Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using sonic or ultrasonic energy
Reexamination Certificate
2001-03-29
2003-01-07
Warden, Sr., Robert J. (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using sonic or ultrasonic energy
C422S022000, C422S028000, C424S405000
Reexamination Certificate
active
06503449
ABSTRACT:
The present invention relates to a process for the elimination of microbial contamination from water-based suspensions of solid particles, especially organic and inorganic pigment dispersions, and the colourant formulations containing such suspensions.
Microbial organisms, especially bacteria, yeasts and fungi, are present in all aspects of the environment and are capable of existing under the most extreme conditions. Spore-forming organisms can exist in a dormant state for many years, ready to come into growth when the environment is friendly. Others will exist when the moisture content of the environment is sufficient to sustain growth. All are capable of metabolising organic substrates as sources of nutrient.
Microbial spoilage in the food industry is well known and extreme measures are typically employed for its elimination and prevention. For example, heat treatment, often under pressure (autoclaving), and gamma irradiation can be used to achieve decontamination.
Systems that are water-based and contain compounds of carbon, nitrogen, oxygen and sulphur are ideal breeding grounds for microbial organisms. The subsequent manifestations for such contamination can be mal odours, mycelial mats, settling of the solids in paints (due to digestion of the thickeners), blocking of filtration systems, and the like. As legislation and environmental pressures on volatile organic compounds (VOC's) increase, an increasing number of systems such as, for example, paints, printing inks and the like are converting from solvent-based to water-based formulations.
Most of the colour in every-day life derives from organic or inorganic pigments. These are very small particles (ranging from a few nanometres to several hundreds of microns in size) which are dispersed in synthetic or natural substrates (inks, paints, fibres, cosmetics and the like), and those in turn, are susceptible to microbial attack. The conventional methods for resisting such attacks have been to add chemical biocides to the formulations. These biocides are toxic to the micro-organisms, and either kill, or put the microorganisms into a condition of stasis. These chemical biocides, by their very natures, can be toxic to humans, causing secondary effects such as skin sensitisation, and are themselves becoming subject to increasing legislation and restriction in use. Furthermore, as the most effective chemical biocides can be adversely affected by the typical conditions of industrial processing (heat, pH, amines, thiols, and the like), even higher biocide levels are then required to overcome these factors. When solid particles are present in the medium the biocides can be adsorbed on the surface of the particles which can also have a negative effect on their efficacy.
Aqueous pigment dispersions and the formulations they colour are by their very nature unsuited to any degree of heat treatment because of both the cloud points of the additives which they contain, and because of gamma irradiation due to the susceptibility of the chemical chromophore to high-energy breakdown, and, as such, aqueous pigment dispersions are normally dependent on chemical biocides. Pigment powders, because of their very small particle size (measured in nanometres), high surface area and propensity to adsorb moisture, can carry varying levels of microbial contamination either in the vegetative or dormant states. When such pigment dispersions are dispersed into water containing organic surface-active agents the environment becomes conducive to the active propagation of microbial contaminants, particularly in the warmer climates, in warehouses, the holds of ships, and other typical storage conditions. Contamination levels of up to 10
8
colony-forming units per millilitre can typically be reached. To counter this, chemical biocides are normally added in sufficient levels to minimise the growth of contaminants, and if not consumed, remain present as potentially toxic substances in the application system. This presents a dilemma to the manufacturer as products containing more than a specified amount of a particular biocide must carry a warning label identifying the product as toxic (for example:—R43—Skin Sensitiser) even when the main product itself is not toxic. Thus, it would be a significant technical advantage to develop a process for the production of water-based suspensions of solid particles that are free of microbial contamination at the point of manufacture; during and after storage; in final formulation with additional materials. It would be a further advantage to develop such a process wherein the levels of chemical agent (biocide) employed are below the regulatory labelling level while still being sufficient to control microbial growth.
The present invention relates to a process using ultrasound in conjunction with very low levels of chemical biocide for the control of biological activity from suspensions of solid particles in water-based fluids, especially pigment and dye colourants. The process according to the present invention allows for a significant reduction in the processing time for control of biological activity at biocide levels well within regulatory labelling limits, and provides a more effective and efficient throughput of pigmented material. Furthermore the present invention additionally provides means for further improvements in process efficiency by careful selection of chemical biocide to suit the components in any particular coloured aqueous formulation.
Accordingly, the present invention provides a process for the production of biologically inactive dispersions of coloured particles in aqueous formulations at ambient temperatures when the level of contamination is as high as 10
9
colony-forming units per millilitre via ultrasonic treatment of a mixture of the solids dispersion and chemical biocide.
Water-based solids suspensions suitable for use in the process according to the present invention include dispersions of organic and inorganic pigments and dyestuffs in water containing additives that enhance processing and applicational properties. Examples of such additives are ethoxylated fatty alcohols and phenols, sulphonated naphthalenes and their derivatives, acrylic acid polymers and copolymers with styrene, both water-soluble and emulsion. The term “solid” as defined herein includes particles of pigments and dyes where the particle can be an individual crystal, aggregate of crystals or agglomerate of aggregates ranging in size from a few nanometres to hundreds of microns together with additives which themselves are solutions or emulsions in water. Any level of solid may be employed in the suspensions. However, at very high solids contents, typically greater than about 65%, highly viscous materials are typically formed which, although usable in the present process, provide specific difficulties in the manufacturing process due to pumping limitations. Similarly, highly diluted suspensions, typically containing solids at levels of less than about 5%, may be processed (pumped) more easily but their low solids content can limit their utility for economic reasons. Thus solids suspensions containing from 10% to 80% of solids, preferably 20% to 60% by weight of the dispersion are preferred for use in the process of the present invention.
Any level of chemical biocide may be employed in the dispersions/formulations to be processed according to the present invention. Preferably the total level of chemical biocide used is lower than the level requiring an R43 skin sensitising label. Typically the chemcial biocide is present at levels of from about 5 parts per million (ppm) by weight of the dispersion to about 500 ppm, most preferably from about 50 ppm to about 250 ppm by weight of the dispersion/formulation.
Chemical biocide as defined herein means a material which is capable of inhibiting the growth of microbiological contaminants in water-based systems. Examples of microbiological contaminants as defined herein include Gram positive and Gram negative bacteria, yeasts and fungi. Suitable chemical biocides include aldehydes and i
Ciba Specialty Chemicals Corporation
Mansfield Kevin T.
Soubra Imad
Warden, Sr. Robert J.
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