Cleaning method

Abstract: The invention relates to a method for the cleaning, washing, degreasing, deoiling, removal of swarf or of pigment, of an object which comprises: bringing the object into contact with a two-component system comprising a water-immiscible organic solvent, and water in the substantial absence of a surface tension lowering agent, and in the substantial absence of a substance increasing the alkalinity, and subsequently separating the object from the two-component system, and allowing the two-component system to separate in contaminated organic solvent and water.

Description: The present invention relates to a method for the cleaning, washing, degreasing, deoiling, removal of swarf or of pigments of objects. Cleaning operations of metals, plastics, ceramics, glass or textiles are usually performed in a continuous one-phase system, which is a solvent or a solvent mixture or an aqueous system comprising dissolved ingredients, such as detergents, pH-modifiers, complexing agents, etc. Solvents are also used with dissolved ingredients or as emulsions in water. Two-phase systems have been described in the patent literature, but the described systems comprise additional phases, which make the systems only quasi-two-phase systems. UK Patent Application 2,026,551 discloses a method for the cleaning of surfaces which are contaminated with oil comprising contacting the oily surfaces with a cleaner comprising an organic solvent and an aqueous solution of a substance which decreases the surface tension and/or increases the alkalinity of the solution, and in which subsequent to the cleaning operation the contaminated cleaner is separated from the bodies being cleaned and on standing separates into organic and aqueous phases. According to the description and the example of the UK Patent Application 2,026,551 there are in fact three phases. A metastable intermediate phase has been formed, which hampers the recycling process as a whole. US Patent Specification 4,619,706 discloses a two-phase liquid both comprising either glycol phenol ether or ethoxylated furfuryl alcohol as organic phase and an aqueous phase, said phases being relatively insoluble in one another. According to the description ethoxylated furfuryl alcohol has a significant degree of solubility in aqueous solutions having low alkaline concentrations and furthermore 2-phenoxyethanol has a solubility of 2.69 in 100g of water. The compounds have a too great solubility to be used in the process according to the invention. The system is not a true two-phase system. German Patent Publication 2056341 discloses an unstable emulsion comprising a water-insoluble organic solvent and an aqueous solution of washing-active ingredients, aralkylsulfonates, phosphates and alkali. The emulsion disintegrates after a few minutes. The disintegration still proceeds too slowly. US Patent Specification 1,927,496 relates to a process of cleaning involving the forceful impingement against the surface to be cleaned, of a permanent colloidal suspension of oil in water. A small amount of oil, namely 1 part of oil per 50 to 150 parts of water, is suspended in the water. The suspension has a permanent character. Furthermore all systems of the prior art have the disadvantage that the compounds added to the water give rise to effluent problems. It is an object of the invention to have a method for the cleaning, washing, etc. of objects, which is from environmental point of view more acceptable and gives no rise to effluent problems. The invention relates to a method for the cleaning, washing, degreasing, deoiling, removal of swarf or of pigments of an object which comprises bringing the object into contact with a suspension, characterised in that the suspension comprises a true two-phase system, the two phases existing in finely divided form next to each other and comprising a water-immiscible organic solvent and water in ratio of from 9:1 to 1:9, in the absence of a surface tension lowering agent and in the absence of a substance increasing the alkalinity, and subsequently separating the object from the two-phase system, and allowing the two-phase system to separate in contaminated organic solvent and water. The two-phase system may be defined as a true two-phase system with the two phases being immiscible with each other, which further exist in finely divided form next to each other (in a dispersed form) and are maintained in this form by mechanical force generally. Since the two phases exert their working in the dispersed form, the phases should be maintained at least during a certain time in that form. Later the system may disintegrate after it has exerted its action on the surface of an object. No specific conditions are set to the water, which must not contain compounds which make the composition worthless. The composition may comprise water from different sources, like tap-water, distilled water or desalted water. But fluoridated water will be of no hindrance. In the process according to the invention the phases stay apart by virtue of their immiscibility and on hitting the surface of the object the phases exert a stress tension on the dirt layer according to their original surface tension, namely the water droplets at 73 dynes/cm (mN/sec) and the hydrocarbon droplets at about 25 dynes/cm (mN/sec). This helps enormously to remove thick layers (particularly pigment layers) in a short time. Moreover since the low surface tension of the small hydrocarbon droplets is maintained it helps to remove splinters and pigments from small bores and holes. Furthermore after the surface of the object has been into contact with the two phase system, the latter disintegrates very quickly, generally within about half a minute, and spontaneously and the separate phases may be used again in the cleaning process. The separation of the two phases, water-immiscible organic solvent and water, follows Stoke's law when both have been intimately mixed. This means that the smaller the particles are, the longer the time is, needed for separation. Stoke's law describes the rate of fall of a small sphere in a viscous fluid. When a small sphere falls under the action of gravity through a viscous medium it ultimately acquires a constant velocity. where a is the radius of the sphere, d₁ and d₂ the densities of the sphere and the medium respectively and η the coefficient of viscosity, g the acceleration due to gravity. The water-immiscible organic solvent preferably is a mixture of a non-aromatic hydrocarbon and a minor amount of an alkylated aromatic containing at least one alkyl group of from 8 to 18 carbon atoms. More preferably the organic solvent contains from 85 to 98 parts by weight of a non-aromatic hydrocarbon liquid having an atmospheric initial boiling point of at least 150 °C, and from 2 to 15 parts by weight of at least one alkylated aromatic containing at least one alkyl group with from 8 to 18 carbon atoms. The alkylated aromatics include alkylated xylenes, toluenes and benzenes. Preferred are alkylbenzenes, in particular benzenes containing one linear alkyl group with from 8 to 18, preferably from 10 to 16 carbon atoms. Of course it is possible to apply one pure alkylbenzene. Such pure alkylbenzenes are rather expensive. Therefore it is cheaper and more feasible to employ mixtures of alkylbenzenes. Further it is often advantageous to use such mixtures since due to their different structures the alkylbenzenes show slightly different solubilizing properties. The non-aromatic hydrocarbon liquid includes aliphatic and/or cyclo-aliphatic compounds. Saturated hydrocarbons are substantially non-toxic and are therefore very suitable. The non-aromatic hydrocarbon liquid has an atmospheric initial boiling point of preferably at least 150 °C. Therefore, the mixture will have a rather high flash point. This is desirable for then it is possible to safely use the mixture even on warm equipment. Preferably, the flash point of the mixture is at least 55 °C. (The flash point can be determined e.g. by the well-known Abel-Pensky Closed Cup method). The end boiling point of the non-aromatic hydrocarbon liquid is suitably below 320 °C, preferably the boiling range is from 180 °C to 280 °C. To make the two-phase system ready for use, the water-immiscible organic solvent and the water should be intimately mixed, so that the one fluid is dispersed into the other. This requires mechanical force, such as a pump, a nozzle/jet, ultrasonic waves, stirrer or other equipment. The volume ratios of the amounts of organic solvent and water may vary from 9:1 to 1:9, more preferably from 3:1 to 1:3. The nozzle to be employed in the process according to the invention may be of any kind, e.g. as used in the well known preparation of polyurethanes. The object to be cleaned can be simply hung in a reservoir, a stream of the two-phase system just prepared, is directed to the object and exerts its cleaning action, whereafter two-phase system disintegrates and forms two layers in the reservoir. After tapping off both layers from the reservoir the components can be used again. Another method consists of immersing the object to be cleaned in a reservoir while the two phases are put in the reservoir. Ultrasonic vibration is generated in the fluid of the reservoir by suitable means, e.g. placed on the inner walls of the reservoir. The two phases are hereby intimately mixed at a place where the object is hung. As soon as the ultrasonic vibration is stopped the two-phase system disintegrates. The object is taken away from the reservoir and rinsed. The reservoir can be used several times. The process according to the invention may be carried out at a temperature ranging from 10 °C to 80 °C, preferably from 20 °C to 60 °C. Examples All kinds of objects, which were contaminated with oil, grease, chips, turnings, pigments etc., were subjected to the action of a two-phase system comprising Shell cold cleaning agent UKR A 151 and water. The two-phase system was a dispersed mixture of the two phases, obtained by an intimate mixing procedure in nozzles or via ultrasonic waves. The system was sprayed, dip-sprayed under sufficient pressure, sometimes under high pressure, or the system was brought under ultrasonic vibration in immersed state. Shell UKR A 151 consisted of a mixture of 93% vol. "Shellsol D60" (an aliphatic hydrocarbon with initial boiling point of 180-190 °C and an end boiling point of 200-220 °C) and of 7% vol. "Dobane 45" (a mixture of linear alkylbenzenes with mainly C₁₄ and C₁₅ alkyl groups). In the tables are given the working conditions and the results obtained by the several processes:

Claims: A method for the cleaning, washing, degreasing, deoiling, removal of swarf or of pigment of an object which comprises: bringing the object into contact with a suspension, characterised in that the suspension comprises a true two-phase system, the two phases existing in finely divided form next to each other and comprising a water-immiscible organic solvent and water in a ratio of from 9:1 to 1:9, in the absence of a surface tension lowering agent, and in the absence of a substance increasing the alkalinity, and subsequently separating the object from the two-phase system, and allowing the two-phase system to separate in contaminated organic solvent and water. A method as claimed in claim 1, wherein the true two-phase system comprises a water-immiscible hydrocarbon solvent and water unaccompanied by an added substance which destroys the nature of the true two-phase system. A method as claimed in claim 1 or 2, wherein the two-phase system comprises a water immiscible hydrocarbon solvent and tap-water, distilled water or desalted water. A method as claimed in one or more of the claims 1-3, wherein the organic solvent comprises a non-aromatic hydrocarbon and a minor amount of an alkylated aromatic containing at least one alkyl group of from 8 to 18 C atoms. A method as claimed in one or more of the claims 1-4, wherein the two-phase system is allowed to separate within one minute into organic solvent and water layers. A method as claimed in claim 5, characterized by the absence of a metastable intermediate layer. A method as claimed in claim 1, wherein the two-component system is maintained in the form of a dispersion of the one fluid in the other fluid. A method as claimed in claim 7, wherein mechanical force is applied, in order to maintain the dispersion. A method as claimed in one or more of the claims 1-8, wherein the treated object is rinsed with water.

Inventors: HERTLEIN KURT, HERTLEIN, KURT
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1989
Main classification: C23G5
IPC codes: C11D7, C23G5, B08B3