Patent ID: 7704530

Claim:
A method of inhibiting coloring of an antimicrobially-treated plastic preform having contact with water or containing water, comprising: providing a plastic preform that can develop undesired coloring due to the effect of silver ions when admixed with an aqueous medium in the presence of a silver-based antimicrobial agent which dissociates silver ions in the aqueous medium; providing (A) a silver-based antimicrobial agent which dissociates silver ions in the aqueous medium; providing (B) a silver ion trapping agent comprising adenine, guanine, cytosine, thymine, and/or uracil in free base form; and mixing and dispersing (A) and (B) into the plastic preform; wherein (1) the ratio of (A)/(B) is 1/1 to 100/1 by weight, (2) (A) and (B) are contained at a ratio of 0.05 to 5.0% by weight in total, relative to 100% by weight of said plastic preform, and (3) said silver-based antimicrobial agent is selected from the group consisting of silver zeolite, silver apatite, silver zirconium phosphate, and silver glass; whereby said undesired coloring of the antimicrobially-treated plastic preform is inhibited.