Abstract:
An apparatus and process for the continuous preparation of a mixture of two or more fluids, such as paints, enamels and dyes, to produce a resulting fluid having desired pre-defined physical properties, such as a particular color, opacity, hue, saturation, luminosity, density and/or viscosity, with automatic adjustment of the physical characteristics of the resulting fluid mixture. The apparatus comprises storage devices, a mixer, a fluid supply device, a detector, and a control device. The control device is adapted to receive a signal from the detector, the signal representing the detected physical characteristic of a fluid supplied by the fluid supply device, and to compare the detected physical characteristic with a desired physical characteristic of the fluid. Depending on the comparison between detected and desired physical characteristics, a fluid supply control signal is sent to the fluid supply device which varies the proportion of each component of the fluid supplied to the mixer, until the detected physical characteristic is substantially the same as the desired physical characteristic.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and process for the continuous preparation of a mixture of two or more fluids, such as paints, enamels and dyes, to produce a resulting fluid having desired pre-defined physical properties, such as a particular color, opacity, hue, saturation, luminosity, density and/or viscosity. 
     BACKGROUND ART 
     Paint production processes have, over the years, evolved from the traditional method of using joint dispersion of pigments to the use of colorimetric processes where there is dispersion of each of the pigments separately to form a set of concentrated pigments (concentrates) and bases which are mixed together at the time of production of the paint to give a determined color. Such colorimetric processes can be classified in two categories, those with adjustment and those without adjustment. 
     In paint production processes with adjustment, the concentrates are mixed with resins and solvents, or, optionally, with determined bases, and the properties of the resulting mixture are measured. If the measured properties vary from the required specifications, an adjustment is made by the addition of ingredients capable of correcting the variations. 
     Paint production processes with adjustment are used in factories for the production of medium to large quantities of paints. Mixing occurs in large vats and the end product is only transferred to the final container after confirmation that its properties are within the specified limits. 
     In paint production processes without adjustment, the base and concentrates are supplied directly to the final container, after which the mixture is homogenised and the paint is ready for use. In such a production process there is no possibility for verification of and adjustments to the end product, and for this reason the base and concentrates have to have rigorously specified properties, and dosage of the base and concentrates has to be carefully controlled so that the end product meets the required specifications. 
     Paint production processes without adjustment are used, where the paint is to be produced at point of sale, for the supply of relatively small quantities of paint, having a wide range of colors and shades. Such processes can also be used in the factory for the production of small batches of paint. 
     In processes without adjustment, it is essential that the bases and concentrates are produced within strict limits of variation in color, opacity or hiding power, viscosity and density. The problem with such processes is that it is very difficult to produce the concentrates and bases within such strict limits of variation, only being possible with rigorous control and adjustment, making the process expensive and slow. 
     The need for such stringent standards of control and the requirement for adjustment mean that the process of producing the bases and concentrates is lengthy and expensive. 
     The normal methods of controlling and adjusting the bases and concentrates of each batch of paint consist of preparing the concentrate, or base, by culling with standard bases, applying a coat of paint to a substrate, then drying the paint followed by analysis of the color, hiding power and opacity (in the case of the bases) of the dried coat of paint, using visual or preferably spectrophotometric reflection methods. If the paint varies in any of its properties from that which is required, then further ingredients are mixed to compensate for the variation. Once these further ingredients have been added, the resulting concentrate or base is again analysed, and if it is still outside the tolerances for variation of any of the paint properties, another cycle of compensation and analysis is begun. Such a procedure is normally very time consuming, taking days before the paint batch is within its specified tolerance limits. 
     Also, apart from being time consuming, the traditional methods tend to be very wasteful of paint, because each test batch that does not meet the necessary requirements for color, opacity or hiding power is discarded, without re-using the paint. This can be extremely expensive where a large number of adjustments have to be made before the paint comes within the required specifications. 
     Efforts to solve such problems have been made, notably, U.S. Pat. No. 4,403,866 describes an apparatus and process for automatically making a paint having the color values of a standard paint, in which components of paint are fed into a mixer where they are combined, and the resulting combination is analysed spectrophotometrically to determine whether it comes within a desired color value. If the paint is not of the desired color, the ratio of paint components fed to the mixer is adjusted until the paint has the required color. Paint mixture that has been analysed and which does not meet the requirements is recycled continuously back into the mixer so that no paint is wasted. However, because the analysed paint is pumped directly back into the mixer the desired component ratio cannot be determined exactly. 
     There is, therefore, a need for a process in which both concentrates and bases can be analysed and their component ratios can be corrected quickly and simply, and in which paint that does not meet the specified requirements can be re-utilised by the system without adversely affecting the determined component ratios. 
     In order to cut down paint production costs to a minimum such a process needs to be automatic, with the minimum of human intervention, and to use apparatus which is capable of measuring the properties of the concentrates and bases, determining the ingredients, and quantities thereof required to correct any variations from the required physical properties of the concentrate or base, automatically supplying the correct amount of ingredients necessary to make the correction, and needs to be capable of guaranteeing that the final product has properties that are within the specified limits for the paint. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to provide an apparatus and a process for the continuous preparation of fluids, such as paints, enamels and dyes with automatic adjustment of the physical properties of the fluid, and re-utilisation of any fluid that does not have the required physical properties, in order to overcome the above mentioned problems in the state of the art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, an apparatus for the continuous preparation of a fluid with automatic adjustment of the physical characteristics thereof, comprises: 
     a storage means, for storing a first component of the fluid; 
     at least one further storage means, for storing at least one further component of the fluid; 
     mixing means, for mixing the first component with at least one further component of the fluid, the mixing means having a fluid input and a fluid output; 
     fluid supply means, connected between the storage means and fluid input of the mixing means, for supplying a specified proportion of each of the components of the fluid to the mixing means; 
     detector means, for detecting a physical characteristic of the fluid, the detector means being capable of producing a signal representing the detected physical characteristic, the detector means having a fluid input in communication with the fluid output of the mixing means and having a fluid output; 
     control means, adapted to receive the signal representing the detected physical characteristic, the control means being capable of comparing the detected physical characteristic with a desired physical characteristic of the fluid, and of producing a fluid supply control signal, dependent on the comparison between detected and desired physical characteristics, the fluid supply means being responsive to the fluid supply control signal to vary the proportion of each component of the fluid supplied to the mixing means, until the detected physical characteristic is substantially the same as the desired physical characteristic; and 
     fluid recycling means, connected between the fluid output of the detector means and the input of the mixing means to allow fluid to return to the mixing means; 
     wherein the recycling means comprises buffer means, for temporary storage of the fluid, the control means being adapted to produce a buffer control signal and the buffer means being responsive thereto, for controlled supply of the diluted fluid to the mixing means. 
     For preference, the apparatus additionally comprises fluid dilution means, connected between the output of the mixing means and input of the detector means, for controlled dilution of the fluid before detection of the physical characteristic thereof. 
     Preferably, the fluid dilution means comprises further mixing means. 
     More preferably still, the detector means is adapted to measure the transmission of electromagnetic radiation through the fluid, and the signal representing the physical characteristic is obtained by measurement of the transmission of electromagnetic radiation through the fluid. 
     According to a second aspect of the present invention, a process for the continuous preparation of a fluid with automatic adjustment of the physical characteristics thereof, comprising the steps of: 
     (i)—supplying a first component of the fluid to a mixing means; 
     (ii)—supplying at least one further component of the fluid to the mixing means, each of the components of the fluid being supplied in specified a proportion; 
     (iii)—mixing the components of the fluid; 
     (iv)—supplying the mixed fluid to a detector means; 
     (v)—detecting a physical characteristic of the fluid; 
     (vi)—comparing the detected physical characteristic of the fluid with a desired physical characteristic thereof; 
     (vii)—varying the specified proportion of the components of the fluid being supplied to the mixing means, until the detected physical characteristic is substantially the same as the desired physical characteristic; and 
     —(viii) recycling the mixed fluid supplied to the detector means; 
     such that the step of recycling the mixed fluid supplied to the detector means includes the steps of supplying the fluid to a buffer means and controlling the supply of the fluid from the buffer means to the mixing means, for mixing with the components of the fluid. 
     For preference, the process further includes the step of diluting the mixed fluid before it is supplied to the detector means. 
     Preferably, the step of diluting the mixed fluid includes supplying it to a further mixing means. 
     More preferably still, the step of detecting a physical characteristic of the fluid includes measuring the transmission of electromagnetic radiation therethrough. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 shows a schematic diagram of an apparatus for the continuous preparation of a fluid with automatic adjustment of the properties of thereof, according to the present invention; 
     FIG. 2 shows a schematic diagram of a fluid supply unit for supplying a specified amount of a component of the fluid; and 
     FIG. 3 shows a schematic diagram of a fluid analysis unit for measuring the characteristic properties of the fluid, and a system control unit for controlling the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1 of the drawings, an apparatus for the continuous preparation of a fluid, according to the presently preferred embodiment of the invention, comprises a fluid supply unit  1 , connected to a mixer unit  2 , for mixing the components of the fluid, mixer unit  2  being connected to a fluid analysis unit  3 , for detecting and analysing a specified physical characteristic of the fluid, such as its color, opacity, hue, saturation, luminosity, density, viscosity and/or temperature. Fluid analysis unit  3  is described in detail in patent application PCT/BR96/00046 (see also US national stage patent U.S. Pat. No. 6,288,783, and is included herein by reference. Fluid supply unit  1 , mixer unit  2  and fluid analysis unit  3  are connected to a system control unit  4 , for controlling the functions of units  1 ,  2  and  3 . 
     Fluid supply unit  1  comprises fluid storage tanks  101 ,  102 ,  103 ,  104  and  105 , used for storing the various components of the fluid to be produced. Where the fluid to be produced is a paint, storage tank  101  is typically a large vat which is used for storing a large quantity of either a concentrate or a base that is to have its characteristic physical properties measured and adjusted should they not be according to a previously determined standard. Storage tank  101  is supplied with a fluid stirrer  106 , for ensuring that the fluid is homogenised, and is connected to a valve  107  for controlling release of the fluid to mixer unit  2 . A pump  108  is connected to valve  107  and is used to pump the fluid to mixer unit  2  at a flow rate which, depending on specific requirements, can be varied in the range from 1 to 100 litres/min. Pump  108  is connected to a flow rate meter  110  which measures the flow rate of the fluid being pumped by pump  108  from storage tank  101 . Control unit  4  controls operation of pump  108  depending on the detected flow rate measured by flow rate meter  110 , to ensure that the rate of flow of fluid to mixer unit  2  is constant. 
     Referring now to FIG. 2, each one of fluid storage tanks  102 ,  103 ,  104 ,  105  to n is connected to a dosing apparatus  112 . Dosing apparatus  112  is connected to control unit  4  such that a specified amount of each of the fluid components, required to be added to the fluid for adjustment thereof, can be supplied to mixer unit  2 . 
     Each dosing apparatus  112  comprises a pump  113 , connected to respective storage tank  102 ,  103 ,  104  or  105 . Pump  113  is connected to a control valve  114  and via a first pressure transducer  115  to a filter  116 . Filter  116  is used to filter out solid particles from the fluid and is connected via a second pressure transducer  117  to a set of pumps  118  comprising, three dosing pumps  119 ,  120  and  121 , connected in parallel with each other. During operation, filter  116  can become saturated with particulate matter, and in order to know when this is happening, the pressure difference between pressure transducers  115  and  117  is calculated in real time. Dosing pumps  119 ,  120  and  121  are positive displacement pumps, each having a different operating range. For example, 0-80 ml/min, 0-2500 ml/min, and 0-10000 ml/min. Set of pumps  118  is connected via a third pressure transducer  122  to a valve  123  having two outputs, one connected to mixer unit  2 , the other connected to control valve  114 . Valve  123  allows fluid to be directed either into mixer unit  2 , transducer  122  providing information regarding the pressure of injection into mixer unit  2 , or to be returned to its respective storage tank  102 ,  103 ,  104 , or  105 , in order to avoid sedimentation of the fluid in the connecting pipes when not in use. Control valve  114  is connected to a fluid inlet  124  of storage tank  102 ,  103 ,  104  or  105 , and is used to guarantee supply of fluid to dosing pumps  119 ,  120 , and  121  when the fluid is being injected into mixer unit  2 . Control valve  114  is controlled automatically by pressure transducer  117 . 
     In operation, dosing apparatus  112  receives a control signal from control unit  4  to supply a specified amount of the fluid stored in storage tank  102 ,  103 ,  104  or  105  to mixer unit  2 . Initially, fluid is pumped from storage tank  102 ,  103 ,  104  or  105  by pump  113  and returned via control valve  114  to fluid inlet  124  of storage tank  102 ,  103 ,  104  or  105  until the fluid pressure stabilises at 3 kg/cm 2 . The pressure is regulated by controlled opening of control valve  114 , and is measured by first pressure transducer  115 . Once the pressure has stabilised at 3 kg/cm 2 , one of dosing pumps  119 ,  120  or  121  is activated depending on the dosage of fluid required to be supplied to mixer unit  2 , and valve  123  is opened to allow the fluid to flow in a closed circuit back to fluid inlet  124 . Dosing pump  119 ,  120  or  121  is controlled to vary the pressure of the fluid flowing in the closed circuit until the pressure, measured by third pressure transducer  122 , reaches a pressure of 1 kg/cm 2  above that in mixer unit  2 . Once this pressure has been reached, valve  123  is switched to allow the fluid to flow to mixer unit  2 . The percentage of dosing is related to the velocity of either of dosing pumps  119 ,  120 , or  121 , which are controlled using invariable frequency drives. 
     Referring to FIG. 3 of the drawings, fluid analysis unit  3  comprises an optical unit  5 , for providing a source of electromagnetic radiation to a detection unit  6  and for sensing electromagnetic radiation emitted therefrom. Both optical unit  5  and detection unit  6  are connected to control unit  4 , used for data acquisition and control of the functions of units  5  and  6 , as well as for controlling units  1  and  2 . 
     Optical unit  5  comprises a light source  509  having three outputs  502 ,  503  and  504  for emitting electromagnetic radiation in the visible region of the electromagnetic spectrum. Outputs  502  and  503  are connected to inputs of fiber optic cables  507  and  508  respectively of a standard spectrometer  501 . Source  509  comprises an incandescent halogen lamp or xenon flash lamp emitting a range of wavelengths from 400 to 700 nm, the supply for the lamps being electronically stabilised, and the lamps themselves being monitored with respect to their performance so that they may be changed as soon as they go below specification. 
     Output  504  also receives light from source  509 , which is directed by a fiber optic cable (not shown) to an input  510  (reference channel of spectrometer  501 ). Output  504  serves as a reference for the measurement of the spectra received from detection unit  6 . 
     Optical unit  5  is also provided with an input  511  connected to a fiber optic cable  512  which directs light from detection unit  6  to a detector (not shown). 
     Detection unit  6 , comprises a fluid analysis cell  601  which has a fluid inlet  602  connected to mixer unit  2  and a fluid outlet  603  also connected to mixer unit  2 . Light from optical unit  5  is directed via fiber optic cables  507  and  508  to inputs  604  and  605  for transmission and reflection analysis respectively of the fluid in analysis cell  601 . Input  604  also acts as output for the light transmitted through or reflected from the fluid and is connected to fiber optic cable  512 . 
     Referring to FIGS. 1 and 3, mixer unit  2  comprises a first mixer  201  having an impeller  201   a , a second mixer  202 , having an impeller  202   a , and a fluid buffer unit  203 . First mixer  201  has fluid inlets  204 , connected to the dosing apparatus  112  of each of fluid storage tanks  101 ,  102 ,  103 ,, 104  and  105 , and has two fluid outlets  205 , one connected to a valve  206  and the other, via a flow rate meter  207 , to a first fluid inlet  208  of second mixer  202 . 
     Valve  206  is connected via a pressure transducer  209  and flow rate meter  210  to a system outlet valve  211  which in turn is connected to a fluid return conduit  212  and to a system outlet  213 . 
     Second mixer  202  has a fluid outlet  214  connected to inlet  602  of fluid analysis cell  601  of detection unit  6 , and a second fluid inlet  215  connected via a fluid flow meter  216  to a valve  217 . Valve  217  is connected to the dosing apparatus  112  of each of storage tanks  104  and  105 . 
     Fluid buffer unit  203  comprises a temporary storage tank  203   a , and a dosing pump  220 . Temporary storage tank  203   a  has a capacity of approximately 5 litres and has a fluid inlet  218  connected to outlet  603  of fluid analysis cell  601 , and a fluid outlet  219  connected to dosing pump  220 . Pump  220  is connected to fluid inlet  204  of first mixer  201 , and is activated, depending upon the signal from a level transducer (not shown) provided in storage tank  203   a , so that it continuously re-injects the fluid, which has been sampled and analysed by fluid analysis unit  3 , recycling this sampled fluid into first mixer  201 . 
     The entire system is controlled by control unit  4 , which comprises a programmable microprocessor  401  connected to a microcomputer  402 , for operator control thereof. Microcomputer  402  is provided with analysis and supervision software for analysis and display to an operator of the various parameters of the system. Microprocessor  401  receives and processes both analogical and digital data provided by the various system units  1 ,  2  and  3 , and automatically responds to these signals. Microprocessor  401  activates pump  113  and set of pumps  118  of dosing apparatus  112 , controls the pressure of the fluid in dosing apparatus  112  and the level of the fluids in storage tanks  101 ,  102 ,  103 ,  104  and  105 . Microprocessor  401  also controls the operation of mixer unit  2 , including control of pressure, temperature, rotation of impeller  201   a  and  202   a  etc., and receives signals from optical unit  5  and detector unit  6  of fluid analysis unit  3 . 
     Microcomputer  402  receives analogical signals from microprocessor  401  containing data with respect to the intensity of the light passing through the fluid or reflected thereby and converts these signals into digital data representing the transmission or reflection curve of the liquid as a function of wavelength of the light. This data is sent to a calorimeter software, also provided in microcomputer  402 , which processes and compares these curves with standard transmission or reflection curves contained in a database. The result of this comparison is sent to the supervision software which has a graphical interface for presentation of data relating to each component of the apparatus (units  1 ,  2  and  3 ) to an operator. The supervision software comprises a database containing formulae for the fluid products that the apparatus can produce. 
     With reference to FIGS. 1 to  3  the preferred embodiment of the process for continuous production of a fluid with automatic adjustment of the physical characteristics thereof comprises the following steps: 
     Initially, the operator, using microcomputer  402 , chooses the fluid product which is to be produced from the list of available products in the database of the supervision software. The database contains the formula for the product giving the proportions of each of the fluid components. As soon as the operator instructs the supervision software that a particular product is required, microprocessor  401  sends a signal to fluid supply unit  1  activating pump  108  to pump the fluid to be analysed and adjusted at a rate of 10 litres/min. At the same time, microprocessor  401  sends signals to dosing apparatus  112  of storage tanks  102 ,  103 ,  104  and  105  to provide the correct proportion of fluid components therefrom, depending on the formula for the liquid product stored in microcomputer  402 . Dosing apparatus  112  operates as described previously initially to supply a non-adjusted proportion of each of the required components of the fluid to mixer unit  2 , the non-adjusted proportion of the components being given by the idealised formula stored in the database. 
     Mixer unit  2  receives a signal from microprocessor  401  to operate first mixer  201  by rotating fluid impeller  201   a  to homogenise the fluid which exits from fluid outlet  205 . Initially, valve  206  is adjusted to allow a sample of the mixed fluid to flow, at a flow rate of 0.1 litres/min, to second mixer  202 . The flow rate of the sample is monitored by flow meter  207 , and is used to control the opening of valve  206 , via microprocessor  401 , to maintain a fixed flow rate of sample fluid to second mixer  202 . 
     At the same time as the fluid sample is supplied to mixer  202 , dosing apparatus  112  of either or both of storage tank  104  and/or  105  is activated to supply a fluid dilution component at a flow rate of, for example, 0.9 litres/min to produce a dilution of 900%. The flow rate of the dilution fluid is monitored by flow meter  216 , which provides a signal that is used to control the RPM of metering pumps  104   a ,  104   b  and  105   a ,  105   b  of storage tanks  104  and  105  respectively, via microprocessor  401 , in order to maintain a fixed flow rate of dilution fluid to second mixer  202 . Dilution of the sample is only necessary where the sensitivity of detection unit  6  needs to be increased to produce a transmission spectrum. Such would be the case where the fluid to be produced is a paint concentrate with a high saturation. 
     The fluid sample (undiluted or diluted) passes through fluid analysis cell  601  where it is analysed, the results of the analysis being used by microprocessor  401  to increase or diminish the flow of each of the components of the fluid from dosing apparatus  112 . The delay time, between making an adjustment to the proportion of each of the fluid components and receiving the results of the spectral analysis of the resulting fluid, is calculated as 25.5 seconds. Thus, analysis of the fluid should be carried out every 30 seconds or less. 
     Fluid analysis unit  3  is provided continuously with a sample of the fluid to be analysed coming from second mixer  202 . On exiting from fluid analysis unit  3 , the sampled fluid is directed to temporary storage tank  203   a  of fluid buffer unit  203 , from which it is pumped by pump  220  at a controlled low flow rate into first mixer  201 . As soon as pump  220  is activated the flow rate of dilution fluid, supplied from storage tanks  104  and/or  105  by respective fluid supply apparatus  112  to first mixer  201 , is proportionally decreased in order to compensate for the addition of dilution fluid from buffer  203 . The rate of flow of the diluted sample fluid from buffer  203  to mixer  201  is controlled so that buffer  203  is empty when the required adjustments have been made to the fluid such that it has the required properties. 
     While the fluid sample, mixed by mixer  202  and analysed by fluid analyser unit  6 , does not correspond to the required fluid product, the rest of the fluid exiting from mixer  201  is directed via system outlet valve  211  through fluid return conduit  212  to fluid storage tank  101 . As soon as the fluid sample corresponds to the required product, valve  211  is moved to the discharge position to allow all the fluid flowing from first mixer  201  to flow to system outlet  213 . 
     Sampling of the fluid may be carried out at intervals during production of a batch of the fluid to ensure that it has the required properties. 
     Once a particular batch of fluid has been produced, the apparatus is cleaned automatically by injecting solvent into the system, at a pressure of 7 kg/cm2, together with a nitrogen/air mix. 
     It should be observed that advantageous physical changes to the apparatus itself may be apparent to those skilled in the art, and as such, the scope of the present invention should be limited only by the terms and interpretation of the following claims.