CA2108679A1 - Process and device for washing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The invention concerns a process for washing fibrous materials, skins, textile materials or the like using an aqueous, surfactant containing washing liquid obtained by adding washing agents to water. The minimal dispensed amounts as determined in subsequent washing tests are always obtained automatically, without the cleaning power and the cleaning efficiency being reduced to unacceptable levels. To this end, the surface tension of the washing liquid is measured during the washing processusing a tensiometer. The actual washing agent concentration is derived from these measured values and an initial concentration is derived from the quantity of washing agent added. The detergency is calculated from this initial concentration. The addition of a washing agent is discontinued when no further increase occurs in the detergency. The invention also concerns a device for carrying out the process. The device has capillaries connected to constant gas flow sources and immersed to the same depth in the washing liquid. The capillaries are connected to a device for determining the pressure or the frequency of pressure variations which controls a dispensing unit via an evaluation unit.

Description

PROCESS AND DEVICE FOR WASHING

This invention relates to a process for washing fibrous materials, skins, textile materials or the like with a water-based surfac~ant-containing washing liquid which is obtained by addition of detergents to water.
For some time, the washing processes carried out in the institutional sector ands in the home have been the target of efforts to achieve ecological and economic im-provements in lhe processes. These efforts have been aimed at reducing the consump-tion of energy, detergent, water and time. To achieve these objectives, special dis-pensing syslems and dispensing processes are often used. A particular difficulty in-volved in the use of special dispensing processes is that, on the one hand, as little de-.o te~nt and water and possible should be used although, on the other hand, the 7.g amounts dispensed should nol fall below the minimum levels dependent on a numberof paramelers to ensure that delergency and washing performance do not to fall to un-acceptablc levels. There is an optimal detergent concentration for every ~ype of mater-ial to be washed, soils, waler hardnesses and delergents and also temperalures and the type of mechanical agitation. This concenlralion can be determined purely empirically from Ihe fact that, if the concenlration falls below this optimum, the washing result falls to unacceptable levels and, if the optimum is exceeded, no improvement is ob-tained in the washing result. In order always to achieve the optimal dispensing of de-tergent in practice under highly variable conditions, the optimal washing point men-tioned has to be automatically determined during the washing process itself.
It is known from MOCS, Vol. 1963, 1986, pages 931 to 943, that the surface tension of the washing water used in a mechanical washing machine can be measured and the result of the measurement subsequently used to control the addition of deter-gents. However, it is not known whether and in what way the optimal washing point s can be determined in a process for washing fibrous materials, skins, textile materials or the like by lhe measurement of surface tension and then used to control the addition of detergents. In other known washing processes, dispensing of the detergent is con-trolled by measurement of the conductivity, the pH value and the degree of clouding (Laboratory Practice, 1984, page 69). Unfonunately, these known dispensing process-es give unsadsfactory results. US-PS 3,881,344 and US-PS 4,416,148 are cited as fur-ther relevant prior an.
Accordingly, the problem addressed by the present invention was always to achieve the minimum dispensed amounts determinab1e in subsequent washing tests au-tomatically without a reduction in detergency and washing performance to unaccepta-ble levels. In addition, this problem was to be solved irrespective of the washing con-ditions, such as the type of materials to be washed, the detergent, the water hardness, the mechanics, the soils, etc., without the process according to the invention having to be spccially adapted to these washing conditions.
According to the invention, the solution to this problem is characterized in that ~o the surface tension of the washing liquid is measured, more panicularly continuously, with a tensiometer during the washing process; that the actual detergent concentration (Value 1) is ascertained from these measured values; that from the quantity of ~ 08~79 detergenl added, a concenlralion with mspect to delergent (Value 2) is ascerlained, more particularly continuously; ~hat the Detergen~ Effect (Value I - Value 2)/Value 2 is calculated; and that the addition Or detergent is terminated when there is no further increase in the De~ergenl Efrecl. A bubble lensiomeler operaled with suffi-cienlly conslanl gas slreams, parlicularly air slreams, is advanlageously used for this purpoæ.
Il is importanl in this regard lhat only the change as a funclion of lime and not lhe absolule value of the Delergenl Efrect goes inlo lhe control Or lhe amount of deter-gent dispensed. Because the maximum detergent efrecl is dependent upon the degree o of soiling, the delergent and other washing conditions, the process can thus be univer-sally used, without having to be specially adapted to certain washing conditions. The bubble tensiometer mendoned is known per se and is described, for example, by F.J.
Schork and W.H. Rey in Journal of Applied Polymer Science, Vol. 28, 1983, pages 407 to 430, so that there is no need for any further description in the present specifica-s tion.
The oplimal washing poinl mentioned above is reached automatically in the process according to the invention becauæ, as shown hereinafter, this point coincides wilh the maximum of the magnitude of the Detergent Effect, i.e. with ils optimum.
In one advantageous embodiment in which the Detergent Effect can be deter-mined very accurately. the detergent is added discontinuously in several individual portions and the Detergent Effect is determined from a point in time when there is no further significant increaæ in surface tension afler the addition of one of the portions.
A further saving of time and energy is achieved if the wash cycle is terminated during or after termination of addition of the delergent. Pumping off and/or rinsing 2s can then be commenced.
In the delermlnation of surface tension, it is possible on the one hand to mea-sure the Wference belween the ma~imum bubble pressures and, on the other hand, to determine the rate at which the bubbles flow from the bubble tensiometer as a func-don of dme. The first of theæ lwo methods is preferred.
It is also important that the tensiometer is operated with constant gas streams.TlKse can be produced by regulation of variable gas streams or even by uniformly op-erating pumps.

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The process according lo the invention is suitable ror dispensing both liquid and solid or paste-form detergents.
According to lhe invention, various possibilities are available for regula~ing the amoun~ of detergent dispensed. In one simple version, the washing liquid may be agi-s tated and the surface tension measured in an alternating sequence. Depending on theresult of the measurement, more detergent is added or the addition of detergent is stopped. On the other hand, in a washing process where the washing liquid is conlin-uously circulated, the surface tension of the circulating part of the washing liquid can be measured, more particularly continuously. The only requirement governing the 10 measurement of surface tension is that the liquid should not be agitated too vigorously in the vicinity of the tensiometer. On the other hand, however, a major advantage of the process according to the invention lies in the extremely small volume of washing liquid required for the tensiometer so that, by simple modification, the process accord-ing to the invention as claimed in the first claim can be carried out in a number of dif-5 ferent types of washing machines without having to change the programs or controlsor the washing effect properdes of the washing machines. Thus, on the other hand, surface tension can also be measured in the liguor pumped off.
In another embodiment of the invention, the dependence of surface tension on temperature is corrected during the measurement. This can be done by incorporadon 20 of the values measured by a thermosensor in the regulation of the amount dispensed.
According to the invention, not only can the necessary quantily of detergent and hence the necessary washing time be reduced, which also minimizes energy, the quantity of rinsing water required for the washing process can also be reduced. This is because, in another embodiment, rinsing is terminated when the measured surface 2s tension e~ceeds a predetermined maximum value.
The invention relales nol only lo the washing process described in the forego-ing, bul also to apparalu8 for carrying out the process. In this apparatus, the solution ~o lhe problem addre~sed by the invention is characterized in that capillaries connected to constanl gas stream sources and dipping to equal depths into the washing liquid are S'D provided and are connected lO means for measuring the pressure or the frequency of changes in pressure which control a dispensing unil for the detergent via an evaluation unit.

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To reduce Ihe quanlily of rinsing waler, lhe evalualion unit of the apparalus ac-cording lo the invenlion is connecled to a conlrol element which actuates rinsing.
Embodiments of lhe invenlion are described in delail in lhe following with ref-erence lo lhe accompanying drawings, wherein:
s Figure 1 shows washing results delermined by a standard process for powder-form universal detergent plotted against the amount dispensed.
Figure 2 shows washing results for liquid universal detergents likewise deter-mined by a standard melhod plolled againsl lhe amounl dispensed.
Figure 3 shows the relationship belween the concentralion of a powder-form o universal detergent and the measured pressure difference of the tensiometer.
Figure 4 shows the same for a liquid universal detergent.
Figure 5 shows the changes in concentration of a wash liquor in consequence of the washing process as a function of the concentration for a powder-form universal detergent.
s Figure 6 shows the same for a liquid universal detergent and laundry without standard soils.
Figure 7 shows the same for a liquid universal detergent and laundry with standard soils.
Figure g shows the relative Detergent Effect as determined from tensiometer measurements for a powder-form universal detergent.
Figure 9 shows the same for a liquid universal detergenl and laundry without standard soils.
Figure 10 shows the same for laundry with standard soils.
Figure 11 shows the reduction in the washing reserve during a wash cycle 2C plolted against time and measured with the tensiometer.
Pigure 12 schematically illustrates one embodiment of the apparatus according to the invention.
lhe washing tests described in the following were carried out wilh a powder-form universal detergent and with a liquid universal detergent. The laundry to be wa8hed consisted of 3.S kg of normally soiled domestic wuhing with and wlthoul ad-ditional standard soils. A one-wash cycle was used with an amounl of S0 to 170 gof the powder-form detergent divided into portions of 20 g and S0 to 17S ml of the S

210~7.~
liquid delergent divided imo porlions of 25 ml. The washing temperature was 60 C.
To evaluate the washing tests, samples of I liter of wash liquor were removed during the first pumping-off phase.
To ascertain the optimal amount of detergents, washing tests are usually carrieds out with different amounts and different items of laundry and the reflectance spectra of the laundry items is subsequently measured. Figures I and 2 show results such as these obtained in known manner. Figure 1 shows the Berger whiteness values for terry towels, tea cloths and huckaback towels after 15 washes with a powder^forrn uni-versal detergent in a one-wash cycle al 60 C. It can be seen from this graph that the ~o whiteness values increase with increasing dosage until a plateau is reached with an amount of around 110 g. This amount represents the optimal washing point marked with an arrow 1. Accordingly, ~hese measurements can only be carried out on com-pletion of the washing process.
Figure 2 shows a corresponding graph for a liquid universal detergent. In this case. reflectance is plotted in percent against the amount of detergent. The wæhing results were again obtained in a one-wash cycle at 60 C. As in Fig. 1, the washing result, the single wash cycle perfor nance, increases until it reaches a plateau at an amount of 125 ml. In this case, therefore, this amount forms the optimal washingpoint marked by the arrow 1.
It is shown hereinafter how, in accordance with the invention, this optimal washing point can actually be determined during the washing process and used for aut-omatically controlling the dispensing of a washing machine. To this end, the concen-tration of detergent in the wash liquor has to be determined from the values obtained with a tensiometer. As shown in Figs. 3 and 4, there is a clear and unambiguous rela-2- tionship between this concentration and the pressure difference as measured with the tensiomcter. A corresponding relationship e~ists between the concentration and the pressure variation rate as measured with the tensiometer, so that it could also be used as an alternative in the process according to the invention. Accordingly, Fig. 3 shows a calibration curve for a powder-form udversal detergent whi1e Fig. 4 shows a corre-:10 sponding curve for a liquid udversal detergent.
The graphs in Figs. S, 6 and 7 e~plain the principle on which the optimal washing point can be determined with a tensiometer in accordance with the present 21~7 ~

invention. In Fig. 5, the concemration values of wash liquors obtained from ten-siomeler measurements, which were ref~rred to earlier as Value 1, are plolted against the concenlralion calculated from the quantily of delergenl added and the quantily of water. These values were measured for wash liquors obtained after the washing of 3.5 kg of normally soiled domestic washing with a powder-form universal delergent. The concenlration values calculated from the quantity of detergent added and the quandty of water correspond to the concentration values with respect to the wash liquor before the washing process and were referred to earlier on as Value 2.
Without the influence of the soiled domesdc washing, the line 2 of equal con-centration would be obtained. In fact, however, the line 3 is obtained after the wash-ing process. The difference between ~he two lines 2 and 3 marked by the double ar-row 4 represents the quandty of de~ergent which was adsorbed onto soil and fabrics.
By contrast, the double arrow 5 marks the quantity of detergent remaining behind in the liquor after washing. It can be seen from Fig. 5 that line 3 curves upwards at a concentration of 5.5 g/l. This effect can be explained by the fact that, with relatively high concentrations, no further detergent is adsorbed onto soil and fabrics and any de-tergent additionally introduced passes straight into the wash liquor. The concentradon of 5.5 g/l corresponds to an addition of 110 g for 3.5 kg of normally soiled domestic washing and hence to the opdmal washing point, as shown in Fig. 1. Accordingly, ~o this opdmal dosage is again marked by the arrow 1. Both here and in the other Fig-ures, the same items are denoted by the same reference numerals.
Figure 6 shows the same relationship as Fig. 5, but for liquid universal deter-gents and normally soiled domesdc washing without standard soils. In this case, the bend in line 3 occurs at a Value 2 of 5.2 ml/l which corresponds to an addidon of 104 ml for 3.5 kg of normally soiled domesdc washing. The value also corresponds fairly closely to the opdmal washing point determined by standard methods as shown in Figs. I and 2.
Figure 7 shows the same reladonship as Fig. 6, bul for normally soiled domes-tic washing with additional standard soils. In this case, the bend in line 3 occurs at a Value 2 of 6.1 mVI, wbich corresponds to an addidon of 122 ml for 3.5 kg of normally soiled domesdc washing. A compa ison with Fig. 2 shows thal in this case, too, the bend in curve 3 occurs at the opdmal washing point.

21~79 In order lo u~ilize the rela~ionships just described to develop an automatic dis-pensing or metering system, the variable "Detergent Effect" (DE) is defined æ the quotient from the difference in concentration before and after washing, which ismarked in Fig. 5 by the double arrow 4, and the concentration before washing.
s Accordingly, the variable in question is (Value 2 - Value l)/Value 2. As will be shown, the optimal washing point is situated at that quantity of detergent for which the Detergent Effect DE reaches its maximum. At this washing point, as much detergent as necessary is used for adsorbing soil, although at the same time as little detergent as possible passes unused into the wastewater.
Accordingly, the following information can be derived from the results illus-trated in Figs. 5 to 7. The quantity of detergent used to adsorb soil increases with in-creasing input of detergent, as does the quantity of detergent remaining in the liquor after washing. Beyond a cer~ain limiting concentration, however, the quantity of de-tergent remaininB in the liquor increases to a greater extent than the quantily required 15 to adsorb soil. Accordingly, there is an optimal ratio between the quantity of deter-gent used for dispersing or emulsifying soil and the quantity of detergent remaining behind in the wæh liquor which does not contribute towards soil adsorption.
In Figs. 8 to 10, the Detergent Effect is illustrated as a function of the dosage under certain conditions. Irl tbis case, the "Reladve Detergent Effect" is recorded as 2D the quodent from the Detergent Effect and the ma~imum Detergent Effect under the particular washing conditions prevailing. The results in Fig. 8 were obtained with powder-form universal detergent while the results in Figs. 9 and 10 were obtained with liquid universal detergent - in Fig. 9 for washing without standard soils and in Fig. 10 for washing with addidonal standard soils. Comparison of the mal~imal values 2~ of the Relative Detergent Effect with the optimal washing points determined in Figs.
I and 2 leads to Ihe conclu~ion tha~ the ma1~imum of the Relative Detergent Effect co-inclde8 e~actly with this optimal washing point. If, therefore, the particular relative or absolute Detergent Effects are determined from concentration measurements during the washing process in dependence upon the addidon of detergent, the amount dis-~o pen~ed csn be adjusted during the actual washing process in such a way that the opti-mal washing effect is ach}eved although the degree of soiling of lhe laundry and other parameters can differ from one wash to another.
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Thus, in one prcferred embodiment of lhe process according to the inven~ion, lhe delergent is added in porlions, for example in portions of lO g or 10 ml. After each addition, surface lension inilially decreases, but then increases again during the dispersion of soil. When lhe surface tension has reached a substantially constant val-5 ue, the Delergen~ Effect is determined from lhe quantity of detergent and wa~er addedup to that point and from the result of the lensiometer measurement now carried out.
After another portion of the deler,gent has been added and the surface tension has fallen and risen again, the Detergent Effect is again determined when the surface ten-sion reaches a substantially constant value which does not have lo coincide with the 10 previous conslant value. If the value obtained for the Delergent Effect is lower than on the last occasion, the addition of detergent and the washing process are terminated.
If, however, the Detergent Effect increases, the cycle is repeated. In Fig. 11, the re-duction in the washing reserve during the washing process, measured as the differen-tial pressure of the tensiometer, is plotted against time. Il can be seen how the surface s tension increases during soil dispersion after the addition of a portion of detergent, reaching a substantially constant value after a certain time, as just e~plained.Figure 12 shows one embodiment of apparatus according to the invention. In this case, the tensiometer was operated with compressed air. To achieve constanl air streams, the compressed air is regulated by the valves 6 and 7 before being delivered 2D to two capillaries 8 and 9. These capillaries dip inlo the wash liquor 11. The pres-sure difference between the feeds to the two capillaries 8 and 9 is determined by a measuring instrument lQ The measurements are evaluated by a computer 12 to obtain the surface tension, the concentration of surfactant and the Detergenl Effect. These values are fed to a dispensing control unit 13 which is connected to a dispensing unit 25 14 for liquid or solid detergent.

Claims (15)

1. A process for washing fibrous materials, skins, textile materials or the like with a water-based surfactant-containing washing liquid which is obtained by addition of detergent to water, characterized in that the surface tension of the washing liquid is measured, more particularly continuously, with a tensiometer during the washing process, in that the actual detergent concentration (Value 1) and a concentration with respect to detergent (value 2) are determined, more particularly continuously, respec-tively from the measurements obtained and from the quantity of detergent added and that the Detergent Effect (Value 1 - Value 2)/Value 2 is calculated and in that the ad-dition of detergent is terminated when there is no further increase in the Detergent Effect.

2. A process as claimed in claim 1, characterized in that the tensiometer used is a bubble tensiometer operated with sufficiently constant gas streams, particularly air streams.

3. A process as claimed in claim 1 or 2, characterized in that the detergent is add-ed discontinuously in several individual portions and the Detergent Effect is deter-mined from a point in time when, after addition of one of the portions, there is no fur-ther significant increase in surface tension.

4. A process as claimed in claim 1 or 3, characterized in that the washing process is terminated during or after termination of the addition of detergent.

5. A process as claimed in any of claims 2 to 4, characterized in that, to deter-mine surface tension, the difference between the maximum pressures of the bubbles produced in the bubble tensiometer is measured.

6. A process as claimed in any of claims 2 to 4, characterized in that, to deter-mine surface tension, the rate at which the bubbles flow from the bubble tensiometer is measured as a function of time.

7. A process as claimed in any of claims 2 to 6, characterized in that the constant gas streams are produced by regulation of variable gas streams or by uniformly operat-ing pumps.

8. A process as claimed in any of claims 1 to 7, characterized in that liquid, solid or paste-form detergent is added.

9. A process as claimed in any of claims 1 to 8, characterized in that the washing liquid is agitated and surface tension is measured in an alternating sequence.

10. A process as claimed in any of claims 1 to 8, characterized in that, where the washing process is carried out with continuously circulating washing liquid, the sur-face tension of the circulating part of the washing liquid is measured, in particular continuously.

11. A process as claimed in any of claims 1 to 9, characterized in that surface ten-sion is measured in the liquor pumped off.

12. A process as claimed in any of claims 1 to 11, characterized in that the de-pendence of surface tension on temperature is corrected during the measurement.

13. A process as claimed in any of claims 1 to 12, characterized in that rinsing is terminated when the measured surface tension exceeds a predetermined maximal value.

14. Apparatus for carrying out the process claimed in any of claims 1 to 13, char-acterized by capillaries which are connected to constant gas stream sources and which dip to equal depths into the washing liquid, being connected to means for measuring the pressure or the frequency of changes in pressure which control a dispensing unit for the detergent via an evaluation unit.

15. Apparatus as claimed in claim 14, characterized in that the evaluation unit is connected to a control element which actuates rinsing.