It has been known for a long time that some metal ions such as silver ion, copper ion, and zinc ion have antibacterial properties. For example, silver ion has been widely utilized as a disinfectant or a germicide in the form of a solution of silver nitrate. However, the use of silver nitrate as a solution is inconvenient for handling and further there is the disadvantage that such a solution can be used only for restricted purposes.
Then, a polymeric substance holding the metallic ions was proposed for use in various fields to reduce the aforementioned disadvantages. Many methods of incorporating the metal ions into a polymeric substance are known, for example, the method of binding or adding fine wires or powder of the metals themselves to a polymer and the method of incorporating compounds of the metals into a polymer.
However, in the methods in which the metals themselves are used as mentioned above, there is the disadvantage that the metals show poor compatibility with polymers because the specific weights and Young's moduli of metals are usually very high compared with those of conventional polymers. In addition, such metals lead to very expensive products, with heavy weights as they are necessarily used in a large amounts.
In the method wherein compounds of the metals are used, the products obtained can be utilized only for restricted purposes because of the great influence of the compounds on polymer properties, or else the product shows poor durability of antibacterial performance because the metal ions are merely contained in or attached to the polymer and, accordingly, they easily fall away from the polymer while being used.
For no or less disadvantages such as those mentioned above, a method was proposed wherein a polymer contains organic functional groups having an ion exchange function or a complex forming function and, in turn, these groups retain the metal ions (for example cf. DE-C-963 192). However, in this method, the adverse effect of these functional groups on physical properties of the polymer cannot be disregarded.
Whether the functional groups are chemically introduced into a polymer or compounds having the functional groups are added in a polymer, the type of polymers and the type and amount of functional groups capable of being used are limited to avoid noticeable changes in physical properties of polymers.
U.S. Pat. No. 4,115,130 and FR-A1 061 158 describe a biocidal composition suitable for use in marine antifouling coatings, which comprises a water-insoluble mineral having an internal pore structure, e.g. zeolites, which contains within the pores or is saturated with a biocidal compound effective against marine growth, e.g. metals, metal compounds or organo-metal compounds.
In U.S. Pat. No. 4,525,410, one of the present inventors and others proposed a particle-packed fiber article having antibacterial properties. Specific zeolite particles retaining therein a metal ion having a bactericidal activity are packed and retained in a mixed fiber assembly composed of low-melting thermoplastic synthetic fibers and ordinary fibers. The zeolite particles are retained by welding of the low-temperature thermoplastic synthetic fibers in a state of allowing the contact thereof with an external fluid.
In order to provide fiber articles having antibacterial properties, it has been known for a long time to after-treat the fiber articles with antibacterial agents or antifungous agents. However, such after-treatment fails to provide durable antibacterial effects.
One of the present inventors and others also proposed a polymer article having antibacterial properties comprising at least one organic polymer and zeolite articles contained in the polymer and retaining at least one metal ion having antibacterial properties at ionexchangeable sites of the zeolite (EP-B1-116, 865, and U.S. Pat. No. 4,775,585 filed Jan. 29, 1987). The illustrated polymer article has the shape of granules, films, fibers and so on. In the case of fibers, it is described that the zeolite may be contained in a sheath component of sheath-core conjugated fibers.