Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Heterogeneous arrangement
Reexamination Certificate
2002-08-23
2004-09-28
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Heterogeneous arrangement
C510S446000, C510S447000
Reexamination Certificate
active
06797686
ABSTRACT:
TECHNICAL FIELD
The present invention relates to coated solid bodies, in particular to coated solid bodies in the form of tablets, capsules, micro-tablets, powders, agglomerates and the like. In particular, it relates to coated solid bodies having improved dissolution characteristics together with excellent strength, surface hardness and storage stability. The invention also relates to a process for coating solid bodies, both water-soluble or dispersible bodies and other water-impermeable substrate. The coated solid bodies are suitable for a variety of uses including pharmaceuticals, detergents, food applications, etc. In the following, however, the invention will be primarily described in terms of detergent tablets.
BACKGROUND
Compositions in tablet form are well known in the art. Tablets hold several advantages over liquid and particulate composition forms, such as ease of dosing, handling, transportation and storage. Two main issues can still be improved in tablet formulation: dissolution rate and tablet strength. The most usual way to make tablets is by compression of particulate solids usually with a binder. However, a dichotomy exists in that as compression force is increased, the rate of dissolution of the tablets becomes slower. A low compression force, on the other hand, improves dissolution but at the expense of tablet strength. The presence of an external coating can enhance the tablet strength, allowing tabletting at a reduced compaction force which in turn enhances the speed of disintegration of a tablet. While tablets without a coating can be entirely effective in use, they usually lack the necessary surface hardness to withstand the abrasion that is a part of normal manufacture, packaging and handling. The result is that uncoated tablets can suffer from abrasion during these processes, resulting in chipped tablets and loss of active material. Also, especially in the case of highly alkaline compositions, the outer surface of an uncoated tablet may be aggressive to the skin and even somewhat hazardous to handle.
In such cases, tablet coating is highly desirable. Finally, coating of tablets is often desired for aesthetic reasons, to improve the outer appearance of the tablet or to achieve some particular aesthetic effect.
Numerous methods of tablet coating have been proposed for detergent tablets. GB-A-983,243 and GB-A-989,638 describe the use of a readily water-soluble organic film forming polymer as a coating material for detergent tablets to make the tablet resistant to abrasion and accidental breakage. The polymeric film is formed by spraying the tablet with an aqueous solution containing between 10 and 25% of polyalcohol and then drying with forced air, heated air or infra-red rays to harden the coating and evaporate the solvent.
GB-A-1,013,686 discloses a detergent tablet surrounded by a coating of an organic water-dispersible binder selected from of vinyl alcohol homopolymers and copolymers.
U.S. Pat. No. 5,916,866 describes tablets with a coating of a film-forming water-soluble organic polymer selected from the group consisting of polyethelene glycol, copolymers of vinyl pyrrolidone and vinyl acetate, and copolymers of maleate and acrylate.
U.S. Pat. No. 4,219,435 discloses a detergent tablet provided with a coating of a hydrated salt having a melting point in the range from 30° C. to 95° C., such coating being applied to the tablet in the form of a melt.
Polymer film-coatings as those described in the prior art usually exhibit good mechanical properties (i.e. strength and elasticity) but they have relatively poor dissolution characteristics in water. Film coatings can tend to slow down the dissolution rate of the tablet by opposing water penetration into the tablet core.
Hydrated salt coatings have a crystalline structure and present a very fast disintegration rate in contact with water. However, they are relatively weak and brittle due to their crystalline nature. Therefore, these coatings do not generally provide good tablet integrity.
As can be seen from the prior art, there is still a need to provide tablets having, at one and the same time, good dissolution rate, surface hardness, strength and integrity. One object of the present invention, therefore, is to provide coated tablets and other solid forms having good mechanical properties as well as having excellent dissolution and disintegration characteristics. Another object is to provide a method of coating solid bodies in order to provide improved protection for the body.
SUMMARY OF THE INVENTION
It has now been found that coating tablets and other water-soluble or water-dispersible solid forms with a water-soluble or dispersible micro-porous coating allows for excellent dissolution features at the same time as providing good mechanical strength and integrity. The coating structure is permeable to water, therefore water can penetrate rapidly into the core of the body and consequently the dissolution process is not delayed by the presence of the coating.
According to one aspect of the present invention, there is provided a coated solid body comprising a core of an active composition and having a water-soluble or dispersible micro-porous coating. The term “micro-porous” herein indicates that the coating is permeable to water under ambient conditions and comprises pores or interstices (hereinafter referred to as pores) of generally microscopic size. In general terms, the pores have an average pore diameter in the range from about 1 to about 500 &mgr;m, preferably from about 5 to about 200 &mgr;m and more preferably from about 10 to about 100 &mgr;m.
In highly preferred embodiments, the solid body is coated with a network of fibres, the meshes of which define the pores of the coating. Thus according to another aspect of the invention, there is provided a coated solid body comprising a core of an active composition and having a porous water-soluble or dispersible fibre network coating (sometimes referred to herein as a “net-coating”). Preferably, the net-coating has an average mesh size in the range from about 1 to about 500 &mgr;m, preferably from about 5 to about 200 &mgr;m and more preferably from about 10 to about 100 &mgr;m. The terms poro size and mesh size are used interchangeably herein and expressed as the square root of the cross-sectional area of the pore or mesh in the plane of the coating.
The micro-porous or net coating structure is formed from a concentrated solution of polymers sprayed onto the body, generally under conditions which lead to fast evaporation of the solvent. The precise nature of the coating including the size of the pores depends on the nature of the solvent, on the chemistry of the polymers, the concentration of the polymeric solutions and on the process conditions, especially the drying conditions.
The micro-porous or net coating is preferably formed from a solution comprising a water-soluble or dispersible polymer. Suitable polymers for use herein include polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl acetates and partially hydrolysed polyvinyl acetates, polyvinyl amides, biopolymers and biopolymeric polyelectrolytes including carrageenans, pectins, gelatin, xanthan, alginates, agar, starch, latex, polymers derived from cellulose such as microcrystalline cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose and mixtures thereof. Preferred polymers for use herein are thermoplastic polymers.
The coating solution preferred for use herein is a concentrated water-soluble or water-dispersable polymer solution, containing the polymer in a proportion of from about 15% to about 70%, more preferably from about 20% to about 60% and most preferably from about 25% to about 50% by weight thereof.
The polymer solution will normally comprise from about 30% to about 85% preferably from about 40% to about 80% and more preferable from about 50% to about 75% of solvent selected from organic and aqueous solvents and mixtures thereof. Organic solvents may require complex drying steps, in addition to health, safety and environmental consideration
Genix Lionel Bernard Michel
Gossens Christian
Romero Angelina Rena
Gupta Yogendra N.
Petruncio John M
The Procter & Gamble & Company
Zerby Kim W.
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