AU714410B2 - A process for the machine cleaning of returnable containers soiled with stubborn soils - Google Patents

Description

A Process for the Machine Cleaning of Returnable Containers Soiled with Stubborn Soils This invention relates to a process for the machine cleaning of returnable food containers soiled with stubborn soils, more particularly particulate soils, in which the containers are treated in a washing machine with cleaning chemicals known per se in the food industry.

Food containers intended for re-use are machine-cleaned in large installations after their return from the consumer. In many cases, not all the soils adhering to the containers can be removed with the cleaning chemicals used therein, such as caustic soda in conjunction with surfactants, under the prevailing conditions, namely temperature, time, etc. The stubborn soils in question are not only soils typical of the particular container, but also difficult soils which are formed by excessively long and inappropriate storage of only partly empty containers and by the use of the food containers for other purposes by the customer. Examples of such stubborn soils include yeasts, moulds, caked-on organic residues, glue residues emanating from labels, oil, fats, foreign flavours and aromas, inorganic salts, dyes, etc.

In view of the stringent hygiene requirements imposed in the food industry, microorganism-containing soils represent a particularly serious problem which is explained in more detail in the following with reference by way of example to returnable beverage containers made of plastic. However, the invention is by no means confined to the removal of microorganisms from plastic containers.

In known processes, the returnable bottles are cleaned in bottle washing machines with caustic soda heated to 85 0 C in conjunction with additives. In the summer months in particular, the returnable bottles contain a large number of microorganisms when they come back empty from consumers. The bottles are often exposed for several days or even weeks to temperatures favourable to the growth of microorganisms. Yeasts are thus able to proliferate and to ferment the remains of the beverage while moulds form lawns in the bottles.

To remove the usual soils and beverage remains, the bottles are washed with water (preliminary cleaning) and then treated with 1.5 to 3.0% caustic soda heated to 50 to 85 0 C in corresponding baths. However, this cleaning step is not sufficient to remove all the microorganisms and other stubborn soils. Because of this, complexing agents, for example EDTA (ethylenediamine tetraacetic acid) and/or NTA (nitrilotriacetate), are added to the caustic baths to enable the microorganisms to be satisfactorily removed in the case of glass bottles.

However, in the cleaning of refillable plastic bottles consisting, for example, of PET (polyethylene terephthalate), the use of caustic baths containing added complexing agents, such as those already mentioned, does not have the required ~2ffect. After cleaning, unacceptable residues of moulds and dead yeast cells C00162 remain on the surfaces of the plastic bottles where they can be seen, for example, in the form of black spots.

Other stubborn soils, for example rust residues on or in glass containers, are also resistant to normal machine cleaning processes for returnable containers in the food industry. Another difficulty involved in solving this problem is that only those cleaning chemicals or additives which satisfy both the anti-corrosion and processrelated requirements of the washing machine and the cleaning process and also economical and ecological criteria can be used in the washing machines routinely employed in the food industry. For example, no acids can be used in the highly alkaline cleaning baths. The introduction of high-quality additives, which are consumed by the soiling of the cleaning bath itself, is also out of the question for economic reasons. In addition, for reasons that need not be explained here, the choice of the cleaning formulation and its composition is further limited by the particular machine-cleaning process and the washing machine itself.

It has surprisingly been found that the problem of effectively removing microorganisms from plastic bottles can be solved by using oxidising agents which release available oxygen, for example perborates or hydrogen peroxide. It is specifically pointed out that the present invention is not directed to disinfection by destruction of the microorganisms, but rather to the mechanical detachment and removal of soils adhering firmly to the surfaces of the containers, for example the black spots encountered in practice and also other stubborn soils. It has been found that the soils, particularly microorganisms, are thoroughly and satisfactorily detached from the plastic surfaces after exposure for only a few minutes to the oxidising agents in question.

The use of oxidising agents in connection with the cleaning of returnable plastic food containers is known from DE 43 22 328 Al. In this case, however, the oxidising agent is not used to clean the containers, but instead to treat the containers after they have been cleaned in order to eliminate constituents which have migrated, more particularly flavour components. This is because if, for example, a plastic bottle is refilled with a different beverage, the taste of the beverage in question can be affected by flavour constituents which have migrated into the plastic. In order to obviate this disadvantage, the proposal disclosed in the cited document is characterised in that, whenever the beverage is changed, all the cleaned containers are subjected to a treatment with oxidising agents. Accordingly, the known process does not seek to clean the containers by removing stubborn soils, but rather to subject containers which have already been cleaned to an aftertreatment.

However, if the oxidising agents releasing available oxygen are incorporated N the cleaning liquids known per se, for example by addition to the cleaning baths bottle washing machines, further problems arise. The oxidising agents C00162 3 decompose very quickly in the generally heavily polluted cleaning baths so that relatively large quantities of oxidising agent have to be continuously added. The consumption of oxidising agent is so high that the process cannot be used to remove the soils with oxidising agents on economic grounds. A variant of the process, in which a solution containing the oxidising agents is introduced onto or into the containers through separate spray pipes, is also uneconomical because the oxidising agent can only be used once for a single container.

The invention is concerned not only with the special problem of achieving the satisfactory removal of microorganisms from returnable food containers in a thorough and, at the same time, economical manner, but also with the thorough and economic removal from such containers of stubborn soils which cannot be removed during normal automatic machine cleaning for technical or economic reasons. As mentioned above, the soils to be removed are not only microorganisms, but also for example stubborn organic residues, glue residues, oils, fats, flavours and aromas, inorganic salts, dyes, etc.

Accordingly, the problem addressed by the present invention was to achieve thorough and satisfactory removal from returnable containers of stubborn soils, which cannot be economically removed by normal machine cleaning, in a particularly economical, inexpensive and ecologically friendly manner in the process mentioned at the beginning.

According to the invention, the solution to this problem is characterised in that the containers soiled with the stubborn soils, more particularly particulate soils, are detected by a sensor before and/or after cleaning with known cleaning chemicals in the washing machine, are automatically removed from the line and only the containers which have been removed are treated one or more times in at least one separate step with at least one chemical which is not used in the washing machine (separate treatment) and which is suitable for removing the soils.

Instead of the simultaneous treatment of all the returnable containers both with the cleaning chemicals known per se and with a chemical which detaches the stubborn soils or residues, the invention proposes firstly a treatment separate from the cleaning known per se to remove these special soils and, secondly, a limitation of the treatment to containers which have been automatically removed from the line beforehand. Accordingly, the consumption of the special chemical on the one hand is dramatically reduced by comparison with the use of this chemical in the normal machine cleaning process, because some of these chemicals decompose in the presence of the highly polluted cleaning bath. On the other hand, even those chemicals which have no effect when added to the cleaning bath, for example acids in the case of the usual alkaline cleaning baths, and/or which should not be used in A, rmal machine cleaning, for example on corrosion grounds, may be used in the p cess according to the invention. Finally, not all containers, but only problem C00162 4 containers are subjected to the treatment with the special chemical. In addition, the treatment step separate from the actual cleaning processes enables the special chemical to be repeatedly used, irrespective of whether the process is carried out continuously or discontinuously, and provides for the economic use of otherwise overly expensive mechanical cleaning steps because only the heavily soiled containers have to be subjected to this separate treatment.

The following preferred examples are mentioned as special chemicals for removing stubborn soils. Stubborn organic residues, glue residues emanating from labels, oils, fats and dyes can be removed by oxidising agents, surfactants and/or complexing agents. Oxidative chemicals are particularly suitable for removing flavours and aromas. Complexing agents and acids are preferably used for removing inorganic salts adhering firmly to the containers.

Accordingly, the containers removed from the line are treated in the separate step with oxidising agents and/or acids, optionally in conjunction with other chemicals, such as surfactants or complexing agents.

The process according to the invention can be carried out with particular advantage when the containers consist of plastic and, more particularly, are plastic bottles which are cleaned in bottle washing machines, because these containers lend themselves particularly well to thorough and economic cleaning. This applies in particular to microorganisms adhering firmly to the plastic containers.

Accordingly, one particularly preferred embodiment of the invention is characterised in that containers stubbornly soiled with microorganisms, such as yeasts, moulds and the like, are removed from the line and the containers removed from the line are treated with at least one oxidising agent yielding available oxygen.

In order to intensify the separate treatment of these containers, the containers removed from the line are additionally treated with inorganic and/or organic acids and/or surfactants and/or complexing agents. Suitable complexing agents are, for example, EDTA, NTA, phosphates, gluconates, etc.

By way of clarification, it is pointed out that the term "cleaning chemical" used in the present application applies to the cleaning concentrate while the term "cleaning liquid" applies to the ready-to-used dilute solution of the cleaning concentrate in water.

The following factors were taken into consideration in the choice of the special chemicals used in accordance with the invention for the separate treatment of the containers removed from the line. The chemicals used in the process and their decomposition products are readily soluble in water, odourless and tasteless and, in addition, do not represent any threat to the environment. Discolouration of the plastic container and/or attacks on the surface of the plastic material are avoided.

ALQ the process according to the invention, the plastic materials of the container are o? ly exposed to relatively low temperatures or only briefly to relatively high C00162 temperatures, so that no deformation occurs. The process according to the invention is suitable for cleaning glass or plastic containers for accommodating beverages and/or milk products, the containers preferably consisting of polyethylene terephthalate (PET), polycarbonate polypropylene

(PP),

polyacrylonitrile (PAN), polyethylene naphthalate (PEN) or polyvinyl chloride (PVC).

In one particularly preferred variant of the process, the stubbornly soiled containers are only detected after cleaning in a washing machine which uses cleaning chemicals known per se (in the case of bottles, a bottle washing machine known per se), the containers are removed from the line and are then subjected to the separate treatment. In this case, only those containers which have already passed once through the washing machine are subjected to the separate treatment, so that the solution preferably used repeatedly for the separate treatment is only lightly polluted with organic residues. In the case of oxidising agents, it is possible through degradation curves to show that these solutions, for example containing perborate or peroxide, show very high stability, so that the quantities of oxidising agent required are relatively small.

The separately treated containers are preferably returned to the beginning of the washing machine. This "recirculation" ensures that only cleaned containers which have been freed from the stubborn soils and which, in particular, are in a microbiologically satisfactory state collect at the exit of the washing machine. The containers still containing residues pass through the treatment stage with the oxidising agent several times.

In another advantageous embodiment of the process according to the invention, the stubbornly soiled containers are detected before cleaning in the washing machine, removed from the line, subjected to the separate treatment and then returned to the beginning of the washing machine. In this variant, too, it is of advantage to return the separately treated containers to the beginning of the sensor unit in order to ensure complete removal of the stubborn soils in every case.

In one particularly economic variant of the process according to the invention, the containers removed from the line pass directly to the filling and labelling stations after the separate treatment, and, optionally, a subsequent rinsing step.

The sensor unit used in the process according to the invention for detecting the stubbornly soiled and, in particular, microorganism-infested containers can assume different forms. Thus, these containers may be detected by an optical and/or chemical detector. In the first case, a so-called bottle inspector operates by a transillumination method. In the second case, the door is detected by a so-called sniffer. These sensors are known per se and, accordingly, need not be described in detail here. However, other sensors are also suitable for use in the process cording to the invention.

C00162 6 In another embodiment, the chemical used in the separate treatment is sprayed into and/or onto the containers and/or the treatment is carried out in a bath.

An optimal combination of chemical and mechanical effects is achieved in the spraying process.

The stubbornly soiled containers are preferably treated with an aqueous solution.

In addition to the principal component, such as oxidising agent and/or acid, the chemical used for the separate treatment may with advantage additionally contain surfactants, for example anionic, cationic and/or nonionic surfactants, sugar surfactants, and polyacrylates, phosphates and phosphonates which facilitate or improve detachment of the stubborn soils and, in particular, the microorganisms from the surfaces of the containers. In addition, the presence of complexing agents, for example EDTA, and terpenes and/or solvents, for example alcohols or dimethylsulfoxide, is of advantage. The additional ingredients may be present separately or in combination in the liquid phase. In particular, they improve the effect of the oxidising agent in detaching the microorganisms from the plastic surfaces.

The process according to the invention for separately treating the containers may be carried out over a wide temperature range. Generally speaking, the higher the temperature used, the more effective the detachment of the stubborn soils from the containers, more particularly from the interior of bottles. In the separate treatment of plastic containers, temperatures towards the upper end of the range shown below may be applied. At all events, however, the stability of the containers depending on the particular plastic must be guaranteed. The separate treatment of the containers with oxidising agents at temperatures of 0 to 900C and preferably in the range from 20 0 C to below the softening temperature of the particular plastic is preferred. For example, the upper limit of the temperature range for PET material is below 600C and, for PC material, up to 80 0

C.

It has been found to be favourable to allow the separate treatment chemical, more particularly the oxidising agent, to act on the containers for 0.5 to 10 minutes and preferably for 1 to 8 minutes. These times apply both where the containers are exposed to the liquid phase in a bath and where the liquid phase is applied to the containers by spraying.

In one preferred embodiment of the invention, the oxidising agents are selected from organic peracids, alkaline hypochlorites, hydrogen peroxide, alkaline perborates and alkaline percarbonates. Perborates, for example sodium perborate, are particularly preferred.

It has also been found to be of particular advantage to use perborates in the ,17 4m of an aqueous solution with a concentration of 0.001 to 2% by weight, C00162 preferably 0.01 to 1.5% by weight and more preferably 0.1 to 1% by weight, as the oxidising agent.

In another preferred embodiment, organic per acids in the form of an aqueous solution, more particularly peracetic acid and/or perpropionic acid, are used as the oxidising agent, the per acid content of the aqueous solution being between 0.001 and 40% by weight, preferably between 0.01 and 5% by weight and more preferably between 0.05 and 2% by weight.

In the process according to the invention, the chemical used for the separate treatment may be added to an aqueous treatment solution in the form of a watercontaining or powder-form concentrate.

The particular advantages of the process according to the invention may be summarised as follows. Soils which require reactive cleaning chemicals can be removed in an economical and thorough manner, only relatively small quantities of the cleaning chemicals being required. Cleaning chemicals which attack normal washing machines, for example acids, may even be used. Even cleaning chemicals which are ecologically unfavourable in normal cleaning processes may be safely used in the process according to the invention because the pollution level of the wastewater is considerably lower by virtue of the small quantity of cleaning solution and, for this reason, the wastewater can also be treated particularly inexpensively. According to the invention, even processes which can only be carried out to a limited extent, if at all, in the usual, very much larger washing machines on technical and/or economical grounds may be used for the separate treatment.

Examples of embodiment of the invention are described in detail in the following with reference to the accompanying drawings, wherein: Figure 1 is a schematic flow chart of a first continuous embodiment of the invention where the containers are removed from the line before passing through the washing machine.

Figure 2 shows a flow chart corresponding to Fig. 1 of a second embodiment of the invention where the containers are only removed from the line after passing through the washing machine.

Figure 3 is a flow chart of a third embodiment of the invention.

Figure 4 is a flow chart of a fourth embodiment of the invention.

Figure 5 is a flow chart of a fifth embodiment of the corresponding to Fig. 2 except that the process is carried out discontinuously.

Figure 6 is a flow chart of a fourth embodiment of the invention corresponding to Fig. 5 where the containers are removed from the line before passing through the washing machine.

In all the drawings, the same reference numerals have the same meanings and accordingly, are explained only once.

C00162 8 In the process shown in Fig. 1 which is particularly suitable for removing flavours from the containers, the returnable plastic containers to be cleaned are sniffed by a sniffer 1 to determine whether any door-emitting soils are present in the bottles. The sniffer could be replaced by an optical inspector which is capable of recognising black spots. The sensor is set up in such a way that a certain number of bottles are removed from the line and delivered by a secondary conveyor 2 to a separate treatment 3 with a special chemical. When setting up the sensor 1, it is important to ensure that although, with a particularly sensitive setting, all the required problem containers are detected, containers with no stubborn soils are not unnecessarily removed from the line at the same time. In practice, the ratio of containers removed from the line to containers remaining in the line can be optimally adjusted to meet requirements.

After the separate treatment 3, the problem bottles are returned to the beginning of the sniffer 1 or, alternatively, pass directly to the bottle washing machine as indicated by the chain line in Fig. 1. If, in the first case, the soils have been adequately removed, the bottles pass together with the unproblematical containers into the bottle washing machine 4 and then pass via a bottle inspector known per se to the packing station.

The separate treatment 3 may be carried out in a small washing machine or even in a simple immersion bath or in a spray arrangement, optionally together with an immersion bath.

By virtue of the considerably smaller cleaning bath volume of the separate treatment 3, the consumption of the special chemical is significantly reduced compared with the use of the same chemical in the bottle washing machine 4.

Another contributory factor in this regard is that only a fraction of the total number of bottles is subjected to the separate treatment.

The particularly preferred process shown in Fig. 2, which is particularly suitable for removing particulate soils, is similarly carried out. In this case, however, only those bottles which, on the one hand, have already been cleaned in the bottle washing machine 4 and which, on the other hand, still contain a certain amount of stubborn soil are subjected to a separate treatment 3. In this way, the bath used in the separate treatment 3 is only minimally polluted with organic residues, so that the stability of the special chemical is not affected, even after repeated use. Accordingly, this process is particularly economical in regard to the consumption of the special chemical, for example the oxidising agent, required.

One advantage of the sensor 5 arranged after the washing machine 4 is that labels or the like glued to the containers are unable to interfere because they have already been removed in the washing machine 4.

RA In the process shown in Fig. 2, the sensor assumes the form of a bottle 1 pector 5 capable of detecting particulate soils.

000162 The process according to the invention illustrated in the flow chart in Fig. 3 is carried out similarly to the process shown in Fig. 2 except that, after the separate treatment 3, the containers pass directly to the exit of the bottle inspector In the process according to the invention shown as a flow chart in Fig. 4, the bottles soiled with stubborn soils are sniffed by a sniffer 1 in the same way as in the process shown in Fig. 1, conveyed by a secondary conveyor belt 2 to the separate treatment station 3 and in contrast to the process shown in Fig. 1 finally pass directly to the entrance of the bottle inspector 5 positioned after the bottle washing machine 4.

The variants of the process according to the invention shown in Figs. 5 and 6 operate discontinuously in contrast to the embodiments described in the foregoing.

The heavily soiled bottles are detected by the bottle inspector 5 or by the sniffer 1, removed from the line and periodically subjected to a discontinuous separate treatment.

is The process shown in Fig. 5 is particularly suitable for removing particulate soils. The bottles removed from the line are conveyed by a secondary conveyor belt to a packing station 6. The soiled bottles are collected. The stubbornly soiled bottles collected, and only these bottles, are passed at regular intervals through the bottle washing machine 4 in which they are subjected to the separate treatment. To this end, the special chemicals, for example oxidising agents and/or acids, are added to the treatment liquid in the bottle washing machine 4. The treatment liquid is preferably freshly prepared in order to guarantee stability, particularly in the case of the oxidising agent, throughout the treatment period.

In addition to the advantages already mentioned with regard to Fig. 2, there is no need for an additional washing machine for carrying out the separate treatment.

The process shown in Fig. 6 is carried out in the same way as the process shown in Fig. 5 and has the same advantages. This process is preferably used to remove flavours from the containers.

Apart from the described embodiments, the processes mentioned may also be combined. For example, the processes shown in Figs. 1 and 5 or in Figs. 4 and the processes shown in Figs. 2 and 6 or in Figs. 3 and 6 and the processes shown in Figs. 5 and 6 or in Figs. 1 and 2 may be combined.

List of Reference Numerals 1 sniffer 2 secondary conveyor belt 3 separate treatment 4 bottle washing machine A inspector 4 packer C00162

Claims (19)

1. A process for the machine-cleaning of returnable food containers which are soiled with stubborn soils, more particularly particulate soils, and of which the stubborn soils consist of microorganisms, such as yeasts, moulds and the like, the containers being treated in a washing machine with cleaning chemicals known per se in the food industry, characterised in that the containers soiled with the stubborn soils are detected by means of a sensor before and/or after cleaning with the cleaning chemicals known per se in the washing machine, automatically removed from the line and only those containers removed from the line are treated one or more times in at least one separate step with at least one chemical which is not used in the washing machine (separate treatment) and which contains oxidising agents and/or acids.

2. A process as claimed in claim 1, characterised in that the containers removed from the line are treated in the separate step with other chemicals, such as surfactants and complexing agents.

3. A process as claimed in claim 1 or claim 2, characterised in that the °o containers consist of plastic and, in particular, are plastic bottles which are cleaned in bottle washing machines. i 4. A process as claimed in any one of the preceding claims, characterised •:2e in that the containers removed from the line are treated with at least one oxidising oo•• o agent releasing available oxygen.

5. A process as claimed in claim 4, characterised in that the containers removed from the line are additionally treated with inorganic and/or organic acids and/or surfactants and/or complexing agents.

6. A process as claimed in any one of claims 3 to 5, characterised in that oo containers of polyethylene terephthalate, polycarbonate, polypropylene, o polyacrylonitrile, polyethylene naphthalate or polyvinyl chloride for accommodating o o beverages and/or milk products are treated. S0 7. A process as claimed in any one of the preceding claims, characterised in that the stubbornly soiled containers are only removed from the line after cleaning in the washing machine which uses cleaning chemicals known per se and °are then subjected to the separate treatment. *41 8. A process as claimed in claim 7, characterised in that the separately treated containers are returned to the beginning of the washing machine.

9. A process as claimed in any one of the preceding claims, characterised in that the stubbornly soiled containers are detected before cleaning in the washing machine, removed from the line, separately treated and then passed to the beginning of the washing machine. A process as claimed in claim 9, characterised in that the separately ated containers are returned to the beginning of the sensor. C00162

11. A process as claimed in any one of the preceding claims, characterised in that, after the separate treatment and, optionally, a subsequent rinsing step, the containers removed from the line are passed directly to filling and labelling stations.

12. A process as claimed in any one of the preceding claims, characterised in that the stubbornly soiled and, in particular, microorganism-infested containers are detected by an optical and/or chemical detector.

13. A process as claimed in any one of the preceding claims, characterised in that the chemical used in the separate treatment is sprayed into and/or onto the containers and/or the treatment is carried out in a bath.

14. A process as claimed in any one of the preceding claims, characterised in that the stubbornly soiled containers are treated with an aqueous solution. A process as claimed in any one of claims 3 to 14, characterised in that the separate treatment of the plastic containers is carried out at temperatures of 0 to

16. A process as claimed in claim 15, characterised in that the separate S treatment of the plastic containers is carried out at temperatures in the range from S 20'C to below the softening temperature of the particular plastic material.

17. A process as claimed in any one of the preceding claims, characterised in that the chemical used for the separate treatment, is allowed to act on the :to containers for 0.5 to 10 minutes.

18. A process as claimed in claim 17, characterised in that the chemical used for the separate treatment is an oxidising agent.

19. A process as claimed in claim 17 or claim 18, characterised in that the chemical used for the separate treatment, is allowed to act on the containers for 1 to 8 minutes, "•6020. A process as claimed in any one of claims 2 to 19, characterised in that •0 the oxidising agents are selected from organic peracids, alkaline hypochlorites, hydrogen peroxide, alkaline perborates and alkaline percarbonates. S"21. A process as claimed in claim 20, characterised in that perborates in the form of an aqueous solution with a concentration of 0.001 to 2% by weight, are 46 used as the oxidising agent. 0• 22. A process as claimed in claim 21, characterised in that perborates in the form of an aqueous solution with a concentration of 0.01 to 1.5% by weight are used as the oxidising agent.

23. A process as claimed in claim 21 or claim 22, characterised in that perborates in the form of an aqueous solution with a concentration of 0.1 to 1% by weight are used as the oxidising agent. Sa24. A process as claimed in claim 20, characterised in that an organic 'acid in the form of an aqueous solution, is used as the oxidising agent. C00162 12 A process as claimed in claim 24, characterised in that peracetic acid and/or perpropionic acid, is used as the oxidising agent.

26. A process as claimed in claim 24 or claim 25, characterised in that the peracid content of the aqueous solution is between 0.001 and 40% by weight.

27. A process as claimed in claim 24 or claim 25, characterised in that the peracid content of the aqueous solution is between 0.01 and 5% by weight.

28. A process as claimed in claim 24 or claim 25, characterised in that the peracid content of the aqueous solution is between 0.05 and 2% by weight.

29. A process as claimed in any one of the preceding claims, characterised in that the chemical used for the separate treatment is added to an aqueous treatment solution in the form of a water-containing or powder-form concentrate. A process for the machine-cleaning of returnable food containers which are soiled with stubborn soils, substantially as hereinbefore described with reference to the accompanying drawings. Dated 29 January 1999 HENKEL-ECOLAB GMBH Co. OHG Patent Attorneys for the Applicant/Nominated Person SPRUSON&FERGUSON C00162