pressurized by means of compressed air to a predetermined starting pressure and measured values from a density sensor (31) are sampled until a first constant density signal is reached, after which the pressure from the compressed air is increased to a second predetermined value and a new reading of density values is carried out until a second constant density signal is reached.

8. A procedure according to claim 7, characterized in that if the two constant density signals are not equal, the pressure from the compressed air is increased to a third predetermined value and a new reading of density values is carried out until a third constant density signal is reached, which is compared with the second constant density signal.

9. A procedure according to any of claims 6-8, characterized in that the density is measured with a nuclear density meter (31).

10. A procedure according to any of claims 6-9, characterized in that after any required processing the read-in measured values are presented as dry content, air content, temperature, and viscosity.

11. A coating colour analyzer for on-line analysis of coating colour, comprising a. a measurement vessel (21), b. means for removing a sample of coating colour from a flow of deaerated coating colour to a coater (1), which means comprises an inlet conduit (22) to the measurement vessel and an outlet conduit (23) the from measurement vessel (21), b. means for sealing the measurement vessel (21), which sealing means comprises a first valve (Vl) in the inlet conduit (22) and a second valve (V2) in the outlet conduit (23), c. means (24, V3) for exposing the coating colour sample in the measurement vessel (21) to a predetermined increase of pressure that, when the sample of coating colour still contains captured air, decreases the volume of the sample of coating colour and increases its density, and d. means (28, 31) for determining the decrease of volume / increase of density with the predetermined increase of pressure, characterized in that e. the means for exposing the sample of coating colour to the predetermined increase of pressure comprises means (24, V3) for applying compressed gas preferably compressed air, in direct contact with the sample of coating colour sample.

12. A coating colour analyzer according to claim 11, characterized in that the means for applying compressed air comprises a conduit (24) provided with a third valve (V3) from a compressed air source, which compressed air conduit (24) is connected with the outlet conduit (23) from the measurement vessel (21) at a point upstream the second valve (V2).

13. A coating colour analyzer according to claim 12, characterized in that it further comprises a pressure release conduit (25) provided with a fourth valve (V4), which conduit (25) is connected to the compressed air conduit (24) at a point downstream the third valve (V3).

14. A coating colour analyzer according to any of claims 11-13, characterized in that it further comprises a conduit (26) provided with a fifth valve (V5) from a water source, which water conduit (26) is connected to the supply conduit (22) for coating colour to the measurement vessel (21) at a point downstream the first valve (Vl) and a conduit (27) provided with a sixth valve (V6) for outlet of used water.

15. A coating colour analyzer according to any of claims 11-14, characterized in that the means for determining the decrease of volume / increase of density comprises a PLC (28) and sensors (29-31) mounted in the measurement vessel (21) for detection of temperature, pressure, and density, which are connected to the PLC (28).

16. A coating colour analyzer according to claim 15, characterized in that the density sensor (31) is a nuclear density sensor.

17. A coating colour analyzer according to claim 15 or 16, characterized in t h a t a sensor (34) for detection of viscosity is also mounted in the measurement vessel (21) and connected to the PLC (28).

18. A coating colour analyzer according to any of claims 15-17, characterized in that all valves (V1-V6) are arranged to be opened and closed by the PLC (28).

19. A coating colour analyzer according to claim 18, characterized in that the first and the fourth valve (Vl resp. V4) are regulation valves and the remaining ones (V2, V3, V5,V6) are shut-off valves.