シリコーンオイルフリー注射器実現のための光化学的フッ素化処理ガスケットの最適化

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In the medical field, plastic syringes are used with silicone oil for the sliding area between a barrel and gasket, where barrels are typically plastics such as PP (Polypropylene) and gaskets are made of TPE (Thermoplastic elastomer). However, silicone oil is considered to have some demerits: accumulation in the body and adsorption of medicine's constituent. Therefore, the development of unlubricated plastic syringes is desired. We reported in 2009 that the friction coefficient between TPE and PP flat specimens without silicone oil at normal load of 1 N was decreased by 50 % by photochemical fluorination of TPE. The test with an actual syringe, or the indentation of a fluorinated TPE gasket into a silicone oil-free PP barrel showed that the resistance force during indentation was decreased from 50.7 N to 30.4 N; the reduction ratio of resistance force was 40%. In this work, the effect of gasket deformation ratio α (=[DG-DB]/DG×100 %, DG: diameter of gasket, DB: inner diameter of barrel) on the fluorination effect in silicone oil-free syringes was further investigated by changing the inner diameter of barrel so that the contact pressure between gasket and barrel are changed. As a result, it was confirmed that the reduction ratio of resistance force due to photochemical fluorination increased from 43 to 75%, with the inner diameter of barrel DB changed from 20.3 mm (α=2.64 %) to 20.7 mm(α=0.72 %) against a fixed gasket diameter of DG=20.85 mm. At the inner diameters DB≥20.65 mm (α≤0.96 %), the resistance force between fluorinated gasket and barrel was less than 10 N, which is the maximum acceptable value for practical syringes. Moreover, at the inner diameter DB=20.65 mm (α=0.96 %), leak load, above which water leak occurs between gasket and barrel during indentation, was more than the minimum acceptable value of 76.9 N for practical syringes. In other words, the requirements for practical syringes in the resistance force and leak load were both satisfied at α=0.96 % with fluorinated gaskets; on the other hand, these requirements were not satisfied together at any α values with non-treated gaskets.

シリコーンオイルフリー注射器実現のための光化学的フッ素化処理ガスケットの最適化

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