Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Tablets – lozenges – or pills
Reexamination Certificate
1999-01-08
2002-02-05
Spear, James M. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Tablets, lozenges, or pills
C424S401000, C424S465000, C424S470000, C424S489000, C514S944000, C514S951000
Reexamination Certificate
active
06344216
ABSTRACT:
The present invention relates to carboxylic acid polymer compositions and particularly relates to concentrates of acrylic acid polymers and their use to prepare gels of diluted and neutralized polymer.
The polymers to which the invention relates include cross-linked polymers of acrylic acids which are widely used as thickeners, stabilizers and emulsifiers in many industries. Said cross-linked polyacrylic acids are produced and sold under a number of trade names for example Carbopol (B F Goodrich), Acrisint (Sigma), Pemulen (B F Goodrich), Junlon (Nihon Kogakyu) etc. They are however most often referred to by either of the generic terms carbomer and cross-polyacrylate, (developed by the Cosmetics, Toiletries or Fragrances Association). The polymer products are referred to by these names in this application.
Said products so described are supplied in the form of very fine powders with poor flow properties, and handling of these products is not easy. However, it has always been considered that the products must be in the form of very fine powder if complete wetting and reasonably rapid hydration of each particle is to take place when the products are added to a liquid medium, such as water, to form a gel from which products such as liquid detergents, cosmetics, toiletries or pharmaceutical products can be made. A consequence of the products being in the form of a very fine powder is that they have a pronounced tendency to dust and fly about the work place even when care is taken to minimise this.
It is conventionally regarded therefore that, despite the handling difficulties, the products must be supplied in the form of fine powders since, when they are to be converted to a gel, and in the initial stage of hydration for this conversion i.e., wetting of the powders, the formation of a very stiff gel on the outside of the powder particles occurs which delays and restricts the entry of further water to hydrate the remainder of the particle. The stiff gel on the outside of the particle therefore tends to prevent further water ingress into the particle, thereby retarding the formation of a smooth gel. In addition, agglomerates of the powder particles form lumps which increases the problem of wetting out and dispersion.
Furthermore, when disturbed, the dry powder tends to develop strong electrostatic charges which impairs further the ability of the powder to flow in the required direction and, in the extreme, causes small agglomerates to fly about which results in loss of material. This makes the automatic measuring out of the carbomers virtually impossible.
As a result of these problems, manufacturers of the products always advise that the said product be carefully sifted into the water in an attempt to break up the dry agglomerates which tend to form during storage. Furthermore, these carbomers, when fully swollen and hydrated, have the property of suspending insoluble gases, liquids and solids. This property, although very desirable in most instances, can make the removal of air bubbles from the mixture very difficult, if not impossible, within a reasonable period of time.
In an attempt to overcome this problem it has been proposed to prepare concentrated dispersions of resins in water. However, due to the high viscosity of said resins, they are extremely difficult or impossible to handle. A further initiative, as described in co-pending application No 9114095.4 provides, by incorporating small proportions of salts of multi-valent cations in these dispersions either by dry blending the polymer and salt together before adding them to the water, or by mixing the salt, powdered carbomer, and water in any order, a concentrate which has been found to be extremely effective and to have gained acceptance as a workable alternative.
The provision of said multi-valent cations in the blend has been found to be acceptable but further research has shown that the important factor of handling difficulties of the powdered carbomer in a dry state is not properly addressed. The addition of additional matter to the carbomer, although having an important effect on the characteristics of the carbomer, does not solve many of the other inherent handling problems of the carbomer, and also meets resistance from users reluctant to change to a product which requires new certification and approval. For example, the form in which the carbomer is provided is important in allowing improvements both in the mixing of the carbomer in a liquid medium to form the gel and also in improving the storage characteristics of the carbomer.
The aim of the present invention therefore is to provide an improvement in the form in which a polymer is provided such that the ease of mixing or blending of the polymer in a liquid medium to form a gel is improved in relation to existing powdered polymers and the polymer in its improved form is non-dusting, non-static and has improved flow-characteristics.
The present invention provides for the conversion of a powdered polymer wherein said polymer is converted to a granular, pelletised or tablet form.
Typically said polymer will be a powdered carbomer or cross polyacrylate and will, in a first embodiment, be comprised wholly of carbomer, or cross-polyacrylate.
The carbomer in its converted form will be capable of rapid dispersion when added to a liquid medium to form a gel substance.
In a second embodiment, the polymer will comprise a carbomer or cross-polyacrylate with which is blended an electrolyte to form a composition which is subsequently converted to a granular, pelletised, or tablet form.
Typically said electrolyte will have any of the following characteristics, namely it is;
readily soluble in liquid,
an acid or salt or acid salt of mono-or poly-valent cations or combinations thereof,
a salt, acid or acid salt, whose pK value is at least 0.5 units and preferably 1.0 unit, less than the pK value of the carbomer itself which is typically 4.3,
preferably solid and non-volatile at normal temperatures,
preferably non-toxic,
stable under normal storage conditions and preferably does not discolour, polymerise or change in any other way.
Typically, said electrolyte will also be non-hygroscopic.
When said electrolyte is an acid, or an acid salt, the pK value of the acid, a measure of its acidity, will, be at least equal to, and preferably 1.0 unit less than the pK value of the carbomer.
Preferably, the pK value of the acid will be 2.0 units less than the pK value of the carbomer, which typically has a pK value of 4.3.
In a further aspect of the invention, the electrolyte used in a blended form with the carbomer, will be an acid salt of mono-valent or multivalent cations.
Typically said blend will be easily granulated or pelletised and will be supplied in that form. To form said pellets, tablets, or granules into the required gel will require the conventional addition and mixing with a liquid medium followed by neutralisation of the mixture. Typically said liquid medium will be water but may also be any of an organic solvent such as ethanol, propylene glycol or a blend of a polar hydroxylic solvent and a non-swelling solvent.
Preferably, the polymer will be provided in a granular form. Typically to form granular products, either wet or dry granulation methods can be employed. Dry granulation involves the use of high pressure to force the particles into contact with each other and can be carried out either in moulds by means of a ram or by forcing the powder through a screen with rollers. Subsequently the material may be reduced in size and put through screens to enable a selected size range to be obtained. Wet granulation typically involves treatment with a small proportion of water to assist binding of the particles which then occurs without the need for high pressures. Other solvents can be used, but in this instance would be considered undesirable. Drying of the granular material may also be carried out as part of the process.
Conventionally it is generally held that for materials of the type of this invention, small particle size is essential if the rate of hydration of the said mate
Minister Peter E.
Stead Stanley Gordon
Rohm & Monsanto, PLC
Spear James M.
Surfachem Group PLC
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