Abstract:
A stable, cleaning solution for acoustic material such as porous tile, fabric, etc., is disclosed that contains an inorganic oxidizer, such as ammonium persulfate as the active ingredient in the solution, that may be applied by spraying. Potable tap water is used as the diluent, and various ingredients are utilized in the cleaning solution to clean the tile and maintain the solution as a clear, single phase solution having a relatively long term activity life of about 5-10 days, at a pH typically at least about 8-9.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a composition and process for cleaning acoustic materials, which may include porous cellulosics such as acoustic ceiling tile, wood fiber matrices, blown acoustic mineral matrices comprising perlite combined with white portland cement, cement and lime, fabrics, painted acoustic surfaces, vinyl and plastic materials, cork, mineral fibers and mineral wool, plastic coated metals, metals, and the like. 
     Cleaning solutions that are presently employed to clean these acoustic materials contain a solution of chlorine bleach or other solutions that contain releasable chlorine as the active ingredient. Obviously, a cleaning solution is desired that can function in a manner similar to chlorine but without the dangerous side effects. If chlorine could be eliminated, the cleaning operation would be safer and would require less governmental regulations. 
     Ammonium persulfate and similar inorganic persulfates that are water soluble are known as oxidizing agents, and these persulfate solutions are relatively stable when used alone. However, when used in conjunction with many common cleaner ingredients, the persulfate decomposes over a fairly short period, following solution make-up. The solution stability should be long enough to allow a work crew sufficient flexibility in the cleaning operation without being concerned about the cleaning solution losing its strength over a short period of time. 
     It is preferable, on a long term basis, to be able to store the oxidizer, in this case the persulfate, in the solid dry form. This would increase the oxidizer storage life considerably, compared to storing a solution. Furthermore, if the persulfate can be transported as a dry solid instead of a liquid, and if the dirt removing portion of the cleaning solution can be shipped as a concentrate, this would save shipping costs. 
     THE INVENTION 
     According to the invention, a cleaning solution and method for cleaning porous acoustic materials is provided containing one or more water soluble persulfates as the active oxidizing ingredient. This solution is much safer to use than chlorine and is equivalent in cleaning effectiveness compared to solutions containing chlorine bleach or releasable chlorine. 
     Typical inorganic persulfates that are suitable include ammonium persulfate (NH 4 ) 2  S 2  O 8 , potassium persulfate KSO 5 , K 2  S 2  O 8 , and sodium persulfate NaSO 5 , Na 2  S 2  O 8 . The ammonium persulfate is preferred due to its relatively low cost and high and rapid water solubility. About 2.0%-10% of the ammonium persulfate may be employed, and a range of about 5.0%-7.0% is preferred. All percentages herein refer to parts by weight of the final cleaning solution used for application onto the acoustic material, such as by spraying. The solution has a reasonably long term stability period of about 5-10 days, depending on the water purity and storage temperature. 
     Initially, the cleaning solution is made up in two portions, one portion containing the oxidizing persulfate. The other portion containing various dirt dissolving compounds, a caustic pH adjusting agent, and stabilizing compounds, is quite stable and relatively free of particulate matter such as precipitates, crystallization, colloidal materials, and the like. The dirt dissolving portion of the solution thus has a relatively long term storage life, and this property enables it to be readily formulated at a factory as a concentrate, shipped and then stored. The final cleaning solution is produced by mixing appropriate amounts of persulfate and dirt dissolving concentrate with water. 
     The stability of the cleaning solution of this invention is quite surprising since a technical bulletin published by FMC Corporation concerning ammonium persulfate advises that the dry persulfate should not contact solvents, oils, greases and oxidizable organic compounds; the FMC bulletin also states that a solution of ammonium persulfate should not contact strong caustic solutions. Notwithstanding the FMC bulletin, the cleaning solution of this invention containing persulfate can be stabilized in the presence of a variety of organic compounds including solvents, emulsifiers, surfactants, and also caustic solution, and be utilized to safely remove greases, dirt, stains, and so forth. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Since many impurities may be contained in tap water that could catalyze the decomposition of ammonium persulfate, or otherwise reduce its effectiveness, these compounds should be either eliminated or neutralized. Such compounds include bacteria in concentrations that would render the water non-potable, ions such as Ca +2 , Mg +2 , etc., that will react with the cleaner to precipitate alkali or other solution components, or Cu +2  ions that are potent catalysts for the decomposition of the persulfate. Usually, if a solution of potable tap water is employed, the problem of bacterial reaction with the persulfate will be minimized. Use of a chelating agent such as a nitriloacetic acid derivative will reduce the effect of hard water ions; usually, a concentration of about 0.03%-0.3%, and preferably about 0.05%-0.1% will be effective. A preferred chelating agent is hydroxyethyl ethylene diamine triacetic acid tri-sodium salt that is sold by the Dow Chemical Co. as &#34;VERSENOL 120,&#34; and by Hampshire Chemical Division of W. R. Grace Co. as &#34;HAMPOL 120&#34;.  The VERSENOL 120 or HAMPOL 120 appears to aid in the removal of tobacco residue stains more effectively than the more commonly used &#34;VERSENE 100&#34; (Dow Chemical Co.) which is ethylene diamine tetra acetic acid tetra sodium salt. 
     A hydrotrope is employed in the dirt dissolving solution to maintain this solution as a single phase and also to stabilize the cleaning solution formed by combining the oxidizing agent and the dirt dissolving solution. A preferred hydrotrope may be a Na or K xylene sulfonate, a phosphate ester surfactant, or mixtures thereof. The hydrotrope may be used in the cleaning solution at a concentration range broadly speaking of about 0.5%-3.0%, and preferably about 0.8%-1.3%. 
     Cleaning compounds such as surfactants or emulsifiers are used to emulsify dirt particles which remain on the acoustic material after an initial physical cleaning such as by vacuuming, brushing, etc. The surfactant or emulsifier is non-reactive with the persulfate and is preferably one or more of: ethoxylated alkyl phenols including octyl or nonyl phenols, ethoxylated fatty acid esters, ethoxylated alcohols, fatty acid sulfates, ether sulfates, and mixtures thereof. When an emulsifier is employed in conjunction with a surfactant, a suitable type that may be used is polyethyleneglycol 400 sesquioleate, sold by Emery Industries, Inc. as &#34;EMEREST 2647&#34;. A concentration range of about 0.5%-4.0% of the surfactant and/or emulsifier in the cleaning solution is useful, and preferably, about 0.5%-1.5% is used. 
     An inorganic soil suspender is used to produce a suspension of solids that are removed from the acoustic material; this minimizes formation of a thick residue that tends to be impervious to an oxidizer because of its thickness. Preferred soil suspenders include tetrapotassium pyrophosphate, sodium tripolyphosphate, Na or K hexametaphosphate, Na and K silicates, etc. Typical soil suspender concentrations vary from about 0.1%-4.0%, and preferred concentrations vary from about 0.2%-0.5%. 
     A water miscible solvent is used to dissolve organic components in the dirt. Typical solvents include isopropyl alcohol, acetone, ethyl alcohol, ethyl and butyl monoesters of ethylene glycols, methyl ethyl ketone, etc. The solvent and detergent are coupled by the hydrotrope, the latter also coupling the aqueous phase with the non-aqueous phase of the dirt dissolving solution. About 1.0%-6.0%, and preferably about 1.5%-3.5% of the solvent is employed in the cleaning solution. 
     A base such as NaOH or KOH is added to the dirt dissolving and stabilizing solution in a sufficient amount so that the pH of the cleaning solution will be adjusted to about 8-9; this optimizes the activity of the ammonium persulfate, and prevents the odor of ammonia. When using ammonium persulfate, a typical concentrate solution pH when formulated at the factory is about 13-14; usually, the KOH concentration in the cleaning solution may vary from about 1%-6%, but this range can vary widely, depending on the choice of ingredients. If the ammonia odor is not objectionable, or if a persulfate other than ammonium persulfate is used, the pH may be increased to about say, 9-11. This will increase the persulfate activity somewhat, but will shorten the useful life of the cleaning solution, and will slightly increase the potential skin hazard to the user. 
     The acoustic material such as porous acoustic tile is initially brushed and/or vacuumed. The cleaning solution is prepared from the concentrate and dry ammonium persulfate, and then applied to the physically cleaned tiles, preferably by spraying. With the exception of metal fittings that may catalyze the decomposition of the persulfate, such as mild steel, copper, copper alloys, nickel, etc., the same spraying equipment may be used as that for chlorine, thus obviating the need for new equipment. The detergent and solvent action of the cleaning solution will loosen the dirt from the tile surface and then redistribute the dirt over the tile in an even manner. This facilitates a uniform oxidation of the dirt, tobacco and cooking residues, etc., by the persulfate and conversion of these materials to a neutral color. The tiles are then simply allowed to dry. 
     When applying the aqueous cleaning solution containing persulfate, it is preferred to avoid direct contact with the spray, and use of common painter&#39;s spray or dust goggles and face mask, and possibly rubber gloves is accordingly recommended. However, unlike chlorine, the spray of this invention does not pose a problem to persons outside the work area because it is not disseminated as a hazardous gas, with the exception of minor amounts of solvent. 
     Obviously, various embodiments of this invention are possible without departing from the inventive spirit thereof. For example, if the tap water is of very good quality and low hardness, the use of a chelating agent may be reduced below the specified concentration levels. Furthermore, the amount of phosphate ester (or similar) surfactant used as the hydrotrope may be increased beyond the concentration limits shown and thereby function partly or completely in place of the polyoxyethylene-9-octyl (or nonyl) phenol surfactant. Also, if the acoustic tiles are extremely dirty, a stronger concentration of persulfate, or higher pH may be used, or a second application of the cleaning solution might be necessary. If desired, an optical brightener may be included in the cleaning solution to enhance the brightness of the acoustic tile surface.