  A liquid scintillator base experiment KamLAND-Zen has set a lower limit on
neutrinoless double beta decay half-life, and upgrade project KamLAND-Zen 800
has started in 2019. Unfortunately, this project expects some backgrounds, and
one of the main backgrounds is beta/gamma-ray from 214Bi in container of xenon
loaded liquid scintillator (mini-balloon). In order to reject the background,
we suggest using scintillation film for the future mini-balloon. If we can tag
alpha-ray from 214Po by scintillation detection, we can eliminate 214Bi events
by delayed coincidence analysis. Recently, it was reported that polyethylene
naphthalate (PEN) can be used as a scintillator with blue photon emission. PEN
has chemical compatibility for strong solvent, thus it has a possibility to use
in liquid scintillator. In this presentation, we will mention the results for
feasibility studies about transparency and emission spectra, light yield,
radioactivity, strength of film etc.. We also show the test-sized scintillation
balloon with an 800-mm diameter and discussions about how to use the
scintillation balloon in KamLAND.
