Aqueous cleaning processes are a mainstay of both domestic and industrial textile fabric washing. On the assumption that the desired level of cleaning is achieved, the efficacy of such processes is usually characterised by their levels of consumption of energy, water and detergent. In general, the lower the requirements with regard to these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption is also significant, as this minimises the need for disposal of aqueous effluent, which is both extremely costly and detrimental to the environment.
Such washing processes involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, within practical limits, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. The key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter; this is the agitation of the cloth surface during washing, which plays a key role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level in combination with the drum design for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. reduce energy, water and detergent consumption), and the need for efficient mechanical action in the wash. For domestic washing in particular there are defined wash performance standards specifically designed to discourage the use of such higher levels in practice, in addition to the obvious cost penalties which are associated with such usage.
Current efficient domestic washing machines have made significant strides towards minimising their consumptions of energy, water and detergent. EU Directive 92/75/CEE sets a standard which defines washing machine energy consumption in kWh/cycle (cotton setting at 60° C.), such that an efficient domestic washing machine will typically consume<0.19 kWh/kg of washload in order to obtain an ‘A’ rating. If water consumption is also considered, then ‘A’ rated machines use <9.7 liters/kg of washload, whilst the most efficient modern machines are now capable of using even less water—e.g. model number F1480FD6 manufactured by LG (see www.lg.com). This machine typically uses 63 liters for a 9 kg washload, i.e. 7 liters/kg.
Detergent dosage is then driven by manufacturer recommendations but, again, in the domestic market, for a concentrated liquid formulation, a figure of 35 ml (or 37 g) for a 4-6 kg washload in soft and medium hardness water, increasing to 52 ml (or 55 g) for a 6-8 kg washload (or in hard water or for very dirty items) is typical (see, for example, Unilever pack dosage instructions for Persil® Small & Mighty). Hence, for a 4-6 kg washload in soft/medium water hardness, this equates to a detergent dosage of 7.4-9.2 g/kg whilst, for a 6-8 kg washload (or in hard water or for very dirty items), the range is 6.9-9.2 g/kg.
Energy, water and detergent consumptions in the industrial washing process (washer-extractors) are considerably different, however, and usages of energy and water are less constrained in such environments, since these are principal factors in reducing cycle time—which is, of course, more of a consideration than in the domestic scenario. There is a similar pressure on detergent levels, however, but this is mostly due to a desire to reduce cost.
Thus, it can be taken from the above discussion that the performance levels which set the highest standard for an efficient fabric washing process are an energy consumption of <0.19 kWh/kg, a water usage of approximately 7 liters/kg, and a detergent dosage of approximately 8 g/kg. However, as already mentioned, it is becoming increasingly difficult to reduce the water (and, hence, energy and detergent) levels in a purely aqueous process, due to the minimum requirement to wet the fabric thoroughly, the need to provide sufficient excess water to suspend the soil removed in an aqueous liquor and, finally, the need to rinse the fabric.
Heating of the wash water is then the principal use of energy, and a minimum level of detergent becomes necessary in order for an effective concentration to be reached at the operating wash temperature. If a means to improve mechanical action could be achieved without increasing the water level used, then the aqueous wash process could become significantly more efficient (i.e. yield further reductions in energy, water and detergent consumption). It should be noted that mechanical action itself has a direct effect on the detergent level, since the greater the level of soil removal which is achieved through physical force, the less that is required of the detergent chemistry. However, increasing the mechanical action in a purely aqueous washing process has certain associated drawbacks. Fabric creasing readily occurs in such processes, and this acts to concentrate the stresses from mechanical action at each crease, resulting in localised fabric damage. Prevention of such fabric damage (i.e. fabric care) is of primary concern to the domestic consumer and the industrial user.
Various different approaches to the development of new cleaning technologies have been reported in the prior art, including methods which rely on electrolytic cleaning or plasma cleaning, in addition to approaches which are based on ozone technology, ultrasonic technology or steam technology. Thus, for example, WO-A-2009/021919 teaches a fabric cleaning and disinfection process which utilises UV-produced ozone along with plasma. An alternative technology involves cold water washing in the presence of specified enzymes, whilst a further approach which is particularly favoured relies on air-wash technology and, for example, is disclosed in US-A-2009/0090138. In addition, various carbon dioxide cleaning technologies have been developed, such as the methods using ester additives and dense phase gas treatments which are described in U.S. Pat. No. 7,481,893 and US-A-2008/0223406, although such methods generally find greater applicability in the field of dry cleaning. Many of these technologies are, however, technically complex and not readily suited to domestic applications, in particular.
In the light of the challenges which are associated with aqueous washing processes, the present inventors have previously devised a new approach to the problem, which is technologically straightforward, and yet still allows the deficiencies demonstrated by the methods of the prior art to be overcome. The method which is provided eliminates the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal, whilst also yielding economic and environmental benefits.
Thus, in WO-A-2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. Preferably, the substrate is wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation additionally comprises at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. In preferred embodiments, the substrate comprises a textile fibre and the polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, but are most preferably in the form of nylon chips.
The use of this cleaning method, however, presents a requirement for the cleaning chips or beads to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation, and this issue was initially addressed in WO-A-2010/094959, which provides a novel design of cleaning apparatus requiring the use of two internal drums capable of independent rotation, and which finds application in both industrial and domestic cleaning processes.
With a view to providing a simpler, more economical means for addressing the problem of efficient separation of the cleaning media from the substrate at the conclusion of the cleaning process, however, a further apparatus is disclosed in co-pending PCT Patent Application No. PCT/GB2010/051960. The apparatus of PCT Patent Application No. PCT/GB2010/051960, which finds application in both industrial and domestic cleaning processes, comprises a perforated drum and a removable outer drum skin which is adapted to prevent the ingress or egress of fluids and solid particulate matter from the interior of the drum. The cleaning method requires attachment of the outer skin to the drum during a first wash cycle, after which the skin is removed prior to operating a second wash cycle, following which the cleaned substrate is removed from the drum.
The apparatus and method of PCT Patent Application No. PCT/GB2010/051960 is found to be extremely effective in successfully cleaning substrates, but the requirement for the attachment and removal of the outer skin detracts from the overall efficiency of the process and the present inventors have, therefore, sought to address this aspect of the cleaning operation and to provide a process wherein this procedural step is no longer necessary. Thus, by providing for continuous circulation of the cleaning chips during the cleaning process, it has been found possible to dispense with the requirement for the provision of an outer skin.