Heat shrinkable plastic products have the property of shrinking when heated and are widely utilized for films such as shrink packages, shrink labels, etc. In particular, polyvinyl chloride (PVC), polystyrene, and polyester based plastic films have been used to label or cap seal a variety of vessels or to directly package them.
However, films made of PVC are subject to environmental restrictions because their incineration may generate hydrogen chloride gas and a dioxin-causing material. If this product is used as a shrink label of a PET vessel, the recycling of the vessel can be carried out only after the cumbersome separation of the label and the vessel from each other.
Also, polystyrene based films may be very stably worked when undergoing the shrinking process and have a good external appearance, but have poor chemical resistance, undesirably requiring that an ink having a specific composition be used for printing. Furthermore, this film is problematic because it shrinks spontaneously because of poor storage stability at mom temperature, undesirably deforming the dimensions thereof.
Films made of polyester resin without such problems are receiving considerable attention as a shrink label while substituting for the films made of the above two materials. Moreover, as the use of PET vessels increases, polyester films which may be easily regenerated without the need to separately remove the label upon recycling of the vessels are being increasingly used.
However, the shrinking properties of conventional heat-shrinking polyester films must be improved. Because of drastic changes in shrinkage behavior, these films may wrinkle or shrink non-uniformly, undesirably causing frequent problems during a molding process of their shape deviating from an intended design. Also, compared to PVC based films or polystyrene based films, polyester films have relatively higher maximum shrinkage rate but are poor in terms of shrinkability at low temperature, and thus should be shrunk only at high temperature. Furthermore, because polyester has high heat shrinkage stress, PET vessels are undesirably deformed or becomes white turbid.