A polyorganosiloxane composition which is cured at normal temperature to fore a rubbery elastic material has been widely used as electrically insulating sealants, sealants for construction, etc. However, since such a kind of composition is spoiled by microorganisms such as fungi, bacteria, etc., according to environmental conditions after curing, the composition is discolored or stained, whereby not only the appearance of the composition is spoiled but also it frequently happens that a sealing property, an electrically insulating property, etc. , which are the essential functions of the composition, are decreased.
For preventing occurrence of those disadvantages, it has been practiced to add a material having an effect of killing microorganisms to the composition. However, in a composition having added thereto a conventional fungicide, it is impossible to sufficiently prevent growth of microorganisms and keep the effect for a long period of time. Also, when such a fungicide is added to the composition, according to the kinds of the base polymer and a crosslinking agent used for the polymer, there is a problem that the fungicide adversely affects the storage stability, the color tone, the adhesive property, etc., of the composition.
To overcome the above problems, JP-A-56-38348 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses use of an N-substituted benzimidazole carbamate as a fungiproofing agent for a room-temperature curing polyorganosiloxane composition. This compound does not color the composition when the composition contianing the compound is stored for a long period of time and is excellent in the fungus resistance, but the fungus resistance after a warm water deterioration test, etc., for a long period of time is yet insufficient according to a purpose. Hence a further improvement has been required.
JP-A-2-306907 discloses use of p-chloro-m-xylenol together with bis(2-pyridylthio-1-oxide) zinc salt as an anti-fungus agent for a modified silicone sealant. Since in the modified silicone sealant, polyoxypropylene is the base polymer and a crosslinked point only is the disiloxane bond, the modified silicone sealant is chemically different from a polyorganosiloxane sealant and is rather similar to a polyurethane sealant. Therefore, JP-A-2-306907 does not suggest that such an antifungus agent is effective for a polyoxyorganosiloxane sealant. In fact, in the case of a polyorganosiloxane sealant, bis(2-pyridylthio-1-oxide) zinc salt itself does not show a sufficient fungus resistance. On the other hand, in the case of using p-chloro-m-xylenol as an antifungus substance for a polyorganosiloxane sealant, when a silane or a siloxane having an oxime group in the molecule is used as a crosslinking agent, the sealant increases the viscosity during the storage, whereby the storage stability of the sealant is reduced. Accordingly, there is a disadvantage that the selection of a crosslinking agent is restrained.