CLEANING METHOD

Abstract: In a method of cleaning glass containers in a continuous feed process, an aqueous composition comprising an alkaline agent and a weak sequestrant. A typical alkaline agent is NaOH. Typical weak sequestrants are polyacrylates (e.g. MW < 10,000) and phosphonates.

Description: CLEANING METHOD The present invention relates to a method of cleaning glass containers. Many glass containers such as bottles which are used for selling beverages, for example beer, milk or soft drinks, are recycled. Before refilling, they are washed in an industrial bottle washer. These industrial washers conventionally consist of a multiplicity of pockets arranged along a conveyor which conveys the items to be washed through a tortuous path where they are treated with a cleaning solution and then rinsed. They are loaded into the pockets by an automatic mechanism such as a turntable. Typically, these machines can handle from 5,000 to 100,000 bottles per hour, or more, depending on machine capacity. The conventional cleaning solution usually contains about 1% by weight of sodium hydroxide and an anti-foam agent and is applied at a temperature of around 80°C. It is often applied by a soaking stage followed by a spray stage, prior to rinsing, or else by just spraying before rinsing. Many people will*be familiar with the phenomenon of scuffing, which produces whitish circles or part-circles around the exterior of the bottle. It is believed that scuffing is produced partly by chemical errosion of the glass surface by the cleaning solution and partly by mechanical abrasion, e.g. between the bottles themselves or between the bottles and parts of the cleaning apparatus. The aforementioned problem has now been solved in accordance with a first aspect of the present invention, by a method of cleaning glass containers in a continuous-feed process, the method comprising the step of applying to the containers, an aqueous composition comprising an alkaline agent and a weak sequestrant. Cleaning with such a composition has been found to reduce scuffing significantly. It should be noted that glass items (e.g. drinking glasses) are often mechanically cleaned using domestic or industrial warewashing compositions which contain inter alia alkaline agents and sequestrants. However, this is not in a continuous-feed process where the aforementioned scuffing problem occurs. Preferably, the aqueous composition contains from 0.1% to 10% by weight of the alkaline agent, more preferably from 0.5% to 5% by weight and especially from 0.75% to 2% by weight. Preferably also, the aqueous composition contains from 50 to 1000 pp by weight of the weak sequestrant, more preferably from 100 to 500 ppm by weight and especially from 200 to 400 ppm by weight. The weak sequestrant may for example comprise one or more agents selected from polyacrylate-type sequestrants and phosphonate sequestrants. Preferred polyacrylate-type sequestrants include polyacrylic acids or polyacrylates, especially low molecular weight polyacrylates, e.g. MW<10,000, e.g. Sokalan PA15 ex BASF or Norasol LMW45 ex Norso-Haas, and maleic anhydride/(meth)acrylic acid copolymers, e.g. Sokalan CP5 ex BASF. Suitable phosphonate sequestrants include the range sold under the "Dequest" Trade Mark, ex Monsanto. Suitable alkaline agents include alkali metal hydroxides, e.g. sodium or potassium hydroxides, alkali metal silicates, including metasilicates, e.g. sodium silicate having a mole ratio of Si0 2 :Na 2 0 of about 3.3:1 or less, including from about 1.8:1 to about 2.2:1 (normally referred to as sodium disilicate) . Sodium hydroxide is especially preferred. However, the alkaline agent could comprise two or more different such materials. According to a second aspect of the invention, there is provided an aqueous composition for continuous- feed cleaning of glass containers, the composition comprising from 0.5% to 10% by weight of an alkaline agent and from 50 to 1000 ppm by weight of a weak sequestrant. Particularly preferred amounts and type of alkaline agent and weak sequestrant for such a composition are as indicated above. The composition used in the method of the present invention may also contain some non-ionic anti-foam and/or wetting agent, for example in a weight ratio of from 1:50 to 1:10 relative to the weak sequestrant. It is also possible for the composition to contain one or more other minor ingredients which are usual in such compositions. However, often the composition will be substantially free of other ingredients. Usually, the step applying the aqueous composition to the glass containers, will be followed by a rinsing step, preferably using water, optionally including a rinse aid. This could be a two-stage process using first warm, and then cold water. The aqueous composition itself is conveniently prepared by diluting a pre-concentrated aqueous solution of the weak sequestrant with an aqueous solution of the alkaline agent. The latter will normally contain all of the alkaline agent to be present in the final solution and all of the water, except for the amount contained in the pre-concentrated aqueous solution of the sequestrant. The method of the present invention can be applied to the continuous-feed cleaning of any glass containers, for example beverage containers but one useful example is in the cleaning of beer bottles. The present invention will now be explained in further detail by way of the following non-limiting experiments: Experiment 1 An aqueous solution of 15% by weight weak sequestrant, (being either variant (a) polyacrylate sequestrant, i.e. Sokalan PA15 ex BASF, av MW 1500 or variant (b) phosphonate sequestrant, i.e. Dequest 2000 ex Monsato) was diluted in a bath with a 2% by weight aqueous solution of sodium hydroxide containing non-ionic anti-foam agent, such that the amount of weak sequestrant in final solution was 300 ppm by weight. The amount of anti-foam in final solution was in the weight ratio of 2:15 relative to the sequestrant. The final solution, in each case was applied to beer bottles in an industrial bottle washing machine at a maximum temperature of 80°C, first in a soaking step and then in a spray step. This cleaning process was followed by rinsing using softened water at 40°C as a first rinse step and then cold fresh softened water as a second rinse step. Experiment 2 0.3 litre Dutch standard beer bottles were subjected to alternate mechanical and chemical conditions, for both a control bottle batch and a bottle batch subjected to chemical conditions according to the present invention, whereafter the level of scuffing was assessed both visually and by a charge coupled device (CCD) camera. The CCD camera recorded the number of non reflective pixels on the bottle. On the basis of this figure the bottle was classified into a scuffing category. The bottles were subjected to mechanical conditions by placement on a 10 meter conveyor loop for 10 minutes. Chemical control conditions consisted of soaking 50 control bottles in a 1% solution of NaOH in soft water (<1° german hardness) at 80°C. According to the present invention, the chemical conditions consisted of soaking 50 bottles in 1% solution of NaOH plus 0.2% of the formulation A. Formulation A: Nitrilotri ethylene phosphonic acid 15.0% Sodium cumene sulphonate 3.6% Non ionic surfactant 2.0% Distilled water rest Every 5 cycles, 5 bottles were removed from the test and visually classified in comparison to reference bottles, wherein a cycle consisted of exposure to the mechanical conditions for 10 minutes, followed by exposure to the chemical conditions for 10 minutes, and the reference bottles were beer bottles considered visually acceptable by Heineken. Visual level 5 is considered to be the maximum acceptable level for bottles. To minimize thermal stress, the bottles were exposed to a soak bath between the mechanical and chemical treatments, wherein the temperature change was limited to 35°C between the respective treatments. Table 1. Results experiment 2 Test Number of Visual level Visual level cycles of scuffing of scuffing (control) (invention) 1 5 2 1 2 10 2 2 3 15 2 2 4 20 3 2 5 25 4 3 6 30 4 4 7 35 5 4 8 40 5 5 i n 9 45 6 The scuffing category found by the instrumental method correlated very well with that of the visual assessment Experiment 3 As a control, standard 0.3 litre beer bottles were subsequently subjected to production bottlewashing conditions. Each test was started with 50 bottles per condition to be examined. The bottles were put into crates which were put at the beginning of the washing line. The bottles followed the standard route of: decrater, bottlewasher, filler, tunnel pasteurizer, labeling machine, crate packer. The bottles were collected from the filled crates, emptied and reintroduced at the beginning of the line. The chemical treatment consisted of washing the bottles in a regular bottlewasher at the conditions and temperatures prescribed. Every 5 cycles, 5 bottles were removed from the test and visually classified in comparison to the reference bottles as in experiment 2. The bottles were also assessed by using the CCD camera to determine scuffing levels as described before. The bottlewashing conditions in the control were: 1 ± 0.1% NaOH solution, temperature 80 ± 1°C. Table 2. Results control Test Number of Number of Visual cycles pixels scuffing level 1 5 170 2 2 10 327 2 3 15 808 2 4 20 2512 3 5 25 4207 4 6 30 5979 4 7 35 7789 5 8 40 9727 5 9 45 14259 6 50, 0.3 litre Dutch standard beer bottles were subsequently subjected to the same test production bottlewashing conditions as above, but using the bottles washing formulation A under the following conditions: 1 ± 0.1% NaOH solution, 0.2 ± 0.05% of formulation A, and a temperature of 80 ± 1°C. The results of this are shown in table 3. Table 3. Test Number of Number of Visual cycles pixels scuffing level 1 5 49 1 2 10 195 2 3 15 492 2 4 20 1640 3 5 25 4667 4 6 30 5880 4 7 35 8728 5 8 40 10229 5 9 45 10587 5 10 50 14326 6

Claims: CLAIMS I. A method of cleaning glass containers in a continuous-feed process, the method comprising the step of applying to the containers, an aqueous composition comprising an alkaline agent and a weak sequestrant. 2. A method according to claim 1, wherein the aqueous composition contains from 0.1% to 10% by weight of the alkaline agent. 3. A method according to claim 2, wherein the aqueous composition contains from 0.5% to 5% by weight of the alkaline agent. 4. A method according to claim 3 , wherein the aqueous composition contains from 0.75% to 1.5% by weight of the alkaline agent. 5. A method according to any preceding claim, wherein the aqueous composition contains from 50 to 1000 ppm by weight of the weak sequestrant. 6. A method according to claim 5, wherein the aqueous composition contains from 100 to 500 ppm by weight of the weak sequestrant. 7. A method according to claim 6, wherein the aqueous composition contains from 200 to 400 ppm by weight of the weak sequestrant. 8. A method according to any preceding claim, wherein the weak sequestrant comprises a polyacrylate sequestrant. 9. A method according to claim 8, wherein the polyacrylate sequestrant has an average molecular weight of less than 10,000. 10. A method according to any of claims l to 7, wherein the weak sequestrant comprises a phosphonate sequestrant. II. A method according to any preceding claim, wherein the alkaline agent comprises sodium hydroxide. 12. A method according to any preceding claim, wherein the step of applying the aqueous composition is followed by a rinsing step. 13. A method according to any preceding claim, wherein the aqueous composition is prepared by diluting a pre-concentrated aqueous solution of the weak sequestrant with an aqueous solution of the alkaline agent. 14. A method according to any preceding claim, wherein the glass containers are in the form of bottles.

Inventors: GEERLINGS DETLEF HEIKO MICHAEL, JAKOBS RUBEN EMIEL MARCO JULIU, GEERLINGS, DETLEF, HEIKO, MICHAEL, JAKOBS, RUBEN, EMIEL, MARCO, JULIUS
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1995
Main classification: C11D7
IPC codes: C11D3, C11D7