Patent Application
20080214429
This invention relates to rapid dissolving film formulations for the quick and convenient delivery of surfactants upon the addition of water, e.g. a soap for personal washing applications.
Although a number of carbohydrate based hydrocolloids have been proposed as the polymer basis for film-form compositions for delivery of soaps, detergents, etc., I have found that hydroxypropyl methycellulose (HPMC) is an unusually good choice owing to its strength, rapid dissolution in water and natural foaming properties. Unlike materials such as carboxymethyl cellulose, HPMC is compatible with cold mixing and the production of soap films which will not stick together.
I have found that the water soluble polymer hydroxypropyl methyl cellulose (HPMC) in combination with sodium isothionate as the primary surfactant provides a basis for films of superior properties that function as soap for personal hygiene applications. Compositions according to the present invention are in the form of a thin film which dissolves on contact with water and are, as such, very convenient to use.
Personal wash films according to the present invention comprise the following essential components:
Low molecular weight HPMC (12-18 cps, in 2% aqueous solution at 20° C.) is preferred, as it dissolves more rapidly and rinses cleanly, with little or no “slimy” sensation. Methocel A15™ (Dow Chemical Corporation), and Metolose™ MCE-15 (Shin-Etsu Chemical Co. Ltd.), are examples of suitable HPMC polymers.
Propylene glycol is preferred as a plasticizer, as it has natural surfactant properties and does not suppress foam production, as is the case with other humectants such as glycerol.
Sodium isothionate is unusually suitable as the primary surfactant in personal wash films, owing to its mildness (derived from natural sources), compatibility with HPMC and most important—it's tendency to produce a very dense, stable foam.
A lesser amount of one or more co-surfactants is required to improve performance by accelerating lather production and providing a more “open” foam.
1. Cold mixing is carried out in three stages:
2. Casting of slurry mix to form a film
3. Die-cutting & embossing (or optionally, printing) of the soap film
HPMC must be mixed in cold water (less than 30° C.), and separately from surfactants in order for thorough hydration of the polymer to occur. The polymer should be mixed under rapid agitation, until smooth and for a minimum of about 30 minutes before addition of surfactants and fragrance.
Once polymer hydration is complete, surfactants can be blended into the mix. This results in a slurry which is very stable, and can be held for several weeks under ambient (5-30° C.) storage conditions, until needed.
Aeration, as a third and final stage of mixing, may be carried out to reduce the specific gravity from an initial level of about 0.9 g/ml. A specific gravity of less than 0.86 vastly improves dissolution rate, and most important—produces a dry cast film which is bright white (no color is added), opaque, and can be easily embossed (see below).
The specific combination of HPMC and sodium isothionate, results in a film with performance characteristics which are exceptionally well suited to personal wash applications, but with adequate strength to allow for unsupported casting (eg. cast directly onto stainless steel belt or other suitable drying surface, without need for a carrier backing film).
If a carrier film is required (eg. for production of film in roll stock form), bare aluminum foil and/or poly-coated aluminum foil is used. Film tends to stick to conventional polyethylene-based carriers, and Mylar™).
Film can be sheeted and stored for die cutting and embossing at a later stage, or die cut immediately off the production line.
Embossing of the film is achieved by compression of the aerated film with a rubber stamp, or means similar to that used in flexographic printing processes. Initial film thickness is approximately 150 microns. Upon embossing, the affected area compresses to a thickness of about 80 microns, giving a relief to the surrounding film and allowing the improved image (e.g. trademark) to be clearly visible.
Alternatively, films may be printed on by one of several means, including ink jet, or flexographic printing.
Embossing of film strips may be conveniently achieved during the die cutting stage, which allows for improved production efficiency and correct registration of the logo (embossed image) on the finished strip.
| Number | Date | Country | |
|---|---|---|---|
| 60886703 | Jan 2007 | US |
