Abstract:
A process of cleaning a polycarbonate bottle includes 
     (a) washing the bottle with a composition consisting essentially of an aqueous basic solution containing the members: alkali metal carbonate, alkali metal bi-carbonate and a low foaming detergent, and 
     (b) then rinsing the bottle with water.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to cleaning of poly carbonate drinking water bottles, and more particularly concerns cleaning compositions of this type that are free of chlorine and will not cause stress cracking or crazing of such containers. 
     The problems of chlorine fume production, and stress cracking and crazing of polycarbonate containers arise during washing or cleaning of same, using conventional cleaning compositions. Such containers are commonly used for drinking water, they are considered re-usable, and therefore must be washed or cleaned. Public health regulations require an alkalinity titration equivalent to 0.35% as sodium hydroxide; however, a pH higher than 11.0 can be detrimental and cause the described crazing and stress cracking. Also, since the bottles are used for drinking water, the cleaning compositions must be non-toxic and leave no objectionable odor or taste. No way was known to avoid such problems, using conventional cleaning compositions. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide a cleaning composition, and process, that avoids the above problems. 
     In its composition aspects, the invention concerns the provision of alkali metal salts so combined that they have, at use concentrations, a pH of 11.0 or less and an adequate reserve of titratable alkalinity, at least equivalent to 0.35 percent caustic soda (sodium hydroxide), when titrated to the colorless phenolphthalein end point, which is about pH 8.0. 
     In its process aspects, the invention involves the steps: 
     (a) washing the poly carbonate bottle with a composition consisting of a basic solution containing an alkali metal carbonate, an alkali metal bi-carbonate and low-foaming surfactant, and 
     (b) rinsing the bottle with water. 
     As will appear, the solution pH is adjusted below 11.0 by adjustment of ingredient weight percentages. 
     DETAILED DESCRIPTION 
     The aqueous washes or solutions of the present invention are based on use of mixtures of sodium carbonate, sodium bi-carbonate and a small percentage of low foaming surfactant. As will appear, a cleaning composition or concentrate is prepared or supplied, for example, and added to or combined with a much larger (relative) volume of water. For example, between 1.6 2.0 ounces of concentrate is added to or combined with a gallon of water, these being relative proportions. 
     One basic concentrate formula is: 
     
         ______________________________________            Range (weight %)Ingredient         Broad    Preferred______________________________________sodium carbonate   84-90%   88%sodium bi-carbonate              10-12%   11%low-foaming surfactant               .5-1.5%  1%(BASF PLURAFACRA-40, or equivalent)______________________________________ 
    
     A second concentrate formula, by way of example is: 
     
         ______________________________________            Range (wt. %)Ingredient         Broad    Preferred______________________________________potassium carbonate              86-90%   89%potassium bi-carbonate               9-11%   10%low-foaming surfactant               .5-1.5%  1%(BASF PLURAFACRA-40, or equivalent)______________________________________ 
    
     A third concentrate formula, by way of example is: 
     
         ______________________________________            Range (wt. %)Ingredient         Broad    Preferred______________________________________lithium carbonate  87-91%   90.7%sodium bi-carbonate               8-10%   8.3%low-foaming surfactant               .5-1.5% 1.0%(BASF PLURAFACRA-40, or equivalent)______________________________________ 
    
     Other usable surfactants are: 
     Polyoxyethylene glycols such as Pluronic L-61, a product of Wyandotte Chemical Co., and Witconnol 171, a product of Witco Chemical Corp; Linear primary alcohol polyether, such as Antarox BJ-225, a product of GAF (General Aniline &amp; Film Corp.); nonyl phenoxy polyethoxy ethanol, such as Triton N-101, a product of Rohm &amp; Haas Company; or any low foaming surfactant that does not craze polycarbonate plastic material. 
     The above concentrate, which is a free flowing, granular, alkaline powder, mixed with a relatively large volume of water, as referred to, provides a poly carbonate bottle wash solution having a pH below 11.0 and preferably about 10.5. The sodium carbonates and bi-carbonates are readily available and low priced; however, the alkali metal carbonates and bi-carbonates or mixtures of same may used (potassium and lithium for example). 
    
    
     EXAMPLE 
     The above solution is sprayed onto poly carbonate bottle surfaces, as by means of a spray washer having a spray nozzle, at a temperature or temperatures between 120° F. and 150° F., and preferably about 130° F. The spray wash is continued for 1.5 to 3 minutes. Thereafter, the bottle is rinsed with distilled water, or soft water, for at least about 30 seconds. 
     A graph of the pH requirements and the alkalinity requirements is given by a plot of the variation of the pH as the alkalinity is reduced by titration with a standard acid. See FIG. 1. Curve A, sodium hydroxide, has a pH much above 11 until nearly all of its alkalinity is used up. Curve B, the basic concentrate formula of the present invention, starts out with a pH below 11.0, which slowly drops as the alkalinity is used up and does not drop below the effective alkali range at pH 8.0 until after more acid is consummed than is used by sodium hydroxide. 
     The materials of choice are sodium carbonate and sodium bicarbonate; however, other alkali metals such as potassium and lithium give similar acceptable curves. 
     The above composition and process provide the following benefits. 
     1. Preparations of the wash solution is readily carried out by mixing of concentrate with cold water. 
     2. The wash solution is non-foaming at the described concentrations and temperatures. 
     3. The solution is free of chlorine and thus free of such fumes. 
     4. The solution removes most paper labels from containers. 
     5. The solution does not leave odor or after-taste in container, particularly after rinsing. 
     6. The containers do not become crazed or cracked as a result of washing as described.