WO1993005135A1

WO1993005135A1 - Use of strongly alkaline agents to prevent silver cutlery from tarnishing in washing-up machines

Info

Publication number: WO1993005135A1
Application number: PCT/EP1992/001906
Authority: WO
Inventors: Josef Penninger; Beatrix Kottwitz; Dagmar Zaika
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1991-08-29
Filing date: 1992-08-20
Publication date: 1993-03-18
Also published as: DE4128672A1; EP0600969A1

Abstract

To prevent silver cutlery from tarnishing when washed in washing-up machines, the invention proposes the use of strongly alkaline agents (pH ⊃ 11) containing per-acids, or peroxy compounds mixed with organic bleach activators, and optionally, low-foaming non-ionic surfactants without the addition of corrosion inhibitors.

Description

"Use of strongly alkaline agents to prevent tarnishing of silver cutlery in dishwashers"

When cleaning dishes in household dishwashers (HGSM) food waste and thus u. a. mustard, peas, egg and other sulfur-containing compounds such as mercaptoamino acids are also added to the washing liquor. These contaminants are the cause of tarnishing of silver cutlery, which is due to the formation of colored silver complex compounds. When using active chlorine-containing cleaners, this secondary reaction could be avoided by oxidizing the sulfidic functions to sulfones or sulfates. The problem became acute, however, when active oxygen compounds such as sodium perborate or sodium percarbonate were used as an alternative to the active chlorine compounds.

From "Soap & Chemical Spec", 46, Issue 4 (1970), page 33, automatic dishwashing agents containing pentasodium triphosphate, sodium metasilicate, alkali carbonate and alkali perborate are known. German Patent Application No. 1 279877 describes a method for mechanical dishwashing using detergents in which per compounds and activators for them are present in the form of granules which are separated from one another. Organic peracids or their salts are also suitable as per-compounds. Such means are said to eliminate even stubborn starch films. An additional addition of anti-corrosion agents is recommended.

German patent application 1 302 394 describes dishwasher detergents which can be used in machines and which can contain alkali metal salts and a bleach activator. They also contain enzymes and therefore may only have a pH value of 7-9 instead of the usually strongly alkaline pH value. In US Pat. No. 3,549,539, strongly alkaline, machine-applicable dishwashing detergents are described, which can contain, among other things, perborate with an organic bleach activator as the oxidizing agent. Additives such as benzotriazole are recommended as anti-tarnish agents. Application examples for this are missing. From German Auslegeschrift 1695219 it is known that acylated organic substances can be used as activators for per compounds wherever peroxy compounds are used, for example in the passivation of aluminum or other light metal surfaces. PH values of preferably 7-11.5 are mentioned. European Patent Specification 145 090 protects alkaline detergent compositions which can also be used for machine dishwashing and which contain peroxy compounds and, as an activator for them, a compound which provides manganese (II) ions in aqueous solution and sodium etasilicate and whose aqueous solutions have a pH of 9.5 - have 13. They can also contain surface-active compounds and additionally known organic peroxide activators, but this is not demonstrated by examples. The bleaching effect of the peroxy compounds on tea stains is enhanced there by the addition of manganese (II) salt activators.

It is not apparent from the prior art that peroxy compounds, which are activated by adding known organic bleach activators, prevent tarnishing of silver cutlery during cleaning in dishwashers. Instead, it has always been recommended to add corrosion inhibitors, most of which were heterocycles, but which occasionally encounter toxicological and physiological concerns. Additions of unsaturated fatty acids also have an insufficient effect.

It has now surprisingly been found that the use of strongly alkaline agents containing peracids or of peroxy compounds mixed with organic bleach activators and, if appropriate, known low-foaming nonionic surfactants can prevent silverware from tarnishing in the HGSM. This is all the more surprising since normally the per Acids are relatively stable at high pH values of 11, so they are not very effective (see G. Reinhardt and W. Schuler in "Official Congress of SEPAWA eV", 35th Annual Meeting from October 5 to 6, 1989, page 29).

The effect of a bleaching system can be differentiated by visual assessment of the silver cutlery washed with the appropriate formulation in a household dishwasher. The corresponding procedure is described in the examples below.

The composition of the agents used according to the invention essentially corresponds to the known alkaline, machine-applicable dishwashing agents based on peracids or per compounds such as sodium perborate or sodium percarbonate. Sodium perborate monohydrate is preferred (cf. "Tenside" 27 (1990), pages 52 to 56). Polymeric alkali phosphates, alkali silicates and alkali carbonates are used as builders, and small amounts of low-foaming nonionic surfactants may be added to improve the wetting effect. It is also known to replace phosphates with various organic complexing agents which also serve as builders and which include, for example, ethylenediaminetetraacetic acid and the like.

Suitable polymeric alkali metal phosphates are the condensed phosphates which are customarily used in washing-up and cleaning agent mixtures and which can be present in the form of their alkaline neutral or acidic sodium or potassium salts. Examples include: tetrasodium pyrophosphate, disodium dihydrogen pyrophosphate, pentasodium triphosphate, sodium hexametaphosphate and the corresponding potassium salts or mixtures of sodium and potassium salts. Their amounts are expediently in the range from 0 to about 50% by weight, preferably 0 to about 35% by weight, based on the total composition.

Anhydrous sodium or potassium silicates are preferably used as alkali silicates, in which the ratio of alkali oxide to silicon dioxide is approximately 1: 0.5 to 3.5, preferably 1: 1. To the extent that alkali carbonates are used in the mixtures, Na is the primary choice trium-potassium carbonates. However, no more than 30 percent by weight of the alkali silicates should be replaced by alkali carbonates, since the stronger alkaline reaction achieved in this way can lead to an increased corrosion effect of the cleaner. The amount of the alkali silicates in the total average is expediently about 20 to 80, preferably about 30 to 75,% by weight.

Anhydrous, but also water containing compounds can preferably be used as alkali metal carbonates. Sodium carbonate and sodium bicarbonate, the amounts of which are 3 to 30, preferably 6 to 15,% by weight, based on the total composition, are preferred.

Organic polymers, especially polycarboxylates, which also act as co-builders, are also preferably used. Polyacrylic acids and copolymers of maleic anhydride and acrylic acid and the sodium salts of these polymer acids are suitable. Commercial products are e.g. B. Sokalan (R) CP 5 and PA 30 from BASF, Alcosperse ^(R) 175 or 177 from Alco, LMW ( ^R ) 45 from NorsoHAAS.

The foam behavior is decisive for the surfactants that can be used. Low-foam connections are preferred because of the machine mechanics. These are primarily non-ionic surfactants. All compounds known for this area of application, in particular adducts of 4 to 10 moles of ethylene oxide or 2 to 6 moles of ethylene oxide and 2 to 6 moles of propylene oxide with C ₁₀ -C ₂₀ , preferably C ₁₂ -C ₁₈ fatty alcohols, can be used as nonionic surfactants, which can in each case be end-capped with C ₁ -C ₄ -n-alkyl radicals, and alkyl glucosides having 8 to 18, preferably 8 to 14 carbon atoms in the alkyl radical and 1 to 4, preferably 1 to 1.4, glucoside radicals in the molecule.

The total amount of surfactants in the cleaning agent is expediently from 0 to about 5, preferably from 0.5 to about 2,% by weight.

If the cleaning agents foam too much during use, they can still contain about 0.1 to 6, preferably about 0.5 to 4% by weight of one foam-suppressing compound, preferably from the group of paraffins, hydrophobized silica and bisstearic acid amides, can be added.

The known alkali perborates and percarbonate, which are activated according to the invention by activators such as, for example, tetraacethylethylenediamine, tetraacetylglycoluril, pentaacetylglucose or diacetyldioxohexahydrotriazine, can also be used as peroxy compounds, but also peracids or their salts such as alkali persulfate or magnesium monoperphthalate additive can be omitted, with additional activator being used. The amounts of the peroxy compounds can be about 3 to 10, preferably about 5 to 9,% by weight, based on the total agent. The amount of organic bleach activators is suitably about 0.5 to 5, preferably about 1 to 3 wt .-%, based on the total agent. Manganese (II) salts are not an option here. They decompose the per connection and use it up with it. Braenstein fails.

In addition to the constituents mentioned, the mixtures to be used can contain further components, in particular inorganic salts, such as sodium sulfate, as blending agents. Other possible additives are substances with a buffering action, dyes, perfumes, and, if appropriate, enzyme-inactivating additives, such as ammonium chloride or the like.

If the agents to be used according to the invention are preferably in powder form, they are packaged in a known manner by grinding and mixing the constituents. In order to achieve an intimate connection of the powder constituents, it may be appropriate to mix the powder with an aqueous solution of crystallizing salts, e.g. As sodium sulfate, or to spray one of the nonionic surfactants mentioned. This treatment also reduces the tendency of the powder to dust.

The agents to be used can be used both in household dishwashers and in commercial dishwashers. They are added by hand or using suitable dosing devices. The application con concentrations in the cleaning liquor are about 0.5 to 10 g / l, preferably 2 to 5 g / l.

The rinse program is generally supplemented and ended by a few intermediate rinse cycles with clear water following the cleaning cycle and a rinse cycle with a customary rinse aid. After drying you get not only a completely clean and hygienically perfect tableware, but above all also practical bright silver cutlery.

Examples

In the examples:

Sokalan ^(R) CP 5: Acrylic acid / maleic acid copolymer from BASF

Plurafac ^R LF 403: fatty alcohol alkoxylate from BASF

TAED: tetraacetylethylenediamine

PAG: pentaacetyl glucose

DADHT: 1,5-diacetyl-2,4-dioxo-hexahydro-1,3,5-triazine

ISA: isatoic anhydride

H-48: Mg monoperoxyphthalate

DPDDA: diperoxydodecanedioic acid

Caroat: 2KHSO ₅ -KHSO ₄ .K2SO ₄ (e.g. from Degussa)

example 1

Three silver spoons (type WMF, hotel cutlery, form Berlin) were cleaned with a silver cleaner, degreased with petrol and dried. The spoons were then placed in the cutlery basket of a HGSM type Bosch 5712. The cleaning program (65 ° C, 3 - 4 ° dH) was now started and after the pre-rinse cycle 10 g mustard and 30 g phosphate cleaner with one of the additives listed in table 1 or 2 were dosed directly into the machine. After the rinsing and drying process has ended, the HGSM is opened for 10 minutes, the machine is closed again and rinsed again in the same way. After this second rinse, the spoons are removed and evaluated. For this purpose, the tarnish colors are rated in the range from 0 to 10 (0 = no tarnishing, 6 = gold-brown discoloration, 10 = violet discoloration).

Detergent composition

28% pentasodium triphosphate

38% Na metasilicate, anhydrous

14% Na ₂ H2SiO ₄ . 4H ₂ O

7% sodium perborate monohydrate

5% sodium carbonate, anhydrous

6% water

2% additive

pH (1% in dist. H ₂ O): 12.6

-------------------------------------------------- ----------

Example 2

The procedure was as described in Example 1; in this example, the cleaner is a phosphate-free formulation. The results are shown in Table 2.

Detergent composition

49% sodium metasilicate

15% Na ₂ H ₂ SiO4. 4H ₂ O

15% sodium carbonate, anhydrous

8% Sokolan ^(R) CP 5

7% sodium perborate monohydrate

1% Plurafac ^R LF 403

3% water

2% additive

pH (1% in des. H ₂ O): 12.5

Comparative Examples

The following examples show that when using cleaning agents according to the state of the art according to German patent specification 1 279 877 and European patent specification 145 090, where manganese (II) salts were used as activators for per compounds, no silver protection he follows.

The system described in Example 1 was used for testing and evaluation. The results are summarized in Table 1. The addition of Mn (II) salts did not lead to a reduction in tarnishing of silver cutlery.

Detergent composition:

28% pentasodium triphosphate

38% Na metasilicate, anhydrous

14% Na ₂ H ₂ SiO ₄ ^. 4H ₂ O

7% Na perborate monohydrate

5% sodium carbonate, anhydrous

0.036 1.80% Mn (II) salt

ad 100 water

Claims

1. Use of strongly alkaline agents containing peracid or of peroxy compounds mixed with organic bleach activators to prevent tarnishing of silver cutlery in dishwashers.

2. Use of agents mixed with organic bleach activators containing acyl groups according to claim 1.

3. Use of agents according to claim 1 and 2 with a further content of low-foaming nonionic surfactants.

4. Use of agents according to claims 1 to 3 with a pH> 11.

5. Use of agents according to claim 1 to 4 containing about 3 to 10 wt .-% of peroxy compound, based on the total agent.

6. Use of agents according to claim 1 to 5 containing about 0.5 to 5 wt .-% of organic bleach activators, based on the total agent.