Coating processes – Medical or dental purpose product; parts; subcombinations;... – Particulate or unit-dosage-article base
Reexamination Certificate
1997-11-10
2002-06-18
Beck, Shrive P. (Department: 1762)
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Particulate or unit-dosage-article base
C427S189000, C427S212000, C427S201000, C427S562000, C427S460000, C427S461000, C427S469000, C427S202000, C427S203000, C427S289000, C427S424000, C427S128000, C427S129000, C427S130000
Reexamination Certificate
active
06406738
ABSTRACT:
This invention relates to the electrostatic coating of pharmaceutical substrates with a powder coating material and to powder coating materials for coating the pharmaceutical substrates. In particular, but not exclusively, the invention relates to the electrostatic coating of cores of pharmaceutical tablets with a powder coating material and to powder coating materials for coating the cores of pharmaceutical tablets. While reference is made throughout the specification to pharmaceutical tablets and the invention is of particular application to pharmaceutical tablets of conventional shape, it should be understood that the term is to be interpreted in a broad sense as covering also other products to be taken orally such as pellets, capsules or spherules.
Electrostatic coating of electrically conducting substrates such as metal objects is well known. For example in certain paint spraying processes, paint is electrically charged and droplets of paint are sprayed onto an earthed metal object. Such methods have been successful in obtaining a uniform coating on the substrate.
Electrostatic coating of electrically non-conducting substrates, and pharmaceutical tablet cores in particular, is more difficult. There have been proposals for electrostatic coating of tablets for many years. For example, GB 1 075 404 proposes an apparatus for coating tablets in which an atomiser is used to spray finely divided particles of a coating solution onto tablets in a high potential field. The coating is dried using, for example, an infra-red heater. Such proposals have not however been practised on any substantial commercial scale and the coating of pharmaceutical tablet cores is most commonly carried out as a batch process by applying a liquid coating in a revolving drum. The liquid coating material may of course be supplied in some cases in powder form but, if so, it is then dissolved or dispersed in a liquid prior to application. It is not, therefore, applied to the tablet core in powder form.
It is in many ways easier to apply a liquid rather than a powder coating to the core of a pharmaceutical tablet. It is difficult to obtain adhesion of the powder to the tablet and in order to secure the coating to the core, the powder must be transformed into a film without damaging the tablet core, which usually will include organic materials. Furthermore an even coating is required and it is difficult to obtain an even coating of powder on a tablet core.
When a liquid coating is used, the coating must be dried. Theoretically such drying could in some circumstances be carried out at room temperature but in commercial practice it is important, for example because of the rate at which the process must be carried out, to heat the tablets and that is expensive because of the large input of energy required to vaporise the solvent used in the liquid coating. Another disadvantage of liquid coating is that it cannot be used for coating materials that are not soluble or suitably dispersible in a usable liquid, preferably water.
WO92/14451 is concerned with electrostatic powder coating of pharmaceutical tablets and describes and illustrates a process in which the cores of pharmaceutical tablets are conveyed on an earthed conveyor belt and electrostatically charged powder is sprayed towards the cores to form a powder coating attached to the surfaces of the cores. The powder coating is then fused to give a fused film coating secured to the core.
A disadvantage of such a method is that the majority of the powder sprayed towards the cores is not charged and is not deposited on the cores. That leads to overspray and to wastage of the powder material and makes it difficult to obtain a uniform coating.
In a first aspect, the present invention seeks to provide a powder coating material suitable for use in the electrostatic powder coating of a pharmaceutical tablet core and to provide a method for the electrostatic coating of a pharmaceutical tablet core in which a special powder coating material is used to facilitate the electrostatic coating.
The first aspect of the invention provides a powder coating material for use in the electrostatic powder coating of a tablet core, especially for use in a coating method as defined below, and having special properties to make it suitable for use in such a method. The special properties which the powder coating material advantageously has are further defined below and where the advantages provided by those properties are dependent upon the coating method employed, that method is also further defined.
According to a first aspect of the invention there is provided a powder coating material suitable for use in the electrostatic powder coating of a pharmaceutical tablet core in which the material is pharmaceutically acceptable, is treatable to form a film coating and includes composite particles, the composite particles comprising two or more components having different physical and/or chemical properties.
It is important that the powder coating material is a pharmaceutically acceptable material. That in itself imposes severe constraints on the powder coating material since at least most powder coating materials that are commercially available for use in electrostatic powder coating processes are not physiologically tolerable or pharmaceutically acceptable and materials that are commercially available for use as coating materials for pharmaceutical tablet cores are not in a form suitable for electrostatic powder application because other properties of the material are not suitable.
The powder coating material of the invention includes at least two different components, each different component having different physical and/or chemical properties. It is much simpler to provide a powder material having the desired properties referred to above and elsewhere in the specification by providing a material composed of more than one component than by providing a single component material. For powder materials including two or more different components, we have found that improved coatings may be achieved where the powder includes composite particles of the components.
It is particularly important for the particles of the coating material to include more than one of the components where one or more of the components do not have the necessary electrical properties to become coated onto the core when, for example, the method of coating used is as described in the example below. Where the particles are not composite particles those particles of components that do not have the necessary electrical properties may simply remain at the source of powder and will not become coated onto the tablet core. The inclusion of the composite particles is thought to improve the efficiency of coating of the substrate as well as the uniformity of coating applied. The improved efficiency of coating can help to reduce the time required for coating each substrate.
The term “composite particles” as used in this specification refers to particles which have been formed from two or more different components. The composite particles are not homogeneous, that is they have two or more regions each comprising different components of the particle. The composite particle may have the form of a discrete composite particle or may be in the form of agglomerates or aggregates of discrete particles of the different components, the agglomerates or aggregates behaving as discrete composite particles.
Advantageously at least 50% by weight of the particles of the powder are composite particles. Ideally, substantially all of the particles are composite particles but that may not be feasible, in particular where the particle size of the composite particle is small. Where the powder includes more than two components having different physical and/or chemical properties, advantageously the composite particle also includes those other components. Ideally, substantially all of the composite particles would comprise discrete particles including each of the different components. However, in practice, satisfactory coatings can be achieved where the ind
Hogan John E.
Page Trevor
Reeves Linda
Staniforth John N.
Beck Shrive P.
Kolb Michener Jennifer
Nixon & Vanderhye
Phoqus Limited
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