Abstract:
A process for reducing the corrosive action of hypochlorite on metal surfaces in hypochlorite-containing aqueous liquid cleaning agents by the use of a combination of alkali hydroxide, alkali silicate, and alkyl(alkoxy) n  sulfate, where n=0.5 to 10.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation under 35 U.S.C. Section 365(c) and 35 U.S.C. Section 120 of International Application No. PCT/EP2006/011960, filed Dec. 13, 2006. This application also claims priority under 35 U.S.C. Section 119 of German Patent Application No. DE 10 2005 063 065.0, filed Dec. 29, 2005. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    The present invention relates to reduction of the corrosiveness of hypochlorite on metal surfaces when hypochlorite-containing liquid cleaning agents are used to clean metal surfaces. 
         [0005]    Cleaning agents for hard surfaces, for example kitchen and bathroom cleansers, have in the past been highly abrasive powders that optionally contained small quantities of surfactants and were appropriately referred to as scrubbing powders. They were aggressive not only to the user&#39;s hand, but also to the surface with which they were brought into contact for cleaning purposes. In some cases, a bleaching agent was incorporated into such scrubbing powders in order to break up stains oxidatively, thereby making them easier to remove. Even though modern abrasive cleaners are now much friendlier to the skin in terms of their composition, these cleaners nevertheless rely substantially on the action of the abrasive substance in order to remove stains; this includes, in particular, the removal of soap deposits—which, as a rule, derive substantially from personal hygiene—from hard surfaces such as, for example, bathroom tiles or sinks. 
         [0006]    After application of the cleaning agent, subsequent wiping with a moist or even dry cloth is usually necessary in order to remove the stains. It is furthermore desirable that the cleaning agent penetrate through the stain present on the hard surface, and thus facilitate the lifting of the stain from the surface. Sodium hypochlorite is known as a highly effective bleaching agent and has been used for a long time, if applicable together with soaps and/or synthetic surfactants, to remove spots and all types of stains when laundering textiles and also when cleaning hard surfaces. For use in households, it is marketed normally in concentrations of approximately 2 to 10 wt % in water. While excellent disinfection performance and very good cleaning results on hard surfaces are obtained with the use of hypochlorite-containing agents, on sensitive cleaned items a change in the surface is observed in some cases. This can range from a slight impairment of the visual impression to the occurrence of depressions in the surface or even pitting; severe cases normally occur only when the agent is used improperly. 
         [0007]    Among the sensitive surfaces discussed here are, in particular, those made of metal, for example steel surfaces, such as those that may be found, for example, in kitchen sinks, as housing surfaces of household appliances, or as exterior surfaces of kitchen or bathroom cabinets. When such surfaces are cleaned, the risk exists that damage to the surface may occur because of the metal corrosiveness of the hypochlorite, especially when an agent normally to be used after dilution with water is applied in undiluted fashion onto the metal surface and left there for a longer time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Surprisingly, it has now been found that adaptation or specific selection of the other ingredients of hypochlorite-containing cleaning agents positively influences the corrosion behavior. 
         [0009]    The subject matter of the present invention is the use of a combination of alkali hydroxide, alkali silicate, and alkyl(alkoxy) n  sulfate, where n=0.5 to 10, in a hypochlorite-containing aqueous liquid cleaning agent, in order to reduce the corrosiveness of hypochlorite on metal surfaces. The metal surface in this context is preferably a steel surface, since the improvement effect of the combination used according to the present invention is then particularly pronounced. The combination used according to the present invention is preferably a constituent of the hypochlorite-containing cleaning agent. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0010]      FIG. 1  shows the appearance of steel panels treated with sodium hypochlorite after 14 days, 21 days and 25 days. 
           [0011]      FIG. 2  shows the appearance of steel panels treated with an aqueous agent according to the invention after 14 days, 21 days and 25 days. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    In a preferred embodiment of the invention, the cleaning agent contains 0.5 wt % to 10 wt %, in particular 2 wt % to 5.5 wt %, alkali hypochlorite. Although other alkali hypochlorites such as, for example, potassium hypochlorite may be used, it is nevertheless preferred to use sodium hypochlorite according to the present invention. Commercially used aqueous sodium hypochlorite solutions often contain considerable quantities of chloride salts. These can certainly be used for the manufacture of corrosion-improved agents according to the present invention, so that it is not absolutely necessary to resort to the use of high-purity NaOCl. 
         [0013]    The hypochlorite-containing agents are alkaline, it being preferred according to the present invention if the cleaning agent contains from more than 0 wt % to 5 wt %, in particular 0.1 wt % to 2 wt %, alkali hydroxide. 
         [0014]    By preference, from more than 0 wt % to 5 wt %, in particular 0.1 wt % to 2.5 wt %, alkali silicate is contained in the agent. This not only improves the corrosion behavior but also enhances the shelf stability of the hypochlorite. 
         [0015]    A further component of the combination used according to the present invention is a surfactant in the form of an alkyl(alkoxy) n  sulfate, which can also be referred to as an alkyl ether sulfate and is obtainable by the reaction of alcohols (by preference having 6 to 22 carbon atoms) with alkylene oxide, in particular ethylene oxide, and subsequent sulfatization and neutralization, in particular with alkaline alkali salts such as alkali hydroxides. A C 12-14  fatty alcohol ether sulfate alkoxylated with two equivalents of ethylene oxide is particularly suitable. Alkyl(alkoxy) n  sulfate is contained in the cleaning agent by preference at from more than 0 wt % to 5 wt %. The alkyl(alkoxy) n  sulfate preferably comprises a C 8-18 , in particular C 12-16  alkyl group, —OCH 2 CH 2 —, and/or —OCHCH 3 CH 2  alkoxy group(s), n being by preference a number from 1 to 6, in particular 2 to 5. 
         [0016]    The preferred alkali hydroxide is sodium hydroxide. The alkali salts recited in conjunction with the other ingredients of the agents are also preferably the sodium salts. In particular, for example, the alkali silicate is sodium silicate, and/or the alkali metal counterion of the ether sulfate is the sodium ion. 
         [0017]    The cleaning agent can, if desired, contain up to 5 wt % additional bleach-stable surfactant. Betaines are preferred, in particular those of the general formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which R 1  is an alkyl or alkenyl group having 6 to 22 carbon atoms or an R 4 CO—NH—(CH 2 ) n  group, R 2  is hydrogen or an alkyl group having 1 to 4 carbon atoms, R 3  is hydrogen or an alkyl group having 1 to 4 carbon atoms, R 4  is an alkyl or alkenyl group having 6 to 22 carbon atoms, m is a number from 1 to 6, and n is a number from 1 to 3. Examples of particularly suitable representatives of this class of surfactants encompass C 12-18  alkyldimethylbetaine, commercially obtainable as coconut betaine, and C 10-16  alkyldimethylbetaine, commercially obtainable as lauryl betaine. 
         [0018]    The preparations can additionally contain sequestering agents, by preference phosphates, alkyl phosphates, alkylphosphonic acids, and among the latter, in particular those having at least one amine oxide substituent on the alkyl group (referred to here as amine oxide phosphonic acids), polyacrylic acids, and/or polyacrylic acids comprising phosphono groups, which acids can also be present in the form of their alkali salts. The incorporation of such complexing agents results, surprisingly, in particularly good shine retention on the hard surfaces that are treated. This is not observed when other complexing agents, for example, methyl glycine diacetic acid or nitrilotriacetic acid, are used instead. Amine oxide phosphonic acids are normally manufactured by the oxidation of aminoalkylphosphonic acids. They preferably belong to the group of compounds according to the general formula (II) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which R 5  is hydrogen, a —(CH 2 ) x (CHCH 3 ) y —NH 2 -&gt;O group, or an alkali metal, x is a number from 1 to 4, and y is 0 or 1. Among the particularly preferred amine oxide phosphonic acids is the amine oxide based on aminotrimethylenephosphonic acid. By preference, 0.01 wt % to 2 wt % of such sequestering agents are present. 
         [0019]    It is additionally preferred if the agents contain 0.1 wt % to 2 wt % carbonate, in particular alkali carbonate. 
         [0020]    In addition to the aforesaid constituents, the corrosion-improved preparations according to the present invention can contain small quantities of one or more bleach-stable dyes or odorants. The fragrance component that is optionally contained preferably has a higher relative volatility than the constituents that are, if applicable, responsible for a bleach odor. 
         [0021]    The agents stabilized according to the present invention can easily be manufactured by mixing the aforesaid ingredients in the quantities indicated. They are utilized after dilution with water, or, if desired, also undiluted. 
         [0022]    The corrosion behavior of hypochlorite-containing preparations was examined. For this, small panels of sheet steel were placed into the undiluted preparations, and the relative corrosion rate after 14 days, 21 days, and 25 days was determined. The appearance of the steel panels is reproduced in  FIGS. 1 and 2 :  FIG. 1  shows the surface after being placed sodium hypochlorite (2 wt % in water), and  FIG. 2  shows the surface after being placed an aqueous agent that contained 2 wt % sodium hypochlorite, 1.5 wt % NaOH, 3 wt % Na—C 14/16  alkyl(ethoxy) 2  sulfate, and 2 wt % sodium silicate. Sample  3  was obtained after 14 days, sample  4  after 21 days, and sample  5  after 25 days. It is clearly apparent that the use according to the present invention of the combination results in much less damage to the metal surface.