Single-layer elastic tubular film of polyamide used for packaging paste substances and a process for the production of such film

A single layer tubular film of polyamide used for packing and casing foodstuffs in paste form, especially foodstuffs that are packed when hot or are subject to heat treatment after packing, wherein the tubular film:

• consists of at least one polyamide that can absorb at least 5% of its weight in water up to saturation;
• is completely thermofixed;
• and
• displays the following elastic behaviour:
• (i) at room temperature, when saturated with water, at an internal pressure between 0 and 0.6 bar, expands cylindrically and evenly according to the equation (1) .DELTA.D=m.times.p+c;
• and
• (ii) when the internal pressure is released to between 0.6 and 0 bar, contracts cylindrically according to the equation (2) .DELTA.D'=m'.times.p+c', wherein:
• .DELTA.D is the difference in diameter expansion in (mm) during internal pressurization;
• .DELTA.D' is the difference in diameter contraction in (mm) during internal pressure release;
• m is the upward slope of a plot of ?.DELTA.D vs internal pressure;
• m' is the upward slope of a plot of .DELTA.D' vs. internal pressure;
• p is the internal pressure in (bar);
• c is the ordinate intersection of equation (1), with c equal to zero;
• c' is the ordinate intersection of equation (2);
• the absolute values for m and m' lie between 23 and 6, and for a given diameterr the values for m and m' vary by no more than 20%;
• c' is always less than 4.5 mm;
• and
• equations (1) and (2) apply in the internal pressure range between 0 and 0.6 bar, respectively.