EP2821473A1

EP2821473A1 - Process for cleaning a surface and cleaning concentrate for use therein

Info

Publication number: EP2821473A1
Application number: EP13174569.7A
Authority: EP
Inventors: Hermann Becker; Matthias Reihmann
Original assignee: Becker Bernhard; Becker Peter Philipp; Gelita AG
Current assignee: Becker Bernhard; Becker Peter Philipp; Gelita AG
Priority date: 2013-07-01
Filing date: 2013-07-01
Publication date: 2015-01-07
Anticipated expiration: 2033-07-01
Also published as: EP2821473B1

Abstract

The present invention relates to a method for cleaning an article comprising a surface, in particular a train, and a cleaning concentrate for use in this method. In a first cleaning cycle of the cleaning method the surface of an article is a) cleaned with a cleaning composition and b) cleaned with a low concentrated polypeptide containing cleaning composition. After recontamination of the surface it is only necessary in a second and further cleaning cycles to repeat step b).

Description

The present invention relates to a method for cleaning an article comprising a surface and a cleaning concentrate for use in this method.
Accumulation of dirt on surfaces of articles is a common problem in diverse fields. For example, articles used outdoor such as vehicles and particularly rail vehicles (such as trains) are exposed to e.g. inorganic substances such as flash rust, dust generated by abrasion of brakes, rails or wheels, biological substances such as insects and other organic substances such as oil and grease. The type and way of formation of the contamination on the surface of e.g. rail vehicles, where dirt is deposited under significant impact force, in combination with a high frequency of use as well as the exposure to any weather and temperature conditions can lead to contamination on the surface which is particularly difficult to remove by the combined use of mechanical and chemical measures.
Different methods of cleaning for contaminated surfaces of articles, i.e. articles whereon dirt has accumulated, have been proposed in the prior art. For example, highly alkaline or highly acidic and surfactant containing cleaning compositions have been used. They are applied to the contaminated surface, left there for a certain dwell time and, after application of mechanical cleaning tools such as brushes, they are rinsed off.
DD 47897 discloses a combined cleaning method, particularly for the painted surface of trains, wherein the surface to be cleaned is alternately treated with alkaline and acidic cleaning compositions instead of a treatment with only one cleaning composition, being either alkaline or acidic.
DE 19651319 is also directed to a method for cleaning vehicles and discloses the combined cleaning of the contaminated surface with an acidic and an alkaline cleaning composition wherein the cleaning compositions are applied to the surface one directly after the other without an intermittent step wherein the first cleaning composition would be rinsed off the surface before the second cleaning composition would be applied.
The application of highly acidic or alkaline cleaning compositions may increase cleaning efficiency and may reduce the dwell time of the cleaning composition on the surface prior to rinsing off.
However, such cleaning compositions have several disadvantages. First of all, they are aggressive and may react with the surface material and negatively affect it, e.g. particularly in case of a coated surface with e.g. paint (lacquer), metal, glass or polymer surfaces. Especially at temperatures above 40°C damage to the surface may increase. Warm/hot surfaces thus have to be cooled before cleaning. This becomes particularly relevant during summer when the surface of vehicles can heat up significantly due to sunlight. In motorized vehicles hot surfaces may also arise from heat from the motor. Furthermore, certain security measures have to be adhered to when using highly acidic or alkaline cleaning compositions. For example, personal protective equipment and a closed cleaning line may be necessary. Certain waste management rules have to be complied with. The pH of waste water may not be extreme (too acidic or too alkaline) for environmental reasons. The pH may e.g. influence precipitation of contaminants in the waste water system. pH correction in waste water plants is costly and if pH correction leads to the formation of waste slags further costs may incur for their separate disposal.
Instead of cleaning contaminated surfaces itself proposals have been made in the prior art for providing surfaces in danger of contamination with a protective layer (also termed film or coating) for protection against contamination. US 2,986,471 suggests to apply a water-soluble protective film based on sodium carboxymethylcellulose to the surface of automobiles in order to prevent particularly insect-remains to penetrate to the paint. Such contaminants will instead be supported on the film and the film together with the contaminants thereon can then be washed off the surface by simple application of water. After the automobile has been washed, a new film has to be applied by treating the automobile surface with a solution containing 3-7% sodium carboxymethylcellulose. While this approach avoids detergents or strong solvents one specific disadvantage is that the film due to its water-solubility has to be renewed after each exposure to water including rain.
In AU 70178/74 surfaces are coated for protection against contamination with a protective layer which is insoluble in neutral and slightly acidic aqueous solutions, but is at least partially soluble in alkaline solutions. It is thus described that - after contamination - the protective layer can be removed together with the dirt by treatment with an alkaline cleaning solution. After drying, the clean surface may then be treated with fresh film-forming solution. The film formed may comprise a polymeric film, for example vinyl acetate-unsaturated acid polymer. An example is provided for such composition to be applied to a surface with a polymer content of above 10 wt.-%.
DE 2723493 discloses a protective layer that is applied to a surface that should be kept clean, optionally after fundamental cleaning of the surface. The protective layer is formed from a film-forming composition containing a film-forming agent in a concentration of preferably 10 wt.-%. The film forming compositions also preferably contain organic solvents. A similar disclosure is made in GB 1604562 , which suggests that after contamination (of the protective layer), the protective layer is not completely removed, but only the surface of the protective layer is removed during cleaning so that the surface of the article is not exposed to any treatment when the protective layer is partially replaced. The concentration range of film-forming agents in the compositions is very broadly indicated to be 0.5-80 wt.-%. Exemplary film forming compositions are described with cellulose ethers, polymethylvinyl ether maleic acid anhydride, urea formaldehyde condensate, polyacrylates and silicates. The description also enumerates polyamides as potential film-forming agents in a row with e.g. polyesters. Polypeptides are not named and from the listing of potential film-forming agents it is not to assume that the term polyamides should include polypeptides which are usually able to build hydrogen bonds in contrast to the film forming agents described in GB 1604562 .
All of the methods described above using protective films, which are fully or partially removed when dirt has accumulated thereon, have certain disadvantages. In particular, they use high concentrations of film-forming agents in the cleaning compositions applied to the surface, which can be costly. High concentrations of the film-forming agents can also negatively influence the applicability for spraying the compositions onto a surface due to higher viscosities of the compositions. Furthermore, the described protective layers are continuous films which have to exhibit a certain thickness to ensure that no contamination will come in contact with the underlying surface to be protected as the methods do not provide for "cleaning" the surface, but only for applying and exchanging a contaminated protective film. Drying for formation of these films of a certain thickness takes time. Moreover, the appearance of the surface of the article may be negatively influenced by the protective film, which completely covers the surface. In this respect, it is also to be noted that none of the mentioned methods using a protective film describes the separate application of a finishing agent to obtain a surface with good drying properties which looks optically attractive after final drying.
It can be summarized that neither the cleaning methods described above using highly acidic or alkaline cleaning compositions nor the methods which avoid contamination of a surface by providing it with a protective film that is fully or partially exchanged when contaminated are fully satisfactory. There is still a need for an improved method for cleaning an article comprising a surface, in particular wherein the article is a vehicle. The cleaning method should be efficient time wise and economically. It should be safe and reduce recontamination measurable in terms of cleaning intervals and type and intensity of further cleaning required after recontamination. More particularly, such improved method for cleaning should have a high and fast cleaning efficiency for different kinds of contaminants (alone or in combination). The cleaning compositions applied therein should have good dissolving and/or complexing properties for contaminants during application and also in the generated waste water (also when pH or temperature change), a moderate pH when applied to the surface, good compatibility with surface materials (not being too aggressive), good properties for spraying, applying and wetting, and low aerosol formation when sprayed. The cleaning method should provide in the end for good draining properties of the treated surface, which should appear optically immaticulate. Furthermore, it should provide for long-lasting cleaning efficiency and cleaning intervals should be prolongable without the need to apply environmentally critical substances. The cleaning method and cleaning compositions used therein should be compatible with environmental guidelines and guidelines regarding waste water and waste water plants. Waste water should be recyclable with little formation of waste slags. Ideally, the cleaning method and the compositions used therein should not only passively comply with regulations regarding waste water treatment, but the cleaning method and compositions should be optimized to exceed existing standards. The cleaning method should be cost attractive in terms of procedure and the cleaning compositions used.
The inventors of the present invention have now surprisingly found an improved cleaning method. In a first cleaning cycle of the cleaning method the surface of an article is a) cleaned with a cleaning composition, b) cleaned with a low concentrated polypeptide containing cleaning composition and optionally c) treated with a drying aid. After recontamination of the surface it is only necessary in a second and further cleaning cycles to repeat step b) and optionally step c). Surprisingly, the polypeptide containing cleaning composition is highly effective for cleaning and the polypeptide concentration in the second cleaning composition can be low, considerably lower than concentrations of film-forming agents suggested in methods of the prior art for keeping a surface clean by providing it with a protective layer. Treatment with the drying aid can serve as finishing to obtain an optically immaculate surface with favorable draining properties. The cleaning method of the invention is highly effective in terms of time and media used as well as it allows for increased intervals of cleaning with a cleaning agent. The method is also of low aggressivity to the surface of the article and optimized in terms of waste management.
The present invention is thus directed to a method for cleaning an article comprising a surface wherein the method comprises a first cleaning cycle comprising

(a) cleaning the surface with a first cleaning composition,
(b) cleaning the surface with a second cleaning composition containing at least one polypeptide, wherein the total amount of polypeptide in the second cleaning composition is from 9.9*10^-6 wt.-% to 1.2*10^-2 wt.-% based on the total weight of the second cleaning composition and wherein the second cleaning composition is different from the first cleaning composition, and
(c) optionally treating the surface with a drying aid,

In this specification, "parts" and "%" are on a weight by weight basis, if nothing else is explicitly stated or evident for a skilled person in the specific context.
In step (a) of the first cleaning cycle the surface undergoes a basic cleaning. Existing dirt on the surface can thereby be removed. Conventional cleaning compositions may be applied in this cleaning step. Often, the first cleaning composition is an acidic or alkaline cleaning composition. Acids used in the acidic cleaning composition are e.g. hydrochloric acid, sulphuric acid, amido sulfonic acid, phosphoric acid or oxalic acid. Cleaning compositions with e.g. acetic acid, haloacetic acid, citric acid, glycolic acid, gluconic acid, boric acid and/or phosphonic acid may also be used. An alkaline cleaning composition usable as first cleaning composition may e.g. contain hydroxides of alkali metals, particularly sodium hydroxide or potassium hydroxide, sodium carbonate and/or alkanolamines. The first cleaning composition may also contain other substances which are typically contained in cleaning compositions such as e.g. surfactants, complexing agents, dispersing agents and/or corrosion inhibitors. In a preferred embodiment of the invention, the first cleaning composition is an aqueous acidic cleaning composition containing oxalic acid.
The first cleaning composition preferably is an aqueous acidic cleaning composition with at least 50 wt.-% water based on the total weight of the aqueous cleaning composition. The cleaning composition has a pH of preferably 0.2 to 2. The pH of the cleaning composition can e.g. be in between 0.6 and 1.2. For example, the cleaning composition can have a pH of 0.9. In another preferred embodiment the first cleaning composition is an aqueous alkaline cleaning composition with at least 50 wt.-% water based on the total weight of the aqueous cleaning composition, and with a pH of 7.5 or more, preferably 8-10. Preferably, the aqueous cleaning compositions as defined above contain at least 70 wt.-% water based on the total weight of the aqueous cleaning composition. When the pH is indicated in this specification it is measured at 25°C if it is not stated otherwise.
Cleaning efficiency in step (a) can be increased e.g. by the use of brushes, sponges and/or cleaning clothes. The first cleaning composition can be sprayed onto the dry or prewetted surface to be cleaned, be brushed or rubbed in mechanically (to loosen strongly adhering dirt) and then be rinsed off, eventually after some dwell time. Rinsing and prewetting (if applicable) is preferentially done with water.
While step (a), step (b) and, if optional step (c) is carried out, optional step (c) of the first cleaning cycle of the method are performed in this order, the method can of course comprise additional steps before step (a), in between the steps or after step (b) or optional step (c). The method may e.g. comprise prior to step (a) a step of diluting a first cleaning concentrate to obtain the first cleaning composition. The method of the invention may also comprise a further cleaning step between steps (a) and (b), e.g. when the surface is cleaned in step (a) with an acidic cleaning composition (or an alkaline cleaning composition, respectively) as first cleaning composition the surface may then be additionally cleaned with an alkaline cleaning composition
(or an acidic cleaning composition, respectively) before cleaning is continued in step (b). The different steps of the cleaning method may also be repeated.
In step (b) the surface of the article is cleaned with a second cleaning composition. The second cleaning composition contains at least one polypeptide. A polypeptide as used herein also encompasses proteins which are long chained polypeptides. Preferably, the at least one polypeptide contained in the second cleaning composition has a molecular weight (M_R) of at least 1000 g/mol and not more than 600000 g/mol, more preferably, the molecular weight of the at least one polypeptide contained in the second cleaning composition is from 20000 g/mol to 600000 g/mol. The molecular weight of the at least one polypeptide can e.g. be from 20000 g/mol to 300000 g/mol. It is of course also possible that the second cleaning composition contains a mixture of polypeptides, preferably of polypeptides as defined above. The total amount of polypeptides in the second cleaning composition is in the range from 9.9*10^-6 wt.-% to 1.2*10^-2 wt.-% based on the total weight of the second cleaning composition. Higher concentrations may lead to streaks (wavy lines also called schlieren) on the surface to be cleaned. Preferably, all polypeptides in the second cleaning composition have a molecular weight (M_R) of at least 1000 g/mol and not more than 600000 g/mol, more preferably from 20000 g/mol to 600000 g/mol, e.g. from 20000 g/mol to 300000 g/mol. As polypeptides are biodegradable the application of polypeptide containing cleaning compositions in a cleaning method can be advantageous over the application of some polymer containing compositions in methods of the prior art for keeping a surface clean by providing it with a protective layer of a polymer which is no polypeptide. The polypeptide concentration of the second cleaning composition can also be considerably lower in the method of the present invention than polymer concentrations used in the prior art for building a protective layer to keep a surface clean. Preferably, the second cleaning composition has a total amount of polypeptide from 9.9*10^-5 wt.-% to 2.4*10^-3 wt.-%, more preferably from 3.0*10^-4 to 1.2*10^-3 wt.-% based on the total weight of the second cleaning composition.
The second cleaning composition containing at least one polypeptide is usually an aqueous liquid containing at least 50 wt.-%, preferably at least 70 wt.-% of water. It usually has good spraying properties so that it can be easily applied to the surface to be cleaned. It is preferred that the second cleaning composition is brushed or rubbed onto the surface mechanically. It is assumed that the polypeptide smoothes surface roughness. It also seems to contribute to a shiny effect of the surface by reduced light scattering.
In one embodiment, at least one polypeptide contained in the second cleaning composition is contained as a molecular dispersion (i.e. dissolved) or as a colloidal dispersion with a particle size in the range from 1 nm to 1000 nm. Preferably the second cleaning composition does not contain encapsulated substances.
The second cleaning composition may also contain e.g. one or more buffer(s), tenside(s), solubilizer(s), surface modifier(s), fragrance(s), solvent(s) and/or dye(s). The second cleaning composition thus e.g. contains potassium sodium tartrate, alkyl ether sulfate C12-14 with EO, sodium salt, isotridecanol, ethoxylated (>5-20 EO), sodium p-cumenesulfonate, Rewocare 755 (Evonik Industries, Germany), orange terpenes, ethylene glycol, butyl digylcol, a dye, a preservative and/or other known additives for cleaning compositions for cleaning the surface of trains, such as wetting agents and here reference is made to the commercial product Rewocare 755, obtainable form the company Evonik Industries AG, 45127 Essen, Germany.
In step (c) the surface is treated with a drying aid. Drying aids (or rinse aids) for use in cleaning processes in particular for vehicles are principally well known in the art. In general drying properties of a surface after cleaning away the dirt on the surface can be influenced by applying drying aid in the last step of a cleaning method in lipophilic layers to the surface to favor water droplets to roll off. Lipophilic or lipophilising substances can be used therefore, which should reduce the adhesion of water. According products (mostly from the car wash industry) are, however, not uncritical with respect to environmental compatibility and waste water treatment. In the present invention, the drying aid preferably does not render a surface lipophilic, but in contrast render it hydrophilic so that water rather runs off the surface as a film instead of droplets. Accordingly, the drying aids preferably used in the present invention provide hydrophilic properties to the surface to be cleaned. The drying aid used in the present invention is therefore preferably selected from a drying aid containing at least one tenside and/or at least one hydrophilic polymer. Examples of suitable tensides and hydrophilic polymers used as drying aids are discussed later.
It is possible to use very low concentrated drying aids in the present invention. The polymer concentration of the drying aid of optional step (c) is e.g. low compared to the concentrations of polymer compositions used in the prior art in methods for keeping a surface clean by providing it with a polymer protective layer. The concentration is also low compared to concentrations of polymer used in glazing compositions/water repellency compositions of the prior art.
The method of the invention preferably also comprises a step of diluting an aqueous drying aid concentrate in order to produce the drying aid used in step (c). Dilution is usually made with water.
The drying aid used in step (c) of the method of the present invention also has good spraying properties.
In one embodiment of the method of the invention, the second cleaning composition is an aqueous cleaning composition of low alkalinity with at least 50 wt.-% water based on the total weight of the second cleaning composition, which has a pH in the range from 7.5 to 9.5, preferably in the range of 9 to 9.5, and the drying aid used in step (c) is an aqueous drying aid with at least 50 wt.-% water based on the total weight of the drying aid, which has a pH lower than the pH of the second cleaning composition. The drying aid, for example, has a pH of 7. Preferably, the aqueous cleaning composition and the aqueous drying aid as defined above contain at least 70 wt.-% water based on the total weight of the aqueous cleaning composition and the aqueous drying aid, respectively. The different pH values can cause the polypeptide which was applied to the surface in step (b) to be less soluble in the drying aid of step (c) than in the second cleaning composition.
Treatment of the surface with the drying aid in step (c) may also affect that polypeptide from the second cleaning composition which adheres to the surface after step (b) is not easily removed from the surface during use of the article. The drying aid may stabilize polypeptide on the surface of the article.
Reduced solubility of the polypeptide (at maintained swelling ability and hydrophilicity) on the surface may also be achieved by treatment of the surface with tanning agents. Such tanning agents may e.g. be tanning agents from plants, such as extracts from leaves, lumbers, cortices, fruits and roots, mineral tanning agents, such as alum, aluminum salts, particularly aluminum sulfate, and polysulfate, metal salts in combination with the addition of a complexing agent, such as iron and titanium salts, and aldehydes, such as formaldehyde and glutaraldialdehyde. Furthermore, solubility of the polypeptide may be affected by UV-exposure.
In a preferred embodiment of the method of the invention the surface is neither rinsed (e.g. with water) nor dried in between steps (a) and (b) of the first cleaning cycle. Preferably steps (a), (b) and (c) are performed without taking any further steps in between except for eventual dilution steps to prepare the second cleaning composition of step (b) and the drying aid of step (c) from a cleaning concentrate (second cleaning concentrate) and a drying aid concentrate, respectively and rinsing the surface with fresh water or process water in between steps (b) and (c).
After recontamination of surfaces of articles cleaned as described above in a first cleaning cycle cleaning in a second and further cleaning cycle is facilitated. In a preferred cleaning method according to the present invention the method additionally comprises a second cleaning cycle which is carried out after the surface of the article became contaminated after the first cleaning cycle, the second cleaning cycle comprising carrying out step (b) and optionally step (c) as defined above, wherein step (b) and optional step (c) are performed in this order if optional step (c) is carried out. In another embodiment, the afore described method additionally comprises one or more further cleaning cycles, each cleaning cycle being performed after contamination of the surface of the article after completion of the previous cleaning cycle, each further cleaning cycle comprising carrying out step (b) and optionally step (c) as defined above, wherein step (b) and optional step (c) are performed in this order if optional step (c) is carried out. No step (a) as described for the first cleaning cycle is performed in the second and further cleaning cycles. According to the invention a cleaning of the surface with a cleaning composition according to step (a) of the process of the invention is only necessary after e.g. 5 cleaning cycles (not including the first basic cleaning cycle), preferably after 10 cleaning cycles (not including the first basic cleaning cycle). However, step (a) should be repeated usually after not more than 50 cleaning cycles (not including the first basic cleaning cycle), preferably not more than 30 cleaning cycles (not including the first basic cleaning cycle).
In a preferred method of the invention step (c) is performed in any cleaning cycle.
Brushes or similar means may be used during cleaning in step (b) of the method of the invention. The applied mechanical energy via brushes or similar means helps in e.g. removing the drying agent used in optional step (c) of the previous cleaning cycle. Furthermore, the brushes also help to apply new polypeptide to the surfaces of articles in step (b) by an exchange of remaining polypeptide deposited on the surface from a previous cleaning cycle (old polypeptide) due to the mass ratio of new polypeptide and old polypeptide.
The method of cleaning of the present invention thus provides multiple advantages. Basic cleaning according to step (a) as described above can be omitted in following cleaning cycles which is environmentally friendly and which allows to save money and time. While the prior art describes cleaning methods that require 40 minutes for cleaning 100 m of train (due to a low velocity of the train required when moving through the cleaning line; if the velocity is increased in conventional methods, cleaning results may be negatively affected or higher concentrations of conventional cleaning compositions have to be used to obtain proper cleaning results), the method according to the invention surprisingly allows to clean 100 m of train in less than 20 minutes, e.g. when using a velocity of 15,2 m/min of the train (length: 100 m) when moving through the cleaning line (length: 70 m) (100 m train + 70 m washing line / 15,2 m/min = 11.2 min) and using 4 min cleaning time each for cleaning the front and the rear of the train during which the train is stopped in the cleaning line (11.2 min + 4 min + 4 min = 19.2 min).
Cleaning cycles can furthermore be increased. The cleaning method of the present invention only makes re-cleaning of a train with a cleaning agent used in step (a) necessary after 12 months. Preferably, re-cleaning with a cleaning agent used in step (a) is done after 5-6 months. In between, the train can be cleaned every 3 to 4 weeks with a cleaning cycle which comprises only step (b) and optionally step (c) (maintenance cleaning). If a conventional cleaning composition was used the recontaminated (after basic cleaning) surface of the article in case of trains would have to be cleaned again every 7 days.
When it is described in the second and further cleaning cycles that step (b) is carried out as defined in the first cleaning cycle this means that the second cleaning composition used in step (b) in the second and further cleaning cycles can be the same as the second cleaning composition used in step (b) of the first cleaning cycle. It can, however, also be different as long as the second cleaning composition contains at least one polypeptide, wherein the total amount of polypeptide in the second cleaning composition is from 9.9*10^-6 wt.-% to 1.2*10^-2 wt.-% based on the total weight of the second cleaning composition and wherein the second cleaning composition is different from the first cleaning composition. Using a cleaning composition in step (b) of all cleaning cycles which contains the same components (the concentrations of the components may differ) is preferred. The drying aid used in optional step (c) in the second and further cleaning cycles can be the same as the drying aid used in step (c) of the first cleaning cycle. This is preferred.
In a preferred embodiment the cleaning method of the present invention is a method comprising a step of diluting a first cleaning concentrate containing at least one member of the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and glycerine and at least 11 wt.-% of oxalic acid, wherein wt.-% is based on the total weight of the cleaning concentrate in order to produce the first cleaning composition, which is used in step (a) of the method. More preferably, a first cleaning concentrate containing at least 15 wt.-%, even more preferably at least 20 wt.-% of dissolved oxalic acid based on the total weight of the cleaning concentrate is diluted in this step. One advantage of the use of oxalic acid is that it is biodegradable. The ethylene glycol content of the concentrate is preferably at least 50 wt.-% based on the total weight of the concentrate. The high amount of ethylene glycol allows the provision of cleaning concentrate solutions with high concentrations of oxalic acid, which are stable at a broad range of temperatures; particularly at e.g. temperatures ≤ 5°C or even ≤ 0°C. In one embodiment of the invention, the method of the invention thus comprises a step of diluting a cleaning concentrate containing at least 50 wt.-% of ethylene glycol, at least 15 wt.-% of oxalic acid and at most 30 wt.-% of water wherein wt.-% is based on the total weight of the cleaning concentrate in order to produce the first cleaning composition, which is used in step (a) of the method. This cleaning concentrate may also contain one or more tensides and phosphoric acid, which is an acid of only medium strength as compared to potentially more harmful strong mineral acids, which are rather avoided in the present invention.
Dilution of the cleaning concentrate can be made with water to a concentration of 1.5 wt.-% to 3 wt.-% oxalic acid based on the total weight of the diluted cleaning composition which can e.g. be sprayed on the surface of an article to be cleaned. Such composition only needs a very short contact time on the surface to be cleaned for efficient cleaning. It has been found that e.g. 15.2 m of a contaminated train may be cleaned with such composition per minute. With conventional cleaners for trains only 2.5 m of a contaminated train may be cleaned per minute in some cleaning lines. This is the case when high concentrations of cleaning compositions should be avoided (higher concentrations may provide for better soil removal, but may damage the surface of articles to be cleaned or generate streaks on the surface). To compensate for less effective soil removal of lower concentrated cleaning compositions, dwell time may be increased by reducing the velocity of a train that moves through the cleaning line to e.g. 2.5 m/min instead of 15.2 m/min.
An oxalic acid and ethylene glycol containing cleaning composition can also advantageously be used on hot surfaces without prior cooling of the surfaces. This is important with trains, since the motor coach after use can be very hot, but also the entire train surface may significantly heat up upon exposure to the sun. In winter, the cleaning concentrate used in the present invention is stable during storage and application of the cleaning composition may be possible around 0°C at which usually only highly aggressive "acidic winter cleaning compositions" (containing e.g. hydrochloric acid, sulphuric acid and/or amido sulfonic acid) are used for cleaning. The invention is therefore also directed to a method of cleaning comprising a step of diluting a first cleaning concentrate containing at least one member of the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and glycerine and at least 11 wt.-% of oxalic acid, wherein wt.-% is based on the total weight of the cleaning concentrate in order to produce the first cleaning composition, which is used in step (a) of the method, wherein the surface cleaned in step (a) of the method has a temperature of 5°C or lower or of 30°C or higher, preferably of 40°C or higher. The surface of the vehicle can e.g. have a temperature of 30°C to 60°C.
It has been pointed out before that the method of the invention is environmentally friendly. When the cleaning composition of step (a) is produced as described above by diluting a cleaning concentrate containing at least one member of the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and glycerine and at least 11 wt.-% of oxalic acid in order to produce the first cleaning composition, which is used in step (a) of the method, and the washing solvent is collected, the oxalic acid may be removed from the waste water completely by addition of hydrogen peroxide which allows to reuse the water.
As the pH of the second cleaning composition can also be moderate (e.g. low alkalinity), this further contributes to an environmentally friendly method of cleaning. The method of the invention therefore also includes a method comprising a step of diluting a second cleaning concentrate having a pH in the range from 7.5 to 9.5 and containing at least one polypeptide, wherein the total amount of polypeptide is from 0.001 wt.-% to 0.5 wt.-% based on the total weight of the concentrate, in order to produce the second cleaning composition which is then used in step (b) of the method of the invention. The second cleaning concentrate is usually an aqueous cleaning concentrate with at least 50 wt.-% water based on the total weight of the cleaning concentrate. It preferably contains at least one tenside. The total tenside concentration may e.g. be up to 11 wt.-% based on the total weight of the cleaning concentrate. The tenside(s) can be, for example, alkylbenzene sulfonate, a-methylester sulfonate, a-sulfonated fatty acids, secondary alkane sulfonate, alcohol sulfate, alcohol ether sulfate, a-olefin sulfonate, sulfo succinic acid ester and/or salts of carboxylic acids. Dilution of cleaning concentrates is usually made with water. Usually, the concentrates are diluted by mixing 1 part by volume of second cleaning concentrate with 40 to 100 parts by volume of water.
It is preferred that the second cleaning concentrate, from which the second cleaning composition used in step (b) may be prepared by dilution, has a high buffering capacity so that at least 0.175 equivalent amount (Val) of acid per liter of cleaning concentrate, preferably at least 0.204 equivalent amount (Val) of acid per liter of cleaning concentrate has to be added to adjust the pH of the cleaning concentrate to 7. This ensures that after dilution of the cleaning concentrate, the final cleaning solution still has a moderate pH-value which facilitates cleaning but is not environmentally harmful.
The pH of the polypeptide containing cleaning composition (second cleaning composition) may affect a shift of the pH on the surface to be cleaned. Polypeptide from a previous cleaning cycle may thus be removed more easily from the surface. Preferably polypeptides of different cleaning cycles do not layer up on the surface to be cleaned.
The at least one polypeptide contained in the second cleaning composition is preferably selected from the group consisting of gelatine, collagen, albumin, casein, soy polypeptide (i.e. soy protein), pea polypeptide (i.e. pea protein), potato polypeptide (i.e. potato protein), wheat polypeptide (i.e. wheat protein), whey polypeptide (i.e. whey protein) or canola polypeptide (i.e. canola protein). Although e.g. soy polypeptide may comprise a mixture of different polypeptides it is considered one polypeptide (in the sense of one kind of polypeptide) for the purpose of the present invention. Similar considerations apply to the other members of the group of polypeptides as defined above. For example, although gelatine may comprise different polypeptides it is considered one polypeptide (in the sense of one kind of polypeptide) for the purpose of the present invention. Gelatine, collagen and albumin may be obtained from animals, such as e.g. cattle, chicken, horse, pig or fish. Gelatine is usually obtained from connective tissue or bones of animals, particularly from the skin or bones of pig or cattle or also from poultry and fish. In a preferred method of the invention, the at least one polypeptide contained in the second cleaning composition is gelatine, more preferably gelatine which creates a pH of 5.50 to 6.00 at 60°C in an aqueous solution of 6.67 wt.-%. The at least one polypeptide contained in the second cleaning composition is preferably gelatine with a molecular weight (M_R) of at least 1000 g/mol and not more than 600000 g/mol, particularly more than 20000 g/mol and not more than 600000 g/mol. The at least one polypeptide can e.g. be gelatine having a molecular weight from 20000 g/mol to 300000 g/mol. The nitrogen content of the gelatine is preferably 16 wt.-% to 19 wt.-%. The hydroxyprolin content is preferably 10 wt.-% to 15 wt.-%. As the at least one polypeptide contained in the second cleaning composition particularly gelatine with one or more of the following features has proved to be successful:

Gel strength (according to AOAC): ≥ 120 g Bloom
Viscosity (6.67 %; 60°C): 3.00 - 4.00 mPa*s
pH (6.67 %; 60°C): 5.50-6.00
transmission (620 nm 6.67 %): ≥ 88 %
transmission (450 nm 6.67 %): ≥ 68 %
conductivity (1.00%; 30°C): ≤ 150 µS/cm
Calcium (Ca complexometric): ≤ 750 ppm

Particularly good cleaning results were obtained with the gelatine having the described features.
As it has been described before, the drying aid used in the present invention is preferably selected from a drying aid containing at least one tenside and/or at least one hydrophilic polymer. A tenside as used herein is considered a compound having amphiphilic properties. For the purpose of the invention a compound which might be considered as both, a tenside or a polymer is designated as tenside. The tenside is preferably a fatty alcohol polyalkylene glycol ether. For example, a C8-C18 alcohol polyalkylene glycol ether is used as drying aid in the present invention. The fatty alcohol polyalkylene glycol ether has preferably less than 100 C-atoms. The hydrophilic polymer is preferably selected from the group consisting of polyvinylalcohol, polyvinylacetate, poly(meth)acrylate, poly(meth)acrylic acid, polyurethane, polyisocanate, polyisothiocyanate and polysuccinimidester. It is more preferably selected from the group consisting of polyvinylalcohol, polyvinylacetate, poly(meth)acrylate and poly(meth)acrylic acid.
A preferred embodiment of the invention is thus a method for cleaning an article comprising a surface wherein the method comprises treating the surface with a drying aid, wherein the drying aid contains at least one tenside as defined above. Preferably, the total amount of tenside contained in the drying aid is from 10^-8 wt.-% to 10^-6 wt.-%, more preferably from 5*10^-8 wt.-% to 5*10^-7 wt.-% based on the total weight of the drying aid.
Another preferred embodiment of the invention is a method for cleaning an article comprising a surface wherein the method comprises treating the surface with a drying aid, wherein the drying aid contains at least one hydrophilic polymer as defined above. Preferably, the total amount of hydrophilic polymer contained in the drying aid is from 10^-8 wt.-% to 10^-6 wt.-%, more preferably from 5*10^-8 wt.-% to 5*10^-7 wt.-% based on the total weight of the drying aid.
A further preferred embodiment of the invention is a method for cleaning an article comprising a surface wherein the method comprises treating the surface with a drying aid, wherein the drying aid contains at least one tenside and at least one hydrophilic polymer as defined above. Preferably, the total amount of tenside and the total amount of hydrophilic polymer contained in the drying aid is from10^-8 wt.-% to 10^-6 wt.-% each, more preferably from 5*10^-8 wt.-% to 5*10^-7 wt.-% each, based on the total weight of the drying aid.
Preferably, the drying aid contains no polypeptide.
A preferred drying aid of the present invention can be obtained by diluting the commercial product Bedos 690 (Boss Chemie, Wittenbach, Switzerland) or the commercial product Propetal 105 (Zschimmer & Schwarz GmbH & Co KG Chemische Fabriken, 56112 Lahnstein, Germany). For use in the process of the method of the present invention Bedos 690 is diluted with water prior to its application. For example, the product Bedos 690 is diluted with about 10000000 part of water (per part of Bedos 690).
The method of the invention is widely applicable. Examples of articles comprising a surface that can be cleaned with the method of the present invention include vehicles such as e.g. a rail vehicle (train, tram etc.), a car, a motor-cycle, a truck, a hanger, and a bus as well as other means of transportation such as an airplane and a ship. The surface itself may e.g. be a metal surface, preferably a coated surface e.g. with paint (lacquer), an anodized surface or a stainless steel surface, etc. It is usually the external surface of articles which is cleaned by the method of the invention. The method of the invention can also be used for cleaning articles comprising a surface wherein the article is e.g. a wind turbine, a traffic sign, a facade of a house, a canvas of a truck or of a marquee. In a preferred method of the invention the article is a vehicle, more preferably a train.
The method of the invention is usually performed within an automated cleaning line.
It has been explained above that the method of the invention is particularly advantageous because it employs only cleaning compositions with moderate pH values. The current invention is therefore also directed to a cleaning concentrate comprising a tenside and a buffering system, wherein the cleaning concentrate has a pH in the range from 7.5 to 9.5 and a buffering capacity so that at least 0.175 equivalent amount (Val) of acid per liter of cleaning concentrate, preferably at least 0.204 equivalent amount (Val) of acid per liter of cleaning concentrate has to be added, to adjust the pH of the cleaning concentrate to 7. If monoprotic acids are used for determining the buffering capacity the equivalent amount (Val) of acid corresponds to the molar amount of acid per liter of cleaning concentrate that has to be added to adjust the pH of the cleaning concentrate to 7. To determine the buffering capacity, the acid (e.g. HCI or H₂SO₄) is added to the cleaning concentrate as a solution of a concentration of 0.1 val/I. When the buffering capacity is thus determined with an HCI solution (monoprotic acid), an HCI solution of 0.1 mol/I is used. When the buffering capacity is determined with H₂SO₄ solution, an H₂SO₄ solution of 0.05 mol/I is used. In one embodiment, the cleaning concentrate of the present invention comprises a tenside and a buffering system, wherein the cleaning concentrate has a pH in the range from 7.5 to 9.5 and a buffering capacity so that at least 0.182 mol of HCI per liter of cleaning concentrate, preferably at least 0.216 mol of HCI per liter of cleaning concentrate has to be added to adjust the pH of the cleaning concentrate to 7, whereby the HCI is added to the cleaning concentrate in form of a 0.1 mol/I solution to determine the buffering capacity. A buffering system based on a multicarboxylic acid such as citric acid, malic acid, fumaric acid, succinic acid or maleic acid may be used. A borate buffer may also be used. Preferably the cleaning concentrate of the invention comprises as buffering system based on tartaric acid or citric acid. From the cleaning concentrate of the present invention the second cleaning composition to be used in step (b) of the method of the present invention may be prepared upon addition of a polypeptide and dilution.
The cleaning concentrate according to the invention is an aqueous cleaning concentrate. It contains preferably at least 50 wt.-% water based on the total weight of the aqueous cleaning concentrate. The cleaning concentrate of the present invention can be diluted to different extents, preferably with water, to obtain a cleaning composition which is particularly useful in the method of the present invention. The cleaning concentrate itself is preferably not directly applied to a surface of an article. The cleaning concentrate of the present invention having a moderate pH value and a high buffering capacity is particularly advantageous because it allows to carefully control the pH-value of the cleaning composition after dilution. A moderate pH-value in the second cleaning composition used in step (b) of the method of the invention is particularly advantageous to make best use of the polypeptide in this cleaning composition. Many polypeptides, in particular the most preferred gelatine are pH-sensitive and thus work best at a moderate pH, e.g. in the range of 4 to 10. Furthermore, when the cleaning composition to be applied to a surface, which is prepared from the cleaning concentrate of the invention, still has a high buffering capacity, it is less affected in terms of pH by eventual remnants of a cleaning composition of a different pH of a previous cleaning step, which might not have been rinsed off the surface with water before the following cleaning step. A rinsing step may thus become omissible speeding up the procedure.
It is particularly advantageous to add the polypeptide already to the cleaning concentrate of the present invention. In a preferred embodiment, the invention thus concerns a cleaning concentrate containing at least one polypeptide, wherein the total amount of polypeptide in the cleaning concentrate is from 0.001 wt.-% to 0.5 wt.-% based on the total weight of the cleaning concentrate. At least one polypeptide contained in the cleaning concentrate of the invention is preferably contained as a molecular dispersion (i.e. dissolved) or as a colloidal dispersion with a particle size in the range from 1 nm to 1000 nm. Preferably, the cleaning concentrate of the present invention does not contain encapsulated substances. In one embodiment, the total amount of polypeptide is from 0.01 wt.-% to 0.1 wt.-% based on the total weight of the cleaning concentrate, more preferably from 0.03 wt.-% to 0.05 wt.-% based on the total weight of the cleaning concentrate. The at least one polypeptide in the cleaning concentrate of the invention is preferably gelatine, more preferably gelatin which creates a pH of 5.50 to 6.00 at 60°C in an aqueous solution of 6.67 wt.-%. The cleaning concentrates as defined above can be used in the method of the invention, when it comprises a step of diluting the cleaning concentrate to obtain the second cleaning composition. The invention is thus also directed to a cleaning method comprising a step of diluting a polypeptide containing cleaning concentrate in order to produce the second cleaning composition which is used in step (b) of the method. If the polypeptide is not already a component of the cleaning concentrate of the present invention, the polypeptide has to be added to the cleaning composition after or during dilution of the cleaning concentrate. Concentrates are generally advantageous (provided that they are safe, e.g. they do not have extreme pH values which are avoided in the present invention) as they have lower transport and storage costs than voluminous diluted compositions.
The following examples are intended to illustrate the invention without however limiting it.
Figures 1 and 2 show schematically conventional cleaning lines that have been used for cleaning a train in the following examples

Example 1

First cleaning concentrate

A first cleaning concentrate was prepared as follows: 27 parts by weight of oxalic acid dihydrate were dissolved in 59.21 parts by weight of ethylene glycol at about 30°C. 13.5 parts by weight of ortho phosphoric acid 75%, 0.27 parts by weight of alkyl benzene sulfonic acid and 0.02 parts by weight of Rewocare 755 (Evonic Industries, Germany) were added to the solution.
Samples of the cleaning concentrate were stored at temperatures of -5°C, -10°C and -15°C for 14 days each. After storage the samples showed no change such as turbidity, precipitation etc. The samples were still clear solutions. Another sample of the cleaning concentrate was stored at 60°C for 24 h and subsequently slowly cooled to 5°C. No layering, precipitation and color change could be observed in the sample

First cleaning composition

For cleaning a train as described below, 1 part by volume of the first cleaning concentrate was mixed with 8 parts by volume of water (when it is referred to water without further specifying the type of water, fresh water is meant hereafter) to obtain the first cleaning composition as applied on the train surface in the cleaning process (cleaning step (a)). Alternatively, the first cleaning composition could be prepared directly in the concentration of use on the train surface, thus omitting the preparation of a first cleaning concentrate and its dilution.

Second cleaning concentrate

A second cleaning concentrate was prepared as follows: 10 parts by weight of potassium hydrogen tartrate were mixed with 35 parts by weight of water at about 40°C. The forming precipitate was dissolved by addition of sodium hydroxide until a pH of 10.2 was obtained. 1.5 parts by weight of alkyl ether sulfate C12-14 with EO, sodium salt (content ≥ 20 % - < 30 %) (Texapon NSO UP), 2.1 parts by weight of isotridecanol, ethoxylated (>5-20 EO) (Marlipal O 13/90), 7 parts by weight of sodium cumene sulfonate (content ≥ 25 % - < 50 %) (Lutensit TC-CS 40), 0.07 parts by weight of Rewocare 755 (Evonik Industries, Germany), 0.02 parts by weight of orange terpenes, 3 parts by weight of ethylene glycol and 2 parts by weight of butyl diglycol were added to the mixture. Furthermore, 0.038 parts by weight of gelatine were added to the mixture. Therefore gelatine (Novotec® 100, Gelita Deutschland GmbH, Eberbach Germany) was soaked in cold water for 20 min and subsequently dissolved at 60°C and this preparation was added to the mixture. Finally, 0.05 parts by weight of Parmetol A26 (Schülke & Mayr GmbH, Norderstedt, Germany) were added to the mixture and the pH of the mixture was adjusted to < 9.5. In total (including the sodium hydroxide used in the beginning of the preparation of the second cleaning concentrate, see above), 2.2 - 2.25 parts by weight of sodium hydroxide were thus used to prepare the second cleaning concentrate. The remaining parts by weight of the cleaning concentrate is water. A dye may be added.
This second cleaning concentrate was stored for 14 days without showing any visible change such as turbidity, precipitation etc.

Second cleaning compositions

For cleaning a train as described below, the second cleaning concentrate was diluted with water as follows to obtain the second cleaning compositions (table I) as applied at the different stands on the train surface in the cleaning process, see below (cleaning step (b)):
Alternatively, second cleaning compositions could be prepared directly in the concentrations of use on the train surface, thus omitting the preparation of a second cleaning concentrate and its dilution.

Drying aid

A drying aid concentrate was prepared as follows: 0.454 parts by weight of Bedos 690 (Boss Chemie, Wittenbach, Switzerland) were mixed with 99.496 parts by weight of water. 0.05 parts by weight of a preservative (Parmetol A 26, Schülke & Mayr GmbH, Norderstedt, Germany) were added to avoid formation of streaks in the composition and development of bad odor.
The drying aid concentrate was stored for 14 days without showing any visible change such as turbidity, precipitation etc.
For cleaning a train as described below, 1 part by volume of the drying aid concentrate was mixed with 46500 parts by volume of water to obtain the drying aid as applied on the train surface in the cleaning process (cleaning step (c)). Alternatively, the drying aid could be prepared directly in the concentration of use on the train surface, thus omitting the preparation of the drying aid concentrate and its dilution.

Cleaning process

A conventional cleaning line (Figure 1) for trains was used to show the effectiveness of the method of the invention using the compositions as defined above. A standard train (two-part diesel railcar (series 628 by Düwag, Waggon-Union, AEG i.a.)) having a length of 46 m was used for this example. The train had visible contamination on the train surface. The train moved through the cleaning line with a velocity of 15.2 m/min. The cleaning line had a length of 70 m and the complete cleaning cycle was finished after 23.63 minutes.
The train was moved through the cleaning line with a constant velocity (by a tow carriage via a rope).
At the precleaning stand, first cleaning composition (composed of 1 part by volume of the first cleaning concentrate and 8 parts by volume of water) was sprayed onto the train (cleaning step (a)). After 3.3 m the front of the train reached washing stand A where first cleaning composition (composed of 1 part by volume of the first cleaning concentrate and 8 parts by volume of water) was applied to the entire side area of the train and brushed in via side brushes.
In between, after the front of the train had passed washing stand A by about 3-4 m, the entire process (spray arch at precleaning stand and application of first cleaning composition and brushing in via side brushes at washing stand A) was interrupted and second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 72 parts by volume of water) was applied to the front of the train and brushed in via the top brush of cleaning stand A by relative movement of washing stand A to the train which was stopped in the cleaning line for this procedure (the tow carriage stands still). This procedure took 8 minutes, which could, however, also be shortened if desired while still obtaining good cleaning results. Subsequently, the train was moved further through the cleaning line and reached washing stand B after 46 m. At washing stand B, second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 85 parts by volume of water) was applied to the train and brushed in via the side brushes. Immediately after washing stand B the surface of the train was rinsed with process water at postcleaning stand I.
After 6 m the train reached postcleaning stand II, where it was rinsed with drying aid (composed of 1 part by volume of the drying aid concentrate and 46500 parts by volume of water). After 3 more meters the train was again rinsed with process water at postcleaning stand III.
After the train had passed washing stand B, the entire process was interrupted and second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 85 parts by volume of water) was applied to the rear of the train and brushed in via the top brush by relative movement of washing stand B to the train which was stopped in the cleaning line for this procedure (the tow carriage stands still). This procedure took 8 minutes, which could, however, also be shortened if desired while still obtaining good cleaning results.
Thereafter, the train was further moved through the cleaning line so that the rear of the train finally also passed the postcleaning stands and the entire train left the cleaning line after 23.63 min.
From the following Table II the details regarding the amount of composition sprayed, spray pressure, spray temperature and spray time etc. can be seen.
After the train had left the cleaning line it showed no visible contaminations and had a clean and very shiny surface.
The train was then used in a conventional manner for 28 days. After this time visible contamination could be seen on the train surface.
The contaminated train was again brought to a cleaning line for carrying out a second cleaning cycle. During this second cleaning cycle no first cleaning composition was used, but the train was only treated with second cleaning composition - containing the polypeptide - and the drying aid and rinsed.
The train was moved through the cleaning line with a constant velocity.
At the precleaning stand, second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 100 parts by volume of water) was sprayed onto the train. After 3.3 m the front of the train reached washing stand A where second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 80 parts by volume of water) was applied to the entire side area of the train and brushed in via side brushes.
In between, after the front of the train had passed washing stand A by about 3-4 m, the entire process (spray arch at precleaning stand and application of second cleaning composition and brushing in via side brushes at washing stand A) was interrupted and second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 50 parts by volume of water) was applied to the front of the train and brushed in via the top brush of cleaning stand A by relative movement of washing stand A to the train which was stopped in the cleaning line for this procedure (the tow carriage stands still). This procedure took 8 minutes, which could, however, also be shortened if desired while still obtaining good cleaning results. Subsequently, the train was moved further through the cleaning line and reached washing stand B after 46 m. At washing stand B, second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 85 parts by volume of water) was applied to the train and brushed in via the side brushes. Immediately after washing stand B the surface of the train was rinsed with process water at postcleaning stand I.
After 6 m the train reached postcleaning stand II, where it was rinsed with drying aid (composed of 1 part by volume of the drying aid concentrate and 46500 parts by volume of water). After 3 more meters the train was again rinsed with process water at postcleaning stand III.
After the train had passed washing stand B, the entire process was interrupted and second cleaning composition (composed of 1 part by volume of the second cleaning concentrate and 85 parts by volume of water) was applied to the rear of the train and brushed in via the top brush by relative movement of washing stand B to the train which was stopped in the cleaning line for this procedure (the tow carriage stands still). This procedure took 8 minutes, which could, however, also be shortened if desired while still obtaining good cleaning results.
Thereafter, the train was further moved through the cleaning line so that the rear of the train finally also passed the postcleaning stands and the entire train left the cleaning line after 23.63 min.
From the following Table III the details regarding the amount of composition sprayed, spray pressure, spray temperature and spray time etc. can be seen.
The whole second cleaning cycle (maintenance cleaning) took < 23.63 minutes.
After leaving the cleaning line the train had again the same clean and shining surface as after the first cleaning cycle (basic cleaning).
Use and contamination of the train and applying a cleaning cycle without using the first cleaning composition was repeated for 5 (it may also be possible to repeat even for 11) times before the cleaning result was considered not being satisfactory. At that time the whole cleaning process including cleaning step (a) was repeated (basic cleaning).
Compared with a conventional use of a cleaning line a total of about 1000 liters of concentrates could be saved and a total of about 40 hours of cleaning time could also be saved per year for cleaning a train as described above, while still having the same excellent cleaning result as with a conventional cleaning method (table IV). For comparison of the conventional method with the method of the invention, a maintenance cleaning interval of 7 d must be considered for the conventional method. Only with such short cleaning intervals, the appearance of the train at the end of the interval is still acceptable. In practice, however, maintenance cleaning with the conventional method is only performed every 14 days despite the trains being very dirty after 14 days. Nevertheless, when comparing the method of the invention with the conventional method as usually practiced (re-cleaning every 14 days), the method of the invention still saves a total of about 450 liters of concentrates and a total of about 30 hours of cleaning time per year for cleaning a train as described above (table IV). One reason for this is that the method of the invention allows maintenance cleaning intervals of 28 (instead of 7 or 14 days) with a still acceptable appearance of the trains at the end of the 28 day use-period.

Comparative example 1

The same standard train as used in example 1 was subjected to a conventional cleaning process.
For basic cleaning, the train was sprayed step-by-step with an alkaline cleaning composition (composed of 1 part by volume of an alkaline cleaning concentrate and 3 parts by volume of water) using manual spray equipment. The cleaning concentrate contained butyl diglycol (< 5 wt.-%), coconut acid, diethanolamide (< 5 wt.-%), 2-aminoethanol (< 5 wt.-%), a mixture of anionic and non-ionic tensides (< 5 wt.-%). Depending on the ambient temperature the sections to be sprayed have to be adjusted as such that the cleaning concentrate does not dry on the surface of the train.
Subsequently, the entire train surface was rubbed with manual cleaning sponges. The procedure was repeated until all soil was removed. Thereafter, the surface of the train was rinsed with water. Windows and window frames were cleaned with pumice powder (quartz free) under addition of alcohol using white scouring sponges. Subsequently, they were rinsed with water.
For maintenance cleaning, the train was moved through a conventional cleaning line (Figure 2) with a constant velocity of 15.2 m/min. The cleaning line had a length of 70 m.
At the precleaning stand, the front of the train was sprayed with an insect removing composition (composed of 1 part by volume of an insect removing concentrate and 14 parts by volume of water; the insect removing concentrate containing a mixture of ionogenic and non-ionogenic tensides (< 5 wt.-%), butyl diglycol (< 5 wt.-%) and solvents (< 5 wt-%). 20 cm further along the cleaning line, the entire train was sprayed with water to decrease the surface temperature. After 3.3 m the front of the train reached washing stand A where a cleaning composition (composed of 1 part by volume of the cleaning concentrate and 14 parts by volume of water; the cleaning concentrate containing aluminum sulfate, 18 hydrate, oxalic acid dihydrate ( 5 - 15 wt.-%), citric acid (< 5 wt.-%), sodium isoalkyl sulphate (< 5 wt.-%), alkane sulfone sodium salt (< 5 wt.-%) was applied to the entire side area of the train and brushed in via side brushes.
In between, after the front of the train had passed washing stand A by about 3-4 m, the entire process (spray arch at precleaning stand and application of cleaning composition and brushing in via side brushes at washing stand A) was interrupted and cleaning composition (composed of 1 part by volume of the cleaning concentrate as described above and 14 parts by volume of water) was applied to the front of the train and brushed in via the top brush of cleaning stand A by relative movement of washing stand A to the train which was stopped in the cleaning line for this procedure. This procedure took 8 minutes.
Subsequently, the train was moved further through the cleaning line and reached washing stand B after 46 m. At washing stand B, the side areas of the train were brushed thoroughly via the side brushes of the washing stand B while adding water.
Immediately after washing stand B the surface of the train was rinsed with process water at postcleaning stand I.
After 6 m the train reached postcleaning stand II, where it was rinsed with water. After 3 more meters the train was again rinsed with process water at postcleaning stand III. After 4 m, the windows of the train were rinsed at an additional postcleaning stand IV with water.
After the train had passed washing stand B, the entire process was interrupted and the rear of the train was brushed thoroughly via the top brush of washing stand B without application of cleaning composition. The train was stopped in the cleaning line for this procedure which took 8 minutes.
Thereafter, the train was further moved through the cleaning line so that the rear of the train finally also passed the postcleaning stands and the entire train left the cleaning line after 23.63 min.
The train was used under essentially the same conditions as the train that has been cleaned in example 1. After 2 weeks the train surface showed clear signs of contamination and the train had to be subjected to the same conventional maintenance cleaning method as described above.

Claims

A method for cleaning an article comprising a surface wherein the method comprises a first cleaning cycle comprising
(a) cleaning the surface with a first cleaning composition,

(b) cleaning the surface with a second cleaning composition containing at least one polypeptide, wherein the total amount of polypeptide in the second cleaning composition is from 9.9*10^-6 wt.-% to 1.2*10^-2 wt.-% based on the total weight of the second cleaning composition and wherein the second cleaning composition is different from the first cleaning composition, and

(c) optionally treating the surface with a drying aid,
wherein step (a), step (b) and, if optional step (c) is carried out, optional step (c) are performed in this order.
Method according to claim 1 wherein the method additionally comprises a second cleaning cycle which is carried out after the surface of the article became contaminated after the first cleaning cycle, the second cleaning cycle comprising carrying out step (b) and optionally step (c) as defined in claim 1, wherein step (b) and optional step (c) are performed in this order if optional step (c) is carried out.
Method according to claim 2 wherein the method additionally comprises one or more further cleaning cycles, each cleaning cycle being performed after contamination of the surface of the article after completion of the previous cleaning cycle, each further cleaning cycle comprising carrying out step (b) and optionally step (c) as defined in claim 1, wherein step (b) and optional step (c) are performed in this order if optional step (c) is carried out.
Method according to any of claims 1-3 wherein step (c) is performed in any cleaning cycle.
Method according to any of claims 1-4 comprising a step of diluting a cleaning concentrate containing at least one member of the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and glycerine and at least 11 wt.-% of oxalic acid, wherein wt.-% is based on the total weight of the cleaning concentrate in order to produce the first cleaning composition, which is used in step (a) of the method.
Method according to claim 5 wherein the surface cleaned in step (a) of the method has a temperature of 5°C or lower or of 30°C or higher, preferably of 40°C or higher.
Method according to any of claims 1-6 comprising a step of diluting a cleaning concentrate having a pH in the range from 7.5 to 9.5 and containing at least one polypeptide, wherein the total amount of polypeptide is from 0.001 wt.-% to 0.5 wt.-% based on the total weight of the concentrate, in order to produce the second cleaning composition which is used in step (b) of the method.
Method according to any of claims 1-7 wherein the at least one polypeptide contained in the second cleaning composition is gelatine, preferably gelatine which creates a pH of 5.50 to 6.00 at 60°C in an aqueous solution of 6.67 wt.-%.
Method according to any of claims 1-8 comprising treating the surface with a drying aid, wherein the drying aid contains at least one tenside and/or at least one hydrophilic polymer.
Method according to claim 9 comprising treating the surface with a drying aid, wherein the drying aid contains at least one tenside and the total amount of tenside in the drying aid is from 5*10^-8 wt.-% to 5*10^-7 wt.-% based on the total weight of the drying aid.
Method according to claim 9 comprising treating the surface with a drying aid, wherein the drying aid contains at least one hydrophilic polymer and the total amount of hydrophilic polymer in the drying aid is from 5*10^-8 wt.-% to 5*10^-7 wt.-% based on the total weight of the drying aid.
Method according to any of claims 1-11, wherein the article is a vehicle, preferably a train.
Cleaning concentrate comprising a tenside and a buffering system, wherein the cleaning concentrate has a pH in the range from 7.5 to 9.5 and a buffering capacity so that at least 0.175 equivalent amount (Val) of acid per liter of cleaning concentrate has to be added to adjust the pH of the cleaning concentrate to 7.
Cleaning concentrate according to claim 13 wherein the buffering system is based on tartaric acid or citric acid.
Cleaning concentrate according to claim 13 or 14 containing at least one polypeptide, wherein the total amount of polypeptide in the cleaning concentrate is from 0.001 wt.-% to 0.5 wt.-% based on the total weight of the cleaning concentrate.
Cleaning concentrate according to claim 15 wherein the at least one polypeptide contained in the cleaning concentrate is gelatine, preferably gelatine which creates a pH of 5.50 to 6.00 at 60°C in an aqueous solution of 6.67 wt.-%.
Method according to any of claims 1-12 comprising a step of diluting a cleaning concentrate according to claim 15 or 16 in order to produce the second cleaning composition which is used in step (b) of the method.