Heat-shrinkable polyester film roll and a process for producing the same

Abstract

A film roll of a heat-shrinkable polyester film meeting the following requirements: (1) when samples are cut off therefrom at an almost equal interval along the longitudinal direction, and immersed in hot water at 85° C. for 10 seconds, subsequently in water at 25° C. and withdrawn, heat-shrinkage percentages in the maximum shrinkage direction of all the samples are 20% or more; and (2) when raw polymers used for production of the film above comprises of a major constitutional unit and one or more sub constitutional units different therefrom, and the content of the primary sub constitutional unit in each sample is more than 7 mole % in 100% of all constitutional units, and the contents of the primary sub constitutional unit of all the samples fall within a range of ±2 mole % relative to the average.

1 . A process for producing a film roll of a heat-shrinkable polyester film comprising the steps of blending a polymer used in the greatest amount and one or more polymers different in compositions therefrom, and extruding the mixture in a molten state, raw chips of each polymer being cylindrical members having elliptical cross-sections with major and minor axes, averages of the major axis, the minor axis and the length of the raw chips of the polymers different from the polymer used in the greatest amount falling, respectively, in the range of ±20% relative to the averages of the major axis, the minor axis and the length of the raw chips of the polymer used in the greatest amount. 
   
   
       2 . A process for producing a film roll of a heat-shrinkable polyester film comprising a step of extruding polyester in a molten state into a film by an extruder mounted with a funnel-shaped hopper as a raw chip supplier, the hopper having an inclination angle of 65° or more relative to the ground. 
   
   
       3 . A process for producing a film roll of a heat-shrinkable polyester film comprising a step of extruding polyester in a molten state into a film by an extruder mounted with a funnel-shaped hopper as a raw chip supplier, the hopper having an internal capacity of holding 15 to 120 mass % of polyester relative to a discharge amount of the extruder per hour. 
   
   
       4 . A process for producing a film roll of a heat-shrinkable polyester film comprising the steps of melt-extruding raw polymer into film, cooling the film, and drawing the film, or additionally rewinding the film into a roll between the cooling and the drawing, variations in surface temperature of the film measured at any point in a preheating step, a drawing step, and a heat-treating step after the drawing step, are controlled, respectively, in a range of ±1° C. relative to the average temperatures with respect to preheating, drawing, and heat-treating zones over an entire length of the film.