DE69514824T2 - METHOD FOR WASHING DISHES WITHOUT THE USE OF FASTENERS - Google Patents

Description

METHOD OF WASHING DISHES WITHOUT USING BLEACH Field of the invention

The present invention relates to a method for dishwashing in industrial systems or systems for larger establishments, as opposed to automatic domestic dishwashers.

Background of the invention

A typical conventional industrial dishwashing system consists of a transport system separated into prewash, wash, rinse and dry stations. The wash water is typically introduced into the rinse zone of this system and is cascaded to the prewash zone while the dishes are transported in a countercurrent direction.

Dishwashing detergents used in such systems generally contain a chlorine bleach combined with a cleaning ingredient such as an aqueous solution of a basic agent and a sequestering agent or builder such as sodium tripolyphosphate.

Although these systems provide an excellent level of tea stain removal, the incomplete removal of starch soils is a problem. Starch soils are particularly difficult to remove when ware is subjected to high temperatures during food preparation and such foods are left on the heated substrates for long periods during dispensing.

A proposed solution to this problem is described in EP-A-282 214 (Diversey). This document discloses a method for cleaning dirty dishes with an undirected, mist-like spray of a strongly alkaline cal solution. However, a strong alkaline spray is potentially dangerous for the operator.

An industrial dishwashing process using a low alkaline detergent and an enzyme dosed into either a rinse or a wash bath of the system is described in WO-A-94/27488 (Henkel-EcoLab). The publication describes a means of compensating for the degradation of enzyme, in particular an amylase, during downtimes of the system by adding burst doses of the enzyme to the wash zone.

DE-C-43 24 106 discloses a method for dishwashing for industrial dishwashing machines or dishwashing machines for larger establishments, wherein an enzyme component Thermamyl 300L and a phosphate or a low alkaline cleaning component based on NTA are added to the cleaning liquid in order to optimize the cleaning results.

German patent application DE-A-42 19 620 describes a household dishwashing detergent wherein bleach and enzyme-containing components are dosed at different stages of the washing process. The enzyme is added during the pre-rinse or at the beginning of the washing cycle. The bleach is only added during the cleaning cycle after a predetermined time after which the washing liquor has reached a desired temperature. Thus, the negative interaction between the bleach and the enzyme is avoided. This approach is not feasible in industrial dishwashing detergents where a cascade flow of water from one container to another occurs and where the cleaning process is a continuous process.

One possible approach to minimize the negative interactions between the active ingredients while maximizing cleaning performance in industrial dishwashing machines for larger facilities is to introduce the active ingredients into the system one at a time. In sequential dosing, the components of the detergent are introduced separately into different chambers of the machine. Sequential dosing separates the active ingredients to minimize negative interactions and thereby maximize the cleaning performance of each individual component.

Bleaching agents have been separated from the dishwashing detergents to minimize deactivation of the enzyme components. It is known that in the absence of a bleach, good stain removal (e.g. tea stain removal) can be achieved over a wide range of water hardness by using a strong builder or sequestrant at a relatively high wash pH. Thus, the negative interaction between bleach and enzyme can be avoided while maintaining good cleaning performance.

However, it is also known in the art that many enzymes, particularly amylase enzymes, which are useful for starch removal, are unsuitable for use in cleaning systems when the pH of the agent is above 10. Such high pH values minimize enzyme activity and stability. See GB-A-1 296 839 (Novo).

Therefore, there is a need for a cleaning system that provides effective cleaning performance for both starch and tannin removal while minimizing those negative interactions responsible for deactivation of the active ingredients within the system.

Brief description of the invention

An object of the invention is to provide an industrial dishwashing process or a dishwashing process involving a chemical cleaning system containing at least two separate components. Each component is dissolved or diluted in an aqueous solution to a concentration useful for cleaning.

The chemical cleaning system has essentially no bleach among its components.

Accordingly, the present invention provides methods for washing dishes in an industrial multi-container machine or a multi-container machine for larger facilities, comprising the steps of:

a) selecting a chemical cleaning system comprising at least two separate components for aqueous dissolution or dilution to the appropriate use concentration in two separate zones of a dishwasher, the first component comprising a detergent and the second component comprising an enzyme, the system being substantially free of added bleach and a 1% aqueous solution of the first component being at least 1 pH unit more alkaline than a 1% aqueous solution of the second component;

b) introducing the first component into a washing zone for cleaning dirty dishes;

c) subsequently introducing the second component into a second washing zone for further cleaning of the dishes and

d) Rinsing the dishes with an aqueous solution to substantially rinse away the chemical cleaning system.

Description of the preferred embodiments in detail

Typical industrial dishwashing processes are either continuous or non-continuous and are carried out in either a single-bin or multi-bin/transport type machine. In the transport system, a prewash, wash, rinse and dry zone are generally arranged using partitions. The wash water is introduced into the rinse zone and is cascaded back to the prewash zone while the dirty dishes are transported in a counter-current direction.

The method of washing dishes according to the invention is particularly effective in multi-container/transport type systems. In these types of systems, the contact time between the detergent and the items to be washed is relatively short. Means of maximizing these contact times are continually being sought, while at the same time reducing periods of negative interaction of the detergent actives. composition must be minimized to provide the best cleaning performance.

In the present invention, sufficient cleaning performance is achieved despite the removal of bleach. The reason is that bleaches generally create a negative interaction with other cleaning components, such as enzymes.

The enzymatic component

Amylolytic enzymes are used to remove starch soils. The applicable amylolytic enzymes may be derived from bacteria or fungi. Preferred amylolytic enzymes are those produced and described in GB-A-1 296 839, which are cultured from the strains Bacillus licheniformis NIB 8061, NIB 8059, ATCC 6334, ATCC 6598, ATCC 19945, ATCC 8480 and ACTT 9945 A. Examples of such amylolytic enzymes are those produced and sold under the trademark Termamyl® by Novo Industri A/S, Copenhagen, Denmark.

Also useful in the invention are α-amylase enzymes mutated by modifying one or more amino acid sequences as in WO-A-94/14951 and WO-A-94/02597 and sold by Novo Industri under the trade name Durmamyl. Other α-amylase enzymes useful in the invention are described in EP-A-208 491 (Genencor Int'l).

The amylolytic enzymes can be used in either granular or liquid form and have enzymatic activities of 2 to 25 maltose units/milligram. They can be incorporated into the cleaning systems of the invention in an amount such that the final composition has an amylolytic activity of 10³ to 10⁸ maltose units/kilogram, preferably 10⁵ to 10⁸ maltose units/kilogram, and most preferably 10⁶ to 10⁸ maltose units/kilogram.

The amylolytic activity mentioned herein can be determined by the method described by P. Bernfeld in "Method of Enzymology", Volume 1 (1955), page 149.

Proteolytic enzymes may also be incorporated into the cleaning system to remove protein stains. Useful proteolytic enzymes include the subtilisin obtained from the strains Bacillus subtilis licheniformis, such as the commercially available subtilisins Maxatase, sold by Gist-Brocades N. V., Delft, Holland, and Alcalase, sold by Novo Industri A/S, Copenhagen, Denmark. Particularly suitable proteases are those obtained from a strain of Bacillus with maximum activity over a pH range of 8 to 12 and are commercially available from Novo Industri A/S under the trade names Esperase and Savinase. Also useful is a protease sold under the trade name OxP by Genencor Int'l. The preparation of these analogous enzymes is described in GB-A-1 243 784. Proteolytic enzymes are generally presented as granules such as marumen, prills or p-granules, or in liquid form. The proteolytic enzyme activities of these samples are 500 to 6000 glycine units per milligram. The proteolytic enzyme activity can be determined by the method described by M. L. Anson in "Journal of General Physiology", Volume 22 (1938), page 79 (1 Anson unit/gram = 733 glycine units per milligram).

In the cleaning composition of the invention, proteolytic enzymes may be present in amounts such that the final composition has a proteolytic enzyme activity of about 10³ to 10¹⁰ glycine units/kilogram, preferably 10⁵ to 10¹⁰, more preferably 10⁶ to 10⁹⁰.

Other enzymes that can be incorporated into the cleansing system are lipolytic enzymes that can be used to enhance fat removal. Commercially available lipolytic enzymes include Lipase YL, Amano CE, Wallerstein AW, Lipase MY and Lipolase, sold by Novo Industri.

The enzyme-containing component, particularly amylolytic enzyme-containing component, is dosed into the dishwashing system upon aqueous dissolution or dilution to its use concentration such that the pH of a 1% aqueous solution is desirably less than 9, preferably 7 to 9, more preferably 8 to 9. The enzyme-containing component should be introduced into the system separately from the other active components of the cleaning system. Generally, the component is applied in a wash zone of the system using any conventional means such as suitable spray nozzles or jet nozzles directed upwardly or downwardly against the dishes. In a preferred embodiment, the enzyme-containing component is sprayed directly onto the dishes as they move, countercurrent to the metered component. Careful rinsing of the enzyme from the dishes when the contact time is complete should follow.

In order to avoid excessive exposure of the second component to the detergents, the enzyme-containing component is gradually dosed into the dishwashing process after the detergent containing the component in a container separate from the container into which the detergent-containing component is introduced.

Component containing cleaning agent

An aqueous solution of the component containing the cleaning agent must have a higher alkalinity than that of the enzyme component by at least one unit, preferably more than one pH unit. Thus, a 1% aqueous solution of the cleaning component resulting from its dissolution or dilution to use concentration should have a pH at least 1 pH unit more alkaline than a pH of a 1% aqueous solution of the enzymatic component. Preferably, the cleaning agent component solution should have a pH of 9.5 or greater, preferably 9.5 to 13.

It is understood that more than one component may contain a cleaning agent, so that the component containing the greatest total amount (i.e., weight percent) of the cleaning agent is referred to as "the component containing the cleaning agent or the component containing the cleaning agent". It is It is also understood that the overall cleaning agent may comprise, in any given component, two or more different and individual cleaning agents as described below.

The concentration of the cleaning agent following dissolution or dilution is such that the weight of the component per unit volume of water should be in the range of 1 to 5 grams per liter, preferably 1 to 4 grams per liter, most preferably 1 to 3 grams per liter.

The cleaning agent may be selected from a basic or strongly alkaline material, a detergent builder, a surfactant or a mixture thereof.

Suitable basic agents include alkali metal hydroxides such as sodium or potassium hydroxides, alkali metal silicates such as metasilicates, preferably sodium metasilicate, and other alkaline basic materials such as borax. Particularly effective is sodium silicate having a molar ratio of SiO2:Na2O of 1:3.3, preferably 1.8:2.2, generally preferred as sodium disilicate.

Suitable builder materials are well known in the art and many types of organic and inorganic compounds have been extensively described in the literature. Builder materials include both phosphate and non-phosphate compounds. They are generally employed in cleaning compositions to provide alkalinity and buffering capacity, prevent deflocculation, maintain ionic strength, extract metals from soils, remove alkaline earth metal ions from washing solutions.

The builder material useful herein may be one or more mixtures of the various phosphate and non-phosphate builder materials. However, the non-phosphate builder materials may also be used, such as the alkali metal citrates, carbonates and bicarbonates, and the salts of nitrilotriacetic acid (NTA), dipicolinic acid (DPA), oxydisuccinic acid (ODS), succinic acid alkyl and alkenyl esters (AKS), ethylenediaminetetraacetates, oxy denatured heteropolymeric polysaccharides, polycarboxylates such as polymaleates, polyacetates, polyhydroxyacrylates, polyacrylate/polymaleate and polyacrylate; polymethacrylate copolymers and the terpolymer of polyacrylate/polymaleate and vinyl acetate (ex Hüls) and zeolites, layered silicates and mixtures thereof. They may be present in more than one component of the system, but in the only component containing builder or in the component containing most of the total builder material, in the range of 1 to 50, preferably 5 to 40, more preferably 10 to 30 (in weight percent).

Particularly preferred builders are citrates, DPA, ODS, succinic acid alkenyl esters, carbonates, bicarbonates, the higher molecular weight block copolymers, ITA/VA, with Mw greater than 60,000, maleic anhydride/(meth)acrylic acid copolymers, for example Sokalan CP5, from BASF, NTA and the terpolymer of polyacrylate/polymaleate and vinyl acetate (from Hüls).

Scale formation on dishes and machine parts is a significant problem that needs to be solved or at least reduced in the formulation of a machine dishwashing product, particularly in the case of low phosphate dishwashing detergents (e.g. less than the equivalent of 20% by weight, particularly 10% by weight of sodium triphosphate) and phosphate-free, particularly zero-P machine dishwashing compositions.

To reduce this problem, co-builders, such as polyacrylic acids or polyacrylates (PAA) and the various organic polyphosphonates, for example of the Dequest series, can be incorporated into one or more system components. For improved biodegradability (as co-builders), the block copolymers of formula (I) as set out in published PCT patent specification WO-A-94/17170 can also be used. For each component, the amount of co-builder can range from 0.5 to 10, preferably 0.5 to 5 and more preferably 1 to 5 percent by weight.

Furthermore, the cleaning agent may comprise one or more surfactants. The surfactant may also be present in a or more component(s) of the system. However, in the component(s) containing the most surfactant, there may be in the range of 0.5 to 20, preferably 1 to 15, and most preferably 3 to 15 weight percent. Such surfactant (if present) is of course separate from any surfactant used as a rinse aid in the rinse phase after use of a system according to the invention.

Normally, in a suitably built or highly built composition, it is common to add only small amounts of low to non-foaming non-ionic surfactant to assist in detergency and in particular to suppress extensive foaming caused by some protein soils. Higher amounts of highly detersive surfactants, such as the high HLB non-ionic surfactants, the anionic sulfate or sulfonic surfactants and the alkyl polyglycoside class of surfactants, may be employed in less built, active/enzyme based compositions.

These compositions may further include a defoamer. Suitable defoamers include mono- and distearyl acid phosphate, silicone oil and mineral oil. The compositions may include 0.02 to 2% by weight defoamer, or preferably 0.05 to 1.0%.

In the method according to the invention it will be normal that the application of all system components is followed by a final rinse using water which preferably contains a rinsing aid.

Any known silver anti-tarnish agents may also be included, such as benzotriazole or 1,3-N-azole compounds described in WO-A-95/10588.

Small amounts of various other components may be present in the chemical cleaning composition. These components include solvents and hydrotropes such as ethanol, isopropanol and xylene sulfonates, flow control agents, enzyme stabilizing agents, soil suspending agents, anti-redeposition agents, anti-tarnish agents, anti-corrosion agents, colorants, bleach scavengers (e.g. sulfite) and other functional additives. The use of bleach scavengers in the process and system of the invention could be advantageous since even in a non-bleach system traces of bleach could unexpectedly be present as residue from previous runs.

The components used in the present invention can be independently formulated in the form of solids (optionally to be dissolved before use), aqueous liquids or non-aqueous liquids, also to be diluted before use.

The present invention will now be further described in more detail with the aid of the following non-limiting examples in which parts and percentages are by weight unless otherwise indicated.

example 1

In a non-bleach system, it was observed that tea stain removal was significantly improved when formulations contained a builder formulated at a strongly alkaline wash pH, i.e., greater than about 10. The following dishwashing compositions were prepared:

¹ A terpolymer of acrylate/maleate and vinyl acetate, sold by Hüls.

None of the sample formulations contained a bleach or an enzyme. The pH of a 1% aqueous solution of each of the samples was adjusted to a pH between 7 and 11 by the addition of either NaOH or H2SO4.

The cleaning performance of the two compositions was compared using the residual tea stain test.

Porcelain cups were soiled with tea three times before washing. Cleaning tests were carried out in a dishwasher. The temperature of the water in the main wash cycle was 55ºC and the washing time was 1 minute.

The cleaned dishes were then compared to a chart that rates tea stain removal on a scale of 0 to 5, with 0 indicating no visible tea staining and 5 indicating severe staining. The results according to the chart are as follows:

It was thus observed that as the pH of the aqueous solutions of the detergent compositions increased, tea stain removal improved for both compositions containing NTA or Huls polymer builder materials without the presence of either bleach or an enzyme. Thus, at high alkalinity, tea stain removal is very effective in the presence of only a builder.

Example 2

However, high alkalinity and the presence of a builder material can have a negative influence on amylase enzyme stability and starch removal, as shown below.

Sample 1, described in Example 1, was prepared with the addition of an amylase enzyme (sold as Termamyl 300L by Novo) to provide an enzymatic activity of 2 x 10⁷ maltose units per kilogram. A second sample was prepared with the Termamyl enzyme but no builder was present. Each sample was adjusted to pH values of 8.5 and 10 and the four samples were observed for enzyme stability and starch removal as follows.

Porcelain plates were soiled with potato starch. An industrial single-tray dishwashing machine was run for approximately 30-40 minutes while 11 wash cycles were completed. At the end of each wash cycle, fresh product was dosed to compensate for the dilution of the wash solution by rinse water.

The enzyme stability of amylase was measured using conventional means.

Residual starch on the cleaned dishes was graded by a chart in percentage terms with 100% indicating residual soiling over the entire surface of the plate and 0 indicating complete removal of soil. The observed amylase stability and cleaning efficacy in four samples were as follows:

Sample residual thickness (% area)

NTA and Amylase pH 10 80%

NTA and Amylase pH 8.5 45%

Amylase pH 10 60%

Amylase pH 8.5 25%

These data show that the starch removal benefit is generally greater at pH 8.5 compared to pH 10. and that at both wash pHs the NTA builder had a negative effect on starch removal. The presence of NTA resulted in a significant reduction in the stability of the enzyme at a wash pH of 10. A less negative effect on the enzyme stability builder was observed at a pH of 8.5.

Example 3

A significant effect of the presence of a strong builder on amylase enzyme stability at high alkalinity was again observed in wash solutions of 65ºC. High temperature washes are commonly used in industrial dishwashing machines and in dishwashing machines for larger establishments and in a multi-chamber machine they will most likely be present in the final wash tank. The four compositions of Example 2 were prepared and amylase stability was measured at a temperature of 65ºC with the following results (expressed as % residual amylase activity):

Thus, at pH 10 and 65ºC, the effect of the presence of a strong builder on amylase stability is enormous and would have a significant negative influence on starch removal by the enzyme.

Furthermore, although amylase stability is significantly improved at pH 8.5 compared to pH 10, even at pH 8.5 there is a clear advantage to the absence of a strong sequestrant present in the wash tank when the amylase enzyme is dosed.

Example 4

The cleaning effectiveness of a composition used according to the invention was compared with the cleaning of a conventional composition used in dishwashing. The evaluation was carried out in a multi-chamber machine (from Hobart) in order to evaluate the real advantages obtained from the sequential dosing of the components and a pH difference between the washing zones into which the cleaning and enzyme components are dosed.

The two (2) component, bleach-free composition used in accordance with the present invention (hereinafter referred to as the inventive composition) was prepared as follows:

A. Detergent component

Ingredients % Active ingredient

Potassium hydroxide 2.8

Anti-scale agent (Dequest-2000) 1.0

Nitrilotriacetate (NTA) 28.0

Potassium silicate 4.0

Water as a balance

The pH of a 1% aqueous solution of the cleaning component was adjusted to pH 9.8. The cleaning component was dosed into a washing zone in an amount of 2 g/l, followed by sequential dosing of an enzymatic component.

B. Enzymatic component

100 ppm of an amylase (Termamyl 300L, sold by Novo) was dosed to the last washing zone following the dosing of the cleaning component. The pH of a 1% aqueous solution of the enzymatic component was 8.5.

The cleaning effectiveness of the composition according to the invention was compared with a conventional composition of State of the art compared with the following cleaning and bleaching components:

A. Cleaning component

Ingredients %Active ingredient

Sodium hydroxide (50%) 70

Phosphono-1,2,4-butanetricarboxylic acid 6

Polyacrylic acid, sodium salt 8

Water to 100

B. Bleaching component

Ingredients % Active ingredient

Potassium hydroxide 3.0

Potassium triphosphate 1.5

Neutral sodium silicate 4.0

Sodium hypochlorite (as active chlorine) 6.0

Water to 100

The pH of a 1% aqueous solution of the cleaning component was about 11. The bleach-containing component was first dosed into a prewash or wash zone in an amount of 0.5 g/l, followed by sequential dosing of the cleaning component into a wash zone in an amount of 2 g/l.

Porcelain cups were soiled with tea three times before washing. Porcelain plates were soiled with potato starch. To simulate the gradual build-up of starch soil due to incomplete starch removal in a wash cycle, starch plates were re-soiled after the first wash cycle and then subjected to further sequential washing/starch soiling procedures.

The cleaning performance of the two compositions was evaluated using a panel. The following results were observed:

Thus, the formulation according to the invention, which does not contain bleach but has an enzymatic component that has a pH of at least one unit below the pH of the cleaning component, shows significantly better cleaning performance compared to the performance of the commercial product with bleach.

Example 5

The cleaning efficiency of a composition used in accordance with the invention, in which the cleaning agent and the enzymatic component were dosed sequentially into separate wash tanks, was compared with a system in which the same cleaning agent and enzyme components were used, but were dosed into the same (final) wash tank instead. The composition of the cleaning agent and the enzyme component and the test procedure are as described in Example 4. Both systems are free of bleaching agents. The following results were observed:

Sequential dosing of the detergent and the enzyme components in separate wash tanks results in significantly improved starch removal compared to the situation when detergent and enzyme are dosed separately into the same wash tank.

Claims (7)

1. A method for washing dishes in an industrial multi-container machine or a multi-container machine for larger establishments, comprising the steps of: a) selecting a chemical cleaning system comprising at least two separate components for aqueous dissolution or dilution to the appropriate use concentration in two separate zones of a dishwasher, the first component comprising a detergent and the second component comprising an enzyme, the system being substantially free of added bleach and a 1% aqueous solution of the first component being at least 1 pH unit more alkaline than a 1% aqueous solution of the second component; b) introducing the first component into a washing zone for cleaning dirty dishes; c) subsequently introducing the second component into a second washing zone for further cleaning of the dishes and d) Rinsing the dishes with an aqueous solution to substantially rinse away the chemical cleaning system. 2. The method of claim 1, wherein the aqueous solution of the first component has a pH of 9.5 or more. 3. The method of claim 1 or 2, wherein the aqueous solution of the second component has a pH of less than 9.0. 4. A method according to any one of claims 1-3, wherein the first component is selected from the group consisting of a basic or strongly alkaline material, a detergency builder, a surfactant and a mixture thereof. 5. A method according to claim 4, wherein the detergency builder is a phosphate or non-phosphate material. 6. The method of claim 5, wherein the non-phosphate builder is selected from the group consisting of the salts of nitrilotriacetic acid, dipicolinic acid, oxydisuccinic acid, alkyl succinates, alkenyl succinates, ethylenediaminetetraacetate, oxidized heteropolymeric polysaccharides, polycarboxylates, zeolites, layered silicates and mixtures thereof. 7. The method according to any one of claims 1-6, wherein the enzyme is selected from the group consisting of an amylase, a protease, a lipase and mixtures thereof.