As you may know, use of ambiguous words, such as “about”, “approximately”, “preferably”, “optionally”, etc., in claims is basically impermissible in Japan.
We often receive Office Actions in which the Examiner is of the opinion that the word “about” in the claims makes the scope of the claimed invention indefinite. In such cases, in general, we propose to simply delete the word “about” in the claims.
Meanwhile, with regard to the term “substantially consisting of” interpreted in JP, it means that it cannot contain any other element that will have some influence on the claimed composition regarding the aimed object of the claimed invention. For example, if a fining agent is included in a glass composition, it may still fall within the scope of the glass composition claim since inclusion of a fining agent is not special and it may not have a special effect or performance on the claimed glass composition. If the patent should say that the claimed invention is free of fining agent, of course, a glass composition including a fining agent will not fall within the scope of the claim. Further, inclusion of impurities will not change the situation.
Similarly, under the Japanese patent practice, “A consists essentially of X” is interpreted to mean that A may include, in addition to X, minor impurities that cannot technically be completely removed from the batch or a trace amount of components that do not affect the aimed object or the intended results of the claimed invention. Bearing the above in mind, for example, if graphite is included in a glass composition, it may still fall within the scope of the glass composition claim as long as the amount of included graphite is very minor and graphite does not at all affect the performance of the claimed batch mixture in terms of the intended results of the present invention.