Bactericidal/fungicidal plastic articles

Details Bactericidal/fungicidal plastic articles Bactericidal/fungicidal plastic articles

1999-11-01

2003-04-08

Hartley, Michael G. (Department: 1616)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Wearing apparel, fabric, or cloth

C424S404000

Reexamination Certificate

active

06544536

ABSTRACT:

This invention relates to processes for producing plastic bodies that can be further processed, particularly for use in the medical field, and exhibit an antimicrobially effective content of metals or metal compounds (in the following called active agents).
These are especially materials and/or compounds thereof whose oligodynamical effect is known, such as silver, copper and gold, but also other heavy metals such as zinc and also lanthanides that have an effect on bacteria and/or fungi as desired according to this invention, i.e. they eliminate them, they prevent them from multiplying as well as from sticking to or embedding themselves in the plastic, or at least largely keep them from doing so.
A look at the present situation on the market shows that pre-products or finished parts made of such plastics are not yet commercially available, but according to the state of the art they can indeed be produced to function.
One reason why these products have not yet been introduced on the market to a considerable extent, is most likely the question of time and/or energy and thus costs involved in the production of such plastics.
On the one hand, this holds true for the costs of the amounts of metal and/or metal compound necessary for the desired purpose, in particular of silver, when these substances are to be included in the plastic in the powder form, in which case the lower limit for the metal and/or metal compound to be effective is frequently stated to be in an order of magnitude of 1 wt. % of the plastic; however, larger amounts are always stated to be even more effective. In this context, reference is made to the pate publications U.S. Pat. No. 4,054,139, WO-A-84/01721, EP-A-0 190 504, DE-A-37 25 728, EP-A-0 251 783 and DE-A-39 42 112.
On the other hand, this holds true for the costs of the actually rather elaborate wet process for the treatment of plastics, e.g. according to DE-C-42 26 810, which correspondingly is only to be used in special cases and in which very small amounts of the active agent are sufficient.
Another way of avoiding the high material costs for antimicrobial finishing is not to subject the plastic as a whole to antimicrobial finishing but to coat the finished objects produced from this plastic with active agents.
However, all physical methods (such as vapor deposition, cathodic sputtering, plasma-assisted vapor deposition, ionic plating, ion implantation) and also the chemical methods (e.g. currentless electro-plating, reactive vapor deposition, reactive cathodic sputtering, CVD, PACVD) work such that only the surfaces facing the source of the active substance to be applied or, e.g. in the case of plasma-assisted methods, at least only the surfaces openly facing the environment are coated. The internal surfaces of objects, which are usually particularly important for medical applications, e.g. the internal surfaces of catheters, however, cannot be reached by the aforementioned methods and thus remain uncoated.
The problem underlying the present invention is thus to provide a method for producing oligodynamically active plastic bodies not exhibiting the aforementioned disadvantages, i.e. that are easy to produce, require only small amounts of oligodynamical metal and/or the compound(s) thereof and uniformly act on all surfaces, also on those that are hard to get to.
This problem is solved by a method for producing plastic bodies having a content of one or several oligodynamically active metal(s) or metal compounds as an active substance, characterized in that the active substance is embedded in the plastic in the form of discrete particles, wherein the amount of active substance is no more than 1.0 wt. %, preferably no more than 0.5 wt. %, based on the total weight of the plastic body, and the maximum size of the discrete active substance particles is less than 500 nm.
Active substances in powder form of any kind that are easy to handle are only produced and for sale with finenesses of grain up to the micron range (i.e. ≧1 &mgr;m) and sub-micron range (i.e. >0.1 &mgr;m). According to the manufacturer's information, the thus achieved specific surface, for instance in the case of the finest commercially available silver powder having a rated grain size of 2-3.5 &mgr;m, which of course comprises also a certain portion of coarser particles and sub-micron particles, which is unavoidable, amounts to 0.5 to 1 m
2
/g. Other frequently used and also less expensive silver powders have even larger particles and correspondingly lower specific surfaces.
Even finer, colloidal preparations can generally only be prepared as sols or gels. The thus present portion of protective colloid during further processing and use usually involves considerable undesired side effects. Besides, such colloidal preparations are often rather unstable and, in addition, often relatively expensive.
In the process of this invention, plastic bodies are therefore preferably produced such that the blank is coated with the bactericidally and/or fungicidally (oligodynamically) active substance by means of a chemical or physical process, the obtained blank (pre-product) is comminuted and/or molten down, from which mass the desired plastic body is then produced according to common methods.
Very thin and, depending on the process, fine and even extraordinarily fine structures of the deposited material can be achieved by means of physical and chemical methods for coating surfaces, which structures correspond to or at least come close to the fineness of colloidal preparations. This holds true especially when the deposited layers are very thin.
The resulting minimum value of the specific surface is 19 m
2
/g for such coatings, for instance just by mathematic calculation of the outer geometry at a layer thickness of 10 nm e.g. for the deposition of silver. Preferably the layer thickness is 1 to 50 nm.
If also those surfaces are taken into account that arise perpendicular to the main surface due to open laying grain edges and due to fracturing of the surface due to errors in the uniformity of the deposition, the resulting value for the specific surface is even higher in practice.
Preferably, the maximum particle size distribution of the active substance is below 100 nm in at least one dimension (e.g. in particles present in the form of flocks or flakes), more preferably 10 nm. In thin layers, the grain size may even be smaller than 1 nm.
Crystalline materials (PTFE, some polyimides) must e.g. be comminuted by grinding; remelting is not possible (in practice). They are then shaped as desired by e.g. (pressure) sintering.
Tests showed that plastics having principally a low but most finely dispersed content of metal particles (or particles of metal compounds) with a correspondingly large specific active surface have the same effect as plastics having a considerably higher but less finely dispersed content of metals (or metal compounds) with a correspondingly smaller specific active surface.
Since, however, the supply of these active substances, which is decisive for their long-term effect, is undoubtedly larger when the particles are coarser, it can be mentioned as another advantage of the plastics produced according to the above-mentioned method that for particularly critical cases these plastics may be equipped with metal (or metal compounds) having particles whose size may be influenced for an optimum long-term effect from the very beginning by a suitable process for the production of the layer.
The coating can take place on film (see Example), which can then be re-comminuted and further processed. It may also be applied to fibers or granules with the same end result of the production of the desired final concentration of the active substance in the plastic.
Plastic blanks that already contain fillers may also be used. Preferred are plastic blanks whose fillers do not considerably alter the chemical and physiological properties of the plastic used as a pre-product. Preferred fillers are those that result in the end products produced therefrom being easily recognizable by means of X-rays and/or h

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