Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
1999-07-07
2001-06-19
Douyon, Lorna M. (Department: 1751)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S025200, C134S025400, C134S035000, C134S022190, C134S025100, C510S219000, C510S243000, C510S405000, C510S421000, C510S434000, C510S435000, C510S436000, C510S477000, C510S480000
Reexamination Certificate
active
06247478
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to methods and compositions for cleaning polyethylene terephthalate containers. More specifically, the invention relates to methods and compositions which remove mold, present on polyethylene terephthalate containers, with reduced hazing.
BACKGROUND OF THE INVENTION
As with many industries, the drive towards economy has also effected the beverage industry and has resulted in certain real changes in the way in which beverages are bottled, distributed and dispensed. In the last decade the beverage industry has seen a switch from glass to plastic containers. Plastic containers may be made from any number of materials depending on the application. One material is polyethylene terephthalate, “PET”. Two types of PET bottles that are commonly used are single trip and multi-trip bottles. Single trip bottles are those which are filled, used, and then discarded. Multi-trip bottles are collected and reused and must be washed before refilling.
PET bottles offer several advantages over glass. Their light weight reduces freight costs. When dropped onto a hard surface they do not shatter like glass and generally do not break. Conveyor wear caused by the containers in the packaging plant is also reduced. The closure is also generally reusable after a bottle has been opened.
Disadvantages are that PET bottles are easily scratched, and susceptible to chemical attack when they are washed. PET containers also do not tolerate conditions above 60° C. Exposing them to higher temperatures than 60° C. causes deformation and/or shrinkage of the bottles.
Recycling of PET containers was recently approved by the FDA in the USA to permit turning used containers into new ones. Because new resin costs 50 to 75 cents per pound, recycling used bottles is economically attractive. In time, glass soft drink bottles are expected to disappear from the market. This heightens the relevance of PET container processing even further.
The cleaning of PET bottles takes place over a series of steps using caustic immersion tanks and spray wash stages in a bottlewasher. In the wash tanks, product residue, dirt, labels and labeling adhesive are removed. Because the surface of PET bottles is hydrophobic, cleaning them is more difficult than glass bottles. Also, the lower washing temperature decreases the chemical activity of the bottle washing solution.
Two principle problems in the cleaning of PET bottles are touched on by Laufenberg et al., “Cleaning, Disinfecting, and Transporting Pet Returnables”, Brew Bev. Ind. Int. 1, 40-4 (0 ref.) January, 1992.
In this article, the author outlines the susceptibility of the PET bottles to corrosion or hazing. Hazing results from the chemical etching of the surface of the PET container by the caustic present in the wash bath.
An especially challenging problem which affects reusable PET bottles is the occurrence of mold in returned bottles. To simply discard all bottles from which mold can not be removed is prohibitively expensive. Reject rates of 40 to 50% have occurred at certain times of the year in countries located in tropical climates.
The necessary cleaning temperature for PET bottles is 60° C. or less due to the glass transition temperature of PET. If exceeded, PET bottles deform and shrink. The cleaning power of a bottle washing solution at 60° C. is only one quarter that at 80° C. Bottles returned with product residue, i.e., those bottles that have not been rinsed, are almost always contaminated with microbiological forms of life. The bottle washing solution eliminates the presence of microbiological forms of life such as bacteria, spores, molds, and yeasts present in the bottle. However, at the reduced temperature of 60° C., molds often present a persistent problem in the cleaning and reuse of PET bottles.
PET bottles simply cannot be washed like glass. Glass bottles are normally washed at 80° C. Glass can also be washed with a relatively high concentration of caustic. While glass may be washed with up to 5.0% caustic, as little as 1.5% caustic can cause hazing in a PET container. With glass the washing temperature, the caustic concentration, and the washing time may be adjusted to allow for variability within the environment. In contrast, PET containers cannot withstand high levels of any of these variables.
While various alternatives have been proposed such as lowering the level of caustic, there remains a need in the industry for compositions and methods which allow for the efficient cleaning of PET containers and multiple reuse events.
SUMMARY OF THE INVENTION
The first aspect of the invention is a method for cleaning a polyethylene terephthalate container. The method includes combining a first concentrate with a second concentrate in an alkaline wash solution. The first concentrate includes from about 0.3 to 25 wt-% of a surfactant and from about 5 to 30 wt-% of an acid. The second concentrate includes from about 8 to 60 wt-% of a builder. The method further includes the step of contacting the PET container with the wash solution wherein the removal of soil is undertaken with minimal hazing of the container.
An additional aspect of the invention is a method for cleaning plolyethylene terephthalate containers which includes contacting the container with an alkaline wash solution having a temperature ranging from about 50° C. to 60° C. The alkaline wash solution is formulated from a first concentrate, a second concentrate, an alkalinity source, and a balance of water. The first concentrate includes a nonionic surfactant, a first builder, and acid in an amount effective to provide a phase stable solution. The second concentrate includes a nonionic surfactant and a second builder. The first and second concentrate are present in the wash solution in a concentration ranging from about 0.5 wt-% to 1.2 wt-%, and the first nonionic surfactant has a cloud point ranging from about 5° C. to 60° C.
A further aspect of the invention is an alkaline wash solution for cleaning polyethylene terephthalate bottles. The wash solution includes from about 1 to 5 wt-% of a source of alkalinity, from about 480 to 4000 ppm of a builder, from about 6 to 500 ppm of a surfactant, and from about 20 to 800 ppm of a coupler.
The invention is compositions and methods for cleaning polyethylene terephthalate (PET) bottles with enhanced removal of mold and reduced hazing. In addition to the 1 to 3 wt-% caustic commonly used in PET bottle washing procedures, the compositions of the invention include surfactants and builder combination, which heightens cleaning and removes mold.
Hazing generally results from chemical etching caused by caustic present in the wash solution. Hazing is a clouding or dulling of the PET container surface which detracts from the aesthetic character of the container. Surprisingly, it has been found that by using surfactants with appropriate cloud points, hazing may be substantially reduced. Preferably, PET containers treated with the wash solution of the invention are substantially free of hazing.
Further, mold growth, particularly in the inside of returned PET bottles, proves to be a major challenge in bottle washing. Molds are very difficult to remove, even with a solution having as much as 3% caustic. Good cleaning usually removes most of the organic components of mold. However, the inorganic residues of mold may remain on the PET container surface. This may cause a problem similar to water spots. This condition gives a positive test result by methylene blue staining, (Industrial Code of Practice for Refillable PET Bottles, Edition 1 (1993-1994 UNESDA/CESDA, pg. V-18). The compositions and methods of the invention substantially remove soils and both the organic and inorganic residues of mold.
DETAILED DESCRIPTION OF THE INVENTION
The Composition
Generally, the wash solution of the invention is formulated from two concentrate compositions. These two concentrate compositions are combined in an aqueous wash solution with an alkalinity source, before use. These concentrate compositions generally comprise surfactants, an acid, buil
Cords Bruce R.
Herdt Brandon L.
McSherry David D.
Valencia Arturo
Wei Guang-jong Jason
Douyon Lorna M.
Ecolab Inc.
Merchant & Gould P.C.
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