Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Solid – shaped macroscopic article or structure
Reexamination Certificate
2001-01-17
2004-02-03
Douyon, Lorna M. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Solid, shaped macroscopic article or structure
C510S224000, C510S294000, C510S298000
Reexamination Certificate
active
06686328
ABSTRACT:
TECHNICAL FIELD
The present invention relates to multi-phase detergent tablets. In particular, it relates to multi-phase detergent tablets having improved robustness and product integrity together with excellent dissolution characteristics.
BACKGROUND
Detergent compositions in tablet form are known in the art. It is understood that detergent compositions in tablet form hold several advantages over detergent compositions in particulate form, such as ease of dosing, handling, transportation and storage.
Detergent tablets are most commonly prepared by pre-mixing components of a detergent composition and forming the pre-mixed detergent components into a tablet using any suitable equipment, preferably a tablet press. Tablets are typically formed by compression of the components of the detergent composition so that the tablets produced are sufficiently robust to be able to withstand handling and transportation without sustaining damage. In addition to being robust, tablets must also dissolve sufficiently fast so that the detergent components are released into the wash water as soon as possible at the beginning of the wash cycle.
However, a dichotomy exists in that as compression force is increased, the rate of dissolution of the tablets becomes slower. The present invention therefore seeks to find a balance between tablet robustness and tablet dissolution.
Solutions to this problem, as seen in the prior art, have included compressing the tablets with low compression pressure. However tablets made in this way, although having a fast relative dissolution rate, tend to crumble, becoming damaged and unacceptable to the consumer. Other solutions have included preparing tablets using a high relative compression pressure, in order to achieve the required level of robustness, and comprising a dissolution aid, such as an effervescent agent.
Multi-phase detergent tablets described in the prior art are prepared by compressing a first composition in a tablet press to form a substantially planar first layer. A further detergent composition is then delivered to the tablet press on top of the first layer. This second composition is then compressed to form another substantially planar second layer. Thus the first layer is generally subjected to more than one compression as it is also compressed during the compression of the second composition. Typically the first and second compression forces are in the same order of magnitude. The Applicant has found that where this is the case, because the compression force must be sufficient to bind the first and second compositions together, the force used in both the first and second compression steps must be in the range of from about 4,000 to about 20,000 kg (assuming a tablet cross-section of about 10 cm
2
). A consequence of this is a slower rate of tablet dissolution. Other multi-phase tablets exhibiting differential dissolution are prepared such that the second layer is compressed at a lower force than the first layer. However, although the dissolution rate of the second layer is improved, the second layer is soft in comparison to the first layer and is therefore vulnerable to damage caused by handling and transportation. Moreover, the two layers are found to have poor adhesion characteristics and can break up under the relatively mild stress conditions found in storage or transportation.
The present invention therefore provides multi-phase detergent tablets for use in automatic dishwashing, laundry, etc and which have improved integrity and robustness together with excellent dissolution characteristics.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a multi-phase detergent tablet for use in a washing machine, the tablet comprising a first phase in adhesive contact with one or more second phases, at least one second phase being in the form of a compressed particulate solid incorporating liquid adhesive and having an average porosity of less than about 0.15 ml/g, preferably less than about 0.13 ml/g and more preferably less than about 0.11 ml/g.
Porosity can be measured by known methods including image analysis, mercury porosimetry, determination and comparison of volume and mass, determination and comparison of surface area and diameter, gas chromatography, x-ray small angle scattering and displacement methods. A preferred method of measuring porosity is the mercury porosimetry method, average porosity being defined as the total intrusion volume of the particulate solid (prior to introduction of the liquid adhesive) for pore volumes below 30 &mgr;m. Preferably, the compressed particulate solid has an average porosity of less than about 0.09 ml/g, more preferably less than about 0.07 ml/g and especially less than about 0.05 ml/g.
In preferred embodiments, the adhesive is liquid or fluid at or close to ambient temperatures (preferably 28° C., more preferably 25° C. and above). It is also preferred herein to use adhesives that are water-frangible or water-sensitive, for example, adhesives based on water-soluble or water-emulsifiable polymers. It will also be understood that water and other solvent-based adhesives, for example, adhesives comprising aqueous polymeric solutions or emulsions, are also suitable for use herein. However, the preferred adhesives are either water-free or are used in conjunction with a water-sink (for example, anhydrous builder salts) in order to minimise the free moisture content of the final tablet compositions which is preferably less than about 1% by weight. The liquid adhesive is incorporated by post-addition, preferably as a spray-on, to the particulate solid prior to compression. The level of liquid adhesive is preferably from about 0.1% to about 3%, more preferably from about 0.5% to about 1.5% by weight of the second phase particulate solid.
In preferred embodiments, the first phase also takes the form of a compressed particulate solid, the average porosity of which is greater than that of the second phase particulate solid by at least 10%, preferably at least 30%, and more preferably at least 60%, this being valuable for optimum adhesion. In general, the average porosity of the first phase is at least 0.1 ml/g, preferably at least 0.12 ml/g, more preferably at least 0.14 ml/g, especially at least 0.16 ml/g and more especially at least 0.18 ml/g. Preferred adhesives for use herein are selected from water-soluble poly(C
2
-C
4
)-alkylene oxide polymers and copolymers, poly(C
2
-C
4
)-alkoxylated nonionic surfactants, aqueous polymeric solutions and emulsions, and mixtures thereof. Of these, highly preferred from the viewpoint of optimum product integrity, robustness and dissolution characteristics are the polyethylene glycols having an average molecular weight in the range from about 200 to about 700, preferably from about 250 to about 600, although polyethylene glycols of a somewhat higher average molecular weight, for example up to about 900, can be used if the detergent tablet is prepared at a temperature slightly above ambient, for example up to about 28° C.
Thus according to second aspect of the invention, there is provided a multi-phase detergent tablet for use in a washing machine, the tablet comprising a first phase in adhesive contact with one or more second phases, at least one second phase being in the form of a compressed particulate solid incorporating liquid adhesive selected from polyethylene glycols having an average molecular weight in the range from about 200 to about 700.
The detergent tablets herein comprise at least one first phase in adhesive contact with one or more second phases (sometimes referred to herein as ‘optional subsequent phases’). In preferred embodiments, the first phase is a compressed shaped body prepared at an applied compression pressure of at least about 250 kg/cm
2
, preferably at least about 350 kg/cm
2
(3.43 kN/cm
2
or 34.3 MPa), more preferably from about 400 to about 2000 kg/cm
2
, and especially from about 600 to about 1200 kg/cm
2
(compression pressure herein is the applied force divided by the cross-sectional area of the tablet in a
Douyon Lorna M.
Matthews Armina E.
The Procter & Gamble & Company
Waugh Kevin L.
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