Hydrophilic pressure sensitive hot-melt adhesives

Details Hydrophilic pressure sensitive hot-melt adhesives Hydrophilic pressure sensitive hot-melt adhesives

1996-11-13

2001-02-20

Kishore, Gollamudi S. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Web, sheet or filament bases; compositions of bandages; or...

C424S447000, C424S449000

Reexamination Certificate

active

06190689

ABSTRACT:

SPECIFICATION
The present invention relates to devices for the release of substances from pressure sensitive hot-melt adhesives having an uneven or even distribution of the substances.
Typical representatives of devices for the release of substances from adhesives are self-adhesive products for the application on intact skin, for example, medicinal patches for the controlled dermal or transdermal release of substances and cosmetic patches for the release of active or odorous substances; self-adhesive products for the application on injured skin, e.g., patches, wound dressings, or surgical films for the release of substances to wounds.
Pressure sensitive adhesive layers comprising pharmaceutical or other active substances are for the most part formed by coating a solution or dispersion with subsequent evaporation of the solvent or dispersant.
The use of solvents or dispersing agents in the production of adhesive layers for devices of the above-mentioned type is disadvantageous for many reasons; this applies to both the economic point of view because of expensive drying lines, extracting plants, recovery and disposal facilities, and to the ecological point of view because of the environmental impact caused by solvents and dispersing agents as well as their degradation products.
In contrast to this, adhesive layers manufactured from a melt of the formulation components have advantages with respect to economy and ecology. However, there is the disadvantage that very high temperatures are necessary to melt the commonly used pressure sensitive hot-melt adhesive formulations so that the pharmaceutical or other active substances to be incorporated are decomposed, modified or evaporated, at least partially.
In addition, the conventional pressure sensitive hot-melt adhesive formulations—as well as adhesive formulations bound by solvents or dispersants—have further disadvantages, in particular when used in man; in general, these become apparent in the form of skin reactions and painful rubors during the application or after removal of the device.
In case of aggressively adhering devices, these skin irritations may be due to an injury of the corneum when the adhesive device is removed from the skin. Most frequently, however, skin reactions result from the fact that the base components of adhesive formulations are of a lipophilic nature; this in particular applies to pressure sensitive adhesives. When applied to the skin, these adhesives have the effect of occlusive films or foils which completely prevent the cutaneous respiration and evaporation of water and thus suppress the mechanisms of thermoregulation at the application site. Since the water released by the skin cannot evaporate, thin water films and water islands form between the adhesive layer and the skin and these represent an optimum environment for the growth and multiplication of skin germs. Once a certain population size is reached, the amount of skin germs decomposing per time unit is such that the concentration of toxic catabolic products and decomposition products drastically increases, again resulting in massive skin reactions.
There were attempts to combat these phenomena, e.g., in case of the pressure sensitive adhesive formulation for self-adhesive wound dressings, by incorporating so-called hydrocolloidal particles into pressure sensitive hot-melt adhesives, i.e., hydrophilic substances, in particular polymers, which absorb and withdraw water from the surface of the skin.
But even these formulations cannot avoid another serious disadvantage of conventional pressure sensitive hot-melt adhesives. In addition to the above-mentioned, rather physical reasons resulting in skin irritations, it is first of all the allergic skin reactions that cause problems, and these are usually caused by the chemical properties of the lipophilic adhesive resins used. Up to the present, this problem has not been solved satisfactorily, since these adhesive resins cannot be omitted when a reliable adherence to the skin is required.
Owing to their lipophilic nature, prior art pressure sensitive hot-melt adhesive formulations for the release of substances have another disadvantage: with respect to the controlled release of substances they are suitable only for lipophilic substances. In the case of hydrophilic substances it is hardly possible to create the preconditions for the release control relating to the thermodynamic activity in the pressure sensitive hot-melt adhesive. These substances must be dissolved in the adhesive formulation, at least partially, so that they can diffuse within an adhesive formulation, reach the interface and be released; in general, this cannot be achieved when hydrophilic substances and lipophilic pressure sensitive hot-melt adhesives are combined.
Accordingly, it was the object of the present invention to find a device for releasing substances from pressure sensitive hot-melt adhesives, which comprises a pressure sensitive hot-melt adhesive that reliably adheres to the desired surface at room temperature after slight pressure, does not leave any residue on the surface after removal, absorbs cutaneous moisture, comprises non-allergenic adhesive resins, and permits the incorporation of hydrophilic substances in dissolved form.
In a device for the release of substances from hydrophilic pressure sensitive hot-melt adhesives having an even or uneven distribution of these substances, this object is achieved with the present invention by the fact that the pressure sensitive hot-melt adhesive is hydrophilic and comprises at least one water-soluble or at least water-swellable polymer, at least one water-soluble, meltable adhesive resin, and substance to the released.
Most surprisingly, it turned out that it is possible to produce pressure sensitive hot-melt adhesives complying with the above-mentioned requirements by combining water-soluble, or at least water-swellable, polymers with water-soluble, meltable adhesive resins under addition of the substances to be released; and in this connection water-soluble, meltable tacky substances, which are low-viscous and ropy per se—when combined with hydrophilic polymers—form coherent layers of an excellent cohesion which, in addition to that, have adhesive forces absolutely comparable to those of conventional adhesives.
Pressure sensitive hot-melt adhesives within the meaning of the present invention are those by means of which coated devices can reliably be joined with surfaces at room temperature under slight pressure, and which have a cohesion permitting a residual-free removal of the adhesive-coated device from the application surface by simply stripping it off. In order to avoid undesired modifications of the substances to be released or of other formulation components, the pressure sensitive hot-melt adhesives of the kind specified herein are preferably processed at temperatures between 40 and 150° C., most preferably at temperatures between 80 and 120° C., in molten condition, and they solidify under formation of adhesive and cohesive forces.
Pressure sensitive hot-melt adhesives of the type mentioned herein differ greatly from hydrophilic, water-soluble adhesives known from the production of so-called gummed surfaces, e.g., envelopes or labels. These adhesives which build up cohesive but no adhesive forces after melting, processing, and setting are activated only when moistened with water or saliva, and they are brought into contact with the application surface in moist condition. After drying of the adhesive, adhesive forces build up which firmly join the respective surfaces, e.g., paper labels with glass surfaces. In contrast to surfaces joined by pressure sensitive hot-melt adhesives, said adhesive forces between device and surface cannot be eliminated by simply pulling the adhesive-coated device off the application surface; in these cases neutralization of the adhesive forces can only be effected by redissolving or slightly solving the adhesive, e.g., by moistening with water, removal in a water-bath or over water vapor.
When formulating the pressure sensitive hot-melt

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