Abstract:
A composition comprising 2-n-octyl isothiazolone 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one has been found to provide superior preservative performance as compared to the individual components.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the preservation of aqueous products such as liquid dishwash detergents, surfactants, and liquid soaps against microbial degradation. More specifically, the invention relates to the use of compositions comprising 2-n-octylisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one for the preservation of materials susceptible to microbial degradation. 
     Materials containing organic material in aqueous solutions may be highly susceptible to attack from microorganisms. Materials such as liquid dishwash detergents, surfactants, liquid soaps, adhesives, metal working fluids, hand cleaners, paints, mineral slurries, polymer emulsions and shampoos are routinely formulated with antimicrobial agents to prevent the growth of putrifying microorganisms. 
     Numerous materials are known in the literature for use in preventing microbial growth in susceptible materials. Some example are found in U.S. Pat. Nos. 4,105,431 and 4,135,945 and in 4,725,611. 
     SUMMARY OF THE INVENTION 
     This invention relates to the discovery that a combination of isothiazolones when used at extremely low amounts is more effective than any of the components at similar dosage rates. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of this invention comprises: 
     a. Component 1: comprises a mixture of 75% 5-chloro-2-methyl-4-isothiazolin-3-one and 25% 2-methyl-4-isothiazolin-3-one; and 
     b. Component 2: 2-n octyl-4-isothiazolin-3-one. 
     These two components may be mixed in a range of ratios from 1 part Component 1: 10 parts Component 2 to 10 parts Component 1: 1 part Component 2. The most preferred ratio is in the range 2 parts Component 1: 1 part Component 2 to 5 part Component 1: 1 part Component 2. Typical use levels are in the range of 1 to 15 ppm of Component 1 plus Component 2 as the active ingredient with preferred use levels in the range of from 1 to 4 ppm of the compositions. 
     EXAMPLES 
     The following experiments demonstrate the invention. 
     Various levels of the two components are added to a liquid dish detergent formulation. The test samples are inoculated with bacteria that has been previously shown to be able to degrade the liquid dish detergent. Additional microbial inoculum is added to the samples every week for four weeks. The level of microbial growth present in the samples is determined each week. Standard plate counting techniques are employed using trypticase soy agar and rose bengal chloramphenicol agar plates. Samples are evaluated to determine the number of weeks that the samples remained free of microbial growth. Any growth in these products is not acceptable and is judged a failure. 
     MIC Component 1 
     Component 1 is known to have a broad spectrum of antimicrobial activity. Minimum inhibitory concentrations (MIC) of Component 1 for various types of microorganisms appear in Table 1: 
     
                       TABLE 1______________________________________         MIC (ppm active ingredient)______________________________________Gram Positive Bacteria           2.0-9.0Gram Negative Bacteria           2.0-9.0Fungi           2.0-9.0______________________________________ 
    
     MIC Component 2 
     Component 2 is known to be effective in the control of fungi but is much less effective in the control of bacteria, particularly gram negative bacteria. Minimum inhibitory concentrations for various types of microorganisms appear in Table 2. 
     
                       TABLE 2______________________________________         MIC (ppm active ingredient)______________________________________Gram Positive Bacteria           8.0-32.0Gram Negative Bacteria           125.0-1000.0Fungi           0.6-16.0______________________________________ 
    
     By itself Component 2 is not effective in preventing microbial growth in a susceptible material which typically becomes contaminated with fungi and bacteria, particularly gram negative bacteria. Component 1 is known to be effective at a dosage level of at least 4 ppm. A mixture of Component 1 and Component 2 has been found, however, to be more effective than would be predicted based on the spectrum of activities of the two separate components. 
     Table 3 shows results of a comparative test in a liquid dishwashing detergent. (Weeks until the onset of microbial growth is presented as a function of concentration of the two components.) 
     
                       TABLE 3______________________________________Comparison of ActivitiesConcentration     Concentration  Total     Weeksof Component 1     of Component 2 Active    Until(ppm active)     (ppm active)   Ingredient                              Failure______________________________________1.0       0              1.0       02.0       0              2.0       04.0       0              4.0       &gt;41.0       0.2            1.2       41.0       0.5            1.5       42.0       0.4            2.4       &gt;42.0       1.0            3.0       &gt;4______________________________________