GB2232418A - Manufacture of highly structured paints - Google Patents

Abstract

A method and apparatus are described for making highly structured paints, of the type popularly referred to as "solid" paints. These paints consist of substantially ordinary water-based paints to which a gelling agent has been added to give the paint a shape-retaining quality. The invention relates to a method and apparatus for improved mixing of the base paint and gelling agent by pumping both in a substantially continuous flow into and through a mixing chamber thus removing the need for any batchwise mixing.

Description

Manufacture of highly structured paints This invention relates to a method and apparatus for making highly structured paints, known in the trade nowadays as "solid" paints. Although solid paints are currently in vogue commercially they have been known for many years as "jelly" paints and simply consist of substantially ordinary water-based paints to which a relatively large amount of structuring, or gelling, agent is added to give the paint a shape retaining quality.

Such paints have conventionally been made in batches. The base paint is run into a mixing vessel, the gelling agent is added and the already gelling paint is pumped or run into the eventual packaging containers where it is allowed to set for a few weeks before being dispatched and sold. However this manufacturing method suffers from drawbacks which make the resultant paint of varying quality and more expensive than necessary, for the following reasons.

The relatively large proportions of gelling agent necessary to achieve the final desired gel strength causes the paint to begin to set very quickly. In order to keep the mix suitably liquid in order to flow into the packaging containers, it is necessary to keep stirring it. This keeps the paint liquid but the paint is sensitive to the shearing effect of stirring and this reduces the final gel structure. For this reason a greater quantity of gelling agent is added that would otherwise be required so that the last of the batch, after stirring, retains a sufficiently high gel strength. However this greater quantity of gelling agent causes the first containers of the batch to have a gel strength greater than intended, and therefore inconsistent structure throughout the batch.

A compromise must therefore be reached whereby the first of the batch is not too solid and the last of the batch does not have its gel structure broken down too much. As part of this compromise, the stirring time is reduced to a minimum, and as there is a limit to the speed of packaging this means that, of necessity, the batches have to be kept small, such as for example to 250 litres. For volume production this means that a large number of mixing vessels must be used and a corresponding number of staff employed to operate them.

Thus the manufacturing cost of such paints is increased by (a) the extra amounts of gelling agent required and (b) the extra labour costs.

It is an object of this invention to provide a method and apparatus for manufacturing highly structured paints which is free of the above disadvantages and leads to an improved quality of product and lower manufacturing costs.

According to the invention there is provided a method of making a highly structured paint comprising the following steps: (a) pumping base paint from a storage container in a substantially continuous flow into and through a mixing chamber, (b) pumping a controlled quantity of gelling agent in a substantially continuous flow into and through said mixer chamber whereby the gelling agent is combined and mixed with said base paint, (c) passing said mixture into a collecting vessel for transient storage therein, and (d) transferring said mixture from the collecting vessel into packaging containers.

The advantages afforded by the invention will be immediately apparent. The improvement lies basically in the omission of any batchwise mixing. Because the paint mixture moves in a substantially continuous flow according to the invention it is possible to dose into the base paint the precise amount of gelling agent required to attain the final consistency, and this amount, for example 0.8% of the total mix can be preset and will remain constant.

The invention also extends to apparatus for carrying out the method, and accordingly viewed from another aspect the invention provides apparatus for manufacturing highly structured paint comprising the following: (a) a storage vessel for base paint connected by a line to a drive pump, (b) a storage vessel for gelling agent connected by another line to a drive pump, (c) outlet lines from said pumps leading to a common mixing chamber, (d) an outlet line from the mixing chamber passing to a storage vessel where the mixed paint can be transiently stored, (e) an outlet line leading from said storage vessel to a filling station where the mixed paint is transferred to packaging containers.

Again it will be seen that this apparatus enables the paint to be thoroughly mixed in a continuous stream and require only transient storage before being passed into packaging containers for subsequent gellation. The mixing process is completed relatively quickly so that the paint remains liquid even in its transient storage so that it remains sufficiently liquid to make it readily handlable at the filling station.

In a preferred embodiment the pumps for the base paint and the gelling agent are driven by a common motor and drive shaft. This is an important feature because it ensures that once the machine is set up the relative proportion of gelling agent to base paint remains constant no matter what the speed of the motor is. If for example the pumps are of the cylinder/piston kind the cross-section of the gelling agent pump is of course considerably smaller than that of the base paint pump but their strokes are synchronised so that precisely the right quantity of gelling agent can be injected into the main stream.

A further preferred feature is that the mixing chamber is that of a static mixer rather than a dynamic mixer. A static mixer consists basically of a tube with a number of internal inwardly directed elements around which the continuously flowing mixture streams causing turbulence and eddies imparting to the mixture a thorough mixing effect.

In one embodiment the gelling agent line passes directly into the static mixer whereas in another preferred arrangement the line passes into the base paint line upstream of the mixer. In either arrangement the actual injection is preferably accomplished by a transverse tube in the base paint stream and having a plurality of downstream directed fine apertures. In this way the gelling agent is injected into the flowing base paint at a high velocity causing local turbulence and reducing the risk of localised gelling.

In order to ensure that the velocities of the base paint and gelling agent are equal and constant as they enter and pass through the static mixer, there is preferably provided a constant pressure check valve downstream of the mixer in the outflow line.

In order to prevent base paint flowing backstream in the line from the gelling agent pump and clogging the same, there is preferably provided in that line a nonreturn valve.

The speed of the double pump is preferably controlled by an AC inverter which may provide for damped or adjustable acceleration and deceleration. The speed of the pumps is adjusted via the AC invertor to match the throughput of the filling station and ensure that the level of mixed paint in the temporary storage vessel remains substantially constant. However should the filling station cease functioning for any reason and the level of paint in the storage vessel therefore rise, there may be provided a level switch in the vessel serving to turn off the pumps via the AC invertor until the filling station recommences operation and the level of mixed paint in the storage vessel falls.

Conventionally, paint of the kind with which the invention is concerned is sold in flat trays rather than cans. Because the paint is already thickening when it reaches the filling station, it has in the past exhibited a tendency to heap in the tray when the metered amount is pumped in. This means that the tray must be shaken and perhaps a comparatively long period of time must elapse before a lid can be placed on the tray. In a particularly preferred embodiment of the invention this difficulty is overcome by providing at the filling station two filling nozzles above each packaging tray. This arrangement has been shown to substantially reduce the heaping effect. The nozzles may be a twin pair fed by a common line and pump, or alternatively each nozzle may be associated with its own pump.

A number of further advantages are obtained by the invention. For example, highly structured paint made by prior art methods needed about three weeks gellation time to attain its desired structure. In contrast, paint made according to the invention requires only about two weeks storage. This brings an economic advantage because it reduces the amount of stock required to be kept in hand. There is a more consistent uniformity of product according to the invention, and less labour is required, particularly in cleaning, than in the previous batching process. Less gelling agent is needed than in the prior art, and although this may only make a saving of one or two pence per packaging container, over a year and in the quantities which a modern plant needs to put through this can amount to a saving of tens of thousands of pounds.

In order that the invention may be readily understood an embodiment thereof will now be described with reference to the accompanying drawing which shows schematically an apparatus according to the invention for producing a highly structured paint.

Base paint is stored in the left hand storage vessel 1 which is provided with a stirrer 2 driven by a motor 3 mounted on the vessel. The base paint enters via a port 4. The vessel is mounted on a weighing assembly 5 enabling the amount of paint left in the vessel to be determined.

A base paint line 6 leaves the vessel and contains a control valve 7 and a expandable and contractable portion 8 allowing the vessel 1 to move up and down on its weighing assembly 5. The line, which is a 7.5 centimetre line then passes to a second control valve 9, through a filter 10 before reaching the base paint pump 11 between the filter 10 and pump 11 is a water supply inlet 12 allowing water to be pumped in to flush the system out.

The gelling agent is stored in the right hand storage vessel 13 whose outflow line leaves through a pair of control valves 14, 15 to a filter 16 before reaching gelling agent pump 17. Again there is a water supply inlet 18 for flushing through the system.

The pumps 11 and 17 are mounted on a common shaft 19 driven by motor 20 which itself is controlled by an AC inverter (not shown). The individual strokes of the respective pumps can be adjusted but once set remain in constant proportion to each other ensuring that precisely the right proportion of gelling agent to base paint is provided.

In the outflow line 21 from the pump 17 is a nonreturn valve 22 preventing base paint from flowing back into the pump where it might react and set causing difficulty. The outflow line 21 passes into a static mixer 23 which is also supplied with base paint by the line 24 leading from pump 11. The static mixer 23 comprises for example a STATFLOW 316 (Trade Mark) which is a stainless steel mixer having sixteen elements or baffles. The line 21 passes into the mixer and is connected to a transverse pipe containing downstream directed fine apertures whereby the gelling agent is squirted into the main flow.

The base paint and gelling agent are mixed thoroughly in the mixer 23 under pressure provided by the constant pressure check valve 25 disposed in the outflow line 26 from the mixer. The outflow line then continues to enter the collecting vessel 27 where the mixed paint is transiently stored before being passed on to the filling station (not shown). The collecting vessel 27 is provided with a level limit switch 28 operated by a float 29 whereby power to the motor 20 is turned off if the paint level in vessel 27 exceeds a predetermined amount.

Collecting vessel 27 is in the form of a hopper and the outflow line 30 after a control valve 31 contains a filter 32 upstream of a metering pump 33 which supplies the correct quantity of paint in discrete doses to a filling head whence it passes into its storage trays.

As mentioned above, two filling heads per tray are preferably provided in order to avoid heaping and indeed two pumps may be provided one for each filling head.

Claims (11)

1. A method of making a highly structured paint comprising the following steps: (a) pumping base paint from a storage container in a substantially continuous flow into and through a mixing chamber, (b) pumping a controlled quantity of gelling agent in a substantially continuous flow into and through said mixer chamber whereby the gelling agent is combined and mixed with said base paint, (c) passing said mixture into a collecting vessel for transient storage therein, and (d) transferring said mixture from the collecting vessel into packaging containers.

2. Apparatus for manufacturing highly structured paint comprising the following: (a) a storage vessel for base paint connected by a line to a drive pump, (b) a storage vessel for gelling agent connected by another line to drive pump, (c) outlet lines from said pumps leading to a common mixing chamber, (d) an outlet line from the mixing chamber passing to a collecting vessel where the mixed paint can be transiently stored, (e) an outlet line leading from said collecting vessel to a filling station where the mixed paint is transferred to packaging containers.

3. A method or apparatus according to claim 1 or 2 in which the pumps for the base paint and the gelling agent are driven by a common drive.

4. A method or apparatus according to claim 1, 2 or 3 in which the mixing chamber is that of a static mixer.

5. A method or apparatus according to claim 4 in which the gelling agent line passes directly into the static mixer.

6. A method or apparatus according to claim 4 in which the gelling agent line passes into the base paint line upstream of the mixer.

7. A method or apparatus according to claim 5 or 6 in which injection of the gelling agent is accomplished by a transverse tube in the base paint stream and having a plurality of downstream directed fine apertures.

8. A method or apparatus according to any of the preceding claims including a constant pressure check valve downstream of the mixing chamber.

9. A method or apparatus according to any of the preceding claims in which the speed of the pumps is controlled by an AC inverter.

10. A method or apparatus according to any of the preceding claims in which the paint is deposited into packaging trays and in the filling station two filling nozzles are provided above the tray filling position.

11. A method or apparatus for manufacturing a highly structured paint substantially as hereinbefore described with reference to the accompanying drawing.