Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
1998-01-08
2001-06-05
Gupta, Yogendra (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S320000, C435S177000, C435S188000, C523S201000
Reexamination Certificate
active
06242405
ABSTRACT:
This invention relates to enzyme containing particles wherein the enzyme can be controllably retained within the particles despite migration of other materials through the walls of the particles. In particular the invention relates to liquid detergent concentrates which contain particles which contain an enzyme whereby the enzyme is protected in the concentrate but is released when the concentrate is diluted in wash water. In particular it preferably relates to such concentrates which contain two enzymes wherein one would normally deactivate the other but which are protected from each other in the concentrate and which are available upon dilution in wash water.
There is extensive prior art on encapsulating active ingredients in polymeric particles so as to attempt to protect the active ingredient from the environment during storage but to permit release when required. In some processes the active ingredient is distributed through a polymeric matrix. In other processes the active ingredient is present in the core of a particle which has a polymeric shell. In some processes there is a polymeric shell surrounding a core containing a polymeric matrix and the active ingredient.
Particular difficulties arise in those instances when it is intended that release of the active ingredient should occur solely as a result of a change in the ambient environment, without any deliberate application of a release mechanism such as the application of external rupturing pressure. Particular problems also arise when the capsules are very small, for instance below 30 &mgr;m, since the capsules then have an extremely large specific surface area, ie surface area per unit mass of particles. Accordingly, even a very low permeation rate from the surface of the particles may be unacceptable with these small particles, whereas the same permeation rate from the surface of larger particles, having a much smaller specific surface area, may be acceptable.
It is known to be desirable to include detergent enzymes in liquid detergent concentrates. There have been many proposals in the literature to protect the enzyme from the continuous phase of the concentrate and/or water by providing a continuous shell and/or a matrix which is intended to protect the enzyme from the concentrate but to release it when the detergent concentrate is added to water to provide wash water. Examples are given in EP 356,239 and WO92/20771, and the prior art discussed in those. These and other known methods generally involve forming the shell by coacervation.
Although there have been proposals to include coarse particles, for instance having a size up to 1,000 &mgr;m, in detergent concentrates, in practice this is commercially unacceptable because the particles settle out from the concentrate. It is, instead, necessary that the particles could be so small that they can be stably dispersed in the concentrate, and in practice this means that they should generally have a size at least 90% by weight below 30 &mgr;m (dry size). Accordingly the particles have a very high specific area.
Unfortunately it is very difficult to select a coacervation polymer and its conditions of use on the one hand, and a polymeric or other core composition on the other, so as to obtain in particles of high specific area the optimum protection and release performance that is required. In general, either the shell is too impermeable to give effective release when required or the shell permits premature relase.
A somewhat similar problem exists in systems for immobilising enzymes for use as, for instance, catalysts in chemical (including biochemical) reactions. Either the enzyme escapes prematurely through the shell of the immobilising particles or the shell is so impermeable that it severely interferes with the necessary migration through the shell of reactants and reaction products.
A particular problem seems to arise in liquid detergents because of the tendency of the enzyme to permeate during storage through the high surface area of the coacervate shell, if the shell is capable of giving full release when required. This is probably due in part to the rather low molecular volume of the enzyme (since detergent enzymes typically have a molecular weight of the order of 20,000 to 100,000) combined with the fact that many polymer films are likely to be permeable or semi-permeable to molecules of this size. Accordingly on prolonged storage a significant amount of the enzyme may migrate through the large surface area of the shell even if the permeability of the shell appears to be low. If the shell is made sufficiently thick or cross-linked to minimise the risk of this happening it is then very difficult to achieve adequate release of the enzyme.
Various encapsulation techniques other than coacervation are known for various purposes and one such technique which has been used for other processes is inter facial condensation (IFC) polymerisation. IFC encapsulation techniques are generally conducted in oil-in-water dispersions (so that the oil phase becomes the core) but it is also known to conduct IFC encapsulation on a water-in-oil dispersion (so that the water phase becomes the core).
JP-A-63-137996 describes liquid detergents containing encapsulated materials wherein the encapsulation can be by coacervation or by IFC polymerisation. It is stated that the particle size can be from 1 &mgr;m to 30,000 &mgr;m but in each of the examples the particle size range is from 20 &mgr;m up to 100 &mgr;m or more. Accordingly it is clear that the products which are made by this process will have a coarser particle size, and therefore a very much lower specific surface area, than we require.
The objective in JP 63-137996 is to include in the core a water-soluble or water absorbent polymer that will swell sufficiently when the detergent is put into wash water to cause rupture of the capsules, with consequential release of the core. Two of the examples show relatively coarse capsules having a shell made by coacervation and having enzyme in the core. They show significant loss of activity during storage but also show that the residual activity is released quickly upon adding the detergent to water.
The other example shows coarse particles of an IFC polyester polymer shell wherein the core includes a high molecular weight dye (molecular weight 2 million) as the active ingredient together with anionic surfactant and cross-linked insoluble polymer. The coarse particles are made as a powder and are then dispersed in a shampoo. It is shown that there is no dye release during storage but that there is rupture and rapid release of the dye when the shampoo is added to water. The large particle size and the high molecular weight of dye probably contribute to the failure of the dye to permeate out of the polyester shell wall during storage.
The fact that anionic surfactant was included in the core composition indicates that the authors assumed that the shell would provide a complete barrier to the permeation of anionic surfactant through the shell. Accordingly this example suggests a shell of low specific area which is totally impermeable (inwards or outwards) to surfactant and dye while in the concentrate and which ruptures on contact with water. The shell is formed around a pre-formed particle of the cross-linked polymer. Because the dye has a molecular weight very much larger than a detergent enzyme, the fact that the dye did not permeate out of these large capsules on storage gives no useful information about how to retain and release enzyme in microcapsules having much larger surface area.
The use of block copolymers in IFC polymerisation is described in EP-A-671206.
We have found that it is not easily possible to achieve the desired result using any of the micro encapsulation procedures previously described for encapsulating detergent enzymes. In practice, either the shell wall is generally too permeable to prevent migration of the relatively low molecular weight enzyme through the high specific surface area provided by the shell wall or the shell wall is so impermeable and strong that it
Lykke Mads
Mistry Kishor Kumar
Simonsen Ole
Symes Kenneth Charles
Gupta Yogendra
Novo Nordisk A S
Sughrue Mion Zinn Macpeak & Seas, PLLC
Webb Gregory E.
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