EP0057968A2

EP0057968A2 - Making paint or the like

Info

Publication number: EP0057968A2
Application number: EP82300057A
Authority: EP
Inventors: Robert William English
Original assignee: MASTERMIX ENGINEERING Co Ltd
Current assignee: MASTERMIX ENGINEERING Co Ltd
Priority date: 1981-02-11
Filing date: 1982-01-07
Publication date: 1982-08-18
Also published as: EP0057968A3

Abstract

Dispersion apparatus for making paint has the powder delivered to the pot containing the solvent through a tube which dips slightly below the surface of the solvent, and the interior of the pot is maintained at sub-atmospheric pressure to cause induced flow of powder directly into the solvent. This greatly reduces ambient atmospheric pollution and rapid and efficient dispersion.

Description

This invention relates to the manufacture of suspensions of solids in liquids, for example paints, inks and the like in which powdery material is dispersed in solvent.
It is known to use an apparatus comprising a pot or container, and one or more impellers which are rotatable about a vertical axis or axes, at least one of the impellers being mounted for vertical movement so that the location of the maximum agitation zone relative to the depth of the pool of liquid can be adjusted. Commonly the container is closed by a cover which may have one or more inlet openings through which the powdery material can be delivered, often in stages. Where paint is being made to a particular specification, the various ingredients will be charged into the container successively, usually with dispersion of each previous increment completed before the next commences.
Our European Patent No. 0000827 describes an apparatus of this kind with the additional feature that the impeller or agitator is adjusted in position automatically.
Where large volumes of the same material are to be made, it is known to feed powders by screw conveyors or pneumatically from silos, to discharge through the cover into the container. Where small .quantities are to be made, or even if large quantities are to be made but in batch fashion with a change to a different type of material being made in the next use of the apparatus, these methods are inconvenient because of the risk of the materials used in one operation contaminating those used in a successive t operation: in such cases the materials are usually loaded manually.
All of these methods are in fact prone to contamination and create environmental pollution in the vicinity of the apparatus.
The object of the present invention is to provide improvements and avoid these difficulties.
In accordance with the invention a method of making a viscous liquid or paste using a dispersion apparatus includes the steps of introducing the solvent or other liquid into the dispersion vessel, closing the same, reducing the pressure in the vessel, and by the reduced pressure inducing flow of powder material into the vessel through an outlet disposed below the surface of the liquid.
Also in accordance with the invention, apparatus for making a viscous liquid or paste comprises a closed container, at least one agitator in the container, means for raising and lowering the agitator, and is characterised in that the container is connected to an extractor for lowering the pressure in the container, and in that at least one powder supply duct extends into the vessel so as to terminate below the liquid surface in the vessel.
Further features of the invention will become more apparent from the accompanying description of a presently preferred embodiment of the invention, illustrated in the accompanying drawing wherein the sole figure is a somewhat diagrammatic and part sectional elevation.
Referring to the drawing, the dispersion apparatus comprises a container 10 provided with a sealed lid 12 and a first low speed impeller 14 which is spaced close to the wall and base of the vessel. The impeller 14 may be driven by an underslung motor (not shown).
The apparatus is also provided with a high speed agitator or impeller 16 carried on a shaft 18 driven from a motor 20 and the whole of the parts 16 to 20 are arranged to be raised and lowered by a hydraulic system 22 mounted on the exterior wall of the vessel.
In accordance with the invention and in this particular embodiment, the shaft 18 runs co-axially in a powders delivery tube 24 which terminates very slightly above the agitator 16, and which slides in an appropriate gland 26 in the lid of the container. The duct 24 is connected through a flexible hose 28 and a fixed hose system 30 to a silo 32, and the silo may be located in a different room or even in a different building, and the wall 34 is simply illustrative of the fact that it is unnecessary for the silo to be located in the same confines as the dispersion apparatus per se.
The container 10 is connected to an extractor fan (not shown) by way of a pipe 36 opening from the container cover. An atmospheric pressure within the container of about minus 0.2 bar has been found to be very suitable.
It will be appreciated by the skilled engineer that there is a relationship between the pressure differential (between the interior of the container and atmosphere) and the extent of immersion of the tube 24, but in any event it is preferred to arrange so that the bottom end of the tube 24 is only a few centimeters (typically of the order of 3 to 6 centimeters) below the surface of the liquid whilst the agitator is in use - and it will be borne in mind that the surface is not then level and planar but may be somewhat as indicated in the drawing.
The arrangements for powder supply may include a fluidising valve ensuring free flow from the silo into the duct 30, and effectively air admitted at the end of the duct for example via valve 38 and used in conveying the powder through the duct is subsequently extracted via the pipe 36 in order to maintain the pressure differential.
Experiments have shown that large amounts of powdery material can be dispersed into the solvents extremely efficiently, economically, and rapidly. On stripping the experimental apparatus subsequently, it has been found that very little trace remain in the duct system including the tube 24 even when notoriously difficult to handle powders have been used.
However, to simplify cleansing of the apparatus when it is to be used for batch treatment and to produce batches of different materials from time to time, there may be an additional solvent inlet provided in the vicinity of the valve 38 and again in the vicinity of the joint between the hose 28 and the tube 24, so that solvent may be flowed over the surfaces to remove final traces of previously used powders.
It is desirable to provide a particularly efficient seal at the top end of the shaft 18 and between it and the motor 20, but again, the motor design may be such as to allow bleed of air around the shaft via the seal so that there is a positive flow downwardly of the shaft 18 and this itself reduces the risk of loss of powder, or of contaimination of the motor with powder.
The drawing illustrates an arrangement in which a single powder store is connected via a single hose and duct system. In practice, it will be appreciated, a plurality of hose systems will be useful, for example connected to different silos or powder storage hoppers', or possibly the hose 30 may be provided with a number of branches connected to different powder supply sources, and with appropriate valves to control the flow therefrom, so that (usually) one ingredient is dispersed in the solvent before the second one is introduced, and so on.
Where a plurality of ducts extend through the lid into the container, they may be grouped about the impeller shaft 18 instead of being concentric therewith.
The automatic control system of said European Patent No. 0000827 may be found particularly useful with the present invention, in enabling the dip tube or tubes conveying the powders to be automatically raised with the agitator so that the extent of their immersion is maintained substantially constant.

Claims

1. A method of making a viscous liquid or paste using a dispersion apparatus includes the steps of introducing the solvent or other liquid into the dispersion vessel and closing the same, and is characterised in that the pressure in the vessel is reduced, and flow of powder material into the vessel through an outlet disposed below the surface of the liquid is induced by the reduced pressure.

2. Apparatus for making a viscous liquid or paste comprises a closed container, at least one agitator in the container, and means for raising and lowering the agitator, and is characterised in that the container is connected to an extractor for lowering the pressure in the container, and in that at least one powder supply duct extends into the vessel so as to terminate below the liquid surface in the vessel.

3. Apparatus as claimed in Claim 2 wherein the impeller shaft extends co-axially of and through the duct.

4. Apparatus as claimed in Claim 2 wherein the powder supply duct is provided with an air inlet at the end remote from the apparatus.